Study On Design And Manufacturing Technology For Steel Pressure Sensors Based On Thick Film Process

Pressure sensors, with demand being the largest among all sensors, are widely used in various industry fields. However, most of the products currently available are not perfect enough to meet the requirements of some specific occasions.Taking the technical weaknesses of mainstream pressure sensors and the development stages at home and abroad into consideration, two types non-traditional steel pressure sensors based on thick film technology are proposed and investigated in this thesis. First, thick film resistors (TFRs) on430stainless steel substrate for strain sensor applications are investigated. The material parameters related to the sensors are tested and the steel pressure sensors are designed and manufactured by using finite element method (FEM). Second, a novel pressure sensor design using epitaxial silicon strain gages bonded on17-4PH stainless steel diaphragm based on thick film technology is also proposed and evaluated, and effects of the microstructure of the adhesive on the sensor performances are analyzed. The main research efforts are as follows:(1) Nanoindentation test with the continuous stiffness method (CSM) is conducted on the dielectric-on-430steel-substrate to obtain its mechanical properties. Test results show that the average elastic modulus of the dielectric-on-steel substrate is126.56GPa and the average hardness is8.364GPa. The performance parameters of the thick film resistors (TFRs) are measured to verify their feasibility as strain gages for pressure or force sensors. Results show that gauge factor (GF) and noise indices (NI) of TFRs are10.2and-20dB, respectively. And the temperature coefficients of resistivity (TCRs) are230ppm/K (-40-125℃) and250ppm/K (125～220℃).(2) Reliable bonding between the dielectric and430steel substrate is confirmed by free fall test and thermal shock test. Microstructure analysis shows the compatibility of TFRs and the dielectric on steel substrate, which indicates the feasibility of manufacturing thick film steel pressure sensors.(3) The thickness of the dielectric and the positions of TFRs on the dielectric-on-steel are obtained by FEM. Effects of the thermal stresses and the self-heating of TFRs on the performance and reliability of the steel pressure sensors are evaluated, and the corresponding improvement measures are proposed.(4) Thick film based steel pressure sensors are designed and manufactured, and the performance characteristics are evaluated. Test results show that the temperature drifts of the sensors are less than2.5%full scale (FS), and the accuracy-related parameter errors are no more than0.15%FS from-40℃to125℃. And from125℃to220℃, the temperature drifts of the sensors are less than2.85%FS, and the accuracy-related parameter errors are no more than0.3%FS.(5) The strain gages with uniform resistance are obtained by growing an epi-silicon layer on a single crystal silicon wafer using epitaxial deposition technique rather than conventional photolithography and etching techniques. The inorganic glass frits rather than organic adhesives are used as the bonding material between the strain gages and the17-4PH SS diaphragm. Results show that the hysteresis and repeatability errors of sensors are less than0.05%FS and0.12%FS at125℃, respectively, which are almost equal to those at room temperature, showing the robust high temperature stability. Experimental results show that the defects in the organic adhesive greatly deteriorate the hysteresis and repeatability errors of the sensors.