A high-temperature thermopile fabrication process for thermal flow sensors

A new high-temperature fabrication process for thermopile-based flow sensors is presented. The high-temperature passivation of LPCVD silicon nitride leads to an improvement for liquid applications because of the low tendency towards pinholes and the good step coverage. The thermopiles are made of p-doped polysilicon and titanium-tungsten. The nitride membrane was released by a DRIE process to achieve a reduced chip size and higher yield compared to established thermal flow sensors. Devices for different flow rates were fabricated and successfully tested, showing good sensitivity and very short reaction time.