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Traditional radio frequency filters cannot meet the demands of miniaturization, high frequency operation, integration, and broadband capacity in new-generation communication system owing to their larger volumes. A thin film bulk acoustic resonator (FBAR) is therefore suggested as an optimum solution because of its small volume and a good performance. In this study, the COMSOL multiphysics software was used to build 2 D and 3 D finite element models to analyze the harmonic characteristics of the FBAR. Based on the optimized structural parameters, the FBAR was fabricated with series resonant frequency, parallel resonant frequency, and effective coupling coefficient values of 3.705, and 3.82 GHz, and 7.4%, respectively. Compared with the simulated FBAR results, the effective coupling coefficient of the fabricated FBAR declined by only 0.1%, almost achieving the desired performance.

Ultracompact and ultrastable clock chips are essential for beyond 5G/6G (b5G/6G) telecommunication systems, and we are studying 3-GHz-band thin-film bulk acoustic resonator (FBAR) oscillators for the development of such clock chips. Good frequency instability of less than 10−11 can be obtained by stabilizing the 3-GHz-band RF signal from the FBAR oscillator with the sharp resonance line called the clock transition of the Rb atom by feedback control. Here, to reduce the cost of such a frequency stabilization system due to mass production, the FBAR oscillator was redesigned using the 180 nm CMOS rule, and its oscillation characteristics were evaluated. We also developed an FBAR two-divider oscillator to simplify the above stabilization loop and elaborately evaluated the locking range of the dividers.

This paper presents a thin film bulk acoustic resonator (FBAR) with a supporting column structure. The supporting column structure is placed at the vertex of each side of the resonator. The area around the active area of the resonator can be etched to form a trench structure. This structure can reduce the transmission of the lateral acoustic wave to the inactive area and increase the quality factor (Q-factor) of the resonator. Different dimensions of the square supporting column structure are compared in this paper and results show that as the width of the square supporting column increases, the Q-factor of the resonator increases accordingly. Because of the influence of the coupling capacitance at the supporting column, the effective coupling coefficient $(\boldsymbol{K}_{eff}^{2})$ of the resonator gradually decreases as the width of the supporting column increases.

An injection‐locked divider oscillator that converts a 6‐GHz‐band signal into a 3‐GHz‐band signal was developed. The injection‐locked divider oscillator was specifically designed to lock on the clock transition frequency of 87Rb of 6.824 GHz to provide a laser modulation signal at 3.417 GHz for an on‐chip coherent population trapping atomic clock system. To obtain high frequency stability and low‐phase noise with low power consumption in the super‐high‐frequency band, a thin‐film bulk acoustic resonator is used instead of the conventional LC tank circuit. The fabricated oscillator operated well with a power consumption of 4.5 nW. The maximum lock range was 1.5% in fractional frequency. Also, unlike the conventional injection‐locked divider oscillator with an LC tank, the bifurcation of the lock range width was observed when sweeping the injection power of the 6‐GHz‐band signal, and in the down sweep, the locking operation was maintained even at an injection power of −20 dBm.

The dependence of the performance of thin film bulk acoustic resonator (FBAR) and solidly mounted resonator (SMR), on their areas is studied with the aid of finite element method (FEM) software. Dual step frame method is applied for both types of the resonators in order to improve their quality factors at resonance and at antiresonance frequency when they are miniaturized. The important role of the material quality in promoting the benefit of this method is also emphasized in this study.

Thin film bulk acoustic resonator (FBAR) plays a very important role in radio frequency (RF) filters used in cell phone and other wireless systems. Although FBAR is commercialized, the design/process interactions on the frequency response variation in FBAR device are still lacking. Design and fabrication are two crucial aspects affecting FBAR device performance. In this report, various solidly mounted resonators (SMR) were designed, fabricated and analyzed to study wafer-level site-to-site RF variation on design and fabrication process. As a key process step for SMR FBAR, the optimization process of Mg-doped ZnO piezoelectric thin film deposition was studied by varying thin film sputtering conditions using various sputtering targets and by post annealing treatment after the deposition. The quality of this crucial layer was verified by XRD on its (0 0 2) crystallization and wafer-level FBAR RF characterization. FBAR devices with high quality were fabricated with an excellent resonant behavior near 2 GHz and a maximum return loss of −15 to 25 dB. Quality factor Q ranges from 400 to 800, with a coupling coefficient keff2 of 1.5–3%. Wafer-level and wafer-to-wafer variation of central frequency are within 1.8–2.1 GHz. Computer simulation verified that this frequency variation correlates to the piezoelectric film variation of 1.6–1.9 μm. Process control on this piezoelectric thin film is essential to maintaining the resonator frequency-controlled value when building duplexer RF circuits. The dependency of RF performance on FBAR size, density and orientation is not obvious, compared to that of the wafer-level FBAR device variation on fabrication process. Regarding to the Mg-doping effect in MgxZn1-xO piezoelectric film, the amount of Mg in MgxZn1-xO film during the sputtering process must be properly controlled within 30% to keep the piezoelectric quality. The average acoustic speed of the Mg-doped ZnO film is 6870 m/s with the estimated range of 5760–7980 m/s, which is better than that of pure ZnO film (6330 m/s).

