Non-radiative Multi-phonon Theory Research Articles

Comphy v3.0—A compact-physics framework for modeling charge trapping related reliability phenomena in MOS devices

Charge trapping plays an important role for the reliability of electronic devices and manifests itself in various phenomena like bias temperature instability (BTI), random telegraph noise (RTN), hysteresis or trap-assisted tunneling (TAT). In this work we present Comphy v3.0, an open source physical framework for modeling these effects in a unified fashion using nonradiative multiphonon theory on a one-dimensional device geometry. Here we give an overview about the underlying theory, discuss newly introduced features compared to the original Comphy framework and also review recent advances in reliability physics enabled by these new features. The usefulness of Comphy v3.0 for the reliability community is highlighted by several practical examples including automatic extraction of defect distributions, modeling of TAT in high-κ capacitors and BTI/RTN modeling at cryogenic temperatures.

Charge Trapping and Emission Properties in CAAC-IGZO Transistor: A First-Principles Calculations.

The c-axis aligned crystalline indium-gallium-zinc-oxide field-effect transistor (CAAC-IGZO FET), exhibiting an extremely low off-state leakage current (~10-22 A/μm), has promised to be an ideal candidate for Dynamic Random Access Memory (DRAM) applications. However, the instabilities leaded by the drift of the threshold voltage in various stress seriously affect the device application. To better develop high performance CAAC-IGZO FET for DRAM applications, it's essential to uncover the deep physical process of charge transport mechanism in CAAC-IGZO FET. In this work, by combining the first-principles calculations and nonradiative multiphonon theory, the charge trapping and emission properties in CAAC-IGZO FET have been systematically investigated. It is found that under positive bias stress, hydrogen interstitial in Al2O3 gate dielectric is probable effective electron trap center, which has the transition level (ε (+1/-1) = 0.52 eV) above Fermi level. But it has a high capture barrier about 1.4 eV and low capture rate. Under negative bias stress, oxygen vacancy in Al2O3 gate dielectric and CAAC-IGZO active layer are probable effective electron emission centers whose transition level ε (+2/0) distributed at -0.73~-0.98 eV and 0.69 eV below Fermi level. They have a relatively low emission barrier of about 0.5 eV and 0.25 eV and high emission rate. To overcome the instability in CAAC-IGZO FET, some approaches can be taken to control the hydrogen concentration in Al2O3 dielectric layer and the concentration of the oxygen vacancy. This work can help to understand the mechanisms of instability of CAAC-IGZO transistor caused by the charge capture/emission process.

Comphy — A compact-physics framework for unified modeling of BTI

Metal-oxide-semiconductor (MOS) devices are affected by generation, transformation, and charging of oxide and interface defects. Despite 50 years of research, the defect structures and the generation mechanisms are not fully understood. Most light has been shed onto the charging mechanisms of pre-existing oxide defects by using the non-radiative multi-phonon theory. In this work we present how the gist of physical models for pre-existing oxide defects can be efficiently abstracted at a minimal loss of physical foundation and accuracy. Together with a semi-empirical model for the generation and transformation of defects we establish a reaction-limited framework for unified simulation of bias temperature instabilities (BTI). The applications of the framework we present here cover simulation of BTI for negative (NBTI) and positive (PBTI) gate voltages, life time extrapolation, AC stress with arbitrary signals and duty cycles, and gate stack engineering.

Short Distance Channel Defect Intractions in Graphene Nanoribbon Field Effect Transistors

We have studied theoretically the channel defect interaction and for this we have used correlated nonradiative multiphonon theory in conjunction with the coulomb energy. We have presented the charge capture rate. To calculate the value of coulomb energy we have developed a quantum capacitive circuit considering the effect of the fringing electrical field distributed spatially in the dielectric. The calculated short distance charge capture rate for the channel subbands at room temperature revealed a significant correlation between the capture rate and singularity characteristics of the one dimensional density of states. Charge capture through the nonradiative multiphonon transition is responsible for the shortdistance interactions between the channel carriers and the interfacial dielectric defects that are typically located within a few nanometers of the dielectric channel interface.

Coulomb-energy featured capture kinetics in graphene nanoribbon field-effect transistors

Charges trapped in the gate dielectric and acting as long-range scatterers can have a significant effect on carrier transport in graphene-based nanodevices. In this study, we theoretically investigated the charge capture kinetics of short-distance channel-defect interactions in graphene nanoribbon nanodevices by employing the nonradiative multiphonon theory in conjunction with the Coulomb energy ($\ensuremath{\Delta}E$). The peaks that emerged from the electron capture rate strongly correlated with the singularity characteristics of a one-dimensional (1D) density of states. Furthermore, we elaborate herein on how the value of $\ensuremath{\Delta}E$ plays a decisive role in determining the capture kinetics for the trapping of channel carriers in the interface dielectric defects in 1D nanodevices.

A multi scale modeling approach to non-radiative multi phonon transitions at oxide defects in MOS structures

We discuss a novel approach to predict non-radiative multi phonon (NMP) transition rates for oxide defects in semiconductor devices in the context of device reliability. In accordance with NMP theory, the influence of the atomic vibration on the electronic transition is assumed to be fully described by the line shape function. This line shape is calculated from density functional theory for a given defect structure and then combined with the carrier spectrum from a non-equilibrium Green's function model of the semiconductor device. Hole capture rates at different temperatures and bias conditions are computed for two well-studied defect structures, the oxygen vacancy and the hydrogen bridge, at different positions in the oxide of an MOS structure.

Recent trends in bias temperature instability

Several trends occurring in the past few years in our understanding of bias temperature instability (BTI) are reviewed. Among the most important is the shift toward analyzing BTI relaxation with the tools originally developed for describing low-frequency noise. This includes the interpretation of the time, temperature, voltage, and duty cycle dependences. It is shown that a wealth of information about gate oxide defect properties can be obtained from deeply scaled devices and correctly modeled based on nonradiative multiphonon theory. It is then shown how detailed understanding of individual defect properties can allow interpreting the variability issues of future complementary metal-oxide semiconductor technologies. This is complemented by showing the most promising technological solutions for BTI.