Si-Ty Lam

Dot-product engine for neuromorphic computing: programming 1T1M crossbar to accelerate matrix-vector multiplication

Vector-matrix multiplication dominates the computation time and energy for many workloads, particularly neural network algorithms and linear transforms (e.g, the Discrete Fourier Transform). Utilizing the natural current accumulation feature of memristor crossbar, we developed the Dot-Product Engine (DPE) as a high density, high power efficiency accelerator for approximate matrix-vector multiplication. We firstly invented a conversion algorithm to map arbitrary matrix values appropriately to memristor conductances in a realistic crossbar array, accounting for device physics and circuit issues to reduce computational errors. The accurate device resistance programming in large arrays is enabled by close-loop pulse tuning and access transistors. To validate our approach, we simulated and benchmarked one of the state-of-the-art neural networks for pattern recognition on the DPEs. The result shows no accuracy degradation compared to software approach (99 % pattern recognition accuracy for MNIST data set) with only 4 Bit DAC/ADC requirement, while the DPE can achieve a speed-efficiency product of 1,000× to 10,000× compared to a custom digital ASIC.

Multilayer structured polymer light emitting diodes with cross-linked polymer matrices

Currently, there is great interest in manufacturing multilayer polymer light emitting diode (PLED) structures via low-cost solution-based spin-casting or printing methods. The difficulty with this approach is that solvent from freshly deposited films often dissolves the underlying layers. This letter demonstrates that fully operational multilayer PLED structures can be fabricated via a solution process by embedding the hole transport material in cross-linked inert polymer matrices that protect the functional material while subsequent layers are deposited using the same solvent. The resulting devices exhibited greatly improved quantum efficiency compared with devices that did not employ cross-linked polymer matrices.

Temperature and field-dependent transport measurements in continuously tunable tantalum oxide memristors expose the dominant state variable

Applications of memristor devices are quickly moving beyond computer memory to areas of analog and neuromorphic computation. These applications require the design of devices with different characteristics from binary memory, such as a large tunable range of conductance. A complete understanding of the conduction mechanisms and their corresponding state variable(s) is crucial for optimizing performance and designs in these applications. Here we present measurements of low bias I–V characteristics of 6 states in a Ta/ tantalum-oxide (TaOx)/Pt memristor spanning over 2 orders of magnitude in conductance and temperatures from 100 K to 500 K. Our measurements show that the 300 K device conduction is dominated by a temperature-insensitive current that varies with non-volatile memristor state, with an additional leakage contribution from a thermally-activated current channel that is nearly independent of the memristor state. We interpret these results with a parallel conduction model of Mott hopping and Schottky...

Nanosphere lithography based technique for fabrication of large area well ordered metal particle arrays

Nanosphere lithography is an effective technique for high throughput fabrication of well-ordered patterns, but expanding the method to large area coverage of nanoparticles less than 300 nm in diameter while maintaining good order has proven challenging. Here we demonstrate a nanosphere lithography based technique for fabricating large area, wellordered arrays of hemispherical metal particles which pushes the limits of these size constraints. First, large area monolayers of polystyrene (PS) nanospheres are assembled at an air-water interface and then transferred to a submerged substrate. The submerged substrate is supported at a 10° angle so that the water draining speed can be used to control the transfer rate, which is essential for hydrophobic substrates such as the polymer-coated glass used in our work. A double liftoff procedure was used to transfer the PS pattern to a silver particle array on an arbitrary substrate, achieving tunable control over the final metal particle diameter and spacing in the range of 50-150 nm and 100-200 nm, respectively. Additional control over particle shape and diameter can be obtained by modifying the substrate surface energy. For example, depositing silver on ITO-coated glass rather than a more hydrophilic clean glass substrate leads to a more hemispherical particle shape and a diameter reduction of 20%. Peak wavelength-selective reflection greater than 70% and total extinction greater than 90% were measured. The intensity, position and bandwidth of the main plasmon resonance of the arrays were shown to have minimal angle dependence up to at least 30° off normal.

Ultracompact electron-beam column

An electron optical system with an array of columns was developed for an electron-beam addressable data storage device that has the form factor of Compact Flash and a capacity >10GB. The electron optical column occupies an area <2500μm2 and produces a focused beam with current <100nA and a diameter <40nm. An extended-area electron source that consists of an array of randomly distributed hemispherical-grain polysilicon nodules was developed. The field at the nodules is enhanced by a factor of 3–5 compared with metal-insulator-semiconductor structures with smooth cathodes. Electron emission consequently occurs predominantly at the nodules. A maximum current density of ∼20A∕cm2 was achieved with this electron source. The multiplicity of emission sites helps us to reduce significantly the emission current noise. An electron optical column to focus the emission from this extended source into a diameter <30nm was also developed. The column consists of a single main lens and an array of auxiliary nanolenses. The...

Facile Synthesis of Functionalized Bis(arylethynyl)benzene Derivatives via Sila–Sonogashira Reaction

Abstract This article describes a facile synthesis of a new series of symmetrical bis(arylethynyl)benzene derivatives via a one-pot coupling reaction between trialkylsilyl protected arylalkynyes and aryldihalides bearing both electron-withdrawing (EW) and electron-donating groups (ED) in the presence of PdCl2(PPh3)2(5%) / CuI/tetrabutylammonium fluoride / triethylamine / tetrahydrofuran (sila–Sonogashira reaction) at room temperature. GRAPHICAL ABSTRACT

Field emission information storage technology

Field emission information storage devices (FEISD) present exciting possibilities in an era of mobile computing and applications. Ultra high storage densities of greater than one terabit per square inch may be realized from this type of device. The device comprises three major components: a field emission tip array, a storage medium and a micromover (MEMS-based micromotor). This paper discusses results and issues of the array of field emitters for the FEISD.

An ultra-compact electron-beam column

In this paper, an electron optical system with an array of columns was developed for an electron-beam addressable data storage device that has the form factor of compact flash and capacity > 10 GB. The columns were analyzed with a single Spindt emitter and a three-aperture focusing structure that focuses the beam into a 40 nm core that contains /spl sim/ 60% of the beam current and a tail that spreads to several hundred nanometers. The focusing structure and the emission characteristics for Spindt emitters were presented. An extended electron source that consists of an array of regularly or randomly distributed point emitters which consists of a randomly distributed hemi-spherical poly-silicon nodules (NPS) with 20 /spl plusmn/ 5 nm radius. The physical and electron emission characteristics of NPS were also presented. A novel electron optical column to focus the emission from the NPS extended electron source into a diameter < 30 nm was developed.