Recently, scandium-doped aluminum nitride $(\text{Sc}_{\mathrm{x}}\text{Al}_{1^{-}\mathrm{x}}\mathrm{N})$ has drawn a lot of attention as a promising material for RF-MEMS due to its large piezoelectric constants. In this paper we present the study of electrode effect on material constant extraction of $\text{Sc}_{\mathrm{x}}\text{Al}_{1^{-}\mathrm{x}}\mathrm{N}$ by measuring parallel resonant frequency of thickness-extensional mode thin film bulk acoustic resonator. Analytical method based on Mason model was adopted to investigate the effect of electrode material and thickness on the impedance spectrum of resonator. The accuracy of elastic constant $C_{33}{}^{D}$ extraction for ignoring the electrode was evaluated. The results show that electrode has a great effect on the impedance of resonator, a correction to electrode effect should be made for accurate extraction of $C_{33}{}^{D}$ .

Temperature and magnetic sensors based on MEMS technology benefit from their advantages such as small size, low power consumption and low cost, and are getting more and more attention. The dual-mode sensor based on thin film bulk acoustic resonator (FBAR) uses a Mo/AlN/FeGa sandwich structure as the resonant region, and has two resonant modes: $\mathrm{f}_{\mathrm{A}}$=2.3946 GHz and $\mathrm{f}_{\mathrm{B}}$=2.4628 GHz. The temperature sensitivities of frequency of modes A and B are 120 kHz/oC and 116 kHz/oC, the S11 intensity temperature sensitivities are 0.0014 dB$/^{\circ}$C and 0.0025 dB$/^{\circ}$C, respectively; the frequency magnetic field sensitivities are 2.72 kHz/Oe and 0.47 kHz/Oe, S11 intensity magnetic field sensitivities are 7E-5 dB/Oe and 6E-5 dB/Oe respectively. The dual-mode sensor has several sensing modes, in addition to detecting temperature and magnetic field independently, it can also correct the influence of temperature on magnetic sensing characteristics, which has important application value.

This work presents the high-temperature characterization of ferroelectric wurtzite Aluminum Scandium Nitride films and acoustic devices. Compared to the room temperature measurements, we observe up to 3 times reduction in the measured coercive field of the sputtered Mo (100nm)/Al0.7Sc0.3N (900nm)/Mo (100nm) capacitors at elevated temperatures up to 600K. Such coercive field reduction translates into significantly lower polarization switching voltages required for a given ferroelectric film thickness. Here, we study the dependency of the coercive field on the device temperature and propose to use temperature control to fine-tune the coercive field and the associated polarization switching voltage. Furthermore, two types of acoustic devices are cofabricated on the same piezo-stack on silicon-on-insulator (SOI) platform: (i) Al 0.7 Sc 0.3 N thin film bulk acoustic resonator (FBAR) released from the front side by etching the Si device layer, with an overall resonant stack thickness of 1.1 μ m. (ii) Al 0.7 Sc 0.3 N-on-Si composite FBAR (CFBAR), released from the backside, with the resonant stack including a passive 3.5 μm-thick Si device layer. The hightemperature frequency responses of the two acoustic devices are studied showing an excellent temperature coefficient of frequency (TCF) match between COMSOL finite element analysis (FEA) and measured results. Finally, the frequency tunability of the ferroelectric FBAR is tested at 600K with the DC bias ranging from 0 to -100V, showing 3 times higher frequency tuning than at room temperature under the same DC bias conditions. This proves that a larger tuning range and polarization switching can be achieved with lower DC voltages at higher temperatures.

Micro-electromechanical systems (MEMs) started to dominate the interests of the industry due to the high growth of the various radio frequency (RF) systems, such as mobile telecommunication, satellite communication and other wireless devices that accrues high frequency range. In addition to the race of miniaturizing the device feature size. However, the main obstacle of enabling such devices is that not all of the MEMS technologies are compatible with integrated circuits (IC) manufacturing process. MEMs' devices that are based on acoustics waves like surface acoustic wave (SAW) and bulk acoustic wave (BAW) overcome aforementioned limitations while providing an outstanding performance. BAW resonator is a new technology raised during the last decade which shows better temperature stability compared to SAW, better selectivity, IC manufacturing process compatibility, and lower insertion loss. Filters based on BAWs show very promising results as well. However, BAW resonators still need optimization to achieve the high-quality factor also the temperature dependency is still a big problem. A novel Thin Film bulk acoustic resonator (FBAR) design is presented in this paper using aluminum nitride (AlN) as peizoelectric material and Tungsten (W) for the electrodes, with detailed electrical model and FEM simulations using COMSOL MULTIPHYSICS. In addition, Cadence Virtuoso is used to implement and simulate the electrical model. A resonance frequency of 2.4 GHZ is achieved with quality factor (QF) of 1548 and Temperature coefficient of frequency (TCF) ∼ 4.6 (ppm/ oC).

In this paper, an infinite circular ZnO thin film bulk acoustic resonator (FBAR) with a frame-like electrode operating at the thickness-extensional (TE) mode is studied. Two-dimensional scalar differential equations established for the problem in the Cartesian coordinate system are successfully solved by transforming them into normal Bessel equations and modified Bessel equations in the cylindrical coordinate system. Resonant frequencies and vibration distributions are obtained for this frame-like FBAR sensor. A nearly uniform mass sensitivity distribution in the active area is achieved by designing proper electrode size and mass ratio of the driving electrode to the ZnO film. Numerical results show that compared with the reported ring electrode FBAR sensor, the novel frame-like electrode FBAR can achieve a maximum optimization ratio (up to 97.90%) on the uniformity of the mass sensitivity distribution in the active area under the same structural parameters, which is also higher than the optimization ratio 77.63% obtained by the reported double-ring electrode design. Moreover, the mechanism to achieve a very uniform mass sensitivity distribution in the active area by the frame-like electrode is explained in detail according to dispersion curves. Namely, when the resonant frequency of the FBAR sensor is close to the cut-off frequency of the active region in the dispersion curve, the mass sensitivity distribution is nearly uniform. These conclusions provide a theoretical guidance for the design and optimization of ZnO FBAR mass sensors with high performance.

