Microheater

About: Microheater is a research topic. Over the lifetime, 814 publications have been published within this topic receiving 12478 citations.

Temperature control and readout circuit interface for Mox based NH3 gas sensor

Abstract: This work demonstrates a handheld, micro-heater integrated metal oxide (MOX) based gas sensor interface system that includes digital set point, a precise closed loop temperature control and a wide range resistance readout circuit. The implementation of proposed system, constitutes two circuits. First, the temperature control loop circuit, able to set the platinum micro heater temperature over a range from ambient temperature to 300 °C, with a maximum peak to peak deviation less than 2.0 °C. An ON---OFF control technique is used to control the temperature of microheater since the heat transfer characteristics of micro heater are difficult to model. Second, a resistance to time conversion based resistance readout circuit is designed that measures the resistance over a range of 1 K? to 100 M?. The overall system is flexible and can be interfaced with integrated sensors having different power requirements and fabrication parameters. Gas sensing film used for gas detection is made of Tin oxide (SnO2). Since, the metal oxide sensor works at elevated temperatures, it can detect different gases like, ammonia (NH3) at 230 °C, nitrogen dioxide (NO2) at 80 °C and carbon mono-oxide (CO) at 270 °C. Various experiments were conducted to test the above mentioned circuit by first connecting discrete known resistive components and also, its response with NH3 is recorded with various concentrations. The resistance readout circuit output has an excellent accuracy with an error of less than 2 % in sensor resistance measurement and hence in measurement of gas concentration.

High-temperature gas sensor using perovskite thin films on a suspended microheater

Abstract: Suspended microstructures consisting of a thin oxide/nitride diaphragm with embedded polysilicon heaters were designed and fabricated using a standard complementary metal–oxide–semiconductor process and simple postprocessing. Thin films of gas sensitive materials based on the SrFeO2.5+x nonstoichiometric perovskite family were deposited onto the diaphragms by room-temperature pulsed excimer laser deposition. Successful chemical sensor functionality was demonstrated. With applied power up to 30 mW, estimated temperatures of the gas sensor film up to 900 °C were reached. When the device was exposed to volatile organic compounds (VOCs) such as acetone and methanol, a reversible ten to 100-fold increase in sensor film resistance was observed, with response times from less than 1 s to a few minutes. Sensor response sensitivity depended on applied power and on the nature of the VOC analyte. This sensor device has the potential for use in multiarray configurations such as in an electronic nose.

Ultrasensitive Pd–Ag/ZnO/Nickel Alloy-Based Metal–Insulator-Metal Methane Sensor on Micromachined Silicon Substrate

Abstract: A novel Pd-Ag/ZnO/Nickel alloy Metal-Insulator-Metal (MIM) sensor on micromachined silicon platform, for efficient methane detection, is reported in this letter. The co-planar microheater and lower electrode of the MIM sensor were fabricated using an alloy (called DilverP1) of nickel. The Ni-alloy was found to offer an Ohmic contact with ZnO sensing layer. Nanostructured ZnO was deposited on lower electrode by a low temperature chemical process and Pd-Ag (70%) was used as the top catalytic electrode to ZnO. A study of the current-voltage characteristics of the MIM structure in pure N2 with the presence and absence of desired concentration of methane revealed that the device can be used as a low-temperature methane sensor with ultrahigh sensitivity and fast response. The response magnitude and response/recovery time were studied at different temperatures (100, 130, 160, 190, and 220°C) for different methane concentrations. 190°C was found to be the optimum temperature for maximum response of ~316% and minimum time of response of 18 s at 1% methane in N2.

Micromachined field emission cathode with an integrated heater

Abstract: We report on the fabrication and operation of integrated micromachined and suspended field emission cathode tips. The emitter tips are suspended at the center of a silicon beam using multiple patterning methods of high aspect ratio silicon structures using a single layer silicon dioxide etch mask. The integrated, suspended silicide microheater is used to clean and to activate the cathodes. The silicon tips are subsequently modified to improve their emission properties. The modified cathodes exhibit a significantly lower turn on voltage of about 50 V (∼100 V for silicon cathodes), and need no chemical tip cleaning prior to emission. A much larger emission current with reduced emission noise has been observed when a single tip is cycled through the tip forming process.

SOI-CMOS compatible low-power gas sensor using sputtered and drop-coated metal-oxide active layers

Abstract: In this paper, a Silicon-On-Insulator (SOI) solid-state gas-sensor with an original design of a polysilicon loop-shaped microheater fabricated on a thin-stacked dielectric membrane is presented. The microheater ensures high thermal uniformity and very low power consumption (25 mW for heating at 400°C). Sensitive films are based on tin and tungsten oxides deposited either by RF sputtering or drop coating methods. The fabricated sensors are tested to a wide variety of contaminant species and promising results are obtained. The use of completely CMOS compatible TMAH-based bulk micro-machining techniques during the fabrication process, allows easy smart gas sensor integration in SOI-CMOS technology. This makes SOI-based gas-sensing devices particularly attractive for use in handheld battery-operated gas monitors.