Large grain poly-Silicon (p-Si) films have been evaluated for high speed TFT for flat panel displays [1,2]. It is expected that with good quality p-Si, “System on Glass” products, in which entire electronic circuitry is incorporated directly onto glass are achievable [3]. This approach therefore has the potential to fabricate Integrated AMLCD's (IAMLCD) and bypass conventional Si wafer based products and integrate CMOS circuits with direct view TFT LCD manufacturing. To realize this potential; it is necessary to develop a production process for depositing repeatable, good quality p-Si films on to large area glass substrates.

The glass substrate plays a crucial role in the successful performance of advanced flat panel displays (FPDs). These FPD technologies include active-matrix liquid crystal displays (AMLCD) and Plasma Displays (PDP). Although these displays are different in the way in which they operate, there are several common substrate requirements, all of which are determined by the process for making the entire display. These include issues relating to substrate size, thermal shrinkage, high temperature stability, and substrate surface quality.

While AMLCD technology is moving toward larger sizes, PDPs are currently large size displays, requiring large glass substrates. The primary issue in using larger substrates is minimizing distortion of the glass during high temperature processes, both viscous sag and shrinkage. These are related to the high temperature thermal stability which, in turn, is largely determined by the strain point and thermal history of the substrate. Finally, thickness uniformity and surface flaws are critical to the performance of the final display.

Coming's Code 1737 glass substrate meets the requirements for AMLCDs and has become the industry standard. Corning/Saint-Gobain Code CS25 glass is a new glass that has significant benefits over soda-lime glass for PDP applications. This paper will discuss these two glasses in terms of the above-mentioned issues.

For many flat panel display applications, traditional glass substrates for the TFT backplane are not sufficiently rugged. Therefore, we have begun to explore the use of steel foils as TFT substrates for emissive or reflective displays. We report the fabrication of high quality a-Si:H TFTs on lightweight, flexible 75 μm thick stainless steel foils. The electrical characteristics of the TFTs were good and were not significantly affected by either dropping over 15 meters to a concrete floor or being bent to a radius of curvature of 8.25 cm for a period of over 400 hours. Typical device characteristics were: ION/IOFF > 107, IOFF ∼ 1012 A, VT ∼ 3.2 V, and μEFF ∼ 0.9 cm2/Vs. We also discuss our recent work on the successful integration of organic light-emitting diodes (OLEDs) with TFTs on steel substrates, resulting in a new form of emissive display.

We have evaluated the electrical and the optical properties of a planarization polymer (benzocyclobutene; BCB) having a dielectric constant of 2.65 for the application to high aperture-ratio a-Si:H TFT-LCDs. An average optical transmittance of 96 % was found for the BCB film having a thickness of 3 μm in the visible-light region (400–700 nm) of the absorption spectrum. Experimental results showed that the back-channel etched a-Si:H TFT electrical performance was not significantly affected by the BCB passivation. In addition, the three-dimensional analysis of the coupling capacitances between ITO pixel electrode and metal bus lines have indicated that the low dielectric constant of planarization polymer is necessary for the application of this material to the high-aperture-ratio a-Si:H TFT-LCDs. Finally, we have established that for a given tolerance margin, a certain value of polymer thickness is needed to suppress the feed-through voltage and the vertical cross-talk between pixel electrode and metal bus lines.

We adapted a new technique for depositing copper lines, at a maximum process temperature of 200°C. The technique is based on the decomposition of copper hexanoate by UV light, followed by annealing in H2 [1]. A copper film resistivity of 8 μΩcm is obtained. We patterned this copper metallization on Corning 7059 glass substrates by three different techniques, including exposure through a shadow mask, lift-off of xerographic toner, and direct writing.

In a conventional liquid crystal display (LCD), glass substrates coated with an indium tin oxide (ITO) layer are typically used for the application of an electric field to the liquid crystal material. For many applications, there is a need for a LCD with a plastic substrate. While ITO works well with glass, it does not adhere as well to plastic. It is brittle, and has a tendency to crack under constant bend conditions. Polypyrrole is well known for its good conductivity and chemical stability. Moreover, as an organic polymeric material, polypyrrole film can also flex and bend with the plastic substrate. Therefore, it is a good candidate for plastic LCDs. We present here the results on the development of polypyrrole films deposited on plastic substrates which are suitable for reflective LCDs.

