Investigate the radiation response of Heterojunction Bipolar Transistors : impact of X-ray irradiation on DC and Low Frequency Noise characteristics

Abstract

SiGe HBTs have emerged to meet the burgeoning demand of wireless communication and high-speed niche applications at a compelling cost advantage. The high integration capability of SiGe technology with CMOS provides a favorable opportunity to leverage the advantages of both technologies. But in recent years, the fast scaling of transistor dimensions has increased the 1/f noise and sets a minimum signal level of electronic devices. In addition, the detrimental effects of radiation on the performance and reliability of electronic devices have been an issue in the radiation society. Consequently, this is my main motivation to characterize, model and analyze the SiGe:C HBT devices to design rad-hard devices and to find a solution that reduces low-frequency noise. I have evaluated the impacts of x-ray irradiation on the DC characteristics and low-frequency noise of 55 nm advanced SiGe:C HBTs. The HBTs, which exhibit a fT/fMax of 320/370 GHz, are issued by STMicroelectronics. Three samples, which covers an emitter area range of 0.2\times 5 µm² to 0.42 \times 10 µm² were irradiated to 240 krad(air), 280 krad(air) and 520 krad(air), which is far more than the prior study on this device (i.e., 151 krad (air)). The DC parameters such as forward Gummel characteristics, current gain (hFE), relative excess base current (∆ib/ib) and relative excess collector current (∆ic/ic) were examined before and after irradiation. Moreover, the impacts of annealing at 100 \degc and 130 \degc have been evaluated to examine the possible recovery mechanisms of induced radiation traps. Concerning low frequency noise (LFN) the dependence of base current noise spectral density (Sib) of 1/f noise and generation-recombination noise (g-r noise) on base current is evaluated. To extract Kb, a figure of merit representing the 1/f noise amplitude, and locate the low-frequency noise sources, the impact of emitter geometry and collector doping is analyzed using compact SPICE modeling. I present that the radiation- induced traps majorly affect the low injection region of the base current. This is confirmed by the plot of ∆ib/ib with TID at different base emitter voltages, Vbe, and our post-irradiation model. In addition, the dependence of ∆ib/ib with emitter geometry locates the induced-radiation trap centers. The compact SPICE modeling of the 1/f noise of the device under test (DUT) shows that Sib is proportional to the quadratic dependence of base current and Kb is in the range of 10-9 µm².