High-overtone Bulk Acoustic Resonator Research Articles

Shear mode electromechanical coupling coefficient k15 and crystallites alignment of (112¯) textured ZnO films

ZnO film, in which the crystallite c axis lies in the substrate plane [(112¯0) textured ZnO], is a good candidate for application in shear mode piezoelectric devices. The relationships between the degree of crystallites alignment and the shear mode electromechanical coupling coefficient k15 in (112¯0) textured ZnO films have been investigated. Forty pure-shear mode high overtone bulk acoustic resonators consisting of the (112¯0) textured ZnO film were prepared. The film was varied in crystallites alignment and film thickness. The degrees of crystallites alignment of the films were determined by x-ray pole figure analysis. The k15 values of the films were estimated from the conversion loss characteristics of the resonators. A significant correlation was observed between dispersion of the x-ray poles and the k15 values. However, the k15 values in the thinner films were clearly reduced as compared with those in the thicker films despite their similarities in crystallites alignment. In addition, unexpected second harmonic mode resonance was detected in the thinner films. We concluded that the piezoelectrically inactive layer in the initial film growth deteriorated the k15 value in thinner films.

Electrode effects on general modes in high-overtone bulk acoustic resonators

Generally, in theoretical calculations of high-overtone bulk acoustic resonators (HBAR), metal electrode effects were always ignored. However, the acoustical impedance, thickness and loss of the electrodes affect practically the performances of HBAR operating at high-frequency. For very high-frequency cases, the thickness of the metal electrode is always on the same order of that of the piezo-film and the electrode effects on modes cannot be negligible. In this paper, based on the resonance frequency spectra and Butterworth Van Dyke equivalent circuit of HBAR, the effects of the material, loss, and thickness of the electrodes on the figure of merit, effective electromechanical coupling factor, quality factor, etc. are analyzed. It is demonstrated that the performance of HBAR can also be optimized by using the electrodes with proper impedance, loss and thickness.

Electrode effects on frequency spectra and electromechanical coupling factors of HBAR

In this paper, effects of electrodes on the spectra of high-overtone bulk acoustic resonator are analyzed phenomenologically by numerical simulations. Acoustic impedance ratio of the substrate to piezo-film, Zsb/Z0, and acoustic impedance ratio of the electrode to piezo-film, Ze/Z0, are taken as the category parameters for different combinations of three kinds of substrates, three kinds of piezo-films, and seven kinds of electrodes. The numerical simulations for all of the combinations are carried out. The results indicate that the acoustic impedance ratio of the substrate to piezo-film is a key factor for the variations of the space of parallel resonance frequency and the effective coupling factor versus the mode order. The mechanical effects of the electrodes have significant contribution as well. Several approximate formulae are given to evaluate the effective coupling factor for different combinations.

Parameter characterization of high-overtone bulk acoustic resonators by resonant spectrum method

Effects of electrode on high-overtone bulk acoustic resonator (HBAR) spectra are analyzed by numerical simulation. The figure of merit (FOM), the effective electromechanical coupling factor, k eff 2 ( m ) , and the quality factor Q s of the unique mode are discussed based on the resonance spectra of the HBAR. It is demonstrated that electrodes with proper acoustic impedance and thickness could improve the performance of the HBAR, or degrade the performance if the electrodes are not properly chosen.

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.

Extremely low phase noise UHF oscillators utilizing high-overtone, bulk-acoustic resonators

High-overtone, bulk acoustic resonators (HBAR) have been designed that exhibit 9-dB insertion loss and loaded Q values of 80000 at 640 MHz with out-of-phase resonances occurring every 2.5 MHz. These resonators have been used as ovenized frequency-control elements in very low phase noise oscillators. The oscillator sustaining stage circuitry incorporates low-1/f noise modular RF amplifiers, Schottky-diode ALC, and a miniature 2-pole helical filter for suppression of HBAR adjacent resonant responses. Measurement of oscillator output signal flicker-of-frequency noise confirms that state-of-the-art levels of short-term frequency stability have been obtained. Sustaining stage circuit contribution to resulting oscillator flicker-of-frequency noise is 7-10 dB below that due to the resonators themselves. At 16-dBm resonator drive, an oscillator output signal white phase noise floor level of -175 dBc/Hz is achieved.

Frequency stability of high-overtone bulk-acoustic resonators

The results of phase noise measurement for high-overtone bulk-acoustic resonators (HBARs) for use in high-performance oscillators, operating at 640 MHz with insertion losses of 10-15 dB and unmatched Qs greater than 110 K are reported. Noise measurements made on these resonators with input drive levels of 16 dBm have shown self-noise levels of S(y)(f=100 Hz)=8.0x10(-26) for 1/f noise which represents state-of-the-art for a UHF resonator.

Magnetically tuned high overtone bulk acoustic resonator

Electroacoustic resonating apparatus capable of generating resonances of tunable frequencies. The apparatus includes two transducers coupled to a ferrimagnetic substrate at opposite ends thereof. The first transducer converts an input signal into a signal that produces bulk acoustic waves in the ferrimagnetic substrate. The second transducer receives the bulk acoustic waves and converts them into electrical signals, or alternatively a single transducer which performs both input and output functions. Variable magnetizing means located proximate to the ferromagnetic substrate induces a magnetic field throughout the substrate wherein the magnetic field alters the frequencies of the resonance of the acoustic waves. By varying the magnitude of the magnetic field, the frequencies of the resonances may be varied, thereby allowing tuning of the apparatus.