LED-microarrays
We are working in close collaboration with Prof. P. Barviz's group in University of Washington on integrating LED-microarrays in contact lens displays. Our long-term goal is to create a display that can be comfortably worn in the form of a contact lens, which will include a pixel array, focusing optics, an antenna, and circuitry for power harvesting, radio communication, and pixel control.
Integrating displays on contact lenses present several challenges. First, as the display is standalone, power must be provided and stored for system operation without a wired connection. Second, the lens system must be biocompatible and meet regulations for radio frequency radiation. A third challenge is mechanical and electrical integration of micrometer-scale LED microarrays on a polymer substrate. Furthermore, all components must fit within the volume of standard contact lenses, ∼1.0 cm2 in area with thicknesses of 200 μm or smaller. Additionally, the human eye, with its minimum focal distance of several centimeters, cannot resolve objects on a contact lens. Thus the light from LEDs needs to be focused using subsidiary lenses.
LED-microarrays are fabricated on GaN LED structure grown on sapphire substrate. The LED structure consists of GaN buffer layer, n- and p- type layers of the diode and InGaN QWs that are responsible of the light generation. The structure is grown by metallo-organic vapor phase epitaxy. Post-growth processing of the LED-microarrays is started with thinning the sapphire wafer to approximately 200 μm. The surface of the LED structure is then etched and metal contacts are deposited on p- and n- layers.
Fabrication process of a single LED pixel
The dimensions of a single LED pixel are in the order of tens of micrometers. Several adjacent pixels can be processed into a microarray. In the microarray each pixel can be controlled individually, so forms a pixel display. The first prototypes we have fabricated consist of 4x4 and 3x4 pixels.
Microarrays of 50 micrometer radius pixels.
The LED structure growth and microarray processing is done in Aalto University laboratories located in Micronova by the optoelectronics group. The LED microarrays are incorporated into contact lenses by prof. Babak Parviz's group in University of Washington. The active contact lens contains RF-antenna for wireless energy and information transfer to the lens, control circuitry and interconnects to the LED microarray. The light emitted by the LED pixels is focused to the retina by Fresnel lenses on each pixel. All subsustems are encapsulated in a trasparent polymer material.
Antenna, control circuitry and interconnects for LED microarrays on a contact lens. (Professor Babak A. Parviz, University of Washington )
The wireless energy transfer has range of approximately one meter in free air. The antenna design is constrained by contact lens size and eye physiology. In the prototype a 5.0 mm radius loop antenna is used to harvest radio frequency energy which leaves the pupil unobstructed.
The active contact lens was tested in a rabbits eye with no observed adverse effects. (Professor Babak A. Parviz, University of Washington )
Further information: