Fabrication of sub-100 nm IDT SAW devices on insulating, semiconducting and conductive substrates

This work describes the electron-beam (e-beam) lithography process developed to manufacture nano interdigital transducers (IDTs) to be used in high frequency (GHz) surface acoustic wave (SAW) applications. The combination of electron-beam (e-beam) lithography and lift-off process is shown to be effective in fabricating well-defined IDT finger patterns with a line width below 100 nm with a good yield. Working with insulating piezoelectric substrates brings about e-beam deflection. It is also shown how a very thin organic anti-static layer works well in avoiding this charge accumulation during e-beam lithography on the resist layer. However, the use of this anti-static layer is not required with the insulating piezoelectric layer laying on a semiconducting substrate such as highly doped silicon. The effect of the e-beam dose on a number of different layers (of insulating, insulating on semiconducting, semiconducting, and conductive natures) is provided. Among other advantages, the use of reduced e-beam doses increases the manufacturing time. The principal aim of this work is to explain the interrelation among e-beam dose, substrate nature and IDT structure. An extensive study of the e-beam lithography of long IDT-fingers is provided, in a wide variety of electrode widths, electrode numbers and electrode pitches. It is worthy to highlight that this work shows the influence of the e-beam dose on five substrates of different conductive natur

Quasi-static stop band with flexural metamaterial having zero rotational stiffness

Metamaterials realizing stop bands have attracted much attentions recently since they can break-through the well-known mass law. However, achieving the stop band at extremely low frequency has been still a big challenge in the fields of elastic metamaterials. In this paper, we propose a new metamaterial based on the idea of the zero rotational stiffness, to achieve extremely low frequency stop band for flexural elastic waves. Unlike the previous ways to achieve the stop band, we found that the zero rotational stiffness can provide a broad stop band at extremely low frequency, which starts from even almost zero frequency. To achieve the zero rotational stiffness, we propose a new elastic metamaterial consisting of blocks and links with the hinge connection. Analytic developments as well as numerical simulations evidence that this new metamaterial can exhibit extremely low and broad stop band, even at the quasi-static ranges. In addition, the metamaterial is shown to exhibit the negative group velocity at extremely low frequency ranges, as well as the quasi-static stop band, if it is properly designed.ope

Optimization of AlN thin layers on diamond substrates for high frequency SAW resonators

AlN/diamond heterostructures are very promising for high frequency surface acoustic wave (SAW) resonators. In their design, the thickness of the piezoelectric film is one of the key parameters. On the other hand, the film material quality and, hence, the device performance, also depend on that thickness. In this work, polished microcrystalline diamond substrates have been used to deposit AlN films by reactive sputtering, from 150 nm up to 3 μm thick. A high degree of the c-axis orientation has been obtained in all cases. SAW one port resonators at high frequency have been fabricated on these films with a proper combination of the film thickness and transducer size

Locally Resonant Metagrating by Elastic Impedance Modulation

The optical and acoustic metagratings have addressed the limitations of low-efficiency wave manipulation and high-complexity fabrication of metamaterials and metasurfaces. In this research, we introduce the concept of elastic metagrating and present the theoretical and experimental demonstration of locally resonant elastic metagrating (LREM). Remarkably, the LREM, with dimensions two orders of magnitude smaller than the relevant wavelength, overcomes the size limitations of conventional metagratings and offers a unique design paradigm for highly efficient wave manipulation with an extremely compact structure in elastic wave systems. Based on a distinctive elastic impedance engineering with hybridization of intrinsic evanescent waves, the proposed LREM achieves wide-angle perfect absorption. This tackles a fundamental challenge faced by all elastic metastructures designed for wave manipulation, which consists in the unavoidable vibration modes in finite structures hindering their implementations in real-world applications

WIRELESS AND BATTERYLESS SURFACE ACOUSTIC WAVE SENSORS FOR HIGH TEMPERATURE ENVIRONMENTS

International audienceSurface acoustic wave (SAW) devices are widely used as filter, resonator or delay line in electronic systems in a wide range of applications: mobile communication, TVs, radar, stable resonator for clock generation, etc. The resonance frequency and the delay line of SAW devices are depending on the properties of materials forming the device and could be very sensitive to the physical parameters of the environment. Since SAW devices are more and more used as sensor for a large variety of area: gas, pressure, force, temperature, strain, radiation, etc. The sensors based SAW present the advantage to be passive (batteryless) and/or wireless. These interesting properties combined with a small size, a low cost radio request system and a small antennas when operating at high frequency, offer new and exiting perspectives for wireless measurement processes and IDTAG applications. When the materials constituting the devices are properly selected, it becomes possible to use those sensors without embedded electronic in hostile environments (as high temperature, nuclear site, …) where no solutions are currently used. General principle of the SAW sensor in wired and wireless configurations will be developed and a review of recent works concerning the field of high temperature applications will be presented with specific attention given to the choice of materials constituting the SAW device

Perfect anomalous splitter by acoustic meta-grating

As an inversely designed artificial device, metasurface usually means densely arranged meta-atoms with complex substructures. In acoustics, those meta-atoms are usually constructed by multi-folded channels or multi-connected cavities of deep sub-wavelength feature, which limits their implementation in pragmatic applications. We propose here a comprehensive concept of a perfect anomalous splitter based on an acoustic meta-grating. The beam splitter is designed by etching only two or four straight-walled grooves per period on a planar hard surface. Different from the recently reported reflectors or splitters, our device can perfectly split an incident wave into different desired directions with arbitrary power flow partition. In addition, because ultrathin substructures with thin walls and narrow channels are avoided in our design procedure, the proposed beam splitter can be used for waves with much shorter wavelength compared to the previous suggested systems. The design is established by rigorous formulae developed under the framework of the grating theory and a genetic optimization algorithm. Numerical simulation and experimental evidence are provided to discuss the involved physical mechanism and to give the proof-of-concept for the proposed perfect anomalous acoustic splitter.Comment: 5 figure