Radio Frequency Liquid Viscosity Sensor Based On AlN Thin Film

As one of the important physical parameters of liquid properties,liquid viscosity is widely used in unlabeled chemical detection,industrial production,energy and power,biological health and other fields.At present,for liquid viscosity detection of the most common methods have the following several: capillary method,falling ball method,rotating barrel method and so on.However,these methods all require large volume of moving parts or power sources,which do not conform to the development trend of sensors.With the characteristics of high sensitivity,small volume and low cost,acoustic liquid viscosity sensor has gradually become an important means of liquid viscosity measurement.Based on the purpose of liquid viscosity measurement,a Lamb wave liquid viscosity sensor with protective layer is designed.The special vibration mode of high order Lamb wave is used to measure the liquid viscosity,and the reliability of the device is enhanced.In this paper,based on the aluminum nitride(AlN)piezoelectric film,the design and preparation of liquid viscosity sensor are studied.The main research contents are as follows:1.The relationship between the mechanical parameters of liquid and the velocity and attenuation of sound wave is analyzed,and the feasibility of applying high-order Lamb wave to the measurement of liquid viscosity is discussed.Through modeling and simulation,the vibration modes of the device and the motion of the particles under different substrate thicknesses are studied,and the vibration modes suitable for liquid viscosity sensing are found.2.According to the simulation results,a Lamb wave liquid viscosity sensor with SiO2 protective layer is designed.This design can protect the cross finger electrode of the sensor,increase the applicable environment of the sensor,and still maintain the good performance of the sensor in a long time.Then the viscosity sensor is fabricated based on MEMS technology.3.Set up a sensor test system to test the sensor's viscosity perception ability.In viscosity testing,the sensor has the ability to distinguish glycerine solutions with different viscosities,and the frequency response of the sensor is linearly related to the viscosity values within a specific viscosity range,with a viscosity frequency coefficient of -182.6 PPM/mPa·s,a sensitivity of -58.26 kHz/mPa·s,and a maximum error of 0.34%.The test results show that the liquid viscosity sensor has good performance,which provides guidance for further research.