AlN/GaN/Sapphire heterostructure for high-temperature packageless acoustic wave devices

Abstract

Surface acoustic waves (SAW) technology is very promising to achieve wireless sensors able to operate in high temperature environments up to possibly 1000°C. However, there is currently a bottleneck related to the packaging of such sensors. The current high-temperature packaging solutions can withstand 600°C at most. This limitation could be overtaken by the development of packageless devices, based on the waveguiding layer acoustic waves (WLAW) principle. In such devices, the acoustic wave is confined inside an inner layer and is then isolated from undesired surface perturbations like dust deposition. In this paper, we investigate the performance of an AlN/IDT/GaN/Sapphire WLAW device used as a temperature sensor able to operate up to 500°C. After validating a room-temperature GaN material constant set with basic SAW measurements performed on IDT/GaN/Sapphire structure, the AlN/IDT/GaN/Sapphire device is simulated to determine the optimal relative thicknesses of AlN and GaN films in order to obtain a good wave confinement. Based on these calculations, an experimental WLAW device is performed and electrically characterized. The full wave confinement is experimentally confirmed by the lamination of an acoustic absorber on top of the device: no change in the scattering parameters was observed. The WLAW device is then electrically characterized between the ambient temperature and 500°C. A temperature coefficient of frequency (TCF) value of-34.6 ppm/°C is obtained, demonstrating the potential of the WLAW AlN/IDT/GaN/Sapphire structure as a packageless temperature sensor. Finally, the theoretical TCF of the AlN/IDT/GaN/Sapphire structure was numerically calculated by changing the material constants of AlN, GaN and Sapphire according to the temperature coefficients available in the literature. The theoretical and experimental data were found in good accordance.

Design and Characterization of High-Q SAW Resonators Based on the AlN/Sapphire Structure Intended for High-Temperature Wireless Sensor Applications

“…Their frequency evolution up to 593°C has a slight curvature, with a first-order TCF of -28 ppm/°C, and a second-order TCF of -36 ppb/°C 2 (25°C being used as the reference temperature). This frequency behavior is in good accordance with previously published, experimental and calculated TCF results, for a relative AlN thickness around 0.46 [25]. The aluminium IDTs can still show enough stability in their electrical behavior up to 600°C.…”

“…The first-order TCF is -57 ppm/°C, while the second-order TCF is -17 ppb/°C 2 . This is again in good agreement with previous results, for a relative AlN thickness of 0.24 [25]. The temperature reading errors are particularly low, in spite of the limited resolution of the chuck's temperature display (1°C), that served as a reference.…”

AlN/Pt/LN-Y128 Packageless Acoustic Wave Temperature Sensor

“…This technological barrier could be elegantly broken by the development of so-called "packageless" sensors. It has already been shown theoretically and experimentally that a packageless solution is achievable using Waveguiding Layer Acoustic Waves (WLAW) [5][6][7][8]. In a WLAW structure, the wave propagates in a low velocity layer "sandwiched" between two high acoustic velocity layers [5].…”

An Experimental and Theoretical Study of Impact of Device Parameters on Performance of AlN/Sapphire-Based SAW Temperature Sensors

“…Figure8shows the flowchart of the simulation technique implemented, combining Euler transformation and COM theory with the Christoffel equation to describe the boundary conditions of AlN/sapphire based-SAW sensors[25,26]. Device and material parameters for the simulation can be divided into tensors and scalars.…”

“…[25]. Then the |Y11| from the COM simulation was adjusted by modifying the tensors of AlN until it fitted well with the measured |Y11| of sensors along the m-direction, as shown inFigure 9a.…”