Alison Chaiken

Phase-change recording medium that enables ultrahigh-density electron-beam data storage

An ultrahigh-density electron-beam-based data storage medium is described that consists of a diode formed by growing an InSe/GaSe phase-change bilayer film epitaxially on silicon. Bits are recorded as amorphous regions in the InSe layer and are detected via the current induced in the diode by a scanned electron beam. This signal current is modulated by differences in the electrical properties of the amorphous and crystalline states. The success of this recording scheme results from the remarkable ability of layered III-VI materials, such as InSe, to maintain useful electrical properties at their surfaces after repeated cycles of amorphization and recrystallization.

Crystal structure of κ-In2Se3

Structural properties of single-phase films of {kappa}-In{sub 2}Se{sub 3} and {gamma}-In{sub 2}Se{sub 3} were investigated. Both films were polycrystalline but their microstructure differed considerably. The a-lattice parameter of {kappa}-In{sub 2}Se{sub 3} has been measured. Comparison between these two materials indicates that {kappa}-In{sub 2}Se{sub 3} has a significantly larger unit cell ({Delta}c = 2.5 {+-} 0.2 % and {Delta}a = 13.5 {+-} 0.5%) and a structure more similar to the {alpha}-phase of In{sub 2}Se{sub 3}.

Roll-to-roll manufacturing of electronics on flexible substrates using self-aligned imprint lithography (SAIL)

Abstract— The manufacture of large-area arrays of thin-film transistors on polymer substrates using roll-to-roll (R2R) processes exclusively is being developed. Self-aligned imprint lithography (SAIL) enables the patterning and alignment of submicron-sized features on meter-scaled flexible substrates in the R2R environment. SAIL solves the problem of precision interlayer registry on a moving web by encoding all the geometry information required for the entire patterning steps into a monolithic three-dimensional imprint with discrete thickness modulation. The pre-aligned multiple-step mask structure maintains its alignment regardless of subsequent substrate distortion. Challenges are encountered in relation to the novel nature of using flexible substrates and building toolsets for the R2R processing. In this paper, methods of the SAIL process, the resulting active-matrix backplanes, the trajectory of SAIL process development, and the remaining issues for production are presented.

Structural and electronic properties of amorphous and polycrystalline In2Se3 films

Structural and electronic properties of amorphous and single-phase polycrystalline films of γ- and κ-In2Se3 have been measured. The effect of deposition conditions on the film phase was studied extensively. The stable γ phase nucleates homogeneously in the film bulk and has a high resistivity, while the metastable κ phase nucleates at the film surface and has a moderate resistivity. The microstructures of polycrystalline hot-deposited and postannealed, cold-deposited γ films are quite different but their electronic properties are similar. The increase in the resistivity of amorphous In2Se3 films upon annealing is interpreted in terms of the replacement of In–In bonds with In–Se bonds during crystallization. Great care must be taken in the preparation of In2Se3 films for electrical measurements as the presence of excess chalcogen or surface oxidation may greatly affect the film properties.

23.4: Invited Paper: Active‐Matrix Backplanes Produced by Roll‐to‐Roll Self‐Aligned Imprint Lithography (SAIL)

Progress in the development of a fully roll-to-roll self-aligned imprint process for producing active matrix backplanes with submicron aligned features on flexible substrates is reported. High performance transistors, crossovers and addressable active matrix arrays have been designed and fabricated using imprint lithography. Such a process has the potential of significantly reducing the costs of large area displays. The progress, current status and remaining issues of this new fabrication technology are presented.

Using a Microcantilever Array for Detecting Phase Transitions and Stability of DNA

We report the extension of the microcantilever platform to study the thermal phase transition of biomolecules as they are heated. Microcantilever-based sensors directly translate changes in Gibbs free energy due to macromolecular interactions into mechanical responses. We observe surface stress changes in response to thermal dehybridization of double-stranded DNA oligonucleotides that are attached onto one side of a microcantilever. Once the cantilever is heated, the DNA undergoes a transition as the complementary strand melts, which results in changes in the cantilever deflection. This deflection is due to changes in the electrostatic, ionic, and hydration interaction forces between the remaining immobilized DNA strands. This new technique has allowed us to probe DNA melting dynamics and leads to a better understanding of the stability of DNA complexes on surfaces. (JALA 2006;11:222–6)

Electron-beam detection of bits reversibly recorded on epitaxial InSe/GaSe/Si phase-change diodes

We demonstrate a data read-back scheme based on electron-beam induced current in a data storage device that utilizes thermal recording onto a phase-change medium. The phase-change medium is part of a heterojunction diode whose local charge-collection efficiency depends on the crystalline or amorphous state of a bit. Current gains up to 65 at 2 keV electron beam energy have been demonstrated using InSe/GaSe/Si epitaxial diodes. Fifteen write–erase cycles are obtained without loss of signal contrast by using a protective cap layer and short write pulses. 100 write–erase cycles have been achieved with some loss of contrast. Erasure times for the bits are longer than in similar polycrystalline In–Se media films. Possible reasons for the long erasure times are discussed in terms of a nucleation- or growth-dominated recrystallization. Prospects for extension to smaller bit sizes using electron-beam writing are considered.

Electronics Produced by Roll-to-roll Self-Aligned Imprint Lithography

In this presentation, we present a method for fabrication using self-aligned imprint lithography (SAIL). The self-aligned process solves the layer-to-layer registration issues arising from the dimensionally changes of flexible substrates. The imprint process eliminates the need for photolithography and greatly lowers the cost for large area electronics because it is compatible with roll-to-roll processing. The basic concepts of the SAIL process are presented along with electrical characteristics of devices produced by roll-to-roll SAIL processes.

Heteroepitaxy of InSe/GaSe on Si(111) Substrates

High quality growth of InSe on Si(111) was achieved by insertion of GaSe buffer layer. Rhombohedral polytypes were formed in both the InSe and GaSe layers. Twinning and stacking disorder was often detected in these materials due to their layered structure. Moreover, in samples with a thin GaSe layer, strong interdiffusion of indium into the GaSe layer was detected that resulted in the formation of an In x Ga y Se phase. The dominant threading defects present in these InSe/GaSe heterostructures were screw dislocations, which may act as nonradiative recombination centers.