Easy monitoring of prostate specific antigen (PSA) directly from blood samples would present a significant improvement as compared to conventional diagnostic methods. In this work, a split mode thin film bulk acoustic resonator (TFBAR) device was employed for the first time for label-free measurements of PSA concentrations in the whole blood and without sample pre-treatment. The surface of the sensor was covalently modified with anti-PSA antibodies and demonstrated a very high sensitivity of 101 kHz mL ng-1 and low limit of detection (LOD) of 0.34 ng mL-1 in model spiked solutions. It has previously been widely believed that significant pre-processing of blood samples would be required for TFBAR biosensors. Importantly, this work demonstrates that this is not the case, and TFBAR technology provides a cost-effective means for point-of-care (POC) diagnostics and monitoring of PSA in hospitals and in doctors' offices. Additionally, the accuracy of the developed biosensor, with respect to a commercial auto analyser (Beckman Coulter Access), was evaluated to analyse clinical samples, giving well-matched results between the two methods, thus showing a practical application in quantitative monitoring of PSA levels in the whole blood with very good signal recovery.

Mode-coupled vibrations in an ultra-high frequency (UHF) ZnO thin film bulk acoustic resonator (FBAR) operating at thickness-extensional (TE) mode are studied by employing weak boundary conditions (WBCs), constructed based on Saint-Venant’s principle and mixed variational principle in the piezoelectric theory. The frequency spectra, describing the lateral size-dependence of mode couplings between the main mode (TE) and undesirable eigen-modes, for clamped lateral edges are compared with the existing frequency spectra for free lateral edges to illustrate the boundary influence. The displacement and stress variations in FBAR volume are also presented to intuitionally understand and distinguish the difference of frequency spectra between these two different lateral edges, and then we discuss how to select outstanding lateral sizes to weaken the mounting effect. The frequency spectra predicted from our approximate WBCs are also compared with and agree well with those predicted by the finite element method (FEM) using COMSOL, which proves the correctness and accuracy of our theoretical method. These results indicate that the WBCs could have potentials in the valid predictions of lateral size-dependence of mode couplings in piezoelectric acoustic wave devices.

The present work focusses on the design and simulation of a thin film bulk acoustic resonator (TFBAR) and a polyimide based TFBAR (PI-TFBAR) and compares the radio frequency (RF) bandpass filter response designed from these resonators. The Polyimide layer in the PI-TFBAR acts as an acoustic wave reflector along with providing mechanical strength to the device. The designed third order bandpass filter has a ladder topology. The insertion loss of the TFBAR filter is 1.69 dB and the return loss is 39.60 dB whereas the insertion loss and return loss are 1.71 and 23.7 dB respectively for the PI-TFBAR filter. The bandwidth of the TFBAR filter is 68.0 MHz and for PI-TFBAR it is 25 MHz. The proposed filter designs, with further optimization, may have application in the 2.6 GHz band, which has been identified by the International Telecommunication Union as a global band for International Mobile Telecommunications and is one of the core bands of LTE-Advanced technology.

Carbon dioxide (CO2) is a gas that well represents air quality in indoor environments as well as being an important greenhouse gas. However, the reliable and affordable sensing of environmental CO2 at room temperature, with techniques other than optical spectroscopy, remains an unsolved problem to this day. One major challenge for solid state sensors is the realisation of adequate selectivity, especially towards changing humidity. The thin film bulk acoustic resonator (FBAR) is a MEMS (Microelectromechanical systems) device that can not only detect gas-induced mass changes but also changes in the acoustic velocity and density of its layers. This multi-sensing provides a suitable platform for selective gas sensing. In this work we present studies done on polyaminosiloxane- and ethyl cellulose-functionalised FBARs regarding CO2 sensitivity, selectivity towards humidity, and stability. We demonstrate how CO2 and humidity signals can be separated and that CO2 can be sensed with a resolution of 50 ppm between 400 and 1000 ppm. Using the Mason model, we show how the acoustic velocity and density of an absorption layer can be determined and how changes in those parameters affect the resonance frequency shift. The understanding of these results ultimately presents a tool to theoretically separate any number of gas analytes.

Thin film bulk acoustic resonator (FBAR) higher quality factor (Q) provides steep skirt and low insertion losses in the pass band. In this paper, three different loss sources are identified and FBAR is design and simulated in order to reduce the losses. Firstly, the FBAR’s top electrode is simulated for the areas of 150 × 150, 300 × 300 and 400 × 400 μm2 and the quality factor is improved as the area increased to 102, 432.6 and 743.7 respectively. The impedance of the FBAR is reduced as the area of the electrode is increased. Secondly, the anchor width is reduced from 60 to 45 μm and the quality factor is increased from 341 to 432.6 respectively. The losses through the anchor reduce as the anchor reduces. Electrode area and anchor area simulation are showing the notable effect and no other paper is reported for the comparison. Thirdly, the damping factor coefficient (β) is varied as 4.7e−14, 3.84e−14 and 2.5e−14. The quality factor is increased as the damping factor reduces and reported as 283.2, 341.2 and 444.5 respectively. The damping reduction leads the FBAR structure to vibrate more freely at the resonance. The losses through damping are reduced and more energy has stored at the resonance so it increases the quality factor.

