This paper reviews advanced excimer-laser crystallization techniques and its application to crystal-Si thin film transistors (TFTs). Combined microstructure and time- resolved optical reflectivity investigations during conventional excimer-laser crystallization showed that explosive crystallization occurs during excimer-laser irradiation. Two methods enabling location-control of large silicon islands will be reviewed. One of the methods uses local thermal relief by modifying locally the heat extraction rate towards the substrate. A small unmolten region remains at the center of high heat extraction part which then acts as a seed for radially grown Si grain with a diameter of 6 micrometers . One of the other methods use geometric selection through a vertical narrow constriction. In this method, upon laser irradiation, a small unmolten Si region remains at the bottom of narrow holes etched in the underlying isolation layer. During vertical regrowth, a single grain is filtered out which subsequently seeds the lateral growth of large grains. We will also discuss the performance of crystal-silicon TFTs that are formed in the location-controlled Si grains. The field-effect mobility for electrons is 450 cm²Vs, which is very close to that of TFTs made with silicon-on-insulator wafers.

Changing the TFT backplate from a glass to a plastic substrate will reduce the weight of a Flat Panel Display (FPD), but transparent plastic substrates are generally only temperature-resistant up to 125 degrees C. We have focused therefore on reducing the maximum processing temperature to 110 degrees C. Sputtered a-Si films are more suitable for laser crystallization on plastic, because they contain no hydrogen and can be crystallized by an excimer laser even if deposited at room temperature. We report high-quality poly- Si obtained by pulse laser crystallization on a plastic substrate coated with a buffer layer. A doping technique for source and drain compatible with a low temperature wide area substrate, based on excimer laser annealing, has been developed. The results of UV reflectivity, SEM, TEM, AFM, and Raman spectroscopy studies are summarized. Self-aligned top-gate TFTs fabricated on a plastic substrate at a substrate temperature of 110 degrees C are reported. Transistor field effect mobility of 250 cm²/V.s and a sub-threshold swing of 0.16 V/decade have been reported. Work on TFT s fabricate don plastic substrates is summarized.

The excimer-laser-based machine developed by SOPRA for the Low Temperature Poly Silicon (LTPS) exhibit unique characteristics described in the present paper. The machine consists in a laser source, an optical set-up to homogenize the beam and a motion stage. The laser source is able to deliver up to 20 J per pulse. A shot to shot stability currently better than 4 percent ensures a high reproducibility of the annealing. The pulse duration of 200 ns is also known to improve the process in terms of resulting Si grain size. Due to the high energy per pulse, a large surface of typically 18 cm² is annealed at once. Recent studies pointed out the good reproducibility of the TFT made of Si annealed by mean of this system: a deviation of the mobility of only 7.6 percent has been obtained for several tens of TFT which average mobility is of 234 cm²/V.s. Performances of TFT can be improved by annealing the a-Si in controlled atmosphere. TFTs submitted to an electrical stress, exhibit a much better stability than that of TFTs obtained by Solid Phase Crystallization. The variation of the slope of the 'laser processed' TFTs is two to three times lower than that of 'SPC' TFTs.

Liquid-crystal displays (LCDs) especially active-matrix LCDs are conquering the display market. The market has forced a continuous process development to fulfill all of the demands from the various fields like car navigation systems, multi- media applications, laptop computers or PC displays. The LCD manufacturers face a constant challenge to produce higher performance display at lower costs. Therefore, they are looking for the most cost effective and best production technique.

We have developed excimer-laser-annealing modeling capability by broadening the computational ability of a standard finite-element based computational-fluid-dynamics software package to adopt to the specific demands of very rapid heating of thin a-Si films. This was achieved by the incorporation of a subroutine employing a phase function and a set of rules for determining latent heat absorption or release. Wit this enhancement the model was able to correctly calculate the degree of superheating/undercooling in the film and track the melt-solid interface velocity. The model also provided reasonable estimates of the expected poly-Si lateral growth length as a function of the laser irradiation scenario. The model in its current form is a useful tool for first order calculations and for supporting relevant experimental studies.

