\r\n\tIn sum, the book presents a reflective analysis of the pedagogical hubs for a changing world, considering the most fundamental areas of the current contingencies in education.
",isbn:"978-1-83968-793-8",printIsbn:"978-1-83968-792-1",pdfIsbn:"978-1-83968-794-5",doi:null,price:0,priceEur:0,priceUsd:0,slug:null,numberOfPages:0,isOpenForSubmission:!1,hash:"b01f9136149277b7e4cbc1e52bce78ec",bookSignature:"Dr. María Jose Hernandez-Serrano",publishedDate:null,coverURL:"https://cdn.intechopen.com/books/images_new/10229.jpg",keywords:"Teacher Digital Competences, Flipped Learning, Online Resources Design, Neuroscientific Literacy (Myths), Emotions and Learning, Multisensory Stimulation, Citizen Skills, Violence Prevention, Moral Development, Universal Design for Learning, Sensitizing on Diversity, Supportive Strategies",numberOfDownloads:null,numberOfWosCitations:0,numberOfCrossrefCitations:null,numberOfDimensionsCitations:null,numberOfTotalCitations:null,isAvailableForWebshopOrdering:!0,dateEndFirstStepPublish:"September 14th 2020",dateEndSecondStepPublish:"October 12th 2020",dateEndThirdStepPublish:"December 11th 2020",dateEndFourthStepPublish:"March 1st 2021",dateEndFifthStepPublish:"April 30th 2021",remainingDaysToSecondStep:"3 months",secondStepPassed:!0,currentStepOfPublishingProcess:4,editedByType:null,kuFlag:!1,biosketch:"Dr. Phil. Maria Jose Hernandez Serrano is a tenured lecturer in the Department of Theory and History of Education at the University of Salamanca, where she currently teaches on Teacher Education. She graduated in Social Education (2000) and Psycho-Pedagogy (2003) at the University of Salamanca. Then, she obtained her European Ph.D. in Education and Training in Virtual Environments by research with the University of Manchester, UK (2009).",coeditorOneBiosketch:null,coeditorTwoBiosketch:null,coeditorThreeBiosketch:null,coeditorFourBiosketch:null,coeditorFiveBiosketch:null,editors:[{id:"187893",title:"Dr.",name:"María Jose",middleName:null,surname:"Hernandez-Serrano",slug:"maria-jose-hernandez-serrano",fullName:"María Jose Hernandez-Serrano",profilePictureURL:"https://mts.intechopen.com/storage/users/187893/images/system/187893.jpg",biography:"DPhil Maria Jose Hernandez Serrano is a tenured Lecturer in the Department of Theory and History of Education at the University of Salamanca (Spain), where she currently teaches on Teacher Education. She graduated in Social Education (2000) and Psycho-Pedagogy (2003) at the University of Salamanca. Then, she obtained her European Ph.D. on Education and Training in Virtual Environments by research with the University of Manchester, UK (2009). She obtained a Visiting Scholar Postdoctoral Grant (of the British Academy, UK) at the Oxford Internet Institute of the University of Oxford (2011) and was granted with a postdoctoral research (in 2021) at London Birbeck University.\n \nShe is author of more than 20 research papers, and more than 35 book chapters (H Index 10). She is interested in the study of the educational process and the analysis of cognitive and affective processes in the context of neuroeducation and neurotechnologies, along with the study of social contingencies affecting the educational institutions and requiring new skills for educators.\n\nHer publications are mainly of the educational process mediated by technologies and digital competences. Currently, her new research interests are: the transdisciplinary application of the brain-based research to the educational context and virtual environments, and the neuropedagogical implications of the technologies on the development of the brain in younger students. Also, she is interested in the promotion of creative and critical uses of digital technologies, the emerging uses of social media and transmedia, and the informal learning through technologies.\n\nShe is a member of several research Networks and Scientific Committees in international journals on Educational Technologies and Educommunication, and collaborates as a reviewer in several prestigious journals (see public profile in Publons).\n\nUntil March 2010 she was in charge of the Adult University of Salamanca, by coordinating teaching activities of more than a thousand adult students. She currently is, since 2014, the Secretary of the Department of Theory and History of Education. Since 2015 she collaborates with the Council Educational Program by training teachers and families in the translation of advances from educational neuroscience.",institutionString:"University of Salamanca",position:null,outsideEditionCount:0,totalCites:0,totalAuthoredChapters:"0",totalChapterViews:"0",totalEditedBooks:"0",institution:{name:"University of Salamanca",institutionURL:null,country:{name:"Spain"}}}],coeditorOne:null,coeditorTwo:null,coeditorThree:null,coeditorFour:null,coeditorFive:null,topics:[{id:"23",title:"Social Sciences",slug:"social-sciences"}],chapters:null,productType:{id:"1",title:"Edited Volume",chapterContentType:"chapter",authoredCaption:"Edited by"},personalPublishingAssistant:{id:"301331",firstName:"Mia",lastName:"Vulovic",middleName:null,title:"Mrs.",imageUrl:"https://mts.intechopen.com/storage/users/301331/images/8498_n.jpg",email:"mia.v@intechopen.com",biography:"As an Author Service Manager, my responsibilities include monitoring and facilitating all publishing activities for authors and editors. From chapter submission and review to approval and revision, copyediting and design, until final publication, I work closely with authors and editors to ensure a simple and easy publishing process. I maintain constant and effective communication with authors, editors and reviewers, which allows for a level of personal support that enables contributors to fully commit and concentrate on the chapters they are writing, editing, or reviewing. I assist authors in the preparation of their full chapter submissions and track important deadlines and ensure they are met. I help to coordinate internal processes such as linguistic review, and monitor the technical aspects of the process. As an ASM I am also involved in the acquisition of editors. 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Venkateswarlu",coverURL:"https://cdn.intechopen.com/books/images_new/371.jpg",editedByType:"Edited by",editors:[{id:"58592",title:"Dr.",name:"Arun",surname:"Shanker",slug:"arun-shanker",fullName:"Arun Shanker"}],productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"878",title:"Phytochemicals",subtitle:"A Global Perspective of Their Role in Nutrition and Health",isOpenForSubmission:!1,hash:"ec77671f63975ef2d16192897deb6835",slug:"phytochemicals-a-global-perspective-of-their-role-in-nutrition-and-health",bookSignature:"Venketeshwer Rao",coverURL:"https://cdn.intechopen.com/books/images_new/878.jpg",editedByType:"Edited by",editors:[{id:"82663",title:"Dr.",name:"Venketeshwer",surname:"Rao",slug:"venketeshwer-rao",fullName:"Venketeshwer Rao"}],productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}},{type:"book",id:"4816",title:"Face Recognition",subtitle:null,isOpenForSubmission:!1,hash:"146063b5359146b7718ea86bad47c8eb",slug:"face_recognition",bookSignature:"Kresimir Delac and Mislav Grgic",coverURL:"https://cdn.intechopen.com/books/images_new/4816.jpg",editedByType:"Edited by",editors:[{id:"528",title:"Dr.",name:"Kresimir",surname:"Delac",slug:"kresimir-delac",fullName:"Kresimir Delac"}],productType:{id:"1",chapterContentType:"chapter",authoredCaption:"Edited by"}}]},chapter:{item:{type:"chapter",id:"61873",title:"Food Safety Legislation in Some Developing Countries",doi:"10.5772/intechopen.75587",slug:"food-safety-legislation-in-some-developing-countries",body:'Food safety systems in developing countries are weak, fragmented, and not effective to protect consumer’s health or help countries competing for export markets. Improving food safety often costs much (or is associated with additional costs which could only be recouped by the items fetching more money) and many developed countries experience real challenge in making food safety legislations work. At least, this is the perception of majority of SMEs. Many years later after the unveiling of codex and ISO standards, these countries’ domestic markets suffer from sustained food safety-related issues ranging from food-borne illnesses to food fraud. In spite of this, a lot of stride has been made with regard to development or adoption of international standards; however, what remains to be seen is the full implementation and hence marked decrease in food safety-related incidences [1].
