Bulk Acoustic Resonator Research Articles

Piezo-optomechanical coupling of a 3D microwave resonator to a bulk acoustic wave crystalline resonator

We report the observation of coupling between a 3D microwave cavity mode and a bulk mechanical resonator mediated by piezoelectric and radiation pressure effects. The system is composed of a quartz bulk acoustic wave resonator placed inside a microwave re-entrant cavity, which is designed to act as both the electrodes for piezoelectric actuation and a 3D resonator. The cavity electromagnetic mode is modulated by a 5 MHz bulk acoustic wave shear mode, which is modeled and experimentally verified using the input-output formalism. Through finite element method simulations, we calculate the various contributions to the electromechanical coupling and discuss the potential of the system to reach high cooperativities as well as suitable applications.

A general approach for dispersion relations in multilayered structures with an arbitrary number of piezoelectric layers and elastic layers

A general approach, which can efficiently and automatically derive dispersion relations for infinite layered structures with any number of piezoelectric and elastic layers, is proposed in this paper. Based on the Stroh formalism and the dual variable and position method, the general relationship between top and bottom variables of a single layer is obtained first. Considering the different layups possibly appearing in multi-structures, three base cases are presented in detail. By combining these base cases repeatedly from the bottom of the plates to the top, we can easily write programming codes to derive dispersion relations for any general multilayered structure automatically. To verify this approach, dispersion curves and mode shapes for the film bulk acoustic resonator and the stacked crystal filter are presented in this paper. The results show good conformity with reported works and simultaneously prove the ability of our approach for complex and generally anisotropic multilayered structure. Above all, this general approach is efficient and superior to get the dispersion relations, which is convenient for further study of wave propagation characteristics in general multilayered structures.

Hydrophobin-functionalized film bulk acoustic wave resonators for sensitive and polarity-sensitive sensing of volatile organic compounds

Film bulk acoustic wave resonators have demonstrated great potential in the detection of volatile organic compounds owing to their high sensitivity, miniature size, low power consumption, capacity for integration, and other beneficial characteristics. However, it is necessary to functionalize the surfaces of these resonators to enhance the adsorption and discrimination of volatile organic compounds. Here, we report a convenient and reliable method for functionalizing the surfaces of film bulk acoustic wave resonators with hydrophobins via self-assembly to enable highly sensitive and polarity sensitive detection of volatile organic compounds. Experiments conducted using various concentrations of five volatile organic compounds possessing different polarities demonstrated that the hydrophobin coating enhanced the responsivity of the proposed sensor. The obtained results were in good agreement with the Brunauer–Emmett–Teller model of multilayer physisorption, which suggests that the hydrophobin coating enhanced the sensitivity by improving the monolayer adsorption capacity. Our work demonstrates that the combination of multifunctional biosurfactants and microelectromechanical devices can permit high-performance gas sensing.

An Overview of High Frequency Acoustic Sensors-QCMs, SAWs and FBARs-Chemical and Biochemical Applications.

Acoustic devices have found wide applications in chemical and biosensing fields owing to their high sensitivity, ruggedness, miniaturized design and integration ability with on-field electronic systems. One of the potential advantages of using these devices are their label-free detection mechanism since mass is the fundamental property of any target analyte which is monitored by these devices. Herein, we provide a concise overview of high frequency acoustic transducers such as quartz crystal microbalance (QCM), surface acoustic wave (SAW) and film bulk acoustic resonators (FBARs) to compare their working principles, resonance frequencies, selection of piezoelectric materials for their fabrication, temperature-frequency dependency and operation in the liquid phase. The selected sensor applications of these high frequency acoustic transducers are discussed primarily focusing on the two main sensing domains, i.e., biosensing for working in liquids and gas/vapor phase sensing. Furthermore, the sensor performance of high frequency acoustic transducers in selected cases is compared with well-established analytical tools such as liquid chromatography mass spectrometry (LC-MS), gas chromatographic (GC) analysis and enzyme-linked immunosorbent assay (ELISA) methods. Finally, a general comparison of these acoustic devices is conducted to discuss their strengths, limitations, and commercial adaptability thus, to select the most suitable transducer for a particular chemical/biochemical sensing domain.

