New generation of Flat Panel Displays, Organic Light Emitting Diode (OLED) with fast response, high brightness, high contrast plays an important role gradually in the further market of flat penal display (FPD). The characteristics of OLED like as bright light¡Bthin¡Bshort¡Bsmall subverts the concept of LCD displays. But the life time of organic materials become the obstruction on the further development of OLED-FPD. In addition, the non-uniformity of OLED Panel could cause the quality of frames worse. Hence, for solve the problem, A more powerful Pixel driving circuit will be designed for achieving the high performance of OLED based FPD. Recently, many researches were related to the compensating pixel driving circuits have reported. The catalogs of pixel driving circuits were divided into two types as voltage-driving circuit and current-driving circuit, which were used to solve the problems like the variation of the threshold voltage, the electronic mobility and the long time with storing capacitors charge and discharge. In this study, a novel pixel driving circuit with new discharged paths was design in order to solve the long time of charge and discharge. Theoretical and circuit simulation show this design can enhance the frame rates effectively. At the same time, it also achieves better performance such as higher resolution and quality of frame rate for the large size OLED panels.

Rapid progress over the last decade on thin film transistor (TFT) active matrix organic light emitting (AMOLED) displays led to the emergence of high-performance, low-power, low-cost flat panel displays. Despite the shortcomings of the active matrix that are associated with the instability and low mobility of TFTs, the amorphous silicon TFT technology still remains the primary solution for the AMOLED backplane. To take advantage of this technology, it is crucial to develop driving schemes and circuit techniques to compensate for the limitations of the TFTs. The driving schemes proposed in this thesis address these challenges, in which, the sensitivity of the OLED current to the transistor variations is reduced significantly. This is achieved by comparing the data signal with a feedback signal associated with the pixel current by means of an external driving circuit through a column feedback line. Depending on the nature of the feedback signal, (i.e. current or voltage) several pixel circuits and external drivers are proposed. New AMOLED pixel circuits with voltage and current feedback are designed, simulated, fabricated, and tested. The performance of these circuits is analyzed in terms of their stability, settling time, power efficiency, noise, and temperature-dependence. For the pixel circuits with current feedback, an operational transresistance amplifier is designed and implemented in a high-voltage CMOS process. Measurement results for both voltage and current feedback driving schemes indicate less than a 2%/V sensitivity to shifts in the threshold voltage of the TFTs. By using current feedback and an accelerating pulse, programming times less than 50 s are achieved.

Rapid progress over the last decade on thin film transistor (TFT) active matrix organic light emitting (AMOLED) displays led to the emergence of high-performance, low-power, low-cost flat panel displays. Despite the shortcomings of the active matrix that are associated with the instability and low mobility of TFTs, the amorphous silicon TFT technology still remains the primary solution for the AMOLED backplane. To take advantage of this technology, it is crucial to develop driving schemes and circuit techniques to compensate for the limitations of the TFTs. The driving schemes proposed in this thesis address these challenges, in which, the sensitivity of the OLED current to the transistor variations is reduced significantly. This is achieved by comparing the data signal with a feedback signal associated with the pixel current by means of an external driving circuit through a column feedback line. Depending on the nature of the feedback signal, (i.e. current or voltage) several pixel circuits and external drivers are proposed. New AMOLED pixel circuits with voltage and current feedback are designed, simulated, fabricated, and tested. The performance of these circuits is analyzed in terms of their stability, settling time, power efficiency, noise, and temperature-dependence. For the pixel circuits with current feedback, an operational transresistance amplifier is designed and implemented in a high-voltage CMOS process. Measurement results for both voltage and current feedback driving schemes indicate less than a 2%/V sensitivity to shifts in the threshold voltage of the TFTs. By using current feedback and an accelerating pulse, programming times less than 50 s are achieved.

In this thesis, the dimension effects and reliabilities of the p-channel poly-Si TFTs for AMOLED are successfully characterized. We have measured and compared the electrical behaviors of devices to study dimension and temperature effects in this experiment. The influences on the narrow channel width effects are also discussed and explained. It is found that the devices with narrow channel width, exhibit promotional turn-on current and smaller threshold voltage. In addition, the stress effects in p-channel poly-silicon thin-film transistors are investigated and characterized with various applied voltages. The stress effects are clearly analyzed by different methods, such as activation energy of leakage current, changing the definition of source and drain for Vg-Id curve, and C-V measurements. Finally, a physical model was proposed to well explain the results we observed.

