LATTE

LAboratory for Terascale and Terahertz Electronics (LATTE)

P.I. Roger Lake

Members
Khairul Alam
Nick Bruque
Rajeev Pandey
Yun Zheng

Former Members
Cristian Rivas
Tao Gong
Junjie Yang

LATTE Group Summer 04.

Nick's summer project. Building the
LATTE Beowulf cluster.

Chemical and Biological Self-Synthesis of Molecular Integrated Circuits

Integration is a critical problem facing molecular electronics. Discrete molecular and CNT FETs have been demonstrated placing us at the circa 1940s transistor develop stage. We now need a "Jack Kilby" for inventing an integration process for molceular electronics. We are pursuing an approach of chemical and biological self-synthesis for molecular electronics using technology from biosensing and NEMS. Our group is modeling the electronic properties of the materials and devices. We use the nonequilibrium Green function formalism with a variety of models ranging from the pi-bond model, to empirical sp3d5s*, to DFT, to ab-initio quantum chemistry.

Functionalized
CNT

QD RTD / SET with
base or gate contact

Inverter

MARCO Focus Center on Nano Materials (FENA)

Pror Art (from C. Ozkan)

QD functionalized with metalized single strand oligos.

3D Atomistic Modeling of Si/SiGe Nanostructures

The scaling and miniaturization of CMOS has continued unabated, overcoming perceived technical obstacles ahead of schedule. It now appears that tunneling, the finite, countable number of electrons, and the random statistical fluctuations of dopants and alloys determine the ultimate limits of this trend. Modeling software should be developed now that can address the physics associated with Si-based device sizes at the ultimate quantum limit and to investigate nano-device concepts beyond traditional CMOS. Our objective is to develop a three-dimensional (3D), atomistic, full-band, full-quantum device simulator to model electron and hole transport through strained, nano-scale Si-based structures. At this level, there is a natural merging of device and material simulations. The immediate ‘device under test’ is the ‘self-assembled’ Si / SiGe nanopillar. It consists of a core of SiGe within an oxidized Si nanowire. To address the issues of electronic modeling and design of such structures, we have developed two different approaches both within the non-equilibrium Green function (NEGF) framework. The first approach is based on a three-dimensional (3D) discretization of the single-band effective mass equation. The second is based on the full-band sp3s*d5 localized orbital model. A H-passivated Si pillar with its cross section is shown at right.

Three-Dimensional, Full-Band, Quantum Modeling of Electron and Hole Transport through Si / SiGe Nano-Structures, Proceedings of NanoTech 2003, San Francisco, CA, Feb. 23-27, 2003.

NSF NIRT: Self-aligned and self limited quantum dot nanoswitches

Si Nanowire

Molecular Quantum Computing

The recent trend in proposals for “on chip” quantum computers has favored a combination of physically confined and electrostaticly confined semiconductor quantum dots or shallow donors in Si. Such schemes require spatial control of at least two spatially separated single electrons. We believe that this will be a difficult technological challenge, and if it is not solved, it will be a show stopper for that line of approach. Our implementation consists of a self assembled monolayer (SAM) of identical molecules containing the nuclear quantum bits that will be manipulated with locally generated (on-chip) magnetic field pulses. The qubits are embodied in the states of the spin 1/2 nuclei in each molecule. Readout of the nuclear state is accomplished by a “trigger method” in NMR terminology. The nuclear spin information is transferred to the electron spin via the hyperfine interaction and the electron exchange energy.
Center for Nanoscale Innovation for Defense (CNID)

High Speed Devices for Millimeter Wave and Mixed Signal Applications

We are performing both device design and circuit models for high speed InP and InAs based devices. The figure at right shows the CV cureve of an RTD with the peak in the capacitance in the NDR region which we refer to as the quantum capacitance. For the effect of the quantum capacitance on an RTD see "A Physics Based Model for the Quantum Capacitance of an RTD." For the effect of transit time effects in the collector see "A self consistent transit time model for the RTD."
Raytheon

Si/SiGe Tunnel Diodes

Recent demonstrations of Silicon based tunnel diodes fabricated with low-temperature molecular beam epitaxy (LT-MBE) have exhibited a maximum current density of 150 kA/cm² and maximum peak to valley current ratio (PVCR) of 6. These demonstrations have important electronic device implications. The fabrication process is compatible with the complementary metal-oxide-semiconductor (CMOS) or Si/Si_xGe_1-x bipolar technology. The current density and PVCR are sufficient for high speed switching applications. In contrast to the alloy construction techniques of the 1960s, the LT-MBE process allows one to engineer the junction potential for investigation of its effect on the current and peak-to-valley current ratio. We are modeling these devices using the non-equilibrium Green function formalism in a planar orbital basis. At right are full-band NEGF calculations of the phonon-assisted tunneling current showing the effect of bandtails in the contacts on the excess current and PVCR.

Full Band simulation of indirect phonon assisted tunneling in a silicon tunnel diode with delta-doped contacts.

Full Band Modeling of the Excess Current in a Delta-Doped Si Tunnel Diode.