Development of 8‐in. oxide‐TFT‐driven flexible AMOLED display using high‐performance red phosphorescent OLED

An 8‐in. flexible active‐matrix organic light‐emitting diode (AMOLED) display driven by oxide thin‐film transistors (TFTs) has been developed. In‐Ga‐Zn‐O (IGZO)‐TFTs used as driving devices were fabricated directly on a plastic film at a low temperature below 200 °C. To form a SiO_x layer for use as the gate insulator of the TFTs, direct current pulse sputtering was used for the deposition at a low temperature. The fabricated TFT shows a good transfer characteristic and enough carrier mobility to drive OLED displays with Video Graphic Array pixels. A solution‐processable photo‐sensitive polymer was also used as a passivation layer of the TFTs. Furthermore, a high‐performance phosphorescent OLED was developed as a red‐light‐emitting device. Both lower power consumption and longer lifetime were achieved in the OLED, which used an efficient energy transfer from the host material to the guest material in the emission layer. By assembling these technologies, a flexible AMOLED display was fabricated on the plastic film. We obtained a clear and uniform moving color image on the display.     

An OTFT‐driven rollable OLED display

Abstract— An 80‐μm‐thick rollable AMOLED display driven by an OTFT is reported. The display was developed so as to be rollable in one direction with an integrated OTFT gate driver circuit. It was successfully operated by an originally developed organic semiconductor, a peri‐xanthenoxanthene derivative. The display retained its initial electrical properties and picture quality even after being subjected to 1000 cycles of a roll‐up‐and‐release test with a radius of 4 mm.     

Low‐temperature fabrication of 5‐in. QVGA flexible AMOLED display driven by OTFTs using olefin polymer as the gate insulator

Abstract— A 5‐in. QVGA flexible AMOLED display driven by OTFTs has been fabricated at a low temperature of 130°C. A polyethylene naphthalate film was used as the flexible substrate and an olefin polymer was used as the gate insulator for the OTFT. This layer was formed by spin‐coating and baking at 130°C. Pentacene was used as the organic semiconductor layer. The OTFT performance to drive the flexible display with QVGA pixels in terms of current on/off ratio, carrier mobility, and spatial uniformity on the backplane have been obtained. Phosphorescent and fluorescent OLEDs were used as light‐emitting devices on a flexible display. Those layers were formed by vacuum deposition. After the flexible display was fabricated, a clear and uniform moving image was obtained on the display. The display also showed a stable moving image even when it was bent.     

System design for a wide‐color‐gamut TV‐sized AMOLED display

Abstract— By using current technology, it is possible to design and fabricate performance‐competitive TV‐sized AMOLED displays. In this paper, the system design considerations are described that lead to the selection of the device architecture (including a stacked white OLED‐emitting unit), the backplane technology [an amorphous Si (a‐Si) backplane with compensation for TFT degradation], and module design (for long life and low cost). The resulting AMOLED displays will meet performance and lifetime requirements, and will be manufacturing cost‐competitive for TV applications. A high‐performance 14‐in. AMOLED display was fabricated by using an in‐line OLED deposition machine to demonstrate some of these approaches. The chosen OLED technologies are scalable to larger glass substrate sizes compatible with existing a‐Si backplane fabs.     

Improvement in image quality of a 5.8‐in. OTFT‐driven flexible AMOLED display

Abstract— The image quality of an OTFT‐driven flexible AMOLED display has been improved by enhancing the performance of OTFTs and OLEDs. To reduce the operating voltage of OTFTs on a plastic film, Ta²O⁵ with a high dielectric constant was used as a gate insulator. The organic semiconductor layer of the OTFT was successfully patterned by a polymer separator, which is an isolating wall structure using an organic material. The OTFT performance, such as its current on/off ratio, carrier mobility, and spatial uniformity on the backplane, was enhanced. A highly efficient phosphorescent OLED was used as a light‐emission device. A very thin molybdenum oxide film was introduced as a carrier‐injection layer on a pixel electrode to reduce the operating voltage of the OLED. After an OTFT‐driven flexible AMOLED display was fabricated, the luminance and uniformity on the display was improved. The fabricated display also showed clear moving images, even when it was bent at a low operating voltage.     

Polysilicon TFT technology on flexible metal foil for AMPLED displays

Abstract— 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.     

Flexible AMOLED displays on stainless‐steel foil

Abstract— The world's thinnest flexible full‐color 5.6‐in. active‐matrix organic‐light‐emitting‐diode (AMOLED) display with a top‐emission mode on stainless‐steel foil was demonstrated. The stress in the stainless‐steel foil during the thermal process was investigated to minimize substrate bending. The p‐channel poly‐Si TFTs on stainless‐steel foil exhibited a field‐effectmobility of 71.2 cm²/N‐sec, threshold voltage of ?2.7 V, off current of 6.7 × 10¹³ A/μm, and a subthreshold slope of 0.63 V/dec. These TFT performances made it possible to integrate a scan driver circuit on the panel. A top‐emission EL structure was used as the display element, and thin‐film encapsulation was performed to realize a thin and flexible display. The full‐color flexible AMOLED display on stainless‐steel foil is promising for mobile applications because of its thin, light, rugged, and flexible properties.     

Bezel free design of organic light emitting diode display via a‐InGaZnO gate driver circuit integration within active array

In this article, we described an innovative design technology of active matrix organic light emitting diode (AMOLED) display, to provide a bezel free design. We designed gate driver circuit of amorphous indium‐gallium‐zinc oxide thin‐film transistors (TFTs) not on the bezel area but within the active array. Although we applied challengeable design, no degradation of electrical/optical properties of panel was observed. Because we effectively prevented capacitive coupling and interference between the emission circuit and integrated gate driver circuit in active array, finally, we successfully demonstrated a bezel free designed AMOLED display of 18.3″ HD (1366 × 768) driven by a‐InGaZnO TFTs.     

a‐InGaZnO thin‐film transistors for AMOLEDs: Electrical stability and pixel‐circuit simulation

Abstract— Inverted‐staggered amorphous In‐Ga‐Zn‐O (a‐InGaZnO) thin‐film transistors (TFTs) were fabricated and characterized on glass substrates. The a‐InGaZnO TFTs exhibit adequate field‐effect mobilities, sharp subthreshold slopes, and very low off‐currents. The current temperature stress (CTS) on the a‐InGaZnO TFTs was performed, and the effect of stress temperature (TSTR), stress current (ISTR), and TFT biasing condition on their electrical stability was investigated. Finally, SPICE modelling for a‐InGaZnO TFTs was developed based on experimental data. Several active‐matrix organic light‐emitting‐display (AMOLED) pixel circuits were simulated, and the potential advantages of using a‐InGaZnO TFTs were discussed.     

High refresh rate and low power consumption AMOLED panel using top‐gate n‐oxide and p‐LTPS TFTs

A pixel circuit and a gate driver on array for light‐emitting display are presented. By simultaneously utilizing top‐gate n‐type oxide and p‐type low‐temperature polycrystalline silicon (LTPS) thin‐film transistors (TFTs), the circuits provide high refresh rate and low power consumption. An active‐matrix LED (AMOLED) panel with proposed circuits is fabricated, and driving at various refresh rate ranging from 1 to 120 Hz could be achieved.