Interface-trap Buildup Research Articles

Total-Ionizing-Dose Effects in IGZO Thin-Film Transistors

Total-ionizing-dose (TID) effects are evaluated in back-gated IGZO thin-film transistors irradiated under different gate biases. Negative-bias irradiation leads to worst-case degradation of TID response in these devices, primarily as a result of enhanced charge trapping in the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> overlayer. The relatively small peak transconductance decrease after irradiation illustrates that IGZO transistors are much less sensitive to interface-trap buildup and other instabilities due to hydrogen release and transport than amorphous Si thin film transistors examined previously. The TID response of devices with different gate sizes is also investigated. No significant geometry dependence is observed, which is promising for future scaling down of the technology.

Total-Ionizing-Dose Effects on 3-D Sequentially Integrated FDSOI Ring Oscillators

Total-ionizing-dose responses are investigated for fully-depleted silicon-on-insulator (FDSOI) ring oscillators (RO), in three-dimensional (3D) architectures. Operational frequencies decrease after irradiation in these devices due primarily to threshold voltage shifts and transconductance degradation due to interface-trap buildup in the pull-up <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> MOSFETs. 3D sequentially-integrated FDSOI ROs fabricated in the bottom layer of the 3D structure show the most significant frequency degradation. AC-bias irradiation leads to greater shifts than static-bias irradiation in these devices due to enhanced interface-trap buildup. Circuit simulations reinforce the relative importance of transconductance degradation in pull-up <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> MOSFETs to the TID response of these ROs.

Effects of Bias and Temperature on Interface-Trap Annealing in MOS and Linear Bipolar Devices

This article reviews the effects of applied bias and temperature on Si/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> interface-trap buildup and annealing rates. Electrical and spectroscopic methods are described to estimate interface-trap densities at oxidized Si surfaces, in MOS capacitors and transistors, and in linear bipolar devices. Illustrative results provide insights into the kinetics and energetics of interface-trap annealing. Interface traps in MOS and linear bipolar devices anneal much more easily at 0 V bias than at positive or negative applied bias. Hydrogen transport and reactions play critical roles in interface-trap buildup and annealing processes. The complex interplay between H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> diffusion and H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> drift is illustrated via coupled experimental and theoretical studies. Interface-trap annealing imposes significant constraints on hardness-assurance techniques. Current MOS standard tests that incorporate accelerated aging at elevated temperature at worst case, static, positive bias enable successful assessment of MOS devices in low-dose-rate environments. However, it is not similarly possible to use elevated-temperature irradiation and/or annealing at worst case, 0 V bias to predict low-dose-rate response for linear bipolar devices and ICs. Temperature-switching during irradiation appears to be a promising approach to address this issue.

Aging Effects and Latent Interface-Trap Buildup in MOS Transistors

Effects of ~35 years of aging during storage are investigated on the radiation response and 1/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f$ </tex-math></inline-formula> noise of Oki nMOS and pMOS transistors with high oxygen vacancy densities in SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . Short-term interface-trap buildup during irradiation is enhanced significantly, relative to that observed in 1989, 1997, and 2008. In contrast, a similar latent interface-trap buildup is observed for aged pMOS devices irradiated and annealed at room and elevated temperatures at positive bias in this and earlier studies. The significant latent interface-trap buildup is observed for nMOS devices irradiated at 0 V and annealed at room and elevated temperatures under positive bias, a condition not evaluated in prior work. Results strongly suggest that latent interface-trap buildup is due to H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> diffusion and dissociation at charged or dipolar O vacancies in SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , followed by proton transport to the Si/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> interface and reactions with Si–H complexes. Models that attribute latent interface-trap buildup to long-term proton trapping at O vacancies in SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> appear to be ruled out by these results. Additional insight is provided into mechanisms of postirradiation interface- and border-trap buildup after long-term MOS device storage.

