microLED displays closer to commercialisation

Technology advancements pave the way for various cost reduction paths toward volume manufacturing,” commented Eric Virey, PhD, Senior Market and Technology Analyst at Yole. “But none are straightforward.” 

Yole had a chance to visit glō’s private suite and see an impressive series of demos and working prototypes such as a 1.5” 264 ppi RGB wearable display on a LTPS glass backplane, and a 0.7” 1000ppi RGB display for AR / HUD on a CMOS backplane.

Despite a high profile investment from Google in 2017, glō had remained quiet regarding its technology and activities. Following CES, Virey had a chance to interview Fariba Danesh and Aniruddha Nazre, respectively CEO and executive chairman of glō to discuss the company’s recent progresses as well as its manufacturing and commercialisation strategy.

Eric Virey (EV): Could you please introduce glō to our readers?

Fariba Danesh (FD) & Aniruddha Nazre (AN): glō started as a compound semiconductor company that was founded in Sweden and moved to Silicon Valley eight years ago. Its investors include FAM, Wellington Partners, Nano Future Invest, TeknoInvest and Google.

EV: How long have you been working on microLEDs, and more specifically on display applications?
FD & AN: The company has worked on developing highly efficient microLEDs made from InGaN for more than a decade. Most of the effort has been on developing green microLEDs and later red microLEDs. Over the last four years glō has also invested in significant R&D toward developing a selective direct wafer transfer technology, building a complete display technology portfolio.

EV: What are glō’s key elements of differentiation in the microLED display field?
FD & AN: glō makes all three colours (RGB) from InGaN, in sizes from 20 down to 1.5μm. The unique characteristic of glō microLEDs is that they peak at current densities that are 1/100th that of traditional LEDs, making them ideally suited for displays being driven by transistors on LTPS glass substrates or CMOS substrates. Being able to use commercial backplanes in LTPS and CMOS allows glō to make displays of various sizes and resolutions with the best performance possible in terms of brightness, efficiency, colour gamut, contrast, refresh rates and life time.

EV: Do you focus specifically on epitaxy and chip design or are you also working on other aspects of microLED technologies such as transfer, drivers etc?
FD & AN: glō is vertically integrated in terms of systems design. glō designs its own InGaN microLEDs to optimise light extraction and render uniform colour with the right emission angles. In addition, glō has developed its own direct wafer transfer technology that allows it to make display panels with sizes from 0.1” to 75” with resolutions up to 3000ppi on either glass LTPS or silicon CMOS backplanes.

Since we leverage commercial backplane and related drivers, we do not work on those items.

EV: Could you briefly describe the demos and prototypes you recently showed at CES? How do they compare with LCD and OLED in term of performance?
FD & AN: The working displays presented at CES were:

• A 1.5” diagonal RGB smart watch display with 20 micron microLEDs at 264ppi on a LTPS glass backplane. This display produces 4000 nits brightness, has infinite contrast, 120Hz refresh rate, 121% of DCI-P3 colour gamut and uses less than 1W of power.
• A 0.7” diagonal RGB display for AR glasses and HUD applications with ten micron microLEDs at 1000ppi on a CMOS backplane. This display produces 100,000 nits of brightness, has infinite contrast, 120% DCI-P3 colour gamut, 120 Hz refresh rate and uses 3.25W power.

The best OLED display can produce a brightness of 1000 nits, but the organic LEDs degrade rapidly because they cannot withstand the higher currents required. An equivalent LCD display would have to use over ~85W of power, which is obviously not practical for any wearable display. A LCD display also does not offer the same colour gamut, contrast or refresh rate. To summarise: glō microLED displays offer 10x more brightness and 5x better power efficiency with equal or better colour quality than the best OLED

EV: Are those displays using 2D chips or your nanowire technology ?
FD & AN: glō uses its unique epitaxy technology developed over the many years of nanowire work in all its microLEDs. The technology can be used to make both LED types, depending on the application. This month in Photonics West, our 100,000 nits HUD demo show cases our latest 2D LEDs, while the smartwatch display show cases the same technology in our latest 1D rendition.

EV: In its ‘microLED Displays 2018 report’, Yole highlighted the challenges of driving microLEDs, especially with traditional TFT backplanes such as LTPS or Oxide (Yole will also discuss the topic at the upcoming SID –Display Week Conference in San Jose in May). glō seems to have made significant breakthroughs in that regard. How are you addressing the challenge of microLED non-linearity? What kind of compensation circuits might be needed and how do they differ from other emissive technologies such as OLEDs?
FD & AN: The standard compensation circuitry needed for OLED LTPS and CMOS uniformity are suitable for glō’s LEDs. There are two attributes in glō’s technology that allow us to use standard LTPS driver electronics and compensation:

• glō microLEDs are specifically designed to be efficient in the low current regimes offered by LTPS and CMOS back planes.
• All colours of glō microLEDs, including red, are made with InGaN material, simplifying the demands on compensation circuits. The InGaN semiconductor material also has the advantage of longer life times and better temperature stability, reducing the burden on compensation circuitry.

