Gray Scale Capability Research Articles

(Invited) Amorphous Zr-Doped HfO2 high-K Dielectric Thin Film for Electronic and Optoelectronic Applications

Metal oxides have been used as the high-k dielectric materials in ICs and TFTs for several decades. Recently, they are used as the gate dielectric in the nano-sized MOSFET to take the advantage of the low leakage current and other device properties. HfO2 is the most popular high-k gate dielectric for sub 1 nm EOT transistors and circuits. One of its main drawbacks is the low crystallization temperature, i.e., < 700°C, which can be a serious reliability problem. We have solved this problem by adding Zr into HfO2 to form the Zr-doped HfO2 (ZrHfO) film. This kind of high-k film can remain amorphous after been heated to above 900ºC. The material and electrical properties can be optimized by controlling the concentration of Zr in the film and the post deposition annealing (PDA) condition. In this talk, the author reviews his works in dielectric and non-dielectric applications of the amorphous ZrHfO thin film. They are highly dependent on the structure of the film. The amorphous ZrHfO high-k thin film can be transformed into heterogeneous structures for non-dielectric applications. For example, one or more of the nanocrystalline materials have been embedded into the ZrHfO thin film to serve as charge trapping media. Electrons and holes can be stored in this kind of film separately with the selection of the proper nanocrystal materials and the gate bias condition. This kind of nonvolatile memory device has a lifetime more than 10 years The amorphous ZrHfO high-k thin film can be prepared into another type of heterogeneous structure. After the hard breakdown process, many nano-resistors can be permanently and uniformly formed in the high-k thin film. Light can be emitted from nano-resistors upon the application of a voltage. This is a solid state incandescent light emitting device (SSI-LED) became the principle of light emission is the black body emission. The emitted light has the broad-band spectrum covering the whole visible and part of the near-IR wavelength range. Applications of SSI-LEDs include lighting, on-chip optical interconnect, and others. The nano-resistor structure can also be used as one-time-programmed memory devices, i.e., antifuses, because the leakage current ratio after and before the breakdown process can be larger than 105. Separately, the nano-resistor structure has the current rectification function, which makes it a diode device. However, different from the on-off function of the conventional p-n junction diode, which has a drastic change of the current upon a small increase of the driving voltage, the nano-resistor based diode has the gray-scale capability because of the gradual change of the current vs. voltage curve. There are many other possible applications of the amorphous ZrHfO high-k thin film beyond the conventional electronics and optoelectronics, which will also be discussed. This talk is dedicated to the memory of Prof. Samares Kar for his seminal contribution to this important ECS symposium series.

Fabrication of a curved microlens array using double gray-scale digital maskless lithography

Digital maskless lithography is considered to be a high-efficiency and low-cost approach for the fabrication of microstructures, but is limited by the gray scale capability of spatial light modulators. In this work, a novel method of double gray-scale digital maskless lithography is presented for forming a curved microlens array. The target exposure dose profile of the curved microlens array is first split into two individual 3D energy profiles, and then each 3D energy profile can be respectively realized by a single gray-scale digital lithography. Two gray-scale digital masks obtained by projection calculation are superposed on the substrate so as to realize the exposure dose profile of the curved microlens array. Thus, the effective steps that are achieved through the photoresist response to the modulated UV exposure are doubled, so a smoother profile with a steep gradient can be formed by the precise modulation of double gray-scale masks. As a result of the double gray-scale method, a curved microlens array with 183 micro lenslets on a 1024 µm × 768 µm spherical surface has been successfully fabricated.

