Jeremy Masson

Real-time imaging of acoustic waves on a bulk acoustic resonator

Time resolved images of acoustic waves in the 100 MHz–2.2 GHz range are obtained for an electrically excited thin-film bulk acoustic wave resonator by means of an ultrafast optical technique. Electrical pulses, synchronized to ultrashort laser pulses, piezoelectrically excite the device, and synchronous near-infrared laser pulses interferometrically detect surface motion. The frequency dispersion is extracted using spatiotemporal Fourier transforms, revealing both longitudinal and surface acoustic modes.

Development of Absorbing Conditions for the Analysis of Finite Dimension Elastic Wave-Guides

A perfectly matched layer approach was developed for piezoelectric problems simulated by finite element and compared with a distributed viscosity absorption method. The development is self-consistent and allows for absorbing energy at the edges of a mesh without spurious reflection due to non appropriated boundary conditions. ID and 2D validation are reported and the method is applied to analyze a finite length Lamb wave transducer and a 2D FBAR structure.

Frequency sources and filters applications using high overtone bulk acoustic resonators exhibiting high Q.f product

Bulk acoustic waves excited in thin piezoelectric films have revealed their capabilities for addressing the problem of high frequency RF filters and frequency sources (above 1 GHz). In this paper, we propose an alternative to thin film deposition consisting in single crystal wafers bonded on substrate (high quality) and thinned down, allowing for plate thickness close to 30 mum. This has been achieved on 3 inches wafers and allows for an accurate selection of the wave characteristics.

On the dispersive behaviour of AlN/Si High Overtone Bulk Acoustic Resonators

Harmonic bulk acoustic resonators are build on a SOI to allow for a good spectral separation of the device resonance. SOI is etched back to allow for the fabrication of well defined resonance in the vicinity of 2.45 GHz. Thermal sensitivity close to -25 ppm/K also was measured. The analysis of experimental data obtained for resonance taking place in the whole stack allows for emphasizing a dispersive behavior of the harmonic modes of the structure.

High Overtone Bulk Acoustic Resonators Based on Thinning Single-crystal Piezoelectric Layers

Bulk acoustic waves excited in thin piezoelectric films have revealed their capabilities for addressing the problem of high frequency RF filters (above 1 GHz). In this paper, we propose an alternative to thin film deposition consisting in single crystal wafers bonded on a substrate (for instance silicon) and thinned, allowing for plate thickness close to 10 mum. This has been achieved on 3 inches wafers and allows for an accurate selection of the wave characteristics. More, the properties of the piezoelectric material are found conform with tabulated values, enabling one to reliably design any passive signal processing device.

Electron-beam processed SAW devices for sensor applications

In this paper, electron-beam (e-beam) lithography for processing of surface acoustic wave devices is investigated, and its suitability for large-scale processing discussed. Electron-beam lithography is used for exposure of surface acoustic wave (SAW) resonator patterns on polymethyl methacrylate (PMMA) coated piezoelectric substrates. Electron-beam lithography can be used for high frequency SAW designs, due to a minimal finger width of 100 nm to 400 nm. Such SAW devices can be used for high-frequency sensor applications. This contribution will consider processing, on-wafer characterization, and characterization of sensor effects in instrumentation applications.

Hybrid resonant structures for wireless sensor applications

In this work, we report on an original approach for increasing the coupling factor of Harmonic Bulk Acoustic Resonators (HBARs). It consists in adding a layer onto the top electrode to optimize the operation of the device. We avoid using metal layers and used an extra Aluminum Nitride (AlN) film to optimize the excitation energy localization in the stack and try and preserve the Q factor of the structure. We present simulation results demonstrating the efficiency of the optimization approach. Based on these simulations, test devices have been manufactured and tested, demonstrating the possibility to gain more than a factor of 2 on the coupling along the proposed approach. Finally, the possibility to wirelessly interrogate these resonators is demonstrated.

High Overtone Bulk Acoustic Resonators Based on Thinned Single‐crystal Piezoelectric Layers: Filters and Frequency Sources Applications

The thin film bulk acoustic wave resonators exploiting the thickness-extensional vibration mode of piezoelectric thin films is a key technology as alternative solutions to standard SAW resonators. Lakin have emphasized the capability of High Overtone Bulk Acoustic Resonators to present high quality factors at frequencies in the GHz range. HBAR spring from the conjugation of the strong coupling coecient of deposited piezoelectric thin films and of the high intrinsic quality of used substrates. The piezoelectric film and the two electrodes on its both sides are used as transducer whereas the acoustic energy is mainly trapped in the substrate. The resonant frequency corresponds to a half wavelength in the entire thickness of the device and, in opposition to FBAR, we can utilized both odd and even harmonics. The fundamental, generally in the vicinity of 10»MHz, has no specific interest but Q.f products around 1.1◊10 14 have already been obtained for high overtones using aluminum nitride thin films deposited onto sapphire. In view of improving the Q factor of thin films, it is desirable to use a single-crystal piezoelectric material such as lithium niobate. We show and compare the fabrication in both approaches. Dierent measurement results are exposed for both approaches for the fabrication of oscillator and filters are shown and discussed.

High-overtone bulk acoustic wave resonator on galliumnitride

In our previous research we already demonstrated micro acoustic devices, such as membrane based thin film bulk acoustic shear wave resonators and surface acoustic shear wave resonators, based on Metal-Organic-Vapour-Phase-Epitaxial (MOVPE) grown highly oriented a-plane piezoelectric material. Although MOVPE is a well established process for compound semiconductor layer growth especially of III–V semiconductors as InP, GaAs, and the nitrides GaN or AlN as also design and simulation of micro acoustic devices is nowadays a well established knowledge, the linkage between both is quite a technological challenge. Using an adapted MOVPE growth process for a-plane GaN on r-plane sapphire with a process linked improved surface quality; the challenge to build up high-overtone bulk acoustic wave resonators (HBAR) with a shear polarization of the acoustic wave was risen within this research. Different designs of MEMS-based prototypes of HBARs were processed on a-plane GaN after intensive simulations, their acoustic electrical behaviour analyzed and the temperature coefficient of frequency determined.

Comprehensive characterization of Surface acoustic wave trapping in a periodic array of high aspect ratio electrodes

A comprehensive characterization of surface acoustic waves trapped under high aspect ratio electrode gratings atop LiNbO3 (YXl)/128deg has been achieved. We have analyzed the motion of the electrodes corresponding to the excited modes and we have reported the quality factor and the coupling coefficient evolution versus phase velocity. Very high coupling coefficients can be obtained for low velocity (1000 m.s-1) elliptically polarized modes. TCF of some mode also were measured and found close to the sensitivity of standard SAW.