Compared to flexible lateral µLEDs, the flexible vertical LEDs can be designed in denser arrays, with a comparatively simple top and bottom interconnect layout, the paper reports. Obtained through a monolithic fabrication technique, the ultrathin GaN LED arrays were demonstrated to output up to 30mW mm−2 of optical power, characterized with an estimated lifetime of about 12 years, with excellent thermal and mechanical stability up to 100 000 flexing cycles. The Flexible vertical microLED owe their high electrical power efficiency to their shorter current path and a lower internal resistance compared to those of lateral microLED, explain the authors. What’s more, the simple top and bottom electrode configuration lends itself very well to cooling through a bottom heat sink.
The aim of this research was to develop tiny arrays of LEDs flexible enough to be implanted and conform to the surface of the brain, for direct optical stimulation of surface neurones. In one experiment, the blue micro LED array was powered wirelessly through a coil, with both the f-VLEDs and the coil flexibly integrated on a transparent biocompatible substrate directly affixed onto a living mouse cortex.
The low cost f-VLEDs production technology could not only be applicable to neurosciences but also to high density microdisplays for wearables. By the end of 2018, the researchers hope they’ll be able to demonstrate full-colour micro LED displays in smart watch sizes.