Thin Film Transistors as Driving Devices for Attached Devices

TFTs have been the most popular devices for the large area active matrix flat panel displays for the past 20 years. The a-Si:H TFT is suitable for driving the liquid crystal in the pixel level because of its characteristics of low power consumption, gray scale capability, low leakage current, etc. [1]. The a-Si:H TFT array can be easily fabricated on the large area glass substrate with a high throughput at a low temperature. However, the low mobility limits its applications in many areas. For example, the OLED has been widely studied as a potential replacement of the LCD for its low power consumption, contact size, and good color quality. However, for the high quality displays, TFTs are required to drive the OLED pixels [2]. It is difficult or impossible to drive each OLED pixel with a single a-Si:H TFT. The high mobility poly-Si or oxide TFTs are proper for this application. In addition, there are many studies on using the TFT as a driving or sensing device for purposes of chemical or biological sensing, detection, or imaging [2,3]. For some new applications, the high mobility is often required. In this paper, authors investigated limitations on applying a single TFT to driven a device.Figure 1 shows a simple system of a TFT attached with a resistor to the drain electrode. Since a large number of the attached devices change their conductivities upon exposure to selected chemicals, biological agents, optical intensity, or mechanical stress, the resistance is used as a reference of the change. Figure 2 shows the drain current change with the resistance (r) of the resistor attached to the TFT. The poly-Si TFT (W/L = 12m/6m) has a field effect mobility (meff ) of ~ 235 cm2/V.s, an on current (Ion ) of 1.8x10-4 A , a threshold voltage (Vt ) of 0.45V, and a subthreshold slope (S) of 0.26 V/dec. The TFT gate voltage (Vg ) was fixed at 9 V and the complete system was driven at VD’ = 10V. Both the current passing the resistor, i.e., ID , and the drain voltage (VD ) decrease monotonically with the increase of r. Since the ID ’s in Fig. 1 are below that of the TFT without the attached resistor, the performance of the system is controlled by the resistor. This kind of system can be used to detect the change of the environment, such as the light intensity or gas composition, when the resistor responds to the variation of a parameter. For the Fig. 1 system, the power applicable to the resistor is limited. For example, Figure 3 shows that the maximum power is obtained when the resistance is about 100 ohm. TFTs are usually used as switching devices. However, there are limits on the physical characteristics of the attached device. If the power required for the attached device is beyond the peak power in Fig. 3, it cannot be fully turned on although the complete system can be built. For certain applications, such as MEMS or LEDs, the peak power can be a good guideline on selecting the TFT or designing the attached device. The peak power can be increased with the improvement of the TFT characteristics, such as the meff or W/L ratio, however, with limits. The reliability of the TFT is an important issue in the Fig. 1 system. In addition to the environmental factors, e.g., humidity, light, and temperature, the lifetime has to be kept long. For example, the TFT can deteriorate, e.g., increasing the off current, the threshold voltage, or the subthreshold slope, during the driving of the attached device with a high current or for an extended period of time. Possible solutions and limitations will be discussed. Geng-Wei Chang thanks the National Science Council Graduate Students Study Abroad Program for supporting his study in Prof. Yue Kuo’s Thin Film Nano & Microelectronics Research Laboratory. [1] Y. Kuo, ECS Interface, 22(1), 55 (2013).[2] Y. Kuo, Chap. 13, Thin Film Transistors, Vol. 2, p. 464, Kluwer Academic Publishers (2004).[3] Y. Kuo, Chap. 11, Thin Film Transistors, Vol. 1, p. 485, Kluwer Academic Publishers (2004).

Study on Fabrication Conditions of Polymer-Stabilized V-Mode FLCD

In this research, we focus on the polymer-stabilized V-mode FLC (PSV-FLC) in which a doped monomer is photocured in the SmA phase. PSV-FLC may show monostable and V-shaped electrooptical characteristics with a grayscale capability. In this paper, we investigate the dependence of the monostable capability on the fabricating conditions such as monomer materials, polymer concentration, and UV energy. Furthermore, in order to increase the contrast ratio, we introduce a photo-alignment technique. As a result, it is found that the monostable capability of PSV-FLC strongly depends on their conditions. Furthermore, the more uniform molecular alignment without rubbing scratch pattern was obtained by using the photo-alignment film.