Generation and Propagation of Superhigh-Frequency Bulk Acoustic Waves in GaAs

Coherent super-high-frequency (SHF) vibrations provide an excellent tool for the modulation and control of excitations in semiconductors. Here, we investigate the piezoelectric generation and propagation of longitudinal bulk acoustic waves (LBAWs) with frequencies up to 20 GHz in GaAs crystals using bulk acoustic wave resonators (BAWRs) based on piezoelectric thin ZnO films. We show that the electro-acoustic conversion efficiency of the BAWRs depends sensitively on the sputtering conditions of the ZnO films. The BAWRs were then used for the study of the propagation properties of the LBAWs in GaAs in the frequency and temperature ranges from 1 to 20 GHz and 10 and 300 K, respectively, which have so far not been experimentally accessed. We found that the intrinsic acoustic absorption of GaAs in the temperature range from 80 K to 300 K is dominated by scattering with thermal phonons. At lower temperatures, in contrast, the intrinsic acoustic absorption saturates at a frequency-dependent value. Experiments carried out with different propagation lengths indicate that the saturation is associated with losses during reflection at the sample boundaries. We also demonstrate devices with high quality factor fabricated on top of acoustic Bragg-reflectors. The results presented here prove the feasibility of high-quality acoustic resonators embedding GaAs-based nanostructures, thus opening the way for the modulation and control of their properties by electrically excited SHF LBAWs.

Enhancing RF Bulk Acoustic Wave Devices: Multiphysical Modeling and Performance

The rapid proliferation of smartphones, tablets, and intelligent wearables is proof of the global success of high-performance RF acoustic devices based on bulk acoustic wave (BAW) and surface acoustic wave (SAW) technologies. Advanced wireless communication standards, such as 4G/LTE and the upcoming 5G, make the implementation of new RF features (power handling, wider bandwidth, and reconfigurability) mandatory in modern end-user equipment for mobile communications. This leads to an increasing demand for SAW and BAW components due to their compatibility with higher frequencies. In the year 2020, shipments of RF filters will exceed 68 billion (Figure 1), of which about 40 billion will be high-performance filters, such as film bulk acoustic resonators (FBARs), high quality factor (Q) BAW components, temperature-compensated (TC) SAW components, and thin-film SAW components [1]-[3].

Testing the generalized uncertainty principle with macroscopic mechanical oscillators and pendulums

Recent progress in observing and manipulating mechanical oscillators at quantum regime provides new opportunities of studying fundamental physics, for example, to search for low energy signatures of quantum gravity. For example, it was recently proposed that such devices can be used to test quantum gravity effects, by detecting the change in the [x,p] commutation relation that could result from quantum gravity corrections. We show that such a correction results in a dependence of a resonant frequency of a mechanical oscillator on its amplitude, which is known as amplitude-frequency effect. By implementing this new method we measure amplitude-frequency effect for 0.3 kg ultra high-Q sapphire split-bar mechanical resonator and for 10 mg quartz bulk acoustic wave resonator. Our experiments with sapphire resonator have established the upper limit on quantum gravity correction constant for $\beta_0<5 \times10^6$ which is a factor of 6 better than previously detected. The reasonable estimates of $\beta_0$ from experiments with quartz resonators yield an even more stringent limit of $4\times10^4$. The data sets of 1936 measurement of physical pendulum period by Atkinson results in significantly stronger limitations on $\beta_0 \ll 1$. Yet, due to the lack of proper pendulum frequency stability measurement in these experiments, the exact upper bound on $\beta_0$ can not be reliably established. Moreover, pendulum based systems only allow testing a specific form of the modified commutator that depends on the mean value of momentum. The electro-mechanical oscillators to the contrary enable testing of any form of generalized uncertainty principle directly due to much higher stability and a higher degree of control.

Suppression of Spurious Lateral Modes and Undesired Coupling Modes in Frame-Like FBARs by 2-D Theory.

Thin-film bulk acoustic wave resonators (FBARs) are of significant interest for wireless applications due to their good performance. To achieve excellent characteristics, the frame-like FBARs were previously invented by researchers in this field to suppress the resonances of spurious lateral modes (or spurious modes). Another aspect that has an impact on the working performance of FBAR is the undesired coupling modes, which were rarely studied due to the lack of proper theoretical tools. In this article, we thoroughly investigate the coupling modes and spurious modes in frame-like FBARs by 2-D theory, which was already derived in our previous work. The widely used state-vector approach is applied here and both free and forced vibration problems are analyzed. Frequency spectra and mode shapes obtained from free vibration analysis show the coupling vibration characteristics in this structure. Moreover, the admittance resonance obtained from the forced vibration analysis shows the efficiency of the designed structure on the suppression of both undesired coupling and spurious modes. Results in this article provide a thorough understanding of the vibration in frame-like FBAR, and the method presented can work as an effective tool in engineering design process.

