Carlos Pina-Hernandez

High-Resolution Functional Epoxysilsesquioxane-Based Patterning Layers for Large-Area Nanoimprinting

Epoxysilsesquioxane (SSQ)-based materials have been developed as patterning layers for large-area and high-resolution nanoimprinting. The SSQ polymers, poly(methyl-co-3-glycidoxypropyl) silsesquioxanes (T(Me)T(Ep)), poly(phenyl-co-3-glycidoxypropyl) silsesquioxanes (T(Ph)T(Ep)), and poly(phenyl-co-3-glycidoxypropyl-co-perfluorooctyl) silsesquioxanes (T(Ph)T(Ep)T(Fluo)), were precisely designed and synthesized by incorporating the necessary functional groups onto the SSQ backbone. The materials possess a variety of characteristics desirable for NIL, such as great coatability, high modulus, good mold release, and excellent dry etch resistance. In particular, the presence of epoxy functional groups allows the resists to be solidified within seconds under UV exposure at room temperature, and the presence of the fluoroalkyl groups in the SSQ resins greatly facilitate mold release after the imprint process. In addition, the absence of metal in the resins makes the materials highly compatible with applications involving Si CMOS integrated circuits fabrication.

Facile route of flexible wire grid polarizer fabrication by angled-evaporations of aluminum on two sidewalls of an imprinted nanograting

In this study, we report a new method to fabricate a wire grid polarizer (WGP) that greatly relaxes the requirement on patterning and etching, and can be easily applied to produce flexible WGPs. The technique is to pattern a high aspect ratio and narrow linewidth grating by nanoimprint lithography followed by two angled aluminum depositions in opposite directions to produce the narrow spacing between the aluminum lines required for a visible band WGP. Anisotropic reactive ion etching is used to remove the aluminum deposited at the top of the grating but leave the aluminum layer on the grating sidewalls, thereby forming a metal wire grid with much smaller spacings than a lithographically defined grating. As a result, the fabricated WGP showed good performance in a wide range of visible wavelength.

Continuous patterning of nanogratings by nanochannel-guided lithography on liquid resists.

Department of Mechanical Engineering University of Michigan Ann Arbor, MI 48109, USA H. J. Park , Dr. C. A. Pina-Hernandez , Prof. L. J. Guo Macromolecular Science and Engineering University of Michigan Ann Arbor, MI 48109, USAE-mail: guo@umich.edu Dr. M. K. Kwak , Prof. L. J. Guo Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor, MI 48109, USA [ +] Present address: Molecular Imprints, Inc., Austin, TX 78758, USA

Printable planar lightwave circuits with a high refractive index

We report a novel nanofabrication method to fabricate printable integrated circuits with a high refractive index working in the visible wavelength range. The printable planar ligthwave circuits are directly imprinted by ultra-violet nanoimprinting into functional TiO2-based resist on the top of planar waveguide core films. The printed photonic circuits are composed of several elementary components including ridge waveguides, light splitters and digital planar holograms. Multi-mode ridge waveguides with propagation losses around 40 dB cm(-1) at 660 nm wavelength, and, on-chip demultiplexers operated in the visible range with 100 channels and a spectral channel spacing around 0.35 nm are successfully demonstrated.

Ultrasmall Structure Fabrication via a Facile Size Modification of Nanoimprinted Functional Silsesquioxane Features

We propose a simple and robust scheme for a precise and controlled fabrication of ultrasmall structures through the direct size modification (either reduction or increment) of functional nanoimprinted silsesquioxane (SSQ) patterns. The size modification of nanopatterned SSQ polymer features was achieved according to two different independent approaches. In the first approach, feature size was reduced by a simple heat-induced mass loss mechanism; in the second approach structure size increment was achieved by building multiple polymeric layers on top of imprinted patterns. The fabricated arrays follow the shape contour of the patterned structures so the original imprinted profile is preserved. The engineered capabilities were applied to produce high resolution stamps for nanoimprinting. These approaches free the need for sophisticated nanofabrication techniques and expensive facilities required for nanopatterning.

