Sense Transistor Bypass Diode Structure for ESD-Rugged Current Sensing
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Solution Overview
Problem
Current current sensing in power transistors is prone to inaccuracies and reliability issues due to the small size of sense transistors, which can lead to spurious turn-on and sensitivity to electrostatic discharge (ESD) events, affecting the accuracy of current measurement in high-performance applications like server systems.
Innovation Solution
Incorporating a bypass diode structure in parallel with the sense transistor to provide a bypass for unwanted charges and increase the area for avalanche ruggedness, thereby improving the sense transistor's reliability and ESD resistance, while maintaining similar design rules to the main transistor for effective current mirroring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a small sense transistor is used for current sensing, then the current measurement function is achieved, but the transistor becomes sensitive to ESD events and spurious turn-on
Solution Approach 1:
A bypass diode structure is introduced as an intermediary protective element connected in parallel with the sense transistor. The diode acts as a mediator that captures and dissipates ESD energy and unwanted charges before they can affect the sense transistor, thereby protecting the sensitive current sensing element while maintaining its small size and measurement accuracy.
Solution Approach 2:
The bypass diode structure is pre-configured in parallel with the sense transistor to provide beforehand protection against ESD events and spurious turn-on. The diode is positioned and biased to be ready to capture and divert harmful charges before they can reach and damage the sense transistor, cushioning it against potential electrical stress.
2Reliability
If the sense transistor area is increased to improve ESD ruggedness, then the ESD resistance improves, but the current sensing accuracy and response may deteriorate
Solution Approach 1:
The device is segmented into two functional parts: a small sense transistor dedicated to accurate current sensing and a separate bypass diode structure dedicated to ESD protection. This segmentation allows each component to be optimized for its specific function - the sense transistor remains small for accuracy while the diode provides the necessary protection area without compromising the sensing element.
Solution Approach 2:
The bypass diode serves as an intermediary protective structure that provides ESD ruggedness without requiring the sense transistor itself to be enlarged. The diode captures the ESD energy in parallel, allowing the sense transistor to maintain its small, accurate dimensions while still benefiting from enhanced protection.
3Reliability
If a bypass diode structure is added in parallel with the sense transistor, then the ESD resistance and ruggedness improve, but the device complexity increases
Solution Approach 1:
The bypass diode structure is merged with the sense transistor fabrication process and layout, sharing common diffusion regions and being formed in the same semiconductor body. The diode is integrated alongside the sense transistor using similar processing steps, combining the protection function with the sensing function in a unified device structure rather than adding a completely separate component.
Solution Approach 2:
The bypass diode structure serves multiple functions: it provides ESD protection, captures unwanted charges, prevents spurious turn-on, and can also function as an additional current path during normal operation. This multi-functionality justifies the added structural element by providing several benefits simultaneously, reducing the net complexity increase.
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 bypass diode structure enhances the sense transistor's ruggedness against spurious turn-on and ESD events, ensuring more accurate and reliable current measurement by displacing current through the diodes during voltage changes and ESD events, thus improving the overall performance in high-performance applications.
Implementation Method 1
at least one bypass diode structure for protecting the sense transistor. The at least one bypass diode structure is electrically coupled in parallel with the sense transistor
Data Source
AI summary
In an embodiment, a semiconductor device includes: a main transistor having a load path; a sense transistor configured to sense a main current flowing in the load path of the main transistor; and a bypass diode structure configured to protect the sense transistor and electrically coupled in parallel with the sense transistor. A sense transistor cell of the sense transistor includes a sense trench and a sense mesa. The sense trench and a bypass diode trench of the bypass diode structure form a common trench. The sense mesa and a bypass diode mesa of the bypass diode structure form a common mesa.