Investigation of Temperature Sensing Capabilities of GaN/SiC and GaN/Sapphire Surface Acoustic Wave Devices

George Boldeiu,Alexandra Nicoloiu,Claudia Nastase,Adrian Dinescu,Ioana Zdru,Alexandru Muller,George E Ponchak

doi:10.1109/access.2021.3137908

Abstract

This paper proposes high sensitivity temperature sensors based on single port surface acoustic wave (SAW) devices with GHz resonance frequencies, developed on GaN/SiC and GaN/Sapphire, which permit wide range, accurate temperature determinations. In contrast with GaN/Si SAW based temperature sensors, SiC and Sapphire substrates enable the proper functionality of these devices up to 500°C (773 K), as the high resistivity Si substrate becomes conductive at temperatures exceeding 250°C (523 K) due to the relative low bandgap (and high intrinsic carrier concentrations). Low temperature measurements were carried out using a cryostat between -266°C (7 K) and room temperature (RT) while the high temperature measurements are made on a modified RF probe station. A polynomial fit was used below RT and a linear approximation was evidenced between RT and 500°C (773 K). The structures were simulated at different selected temperatures based on a method that couples Finite Element Method (FEM) and Coupling of Modes (COM). The measured temperature coefficient of frequency (TCF) is about 46 ppm/°C for GaN/SiC SAWs and reaches values of 96 ppm/°C for GaN/Sapphire SAW in the temperature range 25 – 500°C (298 K – 773 K).

Highlights

Surface acoustic wave (SAW) sensor devices capable of operating at very low temperatures and at high temperatures bring the possibility of harsh environment applications in industry and in space, due to their full compatibility with wireless data transmission and batteryless operation
COMSOL Multiphysics takes into consideration the periodicity of the structure, allowing us to reduce the model even more, to one period, λ = 4·w, where w represents the width of the finger and the interdigit spacing of the IDT)
The simulation method based on Finite Element Method (FEM) and Coupling of Modes (COM) techniques was described in detail and the simulated results, at room temperature, were compared to measurements and to FEM simulations in order to evidence the importance of the coupled technique

Summary

Introduction

Surface acoustic wave (SAW) sensor devices capable of operating at very low temperatures and at high temperatures bring the possibility of harsh environment applications in industry and in space, due to their full compatibility with wireless data transmission and batteryless operation. GaN/Si, GaN/SiC and GaN/Sapphire layered structures are fully compatible with nanolithographic and micromachining processes that can be introduced in the fabrication protocol of the acoustic devices (SAW or thin film bulk acoustic resonators). These substrates are intensively used in industrial fabrication of Monolithic Microwave Integrated Circuits (MMICs). An application of temperature SAW sensors might be the temperature monitoring in high power GaN based MMICs for radar applications. A high resonance frequency is an advantage since the sensitivity is proportional with the resonance

Methods

Results

Conclusion