MEMS-based IR thermopile resolves to 0.01°C

-- EDN, 4/13/2000

A micromachined membrane thermopile from Melexis provides accurate noncontact temperature measurement. The MLX90247 uses Seebeck-coefficient materials for the thermopile.

The company claims that the materials yield two to four times greater output than other materials currently in use. The high output, coupled with appropriate signal conditioning, allows measurement resolution to 0.01°C. The IC provides two options for temperature measurement: a linear on-chip PTC thermistor and a separate, internal base-mount NTC thermistor. The MLX90247 (picture) consists of a thin membrane embedded with semiconductor thermocouple junctions, connected in series to increase output. The hot junctions of the thermopile are near the center of the membrane; the cold junctions extend onto the bulk-silicon edge. When you aim the IC at a hot or cold object, the low thermal conductivity of the membrane allows absorbed heat to cause more of a temperature increase at the center of the membrane than at the edge of the bulk silicon. The Seebeck-coefficient thermocouples generate a dc voltage in reponse to the temperature differential. The IC is compatible with the full capabilities of Microcosm's MEMCAD (www.memcad.com) thermopile-modeling software.The MLX90247 is manufactured to QS9000 standards and comes in a TO-39 package. In automotive grade, the IC costs $2 (100,000).

Melexis Inc, 1-603-223-2362, www.melexis.com.

-by Bill Travis