Temperature and Humidity Dependence of Response of PMGI-Encapsulated Pt-AlGaN/GaN Diodes for Hydrogen Sensing

Polydimethylglutarimide (PMGI), a photosensitive positive type resin used in photoresists, is shown to be an effective moisture barrier for mitigating the effect of humidity on the sensitivity of Pt-AlGaN/GaN Schottky diodes for hydrogen detection. The maximum relative current change observed in PMGI-encapsulated diodes forward biased at 1.3 V and exposed to 500 ppm of dry or humid H
₂
is identical within experimental error over the temperature range 25 °C-300°C and peaks at 200 °C in both cases (4.4 × 10
⁶
% increase compared with the current under N
₂
ambient). Unencapsulated diodes exhibit a decrease of approximately one ninth of the current signal for detection of 500 ppm of H
₂
in the presence of water. The PMGI is easily spun-on to the sensors, and does not degrade until temperatures of 335 °C or higher, making it a suitable moisture barrier for most hydrogen sensing applications.