Bulk Acoustic Wave Resonators Research Articles

Design and Fabrication of a Film Bulk Acoustic Wave Filter for 3.0 GHz-3.2 GHz S-Band.

Film bulk acoustic-wave resonators (FBARs) are widely utilized in the field of radio frequency (RF) filters due to their excellent performance, such as high operation frequency and high quality. In this paper, we present the design, fabrication, and characterization of an FBAR filter for the 3.0 GHz-3.2 GHz S-band. Using a scandium-doped aluminum nitride (Sc0.2Al0.8N) film, the filter is designed through a combined acoustic-electromagnetic simulation method, and the FBAR and filter are fabricated using an eight-step lithographic process. The measured FBAR presents an effective electromechanical coupling coefficient (keff2) value up to 13.3%, and the measured filter demonstrates a -3 dB bandwidth of 115 MHz (from 3.013 GHz to 3.128 GHz), a low insertion loss of -2.4 dB, and good out-of-band rejection of -30 dB. The measured 1 dB compression point of the fabricated filter is 30.5 dBm, and the first series resonator burns out first as the input power increases. This work paves the way for research on high-power RF filters in mobile communication.

Analysis of lattice deformation originated from residual stress on performance of aluminum nitride-based bulk acoustic wave resonators

With the development of MEMS technology to the nanometer scale, the influence of different process conditions on the performance of nano-devices can be calculated through the microscopic changes of materials. During the manufacturing process, the large residual stress from the film stack significantly influences the performance of devices, thereby reducing the wafer yield. Herein, we apply density functional theory to MEMS processes to reveal the intrinsic mechanism of how residual stress affects the performance of aluminum nitride-based bulk acoustic wave (BAW) resonators on an 8-inch high-resistance silicon wafer. The variation rule of physical properties of piezoelectric material aluminum nitride with different residual stresses is calculated via first-principles calculations. Through theory formula derivation, the piezoelectric-coupling constant (Kt2) of the bulk acoustic wave resonator is positively correlated with tensile residual stress, and the resonant frequency (fp, fs) is negatively correlated with tensile residual stress. The measurement results show that the average shifts of Keff2 is 0.12 % within −137 MPa and 183 Mpa residual stress, which is an excellent match with the theory prediction.

High Figure-of-Merit Film Bulk Acoustic Wave Resonator Based on Al0.87Sc0.13N Film Prepared Using a Novel Dual-Stage Method

High Figure-of-Merit Film Bulk Acoustic Wave Resonator Based on Al_0.87Sc_0.13N Film Prepared Using a Novel Dual-Stage Method

Ultra-low power, high-data rate, fully on-chip radio frequency on-off keying receiver for internet-of-things applications

Despite the enormous potential of energy-efficient receivers for wireless sensor networks, the large power consumption or limited data rate support impedes its extensive applications. Here, we present an energy-efficient, ultra-low power, higher data rate supporting, completely on-chip radio-frequency receiver frontend for on-off keying modulated signals in the 2.4 GHz industrial, scientific, and medical band. This compact-sized receiver is achieved by implementing temperature-resilient oscillator, pseudo-differential mixer, and a wideband detector while avoiding bulky external components such as bulk-acoustic wave resonators, crystal oscillators. Measurement results demonstrate that the proposed on-off keying receiver can decode low power level radio-frequency signals up to 5 Mbps data rate while consuming only 178 µW power. This work also demonstrates support for lower data rates at reduced power. Since the proposed receiver operates in different power modes, it can be integrated in diverse applications including internet-of-things devices and continuously monitoring biomedical/wearable implants.

Aluminium Scandium Nitride Thin Film BAW Resonators (FBAR) for 5G Applications

With the growing impact of 5G communication system, Radio-Frequency Micro-Electro-Mechanical-Systems (RF MEMS) technologies are becoming increasingly important in our daily lives. Development of filters in the 5G frequency range is being carried out tremendously. The rapid rise in smartphone usage, heightened data demands, congestion in the frequency spectrum, and advancements in technology have posed numerous challenges for the development of RF filters. The ultimate goal is to simplify the RF Front End Module used in smart phones, thereby achieving better selectivity. In this paper, a high frequency - high Q thin film bulk acoustic wave resonator of piezoelectric material Aluminium scandium nitride (AlScN)based FBAR is designed for 5G Application. Finite element analysis conducted using the COMSOL Multiphysics software assess the characteristics of the constructed FBAR. The outcomes indicate that the device resonates effectively at 5 GHz, exhibiting commendable return loss and a Q-factor of 1490. A high-resonance-frequency FBAR device offers advantages for 5G mobile technology.

