Spectral interferometry-based microwave-frequency vibrometry for integrated acoustic wave devices

We experimentally demonstrate Aluminum Nitride (AlN) cross-sectional Lame mode resonators (CLMRs) operating in the microwave frequency range and showing high Qkt2 products (FoM) in excess of 85. Such feature enables low motional resistance (Rm) values (37 Ω) in CLMRs characterized by low static capacitance (Co) approaching 66 fF. In addition, the ability of CLMRs to simultaneously achieve high kt2 (> 4%) and a lithographic frequency tunability (> 260 MHz around 900 MHz) is experimentally demonstrated, for the first time, in this work. Such important feature renders CLMRs promising candidates to replace off-chip Surface Acoustic Wave (SAW) devices in lithographically defined filters for next-generation wireless communication platforms.

SiO_2 with the alpha-quartz structure is one of the most popular piezoelectrics. It is widely used in crystal oscillators, bulk acoustic wave (BAW) devices, surface acoustic wave (SAW) devices, and so on. GeO_2 can also be crystallized into the alpha-quartz structure and it has better piezoelectric properties, with higher piezoelectric coefficient and electromechanical coupling coefficients, than SiO_2. Experiments on bulk crystals and theoretical studies have shown that these properties can be tuned by varying the Si/Ge ratio in the Si_xGe_{1-x}O_2 solid solution. However, to the best of our knowledge, thin films of Si_xGe_{1-x}O_2 quartz have never been reported. Here we present the successful crystallization of Si_xGe_{1-x}O_2 thin films in the alpha-quartz phase on quartz substrates (SiO_2) with x up to 0.75. Generally, the films grow semi-epitaxially, with the same orientation as the substrates. Interestingly, the Si_{0.75}Ge_{0.25}O_2 composition grows fully strained by the quartz substrates and this leads to the formation of circular quartz domains with an ordered Dauphiné twin structure. These studies represent a first step towards the optimization of piezoelectric quartz thin films for high frequency (> 5 GHz) applications.

Direct full-scale computational simulation of electronic acoustic wave devices is among the most challenging problems for designing high performance devices. The problem also becomes urgent as the conventional methods fail to characterize the behavior of miniaturized devices that operate at high frequency for demanding applications. The effective computational methodology has not yet been developed for the full-scale simulation of multi-physical phenomena in many micro-electromechanical devices of complex geometric structure on the nano- and micro-scale. Here a direct finite element model for the full-scale analysis of the frequency response of surface acoustic wave (SAW) devices is presented. The ability of the method to quantitatively evaluate the influence of the bulk waves at the high-frequency end of the filter passband and the influence of the number of electrodes on insertion loss is noteworthy. Some practical computational challenges of finite element modeling of SAW devices are also discussed parenthetically.

This paper presents a novel mixing surface acoustic wave (M-SAW) device using multiple Aluminum (Al) interdigital transducer (IDT) layers for liquid sensing applications. The stronger mechanical wave beam generated by the multiple input-IDT layers on the thin film (1 μm) Aluminum Nitride (AlN), consists of different-phase acoustic waves that can travel through a liquid medium. In contrast to the whole signal leaking into liquid medium as in typical SAW devices, the signal obtained at the receiver of the M-SAW device only has a decline in the Rayleigh component. The experimental results show that it is possible to interact with the liquid medium placed on the surface and extract information about the liquid volume based on the phase change. Phase shifts of −16.35°, −11.23°, −4.84°, and −0.86° are obtained for different volumes of demi-water after 10 seconds, 2, 4 and 5 minutes of vaporization, respectively.

In this paper, we describe the study of time to failure (TTF) evaluation of radio frequency (RF) surface and bulk acoustic wave (SAW/BAW) devices for the International Electrotechnical Commission (IEC) standardization. As the passband shifts with T due to the nonzero temperature coefficient of frequency (TCF), its influence must be taken into account at the acceleration test. A technique to estimate the frequency-dependent TCF of RF SAW/BAW devices for the acceleration test of the TTF estimation is proposed. First, it is shown how the filter passband shifts with T, and its numerical model is proposed. Then, its impact on the power durability test is presented.

The distributed capacitance of the periodic grating, the 2- electrode, and the 3-electrode stripline waveguide modulators are derived exactly using conformal mapping techniques. The capacitance formulas are shown to have a common form; they differ in a single parameter which is simply related to the electrode width and spacing. Discrepancies previously found in the capacitance expressions used for the 2-electrode structure are resolved. For the finite 3-electrode structure studied here, a self- and a mutual distributed capacitance are defined. Techniques for switching a 3-electrode directional coupler are suggested. The closed form mapping function derived here will be useful in the design of waveguide directional couplers. The electrode structures examined here are similar to those used in surface acoustic wave devices; therefore, the capacitance calculations should also be applicable.

In this paper, flexible ZnO/ Al Lamb wave device was used to detect and eliminate surface condensations, commonly occurring in chemical process, agriculture, automobile and pipelines. The flexible and smart patch based on acoustic wave devices can identify dew formation through the change of frequency spectrum and then actuate to remove the condensation through acousto-thermal effect. To distinguish the differences between environmental interference (temperature and humidity) and the real condensation, a specified 3D space was built to quantify the degree of distortion of the transmission spectra. For droplets uniformly distributed on the surface of the device with an input power of ∼0.6 W, the evaporation time was significantly reduced to ∼ 1/13 of the natural evaporation time.

