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To find its practical use in ultrahigh density optical data storage, superresolution (SR) technique needs a material that can render a high SR capability at no cost of durability against repeated readout and write. Thermoelectric materials appear to be promising candidates due to their capability of yielding phase-change-free thermo-optic changes. A feasibility study was carried out with PbTe for its large thermoelectric coefficient and high stability over a wide temperature range as a crystalline single phase. Under exposure to pulsed red light, the material was found to display positive, yet completely reversible changes of optical transmittance regardless of laser power, fulfilling basic requirements for SR readout and write. The material was also shown to have a high endurance against repeated static laser heating of up to 106–107 cycles tested. A read only memory disk with a PbTe SR layer led to the carrier to noise ratio value of 47dB at 3.5mW for 0.25μm pit; below the optical resolution limit (∼0.2...

An approach is proposed to develop recording materials for high speed phase change optical data storage. It utilizes a thin film alloy mixture between a stoichiometric GeSbTe alloy and an additive ternary telluride alloy. Selection rules for an additive alloy are suggested. For a test, (Ge1Sb2Te4)1−x(Sn1Bi2Te4)x thin films are deposited by co-sputtering and their structural and thermal properties are studied. Ge1Sb2Te4 and Sn1Bi2Te4 are found to form a completely soluble pseudo-binary system, whose crystalline lattice parameters obey Vegard’s rule over the entire range of x (0

To better understand the role of nitrogen (N) during crystallization of Sb-rich phase change materials, a study was conducted using Sb and Sb70Te30 as host materials of N. Crystallization of the as-sputtered Sb–N films of varying N content was examined to reveal that Sb–N bonds are formed in the as-sputtered states, enhancing amorphous phase stability increasingly with N content. Crystallization appeared to proceed with irreversible dissociation of these bonds to form N2 molecules that may then exist stably during the subsequent memory operations. N2 molecules are considered to play as growth-retarding agents as demonstrated with memory operations of N-doped Sb70Te30.

Superresolution (SR) phenomena due to Ge2Sb2Te5 films were examined by combined analysis of the transmission electron microscopy (TEM) microstructures of the laser-irradiated films and the results from dynamic and static tests using blue lasers. A new finding was made that comprises a complementary case of the classical SR readout by Ge2Sb2Te5 film; an amorphous band instead of a closed aperture of melt in the crystalline background forms behind a moving laser but still produces a high SR signal. A complete carrier-to-noise-ratio curve of a SR-read-only memory employing Ge2Sb2Te5 may be derived from a nonlinear optical effect, specifically thermally assisted saturable absorption.

We investigated the bias polarity dependence of the characteristics of a phase change memory device and found that the device showed higher resistance both at programed and erased states, extended erasing time, and higher threshold voltage (Vth) under negative bias than those under the conventional positive bias. Taking advantage of this dependence, we were able to obtain four highly distinguishable resistance states in such a reproducible manner that may be utilized for a reliable multilevel storage. We explain this polarity dependence in terms of the difference in the density of trap states at the interfaces between the phase change material and electrodes.

Polarization-dependent optical properties of slab waveguide films, which are composed of Au nanoparticles dispersed in a SiO2 matrix, were investigated using a prism coupler. The optical spectra and the mode profiles of the nanocomposite films prepared by alternating sputtering were compared with those of cosputtered films, and the optical anisotropy of the films were modeled and analyzed on the basis of an effective medium theory with Maxwell–Garnett geometry and a layer-by-layer photonic band-gap structures.

The resonance properties due to the surface plasmon excitation of metal nanoparticles make the nanocomposite films promising for various applications such as optical switching devices. In spite of the well-known ultrasensitive operation of optical switches based on a guided wave, the application of nanocomposite film has inherent limitation originating from the excessive optical loss related to the surface plasmon resonance. In this study, we address this problem and present the experimental and theoretical analyses on the pump-probe optical switching in prism-coupled Au(1vol%):SiO2 nanocomposite waveguide film.

A technique to develop an undoped homojunction chalcogen thin-film transistor (UHJ-c-TFT) on glass is described. The UHJ-c-TFT is based on ternary chalcogenide alloy amorphous (α) Ge2Sb2Te5 (GST) and the positively cooled crystalline (χ) GST. The α-GST and the positively cooled χ-GST are used as a channel layer and ohmic contact layer, respectively. In the UHJ-c-TFT, the authors realize electric rectification by the energy difference from the Fermi level of the α-GST and the Fermi level of the positively cooled χ-GST. The UHJ-c-TFT shows the clear gate characteristics of a typical p-channel enhancement mode.

An experimental investigation was carried out on the kinetic nature of the set process in a phase change memory device by combined analyses of set voltage wave forms and time-resolved low-field resistances. As it turned out, the progress of a set process may be measured in terms of three characteristic times in sequence i.e., threshold switching time tth, incubation time for crystallization tinc, and complete set time tset. These characteristic times are supposed to demarcate, in some measure, different stages of crystallization in the memory material during a set process. Each of these times has a strong dependence on input pulse voltage and particularly threshold switching time tth was found to have an exponentially decaying dependence. The latter may be related to the decreasing capacitance of an amorphous phase-change material with approaching threshold switching.