This paper aims to achieve the uniform displacement variations in a rectangular ZnO thin film bulk acoustic resonator (FBAR) with frame-like electrodes operating at the thickness-extensional (TE) mode. The variational formulation based on two-dimensional scalar equations provides a theoretical foundation for the Ritz method adopted in our analysis, and the resonant frequencies and vibration distributions of TE modes are obtained. A nearly uniform displacement distribution at the active area of the frame-like electroded FBAR is achieved by designing proper electrode size, which exhibits more uniform displacement distributions than ring electroded FBAR under the same structural sizes. Moreover, the principle of the achievement of a very uniform displacement distribution in the active area is illustrated. These conclusions provide a theoretical guidance for the design and optimization of ZnO FBAR mass sensor with high performance.

Using first principles and the constitutive equations for a piezoelectric, we solve the 2-D acoustic wave inside a single, infinite, piezoelectric membrane to study the dispersion of thin film bulk acoustic resonator (FBAR) lateral modes, with and without infinitely thin electrodes. The acoustic eigenfunction is a dual wave, composed of longitudinal and shear components, able to satisfy the 2-D acoustic boundary conditions at the vacuum interfaces. For the single piezoelectric slab, we obtain analytical expressions of the dispersion for frequencies near the longitudinal resonant frequency (Fs) of the resonator. These expressions are more useful for the understanding of dispersion in FBARs and more elegant than numerical methods like finite-element modeling and various matrix methods. We additionally find that the interaction between the resonator’s electrodes and the acoustic wave modifies the lateral-mode dispersion when compared to the case with no electrodes. When correctly accounting for these interactions, the dispersion zero is placed clearly at Fs, unlike what is calculated from a 2-D model without electrodes where the dispersion zero is placed at Fp. This is important since all experimental evidence of measures FBAR resonators shows that the dispersion zero is at Fs. Furthermore, we introduce an electrical current-flow model for the propagating acoustic wave inside the electroded piezoelectric, and based on this model, we can discuss an electrode-loss mechanism for FBAR lateral modes which depends on dispersion. From our model, it results that lateral modes with real $k_{x}$ have higher electrode dissipation if they are closer to the resonant frequency. This is consistent with the typical behavior of measured FBAR filters where the maximum lateral mode damage on the insertion loss takes place for frequencies immediately below Fs.

Defects in efficiency or usability have come into being when using the maximum stress on FBAR structure as the reference stress or using the so called "Calculus-like analysis method" to calculate the sensitivity of FBAR transducer. The former does not consider the influence of the strain in the thickness direction, which overestimates the sensitivity. The latter learns from FEM, but it is too complicate and heavy-workload. In order to eliminate these deficiencies, the improved sensitivity prediction method for FBAR transducer is put forward. The whole calculation process is completed with COMSOL (R) FEM software to avoid the complex data processing. The energy weighted average method is used to calculate the average strain of every single layer in FBAR and the average internal pressure of piezoelectric layer. The average strain is used to modify the thickness of FBAR, and the internal pressure is used to modify the elastic constant of piezoelectric material. Then the eigenfrequency solving method is carried out to solve the eigenfrequency of FBAR. The former improves the speed of solving, and the latter enhance the accuracy of the calculation results. The sensitivity of both circular membrane type FBAR transducer and FBAR micro-accelerometer can be calculated through the improved method. The expected sensitivity of the membrane type FBAR transducer is 46.5 MHz/N, which is close to the experimental result, 50 MHz/N. However, due to unawareness of the actual structure parameters, the expected sensitivity of the micro-accelerometer is 27 kHz/g, which is different from the experimental result, 100 kHz/g. The two calculation cases indicate that the improved sensitivity prediction method for FBAR transducer is both effective and available.

Intrinsically switchable thin film bulk acoustic resonator (FBAR) filters based on ferroelectric barium strontium titanate (BST) are presented. A 1.5-stage $\pi$ -network intrinsically switchable FBAR filter unit cell with a 3-dB fractional bandwidth of 3% at 2 GHz is systematically designed, simulated, and fabricated. The minimum insertion loss (IL) for the filter unit cell is 2.25 dB, representing the lowest IL reported for BST bulk acoustic wave filters to date, which is mainly due to its high $Q \times K_{t}^{2}$ BST resonators. Two 1.5-stage filter unit cells are connected in series to form a 2.5-stage filter, providing more than 25 dB of out-of-band rejection and OFF-state isolation between the input and the output ports. The measured input third-order intercept point (IIP3) of the 2.5-stage filter is 47 dBm. Furthermore, the footprint of the fabricated filters is notably small, due to the high permittivity of BST.

