High-Definition, Low-Power Consumption Display Achieved with Crystalline Oxide Semiconductor (OS)


SEL develops and prototypes various displays with crystalline oxide semiconductor CAAC-OS. FETs made with crystalline oxide semiconductors enable high-resolution and low-power consumption displays[1].
Our OLED display prototypes, such as 8K displays, ultra-small and high-resolution displays, flexible displays (foldable display®s and multi-displays), and touch-sensor-embedded displays, are characterized by their high resolution and high contrast. There is a high expectation for these technologies to be used in the mobile devices and medical devices.

Liquid crystal displays including our crystalline oxide semiconductors are in widespread use across the display industry, an example of which is its adoption in smartphone displays in 2012 as the world's first liquid crystal displays including OS.

Now, we are also considering expanding our crystalline oxide semiconductor technology to micro-LED displays, which are attracting attention as third generation displays after LCDs and OLEDs.


OLED Display


8K display

World's Smallest Direct-View 8K Display with High-Aperture Ratio using
HarPOS® Technology

SEL have developed high-resolution OLED displays exceeding 1000ppi by application of thin-film transistors using crystalline oxide semiconductors to drivers[1].We also achieved ultra-high-resolution 13.3-inch 8K display creating a greater feeling of depth in images and stereoscopic effect. We have further increased the resolution to realize 8K displays in various sizes, including an 8.3-inch display exceeding 1000ppi[4],[5].
Initially, color displays were fabricated by combination of white-emission OLED devices and color filters, but now OLED materials for different colors are separately patterned by a photolithography technique, thereby achieving a higher aperture ratio, lower power consumption, and higher color purity.
We call this new technology high aperture ratio patterned organic semiconductor, "HarPOS."

HarPOS
▲ HarPOS- 8.3-Inch 8K Display (10.4 cm×18.5 cm, pixel count of 7680×4320)

[1] K. Yokoyama et al., “A 2.78-in 1058-ppi Ultra-High-Resolution OLED Display Using CAAC-OS FETs”, SID Symp. Dig. Tech. Pap., 46, 1039 (2015).
[2] S. Kawashima et al., “13.3-in. 8K x 4K 664-ppi OLED Display Using CAAC-OS FETs”, SID Symp. Dig. Tech. Pap., 45, 627 (2014) , Received SID Distinguished Paper Award.
[3] R. Yamamoto et al., “13.3-inch 8k4k 664-ppi 120-Hz 12-bit OLED Display”, SID Symp. Dig. Tech. Pap. 47, 53 (2016), Received SID Distinguished Paper Award.
[4] M. Shiokawa et al., “A 1058 ppi 8K4K OLED Display Using a Top-Gate Self-Aligned CAAC Oxide Semiconductor FET”, SID Symp. Dig. Tech. Pap. 47, 1209 (2016).
[5] T.Aoyama et al., “An 8.34-inch 1058-ppi 8K x 4K Flexible OLED Display”, SID Symp. Dig. Tech. Pap. 48 [1], 338 (2017).



Ultra-small and high-resolution displays for AR/VR

AR/VR displays require higher resolution and higher brightness. We are developing a circuit board where a pixel circuit using our original OSLSI® and a driving circuit using silicon (Si) are stacked, aiming to further miniaturize displays. We also succeeded in developing ultra-high-resolution displays exceeding a resolution of 3000 ppi and a luminance of 5000 cd/m2 by combination of the stacked structure and HarPOS technology.


▲ Stacked Structure of Display Area and Driver Circuit


▲ Three-Dimensional View of Stacked Structure

[6] S.Katsui et al., “5291 ppi organic light-emitting diode display using field-effect transistors including a c-axis aligned crystalline oxide semiconductor,” J. Soc. Inf. Disp., 50(1), 311 (2019).
[7] K.Kato et al., “5291-ppi OLED Display Enabled by Monolithic Integration of C-axis-aligned Crystalline IGZO FET and Si CMOS,” IDW '21 Proc., 177 (2021).