Engineering Electron–Phonon Coupling of Quantum Defects to a Semiconfocal Acoustic Resonator

Diamond-based microelectromechanical systems (MEMS) enable direct coupling between the quantum states of nitrogen-vacancy (NV) centers and the phonon modes of a mechanical resonator. One example, a diamond high-overtone bulk acoustic resonator (HBAR), features an integrated piezoelectric transducer and supports high-quality factor resonance modes into the gigahertz frequency range. The acoustic modes allow mechanical manipulation of deeply embedded NV centers with long spin and orbital coherence times. Unfortunately, the spin-phonon coupling rate is limited by the large resonator size, >100 μm, and thus strongly coupled NV electron-phonon interactions remain out of reach in current diamond BAR devices. Here, we report the design and fabrication of a semiconfocal HBAR (SCHBAR) device on diamond (silicon carbide) with f × Q > 1012 (>1013). The semiconfocal geometry confines the phonon mode laterally below 10 μm. This drastic reduction in modal volume enhances defect center coupling to a mechanical mode by 1000 times compared to prior HBAR devices. For the native NV centers inside the diamond device, we demonstrate mechanically driven spin transitions and show a high strain-driving efficiency with a Rabi frequency of (2π)2.19(14) MHz/Vp, which is comparable to a typical microwave antenna at the same microwave power, making SCHBAR a power-efficient device useful for fast spin control, dressed state coherence protection, and quantum circuit integration.

Two-Dimensional Coupling Vibration Analysis of Laterally Acoustically Coupled Two-Port Thin-Film Bulk Acoustic Resonators

In this paper, we present an approach to studying the mode coupling vibrations in two-port thin-film bulk acoustic wave resonator (FBAR) devices with two pairs of electrodes deposited on the zinc oxide film. The two-dimensional plate theory established in our previous work is employed, which takes into account the coupling of the operating thickness-extensional mode with the extensional, flexural, fundamental and second-order thickness-shear modes. The propagation of straight-crested waves in the plate is studied, and the state-vector approach is successfully used to simplify the derivation process. For a structurally symmetric device, the modes are separated into quasi symmetric and antisymmetric ones. Frequency spectra and corresponding mode shapes are obtained under the stress-free boundary conditions, respectively, and then coupling effects and energy trapping phenomenon are discussed in detail. Some results for structures with asymmetric electrode distributions are also shown. It is found that the choice of aspect ratio has a great effect on mode couplings of FBAR devices. This study will be useful for the design of FBAR filters and sensors.

FlexMEMS-enabled hetero-integration for monolithic FBAR-above-IC oscillators

In this work, a monolithic oscillator chip is heterogeneously integrated by a film bulk acoustic resonator (FBAR) and a complementary metal-oxide-semiconductor (CMOS) chip using FlexMEMS technology. In the 3D-stacked integrated chip, the thin-film FBAR sits directly over the CMOS chip, between which a 4 μm-thick SU-8 layer provides a robust adhesion and acoustic reflection cavity. The proposed system-on-chip (SoC) integration features a simple fabrication process, small size, and excellent performance. The oscillator outputs 2.024 GHz oscillations of −13.79 dBm and exhibits phase noises of −63, −120, and −136 dBc/Hz at 1 kHz, 100 kHz, and far-from-carrier offset, respectively. FlexMEMS technology guarantees compact and accurate assembly, process compatibility, and high performance, thereby demonstrating its great potential in SoC hetero-integration applications.

Ultrathin Ceramic Piezoelectric Films via Room-Temperature Electrospray Deposition of ZnO Nanoparticles for Printed GHz Devices.

