Vertical MOSFET and LED on Silicon Substrate
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Solution Overview
Problem
Existing LED modules with separate current sources require extra space and interconnections, leading to increased cost and potential component mismatching, and suffer from power loss due to long vertical conduction paths and the need for laser drilling.
Innovation Solution
A compact LED module design where a MOSFET and LED are formed on the same substrate with a vertical channel MOSFET, using a trench formed by reactive ion etching, eliminating the need for laser drilling and enabling uniform current supply for consistent brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a separate current source is used to control LED brightness, then the LED can be controlled independently, but extra space and interconnections are required, increasing cost and complexity
Solution Approach 1:
The patent merges the LED and current source into a single integrated module, where the MOSFET and LED share the same substrate. This integration eliminates separate interconnections and reduces overall module complexity while maintaining independent LED control capability through the MOSFET gate terminal.
Solution Approach 2:
The substrate serves multiple functions simultaneously: it acts as both the mounting platform for the LED and the current source, provides electrical connections for both components, and serves as the heat dissipation path. This multi-functionality reduces the need for separate structural elements.
2Ease of manufacture
If laser drilling is used to create vertical conduction paths, then current can be conducted vertically, but considerable expense and power loss are incurred
Solution Approach 1:
The patent extracts the need for laser drilling by utilizing the substrate's natural vertical conduction properties. Instead of creating artificial conduction paths through laser drilling, the design leverages the existing substrate structure to provide vertical current flow, eliminating the harmful laser drilling process and associated energy losses.
Solution Approach 2:
The patent employs a simpler, more cost-effective manufacturing approach by using standard substrate processing techniques instead of expensive laser drilling. The vertical conduction is achieved through conventional fabrication methods that are less costly and energy-intensive.
3Ease of manufacture
If lateral MOSFET channels are used, then the LED module can be formed on the substrate, but the surface area is relatively large, adding expense and size
Solution Approach 1:
The patent transitions from lateral MOSFET channels to vertical channels, changing the dimensional orientation of the conduction path. This vertical configuration allows current to flow through the thickness of the substrate rather than across its surface, significantly reducing the required surface area while maintaining manufacturability.
4Productivity
If multiple LEDs are fabricated on a single wafer, then productivity increases, but uniform brightness across all LEDs becomes difficult to achieve
Solution Approach 1:
The patent implements local quality control by providing each LED with its own dedicated MOSFET current source on the same substrate. This localized current control ensures that each LED receives precisely controlled current, achieving uniform brightness across all LEDs fabricated on a single wafer while maintaining high productivity.
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 results in a compact, efficient LED module with reduced power loss and cost, allowing for more LEDs to be fabricated on a single wafer with uniform brightness across the module.
Implementation Method 1
The vertical channel MOSFET has a high conductivity in the vertical direction and uses a trench that may be formed using a reactive ion etch (RIE).
Data Source
AI summary
An LED module is disclosed containing an integrated MOSFET driver transistor in series with an LED. In one embodiment, GaN-based LED layers are epitaxially grown over an interface layer on a silicon substrate. The MOSFET gate is formed in a trench in the silicon substrate and creates a vertical channel between a top source and a bottom drain when the gate is biased to turn on the LED. A conductor on the die connects the MOSFET in series with the LED. One power electrode is located on a top of the die, another power electrode is located on the bottom of the die, and the gate electrode may be on the top or the side of the die.