A Study On The Design And Fabrication Of Micro Pressure Sensors

Micro pressure sensor is simple but widely used, and it is studied and industrialized very early. Micro machining technology is important for fabrication of some MEMS products. In this paper, three micro pressure sensors are designed and one of them is fabricated by the micro machining technology. The main contents of the paper are as follows:1. Based on the piezoresistive effect, large or small deflection theory, thin film's stress theory and other mechanics or electricity knowledge, a piezoresistive micro pressure sensor is designed. It is sensitive to pressure and the measurement range of pressure can be changed.2. A micro differential capacitance and a micro harmonic oscillator are studied and designed. The structure of the micro differential capacitance is optimized by use of the ANSYS software.3. When SiH4 reacts with NH3 in a Plasma-Enhanced Chemical Vapor Deposition(PECVD) equipment, a thin film of Si3N4 is deposited on the Si film. Process parameters related to the film quality are discussed; Relations are found between the etching rate and different process parameters when SiO2 and Cr thin films are etched in an Inductively Coupled Plaslma (ICP) etching equipment; The TMAH eroding solution's PH value under different temperatures and concentrations are studied, since the etching process can be controlled by the PH value.4. According to micro machining processes, a process flow is planed to make the piezoresistive sensor chip successfully. The process flow is simple and feasible.5. Based on the testing principle of Wheatstone bridge, a simple testing system is set up with two cascaded amplifiers and two cascaded Butterworth lowpass filters. The varying voltage is tested by the system as the pressure is changed. Experiment data are obtained, which also prove the feasibility of the design and the process flow.Results of the research and experiments in this paper are beneficial to deign and fabrication of micro pressure sensors. The micro machining technology can also be used for other MEMS products.