Comparison of aluminum nitride thin films prepared by magnetron sputter epitaxy in nitrogen and ammonia atmosphere

Wurtzite-type aluminum nitride (AlN) thin films exhibiting high thermal conductivity, large grain size, and low surface roughness are desired for both bulk acoustic wave and surface acoustic wave resonators. In this work, we use ammonia (NH3) assisted reactive sputter deposition of AlN to significantly improve these properties. The study shows a systematic change in the structural, thermal, and morphological properties of AlN grown in nitrogen (N2) and N2 + NH3 atmosphere. The study demonstrates that NH3 assisted AlN sputtering facilitates 2D growth. In addition, the study presents a growth model relating the 2D growth to improve the mobility of aluminum (Al) and nitrogen (N) ad-atoms in NH3 atmosphere. Consequently, the thermal conductivity and roughness improve by ≈76%, and ≈35%, while the grain size increases by ≈78%.

Design and Fabrication of 3.5 GHz Band-Pass Film Bulk Acoustic Resonator Filter

With the development of wireless communication, increasing signal processing presents higher requirements for radio frequency (RF) systems. Piezoelectric acoustic filters, as important elements of an RF front-end, have been widely used in 5G-generation systems. In this work, we propose a Sc0.2Al0.8N-based film bulk acoustic wave resonator (FBAR) for use in the design of radio frequency filters for the 5G mid-band spectrum with a passband from 3.4 to 3.6 GHz. With the excellent piezoelectric properties of Sc0.2Al0.8N, FBAR shows a large Keff2 of 13.1%, which can meet the requirement of passband width. Based on the resonant characteristics of Sc0.2Al0.8N FBAR devices, we demonstrate and fabricate different ladder-type FBAR filters with second, third and fourth orders. The test results show that the out-of-band rejection improves and the insertion loss decreases slightly as the filter order increases, although the frequency of the passband is lower than the predicted ones due to fabrication deviation. The passband from 3.27 to 3.47 GHz is achieved with a 200 MHz bandwidth and insertion loss lower than 2 dB. This work provides a potential approach using ScAlN-based FBAR technology to meet the band-pass filter requirements of 5G mid-band frequencies.

Plasma-enhanced chemical vapor deposition a-SiOCN:H low-Z thin films for bulk acoustic wave resonators

The 5th generation (5G) wireless telecommunication standards with newly defined frequency bands up to 6 GHz are currently established around the world. While outperforming surface acoustic wave (SAW) filters above 1 GHz, bulk acoustic wave (BAW) resonators in multiplexers for radio-frequency front-end (RFFE) modules continuously face higher performance requirements. In contrast to free-standing bulk acoustic resonators (FBARs), solidly mounted resonator (SMR) technology uses an acoustic Bragg mirror, which has already been successfully applied for several GHz applications. In this work, we investigate the potential of amorphous hydrogenated silicon-oxycarbonitride (a-SiOCN:H) thin films synthesized with low-temperature plasma-enhanced chemical vapor deposition (PECVD) as a low acoustic impedance (low-Z) material. Compared to the state-of-the-art where in Bragg mirrors up to now SiO2 is used as standard, the acoustic impedance ratio against the high-Z material tungsten (W) is enhanced for a better device performance. To limit the expected increase in viscous loss when the acoustic impedance is reduced, to a minimum, predominantly the mass density was reduced while keeping the mechanical elasticity high. By doing so, acoustic impedance values as low as 7.1 MRayl were achieved, thereby increasing the impedance ratio of high-Z to low-Z materials from 8:1 up to 14:1.

Analytically assisted FEM approach for the design and optimization of laterally excited bulk acoustic wave resonators (XBARs) with a high electromechanical coupling

Analytically assisted FEM approach for the design and optimization of laterally excited bulk acoustic wave resonators (XBARs) with a high electromechanical coupling

Single-Crystalline Bulk Acoustic Wave Resonators Fabricated With AlN Film Grown by a Combination of PLD and MOCVD Methods

Single-Crystalline Bulk Acoustic Wave Resonators Fabricated With AlN Film Grown by a Combination of PLD and MOCVD Methods

Use of periodic 2D pillar array for performance enhancement of AlN-based SMR BAW resonators

This paper discusses the applicability of a two-dimensional (2D) periodic pillar array as the first layer of an acoustic mirror for AlN-based solidly mounted resonators of bulk acoustic waves. It is based on the idea that the periodic pillar array behaves like a uniform layer when the period is much smaller than the wavelength and its behavior is given by the ensemble average of pillar materials. The simulation shows that the effective electromechanical coupling factor can be enhanced close to that of AlN-based film bulk acoustic resonators when the slot ratio is large. It is also shown that the use of a 2D pillar array can enhance the reflectivity of the Bragg reflector. It should be noted that the periodic 2D pillar array can also control the anisotropy of wave propagation along the surface. Owing to this, transverse mode resonances can be suppressed well by adjusting the wave dispersion curve properly.

