Study On Surface Acoustic Wave Temperature Sensor Of AlN Film

In recent years,the development of temperature sensors is very rapid,with the detection requirements in some harsh special environments,active wired sensors are easy to be constrained,such as in high-speed running objects or confined space,traditional temperature sensors need to solve the wiring and other problems And some of the active and passive wireless sensor system wireless temperature measuring range is not big,and active will increase the volume of a sensor,can also affect the service life To solve above problems,this paper on the surface acoustic wave（SAW）temperature sensor is studied and the preparation,can be achieved in a wide temperature range temperature measurement,which laid a foundation for subsequent wireless detection.Firstly,the effect of argon nitrogen ratio and argon nitrogen flow rate on the orientation of ALN films deposited on（002）crystal plane by RF magnetron sputtering at different substrate temperatures was investigated.The optimal sputtering parameters were obtained as substrate temperature 375℃sputtering pressure 0.35Pa argon nitrogen ratio 4:1.The ALN film（002）deposited by argon nitrogen flow rate of 20sccm and 5sccm has a strong diffraction peak and a FWHM of 0.217°,which has good piezoelectric properties.In order to explore the influence of temperature on ALN film,the substrate is deposited at 1000 The results show that the gap between grains and the surface roughness increase with the increase of temperature,the intensity of（002）diffraction peak decreases,and a small amount of O element penetrates into the ALN film at 1000℃,but it is still piezoelectric.Then,the structural parameters of the sensor were designed and simulated by COMSOL software.Under the condition of 20μm wavelength,the influence of different metal electrode thickness on Rayleigh wave velocity and electro-mechanical coupling coefficient was investigated.The Pt electrode thickness was 100nm and the metallization ratio was 0.5.When the ALN film is very thin,the temperature frequency coefficient（TCF）of the sensor is negative and increases with the increase of the thickness.In order to improve the sensitivity of the device,the thickness of the ALN piezoelectric layer is determined to be 2μm,and the TCF value is-57.23 ppm/℃.Then,the substrate after deposition of ALN film was used to fabricate the sensor and the mask was designed using the simulated parameters.The photolithography on the substrate surface was graphically used,and then the 10nm transition layer Ta and 100nm electrode layer Pt were deposited.Finally,the Interdigital transducer and reflection gate on the sensor surface were stripped.At last,muffle furnace and vector network analyzer were used to test the temperature and frequency response of the sensor.Platinum wire and platinum paste were used to lead the sensor and fixed on the ceramic plate.The TCF value was-54.65ppm/℃in the range of 23～800℃,and the sensor was found to fail at 800 In order to improve the working temperature of the sensor,400nm thick Si O₂and AL₂O₃protective layers are sputtered respectively.The test results show that the characteristic frequency and absolute value of TCF of the sensor with protective layer are reduced to 1000℃.The electrode on the sensor surface did not agglomerate after 1h of insulation,which proves that the protective layer can effectively improve the working temperature,but there will be defects in some areas of the busbar,because the binding force between Ta and ALN of the transition layer decreases.