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

Abstract

Abstract. Classically gated infrared (IR) detectors have been implemented using charge-coupled devices (CCD). Bipolar complementary metal-oxide semiconductor (BiCMOS) technology emerged as a viable alternative platform for development. BiCMOS technology has a number of advantages over CCD and conventional CMOS technology, of which increased switching speed is one. The pixel topology used in this work is a reversed-biased diode connected heterojunction bipolar transistor. The disadvantage of CMOS detectors is the increased readout noise due to the increased on-chip switching compared to CCD, which degrades dynamic range (DR) and sensitivity. This yields increased switching speeds compared to conventional bipolar junction transistors. Sensitivity improved from 50 mA∕W (peak) at 430 nm in CCD detectors to 180 mA∕W (peak) (or 180; 000 V∕W) at 665 nm in BiCMOS detectors. Other CMOS IR detectors previously published in the literature showed sensitivity values from 2750 to 5000 V∕W or 100 mA∕W. The DR also improved from 47 and 53 dB to 70 dB. The sensitivity of conventional CCD detectors previously published is around 53 mA∕W. The second advantage is that detection in the near-IR band with conventional silicon integrated technology is possible. This work has shown increased detection capabilities up to 1.1 μm compared to Si detectors.

Characterization of diode-connected heterojunction bipolar transistors for near-infrared detecting applications

“…As mobility is increased due to the lower base resistance as a result of the germanium doping, sensitivity in the near-infrared range using SiGe HBTs as detecting elements peaked at 665 nm, which is about 9.5 dB higher than a Si pin-diode measured on the same prototype IC. 8 It must be noted that the given measurements were from two detector arrays with readout circuitry, where the one included SiGe diode-connected HBTs and the other one included Si pin-diodes. In both instances, a 2 × 2 array was used where the total detecting area was the same.…”

“…23 For I-V measurements where reverse biasing is applied to base-emitter and base-collector shorted HBTs, the results show that little deviation occurs as the device is cooled down to 77 K. This work can be used to estimate the DR and sensitivity of diode-connected SiGe HBTs. 8 Sensitivity is directly proportional to the current flow.…”

“…Prototyping was formerly accomplished and also published. 8 As shown in Fig. 6, the same prototype has been used and subjected to the experimental findings reported through this paper.…”

“…Silicon germanium (SiGe) IC technology presents a favorable platform for nearinfrared photodetector development because of the ease of integration with a standard Si technology. 8 Characterization of SiGe diode-connected heterojunction bipolar transistors (HBTs) using two configurations with measurements at room temperature (293 K) and cryogenic temperature (77 K) are presented in this paper. Cryogenic small-signal modeling of SiGe HBTs 9 using non-CMOSbased technology has been reported in the literature.…”

“…10 Specifically, the use of SiGe shows improved performance over other CMOS technologies for dynamic range (DR) and sensitivity. 8 SiGe HBTs exhibit decreased base resistance, increased maximum oscillation and cutoff frequency, increased Early voltage and increased current gain compared with Si bipolar junction transistors (BJTs). The same collector current density (J C ) and base current density (J B ) are seen at lower base-emitter voltages (for a 10 −5 mA∕μm 2 J B and J C , measured at 0.7 and 0.55 V, respectively, for SiGe HBTs and at 1.05 and 1 V, respectively, for Si BJTs).…”