Solving the Mass-Transfer Problem for MicroLED Displays
Many observers predict microLED technology will ultimately win in key segments of the display market. Inorganic LEDs can be up to 1000 times brighter, more robust and long-lived, allowing much higher efficiency and lower power consumption, particularly for mobile devices that are viewable in bright daylight like smartphones, wearables, and AR/VR apps, as well as in larger displays. Fundamentally the same tech dominating solid-state lighting (SSL) scaled down to individual, addressable display pixels, it is already prevalent in large format displays for sports stadiums, advertising, signage, and may ultimately displace projection in Cinema or other venues.
While in larger displays the pixels can also be large, the trend is to increased resolution and smaller microLED pixels, ultimately for smartphones, smartwatches, and microdisplays for AR/VR, as well as 8K+ resolution in larger displays. But there are significant manufacturing and cost challenges as (die sizes) shrink to below 10 um, the sizes typically needed for a smartphone display is over 400+ PPI range. For example, Apple acquired LuxVue in 2014 and is still working hard on microLED displays to displace the OLED screens in their smartphone models.
Among the several major manufacturing challenges with microLED displays, first and foremost may be the so-called Mass-Transfer problem: how to very rapidly, reliably assemble pre-made microLED die into precisely ordered arrays on a control backplane to form a display. Massively parallel techniques are needed, with few to no bad pixels allowed, a major challenge that is more difficult than it appears if throughput and commercial viability are considered. Other challenges include color conversion, an area where VerLASE had originally been focused both for microdisplays as well as larger displays. In larger displays, such as in smartphones, however, Mass-Transfer becomes the major hurdle, severely limiting microLED market development. We have been quietly working on that challenge, recently filing IP on a new, novel approach to solve the mass-transfer problem in a commercially viable way. Display densities over 400 PPI (meaning < 10-20 um subpixels where microdie sizes are even smaller) should be readily achievable for smartphone sizes, with very high thruputs, much higher than other known techniques, with provisions for in-line metrology and in-process repair, a differentiator in leading approaches.
If the manufacturing problems are solved in a commercially feasible way, they can be very price competitive. A cheap 6-inch standard LED wafer can be sub-divided into MANY much smaller microLED dies, then re-populated over a much larger surface area, where each microLED die representing a sub-pixel of a larger display. For example, a single such wafer yields enough 10 um die to populate about 100 displays at 2 Million pixels each!
Displays also come in many different resolutions and sizes with differing needs depending on size. The microLEDs that would form the emissive sub-pixels in these displays will be of different sizes; “Wall” sized displays could be made with mini dies, but for 4K or 8K high resolution microdies would sooner apply. A Mass-Transfer technique that can handle smaller microdies, can be adapted to mass transfer of larger micro or mini-dies; however, the reverse is not true, it’s not always possible to scale a given method to mass transferring smaller microdies.