Quartz Microhotplate Methane Sensor Array With In-situ Printed Nanocatalyst

Catalytic combustion gas sensors are widely utilized for methane and other flammable/toxic gas detection.The sensor performance is highly related with the planer microhotplate and micro/nano catalyst.Drawbacks of conventional silicon-based membrane microhotplates are complicated structure,complex fabrication processes,and unstable constructions against vibration or high temperature.Moreover,the limitation of traditional loading methods in material ingredients and micro structures impede the in-situ fabrication of high performance catalyst.In addition,long term high temperature working mode principally results in catalytic sensors degradation.These issues limit the application of micro catalytic sensor in mass production.A non-membrane fused quartz microhotplate was proposed as a general heating/sensing micro platform.A 2-D planer microhotplate with simplified structure and a 3-D cone-cavity microhotplate with optimized performance were constructed by multi-physics simulation and were micro fabricated by standard MEMS processes,with performances including the power consumption,response time,high temperature resistance,vibration stability,and fabrication yield investigated.Based on the low thermal conductivity of quartz substrate,the low power device is available without the need of fragile membrane structure,avoiding high temperature degradation or vibration failure,with the construction significantly simplified and the compatibility with nonstandard micro processes.The 3-D cavity etched by abrasive sand blasting further enhanced the power consumption,response time,and yield,with good prospect to replace traditional silicon-based microhotplate.An novel in-situ printing method for synthesizing and loading high performance catalyst system was proposed based on screen-inkjet hybrid printing and micro impregnation.?-Al₂O₃ supported Pd-Pt bimetallic mesoporous catalyst and CeO2 nano promoter were in-situ fabricated on as fabricated microhotplate,with morphology,constitution,catalytic activity,thermal resistance,and long term stability characterized,demonstrating co-catalyst with high porosity,high repeatability,picolitre quantity,and micro meter position can be achieved by the proposed in-situ printing,which is compatible with standard MEMS electrode.Furthermore,a newly proposed core-shell Pd-Pt@CeO2 nanocatalyst based on the in-situ printing utilized for micro sensor made comprehensive enhancement of working temperature?as low as 300 oC?,sensitivity,thermal stability,response time,signal noise ratio,and long term lifetime.A multi-units sensor array working at the one-hot mode was designed and fabricated based on the above proposed quartz-based microhotplate and in-situ hybrid printing,focused on the long term lifetime in coal mine gas monitoring.The alternate one-hot mode was maintained by the large temperature gradient and was verified with micro characterization and long term gas sensing test.Besides,the chip was integrated into a self-developed gas detection system,with engineering availability verified,which shown good prospect for long term high temperature application.This thesis provides a general platform and a long term working mode for high temperature MEMS,and proposes a high performance nanocatalyst together with its in-situ fabrication method for catalytic MEMS,as an important guideline for non silicon-based MEMS and printed MEMS.