Solidly Mounted Resonator Research Articles

Dual-Mode Solidly Mounted Resonator-Based Sensor for Temperature and Humidity Detection and Discrimination.

Sensors based on solidly mounted resonators (SMRs) exhibit a good set of properties, such as high sensitivity, fast response, low resolution limit and low production cost, which makes them an appealing technology for sensing applications. However, they can suffer from cross-sensitivity issues, as their response can be altered by undesirable ambient factors, such as temperature and humidity variations. In this work we propose a method to discriminate humidity variations from the general frequency response using an SMR specifically manufactured to operate in a dual-mode (displaying two close resonances). The two modes behave similarly towards humidity changes (-1.94 kHZ/(%RH)) for resonance one and -1.62 kHZ/(%RH) for resonance two), whereas their performance under temperature changes is significantly different, displaying 2.64 kHZ/°C for resonance one and 34.21 kHZ/°C for resonance two. This allows for the decoupling process to be carried out in a straightforward manner. Frequency response is tracked under different humidity conditions, in the -20 °C to room temperature region, proving that this behavior is reproducible in any given environment.

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.

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.

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.

Use of periodic trenches in SMR-type XBAR for suppression of transverse mode resonances and lateral leakage

This paper discusses the use of periodic trenches to the top SiO2 layer of the Bragg reflector in solidly-mounted-resonator type laterally-excited-bulk-wave-resonators for the slowness manipulation to suppress both transverse mode resonances and lateral leakage. First, it is shown that the SAW slowness surface can be flattened by the application of periodic trenches, and this is owing to the coupling of the propagating SAW mode with resonances of periodic trench walls. It is also shown that flattening the SAW slowness surface enables us to suppress transverse mode resonances well. However, its impact on lateral leakage is not obvious. Then, the broadband piston mode design is applied, and its effectiveness is demonstrated for the suppression of both transverse mode resonances and lateral leakage. Deposition of a dielectric layer to the gap regions is also proposed as an alternative for leakage suppression, and it is shown that Si3N4 is appropriate as a dielectric material.

Mechanically Driven Solidly Mounted Resonator‐Based Nanoelectromechanical Systems Magnetoelectric Antennas

The miniaturization of antennas has been a significant challenge in the field of electronics and telecommunications. In recent years, mechanically driven thin‐film bulk acoustic resonator (FBAR) magnetoelectric (ME) antennas have emerged as a promising solution, demonstrating superior miniaturization capabilities compared to conventional state‐of‐the‐art compact antennas. While nanoelectromechanical systems (NEMS) FBAR ME antennas exhibit high miniaturization potential, their suspended thin‐film heterostructures render them fragile and exhibit low power handling capabilities. The findings demonstrate that solidly mounted resonator (SMR) NEMS ME antennas on a Bragg acoustic resonant reflector offer a compelling solution. With a circular resonating disk of 200 μm diameter operating at 1.75 GHz, these SMR‐based antennas display a high antenna gain of −18.8 dBi and a 1 dB compression point (P1dB) of 30.4 dBm. Compared to same‐size FBAR ME antennas with a free‐standing membrane, SMR‐based antennas exhibit significantly higher structural stability and 23.3 dB stronger power handling capability, in addition to easier fabrication processes. The compatibility of the simple fabrication processes with complementary metal–oxide–semiconductor technology, along with the dramatic miniaturization, high power handling, robust mechanical properties, and much higher antenna radiation gain, make these SMR‐based ME antennas a promising candidate for future antenna systems.

Solidly Mounted Resonators with Ultra‐High Operating Frequencies Based on 3R‐MoS2 Atomic Flakes

AbstractConventional bulk and thin piezoelectric materials based film bulk acoustic resonators (FBARs) are facing an insurmountable challenge for millimetric frequency applications due to the poor piezoelectric properties of the materials when their thickness reaches the sub‐micron regime. Novel FBARs for ultra‐high working frequencies are in urgent demand to meet the requirements of the fast‐growing 5/6G telecommunication techniques. Recent advances in 2D piezoelectric nanomaterials create an opportunity in this perspective. Here, the first FBAR chip based on 2D 3R‐MoS2 ultrathin piezoelectric flakes with a solidly mounted resonator (SMR) architecture is reported. The typical resonant frequency for an SMR device based on ≈200 nm 3R‐MoS2 flake reaches over 25 GHz with high reproducibility. Theoretical and finite element analysis suggest that the observed resonance is of longitudinal acoustic modes. This study demonstrates for the first time that the access to 2D piezoelectric nanomaterials makes high performance piezoelectric devices feasible for various promising applications including high‐speed telecommunication, acousto‐optic, and sensor fields,etc.

