Surface Acoustic Wave Devices in Electronic WarFare

Acoustic waves based MEMS devices offer a promising technology platform for a wide range of applications due to their high sensitivity and the capability to operate wirelessly. These devices utilize an acoustic wave propagating through or on the surface of a piezoelectric material, as its sensing mechanism. Any variations to the characteristics of the propagation path affect the velocity or amplitude of the wave.

The presence of organic or inorganic chemical species can be detected by their reaction with a suitable reagent. In acoustic sensors where the sensor reagent is immobilized on the device, the associated mass increase is detected by a change of the propagation characteristics of an acoustic wave. Acoustic surface wave (SAW) devices promise an advantage over the commonly used quartz oscillators because of their inherent higher sensitivity associated with their high operating frequency of up to several hundred MHz. Until now SAW devices have not found widespread application, mainly because of handling difficulties associated with the necessity to mount these devices on sockets and to connect them electrically with bonding wires. In this contribution, techniques will be presented to overcome problems associated with the operation of SAW sensors in aggressive liquids or in gases at elevated temperatures. A new type of SAW device has been developed in which no ohmic electrical contacts are required. Instead, electrical connection between the device and the electronic circuitry is achieved by inductive coupling. In this way, operation and preparation of the devices is considerably eased. Data will be presented on immunosensing in buffer solutions, and on gas sensing at temperatures up to 500 °C.

Acoustic surface wave (SAW) devices have an irreplaceable role in modern mobile communication due to their excellent performance. It is important to analyze and design SAW devices accurately. Coupling-of-Modes theory (COM) and P-Matrix are common methods to simulate the frequency response of SAW devices. Finite element method (FEM) is also an effective method to solve piezoelectric devices. It is very meaningful to combine these methods to improve the speed and accuracy of calculation. In order to extract COM parameters, an effective connection between admittance obtained by P-matrix and FEM basing on COM equation and P-Matrix was established. COM parameters are extracted by modal and harmonic analyses in FEM. The admittances result from COM with these COM parameters agree well with that from FEM in a wide frequency range. It illustrates the effectiveness of the novel method.

For the last 60 years, acoustic wave devices have been used. In the last two decades, surface acoustic wave (SAW) devices have gained interest for sensor applications. The velocity and damping are sensitive to the outside parameter of SAW devices; therefore, they are attracting the people toward their use. A SAW device is consisting of a piezoelectric material with metal inter-digital transducer on its surface. When an electrical signal is applied, it converts into an acoustic wave.

Ultra high frequency acoustic wave propagation in fully polymer based surface acoustic wave device

Surface acoustic wave (SAW) devices are powerful platforms for mass sensing, chemical vapor or gas detection, and biomolecular identification. Great efforts have been made to achieve high sensitivities by using super-high-frequency SAW devices. Conventional SAW sensing is based on mass-loading effects at the acoustic wave propagation (or delay line) region between two interdigitated transducers (IDTs). However, for many super-high-frequency SAW devices with their small sizes, there is a huge challenge that the sensitivity is difficult to be further increased, simply because there are very limited areas between the IDTs to deposit a sensing layer. Herein, we proposed a novel strategy based on giant mass-sensitivity effects generated on the global area of acoustic wave device (defined as areas of both delay line region and IDTs), which significantly enhances sensitivity and reduces the detection limit of the SAW device. Both theoretical analysis and experimental results proved this new strategy and mechanism, which are mainly attributed to the efficient energy confinement at the IDTs’ region for the super-high-frequency SAW devices. The achieved mass sensitivity using this new strategy is as high as 2590 MHz <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot $ </tex-math></inline-formula> mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{{2}} \cdot \mu \text{g}^{-{1}}$ </tex-math></inline-formula> , which is about 500 times higher than that obtained from only using the acoustic wave propagation region with a SAW frequency of 4.43 GHz. Hypersensitive humidity detection has been demonstrated using this newly proposed sensing platform, achieving an extremely high sensitivity of 278 kHz/%RH and the fast response and recovery times of ~37 and ~35 s, respectively.