Toward real-time spectral imaging for chemical detection with a digital micromirror device-based programmable spectral filter

Hyperspectral imaging sensors have proven to be powerful tools for highly selective and sensitive chemical detection applications, but they have significant operational drawbacks including slow line-scanning acquisition, large data volume of the resulting images, and a detection time lag due to the computational overhead of the matched-filter analysis. We have recently developed and demonstrated a high-speed, high-resolution, programmable spectral filter based on the Texas Instruments DLP® digital micromirror device (DMD) that is capable of performing matched-filter image processing across a two-dimensional (2-D) field-of-view directly in the optical hardware and will enable real-time chemical detection without slow scanning, large data volumes or expensive postprocessing requirements. Based on traditional optical techniques, our spectral filter encodes the spectral information orthogonal to the spatial image information, enabling the DMD to encode matched-filter information into the spectral content of the scene without disturbing the underlying 2-D image. With this new technology, everything from simple multiband filters to very complicated hyperspectral matched filters can be implemented directly in the optical train of the sensor, producing an image highlighting a target signature within a spectrally cluttered scene in real time without further processing. We will first describe the implementation of a DMD as a multiplexing spectral selector for a 2-D field-of-view, discuss its utility as a multiband spectral filter, and show how the DLP’s® duty cycle-based grayscale capability enables the direct measurement of the adaptive matched filter. We will also show examples of multispectral and hyperspectral matched-filter images recorded with our visible spectrum prototype.

P.97: Low Driving Voltage and Gray Scale Capability of Nanostructure Enhanced Cholesteric Liquid Crystal Device

AbstractA nanostructure surface treatment is proposed to improve the response time and driving voltage of cholesteric liquid crystal (CLC) devices. With nanostructure surface, threshold Voltage (Vth) can be reduced ∼10% with minimum reflectance loss. The transition time can be greatly reduced by 80% and multi‐level gray scale can be achieved with new driving scheme in the nanostructure enhanced CLC cell.

The electro-optical characteristics and applicability evaluation of a photo-induced vertical alignment negative-type liquid crystal/photo-curable acrylic pre-polymer mixture system mixed with chiral smectic A phase liquid crystal

In this study, we have investigated newly synthesised chiral smectic A (SmA*) liquid crystals (LCs) with a lactic acid structure with polarised optical microscopy (POM). We started cooling from the clear point until a SmA* phase emerged as the temperature dropped to the range 55.7–88.6°C. At this point, the alignment of the LC molecules resulted in a homeotropic texture. To take advantage of this characteristic, we then mixed the SmA* LC into a negative dielectric anisotropy nematic-type liquid crystal (NLC)/photo-curable acrylic pre-polymer mixture system (the NLC mixture system) with photo-induced vertical alignment, to realise the vertical alignment effect among the NLC molecules. This multi-component LC mixture system gave rise to a special, unknown twist grain boundary AX (TGB AX *) phase with rather broad temperature range, which maintained its helix structure even after crystallisation. In addition, we also utilised the electrical field induced molecular tilt effect (the electroclinic effect) within the SmA* LC to improve the response time of the LC device and gray-scale capability of the NLC mixture system. We further observed this multi-component LC mixture system after ultraviolet light irradiation treatment with POM, to investigate the alignment of the LC molecules, device display and electro-optical properties.

A Fast Transflective Ferroelectric Liquid Crystal Display with Gray Scales in a Single Gap Geometry with Dual Transverse Electric Fields

A transflective display with high speed and gray scale capability is demonstrated using a vertically aligned deformed helix ferroelectric liquid crystal (VA-DHFLC) mode in a single gap geometry. In order to compensate the optical path difference between transmissive (T) and reflective (R) regions, dual types of transverse electric fields are produced from in-plane electrodes prepared on two substrates in T regions and on only one substrate in R regions. The VA-DHFLC mode employed in such electrode configuration provides several unique features such as defect-free alignment over large area, fast response, and gray scale capability without hysteresis.

