Characterization of Gallium Nitride Heterostructures for Strain Sensing at Elevated Temperatures

Abstract

Structural health monitoring of physical stimuli such as strain within extreme harsh environments (high temperature, chemically caustic, high shock, high pressure, and high radiation) is currently limited. More specifically, critical structural components used in aircraft, combustion engines, and down-hole environments can utilize strain sensors to monitor structural state of health to prevent catastrophic failures and study mechanical fatigue within extreme environments. Unfortunately, traditional metal foil strain gauges have low sensitivity and silicon-based devices are limited to temperatures below 200 °C and benign environments due to junction leakages and material degradation. Primarily due to its large bandgap (3.4 eV) gallium nitride (GaN) offers a promising material platform for sensing within extreme environments because it is temperature resistant (electrically stable above 600 °C), chemically stable, and radiation-hardened. Additionally, when aluminum gallium nitride (AlGaN) is grown on GaN it creates a high electron density sheet at the interface known as a 2-dimensional electron gas (2DEG) layer. The gauge factor for AlGaN/GaN heterostructure devices is comparable to silicon devices and higher than metal foil gauges. This paper will examine how the GaN heterostructure devices are affected by elevated temperatures; this is done by fabricating 2DEG GaN resistors on cantilevers and applying known loads at the end while under temperatures from room temperature to 92 °C. The gauge factor of the device was found to increase in a linear relationship from -17.6, -52.6, and -80.7 for 25 °C, 48 °C, and 70 °C, respectively. However, the gauge factor appears to saturate at 70 °C only varying to -83.4 for 92 °C.