Research And Fabrication Of Ultraviolet Sensor Based On FBAR

With the development of the information age,thin film bulk acoustic resonators（FBARs）have the advantages of small size,high frequency and high Q value,and are widely used in radio frequency and sensing fields.Because of its strong anti-interference ability and high sensitivity,ultraviolet sensing technology has great application potential in civil and military fields.AlN has the advantages of high speed of acoustic,stable physical and chemical properties,and compatibility with COMS process.It is expected to integrate with other components to prepare small size passive high-sensitivity UV sensors,which has research value and application prospects.In this thesis,a UV sensor that combines metal-semiconductor-metal（MSM）and FBAR is proposed to study the performance of the device and explore the fabrication process of the device.The main research contents of the thesis are as follows:（1）The UV sensing mechanism of the combination of MSM and FBAR is studied,and the theoretical performance of the device is calculated by simulation.The MSM UV detector and FBAR were combined to form the MSM-FBAR UV detector by the equivalent circuit method,the influence of the connection method on its UV detection performance was simulated,and the design method of the parallel structure device was explored.The results show that when the electrode width of the Ni-ε-Ga₂O₃ MSM device is 5μm and the interdigital spacing is 4μm,the parameters in the FBAR are:k_t² is 12%,R_s is 0,C₀ is 0.7 p F,fs is 500 MHz,When Q_pis 2000 and Q_p is 5000,the device obtains the best impedance sensitivity of 100 kΩ/（μW/mm²）;when kt² is 20%,Rs is 0,and the static capacitance is equal to the MSM equivalent capacitance,the device obtains the best frequency sensitivity 1.4MHz/（μW/mm²）.（2）The etching process of Al_0.8Sc_0.2N and epitaxial AlN was studied.By optimizing the Inductively Coupled Plasma（ICP）etching equipment program,the etching selectivity ratio of Al Sc N to photoresist is 0.7:1,the etching rate is 79 nm/min,and the etching rate is 79nm/min.The inclination angle is 20.2°,and the surface roughness is 1.28 nm.The removal process of the epitaxial AlN film was studied,the etching morphologies of the dry and wet methods,and the wet etching of the film in different etching solutions were compared.Finally,the optimal surface roughness was obtained in KOH solution of 1.3 nm.（3）AlN seed/Mo/AlN/Mo/AlN FBAR devices and epitaxialε-Ga₂O₃-based MSM devices were fabricated by MEMS technology,their UV detection performance was characterized,and the UV response of the devices after the combination was studied.This structure was prepared and the resonant frequency of the fabricated FBAR device is 2.49GHz,the Q_p value is 369 and k_t²=6.4%.The resonant frequency of the prepared MSM-FBAR device is 2.5 GHz,the Q_p value is 31 and k_t²=3%,the impedance sensitivity is 0.9MHz/（μW/mm²）,and the impedance sensitivity is 27Ω/（μW/mm²）.Finally,the MSM FBAR hetero-integrated UV sensor is designed.