Evidence of Interface Trap Build-Up in Irradiated 14-nm Bulk FinFET Technologies

Total ionizing dose response of 14-nm bulk-Si FinFETs has been studied with a specially designed test chip. The radiation testing shows evidence of interface trap build-up on 14-nm Bulk FinFET technologies. These defects created in the isolation layer give rise to a new radiation-induced leakage path which might lead to a reliability issue in CMOS technologies at or below the 14-nm node. TCAD simulations are performed and an analytical model for TID-induced leakage current is presented to support analysis of the identified TID mechanism. TCAD simulation and analytical model results are consistent with the experimental data.

Temperature-Switching During Irradiation as a Test for ELDRS in Linear Bipolar Devices

A temperature-switching irradiation (TSI) sequence has been developed that is based on a first-principles understanding of interface-trap buildup and annealing. The dynamics of interface-trap buildup and annealing during elevated temperature irradiation are described in detail to provide background, context, and enhanced understanding of the TSI method. The method is shown to be a practical and conservative test for enhanced low-dose-rate sensitivity (ELDRS) in linear bipolar devices and ICs. Examples of TSI sequences are shown for target doses up to 200 krad(Si), a range of great practical interest for space applications. The method can be adapted for higher dose applications via similar approaches. Devices that do not exhibit ELDRS respond similar to TSI and high-dose-rate irradiation.

Hydrogen Soaking, Displacement Damage Effects, and Charge Yield in Gated Lateral Bipolar Junction Transistors

The effects of 70-keV and 1-MeV electron irradiations on gate-controlled lateral PNP (GLPNP) transistors are evaluated with and without molecular hydrogen (H2) soaking. At a given ionization dose, 1-MeV electron irradiation causes more degradation of current gain in GLPNP transistors that have not been soaked in H2 than 70-keV electrons. This is because linear bipolar transistors are sensitive to both ionization and displacement damage effects, and because 1-MeV electrons induce significant displacement damage in Si-based bipolar junction transistors and 70-keV electrons do not. In H2-soaked transistors, the degradation is much larger than in unsoaked devices, and similar amounts of degradation are observed for 70-keV electron irradiation and 1-MeV electron irradiation. This occurs because ionization–induced release, transport, and reactions of hydrogen in the bipolar-base oxide greatly enhance interface-trap buildup and dominate device response in H2-soaked devices, and because charge yield ratios for 70-keV and 1-MeV electron irradiations differ by less than ~20%.

In-Situ Measurement of Total Ionising Dose Induced Changes in Threshold Voltage and Temperature Coefficients of RADFETs

This work presents results of a total ionising dose experiment, during which p-channel RADFETs were irradiated and measured under different gate bias conditions using an in-situ technique. The measurement system allowed threshold voltage shifts and temperature sensitivity of the shift to be measured during irradiation to 60 krad(Si) and the subsequent 55 day period of annealing. The experimental results obtained allow improved insight into temperature sensitivity related problems of RADFET based dosimetry systems for space and terrestrial applications. The results show that the radiation-induced decrease in mobility, caused by the interface trap build-up, has a predominant effect on RADFET temperature coefficients.

Conversion model of radiation-induced interface-trap buildup and the some examples of its application

It is supposed that the rechargeable radiation-induced positive centers in the oxide must have energy levels within the Si forbidden gap. These assumptions served as the basis for the physical model of the interface-trap build-up and enhanced low dose rate sensitivity (ELDRS) in bipolar devices. As examples of using the proposed conversion model is considered for bipolar devices space application.

Activation Energies for Oxide- and Interface-Trap Charge Generation Due to Negative-Bias Temperature Stress of Si-Capped SiGe-pMOSFETs

We investigate negative-bias temperature instabilities in SiGe pMOSFETs with SiO 2/HfO 2 gate dielectrics. The measured activation energies for interface-trap charge buildup during negative-bias temperature stress are lower for SiGe channel pMOSFETs with SiO 2/HfO 2 gate dielectrics and Si capping layers than for conventional Si channel pMOSFETs with SiO 2 gate dielectrics. Electron energy loss spectroscopy and scanning transmission electron microscopy images demonstrate that Ge atoms can diffuse from the SiGe layer into the Si capping layer, which is adjacent to the SiO 2/HfO 2 gate dielectric. Density functional calculations show that these Ge atoms reduce the strength of nearby Si–H bonds and that Ge–H bond energies are still lower, thereby reducing the activation energy for interface-trap generation for the SiGe devices. Activation energies for oxide-trap charge buildup during negative-bias temperature stress are similarly small for SiGe pMOSFETs with SiO 2/HfO 2 gate dielectrics and Si pMOSFETs with SiO 2 gate dielectrics, suggesting that, in both cases, the oxide-trap charge buildup likely is rate-limited by hole tunneling into the near-interfacial SiO 2.

