13 January 2023
SmartKem creates first monolithic micro-LED display using organic thin-film transistors
UK-based electronics materials and process technology firm SmartKem claims that it has created the first monolithic micro-LED display using organic thin-film transistors (OTFTs).
The new method of processing a thin-film transistor backplane on top of gallium nitride LEDs has the potential to accelerate the commercialization of micro-LED displays, it is reckoned.
Consumer electronics companies are actively developing micro-LED displays since they promise higher brightness, lower power consumption and longer lifetime. This is particularly important for portable powered displays such as smartwatches and augmented-reality/virtual-reality (AR/VR) displays which cannot accommodate large batteries.
Existing VR and AR headsets use liquid-crystal displays (LCD) and organic light-emitting diode (OLED) displays, which lack brightness, resolution, power efficiency and lifetime. Efforts to establish micro-LED manufacturing use physical transfer of LEDs from the wafer upon which they are manufactured to the TFT display backplane, where they must be laser welded to the contact pad of the transistor to make an electrical connection.
For high-resolution displays, millions of tiny LEDs need to be transferred from one place to another, so the potential for placement error is large. If a 99.9% placement yield is achieved, then a full-HD color display will have over 6000 faulty sub-pixel LEDs that would need to be identified, removed and re-attached. Once the 6000 faulty LEDs have been replaced, a 99.9% yield will still mean six of these will be faulty, so the task of manufacturing a perfect display is not yet finished. It is the process of seeking out the faults and then replacing them one by one which is slowing down commercialization of this new type of display.
SmartKem says that its patented core chemistry allows its semiconductor inks to be processed at the low temperature of 80°C. With its lower temperature, transistors can be processed directly on top of the micro-LEDs. This eliminates the mass transfer and laser welding processes, and the fabrication of OTFTs can use existing low-cost manufacturing tools currently used for LCD backplane manufacturing. This approach cannot be carried out with other types of thin-film transistors as they are processed at the much higher temperature of 300°C, which damages the micro-LEDs, and which is why you need to make them separately and then laboriously join them together one by one, notes SmartKem.