No abstract

A polysilicon transistor based active matrix organic light emitting diode (AMOLED) pixel with high pixel to pixel luminance uniformity is reported. The new pixel powers the OLEDS with small constant currents to ensure consistent brightness and extended life. Excellent pixel to pixel current drive uniformity is obtained despite the threshold voltage variation inherent in polysilicon transistors. considerations in the design for high information content displays are discussed.

Measurements of breakdown voltage in p-i-n diodes with thin i regions are compared with local and non-local theoretical calculations. It is found that overshoot effects compensate for the dead space at high fields close to breakdown but that non-local aspects become stronger at lower fields.

The design of an active matrix organic light emitting diode (AMOLED) display using a polysilicon thin film transistor pixel is described. Characteristics of the OLED response in the low current regime are described and their impact on the design of integrated driver circuitry is discussed. Integrated data and select scanners which generate the signals necessary for data capture and pixel calibration are presented.

Organic thin film transistors (OTFTs) have made impressive progress over the past decade, and it appears increasingly likely that OTFTs will find use in a number of low-cost, large-area electronic applications, such as active-matrix displays, smart cards, price and inventory tags, and large-area sensor arrays. OTFTs provide two principle advantages over TFTs based on inorganic semiconductors: they can be fabricated at lower temperature and, potentially, at significantly lower cost. Low processing temperatures allow OTFT device and circuit fabrication on polymeric or other inexpensive substrates, rather than glass. The prospect of a flexible, rugged, light-weight active-matrix display at relatively low cost has spurred a number of manufacturers and government agencies to consider plastic displays for a variety of military, medical, industrial, and consumer applications.We report here on the design and fabrication of a flexible active-matrix OTFT backplane suitable for use in flexible polymer-dispersed liquid crystal displays. 75 pm thick flexible polyethylene naphthalate (PEN) film was used as the substrate, and OTFT and pixel arrays with good electrical performance, yield, and uniformity were obtained.The pentacene TFT and pixel structure is shown in Figure 1. Nickel was used for the gate electrodes, silicon dioxide was deposited to form the gate dielectric layer, transparent indium tin oxide (ITO) was used for the pixel electrodes, and palladium was deposited for the source and drain contacts [l]. To form the organic active TFT layer, pentacene was thermally evaporated in vacuum at a pressure near Pa with a deposition rate near 1 as. The silicon dioxide gate dielectric surface was vapor-treated with octyldecyltrichlorosilane prior to pentacene deposition. During pentacene deposition, the substrate was held at 60 "C to improve molecular ordering in the pentacene film, which leads to increased carrier mobility and improved device characteristics. To passivate and pattern the pentacene layer without exposure to common solvents and resist developers, a photolithographic process based on polyvinyl alcohol (PVA) was used. A water-based solution of PVA with an ammonium dichromate photosensitizer was spun onto the pentacene layer to serve as a negative-tone photoresist. The PVA was exposed with UV light and developed in water, and pentacene outside the active TFT regionsunprotected by the PVA maskwas removed in an oxygen plasma. Prior to all device processing, the PEN substrates are pretreated at 150 "C for 2 hours to improve thermal dimensional stability; the maximum temperature used for device processing is 1 10 "C.A display test chip was designed that includes four types of 16 x 16, 250-pm-pitch pixel arrays with clear aperture between 38% and 58%, a number of OTFT circuits, such as differential amplifiers, fkequency dividers, and ring oscillators, a 1 cm2, 200-OTFT parameter test array (density limited by test probe structure), and a variety of process test structures. Completed test chips were analyzed using automa...