Food safety concept continues to gain attention particularly in developing countries. Many countries rely purely on small scale (subsistence) and street vendors to feed their populations. Yet, these traders are not usually included in the mainstream food safety systems. In flow of substandard and poor quality goods, corruption, low income, unjust trade, and political turmoil are ills deviling developing economies, and this adds to the challenge of food safety systems’ operation. Generally, few of the developed countries have formalized agriculture systems. To this extent, farm implements, fertilizers, seeds crop management practices, and manufacturing are scattered across vast geographical locations. Food insecurity, political instability, outbreaks of communicable diseases and natural disasters are challenges that compete for government attention; hence, food safety is often not prioritized. Yet, the definition of food security from the 1996 World Food Summit Plan of Action mentions access to sufficient, safe, nutritious and affordable food to all people at all times. Often, it seems that in developing countries, not enough emphasis is put on the safety aspect of food security [2].
According to published data by FAO and WHO, about 2000 food-borne-related deaths occur daily in Africa. Over 700,000 food-borne illnesses recorded annually are due to diarrheal-related illnesses and from contaminated food and water. Salmonella, Shigella flexneri, Shigella sonnei, Clostridium perfringens and other parasites are major culprits. An alarming average of 3.3–4.1 episodes of diarrheal diseases among children in Africa has also been recorded annually. Coupled with malaria, HIV, TB, these become more debilitating, creating a huge dent on the public health’s integrity. Food-borne illnesses lead to reduced productivity, disability, early deaths, low incomes and hence low access to food and the problem becomes cyclic. Illegal use of food additives, (E110, E102, E104, and E124) in local and imported foodstuff including infant foods, is an alarming case. Unless an approach that understands the unique challenges of developing economies are employed, the great food safety legislations may remain in revered books of codex without having a real impact on food safety situation in the developing world [2].
First, developing countries bear the greatest global burden of food-borne illnesses and death. The strain this adds to an already stretched public health services is huge. Second, regional and international trade is becoming extremely invaluable. For this reason, more sensitivity to food safety is needed. Benefits of safe, adequate, and nutritious food abound. It is crucial to long-term economic growth, good health, and productivity. It is also associated with a happier population that would enjoy reduced conflict. Countries in Africa and the rest of the developing world have some form of legislation regarding food safety. Some of this, however, are most rudimentary, archaic and at times not based on sound science. For these legislations to benefit the rest of the countries, there must be a push to align them to World Trade Organization (WTO)’s agreement on the application of Sanitary and Phytosanitary (SPS) and Technical Barriers to Trade (TBT) agreements and the Codex standards and codes of practice. Some of the standards are not science-based as required by Codex in a bid to help facilitate regional and international trade among different countries. This then curtails international trade and sometimes creating a bad notion of standards among processors. Several factors hamper the push to realize the implementation of food safety legislations in the countries such as inadequate technical capacity, lack of awareness of economic loss arising from poor quality foods, and weak enforcement of regulations among others [1]. The unveiling of the ISO allowed for HACCP to be upgraded through the International Standard ISO22000:2005 (Food Safety Management Systems—Requirements for any organization in the food chain). The ISO technical committee on food safety created in 1947 is one of ISO’s oldest and most fruitful committees, with over 830 published regulations and 125 more in the pipeline. ISO standards have played a crucial role in promoting global standards, development of harmonization and awareness creation. In many developing countries, ISO 22000:2005 is not a mandatory food safety requirement and perhaps due to its complexity, cost of compliance or technicalities, only few companies that most of the times have qualified food safety experts manage to get the certification.
Africa has been reported to enjoy over 5% annual economic growth in the recent decade, and this growth rate is predicted to continue or even improve in the next couple of years. For African countries, opulence and affluence among her populace is creating a reason for demand of high quality safe and mostly longer lasting products [2]. This can also be said accurately of the rest of the developing economies especially in Asia as well as South America. The Sanitary and Phytosanitary (SPS), World Trade Organization (WTO)’s—Technical Barriers to Trade (TBT) agreements are some of the regulations that require attention of all countries involved in any trans-border trade particularly of agricultural produce. The developing economies are huge exporters of raw or semi-processed agricultural goods, and these put them directly under the requirements of these legislations. Though there exists food safety standards in almost every country in one form or the other, these standards do not adequately help to improve food safety because of two main reasons. First, imports even of poor quality foods are not curtailed sometimes due to laxity, incapacity, or corruption. Some of the regulations are far stricter even beyond the codex requirements this more often than not hinders trade especially inter-regional trade. Second, there is very low level of implementation of regulations across board. This is why the regularization of laws and their harmonization should come into play. There are few global organizations that are at the forefront and with the expertise and neutrality to help countries navigate this concept of global standards harmonization. One such initiative is the Global Harmonization Initiative (GHI). More about the structure strategies and aims of the GHI and other such bodies are discussed in a later subheading.
In general, it can be surmised that there are three major models adopted by countries in national food control systems: the single agency model relies on one organization or umbrella body which is mandated with all the functions of controlling food safety. This model has the advantage that food safety issues are accorded priority, and they can be highly effective. The second model implies multiple agency scenarios. In this case, the role of food safety is sector and commodity-specific. In this system, the roles could also be devolved to federal, local governments or counties and the national level. Some challenges with this model are: duplicity of functions, conflicts, and differing expertise at national and at the regional level, reduced domestic consumer confidence and confusion among stakeholders as to which laws to comply with. The third model is an integrated system: in this system, agencies are assigned jurisdiction based on aspects of food safety which cut across all the sectors such as policy development, coordination, inspection, education, and training. Irrespective of the model that best suits a country, it must be based on the principles of transparency, inclusiveness, integrity; clarity of roles, accountability, science/risk-based approach and equivalence as the benchmarks against which its success is measured [3].
This gives the general direction and thrust to the food industry in a country and defines the collective vision for all the actors in the food chain in a country. The presence of a Food Safety policy (FSP) is critical to coordinated function of all the organizations charged with the responsibility to deliver food safety. It is in this document that governments must state and demonstrate food safety and its relation to economic and public health. The case studies of the developing countries here demonstrate at least governments’ understanding and commitment to setting up a food safety and nutrition policy.
Once a food safety policy is in place and adopted, this gives room for appropriate accompanying legislation. The legislation must be updated, based on science; give spell out clearly the roles and obligations of each concerned organization, and above all be enforced. For many developing countries, the full enforcement is a missing ingredient. For food safety legislations to succeed, they must cover all components of the food supply chain. Often in Africa, and the rest of the developing countries, food safety legislations leave out the informal sector which is a major contributor to food value chain and hence any accompanying ills.
There is great variety of indigenous foods in the developing world. Many countries do not have standards that govern preparation and trade of these indigenous foods. Effort is put currently through Codex Alimentarius Commission’s (CAC) Working Groups to change this. This move should be encouraged and many countries ought to bring on the table several of their native foods. However, the standards development process must be supported by scientific data on nutritional and safety aspects of food which is a gap that needs to be filled. In addition, the standards development must be responsive and internationally oriented and the body responsible be accorded a clear mandate.
