Piezoresistive Properties Study On A GaAs HEMT-embedded Beams-mass Structure

The study of MEMS devices based on the piezoresistive effect of silicon has several ten years history with widely applications. However, the sensitivity of piezoresistive effect of silicon can not meet the seismic wave detection, navigation guidance, platform stability and other high-precision, highly sensitive sensor's demands. In this paper, a GaAs high electron mobility transistors (HEMT)–embedded beams-mass structure is designed, which is cross beam structure, with the advantages of high sensitivity, adjustable resistance.Based on the piezoresistive effect theory, n +-AlGaAs/i-AlGaAs/i-InGaAs/i-GaAs HEMT structure is designed and grown; and the mechanical parameters of beams-mass structure is analyzed and simulated by ANSYS. This structure is processed with the processing technology of body and surface combination technology, such as the double groove technology, the air bridge technology and hole controling technology. Finally, experimental results on the original structure has been optimized and improved.In the experiments, the HEMT parameters characteristic experiment, the depth of gate groove experiment, the piezoresistive coefficient experiment and the temperature experiment are studied based on the piezoresistive effect theory. The results show that: the piezoresistive coefficient of GaAs HEMT under different bias voltage is different. And the change of saturation region is larger obviously than the linear region. The maximum piezoresistance coefficient of GaAs HEMT is three orders of magnitude higher than that of silicon; the piezoresistive coefficient of GaAs HEMT decreases with increasing temperature . This will be very useful for the design of new high-sensitivity and adjustable resistance Micro-Electro-Mechanical Systems piezoresistive device. In this paper, innovation is mainly reflected in: (1) We design firstly a new stress loading system to obtain the piezoresistive coefficient, including an Agilent 4156C semiconductor characteristic analyzer, a Polytec microsystem analyzer and an ANSYS simulation software. (2) A series of optimization based on the original structure are made: to remove the air bridge technology, to change the location of gate electrode leads, and to consider the relationship of piezoresistive coefficient and crystal.