LDMOS Isolation Ring Diode Biasing for Breakdown Voltage
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Solution Overview
Problem
Conventional LDMOS devices face challenges in achieving high breakdown voltage due to limitations in epitaxial layer thickness, which complicates fabrication and alignment, and increases the difficulty of forming a robust electrical connection between the isolation ring and the buried layer.
Innovation Solution
The solution involves dynamically biasing an isolation tub surrounding the LDMOS, electrically coupling it to an integrated diode, which reduces the potential on the isolation ring, thereby improving the breakdown voltage by lowering the potential difference between the buried layer and the well above it, and enhancing the vertical junction breakdown region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the epitaxial layer thickness is increased to improve breakdown voltage, then the breakdown voltage is improved, but the fabrication process becomes more complex and alignment accuracy degrades
Solution Approach 1:
An isolation ring is introduced as an intermediary structure between the epitaxial layer and the buried layer. This isolation ring serves as a mediator to enhance the vertical junction breakdown region and improve breakdown voltage without requiring increased epitaxial layer thickness, thereby avoiding alignment issues associated with thicker layers.
Solution Approach 2:
The invention changes the structural parameters by adding the isolation ring with specific doping characteristics (n-type or p-type depending on device type) and configuring its electrical connection to the buried layer. This parameter change enables improved breakdown voltage through enhanced junction characteristics rather than simply increasing layer thickness.
2Reliability
If the epitaxial layer thickness is increased to improve breakdown voltage, then the breakdown voltage is improved, but forming a robust electrical connection between the isolation ring and the buried layer becomes more difficult
Solution Approach 1:
The isolation ring acts as an intermediary that provides a dedicated electrical pathway between the epitaxial layer and the buried layer. By configuring the isolation ring with appropriate doping and electrical connections (through metal contacts or diffused connections), a robust electrical connection is achieved without requiring excessive epitaxial layer thickness.
Solution Approach 2:
Instead of relying solely on vertical thickness for electrical connection, the invention introduces lateral dimensionality through the isolation ring structure. The isolation ring can be connected to the buried layer through lateral metal contacts or diffused regions, providing an alternative dimensional pathway for electrical connection that avoids the limitations of thick epitaxial layers.
3Reliability
If costly high-energy implanting tools are used to form robust electrical connection with thicker epitaxial layer, then the electrical connection is improved, but the manufacturing cost increases
Solution Approach 1:
The isolation ring provides a cost-effective alternative to expensive high-energy implantation processes. By using standard doping and metal contact techniques to form the isolation ring and its connections, the invention achieves robust electrical connection without requiring costly high-energy implanting tools, thereby reducing fabrication costs.
4Reliability
If the epitaxial layer thickness is increased to improve breakdown voltage, then the breakdown voltage is improved, but alignment issues occur
Solution Approach 1:
The isolation ring serves as an intermediary structure that decouples the breakdown voltage enhancement from the epitaxial layer thickness. By placing the isolation ring at a specific depth and configuring its electrical connections, the invention achieves improved breakdown voltage while maintaining standard epitaxial layer thicknesses that are easier to align during fabrication.
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
This approach results in a higher breakdown voltage for LDMOS devices, as demonstrated by improved I-V characteristics and DC Safe Operation Area (SOA), with reduced sensitivity to gate potential in the 'on' state, and increased integration density without the need for costly high-energy implanting tools.
Implementation Method 1
This diode is positioned outside the device operation area and is constructed by a p-plus active area and the n-type region (e.g., the body region in a p-type LDMOS and the drift region in an n-type LDMOS respectively, which is generally biased with a high potential during the device operation). Such a configuration lowers the potential on the isolation ring by a value equal to or larger than the diode breakdown voltage
Data Source
AI summary
A method for improving breakdown voltage of a Laterally Diffused Metal Oxide Semiconductor (LDMOS) includes biasing a first well of a Field Effect Transistor (FET) to a first voltage. The first well is laterally separated from a second well. An isolation ring is charged to a second voltage in response to the first voltage exceeding a breakdown voltage of a diode connected between the isolation ring and the first well. The isolation ring laterally surrounds the FET and contacts a buried layer (BL) extending below the first well and the second well. A substrate is biased to a third voltage being less than or equal to the first voltage. The substrate laterally extends below the BL and contacts the BL.