Nitrogen Doping Effect for Improving Operation Reliability of Phase Modulator Using Ge2Sb2Te5 Thin Film for Hologram Image Implementation.

A phase modulation device was proposed for the implementation of hologram image for display applications. A Ge2Sb2Te5 (GST) film as thin as 7 nm was prepared between the ITO films to form the cavities corresponding a unit pixel. Nitrogen was incorporated into the GST for improving the thermal stability of the GST active region. The effects of the nitrogen doping on the physical properties of GST was investigated with the variations in doping amounts. The nitrogen incorporation was found to reduce the surface micro-roughness and to improve the thermal stability of the GST even after the crystallization by effectively suppressing the excessive grain growth. As results, the number of repeatable operations for the fabricated phase modulation device was evidently improved from 10 to 69 cycles when a 2.7-at% nitrogen was doped into the GST.

Graphene Electrode Enabling Electrochromic Approaches for Daylight-Dimming Applications.

For environmental reason, buildings increasingly install smart windows, which can dim incoming daylight based on active electrochromic devices (ECDs). In this work, multi-layered graphene (MLG) was investigated as an ECD window electrode, to minimize carbon dioxide (CO2) emissions by decreasing the electricity consumption for building space cooling and heating and as an alternative to the transparent conductor tin-doped indium oxide (ITO) in order to decrease dependence on it. Various MLG electrodes with different numbers of graphene layers were prepared with environmentally friendly poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) to produce ECD cells. Tests demonstrated the reproducibility and uniformity in optical performance, as well as the flexibility of the ECD fabrication. With the optimized MLG electrode, the ECD cells exhibited a very fast switching response for optical changes from transparent to dark states of a few hundred msec.

Holographic image generation with a thin-film resonance caused by chalcogenide phase-change material.

The development of digital holography is anticipated for the viewing of 3D images by reconstructing both the amplitude and phase information of the object. Compared to analog holograms written by a laser interference, digital hologram technology has the potential to realize a moving 3D image using a spatial light modulator. However, to ensure a high-resolution 3D image with a large viewing angle, the hologram panel requires a near-wavelength scale pixel pitch with a sufficient large numbers of pixels. In this manuscript, we demonstrate a digital hologram panel based on a chalcogenide phase-change material (PCM) which has a pixel pitch of 1 µm and a panel size of 1.6 × 1.6 cm2. A thin film of PCM encapsulated by dielectric layers can be used for the hologram panel by means of excimer laser lithography. By tuning the thicknesses of upper and lower dielectric layers, a color-selective diffraction panel is demonstrated since a thin film resonance caused by dielectric can affect to the absorption and diffraction spectrum of the proposed hologram panel. We also show reflection color of a small active region (1 µm × 4 µm) made by ultra-thin PCM layer can be electrically changed.

Design and Fabrication of Integrated Fabry-Perot Type Color Reflector for Reflective Displays.

A Fabry-Perot type integrated color reflector, with red/blue/green colors as subpixels, was designed and fabricated with Si substrate. Ag films were used as reflective mirror layers, SiO2 films were used as Fabry-Perot cavity layers and W films were used as partially reflective layers for the cavity. To minimize the effects of the thickness variation of the oxide cavity layers, the structure of the color reflector was optimized, and the differential deposition scheme was devised and applied in the fabrication process. The integrated color reflector was successfully fabricated with the proposed fabrication scheme. The measured white reflectance was > 45% in the visible spectrum range and -49% at 550 nm wavelength. The fabricated reflector had moderate color gamut of 17% of the National Television System Committee (NTSC) standard and it showed very high white reflectivity. The fabricated color reflector is expected to be applicable to reflective displays.

In situ-grown hexagonal silicon nanocrystals in silicon carbide-based films.

Silicon nanocrystals (Si-NCs) were grown in situ in carbide-based film using a plasma-enhanced chemical vapor deposition method. High-resolution transmission electron microscopy indicates that these nanocrystallites were embedded in an amorphous silicon carbide-based matrix. Electron diffraction pattern analyses revealed that the crystallites have a hexagonal-wurtzite silicon phase structure. The peak position of the photoluminescence can be controlled within a wavelength of 500 to 650 nm by adjusting the flow rate of the silane gas. We suggest that this phenomenon is attributed to the quantum confinement effect of hexagonal Si-NCs in silicon carbide-based film with a change in the sizes and emission states of the NCs.

Size and surface modification effects on the pH response of Si nanowire field-effect transistors.

We investigated the effects of Si nanowire (SiNW) dimensions and their surface modifications on the pH-dependent electronic transport characteristics of SiNW Electrolyte-insulator-Semiconductor Field-Effect Transistors (EISFETs). The threshold voltages, Vth's, of all devices were extracted from the Id-Vg characteristics with Vg applied to the reference electrode immersed in different pH solutions, and their pH-dependences were analyzed for various devices. We found that our devices produce the systematic pH-dependence of Vth with respect to the SiNW's length and show significant changes in a linear pH region and a pH sensitivity upon the Si surface modifications. Particularly in the case of the APTES-treated surface, the linear variation was observed in the wide region of pH = 2 to approximately 11 with the sensitivity of 54.7 +/- 0.6 mV/pH. Also we compared our data to a theoretical result based on the Gouy-Chapmam-Stern-Graham model and found a reasonable agreement between them.

Control of channel doping concentration for enhancing the sensitivity of 'top-down' fabricated Si nanochannel FET biosensors.

The sensitivity of 'top-down' fabricated Si nanochannel field effect transistor (FET) biosensors has been analyzed quantitatively, as a function of the channel width and doping concentration. We have fabricated 130-, 150-, and 220 nm-wide Si FET channels with 40 nm-thick p-type silicon-on-insulator (SOI) layers doped at 8 x 10(17) and 2 x 10(18) cm(-3), and characterized their sensitivity in response to the variation of surface charges as hydrogen ion sensors within buffer solutions of various pH levels. Within the range of channel width and doping concentration investigated, the pH sensitivity of Si channels is enhanced much more effectively by decreasing the doping concentration than by reducing the channel width, which suggests a practical strategy for achieving high sensitivity with less effort than to reduce the channel width. Similar behavior has also been confirmed in the immunodetection of prostate specific antigen (PSA). Combined with excellent reproducibility and uniformity of the channel structure, high controllability of the doping concentration can make the 'top-down' fabrication a very useful approach for the massive fabrication of high-sensitivity sensor platforms in a cost-effective way.