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

Abstract

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 degrees C-300 degrees C and peaks at 200 degrees C in both cases (4.4 x 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 degrees C or higher, making it a suitable moisture barrier for most hydrogen sensing applications.