We have developed a two-dimensional flat-panel imager (FPI) utilizing conventional amorphous silicon (a-Si) thin film transistor (TFT) technology for AM-LCDs, and we have made a prototype. We can experimentally manufacture the FPI basically by utilizing conventional production lines of AM-LCDs, because the imager is based on the TFT array for AM-LCDs. The TFT performs both switching and photo-detecting functions itself. Using the FPI, we can capture monochrome images in real time, and can also achieve full-color images by introducing time-sequential driving based on a color backlight system with RGB-LEDs. The reliability of the TFT under bias and irradiation stress caused by capturing images is maintained by introducing an original driving method and processing the captured image. By making use of advantages the FPI has over conventional imaging systems, we hope that the FPI will be a useful compact imaging device for documents, pictures, fingerprints, and the like.

Location control of grains by µ-Czochralski process with excimer-laser is a powerful tool for realizing high performance single-crystalline Si TFTs (c-Si TFTs). This study reports the behavior of p-channel single-crystalline Si TFTs fabricated inside a location-controlled grain by µ-Czochralski method. Self-aligned p-channel single-crystalline Si TFTs is fabricated with a top gate structure having ECR-PECVD SiO2 as gate insulator. The field effect hole mobility of 250 cm2/Vs and subthreshold swing of 0.29 V/dec. are obtained successfully. Effects of active Si thickness and boron channel doping on the characteristics of the c-Si TFTs were studied.

A novel multi-phase charge-sharing technique is proposed for the dot-inversion method to reduce AC power consumption of the TFT-LCD column driver without requiring any external capacitor for charge conservation. Simple and easy-to-control circuitry is applied in the proposed method, and the power saving efficiency depends on number of charge phases. Increasing the number of charge phases, the saving power efficiency is also raised. Excluding power dissipation of switches, the power saving efficiency is up to 75% theoretically with infinite phases. For previous work, the maximum power saving efficient is 50% without external capacitor. The HSPICE simulation results including power dissipation of all switches show that the proposed method with seven charge phases (eight-column lines as one group) decreases the power consumption of 23-68% and 10-18%, respectively, compared with original circuit (without any low-power scheme) and previous low-power charge-recycling works.

We report, in this paper, on a combined process of photo-oxidation and PECVD using TEOS and O2 gases to produce an SiO2 gate insulator for poly-Si TFTs. Light of 172 nm-wavelength from a Xe excimer lamp generates active oxygen radicals efficiently and selectively without producing ozone. These oxygen radicals efficiently oxidize silicon. In contrast to plasma oxidation, photo-oxidation offers the ability to produce gate oxides without ion bombardment. Oxide-silicon interfaces with interface trap densities of 2-3 1010 cm-2 eV-1 were obtained by photo-oxidation at 200-300. A stack structure was produced using 4.3-nm-thick photo-oxide topped with a 40-nm-thick PECVD oxide film deposited at 300. This stack structure without annealing exhibited excellent interface behavior and the same J-E characteristics as a 100-nm-thick PECVD film annealed at 600.

We have successfully produced laterally-grown grains on large (300 350 mm) glass substrates by means of a newly developed excimer laser crystallization system that features a high-precision mask stage and an auto-focusing system. The original grains were produced with a steep beam edge and their lateral growth was extended by repeated irradiation and translation. TFTs fabricated with these extended grains were found to have mobilities that remained almost constant at 270 cm2/Vs (n-ch. TFTs) and 230 cm2/Vs (p-ch. TFTs) over a wide range of laser fluence (400-600 mJ/cm2).

We present the effects of N2O plasma treatment for hot carrier reliability and gate oxide stability in excimer-laser annealed poly-Si TFTs. N2O plasma treatment between SiO2 and poly-Si suppresses both the reduction in mobility caused by hot carrier stress and the Vth shift caused by gate bias stress. The results of XPS spectra and the energy distribution of the trap state density of stressed TFTs show that the introduction of Si-N bonds plays an important role in poly-Si TFT reliability.