Thin film transistor (TFT) backplanes are being continuously researched for new applications such as active-matrix organic light emitting diode (AMOLED) displays, sensors, and x-ray imagers. However, the circuits implemented in presently available fabrication technologies including poly silicon (poly-Si), hydrogenated amorphous silicon (a-Si:H), and organic semiconductor, are prone to spatial and/or temporal non-uniformities. While current-programmed active matrix (AM) can tolerate mismatches and non-uniformity caused by aging, the long settling time is a significant limitation. Consequently, acceleration schemes are needed and are proposed to reduce the settling time to 20 µs. This technique is used in the development of a pixel circuit and system for biomedical imager and sensor. Here, a metal-insulator-semiconductor (MIS) capacitor is adopted for adjustment and boost of the circuit gain. Thus, the new pixel architecture supports multi-modality imaging for a wide range of applications with various input signal intensities. Also, for applications with lower current levels, a fast current-mode line driver is developed based on positive feedback which controls the effect of the parasitic capacitance. The measured settling time of a conventional current source is around 2 ms for a 100-nA input current and 200-pF parasitic capacitance whereas it is less than 4 μs for the driver presented here. For displays needed in mobile devices such as cell phones and DVD players, another new driving scheme is devised that provides for a high temporal stability, low-power consumption, high tolerance of temperature variations, and high resolution. The performance of the new driving scheme is demonstrated in a 9-inch fabricated display intended for DVD players. Also, a multi-modal imager pixel circuit is developed using this technique to provide for gain-adjustment capability. Here, the readout operation is not destructive, enabling the use of low-cost readout circuitry and noise reduction techniques. In addition, a highly stable and reliable driving scheme, based on step calibration is introduced for high precision displays and imagers. This scheme takes advantage of the slow aging of the electronics in the backplane to simplify the drive electronics. The other attractive features of this newly developed driving scheme are its simplicity, low-power consumption, and fast programming critical for implementation of large-area and high-resolution active matrix arrays for high precision.

Thin film transistor (TFT) backplanes are being continuously researched for new applications such as active-matrix organic light emitting diode (AMOLED) displays, sensors, and x-ray imagers. However, the circuits implemented in presently available fabrication technologies including poly silicon (poly-Si), hydrogenated amorphous silicon (a-Si:H), and organic semiconductor, are prone to spatial and/or temporal non-uniformities. While current-programmed active matrix (AM) can tolerate mismatches and non-uniformity caused by aging, the long settling time is a significant limitation. Consequently, acceleration schemes are needed and are proposed to reduce the settling time to 20 µs. This technique is used in the development of a pixel circuit and system for biomedical imager and sensor. Here, a metal-insulator-semiconductor (MIS) capacitor is adopted for adjustment and boost of the circuit gain. Thus, the new pixel architecture supports multi-modality imaging for a wide range of applications with various input signal intensities. Also, for applications with lower current levels, a fast current-mode line driver is developed based on positive feedback which controls the effect of the parasitic capacitance. The measured settling time of a conventional current source is around 2 ms for a 100-nA input current and 200-pF parasitic capacitance whereas it is less than 4 μs for the driver presented here. For displays needed in mobile devices such as cell phones and DVD players, another new driving scheme is devised that provides for a high temporal stability, low-power consumption, high tolerance of temperature variations, and high resolution. The performance of the new driving scheme is demonstrated in a 9-inch fabricated display intended for DVD players. Also, a multi-modal imager pixel circuit is developed using this technique to provide for gain-adjustment capability. Here, the readout operation is not destructive, enabling the use of low-cost readout circuitry and noise reduction techniques. In addition, a highly stable and reliable driving scheme, based on step calibration is introduced for high precision displays and imagers. This scheme takes advantage of the slow aging of the electronics in the backplane to simplify the drive electronics. The other attractive features of this newly developed driving scheme are its simplicity, low-power consumption, and fast programming critical for implementation of large-area and high-resolution active matrix arrays for high precision.