The past few decades have witnessed the ultra-fast development of wireless telecommunication systems, such as mobile communication, global positioning, and data transmission systems. In these applications, radio frequency (RF) acoustic devices, such as bulk acoustic waves (BAW) and surface acoustic waves (SAW) devices, play an important role. As the integration technology of BAW and SAW devices is becoming more mature day by day, their application in the physical and biochemical sensing and actuating fields has also gradually expanded. This has led to a profusion of associated literature, and this article particularly aims to help young professionals and students obtain a comprehensive overview of such acoustic technologies. In this perspective, we report and discuss the key basic principles of SAW and BAW devices and their typical geometries and electrical characterization methodology. Regarding BAW devices, we give particular attention to film bulk acoustic resonators (FBARs), due to their advantages in terms of high frequency operation and integrability. Examples illustrating their application as RF filters, physical sensors and actuators, and biochemical sensors are presented. We then discuss recent promising studies that pave the way for the exploitation of these elastic wave devices for new applications that fit into current challenges, especially in quantum acoustics (single-electron probe/control and coherent coupling between magnons and phonons) or in other fields.

To improve the performances of surface acoustic wave (SAW) device, the architecture of dual track SAW device was proposed in this paper. The dual track architecture and the multistripe couplers (MSCs) were skillfully applied to the dual track SAW device. The bulk acoustic wave (BAW) excited by input IDT was separated and eliminated by the full transfer MSC. The bidirectional SAW launched by input interdigital transducer (IDT) can be totally received by two output IDTs connected in parallel. The triple transit echo signals were suppressed by dual track in input IDT. Furthermore, the dummy electrodes were used as eliminate the phase front distortion of waves propagating through apodized IDTs, and split electrodes were used as minimize acoustic reflections within transducers. By means of a dual track SAW device with center frequency at 203.559 MHz, the results of test and analysis are presented. Experiments results confirm that the dual track SAW device has good response characteristics in frequency domain and time domain, and the passband ripples and the side lobes are acceptable and better than ones of traditional SAW device.KeywordsSurface acoustic wave (SAW) deviceDual trackBulk acoustic wave (BAW)triple transit echo signals

Acoustic wave devices coated with a thin layer of chemoselective material provide highly sensitive chemical sensors for the detection and monitoring of vapors and gases. In this work, a variety of coating materials and coating deposition techniques have been evaluated on surface acoustic wave (SAW) devices. A novel thin film deposition technique, matrix assisted pulsed laser evaporation (MAPLE), is utilized to coat high quality polymer films on SAW devices, and conventional pulsed laser deposition is used to deposit a passivation layer of diamond-like-carbon on a SAW device surface to prevent water adsorption. In addition, chemoselective coatings are formed by covalent attachment of functionalized species to the silica surface of SAW devices. The self-assembled monolayer or near monolayer structures are designed to populate the SAW device surface with the desirable hexafluoroisopropanol moeity. The rapid kinetic signals achievable with the various coated SAW sensors during vapor tests are examined as a function of the coating material and the quality of the thin films. In parallel to the thin film deposition, growth, and vapor testing, the electrical characteristics of the SAW sensor have been characterized. The quality factor and residual phase noise of polymer coated SAW devices are examined, and a prediction of the theoretical limit of the phase noise performance of the loop oscillator is made.

Flexible surface acoustic wave (SAW) devices have recently attracted tremendous attention for their widespread application in sensing and microfluidics. However, for these applications, SAW devices often need to be bent into off-axis deformations between the acoustic wave propagation direction and bending direction. Currently, there are few studies on this topic, and the bending mechanisms during off-axis bending deformations have remained unexplored for multisensing applications. Herein, we fabricated aluminum nitride (AlN) flexible SAW devices by using high-quality AlN films deposited on flexible glass substrates and systematically investigated their complex deformation behaviors. A theoretical model was first developed using coupling wave equations and the boundary condition method to analyze the characteristics of the device with bending and off-axis deformation under elastic strains. The relationships between the frequency shifts of the SAW device and the bending strain and off-axis angle were obtained, and the results were identical to those from the theoretical calculations. Finally, we performed proof-of-concept demonstrations of its multisensing potential by monitoring human wrist movements at various off-axis angles and detecting UV light intensities on a curved surface, thus paving the way for the application of versatile flexible electronics.

