Low-cost uncooled infrared detectors in CMOS process

This paper reports the implementation and comparison of two low-cost uncooled infrared microbolometer detectors that car be implemented using standard n-well CMOS processes. One type is based on a suspended n-well resistor, which is implemented in a 0.8 mum CMOS process and has a pixel size of 80 mum x 80 mum with a fill factor of 13%; and the other type is based on a suspended p(+)-active/n-well diode, which is implemented in a 0.35 mum CMOS process and has a pixel size of 40 mum x 40 mum with a fill factor of 44%. These detectors can be obtained with simple bulk-micromachining processes after the CMOS fabrication, without the need for any complicated lithography or deposition steps. The diode type detector has a measured dc responsivity (R) of 4970 V/W at 20 muA bias and a thermal time constant of 35.8 ms at 80 mTorr vacuum level, and it has a measured rms noise of 0.52 muV for a 4 kHz bandwidth, resulting in a detectivity (D*) of 9.7 x 10(8) cm Hz(1 /2)/W. The resistive n-well detector can provide the same dc responsivity at 1.68 V detector bias voltage, with about 10 times more self-heating as compared to that of the diode type detector. This detector has a measured rms noise of 0.81 RV for a 4 kHz bandwidth, resulting in a detectivity (D*) of 8.9 x 10(8) cm Hz(1/2)/W, which can be improved further with higher detector bias voltages at the expense of increased self-heating. The diode type detector is better for low-cost large format infrared detector arrays, since it has a superior response even at reduced pixel sizes and lower biasing levels. (C) 2003 Elsevier B.V. All rights reserved.