We also succeeded in developing ultra-high-resolution displays exceeding a resolution of 3000 ppi and a luminance of 5000 cd/m2 by combination of the stacked structure and HarPOS technology[8], [9].
1.50-Inch OLED Display for VR
▲ 1.50-Inch OLED Display for VR (22.81mm×30.41mm, 3207 ppi pixels)

[8] T. Saito et al., “Layout of 1.50-inch, 3207-ppi OLED Display with OSLSI/SiLSI Structure Capable of Division Driving Fabricated through VLSI Process with Side-by-Side Patterning by Photolithography,”SID Symp. Dig. Tech. Pap., 94 (2022).
[9] M. Kozuma et al., “1.5-inch, 3207-ppi Side-by-Side OLED Display Capable of 32-Division Driving with OSLSI/SiLSI Structure Fabricated by Photolithography,” SID Symp. Dig. Tech. Pap., 384 (2022).



foldable display®

We developed CAAC-OS technology, OLED technology, and flexible technology independently, and realized the world's first foldable OLED display. The foldable display incorporates a capacitive touch sensor, which has durability against more than 100,000 times of bending and touch function.


▲Demonstration Video of Foldable Display

8.7-Inch Tri-fold Display with Touch Sensor
▲8.7-Inch Tri-fold Display with Touch Sensor[10]
Image provided by Getty Images

13.3-Inch 8K Bi-fold Display
▲13.3-Inch 8K Bi-fold Display (pixel count of 7680 × 4320)[11]

[10] K. Watanabe et al., “An 8.67-in. Foldable OLED Display with an In-cell Touch Sensor”, SID Symp. Dig. Tech. Pap., 46, 246 (2015).
[11] K. Takahashi et al., “13.3-inch 8k4k 664-ppi Foldable OLED Display Using Crystalline Oxide Semiconductor FETs”, SID Symp. Dig. Tech. Pap., 46, 250 (2015).



Multi-display

Small flexible panels with transparent bezels, expanding the possibility of displays

81-Incn 8K Multi Display
▲ 81-Incn 8K Multi Display (with panels arranged in a 6-by-6 matrix,
and a pixel count of 7680×4320)[12]


[12] D. Nakamura et al., “An 81-in. 8k x 4k OLED Kawara-Type Multidisplay that Provides a Seamless, Continuous Image”, SID Symp. Dig. Tech. Pap., 46, 1031 (2015).

Mockup of a display unit on the dashboard of a car
▲Mockup of a display unit on the dashboard of a car (3 panel units)


Liquid Crystal Display

AQUOS ZETA SH-03G
Smartphone with IGZO:
"AQUOS ZETA SH-03G"
(Distributed by NTT DOCOMO, INC. / Manufactured by Sharp Corporation)

Liquid crystal displays using our crystalline oxide semiconductors (the world's first) have been used in smartphones manufactured by Sharp Corporation since 2012; thus pioneering a new field in the LCD industry.
In addition to the feature of high resolution, LCDs using our crystalline oxide semiconductors can perform idling stop (IDS) driving, which enables low power consumption.


Reflective LCD

5.9-Inch Touch-Sensitive Reflective Display
▲5.9-Inch Touch-Sensitive Reflective Display (pixel count of 1536 × 2048)[13]
Image provided by Getty Images


[13] D. Kubota et al., “Reflective LCD with High Reflectance and Color Reproductivity for Reduced Eye Strain”, SID Symp. Dig. Tech. Pap., 46, 1084 (2015).


1) Idling-Stop (IDS) Driving Technology
IDS driving is a display method for still images, utilizing a feature that a video signal can be held by crystalline OS. In a typical display, over 60 images are displayed per second, which are perceived as a single image or a moving image with human eyes. In other words, many images are actually displayed at high speed to display one still image. With the IDS driving, the number of times an image is re-written while displaying a still image can be reduced to, for example, once every 5 seconds. It is like looking at a natural object or at information on paper. Moreover, when this technology is used in a reflective display, a backlight becomes unnecessary, which enables ultra-low power consumption. This technology provides an electronic book reader with ideal functions such as eye-friendly and long-time driving.



* CAAC-OS, foldable display, HarPOS, and OSLSI are registered trademarks of Semiconductor EnergyLaboratory Co., Ltd.
(Japanese trademark registration No. 5759619, No.5680115, No6473200, and No. 5698906).