A novel technique is presented to simultaneously measure temperature and crystallinity insitu during the rapid thermal annealing of thin Si / SiGe films on transparent substrates for active matrix liquid crystal display applications. The technique uses acoustic waves to monitor temperature, by measuring changes in velocity with temperature. The technique enables accurate tracking of crystalline phase transitions along with temperature, since it is independent of emissivity. This provides a methodology for closed-loop control and end-point detection. The experiments on thin amorphous Si on Quartz demonstrate temperature repeatability of 2%. Also, the technique proved sensitive enough to detect the onset of nucleation, as evidenced by TEM.

Poly-Si TFTs with high field effect mobility are fabricated by using PECVD SiO2 layer deposited with a new method: two-step (graded) oxide deposition. To adjust stoichiometry of the poly-Si/oxide interface and the bulk oxide layer, the double layer oxide films were deposited. The oxide films near the interface were deposited with high N2O/SiH4 gas ratio to obtain the stoichiometric layer for good matching between poly-Si and SiO2. The remaining bulk oxide films were deposited with low N2O/SiH4 gas ratio. The composition of the bulk oxide film was measured by using ESCA and the interface layer was analized with ESR. The poly-Si TFT with the double layer gate oxide resulted to the better performance than conventional TFT wth single layer gate oxde.

The use of the liquid source tetramethylcyclotetrasiloxane (TMCTS) for gate dielectric deposition in low-temperature polysilicon thin film transistor (TFT) processes is investigated. TMCTS was reacted with O2 in an LPCVD furnace at 580°C to form a gate dielectric. For comparison, a low temperature oxide (LTO) was deposited as a gate dielectric using SiH4−O2 LPCVD at 450°C. Capacitance and charge pumping measurements indicate fewer interface states for TMCTS gate dielectric. Both NMOS and PMOS TFTs show comparable or superior performance with TMCTS oxide. Post-deposition annealing has less effect on TMCTS gate oxides. Although TMCTS gate dielectrics appear slightly more susceptible to damage in biastemperature stress tests, TFTs with TMCTS gate oxides still retain better performance after stressing.

The performance and reliability of low pressure chemical vapor deposited (LPCVD) oxides subjected to oxidizing, inert and nitriding annealing ambients is characterized both at low temperature (600°C) and high temperature (950°C). The oxidizing ambient results in worse initial interface state density and charge to break down. We attribute this to the interfacial stress developed during the oxidation, due to the volume mismatch between Si and SiO2. The C-V measurements on poly-Si substrate capacitors and the charge pumping measurements on poly-Si thin film transistors (TFTs) indicate lower trap density for inert and nitriding ambients. The TFTs with inert anneal exhibit lower bias temperature instability compared to oxidizing ambient.

Display devices are one of the key elements of the coming multimedia infrastructure, and Thin-Film-Transistor addressed Liquid Crystal displays are most promising for this application. Physical properties such as dielectric permitivities and electric resistivity are essentially important for TFT-addressing use LC materials. Both theoretical and experimental studies on these properties are reviewed and discussions are made on these in relation to the chemical structure of the liquid crystal substances, providing semiquantitative explanations on the superiority of fluorinated LC materials in respect to the coexistence of the high polarity and the high resistivity. Further studies to improve LC material properties are finally suggested.

We have synthesized compounds of the form M-R-SiCl3 where M is a mesogen based on octyloxy phenyl benzoate, and R is an alkyl chain (tether) that connects M to the silane head group. Tethering lengths from the mesogenic unit to the silane moiety involved 3, 6, or 10 methylene units. These compounds were used to form self-assembled monolayers (SAMs) on silicon wafers, fused silica, and SiO2 coated indium tin oxide (ITO) coated glass. Characterization of these systems includes contact angle measurements, ellipsometry, and atomic force microscopy. Results suggest that the monolayer packing is governed by the lateral interactions between the mesogenic units and not by the tethering length to the solid surface. We have investigated the utility of these chemically-tuned surfaces for liquid crystal alignment. The octyloxy phenyl benzoate self-assembled monolayers induce homeotropic alignment of a nematic liquid crystal.