High-frequency devices are key enablers of state-of-the-art electronics used in a wide and diverse range of exciting applications such as inertial navigation, communications, power conversion, medicine, and parallel computing. However, high-frequency additively manufactured piezoelectric devices are yet to be demonstrated due to shortcomings in the properties of the printed transducing material and the attainable film thickness. In this study, we report the first room-temperature-printed, piezoelectric, ultrathin (<100 nm) ceramic films compatible with high-frequency (>1 GHz) operation. The films are made of zinc oxide (ZnO) nanoparticles via near-field electrohydrodynamic jetting, achieving film piezoelectricity, without high-temperature processing, through a novel mechanism that is controlled during the deposition. Optimization of the printing process and feedstock formulation results in homogeneous traces as narrow as 213 μm and as thin as 53 nm as well as uniform field films as thin as 91 nm; the printing technique can be used with flexible and rigid, conductive and insulating substrates. The crystallographic orientation of the imprints toward the (100) plane increases if the rastering speed during printing is augmented, resulting in a larger piezoelectric response. The resonant frequency of film bulk acoustic resonators increases monotonically with the rastering speed, achieving transmission values as high as 4.99 GHz, which corresponds to an acoustic velocity of 2094 m/s, similar to the expected transverse value in high-temperature-grown ZnO films. Piezoresponse force microscopy maps of printed field films show local variation in the piezoelectric behavior across the film, with an average piezoelectric response as high as 21.5 pm/V, significantly higher than the d33 piezoelectric coefficient of single-crystal, high-temperature-grown ZnO, and comparable with reported values from ZnO nanostructures.

An Investigation on Extraction of Material Parameters in Longitudinal Mode of FBAR

A generalized method for the extraction of longitudinal parameters of materials in a film bulk acoustic resonator (FBAR) is proposed in this brief. Based on the simplification of the equivalent circuit of a Mason model, a compact step impedance resonator (SIR) model without loss resistors or static capacitors is obtained. The resonance of the acoustic layer is also expressed through the resonance condition of a SIR model analytically. Innovatively, the simplified model is used to fit the parallel resonance frequency ( ${f} _{\mathrm{ p}}$ ) of different measured FBARs on a same wafer. Combined with the stack information of five cross section samples and the measured ${f} _{\mathrm{ p}}$ , longitudinal acoustic velocities and densities of AlN and Mo is extracted. The fitted resonance frequency of the simplified model is compared to the measured ${f} _{\mathrm{ p}}$ , and the maximum frequency offset is controlled within 6 MHz. In addition, the extracted material parameters are compared with the reference values and show great matching. This brief analytically reveals the correlation between material parameters and ${f} _{\mathrm{ p}}$ , and the proposed method is useful for accurate frequency fitting and parameter extraction.

Resonant Spin Pumping in an Acoustic Microwave Resonator with ZnO-GGG-YIG/Pt Structure

A theory of acoustic spin pumping in a bulk acoustic wave resonator with a ZnO-YIG-GGG-YIG/Pt structure is presented, with allowance for the exchange contribution to the formation of a coupled magnetoelastic wave spectrum, and the back action of acoustically excited magnetic dynamics in YIG films on the elastic subsystem in all layers. Good agreement is achieved between the theoretical and experimental frequency–field dependences of the resonant frequencies of the resonator and the voltage magnitude of the inverse spin Hall effect in Pt.

Effects of mode couplings on the vibration characteristics of partially electroded thin-film bulk acoustic wave resonators

Mode coupling vibrations in thin-film bulk acoustic wave resonators (FBARs) were systematically analyzed in the series of our work. Previously, the two-dimensional theory of multi-layered FBAR plate has been established and used for the analysis of both free and forced vibrations of a fully electroded plate. In this paper, coupling vibrations in a partially electroded FBAR were taken into account, where the top electrode only covers the central part of the film. The two-dimensional equations were written into matrix form based on the state-vector approach. Transfer matrix functions of the global structure were obtained when continuous and traction-free boundary conditions were satisfied. Aspect ratios of both electroded and unelectroded regions were varied to research the influence of them on the coupling effects. The admittance versus frequency response was also obtained through forced vibration analysis to investigate the coupling effects. Results in this paper show the existence of energy-trapping behavior and the importance of structure size on mode coupling effects, which is important to the design of real FBAR devices.

Frequency-switchable polarity-inverted BAW resonators based on PZT/PTO epitaxial films using difference in coercive field

Electrical frequency switching in bulk acoustic wave resonators based on lead zirconate titanate (PZT)/PbTiO3 epitaxial bilayer films is demonstrated and analyzed. In general, the coercive field of PbTiO3 is higher than that of PZT. Independent polarity inversion of the PZT layers is achieved by applying an intermediate electric field between the coercive fields of PZT and PbTiO3 to the bilayer films. The resonant frequency is switched between the fundamental mode resonance (0.56 GHz) and second mode resonance (1.58 GHz) by applying a negative or a positive electric field to the resonators. The second mode operation can be achieved in the absence of an external electric field. A theoretical model simulated by Mason's equivalent circuit model including the effect of the polarity-inverted structure agreed well with the experimental results. The electromechanical coupling coefficients kt2 of both the PZT layer and the PbTiO3 layer of the polarity-inverted bilayer were estimated to be 17.6% (kt = 0.42) by comparing the experimental results with the theoretical simulations.

