Han-Ping D. Shieh

Magneto‐optic recording materials with direct overwrite capability

The possibility of achieving direct overwrite capability in magneto‐optic thin films is demonstrated. By using films having a compensation temperature tens of degrees higher than the ambient temperature, the demagnetizing field can effectively be used as a bias field for thermomagnetic writing in which writing and erasing of domains are accomplished in the absence of a magnetic field. A read‐before‐write scheme is proposed to facilitate the write/erase laser trigger signal to perform overwriting in real time.

Electrical and Photosensitive Characteristics of a-IGZO TFTs Related to Oxygen Vacancy

The electrical and photosensitive characteristics of amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) related to the oxygen vacancies V̈_O are discussed. With the filling of V̈_O of ratio from 14 to 8, the electron density of the a-IGZO channel decreases from 7.5 to 3.8 ( ×10¹⁶ cm^-3); the saturation mobility of the TFT decreases from 3.1 to 1.4 cm^-2/(V · s); the threshold voltage increases from 7 to 11 V for the TFT with a lower on-current; and the subthreshold slope increases from 2.4 to 4.4 V/dec for the TFT with a higher interface defect density of 4.9 × 10¹¹ cm^-2, the worst electrical stability of V_th ~ 10 V, and a hysteresis-voltage decrease from 3.5 to 2 V. The photoreaction properties of a-IGZO TFTs are also sensitive to the oxygen-content-related absorption of the a-IGZO channel. With the lowest content of oxygen in the channel, the TFT has the largest photocurrent gain of 50 μA (V_g = 30 V; V_d = 10 V) and decrease in V_th ( V_th V) at a high light intensity. The light-induced change of TFT characteristics is totally reversible with the time constant for recovery of about 2.5 h.

30 nm resolution x-ray imaging at 8 keV using third order diffraction of a zone plate lens objective in a transmission microscope

A hard x-ray transmission microscope with 30nm spatial resolution has been developed employing the third diffraction order of a zone plate objective. The microscope utilizes a capillary type condenser with suitable surface figure to generate a hollow cone illumination which is matched in illumination range to the numerical aperture of the third order diffraction of a zone plate with an outmost zone width of 50nm. Using a test sample of a 150nm thick gold spoke pattern with finest half-pitch of 30nm, the authors obtained x-ray images with 30nm resolution at 8keV x-ray energy.

Energy-tunable transmission x-ray microscope for differential contrast imaging with near 60 nm resolution tomography

An energy-tunable transmission hard x-ray microscope with close to 60 nm spatial resolution in three dimensions (3D) has been developed. With a cone beam illumination, a zone plate of 50 nm outmost zone width, a stable mechanical design, and software feedback, we obtained tomographic data sets that are close to 60 nm spatial resolution. Meanwhile, the element specific imaging was also obtained by a differential absorption contrast technique used below and above the absorption of the element. Examples of advanced intergraded circuit devices are used to demonstrate the element selectivity and spatial resolution in 3D of the microscope.

Dynamic Backlight Gamma on High Dynamic Range LCD TVs

A high dynamic range liquid crystal display (HDR-LCD) can enhance the contrast ratio of images by utilizing locally controlled dynamic backlight. We studied the HDR-LCD as a dual-panel display: a backlight module and a liquid crystal (LC) cell. As the gamma of the LC signal, the backlight module was also endowed with a gamma function to control the contrast ratio of HDR images. The inverse of a mapping function (IMF) method proposed as a dynamic gamma mapping curve for the backlight module, has been demonstrated to further improve in HDR image quality. By implementing the IMF method on a HDR-LCD TV with 88 backlight zones, the image contrast ratio can reach while maintaining high brightness, clear image detail, and an average power reduction of 30%.

Photofield‐effect in amorphous In‐Ga‐Zn‐O (a‐IGZO) thin‐film transistors

Abstract We studied both the wavelength and intensity dependent photo‐responses (photofield‐effect) in amorphous In‐Ga‐Zn‐O (a‐IGZO) thin‐film transistors (TFTs). During the a‐IGZO TFT illumination with the wavelength range from 460∼660 nm (visible range), the off‐state drain current (IDS_off) only slightly increased while a large increase was observed for the wavelength below 400 nm. The observed results are consistent with the optical gap of ∼3.05eV extracted from the absorption measurement. The a‐IGZO TFT properties under monochromatic illumination (λ=420nm) with different intensity was also investigated and IDS_off was found to increase with the light intensity. Throughout the study, the field‐effect mobility (μeff) is almost unchanged. But due to photo‐generated charge trapping, a negative threshold voltage (Vth) shift is observed. The mathematical analysis of the photofield‐effect suggests that a highly efficient UV photocurrent conversion process in TFT off‐region takes place. Finally, a‐IGZO mid‐gap density‐of‐states (DOS) was extracted and is more than an order of magnitude lower than reported value for hydrogenated amorphous silicon (a‐Si:H), which can explain a good switching properties observed for a‐IGZO TFTs.

