Researchers are developing an approach that could enable the inexpensive mass manufacture of micro-LED displays
(Nanowerk News) Researchers have demonstrated a continuous roller printing process that can pick up and transfer more than 75,000 micrometer-scale semiconductor devices on a single roll with extremely high accuracy. This new method opens the way for fabricating large-scale optical component arrays and can be used to rapidly fabricate micro-LED displays.
Micro-LED display technology is very attractive because it can achieve highly accurate color rendering at high speed and resolution while using very little power. These views can be implemented in a variety of formats including smartphone screens, virtual and augmented reality devices, as well as large displays several meters wide. For larger micro LED displays, in particular, the challenge of integrating millions of tiny LEDs — which are sometimes smaller than a grain of fine sand — into the electronic control backplane is enormous.
“Transferring micrometer-scale semiconductor devices from their native substrates to various receiving platforms is a challenge being tackled internationally by academic and industrial research groups,” said research team leader Eleni Margariti from the University of Strathclyde in the UK. “Our roll-based printing process offers a way to achieve this in a scalable way while meeting the accuracy demands required for this application.”
In the journal Optical Materials Express (“Continuous roll transfer printing and automatic metrology >75,000 micro-LED pixels in one shot”), the researchers report that their new roller technology can match the layout of a designed device to an accuracy of less than 1 micron. It’s also inexpensive to set up and simple enough to build in a location with limited resources.
“This printing process can also be used for other types of devices including silicon and print electronics such as transistors, sensors and antennas for flexible and wearable electronics, smart packaging and radio frequency identification tags,” said Margariti, who developed the new printing process. . “It could also be useful for creating photovoltaics and for biomedical applications such as drug delivery systems, biosensors and tissue engineering.”
Large-scale device transfers
Today’s semiconductor devices are typically manufactured on wafers using growth techniques that deposit highly detailed and beautifully detailed multi-layer semiconductor thin films onto a semiconductor substrate. Compatibility issues between these thin film structures and the types of substrates suitable for deposition limit how the devices can be used.
“We want to increase the transfer of large numbers of semiconductor devices from one substrate to another to increase the performance and scalability of electronic systems used in applications such as displays and on-chip photonics, where the goal is to incorporate various light-manipulating materials. on a very small scale,” said Margariti. “In order to be used for large-scale manufacturing, it is critical to use a method that can transfer these devices efficiently, accurately, and with minimal errors.”
The new approach begins with a series of tiny devices that are loosely attached to their growth substrate. A cylindrical surface containing a slightly sticky silicon polymer film is then rolled over the suspended device array, allowing adhesive forces between the silicon and the semiconductor to release the device from its growth substrate and assemble it on the cylindrical drum. Because the printing process is continuous, it can be used to print multiple devices simultaneously, which makes it very efficient for large-scale production.
Very accurate printing
“By carefully selecting the properties of the silicon and the surface of the receiving substrate as well as the speed and mechanism of the winding process, the devices can be successfully rolled and released onto the receiving substrate while retaining the spatial arrangement format they had on the original substrate,” explained Margariti. “We also developed a special analytical method that scans for defects in printed samples and provides printing results and positioning accuracy in just a few minutes.”
The researchers tested the new approach with gallium nitride on the semiconductor structure of silicon (GaN/Si). GaN is the predominant semiconductor technology used for micro-LED displays, and using a silicon substrate facilitates the preparation of the device as a suspended structure that can be picked up by a roller. They are capable of transferring over 99% of the device in an array of over 76,000 individual elements with sub-micron spatial precision without significant rotational error.
Next, the researchers are working to further improve the accuracy of the printing process while increasing the number of devices that can be transferred at once. They also plan to test the method’s ability to affix different types of devices to the same receiving platform and determine whether it can be used to print to specific locations from the receiving platform.
