Kopin, a developer and provider of transmissive and reflective active matrix liquid crystal and organic light emitting diode (OLED) microdisplays, announced its latest Lightning® 720p OLED display (1280 x 720 resolution) on silicon has exhibited very high brightness of 7000 nits (candela per square meter) with good color (nearly 100% sRGB) and high contrast (> 4,000: 1). This display combines a duo-stack OLED structure to achieve super high brightness and Kopin’s ColorMaxTM technology for high color fidelity.
A duo-stack OLED is two OLED structures on top of each other and connected in series so that carriers (electrons-holes) pass through the duo-stack OLED and generate photons twice, instead of once like in a conventional single-stack OLED structure currently used in OLED microdisplays. It would be natural to think that a duo-stack OLED can have a Current Efficiency increase of up to 2 times a single-stack OLED. However, a duo-stack structure provides a lot more flexibility in the OLED stack design and OLED materials selection than a single-stack structure, which can result in much higher Current Efficiency (> 5 times in our current estimate), much higher brightness, lower power consumption and longer lifetime.
A major challenge in the duo-stack OLED structure, especially for small pixels, had been serious color mixing among subpixels, resulting in unacceptable color performance. Kopin’s patent-pending ColorMax technology incorporates a specially configured anode structure in the Si backplane to suppress the inherent color mixing among tiny sub-pixels of high-resolution microdisplays. The ColorMax technology, first integrated into Kopin’s 2.6K x 2.6K OLED display, has now been applied to its 0.49-inch-diagonal 720p display with red, green, and blue stripe color sub-pixels of 2.8 µm × 8.4 µm size.
Kopin’s color display is made with a duo-stack white OLED structure and color filters. Kopin has been working with its partner, Lakeside Optoelectronic Technology to optimize the duo-stack OLED structure to output color spectrum to match the bandpass of the color filters for high color fidelity, coupled with very high Current Efficiency and low operating voltage. These 720p displays fabricated from multiple wafers exhibited average Current Efficiency of about 12 candela per ampere (cd/A), with the maximum value about 14 cd/A. These values are much higher than the best publicly available values of the alternative approaches. Kopin’s best 720p display exhibited 7,000 nits with a contrast ratio of >4000: 1. The contrast ratio of the display at 5000 nits is higher than 100,000:1. The power consumption of the display, including the backplane power, is about 500 mW when displaying a full white image at 7000 nits. The 720p display’s color fidelity is about 100% sRGB.
“We are extremely excited that our OLED microdisplay has achieved the very high brightness with good color fidelity by using the duo-stack OLED structure and ColorMax technology. This is truly a shocking achievement,” said Dr. John C.C. Fan, President and CEO of Kopin. “This breakthrough high Current Efficiency is very important for low power consumption and longer lifetime for OLED microdisplays. We now expect the Current Efficiency could be optimized even further which means that our present value of 7,000 nits may be increased further. In addition, the duo-stack OLED structure and ColorMax technology are manufacturable as we have obtained such great results from multiple production ColorMax wafers in Lakeside’s OLED production line. We believe by incorporating another innovative structure on our microdisplay such as a microlens array to enhance the output coupling efficiency, the brightness can be significantly increased further, opening many applications for the OLED microdisplays, especially for the AR/VR wearables.”.