Detection and Discrimination of Volatile Organic Compounds using a Single Film Bulk Acoustic Wave Resonator with Temperature Modulation as a Multiparameter Virtual Sensor Array.

This paper describes the detection and discrimination of volatile organic compounds (VOCs) using an e-nose system based on a multiparameter virtual sensor array (VSA), which consists of a single-chip temperature-compensated film bulk acoustic wave resonator (TC-FBAR) coated with 20-bilayer self-assembled poly(sodium 4-styrenesulfonate)/poly(diallyldimethylammonium chloride) thin films. The high-frequency and microscale FBAR multiparameter VSA was realized by temperature modulation, which can greatly reduce the cost and complexity compared to those of a traditional e-nose system and can allow it to operate at different temperatures. The discrimination effect depends on the synergy of temperature modulation and the sensing material. For proof-of-concept validation purposes, the TC-FBAR was exposed to six different VOC vapors at six different gas partial pressures by real-time VOC static detection and dynamic detection. The resulting frequency shifts and impedance responses were measured at different temperatures and evaluated using principal component analysis and linear discriminant analysis, which revealed that all analytes can be distinguished and classified with more than 97% accuracy. To the best of our knowledge, this report is the first on an FBAR multiparameter VSA based on temperature modulation, and the proposed novel VSA shows great potential as a compact and promising e-nose system integrated in commercial electronic products.

Frequency Spectra of Coupling Vibration in High-Frequency Thickness-Shear ZnO Thin Film Resonator Applied in Sensing Field Based on the Hamilton Principle.

Mode coupling vibration of a multilayered ZnO thin film bulk acoustic wave resonator (FBAR) with its c-axis along the wave propagation direction operating at the fundamental thickness-shear (TSh) mode is studied in this paper. The accurate dispersion curve from 3-D piezoelectric theory indicates that the operating TSh mode could couple to the flexural mode, which influences the performance of a sensing resonator and needs to be eliminated through the so-called frequency spectrum analysis. Frequency spectra of coupling vibration in this FBAR can be obtained by substituting the displacement solutions consisting of the mode branches in the dispersion curve into several weak boundary conditions, which gives the integral boundary conditions across the plate thickness at the side edge of FBARs. The results show that the content of mode couplings to spurious modes depends on the plate length/thickness ratios. The character of desirable values of plate aspect ratios under which the operating TSh mode dominates among all modes is stated specifically, which provides fundamental guidance to the design of structural parameters of FBARs.

A 2-GHz FBAR-Based Transformer Coupled Oscillator Design With Phase Noise Reduction

The oscillator architecture is proposed to reduce the close-in phase noise as well as power consumption. The proposed Colpitts oscillator removes the current source which is the main source of the 1/ $f$ noise conversion. The removal of the current source is compensated by using the transformer and cross-coupled capacitors. The 2-GHz film bulk acoustic resonator (FBAR) is used for the high Q frequency selective elements in the oscillator design. According to measurement results, this FBAR-based oscillator shows $\geq$ 10 dB reduction in close-in phase noise. Specifically, 12-dB lower phase noise is achieved at 100 Hz offset frequency. Measured power consumption is 350 uW, which is almost half of the conventional Colpitts oscillator using same FBAR device.

Sensitivity analysis of multilayered C-axis inclined zigzag zinc oxide thin-film bulk acoustic resonators for CO2 concentration monitoring

This paper proposes a theoretical analysis of an innovative C-axis inclined zigzag multilayered ZnO thin-film bulk acoustic resonator (FBAR) for CO2 concentration monitoring. Analytical study is carried out with 3-D linear piezoelectric equations with appropriate boundary conditions. Numerical results show that the thickness of FBAR has a constant influence on the sensitivity while C-axis inclined angle has a significant influence on the sensitivity for the longitudinal mode of multilayered (double-layered in this paper) FBAR CO2 sensor. The selectivity and sensitivity of the proposed sensor can be further improved by the dopant in ZnO FBAR for real environment monitoring.