| With the development of MEMS technology, micro-heater based on MEMS has gradually gained its wide applications on gas sensors, infrared detectors, infrared sources and some other sensors. By employing some thin films with good thermal insulation as the substrate, the micro-heater presents a series of advantages such as miniaturized size, low power consumption, fast response, high sensitivity, good iteration and feasibility of sensor array integration. With a brief review on the related works in this area, systematic thermal and mechanical design of a MEMS based micro-heater, which concentrates on low power consumption and uniform temperature in a large area, is performed and confirmed through the fabrication and measurements of the actual devices. Devices withnew structures in atmosphere show small temperature difference 0.05℃/μm in a largearea of 500 x 300μm2 with a low power of 25mW for 500 ℃, which are better than thepresent publicated results.In the thermal design, some initial problems concerning power consumption, heating efficiency and thermal time constant etc. are carefully considered according to their different applications. Discussion on temperature uniformity is emphasized. The characteristic of the temperature distribution is theoretically analyzed based on a simplified thermal model in vacuum and atmosphere respectively. Some thermal principles for a micro-heater design have been obtained. On the basis of these principles, some new structures working in vacuum or atmosphere with large-area uniform temperature are presented respectively, and further optimized through simulation work by the FEA method in ANSYS.The theoretical thermal analysis says that, (1) The thermal performance of the micro-heater working in vacuum and atmosphere is definitely different, different structures should be considered in these two distinct applications; (2) In vacuum, thestructure with a ring heater shows good temperature uniformity; which can be further improved by a homogeneous block inside the heater. The simulation work demonstratesthat this structure offers a temperature difference of 0.02 °ci /jm in an area of500 x 600um2 with the maximum temperature of 640K and the supplied power of 20mW on an lOOOxlOOOwm2 closed membrane;(3).In atmosphere; due to the existence of gas convection and conduction; the heater should enter into the central area to increase the inner temperature; which can improve the whole temperature uniformity efficiently. Simulations of the optimized structure in atmosphere shows a temperature difference of0.05°C/{m in an area of 500x300w/n2; with the power 70mW and the maximumtemperature 71 OK.In the mechanical design; a multilayer membrane is designed to compensate the inner stresses for high mechanical stability; which is important in process. Thermal induced stress is also simulated to analyze the stability of the micro-heater's working at high temperature.Some IC processes such as thermal oxidation and LPCVD together with magnetic sputtering of metal Pt; dry etching and wet etching methods are employed to fabricate the devices. The protection for the metal film during the wet etching process is realized by metallization before the etching. The TCR (temperature coefficient of resistivity) of Pt film is tested in a constant temperature cavity. Based on the tested TCR; devices' temperature under different supplied power can be calculated from the resistances of the devices. The results indicated that the devices' electrical and thermal performances of steady state and transient state; as well as the performance of temperature uniformity in atmosphere are well in agreement with the simulations. The devices with the optimized structure in atmosphere demonstrates a high heating efficiency and fast response; with a supplied power of 25mW; temperature as high as 500°C; and the thermal time constant 1.3ms are achieved. All these work build the base for such new micro-heaters' applications in the areas of gas sensing and infrared detecting. |
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