A flip-chip packaged CMOS thermal flow sensor

A flip-chip packaged thermal flow sensor is presented. The sensor chip was fabricated by standard CMOS technology and it consists of polysilicon resistor heaters, Al/polysilicon thermopiles and a substrate bipolar transistor in the center of the sensor chip. The sensor chip was flip-chip packaged on a thin ceramic substrate using copper pillar bump technology. Heat transfer is performed between the polysilicon heaters and the ceramic substrate via the pillar bump. The backside of the ceramic substrate provides a smooth surface for the sensor to contact with the flow. The change of flow-induced temperature distribution on the flow sensing surface is measured by thermopiles and the transistor. Meanwhile, the ceramic substrate holds the sensor chip and protects it from being contaminated or even destroyed by the environment. The packaged flow sensor shows good performances comparing with the unpackaged sensors.