Dynamic range and sensitivity improvement in near-infrared detectors using silicon germanium bipolar complementary metal-oxide semiconductor technology

Abstract

Johan VenterSaurabh SinhaUniversity of PretoriaCarl and Emily Fuchs Institute for MicroelectronicsDepartment of Electrical, Electronic and ComputerEngineeringPretoria, South AfricaE-mail: jwventer@ieee.orgAbstract. Classically gated infrared (IR) detectors have been imple-mented using charge-coupled devices (CCD). Bipolar complementarymetal-oxide semiconductor (BiCMOS) technology emerged as a viablealternative platform for development. BiCMOS technology has a numberof advantages over CCD and conventional CMOS technology, of whichincreased switching speed is one. The pixel topology used in this workis a reversed-biased diode connected heterojunction bipolar transistor.The disadvantage of CMOS detectors is the increased readout noiseduetotheincreasedon-chipswitchingcomparedtoCCD,whichdegradesdynamic range (DR) and sensitivity. This yields increased switchingspeeds compared to conventional bipolar junction transistors. Sensitivityimproved from 50 mA∕W (peak) at 430 nm in CCD detectors to180 mA∕W (peak) (or 180;000 V∕W) at 665 nm in BiCMOS detectors.Other CMOS IR detectors previously published in the literature showedsensitivity values from 2750 to 5000 V∕Wor100 mA∕W. The DR alsoimproved from 47 and 53 dB to 70 dB. The sensitivity of conventionalCCD detectors previously published is around 53 mA∕W. The second ad-vantageisthatdetectioninthenear-IRband withconventionalsilicon inte-grated technology is possible. This work has shown increased detectioncapabilities up to 1.1 μm compared to Si detectors.