The traditional displayer ¡V CRT has already been substituted by liquid crystal displayer (LCD).The a-Si TFT is used to be a switch, while the size of the displayer increases, the require of the performance and quality of TFTs is more and more better. Therefore, it is very important subject to study the stability and to improve the performance of a-Si TFTs. In this study, it simulated the process of the degradation on the TFTs by changing the sizes of TFTs and bias modes to find to stability mechanism of the TFTs. It can be known that under AC stress the degradation depends on the channel length, longer channel length with less degradation. In order to improve the traditional dual-gate structure TFTs, it had made dual-gate TFTs with ITO back-gate, the process of the new structure TFTs are fully compatible with the conventional BCE TFT fabrication process. With dual-channel conduction, the dual-gate TFTs exhibit higher on current and lower photo leakage current performance than the conventional inverted staggered TFTs In this study it also use the dual-gate structure to investigate how the back-channel influence the front-channel conduction. Apply DC bias on the back-gate to from defects at the interface of the active layer and passvation layer, it is found that after stress the on-current show almost the same quantities, and the photo leakage current is obvious decreased.

The charge storage in the a-Si:H PIN photodiode under different light wavelength illuminations has been studied. The leakage current-voltage and capacitance-voltage curves under three fundamental visible light wavelengths, i.e., red, green and blue light were measured. The apparent charge storage density in the negative voltage range was quantified from the capacitance-voltage curve; charges in the positive voltage range were estimated from the leakage current-voltage curve. The measurement was verified with a pre-fabricated circuit which is a charge storage readout device. The diode under the long wavelength light illumination condition stored more charges than that under the short wavelength light illumination condition because the former could penetrate the intrinsic a-Si:H layer deeper than the latter could. The leakage current and charge storage capacity of the diode are determined by the generation of electron-hole pairs and the depletion of charges in the intrinsic layer as well as the supply of charges from the electrodes. A comparison of charge storage capacities of diodes with different intrinsic layer thicknesses is also presented. The number of photogenerated carriers increases with the thickness of the i-layer due to the long penetration depth, but the junction capacitance decreases which results in the decrease of the charge storage capacity. The tradeoff between the photogenerated carriers and the capacitance, combined with thickness-dependent recombination mechanisms increases the complexity of the PIN diode charge storage capacity. The n+- and p+-contact region should be heavily doped so that the storage charge can be confined in the i-layer without diffusing and recombining in the contact region. The n+ and p+ films, prepared by plasma enhanced chemical vapor deposition (PECVD) of a wide range of doping concentration, were fabricated to achieve low bulk resistivity and ohmic contacts with the metal electrodes. Charge storage density was improved after the optimization doped layers in both positive gate voltage and negative gate voltage. The low resistivity contact layers, reduced density of state in the intrinsic layer, and graded p+/i layer account for the enhancement of the charge storage density in the optimized diode.

In this thesis, novel technology for manufacturing high-performance hydrogenated amorphous silicon (a-Si:H) TFT is developed . In the bottom gate light-shied a-Si:H TFT structure, the side edge of a-Si:H island is capped with extra deposition of heavily phosphorous-doped a-Si layer. The new structure a-Si:H TFT process steps is almost unchanged. The masksteops of fabrication new structure TFT are the same as the inverter-staggered TFT. Such an ingenuity can effectively eliminate the leakage path between the parasitic contacts between source/drain metal and a-Si:H at the edge of a-Si:H island. a-Si:H is a well-known photosensitivity material. For driving LCD the TFT must be operated with illuminated environment. It will cause the leakage current. The new TFT structure is similar to the light-shield TFT proposed by Akiyama in 1989. So the new structure TFT can not only reduce the schoktty emission leakage current but also the photo-leakage current. In addition, electrical performance of the novel a-Si:H TFT device exhibits superior effective carrier mobility, as high as 1.05 cm2/Vsec due to the enormous improvement in parasitic resistance. The impressively high performance provides the potential of our proposed a-Si:H TFT to apply for AMLCD and AMOLED technology.

Hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs) are used as switching elements in large area active matrix liquid crystal displays and various image sensing devices for radiation detection. The noise inherent in the a-Si:H TFTs contributes to the overall noise figure of such devices and degrades the signal to noise ratio; therefore, the noise is an important factor in the design of the devices. The noise of the a-Si:H TFTs has been studied experimentally, but the origin of the noise is not understood. <p> This work calculates the noise of the a-Si:H TFTs based on a simulation of operation of the TFTs and the hypothesis that the device noise is due to the intrinsic noise of the a-Si:H material. An a-Si:H TFT with an inverted-staggered structure has been simulated by numerically solving the fundamental transport equations for various gate and drain-source voltages. The drain-source curves derived from the simulation agree qualitatively with the experimental results: both the linear and saturated regions are observed. The low frequency noise was calculated based on the charge density distribution in the channel obtained from the simulation and the known dependence of the noise in the a-Si:H on the charge density, Hooges relation. The calculated noise power increases with the drain-source voltage and is inversely proportional to the gate voltage or the effective channel length. The curves agree qualitatively with the experimental results. The calculated noise power agrees quantitatively with the experiments when the scaling parameter in Hooges relation, , is set to . This value agrees with the experimentally determined value for a-Si:H. The results are consistent with the hypothesis that the low frequency noise in the a-Si:H TFTs is due to the material itself.

Hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs) are used as switching elements in large area active matrix liquid crystal displays and various image sensing devices for radiation detection. The noise inherent in the a-Si:H TFTs contributes to the overall noise figure of such devices and degrades the signal to noise ratio; therefore, the noise is an important factor in the design of the devices. The noise of the a-Si:H TFTs has been studied experimentally, but the origin of the noise is not understood. <p> This work calculates the noise of the a-Si:H TFTs based on a simulation of operation of the TFTs and the hypothesis that the device noise is due to the intrinsic noise of the a-Si:H material. An a-Si:H TFT with an inverted-staggered structure has been simulated by numerically solving the fundamental transport equations for various gate and drain-source voltages. The drain-source curves derived from the simulation agree qualitatively with the experimental results: both the linear and saturated regions are observed. The low frequency noise was calculated based on the charge density distribution in the channel obtained from the simulation and the known dependence of the noise in the a-Si:H on the charge density, Hooges relation. The calculated noise power increases with the drain-source voltage and is inversely proportional to the gate voltage or the effective channel length. The curves agree qualitatively with the experimental results. The calculated noise power agrees quantitatively with the experiments when the scaling parameter in Hooges relation, , is set to . This value agrees with the experimentally determined value for a-Si:H. The results are consistent with the hypothesis that the low frequency noise in the a-Si:H TFTs is due to the material itself.

Abstract Recently, a-Si:H TFT based liquid-crystal display has encroached on the territory of the cathode ray tubes. There is a tendency to fabricate the active matrix LCD on the plastic or flexible substrates. Instead of glass, flexible substrates will make the application of TFT-LCD extensive due to the several advantages: i.e. ultra-slim, light-weight and unbreakable, etc. Nevertheless, the limitation of process temperature for the low-melting substrates is an important issue. In this thesis, the feasibility of a-Si TFT devices fabricated on flexible substrates by using two different technologies have been evaluated. First, a-Si TFT devices were fabricated on glass at 150¢Jsuccessfully and the characteristics of films deposited at lowtemperature have been studied sequentially. For improving the adhesion between organic and inorganic layers and protecting substrate against water or gas during processes, several hot coating layers were investigated. With hot coating layer be introduced, glass was substituted by plastic substrates. We chose PES as the flexible substrate from several candidates due to better optical transmittance and good thermal stability below 200¢J. After direct fabrication on flexible substrate, the stability of electronic characteristics were been investigated with bending examination. In addition, TFT devices were successfully separated from glass and transferred to flexible substrates such as PES or metal foil. Using this technology, temperature limitation has been circumvented and TFT devices still exhibit good electronic characteristic. Furthermore, the bending measurements have been also applied to devices.