Ce travail de thèse a pour sujet l'étude de transistors en couches minces (TFTs) à base d'Indium Gallium Zinc Oxide (IGZO). Nous nous sommes intéressés au procédé de réalisation des TFTs, et à la caractérisation des couches d'IGZO afin d'obtenir les caractéristiques au plus près de l'état de l'art. Nous avons également étudié le processus de passivation, paramètre identifié comme critique pour stabiliser les TFT et atteindre de bonnes performances.Dans un premier temps, nous avons mis au point les conditions du dépôt de la couche active, et de la réalisation des TFTs. Les analyses morphologiques et structurales ont montré l'absence de cristallites de couche, ainsi qu'une surface peu rugueuse. La densité des porteurs de charge de la couche IGZO diminue lorsque le débit d'oxygène, variable durant son dépôt, augmente. La couche active déposée à 200°C et à 4 sccm d'oxygène présente une densité de porteurs de charge de l'ordre de 1E17 cm-3, valeur adaptée au fonctionnement des TFTs.Dans un second temps, nous avons évalué l'influence d'un recuit sur les caractéristiques des TFTs. Nous avons mis en évidence que le recuit sous oxygène conduit à des TFTs opérationnels, tandis que celui sous azote ou en absence de recuit induisent une suppression de l'effet de champ. Nos études ont également montré qu'une température de recuit de 300°C est favorable aux performances des transistors. Les premiers TFTs présentent des mobilités entre 5 et 15 cm2/Vs, des rapports ION/IOFF de l'ordre de 1E7, et des pentes sous le seuil d'environ 0.3 V/décade. Les tensions de seuil (VT), quant à elles, demeurent faibles donc restent à améliorer.Pour finir, nous avons étudié l'impact d'une couche de passivation sur les TFTs, en raison de la dégradation des caractéristiques de ces derniers dans l'atmosphère ambiante. Les couches de SiO2 (déposée par PECVD) et d'Al2O3 (déposée par ALD) ont été étudiées. Nous avons mis en évidence que ces passivations peuvent dégrader les TFTs au lieu de les protéger. VT tend à se décaler dans le sens négatif lorsque l'on augmente l'épaisseur de la couche d'Al2O3 ou le débit de Silane durant le dépôt du SiO2. Une des raisons principales de ce phénomène est la présence de l'hydrogène généré lors de la passivation. Nous avons évalué les solutions pour éviter la dégradation lors du dépôt et assurer une bonne protection du TFT. / This thesis aims to study thin-film transistors (TFTs) based on Indium Gallium Zinc Oxide (IGZO) in the framework of applications in active matrix flat panel LCD and OLED display. The TFT fabrication process and the characterization of IGZO deposited film are two key studies in this thesis in order to obtain TFT electrical characteristics close to the state-of-the-art. We have also studied the passivation which is identified as crucial for stabilizing the TFT and achieving good performance.The deposition of the active layer and the fabrication process of TFT are firstly studied. Smooth surface of deposited films is demonstrated by AFM and the absence of the crystalline peak of the material is shown by X-ray diffraction. The density of charge carriers decreases with the increase of oxygen flow rate. The active layer deposited at 200°C and at 4 sccm of oxygen flow has a carrier density in the order of 1E17 cm-3 which is suitable for TFT operation. This condition is chosen to fabricate IGZO-based TFT in this thesis.In a second step, we have evaluated the influence of annealing condition on TFTs' electrical characteristics. Annealing in oxygen leads to operational TFTs while doing the same under nitrogen or the absence of annealing suppresses field-effect behavior. Our studies have also shown that annealing temperature of 300°C is suitable to obtain good performance of the transistors. From this study, we have obtained TFTs with high mobility (between 5 and 15 cm2/Vs), high ION/IOFF ratios (about 1E7), and reasonable sub threshold slope (about 0.3 V/decade). The threshold voltage (VT) however remains low (between -4 and -2 V) and needs to be improved.Finally, we have investigated the impact of a passivation layer on the performance of IGZO TFTs. SiO2 film (deposited by PECVD) and Al2O3 film (formed by ALD) were studied. We have observed that such passivation can degrade the TFTs rather than protecting them. Concretely, VT shifts in negative direction when increasing the Al2O3 layer thickness or the silane flow during SiO2 deposition. Principal reason for this shift is the presence of hydrogen which is generated during passivation. We have evaluated some solutions to reduce the degradation during deposition and ensure a good protection of the TFTs.

