Integrated Design Of Pressure Sensor Based On SON Structure

MEMS capacitive pressure sensor is widely used due to its short response time,wide temperature range and high sensitivity.With the development of mobile phones,GPS positioning,human health monitoring systems and other portable products,sensors are required to be miniaturized,integrated and multifunctional.Therefore,an integrated pressure sensor based on SON structure was proposed,including absolute pressure sensor and differential pressure sensor.The absolute pressure sensor was fixed in the middle of the film,which was used to improve the linearity of the absolute pressure sensor.The differential pressure sensor had a circular silicon film with a small hole in the middle for sensing dynamic pressure.These two sensors were integrated to achieve simultaneous measurement of absolute and relative pressure,or static and dynamic pressure,which was of great significance to the miniaturization and integration of sensors.The SON?Silicon-on-Nothing?structure was used in pressure sensors to provide a vacuum chamber without sealing and a film with a controllable thickness.This method solved the problems of the stability of the vacuum chamber,and the extraction of electrode wires.The main research contents and results were as follows:?1?Theoretical research on absolute pressure sensor and differential pressure sensor based on SON structure.The working principle of the absolute pressure sensor and the differential pressure sensor were analyzed,and the theoretical calculation model of pressure-deformation and pressure-capacitance were established with using the plate-shell theory and the capacitance calculation formula.The sensitivity coefficient and response time calculation formula of the differential pressure sensor were also given.The influence of structural parameters on performance of absolute pressure sensor and differential pressure sensor were analyzed.The results show that the biggest influence on the performance of the absolute pressure sensor was the radius of the film,followed by the thickness of the film.The strength of the sensor was mainly affected by the size of the middle fixed area.The greatest impact on the damping ratio of the differential pressure sensor was the cavity height,followed by the hole radius of the film opening,and the radius and thickness of the film were less affected.In addition,the response time of the differential pressure sensor can be controlled by adjusting the damping ratio?.The response time,increases with the increasing of damping ratio,and is independent of the pressure difference.?2?The absolute pressure sensor and differential pressure sensor were simulated by ANSYS.The deformation,stress and strain distribution of absolute pressure sensor under uniform pressure load were obtained through static analysis of absolute pressure sensor.The differential pressure sensors of two cavity depths were respectively subjected to unidirectional fluid-solid coupling,and the dynamic change law of the internal pressure of the cavity and the deformation of the pressure-sensitive film under different working modes were obtained,which provided a basis for the optimization of the sensor structure.?3?Production of integrated sensors.The layout design and drawing of the integrated pressure sensor mask was completed with using Auto CAD software.A sensor with a SON structure was produced through photolithographic processing,vacuum and high temperature annealing,silicon and glass anode bonding and other processes,and the electrode was also led out.?4?Test the developed sensor.The test systems of absolute pressure sensor and differential pressure sensor are established respectively.For the absolute pressure sensor,its pressure-sensitive film has a radius of 200?m,a thickness of 2.5?m,a middle fixed radius of 4.2?m,and a gap between electrodes is 5?m.For the differential pressure sensor,its pressure-sensitive film has a radius of 750?m,a thickness of 5?m,a middle opening radius of 5?m,and a gap between electrodes is 5?m.Absolute pressure sensor and differential pressure sensor test systems were built separately.The test results show that under the pressure of 30¹20kPa,the linearity of the 16 absolute pressure sensors was 5.254%,the sensitivity was 4.634pF/Pa,the repeatability error was 6.25%,and the hysteresis error was 4.638%.Simultaneously,the differential pressure sensor characteristics were also tested.In a range of the dynamic pressure from-60 Pa to 60 Pa,the sensitivity coefficient was1.554×10^-4 Pa^-1.With the differential pressure of-40Pa,the response time was about 40s,and the error was 12.5%compared with the theoretical calculation time.With the increasing of differential pressure,the response time of the sensor increases slightly,and the response time of the intake process was longer than the exhaust,causing by the change in the damping of the sensor cavity.The response time and response time difference can be shortened by increasing the volume of the differential pressure sensor cavity.