Legislation and standards that serve the intended purposes in guaranteeing food safety and cross border trade must be science-based. WHO and FAO had earlier, in 1992, stated that risk analysis must be the basis of any food safety framework [12], but in developing countries, lack of expertise, low investment in the requisite infrastructure, and difficulty in collecting own toxicological data is a hindrance to RA. This challenge is a huge one and requires collaborative and innovative efforts from all stakeholders. Toxicological exposure data in many developing countries is very scanty, inaccurate, and usually not timely. To help developing countries to conduct risk assessment, FAO/WHO studies is a great place to start but unless these are closely related to the country’s specific needs, priority may differ from those of FAO and WHO and depending on FAO/WHO’s focus data may take long to finally capture the aspirations of specific countries.
Food quality inspections demonstrate or validate the success or failure of food safety legislations. Legislations that are not enforced are not beneficial at all. This is a major setback in all the aspects of the developing countries. Many factors contribute to this; including low status often awarded to food safety officers, inadequate logistical support, and cumulative tasks required of them hence intermittent attention to the task of inspection. Inadequate geographical coverage in all areas of the country by inspectors of food legislations and neglect of rural community means that their food safety concerns often go unaddressed.
Inspections, and other aspects of food safety monitoring, depend largely on validation, and this is partly conducted by testing of samples to ensure enforcement of legislation. Rapid laboratory testing is also critical to implementation of food-borne illness’ outbreak surveillance. In many cases, laboratory facilities in developing economies whether in Asia or Africa are old, poorly equipped and with either very few personnel or with low competency.
Capacity to implement food safety legislations is a major determiner of success or failure of a food safety management system at the country level. Inadequate capacity is a bottleneck that cuts across many areas. This may be due to lack of competent personnel, lack of funding or poor logistical support to carry out the different aspects dealing in food safety.
Food safety legislation requires regular, planned ongoing training, and upgrading of knowledge for food control officers, law enforcers, consumers and all stakeholders. Many factors regarding food safety change from time to time. This may include status of chemicals for use as food additives, and even specifications like microbial criteria or tolerable daily intakes. Competent, updated and, a responsive team is required to harness these developments for the purposes of making food safety legislations work.
One of the key hurdles to success of food safety legislations is dealing with unreported cases, of illnesses and deaths that arise from food-related illnesses. There must be a link and a close one at that between the food safety enforcing bodies, and the public health departments. Not just that countries must strive to strengthen the epidemiological data collection tools, but also the consumers ought to be well informed about the procedures and benefits of reporting every case even to including suspected cases.
Membership to CAC is voluntary as well as adoption of its standards. It focuses on ensuring consumer safety and promotion of trade. The CAC’s legislation should only be a bare minimum and since they are based on science, they avail the platform that supports countries to provide safe and nutritious foods to their domestic as well as for international market. On this score over 50 African countries are members of CAC and this puts them at a platform to engage on food safety legislation [4].
So far, there are a number of factors that make it difficult for the food safety legislation to work “perfectly” in the developing countries. One of these reasons is minimal application of HACCP to food processing industry and particularly because its implementation is not a mandatory requirement. On the other hand, multinationals and some special food value chains, particularly the export-oriented ones, have adopted HACCP or even stricter systems as has been demanded by their customers in these markets. Of course, this varies across countries with South Africa leading other African countries in embracing third party certification of food companies. Developing countries must be made to understand and appreciate the fact that food safety management systems that work, provide more benefits to the citizenry and is better for the economy. These facts, however, may never have been so clearly stated and understood by those responsible for food safety legislation, implementation, and monitoring [2].
Most developing countries at least host multinational companies that are crucial and that serve a niche market. This includes the likes of Coca Cola, Unilever, Mars Incorporated, and Wrigley’s among others. These are companies whose food safety management systems are extremely strict. In most cases, they are more focused on the use of their internal standards and auditing techniques than they do rely on the inspections mounted by governments. They have systems replete with a robust backup and huge capacity in terms of laboratories, personnel and necessary logistics. Unfortunately, in the developing countries, these lie and operate side by side with the uncoordinated; unregulated street food supply chain that indeed are greater sources of food especially for the urban, poor and middle class dwellers. The existence of the two tier-food safety operations in the developing economies: the multinationals and the local startups, is a phenomenon that must be harnessed as a learning point to enable food safety be addressed to all who are affected by it.
Ghana’s food production system is dominated by informal—very intricate-small- and medium-sized enterprises (SMEs). Hazard Analysis and Critical Control Point (HACCP) systems are not applied by SMEs and occasionally by the large food processors in a reactionary manner, that is, in response to a food safety threatening incident or at the behest of consumers in foreign markets. Most of the local foods and brews are not necessarily included in the standards in Ghana, and this leaves a gap in which food safety programmes cannot be implemented yet these foods contribute massively to the quantity and nutritional intake of the population. These neglected food supply chains could easily be the source of food-borne illnesses and even death. Essentially, there is low literacy that people who are sensitive about food safety are seen to be doing so out of their affluence or to belong to a different class than everybody else. Compared to other challenges like lack of electricity, roads, and food insecurity due to inadequate supplies, food safety is not a priority to most developing countries. This may be the reason why inadequate funding is put toward this endeavor.
This lack of priority means many food supply chains for the majority of the rural areas and town dwellers are not regulated, and to compound this further, traceability mechanisms are almost nonexistent. However, for a few commodities traded formally and internationally, reasonable food safety parameters and legislations are in place. These commodities include; cereals, fruits, vegetables, oil seed, cocoa, and shea nuts. Ghana Food Safety Authority is faced with an inadequate food testing capacity quagmire. This is in reference to equipment, personnel, and the location of the main government laboratory in Accra, serving the whole country [5].
The various Ministries Departments and Agencies have been set up drawing form various legislations. There is, however, a need to have these standards revised and aligned to modern food regulations. Ghana Standards Boards’ mandate is to establish and promulgate standards. It also promotes standardization in industry and commerce thus promoting industrial efficiency. Further, it promotes welfare, health and safety for consumers. In addition, it runs the certification scheme, inspection of food safety operations and metrology. Government of Ghana has several ministries involved in food safety legislation; with the ministry of Environment and Science, Trade and Industry, Ministry of Health, and Ministry of Food and Agriculture taking the leading roles. In the Ghanaian system standards setting formulation/drafting and advice is divorced from the bodies involved in control and enforcement of legislation. There is also separation of risk analysis and advice from the bodies mandated with management and operationalization of the food safety system. However, Ghana has also taken an important step in drafting the National Food Safety Action Plan (NFSAP) to restructure food safety, agriculture, and health institutions to improve efficiency and governance. Such a move allows for a coordinated effort among Ministries, Departments and Agencies, allowing for smooth operations, avoiding duplication of duties, eliminating conflicts and encouraging better enforcement of food safety legislation [5].
Food safety in Nigeria is undermined by inadequate application of Good Agricultural Practices (GAP), abuse of agrochemicals, use of pesticides for fishing, misuse of pesticides for stored grains, chemical contaminants like lead poisoning, and abuse of additives (butylated hydroxyl anisole, nitrates/nitrites). Other challenges include use of toxic packaging material with degradable components, public ignorance, uncoordinated approach and lack of technical expertise, including poor laboratory facilities. On top of this, there is inadequate enforcement of the available legislations. At the same time, food-threatening droughts force inclusion of contaminated food in to the value chain.
The legal framework mirrors that of Ghana with major components being: legislation, policy, institutionalization (institutional framework), inspection, and laboratory testing services. National food safety policy was established in 1999. The establishment of the food safety policy in Nigeria set the country on a path toward well-coordinated food safety legislation. It recognizes the roles of the public sector and that of private sector in addressing challenges of food safety in a multisectoral model [6].
