Wafer level packaging of micro-machined gas sensors

We present a novel approach to combine wafer level packaging (WLP) with micro-machined hotplate gas-sensing elements (Patent Application WO03067241 2003-08-14). This concept allows liquid tight sealing of gas sensor devices, protecting them during production (e.g. wafer dicing) and later in the application, while still allowing the target gases to reach the sensing layer. The basis of the WLP is the combination of a structured Pyrex wafer with a micro-machined substrate wafer. Thereafter, thick film SnO₂ layers are deposited and stabilized before a diffusion membrane is attached, sealing the wafer stack.