Sona P. Kumar

Threshold voltage model for small geometry AlGaN/GaN HEMTs based on analytical solution of 3-D Poisson's equation

A simple and accurate analytical model for the threshold voltage of AlGaN/GaN high electron mobility transistor (HEMT) is developed by solving three-dimensional (3-D) Poisson equation to investigate the short channel effects (SCEs) and the narrow width effects present simultaneously in a small geometry device. It has been demonstrated that the proposed model correctly predicts the potential and electric field distribution along the channel. In the proposed model, the effect of important parameters such as the thickness of the barrier layer and its doping on the threshold voltage has also been included. The model is, further, extended to find an expression for the threshold voltage in the sub-micrometer regime. The accuracy of the proposed analytical model is verified by comparing the model results with 3-D device simulations for different gate lengths and widths.

Device linearity and intermodulation distortion comparison of dual material gate and conventional AlGaN/GaN high electron mobility transistor

Abstract In the work proposed, linearity performance of dual material gate (DMG) AlGaN/GaN HEMT has been analyzed and compared with the corresponding performance of Single Material Gate (SMG) AlGaN/GaN HEMT using ATLAS device simulation. Specifically, we investigate the linearity of DMG and conventional AlGaN/GaN HEMT based on the linearity metrics such as gm, g m 2 , g m 3 , VIP2, VIP3, IIP3, IMD3 and 1-dB compression point. The impact of various device parameters on the device linearity such as the channel length, doping and thickness of the barrier and spacer layer, Al mole fraction and the work function difference of the two gate metals has also been investigated. It is observed that a suitably designed DMG AlGaN/GaN HEMT can considerably improve the linearity performance and minimize intermodulation distortion due to reduced drain induced barrier lowering and high-field effect; and a more uniform electric field for applications in 3-G mobile communication and low noise amplifiers.

Performance assessment and sub-threshold analysis of gate material engineered AlGaN/GaN HEMT for enhanced carrier transport efficiency

The present work explores the features of gate material engineered (GME) AlGaN/GaN high electron mobility transistor (HEMT) for enhanced carrier transport efficiency (CTE) and suppressed short channel effects (SCEs) using 2-D sub-threshold analysis and device simulation. The model accurately predicts the channel potential, electric field and sub-threshold current for the conventional and GME HEMT, taking into account the effect of work function difference of the two metal gates. This is verified by comparing the model results with the ATLAS simulation results. Further, simulation study has been extended to reflect the wide range of benefits exhibited by GME HEMT for its on-state and analog performance. The simulation results demonstrate that the GME HEMT exhibits much higher on current, lower conductance and higher transconductance as compared to the conventional HEMT due to improved CTE and reduced SCEs. This in turn has a direct bearing on the device figure of merits (FOMs) such as intrinsic gain, device efficiency and early voltage. Tuning of GME HEMT in terms of the relative lengths of the two metal gates, their work function difference and barrier layer thickness has further been carried out to enhance the drive current, transconductance and the device FOMs illustrating the superior performance of GME HEMT for future high-performance high-speed switching, digital and analog applications.

3-dimensional analytical modeling and simulation of fully depleted AlGaN/GaN modulation doped field effect transistor

We propose a simple and accurate three- dimensional (3-D) analytical model for the threshold voltage of AlGaN/GaN modulation doped field effect transistor (MODFET) taking into account the short channel effects (SCEs) and the narrow width effects (NWEs) present simultaneously in a small geometry device. The model includes the effect of vital parameters such as doping and thickness of the barrier layer on the threshold voltage. The accuracy of the proposed analytical model is verified by comparing the model results with 3-D device simulations. It has been demonstrated that the proposed model correctly predicts the potential, the electric field distribution along the channel and the threshold voltage.

Two-dimensional analytical sub-threshold modeling and simulation of Gate Material Engineered HEMT for enhanced carrier transport Efficiency

A 2- dimensional analytical sub-threshold model for exploring the novel features of AlGaN/GaN gate material engineered (GME) high electron mobility transistor (HEMT) for reduced short channel effects (SCE) and enhanced carrier transport efficiency (CTE) is proposed. The model accurately predicts the channel potential and electric field (EF) of the conventional and GME HEMT structures. In GME HEMT, the gate is made up of two materials and the work function (WF) difference between the two gate materials results in (1) improved CTE (due to a more uniform electric field along the channel) leading to rapid acceleration of charge carriers and (2) diminished SCEs due to a step in the channel potential. The analytical results have been validated by the device simulator ATLAS.

Analytical Modeling and Simulation of Potential and Electric Field Distribution in Dual Material Gate HEMT For Suppressed Short Channel Effects

In this paper, we present a simple 2- dimensional analytical model for exploring the novel features of the dual material gate (DMG) high electron mobility transistor (HEMT) for reduced short channel effects (SCE). The model accurately predicts the channel potential and electric field for single material gate (SMG) and DMG structures. It is seen that the work function difference of the two metal gates leads to a screening effect of the drain potential variation, by the gate near the drain resulting in suppressed drain induced barrier lowering (DIBL) and hot carrier effect. Moreover, carrier transport efficiency improves due to a more uniform electric field along the channel. The model takes into account the effects of the lengths of the two metal gates and their work function difference. The results predicted by the model are compared with those obtained using ATLAS device simulator to verify the accuracy of the proposed model.

Two-dimensional analytical sub-threshold model of Double Gate MOSFET with gate stack

A two-dimensional (2-D) analytical solution of electrostatic potential is derived for lightly doped Double Gate (DG) MOSFET in the sub-threshold region by solving Poissonpsilas equation using the parabolic profile approach. The analytical model evaluates surface potential, threshold voltage, sub-threshold slope and sub-threshold drain current. Further, to improve the gate control and reduce the gate tunneling leakage currents, the device performance of DG MOSFET is investigated by introducing high k-gate dielectric architecture. A two-dimensional (2-D) analytical solution has also been developed for the DG-gate stack MOSFET design and a performance comparison of both the MOSFET designs have been evaluated. Results reveal enhanced device performance in terms of improved gate control, threshold voltage, sub-threshold slope and sub-threshold drain current.

DMG AlGaN/GaN HEMT: A solution to RF and wireless applications for reduced distortion performance

The study thus proves that DMG AlGaN/GaN HEMT is a potential candidate for growing requirement of high linearity and low distortion in the telecommunication industry due to reduced SCEs and a more uniform electric field distribution. The study also shows that the linearity performance improves further on using lower doping and thickness of the barrier layer and increased metal gate workfunction difference; thus presenting DMG AlGaN/GaN HEMT as a promising solution for high performance RF applications.

Gate Material Engineered-Trapizoidal Recessed Channel MOSFET (GME-TRC) for Ultra Large Scale Integration (ULSI)

In this work, the proposed GME-TRC MOSFET structure has been investigated for different negative junction depths (NJD) and different gate metal workfunction difference and its performance improvement over the TRC MOSFET is studied using ATLAS-3D and DEVEDIT-3D. The result clearly depicts that GME-TRC MOSFET exhibits superior performance as compared to TRC MOSFET in terms of threshold voltage roll-off, reduced punchthrough and DIBL; and improved switching speed of the device and current driving capabilities. Thus, the investigated device structure, in addition to providing SCEs suppression and hot carrier effect immunity, enhances the device reliability and performance in terms of the factors discussed earlier.