A Front-Side Microfabricated Tiny-Size Thermopile Infrared Detector With High Sensitivity and Fast Response

This paper reports a novel tiny-sized (116 mu m x 134 mu m) single-crystalline silicon/aluminum infrared (IR) thermopile detector, which is micromachined only from the front side of (111) wafer for IC-foundry compatible low-cost manufacturing. The tiny-sized detector consists of six serially connected p-silicon/aluminum thermocouples that show significantly higher Seebeck coefficient and lower noise compared with the traditional poly-silicon/aluminum counterparts. With the proposed symmetric helical structure, the length of thermocouple leg length as well as the thermal resistance of the detector can be enlarged within the tiny sensing area. Specific detectivity (D*) is improved by optimizing the cross-sectional area of the two thermoelectric-material layers, which is more practically effective than traditional mathematic analysis methods. The device is fabricated in a (111) wafer [instead of normal (100) wafer] by using a novel single-side micromachining technique. The testing results show that the detector achieves an ultrahigh responsivity of 342 V/W and ultrashort response time of 0.56 ms. Featuring tiny-size, low-cost, and high-performance single-point detection, many thermopile detecting units can be integrated into an IR focal-plane array (IRFPA) for high-resolution imaging.