Kenji Komiya

Transport characteristics of posthard breakdown thin silicon oxide films and consideration of physical models

This article describes the constant-voltage-stress-induced breakdown of thin silicon oxide films, as well as the conduction mechanisms of posthard breakdown oxide films which are characterized by means of the differential resistance technique involving posthard breakdown current and spectral analyses of posthard breakdown current fluctuation. A very thin oxide film still shows a high differential resistance just after the first hard breakdown event; additional current stress pushes the film into the final state. On the other hand, a thicker oxide film enters the final state (breakdown) after the first hard breakdown event. It is also shown that there still exists an energy barrier for electrons after the hard breakdown event as already reported. However, it is also shown that the energy barrier places an asymmetric restriction on electron flow in contrast to the past symmetric assumption. Current fluctuation of posthard breakdown oxide films is characterized in detail. Short-time and long-time observation...

Off-leakage and drive current characteristics of sub-100-nm SOI MOSFETs and impact of quantum tunnel current

This paper estimates the off-leakage current (I/sub off/) and drive current (I/sub on/) of various SOI MOSFETs by simulations based on the hydrodynamic-transport model; the band-to-band tunneling (BBT) effect at the drain is taken into consideration. Here, the simulations are done for SOI structures with a thick channel where the distinct quantization of energy is irrelevant to the present results. It is shown that merging hydrodynamic transport with the BBT effect is indispensable if realistic I/sub off/ estimates are to be achieved. It is shown that the symmetric double-gate SOI MOSFET does not always offer better drivability than other SOI MOSFETs, and that a single-gate SOI MOSFET with carefully selected parameters exhibits superior performance to double-gate SOI MOSFETs. It is also demonstrated that the quantum tunnel current is not significant, even in 20-nm channel SOI MOSFETs. The results suggest that we can still employ the conventional semi-classical method to estimate the off-leakage current of sub-100-nm channel low-power SOI MOSFETs.

Spectroscopic characterization of stress-induced leakage current in sub 5-nm-thick silicon oxide film

This article proposes a spectroscopic characterization technique for examining the stress-induced leakage current in sub 5-nm-thick silicon oxide films. The fluctuation power of stress-induced leakage currents suggests that defects have a single, dominant energy level. Monte Carlo simulations are carried out to verify the defect model and stress-induced leakage current characteristics. It is clearly demonstrated using simulations and spectroscopic analyses that the stress-dependent magnitude of the leakage current is characterized by defect location and defect energy level. Defect distribution is extracted from stress-induced leakage current characteristics based on a physics-based practical defect model; the defect distribution differs from past predictions. It is also identified from simulations that defect regions, which contribute to the stress-induced leakage current observed at high gate voltages, exist mainly at a depth of about 1.2 nm from the SiO2/Si substrate interface with the distribution widt...

Possible influence of the Schottky contacts on the characteristics of ultrathin SOI pseudo-MOS transistors

The paper describes the impact of pseudo-MOS technique on threshold and flatband voltages, and why the threshold and flatband voltages depend on silicon-on-insulator (SOI) layer thickness. Our measurements and simulations suggest that the band-offset-induced depletion beneath the source contact obstructs the local formation of the inversion layer at the SOI/buried oxide interface; this effect becomes significant when the SOI layer thickness is reduced. The SOI layer thickness dependence of flatband voltage is analyzed in a similar manner. The temperature dependence of threshold and flatband voltages is also addressed.

Physics-based analytical model of quantum-mechanical electron wave function penetration into thin dielectric films and capacitance evaluation

We propose an analytical expression of the electron distribution function inside silicon and SiO2 films under the surface-accumulation condition, to simulate the capacitance of a metal–oxide–semiconductor system. We assume a three-dimensional electron gas system and discuss the penetration of the electron wave function into SiO2 or high-k material films. It is demonstrated that the penetration of the wave function into the insulator film slightly influences the capacitance-voltage characteristics. It is also demonstrated that the penetration of the wave function into high-k materials is deeper than that into SiO2 film for identical equivalent oxide thickness (EOT).

Impact of high-k plug on self-heating effects of SOI MOSFETs

A novel SOI device structure that suppresses self-heating effects is proposed. Since it provides effective thermal paths from source to substrate and from drain to substrate, it successfully suppresses the lattice temperature rise throughout the whole device. Since the buried insulator is SiO/sub 2/, it is almost free from the fabrication issues and performance issues in use of high-k material such as high internal charge density, high interface trap density, and drain-induced barrier lowering; the proposed device structure will be easy to fabricate using current trench isolation techniques.

Simulation models for silicon-on-insulator tunneling-barrier-junction metal-oxide-semiconductor field-effect transistor and performance perspective

In this paper, we describe the operation characteristics of a silicon-on-insulator (SOI) tunneling-barrier-junction (TBJ) metal–oxide–semiconductor field-effect transistor (MOSFET) and simulation methods with the aid of the commercial two-dimensional (2-D) device simulator. No scattering (ballistic transport) is assumed in the electron conduction. It is shown that the device exhibits current-voltage characteristics similar to those of the conventional MOSFET. The subthreshold swing and off-leakage current of the device are much smaller than those of modern MOSFETs; short-channel effects are sufficiently suppressed. However, the drive current of TBJ MOSFET is smaller than that of the conventional MOSFET. In order to increase the drive current, the optimization method for the device structure of TBJ MOSFET is discussed in detail.

Spectroscopic analysis of stress-induced defects in thin silicon oxide films

Abstract This paper describes a significant feature of stress-induced defects on the basis of the steady state SILC component and transient characteristics. Fourier transformation of the discharging current strongly suggests, in contrast to past results, that most defects share virtually the same energy level. Assuming that the defect level is 2.1 eV below the SiO 2 conduction band bottom, simple Monte Carlo simulations show the defects lie 1.2 nm from the substrate.

Low‐Frequency Current Fluctuations in Post‐Hard Breakdown Thin Silicon Oxide Films

This paper focuses on the current fluctuation of post‐hard breakdown thin silicon oxide films with thickness ranging from 3 nm to 5 nm. We characterize the post‐degraded structure of silicon oxide films by analyzing current fluctuation spectra after hard breakdown.

Physics-based analytical model of quantum-mechanical electron wave function penetration into thin dielectric films for capacitance evaluation

Recently, quantum-mechanical (QM) effects in MOSFETs have been studied extensively to overcome predicted performance limitation as stated in G. Timp et al. (1999) and A. Pacelli et al. (1999). In MOS structures with a thin gate SiO/sub 2/ film, the dark-space near the Si/SiO/sub 2/ interface influences capacitance-voltage (C-V) characteristics as presented in A. Shimizu et al. (2001). In addition, it is reported that the electron penetration influences C-V characteristics in case of high impurity density based in S. Mudanai et al. (2001). So, simulations should consider several QM effects. Unfortunately, generally speaking, recent numerical calculations including quantum effects spend a long time to get results. In this paper, we derive exact analytical equations or more precise approximation for electron distribution functions. We examine applicability of proposed expressions to C-V analysis.