TFT Backplane Research Articles

Crystalline Orientation Control Enhanced Adhesion of Perovskite to Large‐Area Readout Board for High‐Performance X‐Ray Imaging

AbstractHalide perovskites are reputed as highly promising photoelectronic materials for direct X‐ray detectors, but realizing large‐area flat‐panel imaging requires to address the compatibility issue of the electronic, surficial, and mechanical properties between the perovskite and the readout circuit board. Here, a low‐dimensional MA3Bi2I9 perovskite is chosen to achieve a good match in a balancing act between the two by exploiting an orientation control strategy for perovskite film growth. The most striking consequence of the orientation controlled growth is the excellent adhesion of the thick perovskite film to the electronic board in large area and effectively addresses the charge sharing effect, which has been notoriously difficult to achieve. The resulting detector, exhibits an X‐ray imaging area of 2.8 × 3.2 cm, with a spatial resolution of 4.0 lp mm⁻¹, the highest yet achieved for polycrystalline perovskite detectors based on TFT backplanes, and a sensitivity of 588 µCGyair−1 cm−2 while maintaining a dark current below 10 nA cm⁻2, this is also the highest value recorded to date for polycrystalline zero‐dimensional perovskite detectors. This device clearly revealing the intricate internal structures of both biological specimens and industrial products. This outcome demonstrates the potential of zero‐dimensional perovskites in X‐ray planar imaging and highlights the critical role of orientation control strategies.

68‐1: Distinguished Paper: An Active‐Matrix MicroLED Display Based on Monolithic Integration with IGZO Backplane

We present a method of monolithically integrating GaN microLEDs with an IGZO TFT backplane to produce an activematrix microdisplay. After discussion of the fabrication process, individual LEDs, TFTs, and the integrated system are characterized. Results demonstrate a 32x32 pixel, 78.4 PPI microdisplay with luminance exceeding 1500 nits. This type of monolithic microdisplay forges the path forward for future high luminance integrated displays to enable augmented and mixed reality applications.

14‐3: Late‐News Paper: Channel Etched Coplanar TFTs for Applying a‐IGZO to High‐resolution and IT Applications

Self‐aligned a‐IGZO coplanar TFTs have high mobility, excellent large‐area uniformity, and are structurally free of parasitic caps. Accordingly, it is being adopted and mass‐produced as the backplane of OLED TV. Currently, the scope of application of OLED displays using oxide TFT backplanes is expanding to high‐resolution monitors for gaming. With this expansion, not only the size of the TFT but also its storage capacity has become an important factor in terms of aperture ratio. Instead of using a thick Passivation (PAS) Layer for storage capacity, we developed a structure that maximizes the aperture ratio by using a thin gate insulator (GI). However, GI capacitance must be used as the gate electrode and active layer electrode, but in self‐aligned coplanar structure, the active layer overlapping the gate metal is not conductive. To solve this problem, we succeeded in developing a 27‐inch QHD OLED monitor product for gaming by applying a self‐aligned coplanar structure/process that allows the active layer to simultaneously configure channels and wiring, and controlling degradation of channel characteristics.

Flexible TFT backplane development for extremely small bending radius with organic ILD and novel TFT structures

AbstractA new flexible low‐temperature polycrystalline silicon thin film transistors (LTPS TFTs) on PI substrate with organic ILD layer, island TFT, and TFT channel perpendicular to stress direction was proposed. AMOLED display panel manufactured with organic ILD did not show any visible degradation of panel image after outward rolling cycles of 200,000 at rolling radius of 4 mm or inward folding cycles of 200,000 at folding radius of 1 mm. Another novel structure of TFT with channel perpendicular to stress direction significantly reduced change of threshold voltage of −0.03 V compared with change of threshold voltage of −0.6 V for TFT with channel parallel to stress direction for reliability test of high drain current (HDC) after 100,000 outward‐bending cycles at bending radius of 3 mm. After inward‐bending cycles of 200,000 at bending radius of 1 mm, reliability test results for TFT device with organic ILD layer showed that change of on‐current is 10.07% for hot carrier instability (HCI) test, change of threshold voltage −0.31 V for negative bias thermal instability (NBTI) test, change of threshold voltage −0.24 V for hysteresis test, and breakdown voltage of gate insulator 7.73 MV/cm, respectively, and these performances are similar to those of TFT device with inorganic ILD (SiNx).

Improvement of the Warpage of E-paper Reader TFT Backplane in G8.6 0.5mm Glass

Improvement of the Warpage of E-paper Reader TFT Backplane in G8.6 0.5mm Glass

37‐1: Invited Paper: Manufacturing Readiness of High‐Efficiency and Low‐Cost MicroLED Displays

Applied Materials is pursuing an innovative and manufacturing scalable approach to fabricate full‐color microLED displays on active‐matrix TFT backplanes with four subpixels, high‐efficiency UV‐A microLEDs and in‐situ curing of Cd‐free R/G/B QD formulations. A simplified die‐transfer and much reduced die repair scheme using the 4th subpixel are developed and demonstrated. The readiness of manufacturing tools, materials and processes, and the development of microLEDs with size down to 6µm will be discussed along with progress in assembling smartwatch size displays of superior performance.

78‐2: A flat‐panel‐display compatible ultrasound platform

We present a thin‐film piezoelectric micromachined ultrasonic transducer (PMUT) technology compatible with flat‐panel manufacturing methods. Using the developed flow which is based on a low temperature AlScN piezoelectric layer, we fabricate large area 48x48 element PMUT arrays on glass. Beam steering and ultrasound medical imaging are demonstrated. The developed transducer technology can be combined with a TFT backplane and has the potential of direct integration on top of display size glass sheets, expanding the boundaries of ultrasound application domains.

45‐2: 14.6‐inch 202‐ppi Rollable Micro LED Display with Color Conversion Technology

The 14.6‐inch 202‐ppi rollable micro LED display was fabricated on flexible LTPS TFT backplanes. The tiny micro LEDs, those size are less than 30 um, were bonded on backplanes by flip‐chip soldering technologies. More than 11 million micro LEDs were transferred to achieve brightness of >1000 nits, contrast ratio of >1,000,000:1 and resolution of 2560xRGBx1440. We investigated the structure and mechanism to achieve the rollable capability for micro LED displays.

78‐3: Piezoresistive Area Sensor with Polymer and CNTs Mixture on Oxide TFT Backplane

We demonstrate a highly sensitive, lateral pressure sensor using carbon nanotubes (CNTs) embedded in styrene‐ethylene‐butadiene‐styrene (SEBS) layer on 48 x 48 AM backplane for pressure mapping. The sensor exhibits highly sensitive, piezoresistive performances with current ratio of ~10 6 with a broad detection range of 330 Pa to 28 kPa, and response and recovery times of less than 10 ms and 20 ms, respectively.

25‐1: Distinguished Paper: A Novel Ultra Large Size OLED Display for Premium TVs

In this paper, we present the novel ultra large size OLED display with high image quality for premium TV using an advanced coplanar Oxide TFT backplane, MLA based OLED, small area gate driver in panel for narrow bezel, and pixel charging enhancement method with external compensation. Using these technologies, we improved the luminance efficiency about 20 %, and reduced the gate driver design area to 40%. The pixel charging ratio is more than 80% in all gray levels. Using the developed OLED display, we have successfully developed up to ultra large size 88‐inch 8K, 97‐inch 4K OLED TVs.

67‐2: Adoption of Blue Light Semiconductor Laser Diode (BLDA) in LTPS TFT Manufacturing

We have investigated adoption of CW blue laser diode annealing (BLDA) in manufacturing process of LTPS TFT backplane. Our experiments have shown that except crystallization annealing, BLDA can be adopted in dehydrogenation of precursor amorphous silicon film, and also can be used in the activation after ion implantation. By using BLDA dehydrogenation of H2 content as high as 20% can be implemented. In the activation, BLDA can achieve surface resistance much lower than using conventional RTA.

87‐5: AM Mini‐LED Based on LTPS TFT Backplane with over 5000 Dimming Zones and High Driving Bits

LCD with Mini‐LED backlight performs high brightness and high contrast ratio. In this paper novel Mini‐LED based on LTPS TFT backplane is proposed for LCD backlight with over 5000 dimming zones and excellent image quality. Moreover, based on special driving circuit, 12‐14 driving bits, that is 4096‐16384 gray level, is achieved, which can improve local contrast ratio of the image. Compared to PM Mini‐LED, AM Mini‐LED shows superior performance on high dimming zone design, fewer LED drivers and improvement of image quality.

