Design And Manufacture Of Micro Hotplate-based Gas Sensor

The traditional heater-type gas sensor could become mass production due to itsconvenient manufacture method and low cost. But, a series of shortcomings (such asthe big power consumption, poor consistency, difficult of array and integration) havealso limited its further development. According to the above situation, this workcombined MEMS technology and semiconductor oxide sensing materials preparationtechnique to develop the micro hotplate-based gas sensors, which have the highsensitivity, fast response/recover time, small structure, low power consumption, andthe possibility to be integrated.Firstly, the suspension type micro hotplate with low power consumption and highstability was obtained by the structure design, simulation and MEMS tape-out ofsuspension type micro hotplate. The substrate material was Si; The supporting layerwas composite membrane structure of SiO2and SixNy; The electrodes were Pt; Andthe insulating layer was SiO2. The overall size of device was2mm×2mm×0.4mm;The width and space of electrodes were both10μm; The size of electrode pin was150μm×150μm. The thermal field distribution of suspension type micro hotplatewas uniform. The actual power consumption of device was45.6mW at400℃. Andthe rate of finished micro hotplates was about75%.Secondly, the hierarchical hollow ZnO microspheres and Pd-doped SnO2nanoparticles were prepared by hydrothermal method and coprecipitation methodrespectively. When the operating temperature was275℃, the response time ofhierarchical hollow ZnO microspheres to100ppm ethanol was1s, the recovery timewas19s. And these hierarchical hollow microspheres exhibited a good selectivity toethanol.Thirdly, effectively combining the suspension type micro hotplate and sening materials, micro hotplate-based gas sensor was manufactured by the lead bonding ofmicro hotplate, film formation of sensing materials, welding and aging of device.Then, the gas sensing properties were researched. ZnO-based mirostructure gas sensordisplayed a good performance to NO2. It could detect40ppb NO2with a response ofabout5, which has the potential application value for detecting low concentration ofNO2. The response to500ppb NO2was45.2, with a response time of72s and arecovery time of89s. SnO2-based mirostructure gas sensor displayed a goodperformance to CH4. The response to3000ppm CH4was16.4, with a response timeof1s and a recovery time of5s. And it exhibited a good selectivity to CH4.Finaly, an issue found and solved in the preparation process of sensing materialswas introduced: Phase investigation on zinc-tin composite crystallites. Zinc-tincomposite crystallites (cubes and octahedra) synthesized by conventional methods inearlier literature, were proved to have ZnSn(OH)6structures rather than perovskitestructure ZnSnO3as reported, by XRD, TG, DSC and FTIR analyses.