The mobile display market has been changing with the evolution of the information technology. The display is trying to be more compact and more by integrating new functions. The LPS TFT Is one of the most expected technologies to realize the integrated circuits on the display panels. In this paper, the technologies of TFT-LCD are summarized and the future directions of the technology are discussed, mainly focused to the crystallization and the gate insulator formation.

A novel technology that makes it possible to transfer thin film devices from an original substrate to the other one by using laser ablation/annealing has been developed. This technology is named SUFTLA which stands for surface free technology by laser ablation/annealing. In the process of this technology, polycrystalline-silicon thin film transistors and TAFT circuits, which are firstly fabricated by the low-temperature process below 425 degrees C on quartz or glass substrates, are transferred onto plastic substrates. Any degradation during the transfer process are not observed. By using this technology, CMOS ring oscillators and a TAFT array with integrated drivers for LCD have been developed on plastic substrates and their compete operations were confirmed. This technology is not only applied for displays such as LCD and OELD, but also to any kinds of TAFT circuits including memories and logics on plastics. It also enable us to fabricate a 3D ICs with a very simple manner.

Although it has been developed for more than a decade, low temperature polysilicon technology is far from being as mature as its amorphous silicon counterpart. This is due to much more complex processes, that are not used at all in related industrial areas, such as the microelectronics industry. In this paper, we first present the major critical process steps of the low temperature polysilicon technology, including laser crystallization and MOS-type oxide deposition. In a second part, we show that if high information content displays are to be fabricated with organic light emitting materials, they will certainly use a polysilicon active matrix, because of the inherent stability of this material.

Incorporating low temperature poly-Si (LTPS) technology as an active matrix (AM) in flat panel displays (FPDs) has been a struggle and remains costly. The situation motivates companies to investigate alternative AM technologies. Some projects try to relieve the low temperature constraint by switching the substrate material to a metal foil. Some companies try simply to make the most out of a-Si:H technology. Another strategy is to replace silicons as the TFT channel material. Examples include CdSe and even an organic material like pentacene. When crystalline silicon is considered best, engineers consider how to replace excimer laser annealing (ELA) and its cost. A prominent example is the effort at MIT, which printed devices with a kind of 'semiconductor ink'. The best prospects for inexpensive AM backplanes may be plastic transistors and c-Si block assembly. Current leaders of AM technology, a-Si:H and ELA- LTPS, might still end up offering better overall performance, but their costs will probably be higher.

We report upon the measurement and simulation of the switch- on transient of polycrystalline silicon tin film transistors. The measurement of the switch-on transient reveals an unexpectedly long transient that cannot be explained by the theory adopted for single crystal silicon on simulator devices. In order to explain the experimental findings we have performed simulations of the transient and found that only when energy dependent cross sections are adopted do the calculations correctly reproduce the steady state and overshoot currents and also the transient duration. A physical interpretation of this phenomenon is presented, together with an analysis of the dependence of the transient upon the length of the channel and upon the source-drain voltage.

A key requirement for the development of advanced digital drivers for Low Temperature Poly-Silicon (LTPS) active matrix displays is the provision of a high bandwidth, high resolution Digital to Analogue Converter (DAC) as a prerequisite for higher level integration. For a given panel specification and data rate, the bandwidth and resolution of the conversion process directly influence the efficiency of a digital driver implementation in terms of bezel size, transistor count and power consumption. This paper is concerned with the design and realization of a programmable high performance DAC architecture which meets the requirements for a compact and highly efficient digital data driver. The high performance of the two-stage architecture is achieved by means of a novel pre-charge arrangement that not only increases the speed of operation, but also provides for offset compensation of an analogue buffer with considerably reduced slew rate requirements and power consumption. A switched capacitor implementation of the DAC architecture is presented and the theoretical specifications are verified by simulation. The application of the new architecture to advanced digital drivers with programable input data resolution is briefly discussed.

