The most critical issue in the design of an active matrix organic light emitting diode (AM-OLED) display pixel is the pixel to the pixel luminance uniformity. By substituting four-thin film transistor (TFT) pixel circuit for two-TFT pixel circuit, the luminous uniformity has great improved, but it requires more components than the two-TFT pixel circuit. There are some barriers needed to resolve to utilize hydrogenated amorphous silicon transistor to lit OLED, such as low field effect mobility, low output current and threshold voltage shift. In this article, a two-a-Si:H TFT pixel circuit was designed, which consisted of one named switching TFT and the other named driving TFT. The driving TFT gate line structure modified and a data signal timing improved were reported. The modified driving TFT can provide enough current about 30 microampere to lit OLED and the novel data signal timing can provide a constant current to OLED by restraining the driving TFT threshold voltage variation. In the novel data signal timing, the control signals to the driving TFT gate include a data signal and a reverse data signal. The signals alteration is performed either at a frame rate or at a line rate. By experiments, the driving TFT output current value is plotted as a function of the time in different reversed voltage value. When the magnitude of the positive data signal and the negative data signal is equal, the variety of ΔVth is smallest, about 1.28V after a fixed stressing time of 1.33×104min, which shows the novel data signal timing can improved the driving TFT output-input current stability.
The effect of polymer network polymerized under UV irradiation with electric field application (+/- 50V, 5Hz) to FLC molecule orientation and electro-optic characteristics have been studied. Optical and scanning electron microscope were used to invest the molecule texture and the polymer network structure. The polymer network formed in SmC* phase is anisotropic and fibber-like, a new type texture-striped texture was observed in the cell. The electro-optic performance of the cells was also measured. A fairly good memory state with excellent contrast ratio higher than 20 and a low threshold voltage less than 5V were obtained. At last the striped texture was explained with elastic free energy theory.
A novel structure for an electro-optically controlled Fresnel phase zone plate is proposed. This structure consists of a liquid crystal layer, which takes a homogeneous alignment parallel to the glass substrate surface, and ITO (indium tin oxide) electrode layers on the inner surface of the two glass substrates are formed with the same odd and even zone pattern respectively by using photolithography technology. This kind of zone plate in principle gives nearly 100% diffraction efficiency, and its light gathering power can be electrically adjusted. The detailed fabrication process and primary experimental results are presented.
The image-sticking caused by the asymmetry and shift of current-voltage (I-V) characteristics of the MIM element is a big problem in MIM-LCD. The I-V characteristics couldn't be described accurately and comprehensively by conventional Poole-Frenkel equation, so it is difficult to estimate and optimize various parameters to solve the problems, which means the optimization of the parameters requires many experiments with much effort. In this article, considering the effect of the two interface layers which exist between the two electrodes and the intermediate layer, we introduce a p-n-n+ band model. Using this model, we can explain the reason of the asymmetry and why it is easier to produce Poole-Frenkel effect from the top-electrode to the bottom- electrode than it does on the opposite direction. Meanwhile, we propose that using the weaker electronegative metal as top-electrode or using the sputtered tantalum oxide instead of the anodized tantalum oxides as insulator layer can solve the problem.
A new method of improved viewing angle of STN-LCDs was studied. Adopted method of multi-domain compensating for viewing angle of TN-LCD. In this paper, we reported the double domain STN LCD cells' structure and fabrication process, applied twice rubbing technique and lithography process and accurately orientation. We compared with the viewing angle characteristics of the conventional STN and the DDSTN. Compare with them, you will find that viewing angle of the DDSTN is more improved, it changes wide and uniform, and it is wider than viewing angle of the conventional STN. We also compared the conventional STN with the DDSTN on electric-optics characteristic each other. We analyzed the reason of contrast decrease of the DDSTN LCD, discussed the solvable method.
The afterimage caused by the asymmetry and shift of current- voltage (I-V) characteristic of a metal-insulator-metal (MIM) switching element in the MIM-LCD is a hot and difficult problem which has been being studied until now. The I-V characteristic couldn't be described accurately and comprehensively by the conventional Poole-Frenkel equation, so it is difficult to estimate and optimize various parameters to improve the I-V characteristic in experiments. We introduced a p-n-nPLU band model. The model not only explains some experimental phenomena but also has directive function in experiments. By choosing the weak electronegative metal as top-electrode and Ta with acceptor impurity as bottom-electrode, we not only improve the symmetry of the I-V characteristic but also enhance the current ratio of the on-site and off-state.
A new LCD device called Polymer Stabilized Amorphous (PSA) STNLCD was prepared by one-side rubbing technique and adding a low percentage of a polymer dopant into the cell by curing the photopolymers under the application of an electric. It's shown to introduce a LC polymer network. A wide viewing angle characteristics and reduction of driving voltage have been demonstrated. Comparing with the conventional one-side rubbing STNLCD, the PSA-STNLCD has more stability and adapt to mass production.
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