Hong-Xia Guo

Impact of Bias Conditions on Total Ionizing Dose Effects of

The effect of bias condition on total ionizing dose (TID) of Silicon-Germanium heterojunction bipolar transistors (SiGe HBTs) is investigated. The SiGe HBTs are set at forward, saturated, cutoff, and all-grounded biases during 60Coγ irradiation. After each irradiation stops, the forward Gummel characteristic and inverse Gummel characteristic are measured, and a 3-D simulation of TID for SiGe HBT is performed. The mechanism of TID in different bias conditions is obtained by analyzing normalized excess base current. The results show that the TID damages are different at various irradiation biases of the SiGe HBT, and the worst bias between forward and inverse Gummel characteristics exhibits inconsistently. The reason could be attributed to different defects produced and accumulated in oxide layers by irradiation at various bias conditions. To be specific, the oxide trap charges (Not) in emitter/base (E/B) Spacer is important to the forward Gummel characteristic, yet the Not in LOCOS determines the inverse Gummel characteristic. However, after long time irradiation, the interface states (Nit) both in E/B Spacer and LOCOS dominate the damage to the SiGe HBT despite in forward Gummel mode or inverse Gummel mode.

^{60}{\hbox{Co}}\gamma

Abstract A 3-D simulation of single event effects (SEEs) for domestic Silicon–Germanium heterojunction bipolar transistor (SiGe HBT) in extreme environment is performed with TCAD simulation tools. The influences of environment temperature and linear energy transfer (LET) on SEE are investigated. The combined effects of temperature and LET are also discussed. The results show some interesting phenomena by analyzing collected charges and transient current. The collected charges increase as temperature rises, but the current peaks decline with temperature increasing at base, collector and substrate. However, the peak of emitter transient current rises up and then declines. As LET rises, the collected charges go up linearly, and the transient current peaks also increase but their growth trends are slow. Mobility, carrier ionization and recombination of various regions at different conditions are the main causes of these differences. Current transient is very severe at low temperature. But charge collection is sensitive to high temperature and high LET. Transient pulse caused by diffusion mechanism may have a serious effect on SEEs.

in SiGe HBT

Abstract This paper evaluates enhanced low dose rate sensitivity (ELDRS) in Silicon–Germanium heterojunction bipolar transistors (SiGe HBTs) which are isolated by LOCOS process. The 60 Co gamma irradiations were performed at 80 rad (Si)/s and 0.1 rad (Si)/s respectively in order to investigate dose rate dependence of the SiGe HBT. Devices were set in forward, saturated, cutoff, and all-grounded biases during the irradiation. The degradation mechanism of different dose rate irradiations was analyzed via measurement of forward Gummel mode and inverse Gummel mode both pre- and post- irradiation. The results show that ELDRS exists at forward, saturated, and all-grounded biases irradiations. The dose rate dependences of various irradiated biases are different in the SiGe HBT. The interface-traps both in EB Spacer and LOCOS are the major irradiated damages in the SiGe HBT for the low dose rate irradiation. ELDRS is directly related to the quality, thickness, and shape of oxide layers.

3-D simulation study of single event effects of SiGe heterojunction bipolar transistor in extreme environment

The synergistic effect of total ionizing dose (TID) on single event effect (SEE) in SiGe heterojunction bipolar transistor (HBT) is investigated in a series of experiments. The SiGe HBTs after being exposed to Co-60 gamma irradiation are struck by pulsed laser to simulate SEE. The SEE transient currents and collected charges of the un-irradiated device are compared with those of the devices which are irradiated at high and low dose rate with various biases. The results show that the SEE damage to un-irradiated device is more serious than that to irradiated SiGe HBT at a low applied voltage of laser test. In addition, the gamma irradiations at forward and all-grounded bias have an obvious influence on SEE in the SiGe HBT, but the synergistic effect after cutting off the gamma irradiation is not significant. The influence of positive oxide-trap charges induced by TID on the distortion of electric field in SEE is the major factor of the synergistic effect. Moreover, the recombination of interface traps also plays a role in charge collection.

Investigation of enhanced low dose rate sensitivity in SiGe HBTs by 60 Co γ irradiation under different biases

Silicon-germainum heterojunction bipolar transistor (SiGe HBT) has been demonstrated to be suitable in extreme environment because of its superior temperature characteristics which can operate from 43 K to 400 K [1]. In addition, outstanding hardness to both total ionizing dose (TID) radiation and displacement damage make SiGe HBT technology particularly attractive for space applications [2]. However, it was shown that SiGe HBTs are vulnerable to single event effects (SEEs) [3]. In the last decade, the mechanism of the SEE of SiGe HBT was investigated via TCAD simulation method by a mass of studies. And the representation of SEE was explored by the broad beam heavy-ion tests, for instance, some single event upsets (SEU) of SiGe HBT circuits had been performed by broad beam heavy-ion irradiation [4]. But the SEE sensitive volume can be accurately defined only by the micro-beam heavy ion tests. Furthermore, the micro-beam heavy ion irradiation can observe the actual transient phenomena and the mechanism of single event transient (SET) well. SiGe HBT under test. For this work, the KT9041 SiGe HBTs are employed in the irradiation experiment. The device is similar to vertical NPN Si BJT. But the base region is constituted by gradient SiGe in the SiGe HBT. The thickness of intrinsic base is 0.08 μm. And the heavy doping process is used in the region of the base and the emitter to reduce the area resistance. The lightly doped concentrations of collector and substrate are 6 × 10 and 1 × 10 cm, respectively. Most importantly, there is a collector/substrate (C/S) junction with very large area about 100 μm × 100 μm, which is the most typical structure in this SiGe HBT. In addition, the local oxidation of silicon (LOCOS) isolation process is employed in the SiGe HBT, but the deep trench isolation (DTI) is not used.

Synergistic effect of total ionizing dose on single event effect induced by pulsed laser microbeam on SiGe heterojunction bipolar transistor

Enhanced low dose rate sensitivity (ELDRS) in different process Silicon–Germanium heterojunction bipolar transistors (SiGe HBTs) is investigated. Low and high dose rate irradiations are performed to evaluate the ELDRS of SiGe HBTs manufactured by Tsinghua University (THU). THU SiGe HBTs experience significantly low dose rate sensitivity than that of IBM 8HP SiGe HBTs and behave a “true” dose rate effect. TCAD models were used to explicate the microcosmic structure in THU and IBM 8HP SiGe HBTs. Comparison and discussion show that different SiGe processes may involve different HBT structures and device designs which are the critical influence of ELDRS effect. The different responses of ELDRS should be first attributed to the device structure and design in nature, particularly the geometry of emitter–base junction and the isolation structure.

Heavy ion micro-beam study of single-event transient (SET) in SiGe heterjunction bipolar transistor

Different SiGe processes and device designs are the critical influences of ionizing radiation damage. Based on the different ionizing radiation damage in SiGe HBTs fabricated by Huajie and an IBM SiGe process, quantitatively numerical simulation of ionizing radiation damage was carried out to explicate the distribution of radiation-induced charges buildup in KT9041 and IBM SiGe HBTs. The sensitive areas of the EB-spacer and isolation oxide of KT9041 are much larger than those of the IBM SiGe HBT, and the distribution of charge buildup in KT9041 is several orders of magnitude greater than that of the IBM SiGe HBT. The result suggests that the simulations are consistent with the experiment, and indicates that the geometry of the EB-spacer, the area of the Si/SiO2 interface and the isolation structure could be contributing to the different ionizing radiation damage.