We have successfully fabricated a variety of analog and digital thin film transistor circuits on a flexible stainless steel foil substrate, the majority of which serve display driver purposes. We have modeled the operation of a number of different circuits, in order to determine how the substrate affects their performance. We have verified that a major performance-limiting factor in this type of circuits is the parasitic capacitance to the conductive substrate. The results of our analysis can also provide for some basic guidelines to aid future design and development.

The burgeoning number of mobile consumer electronics has created a demand for lightweight, low-cost, portable displays. The development of a polycrystalline-silicon thin film transistor (TFT) technology compatible with plastic substrates will enable displays and large-area electronics that are low power, rugged and flexible. Significant challenges exist in the development of a polysilicon TFT fabrication process that is compatible with plastic substrates, since plastic has a much lower thermal budget than glass substrates. In general, superior polysilicon TFT performance is achieved with higher temperature fabrication processes because the quality of the polysilicon and gate- dielectric films are very sensitive to process temperature. In this work, an ultra-low-temperature process for fabricating high-quality self-aligned polysilicon TFTs on flexible plastic substrates is described. All fabrication steps are performed at or below 100 degrees C. Polysilicon is formed by crystallizing sputtered amorphous Si films using a XeCl excimer laser with a pulse duration of approximately 35 ns. Gate oxide deposition is formed using high-density plasma CVD, and metal films are deposited by sputtering.

We have successfully fabricated polysilicon thin film transistors on a flexible stainless steel foil substrate. Both - and p-channel devices have been subjected to DC and AC voltage stressing, in order to provide for a basic measurement of their performance. We have compared these characteristics with results obtained from devices we have previously fabricated on quartz substrates, and have found no evidence that the stainless steel substrate has affected the reliability of the transistors. We therefore believe that polysilicon devices and circuits on steel present an attractive alternative to transistors fabricated on more expensive substrates, without any reliability compromise.

Today organic light emitting diodes (OLEDs) are entering the market lace as a competitive flat panel display technology. Rapidly OLED displays are moving from small passive matrices to full color active matrices built on conventional indium tin oxide coated glass. The work in this paper is focused on developing high resolution full color displays on flexible substrates. Presented here will be new developments in high efficiency OLED displays with the application of this technology to flexible substrates thus allowing a whole new generation of display concepts to be realized.

Lateral polysilicon p⁺-n-n⁺ and p⁺-p- n⁺ diodes in a series combination of 2 to 5 were fabricated and their electronic properties such as ON- resistance, reverse current and ideality factor were studied. Since the multiple diodes are in series with each other, they have a reduced reverse current. Such a series combination can be used as a single device in applications such as x-ray sensing arrays, which need switching devices with reverse current lower than 1 by 10^-12 A and forward current more than 1 by 10^-6 A. The ON- resistance and the ideality facto increase linearly with the number of diodes in series. This behavior is attributed to the effect of series combination of diodes.

In order to realize a fully integrated polycrystalline silicon thin-film transistor organic electro-luminescent display (poly-Si TFT-OELD) with good image quality, problems caused by spatially non-uniform device characteristic in TFTs must be addressed. In TFT-OELDs, spatial variation of threshold voltage in TFT driving circuits leads to non- uniform brightness and poor grayscale accuracy. Consequently, special pixel driver circuits are designed to overcome such difficulties. TFT-OELD analog and digital pixel driver circuits are closely examined and design difficulties are pointed out. For example, in an analog driver circuit, one difficulty is to minimize the power consumption given the spread of (Delta) V_(Tau ); whereas in a digital driver circuit, one of the difficulties is how to maximize the number of grayscales. Performance of important circuits are analyzed and compared through circuit simulations using a poly-Si TFT model. Finally, suggestions of grayscale accuracy improvement are made.

