Research On Electric Field And Infrared Frequency Tuning Characteristics Of Aluminum Nitride Based Film Bulk Acoustic Resonator (FBAR)

In recent years,with the acceleration of the mobile Internet and the informatization process,the mobile communication industry has ushered in a rapid development and innovation boom,resulting in huge demand for communication terminal equipment.In wireless communication systems,film bulk acoustic resonators?FBARs?have extensive applications in filters,oscillators,duplexers,and low noise amplifiers?LNA?,due to the advantages of small size,high frequency,high Q value,and CMOS compatibility.Among various research fields of FBAR technology,frequency tuning has always been a hotspot in both academia and industry.Tunability of FBAR has tremendous applications and significant value in frequency consistency,temperature compensation,frequency band expansion and sensing fields.Among various FBAR frequency modulation techniques,the intrinsic electric field tuning and optical tuning methods based on piezoelectric films exhibit unique advantages of flexibility,fast response and no need for additional modulation unit,thus enabling them outstanding advantages and promising applications.At present,there still exist some problems in the study of FBAR's intrinsic electric field tuning and optical tuning characteristics.Current research on intrinsic electric field tuning mainly focuses on the quantitative results of the modulation performance of the presented devices,while it still remains blank in the mechanism of such phenomena.On the other hand,although extensive research about FBAR ultraviolet modulation and visible light modulation has been reported,research on infrared tuning is still rare,especially in the realization of the high sensitivity and reliability of the FBAR based infrared sensor.Therefore,this paper carries out systematically and in-depth study on the electric field and infrared tuning characteristics of AlN based FBAR under the support of the National Key Research and Development Program of China,the National Natural Science Foundation of China,and the Joint Research Fund of Ministry of Education,China.The main work of the dissertation is summarized as follows:?1?Based on the h-type one-dimensional simplified constitutive equation of piezoelectric material,the electromechanical equivalent model of AlN piezoelectric thin film is derived.Combined with the acoustic equivalent models of common material layers,the universal theoretical model of laminated structure FBAR is established.According to this model,the electrical impedance characteristics of the device are analyzed,and FBAR with dual main resonant modes up to GHz is designed by optimization.In addition,finite element simulation software COMSOL Multiphysics is used to analyze the electrical and vibration characteristics of the device under resonant mode.The simulation results are in good agreement with the theoretical model,which indicates that the established theoretical model can effectively predict the resonant characteristics of laminated FBAR.?2?The theory and method for preparing AlN piezoelectric film based on pulsed DC magnetron sputtering is studied.The influence of key process parameters on the crystallization of the c-axis?002?crystal plane are experimentally analyzed,including substrate temperature,sputtering power,gas flow ratio,and process vacuum.AlN piezoelectric films with high c-axis orientation are finally prepared by optimized process parameters.The test results show that the?002?crystal plane orientation diffraction peak intensity of the as-fabricated AlN piezoelectric films is as high as 10⁵counts,meanwhile achieving a full width at half maximum?FWHM?of less than 2°.Furthermore,the integrated micro-nano fabricating technology of FBAR device based on the AlN piezoelectric film is designed,and the designed dual-mode FBAR prototype is fabricated.The test results show that the 1st mode lies around 2.5 GHz,with series resonant Q value of 163,parallel resonant Q value of 249,and electromechanical coupling coefficient of 3.72%.The 2nd mode lies around 3.5 GHz,with series resonant Q value of 211,parallel resonant Q value of 143,and electromechanical coupling coefficient of 4.44%.?3?The electric field tuning characteristics of the dual-mode AlN-FBAR are systematically studied.The experimental results show that the series and parallel resonant frequencies of 1st mode and 2nd mode both are linearly and positively correlated with the applied bias electric field.The tunability of the 1st mode at series and parallel resonant frequency are 48.05 kHz/?MV/m?and 33.13 kHz/?MV/m?,respectively.Meanwhile,2nd mode reaches 68 kHz/?MV/m?and 59.7 kHz/?MV/m?.The dependence of each parameter in the MBVD model on electric field is further studied.The extraction results show that static capacitance C₀ and dynamic capacitance C_m are negatively correlated with the bias electric field,while dynamic resistance R_m and dynamic inductance L_m are positively correlated.The mechanism of electric field tuning of FBAR is systematically analyzed.It is found that electric filed stiffening effect of the AlN piezoelectric thin film plays a major role in the tuning characteristics of FBAR.The dependence of equivalent stiffness coefficient of AlN on electric filed is extracted by iterative algorithm,corresponding to a sensitivity of 333 ppm/?MV/m?in the range of-150 to 150 MV/m.Moreover,for the first time,an atomic interaction mechanism based on inverse piezoelectric effect and Born-Landéequation is proposed to reveal the nature of electric field stiffening effect,suggesting that the nonlinear variation of the interatomic force induced by electric field modulation is the intrinsic reason for this phenomenon in aluminum nitride piezoelectric thin films.Finally,the zero-temperature drift compensation of the device is realized by electric filed tuning.The results show that the zero-temperature drift modulation rates for 1st and 2nd mode are 1.29 V/°C and 0.16 V/°C,respectively.?4?The infrared tuning characteristics of the dual-mode FBAR are studied.The experimental results show that the resonant frequencies of 1st and 2nd mode are linearly and positively correlated with the incident infrared intensity,corresponding sensitivities are 80.88 kHz/?mW/mm²?and 1069.34 kHz/?mW/mm²?,respectively.At the same time,the reflection coefficient of 1st mode is negatively correlated with the incident infrared intensity,while that of 2nd mode is positively correlated.Both of them present nonlinear trend with the change of infrared intensity,and the maximum modulation sensitivity is-13.91 dB/?mW/mm ²?and 1.33 dB/?mW/mm ²?,respectively.The infrared photo-responsive mechanism of FBAR devices was explored,revealing that the photo-heating effect is not the main reason for the infrared photo-sensing of the device.It is inferred that the infrared-sensitive effect of the electrostatic capacitance is the main cause of FBAR infrared tuning.The experimental result indicates that the electrostatic capacitance has a strong dependence on incident infrared intensity,with the modulation sensitivity up to 5.93%/?mW/mm²?.Finally,based on the dual-mode FBAR,infrared detection with four sensing signals is realized,which achieves sensitivities of 3.32Hz/nW,561.21?dB/nW,43.17 Hz/nW and 53.70?dB/nW,respectively.By choosing the reflection coefficient in 1st mode as the sensing signal,the best noise equivalent power of 108 pW/Hz^0.5 can be achieved.