Low-temperature poly-Si thin film transistor with gate-overlapped LDD (GOLD) structure was fabricated. Reliability was evaluated using electrical stress method comparing conventional LDD and single drain structures. As previous researchers have reported, we have confirmed that the degradation of ON current and the field effect mobility was very small compared to conventional LDD or non-LDD structures. We have analyzed the reliability of the GOLD TFT using two-dimensional device simulator. We have clarified that vertical negative field plays a dominant role for improving the reliability in the GOLD TFT. Impact ionization occurs far from the interface between the oxide and poly-silicon by the vertical negative field. GOLD structure is promising for the realization of system on panel.

New positive and negative bias voltage generators for TFT-LCD's drivers utilizing charge pump circuits are introduced. The generators can generate positive or negative voltages with various amplitude by simply changing the number of pumping stages. By using the circuit simulation program HSPICE, it is demonstrated that the introduced generators can provide enough positive or negative voltages for TFT-LCD's drivers.

The a-Si TFT characteristics were studied for process temperatures of as low as 100C. The a-Si TFT kept normal characteristics for process temperature of as low as 150C. The a-Si TFT bias temperature stability was evaluated and degradation of stability initiated at around 150C. The characteristics of a-Si TFT fabricated on plastic substrates were the same as those of a-Si TFT fabricated on glass substrates at low process temperature. TFT-LCD fabricated at a process temperature lower than the glass transition temperature of plastic substrates indicated good display image. These results indicate the possibility of fabricating TFT-LCD on plastic substrates, which would promote the application of a-Si TFT-LCD for mobile devices.

We have proposed and fabricated a new poly-Si TFT employing the selectively doped regions in the active layer. In the proposed poly-Si TFTs, the selectively doped regions where doping concentration is identical to that of the source/drain, reduce the effective channel length during the on-state. Under the off-state, the selectively doped regions may reduce the lateral electric field induced near the drain and reduce the leakage current considerably. The experimental data of the proposed TFT exhibit high on-current, low leakage current and low threshold voltage. The fabrication of the proposed TFT is rather simple; the required steps for the proposed TFT are reduced because high dosage ion-implantation for the source/drain and the selectively doped regions is performed simultaneously prior to excimer laser irradiation step.

This paper demonstrates the slope isn't an appropriate parameter to characterize a signal regarding conducted electromagnetic disturbances. On the other hand, a relevant criterion is made conspicuous: it defines the maximum slope deviation between two segments forming a signal. This criterion is validated by a signal with a maximum slope of 400 mA/µs.

We proposed a new method to evaluate display legibility as a function of resolution. This method was able to evaluated display legibility without being restricted to the display resolution. Using this method, subjective psychological experiments were carried out to investigate display resolution, which provides legibility, in observing small characters. Samples viewed by subjects were images displayed on a high-resolution TFT-LCD that we developed, CRT images and printed documents for comparison. We have found that TFT-LCD legibility was much better than that of CRT, and that minimum resolution of about 175 dpi was needed for use in legible document viewers.

The full liquid crystal display (LCD) simulation with real transistors and other active components is unrealistic. Because a flat panel display (FPD) includes thin-film-transistors (TFT's) whose number is, at least, the number of total pixels. It hits the simulation limit of SPICE if the number of transistors are more than 0.5 million. This paper demonstrates a new, fast, and effective simulation method for a full LCD panel. The method makes it possible to simulate large LCD panels whereas the conventional method cannot handle. The simulation circuit consists of a-Si TFT model presented earlier, the liquid crystal, the pixel macro models, and interconnects. We show the model parameter extraction and the pixel macro modeling process associated with the simulation results. Using the simulation method presented here some larger LCD panels can be accurately simulated in less than a minute on a workstation.

We have analyzed a displayed image of TFT-LCD three-dimensionally in case of low power drive using Multi-Field Driving Method (MFD). We have also proposed a concept of multi-media driving method using MFD in which a displayed image was divided into some interlaced subfield images and the number of interlaced subfields can be changed depending on the moving quantities of displayed images. This method made it possible not only to reduce a driving power consumption in case of still images to less than half, compared to that with conventional methods, but also to maintain high moving image quality.