Flexible and bendable acoustofluidics based on ZnO film coated aluminium foil

ZnO-SiO/sub 2/-Si surface acoustic wave (SAW) devices with polycrystalline ZnO films of high quality at a thickness h between 0.3 and 15 mu m were fabricated using the RF-magnetron bias sputtering technique. X-ray diffraction, rocking curves, and SEM microscopy were used to characterize the ZnO layers. The authors studied the propagation loss and the coupling coefficient of three different types of devices: Rayleigh wave devices with ZnO layers h/ lambda approximately=0.4 and h/ lambda approximately=0.04, and Sezawa wave devices. Measurements were performed in the frequency range between 80 and 600 MHz. It was observed that Rayleigh wave devices with a thin ZnO layer have a much lower frequency dependence of the propagation loss than the other two types of SAW devices. At 550 MHz, devices with thin ZnO layers exhibit a propagation loss of only 7 dB/cm, compared to 24 dB/cm for Rayleigh wave devices with a thick ZnO layer, and 14 dB/cm for the Sezawa wave devices. Phase velocity and coupling coefficient as a function of film thickness were examined and are compared with theoretical values.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Mapping the energy distribution of Surface Acoustic Wave (SAW) devices operating in the Very High Frequency (VHF) and Super-High Frequency (SHF) range provides a quantitative indicator of energy confinement, a core parameter when addressing low loss filters or high quality factor resonators. We here demonstrate the use of Scanning Electron Microscopy (SEM) for mapping Rayleigh wave acoustic field and shear transverse wave (STW) propagating on quartz. Furthermore, the availability of Focused Ion Beam (FIB) for milling the piezoelectric substrate allows for creating obstacles on the acoustic path and hence tune the acoustic wave propagation direction by reflecting the waves along directions which might otherwise exhibit poor electromechanical coupling.

Acoustic waves are currently being used in a wide range of sensor fields including physical sensing, chemical sensing and biosensing. Their implementation requires specific knowledge of materials, acoustic wave properties, device design and the sensing mechanisms involved for a wide range of applications. In this paper, the authors report on commonly used acoustic wave devices in sensor applications as well as the design techniques and fabrication processes. Sensing mechanisms and a portable sensor array system are described. The development of IC-based processes, thin-film deposition and sensitive layer fixation will allow for the integration of a total physical and chemical analysis system in the one IC package, leading to the evolution of smart sensors.

Acoustic wave devices are an attractive technology for use in sensors since acoustic waves present high sensibilities to external parameters in terms of phase velocity and damping. This technology is very interesting in environments such as Internet of Things, where low power consumption is a central requirement. The main drawback of this technology concerns the application and the reliability of the RF signal powering the sensor that makes necessary the use of virtual network analyser or spectrum analyser. Although in literature examples of acoustic wave devices used with external antennas have been discussed, to the best of our knowledge, at the state of the art acoustic devices integrated with an antenna have not been reported yet. This paper will discuss the possibility to realize a wearable, compact remote sensor, totally passive, fully integrated with the antenna. The wearable sensor is based on a Surface Acoustic Wave (SAW) resonator designed to operate at 800 MHz and realized on a flexible and biocompatible polymeric substrate, made of Polyethylene naphthalate (PEN). The SAW resonator consists of a pair of reflecting gratings, defining the acoustic cavity, and an interdigital transducer (IDT) placed at the centre of the cavity. The distributed feedback cavity shows a high Qfactor Q ≈ 2×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> when 200 reflectors are considered.

We present a versatile and accurate chromatic dispersion measurement method for single mode optical fibers over a wide spectral range (200 nm) using a spectral domain white light interferometer. This technique is based on spectral interferometry with a Mach-Zehnder interferometer setup and a broad band light source. It takes less than a second to obtain a spectral interferogram for a few tens of centimeter length fiber sample. We have demonstrated that the relative group velocity, the chromatic dispersion and the dispersion slope of a sample fiber can be obtained very accurately regardless of the zero-dispersion wavelength (ZDW) of a sample after frequency dependent optical phase was directly retrieved from a spectral interferogram. The measured results with our proposed method were compared with those obtained with a conventional time-domain dispersion measurement method. A good agreement between those results indicates that our proposed method can measure the chromatic dispersion of a short length optical fiber with very high accuracy.

A wireless identification system, based on passive surface acoustic wave (SAW) devices, is presented in this paper. Because the system operates at 915 MHz center frequency, we employ a pair of SAW dispersive delay lines to expand and compress the signal. Using this method, we can enhance the processing gain and filter the noise out of the bandwidth. Thus, we can decrease the demands of the receiver sensitivity and improve the system's performance in rejecting interference signals. The testing results show that the maximum readout distance of the interrogator is 20 m.

In this paper, two types of contact-printing methods for micro/nano-lithography are developed and their application on fabricating high-frequency surface acoustic wave (SAW) devices are investigated. First of all, a light-assisted metal film patterning (LAMP) method which transfers a patterned metal film directly from a silicon mold to a substrate is discussed. The pattern transformation relies on both mechanical contact pressure and optical heating at the interface. Metal patterns with 100 nm feature size can be easily transferred in laboratory using simple equipments. Secondly, a contact-transfer and mask-embedded lithography (CMEL) is proposed which cleverly arranges pure mechanical forces and surface energy difference to achieve the patterning of nano-structures on various kinds of substrates. Applications of these two developed methods are demonstrated on the fabrication of high-frequency (~2 GHz) surface acoustic wave (SAW) filters and resonators. Future developments and potential applications of these nanoimprinting and nano-patterning methods will be addressed.