Analysis of spurious peaks at series resonance in solidly mounted resonators by combined BVD-Mason modelling

Solidly Mounted Resonators (SMRs) for high frequency RF filters and sensing applications often display spurious resonances that distort their frequency response. In this work, we try to identify the origin of spurious resonances accompanying the main series resonances in AlN-based SMRs with the help of modified Butterworth Van Dyke (BVD) and Mason’s models. By manufacturing SMRs of different sizes and shapes and studying the influence of the position of the electrical probing spot, we have demonstrated both theoretically and experimentally that devices with larger areas are more likely to display these additional peaks. Our updated models accurately simulate the frequency response of the SMRs, revealing that spurious peaks are mostly related to the resistance of the electrodes. Our study clarifies the origin of the spurious resonances and offers solutions for both, the optimal design and measurement method of SMRs.

Area Dependence of Effective Electromechanical Coupling Coefficient Induced by On-Chip Inductance in LiNbO3-Based BAW Resonators

To solve the problem of filter bandwidth in 5G communication, it is urgent to develop an acoustic resonator with a large effective electromechanical coupling coefficient (Keff2). In this paper, the dependence between the resonance area and the performance of the bulk acoustic wave (BAW) resonator is studied. The solidly mounted resonators (SMRs) based on 43° Y cut lithium niobate (LN) were fabricated by the wafer transfer technique. The on-chip inductor was integrated with the BAW resonator through a pad electrode. Resonators with different resonant areas were fabricated and tested. Finite element modeling (FEM) simulation of acoustic resonators and electromagnetic (EM) simulation of layout were carried out, respectively. The Modified Butterworth Van Dyke (MBVD) model was used to analyze the results, and simulation of the Mason model was adopted. The results show that the dependency relationship between the resonant area and the effective electromechanical coupling coefficient can be induced by on-chip inductance. In the resonant area range of 20 × 20 μm2~160 × 160 μm2, the Keff2 increases from 11.97% to 43.28%.

A method for extracting sole mechanical properties of Bragg reflector by GHz ultrasonic pulse-echo technique

Solidly mounted resonators (SMRs) with an acoustic Bragg reflector should be more suitable for high power RF filters than a self-standing structure because heat can be transferred to the supporting substrate. Thus, even though the demand for SMRs is expected to increase, the evaluation of the properties of the Bragg reflector that comprise them cannot be separated from the properties of the resonator as a whole. A method to evaluate the mechanical reflection coefficient of the Bragg reflector alone before the piezoelectric layer is grown would, therefore, be attractive, as it would be useful in optimizing the Bragg reflector. In this study, a nondestructive evaluation method of the reflector using a GHz ultrasonic pulse-echo technique is proposed. The Sc0.40Al0.60N film ultrasonic transducers with electromechanical coupling coefficient kt2 of 15.8% and longitudinal wave insertion loss of 7.0 dB with 77% fractional bandwidth were employed for the measurement system. Mo/SiO2 Bragg reflector test samples with various number of pairs were evaluated. The experimental mechanical reflectance of the Bragg reflector agreed well with theoretical results simulated by a mechanical equivalent circuit model.

