Joule-heated silicon nanowire for low power hydrogen gas sensor

Abstract

As the demand for measurement of indoor and outdoor air quality has increased, various types of gas sensors have been introduced, and gas sensors having high sensitivity and fast response speed have been developed. The semiconductor type gas sensor has an advantage that it is simple in structure and can be downsized. However, there is a disadvantage of using high power consumption due to the high operating temperature. The gas sensor using self-heating of nanomaterials can reduce power consumption to micro-watts. In order to increase price competitiveness of gas sensors, it should be possible to manufacture with wafer scale. Gas sensors using silicon nanowires can reduce power consumption through the self-heating and can be manufactured in waferscale. Hydrogen gas was detected by using palladium-coated silicon nanowires (Pd-SiNW). The Joule heating of silicon nanowires accelerated the reaction speed and increased the sensitivity. The response time and sensitivity of Pd-SiNW with Joule heating of 1172 $\mu$W for 0.5% hydrogen gas were measured as 1 second and 1.9%, respectively. The hydrogen gas response of Pd-SiNW followed the first order Langmuir isotherm and maximum sensitivity and reaction rate were calculated. Higher sensitivity was observed when using longer Pd-SiNW. The hydrogen detections of Pd-SiNW were investigated for carbon monoxide gas and humidity, which are known to degrade the performance of the hydrogen sensor. It was found that the degradation of hydrogen detection is reduced by applying high Joule heating power of Pd-SiNW. A novel method for measuring the temperature of self-heated silicon nanowires using quantum dots was developed. Quantum dots were coated only on the silicon nanowire using a selective surface modification method and the change in photoluminescence of the quantum dots while Joule heating of the silicon nanowires was measured. Since the emission wavelength of a quantum dot depends on the temperature, the temperature of Joule heated silicon nanowire can be obtained by measuring the emission wavelength of the quantum dots on the silicon nanowire. The temperature of a silicon nanowire having a width of 160 nm and a length of 2 $\mu$m showed a relation of T = 17 + 0.098 × Joule heating power ($\mu$W). The experimental results were verified through simulation results and this method can measure the temperature of silicon microwire. To reduce the power consumption of Joule heated Pd-SiNW, a suspended silicon nanowire was proposed. The response time of a suspended Pd-SiNW with Joule heating power of 147 $\mu$W was similar as the response time of a bounded Pd-SiNW with Joule heating power of 612 $\mu$W. In addition, the sensitivity of suspended Pd-SiNW is 95% higher than that of the bounded Pd-SiNW. The high surface roughness of silicon nanowire can further reduce the Joule heating power of the silicon nanowires.