Micromachined catalytic combustible hydrogen gas sensor

Integrated Ferroelectrics, 2018

In the present work efforts have been made to develop microheater integrated gas sensors with low power consumption. The design and simulation of a single-cell microheater is carried out using ANSYS. Low power consumption (<35 mW) platinum micro-heater has been fabricated using bulk micromachining technique on silicon dioxide membrane (1.5 lm thin), which provided improved thermal isolation of the active area of 250 Â 250 lm 2. The micro-heater has achieved a maximum temperature of $950 C at an applied dc voltage of 2.5 V. Fabricated mircro-heater has been integrated with SnO 2 based gas sensors for the efficient detection of H 2 and NO 2 gases. The developed sensors were found to yield the maximum sensing response of $184 and $2.1 with low power consumption of 29.18 and 34.53 mW towards the detection of 1 ppm of NO 2 gas and 500 ppm of H 2 gas, respectively.

Sensors, 2014

A thermoelectric gas sensor (TGS) with a combustion catalyst is a calorimetric sensor that changes the small heat of catalytic combustion into a signal voltage. We analyzed the thermal balance of a TGS to quantitatively estimate the sensor parameters. The voltage signal of a TGS was simulated, and the heat balance was calculated at two sections across the thermoelectric film of a TGS. The thermal resistances in the two sections were estimated from the thermal time constants of the experimental signal curves of the TGS. The catalytic combustion heat Q catalyst required for 1 mV of ∆V gas was calculated to be 46.1 μW. Using these parameters, we find from simulations for the device performance that the expected Q catalyst for 200 and 1,000 ppm H 2 was 3.69 μW and 11.7 μW, respectively.

IET Circuits, Devices &amp; Systems, 2018

A low-power microelectromechanical system-based metal-oxide gas sensor along with integrated signal conditioning unit is presented in this study to detect and quantify the variation of H 2 gas concentrations. The interface circuit controls the sensor operating temperature, measures the H 2 gas concentration, contributes a user-friendly interface and can be used with any suitable sensor network. A PIC16F877A microcontroller has been used for this purpose. The temperature of the sensors was stabilised by controlling the actuating voltage of the microheater. Temperatures of the microheater depend on the output voltage of the digital-to-analogue converter (DAC) and were measured by sampling the heater resistance through the use of a voltage divider and analogue-to-digital converters (ADCs). A microcontroller accordingly adjusts the output of DAC's in order to apply the appropriate steering voltage to the heaters. The method employed to measure the concentration of gases is to sample the voltage drop over the resistances of the sensors by ADCs. Alarming system for safety measure was also implemented in this design. The preventive action was taken by introducing an additional feature of wireless communication by sending short message service via global system for mobile modem to the designated emergency number.

Gastroenterology, 2005

In this work a microsystem fabrication process for a microheater (MH) and a microhotplate (MHP), as well as their electrical behavior, are reported. This microstructure consists of a SiO2 membrane supported by four cross shaped beams, and two layers of polysilicon (poly1 and poly2); poly1 forms the microheater and the poly2 layer works as a micro hot plate (MHP), whose

Proc. 2002 US DOE …, 2002

The ability to detect gaseous hydrogen is of critical importance to acceptance and utilization of hydrogen as an energy carrier. Micro-machined gas sensors are a new generation of sensor technology combining existing integrated circuit fabrication technology with novel deposition and etching processing. This results in a new device structure, known as a "micro-hotplate", which consists of an integrated hotplate on a suspended thermal isolation structure. This structure allows the sensor to operate at elevated temperatures, and provides a platform where the operating temperature can be rapidly changed to achieve desired response characteristics. ATMI has been developing novel thin film materials to function as hydrogen-selective active layers on top of micro-hotplate devices. This combination of micro-hotplate and novel active thin film materials has led to hydrogen sensors that demonstrate an array of highly desirable features, such as fast response speeds, low-level sensitivity, and amenability to mass production. These sensors are adaptable to a wide variety of sensing applications for a hydrogen-based energy economy, spanning from hydrogen based process monitoring to life safety protection. This paper describes recent efforts and progress made in developing micro-hotplate based hydrogen gas sensors at ATMI. This progress includes designing the sensor geometry to reduce power consumption and investigating the cross sensitivity to several contaminant gases-carbon monoxide, hydrogen sulfide, and isopropyl alcohol. Portable signal conditioning hardware was developed to help study long-term operation stability. Future work will be directed towards continuous improvement of the fabrication process and the development of new application specific operational models.

