This is an article by TechBlick, organizers of the upcoming MicroLED Displays virtual event. MicroLED-Info readers get a 100 Euro discount.

In this article, using select technology slides, we highlight several interesting advancements in MicroLED and/or QD displays. More specifically, we cover 3600PPI “Silicon” Displays | Gravure printed microbumps | Electrohydrodynamically printed QD color converters | Laser LLO and Transfer for MicroLEDs | QD vs Phosphors | Energy saving credentials of microLED

“Silicon” Displays with an incredible 3600ppi full color using microLED and QD technology?

Sharp (HIRANO Yasuakie et al) has developed this technology.

As shown in the slide below, first blue-only uLEDs are formed on a sapphire substrate. Here, one LED array contains 352 x 198 micro LED dies of 24 um x 8 um in size. In parallel, an LSI chip containing the driving circuitry is formed on a silicon wafer. Here, the cathode (N-type electrode) and anode (P-type electrode) are fabricated for each micro LED die to apply driving voltage independently to each die. The Au bump electrodes are fabricated in accordance with the pitch of the LED dies. The two substrates are flip-chip bonded using Au-Au bonding. Here one can already see the parallel to the silicon and optoelectronic industry (vs. the traditional thin film display industry!). Next, the sapphire layer is removed via laser lift off. Finally, Cd-free quantum dots (green and red) are deposited atop the microLED dies to enable R G color conversion. This way one achieves RGB colors.

Kulicke and Soffa Industries (K&S) announced that it has received two purchase orders, from two separate customers, for its LUMINEX, a disruptive laser-based mini and micro LED die-transfer solution.

K&S says that its highly flexible system is capable of single die transfer, multi-die transfer and mass transfer, supporting sorting, mixing, re-pitching and placement process steps. The broad flexibility of this system addresses the growing advanced display value chain and supports needs of LED, OSAT, panel and display suppliers.

Taiwan-based laser micromachining subsystem and equipment manufacturer Bolite Optoelectronics announced its new automated side-wiring system, the laser-based Bolite SW-L, which can be used for the production of tiled microLED displays.

This laser-based tool offers high-precision alignment, advanced process control, and full automation with robotic handling. The minimum line with and spacing is 5 um. Bolite says that this system is highly compatible with TFT production processes. The SW-L systems are now available, and Bolite is already accepting orders.

This is a sponsored post by Coherent

Coherent is a leading global supplier of lasers and photonics technology. For the MicroLED industry, Coherent provides several solutions from a single laser source, optical systems up to an integrated system for the three vital processes in MicroLED fabrication – Laser Lift-Off (LLO), Laser-Induced Forward Transfer (LIFT), and Repair/Trimming.

Coherent recently published a new white paper that provides an update on how high-energy ultraviolet laser beams enable LLO and LIFT processes. The white paper shows the importance of a perfect combination of laser and optical design to a how these lasers ensure placement accuracy and mass transfer that will remain future-proof as microLED chip die size continues to shrink.

The founder and General Manager of Bolite Optoelectronics, Dr. Bowen Cheng, was invited to present at the recent Touch Taiwan 2021 Conference in April. The title of his talk was “Laser Processing Applications for the Manufacturing of Mini and MicroLED Displays.” Since it was presented in Mandarin only, microled-info.com caught up with Dr. Cheng to learn more about this trending subject and the company he started.

Q: Dr. Cheng, can you please tell us a little about your background, prior to starting Bolite?

I was a research engineer at Xerox PARC and helped develop surface micromachined microspring interconnects in a project funded by the U.S. Army Research in collaboration with Oracle. I was also a vital member of the team that successfully demonstrated the world's shortest wavelength diode laser at the time, a 250 nm UV laser for military applications. With these experiences in both semiconductor laser processing and MEMS processing, I decided to start Bolite and build a team to develop state-of-the-art laser solutions for microprocessing applications.

Q: I must admit I’ve not heard of Bolite before. What differentiates you from other laser microprocessing companies?

3D-Micromac announced a new microLED mass transfer tool, called microCETI. The company says its new technology can be used to transfer over 130 million microLEDs per hour.

MicroCETI is based on a laser-induced forward transfer (LIFT) process that can support almost any microLED material and shape. The tool also includes optional modules - a laser lift-off (LLO) module, and a single LED die repair module.

Laser equipment maker Coherent says that it saw a "significant increase" in the level of investment and bookings related to MicroLED displays. These tools are going to be used for process development, as a precursor to mass production.

Coherent reveals that its MicroLED customer base includes almost all current OLED and LCD manufacturers and many well-known MicroLED specific startups and display industry integrators. Coherent is offering multiple UV solutions for four separate MicroLED processes - CLA for high performance low power consumption back planes, laser lift-off for customers using sapphire carrier, laser transfer and laser repair.

Researchers at Zhejiang University developed a laser-driven programmable non-contact transfer printing technique that could be applicable to the transfer of Micro-LED chips. The researchers used an innovative design based on an active elastomeric micro-structured stamp with tunable adhesion.

The tunable adhesive used in this technique features cavities filled with air and encapsulated by a micro-patterned surface membrane, used in easily available sandpapers. The micro-patterned surface membrane can be inflated dynamically to control the interfacial adhesion by heating the air in cavities.

Laser equipment maker Coherent says that its customer have expressed a "reasonable amount of interest " in its Micro-LED solutions. The company is taking orders for R&D tools, but it says that mass production of Micro-LED displays is "still years away".

Coherent offers several laser-based tools used to produce Micro-LED displays, including Laser Lift-Off equipment (LLO) used to separate micro-LEDs from the sapphire wafer and Laser Induced Forward Transfer (LIFT) used to move micro-LEDs from the donor to substrate.

During a presentation at SID Displayweek 2018, laser developer Coherent showed a nice chart that summarizes the performance difference between LCDs, OLEDs and Micro-LED displays.

Coherent says that its lasers could be used in the pick-and-place process when making micro-LEDs. A laser lift-off process (LLO) removes the LED chips from the sapphire growth wafer (or any other carrier wafer) and a the laser-inducted forward-transfer (LIFT) process transfer selected dies from carrier to substrate in a high-precision way that can be massively parallel (over 25,000 dies per shot).