Radio Frequency Bulk Acoustic Wave Research Articles

Analysis and verification on second-order nonlinearity in radio frequency bulk acoustic wave devices employing temperature compensation films

This paper discusses the impact of SiO2/SiOF on second harmonic (H2) generation in temperature-compensated (TC) film bulk acoustic resonators (FBARs). First, two types of TC-FBARs are fabricated and their H2 behavior is compared with that of the standard FBAR. Next, the H2 characteristics of the TC layer are investigated by the use of a series of TC-FBARs where SiOF and Cr layers are placed on the outside of electrodes. The simulations agree very well with the measurements and can explain well how the H2 response changes with Cr thickness. Not only AlN but also SiOF contributes to the generation of H2 response, and H2 becomes very small at an appropriate Cr thickness. Finally, the TC-FBAR filter operating at 5.9 GHz is fabricated and its H2 response is compared with the simulation. The simulation agrees well with the experiment. It is also demonstrated that the insertion of the TC layer is effective in suppressing H2 generation.

Perturbation analysis of second-order nonlinearity and its effectiveness for radiofrequency bulk acoustic wave devices

Suppression of nonlinear signal generation in radiofrequency (RF) surface and bulk acoustic wave devices is one of the most important subjects for the RF front-end modules of recent cellular handsets. In particular, issues with second-order nonlinear products of bulk acoustic waves are well known. In this work, we succeeded in extracting the dominant parameters for second-order nonlinear analysis proposed by Hashimoto et al. [Joint Conf. European Frequency and Time Forum and IEEE Freq. Cont. Symp., 2017, p. 538] and verified that it is applicable in a wide frequency range and also effective for film bulk acoustic resonator (FBAR) device design. Combining the extracted nonlinear coefficients on the perturbation analysis by driving near the fundamental frequency (f0) and half resonant frequency (1/2f0) of the FBAR could reproduce second-order nonlinear characteristics in a wide frequency range. It was also confirmed that the proposed simulations are in good agreement with measurement results for various types of resonators and FBAR filters.

2D scalar wave modelling of apodized RF BAW resonators for transverse mode analysis

This paper proposes the use of a two-dimensional scalar wave model for fast analysis of apodized AlN-based radio frequency bulk acoustic wave devices. First, the working principle and model setup is introduced. Only one particular Lamb mode (S1−) is considered, and its behavior is modeled by a simple scalar wave equation looking from the top surface. Multiple layers are added to the side boundaries so that mode conversion to other modes is treated as leakage to surroundings. The wavenumber of field distribution for each resonance mode is calculated, and then its excitation coefficient, quality factor, and resonance frequency are derived. The device input admittance is calculated by applying derived parameters to the equivalent circuit. A series of oval-shaped AlN-based film bulk acoustic resonator devices are simulated and compared with experimental results. The theoretical results agreed well with the experimental ones, and accuracy and effectiveness of the present analysis are verified.

Emphasis mechanism of nonlinear responses caused by transverse modes in RF BAW devices

It is known that nonlinear responses by transverse resonances are more emphasized than those by the main resonance in radio frequency bulk acoustic wave devices. This paper investigates this mechanism using the LCR-based nonlinear equivalent circuit proposed by the authors. Here a number of acoustic branches are newly added to take multiple transverse resonances into account, and amplitudes of nonlinear voltage sources in the model are determined by summation of currents flowing to acoustic branches. Parameters necessary for the analysis are determined experimentally. It is shown that simulated second and third harmonic responses agree well with the measurement. Next, the magnification mechanism is discussed. It is shown that mth harmonics generated by transverse modes are magnified by m-times approximately, and the factor of m is originated to that at the production between field components of transverse and main modes.

Perturbation Analysis of Nonlinearity in Radio-Frequency Bulk Acoustic Wave Resonators Using the Mass-Spring Model.

This article describes derivation of an equivalent circuit for nonlinear responses in film bulk acoustic resonators from the first-order perturbation analysis using the piezoelectric constitutive equations with the h -form. For simplicity, electrodes and piezoelectric layers are considered as mass and spring, respectively, in the derivation. Then, it is demonstrated that the second- and third-order harmonic responses can be simulated well by the circuit. In addition, nonlinearity in the Si substrate is also taken into account and its impact is discussed. It is also discussed how the frequency dependences vary with the nonlinearity mechanisms as a finding from the derived equivalent circuit.

Impact of Transverse Mode Resonances on Second Harmonic Generation in Radio-frequency Bulk Acoustic Wave Resonators

This paper investigates the impact of transverse mode resonances on second harmonic (H2) generation in radio-frequency bulk acoustic wave devices. Previous work indicated that second-order nonlinearity of the main mode can be well simulated by one-dimensional perturbation analysis using the h-form piezoelectric constitutive equations. This work expands the analysis to the two-dimensional case to investigate the influence of transverse resonances on the H2 generation. The result shows that transverse modes generate strong H2 responses, and this phenomenon is consistent with experimental results. The origin of the strong H2 generation is also discussed.

Radio Frequency Bulk Acoustic Wave Filters: Current Status and Future Prospective

Radio Frequency Bulk Acoustic Wave Filters: Current Status and Future Prospective

Theoretical considerations on influence of circuit impedance on IMD2 measurement of radio-frequency bulk acoustic wave duplexers

This paper discusses theoretically how the impedance of peripheral circuits influences the measurement of second-order inter-modulation distortion (IMD2) generated in RF BAW duplexers. First, IMD2 properties of RF BAW duplexers are expressed by a rank three tensor. Then, the tensor expression is used to evaluate how the port termination affects the IMD2 output. It is shown that variation of IMD2 output is caused mainly by five mechanisms: 1) variation of the transmit (Tx) signal intensity caused by impedance mismatching at the Tx port; 2) variation of the jammer signal intensity caused by impedance mismatching at the antenna (ANT) port; 3) variation of detector read caused by impedance mismatching at the receive (Rx) port; 4) reentry of the IMD2 signal to the ANT port caused by impedance mismatching at the ANT port; and 5) reentry of the Tx signal to the ANT port caused by impedance mismatching at the ANT port. Because input impedance of the ANT port is usually not defined for jammer signals, a large attenuator must be added to the ANT port to suppress the impedance mismatching. This result is consistent with experiments reported previously.

Considerations for measurement setup for second-order nonlinearity in radio-frequency bulk acoustic wave duplexers

This paper discusses the influence of the setup on the measurement reliability and reproducibility for the secondorder inter-modulation distortion (IMD2) generated in RF BAW duplexers. Our measurement results show that the IMD2 level can be reliably and reproducibly measured when the port terminations are properly applied. For example, a filter and a relatively large (>20 dB) attenuator are necessary between an oscillator and the antenna port of the duplexer to suppress the nonlinear mixing and the impedance mismatching. If the order of these two devices were reversed, the IMD2 level would change significantly. Although an isolator is commonly used to stabilize the power amplifier output, our research results show that not using an ISO produced more accurate results.

A circuit model for nonlinear simulation of radio-frequency filters using bulk acoustic wave resonators

This paper describes a circuit model for the analysis of nonlinearity in the filters based on radiofrequency (RF) bulk acoustic wave (BAW) resonators. The nonlinear output is expressed by a current source connected parallel to the linear resonator. Amplitude of the nonlinear current source is programmed proportional to the product of linear currents flowing in the resonator. Thus, the nonlinear analysis is performed by the common linear analysis, even for complex device structures. The analysis is applied to a ladder-type RF BAW filter, and frequency dependence of the nonlinear output is discussed. Furthermore, this analysis is verified through comparison with experiments.