The country boasts of numerous food-related legislations. The laws focus on consumer protection, proper coordination, development of relevant policy, and priority setting in enforcing food legislation. It advocates HACCP as the basis to all food production and processing operations. The other organizations in Nigeria, charged with food safety include the Ministry of Health, National Agency for Food and Drug Administration and Control, the Standards Organization of Nigeria, Ministry of Agriculture and Research and Development and Fisheries, Plant Quarantine Service, the Consumer Protection Council, Federal Ministry of Environment and, Federal Ministry of Trade and Industry. It also recognizes the role of university, research, and local governments in creating awareness and training of personnel for most food safety focused agencies. The key factors to successful food legislation in Nigeria are increased public awareness and customer education about the dangers of neglect of food safety. There should also be better coordination among the bodies charged with responsibilities for food safety. Lastly, capacity building by training of personnel, producers and regulators is vital toward achieving success in implementation of food safety legislation. The SMEs should be urged to form associations for ease of government support in terms of training and awareness creation [6].
Kenya has over 22 Food safety-related legislations under different Departments and Agencies. Kenya became a member of the Codex Alimentarius Commission in 1969. It has since played some crucial functions in various Codex committees and is currently chairing the CCAFRICA region. It has also adopted more than 100 Codex standards. Kenya has developed a National Food and Nutrition Security Policy. Food Safety is a key pillar of the policy document and it can be found under the subtopic of “Food Safety, Standards and Quality Control.” The proposed National Food Safety Authority will be an innovative platform. Chiefly it will be mandated to conduct risk assessment, an area that has been grossly underrepresented in Kenya and the rest of the developing economies. It is also expected to promote human health and ensure better coordination among all the multiple-stakeholders in food safety. The Kenya’s food safety management model is integrated with several bodies across different sectors mandated to ensure safety quality and promotion of trade for specific products in some cases [7]. Kenya is an integral member of the East African Community (EAC). The East African Community has been keen to harmonize several commodity standards with a total of 42 standards recorded as having been harmonized. The thrust has been to facilitate trade and remove barriers allowing for faster movement of goods across borders and thus reducing food losses. Most of these achievements have been through the Working Groups on various commodities. Despite the efforts directed to securing food safety in Kenya, foodborne illnesses, and outbreaks, fraud, and other ills are still reported with regularity [7].
Having looked at some cases of developing countries in Africa, the focus shifts to understanding the food safety scenarios of developing countries in Asia. Two countries that are an important part of the Asian continent, Nepal and India are presented in a bit of depth. Developing countries in Asia have definitely unique food safety scenarios. Nepal, for example, became a member of WTO in the 2004, and hence food safety has acquired a reasonable interest. The most important challenges are as follows:
Poor food safety regulation and enforcement infrastructure
Inadequate technical and regulatory, assessment of conformity
Inspections are difficult as the food producers, processors, traders and retailers are in large numbers and scattered across the country.
Nepal is a member of CAC, WTO, FAO, and South Asian Association for regional cooperation (SAARC). It is also a member of the World Organization for Animal Health (OIE) and Bay of Bengal Initiative for Multi-sectoral Technical and Economic Cooperation (BIMSTEC). The country drafted its first food legislation in 1966. This piece of legislation was called the Food Act. The Food Act spelled out the basis for control of inspection of food premises, destruction of nonconforming products and ensuring safety and quality of imported foods. This was then followed by the Plant Protection Act of 1972 and Animal Health and Livestock Services Act of 1998. The upsurge in international trade and economic liberations in Nepal in the 1990s made food safety a priority as it became critical for acceptance of products traded internationally. Initially, the focus of food safety strategies was toward end product testing. Increasingly though, the knowledge of HACCP and other important food safety systems has resulted in the focus moving to the “farm to fork” continuum. Food safety legislation is increasingly based on HACCP principles even though this is not mandatory yet. Owing to the fact that the country does not have a traceability component, effecting recalls, understanding sources of food contamination, and hence mitigation in times of food-borne outbreaks becomes very cumbersome and may take too long [8].
The Food safety and quality management system in Nepal is under the Ministry of Agriculture and Cooperatives. This it done through the Department of Food Technology and Quality, which is focused on safety and quality of food in the market and ready to eat food. While the Department of Livestock and that of Agriculture are charged mostly with handling safety at primary production of food. The Nepal Council for Standards and the Nepal Bureau of Standards and Metrology are charged with standards development and implementation in Nepal. They are the standards governing body and custodians. Nepal Council for Standards (NCS) is mandated to approve all Nepalese standards while the Nepal Bureau of Standards and Metrology (NBSM) functions as the secretariat that prepares the standards. NBSM has developed and adopted more than 100 standards related to food. Through the South Asian Regional Standards Organization (SARSO), the country is also actively involved in development of regional standards. The Food Standards Board (FSB), advices government on standards and principles and also ensures that they are aligned to international standards. [8].
The food safety and quality management systems in India are under the mandate of the Food Safety and Standards Authority of India (FSSAI). There exists an increased demand for safe, high-quality food and greater choices among the Indian consumers. Food safety incidences like the 2015-withdrawal of Maggi noodles and the governments’ surveillance of food-related illnesses contribute to create awareness on food safety among Indian consumers. Still, over the years, many food-borne illnesses are unreported and foodborne out brakes are erratically reported. In 2006, about 13.2% of households reported food-borne illness. Food Safety Standards Act (FSTA) of 2006 was designed to improve the overall safety of consumers and aid advancement in international trade. Food Safety Standards Authority of India (FSSAI) is wholly responsible for food safety matters. However, even after a decade of transitioning, there are still overlaps of legislations between the Bureau of Indian Standards and FSSAI especially with regard to milk. The same case is observed in fruits and vegetables as both the FSSAI and Agricultural Marketing Standards apply yet both are based on CAC standards. These incidences confuse consumers and make it difficult for producers to distinguish whether the regulations are mandatory or not. Finally, there also exist state-level legislations that require compliance, and this sometimes complicates the intra-state trade [9].
There is a need to improve capacity to enable effective inspection and monitoring of food safety conditions in India. Prosecution and administration of food laws require to be devolved at the state level but currently lies at national level and therefore far flung areas are hardly reached. The country needs to improve laboratory access that currently is deficient and efforts should be made to improve on the number of specialists in the food safety related fields. The main focus in India’s food safety management system is on upgrading laboratories and collaboration between the AGMARK and the FSSAI labs and the sharing of data. This way, only failed samples should be passed on to the national reference laboratory. The universities and FFSAI need to train and employ food safety experts. There is a need to increase awareness of all stakeholders especially on updated regulations. There must be increased emphasis on training of food handlers especially among the informal and small-scale food processors and producers. Currently, awareness is disproportionate among the rural consumers, and yet, these consumers like everyone else deserve good quality food. Use of mass media campaigns to target rural consumers will improve their awareness. Lastly, it is crucial to remove overlap in responsibilities of the organizations and assign clear mandates and modes of collaboration must be agreed [9].
GHI was launched in 2004 by the International Division of IFT and the European Federation of Food Science and Technology (EFFoST) in collaboration with Food Safety Magazine and Elsevier Science. GHI officially achieved the status of a nonprofit, charitable association in 2007 and is registered in Vienna, Austria. GHI aims to harmonize food safety legislations and regulations based on solid science as datum for building consensus. GHI identifies issues presented with justification and evidence, then prioritizes them depending on the availability of experts as Working Groups (WGs) who then evaluate evidence provided to address the specific issue at hand [10]. Making food safety work in the developing countries requires a knowledgeable population. More often than not, the masses are easy to persuade and sometimes fall prey to misleading reports on food safety. Sometimes, politicians are culprits who twist food safety issues for political gain even when the claims are not scientifically sound. A case in point was the anti-GMO crusades conducted in Kenya in 2014–2015 leading up to the government’s ban on production and trade of GMOs. GHI in its approach to promotion of harmonization of food laws is addressing serious issues that could be exploited to make food safety work in developing countries. These are discussed below.