Suspended particle display (SPD) can be controlled in transparency by applying a.c. voltage. We found new synthesized particles for SPD and methods for making them fine. Three new SPD particles showing different colors have been found: δ-herapathite, 1,10-phenanthroline-iodine complex and pyrazinophenanthroline-iodine complex as showing red, blue, purple, respectively. Recrystallization and ultrasonic treatment were found to make them fine crystals. Accordingly, transparency, stability for sedimentation and thermal stability were improved.

The effect of process parameters on the optical property of the chromium/chromium compound multilayered thin film black matrix for liquid crystal display color filter has been investigated. A chromium compound layer was deposited reactively by DC magnetron sputtering, using gas mixture of Ar, CO2, and N2 on soda-lime glass substrate. Metallic chromium layer deposition was followed to enhance the light obstruction of the black matrix. X-Ray diffraction and transmission electron microscopy study showed that CrN is the major phase with unidentifiable oxides and carbides present as minor phases, in chromium compound layer, with nanocrystalline structure. Metallic chromium layer showed columnar growth structure. The ratio of CO2 in the reactive sputtering gas greatly affected the optical property of the multilayer, despite that N2 is the gas which contributes to the formation of the major phase. Delicate change of optical property is due to compositional variation of the compound layer, caused by reaction due to environmental changes. When processed with 10.28% of CO2 and 4.88% of N2 in 3.3 mTorr pressure, film with optical reflectivity of 3.31% at 655 nm of photon wavelength was obtained.

Normal CrOx/Cr type color filter black matrix requires multi-layer sputtering and photo/etch processes which cause several problems such as particles generation, high production cost, and environmental issues. Various kinds of materials are being reviewed to substitute the existing Cr base materials. Especially carbon based organic type and pigment type photo-sensitive materials are actively under development. Our researches are focused on the characterization of material properties, color filter manufacturing techniques which are optimized for liquid crystal process, and the display quality of newly developed materials. Carbon based organic photoresist has excellent optical, material, and process properties which can be used for TFT-LCD color filter products. 14.2″ VGA panel is fabricated by using this organic black matrix technique. It is expected that this technique will lead the color filter production market.

A novel approach to sputter deposit low resistivity indium tin oxide thin films in cost effective way has been made. To reduce the complication of out-gassing from organic substances that are deposited at prior process steps in the flat panel display manufacturing, DC+RF magnetron sputtering was performed with a relatively high base pressure. Introduction of impurity atoms originated from residual air in the chamber into the film produced the change in lattice as well as microstructure of the film. Sputter deposition with higher base pressure resulted in lower resistivity of the film. Increase in the mobility of the carrier resulted in resistivity decrease. Resistivity as low as 1.5×10−4 Ω cm has been achieved with DC 0.67 W/cm2 + RF 0.67 W/cm2 power density and 10−5 Torr base pressure. X-ray diffraction analysis showed as much as 0.2 % increase in lattice constant resulted from higher base pressure sputtering. No further improvement of conductivity was observed for the base pressure over 10−5 Torr, suggesting impurity introduction saturation into the film.

A new kind of amorphous indium tin oxide (ITO) film with good pattern delineation properties and mass production capability, as well as low resistivity and high transparency has been developed. The film was prepared by a cluster-type DC magnetron sputtering apparatus at room temperature with H2O addition to the argon sputtering gas. The amorphous ITO film quality was improved by effective termination of oxygen vacancies with -OH species generated by enhanced decomposition from the added H2O in the plasma.

The effects of the atomic hydrogen treatment (H-treatment) of indium-tin oxide (ITO) and aluminum-doped zinc oxide (AZO) films have been investigated. The atomic hydrogen was generated by hot-wire chemical vapor deposition (HW-CVD) technique. Experimental results have shown that AZO films are chemically very stable under the H-treatment; almost no variation in the optical transmittance and electrical resistivity was observed. On the contrary, ITO films, either prepared by sputtering with ex-situ or in-situ thermal-annealing, have shown severe optical and electrical degradation and surface whitening after the H-treatment. SEM studies of the H-treated ITO surfaces have revealed that the surface whitening was due to the increase in surface roughness and the formation of granule-like metallic balls. Auger electron spectroscopy has indicated that the balls were mainly composed of indium atoms and the areas between balls were rich in oxygen atoms. These results were confirmed by X-ray diffraction and X-ray photoelectron spectroscopy measurements done on ITO before and after the H-treatment. Finally, we have demonstrated that a-SiO, deposited by PECVD will completely suppress the chemical reaction between ITO surfaces and atomic hydrogen generated by HW-CVD technique.

