Electronic devices in space environments can contain numerous types of oxides and insulators. Ionizing radiation can induce significant charge buildup in these oxides and insulators leading to device degradation and failure. Electrons and protons in space can lead to radiation-induced total-dose effects. The two primary types of radiation-induced charge are oxide-trapped charge and interface-trap charge. These charges can cause large radiation-induced threshold voltage shifts and increases in leakage currents. Two alternate dielectrics that have been investigated for replacing silicon dioxide are hafnium oxides and reoxidized nitrided oxides (RNO). For advanced technologies, which may employ alternate dielectrics, radiation-induced voltage shifts in these insulators may be negligible. Radiation-induced charge buildup in parasitic field oxides and in SOI buried oxides can also lead to device degradation and failure. Indeed, for advanced commercial technologies, the total-dose hardness of ICs is normally dominated by radiation-induced charge buildup in either parasitic field oxides and/or SOI buried oxides. Heavy ions in space can also degrade the oxides in electronic devices through several different mechanisms including single-event gate rupture, reduction in device lifetime, and large voltage shifts in power MOSFETs.

Radiation Effects in MOS Oxides

This paper provides a historical review of the literature on the effects of radiation-induced displacement damage in semiconductor materials and devices. Emphasis is placed on effects in technologically important bulk silicon and silicon devices. The primary goals are to provide a guide to displacement damage literature, to offer critical comments regarding that literature in an attempt to identify key findings, to describe how the understanding of displacement damage mechanisms and effects has evolved, and to note current trends. Selected tutorial elements are included as an aid to presenting the review information more clearly and to provide a frame of reference for the terminology used. The primary approach employed is to present information qualitatively while leaving quantitative details to the cited references. A bibliography of key displacement-damage information sources is also provided.

Review of displacement damage effects in silicon devices

The silicon-germanium heterojunction bipolar transistor (SiGe HBT) is the first practical bandgap-engineered device to be realized in silicon. SiGe HBT technology combines transistor performance competitive with III-V technologies with the processing maturity, integration levels, yield, and hence, cost commonly associated with conventional Si fabrication. In the ten-and-one-half years since the first demonstration of a functional transistor, SiGe HBT technology has emerged from the research laboratory, entered manufacturing on 200-mm wafers, and is poised to enter the commercial RF and microwave market. State-of-the-art SiGe HBT's can deliver: (1) f/sub T/ in excess of 50 GHz; (2) f/sub max/ in excess of 70 GHz; (3) minimum noise figure below 0.7 dB at 2.0 GHz; (4) 1/f noise corner frequencies below 500 Hz; (5) cryogenic operation; (6) excellent radiation hardness; (7) competitive power amplifiers; and (8) reliability comparable to Si. A host of record-setting digital, analog, RF, and microwave circuits have been demonstrated in the past several years using SiGe HBT's, and recent work on passives and transmission lines on Si suggest a migratory path to Si-based monolithic microwave integrated circuits (MMIC's) is possible. The combination of SiGe HBT's with advanced Si CMOS to form an SiGe BiCMOS technology represents a unique opportunity for Si-based RF system-on-a-chip solutions. This paper reviews state-of-the-art SiGe HBT technology and assesses its potential for current and future RF and microwave systems.

SiGe HBT technology: a new contender for Si-based RF and microwave circuit applications

An overview is presented of total ionizing dose (TID) effects in MOS and bipolar devices from a historical perspective, focusing primarily on work presented at the annual IEEE Nuclear and Space Radiation Effects Conference (NSREC). From the founding of the IEEE NSREC in 1964 until ~1976, foundational work led to the discovery of TID effects in MOS devices, the characterization of basic charge transport and trapping processes in SiO2, and the development of the first generations of metal-gate radiation-hardened MOS technologies. From ~1977 until ~1985, significant progress was made in the understanding of critical defects and impurities that limit the radiation response of MOS devices. These include O vacancies in SiO2, dangling Si bonds at the Si/SiO2 interface, and hydrogen. In addition, radiation-hardened Si-gate CMOS technologies were developed. From ~1986 until ~1997, a significant focus was placed on understanding postirradiation effects in MOS devices and implementing hardness assurance test methods to qualify devices for use in space systems. Enhanced low-dose-rate sensitivity (ELDRS) was discovered and investigated in linear bipolar devices and integrated circuits. From ~1998 until the present, an increasing focus has been placed on theoretical studies enabled by rapidly advancing computational capabilities, modeling and simulation, effects in ultra-thin oxides and alternative dielectrics to SiO2, and in developing a comprehensive model of ELDRS.

Total Ionizing Dose Effects in MOS and Low-Dose-Rate-Sensitive Linear-Bipolar Devices

Total ionizing dose radiation effects on the electrical properties of metal-oxide-semiconductor devices and integrated circuits are complex in nature and have changed much during decades of device evolution. These effects are caused by radiation-induced charge buildup in oxide and interfacial regions. This paper presents an overview of these radiation-induced effects, their dependencies, and the many different approaches to their mitigation.