The organization believes that meaningful consensus building regarding food safety legislations and regulations can only be achieved if stakeholders have the same understanding of the working definitions of terms used in the area of food science and technology. This is often taken for granted, yet GHI experts prove that even among English-speaking nations like the UK and the USA, some terms used can markedly differ in their meaning. Take the definition of food additives for example, this is markedly different between Canada, US, EU and Japan. GHI has a Working Group Nomenclature on Food Safety and Quality, which had started with harmonization of Russian and English legislations particularly with regard to definitions of terms used in food safety and quality. Such a common definition will lead to a better understanding among food safety experts and enhance consensus building among the developing countries as well with the promise of better implementation of food safety legislation and regulations [11].
The GHI Working Group on Education’s aims to develop a curriculum for educating the public and all stakeholders in the food value chain is very timely. The curriculum is targeting food handlers and also everybody else in the food value chain. The WG aims to create training tools and materials written in simple understandable language and including use of pictorials targeting those who are not able to read. In addressing the knowledge gap, GHI works to ensure that certain key messages in food safety need to be presented in the local languages and in a manner that is understood to the media, political class, and consumers. GHI is of the opinion that food safety legislations and regulations are often written in a manner and a language that is difficult to understand even for trained professionals. Regulations must be “translated” into understandable language, so that people affected can appreciate them.
GHI’s impartiality can be harnessed to help promote consensus on standards and eradicate possible barriers and destruction of an otherwise safe food due to different countries’ legislation. Evidently, it is not for lack of consensus among scientists that differences in food safety legislation occur but rather in the language and communication of the science to various stakeholders. To improve this, building of capacity in terms of personnel, data management, and risk assessment is critical. Most regulations, however, should be the same in all countries; differences may only be needed because of specific eating patterns or genetic issues, like in Japan and Finland where a large part of the population has no beta-galactosidase and therefore cannot digest lactose, which makes too high concentrations of cow’s milk in food products toxic for such people. GHI wants to harmonize the regulations so that trade barriers are removed and food is not destroyed at the border just because the regulations between countries differ [10, 11].
The GHI is developing a Global Incident Alert Network for unauthorized food additives. In such a case, whenever it is found that an illegal (unauthorized) substance that can harm consumers is added to food, in any part the world, the individual who discovered that is tasked with the role of alerting a dedicated committee who will then have the means and the protocol to verify the issue within a short period of time and communicate the same to the relevant authorities who should then take the necessary actions to correct the situation. If necessary, this may be done anonymously, avoiding represailles by the employer. Such an initiative can also help developing economies and enhance transparency and adherence to food safety rules and regulations [11].
Codex Alimentarius Commission (CAC) is an intergovernmental body that is involved in development of food safety standards and is officially recognized by WTO as the arbitrator in conflicts involving food safety legislation between countries or companies at the international level [12]. Though CAC has done a great deal in this regard, it has faced a few challenges that derail its efforts in harmonizing food safety regulations. First, it meets annually and this means the matters agreed at such meetings do not receive speedy progress. Second, the participants to these committees are not always food technologist with grounding on food safety; furthermore, they may strive to secure the interest of the countries they represent as a priority. The African Union (AU) has formed expert committees that mirror those of Codex. These food safety experts’ committees now can offer thoughts considered as Africa’s position on food safety matters. This is a key development as it offers a focal point of responding and dissemination of information. The AU is also fronting the formation of the African Food Safety Authority that will set standards for monitoring Africa’s food supply chain, an equivalent of the European Food Safety Authority (EFSA). There must be a good political will for food safety legislations to work in the developing economies and this initiative being spearheaded by the political arm of AU may just be the right recipe for stimulating local action [2, 11].
The first strategy is the implementation of the rapid alert and response system: that was proposed by GHI in 2014. This system if operationalized can lead to information sharing across the countries. Sharing strategic information could easily save lives by stopping potential food-borne outbreaks before it happens or at least at a very early stage. Analysis of some of the major incidents involving food-borne illnesses in the world indicate that a majority of them would have been prevented had there been a proper reporting channel from those who were involved but who did not talk due to fear of reprisals and possible loss of jobs [11]. Operationalization of such an alert would enthuse consumer confidence leading to increase the economic development. Such a move would stimulate demand for high quality products that puts the whole food safety management system of the developing countries on a higher trajectory. Easier reporting channels, operationalization of help lines, including mobile apps that consumers and small-scale processors can reach to seek help and meet with experts in food safety can provide huge impact.
The second aspect that needs quick redress is regional risk assessment. Due to the nature of funding and capacity required to make this happen, countries and institutional collaborations in this area will help developing countries to not only cost-share requisite infrastructure, but also the ensuing data that may be similar in a number of cases. Such an undertaking will help countries avoid duplication of efforts, reduce unnecessary spending on infrastructure, and enhance better collaboration on matters of risk analysis data among neighboring countries.
Third, knowledge and training of populations on the food safety basics is the most important aspect in making food safety work best in developing economies. Food technologist and the food technology organizations including those adhering to the IUFoST ought to play a bigger role in pushing food safety agenda and particularly in the area of training and education. Both IUFoST and GHI have a training component (the universal food safety curriculum) that is envisaged to greatly improve consumer and other stakeholders’ confidence to play their role of keeping processors and vendors in check with regard to food safety. Creation of awareness to consumers about their rights and privileges confers them confidence and empowers them to keep the food industry and government on toes to deliver on their food safety mandate. All food processors and street vendors, regardless of their remote location and “small” service, must be encouraged to register into clusters of 50–100 or even smaller groups through which expert knowledge on basic hygiene and safe food handling practices can be passed on to them.
Fourth, every single cottage industry that is set up must be made comfortable to realize that the food safety legislations are actually for their good and not meant to keep them away from business. This requires a better working relationship between law enforcing bodies and these food startups. The focus for these legislating bodies should be to midwife these businesses first to profitability through functioning food safety systems, rather than focus on levies when the factories can hardly break even.
Fifth, massive and urgent educational input is required in the area of abuse of additives, or fraud in using chemicals like calcium carbide as an artificial ripening agent in fruits and vegetables by unscrupulous traders in countries like India, and some places in Kenya [13]. Or even the use of formalin in meat preservation, or large doses of sodium metabisulphite in meat preservation to mention a few. The use of these and other cancer causing chemicals must be addressed to consumers and processors and their relation to cancer or the ensuing impact of that, on households and public health explained. It is very critical to make sure that people are made aware of the dangers of the use of such chemicals and their abuse. However, the education must be complete by making consumers understand the relationship between dose, exposure and the possibility of dangers particularly on additives. This way alarmistic remarks that cause panic resulting in loss of what would essentially be good food, will be avoided [11].
Lastly, laboratory facilities are key pillars to ensuring food safety in developing countries. However, they require huge initial investments, high running costs, and very well-trained personnel who are equally expensive to sustain. Developing countries should be encouraged to consider setting up regional centers of analysis, intra-country laboratories, shared regional analytical capacity, and even regional training. This suggestion when implemented will greatly lower the costs and improve access to laboratory analytical facilities. The collaborating countries can also realize a state-of-the-art facility thus enabling quick in-depth analysis that is very important in case of mounting surveillance or diagnostics in cases of disease outbreaks. The private sector involvement and support in availing laboratory analysis and facilities should also be considered seriously as a means to bridging the gap.
