A SILICON-BASED THERMOPILE INFRARED DETECTOR ARRAY CONTAINING ON-CHIP READOUT CIRCUITRY

This dissertation reports a new low-cost infrared detector array which has been realized using standard silicon MOS process technology and micromachining. This array is based on polysilicon-gold thermopiles supported on 1.3 (mu)m-thick dielectric diaphragm windows of SiO(,2) and Si(,3)N(,4). The boron-etch stop is used to obtain 20 (mu)m-thick silicon support rims. This technique not only eliminates sensitivity to misalignment but also allows a highly-packed diaphragm array. While the intrinsic diaphragm stress is strongly affected by the dielectric-film deposition technique and the subsequent high-temperature processes involved, flat diaphragms can be achieved reproducibly for a given process.; A single thermopile on a circular diaphragm window was fabricated using the above-mentioned structure and was also analyzed theoretically to allow better understanding of device performance. The detector responsivity decreases almost linearly as the diaphragm window diameter decreases, while the detectivity decreases in a square-root fashion. The detector time constant can be less than 10 milliseconds when the window diameter is smaller than 1.2 mm.; A typical thermopile element having 40 polysilicon-gold thermocouples supported on a 400 (mu)m x 800 (mu)m dielectric diaphragm window exhibits a responsivity of 12 V/W and a response time less than 10 msec. In the ambient temperature range from 0(DEGREES)C to 90(DEGREES)C, the responsivity decreases with a sensitivity of -1400 ppm/(DEGREES)C. The detector responds to a broad input spectral range and its dynamic range is over 10('6):1. This detector handles an input radiation power of over 5W/cm('2) without any appreciable responsivity degradation. Johnson noise is dominant in this semiconductor thermopile detector and the array packing density is limited by the required detector responsivity and detectivity. The variations in responsivity have been as high as 20% for a given process; however, use of improved deposition and doping techniques should significantly reduce these nonuniformities.; Thirty-two element thermopile arrays with on-chip E/D PMOS multiplexers have been successfully realized using an 8 mask process. It is expected that this type of array will be useful for non-contact, non-destructive product monitoring and automated process control. (Abstract shortened with permission of author.)...