Substrate structure of monolithic gas sensor

Abstract

A substrate structure of a monolithic gas sensor is disclosed, wherein the substrate structure is formed as a thermal resistant and insulating suspended thin plate configuration on a single crystal silicon substrate. The thin plate has formed thereon a heating resistor and coated with tin-oxide-base reducing gas-sensitive material. The thermal resistant thin plate formed on the silicon substrate comprises a native silicon oxide layer, a silicon-rich silicon nitride layer deposited on the native silicon oxide layer, and a top silicon oxide layer formed by thermal oxidation of a surface layer of the deposited silicon-rich silicon nitride layer. An oxide-nitride-oxide sandwiched composited configuration is thus formed that can relieve mechanical stresses internal to the thin plate. The suspended thermal resistantthin plate has corrugation portions formed near the plate edges for relieving mechanical stresses arising from thermal expansion of the silicon substrate and the thin plate when heated to high temperature. The heating resistor formed on the thin plate comprises a polysilicon layer and is covered by a passivation and then by an aluminum oxide layer having a thickness of about several hundred angstroms. The coated tin-oxide-based material is formed by thick-film screen printing to form a sensor film for the single-chip sensing element. Improved thermal and mechanical stress characteristics are obtained while achieving lower electrical power consumption and also maintaining low cost of manufacturing when batched produced.