Education is key area that must be addressed to provide capacity. Safety consciousness as a culture along the entire value chain is key.Food Biosecurity or Defense is increasingly becoming important, yet most developing countries are yet to begin to put policy mechanisms or laws that govern their food value chains and protect it from fresh threats like bio-insecurity or even bioterrorism. This also goes to developing countries’ capacity in responding to biosafety concerns and accompanying legislation. It is high time developing countries begin to deal with the concepts of GMOs based on evidence and perhaps exploit this area that may lead to sufficient foods, thus eliminating the need to allow unsafe foods to enter the value chains due to food insufficiency [11]. Even though the countries have differing opinions on GMOs, the inadequate capacity to test for transgenics in developing economies makes it twice critical that some form of harmonized response based on evaluated and impartial evidence, be reached to facilitate transboundary movement of GMOs.
This chapter has focused on the unique challenges to food safety legislation in some developing economies and the innovative ways in which the stake holders should approach the subject and make it more effective. It has also presented case studies of food safety situations in some developing countries: Asia (India and Nepal), West Africa (Ghana and Nigeria) and East Africa. Finally, it proposes major innovations that could be put into play to make food safety legislation work more effectively in the developing economies.
The authors sincerely wish to thank Professor Huub Lelieveld for his insights into the role of GHI. In addition, we wish to pass our gratitude to Beena Sharma for providing invaluable input into the food industry situation in Nepal and to Vishu Savanth for the help with data regarding food safety situation in India.
The authors have no conflicts of interest in addressing this topic.
Modern computers and electronics, such as smartphones and supercomputers, have been developed in accordance with Moore’s law [1], which implies improvement in cost, speed, and power consumption by scaling down devices. However, the fundamental physical limits and increased fabrication costs pose a hindrance to sustainable development of computing technology [2, 3]. Moreover, with the advent of the big data era, unstructured data and data complexity explosively increases, imposing constraints on the conventional computing technology owing to the von Neumann bottleneck [4, 5]. Neuromorphic systems [6, 7], which mimic the nervous system in the brain, have recently become known as strong candidates to overcome these technical and economic limitations owing to their proficiency in cognitive and data-intensive tasks, together with their low power consumption. To successfully implement these neuromorphic systems, it is of utmost importance to research and develop artificial synapses capable of synapse functions, high reliability, low energy consumption, etc. [8, 9]. In the plethora of possible devices, memristors have gained the spotlight because of their desirable characteristics as artificial synapses [10, 11, 12], including device speed [13], footprint [14], low energy consumption [15], and analog switching [16, 17].
In this chapter, we introduce the basic concepts of neuromorphic systems and memristor synapses. We also describe diverse examples for state-of-the-art artificial synapses in terms of novel functional materials and device architecture. We then briefly review the implemented neuromorphic systems based on memristor synapses.
Conventional computing architecture, that is, von Neumann architecture, forms the groundwork for modern computing technologies [3, 18]. Despite tremendous growth in computing performance, classical architecture currently suffers from the von Neumann bottleneck, which results from data movements between the processor and the memory unit [4, 5]. The memory wall issue, causing high power consumption and low speed, hinders the continuous development of computing technologies [4, 5, 9]. Moreover, artificial neural network (ANN) algorithms, such as deep learning [19], deal with image classification [20, 21], sound recognition [22, 23], specific complex tasks (e.g., the AlphaGo [24]) and so on. Although the ANN algorithms have exhibited superior performance over the conventional computing technologies, they are, at present, constructed on the von Neumann architecture; hence, considerable time and energy resources are required for their operation [8, 9]. Neuromorphic architecture [6, 7], a bio-inspired computing architecture, is one of the most promising candidates to resolve these problems. The neuromorphic systems take advantage of the cerebral nervous system, which consists of a massive parallel connectivity between the neurons (i.e., processor) and the synapses (i.e., memory), indicating the absence of the von Neumann bottleneck [8, 9]. Figure 1 shows the shift of the computing architecture from von Neumann architecture (Figure 1a) to neuromorphic architecture (Figure 1b). The von Neumann architecture shows that the processor and memory are separate, leading to the von Neumann bottleneck. In contrast, in the case of neuromorphic architecture, the neurons and synapses are combined, alleviating the bottleneck issue. The neurons are uncomplicated computing units, the synapses are local memory units, and the communication channels (red line) connect numerous neurons and synapses. It should be noted that the practical purpose of neuromorphic systems is not to replace the von Neumann architecture completely, but to supplement the conventional architecture to make up its leeway, especially for intelligent tasks such as image recognition and natural language processing.
(a) Conventional computing architecture (von Neumann architecture). Data transfer is performed through the bus (memory wall). (b) Neuromorphic architecture. In contrast to von Neumann architecture, von Neumann bottleneck does not exist.
Memristors that consist of a storage layer inserted between the top and bottom electrodes can undergo dynamic reconfiguration within the storage layer with the application of electrical stimuli, resulting in resistance modulation referred to as memory effect [16, 17]. The changed resistance state can be retained even after electrical inputs are removed, and memristors are based on the history of applied electrical stimuli. These capabilities lead to analog switching, which resembles biological synapses where the strength (or synaptic weight) can increase or decrease depending on the applied action potential [25, 26]. When neuromorphic architecture is implemented on the conventional computing architecture, the synaptic weights are stored in the memory unit and are continuously read into the processor unit to transfer information to post-neurons. In other words, practically, the von Neumann bottleneck still remains challenged. However, in case of memristor synapse-based neuromorphic systems, the synapses can not only store a specific weight but also naturally transmit information into post-neurons, overcoming the von Neumann bottleneck and improving system efficiency [8, 9]. In addition to analog switching, memristors have exhibited desirable device properties, including nanoscale footprint [14], long endurance and retention [17, 27], nanosecond switching speed [13, 15], and low power consumption [15]. Owing to these characteristics, memristors have emerged as promising candidates for artificial synapses. However, it should be noted that no specific material/device system has shown all-encompassed characteristics so far.
Depending on their storage layer and electrode, memristors can be broadly classified into two categories: cation-based devices and anion-based devices. It is widely believed that cation-based devices are based on migration of metallic cations (see Figure 2a) [17, 28]. They employ electrochemically active materials such as Ag or Cu as an electrode [29, 30, 31, 32]. The counter electrode is usually an electrochemically inert material, such as Pt, Au, or W, and the storage layer consists of a solid-electrolyte like Ta2O5, SiO2, or Cu2S. For example, when a positive voltage is applied to an Ag top electrode, the atoms from this electrode are electrochemically oxidized to Ag+ cations because of anodic reaction, which are then dissolved into a solid-electrolyte layer. The Ag+ cations migrate across the solid-electrolyte layer toward the counter electrode (e.g., Pt) depending on electric field. At the Pt electrode, the Ag+ cations are electrochemically reduced to Ag atoms because of cathodic reaction and are deposited on its surface. Thus, conductive filaments grow toward the Ag top electrode, and eventually the filaments bridge the anode and the cathode, indicating that the device switches into ON state (low resistance state) as shown in Figure 2a. In contrast, when a negative voltage is applied to the Ag top electrode, the Ag filament begins to dissolve anodically, starting from the interface of the Ag top electrode/Ag filament, which results in OFF state (high resistance state). Owing to this process, cation-based devices are referred to as electrochemical metallization memories and conductive bridging random access memories. It should be noted that the initial formation of conductive filaments is called the electroforming process, which needs a voltage higher than a switching voltage.
(a) Cation-based devices: Through electrochemical reaction, metal cations M+ migrate toward the counter electrode and form conductive filaments between the top and bottom electrodes. (b) Anion-based devices: During electroforming, the soft-breakdown leads to O2− ions (oxygen vacancies V), and the oxygen vacancies form conductive filaments between the top and bottom electrodes.
