Guard Ring Parasitic Bipolar Transistor Surge Protection
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Solution Overview
Problem
Conventional semiconductor devices with parasitic diode surge protection elements are prone to manufacturing variations, leading to uneven avalanche voltages and increased operating resistance, which can result in snap-back and destruction of the device, and require additional chip area for separate surge protection structures.
Innovation Solution
A semiconductor device with a parasitic bipolar transistor formed on the guard ring, acting as a surge protection element, which reduces the impact of manufacturing variations and operating resistance, and integrates the surge protection function within the existing MOSFET structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a parasitic diode is used as a surge protection element in each cell, then surge protection is provided, but manufacturing variations cause uneven avalanche voltages and increased operating resistance leading to snap-back and device destruction
Solution Approach 1:
The invention extracts the surge protection function from individual cell parasitic diodes and relocates it to a dedicated surge protection region formed by the guard ring structure. This separates the surge protection function from the active MOSFET cells, allowing independent optimization and reducing the impact of manufacturing variations on avalanche voltage uniformity.
Solution Approach 2:
The guard ring acts as an intermediary structure that provides a controlled path for surge current. By forming a dedicated surge protection region with specific doping concentrations and geometries, the guard ring mediates between the drain region and the substrate, ensuring uniform avalanche breakdown characteristics independent of cell-to-cell variations.
2Reliability
If separate surge protection structures are added to protect against ESD, then surge protection is improved, but additional chip area is required
Solution Approach 1:
The invention merges the guard ring, which is already present for MOSFET operation, with the surge protection structure. The guard ring is transformed into an active surge protection element by forming a dedicated surge protection region with specific doping concentrations, eliminating the need for separate surge protection structures and reducing chip area requirements.
Solution Approach 2:
The guard ring structure serves dual functions: it provides electrical isolation for the MOSFET cells during normal operation and acts as a surge protection element when ESD or voltage spikes occur. This multi-functionality eliminates the need for dedicated surge protection structures, reducing chip area while maintaining protection capability.
3Reliability
If the distance L4 of the n-type well region between the guard ring and p-type well region is increased, then avalanche occurs in the correct sequence, but the device occupies more area
Solution Approach 1:
The invention applies local quality by forming a dedicated surge protection region with specific doping concentrations (higher concentration in the fourth semiconductor region compared to the third) in the guard ring area. This localized modification creates a preferred breakdown path without increasing the overall device area, controlling the avalanche sequence through local electrical property changes rather than geometric expansion.
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 provides a compact semiconductor device with improved surge protection reliability, reduced operating resistance, and resistance to manufacturing variations, while maintaining the integrity of the MOSFET characteristics and reducing chip area requirements.
Implementation Method 1
This is so that avalanche will occur in a p-n junction D between the p-type well region 54 configuring the cell 54a of the output stage MOSFET 501 and the n-type well region 52 before occurring in a p-n junction C between the p-type well region 30 and n-type well region 52 on the guard ring 32 side when a surge such as an ESD is applied to the n-type drain region 55
Data Source
AI summary
Aspects of the invention provide a compact semiconductor device having a surge protection element, which can reliably protect against surge and is unlikely to be affected by manufacturing variation. By forming a parasitic n-p-n transistor on a guard ring, and adopting the parasitic n-p-n transistor as a surge protection element, it is possible to provide a compact semiconductor device having a surge protection element. Also, by adopting the parasitic n-p-n transistor as a surge protection element, it is possible to reduce the operating resistance in comparison with when using a parasitic n-p-n transistor as a surge protection element, and thus possible to improve the surge protection function. Further, by providing one surge protection element on the guard ring, rather than providing a surge protection element in each cell, it is possible minimize the effect of manufacturing variation (i.e., in-plane variation) on the surge protection function.