Highly improved quality factor of the film bulk acoustic wave resonator by introducing a high quality ZnO buffer layer

The inferior film quality of sputtered AlN has hindered the further development of high-performance film bulk acoustic wave resonators (FBAR). In this work, the ZnO buffer layer was introduced into the FBAR to improve the performance of FBAR for the first time. Compared with its counterpart without the buffer layer, the devices with a buffer layer exhibited a far higher average quality factor (2π times the maximum energy stored in the FBAR/energy dissipated per period) of 2575 ± 136, which was about 64 % larger than that without a buffer layer. Benefiting from the enhanced crystalline quality of AlN, the device also showed an improved effective electromechanical coupling coefficient.

Investigation of phonon lifetimes and magnon–phonon coupling in YIG/GGG hybrid magnonic systems in the diffraction limited regime

Quantum memories facilitate the storage and retrieval of quantum information for on-chip and long-distance quantum communications. Thus, they play a critical role in quantum information processing and have diverse applications ranging from aerospace to medical imaging fields. Bulk acoustic wave (BAW) phonons are attractive candidates for quantum memories because of their long lifetimes and high operating frequencies. In this study, we establish a modeling approach to design hybrid magnonic high-overtone bulk acoustic wave resonator (HBAR) structures for high-density, long-lasting quantum memories, and efficient quantum transduction devices. We illustrate the approach by investigating a hybrid magnonic system, consisting of a gadolinium iron garnet (GGG) thick film and a patterned yttrium iron garnet (YIG) thin film. The BAW phonons are excited in GGG thick film via coupling with magnons in the YIG thin film. We present theoretical and numerical analyses of the diffraction-limited BAW phonon lifetimes, modeshapes, and magnon–phonon coupling strengths in YIG/GGG planar and confocal HBAR (CHBAR) structures. We utilize Fourier beam propagation and Hankel transform eigenvalue problem methods and compare the two methods. We discuss strategies to improve the phonon lifetimes in the diffraction-limited regime, since increased lifetimes have direct implications on the storage times of quantum states for quantum memory applications. We find that ultra-high cooperativities and phonon lifetimes on the order of ∼105 and ∼10 milliseconds, respectively, could be achieved using a CHBAR structure with 10μm YIG lateral area. Additionally, high integration density of on-chip memory or transduction centers is naturally desired for high-density memory or transduction devices. The proposed CHBAR structure will offer more than 100-fold improvement of integration density relative to a recently demonstrated YIG/GGG device. Our results will have direct applicability for devices operating in the cryogenic or milliKelvin regimes. For example, our study will inform the design of HBAR devices that could couple with superconducting qubits for promising quantum information platforms.

9.5–12 GHz solidly mounted bulk acoustic wave resonators utilizing overtone of thickness extension mode

To realize HF bulk acoustic wave (BAW) devices, we have explored the application of integer multiples of overtones (3rd and 6th) of the thickness extension mode in solidly-mounted resonators (SM-BAWRs). When the average thickness of the acoustic films in the Bragg reflector of the SM-BAW device is wavelength (λ)/4, the fundamental mode is strongly excited, but overtone excitation is weak. However, it was found that 0.035λ–0.075λ acoustic layer thickness of a Bragg reflector was suitable for 3rd overtone excitation using a single LiNbO3 (LN) layer and 0.01λ–0.045λ for 6th overtone excitation using a polarization-flipped double LN layer. By using a 1 μm thick LN single thin layer, we successfully excited 3rd overtone at 9.5 GHz. Furthermore, overtones at 9.5 and 12 GHz were excited by bonding 1 μm and 0.9 μm thick LN plates with different polarities.

A Microflow Cytometer Enabled by Monolithic Integration of a Microreflector with an Acoustic Resonator.

Current microflow cytometers suffer from complicated fluidic integration and low fluorescence collection efficiency, resulting in reduced portability and sensitivity. Herein, we demonstrated a new flow cell design based on an on-chip monolithically integrated microreflector with a bulk acoustic wave resonator (MBAW). It enables simultaneous 3D particle focusing and fluorescence enhancement without using shear flow. Benefited by the on-chip microreflector, the captured fluorescence intensity was 1.8-fold greater than that of the Si substrate and 8.3-fold greater than that of the SiO2 substrate, greatly improving the detection sensitivity. Combined with the contactless acoustic streaming-based focusing, particle sensing with a coefficient of variation as low as 6.1% was achieved. We also demonstrated the difference between live and dead cells and performed a cell cycle assay using the as-developed microflow cytometry. This monolithic integrated MBAW provides a new type of opto-acoustofluidic system and has the potential to be a highly integrated, highly sensitive flow cytometer for applications such as in vitro diagnostics and point of care.