Improved frequency response of the 3.5 GHz SMR devices using Ga-doped AlN thin films as the piezoelectric layers

In this paper, the aluminum nitride (AlN) and gallium-doped aluminum nitride (AlGaN) films are adopted to fabricate the 3.5 GHz solidly mounted resonator (SMR) devices. A reactive radio frequency (RF) magnetron sputtering system and a co-puttering subsystem were used to deposit AlN and AlGaN thin films as piezoelectric layers. The sputtering parameters were fixed as sputtering pressure of 35 mTorr and sputtering power of 200 W for AlN piezoelectric layers. For the co-sputtering parameters, the sputtering pressure was set 10 mTorr, and the sputtering powers of Al and GaN targets were 175 W and 25 W, respectively, to deposit AlGaN piezoelectric layers. The X-ray diffraction (XRD) patterns showed that as compared with the 2[Formula: see text] values of the diffraction peaks of AlN thin films, those of AlGaN thin films shifted to lower values. Even the diffraction intensity of (002) peak of AlGaN thin film was higher than that of AlN film, both AlN and AlGaN thin films presented the strongly [Formula: see text]-axis orientated crystallization. The energy dispersive X-ray spectrometer (EDS) analysis showed that the content of Ga element in the AlGaN thin film, ([Formula: see text]), was about 19%. SEM images showed that the obtained AlN and AlGaN thin films exhibited uniform grain sizes and smooth surfaces. Finally, both the frequency responses of the fabricated SMR devices were measured using a network analyzer and the difference in their efficiencies were well compared. The frequency response of the fabricated SMR device with [Formula: see text][Formula: see text]N thin film showed the center frequency of 3.51 GHz, the return loss [Formula: see text] of −10.466 dB, quality factor [Formula: see text] of 170.952, electromechanical coupling coefficient [Formula: see text] of 4.026%, and FoM value of 6.838, respectively. The results show that the frequency response of SMR device has been improved by Ga doped in AlN thin film, although the [Formula: see text] value is still less than that of obtained using single crystalline AlGaN thin film.

Use of heavy dielectric materials in solidly mounted A1 mode resonators based on lithium niobate

This paper discusses the applicability of dielectric materials with high acoustic impedance Z a for use in A1 Lamb mode solidly mounted resonator (SMR) with large electromechanical coupling coefficient k 2 . The study first shows that the use of metal as a reflector creates parasitic capacitance C p, which reduces k 2 significantly. Then, A1 Lamb mode SMRs are designed using HfN, HfO2, WN, WO3 etc., and achievable performances are compared. When either HfN, HfO2, WN, or WO3 is employed, relative large k 2 up to 25% is achievable. For further k 2 enhancement, a hybrid reflector configuration is also examined, wherein HfN is applied only to the top high Z a layer and W is applied to the others. The result indicates that C p caused by the W layers is still significant, and k 2 becomes worse in total.

Thermally Modulated CMOS-Compatible Particle Sensor for Air Quality Monitoring

Combating the health effects of particulate matter (PM) pollution requires affordable and reliable real-time air quality monitoring. The potential for large-scale manufacturing of acoustic-wave-based sensors makes them an interesting option for low-cost, low-power particle sensing applications. This article demonstrates a solidly mounted resonator (SMR) PM sensor with improved sensitivity through thermal modulation of the device. A novel, complementary metal oxide semiconductor (CMOS)-compatible SMR with an integrated microheater was designed, manufactured, and tested. In simulations, it was found that particle deposition increases both the heat loss and the thermal time constant of SMR. The effect of this on the resonant frequency shift of the device caused by particle deposition is investigated closely in this work. The sensitivity of the devices to particle deposition was tested experimentally with and without temperature modulation by placing the device in a test chamber and allowing the randomized settling of aerosolized particles on its surface. The unmodulated sensor demonstrated a particle mass sensitivity of ~40 Hz/ng while the mass sensitivity of the temperature-modulated device was shown to improve by a factor of nearly <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 5$ </tex-math></inline-formula> to 190 Hz/ng. Temperature modulation also improved the detection limit from 100 to 50 ng. Further experiments were conducted by adding an impactor mechanism to have a more controlled measurement setup. To this effect, a thermophoretic particle deposition mechanism was added to the device to enhance its performance. It was demonstrated that the repeatability of measurements was significantly improved, making the device a promising low-cost technology for air quality monitoring.

Fabrication of AlGaN High Frequency Bulk Acoustic Resonator by Reactive RF Magnetron Co-sputtering System.

