Xiaohui Zhao

Integrated Temperature and Hydrogen Sensors with MEMS Technology

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.

Reactive B/Ti Nano-Multilayers with Superior Performance in Plasma Generation.

In this study, reactive B/Ti nano-multilayers were fabricated by magnetron sputtering and the structure and chemical composition were confirmed by transmission electron microscopy and X-ray photoelectron spectroscopy analyses. The periodic multilayer structure can be clearly visible, and the multilayer material is composed of B layers (amorphous), Ti layers (nano-polycrystalline), and intermixed reactants in a metastable system. The as-deposited B/Ti nano-multilayers exhibit a significantly high heat release of 3722 J/g, with an onset reaction temperature of 449 °C. On the basis of these properties, an integrated microigniter was designed and prepared by integration of the B/Ti nano-multilayers with a TaN film bridge for potential applications in plasma generation, and the electric ignition processes were investigated with discharge voltages ranging from 25 to 40 V. The integrated microigniter exhibits improved and stable ignition performances with a short burst time, high plasma temperature, and violent explosion phenomenon in comparison with the TaN film igniter. Overall, the plasma generation of the microigniter can be enhanced substantially by integration with the B/Ti nano-multilayers.

Preparation and evaluation of PdCr thin film resistive strain gauges

Thin film resistive strain gauges using PdCr alloy as sensing material were fabricated on nickel-based alloy substrate, and evaluated for strain response, apparent strain and drift strain over a temperature range to 800 °C. The results indicated that the PdCr thin film strain gauge showed an excellent linear response to applied strain and stable gauge factor at different temperatures. The apparent strain can be estimated and compensated due to its repeatability and low value. The drift strain can be neglected until 600 °C. Even at 800 °C the drift strain can also be corrected since it drifted slightly and linearly. The repeatability of PdCr thin film strain gauge was also evaluated. It showed that the repeatable measurement error was 6.4%.