A thickness longitudinal mode (TLM) thin film bulk acoustic resonator biosensor is demonstrated to operate in water with a high quality-factor, Q. This is achieved using a layer of carbon nanotubes (CNTs) on top of the resonator which has a significantly different acoustic impedance to either the resonator or liquid whilst being susceptible to the binding of biological molecules. This allows the resonance to be decoupled from direct energy loss into the liquid, although still retaining mass sensitivity. AlN solidly mounted resonators (SMRs) having a thickness shear mode (TSM) at 1.1 GHz and TLM at 1.9 GHz are fabricated. CNTs with different forest densities are grown by chemical vapor deposition on the active area with Fe as the catalyst and resulting devices are compared. High forest density CNTs are shown to acoustically decouple the SMRs from the water and in-liquid TLM Q values higher than 150 are recorded even exceeding TSM SMRs without CNTs. The TLM Q in water is remarkably improved from 3 to 160 for the first time by dense CNT forests, rendering the large-scale fabrication of TLM SMRs for liquid-phase sensing applications possible. Despite this partial isolation, SMRs with CNT forests ∼15 μm tall can still detect binding of bovine serum albumin.

We applied a 3.5-GHz-band thin film bulk acoustic resonator (FBAR) to a voltage controlled oscillator (VCO), which is designed as a local oscillator of miniaturized atomic frequency standards (AFSs). This frequency reference instead of a bulky quartz resonator may enable an AFS with a chip component size. By using the 3.5-GHz-band FBAR, the clock frequency at the 87Rb transition (fclock/2=3.42 GHz) was directly generated without a phase locked loop (PLL), reducing the cost, size, and power consumption of the RF control unit. Also, MEMS based Rb gas cells were developed, where the cylindrical cavity was 3 mm in both diameter and length. We observed a coherent population trapping (CPT) resonance. By incorporating the FBAR-VCO into the feedback loop of the CPT system, a sustained clock operation was achieved with a frequency instability of 2.1×10−11 at 1 s.

Bulk acoustic wave (BAW) resonators are widely applied in filters and gravimetric sensors for physical or biochemical sensing. In this work, a new architecture of BAW resonator is demonstrated, which introduces a pair of reflection layers onto the top of a thin film bulk acoustic resonator (FBAR) device. The new device can be transformed between type I and type II dispersions by varying the thicknesses of the reflection layers. A computational modeling is developed to fully investigate the acoustic waves and the dispersion types of the device theoretically. The novel structure makes it feasible to fabricate both type resonators in one filter, which offers an effective alternative to improve the pass band flatness in the filter. Additionally, this new device exhibits a high quality factor (Q) in the liquid, which opens a possibility for real time measurement in solutions with a superior limitation of detection (LOD) in sensor applications.

This work presents the design and simulation of a zinc oxide based thin film bulk acoustic resonator (TFBAR) bandpass filter for 2.6 GHz band applications. Third and fifth-order filters in ladder topology are designed and compared. The third-order filter has an insertion loss of 1.62 dB and return loss of 18.97 dB with a bandwidth of 80 MHz whereas the fifth-order filter has insertion loss, return loss, and bandwidth of 2.85 dB, 25.28 dB, and 60 MHz, respectively. With a central frequency of 2.67 GHz, the designed filter has applications in the 2.6 GHz (2500–2690 MHz) band, which has been identified by the International Telecommunication Union as a global frequency band for mobile broadband services.

The resonance frequency,fs, and the effective electromechanical coupling factor,keff2, of thin film bulk acoustic resonators (FBARs) are derived by transfer matrix method. The effects of thickness and density of electrode onfsandkeff2with different piezoelectric layers are investigated by numerical calculation method. The results show that thickness and density of electrode affectfsobviously, especially in large thickness and density area. Moreover, the effects of thickness, density, and acoustic velocity of electrode onkeff2of FBAR were also studied. The results show that there is a maximumkeff2corresponding to the composition of thickness and density of electrode which is about 20% over the original electromechanical factor of piezoelectric film.keff2is in the direct proportion to the densityρeandveof electrode, respectively. The electrode thickness affectskeff2small with highve; moreover, whenveis high enough, thenkeff2has almost nothing to do withde.keff2always rises with electrode thickness first and then descends with its rising, and the thickness corresponding to the maximumkeff2is different with different electrode, but it always locates in the special area. All above results indicate that the thickness, density, and acoustic velocity of electrode are so important that these results can be applied to design FBAR.

Experiment shows that thin film bulk acoustic resonator (FBAR) is feasible to detect gamma irradiation, but the sensing mechanism is not studied deeply. For this problem, different sensing mechanisms are proposed to explain the resonance frequency shift after gamma irradiation according to two different FBAR structures. One FBAR structure is four - layers stacked (metal layer - piezoelectric layer - oxide layer - metal layer). After gamma irradiation, a voltage will be formed in the radiation sensitive layer (oxide layer), which is equivalent to impose a DC voltage to the piezoelectric layer that makes resonant frequency shift. There is a semiconductor layer between oxide layer and piezoelectric layer in the other FBAR structure, which is the difference between the two structures. A voltage formed in the oxide layer after irradiation will change the surface potential of the semiconductor and then change the space charge layer capacitor in semiconductor that makes the resonant frequency shift. The results of two mechanisms are obtained by simulation and compared with those in related literature, it is found that the trends and magnitudes of frequency shift are the same, so the two mechanisms are feasible.

