Threshold Voltage Shift Model Research Articles

Threshold voltage shift model for p-GaN gate enhancement mode HEMT

In this paper, we based on the gate structure of p-GaN HEMT connected with Schottky diode and PIN diode and analyzed the threshold voltage shift mechanism under the influence of gate voltage. Based on the carrier transport mechanism, the electron injection current and hole injection current of the p-GaN layer is discussed and calculated, while the gate current model and threshold voltage shift model of the p-GaN HEMT are analyzed. The accuracy of the model is verified by comparing with the experimental data. The effects of p-GaN doping concentration, AlGaN barrier layer thickness and Al component on the gate current and VTH shift are discussed based on the model. By optimizing the device structure and process parameters, the gate current of HEMT can be reduced and the stability of VTH can be improved.

Quantitative Analysis of Positive-Bias-Stress-Induced Electron Trapping in the Gate Insulator in the Self-Aligned Top Gate Coplanar Indium–Gallium–Zinc Oxide Thin-Film Transistors

We experimentally extracted the positive bias temperature stress (PBTS)-induced trapped electron distribution within the gate dielectric in self-aligned top-gate (SA-TG) coplanar indium–gallium–zinc oxide (IGZO) thin-film transistors (TFTs) using the analytical threshold voltage shift model. First, we carefully examined the effects of PBTS on the subgap density of states in IGZO TFTs to exclude the effects of defect creation on the threshold voltage shift due to PBTS. We assumed that the accumulated electrons were injected into the gate dielectric trap states near the interface through trap-assisted tunneling and were consequently moved to the trap states, which were located further away from the interface, through the Poole–Frenkel effect. Accordingly, we quantitatively analyzed the PBTS-induced electron trapping. The experimental results showed that, in the fabricated IGZO TFTs, the electrons were trapped in the shallow and deep trap states simultaneously owing to PBTS. Electrons trapped in the shallow state were easily detrapped after PBTS termination; however, those trapped in the deep state were not. We successfully extracted the PBTS-induced trapped electron data within the gate dielectric in the fabricated SA-TG coplanar IGZO TFTs by using the proposed method.

Multi-Coding ECC Algorithm Based on 3D Charge Trap NAND Flash Hot Region Cell Prediction

In this letter, threshold voltage shift model based on 3D Charge Trap NAND flash channel characteristics is built for analyzing the distribution shift and error source of algorithms at different storage time. Multi-Coding BCH based on Hot Region (MC-HR-BCH) is a scheme consists of 3 algorithms. It offers good correction capability (130 to 144 errors per 1276 bytes) based on BCH(n = 9200, k = 8192, t = 72). With the help of MC-HR-BCH, the diversity of data in storage time is well handled.

A Threshold Voltage Model for Charge Trapping Effect of AlGaN/GaN HEMTs

In this paper, a threshold voltage model for charge trapping effect of AlGaN/GaN HEMTs is proposed. The quiescent bias stresses are considered for well modeling the current collapse critical points in pulsed I-V curves. Moreover, the low-frequency dispersions due to the charge trapping effect are well disposed by using the proposed model, which are validated by the scattering parameters (S-parameters). Also, a trapping related parameter α is proposed in the model, which can be conveniently used to describe the current collapse critical points offset due to the different acceptor energy levels of the dopants in GaN buffer. Different from our previous threshold voltage model, the proposed model in this paper can accurately model the dynamic threshold voltage shift due to the fast capture and slow emission processes. The verifications are carried out by comparing with the transient measured drain current. The proposed model is also implemented into a large-signal model for further verifications. The improved large-signal model with the threshold voltage shift model is verified by 0.25 μm process AlGaN/GaN HEMTs with pulsed I-V, S-parameters, power sweep and load-pull measurements. More accurate agreements between measured and modeled results have been achieved in terms of output power (Pout), gain and power added efficiency (PAE).

Threshold-voltage shift model based on electron tunneling under positive gate bias stress for amorphous InGaZnO thin-film transistors

An analytical threshold-voltage (Vth) shift model of amorphous InGaZnO thin-film transistors (a-IGZO TFTs) under positive gate bias stress (PGBS) is reported in this paper. It is demonstrated that electrons in active layers of a-IGZO TFTs can tunnel into gate insulators when PGBS is applied, and a portion of the tunneled electrons would tunnel back. The transfer distance of the tunneled electrons and the time-dependent electron distribution in gate insulators are analyzed with the back-tunneling effect taken into consideration. Finally the Vth shift under PGBS is predicted and the influences of gate voltage and stress time are discussed. The calculated Vth shift under PGBS shows good consistency with the reported experimental data.

A model for threshold voltage shift under negative gate bias stress in amorphous InGaZnO thin film transistors

In the amorphous InGaZnO thin film transistors (a-IGZO TFTs) with high concentration of oxygen vacancy, the energy level of oxygen vacancy-related donor-like states in a-IGZO films near the gate insulator moves upwards under the negative gate bias stress (NGBS). The electrons in the donor-like states above the midgap are emitted to the conduction band, making the donor-like states positively charged. These positively charged donor-like states accumulate near the interface of the a-IGZO films and gate insulator and screen the gate voltage, thus leading to the negative shift of the threshold voltage (V th ) of a-IGZO TFTs. In this article we establish a physical model of V th shift in the negative direction under NGBS, and the results are consistent with the experimental results.

