Christian J. Amsinck’s research while affiliated with North Carolina State University and other places

Interfacing the nanoworld with the microworld represents a critical challenge to fully integrated nanosystems. Solutions to this problem have generally required either nanoprecision alignment or stochastic assembly. A design is presented that allows complete and deterministic fanout of regular arrays of wires from the nano- to the microworld without the need for any critical translational alignment steps. For example, deterministically connecting 10-nm wires directly to 3-mum wires would require a translational alignment to within only about 6 mum. The design also allows for nanowire interconnect and is independent of the technology used to fabricate the nanowires, enabling technologies for which alignment remains very challenging. The impact of potential fabrication errors is analyzed and a structure is fabricated that demonstrates the feasibility of such a design

Two efficient, physically based models for the real-time simulation of molecular device characteristics of single molecules are developed. These models assume that through-molecule tunnelling creates a steady-state Lorentzian distribution of excess electron density on the molecule and provides for smooth transitions for the electronic degrees of freedom between the tunnelling, molecular-excitation, and charge-hopping transport regimes. They are implemented in the fREEDA™ transient circuit simulator to allow for the full integration of nanoscopic molecular devices in standard packages that simulate entire devices including CMOS circuitry. Methods are presented to estimate the parameters used in the models via either direct experimental measurement or density-functional calculations. The models require 6 8 orders of magnitude less computer time than do full a priori simulations of the properties of molecular components. Consequently, molecular components can be efficiently implemented in circuit simulators. The molecular-component models are tested by comparison with experimental results reported for 1,4-benzenedithiol.

Nanoelectronic molecular and magnetic tunnel junction (MTJ) MRAM crossbar memory systems have the potential to present significant area advantages (4 to 6F(2)) compared to CMOS-based systems. The scalability of these conductivity-switched RAM arrays is examined by establishing criteria for correct functionality based on the readout margin. Using a combined circuit theoretical modelling and simulation approach, the impact of both the device and interconnect architecture on the scalability of a conductivity-state memory system is quantified. This establishes criteria showing the conditions and on/off ratios for the large-scale integration of molecular devices, guiding molecular device design. With 10% readout margin on the resistive load, a memory device needs to have an on/off ratio of at least 7 to be integrated into a 64 x 64 array, while an on/off ratio of 43 is necessary to scale the memory to 512 x 512.

Many two terminal molecular devices functioning as diodes have been synthesized with responses similar to solid state devices such as rectifying and resonant tunneling diodes. In this paper, the feasibility of integrating these molecular diodes into current circuit architectures is explored. A bistable latch and memory architecture are simulated using IV data from the 2'-amino-4-ethynylphenyl-4'-ethynylphenyl-5'-nitro-1-bensenethiolate molecule previously published by the Reed group at Yale University. HSPICE simulation results are used to illustrate the performance of a bistable latch and a memory array.

We have demonstrated a new planar edge defined alternate layer (PEDAL) process to make sub-25 nm nanowires across the whole wafer. The PEDAL process is useful in the fabrication of metal nanowires directly onto the wafer by shadow metallization and has the ability to fabricate sub-10 nm nanowires with 20 nm pitch. The process can also be used to make templates for the nano-imprinting with which the crossbar structures can be fabricated. The process involves defining the edge by etching a trench patterned by conventional i-line lithography, followed by deposition of alternating layers of silicon nitride and crystallized a-Si. The thickness of these layers determines the width and spacing of the nanowires. Later the stack is planarized to the edge of the trench by spinning polymer Shipley 1813 and then dry etching the polymer, nitride and polysilicon stack with non-selective RIE etch recipe. Selective wet etch of either nitride or polysilicon gives us the array of an aligned nanowires template. After shadow metallization of the required metal, we get metal nanowires on the wafer. The process has the flexibility of routing the nanowires around the logic and memory modules all across the wafer. The fabrication facilities required for the process are readily available and this process provides the great alternative to existing slow and/or costly nanowire patterning techniques. (P.D. Franzon).

A three-dimensional bottom-up self-assembly technique is developed to use biomolecules such as DNA as scaffolds. The use of viruses as nanoscale scaffolds for devices provide the exquisite control of positioning on the nanoscale. The efficacy of the approach is tested on 3D conductive molecular networks using cowpea mosaic virus (CPMV) as a scaffold. The conductance of the molecular network self-assembled on a single virus is measured using scanning tunneling microscopy (STM), which shows isolated conductive viral nanoblocks (VNB) attached to a gold substrate through a conducting molecule inserted in an insulating C11 matrix. It is observed that red connections are the least important in the formation of the network, such that their removal decreases the network conductance by just 6% to 94% of the maximum. This bottom-up approach uses different types of molecules for functions such as wires, switches, and diodes to build electronic circuits to increase the theoretical device density.

Molecular electronics holds significant potential to outscale bulk electronic devices. However, practical issues have limited that potential to date. This paper reviews the function and design of molecular electronics and evaluates results to date in a circuits context.

An important component to the nanocell, among other self-assembled networks, is the fabrication of a framework by which molecular elements can be interconnected. This framework must be nanometric in scale, created in a material suitable for attachment chemistries and remain electrically discontinuous until molecular attachment. Utilizing the Volmer-Weber mechanism by which gold grows on silicon dioxide surfaces, nanometric islands of gold are fabricated to provide this framework. Using standard photolithography techniques, the regions where these islands are located are well defined. A two-layer photoresist stack is developed that prevents edge shorting around the boundaries of each region. The discontinuous gold films fabricated in this study are repeatable, offer a fill factor of 63%, and are easily patterned down to the one-micron scale.