Devin K. Brown

Process optimization and proximity effect correction for gray scale e-beam lithography

Three-dimensional microstructures find applications in diffractive optical elements, photonic elements, etc., and can be efficiently fabricated by e-beam lithography. Good process control and efficient proximity effect correction are important for achieving the desired structures. With polymethylmethacrylate as the resist, a process optimization of different develop conditions is carried out to identify a process that is most conductive to gray scale features. A novel proximity effect correction scheme called effective dose-depth (EDD) method is proposed. Using the EDD method for grating design and the optimized process, blazed gratings have been fabricated with excellent uniformity and low surface roughness.

Patterning decomposable polynorbornene with electron beam lithography to create nanochannels

Unity® 4671E sacrificial material is a decomposable negative tone polymer sensitive to ultraviolet radiation. In this study, it is shown that Unity® 4671E can also be patterned by electron beam lithography. Nanochannels with a width of 65nm and a pitch of 200nm have been fabricated. The developed Unity® 4671E patterns can thermally decompose and the products can permeate through the encapsulating material leaving nanocavities. This direct write electron-beam process has fewer processing steps than other published fabrication methods.

Fractal Electrode Formation in Metal–Insulator Composites Near the Percolation Threshold

Over the past 20 years, there have been a variety of experiments that have revealed a large increase in the low-frequency capacitance of devices constructed from metal-insulator nanocomposite materials. These capacitive increases are typically reported as dramatic increases in the effective relative dielectric constants of the nanocomposite materials. A class of these materials that operate at room temperature and have metal particle concentrations near the percolation threshold have been shown to have dramatic increases in the effective dielectric constant on the order of 104-1010. The simulations in this paper reveal that electrical contact to large metal clusters inside the composite material near the percolation threshold form fractal-like electrodes that deeply penetrate into the host dielectric material, which result in an effective dielectric constant that is 104-105 times greater than the host dielectric. Furthermore, insulating the planar electrodes so that no electrical contact is made to the metallic clusters inside a near-percolation-threshold composite material reveals a much smaller increase (40×) in the effective dielectric constant. Finally, a new physical scaling model and a simple geometric model for capacitance estimation in metal-insulator composites are developed and used to enhance understanding of the physical effects behind the results of these numerical simulations.

Ratchet effect study in Si/SiGe heterostructures in the presence of asymmetrical antidots for different polarizations of microwaves

Abstract In this work, we studied the photovoltage response of an antidot lattice to microwave radiation for different antidot parameters. The study was carried out in a Si/SiGe heterostructure by illuminating the antidot lattice with linearly polarized microwaves and recording the polarity of induced photovoltage for different angles of incidence. Our study revealed that with increased antidot density and etching depth, the polarity of induced photovoltage changed when the angle of incidence was rotated 90 degrees. In samples with large antidot density and/or a deeply etched antidot lattice, scattering was dominated by electron interaction with the asymmetrical potential created by semicircular antidots. The strong electron–electron interaction prevailed in other cases. Our study provides insight into the mechanism of interaction between microwaves and electrons in an antidot lattice, which is the key for developing an innovative ratchet-based device. Moreover, we present an original and fundamental example of antidot lattice etching through the use of a two-dimensional electron gas. This system deals with a hole lattice instead of an electron depletion in the antidot lattice region.

Novel through-silicon via technologies for 3D system integration

To circumvent the performance and energy bottlenecks due to interconnects, novel interconnect solutions are needed both at the package and die levels. This paper reports (1) novel photodefined polymer-embedded vias within silicon interposers for improved through-silicon via insertion loss, and (2) ultrahigh density low-capacitance nanoscale TSVs with 100 nm diameter and 20:1 aspect ratio for fine-grain 3D IC implementation.

Fabricating millimeter to nanometer sized cavities concurrently for nanofluidic devices

In this study, nanofluidic devices were fabricated using Unity® 4671E, a decomposable, negative tone resist. Cavities as large as 2.5 mm and channels as small as 30 nm were fabricated with the same process. Water was successfully flowed through the devices and the flow was characterized for a 500 nm channel.

Challenges in the fabrication of an optical frequency ground plane cloak consisting of silicon nanorod arrays

The application of transformation optical techniques to photonic crystal-like dielectric structures has facilitated the creation of invisibility cloaks that operate at optical wavelengths. In this article, the authors present the fabrication processes for an all-dielectric ground plane cloak structure that consists of multiple silicon nanorod arrays connected by input and output waveguides. An advantage of this particular design is that it does not use metals to obtain metamaterial-like device behavior. The structure consists only of dielectrics that can be processed by the use of electron beam nanofabrication technologies and is designed to operate in the 1400–1600 nm wavelength range.

Deep ultraviolet photolithography capability of ZEP520A electron beam resist for mix and match lithography

ZEP520A is a positive high resolution electron beam resist enabling nanometer scale features; however, electron beam lithography (EBL) is a characteristically slow process. It is demonstrated that ZEP520A can be exposed by deep ultraviolet (DUV) photolithography and is useful for mix and match lithography schemes. Submicron resolution was achieved, an optical pattern was successfully aligned to an EBL pattern, and 1cm2 was exposed in 11min with DUV compared to 27h with EBL.

Optimization of contact interface resistance for CMOS circuits

In this paper, we demonstrate optimizations within the sintering process window to reduce contact resistance and improve reliability after thermal cycling. A two-phase experiment is outlined to investigate these effects for blanket and localized ion implantation. In addition, a comparison of different aluminum-silicon alloys is performed across the process window of sintering conditions. SEM images are used to verify adequate filling of contact holes and EDS compositional analysis results are presented. I-V characteristics are then used to evaluate electrical performance of the ohmic contact. Recommendations for further improvement of contact formation for back end processes are made. Educational benefits to undergraduates are emphasized.

Geometrically-induced loss suppression in plasmoelectronic nanostructures (Conference Presentation)

Nanostructured metals have utilized the strong spatial confinement of surface plasmon polaritons to harness enormous energy densities on their surfaces, and have demonstrated vast potential for the future of nano-optical systems and devices. While the spectral location of the plasmonic resonance can be tailored with relative ease, the control over the spectral linewidth associated with loss represents a more daunting task. In general, plasmonic resonances typically exhibit a spectral linewidth of ~50 nm, limited largely by the combined damping and radiative loss in nanometallic structures. Here, we present one of the sharpest resonance features demonstrated by any plasmonic system reported to date by introducing dark plasmonic modes in diatomic gratings. Each duty cycle of the diatomic grating consists of two nonequivalent metallic stripes, and the asymmetric design leads to the excitation of a dark plasmonic mode under normal incidence. The dark plasmonic mode in our structure, occurring at a prescribed wavelength of ~840 nm, features an ultra-narrow spectral linewidth of about 5 nm, which represents a small fraction of the value commonly seen in typical plasmonic resonances. We leverage the dark plasmonic mode in the metallic nanostructure and demonstrate a resonance enhanced plasmoelectric effect, where the photon-induced electric potential generated in the grating is shown to follow the resonance behavior in the spectral domain. The light concentrating ability of dark plasmonic modes in conjunction with the ultra-sharp resonance feature at a relatively low loss offers a novel route to enhanced light-matter interactions with high spectral sensitivity for diverse applications.