Thermoelectric CMOS anemometers

We report the fabrication, packaging,and characterization of thermoelectric CMOS anemometers. The sensors are fabricated using the commercial 2 micrometers CMOS process of EM Microelectronic-Marin SA, Switzerland, followed by bulk silicon micromachining. They consist of a membrane of the CMOS dielectrics heated by integrated polysilicon resistors. Integrated p-polysilicon/n-polysilicon thermopiles detect wind-induced temperature differences on the membrane. Two devices are reported. The first, on a 1 mm by 1.3 mm die, measures one component of the wind velocity. The second structure, on a 2 mm by 2 mm die, measures the modulus and the direction of the air flow. We demonstrate packaging solutions for both sensors. They are mounted on a standard TO substrate, embedded in epoxy, and mechanically protected by a wire-mesh. The performance of the 2D device is enhanced by a flow concentrator. The sensor responses were characterized in a wind-tunnel as a function of sensor orientation, air velocity, and mesh parameters. The output signals grow monotonically with the air velocity up to 40 mV at 38 ms-1 at a heating power of 3 mW. Angle detection is demonstrated with standard deviation smaller than 13 degrees. Cost-effective batch production and low power consumption make these thermal devices an interesting alternative to conventional, mechanical, anemometers.