John F. Miner

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.

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.

Air-gaps in 0.3 μm electrical interconnections

A copper/air-gap interconnection structure using a sacrificial polymer and SiO/sub 2/ in a damascene process has been demonstrated. The air-gap occupies the entire intralevel volume with fully densified SiO/sub 2/ as the planar interlevel dielectric. The copper was deposited by physical vapor deposition and planarized by chemical-mechanical planarization. The Ta/Cu barrier/seed layer was deposited by physical vapor deposition; the bulk copper was electrochemically deposited. The resulting structure has an effective intralevel dielectric constant of 2.19.

Beyond the gene chip

We describe a prospective strategy for reading the encyclopedic information encoded in the genome: using a nanopore in a membrane formed from a metal-oxide semiconductor (MOS)-capacitor to sense the charge in deoxyribonucleic acid (DNA). In principle, as DNA permeates the capacitor-membrane through the pore, the electrostatic charge distribution characteristic of the molecule should polarize the capacitor and induce a voltage on the electrodes that can be measured. Silicon nanofabrication and molecular dynamic simulations with atomic detail are technological linchpins in the development of this detector. The sub-nanometer precision available through silicon nanotechnology facilitates the fabrication of the detector, and molecular dynamics provides us with a means to design it and analyze the experimental outcomes.

Microstructure and texture of electroplated copper in damascene structures

The transition from Al to Cu for advanced ULSI interconnects involves changes in architecture and deposition technique that will influence the microstructure and texture of the metal. Cu interconnects are typically formed within the confines of pre-patterned trenches and vias using an electroplating process with a sputtered Cu conduction layer deposited over a refractory metalbased diffusion barrier layer. In this paper, we focus on the influence of the barrier layer (PVD Ti/TiN, Ta, TaN, CVD TiN) and the effect of a vacuum break between barrier and conduction layer depositions, on the texture of the Cu lines, as examined by X-ray diffraction pole figure analysis. A preferred (111) orientation was observed for all samples. The samples with no vacuum break between barrier and conduction layer deposition exhibited in plane anisotropy that was particularly pronounced for the Ta and TaN samples compared with the Ti/TiN sample. Focused ion beam images and transmission electron micrographs showed Cu grain size to be on the order of the trench width with a high degree of twinning, and no boundary could be distinguished between the PVD Cu conduction layer and the electroplated Cu.

Controlling the phase delay of light transmitted through double-layer metallic subwavelength slit arrays

We demonstrate that the phase of light transmitted through double-layer subwavelength metallic slit arrays can be controlled through lateral shift of the two layers. Our samples consist of two aluminum layers, each of which contains an array of subwavelength slits. The two layers are placed in sufficient proximity to allow coupling of the evanescent fields at resonance. By changing the lateral shift between the layers from zero to half the period, the phase of the transmitted electromagnetic field is increased by pi, while the transmitted intensity remains high. Such a controllable phase delay could open new capabilities for nanophotonic devices that cannot be achieved with single-layer structures.

Spatial light modulator for maskless optical projection lithography

Spatial light modulators (SLMs) designed to replace photomasks for optical lithography have been designed, fabricated, and tested. These microelectromechanical devices are fabricated with alternating polycrystalline Si and sacrificial SiO2 layers that are patterned by a 193nm wavelength scanner to dimensions as small as 150nm. Aerial image simulations were used to define the mechanical requirements of the devices. Piston motion of electrically actuated devices was measured with an optical profilometer. The measurements were fit to a simple equation to within 1nm precision, which is adequate for defining 50nm features lithographically. Transient response measurements show that one version of the SLM responds to actuation as quickly as 20μs, fast enough for current 193nm wavelength excimer laser sources.

Transmission enhancement in an array of subwavelength slits in aluminum due to surface plasmon resonances

The coupling of light to surface plasmons through periodic subwavelength metallic structures could strongly modify the optical properties of a metal film. We demonstrate that the optical transmission through an array of subwavelength slits is as high as 80% at resonance, even though the width of each slit is almost 10 times smaller than the wavelength and the slits occupy only 25% of the area of the metal. Numerical calculations suggest that the field intensity is strongly enhanced near the metal surface. The field enhancement could be used for generating nonlinear optical effects and for high sensitivity detection of nanomechanical displacement.

Optical transmission through double-layer, laterally shifted metallic subwavelength hole arrays

We measure the transmission of IR radiation through double-layer metal films with periodic arrays of subwavelength holes. When the two metal films are placed in sufficiently close proximity, two types of transmission resonances emerge. For the surface plasmon mode, the electromagnetic field is concentrated on the outer surface of the entire metallic layer stack. In contrast, for the guided mode, the field is confined to the gap between the two metal layers. Our measurements indicate that, as the two layers are laterally shifted from perfect alignment, the peak transmission frequency of the guided mode decreases significantly, while that of the surface plasmon mode remains largely unchanged, in agreement with numerical calculations.

Optical MEMS devices for telecom systems

As telecom networks increase in complexity there is a need for systems capable of manage numerous optical signals. Many of the channel-manipulation functions can be done more effectively in the optical domain. MEMS devices are especially well suited for this functions since they can offer large number of degrees of freedom in a limited space, thus providing high levels of optical integration. We have designed, fabricated and tested optical MEMS devices at the core of Optical Cross Connects, WDM spectrum equalizers and Optical Add-Drop multiplexors based on different fabrication technologies such as polySi surface micromachining, single crystal SOI and combination of both. We show specific examples of these devices, discussing design trade-offs, fabrication requirements and optical performance in each case.