EV: What kind of brightness levels can be achieved with glō microLED displays on CMOS vs LTPS backplanes? Can they both deliver a wide dynamic range?
FD & AN: To date glō has been able to achieve 4,000 nits from LTPS backplanes and up to 150,000 nits from CMOS backplanes. Both CMOS and LTPS backplanes offer the ability to turn off a pixel completely while the adjacent pixel is fully bright. This enables true high dynamic range (HDR) displays, i.e., the achievable brightness difference between adjacent pixels is orders of magnitude better than OLED.

EV: Your display prototypes feature native RGB LEDs (no colour conversion) that are all made on a GaN material platform. Making red nitride LEDs is notoriously difficult. What kind of efficiency have you achieved so far and how are you tackling that challenge?
FD & AN: glō has spent over a decade perfecting the epitaxial growth and fabrication of green and red microLEDs. glō’s IP in unique device design is the key to have all three colours in InGaN. This capability includes having a red LED with sufficient efficiency to allow us to demonstrate an RGB LTPS panel with 4000 nits and operating at less than 1W.

EV: The low efficiency of small size microLEDs was often seen as a potential show stopper. What kind of performance are you able to achieve for very small die?
FD & AN: Our patented device designs and fab processes are designed to meet this challenge. The display panels we have shown in public, such as our demos at the CES show, set the bar for light output and power efficiency.

EV: You are partnering with various display makers. Could you elaborate more on those partnerships? What is glō business model?
FD & AN: glō is a fully fabless operation. glō has partnered with a leading global LED manufacturer to produce microLEDs in volume for commercial products. In addition, glō has also partnered with few of the largest display panel manufacturers to produce display modules.

EV: What are the next steps for glō in term of technology milestones and product release? What obstacles and challenges are still ahead and which one are you prioritising?
FD & AN: Together with our manufacturing partners, glō is working toward a commercial launch of microLED displays on LTPS backplanes for smartwatches / wearables in the second half of 2019. After the launch of smartwatch displays on LTPS, glō will introduce smartphone displays.

In parallel, we are working with manufacturers of AR glasses and HUD for automotive and defence applications to produce microLED displays based on CMOS backplanes.

Key challenges are reducing time to market by efficiently ramping manufacturing volume together with our partners to produce highest quality microLED displays that are also cost competitive.

EV: microLEDs also bring some challenges in terms of supply chain with a need to bring together 2 different industries and technologies (LED and Displays) and essentially bridge them by creating a 3rd one from scratch: microLED assembly. What do you think the microLED supply chain will look like?
FD & AN: We think that specifically developing the technology to permit the leveraging of existing supply chains is the way to go. With our manufacturing partnerships we plan to use the existing LED and LCD industry equipment and capacity to produce better performing microLED displays than OLED. We believe that microLED displays will breathe new life into the LCD /TFT industry.

EV: Could trade disputes affect this supply chain and your business model if they were to continue or even worsen?
FD & AN: We have deliberately chosen partners that value and respect our intellectual property and that are outside current “dispute zones”. A shortened supply chain with high intellectual property content fits our business model.

EV: Which applications and segments do you think microLED will be applied to? Do you see a clear path to be cost competitive with OLED or other technologies in those segments?
FD & AN: We believe that in the near term, mobile and micro displays are best suited for microLEDs. In the long-term large displays can also be addressed with microLEDs.

• Micro displays (less than one inch diagonal + more than 1000ppi) such as contact lens displays, AR glasses, heads up displays (HUD) .
• Mobile displays (more than one inch to less than eight inch diagonal + 200 to 600ppi) such as wearables, smartphones, and phablets.
• Large displays (more than eight inch diagonal + 80 to 200ppi) such as automotive dashboards, tablets, laptops, 8K, 16K and 24K TVs / wall displays.

EV: Any other comments or messages you would like to add for our readers?
FD & AN: glō microLED displays offer the best performance in terms of brightness, power, colour, dynamic range, contrast and lifetime as compared to LCD or OLED, due to the inherent physics behind the architecture. Inorganic LEDs perform better and last longer than do organic LEDs. They emit more light and are more stable than OLEDs. glō microLED displays offer ten times more brightness and five times better power efficiency with equal or better colour quality than the best OLED.

InGaN LEDs have been used in the lighting industry for decades. The LCD industry has been using LTPS backplanes for displays for decades. glō has brought two disciplines together to make the best of both worlds.