High voltage CMOS backplane for OLED microdisplays
Researchers at Fraunhofer in Germany have developed a high voltage CMOS backplane to boost the brightness of OLED microdisplays.
OLEDs are considered limited at very high brightness in harsh environments so microLEDs are often proposed as an alternative. However, microLEDs experience a significant efficiency loss at very high pixel densities, which are required in high-resolution microdisplays. This means they must be operated with more than 1A/cm². This technology is still not mature, especially for full colour.
The current density for OLEDs during long-lifespan operation is typically below 100 mA/cm². But this can be significantly improved by stacking OLED layers on top of each other, which the researchers showed earlier this year.
However this stacking of OLED layers increases the voltage drop and swing across the OLED stack. To address this, the team at the Fraunhofer IPMS have developed a high-voltage CMOS backplane for high-brightness OLED microdisplays.
“We have developed an innovative pixel cell design that allows for a voltage swing of over 10 volts, enabling the operation of multiple stacked, top-emitting OLED layers,” said Dr. Uwe Vogel, head of Microdisplays and Sensors at Fraunhofer IPMS.
“Depending on the number of stacked units, multiples of the maximum emission can be achieved with high current efficiency while maintaining constant current density. This approach enables full colour maximum brightness of over 10,000 cd/m² while maintaining lifespan and reliability.”
Fraunhofer IPMS has been developing backplanes for various technologies and especially microdisplays for many years with a focus on CMOS technology for mainstream manufacturing. The institute has developed unique expertise in the entire process chain, from feasibility studies to pilot production in OLED microdisplays.
The high voltage CMOS backplane allows stacked OLED microdisplays for augmented reality and virtual reality applications with brightness of 10,000 cd/m², significantly increasing market opportunities.
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