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Space applications using advanced foundry processes require device models that accurately include the dependence of total-ionizing dose (TID) response on process variability and layout. An automated flow is described for TID-aware process design kit generation using new test chips, modeling, and simulation. The variability of TID-induced leakage current and transistor mismatch both increase after irradiation. [ABSTRACT FROM AUTHOR]

The effects of shallow-trench-isolation-induced mechanical stress on radiation-induced off-state leakage current are reported in 90-nm NMOS devices. The radiation-induced leakage current increases with increasing active device-to-isolation spacing. The leakage current also depends on channel width; narrow devices exhibit less leakage before irradiation, but more after irradiation. These geometrical factors affect the mechanical stress in the device, which impact the dopant diffusion and activation and the charge trapping in the STI oxide. The combined effects of these layout-related phenomena affect the sensitivity to radiation-induced charge. [ABSTRACT FROM AUTHOR]

The 1.8-MeV proton radiation responses are compared for AlGaN/GaN HEMTs grown under Ga-rich, N-rich, and NH3-rich conditions. The NH3-rich devices are more susceptible to proton irradiation than the Ga-rich and N-rich devices. The 1/ f noise of the devices increases with increasing fluence. Density functional theory calculations show that N vacancies and Ga-N divacancies lead to enhanced noise in these devices. [ABSTRACT FROM AUTHOR]

The impact of total ionizing dose (TID) is reported on irradiated capacitorless metastable dip RAM (MSDRAM) cells, built in a planar SOI technology. The memory window shifts toward more negative voltages at higher doses. The unconventional gate current peak measured in MSDRAM cells decreases with dose and disappears at 500~\ krad(\ SiO2) for these devices. The retention time of the 0-state decreases with dose, with the greatest decrease for memory cells programmed with high back-gate voltages. The trapped charge in the 400-nm buried oxide changes the potential in the body and interferes with the ability to store a 0-state. The irradiated cells exhibit higher drain currents while reading the 1-state. This increase of the drain current is enhanced for longer programming times. [ABSTRACT FROM AUTHOR]

The total-dose response of Ge p-MOSFETs and p+-n junction diodes is reported for devices fabricated with several process variations. Radiation-induced reduction of the on-off current ratio increases with halo-doping density. Increasing the number of Si monolayers at the substrate/dielectric interface reduces total-dose sensitivity for p-MOSFETs. Reduced mobility degradation is observed after irradiation for devices with a higher number of Si monolayers. The radiation-induced increase in junction leakage is related to the increasing perimeter component of the leakage current. MOSFETs with a higher number of Si monolayers at the dielectric/substrate interface also have reduced perimeter leakage current. Diode leakage current increases with increasing halo-doping density. [ABSTRACT FROM AUTHOR]

The dependence of the subthreshold-swing (SS) degradation on fin width is reported for irradiated 100-nm-gatelength, fully depleted n-channel FinFETs. The wider the fin is, the greater the radiation-induced SS degradation. The higher tolerance to radiation-induced charge for the narrower FinFETs is attributed to the additional lateral gate control over the body potential. The irradiation and room temperature annealing results suggest that the SS increase for wider FinFETs is due primarily to nonuniform trapped charge in the buried oxide (BOX). The subthreshold characteristics of FinFETs with two fins are more likely to exhibit a nonuniform subthreshold slope (NUSS), resulting from fin-to-fin variability, than FinFETs with 20 fins, where the corresponding Id-Vgs curve is the composite of the 20 individual IdVgs curves. [ABSTRACT FROM AUTHOR]

Bipolar test structures were irradiated and annealed with various combinations of molecular hydrogen gas ambients, bias, and thermal conditions. The results show that the buildup and annealing behavior of defects in bipolar base oxides depend strongly on hydrogen concentration. Differences observed in trapped oxide charge annealing rates suggest that the charged defects created in hydrogen-rich environments may be attributed to different types of positive charge in addition to trapped holes. [ABSTRACT FROM PUBLISHER]

