Physical mechanisms contributing to enhanced bipolar gain degradation at low dose rates
- Sandia National Labs., Albuquerque, NM (United States)
- Univ. of Arizona, Tucson, AZ (United States). ECE Dept.
- Phillips Lab./VTE, Albuquerque, NM (United States)
- Analog Devices, Inc., Wilmington, MA (United States)
- Naval Surface Warfare Center, Crane, IN (United States)
- RLP Research, Inc., Albuquerque, NM (United States)
The authors have performed capacitance-voltage (C-V) and thermally-stimulated-current (TSC) measurements on non-radiation-hard MOS capacitors simulating screen oxides of modern bipolar technologies. For 0-V irradiation of [approximately]25 C, the net trapped-positive-charge density (N[sub ox]) inferred from midgap C-V shifts is [approximately]25--40% greater for low-dose-rate (< 10 rad(SiO[sub 2])/s) than for high-dose-rate (> 100 rad(SiO[sub 2])/s) exposure. Device modeling shows that such a difference in screen-oxide N[sub ox] is enough to account for the enhanced low-rate gain degradation often observed in bipolar devices, due to the [approximately] exp(N[sub ox][sup 2]) dependence of the excess base current. At the higher rates, TSC measurements reveal a [approximately]10% decrease in trapped-hole density over low rates. Also, at high rates, up to [approximately]2.5-times as many trapped holes are compensated by electrons in border traps than at low rates for these devices and irradiation conditions. Both the reduction in trapped-hole density and increased charge compensation reduce the high-rate midgap shift. A physical model is developed which suggests that both effects are caused by time-dependent space charge in the bulk of these soft oxides associated with slowly transporting and/or metastably trapped holes (e.g., in E[delta][prime] centers). On the basis of this model, bipolar transistors and screen-oxide capacitors were irradiated at 60 C at 200 rad(SiO[sub 2])/s in a successful effort to match low-rate damage. these surprising results provide insight into enhanced low-rate bipolar gain degradation and suggest potentially promising new approaches to bipolar and BiCMOS hardness assurance for space applications.
- OSTI ID:
- 6559118
- Report Number(s):
- CONF-940726--
- Journal Information:
- IEEE Transactions on Nuclear Science (Institute of Electrical and Electronics Engineers); (United States), Journal Name: IEEE Transactions on Nuclear Science (Institute of Electrical and Electronics Engineers); (United States) Vol. 41:6Pt1; ISSN 0018-9499; ISSN IETNAE
- Country of Publication:
- United States
- Language:
- English
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46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
ELECTRICAL PROPERTIES
HARDENING
JUNCTION TRANSISTORS
MATHEMATICAL MODELS
PHYSICAL PROPERTIES
PHYSICAL RADIATION EFFECTS
RADIATION EFFECTS
RADIATION HARDENING
SEMICONDUCTOR DEVICES
TRANSISTORS
TRAPPING