Polymer LEDs provide a new alternative to LCDs for many display applications, and are particularly attractive because of their high brightness, near-perfect viewing angle, and very fast response time. In this paper, the basic technology used to form the LED structures, and the performance of these devices is presented. Then, the fabrication and driving of passive addressed matrix displays formed using this technology is discussed. Finally, the necessity for active matrix addressing for larger size and higher resolution displays is demonstrated, and it is shown that this is best achieved using low temperature poly-Si technology. The state-of-the-art poly-Si technology used for active matrix addressed LED displays is described, with particular reference to transistor variation, and the resulting non-uniformities in images on displays. A variety of different addressing techniques, and pixel circuits can be used to drive the LEDs in the active matrix, and the performances of these schemes are compared. These include the basic current source circuit; the modified current source circuit; transistor current mirror circuits; and circuits with optical feedback and correction for uniformity variation. Consideration is given both to analogue and to digital drive methods.

A new pixel electrode circuit based on hydrogenated amorphous silicon technology has been designed, fabricated and characterized for the active-matrix organic light- emitting displays. This circuit has four thin-film- transistors (TFTs) and only two external terminals. In addition, a current driver is used to provide the signals to the data line and automatically adjust the current level to compensate for the threshold voltage shifts of both the organic light-emitting devices and the drive TFT. Consequently, this pixel electrode circuit has an excellent electrical reliability even when a large threshold voltage shift is present. Experimental results indicate that a continuous pixel electrode excitation can be achieved with these circuits. Even after a long time circuit aging stress, this circuit only shows an output current level variation less than 1 percent at the high current level and less than 5 percent at the low current levels. Two additional pixel electrode circuits have also been proposed. These new circuits can achieve a higher output current level and a better output-input current linearity without sacrificing the circuit's electrical reliability. All these circuits can potentially be used for the active-matrix organic light- emitting displays.

Recent advances in electronic imaging have led to an increased utilization of soft-copy display for presentation and diagnostic interpretation of medical images in clinical settings. Because of the fundamental importance of display quality in the overall effectiveness of diagnostic imaging, the AAPM has recently formed a Task Group (TG18) to address the acceptance testing and quality control of medical electronic display devices. The purpose of the Task Group is to provide standard guidelines for performing displays evaluation by practicing medical physicists, engineers, and displays investigators, to assure adequate display performance for clinical tasks, and to facilitate inter- and intra-institutional comparisons. The scope of the effort is limited to display devices for monochrome radiological images. The performance characteristics considered include luminance response, luminance uniformity, resolution noise, veiling glare, ambient light response, color uniformity, geometrical distortions, and displays artifacts. For each of the characteristics, three levels of evaluation are considered: visual, quantitative, and advanced. Based on the current standard of practice, suggestions are made for the acceptable ranges of display performance with limited impact on diagnostic efficacy. The purpose of this paper is to provide outline and summary of the TG18 report.

Examinations of the skeletal system have historically used 'detail' x-ray film screen combinations having film-lightbox image quality that is challenging to replicate in a soft- copy environment. A review of the basic diagnostic imaging tasks for this sub-specialty is presented, including resolution and gray scale requirements for visualization of subtle fractures, bone mineral loss, implant loosening, and soft tissue disease. Measurements are made to specify image quality metrics in terms of Michelson contrast, spatial resolution, and dynamic range. Image contrast requirements are presented using Just Noticeable Differences values based on the NEMA and DICOM grayscale softcopy standard of Annex B, Part 14. Image dat is used to calculate modulation transfer function for a type of liquid crystal active matrix display being considered for clinical use.

Color and luminance uniformity testing of displays is often limited to fewer than ten measurements points on the display surface due to the length of time necessary to make a single point measurement. A CCD-based digital imaging tristimulus colorimeter has been developed which is capable of measuring luminance and chromaticity coordinates at over one million spatial locations in several seconds. The Four-Color Method of colorimeter calibration, recently proposed by NIST, has been employed and found to be superior to single point calibration using Illuminant A. Color and luminance uniformity of a CRT and LCD display were measured using the new digital imaging tristimulus colorimeter and a diode array spectrometer. The data show that chromaticity coordinate and luminance measurements using the CCD-based imaging tristimulus colorimeter compare favorably with the point measurements obtained using a diode array spectrometer over the color gamut of a CRT and LCD display.