Transactions on Electrical and Electronic Materials, 2019

Chemoresistive hydrogen gas sensor with zinc oxide (ZnO) thin film as a sensing layer has been studied with a coplanar integrated architecture of microheater and interdigitated electrode (IDE). ZnO thin films are fabricated via a chemical route. The present study is based on the use of a coplanar microheater with IDE's fabricated for the hydrogen sensor. Further, the effect of the integrated architecture over sensing properties of the sensor has been studied. The sensing response of the sensor with film thickness of 150 nm at an operating temperature of 160 °C comes out to be 10.97. The prime aim of the study is to present coplanar integrated architecture of microheater and IDE'sfor a ZnO based hydrogen sensor.

Proceedings

This paper presents a long-term stable thermoelectric micro gas sensor with ligand linked Pt nanoparticles as catalyst. The sensor design gives an excellent homogeneous temperature distribution over the catalytic layer, an important factor for long-term stability. The sensor consumes very low power, 18 mW at 100 °C heater temperature. Another thermoresistive sensor is also fabricated with same material for comparative analysis. The thermoelectric sensor gives better temperature homogeneity and consumes 23% less power than thermoresistive sensor for same average temperature on the membrane. The sensor shows linear characteristics with temperature change and has significantly high Seebeck coefficient of 6.5 mV/K. The output of the sensor remains completely constant under 15,000 ppm continuous H2 gas flow for 24 h. No degradation of sensor signal for 24 h indicates no deactivation of catalytic layer over the time. The sensor is tested with 3 different amount of catalyst at 2 different ...

Sensors and Actuators B: Chemical, 1993

A new integrated catalytic gas sensor for detecting flammable gases or flammable apo rs has been fabricated on silicon with thin film de osition and silicon micromachining techni es. This de ice is reali ed on the rinci le of the con entional catalytic gas sensor known nder the name of `Pellistor'. The detection rinci le of this gas sensor is based on the meas rement of heat emitted by the comb stion of the gas with atmos heric oxygen on a small catalytic s rface. The sensiti e element and the reference element are integrated together on the same chi of si e 2.84x2.46 mm'. This do ble str ct re re ires a ery low electrical ower of ty ically 100 mW at an o erating tem erat re of 400 °C. The excellent thermal ins lation is reali ed by a 0.6 m thin silicon nitride membrane. The sensiti it of the sensor is abo t 13 mV/% methane in air.

Conventional Metal Oxide gas sensors commonly used for sensing inflammable hydrocarbon gases and other toxic gases. However, they suffer from the two limitations, viz. (a) their relatively high operating temperature (≥300° c) and (b) large power dissipation (≥1 Watt). Micromachined silicon based metal oxide gas sensors are being developed to overcome these limitations.The main part of power consumption in a micro-machined gas sensor consists of various thermal losses like conduction through bulk silicon substrate, convection in air from all exposed surfaces and radiation. The thermal characteristics of micro-machined metal oxide based gas sensors have to be optimized with respect to low power consumption, well controlled temperature distribution over the sensing layer and fast transient response. However microheater for the MEMS metal oxide gas sensors have not yet been optimized. In this paper we have developed a methodology (software) for designing and optimizing microheater for MEMS based gas sensor. Using this software we can estimate power requirement for achieving a particular temperature as well as the temperature distribution over the active layer.

Chemosensors

A reduced size thermocatalytic gas sensor was developed for the detection of methane over the 20% of the explosive concentration. The sensor chip is formed from two membranes with a 150 µm diameter heated area in their centers and covered with highly dispersed nano-sized catalyst and inert reference, respectively. The power dissipation of the chip is well below 70 mW at the 530 °C maximum operation temperature. The chip is mounted in a novel surface mounted metal-ceramic sensor package in the form-factor of SOT-89. The sensitivity of the device is 10 mV/v%, whereas the response and recovery times without the additional carbon filter over the chip are &lt;500 ms and &lt;2 s, respectively. The tests have shown the reliability of the new design concerning the hotplate stability and massive encapsulation, but the high degradation rate of the catalyst coupled with its modest chemical power limits the use of the sensor only in pulsed mode of operation. The optimized pulsed mode reduces th...