A Field Sequential Color LCD Based on Color Fields Arrangement for Color Breakup and Flicker Reduction

The field sequential color (FSC) mechanism can effectively generate multi-primary color fields in temporal sequence to form a full-color image. Color breakup (CBU), however, has appeared intrinsically in conventional FSC displays to degrade visual qualities. A novel CBU suppression method, color fields arrangement (CFA), was proposed to eliminate the artifacts for FSC liquid crystal displays (LCDs). The modified order of consecutive color fields results in superimposed color images on a retina without CBU. Additionally, the 4-CFA method with a field rate of 240 Hz was found to avoid the flicker phenomenon on static images. The proposed method was successfully implemented on a 5.6-in optically compensated bend (OCB) LC panel. Our results confirm that the visibility of CBU artifacts can be reduced as the evaluation of dynamic and static models.

Dynamics and factors controlling regularity of thermomagnetically written domains

The reproducibility of thermomagnetically written domains in rare earth–transition metal thin films was studied and as a result films capable of supporting very regular domains were fabricated. To understand the origins of the domains’ size and shape variations, we first studied the nucleation and growth of domains by using a high‐speed magneto‐optical sampling camera having a 10‐ns exposure time. It is observed that the domain is nucleated within 20 ns after the leading edge of the write pulse. The domain grows in size until 50–150 ns after termination of the write pulse, then shrinks, and finally reaches an equilibrium size. For very short write pulses, no shrinkage of the domain is observed after termination of the write pulse. It is found that increased laser power or longer laser pulse duration increases the final domain size, but not in proportion to total energy applied. The domain growth rate varies from film to film, indicating it is influenced by the intrinsic magnetic parameters. The reproducibility and regularity of the final stable domains were then studied as a function of writing and magnetic parameters. Although both influence the regularity of nucleated domains, the latter have been found to have more profound influences than the former. Films with compensation temperature above ambient temperature, larger perpendicular anisotropy constant, smaller magnitude of magnetization, and smaller domain aspect ratio nucleate domains with a higher degree of reproducibility. Higher coercivity films also support more regular domains. Photographs of domains nucleated with different parameters demonstrate these trends. The experimental observations can be qualitatively explained by analyzing the stiffness of the domain wall defining the domains. The wall stiffness is determined by the two competing forces derived from wall energy and demagnetizing energy. When wall energy dominates, the stiffness is large and domains tend to be circular and highly reproducible. When demagnetizing energy dominates, wall stiffness is low and domains become irregular and less reproducible in shape.

Fabrication and nonlinear optical properties of nanoparticle silver oxide films

We report the fabrication of nanoparticle silver oxide thin films by rf magnetron sputtering and characterization of their nonlinear optical properties. The chemical decomposition and reversibility of AgOx compounds were studied by thermogravimetric analysis, differential scanning calorimetry, and x-ray diffraction. Electron spectroscopy for chemical analysis measurements revealed a 0.5 eV negative binding energy shift from AgO to Ag2O phase. The effect of particle plasmon resonance was confirmed by the absorption band shift with increased Ag2O particle size. The measured third-order nonlinear susceptibility (χ3=3.4×10−7 esu) and response time (27 ps) of the Ag2O nanoparticles makes it promising for applications in all-optical switching devices and optical data storage systems.

Design and fabrication of an integrated polarized light guide for liquid-crystal-display illumination

An integrated polarized light guide was designed and fabricated for use as a liquid-crystal backlight with emphasis on uniformity of the light and conversion of p-polarized to s-polarized light. Two different micro-optical structures were fabricated both on the top and the bottom surfaces of the light guide. On the top surface, a subwavelength grating separates s-polarized and p-polarized light to achieve a polarization-conversion efficiency of 69%. A 1.7 gain factor of polarization efficiency was obtained to increase the utility of light for liquid-crystal illumination.