Swift heavy ion (SHI) damage, including single-event gate rupture (SEGR), radiation-induced soft breakdown (RISB), and long-term reliability degradation (LTRD), plays an important role in limiting device lifetime and reliability. However, the atomic-scale physical origins of these phenomena have not been elucidated. In this work, we explain the underlying physical processes responsible for SHI-induced effects in oxides, providing a direct link between atomic motion and macroscopic electrical effects. SRIM 2008 calculations show that SHIs produce low-energy atomic recoils in SiO2. Using parameter-free quantum mechanical calculations, we probe the atomic-scale dynamics of the resulting low-energy atomic displacements. We show that low-energy displacements in SiO2 produce pockets containing high densities of network defects, and that these defects generate electronic states throughout the SiO2 band gap. These spatially correlated defect states represent a low-resistivity ldquoconducting piperdquo through SiO2 layers, and provide an atomistic mechanism for the formation of electrically-active damage that does not rely on thermal spike effects. In the case of SEGR, the conducting pipe allows energy stored on the gate capacitance to be discharged into the oxide, resulting in the permanent damage observed experimentally. The persistence of defects resulting from SHI-induced atomic displacements provides a physical explanation for percolation models of LTRD and RISB. [ABSTRACT FROM PUBLISHER]

Transistors and ICs built in several different captive and commercial facilities were exposed to moisture, irradiated, and annealed. The moisture exposures were performed using highly accelerated stress test (HAST) at 130degC and 85% relative humidity. Irradiation of n-channel transistors exposed to HAST followed by a long-term anneal resulted in some increase in interface-trap and oxide-trapped charge buildup. However, exposing p-channel transistors to HAST preirradiation resulted in extremely large and unexpected voltage shifts immediately following irradiation. They were observed for devices with either doped oxide or nitride final chip passivation. Because of this, nitride passivation may not be sufficient to prevent H2O from causing enhanced radiation-induced degradation over long time periods in some devices (e.g., commercial devices with nitride final chip passivation packaged in plastic packages). The smaller voltage shifts for the n-channel transistors may be related to the formation of phosphosilicate glass (PSG) overlying the sources and drains of the n-channel transistors impeding the diffusion of moisture to the gate oxides. It is shown that, the large radiation-induced voltage shifts for the p-channel transistors can lead to enhanced IC parametric degradation and functional failure at lower radiation levels. Large increases in radiation-induced field oxide leakage current were also observed for transistors exposed to HAST preirradiation. Transistors were also annealed (prior to irradiation) and irradiated in H2. Approximately the same level of radiation-induced degradation was observed for n- and p-channel transistors suggesting that the diffusion kinetics for H2 diffusion are considerably different than for H2O diffusion. These results raise the concern that exposure of devices to moisture or hydrogen can lead to long-term radiation-induced aging effects. [ABSTRACT FROM PUBLISHER]

As integrated circuits become smaller and more complex, it has become increasingly difficult to simulate their responses to radiation. The distance and time scales of relevance extend over orders of magnitude, requiring a multi-scale, hierarchical simulation approach. This paper demonstrates the use of multi-scale simulations to examine two radiation-related problems: enhanced low-dose-rate sensitivity (ELDRS) in bipolar transistors and single-event effects (SEE) in CMOS integrated circuits. Examples are included that demonstrate how information can be passed from simulation tools operating at one level of abstraction to those operating at higher levels, while maintaining accuracy and gaining insight. [ABSTRACT FROM AUTHOR]

Abstract: The peaked evolution of leakage current with total ionizing dose observed in transistors in 130nm generation technologies is studied with field oxide field effect transistors (FOXFETs) that use the shallow trench isolation as gate oxide. The overall radiation response of these structures is determined by the balance between positive charge trapped in the bulk of the oxide and negative charge in defect centers at its interface with the silicon substrate. That these are mostly interface traps and not border traps is demonstrated through dynamic transconductance and variable-frequency charge-pumping measurements. These interface traps, whose formation is only marginally sensitive to the bias polarity across the oxide, have been observed to anneal at temperatures as low as 80°C. At moderate or low dose rate, the buildup of interface traps more than offsets the increase in field oxide leakage due to oxide-trap charge. Consequences of these observations for circuit reliability are discussed. [Copyright &y& Elsevier]

The impact of 63.3 MeV proton and 10 keV x-ray irradiation on the DC and AC performance of complementary (npn + pnp) SiGe HBTs on thick-film SOI is investigated. Proton and x-ray induced changes in the forward and inverse Gummel characteristics, the output characteristics, and avalanche multiplication are reported for both npn and pnp SiGe HBTs, at both room temperature (300 K) and at cryogenic temperatures (down to 30 K). Comparison of room temperature and cryogenic data suggests interface trap formation at two distinct physical locations in the transistors. Experimental data and calibrated TCAD simulations are used to compare the radiation response of both thick-film SOI devices and thin-film SOI SiGe HBTs. [ABSTRACT FROM AUTHOR]