This work reports the structure and electro-optical characteristics of different metal oxide films obtained by spray pyrolysis on heated glass substrates, aiming their application in optoelectronic devices. The results show that this technique leads to thin films with properties ranging from dielectric to degenerate semiconductors, offering the following advantages: simplicity, low cost, high productivity and the possibility of covering large areas, highly important for large area device applications.

A large-area, high power density, high efficiency, and low cost excimer VUV and UV source, which is capable of producing narrow-band radiation tunable between the near UV (λ=354 nm) and the deep UV (λ=126 nm), is described.

This UV source is based on the principle that the radiative decomposition of excimer states created by a dielectric barrier discharge (silent discharge) in a rare gas, such as Ar2* (λ=126 nm), Kr2* (λ=146 nm), Xe2* (λ=172 nm) or molecular rare gas-halide complexes, such as ArCl* (λ=175 nm), KrCl* (λ=222 nm), XeCl* (λ=308 nm). Conversion efficiencies (from input electrical to output optical energy) as high as 22% can be achieved under optimum conditions. This powerful and economical lamp provides a useful UV source for low temperature photon-initiated processes and is an interesting alternative to conventional UV lamps for industrial large-scale low temperature processes. For industrial large-area processing and for the deposition of highly complex structures, these narrow band VUV and UV sources with high photon fluxes have definite advantages. Several applications of these excimer sources are reviewed, including photo-deposition of dielectric and metallic thin films, photo-oxidation of silicon, surface modification, etching of polymer, and photo degradation of pollutants.

Holographically formed polymer dispersed liquid crystal (H-PDLC) displays are investigated in terms of their electro-optic performance parameters and their potential as capable full color display systems. It is demonstrated that the transmission-voltage curve can be modified by low concentrations of chiral dopants, increasing the steepness of the response curve. To probe the details of full-color reflective H-PDLC displays, we invoke a generalized colorimetric/photometric analysis to estimate the display reflectance, white-point, and chromaticity diagram for a vertically integrated stack of red, green, and blue H-PDLC displays.

The widespread use of pigmented color filters in the AMLCD industry has focused attention on their deficiencies, which include marginal film transmittance, significant depolarization and generally poor imaging characteristics for the corresponding imaging resists. These limitations result in diminished color filter contrast and curtailed brightness for the AMLCD device. Incremental color filter contrast improvements have been generated through use of smaller pigment particles which reduce, but do not eliminate, light scattering. As standard pigment synthetic and grind processes give only small color contrast gains, at a cost of protracted pigment manufacture time, another route to more significant gains in color filter contrast is probably necessary. The work herein describes our attempt at defining one viable approach to real improvements in the key color filter responses of reduced depolarization and improved color contrast.

Our approach employs colorants prepared from colloidal suspensions of nanosized, mono-dispersed, dense silica spheres to which appropriate red, green and blue dyes are sorbed. Subsequent dispersion of each colorant nanocomposite in carrier polymer and photoimaging chemistry yields the corresponding negative-tone red, green and blue imageable photoresist. The synthesis and use of monodispersed colorant colloids has been described by Giesche and Matijevic for this and other related areas, but their utility is limited to applications not addressing the more advanced color filter requirements mentioned above. To those ends, our work focused on the synthesis, formulation and optical testing of nanocomposite colorant particles ranging from 10–30 nm in size, using dye chemistry which bridges compatibility between both silica nanosphere and carrier polymer, resulting in clear, highly transparent color films. Two independent optical tests comparing the color contrast on nanocomposite red films with coatings of similar transmittance prepared from reference red pigment dispersion provided rationalization that light scattering is significantly reduced in the nanocomposite film, as evidenced by the 3–10 fold increase in the color contrast ratios.

