We have coated the silicon field emission tips with diamond-like carbon(DLC). The array of tips was made of n-type silicon using conventional dry etch Before DLC coating, the tips were bombarded with argon ion to clean the surface. We found that this bombardment improved the aspect ratio of the tips and the DLC adhesion to the silicon tips. The DLC film was coated using r.f. plasma assisted-CVD using C_6H_6 gas. Initially, the end of the tips was coated with ball-shape DLC. The current-voltage curve was measured in 10^<-6> Torr pressure. The DLC-coated tips emitted current at lower onset voltage than as-prepared silicon tips.
The effect of geometry changes on the field enhancement factor(β) of the field emitter was investigated for the optimum setting of design parameters. For the analysis, a three dimensional field emission simulator and Taguchi statistical methods were used. Unlike the previous reports, there does not exist strong dependence between β and the microtip radius(r). The geometrical changes that produces the greatest effect are the gate to microtip distance(d), cone half angle(θ), vertical tip height(h), and radius(r) in that order. The S/N(signal to noise) ratio results indicate that with design parameter values of as r=30 nm, d=0.7 nm, θ=20-35,and h=1-1.5 μm results in a stable design one with minimum sensitivity to process variations.
We fabricated and characterized silicon field emitter tip arrays by gate etch-back process. A very sharp tip of 1.1 μm height was obtained by two step dry etching process and sharpening oxidation process. Polysilicon was deposited for gate electrodes and spin-on-glass was coated for planarization. After polysilicon etching by dry methods and dipping in buffered HF solution, we obtained a very sharp tip array. While this process is very simple and stable, the device has smaller gap space between the tip and the gate electrode and lower leakage currents than those fabricated by a conventional e-beam evaporated method. The resulting device has been observed by SEM and has been tested in ultrahigh vacuum (< 5×10^<-7> Torr) testing chamber. The measured emission current was 10.9 μA at 85V in 256 tip array.
Strip-shaped diamond field emitter arrays were fabricated by using a transfer mold technique. V-grooves were formed on a single crystalline (100) silicon substrate by an orientation dependent etching(ODE) method. Diamond film was grown on V-grooved silicon substrate by chemical vapor deposition(CVD). Diamond field emitter arrays were formed by etching silicon substrates. I-V characteristics of the fabricated diamond field emitter arrays under 2×10^<-5> Torr showed very sharp turn-on characteristics. It is found from experiment that the transfer mold technique can be used for the fabrication of diamond field emitter arrays. It may be possible to use the strip-shaped diamond field emitter arrays for the field emission display(FED) applications.
Silicon field emission cathodes were fabricated using thin-film techniques and 1.2 μm optical photolithography. With two-step reactive ion etching and thermal oxidation for tip sharpening, 1.2 μm height silicon pillars were formed. Gate oxide layer was deposited using an electron-beam evaporator. And then Ti_<0.1> W_<0.9> was sputtered for gate electrodes. As a result, the gate electrodes easily approach the oxidized cathodes. The gate hole diameter is greatly reduced to sub-halfmicron (< 0.5 μm) from the initial mask size (〜1.2 μm). The I-V characteristics of cathodes show low turn-on voltages (< 55 V) in ultrahigh vacuum (< 3.0×10^<-7> Torr) and the linearity of Fowler-Nordheim plots.
In order to prepare low voltage driving TFELD, the layered BaTiO_3 thin films with high performance were used as the lower dielectric layer. For the layered BaTiO_3,the new stacking method using the continuous cooling of the substrate during the deposition of the amorphous layer after the deposition of the polycrystalline layer at higher temperature was introduced. The layered BaTiO_3 thin film showed higher capacitance per unit area and breakdown strength than the double layered BaTiO_3 thin film prepared by the conventional stacking method. It was confirmed that the insulating ability of the single polycrystalline BaTiO_3 thin film highly depended on its thickness. The ZnS : Mn TFELD using the layered BaTiO_3 thin film showed a turn-on voltage of 〜50 volts and a saturated brightness of 2500 cd/m^2,while the device with the single polycrystalline BaTiO_3 thin film did not show stable emission.