Conversion model of the radiation-induced interface-trap buildup and its hardness assurance application

The model, which confirms that the interaction of trapped positive charges (hydrogenous species) in the oxide and electrons from the substrate is an important component of radiation-induced interface-trap buildup, is presented. The “one-to-Koi” relationship between the number of trapped holes annealed and number of interface-trap generated is used for prediction of MOS device response in space environment. The model of enhanced low dose rate effect (ELDRS) is proposed. ELDRS conversion model is based on the assumption that there are two types of traps: shallow and deep. The time constants of these traps are different and correspond to interface-trap buildup at high dose rates for shallow traps and at low dose rates for deep traps. The possible physical mechanism of ELDRS effect elimination in the silicon-germanium (SiGe) bipolar transistors is described. The original mechanism of interface-trap buildup saturation based on radiation-induced charge neutralization (RICN) effect is presented.

Effects of Proton and X-ray Irradiation on Graphene Field-Effect Transistors with Thin Gate Dielectrics

Charge pumping and drain current-gate voltage ( I D - V G ) measurements are used to investigate degradation and environmental effects in X-ray and proton-irradiated graphene transistors. X-ray irradiation initially degrades mobility due to hole trapping in the oxide, and induces oxygen-related p-type doping that is evident in the increase in ID once trapped holes anneal out; after long times, interface trap buildup dominates device response. Both the drain current and charge pumping current decrease initially after proton irradiation due to displacement damage and dedoping. However, continued degradation indicates further damage to the graphene layer itself, likely from oxygen-related defect creation in the graphene, induced water and gas molecules between the graphene layer and underlying substrate, or some combination of both. These results indicate that the environment can significantly affect the radiation response of graphene devices, and that the long-term response of the device may be quite different from the initial response due to defect creation, charge migration and annealing.

Mechanism of the Saturation of the Radiation Induced Interface Trap Buildup

Ionizing radiation impact leads to degradation of electrical parameters of microelectronic devices. It is necessary to take this fact to account when dealing with microcircuits for space applications and high energy physics. Main physical reason of radiation-induced failures of spaceship and front end electronic equipment is buidup of interface traps at Si-SiO2 interface in semiconductor transistor structures. The original mechanism of interface trap annealing based on radiation induced charge neutralization (RICN) effect is presented. It is supposed that the positive charge of trapped holes in oxide is transformed through electron capture into a new defect (the AD center). The AD centers act as interface traps. The appearance of the A–D+ state leads to the annihilation of the AD center or annealing of interface trap. The annihilation process can be stimulated by radiation induced or substrate electrons. The competitive between accumulation and annihilation processes leads to saturation of the interface trap buildup. The value of density of interface trap in saturation depends on product of interface trap accumulation rate (Kacc)it and constant KAD which is function of thermal velocity, capture cross-section of AD center, generation rate and electron yield of radiation induced electrons. The extraction of these parameters allows explaining a known experimental data. The alternative mechanism of the interface trap saturation connected with the exhaustion of initial interface trap precursors is considered.

The Effects of Proton-Defect Interactions on Radiation-Induced Interface-Trap Formation and Annealing

Interface-trap buildup and annealing are examined as a function of temperature, dose rate, and H2 concentration using a physics-based model. The roles of a number of common oxide defects in radiation-induced interface-trap buildup are evaluated under various conditions. Defects near the interface play a significant role in determining interface-trap buildup by trapping protons as proton concentration and temperature increase.