The electro-optical property of PDLC had been improved by optimizing synthetic conditions such as control of crosslinking density of polymer and formulation. The PDLC materials had low driving voltage, high contrast ratio and high reliabilities for the long-term operation. But there remained some problems for applying to TFT LCD panel. The panel structure of TFT LCD was different from that of the transparent ITO glass because TFT LCD panel had many opaque parts such as transistor elements, metal electrodes and black matrix. Opaque parts of TFT panel shielded UV light and resulted in quite - different phase separation behaviors of PDLC prepared from the transparent ITO glass cell.

The sample preparation conditions in TFT panel had to be changed to obtain similiar electro-optical property with ITO glass cell. Changes of UV intensity and photoinitiator species of the PDLC TFT panel were effective to obtain good results. Contrast of the panel and physical property of the liquid crystal could be improved to the level of ITO glass panel.

The materials characteristics of Al2O3 films grown on Si (100) substrate by traveling wave reactor atomic layer deposition were investigated at the growth temperature ranging from 250 to 500°C. The Al2O3 films grown using Al(CH3)3(TMA) and H2O as precursors were characterized and also compared with the films grown using AlCl3 and H2O. In the study of impurity incorporation, the films grown using TMA showed the C and H count rates of secondary ion mass spectrometry (SIMS) approximately 7–10 times higher than those of the film grown using AlCl3. For the Al2O3 films grown using TMA, the impurity contents and the growth rate decreased and the refractive index increased as increasing the growth temperature. The effect of purge time increase on the impurity incorporation was very small compared with that of growth temperature. The refractive indices were 1.64 and 1.68 at the growth temperatures of 250 and 400°C, respectively. The rough estimation using SIMS data and refractive indices indicated that the H-content decreased from 8.6 at% to 2.9 at% as increasing the substrate temperature from 250 to 400°C. The Al2O3 film grown using AlCl3 and H2O at 500°C contained approximately 0.5% Cl and revealed the refractive index of 1.65.

The effect of the annealing characteristics of MgO thin film, which is used as a protecting layer and known to play an important role to life time and lower the firing voltage in AC plasma displays, was investigated experimentally. MgO films were deposited on glass substrates by an electron beam evaporation method and annealed at different temperatures with varying heat treatment time. The characteristics of the crystallization and surface morphology of MgO films were changed by various annealing conditions, confirmed with X-ray diffraction method and scanning and transmission electron microscopes (SEM & TEM). With increasing annealing time and higher temperature, the intensity of the X-ray diffraction peak and the crystalline grain size of MgO increases. With the change of crystallinity and the decrease in grain boundary area, it is considered that the characteristics of firing voltage and life time of the plasma display panel can be improved with appropriate annealing process.

Solid state bulk processing techniques were used to synthesize various transparent conducting oxides (TCO's) with In, Zn, and Sn cations. Optical and electronic properties of resultant phase-pure TCO's were compared to each other and to bulk samples of Sn-doped In2O3 (ITO). Reduction and heat treatment showed significant effects on optical and electronic performance, indicating optimization of processing conditions will be required for industrial applications.

Comparison of optical and electronic properties in the series of compounds: ZnkIn2O3+k, k = 3,4,5,7,11 revealed trends correlated with the materials’ internal structure. These layered compounds showed improvement of optical properties at higher Zn contents and improvement in conductivity at higher In contents. The trends suggest these materials may be useful for applications where tradeoffs between conductivity and transparency are acceptable.

Annealing effects on Al-Nd (0.19 – 1.82 at. %) thin films deposited on a glass substrate have been investigated. It is found that the resistivity of an Al-Nd-alloy thin film decreases significantly after annealing at 300 °C or higher temperatures. Using cross-sectional transmission electron microscopy (X-TEM), we have observed segregation of Al-Nd inter-metallic precipitates and pure-Al grains during the annealing. The decrease of the resistivity can be attributed to the segregation. Segregation has been also detected from the increase of diffracted X-ray intensities corresponding to Al-Nd inter-metallic compounds in X-ray diffraction (XRD) analysis. Atomic force microscopy (AFM) observation has revealed that the optimum content ratio of Nd in Al-Nd alloys used as interconnect materials for thin-film-transistor liquid crystal display (TFT/LCD) applications is around 0.97 atomic %.

