Development of Cross Beam-Membrane Structure for Silicon-On-Insultor Pressure sensor

• Main Authors: Li-Ren Shin, 施力仁
• Other Authors: 翁宗賢
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/19292894416529696447

碩士 === 國立臺灣大學 === 應用力學研究所 === 104 === Highly stable pressure sensors were developed in this study. The sensors were fabricated via bulk micromachining technology for micro-electromechanical systems. The sensors are designed with piezoresistors situated at the edges of the square diaphragm on a p-type device layer of a silicon-on-insulator wafer. To improve linearity, cross beam membrane are attached on the deformable diaphragm. The backside cavity of the diaphragm was etched by a deep reactive ion etcher up to the designated thickness. This configuration is easy to fabricate, and would possess high sensitivity, simple signal processing, and can achieve good linearity. This research focused on the sensing diaphragm area and thickness, sizes of piezoresistors and their locations, and effect of the doping concentration of the device layer on the measuring sensitivity. After preliminary explorations, five discrete models involving three areas in diaphragm and five sizes in piezoresistor were setup for numerical simulation coupling mechanical and electrical fields. The computational results provide sufficient information to verify that the respondent stresses are within the allowable strength of material and the piezoresistor bridge delivers significant voltage output for accurate measurement. The simulation results also evidence that the diaphragm size of 2300  2300 m2 and thickness of 20 m2 would have a most significant response stress of 178.05 MPa, a sensitivity of 8.75 mV/V/bar. It is obviously that the maximum respondent stress is well within the allowable strength of the material of 300 MPa. With validation of the designs by numerical simulation, five models of pressure sensor were fabricated by semiconductor process technology on a SOI wafer. The processing consisted of E-beam aluminum deposition and lift-off for metal wires, deep etching to define piezoresistor, central bosses, and pressure sensing cavity on the backside. Upon finishing the manufacturing, cutting, and packaging processes, detail calibration were carried out to characterize sensitivity and linearity of the pressure sensor. The correlated data demonstrate that these sensors can stably and accurately measure pressure in the range of 0 to 1.5 bar with a sensitivity of 4.93 ~ 9.98 mV/V/bar. The deviations of sensitivity between test runs were within 0.4 mV/V/bar which shows good repeatability. These sensors also exhibit a very good nonlinearity of 0.33% per full scale output. The output voltage can be magnified by tuning a resistor of the input instrumentation amplifier to a convenient reading corresponding to actual applied pressure. The developed modular pressure sensor and actuator can be integrated into modern instrumentations as well as for intelligent appliances. Since the MEMS processing is compatible with the CMOS manufacturing, the present micro pressure module can be integrated with the other electric control circuits.