Photoluminescence Properties of sythesized inorganic materials were evaluated to find possible phosphors for flat panel display applications. Mg, Zn, and Si_3N_4 powders were mixed and sintered at 800℃, 1000℃, 1200℃, and 1400℃ under N_2 environment after cold pressed to form Mg_XZn_<1〜X>SiN_2 where Tb and Eu were added as luminescent centers. Very sharp emission spectra of Tb^<+3> and Eu^<+2> ions were observed from Mg_xZn_<1-x>SiN_2 : Tb and Mg_xZn_<1-x>SiN_2 : Eu samples sintered at 1200℃, 1400℃ and the maximum intensity of emission spectra occurred at wavelength of 550nm(green light) and 470nm(blue light), respectively.
Hydrogen-free Diamond-Like Carbon (DLC) films were deposited by layer-by-layer technique using plasma enhanced chemical vapor deposition, i.e., deposition of thin DLC layer and subsequent CF_4 plasma exposure on its surface alternatively. The hydrogen-free DLC film could be grown at 200 sec CF_4 plasma exposure on 5 nm DLC layer. The layer-by-layer deposited, hydrogen-free DLC film shows an efficient electron emission ; the onset field emission was found to be 18 V/μm and a barrier energy for emission to be 0.06 eV.
Field emission behaviors from (nitrogenated) diamond-like carbon (DLC) films deposited on p-type Si (100) wafer by r.f. plasma assisted CVD method were investigated. Bias voltage of the substrate was varied from -100V to -900V at a fixed pressure of 10mTorr. Onset field of the film deposited at the bias voltage of -l00V was 10V/μm, while those or the films deposited at higher bias voltage were 20-24V/μm. The effective work functions of all DLC films were 0.05 eV. Nitrogen incorporation to DLC films enhanced the field emission behavior. Depending on the nitrogen source, the effective work functions ranged from 0.02 to 0.04eV. This behavior may be related to more efficient transport carriers from doped Si, through the film, to the emitting surface.
Effect of diamond like carbon (DLC) films coated by pulsed laser deposition technique on the electron emission characteristics of Mo-tips was examined. Turn-on voltage (Vo) was lowered from 80 volts for Mo-tips to 40 volts for DLC coated-tips and saturated anode current (I_<AS>) was increased from 〜44 μA for Mo-tips to 〜2.0 mA or DLC coated-tips. Emission conductance (Ge) has, therefore, been increased from 0.55 μmho with amplified factor of 〜100 due to the DLC coatings on the Mo-tips. Saturated anode current (I_<AS>) dropped rapidly operation. Raman spectrascopy and diffraction in transmission electron microscopy (TEM) revealed that the degradation of electron emission behavior can be ascribed to the conversion of SP^3-bonds, the diamonds, to the SP^2-bonds, graphite. The transformation of the structure, on the other hand, is induced by the local heating of the DLC coatings.
For large area displays, metal FEAs were fabricated with local oxidation of polysilicon. The field emitter arrays(FEAs) with 0.7-μm-diameter gate apertures were made, showing asymmetry of gate edge and roughness on gate surface. However, the electrical characteristics are well compared to the FEAs made from single crystal silicon. The anode current of 62.5 μA(0.1 μA/tip) is measured at the gate bias of 52V for the 625-tip array, while the gate current was less than 0.3 % of the anode current.
These experiments are performed according to the different LC's resistivities to investigate the influence of ionic impurities on the VHR and residual DC voltage using various LC cells which have different polar PI and ITO surface. We found that the increment of VHR depends on the polarity of PIs because the ionic adsorption is related to the polarity of surface, and the residual DC voltage depends mainly on the total ionic quantities rather than the polarity of PIs. In addition, we have known the different tendency of relationship between VHR and residual DC voltage depending on the pairs of LC-PI's.
Simulated annealing (SA) method, an optimization method for finding global minima of multivariable functions, has been applied to design color filters. The color performance of multilayer color filters with regard to their relationship between chromaticity coordinates and luminance, their performance after white balance, white light efficiency, and their chromaticity gamut are discussed. Efforts have been made to evaluate the effectiveness and application of SA method on the design of high performance optical thin films.
