Analysis And Design Of Touch Mode Capacitive Pressure Sensor

Touch mode capacitive pressure sensor (TMCPS) has distinct advantages over normal mode capacitive pressure sensor, and other counterparts. Though bom for more than 10 years, the understanding of the mechanism of its diaphragm deformation after touch in mechanics is not enough. Finite element analysis is employed to model the structural deformation of such a device. Analyzed results show that the deflection of the sensing diaphragm of the sensor tends to be linear, after touch. That is, the post-touch deformation of the diaphragm can be categorized as small deformation.Because of touch between its sensing diaphragm and substrate, touch mode capacitive pressure sensor has a drawback, hysteresis, van der Waal force and electrostatic force are ascribed to the appearance of hysteresis. In order to study the influence of adhesive forces on the output performance of touch mode sensors, small deformation assumption and a simple approach to solve touch problem are used to model the deflection of diaphragms, the feature of hysteresis, and the effect of adhesive forces on other characteristics. Hamaker constant, potential difference, separation distance of touch surfaces, load pressure increment and structural parameters are analyzed respectively. Several ways to reduce hysteresis are presented.To achieve the characteristics of better linearity, a new type of touch mode capacitive pressure sensor named as DDTMCPS is devised, which has a pair of deformable sensing diaphragms. Compared to present touch mode capacitive pressure sensors, the new sensor is characterized by better linearity, and large linear operation range. Such a device also has high sensitivity, and other advantages of normal touch mode capacitive pressure sensor. In the case of such a novel sensor, the second diaphragm served as bottom electrode plays great roles in modifying the deflection of the first diaphragm served as top electrode, furthermore optimizing the performance of touch mode sensors. Proper thickness of the second diaphragm is crucial to achieve a better performance. Silicon fusion bonding technology is advised to fabricate the novel device.