Design Of FBAR Gamma Irradiation Sensors

Due to its advantages of high operating frequency,small size,high quality factor,low loss,high power capacity,high energy conversion efficiency and compatibility with IC technology,the thin film bulk acoustic resonator(FBAR)is also the ideal technology to realize high performance transducer and sensors.This thesis is to design a new type FBAR radiation sensor,including designing of FBAR,sensitive mechanism and designing of readout circuit.Two different stack structure FBARs have been designed as sensor head.Structure one FBAR consists of metal layer-piezoelectric layer-oxide layer-metal layer.The difference between the two stacked FBARs is that there is a semiconductor layer between the piezoelectric layer and the oxide layer in the structure two FBAR and the oxide layer in these two structures is the radiation sensitive layer in these two structures.The process flow of these two stacked FBARs is given at the same time.Different sensing mechanisms are proposed to explain the resonance frequency shift after gamma irradiation according to two different stacked structures FBAR.Mechanism one is DC tuning,the FBAR structure is four-layers stacked(metal layer-piezoelectric layer-oxide layer-metal layer),after gamma irradiation,Electron-hole pairs will be generated in the silicon dioxide radiation-sensitive layer,the generated electrons and holes undergo recombination,separation and trapping.The trapped holes form a DC voltage in the silicon dioxide,and the DC voltage make the resonant frequency of FBAR shift.Mechanism two is tuning by a variable capacitor in series.There is a semiconductor layer between oxide layer and piezoelectric layer in the FBAR stack structure,as a space charge layer capacitance is formed in the semiconductor n-type zinc oxide,which is equivalent to connecte a capacitor to FBAR in series.At different doses,the formed space charge layer capacitance is different,the FBAR resonant frequency shift is not the same.According to these two mechanisms,the relationship between the resonant frequency shifts of FBAR and the total dose are derived.At last,in order to improve the accuracy of the detection,a dual dielectric radiation sensitive layer structure was designed and its mechanism was analyzed.To obtain the performance of the FBAR such as the resonant frequency and quality factor,a test circuit board is designed according to its package size.Because the fixture in the test board will bring errors to the test results,TRL calibration kits are designed to eliminate these errors.To obtain the resonant frequency shift of FBAR,a read-out circuit of FBAR gamma radiation sensor is designed,including oscillator circuit,mixer and filter circuit,amplifying and shaping circuit,FPGA readout circuit.The phase noise of the oscillator is optimized.According to the FBAR equivalent circuit in mechanism two,the output frequency of FBAR oscillator at different doses is obtained.Filter circuit,amplifying and shaping circuit,FPGA readout circuit were designed and simulated at the same time and each circuit module is tested to verify the feasibility,finally the entire circuit is also tested.