Full-epitaxial ScAlN and MgZnO solidly mounted resonators based on epitaxial acoustic Bragg reflector

A full-epitaxial bulk acoustic wave (BAW) resonator is attractive because of its high Q and high-power handling capability. An epitaxial technique is difficult to be employed due to the amorphous SiO2 low acoustic impedance layer in the solidly mounted resonator (SMR), which consists of a piezoelectric thin film on an acoustic Bragg reflector. In this study, we report a full-epitaxial ScAlN or MgZnO SMR based on an epitaxial Ti/Pt or ZnO/Pt acoustic Bragg reflector. The pole figure of epitaxial ScAlN and MgZnO piezoelectric layers showed clear sixfold symmetry. The epitaxial Sc0.43Al0.57N SMR exhibits keff2 of 13.6%. Moreover, the full-epitaxial metal Bragg reflector can act as a thick bottom electrode. This thick electrode is attractive for high frequency operation above 10 GHz in which BAW filter suffers from Q degradation due to the increase in the resistivity of extremely thin electrode.

Epitaxial ZnO piezoelectric layer on SiO2/Mo solidly mounted resonator fabricated using epitaxial Au sacrificial layer

In solidly mounted resonator (SMR) type of bulk acoustic wave resonator, it is difficult to fabricate single crystalline piezoelectric thin films in a bottom-up process due to the amorphous SiO2 in the low acoustic impedance layer of the acoustic Bragg reflector. In this study, single crystalline ZnO piezoelectric layer on amorphous SiO2/polycrystalline Mo acoustic Bragg reflector is fabricated using a wet etching process of the epitaxial Au sacrificial layer. Epitaxial growth of ZnO was confirmed by X-ray diffraction pole figure and transmission electron microscope electron diffraction pattern. Resonance frequency of 1.3 GHz of epitaxial ZnO SMR was observed using a network analyzer.

Lithium Niobate MEMS Antisymmetric Lamb Wave Resonators with Support Structures.

The piezoelectric thin film composed of single-crystal lithium niobate (LiNbO3) exhibits a remarkably high electromechanical coupling coefficient and minimal intrinsic losses, making it an optimal material for fabricating bulk acoustic wave resonators. However, contemporary first-order antisymmetric (A1) Lamb mode resonators based on LiNbO3 thin films face specific challenges, such as inadequate mechanical stability, limited power capacity, and the presence of multiple spurious modes, which restrict their applicability in a broader context. In this paper, we present an innovative design for A1 Lamb mode resonators that incorporates a support-pillar structure. Integration of support pillars enables the dissipation of spurious wave energy to the substrate, effectively mitigating unwanted spurious modes. Additionally, this novel approach involves anchoring the piezoelectric thin film to a supportive framework, consequently enhancing mechanical stability while simultaneously improving the heat dissipation capabilities of the core.

Engineering multimode interactions in circuit quantum acoustodynamics.

In recent years, important progress has been made towards encoding and processing quantum information in the large Hilbert space of bosonic modes. Mechanical resonators have several practical advantages for this purpose, because they confine many high-quality-factor modes into a small volume and can be easily integrated with different quantum systems. However, it is challenging to create direct interactions between different mechanical modes that can be used to emulate quantum gates. Here we demonstrate an in situ tunable beamsplitter-type interaction between several mechanical modes of a high-overtone bulk acoustic-wave resonator. The engineered interaction is mediated by a parametrically driven superconducting transmon qubit, and we show that it can be tailored to couple pairs or triplets of phononic modes. Furthermore, we use this interaction to demonstrate the Hong-Ou-Mandel effect between phonons. Our results lay the foundations for using phononic systems as quantum memories and platforms for quantum simulations.

Theoretical analysis of bulk acoustic wave resonators with emerging ε -Ga2O3 piezoelectric film

In this paper, the theoretical analysis of 2.3 GHz bulk acoustic wave (BAW) resonators with emerging ε-Ga2O3 piezoelectric films was investigated. By using the finite element method to calculate the dispersion curve of the BAW resonator based on ε-Ga2O3, we designed and optimized the Bragg reflector structure as well as the metal frame to suppress transverse energy leakage. When the width of the raised metal frame is an odd multiple of the quarter wavelength of the S1 Lamb mode, the vibration displacement at the boundary of the resonators is significantly suppressed, and the acoustic energy is concentrated as much as possible in the effective area of the resonators, resulting in improvement of the Qp and Qmax. Therefore, the ε-Ga2O3 based BAW resonators with Bode Qmax (∼1488), electromechanical coupling coefficient k2eff (∼15%), and the figure of merit (FoM) coefficient (∼223) are simulated and designed. Detailed theoretical analysis provides the key theoretical guidance and design scheme for the realization of ε-Ga2O3 BAW filters. The above-mentioned results imply that the emerging ε-Ga2O3 piezoelectric semiconductors have application prospects in BAW resonators and radio frequency front-end fields.