Monolithic Ultra-Dense LED Array for Retinal Projection
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Solution Overview
Problem
Conventional LED displays have limitations in achieving high resolution due to large pixel spacing and size, making them unsuitable for ultra-dense applications such as contact lenses or eyewear that require pixel sizes less than 1um^2 and pitches less than 2um to match the density of the human retina.
Innovation Solution
A monolithic ultra-dense LED array is designed with pixel sizes less than 1um^2 and pitches less than 2um, using a 'soda can' shaped LED array with a tall and skinny structure, where the LEDs are taller than their width, and a reflective N-metal is used to electrically contact the N-type layer along the vertical sidewall for efficient current handling and optical isolation, along with photon energy down-conversion or up-conversion materials to create red, green, and blue pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional discrete LED dies are used to form pixels, then the display can be manufactured with standard processes, but the pixel spacing becomes large (25um pitch) and resolution is limited to 500 pixels per inch
Solution Approach 1:
The patent merges multiple LED dies into a single monolithic integrated LED structure where red, green, and blue emitting regions are combined on one substrate. This integration eliminates the need for separate discrete LED dies and their associated bonding processes, achieving ultra-dense pixel packing with pitch less than 2um while maintaining manufacturability through standard semiconductor fabrication processes.
Solution Approach 2:
The patent transitions from planar 2D LED pixel arrangements to a 3D vertical structure with multiple emitting layers stacked along the vertical dimension. This dimensional change allows pixels to be packed densely in the horizontal plane (pitch < 2um) while utilizing the vertical dimension for multiple emitting regions, achieving ultra-high resolution without increasing manufacturing complexity.
2Manufacturing precision
If monolithic LED display technology is used to reduce pixel pitch to 5-10um, then resolution improves, but the minimum achievable pixel pitch is still limited and pixels remain several microns in size
Solution Approach 1:
The patent changes the fundamental parameters of LED pixel structure by reducing pixel pitch from conventional 5-10um down to less than 2um, and pixel area to less than 1um². This is achieved through advanced monolithic integration techniques and vertical cavity designs that allow ultra-small pixel dimensions while maintaining sufficient light output and color purity for high-resolution displays.
3Manufacturing precision
If pixel size is reduced to less than 1um^2 for ultra-dense displays, then resolution matches human retina density, but manufacturing and electrical contact become extremely difficult
Solution Approach 1:
The patent addresses the electrical contact challenge by transitioning to vertical cavity LED structures where current flows vertically through thin semiconductor layers. This vertical geometry allows electrical contacts to be made on the top and bottom surfaces of the ultra-small pixel structure, avoiding the need for lateral contacts that would be impossible at sub-micron dimensions. The vertical cavity design enables standard semiconductor fabrication processes to achieve pixel sizes less than 1um².
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables a high-resolution display that can be embedded in contact lenses or eyewear, projecting images directly onto the retina with improved optical efficiency and mechanical support, maintaining high resolution and color accuracy while being compact enough not to obstruct the wearer's view.
Implementation Method 1
a reflective N-metal is used to electrically contact the N-type layer along the vertical sidewall for efficient current handling
Implementation Method 2
A monolithic ultra-dense LED array is designed with pixel sizes less than 1um^2 and pitches less than 2um
Implementation Method 3
along with photon energy down-conversion or up-conversion materials to create red, green, and blue pixels
Implementation Method 4
along with photon energy down-conversion or up-conversion materials to create red, green, and blue pixels
Implementation Method 5
a reflective N-metal is used to electrically contact the N-type layer along the vertical sidewall
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
There is described a monolithic device comprising a light emitting diode (LED) array. The LED array comprises an array of pillars of semiconductor layers, a fill between the pillars, and a dielectric material. The semiconductor layers include an N-type layer, an active layer, and a P-type layer. The pillars have a height greater than their width. The fill includes a reflective metal. The reflective metal provides mechanical support for the pillars, provides optical isolation between the pillars, and electrically contacts the N-type layer of each pillar along sidewalls of the N-type layers. The dielectric material insulates sidewalls of the P-type layer and the active layer from the reflective metal.