Now that QDs are becoming a mainstream display technology, I am often asked “what’s next” for QDs? Will electroluminescent QDs become a reality? Are QDs on chip really viable? What other applications outside of display technology are QDs good for? I’ll continue to write on these topics in future posts, but for now I will address what I believe is the next hurdle for QD integration into our devices, and if achieved, will blow the doors open on the addressable market for QDs. On Chip.
WHAT IS ON CHIP? Current TV technology (without QDs) rely on a series of blue LEDs with an inorganic phosphor cured into the silicone encapsulating material. On chip QD technology promises to replace the phosphor material with QDs. The hope is that in this form factor, the QDs will deliver the same performance as in other implementation strategies (film or edge implementation – discussed below). If achieved, this would allow any device using LEDs (not OLED) to very easily implement QDs into their product (phones, tablets, TVs, general lighting). LED manufacturers would be able to simply add QD powder instead of phosphor powder to the silicone encapsulating material prior to deposition, allowing for seamless integration of QDs into an LED assembly line.
WHY IS IT SO HARD TO ACHIEVE? Three main reasons: temperature, flux, and atmosphere. The temperature this close to the LED die can be in excess of 100 C! This is, in part, due to the extremely high light flux present in the small area directly above the die (10s of W/cm2). On top of that, the QDs dispersed in the silicone encapsulating materials are constantly exposed to the atmosphere (silicones do not provide a good hermetic barrier). All available displays containing QDs currently implement one of two strategies to exclude atmosphere. 1) QDs sealed inside of a glass tube, or 2) QDs in a polymer film sandwiched between two barrier films. Exclusion of the atmosphere is necessary due to its damaging effect on the QDs, resulting in rapid degradation of the QD optical properties. If on-chip technology is to become a reality, exclusion of atmosphere will need to be part of the solution – and progress is being made.
WHO’S WORKING ON IT? Likely a lot of companies are researching different approaches to overcoming the on chip challenge, although most are being quiet about it for now. Two, in particular, have been fairly open about their quest to be the first to claim on-chip success. Pacific Light Technologies has been focused on this task for many years now and has recently reported some success, although they remain tight-lipped about their approach. Crystallex is currently promoting their “Saphire” quantum dots which contain an alumina protective coating. It should be noted however that there are currently no products on the market containing QDs on-chip, so clearly, there is still some work to be done.
QDs on-chip are not ready for prime time, but as more and more companies put in the resources to solve the challenges of stabilizing QDs for the high temperature, high flux, and oxygen-rich environment, progress will be made. 5 years ago people did not think that QDs would make it to prime time in display technology, but they did, so don’t count them out for on-chip yet either!
Thanks as always for reading!