Better transparent displays coming next
A large number of transparent displays were exhibited at SID 2019, the world’s largest academic conference on display technologies, which took place from May 12 to 17, 2019, in San Jose, the US.
Not only transparent displays using OLED panels, which are used for smartphones and TVs, but also micro-LED transparent displays and dimming-type transparent screens were showcased, indicating that companies are developing transparent displays in various ways.
Micro-LEDs realize high brightness, long product life
In the past, many transparent displays were developed by using OLEDs. OLEDs eliminate the need for backlight, enabling to show images with only one transparent panel.
However, they have problems in brightness and life. Especially, in the case of transparent displays, their backgrounds are bright. So, it is necessary to realize a high brightness for the displays. On the other hand, when their brightness is increased, their product life, which is in a trade-off relationship with brightness, becomes shorter.
To solve such problems of OLEDs, transparent displays using micro-LEDs are emerging. At SID 2019, China-based Tianma Microelectronics Co Ltd, China Star Optoelectronics Technology Co Ltd (CSOT), etc exhibited displays that use inorganic LEDs, which have a much higher brightness and longer life than OLEDs, as pixels.
Tianma’s micro-LED transparent display is driven by low-temperature polycrystalline silicon (LTPS) TFTs (active matrix driving). The company developed the display in cooperation with PlayNitride Inc, a Taiwan-based micro-LED venture firm.
The brightness and transmittance of the display are 600cd/m2 or higher and 60% or higher, respectively. It has a screen size of 7.6 inches, pixel count of 720 x 480, resolution of 114ppi and 116% color gamut on NTSC standards.
CSOT’s micro-LED transparent display is driven by oxide semiconductor IGZO TFTs (active matrix driving). The company claims that the use of IGZO makes it easier to increase the size of the display in the future.
The prototype exhibited this time has a screen size of 3.3 inches, pixel count of 232 x 116, pixel pitch of 0.32mm, gradation of 8 bits, 100% or larger color gamut on NTSC standards and a transmittance of about 45%.
Dimming film realizes vivid image on transparent screen
The ways of realizing transparent displays are not limited to direct-view-type panels such as OLED, micro-LED and LCD panels. There is a method of using a projector to project video on a transparent screen.