Interactive handheld electronic displays use hydrogenated amorphous silicon (a-Si:H) thin film transistor (TFT) as a backplane and a Touch Screen Panel (TSP) on top as an input device. The low mobility and instability of a-Si:H TFT threshold voltage are major two issues for driving constant current as required for Active Matrix Organic Light Emitting Ddiode (AMOLED) displays. Low mobility is compensated by increasing transistor width or resorting to more expensive material TFTs. On the other hand, the ever increasing threshold voltage shift degrades the drain current under electrical operation causing OLED display to dim. Mutual capacitive TSP, the current cell phone standard, requires two layers of metals and a dielectric to be put in front of the display, further dimming the device and adding to visual noise due to sun reflection, not to mention increased integration cost and decreased yield. This thesis focuses on the aforementioned technological hurdles of a handheld electronic display by proposing a dual-gate TFT used as an OLED current driving TFT and a novel phase response readout scheme that can be applied to a one metal track TSP. Our dual-gate TFT has shown on average 20% increase in drive current over a single gate TFT fabricated in the same batch, attributed to the aid of a top channel to the convention bottom channel TFT. Furthermore the dual gate TFT shows three times the Poole-Frenkel current than the single gate TFT attributed to the increase in gate to drain overlap. The dual-gate TFT shows a 50% improvement in threshold voltage shift over a single gate TFT at room temperature, but only ~8% improvement under 75ºC. This is an important observation as it shows an accelerated threshold voltage shift in the dual-gate. This difference in the rate of threshold voltage change under varying temperature is attributed to the difference in interface states, supporting Libsch and Kanicki’s multi-level temperature dependant dielectric trapping model. The phase response TSP readout scheme requires IC only on one side of the display. Cadence Spectre simulation results showed that both touch occurrence and touch position can be obtained using only one metal layer.

Interactive handheld electronic displays use hydrogenated amorphous silicon (a-Si:H) thin film transistor (TFT) as a backplane and a Touch Screen Panel (TSP) on top as an input device. The low mobility and instability of a-Si:H TFT threshold voltage are major two issues for driving constant current as required for Active Matrix Organic Light Emitting Ddiode (AMOLED) displays. Low mobility is compensated by increasing transistor width or resorting to more expensive material TFTs. On the other hand, the ever increasing threshold voltage shift degrades the drain current under electrical operation causing OLED display to dim. Mutual capacitive TSP, the current cell phone standard, requires two layers of metals and a dielectric to be put in front of the display, further dimming the device and adding to visual noise due to sun reflection, not to mention increased integration cost and decreased yield. This thesis focuses on the aforementioned technological hurdles of a handheld electronic display by proposing a dual-gate TFT used as an OLED current driving TFT and a novel phase response readout scheme that can be applied to a one metal track TSP. Our dual-gate TFT has shown on average 20% increase in drive current over a single gate TFT fabricated in the same batch, attributed to the aid of a top channel to the convention bottom channel TFT. Furthermore the dual gate TFT shows three times the Poole-Frenkel current than the single gate TFT attributed to the increase in gate to drain overlap. The dual-gate TFT shows a 50% improvement in threshold voltage shift over a single gate TFT at room temperature, but only ~8% improvement under 75ºC. This is an important observation as it shows an accelerated threshold voltage shift in the dual-gate. This difference in the rate of threshold voltage change under varying temperature is attributed to the difference in interface states, supporting Libsch and Kanicki’s multi-level temperature dependant dielectric trapping model. The phase response TSP readout scheme requires IC only on one side of the display. Cadence Spectre simulation results showed that both touch occurrence and touch position can be obtained using only one metal layer.

This Master's thesis deals with design and a realisation of a device controlling an OLED display, Densitron DD-25664-1A. This display has a resolution of 256 x 64 pixels and allows displaying of 4-bit grayscale. The proposed utility software implements the initialization and termination functions, two sets of fonts { Latin and Greek letters and functions for rendering graphics and text. The result of the project is a device with the controlling software.