A Study of the Geometrical Correction Factor and the Membrane Thickness on the Sensitivity of the Transversal Piezoresistive Pressure Sensor
Keywords:piezoresistive sensors, piezoresistance effect, short-circuit effect, high sensitivity, CMOS microsystem
The sensitivity of four-terminal devices like Hall and piezoresistive sensors is very dependent on its geometric parameters. This dependence is modeled by the Geometrical Correction Factor (G). The majority of these studies take very time-consumption analytical calculations for the analysis of G. In order to simplify this analysis, we present numerical analyses using FEM (Finite Element Method) for the most common geometrical forms of four-terminal devices. This result is general for any fourterminal-shaped sensors and can be used to optimize the sensor aspect ratio leading the maximization of G. In addition, FEM was also used to evaluate the membrane´s thickness influence over the sensor sensitivity by analyzing the in-plane mechanical stress behavior on the sensor active area. Experimental result of a new topology of pressure sensor is also presented, which maximizes G in comparison with conventional four-terminal devices and also improves its sensitivity. A special designed anisotropic wet etching system was used to post-process the sensor membrane. This anisotropic wet etching system allows the fabrication of well-defined membranes with thickness of 20 μm ± 3 μm and roughness as low as 90 nm rms.