arXiv subjects

Imtiaz Ahmed

Publications and source records attributed to Imtiaz Ahmed.

61 records · Page 4Linked to original sources

arXiv2018

Radio-frequency capacitive gate-based sensing

Developing fast, accurate and scalable techniques for quantum state readout is an active area in semiconductor-based quantum computing. Here, we present results on dispersive sensing of silicon corner state quantum dots coupled to lumped-element electrical resonators via the gate. The gate capacitance of the quantum device is configured in parallel with a superconducting spiral inductor resulting in resonators with loaded Q-factors in the 400-800 range. For a resonator operating at 330 MHz, we achieve a charge sensitivity of 7.7 $μ$e$/\sqrt{\text{Hz}}$ and, when operating at 616 MHz, we get 1.3 $μ$e$/\sqrt{\text{Hz}}$. We perform a parametric study of the resonator to reveal its optimal operation points and perform a circuit analysis to determine the best resonator design. The results place gate-based sensing at par with the best reported radio-frequency single-electron transistor sensitivities while providing a fast and compact method for quantum state readout.

physics.app-ph↗

arXiv2014

A Physically Based Analytical Model to Predict Quantized Eigen Energies and Wave Functions Incorporating Penetration Effect

We propose a physically based analytical compact model to calculate Eigen energies and Wave functions which incorporates penetration effect. The model is applicable for a quantum well structure that frequently appears in modern nano-scale devices. This model is equally applicable for both silicon and III-V devices. Unlike other models already available in the literature, our model can accurately predict all the eigen energies without the inclusion of any fitting parameters. The validity of our model has been checked with numerical simulations and the results show significantly better agreement compared to the available methods.

physics.gen-ph↗

arXiv2012

Self Consistent Simulation of C-V Characterization and Ballistic Performance of Double Gate SOI Flexible-FET Incorporating QM Effects

Capacitance-Voltage (C-V) & Ballistic Current- Voltage (I-V) characteristics of Double Gate (DG) Silicon-on- Insulator (SOI) Flexible FETs having sub 35nm dimensions are obtained by self-consistent method using coupled Schrodinger- Poisson solver taking into account the quantum mechanical effects. Although, ATLAS simulations to determine current and other short channel effects in this device have been demonstrated in recent literature, C-V & Ballistic I-V characterizations by using self-consistent method are yet to be reported. C-V characteristic of this device is investigated here with the variation of bottom gate voltage. The depletion to accumulation transition point (i.e. Threshold voltage) of the C-V curve should shift in the positive direction when the bottom gate is negatively biased and our simulation results validate this phenomenon. Ballistic performance of this device has also been studied with the variation of top gate voltage.

physics.gen-ph↗

arXiv2012

Self-Consistent C-V Characterization of Depletion Mode Buried Channel InGaAs/InAs Quantum Well FET Incorporating Strain Effects

We investigated Capacitance-Voltage (C-V) characteristics of the Depletion Mode Buried Channel InGaAs/InAs Quantum Well FET by using Self-Consistent method incorporating Quantum Mechanical (QM) effects. Though the experimental results of C-V for enhancement type device is available in recent literature, a complete characterization of electrostatic property of depletion type Buried Channel Quantum Well FET (QWFET) structure is yet to be done. C-V characteristics of the device is studied with the variation of three important process parameters: Indium (In) composition, gate dielectric and oxide thickness. We observed that inversion capacitance and ballistic current tend to increase with the increase in Indium (In) content in InGaAs barrier layer.

physics.gen-ph↗

arXiv2012

In_xGa_{1-x}Sb MOSFET: Performance Analysis by Self Consistent CV Characterization and Direct Tunneling Gate Leakage Current

In this paper, Capacitance-Voltage (C-V) characteristics and direct tunneling (DT) gate leakage current of antimonide based surface channel MOSFET were investigated. Self-consistent method was applied by solving coupled Schrödinger-Poisson equation taking wave function penetration and strain effects into account. Experimental I-V and gate leakage characteristic for p-channel InxGa1-xSb MOSFETs are available in recent literature. However, a self- consistent simulation of C-V characterization and direct tunneling gate leakage current is yet to be done for both n- channel and p-channel InxGa1-xSb surface channel MOSFETs. We studied the variation of C-V characteristics and gate leakage current with some important process parameters like oxide thickness, channel composition, channel thickness and temperature for n-channel MOSFET in this work. Device performance should improve as compressive strain increases in channel. Our simulation results validate this phenomenon as ballistic current increases and gate leakage current decreases with the increase in compressive strain. We also compared the device performance by replacing InxGa1-xSb with InxGa1-xAs in channel of the structure. Simulation results show that performance is much better with this replacement.

cond-mat.mtrl-sci↗

arXiv2012

A Physically Based Analytical Modeling of Threshold Voltage Control for Fully-Depleted SOI Double Gate NMOS-PMOS Flexible-FET

In this work, we propose an explicit analytical equation to show the variation of top gate threshold voltage with respect to the JFET bottom gate voltage for a Flexible Threshold Voltage Field Effect Transistor (Flexible-FET) by solving 2-D Poisson's equation with appropriate boundary conditions, incorporating Young's parabolic approximation. The proposed model illustrates excellent match with the experimental results for both n-channel and p-channel 180nm Flexible-FETs. Threshold voltage variation with several important device parameters (oxide and silicon channel thickness, doping concentration) is observed which yields qualitative matching with results obtained from SILVACO simulations.

cond-mat.mtrl-sci↗

arXiv2012

Power Allocation for Conventional and Buffer-Aided Link Adaptive Relaying Systems with Energy Harvesting Nodes

Energy harvesting (EH) nodes can play an important role in cooperative communication systems which do not have a continuous power supply. In this paper, we consider the optimization of conventional and buffer-aided link adaptive EH relaying systems, where an EH source communicates with the destination via an EH decode-and-forward relay. In conventional relaying, source and relay transmit signals in consecutive time slots whereas in buffer-aided link adaptive relaying, the state of the source-relay and relay-destination channels determines whether the source or the relay is selected for transmission. Our objective is to maximize the system throughput over a finite number of transmission time slots for both relaying protocols. In case of conventional relaying, we propose an offline and several online joint source and relay transmit power allocation schemes. For offline power allocation, we formulate an optimization problem which can be solved optimally. For the online case, we propose a dynamic programming (DP) approach to compute the optimal online transmit power. To alleviate the complexity inherent to DP, we also propose several suboptimal online power allocation schemes. For buffer-aided link adaptive relaying, we show that the joint offline optimization of the source and relay transmit powers along with the link selection results in a mixed integer non-linear program which we solve optimally using the spatial branch-and-bound method. We also propose an efficient online power allocation scheme and a naive online power allocation scheme for buffer-aided link adaptive relaying. Our results show that link adaptive relaying provides performance improvement over conventional relaying at the expense of a higher computational complexity.

cs.IT↗