Liquid crystal molecules on a photo polymer, PVCN-F irradiated linearly polarized ultra-violet light(LP-UV) are aligned perpendicular to the polarization of UV light. The degeneracy of pretilt angle direction could be broken by liquid crystal injection at nematic phase. To control the magnitude of the pretilt angle, we investigated the values and thermostability of pretilt angle depending on parameters such as LP-UV exposure time, curing temperature and aging temperature. From these results, it is found that the control of pretilt angle can be accomplished by the change of LP-UV exposure time and curing temperature.
There is an increasing need for simple and compact low-power drive solutions for TFT-LCD panels. This demand has led to the development of a nine-channel programmable high-drive reference generator which is appropriate for use with resistor-string DAC based TFT-LCD source drivers. This reference generator greatly simplifies the design and implementation of the external reference circuit required by resistor-string drivers. In addition, it requires less components than discrete implementations. Thus, less PC board space is used, and the reliability of the system is increased. Due to its ability to operate with low supply headrooms, this device also provides a lower power solution than can be achieved with discrete components. It can be used in both 3V and 5V systems and is manufactured in a low-power CMOS process. This reference generator interfaces to an external EEPROM which can be programmed with multiple sets of references voltages for optimization of contrast, power consumption or gamma correction.
We propose two novel methods or improving the yield or TFT LCD. One of the two is as follows. The panel is designed with redundancy, and the display area can be shifted to left or right and upward or downward by the signals from the controller so that the position of the display area may be selected, which enables the avoidance of the defects. The other is a method of preparation against the abnormal operation of the shift register. And this can be implemented using the signals from the controller without any special physical repair unlike the laser-cutting method.
We predict for the first time that a continuous EO effect can exist in achiral Sm C LCs such that the director is made twisted by twice the molecular tilt on going from one substrate to the other. Unlike chiral Sm C^* materials, this external twist is required for producing an induced cone in the Sm C phase so that the molecules rotate continuously along the cone surface formed by the requirement that the molecules are tilted with respect to the layer normal and pinned at the surfaces. As a consequence, a continuous optical modulation can be achieved by means of the dielectric anisotropy with no threshold. This EO effect is predicted in a twisted structure of achiral Sm C materials with either the positive and negative dielectric anisotropy. The basic principles of the optical modulation in such configuration are similar to those in a twist nematic LC geometry except for the existence of smectic layers and the intrinsic biaxiality.
Phosphorous(P) doped hydrogenated microcrystalline silicon (n^+μC-Si : H) films have been prepared by using hydrogen-diluted plasma enhanced chemical vapor deposition technique. 300mm x 400mm CORNING 7059 glass was used as a substrate. A detailed study of the process parameters such as deposition temperature, degree of hydrogen-dilution, RF-power, and deposition time has been investigated. It is found that microcrystalline phase can be obtained for the temperature between 250℃ and 350℃. The existence of μC-Si : H above a critical RF-power(>300W) suggests that RF-power plays an important role for the formation of μC-Si : H. For the film of 94nm thick deposited at 275℃ and 450W of RF-power, resistivity of 0.07 Ω-cm has been obtained which is 3 orders of magnitude lower than normal n^+a-Si : H. The replacement of n^+a-Si : H to heavily P-doped hydrogenated microcrystalline silicon can reduce the metaVa-Si : H contact resistance, but the plasma damage to a-Si : H during n^+uC-Si : H deposition results in the degradation of TFT performance.
Laser-induced crystallization effects on fluorinated microcrystalline silicon films, in which the crystalline fraction is varied, have been investigated. Crystalline fractions of initial films, which has been evaluated from Raman data, is found to influence the laser-induced grain growth behavior. The grain growth is enhanced by the increase of surface melting and solidification times in the film with a critical initial crystalline fraction as well as by the fast lateral grain growth in the film with a relative high initial crystalline fraction.
The PDLCD(polymer dispersed liquid crystal display) panel has a potential for a large area display. A new vacuum filling method for the TFT-PDLCD panels was developed. This new LC filling method does not need an outer vacuum space except for the cell gap-space and is useful for the praparation of large area PDLC panel. Also the temperature dependence of the electro-optical properties of the TFT-PDLC panel was investigated which is used for the high resolution TFT-PDLC projector.