Dielectric loss is inevitable for many piezoelectric materials and it will lead to the dissipation of energy for wave motion. In this paper, we study wave propagation in piezoelectric layered structure of the thin film bulk acoustic resonator (FBAR) with dielectric loss. When the dielectric loss is considered, dielectric constants are complex and the waves are damped which means wavenumber is complex. Thus, the dispersion equations were derived first, and then three dimensional dispersion curves were given in the range of real frequency and complex wavenumber. Further analyses on the characteristics of the wave were made based on the 3D dispersion curves, and the attenuation of the wave was shown. A comparison with the results obtained from the model without dielectric loss was also discussed.

In this paper, the thermal coefficient of frequency (TCF) and the thermal isolation of the BST FBARs for un-cooled resonant IR sensor design are studied. A BST FBAR is fabricated and its temperature-dependent resonance frequency is measured within a wide range of temperature. The TCF of the measured BST FBAR is optimized and values as high as −921 ppm/K is achieved below the BST's phase transition temperature, which is significantly higher than previously reported TCF values for resonant IR sensors. Furthermore, a low thermal conductance between the resonator and the substrate, which is essential for low-noise IR sensors, is achieved by fabricating a BST FBAR with a suspended structure.

In this paper, we presented the study of electrode effects on the performance of thin film bulk acoustic resonator (FBAR)for viscosity sensor application, where the viscosity sensor is with a structure of the top electrode layer/piezo layer/bottom electrode layer, and the sensor's sensitivity (S) and quality factor (Q) was addressed. Simulation results show that, compared with the case of without electrode, adopting electrode with high characteristic acoustic impedance electrode (Z e ) cannot improve S, and S decreases with the thickness of electrode (te); for the case of electrode with low Z, S can be improved by choosing an appropriate te, and there exists an optimal te for the maximization S. Moreover, it was found that both the electrode layer and the viscosity of liquid have a great effect on Q. For low viscosity liquid, Q and S can be simultaneously improved by adopting high mechanical quality factor electrode with low Z and optimization te. For medium viscosity liquid detection, results show that if Z e is specifically chosen in a small certain range, Q and S can also be simultaneously improved with appropriate te, otherwise a balance should be made for the optimization of S and Q through te. For the high viscosity liquid, Q has a great deterioration due to heavy liquid loading and the improvement by electrode is weak. These results can be used for the design and application of FBAR viscosity sensors.

Transmit filters comprising piezoelectric resonators are fabricated in a Thin Film Bulk Acoustic Resonator (FBAR) technology. A filter's 2nd harmonic emissions (H2), generated by the resonators in the filter's output stage must be sufficiently small to prevent the filter from desensitizing a nearby receiver. Anti-parallel and anti-series connected resonator configurations, in which the H2 emissions of a pair of resonators annihilate one another are often used to suppress such emissions. Such topologies are effective in suppressing H2 when the constituent resonators can be modeled as 1-D pistons. But certain resonators exhibit poorly suppressed lateral mode “rattle” behavior over a range of frequencies indicating that they can't be modeled as 1-D pistons. Such resonators produce 2nd harmonic emission “spikes” when they are excited over this same range of frequencies. When pairs of such resonators comprise H2-suppressing circuit configurations, tiny imbalances in the H2 spike emissions of each resonator prevent H2 annihilation. An effort to characterize and to model lateral modes and their corresponding H2 spike emissions in such resonators is warranted in understanding H2 emissions in filters.

A high Q m ×K2 t fundamental mode intrinsically switchable thin film bulk acoustic resonator (FBAR) based on Bao.sSro.sTiOa is designed and fabricated at 2 GHz. High Q m ×K2 t BST FBARs are required for the design of low insertion loss switchable BAW filters. Measurement results for the BST FBAR show a resonator mechanical quality factor (Q m ) of 360 with an electromechanical coupling coefficient (K2 t ) of 8.6%. Q m ×K2 t is 30.8, and to the best of authors' knowledge, it is the highest among the previously reported switchable BST resonators. The measured temperature coefficients of frequency (TCF) for the series and parallel resonance frequencies are −65 and −68 ppm/K, respectively.

Microelectromechanical sensors (MEMS) offer a new way of measuring temperature and infrared (IR) radiation, through measurements of total optical energy, overcoming the obstacles associated with narrow bandgap semiconductor detectors[1]. Specifically, Thin Film Bulk Acoustic Resonators (FBAR) offers a versatile MEMS technology based on resonant devices fabricated using piezoelectric materials [2]. With the addition of an absorbing susceptor and the use of zinc oxide (ZnO) as the piezoelectric it is possible to obtain a higher sensitivity device than previously demonstrated systems, taking advantage of ZnO's higher temperature coefficient of frequency (TCF) [3,4,5]. This work studies the improved sensing ability of an FBAR structure and ease of testing and superior parasitic performance provided in a package using an engineered high TCF FBAR in a monolithically integrated CMOS process.

