Chapters authored
Pulse-Current Electrodeposition of Gold
Pulse-current electrodeposition and a sulfite-based electrolyte were used in fabrication of pure gold films. Surface of the pulse-electrodeposited gold film possessed less defect, lower roughness, smaller grain size, and denser texture when compared with the gold film prepared by constant-current electrodeposition. Microstructures and compressive yield strength of the electrodeposited gold could be controlled by regulating the pulse on-time and off-time intervals in pulse-current electrodeposition. The gold film prepared under the optimum conditions showed an average grain size at 10.4 nm, and the compressive yield strength reached 800 MPa for a pillar-type micro-specimen having dimensions of 10 μm × 10 μm × 20 μm fabricated from the pulse-electrodeposited gold film. Average grain size of the pulse-electrodeposited gold film was much smaller, and the compressive yield strength was much higher than the values reported in other studies. The high strength is due to the grain boundary strengthening mechanism known as the Hall-Petch relationship. In general, the pulse-electrodeposited gold films showed yield strength ranging from 400 to 673 MPa when the average grain size varied by adjusting the pulse-electrodeposition parameters.
Part of the book: Novel Metal Electrodeposition and the Recent Application
Electrodeposition of Gold Alloys and the Mechanical Properties
Strengthening of electrodeposited gold-based materials is achieved by alloying with copper according to the solid solution strengthening mechanism. Composition of the Au–Cu alloys is affected by the applied current density. The mechanical properties are evaluated by micro-compression tests to evaluate the mechanical properties in microscale to take consideration of the sample size effect for applications as microcomponents in MEMS devices. The yield strength reaches 1.15 GPa for the micropillar fabricated from constant current electrodeposited Au–Cu film, and the film is composed of 30.3 at% Cu with an average grain size of 5.3 nm. The yield strength further increases to 1.50 GPa when pulse current electrodeposition method is applied, and the Cu concentration is 36.9 at% with the average grain size at 4.4 nm.
Part of the book: Novel Metal Electrodeposition and the Recent Application
Multi-Physics Simulation Platform and Multi-Layer Metal Technology for CMOS-MEMS Accelerometer with Gold Proof Mass
This chapter describes technical features and solutions to realize a highly sensitive CMOS-MEMS accelerometer with gold proof mass. The multi-physics simulation platform for designing the CMOS-MEMS device has been developed to understand simultaneously both mechanical and electrical behaviors of MEMS stacked on LSI. MEMS accelerometer fabrication process is established by the multi-layer metal technology, which consists of the gold electroplating and the photo-sensitive polyimide film. The proposed MEMS accelerometers are fabricated and evaluated to verify the effectiveness of the proposed techniques regarding sub-1G MEMS and arrayed MEMS devices. The experimental results show that the Brownian noise of the sub-1G MEMS accelerometer can achieve 780 nG/(Hz)1/2 and the arrayed MEMS accelerometer has a wide detection, ranging from 1.0 to 20 G. Moreover, using the developed simulation platform, we demonstrate the proposed capacitive CMOS-MEMS accelerometer implemented by the multi-layer metal technology. In conclusion, it is confirmed that the multi-physics simulation platform and the multi-layer metal technology for the CMOS-MEMS device have a potential to realize a nano-gravity sensing technology.
Part of the book: Novel Metal Electrodeposition and the Recent Application