An Improved Adaptive Subfield Coding Method for Driving AC PDPs

An improved adaptive subfield coding driving method was proposed to reduce the static false contours when the simple-accumulation lighting mode is applied to alternating current plasma display panels (ac PDPs). In the proposed method, when the weighted ratio of the subgrayscale interval to the main grayscale interval is smaller, the gray cumulative probability densities in the subgrayscale interval are sampled in order to locate the sampling gray levels at which the gray probability densities are larger. When the weighted ratio of the subgrayscale interval to the main grayscale interval is larger, the gray levels in the subgrayscale interval are sampled directly so as not to generate larger quantization error brought by the excessive convergence of the sampling gray levels. The simulation results show that the proposed method can eliminate the dynamic false contours in the AC PDPs and has better grayscale expression capability than the existing similar method appearing in the literature. The method proposed in this paper can reproduce the original image information more faithfully.

Multiplexer and Variable Optical Attenuator Based on PDLC for Polymer Optical Fiber Networks

In this work, a combination of a multiplexer and a variable optical attenuator in the same device (VMUX) for use in Polymer Optical Fiber is proposed. Polymer Dispersed Liquid Crystals (PDLC) are polarization independent, have high contrast and gray scale capability. For these reasons, PDLC cells with pixels can be used as switching elements in the device. Characterization of the PDLC has been carried out at two wavelengths. VMUX Complete switching is reached for driving voltages of 20 Vrms, with insertion losses less than 1.6 dB, attenuation larger than 31 dB, rise time less than 2.6 ms and decay time better than 12.4 ms have been obtained.

アダプティブディミング方式を用いたLCDの階調特性改善(画像技術,視覚・画質関連,その他一般)

アダプティブディミング方式を用いたLCDの階調特性改善(画像技術,視覚・画質関連,その他一般)

P‐189: Fast Response Transflective Display Using a Tight Pitch Ferroelectric Liquid Crystal in a Single Gap Configuration

AbstractWe report on a fast response transflective display using a vertically aligned tight pitch ferroelectric liquid crystal (FLC) in a single gap configuration. The optical path difference between transmissive and reflective regions is compensated by adopting in‐plane electrodes on two substrates and on one substrate, respectively. In our transflective FLC display, several unique features such as uniform alignment, fast response, and gray scale capability are demonstrated.

67.3: Electrophoretically Controlled Nematic LCD: Plastic Bistable Technology with Memorized Intrinsic Grey Scale

AbstractHere is presented a nematic LCD based on an electrophoretically controlled orientational effect in suspension of solid nanoparticles in nematic liquid crystal: electrophoretically controlled nematic (EPCN). Polarity controlled electromigration of the nanoparticles, results in the stabilization of the molecular alignment and provides the bistable/multistable switching in a conventional nematic LC cell. The EPCN display allows multiplexing with intrinsic grey scale capability, high resolution and contrast, uses standard LCD materials and techniques and is easily producible by plastic technology.

Molecular Reorientational Motion of a Polymer-Stabilized Ferroelectric Liquid Crystal

The polymer-stabilized ferroelectric liquid crystals (PS-FLC) exhibit monostable and asymmetric electrooptical characteristics with grayscale capability without a threshold. The reorientational motion of FLC molecules can be investigated in terms of two independent optical parameters: the phase difference angle and the angle of the relative amplitude ratio measured with time-resolved ellipsometry. In this study, the time-resolved ellipsometry is applied to the PSFLCs, and we invesitgate the effect of polymer stabilization on the dynamic behavior of molecular reorientation. The measurement results demonstrated the dynamic behavior of PSFLC-molecular reorientation comparatively depends on the tilt angle which FLC takes at the photocure stage.

