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The semiconductor metal oxide (SMO) gas sensors are getting high attention owing to their high sensitivities and fast responses. They require high temperature for the reaction with target gases, and suspended silicon membrane microheaters are typically used to reduce the heating power consumption. However, they have low durability for long-term uses, and high probability of fracture by thermal stress or mechanical impact. In this study, as an alternative to the silicon membrane microheater, anodic aluminum oxide (AAO) based microheater platform gas sensor was fabricated for low power consumption and high thermal/mechanical stabilities. Nanoscale air gaps of the AAO substrate reduce the heat loss transferred to the substrate. Therefore, AAO-based microheater platforms do not require suspended structures sustained by very thin bridges, which dramatically enhances thermal/mechanical stabilities. The temperature of fabricated microheater platform reached to 250℃ by a heating power of 27.4 mW. The excellent thermal/mechanical stabilities of the AAO-based microheater platforms were verified by cyclic on-off and mechanical shock test. The pulsed heating operation was adopted, and it reduced the heating power consumption to 9 mW. The fabricated AAO-based gas sensors showed much higher responses to NO2 gas compared to the SiO2 membrane-based gas sensors.
The semiconductor metal oxide (SMO) gas sensors are getting high attention owing to their high sensitivities and fast responses. They require high temperature for the reaction with target gases, and suspended silicon membrane microheaters are typically used to reduce the heating power consumption. However, they have low durability for long-term uses, and high probability of fracture by thermal stress or mechanical impact. In this study, as an alternative to the silicon membrane microheater, anodic aluminum oxide (AAO) based microheater platform gas sensor was fabricated for low power consumption and high thermal/mechanical stabilities. Nanoscale air gaps of the AAO substrate reduce the heat loss transferred to the substrate. Therefore, AAO-based microheater platforms do not require suspended structures sustained by very thin bridges, which dramatically enhances thermal/mechanical stabilities. The temperature of fabricated microheater platform reached to 250℃ by a heating power of 27.4 mW. The excellent thermal/mechanical stabilities of the AAO-based microheater platforms were verified by cyclic on-off and mechanical shock test. The pulsed heating operation was adopted, and it reduced the heating power consumption to 9 mW. The fabricated AAO-based gas sensors showed much higher responses to NO2 gas compared to the SiO2 membrane-based gas sensors.
I Microhotplates are critical devices in various MEMS sensors that could provide appropriate operating temperatures. In this paper, a novel design of poly-Si membrane microhotplates with a heat compensation structure was reported. The main objective of this work was to design and fabricate the poly-Si microhotplate, and the thermal and electrical performance of the microhotplates were also investigated. The poly-Si resistive heater was deposited by LPCVD, and phosphorous doping was applied by in situ doping process to reduce the resistance of poly-Si. In order to obtain a uniform temperature distribution, a series of S-shaped compensation structures were fabricated at the edge of the resistive heater. LPCVD SiNx layers deposited on both sides of poly-Si were used as both the mechanical supporting layer and the electrical isolation layer. The Pt electrode was fabricated on the top of the microhotplate for temperature detection. The area of the heating membrane was 1 mm × 1 mm. Various parameters of the different size devices were simulated and measured, including temperature distribution, power consumption, thermal expansion and response time. The simulation and electrical–thermal measurement results were reported. For microhotplates with a heat compensation structure, the membrane temperature reached 811.7 °C when the applied voltage was 5.5 V at a heating power of 148.3 mW. A 3.8 V DC voltage was applied to measure the temperature distribution; the maximum temperature was 397.6 °C, and the area where the temperature reached 90% covered about 73.8% when the applied voltage was 3.8 V at a heating power of 70.8 mW. The heating response time was 17 ms while the microhotplate was heated to 400 °C from room temperature, and the cooling response time was 32 ms while the device was recovered to room temperature. This microhotplate has many advantages, such as uniform temperature distribution, low power consumption and fast response, which are suitable for MEMS gas sensors, humidity sensors, gas flow sensors, etc.
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