InAlN/GaN high electron mobility micro-pressure sensors for high-temperature environments

A micro-scale pressure sensor leveraging a ring-shaped In0.17Al0.83N/GaN high electron mobility transistor (HEMT) sensing element was fabricated and characterized under applied pressure. The device design uses InAlN/GaN-on-Si as the material platform to enable monolithic integration with electronics and high-temperature operation. An analytical model of the pressure transduction was used to compare the change in the two-dimensional electron gas (2DEG) sheet carrier concentration for InAlN and AlGaN heterostructures upon applied pressure. The model confirms that the high aluminum content of InAlN and large piezoelectric constants of AlN results in a larger pressure response in InAlN/GaN heterostructures, in comparison to AlGaN/GaN heterostructures. To experimentally examine the InAlN/GaN pressure sensor architecture, a 500-μm-radius pressure sensor was electrically characterized under applied pressures from 0 to 28.5 psig. The current sensitivity of the device increased as gate voltage approached the threshold voltage and as the drain to source bias increased, up to the saturation regime. The maximum change in current (or sensitivity) demonstrated was 0.64%/psig at VGS = −5 V, VDS = 2.2 V. To observe the influence of temperature, the current-voltage (ID-VDS) response of released and unreleased ring-shaped devices was measured up to 300°C. At all temperatures, the current of the released ring-shaped devices decreased when compared to the solid state device, which is attributed to reduced thin film tensile-stress between the underlying GaN buffer layers and the silicon. This work demonstrates the feasibility of using InAlN/GaN sensor architectures for high temperature applications (space exploration, nuclear energy, downhole, and combustion).