In this article, the effect of Mn doping on the permittivity and dielectric loss in 0.67BiFeO3-0.33BaTiO3 (BF-BT) based film bulk acoustic resonator test structures has been investigated. BF-BT thin films were deposited on the fused silica substrates with Pt/TiO2/Ti as bottom electrode. During the study of the BF-BT based parallel-plate structures, it has been revealed that BF-BT is in the ferroelectric state at room temperature. Higher permittivity (ԑ) is observed at a growth temperature of 600 °C and lower dielectric loss is achieved at 0.3 wt% Mn doping contents. These results show that the proposed BF-BT based FBAR test structure has a great potential for applications in tunable thin Film Bulk Acoustic Resonator (FBAR) devices. Comparison of the measured and simulation results has been made by utilizing the Mason equivalent circuit. This work was made possible by GSRA3-1-1116-14016 from the Qatar National Research Fund (a member of Qatar Foundation). The findings made herein are solely the responsibility of the authors. Scopus

This paper describes the fabrication process of the thin film bulk acoustic resonator (FBAR) based on good quality aluminum nitride (AlN) film and the measurement of FBAR by a network analyzer. The AlN film with a highly c-axis orientation and homogeneous surface morphologies is deposited on Bragg reflectors as piezoelectric film by magnetron sputtering. The Bragg reflectors consisted of Ti and W fabricated under the resonator for acoustic isolation improves performance and compatibility of the FBAR and reduces the parasitic resistance of the electrode. The devices are packaged on tube seat and fixed on a high frequency PCB board designed specially for measurement and applications. The FBAR achieved a Q factor of 505 and k2effof 3.42% at a resonant frequency of 2.22 GHz. A high sensitivity of 4.79 kHz·cm2/ng is obtained in the FBAR, which is higher than quartz crystal microbalance.

Coupled structural and fluid flow analysis of bulk acoustic wave (BAW) piezoelectric micropumps is carried out for liquid (water) transport applications. The BAW micropump consists of trapezoidal-prism inlet/outlet elements; the pump chamber, a piezoelectric (PZT-5A) actuator and a thin structural layer (Pyrex glass) between the pump chamber and the actuator. Two-way coupling of forces and displacements between the solid and the liquid domains in the system is considered where actuator motion causes fluid flow. Flow contraction and expansion (through the trapezoidal-prism inlet and outlet sections, respectively) generate net fluid flow. The effect of the back-pressure, actuation frequency, inlet/outlet port angles and driving voltage on the structural–piezoelectric bi-layer membrane deformation and the resulting flow rate are investigated. For the compressible flow formulation considered, an isothermal equation of state for the working fluid is employed. Three-dimensional governing equations for the flow fields and the structural–piezoelectric bi-layer membrane motions are considered. The predicted flow rate increases with actuation frequency up to a critical value. The highest pumping rate is observed at this critical (resonant) actuation frequency due to the combined effects of mechanical, electrical and fluidic capacitances, inductances, and damping. Time-averaged flow rate starts to drop with increase of actuation frequency above the critical value. The present models can be utilized to optimize the design of microelectromechanical system-based micropumps on the basis of fluid flow and structural characteristics.

Film bulk acoustic resonators (FBARs) have received considerable attention for micro-electromechanical systems (MEMS) applications such as RF filters, resonators, and recently, bio-sensors. FBARs consisting of a piezoelectric thin film and an acoustic reflector for acoustic isolation from the surrounding medium are advantageous due to the intrinsic high sensitivity to mechanical, chemical, or electrical perturbation and compatibility with standard CMOS processing. In this work, we investigated the resonance characteristics of acoustic Bragg reflector-type FBARs by the model-based parametric analysis. The effect of various thicknesses and materials of electrodes and structural variation of acoustic Bragg reflectors on the key performance characteristics was studied to identify optimal design parameters for high performance FBAR devices. The key performance characteristics of FBARs include impedance characteristics, reflection coefficients, electro-mechanical coupling coefficients, and Q factors. These results not only offer new insights into design guidelines for high performance FBAR devices but also help better understanding of the fundamental physical phenomenon at resonances of the device.

Integration of a class-E power amplifier (PA) and a thin-film bulk acoustic wave resonator (FBAR) filter is shown to provide high power added efficiency in addition to superior out-of-band spectrum suppression. A discrete gallium arsenide pseudomorphic high-electron-mobility transistor is implemented to operate as a class-E amplifier from 2496 to 2690 MHz. The ACPF7041 compact bandpass FBAR filter is incorporated to replace the resonant LC tank in a traditional class-E PA. To reduce drain voltage stress, the supply choke is replaced by a finite inductance. The fabricated PA provides up to 1 W of output power with a peak power added efficiency (PAE) of 58%. The improved out-of-band spectrum filtering is compared to a traditional class-E with discrete LC resonant filtering. Such PAs can be combined with linearisation techniques to reduce out-of-band emissions.

The manufacturing conditions of a thin-film bulk acoustic resonator (FBAR) filter were investigated to obtain a high Q factor which is stable for mass production. The FBAR consist of patterned electrodes and piezoelectric films. In this study, the influence of edge shape of the films on the anti-resonance characteristics was investigated using a numerical method. Optimized shape was applied to a 2.5-GHz band resonator and filter. As a result, significant improvement of the Q factor and the insertion loss was confirmed.

A ZnO-based film bulk acoustic resonator has been fabricated using a magnetron sputtering technology, which was employed as a biosensor for detection of mucin 1. The resonant frequency of the thin-film bulk acoustic resonator was located near at 1503.3 MHz. The average electromechanical coupling factor \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {K}_{\mathrm{eff}}^2 $$\end{document}Keff2 and quality factor Q were 2.39 % and 224, respectively. Using the specific binding system of avidin-biotin, the streptavidin was self-assembled on the top gold electrode as the sensitive layer to indirectly test the MUC1 molecules. The resonant frequency of the biosensor decreases in response to the mass loading in range of 20–500 nM. The sensor modified with the streptavidin exhibits a high sensitivity of 4642.6 Hz/nM and a good selectivity. Electronic supplementary material The online version of this article (doi:10.1186/s11671-016-1612-5) contains supplementary material, which is available to authorized users.

