Multi-Cathode Thyristor ESD Protection Circuit Design
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Solution Overview
Problem
Thyristor-type electrostatic protection circuits face challenges in rapid triggering without damaging the protection circuit and preventing latch-up during normal use, especially due to insufficient carrier performance and potential gate oxide film damage when static electricity is applied.
Innovation Solution
A protection circuit design incorporating a multi-cathode thyristor with a capacitor element, where the second cathode is positioned to facilitate easier thyristor operation, reducing the holding voltage and preventing latch-up, and optionally replacing the multi-cathode thyristor with a multi-anode thyristor to optimize trigger timing and resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thyristor-type protection circuit is used to provide high discharge capacity, then protection performance is improved, but the circuit is difficult to trigger rapidly when static electricity is applied and may cause latch-up during normal use
Solution Approach 1:
The cathode of the thyristor is divided into two separate cathodes (first cathode and second cathode). The second cathode is connected to the capacitor element while the first cathode is connected to the second terminal. This segmentation allows the thyristor to be triggered more rapidly by the capacitor discharge through the second cathode, while the first cathode provides a stable reference during normal operation, preventing latch-up.
Solution Approach 2:
A capacitor element is introduced as an intermediary component between the second terminal and the second cathode. The capacitor stores energy and provides a rapid discharge path to trigger the thyristor quickly when static electricity is detected, without requiring a high trigger voltage that would cause latch-up during normal operation.
2Speed
If the thyristor is made easy to trigger for rapid protection, then trigger speed is improved, but latch-up becomes more likely during normal use state
Solution Approach 1:
Different regions of the thyristor structure have different doping concentrations optimized for their specific functions. The second cathode region has doping concentration optimized for rapid triggering with the capacitor, while the first cathode region maintains doping optimized for stable operation and preventing latch-up during normal use.
Solution Approach 2:
The holding voltage of the thyristor is adjusted by modifying the doping concentration in the cathode regions. By optimizing the doping concentration in the second cathode connected to the capacitor, the thyristor can be triggered at lower voltages rapidly, while the first cathode maintains parameters that prevent latch-up during normal operation.
3Ease of operation
If a trigger element is added to trigger the thyristor, then trigger capability is improved, but device complexity increases
Solution Approach 1:
The capacitor element serves a dual function: it acts as the trigger element for rapid thyristor activation and simultaneously serves as part of the protection circuit structure. This self-service approach provides trigger capability without adding a separate dedicated trigger element, thereby minimizing circuit complexity.
Solution Approach 2:
The capacitor element is designed to perform multiple functions: energy storage for rapid triggering, voltage reference during normal operation, and participation in the protection discharge path. This multi-functionality eliminates the need for separate trigger components, reducing overall device complexity while maintaining excellent trigger capability.
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 design enables rapid triggering of the thyristor without causing latch-up, enhancing protection against static electricity while maintaining circuit integrity by adjusting the cathode and anode positions and using parasitic capacitance for increased capacity without increasing chip area.
Implementation Method 1
a capacitor element having one end connected to the second terminal
Implementation Method 2
protection against an overvoltage and an overcurrent caused by electrostatic discharge (ESD) or the like
Implementation Method 3
a thyristor (SCR) type protection circuit has been attracting attention recently, because of its excellent discharge capacity
Data Source
AI summary
A protection circuit according to an embodiment of the present invention is provided between a first terminal and a second terminal and includes: a capacitor element having one end connected to the second terminal; and a multi-cathode thyristor formed on a semiconductor substrate, and including an anode connected to the first terminal, a first cathode connected to the second terminal, and a second cathode disposed between the anode and the first cathode and connected to another terminal of the capacitor element.