This work reports on deposition of transparent semi-insulating tin oxide thin films deposited by spray-pyrolysis over large area glass substrates. The precursors used are based on diluted chloride solutions. Bi-doped high resistivity tin oxide thin films are required in the fabrication process of an analog grey scale ferroelectric liquid crystal matrix display. Various parameters have been optimized in order to achieve good reproducibility and uniformity of the electrical and optical properties. Deposition temperature and the properties of the glass substrates have been found as the most critical variables which affect the deposition rate and the quality of the deposited films. The different substrates used, borosilicates and soda-lime glasses, lead to different electrical properties. A further investigation on the stability of the film properties versus different kind of aging procedures have been conducted. Preliminary results of the operation of the complete display making use of our films are shown.

The Field Emission Display (FED) is often portrayed as the emerging alternative to the Active Matrix Liquid Crystal Display (AMLCD). FED displays are based on cold cathodes that emit electrons which are accelerated across a potential in a vacuum to strike a phosphor and emit light. There are numerous material and technology choices at each point of the display system design. Each alternative is characterized by advantages and consequences that affect subsequent choices and system performance. This paper discusses the alternative approaches to cathode material and structure, electron beam focusing, support structure, phosphor and system integration. These choices are related to ultimate display performance and cost.

Uniform and reproducible silicon tip arrays were fabricated using the reactive ion etching followed by the re-oxidation sharpening. Molybdenum was then coated on the some of the silicon tip array. Current-voltage characteristics and current fluctuations were measured in the high vacuum environment. Field emission currents were proved by the Fowler-Nordheim plot studies.

To improve silicon field emitters, diamond and carbon nitride coatings were applied by hot filament CVD and helical resonator CVD, respectively. Helical resonator CVD was first proposed as a new method to grow carbon nitride on silicon tips without damage. Diamond and carbon nitride coatings lowered turn-on voltage and increased emission current. Microstructural and electronic investigations of carbon nitride film were performed. The negative electron affinity of carbon nitride is suggested for enhancing emission current.

Diamond-like carbon is a strong candidate for field emission microcathodes for field emission displays because of its low electron affinity and chemical inertness. The field emission properties of various types of diamond-like carbon such as a-C:H and ta-C are reviewed in the framework of a bonding model of their affinity.

The electron emission properties of a Spindt-type field emitter array have been measured before and after deposition of approximately 100 Å of gold. The workfunction of the emitter decreased by 5% after gold deposition resulting in an 11% reduction in turn-on voltage. Emission stability as measured by RMS current noise improved by 40%. Improvements in emission do not withstand exposure to air. However, baking at moderate temperatures (200°C) restores the emission improvements obtained with the gold overcoating. Fowler-Nordheim plots show that the enhanced emission after baking is due to a increase of the Fowler-Nordheim intercept and not a decrease in slope. Additionally, the gold over coatings resist poisoning as a 50,000 L dose of oxygen only slightly affects emission.

The electron emission behavior of diamond-coated silicon whisker arrays was examined with a point-probe scanner and compared with the behavior of uncoated silicon whiskers as well as with diamond crystallites on a flat Si surface. Emission in all cases was inhomogeneous, and the emission site density was less than the whisker density. Both the diamond-coated and uncoated whiskers displayed a distribution of turn-on fields which peaked at around 10 V/µ, but the uncoated whiskers were observed to burn out if emission outputs exceeded 0.3 µA.

Strip-shaped diamond-tip field emitter array was fabricated by using the transfer mold technique. The sharp turn-on characteristic was observed from the current-voltage measurement of the fabricated diamond-tip field emitter array. The turn-on characteristic of the diamond-tip field emitter array was compared with that of a flat diamond film. High emission current density was obtained from the diamond-tip field emitter array. The threshold voltage of the diamond-tip field emitter array was lower than that of a flat diamond film.