Preparation Process, Finite Element Simulation And Package Inspection Of Ceramic Capacitive Pressure Sensor

With the advent of the Internet of Things era,China’s industry will transform from traditional manufacturing mode to intelligent manufacturing mode.Therefore,advanced manufacturing industry will be focused on in the future development.Pressure sensors are widely used in various fields,such as automotive,energy,petroleum,chemical,aerospace and other fields.In these fields,pressure sensors with ultra-high load,high temperature fatigue resistance,impact corrosion resistance and fast dynamic response are urgently needed.Among various kinds of pressure sensors,ceramic capacitive pressure sensors can meet the above requirements,and their precision,sensitivity and fatigue life are significantly better than similar sensor products.The stability and reliability of ceramic capacitive pressure sensors in the process of packaging and working are mainly studied in this paper,and comprehensively improved through the study of sealing materials and process,the analysis of the packaging stress and fatigue life,the research on the reliability of the electrode and the stability test of the output signal.Firstly,low melting point sealing glass paste of two different systems was designed and prepared,and their physicochemical properties were compared and analyzed.Glass films were prepared on ceramic substrates at different sintering temperatures.The nano scratch tests were used to characterize the bonding strength.The scratch morphology and the failure modes were observed and analyzed.The results show that the physicochemical properties of the glass paste are similar below 800℃,and both of them achieve the most ideal properties when the sintering temperature is about 580℃.Due to the low viscosity and a small amount of low-temperature decomposition substances,the lead-free system has internal stress after sintered and is prone to micro cracks.However,the bonding strength of the lead-containing system is lower than that of the lead-free system,and the lead-containing system is easy to peel off in a wide range.Considering the requirements of bonding reliability and environmental protection,the lead-free system was selected to package the pressure sensing element reliably at 580℃.Secondly,the capacitance cavity and the pressure sensing element of the sensor were modeled and simulated.Finite element software was used to simulate the package stress,high temperature environment and alternating load of the pressure sensor.The simulation results show that the deformation of the ceramic diaphragm at the center is the largest under the load of 1 MPa on the pressure sensing element.In addition,the original structure of the sensor is changed by the packaging stress,and it has no effect on the sensitivity at room temperature,but the temperature sensitivity of the sensors increases sharply under high temperature.When the cyclic alternating load is applied to the pressure sensing element,the ceramic diaphragm appears fatigue failure in the area of the capacitor cavity.In addition,the influence area of fatigue failure is obviously enlarged and the fatigue life is greatly reduced by adding package stress.Thirdly,Au electrodes with a thickness of about 250 nm were prepared on the ceramic substrate by magnetron sputtering.It was found that the number of Au atoms,disorder,surface roughness and resistance on the ceramic surface are increased with the increase of temperature when baked at 150～250℃.With the increase of heat-treated temperature in the range of 560～600℃,the Au atoms attached on the ceramic surface began to agglomerate,the conductivity and the bonding strength of Au electrodes decreased.In addition,the internal stress increases and it is easy to appear large-scale electrode stripping.Finally,the signal of the ceramic capacitive pressure sensor was detected by the self-made pressure sensor test platform.In the static test,with the increase of the pressure on the ceramic diaphragm,the capacitance and voltage were positively correlated,and the linearity was good.But in the dynamic continuous test,the signal fluctuation was obvious and the sensitivity was greatly reduced.In addition,the signal had obvious hysteresis.