On October 27th, the paper entitled "Laser-driven hierarchical "gas-needles" for programmable and high-precision proximity transfer printing of microchips” was published online in Science Advances. The National Key Laboratory of Intelligent Manufacturing Equipment and Technology of our University is the primary organization of this paper. Furong Chen is the first author of this paper. Professor YongAn Huang and Dr. Jing Bian from Nanjing University of Posts and Telecommunications are the co-corresponding authors of this paper. PhD students Mengxin Gai, Haiyang Yu, Zhangyu Xu, and master students Ningning Sun and Lei Liu participated in the research.
Micro–transfer printing (μTP) is the key technology to realize the heterogeneous integration of microelectronics/flexible electronics. How to assemble the micro-scale heterogeneous components in batches and accurately to any receiving substrate with high efficiency and high precision is a great challenge. For example, the MicroLED display technology, which is composed of tens of millions of micro-scale MicroLED self-luminous chips, urgently needs to develop a mass transfer technology with high transfer efficiency (~1 million/h), high transfer accuracy (~ 5μm) and high yield (~99.99%) to meet its large-scale manufacturing needs. Laser-assisted transfer printing is considered to be the most promising mass transfer technology, which can realize ultra-high chip transfer efficiency by using micro-size laser spots and multi-beam high-speed scanning. Currently, two different kinds of μTP (i.e., contact and noncontact) have been developed according to the contact mode between the micro-object and receiver substrate. However, current contact/noncontact μTP techniques fail to simultaneously achieve high selectivity and transfer accuracy, especially on a nonadhesive substrate. Therefore, how to combine high-precision transfer with individual chip control is one of the key bottlenecks for the laser μTP.
Here, a proximity μTP that can change from the noncontact mode to approximatively contact mode is presented for high-precision deterministic microchip assembly. The key idea is the introduction of the hierarchical gas-needles (GNs) stamp, which sequentially changes the initial chip and stamp spacing and interface contact area. This technique is also called dual-laser projection proximity transfer printing (LaserPPT) since the sequential expansion of the hierarchical blisters induced by the UV and IR lasers working together is used as a case for hierarchical GNs. It combines the programmability of noncontact μTP and the high precision of contact μTP. Specifically, because of the highly confined affected zone, the UV laser induces a gas-filled blister with a photothermal-conversion carbon layer (PCL). The PCL can absorb the IR laser to generate a large blister, which reduces the spacing between the microchip and receiver substrate to nearly zero, changing the original noncontact mode to contact mode. At the right moment, massive small-scale blisters reduce the interfacial adhesion and enable the gentle release of a chip onto a non-adhesive substrate due to the pop-up of thermally expandable microspheres (TEMs) on the surface of the large blister. As a result, the proximity transfer mode achieves both high transfer accuracy and wide compatibility with receiver substrates. Systematic analysis has showcased an excellent adhesion switchability of ~1000 times and a high transfer accuracy of ~4 μm.
In combination with the parallel laser operation mode, LaserPPT shows exceptional capabilities for deterministic microarray assembly. Through the self-developed “iGreatTransfer” experimental platform, the research team printed the microchips onto a PDMS substrate to form several complex patterns. Furthermore, a flexible MicroLED display is fabricated via the anisotropic conductive adhesive (ACF) bonding process. These results show the possibility of using LaserPPT for preparing advanced MicroLED displays.
This work not only puts forward a new proximity transfer mode, which assembles the microchips in an approach-and-release manner but also realizes high selectivity and transfer accuracy simultaneously for the first time, pointing out a future direction of laser μTP for the practical application.
The above research work was supported by the National Natural Science Foundation of China.
Original link: https://www.science.org/doi/10.1126/sciadv.adk0244