This paper investigates and compares three methods for the analysis of the thin film bulk acoustic resonator (FBAR) in order to study the propagation of plate waves in the device. The finite element method (FEM) is compared to the Transfer Matrix (TM) and Global Matrix (GM) techniques, which are carefully modified in order to take into account the mixed-multilayer structure of the resonator. To the best of the authors' knowledge, the electrodes and the piezoelectric layer both are treated as layers with fully defined mechanical and electrical properties for the first time.

FBAR (thin film bulk acoustic resonator) filters are widely used in making filters for wireless applications [1]. Until recently, most of the FBAR filters were manufactured on 150mm wafers. In the last couple of years, manufacturing of the FBAR devices started moving onto 200mm wafers. Main reason to move from 150mm wafers to 200mm wafer is that area increases by a factor of about 1.8X. Unfortunately, if the edge exclusion has to be increased in order to avoid bad stress or thickness non-uniformity near the edge of the wafer, it reduces the advantages of the increased area. For example, if the edge exclusion is increased from 3mm to 10mm, it causes 14% yield reduction. This problem has inspired the investigation in the paper. One of the critical parameters for FBAR manufacture is AlN film stress, both, average and across a wafer. If stress varies too much, membranes can develop cracks or peel off. In BAW applications, that don't require stress control for structural reason, it is desirable to keep stress uniform across wafer in order to maintain tight distribution of coupling coefficient. Another critical parameter is film thickness. AlN (aluminum nitride) thickness control of +/−0.2% wafer-to-wafer and across wafer are important in order to obtain high yielding wafers. In this paper we will propose a way to obtain both stress control and film thickness uniformity. Independent stress control is obtained by carefully designing sputtering magnetron with variable magnetic field. Thickness uniformity is independently controlled by ion mill trimming module. By adjusting magnetic field and the length of the plasma discharge (positive plasma column), stress uniformity across 200mm wafer was maintained at less than +/-75MPa. Thickness control on 200mm wafers with only 3mm edge exclusion was demonstrated at

Thin film bulk acoustic resonator (TFBAR) with c-axis tilted AlN finite element modeling was performed using COMSOL Multiphysics simulation software. Depending on the AlN c-axis tilt angle, dual mode TFBAR can be obtained that operate in longitudinal and shear mode: the former mode is a thickness-extensional mode, while the latter is a thickness-in plane-shear mode that is suitable for liquid sensing applications. The acoustic wave displacement, the resonator frequency and equivalent admittance of the TFBARs with different tilt angles and electrode thicknesses were simulated to obtain the optimum design (high electroacoustic coupling efficiency and large quality factor Q) for shear mode operation. Furthermore, AlN films having the c-axis tilted up to about 30 from the substrate normal were successfully grown on silicon (100) substrates by reactive rf magnetron sputtering technique at 200C.

In this paper, the transmitting line method is applied to analyze the properties of FBAR, and the input impedance equation is obtained, and the series resonance frequency fs and the parallel resonance frequency fp are calculated by this method. Moreover, the elastic effects of the electrode on the effective electromechanical coupling factor, k2eff , and the resonance factor, Qs> , of FBAR are investigated by the transmitting line method. Results indicate that the acoustic impedance ratio of the electrode to the piezo-film dominantly determines the behaviors of the k2eff , the variation of Qs versus the thickness of the electrode crucially depends on the acoustic impedance ratio of electrode to piezoelectric films. The results will be applied in the theoretical optimization of FBAR, which are available to optimize the fabrications of FBARs and similar devices.

Sputter deposited aluminum nitride (AlN) thin films have played a central role for the successful development of the thin film electro-acoustic technology. The development has been primarily driven by one device—the thin film bulk acoustic resonator, with its primary use for high frequency filter applications for the telecom industry. Recently, increased piezoelectric properties in AlN through the alloying with scandium nitride have been identified both experimentally and theoretically. This opens up new possibilities for the thin film electro-acoustic technology. Here expectations and discussions are presented on acoustic FBAR sensor performance when based on AlN as well as on such AlN alloys to identify possible benefits and limitations. Inhere, the distinction is made between direct and in-direct (acoustic) use of the piezoelectric effect for sensor applications. These two approaches are described and compared in view of their advantages and possibilities. Especially, the indirect (or acoustic) use is identified as interesting for its versatility and good exploitation of the thin film technology to obtain highly sensitive sensor transducers. It is pointed out that the indirect approach can well be obtained internally in the piezoelectric material structure. Original calculations are presented to support the discussion.

ZnO thin film bulk acoustic resonators (FBARs) with resonant frequency of ∼1.5 GHz have been fabricated to function as an odorant biosensor. Physical adsorption of an odorant binding protein (AaegOBP22 from Aedes aegypti ) resulted in frequency down shift. N,N-diethyl-meta-toluamide (DEET) has been selected as a ligand to the odorant binding protein (OBP). Alternate exposure of the bare FBARs to nitrogen flow with and without DEET vapor did not cause any noticeable frequency change. However, frequency drop was detected when exposing the OBP loaded FBAR sensors to the nitrogen flow containing DEET vapor against nitrogen flow alone (control) and the extent of frequency shift was proportional to the amount of the protein immobilized on the FBAR surface, indicating a linear response to DEET binding. These findings demonstrate the potential of binding protein functionalized FBARs as odorant biosensors.