Abstract
Recently, new imaging devices that take advantage of the TFT array have been developed in the non-display field. The majority of touch-enabled AMLCDs, active matrix liquid crystal display, are based on resistive, capacitive or inductive touch technology. All these solutions require externally added components or screens, which add cost and reduce optical performance. If we can match the passive pixel sensor circuit and use them on the medical image, we can promote the detection rate of the disease by a wide margin. In this way, a photodiode can be integrated into each pixel of the TFT array, or a photoconductive layer can be formed on the TFT array. Thus, the electric charge generated in the photo-detective can be stored in the pixel, depending on the outside of light signals. Then, the charge intensity information can be read out as the imaging data by sequential line-addressing.Passive pixel sensors provide an alternative to the conventional Active Pixel Sensor (APS) for high-density CMOS imaging arrays. Similar to the history of the single-transistor DRAM cell, this one-transistor pixel cell boasts one main advantage over the APS. It can achieve a high fill-factor in a smaller area, leading to a high density array of pixels with high quantum efficiency.Learn in the reports of several experiments, a major weakness in passive pixels is a signal-dependent parasitic current that can contaminate charge signals in different parts of the array. In this thesis we use HSPICE as the tool, and simulate several important parameters in passive pixel sensor circuit in amorphous Si TFT. The simulation result in the thesis demonstrates that, with the photo sensor current as small as 10-12 to 10-15 (A), the signal is not influenced by parasitic current in the circuit and can be conveyed out without deterioration.According to the result of our study, if it can be practically applied to the products design, and if the result is good, we believe that the application of passive pixel sensor with amorphous Si TFT will move a big step forward and be adopted to use widely in different consumer products.