The image photometer measures the photometric characteristics of part or all of a scene stored as photometrically valid image data obtained from a calibrated electronic camera. The technology can offer significant advantages over other photometric methods for measuring visual displays. We review the characteristics of the components of the image photometer and its calibration and discuss how they affect the validity and reliability of its measurements. We also discus how specific design features affect the robustness and ease of use of the display measurement process. The costs and benefits of image photometry are compared to the current alternative photometric measurement technologies.

The appearance of noise on a display is an important usability issue. Sources of noise include electrical interference, display driver artifacts, resampling artifacts, transmission artifacts, compression artifacts, and any intrinsic noise artifacts produced within a display device. Issues for the severity of the noise problem include total magnitude of noise, noise spatial frequencies, proximity of the noise spatial frequencies of the desired information content and the human-eye response to that information content, uniformity of the distribution of noise, and appearance of any visible or regular patterns in the noise. Whatever the source, an accurate method to measure noise may be required to properly assess the influence of the noise. We investigate the intricacies of using a digital camera to accurately measure noise in a static image on a flat panel display (FPD). The electro- optical transfer function of the FPD is measured. A known noise pattern is displayed and measured using the digital camera whereby the predicted noise is compared to the measured noise. Complications and limitations in the metrology will be discussed.

RSD technology is a comparatively new technology. What RSD technology is and how it differs from other display technologies is discussed below. This paper also discusses how to measure contrast of a RSD in a manner that allows comparison of contrast to other types of displays. At first sight, it seems to be a straightforward task involving a simple measurement. However the choice of contrast test procedure and equipment setup determines this number. A contrast ratio test is suggested as a method that allows for fair comparisons between different types of displays.

With the proliferation of liquid crystal displays as the primary instrumentation interface on aircraft flight decks, it becomes important to quantify and control the unique optical parameters, associated with AMLCDs, that affect readability in a critical environment. It has been discovered that image distinctness, in addition to reflected energy intensity, can be a significant detriment to display readability. Consequently, efforts are being made to establish measurement procedures and quantify distinctness- of-image to help control the detrimental effects of this characteristic. Two measurement methods will be discussed that are currently being considered for use in describing the degree of specular distinctness-of-image reflections on avionics AMLCDs.

Flying-spot displays use narrow-spectrum high-power sources that scan the image across the display screen. They can provide a bright display with a large color gamut. When such displays are measure with conventional light-measuring devices (LMDs) such as luminance or illuminance meters, there is concern that the LMD may not accurately measure the display's photometric and colorimetric output. The unique characteristics of the source may exceed the limitations of the instrumentation. A series of diagnostics has been developed that allows for an evaluation of LMDs for use in measuring flying-spot displays. Limitations resulting from LMD saturation, timing, and tristimulus or photopic filters can be revealed, and in some cases, specific causes can be identified. Each diagnostic will be demonstrated using several instruments, including luminance meters, illuminance meters, colorimeters and spectro radiometers. Using a simple comparison box, flying-spot displays can be viewed side-by- side with steady-state sources in a bipartite image. After the sources have been visually matched in color and luminance, the two images can be measured with a particular LMD, and results compared. Any significant difference between results would indicate a limitation of the LMD. Further diagnostics, using integrating spheres, neutral density filters and interference filters, are used to aid in identifying the nature of the limitation, and in some cases, point to solutions.

In active-matrix liquid crystal displays with large pixel array and large number of graylevels, the luminance of a pixel depends on the luminance of the rest of the image. This artifact known as crosstalk is caused by parasitic phenomena in the active-matrix array. When interpreting high information content medical images with subtle features and structured background, crosstalk can affect image fidelity and diagnostic performance. Conventional methods rely on the measurement of the luminance change of small square targets located across the screen when changing the background intensity. We present a method that describes both the magnitude and the spatial extent of the crosstalk artifact. The method is based on the formulation of a response function that corresponds to the differential contribution of a vertical or horizontal line to the luminance of a small centered target. The response function is defined for a given screen position, along the horizontal or vertical display axis. Our measurements show that subtle differences between vertical and horizontal crosstalk can be detected with the proposed method, and that mots of the influence is confined to a 40-pixel region about the target. The results obtained with the proposed characterization method allow for the modeling of crosstalk effects to determine its impact on a variety of visual tasks.

