Overtone Bulk Acoustic Wave Resonator Research Articles

All Acoustical Excitation of Spin Waves in High Overtone Bulk Acoustic Resonator

The hybrid high overtone bulk acoustic wave resonators (HBARs) consisting of a piezoelectric film transducers and gallium gadolinium garnet substrates with yttrium iron garnet films (YIG-GGG-YIG) are used for experimental excitation and detection of acoustically driven spin waves (ADSWs). Two types of HBAR transducers made of Al-ZnO-Al films (differed through the electrodes’ geometry) were deposited onto YIG-GGG-YIG trilayers with different YIG film thicknesses and doping levels and served for excitation of multimode HBAR at gigahertz frequencies. ADSWs were detected by measuring the shifts of resonant HBAR modes in a tangential external magnetic field when the conditions for magnetoelastic resonance (MER) were satisfied. It was shown that the design of the transducer with a continuous bottom electrode provides all acoustical excitation of spin waves (pure ADSWs), suppressing the additional inductive magnetic dynamics excitation due to the electrodes’ geometry. The theoretical study of the HBAR spectrum in a magnetic field showed that the resonance harmonics in the MER region can either almost continuously transfer from one to another, or decay and form an evident magnetoelastic gap. In this case, the shift of resonant frequencies can achieve several intermodal distances. The results obtained are important for applications of HBAR-based devices in spintronics and magnonics.

Microwave Acoustic Attenuation in CTGS Single Crystals.

This article presents a study of special material properties of the single crystalline material Ca3TaGa3Si2O14 (CTGS = Catangasite). The comparatively highly ordered crystal structure and acceptable piezoelectric strength make it a candidate for microacoustic applications under extreme conditions. Obviously, low-loss dynamic behavior is typical for this crystal which consequently enables high-temperature use. As a particular challenge, the behavior at gigahertz frequencies is investigated here. For that, High overtone Bulk Acoustic wave Resonator (HBAR) type measurements in the range of 1-6 GHz are performed. The selection of five distinctive propagation directions for exclusively pure or quasi-longitudinal modes enables to derive the dynamic viscosities from the quality factors of HBAR results. The observed frequency dependences exhibit Akhiezer behavior as the predominant loss mechanism in the cases examined.

Increase of electromechanical coupling coefficient k t 2 in (0001)-oriented AlN films by chromium doping

Piezoelectric AlN films possess high bulk acoustic wave velocity, low acoustic attenuation, and good temperature characteristics. However, AlN film bulk acoustic wave resonators (FBARs) have a relatively small electromechanical coupling coefficient k eff 2. It was recently reported that Cr doping in AlN films increased the piezoelectric constant d 33. The k t 2 of AlN FBARs may thus be enhanced by Cr doping. In this study, we investigated the effect of Cr doping in (0001)-oriented AlN films on k t 2 from the frequency characteristics of high overtone bulk acoustic wave resonators. k t 2 of the Cr-doped AlN films was increased for Cr contents of less than 3%. The maximum k t 2 observed for the Cr0.012Al0.088N film was 5.9%, which was approximately 1.4 times higher than that of pure AlN film (k t 2 = 4.4%).

Frequency and magnetic field mapping of magnetoelastic spin pumping in high overtone bulk acoustic wave resonator

We report on the first observation of microvolt-scale inverse spin Hall effect (ISHE) dc voltage driven by an acoustic spin pumping (ASP) in a bulk acoustic wave (BAW) resonator formed by a Al-ZnO-Al-YIG(1)-GGG-YIG(2)-Pt structure. When 2 mW power is applied to an Al-ZnO-Al transducer, the voltage VISHE ∼ 4 μV in the Pt film is observed as a result of resonant ASP from YIG(2) to Pt in the area ∼ 170 μm. The results of frequency and magnetic field mapping of VISHE(f,H) together with reflectivity of the resonator show an obvious agreement between the positions of the voltage maxima and BAW resonance frequencies fn(H) on the (f, H) plane. At the same time a significant asymmetry of the VISHE(fn(H)) value in reference to the magnetoelastic resonance (MER) line fMER(H) position is revealed, which is explained by asymmetry of the magnetoelastic waves dispersion law.

