Dorian Gachon

Fabrication of High Frequency Bulk Acoustic Wave Resonator Using Thinned Single-Crystal Lithium Niobate 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 or glass) and thinned, allowing for plate thickness close to 10 μ m. 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.

Prediction and measurement of boundary waves at the interface between LiNbO 3 and silicon

Interface acoustic waves (IAWs) propagate along the boundary between two perfectly bonded solids. For a leakage- free IAW, all displacement fields must be evanescent along the normal to the boundary inside both solids, but leaky IAWs may also exist depending on the selected combination of materials. When at least one of the bonded solids is a piezoelectric material, the IAW can be excited by an interdigital transducer (IDT) located at the interface, provided one can fabricate the transducer and access the electrical contacts. We discuss here the fabrication and characterization of IAW resonators made by indirect bonding of lithium niobate onto silicon via an organic layer. In our fabrication process, IDTs are first patterned over the surface of a Y-cut lithium niobate wafer. A thin layer of SU-8 photo-resist is then spun over the IDTs and lithium niobate to a thickness below one micrometer. The SU-8-covered lithium niobate wafer then is bonded to a silicon wafer. The stack is subsequently cured and baked to enhance the acoustic properties of the interfacial resist. Measurements of resonators are presented, emphasizing the dependence of propagation losses on the resist properties. Comparison with theoretical computations based on periodic finite element/boundary element analysis allows for explanation of the actual operation of the device.

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.

Excitation of acoustic waves at the interface between lithium niobate and silicon plates

We discuss the fabrication and characterization of IAW resonators made by indirect bonding of lithium niobate onto silicon. In our fabrication process, IDTs are first patterned over the surface of a Y-cut lithium niobate wafer. A thin layer of SU-8trade photo-resist is then spun over the IDTs and lithium niobate to a final thickness below one micron. The SU-8trade covered lithium niobate wafer is then bonded to a silicon wafer using a wafer bonding machine. Measurements of resonators are presented and compared with theoretical computations based on our periodic finite element/boundary element code allows for explaining the actual operation of the device.

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.

Development of high frequency bulk acoustic wave resonator using thinned single-crystal Lithium Niobate

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 or glass) 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

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.

An acoustic waveguide based on doubly-bonded silicon/PPT/silicon structures

In this paper, we present new results on the development of piezoelectric transducers based on periodically poled ferroelectric domains in a lithium niobate plate bonded between two silicon wafers. The fabrication of the periodically poled transducers operating in the range 50 – 500 MHz has been achieved on a 3 inches 500 µm thick wafer. These devices then have been bonded on silicon wafers to fabricate a waveguide. Guided elliptic as well as partially guided longitudinal modes are excited. The experimental responses of the tested devices are compared to predicted harmonic admittances, showing a good agreement between both results and allowing for a reliable analysis of the nature of the excited modes. We also show interesting studies of material combinations used to guide ultrasonic waves. Dispersion properties have also been studied for a structure Si/PPT/Si.

Predictions and measurement of mass loading effects on quartz bulk acoustic wave resonators

The use of a variational perturbation method combined with finite element analysis is presented here to simulate the influence of mass-loading effects on the resonance frequency of bulk acoustic wave resonator. Computations are conducted on 2D and 3D and any shape of resonator can be considered. Predictions are compared to experimental data