A Bright Future Is Coming
by Stephen P. Atwood
I have been looking forward to this issue ever since we first put it on the calendar because there are so many recent innovations in the field of emissive
technology. My excitement was further piqued when Guest Editor Qun (Frank) Yan (professor, industry advisor, and chair of SID’s emissive display subcommittee) pitched his story ideas, which included one on micro-LEDs and another on quantum dots and quantum rods.
Those of us who remember watching CRT televisions certainly have seen our share of ideas for emissive displays over the years, including electroluminescent
(EL), vacuum fluorescent (VF), light-emitting diode (LED), and, of course, plasma. (I maintain that plasma TVs were one of the best technologies of their time, and I still enjoy my 60-in. plasma TV almost every evening.) But when organic LED (OLED) technology became commercially viable, I began to think that the future could truly be changed by emissive technology. Frank also considers this historical context in his Guest Editorial, where he describes his view of the significance of new emissive technologies for the future of displays. We are very grateful for the excellent effort Frank has made to bring this topic to you this month. OLEDs will certainly be a big part of the future, but as you will read this month, other forms of emissive technology may play as big or even bigger a role
in transforming the current paradigms we work in as display engineers.
I was privileged to get a first look at quantum-dot (QD) technology about a decade ago when a company called QD Vision first began its work up here in New England. Seth Coe-Sullivan, one of the company’s founders, came over to our New England SID chapter meeting with some small vials of fluid that would glow bright red and green when excited by LED light. Being a skeptic, I immediately started looking for the trick behind the demonstration. Was it some kind of optical illusion? Was it a prismatic effect that split the source light and somehow only passed through the color being shown? No, as Seth explained, it really was a secondary self-emitting technology in which the energy was coming from the source light and being re-emitted by the quantum dots at the exact wavelength prescribed by the dots themselves. Wow! I still remember that night and the ideas that were spinning around in my head as I drove home from the meeting.
When the first demonstrations of QD-enhancement films for LCDs were shown, I liked the concept a great deal but felt this was not nearly the goal line for the technology. It is fun to be right once in a while, and I think you will really like our first Frontline Technology article from authors Kai Wang and Xiao Wei Sun
titled “Quantum-Dot and Quantum-Rod Displays – the Next Big Wave,” as much as I did. The authors describe first the current state of the art of QDs as backlight enhancement components for LCDs, including actual QDs embedded on LED chips. They go on to introduce a new structure called a “quantum rod (QR),” which is described basically as “…a kind of core-shell nanocrystal with an aspect ratio of more than 1:1 (e.g,. 5:1).” In other words, a long thin rod that behaves just like the dots, absorbing electric field or light energy and re-emitting at prescribed wavelengths. However, in the form of crystalline rods they have an additional property through which they can emit polarized light along their long axis, potentially making them even more ideal as backlight sources for LCDs.
The fun really begins when the authors discuss the potential to build electroluminescent (EL) displays using quantum-dot-enhanced light-emitting diodes (QLEDs) and describe some recent demonstrations. One such example, which you will recognize from our cover of this issue, are R, G, and B QLED devices made by Najing Technology Company that achieve electrical quantum efficiencies of 20%, 18%, and 14% for red, green, and blue colors, respectively. This technology may become a companion or alternative to OLED in many of the same display form factors being served by OLED today.
Our next Frontline Technology feature is titled “Micro-LED Technologies and Applications” by authors Vincent W. Lee, Nancy Twu, and Ioannis (John) Kymissis. Micro-LEDs describe a class of LED devices that have an emission area smaller than 50 µm × 50 µm and a similar die size. This makes them highly valuable for an almost endless array of display form factors, including flexible, projected, and possibly even three dimensional. They also can achieve an almost unbelievable amount of luminance, making them suitable for an array of demanding high-light-output display applications. But what brings this home for me is that the authors have taken the time not only to explain the technology well but to describe the many ways that creators are actually attempting to develop and commercialize their processes to build these devices into working displays. Some of this manufacturing technology you have no doubt seen before, but some of it is truly original and being developed specifically for micro-LED display manufacturing. Micro-LED technology clearly has a viable foundation and will continue to grow in its potential.
Of course, a lot of the work in emissives comes from fundamental research on new materials. An example of these are the thermally activated delayed fluorescent (TADF) emitters being developed by a company called CYNORA. We had the opportunity to speak with Andreas Haldi, Chief Marketing Officer of CYNORA GmbH, who was eager to talk about the young company’s business and the future prospects for its technology, and we are pleased to offer this installment of Market Insights, a Q&A put together by Jenny Donelan. CYNORA is a great example of the type of highly focused companies that I think we will need to build the eco-system of future emissive-display achievements.
Switching topics, display metrology is a subject that often invokes either groans or glee, depending on who you are and what problem you are trying to solve. Research people love the great performance they can get from high-end metrology setups in their labs – if they can afford them. Manufacturing people often hate the special environments and time requirements needed to implement even a small number of optical measurements in a production line. Those of us close to the subject know there are lots of painstaking ways to get really good measurement results under near-ideal laboratory conditions, but getting high-quality repeatable fast measurements in a production environment can be very challenging. This is particularly true when applied to today’s high-dynamic-range, wide-color-gamut, and high-resolution display products.
As explained in our third Frontline Technology feature, “Next-Generation Metrology Facilitates Next-Generation Displays,” by authors Peter Notermans of Admesy and Nathan Cohen of IMPERX, the solution is to combine the best features of two types of instrumentation: CCD camera and spectro-meter. The authors describe how the development team overcame the shortcomings of high-speed CCD-based photometry: by combining the light paths of a CCD imager with a spectrometer and then implementing a sophisticated calibration technique to allow the system to collect 2-D high-dynamic-range color and gray-scale information much faster than other incumbent methods such as filter-wheel systems. The result is a system that provides the performance advantages of each of the two core instruments with a measurement speed suitable for today’s production demands.
In addition to our features introduced above in this issue, we also have our regular departments of Industry News and SID News, as well as some special coverage of the latest smartphone displays.
As I write this note for the November/ December issue of ID, it is still fall outside my window and the weather has not yet grown too cold. But, like every year before, winter is coming. I am not sad because by the time you get to read this, the holidays we all celebrate will be near at hand. By that time, I’ll be angling to get as much time away from work as I can and eagerly looking forward to special time with my family and now grown children. They are building their own lives from the foundation we gave them, as well as from their own ambitions and passions. I am proud of the people they are today and of what they are striving do for their own futures. As you approach the holidays, I urge you to take the time to cherish your family and recognize them not only for who they are today but who they will become tomorrow, and the day after, and in the years to come. And so, I wish you a wonderful holiday season and a very bright future in the New Year. •