New method to enable mass manufacture of micro-LED displays

Researchers have demonstrated a continuous roller printing process that can pick up and transfer over 75,000 micrometre-scale semiconductor devices in a single roll with high accuracy. The new method could help create large-scale arrays of optical components and could be used to rapidly manufacture micro-LED displays.

Micro-LED display technology can accomplish highly accurate colour rendering with high speed and resolution while using little power. The displays can be applied in a range of formats including smartphone screens, virtual and augmented reality devices and large displays several metres across. For larger micro-LED displays, there are significant challenges in integrated millions of tiny LEDs onto an electronic control backplane.

Research team leader Eleni Margariti said transferring micrometre-scale semiconductor devices from their native substrate to a variety of receiving platforms is a challenge being tackled by academic research groups and industries. “Our roller-based printing process offers a way to achieve this in a scalable manner while meeting the demanding accuracy necessary for this application,” Margariti said.

In the journal Optical Materials Express, the researchers reported that the roller technology can match the designed device layout with an accuracy of less than one micron. The setup is also inexpensive and simple enough to be constructed in locations with limited resources. The printing process could also be used for other devices, including silicon and printed electronics such as transistors, sensors and antennas for a range of applications.

The researchers wanted to improve the transfer of large numbers of semiconductor devices from one substrate to another, to improve the performance and scaling of electronic systems used in applications such as displays and on-chip photonics, where the aim is to combine various materials that manipulate light on a small scale. “To be used for large-scale manufacturing, it is crucial to use methods that can transfer these devices efficiently, accurately and with minimal errors,” Margariti said.

The new approach starts with an array of tiny devices that are attached to their growth substrate. The surface of a cylinder containing a sticky silicone polymer film is then rolled over the suspended array of devices, allowing adhesive forces between the silicone and semiconductor to detach the devices from their growth substrate and array them on the cylinder drum. Because the printing process is continuous, it can be used to print multiple devices, which makes it efficient for large-scale production.

“By carefully selecting the properties of the silicone and receiving substrate surface and the speed and mechanics of the rolling process, the devices can be successfully rolled over and released onto the receiver substrate while preserving the spatially arrayed format they had on the original substrate,” Margariti said.

The researchers tested the new approach with gallium nitride on silicon (GaN/Si) semiconductor structures. GaN is the dominant semiconductor technology used for micro-LED displays and using silicon substrates facilitated the preparation of the devices as suspended structures that could be picked up by the roller. They were able to transfer more than 99% of the devices in an array of over 75,000 individual elements, with no significant rotational errors. Next, the researchers are working to further improve the accuracy of the printing process while also scaling up the number of devices that can be transferred at once.

Image credit: iStock.com/Ladislav Kubeš