Anion-based devices usually require the initial electroforming process and are switched depending on the O2− anions (or positively charged oxygen vacancy V) induced into the storage layer by soft-breakdown (see Figure 2b). These devices consist of a sub-stoichiometric storage layer made of HfOx [33, 34], TaOx [35, 36], WOx [37, 38], etc. When a positive forming voltage is applied to the top electrode, the induced O2− ions migrate toward it. This anion motion causes a change in the valence state of the cation to keep the charge neutral; hence, these devices are also referred to as valance change memories. Throughout the process, the oxygen vacancies continue to form conductive filaments in the storage layer. When the filaments bridge the top and bottom electrodes, current flows through the filaments, with the result that the device switches to ON state. Contrastingly, when a negative voltage is applied to the top electrode, the O2− ions either recombine with oxygen vacancies present in the filaments or oxidize the cation precipitates, with the result that the device switches to OFF state. Thus, memristors could be understood to some extent based on cation- and anion-based mechanisms. However, identifying the precise mechanism of a specific device is a challenge because of the presence of mingled mechanisms and different driving forces or locations. Therefore, further studies are necessary for a deeper understanding of the switching mechanism.
Various properties of memristor synapses that affect the performance of neuromorphic computing need to be discussed in detail. Among them, representative characteristics such as the linearity in weight update, multilevel states, dynamic range (ON/OFF ratio), variation, retention, endurance, and footprint will be addressed in this section as they can substantially affect computing achievements [8, 35]. The linearity of the weight update indicates the linear relationship between synaptic weight change (∆w) and programming pulse. In other words, the conductance of the memristor synapse changes linearly in accordance with the number of programming pulses, which is associated with the mapping of weight in the algorithms for conductance in memristor synapses. Hence, the linearity of weight update affects the performance (e.g., accuracy). Notably, most memristor synapses show a nonlinear weight update, where the conductance change gradually saturates, as shown in Figure 3. Hence, the nonlinearity of weight update should be improved to achieve highly efficient computing.
(a, b) Nonlinearity of weight update. Current abruptly changes in initial pulses and gradually saturates. Most memristors exhibit a nonlinear relationship. All figures are reproduced with permission from Ref [39, 10], respectively. Copyright (2017, 2010) American Chemical Society.
The resolution capability of storage is influenced by multilevel states and dynamic ranges because numerous conductance states can distinguishably store individual pixels of input patterns. Moreover, variations, including cycle-to-cycle and device-to-device variations, could degrade neuromorphic computing, particularly in large-scale systems. However, considering that neuromorphic computing exhibits the fault-tolerant property, neuromorphic architectures could be immune to the variation to some extent, and this is supported by several papers [8, 35, 52]. In addition, memristor synapses are repeatedly updated during the training process and should retain the trained weights (i.e., final conductance). Subsequently, the larger the endurance cycles and retention time, the better are the achievements of the neuromorphic network. Last but not least, it is desirable that device’s footprint is below sub-10 nm because high density leads to more synaptic devices that store learned information under a specific area [8].
Furthermore, it is efficient to improve the characteristics of memristor synapses depending on individual neuromorphic networks, because a desirable memristor synapse capable of being employed into neuromorphic systems is yet to be reported. Supervised learning-based networks [35, 40, 41, 42, 43, 44], for example, are less vulnerable to cycle-to-cycle and device-to-device variations. This is because memristor synapses are updated according to calculated errors under known target values. By contrast, the networks based on unsupervised learning [39, 45, 46, 47] are directly affected by the variation owing to unknown target values. Therefore, memristor synapses need to be designed or selected depending on individual neuromorphic networks.
Memristors for synaptic devices with two-terminal (e.g., vertical/planar-type and gap-type) and three-terminal (e.g., field-effect transistor and lateral coupling type) structures are manufactured by well-established processing technologies [7, 8, 9, 10, 11, 12, 35, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55].
In the case of a two-terminal structure, when different voltages are applied to each of the two electrodes, resulting in current flow through the insulator, varying the conductance of the device enables emulation of biological synapse functions such as synapse plasticity [10, 11, 12, 16, 35, 48]. In particular, the crossbar array of two-terminal devices has received attention because of its characteristics relevant to synaptic devices, such as scalability for high density, simple fabrication process, low cost of fabrication, parallel connection structure, low power, fault-tolerance, and compactness. Thus, they are expected to provide an appropriate structure to support synaptic electronics. The type of two-terminal memristors that are being reffered to as the artificial synapses includes resistive random-access memory, phase change memory, conductive bridge memory, and spin-based memory. Although two-terminal devices are attracting much attention because of their ease of implementation of crossbar arrays, a two-terminal device, as a matter of fact, requires a select device to eliminate the sneak path that occurs in a crossbar array configuration. Additionally, it is difficult to imitate complex synaptic functions such as hetero-synaptic plasticity (e.g., modulatory input-dependent plasticity).
Three-terminal structures (e.g., field effect transistor memory and floating/gate transistor memory) with tunable conductance of channels between the source and the drain are also considered as synaptic devices [49, 50, 51]. The gate electrode acts as the pre-synapse, transferring the stimulus to the insulating layer, indicating the cleft of the synapse, and modulates the conductance of the channel representing the synaptic strength. Although the three-terminal structure is more complicated than the two-terminal structure and is disadvantageous in terms of density, the terminal for the signal transmission process and the learning terminal are separated such that simultaneous signal processing is possible, and complex synapse functions such as hetero-synaptic plasticity can be mimicked. Moreover, they do not require an additional selector device to reduce sneak current in an integrated array architecture.
Recently, going beyond simply implementing a synapse function, researchers have demonstrated advanced concepts of synapse device functions, including self-rectification, photo-assisted synaptic plasticity and neuromodulation to achieve more delicate imitation of the human brain and learning-and energy-efficiency in neurocomputing.
In [35], Choi et al. fabricated a self-rectifying memristor synapse through a two-terminal structure (Pt/TaOy/nanoporous TaOx/Ta), which is capable of suppressing unwanted leakage pathways and then a 16 x 16 crossbar array using only the devices without an additional selector (see Figure 4a and b). The mechanism of memristive switching and synaptic functions, including long-term potentiation (LTP), STDP (spike-timing dependent plasticity), and long-term depression (LTD) were caused by the migration of O2− ions with oxygen vacancies V by applied electric field in the TaOx. In addition, the asymmetric interface contacts of Pt/TaOy and TaOx/Ta prevent the undesired signal by performing the self-rectification function without the selector.
(a) Schematic of a self-rectifying memristor with a Pt/TaOy/nanoporous TaOx/Ta and cross-sectional image of a memristor synapse. (b) I-V curves of the self-rectifying memristor synapse. (a, b) are reproduced with permission from Ref [35] under a Creative Commons Attribution 4.0 International License. (c) Schematics of the suggested mechanism of how a conductive switching filament is formed by the iodine vacancy migration in the presence of light. (d) Synaptic potentiation and depression behavior of the OHP-based synaptic device. (c and d) are reproduced with permission from Ref [52]. Copyright (2018) John Wiley and Sons.
In [51], Huh et al. reported a synapse device that performs the neuromodulator function of a barristor structure using 2D material as shown in Figure 4c. The three-terminal device consisted of a vertically integrated monolithic tungsten oxide memristor, and a variable-barrier tungsten selenide/graphene Schottky diode, termed as a “synaptic barrister.” This synaptic barristor could implement fundamental synaptic functions, including short-term plasticity (STP), paired pulse facilitation (PPF), LTP, and LTD, with external gate controllability, termed as a neuromodulator in bio-synapse. This architecture potentially offers considerable power-saving benefits while significantly tuning the synaptic weights and intrinsically modifying the synaptic plasticity, in comparison with conventional two-neuronal-based synaptic architectures.
