Study On Surface Acoustic Wave Temperature And Mass Dual-parameter Sensor Based On AlN Thin Film

Temperature and quality detection plays an important role in environment,biology,energy and other fields.Based on the aluminum nitride?AlN?piezoelectric thin film,a dual-port delay line temperature and mass dual-parameter SAW sensor is designed,simulated and fabricated.The sensitivities of temperature and mass were studied in principle and experimentally,together with signal extraction method and related interface circuits were also studied and designed.Following works have been completed in the thesis,1.Based on the AlN thin film delay line SAW sensor,the influence of structural parameters on the performance of SAW sensor is theoretically analyzed.The influence of interdigital transducer?IDT?pair numbers on output amplitude and frequency characteristics of the SAW sensor is simulated and analyzed based on IDT's delta function model.The influence of IDT thickness,metallization rate and AlN piezoelectric film thickness on the SAW vibration mode and the output characteristic frequency of SAW sensor is simulated.The results show that the output characteristic frequency of the SAW sensor decreases linearly with the increase of the metallization rate and decreases linearly with the increase of the thickness of the IDT,while increases periodically nonlinearly with the increase of the thickness of the AlN piezoelectric thin film.2.Based on the simulation results,a Al/AlN/Si?100?delay line SAW temperature and mass dual parameter sensor is optimally designed.The parameters of the structure are as follows:the width of the finger strip and the finger distance of the uniform IDT are 10?m,the acoustic aperture is 4mm,the cross finger pair number is 50,the input and output IDT center distance is 5mm,the Al IDT thickness is 0.2?m,and the AlN piezoelectric thin film thickness is 1?m.3.Based on the relationship between temperature and stress and strain is discussed theoretically.The simulation analysis of the sensitive characteristics of temperature and mass loading of the designed SAW temperature quality dual parameter sensor and the numerical simulation of the coupling field are carried out respectively.Simulation works have been carried out for the designed temperature and mass dual parameter SAW sensor and their sensitivity to substrate temperature and mass loading are numerically analyzed.The numerical results show that the output characteristic frequency of SAW dual-parameter sensor has a negative linear relationship with the substrate temperature and a negative linear relationship with mass loading as well.4.A dual parameter SAW sensor with aluminum nitride?AlN?thin film,aluminum?Al?IDT and silicon?Si?100??substrate structure is fabricated based on the DC magnetron sputtering method together with the semiconductor technology compatible with the standard CMOS process.The SEM microstructure characterization results show the fabricated SAW sensor has good accuracy and surface smoothness.5.The fabricated SAW sensor is characterized and analyzed in the temperature range of 0¹50?,and the output characteristic frequency of the SAW sensor has a good negative linear correlation with the temperature.Its temperature sensitivity is-4.3KHz/?,which indicates it could be employed for accurate temperature detection.By the atomic layer deposition method,the Al₂O₃ thin film is deposited in the quality sensitive region of the fabricated SAW sensor to act as the micro-mass load.And the frequency response characteristic to the mass load of the SAW sensor is experimentally obtained.A clear negative linear correlation between the output characteristic frequency and mass load is observed with the experimentally obtained mass sensitivity of296GHz?cm/g,which is better than the SAW mass sensor reported in China.The experimental results laid the foundation for expanding its future applications as biosensor and other multi-parameter sensors.6.A phase difference and frequency difference detection circuit is designed based on STM32F103RTC6 microcontroller and AD9854 high frequency signal source.The hardware circuit and software program of STM32 microcontroller and MC1496 analog multiplier chip are used to measure the frequency difference between input and output signals of sensors.A new solution is proposed for the detection of the output signal of the delay line SAW temperature and mass dual parameter sensor through combining the phase difference detection circuit composed of AD8302 and software algorithm.Innovation points of the paper are summarized as follows:Firstly,the atomic layer deposition of.Al₂O₃ is proposed and used as the micro-mass loading in the experiments to characterize the extraordinarily high mass sensitive of SAW sensor.Secondly,the SAW temperature and mass dual parameter sensor is successfully designed based on the proposed optimal design method.Thirdly,a temperature and quality dual parameter SAW sensor is successfully fabricated with high temperature and mass sensitivity.Research results have great significance in engineering applications,and so far there is no similar reports in China.