Magneto Acoustic Spin Hall Oscillators

This paper introduces a novel oscillator that combines the tunability of spin Hall-driven nano oscillators with the high quality factor (Q) of high overtone bulk acoustic wave resonators (HBAR), integrating both reference and tunable oscillators on the same chip with CMOS. In such magneto acoustic spin Hall (MASH) oscillators, voltage oscillations across the magnetic tunnel junction (MTJ) that arise from a spin-orbit torque (SOT) are shaped by the transmission response of the HBAR that acts as a multiple peak-bandpass filter and a delay element due to its large time constant, providing delayed feedback. The filtered voltage oscillations can be fed back to the MTJ via (a) strain, (b) current, or (c) magnetic field. We develop a SPICE-based circuit model by combining experimentally benchmarked models including the stochastic Landau-Lifshitz-Gilbert (sLLG) equation for magnetization dynamics and the Butterworth Van Dyke (BVD) circuit for the HBAR. Using the self-consistent model, we project up to ~50X enhancement in the oscillator linewidth with Q reaching up to 52825 at 3 GHz, while preserving the tunability by locking the STNO to the nearest high Q peak of the HBAR. We expect that our results will inspire MEMS-based solutions to spintronic devices by combining attractive features of both fields for a variety of applications.

Spin pumping in a composite high overtone bulk acoustic wave resonator

A new way of generating a pure spin current using a magnetoelectric composite high-overtone bulk acoustic-wave resonator (HBAR) based on a layered Al–ZnO–Al–Gd3Ga5O12–Y3Fe5O12–Pt structure is proposed. It is established that the efficiency of generating the rf magnetic field driving the spin current by this method exceeds that of sources which use surface acoustic waves for the excitation of magnetic dynamics and is not inferior to the efficiency of usual electromagnetic ways of exciting a pure spin current that employ microwave cavities.

Resonant spectrum method for characterizing Ba0.5Sr0.5TiO3 based high overtone bulk acoustic wave resonators

This letter reports the use of the resonant spectrum method to characterize a high overtone bulk acoustic wave resonator (HBAR) which has a thin film ferroelectric BaSrTiO3 (BSTO) active layer on a YAG substrate. The HBAR works on the principle of electric field induced piezoelectricity of the thin film ferroelectric BSTO and exhibits switching functionality. From the parallel and series resonant frequencies of each of the multiple peaks in the frequency spectrum of the HBAR, the distribution of spacing of parallel resonance frequency and the distribution of effective coupling coefficient are studied and parameters like acoustic wave velocity, electromechanical coupling coefficient, elastic constant, and density for the thin film are determined. The influence of dc bias voltages on the distribution of the effective coupling coefficient and the electromechanical coupling coefficient is also reported. This letter also establishes the relationship between the relative tunability of the device capacitance and the electromechanical coupling coefficient.

Acoustic spin pumping in magnetoelectric bulk acoustic wave resonator

We present the generation and detection of spin currents by using magnetoelastic resonance excitation in a magnetoelectric composite high overtone bulk acoustic wave (BAW) resonator (HBAR) formed by a Al-ZnO-Al-GGG-YIG-Pt structure. Transversal BAW drives magnetization oscillations in YIG film at a given resonant magnetic field, and the resonant magneto-elastic coupling establishes the spin-current generation at the Pt/YIG interface. Due to the inverse spin Hall effect (ISHE) this BAW-driven spin current is converted to a dc voltage in the Pt layer. The dependence of the measured voltage both on magnetic field and frequency has a resonant character. The voltage is determined by the acoustic power in HBAR and changes its sign upon magnetic field reversal. We compare the experimentally observed amplitudes of the ISHE electrical field achieved by our method and other approaches to spin current generation that use surface acoustic waves and microwave resonators for ferromagnetic resonance excitation, with the theoretically expected values.

Acoustic characterization of AlN films using a High Overtone Bulk acoustic wave resonator

Using the composite resonator with additional thick AlN film with the FWHM of rocking curve of 2.53° under investigation, the bulk acoustic wave attenuation constant and sound velocity along c-axis were directly measured. The method of High Overtone Bulk acoustic wave Resonator (HBAR) spectroscopy based on frequency, measurements of the positions of the resonator peculiarities of phase and amplitude of electromagnetic wave reflection coefficient from composite resonator structure was applied. The method provides attenuation and velocity measurement in a wide frequency band, using the same sample. For the measurements, standard and modified HBAR spectroscopy based on the analysis of only parallel resonance properties of composite resonator structures were used.