The Study Of Micro-structure Gas Sensors Based On Si Substrate

Gas sensors play important roles in air quality control, industry and healthcare as well as security, and they are also very important to measure the flammable and poisonous gases. Recently, microstructure gas sensors, which are based on"Micro-Electro-Mechanical Systems (MEMS)", have gain special interesting due to their compact size, low power consumption, ease of use, and low cost, et al. And they have also proved to be propitious to the integration, intelligentize, multimode function, reliability, and stability of the gas sensors.In this paper, we report the design of micro-heating plate (MHP), which is a part and parcel of microstructure sensor. MHP is simulated by using a finite element analysis method using the software of Ansys. The materials, layouts are studied in detail to improve our microstructure sensor.There are two structures of MHP: membrane-structure and suspending-structure. The suspending-structure MHP owns better stabilization due to the low heat-convection below the MHP. However, the distance between central area and the substrate must be less than the thickness of the chip, thus high technics need to spend on it. In contract, membrane-structure MHP owns our focus due to its easy achievement. In our studies, MHP has been simulated through a finite element analysis method using the software of Ansys. Si and SiO2 are chosen as the substrate and the insulated layer respectively, because of the benefit of heat-convergence and consumption-reduction of the sensor. The heater, signal electrodes are designed on the same plane to avoid the signal cross-talk of the current.We simulated the width, the space between, and the layout of our samples. The idle state is the temperature in the center of MHP is uniformity, which is very import for sensing materials to work. The temperature on the edge of MHP should be low, for the low power consumption of the sensor.Based on our simulations, the performance of sensor, whose width of heater Pt strip, signal Pt strip, space between heater and signal strip is separate 50μm, 50μm, and 25μm, is superior to the other designs. Its central temperature distribution is comparatively even and the power consumption is comparatively lower.We have designed four abecedarian layouts (Ⅰ,Ⅱ,Ⅲ, andⅣ) in our studies. However, the resistance of the heater and the power consumption are found to be high. Subsequently, two new layouts are designed based on our experimental results, the size of them are 2×1×0.253mm and 2×0.5×0.25mm3, respectively. And they are designated as layoutⅤand layoutⅥin this paper.LayoutⅤhas been studied by loading La0.7Sr0.3FeO3 as the sensitive material. The sensor show high sensitivity towards to ethanol: the sensitivity can reach 8.2 to 500 ppm ethanol, the response time and recovery time are 1.5 and 2.5 s, respectively. The power consumption of the sensor is 261 mW, which is 2/3 of the consumption of the sintered sensor.LlayoutⅤandⅥhave also been studied by loading the CO sensing material of doped SnO2. The sensitivity of typeⅤsensor is 8.6 to 50 ppm CO (2.5 times larger than that of sintered sensor), the response time and recovery time are 5 and 22 s, respectively. The power consumption is 82 mW (1/4 of sintered sensor). The sensitivity of typeⅥCO sensor is 11.2 to 50 ppm CO (3.2 times larger than that of sintered sensor), the response time and recovery time are 17 and 30 s, respectively. The power consumption is 39 mW (1/5 of sintered sensor).In conclusion,these novel microstructure gas sensor possess some good gas sensing properties, such as low power consumption, high sensitivity, quick response-recovery. Also, it can avoid the parasitic electric field between heat and signal electrode that are called"sandwich"structure, makes the process technique simple, and enhances the whole performance.Additionally, a temperature measurement based on radialization power for micro-hotplate is designed in our studies. By means of comparing the relation between the radialization power and the temperature, sample surface temperature can be accurately discerned. The experimental result based on this method is quite similar to that of simulation results obtained by Ansys in theory. This measurement is very useful for measuring temperature for these micro samples prone to be untouchable.