| A MEMS based thermopile infrared sensor has been developed using bismuth and antimony. The characteristics of the thermopile were optimized for application in the Low Power Wireless Integrated Microsensor project (LWIM). The critical detector requirements were low power consumption, low cost, room temperature operation, and DC response. Thermopiles ranging from 6 x 6mm with 144 junctions to 10 x 10mm with 196 junctions have been developed and tested. In air at room temperature, the responsivity was measured at 9.6 V/W with a NEP of 5.8 × 10−9 (W/). The corresponding D* was 1.7 × 10 8 (cm/W). In field testing the 10 x 10m thermopile detector was able to detect a person at distances as far as 25 meters with no lens. Using a 32mm lens, the 6 x 6mm detector was able to detect a person as far as 60 meters.; A four-element triangle array thermopile measuring 6 x 6mm has also been developed. In field tests, it was able to detect the motion of a person at distances of 15 meters using a 32 mm lens. The novel triangle array, which was built on a single low stress silicon nitride membrane, was able to provide details on motion as well as simple detection.; In the designing of the thermopiles, a comprehensive heat transfer analysis was performed to optimize the sensor's design. Two-dimensional steady state and one-dimensional transient analysis has been completed which provided accurate temperature profile information on the sensor and agreed well with experimental results. The heat transfer model also illustrated the weakness of the popular lumped heat capacity model when the sensor was driven by a radiation source that was not evenly distributed on the absorber membrane. |
