Ricardo Ruiz

Bit patterned media based on block copolymer directed assembly with narrow magnetic switching field distribution

Electron-beam (E-beam) directed assembly, which combines the long-range phase and placement registration of e-beam lithography with the sharp dot size and spacing uniformity of block copolymer self assembly, is considered highly promising for fabricating templates that meet the tight magnetic specifications required for write synchronization in bit patterned media magnetic recording systems. In our study, we show that this approach also yields a narrower magnetic switching field distribution (SFD) than e-beam patterning or block copolymer self-assembly alone. We demonstrate that the pattern uniformity, i.e., island diameter and placement distributions are also important for achieving tight magnetic SFDs.

High-Resolution PFPE-based Molding Techniques for Nanofabrication of High-Pattern Density, Sub-20 nm Features: A Fundamental Materials Approach

Several perfluoropolyether (PFPE)-based elastomers for high-resolution replica molding applications are explored. The modulus of the elastomeric materials was increased through synthetic and additive approaches while maintaining relatively low surface tension values (<25 mN/m). Using large area (>4 in.(2)) master templates, we experimentally show the relationship between mold resolution and material properties such as modulus and surface tension for materials used in this study. A composite mold approach was used to form flexible molds out of stiff, high modulus materials that allow for replication of sub-20 nm post structures. Sub-100 nm line grating master templates, formed using e-beam lithography, were used to determine the experimental stability of the molding materials. It was observed that as the feature spacing decreased, high modulus PFPE tetramethacrylate (TMA) composite molds were able to effectively replicate the nanograting structures without cracking or tear-out defects that typically occur with high modulus elastomers.

Self-assembly based plasmonic arrays tuned by atomic layer deposition for extreme visible light absorption.

Achieving complete absorption of visible light with a minimal amount of material is highly desirable for many applications, including solar energy conversion to fuel and electricity, where benefits in conversion efficiency and economy can be obtained. On a fundamental level, it is of great interest to explore whether the ultimate limits in light absorption per unit volume can be achieved by capitalizing on the advances in metamaterial science and nanosynthesis. Here, we combine block copolymer lithography and atomic layer deposition to tune the effective optical properties of a plasmonic array at the atomic scale. Critical coupling to the resulting nanocomposite layer is accomplished through guidance by a simple analytical model and measurements by spectroscopic ellipsometry. Thereby, a maximized absorption of light exceeding 99% is accomplished, of which up to about 93% occurs in a volume-equivalent thickness of gold of only 1.6 nm. This corresponds to a record effective absorption coefficient of 1.7 × 10(7) cm(-1) in the visible region, far exceeding those of solid metals, graphene, dye monolayers, and thin film solar cell materials. It is more than a factor of 2 higher than that previously obtained using a critically coupled dye J-aggregate, with a peak width exceeding the latter by 1 order of magnitude. These results thereby substantially push the limits for light harvesting in ultrathin, nanoengineered systems.

Bit-Patterned Magnetic Recording: Nanoscale Magnetic Islands for Data Storage

Bit-patterned recording shows potential as a route to thermally stable data recording at densities greater than 1 Tbit/in2, provided that a number of challenging requirements can be met. Micromagnetic modeling of the write process shows that high write-field gradient (>350 Oe/nm) and tight tolerances on island fabrication and write synchronization (both in the range of ∼1 nm sigma) are required for addressability (the ability to write a given island without detrimentally affecting neighboring islands). Magnetically uniform islands are also required, with tight island switching-field distribution (5−10% of H k ). We show that magnetic multilayer films with perpendicular anisotropy (e.g., Co/Pd multilayers and laminated films of Co/Pd with other materials) are promising candidates for magnetic layer deposition onto pre-patterned substrates. A suitable strategy for patterned media fabrication begins with master pattern generation using electron beam lithography to create chemical contrast guiding patterns for self-assembly; this approach produces higher quality and higher density patterns than e-beam alone. Patterns are replicated over large volumes of disks by UV-cure nanoimprint lithography, followed by etching of the substrate or magnetic layer. Integration of bit-patterned media into a functional recording system requires write synchronization, in which the timing of current switching in the write head is synchronized with the passage of individual islands under the write head. Write synchronization may be implemented using a sector synchronization system, in which the write clock is frequency- and phase-locked to timing bursts read from the disk during periodic interruptions in the writing process.

Line-frequency doubling of directed self-assembly patterns for single-digit bit pattern media lithography

Directed self-assembly is emerging as a promising technology to define sub-20nm features. However, a straightforward path to scale block copolymer lithography to single-digit fabrication remains challenging given the diverse material properties found in the wide spectrum of self-assembling materials. A vast amount of block copolymer research for industrial applications has been dedicated to polystyrene-b-methyl methacrylate (PS-b-PMMA), a model system that displays multiple properties making it ideal for lithography, but that is limited by a weak interaction parameter that prevents it from scaling to single-digit lithography. Other block copolymer materials have shown scalability to much smaller dimensions, but at the expense of other material properties that could delay their insertion into industrial lithographic processes. We report on a line doubling process applied to block copolymer patterns to double the frequency of PS-b-PMMA line/space features, demonstrating the potential of this technique to reach single-digit lithography. We demonstrate a line-doubling process that starts with directed self-assembly of PS-b-PMMA to define line/space features. This pattern is transferred into an underlying sacrificial hard-mask layer followed by a growth of self-aligned spacers which subsequently serve as hard-masks for transferring the 2x frequency doubled pattern to the underlying substrate. We applied this process to two different block copolymer materials to demonstrate line-space patterns with a half pitch of 11nm and 7nm underscoring the potential to reach single-digit critical dimensions. A subsequent patterning step with perpendicular lines can be used to cut the fine line patterns into a 2-D array of islands suitable for bit patterned media. Several integration challenges such as line width control and line roughness are addressed.

Fabrication of templates with rectangular bits on circular tracks by combining block copolymer directed self-assembly and nanoimprint lithography

We combine block copolymer directed self-assembly with nanoimprint lithography to generate templates with rectangular patterns through an original double imprint process. We use a rotary e-beam tool to separately expose circumferential and radial line/space chemical contrast patterns with periodicities commensurate to the natural period of two lamellae-forming poly(styrene-b-methyl methacrylate) (PS-b-PMMA) block copolymers. Line patterns are formed by directed self-assembly of PS-b-PMMA on chemical patterns on two separate submaster templates, one with circumferential lines to define concentric tracks, and a second template on which the block copolymer is used to form radial lines at constant angular pitch. The patterns are subsequently transferred to their underlying Si substrates to form submaster templates. Using two sequential nanoimprinting steps, we combine the radial and circumferential submaster line patterns into a final quartz master template with rectangular bits on circular tracks.

Rapid directed self-assembly of Lamellar microdomains from a block copolymer containing hybrid

Material properties and directed self-assembly of a block copolymer containing hybrid material are presented in this paper. The hybrid material, which is a mixture of poly(styrene-b-ethylene oxide) (PS-b-PEO) and organosilicate (OS), shows morphologies of microdomains similar to those of organic diblock copolymers depending on the fraction of each phase, i.e. PS and PEO+OS. This material system shows very strong segregation between phases, which provides well defined microdomains in thin films even right after spin coating. The strong segregation also makes it possible to generate microdomains of sub-10 nm length scale regime. The hybrid is found to be directed self-assembly (DSA)- friendly, thus typical topographic and/or chemical guiding patterns can be used for DSA of the hybrid.