In this Letter, an active area optimisation technique to improve the performance parameters of the film bulk acoustic resonator (FBAR) is proposed. The active area of the back trench membrane-based FBAR is optimised to remove the spurious modes, higher harmonic modes, and to confine the acoustic signal at its central part during the resonance. The effect of thickness variation of SiO₂ layer on the performance parameters was studied using finite-element analysis (FEA) simulation. The SiO₂ film, on silicon substrate, was used as the support layer and zinc oxide was used as the piezoelectric film for the resonator. The authors have successfully demonstrated the FBAR through FEA for an optimised active area of 320 × 320 µm², series resonance frequency (f _s) 1.249 GHz, and parallel resonance frequency (f _p) 1.273 GHz with an effective electromechanical coupling coefficient of 4.65%.

The use of MEMS resonators for signal processing is relatively new and has the potential to change the topology of newer generation circuits. New materials, design and fabrication processes, and integration with conventional circuitry will need to be considered. This book explores the challenges and opportunities of developing circuits with MEMS resonator filters. The replacement of classical electrical components with electromechanical components is explored in this book, and the specific properties of MEMS resonators required in various frequency ranges are discussed. Materials and their selection, CAD tools for system design and the integration of MEMS with CMOS circuitry, and the design, fabrication, testing and packaging of MEMS filters themselves are addressed in detail. Case studies where resonator MEMS have been used as components have been included to encourage readers to consider the practical applications of this technology. MEMS Resonator Filters is essential reading for the analogue circuit designer community, particularly those who are designing circuits for wireless communications, and CMOS technology researchers and engineers who are involved in the fabrication of circuits. Designers of sensors and interfacing circuits will also be interested since resonators are also being used as sensors.

Microacoustic resonators made on suspended continuous membranes of LiNbO₃ were recently shown to have very strong coupling and low losses at ≥5 GHz, suitable for high-performance filter design. Employing these simple resonator structures, the authors have designed, fabricated, and measured a 4.7 GHz bandpass ladder-type filter having 1 dB mid-band loss and 600 MHz bandwidth to address the 5G Band n79 requirements. The filter is fabricated on a monolithic substrate using standard i-line optical lithography and standard semiconductor processing methods for membrane release, starting with commercially available ion-sliced wafers having 400 nm thickness crystalline LiNbO₃ layers. The filter is well-matched to a 50 Ω network and does not require external matching elements. Through accurate resonator engineering using our finite element method software filter design environment, the passband is spurious-free, and the filter provides better-than 30 dB rejection to the adjacent WiFi frequencies. This filter demonstrates the performance and scalable technology required for high-volume manufacturing of microacoustic filters >3.5 GHz.

In a free-standing 400-nm-thick platelet of crystalline ZY-LiNbO₃, narrow electrodes (500 nm) placed periodically with a pitch of a few microns can eXcite standing shear-wave bulk acoustic resonances (XBARs), by utilising lateral electric fields oriented parallel to the crystalline Y-axis and parallel to the plane of the platelet. The resonance frequency of ∼4800 MHz is determined mainly by the platelet thickness and only weakly depends on the electrode width and the pitch. Simulations show quality-factors (Q) at resonance and anti-resonance higher than 1000. Measurements of the first fabricated devices show a resonance Q-factor ∼300, strong piezoelectric coupling ∼25%, (indicated by the large Resonance-antiResonance frequency spacing, ∼11%) and an impedance at resonance of a few ohms. The static capacitance of the devices, corresponds to the imaginary part of the impedance ∼100 Ω. This device opens the possibility for the development of low-loss, wide band, RF filters in the 3–6 GHz range for 4th and 5th generation (4G/5G) mobile phones. XBARs can be produced using standard optical photolithography and MEMS processes. The 3rd, 5th, 7th, and 9th harmonics were observed, up to 38 GHz, and are also promising for high frequency filter design.

