Analysis and modeling of nonlinear behaviors in piezoelectric surface and bulk acoustic wave devices
Creators: name: Pang, Xiangnan
Publisher: name: No Publisher Supplied
Year: 2021

description: Filters are one of the most important components in the radio frequency front-end (RFFE) wireless communication systems. The acoustic wave-based filters are the dominant technology for mobile devices with small, compact size since acoustic wavelength is about four or five order smaller than the electromagnetic wavelength at the same frequency. There are two solutions of RF filters: surface acoustic wave (SAW) and bulk acoustic wave (BAW) technology. Both SAW and BAW devices are fabricated on the piezoelectric material where the electro-acoustic conversion can be achieved. Along with the emergence of fifth generation (5G) communication, the operation of ultra-high frequency, broadband communication requires that the number of filters in devices increases and the size of each filter/resonator decrease dramatically. The high-power transmission of data in 5G systems also induce a large amplitude acoustic wave propagation at the SAW and BAW filters/resonators. The strict RF module specification require device engineers to consider more factors when simulating and designing the filters. Nonlinearity of SAW and BAW devices is among these.The nonlinear behavior of acoustic wave is at the origin of almost performance instability and sensitivities of devices. Two different classes of nonlinear phenomena exist in terms of propagation behaviors of acoustic waves in piezoelectric devices: (I) The propagation of small amplitude waves in a nonlinear biased medium and (II) the propagation of finite amplitude waves in a nonlinear medium. For the first type nonlinearity, the physical variables change from environment, such as temperature, force, stress, pressure, and static electric field will bias the medium, resulting in the propagation of acoustic waves modified. Of these physical bias fields, the frequency change of the propagated acoustic wave due to temperature variation is especially important for the filter application since the resonators’ frequency change will shift the passband of filters to either higher or lower frequency. This may lead to the violation of filter performance against needed specification. For the second type of nonlinearity, the large amplitude acoustic wave induced by high-power will distort the waveform and lead to a harmonic signal generation. These harmonics, at frequency of integer multiples of fundamental frequency, may interfere with other bands, leading to severe sensitivity problem. Intermodulation effects occurs when more than two signals are applied into the nonlinear medium. The piezoelectric acoustics involves two physics domains of electric and mechanical field. There are various circuit-based models which are extended from the linear ones for the second type nonlinearity, such as coupling-of-modes (COM) model for SAW devices and Mason model or equivalent circuit models for BAW devices. For this dissertation, we investigate the second type nonlinearity from the point of view basic governing physics. Frequency temperature behavior of SAW and BAW devices, which is the first type nonlinearity, will also be studied.More specifically, this study derived and developed the coupled piezoelectric field equation in frequency domain from the basic nonlinear formulation of piezoelectricity. The proposed formulation was implemented using finite element analysis and was employed to study the second type nonlinear problems of the quartz resonators, SAW and BAW resonators. Nonlinear vibration of quartz resonators considering the high order material constants were simulated and validated with experiments and analytical solution in the literatures. The second and third harmonic generation of LiNbO3 based temperature-compensated SAW (TC-SAW) and longitudinal leaky SAW (LLSAW) were investigated. For BAW resonators, the acoustic dispersion relation, the effect of lateral size on the mode coupling, and the frequency-temperature behavior were studied. The most important contribution of this dissertation is proposing a new formulation and method to study the second type nonlinear problems of piezoelectric acoustic devices from the point of view of basic physics.