Lingfeng Mao

Determination of the effective mass of ballistic electrons in thin silicon oxides films using tunneling current oscillations

Abstract A new, simple and accurate method is proposed for the determination of the effective electron mass in thin insulator films from the current–voltage characteristics in fields of the ballistic electron emission regime. The effective mass of electrons was evaluated for oxide films of metal-oxide-semiconductor structures. The effective ballistic electron mass near the conduction band edge of silicon dioxide for different structures changes from 0.52 to 0.84m0 and the experimental data show that the value of the effective mass of the ballistic electron can be treated as a constant while the gate voltage changes at least within a certain voltage range.

Numerical analysis for root-mean-square roughness of SiO2/Si interface on direct tunneling current in ultrathin MOSFETs

Abstract Interface roughness effects on direct tunneling current in ultrathin MOSFETs are investigated by numerical analysis. The interface roughness is described in terms of Gauss distribution. It is shown that the effects of rough surface on tunneling current cannot be neglected while tunneling occurs in the regime of direct tunneling. The effects increase exponentially with oxide thickness or applied voltage across oxide decreasing. This means that the effects become more and more important while the direct tunneling current takes up the main contribution to the gate leakage current.

Study of Fowler-Nordheim tunneling current oscillations of thin insulator MOS structure by wave interference method

Abstract In this paper, a novel method – electron waves interference method – is presented to study Fowler–Nordheim tunneling current oscillations. Using this new analysis, the applied voltage V at the extrema of Fowler–Nordheim tunneling oscillations can be accurately and simply determined. A phase shift of π/4 when electron traverses the forbidden band of perfect medium barrier once is observed by using interference method. Some phenomena observed in experiment can be easy to explain by this method. The extrema of oscillations can be used to determine the barrier thickness in metal-oxide-semiconductor device and the average effective electron mass in the conduction band of the barrier. An important feature of this method is that it is applicable to various shapes of potential barriers and wells.

Thickness measurements for ultrathin-film insulator metal–oxide–semiconductor structures using Fowler–Nordheim tunneling current oscillations

An interference method is introduced to analyze tunneling current oscillations, and a fresh way to extrapolate the oxide thickness in ultrathin-film insulator metal–oxide–semiconductor structures by using the oscillations in the Fowler–Nordheim tunneling currents is presented. A comparison between this extrapolation algorithm and a previous algorithm using tunneling current oscillations shows that the new extrapolation algorithm provides a more accurate and convenient solution to a first principles calculation especially for ultrathin oxide. Another important feature of the proposed method is that it can be applied to various shapes of potential barriers and wells.

The double level calculation of oxygen related donor states in Si and SiO2

Abstract A calculation of the levels related to oxygen donors in Si and SiO 2 has been performed based on a helium-like model. These calculations agree well with the experimental data while the energies of these levels are in the ratio of about 2:1 and the effective radii of these levels are in the ratio of about 2:1.

The effect of image potential on electron transmission and electric current in the direct tunneling regime of ultra-thin MOS structures

Abstract The direct tunneling current through ultra-thin gate dielectrics is modeled by calculating the transmission coefficient of an idealized potential barrier that is modified by the image force. A numerical solution to the Schrodinger equation shows that the barrier lowering induced by image-potential affects the tunneling current largely. An analytical expression for the current is obtained within the Wentel–Kramers–Brillouin approximation. The effects of image force on the direct tunneling current are found to increase with the applied voltage across oxide (Vox) and to decrease with the oxide thickness (Tox).

Effect of SiO2/Si interface roughness on gate current

Abstract In many theoretical investigations of the electric-tunnel effect through an ultrathin oxide in metal-oxide-semiconductor (MOS) structure, it is commonly assumed that the oxide is of uniform thickness. One example of nonuniformity in oxides is interface roughness. Interface roughness effects on direct tunneling current in ultrathin MOS structures are investigated theoretically in this article. The roughness at SiO 2 /Si interface is described in terms of Gauss distribution. It is shown that the transmission coefficient increases with root-mean-square (rms) roughness increasing, and the effect of rms roughness on the direct tunneling current decreases with the applied voltage increasing and increases with rms roughness increasing.

Direct tunneling relaxation spectroscopy in ultra-thin gate oxide MOS structures

Abstract For the first time, a difference analysis method has been applied to separate and characterize interface and oxide traps generated in an ultra-thin direct tunneling (DT) gate oxide. It provides a useful tool to study the mechanism of degradation in ultra-thin MOSFET and extract parameters of interface trap and oxide trap, such as the generation/capture cross-section, centroid and density when a large DT is injected through the gate oxide. This method is an extension of oxide trap relaxation spectroscopy (OTRS) technique. It has the advantage of being direct, fast and convenient in the study of MOSFET reliability.

Stress-induced high-field gate leakage current in ultra-thin gate oxide

Abstract A number of groups have reported that the low-field stress-induced leakage current (SILC) in thin oxides increased after the oxides had been subjected to high voltage stresses. In this study, we observed that high-field SILC increased after the oxides had been subjected to high voltage stresses. The experimental results suggest strongly that SILC must be considered at a high-field region, and the dependence of the high-field SILC on the measurement field E ox is proportional to exp (cE ox ) , as compared to the exp (−c/E ox ) , at a low field which was reported by some researchers. The high-field SILC increases and saturates after a long stress time, when the stress time increases, which is similar to the low-field SILC. Using the method of proportional difference operator, the trap generation/capture time constant can be obtained.

Numerical analysis for the effects of SiO2/Si interface roughness on quantum oscillations in ultrathin MOSFETs

Interface roughness effects on quantum oscillations in ultrathin metal-oxide-semiconductor field transistors (MOSFETs) are investigated by numerical analysis. The interface roughness is described in terms of Gauss distribution. Quantum oscillations in ultrathin gate oxides are shown to be little damped by SiO2/Si interface roughness. The applied voltage shift at the extreme of quantum oscillations increases linearly with SiO2/Si interface roughness increasing. This means that this shift may be used to obtain the information about the interface roughness as an inexpensive and simple tool.