We have studied catalytic thin film resistors made from a Pd and Ni alloy, and propose a method for dramatically reducing the drift of the measured resistance. The resistances of Pd films increase monotonically when exposed to hydrogen, however a stable baseline is difficult to achieve and alpha to beta phase transitions result in hysteresis. It is known that at high hydrogen concentrations, the Pd film cracks and delaminates, however long-term exposures to low concentrations of hydrogen can also result in delaminations. Studies using Pd/Ni alloys show that the phase transition can be suppressed. High temperature anneals in 2 % hydrogen, and the addition of a Ti adhesion layer is shown to reduce drift. Usually long term studies on films are conducted in an ordinary air (oxidizing) atmosphere; however, we report here on studies carried out in a reducing atmosphere of 0.1% hydrogen in nitrogen for 6 months on two sensor structures, field effect transistors (FETs) and resistors. The Sandia Robust Hydrogen Sensor platform containing integrated heaters, temperature sensors, and hydrogen sensitive resistors and FETs was compared to a Sandia Wide Range Sensor containing a 10 atomic percent Ni/Pd (1000Å) alloy resistor with a (100Å) Ti adhesion layer. After six months the two hydrogen sensing resistors on the Robust platform, without an adhesion layer, read a hydrogen concentration of 61% and 2.3%, while the Wide Range Sensor read a hydrogen concentration of 0.102%, which is a dramatic improvement in limiting baseline drift.

Date Published: 26 February 2001
PDF: 11 pages
Proc. SPIE 4205, Advanced Environmental and Chemical Sensing Technology, (26 February 2001); doi: 10.1117/12.417437

Published in SPIE Proceedings Vol. 4205:
Advanced Environmental and Chemical Sensing Technology
Tuan Vo-Dinh; Stephanus Buettgenbach, Editor(s)