Evolution, modelling and simulation of MEMS PWM pressure sensor employing cantilever switch and SOI diaphragm

There are applications that need pressure sensors which produce easily transmittable digital output and are free from inherent disadvantage of conventional piezoresistive and capacitive pressure sensors. This paper presents a micro electro mechanical systems (MEMS) pressure sensor based on pulse width modulation (PWM) technique. The proposed mechanism converts the applied pressure into equivalent PWM signal with an innovative but simple structure. The mathematical model relating the duty cycle of the PWM output signal and the pressure is derived from basic principles first to explain the sensing mechanism theoretically. Simulation studies conducted to validate the proposed sensing principle not only match the theoretical predictions well but also provide the design guidelines for achieving high sensitivity and least non-linearity. The fabrication process flow for the sensor structures has been also developed and presented. Finally this paper presents a design of a PWM pressure sensor and various studies to evaluate the performance of the sensor. Systematic simulation and theoretical studies show that it is possible to achieve a sensitivity of 6.7 mV/kPa with less than 8 % non-linearity using this approach in addition to getting a digital output. These studies further illustrate that this sensing concept paves the way for fabrication of MEMS pressure sensor that needs no complex signal conditioning electronics. Similarly the direct digital output from the sensor make them suitable for applications like Tire pressure monitoring system and process control automation systems.