Design and electro-thermal analysis of surface micromachined perforated membrane hotplate for chemical gas sensor applications

Abstract

This paper presents electrothermal simulation and thermal distribution analysis of Platinum based surface micromachined hotplate with suspended silicon nitride membrane for chemical gas sensing applications. The investigation of power consumption, temperature distribution and transient response of the proposed hotplate structure is carried out using COVENTORWARE®. The heated silicon nitride membrane is thermally isolated from silicon substrate by removal of sacrificial silicon dioxide from front side of the wafer. Operational temperature of 480 °C is achieved at 384.20 mW with a temperature gradient of 1.175 °C/µm across silicon nitride membrane. The result is compared with the same hotplate structure in which silicon nitride membrane is made perforated for ease of membrane release during fabrication and reduction in thermal mass of hotplate. The perforated membrane hotplate showed reduction in power consumption and an operational temperature of 480 °C is achieved at 367.18 mW with a temperature gradient of 1.875 °C/µm over silicon nitride membrane and rise and fall time of 0.068 and 0.091 ms respectively. This improvement in power consumption is lost when silicon nitride membrane thickness is more than 0.7 µm due to increased air thermal conduction from sidewalls of perforation.