Raymond A. Cirelli

The Vertical Replacement-Gate (VRG) MOSFET: a 50-nm vertical MOSFET with lithography-independent gate length

We have fabricated and demonstrated a new device called the Vertical Replacement-Gate (VRG) MOSFET. This is the first MOSFET ever built that combines (1) a gate length controlled precisely through a deposited film thickness, independently of lithography and etch, and (2) a high-quality gate oxide grown on a single-crystal Si channel. In addition to this unique combination, the VRG-MOSFET includes a self-aligned S/D formed by solid source diffusion (SSD) and small parasitic overlap, junction, and S/D capacitances. The drive current per /spl mu/m of coded width is significantly higher than that of advanced planar MOSFETs because each rectangular device pillar (with a thickness of minimum lithographic dimension) contains two MOSFETs driving in parallel. All of this is achieved using current manufacturing methods, materials, and tools, and competitive devices with 50-nm gate lengths (L/sub G/) have been demonstrated without advanced lithography.

Nanoscale organic transistors that use source/drain electrodes supported by high resolution rubber stamps

Soft contact lamination and metal-coated elastomeric stamps provide the basis for a convenient and noninvasive approach to establishing high resolution electrical contacts to electroactive organic materials. The features of relief on the stamps define, with nanometer resolution, the geometry and separation of electrically independent electrodes that are formed by uniform, blanket evaporation of a thin metal film onto the stamp. Placing this coated stamp on a flat substrate leads to “wetting” and atomic scale contact that establishes efficient electrical connections. When the substrate supports an organic semiconductor, a gate dielectric and a gate, this soft lamination process yields high performance top contact transistors with source/drain electrodes on the stamp. We use this approach to investigate charge transport through pentacene in transistor structures with channel lengths that span more than three decades: from 250 μm to ∼150 nm. We also report some preliminary measurements on charge transport through organic monolayers using the same laminated transistor structures.

Measurement of the Casimir Force between a Gold Sphere and a Silicon Surface with Nanoscale Trench Arrays

We report measurements of the Casimir force between a gold sphere and a silicon surface with an array of nanoscale, rectangular corrugations using a micromechanical torsional oscillator. At distances between 150 and 500 nm, the measured force shows significant deviations from the pairwise additive formulism, demonstrating the strong dependence of the Casimir force on the shape of the interacting bodies. The observed deviation, however, is smaller than the calculated values for perfectly conducting surfaces, possibly due to the interplay between finite conductivity and geometry effects.

Optical transmission through double-layer metallic subwavelength slit arrays

We present measurements of transmission of infrared radiation through double-layer metallic grating structures. Each metal layer contains an array of subwavelength slits and supports transmission resonance in the absence of the other layer. The two metal layers are fabricated in close proximity to allow coupling of the evanescent field on individual layers. The transmission of the double layer is found to be surprisingly large at particular wavelengths, even when no direct line of sight exists through the structure as a result of the lateral shifts between the two layers. We perform numerical simulations using rigorous coupled wave analysis to explain the strong dependence of the peak transmission on the lateral shift between the metal layers.

1296-port MEMS transparent optical crossconnect with 2.07 petabit/s switch capacity

A 1296-port MEMS transparent optical crossconnect with 5.1dB/spl plusmn/1.1dB insertion loss at 1550 nm is reported. Measured worst-case optical crosstalk in a fabric was n38 dB and nominal switching rise/fall times were 5 ms. A 2.07 petabit/s switch capacity was verified upon cross-connecting a forty-channel by 40 Gb/s DWDM data stream through a prototype fabric.

Nanopores in solid-state membranes engineered for single molecule detection

A nanopore is an analytical tool with single molecule sensitivity. For detection, a nanopore relies on the electrical signal that develops when a molecule translocates through it. However, the detection sensitivity can be adversely affected by noise and the frequency response. Here, we report measurements of the frequency and noise performance of nanopores </=8 nm in diameter in membranes compatible with semiconductor processing. We find that both the high frequency and noise performance are compromised by parasitic capacitances. From the frequency response we extract the parameters of lumped element models motivated by the physical structure that elucidates the parasitics, and then we explore four strategies for improving the electrical performance. We reduce the parasitic membrane capacitances using: (1) thick Si(3)N(4) membranes; (2) miniaturized composite membranes consisting of Si(3)N(4) and polyimide; (3) miniaturized membranes formed from metal-oxide-semiconductor (MOS) capacitors; and (4) capacitance compensation through external circuitry, which has been used successfully for patch clamping. While capacitance compensation provides a vast improvement in the high frequency performance, mitigation of the parasitic capacitance through miniaturization offers the most promising route to high fidelity electrical discrimination of single molecules.

Chemical modification of the electronic conducting states in polymer nanodevices.

Organic materials offer new electronic functionality not available in inorganic devices. However, the integration of organic compounds within nanoscale electronic circuitry poses new challenges for materials physics and chemistry. Typically, the electronic states in organic materials are energetically misaligned with the Fermi level of metal contacts. Here, we study the voltage-induced change in conductivity in nanoscale devices comprising a monolayer of polyelectrolyte macromolecules. The devices are fabricated using integrated shadow masks. Reversible switching is observed between conducting (ON) and non-conducting (OFF) states in the devices. The open design of our devices easily permits chemical modification of the polyelectrolyte, which we show has a pronounced effect on the ON-OFF switching. We suggest that the switching voltage ionizes the polymers, creating a conducting channel of electronic levels aligned with the contact Fermi level.

Casimir force on a surface with shallow nanoscale corrugations: geometry and finite conductivity effects.

We measure the Casimir force between a gold sphere and a silicon plate with nanoscale, rectangular corrugations with a depth comparable to the separation between the surfaces. In the proximity force approximation (PFA), both the top and bottom surfaces of the corrugations contribute to the force, leading to a distance dependence that is distinct from a flat surface. The measured Casimir force is found to deviate from the PFA by up to 10%, in good agreement with calculations based on scattering theory that includes both geometry effects and the optical properties of the material.

Superhydrophobic membranes with electrically controllable permeability and their application to “smart” microbatteries

Electrically tunable membranes with controllable permeability have been experimentally demonstrated by combining nanostructured and microstructured superhydrophobic surfaces with the phenomenon of electrowetting. Electrowetting allows dynamical tuning of the contact angle that the liquid forms with the membrane nanofeatures and microfeatures, thus controlling the flow of the liquid through the membrane and, therefore, tuning the permeability of the entire structure. “Smart” electrochemical energy storage cells that can be activated on demand have been built by combining these membranes and microfabricated Zn∕MnO2 electrodes. A typical open-circuit voltage of 1.55V and capacity of 200μAh∕cm2 have been demonstrated.

Control of topography, stress and diffusion at molecule?metal interfaces

The transport properties of metal?molecule?metal junctions containing a monolayer of conjugated and saturated molecules with characteristic dimensions in the range 30?300?nm are correlated with microscopic topography, stress and chemical bonding at the metal?molecule interfaces. Our statistically significant dataset allows us to conclude that the conductivity of organic molecules ~1.5?nm long is at least four orders of magnitude lower than is commonly believed.