In this paper, production oriented aspects of using Silicon Dioxide (SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) films in manufacturing of Temperature Compensated Bulk Acoustic Wave (BAW)/ Film Bulk Acoustic Resonator (FBAR) [1], [2] and Surface Acoustic Wave (SAW) devices have been presented. SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> has been used to obtain low Temperature Coefficient (TempCo) in acoustic wave devices for more than three decades [3]. One of the big issues is that depending on the method of deposition and the amount of times SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is exposed to the ambient environment [4], it can significantly alter temperature compensating properties of the film as well as etch rate in a thickness trimming process with focused Ion Beam. Plasma Enhanced Chemical Vapor Deposition (PECVD), RF diode and RF magnetron depositions with in-situ thickness trimming and capping layers were tested on the temperature compensated FBAR and SAW structures. Repeatability of the results was tested with different amount of time before processing steps. Best results were obtained using RF diode sputtered SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> with in-situ trimming process [5] and in-situ aluminum nitride (AlN) sputtered capping layer.

IEEE International Ultrasonics Symposium (IUS), Prague, CZECH REPUBLIC, JUL 21-25, 2013

III Interaction of Light and Acoustic Surface Waves

Surface acoustic wave (SAW) devices are generally fabricated on rigid substrates that support the propagation of waves efficiently. Although very challenging, the realisation of SAW devices on bendable and flexible substrates can lead to new generation SAW devices for wearable technologies. In this paper, we report flexible acoustic wave devices based on ZnO thin films coated on various substrates consisting of thin layers of metal (e.g., Ni/Cu/Ni) and/or polymer (e.g., polyethylene terephthalate, PET). We comparatively characterise the fabricated SAW devices and demonstrate their sensing applications for temperature and ultraviolet (UV) light. We also investigate their acoustofluidic capabilities on different substrates. Our results show that the SAW devices fabricated on a polymer layer (e.g. ZnO/PET, ZnO/Ni/Cu/Ni/PET) show enhanced temperature responsivity, and the devices with larger wavelengths are more sensitive to UV exposure. For actuation purposes, the devices fabricated on ZnO/Ni/Cu/Ni layer have the best performance for acoustofluidics, whereas insignificant acoustofluidic effects are observed with the devices fabricated on ZnO/PET layers. We propose that the addition of a metallic layer of Ni/Cu/Ni between ZnO and polymer layers facilitates the actuation capability for the acoustofluidic applications while keeping temperature and UV sensing capabilities, thus enhancing the integration of sensing and acoustofluidic functions.

For surface acoustic wave (SAW) devices operating at elevated ambient temperatures, piezoelectric crystals that have stable material properties at high temperatures are desirable. The progress in the field of electronic technologies has increased the demand for high-temperature piezoelectric materials for the use in temperature and pressure sensors. Recently, SAW sensors have been operated at room temperature or 100°C ÷ 300°C at most. A new piezoelectric SrLaGa3O7 crystal belongs to tetragonal symmetry class, and has stability of its piezoelectric properties up to the melting temperature of 1650°C. Numerical simulation of the properties of surface and leaky acoustic waves in the SrLaGa3O7 single crystal is performed. The SAW has a maximum value of the electromechanical coupling coefficient (~ 0.25%) on Z+64°-cut and propagation direction along the X-axis. In the same propagation direction, the electromechanical coupling coefficient of the leaky wave is 3.5 times lower than that of SAW. The SAW has large electromechanical coupling coefficient value (~0.24%) on Z, X+45°-cut of the crystal. It is shown that these two cuts of the SrLaGa3O7 single crystal are promising for use in the SAW devices.