Design, fabrication and optimization of a CMOS compatible capacitive pressure sensor

In this paper, some capacitive pressure sensor related work is presented. The theoretical model of the touch mode elastic membrane was firstly derived based on the energy method in the theoretical part. Three capacitive pressure sensors with different sizes are designed and fabricated. The core part of the sensors is an array of capacitors. Each capacitor has an elastic membrane. When pressure is applied, the elastic membranes bend down and the distance between the top and bottom electrodes decreases. Hence, the capacitance of the sensors increases. The fabrication process is based on both CMOS and post-micro-electro-mechanical systems (MEMS) technology. The sensors are characterized under atmospheric pressure ranging from 10 kPa (kilopascal) to 100 kPa. They work well except for having a high nonlinear error, which is mainly caused by the limitation of the sensing mechanism. Inspired by the testing results of these sensors, an attempt is made to improve the linearity of capacitive pressure sensors. This method is based on the complementary sensitivity characterization of touch mode and non-touch mode capacitors. By adjusting the sizes and numbers of the touch mode capacitors and non-touch mode capacitors in the sensor, the nonlinear error of capacitive pressure sensors can be reduced and even eliminated. To verify the feasibility of this method, a structure is designed and simulated with FEM software. The simulation results show that this method is effective at improving the linearity of capacitive sensors. The nonlinear error is remarkably reduced to 2.5%, which is about 28% for the contact mode capacitor and 13.6% for the non-touch mode capacitor. (paper)