A Suitable TFT structure for wide viewingangle displays with in-plane switching mode of nematic LCs has been developed. The structure can be constructed by simplified process reduced the number of electrode layers, suppressing crosstalk generation which is essential for combining the IPS mode with TFTs. A practical aperture ratio was obtained in spite of the existence of interdigital electrodes in a pixel. It has also been adopted into a prototype which have a 10.4 inch diagonal display area with VGA resolution and which display 262,144 colors. This prototype has clarified that these display with the IPS mode have extremely wide viewing-angle characteristic exceeding the polar viewing-angle of 45 degrees satisfying contrast ratio more than 10 without gray-scale inversion in all azimuthal angles. In particular, the color shifting area is very slight in comparison with conventional TFT-LCDs with twisted nematic mode. It has been confirmed that IPS-TFT-LCDs are promising candidates for the next generation LCDs with wide viewing-angles and make it possible to replace CRTS in monitors and televisions.

A 33-cm-Diagonal High-Resolution(1280 1024RGB, which stands for red, green, and blue) TFT-LCD with low, uniform parasitic capacitance between gate electrodes and source/drain electrodes has been developed using Fully Self-Aligned a-Si TFTs. The fabricated TFT-LCD shows no visible seams between block shot exposure regions, even in the display of gray images. In this paper, we describe(1) our full self-alignment technology for the TFTs, including the fabrication process and the technology for reducing OFF current in the TFTs under illumination, (2) SPICE simulation for estimating pixel voltage shift in the fabricated TFT-LCD, and (3) performance results for the fabricated TFT-LCD.

This paper proposes a new duplication redundancy technology, 2 Transistors for 1.5 Gates, that is capable of automatic defect tolerance, so making large, high-resolution, color TFT-LCD panel fabrication both easy and economical. This redundancy technology with automatic defect tolerant capability has a low hardware overhead and is very capable of compensating for open circuit defects in a large active-matrix panel. This technology was confirmed by fabricating a 9.5-inch color TFT-LCD panel with 640480 pixels(960960 dots). This panel showed excellent display performance and produced pictures without defects. The yield improvement effect of this technology was also confirmed by calculation based on the Boltzmann statistics model. Consequently, this technology is clearly seen to have a yield improvement effect equal to defect density reduction of about one order, compared to non redundancy. This technology drastically reduces dot and line defects, enabling fabrication of large, high-resolution, color TFT-LCD panels at a relatively low cost.

The characteristics of a-Si bottom-gate TFT test devices with several kinds of inorganic "quasi-black matrix," such as metal, semiconductor, and insulator, on the top were investigated for various black matrix(BM) resistivities. In the Ia-Vg characteristics, for a BM sheet resistance of about1 1012 Ω/, a high off current and large Vth shift were observed due to the back-gating effects when the BM is charged up. Accrding to the ac dynamic characteristics, there was almost no leakage due to the capacitive coupling between source and drain after 16.6 msec(one frame) when the BM sheet resistance was above 7 1013 Ω/ . It was found that hydrogenated amorphous silicon germanium(a-SiGe:H) film, which has enough optical density, with the sheet resistance above the order of 1014 Ω/ is a promising candidate for an inorganic BM on TFT array.

We have proposed a concept of low power drive system for a multi-media TFT-LCD using MFD in which a displayed image is divided into some interlaced subfield images and the number of interlaced subfields can be changed depending on the moving quantities of displayed images. This method has been applied to a 9.5" TFT-LCD and successful operation has been confirmed without moving image degradation.

We have fabricated a new analog memory for integrated artificial neural networks. Several attempts have been made to develop a linear characteristics of floating-gate analog memorys with feedback circuits. The learning chip has to have a large number of learning control circuit. In this paper, we propose a new analog memory SDAM with three cascaded TFTs. The new analog memory has a simple design, a small area occupancy, a fast switching speed and an accurate linearity. To improve accurate linearity, we propose a new chargetransfer process. The device has a tunnel junction (poly-Si/poly-Si oxide/poly-Si sandwich structure), a thin-film transistor, two capacitors, and a floating-gate MOSFET. The diffusion of the charges injected through the tunnel junction are controlled by a source follower operation of a thin film transistor (TFT). The proposed operation is possible that the amounts of transferred charges are constant independent of the charges in storage capacitor.