Aluminosilicate Structure Thermopile Infrared Detector

A MEMS based thermopile infrared sensor has been developed using Polysilicon/Aluminum. This kind of detectors were characterized as low power consumption, low cost, room temperature operation, and DC response. The 2.1 X 2. 1mm2 thermopiles with 40 junctions, and 0.9 X 0. 9 mm2 absorber area, have been developed and tested. In air at room temperature, the responsivity was measured at 15.36V/W. The corresponding D* was 2.577x 107 cmHz1/2W-1, time constant was 39.5ms, and DC resistance was 29.9K0 <>In the designing of the thermopiles, a comprehensive heat transfer analysis was peroformed to optimize the sensor's design. Two-dimensional steady state analysis has been completed which provided accurate temperature profile information on the sensor and agreed well with experimental results. The heat transfer model also illustrate 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.The thermopile fabrication process combined MEMS technology with semiconductor IC processes. The silicon membrane was fabricated using KOH anisotropic etching and Si-Si3N4/SiO2 'etch-stop' process. The final silicon membrane was about 5000A, which greatly decreased the sensor's thermal conductivity without spoiling its electrical performance.A new design of an additional metal-reflective layer on the cold region and thermopiles' beams is demonstrated and tested. The additional reflective coatings increase the sensor's sensitivity and detectivity by reflecting and transferring the heat absorbed in the cold region to the surrounding air. On the other hand, this design stablize the reference temperature in cold region, largely improves the system reliability.Silicon membrane with good quality is very important for sensors. The silicon oxide membrane usually used in devices is inevitably with large compressive intrinsic stress. The use of an oxide etch mask during heavily boron doped membrane fabrication can alter the state of stress to an apparent compressive state with a positive bending moment. The thermopile devices in this thesis used Si3N4/SiO2 membrane to compensate the intrinsic stress. The last part of this thesis will discuss such situation and the corresponding method to eliminate intrinsic stresses.