Integrated Temperature and Hydrogen Sensors with MEMS Technology

Abstract

In this work, a PdNi thin film hydrogen gas sensor with integrated Pt thin film temperature sensor was designed and fabricated using the micro-electro-mechanical system (MEMS) process. The integrated sensors consist of two resistors: the former, based on Pt film, is used as a temperature sensor, while the latter had the function of hydrogen sensing and is based on PdNi alloy film. The temperature coefficient of resistance (TCR) in both devices was measured and the output response of the PdNi film hydrogen sensor was calibrated based on the temperature acquired by the Pt temperature sensor. The SiN layer was deposited on top of Pt film to inhibit the hydrogen diffusion and reduce consequent disturbance on temperature measurement. The TCR of the PdNi film and the Pt film was about 0.00122/K and 0.00217/K, respectively. The performances of the PdNi film hydrogen sensor were investigated with hydrogen concentrations from 0.3% to 3% on different temperatures from 294.7 to 302.2 K. With the measured temperature of the Pt resistor and the TCR of the PdNi film, the impact of the temperature on the performances of the PdNi film hydrogen sensor was reduced. The output response, response time and recovery time of the PdNi film hydrogen sensors under the hydrogen concentration of 0.5%, 1.0%, 1.5% and 2.0% were measured at 313 K. The output response of the PdNi thin film hydrogen sensors increased with increasing hydrogen concentration while the response time and recovery time decreased. A cycling test between pure nitrogen and 3% hydrogen concentration was performed at 313 K and PdNi thin film hydrogen sensor demonstrated great repeatability in the cycling test.

Low Concentration Response Hydrogen Sensors Based on Wheatstone Bridge

“…The solubility of H in PdNi alloy films decreases with increased test temperature, which results in reducing maximum response of Wheatstone bridge type hydrogen sensor. The response time and recovery time are defined as the consumed time to reach 90% of the final stable value [9]. When exposed to hydrogen, the output voltage of the sensor increases rapidly.…”

“…The annealed sensor still has a detectable output voltage of 600 μV at 10ppm hydrogen. In addition, compared with single PdNi film resistance hydrogen sensor [9], the response time and recovery time of the Wheatstone bridge sensor were significantly reduced and the zero drift was greatly ameliorated. It should be noted that in sharp contrast to previous report [11,12,14], this sensor still had obvious output response under 10ppm hydrogen, which makes it applicable for wide range hydrogen concentration detection (10 ppm -0.4 %).…”

“…Although pure Pd could deliver a high output, fast response and superior selectivity of hydrogen, there are still some shortcomings, such as structural deformations and the consequent hysteretic resistance behavior [2,3]. In order to solve these problems, nanostructured materials and Pd alloy have been used as hydrogen sensitive materials [5][6][7][8][9][10][11][12]. Ozturk et al reported that when exposed to 10% hydrogen, the 2 of 8 6nm Pd films deposited on flexible substrates exhibited good reversibility and good response [13].…”

Integration of SnO2 Nanoparticles with Micro-hotplatform for Low-power-consumption Gas Sensors

“…where R 0 is the initial resistance at the room temperature T 0 , R is the resistance at the temperature T, and α is the temperature coefficient of the resistance of the Pt heater. (29) However, it is a simplified equation; the temperature calculated using Eq. (7) is slightly lower than the actual temperature.…”

Hydrogen Sensing Performance of ZnO Schottky Diodes in Humid Ambient Conditions with PMMA Membrane Layer

“…Gas sensors based on metal oxide (MOX) semiconductors have been widely used for toxic gas detection and quality air control. Extensive efforts have been devoted to developing highly sensitive, selective, reliable, stable, and low-cost sensors [1][2][3][4][5][6][7]. Various MOXs such as SnO 2 , TiO 2 , ZnO, WO 3 , NiO, and Ga 2 O 3 have shown significant change in the conductance through surface interaction and charge transfer between gas molecules and oxide surface atoms.…”