Ta-Ko Chuang

Top-emitting 230dots∕in. active-matrix polymer light-emitting diode displays on flexible metal foil substrates

A top-emitting 230dots∕in. monochrome active-matrix polymer light-emitting diode (PLED) display having the VGA format and fabricated on a flexible steel foil utilizing the polycrystalline silicon thin-film transistor (TFT) technology is reported. The pixel circuitry architecture consists of the conventional two TFT circuitries made of two p-channel metal-oxide-semiconductor (PMOS) transistors and one storage capacitor. The average field-effect hole mobility and threshold voltage of the PMOS polysilicon TFTs fabricated on the metal foil are 37(±4)cm2∕Vs and −1.9(±0.6)V, respectively. The light turn-on voltage of the PLED is 4.0V.

Polysilicon TFT technology on flexible metal foil for AMPLED displays

— A top-emitting 230-dpi active-matrix polymer light-emitting diode (AMPLED) display, having a VGA format and a 3.3-in.-diagonal size, on a flexible stainless-steel-foil substrate is reported. The active-matrix array was fabricated with laser-crystallized polysilicon TFTs at a maximum process temperature of 700°C. The top-emitting PLED diodes were prepared by spin-casting organic light-emitting polymers. This work demonstrates the compatibility of polysilicon-TFT technology with flexible metal-foil substrates for active-matrix organic light-emitting-diode (AMOLED) display applications.

Process Technology for High-Resolution AM-PLED Displays on Flexible Metal-Foil Substrates

The first successful integration of a polysilicon thin-film transistor (TFT) backplane with polymer light-emitting diodes (PLEDs) onto a flexible stainless steel foil is described, and a high-resolution (230 dots/in.) monochrome active-matrix polymer light-emitting diode (AM-PLED) display is demonstrated. The process technology required to implement this high-resolution AM-PLED display onto a flexible metal-foil substrate is discussed. This technology primarily consists of the preparation of flexible metal foil, fabrication of the active matrix polysilicon TFT backplane, and integration with top-emitting PLEDs.

Active-matrix organic light-emitting displays on flexible metal foils

This paper describes the development of a 3.5 inch diagonal Active Matrix Organic Light Emitting Diode Display on flexible metal foils. The active matrix array had the VGA format and was fabricated using the polysilicon TFT technology. The advantages that the metal foil substrates offer for flexible display applications will first be discussed, followed by a discussion on the multilayer coatings that were investigated in order to achieve a high quality insulating layer on the metal foil substrate prior to TFT fabrication. Then the polysilicon TFT device performance will be presented as a function of the polysilicon crystallization method. Both laser crystallized polysilicon and solid phased crystallized polysilicon films were investigated for the TFT device fabrication. Due to the opaque nature of the metal foil substrates the display had a top emission structure. Both small molecule and polymer based organic material were investigated for the display emissive part. The former were evaporated while the latter were applied by spin-cast. Various transparent multi-layer metal films were investigated as the top cathode. The approach used to package the finished AMOLED display in order to protect the organic layers from environmental degradation will be described. The display had integrated polysilicon TFT scan drivers consisting of shift registers and buffers but external data drivers. The driving approach of the display will be discussed in detail. The performance of the finished display will be discussed as a function of the various materials and fabrication processes that were investigated.

Polysilicon TFT technology on metal foils for large area flexible electronics

Flexible electronics is an emerging field that deals with electronic circuits, sensors and actuators that are distributed over a large area. Flexible electronics could find applications in many different fields such as flexible displays, conformal distributed sensors, etc. Flexible electronics rely on the fabrication of silicon thin film transistors on flexible substrates. Depending upon the system performance requirements amorphous or polycrystalline silicon thin film transistors could be utilized. In general polycrystalline silicon or polysilicon is utilized in systems with either high degree of integration or high performance. The high carrier mobility in polycrystalline silicon enables high speed circuitry, while the availability of CMOS circuit architectures in polysilicon enables low power consumption. There are two types of flexible substrates, polymer based and metal foils. The latter can withstand higher temperatures during fabrication of the thin film transistors and have much higher dimensional stability thus enabling small design rules. This paper discusses advances in polycrystalline silicon TFT technology on metal foil substrates. The TFT device characteristics are first discussed followed by circuit applications. Finally the application of polysilicon TFT devices to flexible Active Matrix Organic Light Emitting Displays is shown.

High performance TFT circuits foon-board display driving on flexible stainless steel foils

Displays are one of the preferred flexible electronic applications because of the mechanical and space saving advantages a conformal or foldable display would have (robust, lightweight). These systems would include in the same substrate all or many of the components needed to drive a flat panel OLED display. This study will report results on digital, analog and mixed signal poly-silicon TFT circuits on stainless steel foils that could be used as building blocks for such systems. Some of these circuits include shift registers running at speeds over 10MHz, ring oscillators with stage response frequencies over 1GHz and mixed signal circuits for row and column driving. Pixel circuits for driving organic light emitting diodes are presented as well, with PMOS, NMOS and CMOS topologies implemented for different display resolutions.