Study of structure of Si QDs memory with double barrier and its programming mechanism

SiC x thin films with silicon quantum dots(QDs) were prepared by plasma enhanced chemical vapor deposition (PECVD) and thermal annealing. Transmission electron microscopy (TEM) observation shows that a large number of silicon QDs growing in SiC x films. Memory structure with double barrier which consist of SiC x thin films embedded in silicon QDs were prepared. TEM observations shows that the above process successfully prepared Si 3 N 4 /SiC x /Si-QDs/SiC x /SiO 2 double-barrier memory structure. The programming mechanism of double-barrier silicon quantum dot memory was analyzed theoretically in consideration of coulomb blockade effects and quantum confinement effect of silicon quantum QDs. The threshold voltage shift model of double-barrier structure was established. Simulation of that mode shows that threshold voltage shift of double barrier memory is larger than a single barrier memory and double-barrier memory programming faster too. C - V characteristic tests of storage structure shows that double-barrier structure has good storage carrier storage effect, getting about 10 V's the storage window when the scan voltage is ±12 V.

AIM-Spice Integration of a Recursive Model for Threshold Voltage Shift in Thin Film Transistors

Non-crystalline semiconductor based thin film transistors are the building blocks of large area electronic systems. These devices experience a threshold voltage shift with time due to prolonged gate bias stress. In this paper we integrate a recursive model for threshold voltage shift with the open source BSIM4V4 model of AIM-Spice. This creates a tool for circuit simulation for TFTs. We demonstrate the integrity of the model using several test cases including display driver circuits.

An analytic model for threshold voltage shift due to quantum confinement in surrounding gate MOSFETs with anisotropic effective mass

Threshold voltage shift due to quantum confinement in surrounding gate MOSFETs with anisotropic effective mass is calculated from the solution of 2D Schrödinger equation in elliptic coordinates. The solutions are of the Mathieu function type. It is shown that for some intermediate range of radius in silicon, several subbands need be taken into account to obtain accurate threshold voltage shifts. However, for small radius, only the lowest subband need be considered, and even anisotropic effective mass can be replaced by reduced isotropic effective mass, for which Bessel function is sufficient.

Surface layer effective density-of-states (SLEDOS) and its applications in MOS devices modeling

The concept of surface potential effective density-of-states (SLEDOS) is presented in modeling the quantized inversion layer. Carrier distribution models both in semi-classical and quantum mechanical cases are developed based on SLEDOS. Threshold voltage shift model due to QMEs, a new iteration method to calculate the inversion carrier sheet density and surface potential, as well as a gate capacitance model are built based on the concept of SLEDOS. It is demonstrated that the concept of SLEDOS reveals the physical nature of inversion layer quantization and provides a feasible method to characterize MOS inversion layer.

Analytical model for threshold voltage shift due to impurity penetration through a thin gate oxide

We derived an analytical model for the threshold voltage shift due to impurity penetration through gate oxide and evaluated the thermal budget for pMOS devices with a thin gate oxide. The threshold voltage shift decreases as the channel doping concentration increases, but the decrease is quite small. The allowable surface concentration of the penetrated impurity increases as the gate oxide thickness decreases if the allowable threshold voltage shift is constant. Therefore, the allowable diffusion length normalized by the gate oxide thickness d/sub ox/ increases with decreasing d/sub ox/.

Prediction method for total dose effects on complementary metal oxide semiconductor integrated circuits using impulse response model for threshold voltage shift.

A method is described to predict radiation hardness of general purpose CMOS logic ICs.The method uses an impulse response model for radiation-induced threshold voltage shift of an selected from an IC family. The total dose degradation on ICs can be predicted at any dose rate by simulations using the impulse response model of the threshold voltage shift and their circuit structure data. This method was applied to the prediction of radiation degradation of CMOS logic ICs of HD74HC series, in which an inverter HD74HC04 was selected as the elemental IC. Four inverter samples were irradiated up to 100 Gy (Si) and then annealed to examine the impulse response of the threshold voltage shift of their n- and P-channel MOSFETs. Results predicted by this method represented the static characteristic degradation of the HD74HC04 irradiated up to a large total dose 1 kGy (Si) at two different dose rates 8 and 500 Gy (Si) /h.

Prediction of Total Dose Effects on Sub-Micron Process Metal Oxide Semiconductor Devices.

A method for correcting leakage currents is described to predict the radiation-induced threshold voltage shift of sub-micron MOSFETs. A practical model for predicting the leakage current generated by irradiation is also given on the basis of experimental results on 0.8-μm process MOSFETs. The constants in the threshold voltage shift model are determined from the “true” I-V characteristic of the MOSFET, which is obtained by correction of leakage currents due to characteristic change of a parasitic transistor. In this way, the threshold voltage shift of the n-channel MOSFET irradiated at a low dose rate of 2 Gy(Si)/h was also calculated by using data from a high dose rate irradiation experiment (100 Gy (Si)/h, 5h). The calculated result well represented the tendency of measured data on threshold voltage shift. The radiation-induced leakage current was considered to decay approximately in two exponential modes. The constants in this leakage current model were determined from the above high dose rate experime...