A novel electrically-small bulk acoustic wave (BAW)-mediated multiferroic antenna is proposed based on transverse shear waves instead of the longitudinal ones used in the previously proposed multiferroic antenna [1]. Two in-plane orthogonal pairs of electrodes provide independent excitation of the orthogonal transverse shear modes, enabling the first investigation of polarization control in a BAW-mediated multiferroic antenna. Using this approach, polarization can be controlled simply by adjusting the phase difference between the input RF signals of the two electrode pairs. The proposed design concept is verified numerically via COMSOL simulations and a series of post-processing steps in MATLAB. By assuming ideal input RF signals with equal amplitude and 90° phase difference, broadband circularly polarized radiation is achieved in the subGHz band.

The main purpose of this research is to investigate a novel implementation method for a surface acoustic wave type (SAWT) electrode-area-weighted (EAW) wavelet inverse-transform processor (WITP). The method of EAW is that the electrode areas of the input and output interdigital transducers (IDTs) are proportional to the envelope areas of the wavelet function (i.e. the two IDTs are identical). By this method, the SAWT EAW WITP is fabricated on X-112°Y LiTaO₃ substrate material. In the study, the diffraction problem and phase difference as two key problems are presented and the solution to two problems are implemented.

Surface acoustic wave (SAW) delay lines are commonly used devices, and it is important to characterise them to find the causes of deviations between the experimental and theoretical behaviour in order to consider them during design. The authors present the theoretical characteristics and the characterisation of a SAW delay line through X-ray diffraction, energy dispersive X-ray fluorescence, scanning electron microscopy, atomic force microscopy and the measurement of S-parameters. Using the S-parameters, the Y-parameters were calculated and comparing them with those obtained theoretically, they found disagreement in their magnitudes and also that the experimental SAW velocity was 2.8% larger than the theoretical one. The magnitude of experimental Y11 is smaller than that obtained theoretically because of the ill-defined profile and the metallisation ratio of the electrodes is not ideal due to inherent limitations in the fabrication process, and besides Y21 is smaller than expected because the attenuation of the SAW when it propagates through the delay line. When the electrode defects, the experimental SAW velocity and the attenuation coefficient of SAW in this material are considered in the theoretical calculations, agreement is found between theoretical and experimental results. This procedure is based in the comparison between experimental and theoretical Y-parameters and could be used to estimate attenuation, electrode capacitance and SAW velocity.

Radio-frequency (RF) design techniques for the development of signal-interference microwave bandpass filters (BPFs) with hybridised microstrip and surface-acoustic-wave (SAW) elements are reported. They make use of two original types of transversal filtering sections (TFSs) with embedded one-port SAW resonators. The SAW resonators operate either as non-resonating nodes or as an in-band SAW BPF in their bi-path circuit topologies. These new TFS approaches extend the suitability of signal-interference BPFs to small-fractional-bandwidth (FBW) applications, while offering significant advantages in terms of filtering selectivity and occupied circuit size when compared to traditional solutions for narrow-to-moderate/wide-band specifications. Broader FBWs than those attainable through most of the available all-acoustic-wave BPF configurations are also feasible with them. Moreover, a single type of SAW device is employed in the entire BPF structure, which results in a practical benefit regarding robustness to deviations in the prototype fabrication and assembly processes. The proposed filter design concepts are experimentally verified through the fabrication in microstrip technology and characterisation of two multi-TFS-series-cascade-based high-order BPF prototypes with very-narrow and moderate FBWs.

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.

A novel surface acoustic wave (SAW) resonator integrated on a metal substrate is presented. The devices were fabricated on the aluminium nitride (AlN) thin films deposited by mid-frequency magnetron sputtering on polished TC4 titanium alloy substrates. Using a two-step growth method, AlN film with a full-width at half-maximum of 4.1° had been prepared. The AlN film SAW resonator shows a resonance frequency of 129 MHz and an electromechanical coupling coefficient of 0.28%. The measurement results agree well with the simulation results. This integrated SAW resonator can be used as a good strain sensor in metal structure health monitoring.