In [52], Ham et al. fabricated an organo-lead halide perovskite (OHP)-based photonic synapse in which the synaptic plasticity is modified by both electrical pulses and light illumination. The switching mechanism originates from the presence of a conductive filament by iodine-vacancy mediator, with its switching states controlled by electric-field domination (see Figure 4d). Using diverse electrical stimuli and relative timing between the input pulses, essential synaptic functionalities such as STP, LTP, and LTD were successfully demonstrated. In addition, owing to the accelerated migration of the iodine vacancy inherently existing in the coated OHP film under light illumination, the OHP synaptic device exhibits light-tunable synaptic functionalities with very low programming inputs (≈0.1 V) as shown in Figure 4d. The ability of high-order tuning of the photo-assisted synaptic plasticity in an artificial synapse can offer significant improvements in the processing time, low-power recognition, and learning capability in a neuro-inspired computing system (Figure 4e).
In [12], Wang et al. designed a diffusive memristor for STP synapses and threshold neurons. The devices contain a switching layer doped with Ag nanoclusters (MgOx:Ag, SiOxNy:Ag, and HfOx:Ag) using the co-sputtering method. The switching mechanism is based on the growth and relaxation of Ag nanoclusters depending on whether the voltage pulse is applied, which was experimentally verified by in-situ high-resolution transmission electron microscopy (HRTEM). The designed device mimicked STP under PPF and PPD. Moreover, the device was used as a threshold neuron along with drift memristor synapse based on TaOx to emulate STDP learning rule. Because the conductance of the device gradually increases according to applied voltage and then abruptly decreases under no applied voltage, the device can be used as a threshold neuron. The results give a potential application for simple artificial neurons as compared with CMOS artificial neurons [53, 54].
Prezioso et al. experimentally demonstrated neuromorphic networks based on memristor synapses (see [55]). In their paper, Al2O3/TiO2−x memristor was used to fabricate a 12 × 12 crossbar array to implement a single-layer network [56]. The single-layer network architecture was schematically described as shown in Figure 5a, where 10 input neurons and 3 output neurons are fully linked by 10 × 3 = 30 synaptic weights (Wi,j). Notably, this ANN architecture naturally corresponds to a crossbar array [9, 35]. Input voltages (Vi = 1…9) assigned from pixels of the 3 × 3 input images (see Figure 5b) were applied to each input neuron. After being applied into the network, the input voltages were individually weighted depending on each synaptic weight. Note that V10 is a bias voltage to control the degree of activation of the output neurons. The output neurons received each weighted voltage through linked weights and then integrated the weighted voltages (∑Wi,jVj), where j and i represent the input (j = 1–9) and output (i = 1–3) neurons respectively. The output neurons converted each integrated voltage into output (fi) ranging from −1 to 1 according to the nonlinear activation function: fi = tanh(βIi), where β adjusts the nonlinearity of the activation function and Ii = ∑Wi,jVj. The activation function can be considered as the threshold firing function in a biological neuron. The synaptic weights were represented by a pair of adjacent memristors (Wi,j = Gi,j+ − Gi,j−) for the effectiveness of weight update. The number of selected memristor synapses in 12 × 12 array were 30 × 2 = 60, due to a pair of memristors (Figure 5c). When the network was under the training process, as shown in Figure 5d and e, memristor synapses between input and output neurons were updated based on the Manhattan update rule, which is classified as supervised learning: ∆Wi,j = ηsgn∑[(ti(n) − fi(n)) × df/dI × Vj(n)], where η is the learning rate, ti(n) is the target value, fi(n) is the output value, and n is the nth input image. After the training process was complete, the memristor synapses retained their final conductance, and the test process was performed without weight update (see Figure 5d). From the test process, the neuromorphic network exhibited perfect classification for the first time in 21 epochs (note that one epoch indicates one training process). Although simple and few input images were used to train/test the neuromorphic network, this work greatly contributed to neuromorphic systems based on memristor synapses in terms of experimental demonstration using crossbar arrays.
(a) Input voltages corresponding to an input image (Vi = 1…9) and a bias voltage (V10). These voltages are fed into the single-layer network where 10 input neurons and 3 output neurons are linked by synaptic weights. (b) The “z,” “v,” and “n” input images. Aside from ideal images, other images contain one noise pixel. (c) The schematic of implemented 10 × 6 crossbar array, a pair of adjacent memristors provide one synaptic weight. (d) When an image (e.g., “z”) is fed into network, pixels for black give VR (read voltage) to the network, otherwise, −VR is applied into the network. (e) An instance of weight update according to Manhattan update rule. The synaptic weights corresponding to sign + should be increased, so that the memristors representing G1,1+, G1,2+, G1,5+, G1,6+, and G1,9+ are applied by set voltage. All figures are reproduced with permission from Ref [55]. Copyright (2015) Springer Nature.
It should be noted that the circuit that acquires sgn[ fi(n)] = sgn[∑Wi,jVj] = sgn[∑(Gi,j+ − Gi,j)Vj] could be implemented by a virtual ground circuit and a differential amplifier [43, 57]. Then, the output value is compared with the target value by circuits using a comparator. According to calculated ∆Wi,j, programming memristors of the array, for example, could be performed as shown in Figure 6 [39]. The test board contains four digital-to-analog converters (DACs) providing voltage pulses through the DACs. The DACs 1–4 represent the chosen bottom line, the unchosen bottom line, the chosen top line, and the unchosen top line, respectively. Using matrix switches (Switch 1 and 2), individual memristor is assigned to the corresponding DAC. The multiplexer (MUX) is operated to obtain currents that flow through memristors in the array by delivering the currents into the analog-to-digital converter (ADC). The ADC obtains the applied voltage of the resistor (1 kΩ), and the voltage is changed into the current. The arrows of Figure 6 represent the current flowing through a chosen memristor in case of write, erase, and read processes. Notably, there are non-idealities such as sneak currents and wire resistance in array-level, which could degrade the performance of neuromorphic computing [35, 44, 58, 59, 60]. The sneak currents affect learning accuracy and epochs because of undesired information, especially large-scale array. In Figure 6, in order to avoid sneak currents during read process, unchosen rows and columns are grounded [39]. Moreover, wire resistance consumes input voltages, so that memristors far from points of input voltage could be applied by smaller voltage than input voltage. This influences output currents, leading to degradation of learning performance. The non-idealities in array-level could be overcome by device functions [35, 44], operational scheme [39, 58, 59, 60], or learning algorithms [35, 40, 41, 42, 43, 44] to some degree.
Circuit scheme for write, erase, and read processes. The figure is reproduced with permission from Ref [39]. Copyright (2017) American Chemical Society.
Neuromorphic systems are one of the most promising candidates to deal with the von Neumann bottleneck caused by the memory wall between memory and process units. Using memristor synapses simply classified into cation- and anion-based devices can resolve this bottleneck owing to their storage and transmittance capabilities. To obtain higher performance of neuromorphic systems, representative characteristics, including the linearity of weight update, large multilevel states and dynamic range (ON/OFF ratio), variation and endurance, and retention need to be improved. In this context, different memristor synapses based on novel materials and device structures were introduced. Finally, we have briefly explained neuromorphic networks based on crossbar arrays of memristor synapses, and the network demonstrated perfect classification after 21 epochs. We believe that this chapter offers a deep understanding of the field of memristor synapses.
This work was supported by the National Research Foundation of Korea (NRF-2016R1C1B2007330 and NRF-2019R1A2C2003704), KU-KIST Research Fund, Samsung Electronics, and a Korea University Future Research Grant.
The authors declare no competing interests.
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