(Invited) MEMS Accelerometer Fabricated by Gold Multi-Layer Metal Technology

Abstract

This paper reviews the feature of our proposed MEMS (microelectromechanical systems) accelerometer and the issue of its reliability. In order to realize micro-G (1 G = 9.8 m/s2) level sensing, we have proposed capacitive MEMS accelerometers with gold proof mass using the multi-layer metal technology. Utilizing gold as a high density material of the proof mass reduces the Brownian noise (BN ), which is a crucial factor to determine the resolution of MEMS accelerometer. As a result, we can obtain the low value of 22 nG/√Hz despite the same size of gold proof mass as silicon proof mass. Regarding the reliability, the heat cycle and the vibration cycle tests are conducted. The experimental results suggest that the MEMS accelerometer has potential for a practical use. In conclusion, we confirm that our proposed MEMS accelerometer can make a contribution to a new technical development.

Effective Young’s Modulus of Complex Three Dimensional Multilayered Ti/Au Micro-Cantilevers Fabricated by Electrodeposition and the Temperature Dependency

“…On the other hand, gold is known to be a relatively soft metallic material among materials commonly utilized in electronics, and electrodeposition is a powerful method to strengthening the gold by grain refinement [7,8] alloying [9][10][11] and introduction of nanotwins [12]. Alternately and repeatedly deposition of gold following by a material with higher mechanical strength to realize a multilayered structure is also an effective strategy [13][14][15]. Cantilever-like structures are commonly used in movable components in MEMS devices.…”

“…Gold based MEMS has a complex three dimensional (3D) multilayered Ti/Au structures [2] and the annealing process is often applied in the fabrication of electronic devices, such as 310 • C treatment in fabrication of MEMS accelerometers [13], and the thermal energy could greatly affect the properties of the material and performance of the device [22,23]. Hence, temperature dependency of the effective Young's modulus of micro-cantilevers composed of electrodeposited gold and sputtered titanium is evaluated in this study.…”

Warpage Study of Electrodeposited-Au Micro-Components with Ti/Au Multi-Layered Structures toward MEMS Applications

“…5 Encouraged by these attractive properties of Au, we have devoted our efforts to the development of Au-based MEMS capacitive accelerometers (simply referred to as Au-MEMS). [6][7][8] Due to the high mass density of Au, the Au-MEMS capacitive accelerometers can detect weak accelerations resulting from muscle sounds, which are difficult to detect by commercial accelerometers. 9 On the other hand, the mechanical strength of Au is much lower than most electrodeposited metals commonly used in MEMS, raising concerns about the structural stability in practical applications of Au-MEMS.…”

“…Accordingly, the Au-MEMS capacitive accelerometers are equipped with a titanium/gold (Ti/Au) multi-layered structure. [6][7][8] The mechanical properties, such as yield strength and Young's modulus of Ti are higher than those of gold. 10 The structural stability of the Au-MEMS capacitive accelerometers utilizing the Ti/Au multi-layered structure is expected to be improved.…”

“…The proof masses with four different Ti/Au multi-layered structures and different sizes are fabricated by using the developed lithography and Au electroplating processes. [6][7][8] The warpage in the proof masses is investigated from the height profiles of their top surfaces evaluated by a three-dimensional (3D) optical microscope (OM). For comparison with the experimental results, the warpage behaviors are also discussed by finite element analysis (FEA) simulations.…”