A 256 pixel linear thermopile array using materials with high thermoelectric efficiency

First results are presented concerning a recently developed thermopile array with 256 linearly arranged pixels within a total width of 23 mm. Thermal simulation studies were performed by means of 3-D finite element calculations to optimize the specific detectivity D^* of the pixels and to find the conditions for the crosstalk between adjacent pixels to be as low as possible. Resulting from this, two designs with different element lengths of 1.2 and 0.4 mm, respectively, but equal pixel pitch of 175 mm and pixel width of 89 mm each, have been investigated. Each pixel consists of a thermopile of ten thermocouples built up in a multilayer technology. These thermopiles are arranged on free-standing stress-compensated SiON membranes formed by anisotropic wet-etching of the 4" silicon wafer from the backside. The thermoelectric material combinations typically used are BiSb/Sb and BiSb/BiSbTe, respectively, deposited by vacuum evaporation and patterned microlithographically. The absorbing layer is silver black. To reduce the crosstalk the whole array is built up in a staggered arrangement of two subarrays of 128 pixels shifted by half a pitch against each other and separated by a narrow bar of bulk silicon. Furthermore, the membrane region between the pixels is removed by RIE thus creating a slit