We have studied the current waveform as well as the time- and spectrally-resolved optical emission from a monochrome ac plasma display panel as a function of driving voltage. The voltage driver provided a 18 ns risetime pulse which allowed for a clean separation between the displacement current pulse, ∼25 ns wide, and the discharge pulse. The commercial panel was specially filled with pure He to facilitate comparisons with numerical modeling of the discharge based on relatively new computational procedures which are applied to a local-field approximation for the plasma. The delay in the discharge pulse and the light emission at 668 nm (3d 1D→2p 1P), ranges from ∼100 ns just above the sustain threshold (± 110V) to ∼30 ns at higher voltage (±150 V).

Aluminum metallization incorporating the anodic aluminum oxide has been optimized for high-performance amorphous silicon thin film transistors (a-Si:H TFTs). For such a device, the off-current is less than the picoampere and the ON-OFF current ratio is ∼2×107, the field effective mobility is about 1.25 cm /Vsec in the linear region and the subthreshold swing is about 0.38 V/decade. These electrical performances are acceptable for high-definition AMLCDs.

We have prepared transparent conducting films of cadmium stannate (Cd2SnO4 with resistivity as low as 1.5×10-4 Ω cm. The resistivity of these films is low because of their surprisingly high mobility (60 cm2 V-1 sec-1) at high carrier concentration (7×1020cm-3). We conducted an investigation to determine whether the high mobility is due to unusually low carrier effective mass or to a long carrier relaxation time. The conductivity effective mass and relaxation time were estimated by Drude free-electron modeling of reflectance and transmittance spectroscopie measurements. The Drude model appears to represent the behavior of cadmium tin oxide very well. The optical effective mass of the electrons in cadmium stannate is about 0.35 mo, which is similar to that of other transparent conducting oxides. By varying the doping level, we were able to fabricate films with various levels of degeneracy, but these showed no significant difference in effective mass.

We were also able to determine the carrier effective mass and the relaxation time by measuring four separate electron transport coefficients: conductivity, Hall, Seebeck, and transverse Nernst-Ettingshausen (Nernst). The Fermi level was found to vary from 0.31 to 0.83 eV above the conduction band minimum, and the conduction band was very close to parabolic in this range, with m* ∼ 0.33 mo, in good agreement with the optical result. We conclude that the effective mass of electrons in cadmium stannate is similar to electrons in other transparent conducting oxides and that high mobility results from a relatively long carrier relaxation time.

Polycrystalline silicon (p-Si) TFT offers higher aperture ratio with integrated driver circuits compared to the conventional a-Si TFT in AM-LCD application. The advantages of the p-Si TFT as the pixel switching element will be more pronounced for AM-LCDs with large number of scan lines and/or high pixel density. This paper reviews challenges and issues associated with the technology of p-Si TFT, particularly in active silicon layer deposition, solid phase and laser crystallization, hydrogenation, leakage current, performance of different device architectures and reliability. Critical issues affecting the p-Si TFT AMLCD pixel design are analyzed, including: lithographic resolution and overlay accuracy, pixel density and aspect ratio, display format, storage to LC capacitance ratio, and gate dielectric thickness. Predictions on the regimes of dominance for different flat-panel technologies by advantages in performance and-or cost with respect to panel size and pixel density will be presented.

A new LDD poly-Si TFT structure having symmetrical electrical characteristics independent of the process induced mis-alignment is described in this paper. Based on the experimental results, we have established there is no difference between the forward and reverse characteristics and a low leakage current, comparable to a conventional LDD poly-Si TFT, has been maintained for this new poly-Si TFTs. The maximum ON/OFF current ratio of about 1×108 is obtained for the LDD length of 1.0 μm. In addition, the kink effect in the output characteristics is remarkably improved in the new TFTs in comparison to the conventional non-LDD single- or dual-gate TFTs.