Printable photonic crystals with high refractive index for applications in visible light

Nanoimprint lithography (NIL) of functional high-refractive index materials has proved to be a powerful candidate for the inexpensive manufacturing of high-resolution photonic devices. In this paper, we demonstrate the fabrication of printable photonic crystals (PhCs) with high refractive index working in the visible wavelengths. The PhCs are replicated on a titanium dioxide-based high-refractive index hybrid material by reverse NIL with almost zero shrinkage and high-fidelity reproducibility between mold and printed devices. The optical responses of the imprinted PhCs compare very well with those fabricated by conventional nanofabrication methods. This study opens the road for a low-cost manufacturing of PhCs and other nanophotonic devices for applications in visible light.

Step-and-repeat nanoimprint on pre-spin coated film for the fabrication of integrated optical devices

Abstract. A step-and-repeat nanoimprint lithography (SR-NIL) process on a pre-spin-coated film is employed for the fabrication of an integrated optical device for on-chip spectroscopy. The complex device geometry has a footprint of about 3  cm2 and comprises several integrated optical components with different pattern size and density. Here, a new resist formulation for SR-NIL was tested for the first time and proved effective at dramatically reducing the occurrence of systematic defects due to film dewetting, trapped bubbles, and resist peel-off. A batch of 180 dies were imprinted, and statistics on the imprint success rate is discussed. Devices were optically characterized and benchmarked to an identical chip that was fabricated by electron-beam lithography. The overall performance of the imprinted nanospectrometers is well-aligned with that of the reference chip, which demonstrates the great potential of our SR-NIL for the low-cost manufacturing of integrated optical devices.

Nanoimprinted High-Refractive Index Active Photonic Nanostructures Based on Quantum Dots for Visible Light

A novel method to realizing printed active photonic devices was developed using nanoimprint lithography (NIL), combining a printable high-refractive index material and colloidal CdSe/CdS quantum dots (QDs) for applications in the visible region. Active media QDs were applied in two different ways: embedded inside a printable high-refractive index matrix to form an active printable hybrid nanocomposite, and used as a uniform coating on top of printed photonic devices. As a proof-of-demonstration for printed active photonic devices, two-dimensional (2-D) photonic crystals as well as 1D and 2D photonic nanocavities were successfully fabricated following a simple reverse-nanoimprint process. We observed enhanced photoluminescence from the 2D photonic crystal and the 1D nanocavities. Outstandingly, the process presented in this study is fully compatible with large-scale manufacturing where the patterning areas are only limited by the size of the corresponding mold. This work shows that the integration of active media and functional materials is a promising approach to the realization of integrated photonics for visible light using high throughput technologies. We believe that this work represents a powerful and cost-effective route for the development of numerous nanophotonic structures and devices that will lead to the emergence of new applications.

Nonresidual layer imprinting and new replication capabilities demonstrated for fast thermal curable polydimethysiloxanes

Additional capabilities of a thermal curable polydimethylsiloxane based nanoimprinting resist that allows a fast replication (a few seconds) of 70 nm line width structures at low temperatures and low pressures (20 psi) are reported here. Challenging features such as nanopillars and high aspect ratio structures were accurately replicated. Moreover, a composite stamp was fabricated and successfully used to replicate structures from a DVD master. Additionally, it was found that a substrate with surface treatment by fluorinated silane is appropriate to imprint nanogratings with no residual layer. The residual layer can be eliminated on both a hard and a flexible substrate. The stamping of structures without residual layers can be used to create size controlled polymer nanofibers.

A novel high-refractive index episulfide-thiol polymer for nanoimprinting optical elements

A novel optical polymer with a high refractive index (n = 1.707 at 590 nm) was developed consisting of episulfide and thiol bifunctional monomers. The episulfide derivative of 9,9-bis(4-glycidyloxyphenyl)fluorene, synthesized by the reaction of an epoxide and inorganic thiocyanate, reacts by a ring-opening polymerization with 4,4-thiodibenzenethiol to produce the optical polymer with high transparency over the visible region of the spectrum and thermally stable up to 290 °C. The developed episulfide-thiol optical polymer can be thermally nanoimprinted at 160 °C with nanoscale size resolution. Different nanostructures including sub-micron and nanoscale size gratings, two-dimensional photonic crystals, and plano-convex semispherical microlenses were successfully nanoimprinted with excellent pattern fidelity and low defectivity. These results exhibit the episulfide-thiol optical polymer as a potential candidate for applications in optical and optoelectronic devices.