LDMOS Transistor Layout With STI-Surrounded Drain for High Voltage
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Solution Overview
Problem
Existing high-voltage integrated circuits, such as power amplifiers, require improved laterally-diffused metal-oxide-semiconductor transistors that can withstand high voltages without breakdown, as current devices lack optimal structural features for efficient voltage handling.
Innovation Solution
A laterally-diffused metal-oxide-semiconductor transistor structure is designed with a semiconductor substrate, including a drain, source, and gate, surrounded by shallow trench isolation regions, with specific dopant concentrations and well configurations to enhance voltage handling capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional transistor structures are used in high-voltage integrated circuits, then device fabrication is simpler, but the devices cannot withstand high voltages without breakdown
Solution Approach 1:
The transistor structure is segmented into multiple functional regions including a drift well providing an extended drain, source regions with specific doping concentrations, and shallow trench isolation regions. This segmentation allows each region to handle specific voltage stress, enabling the device to withstand high voltages while maintaining manageable fabrication complexity through modular design
Solution Approach 2:
Different regions of the transistor are assigned different doping concentrations and structural properties optimized for their specific functions. The drift well has a graded doping profile, source regions have higher doping concentrations, and shallow trench isolation regions provide localized electrical isolation. This local optimization enables high voltage withstanding capability without requiring the entire structure to be overly complex
2Reliability
If extended drain structures are added to enhance voltage handling, then voltage handling capability is improved, but current crowding increases
Solution Approach 1:
The drain structure is extended into the drift well region, transitioning from a planar two-dimensional configuration to a three-dimensional structure that utilizes the vertical dimension. This dimensional change distributes the current flow path through both lateral and vertical directions, reducing current density and mitigating current crowding effects while maintaining enhanced voltage handling capability
3Reliability
If shallow trench isolation regions surround the drain, then device breakdown resistance is improved, but manufacturing complexity increases
Solution Approach 1:
Shallow trench isolation regions are formed surrounding the drain structure before final device assembly and operation. This preliminary action pre-establishes electrical isolation and mechanical support structures that prevent breakdown during high-voltage operation, while the standardized isolation trench formation process integrates smoothly into existing fabrication workflows, minimizing additional manufacturing complexity
Data Source
Figure 1
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Figure 2A~2B
AI summary
Structures for a laterally-diffused metal-oxide-semiconductor device and methods of forming a structure for a laterally-diffused metal-oxide-semiconductor device. The structure comprises a drain and a source in a semiconductor substrate. The source includes a source region having a first terminating end, a second terminating end, and a length between the first terminating end and the second terminating end. The structure further comprises a shallow trench isolation region in the semiconductor substrate. The shallow trench isolation region surrounds the drain. The structure further comprises a gate that surrounds the shallow trench isolation region and the drain. The gate has a side section between the drain and the source region, the side section of the gate has a width, and the gate has a length in a direction transverse to the width. The length of the source region is substantially equal to the length of the gate.