Total-ionizing-dose irradiation-induced RF performance degradation is observed in the input-output (IO) and core transistors of a 130 nm SOI NMOS technology. Different MOS structures including Floating Body(FB), T-gate Body(TB) and Tunnel Diode Body Contact(TDBC) SOI structures, were fabricated in a fully-integrated 130 nm SOI process. The radiation-induced DC and RF response of these devices was investigated. The impact of different structures and the use of body contact at PDSOI on the RF TID behavior are discussed by comparing their results to ionizing radiation experiments. • The first study to analyze RF TID response of body contacted and uncontacted body SOI device. • The first study to extract the key parameters in RF TID experiment. • Fmax could degrade more than 50% under irradiation and may cause circuit failure. • Traditional body contact structures not only pay more areas but also degrade TID tolerance both in DC and RF characteristics. [ABSTRACT FROM AUTHOR]

40 years of research on low-frequency (LF) noise and random-telegraph noise (RTN) in metallic and semiconducting nanowires (NWs) demonstrate the importance of defects and impurities to each system. The fluctuating interference of electrons in the local environment of a mobile bulk defect or impurity can lead to LF noise, RTN, and device-to-device variations in metallic and semiconducting NWs. Scattering centers leading to mobility fluctuations in semiconducting NWs include random dopant atoms and bulk defect clusters. Effective energy distributions for the relevant defects and impurities can be obtained from noise versus temperature measurements in conjunction with the Dutta-Horn model of LF noise for both metallic and semiconducting NWs. In semiconducting NWs configured as metal-oxide-semiconductor field-effect transistors, fluctuations in carrier number due to charge exchange with border traps, such as oxygen vacancies and/or their complexes with hydrogen in adjacent or surrounding dielectrics, often dominate or add to bulk noise sources.

Silicon photonics is considered to be an ideal solution as optical interconnect in radiation environments. Our previous study has demonstrated experimentally that radiation responses of device are related to waveguide size, and devices with thick top silicon waveguide layers are expected to be less sensitive to irradiation. Here, we design radiation-resistant arrayed waveguide gratings and Mach-Zehnder interferometers based on silicon-on-insulator with 3 µm-thick silicon optical waveguide platform. The devices are exposed to 60 Co γ-ray irradiation up to 41 Mrad(Si) and 170-keV proton irradiation with total fluences from 1×10 13 to 1×10 16 p/cm 2 to evaluate performance after irradiation. The results show that these devices can function well and have potential application in harsh radiation environments.

In this work, the radiation responses of silicon photonic passive devices built in silicon-on-insulator (SOI) technology are investigated through high energy neutron and 60 Co γ-ray irradiation. The wavelengths of both micro-ring resonators (MRRs) and Mach-Zehnder interferometers (MZIs) exhibit blue shifts after high-energy neutron irradiation to a fluence of 1×10 12 n/cm 2 ; the blue shift is smaller in MZI devices than in MRRs due to different waveguide widths. Devices with SiO 2 upper cladding layer show strong tolerance to irradiation. Neutron irradiation leads to slight changes in the crystal symmetry in the Si cores of the optical devices and accelerated oxidization for devices without SiO 2 cladding. A 2-µm top cladding of SiO 2 layer significantly improves the radiation tolerance of these passive photonic devices.

We investigate the influence of high energy photons and thiol ligands on the photophysical properties of sub-monolayer CdTe/CdS quantum dots (QDs) immobilized in porous silica (PSiO2) scaffolds. The highly disperse, uniform distributions of QDs in a three-dimensional PSiO2 framework ensure uniform interaction of not only radiation but also subsequent surface repassivation solutions to all immobilized QDs. The high optical densities of QDs achieved using PSiO2 enable straightforward monitoring of the QD photoluminescence intensities and carrier lifetimes. Irradiation of QDs in PSiO2 by high energy photons, X-rays, and γ-rays leads to dose-dependent QD photodarkening, which is accompanied by accelerated photooxidative effects in ambient environments that give rise to blue-shifts in the peak QD emission wavelength. Irradiation in an oxygen-free environment also leads to QD photodarkening but with no accompanying blue-shift of the QD emission. Significant reversal of QD photodarkening is demonstrated following QD surface repassivation with a solution containing free-thiols, suggesting reformation of a CdS shell, etching of surface oxidized species, and possible reduction of photoionized dark QDs to a neutral, bright state. Permanent lattice displacement damage effects may contribute toward some irreversible γ radiation damage. This work contributes to an improved understanding of the influence of surface ligands on the optical properties of QDs and opens up the possibilities of engineering large area, low-cost, reuseable, and flexible QD-based optical radiation sensors.