Bonding Transistor Wafer to LED Wafer for Active Modules
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Solution Overview
Problem
Existing LED technologies face challenges in creating compact, cost-effective, and efficient solutions for controlling current through LEDs, especially when driving multi-colored LEDs or forming high-density RGB pixels, due to the need for separate driver circuits and interconnections, which increase size and cost, and can result in excess light emission and reduced contrast in addressable arrays.
Innovation Solution
Integration of a vertical drive transistor with LEDs in a single die, forming a 3-terminal module with a positive voltage terminal, a negative voltage terminal, and a control terminal, allowing active control of current through the LED, enabling parallel or addressable connections of LEDs without the need for separate driver circuits, and allowing each LED to be controlled independently for desired brightness and color.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate driver circuits are used for each LED, then current control precision is improved, but device complexity and size increase
Solution Approach 1:
The patent merges the LED and driver circuit into a single integrated device structure. The driver circuit is formed in a first substrate while the LED is formed in a second substrate, and the two are bonded together to create an integrated LED device. This combining approach maintains precise current control capability while reducing overall device complexity by eliminating separate driver circuit packages and interconnections.
2Measurement precision
If separate driver circuits are used for each LED, then current control precision is improved, but manufacturing cost increases
Solution Approach 1:
The integration of driver circuit and LED into a single device reduces manufacturing cost by eliminating separate packaging, mounting, and interconnection processes. The bonded substrate approach allows for streamlined fabrication where the driver circuit and LED are created in their respective substrates and then permanently joined, reducing assembly steps and associated costs while maintaining precise current control.
3Productivity
If LEDs of different colors are connected in parallel, then high density RGB pixels are achieved, but voltage threshold mismatches cause excess light emission
Solution Approach 1:
The patent integrates individual driver circuits with each LED within a unified device structure, allowing precise independent control of each LED's current. This integration enables high-density RGB pixel arrangements while maintaining proper voltage thresholds for each color LED through dedicated driver control, preventing excess light emission in non-addressed pixels and preserving light-to-dark contrast.
4Adaptability or versatility
If interconnection network is used for addressable arrays, then LED addressing capability is improved, but voltage drops cause incidental forward bias
Solution Approach 1:
The patent combines the LED and its driver circuit into an integrated unit where the driver circuit is formed in a first substrate and the LED in a second substrate, bonded together. This integration eliminates the need for extensive external interconnection networks, reducing voltage drops and preventing incidental forward bias in non-addressed LEDs while maintaining full addressing capability through the integrated driver control.
Data Source
AI summary
LED modules are disclosed having a control MOSFET, or other transistor, in series with an LED. In one embodiment, a MOSFET wafer, containing an array of vertical MOSFETS, is aligned and bonded to an LED wafer, containing a corresponding array of vertical LEDs, and singulated to form thousands of active 3-terminal LED modules with the same footprint as a single LED. Despite the different forward voltages of red, green, and blue LEDs, RGB modules may be connected in parallel and their control voltages staggered at 60 Hz or greater to generate a single perceived color, such as white. The RGB modules may be connected in a panel for general illumination or for a color display.