CEATEC 2023 Micro-LED has emerged as a central player in display field
Perovskite, organic film and DSC have competed in organic series solar cell

October 17 - 20, CEATEC 2023 were held in Makuhari Messe. Main topics of electronics field are closed up in this here.

New demand such as face-to-face communication is exploited by a new transparent TFT-LCD

Pic 1. 20.8-inch transparent display

As concerns display module, Japan Display exhibited a newly transparent display "RealClear". In this system, RGB-LEDs are set on bottom side of TFT-LCD panel. Transparent display was realized by field sequential driving, which was a method to light RGB-LED sequentially. For this reason, optical films such as polarizer and phase difference film are not necessary. Its transmittance is approximate 90%, as a result, see-through property is sufficient. Of course, contrast ratio is relatively low same as 30:1 because of trade-off relationship against transmittance.

In the booth, 20.8-inch panel (1280 × 720 pixel) and 12.3-inch panel (1440 × 540 pixel) were exhibited. It showed to be suitable for face-to-face communication such as shopfront.

E Ink exhibited a flexible e-paper by IGZO-TFT driving for the first time

Pic 2. Flexible 8-inch e-paper by IGZO-TFT driving

With respect to e-paper, E Ink holdings exhibited a flexible color 8-inch e-paper (1920 × 1440 pixel) by IGZO-TFT driving for the first time. In this module, a polyimide film was used as a base substrate. Rewriting speed was foreshortened to 1.5s at color image by IGZO-TFT driving, which had high carrier mobility.

The company exhibited 8-inch color panel with glass substrate and monochrome panel (1920 × 1440 pixel) as IGZO-TFT driving panel, too. IGZO-TFT will be adopted instead of a-Si TFT in required relative speed applications.

Micro-LED chip is directly patterned and mounted on the substrate by laser transfer method

Pic 3. Pilot-produced Green Micro-LED by laser transfer method

As regard Micro-LED, New Energy and Industrial Technology Development Organization (NEDO) introduced a pilot-produced green emission Micro-LED by laser transfer method as achievement of "Post-5G project".

In this project, Toray and Toray Engineering developed laser transfer technology as patterning and mounting method of Micro-LED from an original sapphire substrate with LED to a display substrate by direct laser irradiation. The project pilot-manufactured a small green device with 20 × 30 dot array at 150 μm pitch. Laser transfer speed is 10,000 pieces/sec.

By the way, main subject of this project is to develop advanced mounting process technology of next generation semiconductor.

Micro-LED is used as device of VR/AR/MR display

Fig 1. Structure of Micro-LED and its emission

On the other hand, Meijo University introduced a stack type GaInN series monolithic full-color μLED array, which was possible to manufacture ultra-high resolution and ultra-high brightness VR/AR/MR displays.

Figure 1, monolithic type full-color μLED array has been manufactured on identic substrate by stack of RGB-LEDs through of the intermediary of tunnel junction. 3 primitive color emissions of RGB were obtained. And also, a full-color display with 35 × 15 μm dot array and 330ppi resolution was pilot-manufactured.

In the booth, looking and listening demonstration of head mount display (HMD) using this device was done. In this demonstration, viewer can view virtual image with 4K high resolution and large size. Docent appealed that luminance efficiency of this device was greatly higher than that of the existing OLED.

Micro-LED is manufactured on a newly revolutionary substrate

As concerns material for Micro-LED, Kyocera announced a newly revolutionary substrate "EGOS(ELO GaN on Sapphire)". If this substrate is used as an original substrate of LED device, LED can be manufactured in region with defect-free.

Figure 2 shows process image. As (a), enormous defects of GaN is generated on grown sapphire substrate. And then, as (b) and (c), GaN is grown vertically from opening area of masking layer, as a result, growth core is generated. In this region, enormous defects exist yet. The next, as (d), crystal of GaN is grown from growth core laterally (ELO：Epitaxial Lateral Overgrowth). In this region, layer with defect-free can be formed. Device area and opening area are used as this region and general defect region respectively. As a result, high quality LED can be manufactured.

Fig 2 Manufacturing flow of Micro-LED by use of EGOS substrate

Pic 4. Microscope picture of Micro-LED

In pilot-produced 2-inch device, dot area of 50 × 25 μm was used for ELO region. As a result, it's easy to increase luminous efficiency, brightness, and decrease manufacturing cost. By the way, sapphire substrate was used as a substrate in this sample, but inexpensive silicon wafer can be used due to lost cost manufacturing.

The company will supply EGOS substrate, and also, license out manufacturing technology of Micro-LED using EGOS substrate.

Perovskite solar cell is built in window of high building

As opening sentence, organic series solar cells have competed as a next generation device. First of all, Panasonic appealed an effective demonstration of perovskite solar cell. Main product is an integrated glass window and perovskite solar cell, and then, suitable for high building because of impossibility of setting on roof in Japanese law.

Pic 5. Perovskite solar cell with various transmittances

As picture 5, some samples with different transmittance were exhibited in the booth. Its transmittance can be set at will by laser elimination process after ink-jet printing of perovskite film on the whole. By the way, if perovskite layer is wholly coated (without laser cutting), IPCE (incident photon-to-current efficiency) is 20 %. In short, IPCE is almost same as that of the existing Si series solar cells.

GSI Creos releases a semiconductor polymer ink, is mainly composed of Brilliant Matters's polymer

Pic 6. Flexible organic film solar cell

On the other hand, GSI Creos announced to release polymer inks with Brilliant Matters's semiconductor polymer for organic film solar cell, in Japan.

This polymer has a non-fullerene series accepter, and is bulk-hetero junction type. IPCE at champion data is 17 % because of high light absorption and low energy loss in charge process. Furthermore, in mass-production model, IPCE and lifetime are 7 % and 10 years respectively.

GSI Creos supplies various inks for various coating methods, such as spin-coating, dye-coating, and so on. In the booth, device samples of Brilliant Matters and Yamagata University were exhibited.

Sharp appealed dye-sensitized solar cells with high IPCE same as 20 %

Pic 7. LC-LH

By contrast, Sharp appealed LC-LH (Liquid and Crystal Light Harvesting), which was a dye-sensitized solar cells (DSC). Its IPCE is greatly high same as 20 %, but its reason was not disclosed. It's possible to divert manufacturing process and equipment of LCD. In fact, this device will be mass-produced in the existing LCD factory. For this reason, device can be manufactured by lower cost compared to that of competitors.

Stretchable silicon + Ag ink is suitable for wearable applications

Pic 8. Demonstration of LED lighting by printed DuraQ wiring

As regard material for electronic device, Sumitomo Bakelite introduced a flexible and stretchable wiring paste "DuraQ". It's composed of silicon rubber compound with high strength property and Ag powder. Its tear strength is greatly high same as 40N/m. And also, typical specific resistance is 2 × 10^-4 Ω･cm. In case of 50 % stretch, it's increased at mere 2 times, and also, in case of 100 times at 50 % stretch state, at same times, too. Furthermore, thermal resistance is approximate 300 ℃. It's possible to stack multi-layer, for example, silicon substrate/DuraQ/silicon compound/DuraQ. In this case, its mechanical strength is increased because of same component in all layers.

Picture 8 shows printed sample of DuraQ on silicon rubber substrate. As you see, LED can be normally emitted. It's suitable for wearable applications, and can be sewn on clothes and has resistance against wash.