Mechanisms Separating Time-Dependent and True Dose-Rate Effects in Irradiated Bipolar Oxides

A model for radiation-induced interface-trap buildup distinguishes among the contributions of hydrogen dimerization, electron recombination, and electric field mechanisms, quantitatively explaining time-dependent and true dose rate effects in irradiated bipolar isolation oxides. Hydrogen dimerization is the dominant ELDRS mechanism for devices exposed to medium H2 concentrations (1% per volume), whereas H2 cracking dominates as H2 concentration is increased further. Electron recombination mechanisms contribute at high dose rates ( >; 100 rad(SiO2)/s), but are not the dominant ELDRS mechanism at dose rates lower than 100 rad(SiO2)/s).

Modeling the Effects of Hydrogen on the Mechanisms of Dose Rate Sensitivity

The effects of hydrogen on dose-rate sensitivity are simulated using a one-dimensional (1-D) model that incorporates the physical mechanisms contributing to dose-rate effects in the metal-oxide-semiconductor (MOS) system of gated lateral pnp (GLPNP) bipolar transistors. Calculations show that molecular hydrogen cracking at positively charged defects may be a key reaction relating hydrogen and dose rate response. Comparison to experimental data on bipolar devices is in good agreement with the dose rate calculations of interface trap buildup.

Mechanisms of Interface Trap Buildup and Annealing During Elevated Temperature Irradiation

Both enhanced interface trap buildup and interface trap annealing can occur during elevated temperature irradiation (ETI), depending on the temperature, total dose, and dose rate. In this paper we describe mechanisms that govern the rate-limiting processes of interface trap buildup and annealing during ETI. Hydrogenated oxygen vacancies can facilitate hydrogen dimerization at elevated temperatures. This results in the removal of protons that can create interface traps, so degradation is suppressed. Hydrogen dimerization becomes more competitive with degradation mechanisms as the concentration of protons near the interface increases and/or as temperature increases.

Defect Interactions of ${\hbox{H}}_{2}$ in ${\hbox{SiO}}_{2}$: Implications for ELDRS and Latent Interface Trap Buildup

The energetics of the interactions between molecular hydrogen and common defects in SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> that are typically associated with O deficiency have been obtained using atomic-scale quantum mechanical calculations. H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> does not easily crack at neutral vacancies, but it will crack efficiently at O vacancy sites that have captured a hole and relaxed into the puckered configuration of an E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">γ</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">'</sup> defect, releasing a proton into the oxide. Isolated Si dangling bonds also can play a role in cracking H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , depending on their concentration in the oxides. These results provide significant insight into the underlying causes of latent interface trap buildup in MOS devices and enhanced low-dose-rate sensitivity in linear bipolar devices.

Total ionizing dose effects and annealing behavior for domestic VDMOS devices

Total dose effects and annealing behavior of domestic n-channel VDMOS devices under different bias conditions were investigated. The dependences of typical electrical parameters such as threshold voltage, breakdown voltage, leakage current, and on-state resistance upon total dose were discussed. We also observed the relationships between these parameters and annealing time. The experiment results show that: the threshold voltage negatively shifts with the increasing of total dose and continues to decrease at the beginning of 100 °C annealing; the breakdown voltage under the drain bias voltage has passed through the pre-irradiation threshold voltage during annealing behaving with a “rebound" effect; there is a latent interface-trap buildup (LITB) phenomenon in the VDMOS devices; the leakage current is suppressed; and on-state resistance is almost kept constant during irradiation and annealing. Our experiment results are meaningful and important for further improvements in the design and processing.

Modeling Ionizing Radiation Effects in Solid State Materials and CMOS Devices

A comprehensive model is presented which enables the effects of ionizing radiation on bulk CMOS devices and integrated circuits to be simulated with closed form functions. The model adapts general equations for defect formation in uniform SiO2 films to facilitate analytical calculations of trapped charge and interface trap buildup in structurally irregular and radiation sensitive shallow trench isolation (STI) oxides. A new approach whereby non-uniform defect distributions along the STI sidewall are calculated, integrated into implicit surface potential equations, and ultimately used to model radiation-induced ldquoedgerdquo leakage currents in n-channel MOSFETs is described. The results of the modeling approach are compared to experimental data obtained on 130 nm and 90 nm devices. The features having the greatest impact on the increased radiation tolerance of advanced deep-submicron bulk CMOS technologies are also discussed. These features include increased doping levels along the STI sidewall.