P‐12.4: Low Voltage Switchable Bistable Twist Nematic Display

The most common electronic paper technology is E‐ink, which enables many novel applications such as e‐readers, watches and electronic shelf labels. However, due to the TFT backplane driving and complex production processes, the cost of this technology is high, which limits its popularity. Recently, a low‐cost π‐bistable twist nematic (π‐BTN) liquid crystal display with a high pretilt angle is proposed. It has the same structure and production method as an ordinary liquid crystal display. Passive driving enables the manufacture of high‐resolution bistable displays without the use of thin‐film transistors. Compared with the current bistable twist nematic display technology, the high pretilt angles structure helps to achieve a lowvoltage and fast‐respond bistable display. This wide viewing angle, high contrast and TFT‐free display is a promising candidate for flexible displays.

P‐9.2: ESL products with amorphous silicon solar cells integrated into the backplane

This paper presents a product combining amorphous silicon solar cells and ESL. This product combines the amorphous silicon solar cell process with the TFT backplane of ESL products. At the same time, this product uses solar cells as the device for collecting light energy, and the new energy conversion equipment collects the electric energy generated by solar energy and generates stable output electric energy to provide ESL devices. This scheme is not only environmentally friendly, but also reduces the thickness of products using external solar cells.

33‐2: Invited Paper: Flexible OLED Displays with Ink‐Jet Printing Technology

TCL CSOT has been investing in ink‐jet printing AMOLED technology for many years, and now CSOT has mastered the complete manufacturing process for IJP display technology, including rigid and flexible technology to manufacture middle and large size OLED displays. Flexible technologies such as panel design, substrate, TFT backplane, EL device, thin film encapsulation, module, and compensation have been developed. Attractive flexible prototypes including 14~31‐inch OLED have been demonstrated in the past three years. TCL CSOT expects to provide innovative flexible OLED displays in the near future.

27‐2: Novel LTPS‐TFT Backplane Structure on Glass for 1,443ppi 4.3‐in. AMOLED VR Display

We developed the novel TFT backplane structure on glass for ultra‐high resolution (1443 ppi) AMOLED VR display. The Mixed TFT backplane based on the combination of bottom‐gate poly‐Si TFTs (BGPs) and top‐gate poly‐Si TFTs (TGPs) has solved many issues such as integrating AMOLED pixel circuit in very small area and retaining TFT characteristics on glass for AMOLED VR display.

52‐1: Invited Paper: Technical Progress of OLED Displays for Premium TVs

In this paper, we present novel OLED display technologies with distinctive image quality and design for premium TV using an advanced coplanar IGZO TFT backplane, meta‐lit lens array (MLA) based OLED which increase out‐coupling efficiency, N‐line shared gate driver in panel (GIP), and one scan compensation technology. Using these technologies, we improved the luminance efficiency about 20 %, reduced the size of the panel bezel by 34 %, and have successfully developed world's largest 8K OLED TVs.

2.1: Invited Paper: 16.9‐Inch Flexible AMOLED Display with High Performance Top Gate Oxide TFT

We have fabricated top‐gate IGZO TFTs on PI substrate, which exhibit excellent electrical properties and high mechanical reliabilities to meet the demand for large area flexible display. The ΔVth under PBTS and NBTIS for 10 hours are only +0.26 V and −0.34 V, respectively. The mechanical bending properties of the TFT backplane is investigated. There are almost no change after 200,000 bending cycle test at a curvature radius of 20mm. To improve flexible capability and reduce cost of flexible OLED display, integrated gate driver on array (GOA) circuits with spilt channel structure has been investigated. Finally, we successfully realize 16.9‐inch rollable OLED display with high performance top gate IGZO TFT and GOA circuits

Applications for Flexible TFT Arrays Emerge in the Biomedical Domain

AbstractAs flexible TFT backplane technology increases in utility, can display manufacturing technology make the leap into the biomedical domain?

6‐4: Organic Optical Sensor Based on a‐Si TFT Backplane Used in Fingerprint Identification under OLED Display

The solution‐processed organic optical sensors based on a‐Si TFT backplane have been realized, which indicate the comparable performance compared to a‐Si photodiode optical sensors. Furthermore, the organic sensors demonstrate an extremely low absolute sensitivity threshold (also known as Noise Equivalent Power, NEP), which is down to 2.1 nW/cm2 at 530nm.