Based on the convenience of the use, the traditional display will be replace by the flexible display. According to this reason, it is very important to study on the reliability of the amorphous silicon (a-Si:H) thin-film transistor (TFT) used in LCD under different mechanical strain. In this research, besides of the above-mentioned we also applied AC stress, to understand the influence of AC stress on an a-Si:H TFT under different mechanical strain. The influence of mechanical strain on the performance of an hydrogenated amorphous silicon (a-Si:H) thin-film transistor (TFT) with different channel length and width on metal foil substrate under uniaxial compressive or tensile strain was studied, where the strain is parallel to the TFT source-drain current path. The process of TFT with the maximum temperature 190¢XC exhibited a field-effect mobility of 0.1 cm2/Vs and a threshold voltage of 1.95 V and the leakage current of less than 10-13 A. The TFTs were strained by inward (compression) or outward (tension) cylindrical bending. The mobility had a slightly change under the mechanical strain, which was due to the change in the disorder under bending strain. We also researched on the influence of uniaxial compressive (tensile) strain on the performance of a-Si:H TFTs under different AC stress conditions. When the a-Si:H TFTs were strained and applied AC stress, we found the performance of a-Si:H TFTs were affected more then the flat ones.

The off-state leakage current under back light illumination is, in particular, a serious problem in the multimedia displays that require high intensity backlight illumination. The photo leakage current characteristic of flexible a-Si:H TFTs has been measured in this study . The device activation energy (Ea) of a-Si:H TFTs extracted from various temperature measurements are different from those of typical a-Si:H TFTs, because the Fermi level of a-Si:H TFTs are modulate by the density of states (DOS) in the a-Si:H band gap. The information on DOS is important for understanding the physical mechanisms responsible for the device behavior. It¡¦s related to the threshold voltage,iii subthreshold slope, field effect mobility and the stability of the TFTs. Experimental results show the photo leakage currents of a-Si:H TFTs under tensile stress are less than that of flattened a-Si:H TFTs stemmed the weak light intensity. In addition, the small shifts of threshold voltage and subthreshold swing are resulted from the smaller Ea in a-Si:H channel material.

The widespread use of hydrogenated amorphous silicon (a-Si:H) devices prompted the need for models to identify challenges and solutions early on in the design process.Hydrogenated amorphous silicon photodiodes are commonly used as sensors in large area scanners. It is possible to describe a-Si:H n-i-p photodiodes using an empirical model, which this dissertation presents. Segmented a-Si:H n-i-p photodiodes of varying sizes were fabricated via plasma enhanced chemical vapor deposition. The dark current-voltage characteristics were then measured at different temperatures. Thecapacitance and the quantum efficiency of the devices were also characterized. Using simple semiconductor device equations and the observed empirical behavior, a model is built with a series of parameterized equations. The forward bias current characteristics are represented by the weighted sum of a low bias exponential relationship and a high bias power law relationship. The reverse bias current is modeled as the sum of the bulk thermal component and the edge leakage component. A linear bias dependent equation is used to represent the diode capacitance and a fourth order polynomial is used to model the quantum efficiency. The devices are characterized and the parameters are extracted from the empirical results. Good agreement has been obtained by comparing the results of the proposed model with the experimental results.

The widespread use of hydrogenated amorphous silicon (a-Si:H) devices prompted the need for models to identify challenges and solutions early on in the design process.Hydrogenated amorphous silicon photodiodes are commonly used as sensors in large area scanners. It is possible to describe a-Si:H n-i-p photodiodes using an empirical model, which this dissertation presents. Segmented a-Si:H n-i-p photodiodes of varying sizes were fabricated via plasma enhanced chemical vapor deposition. The dark current-voltage characteristics were then measured at different temperatures. Thecapacitance and the quantum efficiency of the devices were also characterized. Using simple semiconductor device equations and the observed empirical behavior, a model is built with a series of parameterized equations. The forward bias current characteristics are represented by the weighted sum of a low bias exponential relationship and a high bias power law relationship. The reverse bias current is modeled as the sum of the bulk thermal component and the edge leakage component. A linear bias dependent equation is used to represent the diode capacitance and a fourth order polynomial is used to model the quantum efficiency. The devices are characterized and the parameters are extracted from the empirical results. Good agreement has been obtained by comparing the results of the proposed model with the experimental results.