Effects Of Oxide Charges Research Articles

An analytical interpretation of the memory window in ferroelectric field-effect transistors

In this study, we present an analytical equation for describing the memory window of ferroelectric field-effect transistors (FeFETs). The analytical equation is derived based on the effect of oxide charge on the threshold voltage shift of the field-effect transistor and can be expressed by simpler parameters, such as the quantity of polarization switching and trapped charge. We demonstrate that the derived equation is in quantitative agreement with the results of the numerical calculations using a technology computer-aided design simulation tool, which confirms the validity of the equation. Our results show that the analytical equations provide an accurate and practical description of the memory window for FeFETs with various structures.

The effect of interface trapped charge on threshold voltage shift estimation for gamma irradiated MOS device

The ionizing radiation affects the silicon-based electronic devices and leads to the build-up of trapped hole in the oxide and an increase in trap density at the Si–SiO2 interface. These defects cause degradation of device parameters such as threshold voltage shifts, sub-threshold swing and etc. Although the effect of oxide charges on the threshold voltage shift in MOS devices is dominant, accurate estimation requires for modeling of the interface trapped charge effect. In this work, the effect of interface trapped charge on threshold voltage shift in an N-channel MOS transistor device, irradiated at different total ionization doses, was estimated considering proton transport model in gate oxide. The analytical model calculations consider the time dependent buildup of trapped holes and interface trap charges. Furthermore, we used ATLAS as a numerical semiconductor simulation code which only allows modeling oxide trapped charge to calculate the variation of threshold voltage shift with TID without considering the interface trap. Computational results were compared with experimental results at several doses and gate biases. According to the experimental results, ATLAS overestimates threshold voltage shift within 30% approximately. The results based on considering proton transport mechanism in analytical model, showed significantly better agreement with experimental results for total dose level up to 2.87 krad at several different biases. Overall results indicated that considering interface trap charges modeling, substantially improves the accuracy of the threshold voltage shift estimation.

Analytical model for proton radiation effects in bipolar devices

The input bias current response of LM124 operational amplifiers to proton irradiation is shown to correlate with the response of identical part types exposed to neutrons and, subsequently, irradiated with X-rays. Moreover, the bias current responses to proton and combined neutron/X-ray exposures are more sublinear than the sum of neutron and X-ray radiation responses measured independently. These data indicate that the ionization defects introduced by proton irradiation moderate the effects of proton-induced displacement damage in the critical bipolar transistors within the LM124. An analytical model is presented that characterizes the various mechanisms of proton radiation effects in bipolar transistors, including the combined effects of oxide charge and bulk traps on carrier recombination. Prototype transistor responses simulated using the model show good correlation with the sublinear characteristics observed in the experimental data. Furthermore, the model is used to assess whether a bipolar junction transistor (BJT), designed with specific structural characteristics and operating in a proton-rich environment, will suffer the most degradation from damage caused by bulk displacement, ionization damage, or a combination of both.

Three-dimensional simulation of discrete oxide charge effects in 0.1 μm MOSFETs

The threshold voltage fluctuation caused by random distribution of discrete oxide charges is studied using three-dimensional (3D) simulations. It is found that the effect of discrete oxide charges on the terminal current variation depends on their lateral positions in the channel and, for the same number fluctuations of discrete charges, a large threshold voltage fluctuation is introduced in a device with deeper source/drain junction depth (Xj). The effect of 3D current flow is found to give negligible effect on the threshold voltage fluctuation. Finally, the effects of oxide charges and dopants on the threshold voltage fluctuation are compared.

A comprehensive study of hot carrier stress-induced drain leakage current degradation in thin-oxide n-MOSFETs

The mechanisms and characteristics of hot carrier stress-induced drain leakage current degradation in thin-oxide n-MOSFETs are investigated. Both interface trap and oxide charge effects are analyzed. Various drain leakage current components at zero V/sub gs/ such as drain-to source subthreshold leakage, band-to-band tunneling current, and interface trap-induced leakage are taken into account. The trap-assisted drain leakage mechanisms include charge sequential tunneling current, thermionic-field emission current, and Shockley-Read-Hall generation current. The dependence of drain leakage current on supply voltage, temperature, and oxide thickness is characterized. Our result shows that the trap-assisted leakage may become a dominant drain leakage mechanism as supply voltage is reduced. In addition, a strong oxide thickness dependence of drain leakage degradation is observed. In ultra-thin gate oxide (30 /spl Aring/) n-MOSFETs, drain leakage current degradation is attributed mostly to interface trap creation, while in thicker oxide (53 /spl Aring/) devices, the drain leakage current exhibits two-stage degradation, a power law degradation rate in the initial stage due to interface trap generation, followed by an accelerated degradation rate in the second stage caused by oxide charge creation.