This paper proposes the use of tritium-activated light sources made up of CRT phosphors to act as transfer devices between reference spectro radiometers and CRT color measuring instruments. We describe the composition and characteristics of these sources and discuss their suitability as standards. We report on the laboratory measurement and testing of sources of similar nature obtained from a safety sign manufacturer. In these experiments we tried to tag red, green and blue sources with precise tristimulus values in order that they could serve as reference targets for the application of matrix correction methods to colorimeters. We find that chromaticity values can indeed be obtained with adequate accuracy. The establishment of reference luminance values was found to be problematic because the set of sources used showed noticeable spatial non-uniformity, a problem that should be overcome by tighter control of the fabrication process and careful sample selection.

A light source with a programmable spectral output was designed and constructed following the identification of limitations in current display calibration techniques. Current calibration of a display measurement instrument compares the measured spectral output of a pre-calibrated reference light source with the calibration data traceable to national standards. This allows correction factor to be calculated for each wavelength and entered into the measurement instrument. However, the reference light source used to create these correction factors is very dissimilar in spectral output to test display such as cathode ray tubes (CRT) or liquid crystal display (LCDs). The dissimilarity between the reference calibration spectrum and the spectrum of the tested display gives errors at some wavelengths, which leads to inaccurate measurement of color and luminance, and inter-instrument disagreement. The development of a light source with a programable spectrum, will allow display measurement instruments to be calibrated against a reference source that mimics the spectrum of the device under test, improving the accuracy of measurements and the agreement between display measurement instruments. This paper describes the prototype programmable source and demonstrates the feasibility of mimicking both CRT and LCD spectra. The programmable source could be used as a transfer standard to assess display measurement techniques in international laboratories.

In this paper, we describe the implementation of a color calibration method for LCDs where we assume that the angle of vision is normal to the center of the screen. We change the procedure generally used with cathode ray tubes and take into account the high intensity black of an LCD, the variable chromaticities of its primaries and the less than perfect additivity of its colors. This is done by modifying the calibration data and using correction tables. We describe three rendering algorithms which can be used with this implementation. We test them on four IBM LCD models produced in the last four years and conclude that the simplest algorithm is adequate for the latest model.

A prototype display measurement assessment transfer standard (DMATS) is being developed by the NIST to assist the display industry in standardizing measurement methods used to quantify and specify the performance of electronic display. Designed as an idealized electronic display, the DMATS illumination source emulates photometric and colorimetric measurement problems commonly encountered in measuring electronic displays. NIST will calibrate DMATS units and distribute them to participating laboratories for measurement. Analysis of initial interlaboratory comparison results will provide a baseline assessment of display measurement uncertainties. Also, diagnostic indicators expected to emerge from the data will be used to assist laboratories in correcting deficiencies or in identifying metrology problem areas for further research, such as measurement techniques tailored to new display technologies. This paper describes the design and construction of a prototype DMATS source and preliminary photometric and colorimetric characterization. Also, this paper compares measurements obtained by several instruments under constant environmental conditions and examines the effects of veiling glare on chromaticity measurements.

Experimental and theoretical results are reviewed for an excimer-laser-based Si large-grain growth method aiming at a 'system-on-panel' technology. Temperature in the Si thin layer should have a gentle slope along the one direction for growing large grains and should have a steep dip along the other direction for controlling their positions. In order to produce such a temperature distribution using an excimer- laser light pulse, phase-shifter patterns that generate the 2D distribution of the light intensity on the sample surface by Fresnel effects should be independently optimized for both directions. The sample should be of a stacked structure of the heat storage layer, the Si layer and the underlayer with low heat diffusing power. The Si layer thickness is a critical parameter for long grain growth, and should be very thin under the condition of the thick heat storage layer. The growth large grains seem to have excellent crystallinity although experimental data is not sufficient.