Chenjing Lucille Fernando

Physical oxide thickness extraction and verification using quantum mechanical simulation

Physical gate oxide thickness is extracted from TiN gate PMOS and NMOS capacitance voltage measurements using an efficient multi-band Hartree self-consistent Poisson solver. The extracted oxide thicknesses are then used to perform direct tunneling current simulations. Excellent agreement between measured a simulated tunnel current is obtained without the use of adjustable fitting parameters.

An efficient method for the numerical evaluation of resonant states

An efficient technique is presented for numerically evaluating the resonant states of semiconductor heterostructures with an arbitrarily complex potential. It employs the modified quantum transmitting boundary method to couple the boundary conditions into the construction of a non‐Hermitian discrete Hamiltonian matrix. The resonances are the complex‐valued eigenvalues of the corresponding matrix. The boundary terms are energy dependent; therefore the eigenvalue problem is nonlinear. The eigenvalues are located by using a combination of partial‐shift tridiagonal LR algorithm for the initial evaluation of eigenvalues and Newton iteration for refinement of the eigenvalues. For one‐dimensional problems, this technique is efficient and fast enough to be used in an interactive mode, and it has been incorporated into a general‐purpose interactive heterostructure modeling program.

NEMO: general release of a new comprehensive quantum device simulator

Device simulations are essential to explore new device designs, optimize performance, and analyze the underlying physics. Nanoelectronic devices pose a new challenge in this area since conventional drift-diffusion simulators are not applicable, NEMO (NanoElectronic MOdeling) is a new quantum device simulator based on a non-equilibrium Greens function formalism that simulates a wide variety of quantum devices, including RTDs, HEMTs, HBTs, superlattices, and Esaki diodes. Here we announce the general release of NEMO as a national resource freely available to the US scientific community. We present NEMO calculations for InGaAs/AlAs and GaAs/AlAs RTD devices.

Automatic synthesis of equipment recipes from specified wafer-state transitions

Run-to-run and supervisory control algorithms determine the equipment recipe to produce a desired output wafer state given the incoming wafer state and the current equipment model. For simple, low-dimensional equipment models, this problem is not difficult. However, when there are multiple responses for the system and the equipment models are nonlinear, automated synthesis of recipes is complicated by the potential for multiple solutions. While there are standard techniques for handling such inverse problems in general, each of these techniques is optimal only under certain conditions. We present a framework for performing automated synthesis of recipes that integrates database search, local optimization, and global optimization into a consistent methodology that is applicable to a wide range of equipment models and inversion problems in general. The integrated framework imposes quasi-continuity on the extracted recipes, is scalable to systems of high dimensionality, and can be optimized to minimize the expected synthesis time for any given problem. The framework has been implemented in a system that performs statistical optimization of CMOS transistor designs. The integrated framework provides a factor of 16 increase in performance over global optimization and a factor of three increase over exhaustive search and multiple starts of a local optimizer.

Resolution of Resonances in a General Purpose Quantum Device Simulator (NEMO)

Electron transport in quantum devices is governed by discrete quantum states due to electron confinement. A crucial requirement for the modeling of quantum devices is the the numerical identification and resolution of these quantum states. We present an algorithm utilized in our general purpose quantum device simulator (NEMO), where we locate the resonances of the system first and then generate the optimized grid used to integrate over the resonances. We find this algorithm important in the modeling of coherent transport involving ultrafine resonances and crucial for the modeling of incoherent transport.

Writing Research Software in a Large Group for the NEMO Project

The nanoelectronic modeling (NEMO) program is the result of a three-year development effort involving four universities and the former Corporate Research and Development Laboratory of Texas Instruments, now Applied Research Laboratory, Raytheon TI Systems, to create a comprehensive quantum device modeling tool for layered semiconductor structures. Based on the non-equilibrium Green function formalism, it includes the effects of quantum charging, bandstructure and incoherent scattering from alloy disorder, interface roughness, acoustic phonons, and polar optical phonons. NEMO addresses the diverse needs of two different types of users: (i) the engineer/experimentalist who desires a black-box design tool and (ii) the theorist who is interested in a detailed investigation of the physics. A collection of models trade off physical content with speed and memory requirements. Access to this comprehensive theoretical framework is accommodated by a Graphical User Interface (GUI) that facilitates device prototyping and in situ data analysis. We describe a hierarchical software design that allows rapid incorporation of theory enhancements while maintaining a user-friendly GUI, thus satisfying the conflicting criteria of ease of use and ease of development. The theory and GUI modules share data structures that define the device structure, material parameters, and simulation parameters. These data structures may contain general data such as integer and real numbers, option lists, vectors, matrices and the labels for both batch and GUI operation. NEMO generates the corresponding GUI elements at run-time for display and entry of these data structures.

The Effects of Electron Screening Length and Emitter Quasi‐Bound States on the Polar‐Optical Phonon Scattering in Resonant Tunneling Diodes

Polar optical phonon (POP) scattering is one of the dominant scattering mechanisms contributing to the valley current in GaAs and InP based resonant tunneling diodes (RTDs). We systematically explore two model parameters which determine the strength of the POP scattering enhanced valley current: 1. the electron screening length and 2. the length of the emitter electron accumulation region included in the simulation. When emitter quasi-bound states are included in the simulation, reasonable agreements with experiment can be obtained with screening lengths of 15 to 30 nm.

High magnetic field tunneling transport in a double quantum well-triple barrier resonant tunneling diode

We have measured the magnetotransport of double GaAs quantum well-triple AlAs barrier resonant tunneling heterostructures in pulsed magnetic fields up to 48 T, and temperatures down to 0.3 K. The tunneling structure is designed for a near-simultaneous (triple) resonance, under bias, of the quantum well energy levels and the lowest quasi-2D emitter state. The fan chart of the I(V) resonances is more complex than that of a single quantum well since both emitter well and well-well transitions can occur, which can be discriminated by voltage dependence. In addition to transitions corresponding to the emission of an LO phonon, we also observe at high field a transition which may correspond to the absorption of an LO phonon (emitter-well). Shubnikov-de Haas oscillations in the tunnel current of all resonances are observed. At the near-triple resonance, corresponding to a populated 2D well density of ns = 4.5 x 1011 cm-2, a SdH peak (at 0.3 K) is observed at 29 T, assigned to a Landau level filling factor of a z. This peak weakens by 2 K, whereas the integer filling factor peaks are unchanged with temperature.

An application of process synthesis methodology for first-pass fabrication success of high-performance deep-submicron CMOS

This paper describes a methodology to reduce the time and cost of developing deep sub-micron semiconductor manufacturing technology. The methodology consists of following the components: compact models for device performance and reliability, compact models for process modules, and synthesis algorithms that allow the rapid exploration of large design spaces to identify all device and process flow designs that meet the device specifications. This approach is illustrated by applying it to the design of CMOS gate shrinks from 0.35 /spl mu/m to 0.29 /spl mu/m drawn poly gate length. The synthesized devices were manufactured, meeting all performance and reliability requirements in the first silicon run.

Experimentally verified quantum device simulations based on multiband models, Hartree self-consistency, and scattering assisted charging

Accurate predictions of the I-V characteristics of Esaki diodes, resonant tunneling diodes (RTD), and resonant interband tunneling diodes (RITD) require sophisticated models of bandstructure, charging, and scattering. We present direct comparisons of experimental and simulation data based on single, two, and 10 band models and the worlds first calculation of the electrostatic potential obtained self-consistently with scattering-assisted charging. This charge results from the incoherent scattering off of alloy disorder, interface roughness, acoustic phonons and polar-optical phonons.