1/f noise in hot-carrier damaged MOSFET's: effects of oxide charge and interface traps

The 1/f noise in the drain current of hot-carrier damaged MOSFETs biased in weak inversion has been studied. By the use of a biased annealing treatment to simultaneously decrease the density of oxide trapped charge (N/sub ot/) and increase the density of interface traps (D/sub it/), the authors have separated the contributions of these two kinds of defects. The results clearly indicate that, while the low-frequency 1/f noise is correlated with N/sub ot/, the high-frequency 1/f noise is correlated with D/sub it/. >

Time dependence of p-MOSFET hot-carrier degradation measured and interpreted consistently over ten orders of magnitude

Hot-carrier degradation is measured and analyzed over ten orders of magnitude in time for three buried-channel p-MOSFET types with different oxide thicknesses. The effects of oxide charge and interface states are separated by using the charge-pumping technique. Two dominating effects are sufficient to account for the degradation. For worst case degradation, negative oxide charge and interface states are generated by electrons near the drain. This charge is distributed homogeneously over the oxide thickness and it attracts an inversion layer that extends the drain and reduces the effective transistor length logarithmically in time. Simultaneously, this inversion layer prevents substantial degradation related to the interface states, since it masks their effects. A simple model for the logarithmic time dependence is presented. At more negative gate voltages, holes cause interface states that reduce the transconductance with a power-law time dependence, comparable to the worst case n-MOSFET degradation. >

The effect of oxide charges at LOCOS isolation edges on oxide breakdown

The degradation of time dependent dielectric breakdown (TDDB) characteristics at LOCOS isolation edges has been studied using MOS capacitors with and without field oxide edges under gate electrodes. The wear-out mode was shifted toward shorter breakdown time by field oxide etching right after the conventional LOCOS process. An increase in leakage current was observed at the isolation edge, so that the current enhancement is regarded as one of the main causes of the degradation. The current was reduced by constant current stress, suggesting the neutralization of positive charges due to electron trapping. The authors attribute the current enhancement causing the degradation to the buildup of positive charges at the isolation edges. Carrier injection before TDDB tests was found to improve the degradation of the wear-out mode.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Interface and oxide charge effects on DMOS channel mobility

The channel mobility in n-channel DMOS power transistors was examined as a function of interface- and oxide-trappedcharge densities. Interface trapped charge was the primary contributor to mobility degradation. Any apparent dependence of mobility on oxide-trapped-charge density can be attributed to correlation between interface-and oxide-trapped-charge densities.

A Simple Model for Separating Interface and Oxide Charge Effects in MOS Device Characteristics

A simple model to describe radiation effects on MOSFET electrical characteristics is presented. The key assumption is that mobility degradation in an enhancement mode MOSFET is predominantly due to charged interface traps. Model predictions are compared with measured values of interface trap density and device I - V curves.

Effect of oxidation-induced positive charges on the kinetics of silicon oxidation

The oxidation kinetics of silicon is investigated using two-step oxidation in dry O 2. It is found that in an initial state of second oxidation the growth rate of the oxide is different from the oxide's equilibrium growth rate and that the difference in these growth rates is due to the difference in the linear growth rates in these two stages. To explain the difference in the growth rates at the two stages, a model which accounts for the effect of oxide charges on the kinetics of the oxidation of Si is presented. In this model, negatively-charged oxidant species are prevented from reaching the Si/SiO 2 interface by the oxide field near the interface caused by the positive charges generated by the oxidation.

Intersubband spectroscopy of inversion layers in the principal surfaces of silicon: Many-body and “impurity” effects

Frequency domain studies of intersubband transitions have been carried out with a FIR Fourier Transform Spectrometer. The experimental techniques have been applied to several studies including subband spectroscopy in (100) and vicinal planes, and in (111) and (110) inersion layers as well as the effects of oxide charge on the optical properties of (100) inversion layers.