Effect of Polymer Stabilization on Molecular Reorientational Motion of Ferroelectric Liquid Crystals

The polymer-stabilized ferroelectric liquid crystals (PSFLC) exhibit monostable electrooptical characteristics having grayscale capability without a threshold. The reorientational motion of FLC molecules can be investigated in terms of two independent optical parameters: the phase difference angle and the angle of the relative amplitude ratio measured with time-resolved ellipsometry. In this study, the time-resolved ellipsometry is applied to the PSFLCs, and we research the effect of polymer stabilization on the dynamic behavior of molecular reorientation. The measurement results show that the dynamic behavior of PSFLC-molecular reorientation comparatively depends on the tilt angle, which FLC takes during photocuring, in addition to the concentration of polymer.

Ferroelectric Liquid Crystal Cell With Phase Separated Composite Organic Film

We try to adopt a phase separated composite organic film (PSCOF) to a ferroelectric liquid crystal (FLC) cell. It has been found that in order to realize the PSCOF structure, it is important to select an adequate photocure condition such as the concentration of pre-polymer in LC medium, temperature and the UV intensity. The conventional FLC cell shows the so-called bistable hysteresis loop of electrooptical effect, whereas the PSCOF-FLC cell possesses a monostability without threshold. This monostablity is able to realize LC displays which possess grayscale capability.

3차원적 시뮬레이션에 의한 TFT-LCD의 Gray Scale 성능 분석

We analyzed the effect of a pixel and all the inter-electrode capacitances in a unit pixel of TFT-LCDs on the gray scale capability. The pixel and all the inter-electrode parasitic capacitances were obtained from the tree dimensional profiles of potential distribution and molecular director considering lateral fields generated at the edge of the pixel. To obtain the RMS and kickback voltages of the pixel, we constructed an equivalent circuit of the panel containing all the parasitic capacitances. The calculation was performed though H-SPICE. As results, we confirmed that the pixel becomes smaller, the effect of parasitic capacitances on the gray scale capability becomes larger.

10.4: Fast-Response Flexible LCD Panel Driven by a Low -Voltage Organic TFT

A fast-response flexible ferroelectric liquid crystal (FLC) display panel driven by organic TFT (OTFT) was successfully developed. The fabricated OTFT with Ta2O5 gate insulator showed a mobility of 0.3 cm2/Vs and a current on/off ratio of 107 with a low operating drain voltage of −5 V. We obtained fast responses of less than 1 msec and contrast ratio of 14:1 with gray-scale display capability from a 16×16 pixel FLC panel.

Influence of polymer network in polymer-stabilized ferroelectric liquid crystals and its direct observation using a confocal microscope

The paper presents the analysis of the three-dimensional polymer network distribution inside the polymer-stabilized ferroelectric liquid-crystal layer based on the laser scanning fluorescence confocal microscopy and a fluorescent dye tagging of the polymer. The studies of polymer-stabilized ferroelectric liquid-crystal structures described in this paper are focused on the comparison of the influence of polymer network in case that the polymerization is initiated in the chevron as well as in the quasibookshelf liquid-crystal molecular orientation. In the case of the chevron structure the regular distribution of the polymer network within the layer leads to the monostability of the chevron state. On the other hand the specific distribution of the polymer in the polymer-stabilized quasibookshelf stripe textures leads to the perfect bistability, improved multiplex driving, and analog gray scale capability.

33.2: Fabrication and Characterization of Polarization Shielded Smectic (PSS) Liquid Crystal Display

The fabrication and characterization of 1.5″ low temperature poly-silicon (LTPS) gate for polarization shielded smectic (PSS) liquid crystal display are investigated in this paper. Due to the induced polarization nature of smectic C (SmC) layer, the PSS mode exhibits analog gray scale capability and native wide viewing characteristics under specific molecular alignment. Especially, the PSS phase is very broad in temperature range thereby it can be operated during −20 to 80 °C. The inter-gray level response time and contrast ratio of panel are successfully demonstrated to be 500 μs and 240: 1. Moreover, the ultra-fast optical switching behavior and blur free image quality, as well as simple pixel design enable it becoming a promising candidate in niche market for car navigation and TV application.