In this study, aluminum gallium nitride (AlGaN) thin films are used as the piezoelectric layers to fabricate solidly mounted resonators (SMR) for high frequency acoustic wave devices. AlGaN film is deposited on a Bragg reflector, composed of three pairs of Mo and SiO2 films, through a reactive radio frequency (RF) magnetron co-sputtering system at room temperature. The optimized deposition parameters of AlGaN film have a sputtering power of 175 W for Al target, sputtering power of 25 W for GaN target, N2 flow ratio (N2/Ar + N2) of 60%, and sputtering pressure of 10 mTorr. The obtained AlGaN film has a smooth surface, uniform crystal grains, and strong c-axis orientation. The contents of Al and Ga in the AlGaN film, analyzed by energy dispersive X-ray spectroscopy (EDS) are 81% and 19%, respectively. Finally, the frequency response s11 of the obtained SMR device shows that the center frequency is 3.60 GHz, the return loss is about −8.62 dB, the electromechanical coupling coefficient (kt2) is 2.33%, the quality factor (Q) value is 96.93 and the figure of merit (FoM) value is 2.26.

Thickness shear SMR resonator based on Yttrium-doped AlN for high sensitive liquid sensors

AlN doped with transition metals becomes the key for high performance acoustic wave devices due to its improved piezoelectricity after the incorporation of dopants. In this paper, solidly mounted resonator (SMR) based on Yttrium (Y) doped AlN and operates in thickness shear (TS) mode is numerically studied for liquids characterization. The modeling of the TS-SMR is done by finite element analysis and the results are compared to experimental data for validation. After that, the effect of Y concentrations on the acoustic displacement profiles, the resonance frequency and the admittance of the SMR is investigated. The sensitivity of the TS mode resonator to liquids mass loading, viscosity and conductivity is studied for different Y concentrations and different glycerol-in-water contents. The obtained results show that doping AlN with Y enhances the electromechanical and liquids sensing capabilities of TS-SMR and contributes in the development of high sensitive sensors for liquids characterization.

Bulk acoustic wave resonance characteristic modified by reducing the defects in ZnO-based solidly mounted resonators

The c-axis zinc oxide (ZnO) multi-layered films and ZnO-based solidly mounted resonators (SMR) based on high-resistivity silicon substrates have been fabricated by using the combination of sputtering and photolithography with the absence of oxygen and heating. Subsequent annealing procedure was performed to improve the quality of ZnO films and devices. The X-ray diffraction (XRD) measurements reveal that all ZnO films are well crystallized and highly textured, the grain size gradually increases from 18.2 to 20.5 nm with the increasing of annealing temperature (Tann). The X-ray photoelectron spectrometer (XPS) results indicate that the high concentration oxygen defects of as-deposited ZnO films can be reduced through increasing Tann. By comparing the measured electrical properties of the devices before and after various Tann annealing, it was found that the annealing treatment can be used to improve the resonance characteristics, the relative change in return loss (S11) increased from 0 to 0.72 dB and then decreased to 0.07 dB as Tann increases from room temperature to 700 °C. In addition, S11 relative change can also be enhanced from 0.29 to 0.67 by decreasing the effective working area of the devices from 100 × 160 μm2 to 100 × 50 μm2.

Fabrication of a 3.5-GHz Solidly Mounted Resonator by Using an AlScN Piezoelectric Thin Film

In this study, a 3.5-GHz solidly mounted resonator (SMR) was developed by doping scandium in aluminum nitride to form AlScN as the piezoelectric thin film. Molybdenum (Mo) of 449 nm thickness and silicon dioxide (SiO2) of 371 nm thickness were used as the high and low acoustic impedance films, respectively, which were alternately stacked on a silicon substrate to form a Bragg reflector. Then, an alloy target with atomic ratio of 15% Sc was adopted to deposit the piezoelectric AlScN thin film on the Bragg reflector, using a radio frequency magnetron sputtering system. The characteristics of the c-axis orientation of the AlScN thin films were optimized by adjusting sputtering parameters as sputtering power of 250 W, sputtering pressure of 20 mTorr, nitrogen gas ratio of 20%, and substrate temperature of 300 °C. Finally, a metal top electrode was coated to form a resonator. The X-ray diffraction (XRD) analysis showed that the diffraction peak angles of the AlScN film shifted towards lower angles in each crystal phase, compared to those of AlN film. The energy dispersive X-ray spectrometer (EDX) analysis showed that the percentage of scandium atom in the film is about 4.5%, regardless of the sputtering conditions. The fabricated resonator exhibited a resonance frequency of 3.46 GHz, which was a small deviation from the preset resonance frequency of 3.5 GHz. The insertion loss of −10.92 dB and the electromechanical coupling coefficient of 2.24% were obtained. As compared to the AlN-based device, the AlScN-based resonator exhibited an improved electromechanical coupling coefficient by about two times.

