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Performance of AlN-based electroacoustic devices directly tie with piezoelectric and metal electrode film quality. In this paper, sputter techniques for the reactive sputtering of AlN and ScAlN thin films, for the deposition of highly textured metal electrodes, and for the deposition of multilayer Bragg acoustic reflectors for SMR devices using dual-target S-gun magnetrons are described and some film...
A piezoelectric plate, poled along its thickness, that supports on its top surface a periodic grating of electrodes is considered. If wave propagation is assumed along the length of the plate, one demonstrates that an electrical Bragg band gap can be observed, depending on the electrical boundary conditions applied on the electrodes. This gap is associated with a discontinuity of the electric field...
Ultrasounds (US) are a proven medical tool to assess a myriad of biological processes, including breast cancer screening, fetal development and blood flow. However, US also have the potential to deliver power and telemetry capability to deeply implanted devices, surpassing some challenges faced by coils or antennas operating inside the human body. In this study we present an implantable device powered...
In the present study, chirp coded pulses are investigated with respect to high frequency imaging. These pulses were used drive broadband polymer transducers assembled from an adhesive-free layer-be-layer deposition method. The image quality obtained from using a long chirp coded pulse was compared with images generated from shorter pulses. This includes the Ricker wavelet and the square pulse most...
Capacitive micro-machined ultrasonic transducers (CMUTs) offer several advantages over conventional piezoelectric transducers in terms of acoustic performance and circuit integration capability. In this study, we focus on the potential of CMUTs for the high receiving sensitivity which is strongly required for photoacoustic imaging applications. We propose an advanced CMUT cell design with an ultra-narrow...
We have developed a new, fast and simple 3D imaging approach referred to as Simultaneous Azimuth and Fresnel Elevation (SAFE) compounding. The principle behind this technique is to perform conventional plane wave compounding with the bottom set of electrodes, while implementing a reconfigurable Fresnel elevation lens with the top electrodes. While a Fresnel lens would usually result in unacceptable...
This paper reports on the investigation of 1 μm thick films of 20% Scandium-doped Aluminum Nitride (ScAlN) for the making of piezoelectric MEMS laterally vibrating resonators (LVRs). The ScAlN films, which can be sputter-deposited such as undoped Aluminum Nitride (AlN) films, were used to demonstrate high performance resonators. These devices showed quality factor (Qs) in excess of 1000 in air centered...
An original method to measure the acoustic properties of porous Pb(Zr0.53Ti0.47)O3 (PZT) backings at high-frequencies (HF, i.e. between 15 and 25 MHz), was developed. To this end, a piezoelectric PZT-based thick film was deposited onto the porous ceramic backing and directly used to generate an acoustic signal in water. Here, the considered signal is the one that was generated in water, reflected...
A highly sensitive capacitive micromachined ultrasound transducer (CMUT) cell with an ultra-narrow gap was investigated. The electromechanical coupling coefficient (kT) as a figure of merit of sensitivity of ultrasound transducers was 0.67 in a 30-MHz CMUT cell with a 30-nm height vacuum gap and in 100-nm thick dielectric layers, and the coefficient was superior to that of piezoelectric transducers...
Suppression of the SH-SAW response is mandatory to design TC SAW devices on θ degree rotated Y-cut LiNbO3. However, it is not easy because K2 for SH SAW changes rapidly with θ, and its optimal value in terms of the SH-SAW suppression is dependent on electrode and SiO2 thicknesses. The authors found that the optimal θ always locates close to θ where difference in velocities of two SAWs is minimum....
New ultrasound imaging and therapeutic modalities may require transducer designs that are not easily facilitated by conventional design guidelines and analytical expressions. This motivates the investigation of numerical optimization methods that can include the effect of structural layers (e.g. bonding and electrodes), electrical loading, and more than one active piezoceramic layer in the design...
“Acoustic angiography” is a super-harmonic contrast imaging technique, which is based on the fact that when excited with a moderate acoustic pressure near their resonance (2–4 MHz; around MI of 0.5–0.7) ultrasound contrast agents produce broadband content which extends well past 15 MHz. By detecting the higher order harmonic energy while transmitting at a low fundamental frequency, exquisite resolution...
Acoustic delay lines based on Al0.85Sc0.15N thin film hybrid transducers were investigated by finite element modeling. It was found that an acoustic impedance matching between transducer and non-piezoelectric substrate material plays a crucial role to efficiently excite a traveling surface acoustic wave (SAW) through the BAW piston motion. Test devices based on the 2.5 um thick Al0.85Sc0.15N piezoelectric...
3D Ultrasound systems present several technical challenges, particularly the large number of elements in a 2D array, high electrical impedance, and image acquisition time. Crossed electrode arrays address some of these issues, especially the huge reduction in number of elements. However, creating a two-way focused 3D image in real-time is difficult with these arrays because azimuth and elevation dimensions...
In the present work, nonlinearities in temperature compensating (TC) SAW devices are investigated. The materials used are LiNbO3-rot128YX as the substrate and Copper electrodes covered with a SiO2-layer as the compensating layer. In order to understand the role of these materials for the nonlinearities in such acoustic devices, a FEM simulation model in combination with a perturbation approach [1]...
Lithium niobate (LN) based thin film piezoelectrics have being extensively explored [1-3] for the making of high coupling and high performance resonators. The most important bottleneck for the use of LN film is related to fabrication process and it is particularly challenging when a bottom electrode is included in the stack to increase the film capacitance per unit area. We have explored Y-cut LN...
The most important bottleneck for the use of lithium niobate (LN) films for making MEMS resonators is related to the fabrication process and it is particularly challenging when a bottom electrode needs to be included in the film stack to increase the resonator's capacitance per unit area. In this work, we propose to access the bottom electrode by using capacitive coupling rather than a direct resistive...
It is more difficult to nucleate AlN-ScN alloy thin films (AlScN) in pure (0001)-texture than it is with pure AlN thin films. AlN thus can serve as seed layer for AlScN. Equipment limitations may lead to the problem of a vacuum break between AlN and AlScN deposition, as it leads to oxidation of the AlN surface. This issue was studied with high resolution TEM and electron diffraction. The formed oxide...
Ultrasounds are a proven medical tool to assess some biological processes, including breast cancer screening, fetal development and blood perfusion. However, ultrasounds also have the potential to deliver power and telemetry capabilities to deeply implant devices, surpassing some of the challenges faced by coils or antennas operating inside the human body. In this paper, we present a small-form implantable...
A general purpose finite element model that yielded directly the nonlinear frequency response of the second harmonic generation in SAW IDT resonators was developed. The model enabled us to study the effects of the nonlinear material constants, voltage drive, duty factor, and IDT geometry on f-2f nonlinear interactions. Specifically we have applied our model to the study of nonlinear frequency response...
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