Radiation effects and hardening of MOS technology: devices and circuits

The ionizing radiation tolerance of high-performance SiGe HBTs, grown by UHV/CVD and optimized for 77 K, has been investigated for the first time. Results at both 300 K and 77 K indicate that this SiGe technology is inherently radiation tolerant without additional processing steps. Perimeter-to-area analysis show parallel shifts in the collector and base current density for total radiation doses below 1.0 Mrad(Si). Relatively minor degradation in the current gain characteristics is observed for SiGe HBTs exposed to 1.0 Mrad(Si) of Co/sup 60/ gamma radiation, indicating that the technology is robust for many applications requiring a high degree of ionizing radiation tolerance. 1/f noise measurements made pre- and post-radiation show the appearance of a generation-recombination center in some of the SiGe HBTs after a total-dose exposure to 10.0 Mrad(Si).

Ionizing radiation tolerance of high-performance SiGe HBT's grown by UHV/CVD

The effects of 1.0 MeV neutron irradiation on both SiGe heterojunction bipolar transistors (HBTs) and Si CMOS transistors from an advanced ultra high vacuum chemical vapour deposition (UHV/CVD) SiGe BiCMOS technology are examined for the first time over the temperature range of 300 K to 84 K. Results at 300 K indicate that this SiGe technology is robust with respect to neutron radiation. At fluences as high as 10/sup 15/ n/cm/sup 2/ (1.0 MeV equivalent) the devices exhibited a degradation of less than 30% in peak current gain. The SiGe HBTs maintain a current gain of 60 after 10/sup 15/ n/cm/sup 2/ at 84 K, compared to the Si BJT which degrades with cooling to a current gain of 20 at 84 K. The cutoff frequencies of both the Si and SiGe transistors are unaffected by neutron irradiation, and only a slight degradation in the maximum oscillation frequency of the transistors was observed.

Neutron radiation tolerance of advanced UHV/CVD SiGe HBT BiCMOS technology

The effects of 46 MeV proton irradiation induced trap generation and its impact on the electrical characteristics of silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) from an advanced ultrahigh vacuum/chemical vapor deposition (UHV/CVD) SiGe BiCMOS technology are examined and discussed for the first time. At proton fluences as high as 10/sup 14/ p/cm/sup 2/ the peak current gain of the devices degraded by less than 8% compared to the pre-irradiated samples. The maximum oscillation frequency and cutoff frequency of the SiGe HBTs showed only minor degradation after 10/sup 14/ p/cm/sup 2/. Calibration of 2-D device simulation (MEDICI) to measured data in both forward and inverse modes of operation was used to infer the spatial location of the proton-induced traps. Traps in the collector-base space charge region appear as generation/recombination (G/R) centers in the inverse emitter-base region and are the result of displacement damage. Traps at the emitter-base spacer oxide interface appear as G/R centers in the forward emitter-base space charge region and are the result of ionization damage. Taken together, these results suggest that UHV/CVD SiGe HBT technology is robust to proton fluences at least as high as 10/sup 13/ p/cm/sup 2/ without radiation hardening.

An investigation of the spatial location of proton-induced traps in SiGe HBTs

The effects of gamma irradiation on the shallow-trench isolation (STI) leakage currents in a SiGe BiCMOS technology are investigated for the first time, and shown to be strongly dependent on the irradiation gate bias and operating substrate bias. A positive irradiation gate bias significantly enhances the STI leakage, suggesting a strong field assisted nature of the charge buildup process in the STI. Numerical simulations also suggest the existence of fixed positive charges deep in the bulk along the STI/Si interface. A negative substrate bias, however, effectively suppresses the STI leakage, and can be used to eliminate the leakage produced by the charges deep in the bulk under irradiation.

Total dose effects on the shallow-trench isolation leakage current characteristics in a 0.35 /spl mu/m SiGe BiCMOS technology

The effects of proton irradiation on the RF performance of SiGe Heterojunction Bipolar Transistors (HBTs) are reported in this paper. Frequency response and broadband noise properties are investigated in SiGe HBTs for proton fluences up to 5/spl times/10/sup 13/ p/cm/sup 2/. The current gain in the radio frequency (RF) bias region and the cutoff frequency (f/sub T/) show little degradation at even extreme proton fluence (realistic space fluences are 1-5/spl times/10/sup 11/ p/cm/sup 2/). The slight degradation of NF/sub min/ is due to the irradiation-induced increase in the total emitter and base resistance. The associated available gain G/sub A, assoc/ at noise matching is 20.2 dB at f=2 GHz and I/sub C/=2.6 mA for a proton fluence of 5/spl times/10/sup 13/ p/cm/sup 2/. These results suggest that space-borne RF circuit applications of SiGe HBTs should be robust to proton irradiation.

S.D. Clark

Papers

Ionizing radiation tolerance of high-performance SiGe HBT's grown by UHV/CVD

Neutron radiation tolerance of advanced UHV/CVD SiGe HBT BiCMOS technology

An investigation of the spatial location of proton-induced traps in SiGe HBTs

Total dose effects on the shallow-trench isolation leakage current characteristics in a 0.35 /spl mu/m SiGe BiCMOS technology

The effects of proton irradiation on the RF performance of SiGe HBTs