1ppm-detectable hydrogen gas sensors by using highly sensitive P+/N+ single-crystalline silicon thermopiles

Abstract

Hydrogen (H2) is currently of strategic importance in the pursuit of a decarbonized, environmentally benign, sustainable global energy system; however, the explosive nature of H2 requires leakage monitoring to ensure safe application in industry. Therefore, H2 gas sensors with a high sensitivity and fast response across a wide concentration range are crucial yet technically challenging. In this work, we demonstrate a new type of MEMS differential thermopile gas sensor for the highly sensitive, rapid detection of trace H2 gas in air. Facilitated by a unique MIS fabrication technique, pairs of single-crystalline silicon thermopiles (i.e., sensing and reference thermopiles) are batch fabricated with high-density single-crystalline silicon thermocouples, yielding an outstanding temperature sensitivity at the sub-mK level. Such devices ensure the detection of miniscule temperature changes due to the catalytic reaction of H2 with a detection limit as low as ~1 ppm at an operating temperature of 120 °C. The MEMS differential thermopiles also exhibit a wide linear detection range (1 ppm-2%, more than four orders of magnitude) and fast response and recovery times of 1.9 s and 1.4 s, respectively, when detecting 0.1% H2 in air. Moreover, the sensors show good selectivity against common combustible gases and volatile organics, good repeatability, and long-term stability. The proposed MEMS thermopile H2 sensors hold promise for the trace detection and early warning of H2 leakage in a wide range of applications.

Innovative Thermocatalytic H2 Sensor with Double-Sided Pd Nanocluster Films on an Ultrathin Mica Substrate

“…The sensing properties of various H 2 sensors are summarized in Table . ,,,− While the response time of metal oxide semiconductor gas sensors is typically on the order of several seconds, they require heating to very high temperatures. , Some thermochemical H 2 gas sensors exhibit a typical response time of ∼20 s. Many thermal catalytic H 2 sensors also have typical response and recovery times exceeding 10 s. Compared to these previously reported H 2 sensors, even at the operating temperature of 50 °C, our device demonstrates superior H 2 gas-sensing kinetics. To the best of our knowledge, our thermocatalytic H 2 sensor represents the current state-of-the-art in optimized comprehensive sensing capabilities in terms of response and recovery time, sensitivity, and manufacturing technology.…”

Critical Sensing Modalities for Hydrogen: Technical Needs and Status of the Field to Support a Changing Energy Landscape

“…144 The robust selectivity was achieved by embedding the nanowires in a hydrophobic poly(methyl methacrylate) (PMMA) matrix, which likely contributes to the longer response times. 143 Other designs that exploit the thermoelectric effect are emerging due to advances in microfabrication 145,146 techniques that support the production of new intricate thermopiles 142,145,146 consisting of n ∼ 20−30 microthermocouples wired in series. Thermopiles improve the sensitivity to temperature changes by amplifying the associated electrical potential: 149,150 = V n T (19) Zhang et al 146 fabricated thermopiles made from singlecrystalline silicon with a Pt NP@Al 2 O 3 catalyst.…”

“…It is worth noting that combinations of the technologies employed in the associated references may ultimately produce lower detection limits on par with those exhibited by the most sensitive MOS sensors. The lowest detection limits used a conventional catalyst and a sensitive thermopile 146 and it was separately shown that Pt nanoparticle catalysts 142 improve sensitivity and responsiveness while also preventing sensor degradation. It would be particularly interesting to understand how lower operating temperatures effect sensor sensitivity.…”

“…Other catalytic sensors exploit the Seebeck effect to generate a change in potential, Δ V , due to the associated temperature change of a thermoelectric device: − Δ V = α Δ T where α is the Seebeck coefficient. , Hwang et al and Kim et al studied thermochemical hydrogen sensors using Pt-decorated exfoliated graphene sheets and a tellurium nanowire-based thermoelectric (TNTE) layer that is operable at ambient temperature and relative humidity. When hydrogen is present, the Pt nanoparticles catalyze the exothermic combustion of H 2 to create water vapor (Equation ) thereby increasing the TNTE temperature and causing the potential drop as indicated in Equation .…”

“…Other designs that exploit the thermoelectric effect are emerging due to advances in microfabrication , techniques that support the production of new intricate thermopiles ,, consisting of n ∼ 20–30 microthermocouples wired in series. Thermopiles improve the sensitivity to temperature changes by amplifying the associated electrical potential: , Δ V = n α Δ T Zhang et al fabricated thermopiles made from single-crystalline silicon with a Pt NP@Al 2 O 3 catalyst. Air was used as the carrier gas and the optimal operating temperature was determined to be 120 °C requiring about ∼40 mW of power.…”