LDMOS Transistor Guard Ring Isolation Structure
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Solution Overview
Problem
As circuit critical dimensions shrink, LDMOS transistor devices are prone to parasitic circuit elements punching through due to the converse parasitic diode effect, leading to performance degradation and breakdown voltage issues.
Innovation Solution
A LDMOS transistor structure is designed with a guard ring and barrier layer of the same polarity, electrically connected to the source, forming an isolation structure that prevents parasitic circuit elements from latching up with other integrated circuit elements, while also increasing breakdown voltage and reducing on-resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If circuit critical dimensions are shrunk to improve integration density, then device size is reduced, but parasitic circuit elements are more likely to punch through due to converse parasitic diode effect
Solution Approach 1:
A guard ring structure with the same polarity as the source is introduced as an intermediary element between the source and drift region. This guard ring acts as a mediator that prevents direct interaction between the source and parasitic circuit elements, thereby eliminating the punch-through effect while allowing continued miniaturization of the device.
Solution Approach 2:
The guard ring is configured to maintain the same electric potential as the source by using the same polarity doping. This equipotential configuration prevents electric field concentration at the source-drain interface, thereby preventing parasitic diode formation and punch-through effects even in scaled-down devices.
2Reliability
If drift region and field oxide are used to reduce electric field density and improve breakdown voltage, then breakdown voltage is improved, but device complexity increases
Solution Approach 1:
The drift region is segmented into multiple zones with different doping concentrations, creating a graded profile that progressively reduces electric field density. This segmentation allows for improved breakdown voltage while maintaining a manageable structural complexity by dividing the problem into manageable concentration gradients rather than requiring complex multi-layer structures.
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 effectively prevents device punch-through and enhances the performance of LDMOS transistors by forming an isolation structure with an electric potential identical to the source, thereby increasing breakdown voltage and decreasing on-resistance.
Implementation Method 1
parasitic circuit elements formed in the LDMOS transistor device may be more likely punch through due to the converse parasitic diode effect
Implementation Method 2
electric field density around the drain region can be reduced due to the existence of the drift region and the FOX, such that the breakdown voltage of the LDMOS transistor device can be improved
Data Source
AI summary
A lateral diffusion metal-oxide-semiconductor (LDMOS) transistor structure comprises a barrier layer, a semiconductor layer, a source, a first drain and a guard ring. The barrier layer with a first polarity is disposed in a substrate. The semiconductor layer with a second polarity is disposed on the barrier layer. The source has a first polarity region and a second polarity region both formed in the semiconductor layer. The first drain is disposed in the semiconductor layer and has a drift region with the second polarity. The guard ring with the first polarity extends downward from a surface of the semiconductor layer in a manner of getting in touch with the barrier layer and to surround the source and the drain, and is electrically connected to the source.