Broadband piston mode operation of solidly mounted resonator employing A1 Lamb mode on lithium niobate

This paper discusses the impact of etched holes given to the solidly mounted resonator (SMR)-supported A1 Lamb mode resonators. The authors pointed out that the etched holes are effective at suppressing the lateral leakage and the transverse mode resonances for free-standing A1 Lamb mode resonators, and the technique was named the broadband piston mode (BPM). First, the SMR structure is designed for an A1 Lamb mode resonator, and it is shown that the release windows are effective in the suppression of transverse mode resonances even when the SMR is added. Detailed analysis is given to spurious responses that newly appeared by applying the SMR. Then, the discussion is extended to the impact of partial etching of the SMR layers underneath the release windows. The result indicates that the etching of the top SMR layer is enough for recovery of the BPM function.

Plasmon mediated spectrally selective and sensitivity-enhanced uncooled near-infrared detector

Here, we present a high performance uncooled near-infrared (NIR) detector comprising of a giga hertz (GHz) solidly mounted resonator (SMR) and gold nanorods (GNRs) arrays. By coupling the localized surface plasmon resonances of GNRs, the resonator system exhibits optimized optical response to vis-NIR region. Both simulation and experiments demonstrate the hybrid GNRs-SMR exhibit significantly enhanced optical responsive sensitivity of NIR, the tunable aspect ratios (AR) of GNRs enable resonator respond sensitively to selected light. Specially, taking advantage of the acoustofluidic effect of SMR, the GNRs can be controllably and precisely modified on the microchip surface in an ultra-short time, which addresses one of the most fundamental challenges in the localized functionalization of micro/nano scale surface. The presented work opens new directions in development of novel miniaturized, tunable NIR detector.

Evaluation of Mass Sensitive Micro-Array biosensors for their feasibility in multiplex detection of low molecular weight toxins using mycotoxins as model compounds

Mycotoxins produced by Fusarium species including trichothecenes, zearalenone and fumonisins, can co-contaminate food and feed throughout the supply chain, including cereal grains and animal feeds. There is an increasing demand to enhance global food security by improving the monitoring of mycotoxins throughout our food supply chain. For time and cost-efficient analysis, rapid tests capable of detecting multiple toxins from a single sample are ideal. Considering these current trends in mycotoxin testing, this project examined the feasibility of using both a portable and non-portable mass-based biosensor for multiplex mycotoxin detection. The biosensor was a mass sensitive microarray (MSMA) which consisted of 4 × 16 miniaturized mass sensitive transducer pixels based on solidly mounted resonator (SMR) technology. Functionalisation of individual pixels on the sensor surface using nano-spotting technology for the simultaneous and semi-quantitative detection of three regulated mycotoxins: T2-toxin (T2) zearalenone (ZEN), and fumonisin B1 (FumB1) was examined. With the integration of portable and non-portable microfluidic devices for antibody and standard sample injections, competitive inhibition assays were developed followed by singleplex and multiplex calibration curves. The characteristics and performance of the MSMA were evaluated including sensitivity which was determined as the concentration causing 50% inhibition. Sensitivity of singleplex assays using the portable microfluidic device (PMD) were 1.3 ng/ml, 2.0 ng/ml and 6.8 ng/ml for T2, FumB1 and ZEN, respectively. Sensitivity of the multiplex assay again using the PMD was 6.1 ng/ml, 3.6 ng/ml and 2.4 ng/ml for T2, FumB1 and ZEN, respectively. The PMD was an easy to use and highly sensitive screening tool which has been demonstrated for the multiplex detection of three regulated mycotoxins. Analysis was in real time and results were fully digital. Since detection of analytes was by mass it was both a label-free and cost-efficient method proposed method of analysis for mycotoxins.