Stacked Snapback Clamp Trigger Circuit for Low-GIDL ESD Protection
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Solution Overview
Problem
Existing clamp devices for protecting integrated circuits (ICs) from electrostatic discharge (ESD) face issues such as high trigger voltage, excessive gate-induced drain leakage (GIDL), and potential latch-up due to holding voltage being below the IC's maximum operating voltage, which can lead to damage or permanent failure during ESD events.
Innovation Solution
A stacked clamp configuration using multiple NMOS transistors connected in series, with a trigger circuit that optimizes gate voltages to reduce trigger voltage, limit holding voltage, and increase failure current, ensuring reliable snapback operation and minimizing GIDL, is employed. The trigger circuit adjusts gate voltages during ESD events to facilitate bipolar snapback and prevent latch-up.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single clamp device is used to protect ICs from ESD, then the structure is simple, but the trigger voltage is high and GIDL is excessive
Solution Approach 1:
The clamp device is divided into multiple NMOS transistors connected in series, where each transistor shares a portion of the total voltage. This segmentation reduces the trigger voltage and GIDL of each individual transistor while maintaining overall protection capability. The stacked configuration distributes the voltage stress across multiple devices rather than concentrating it in a single clamp.
2Reliability
If the holding voltage is below the IC's maximum operating voltage, then the clamp activates easily, but latch-up occurs causing permanent failure
Solution Approach 1:
The trigger circuit monitors the voltage conditions and provides feedback control to the clamp transistors. During normal operation, the feedback mechanism ensures the clamp remains inactive. During ESD events, the feedback triggers the clamp to activate at appropriate voltage levels and ensures proper deactivation afterward, preventing latch-up conditions while maintaining reliable protection.
3Object-affected harmful factors
If multiple NMOS transistors are stacked in series, then trigger voltage is reduced and GIDL is minimized, but the circuit complexity increases
Solution Approach 1:
The trigger circuit is designed to perform multiple functions: it monitors voltage conditions, activates the clamp transistors during ESD events, controls the timing of activation and deactivation, and prevents latch-up. This multi-functional design reduces the need for separate dedicated circuits for each function, thereby minimizing overall circuit complexity despite the stacked transistor configuration.
4Reliability
If the clamp device conducts high ESD current, then protection effectiveness is improved, but the failure current increases the risk of permanent damage
Solution Approach 1:
The ESD current is distributed across multiple stacked NMOS transistors, with each transistor conducting a portion of the total current. This current segmentation reduces the stress on each individual transistor, lowering the risk of permanent damage while maintaining effective ESD protection. The distributed current path prevents any single device from being overwhelmed by excessive current.
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 stacked clamp configuration effectively limits ESD stress voltage on ICs, reduces GIDL, and prevents latch-up, ensuring reliable protection by distributing voltage across multiple transistors and optimizing bias voltages to maintain high failure currents and low holding voltages within safe operating ranges.
Implementation Method 1
In response to a sudden rise in voltage between the rails due to an ESD event, the clamp device is activated to discharge ESD current, thereby limiting stress voltage applied to ICs
Implementation Method 2
excessive gate-induced drain leakage (GIDL), and potential latch-up due to holding voltage being below the IC's maximum operating voltage
Data Source
Figure 1~2
Figure 3a~3b
Figure 4a~4b
AI summary
An integrated circuit is formed on a substrate, and the integrated circuit includes first and second conductors for providing supply and ground voltages, respectively, a clamp device, and a trigger circuit. The clamp device includes first and second metal oxide semiconductor (MOS) transistors coupled in series between the first and second conductors, wherein the first and second MOS transistors include first and second gates, respectively. The trigger circuit is coupled between the first and second conductors and is configured to drive the first and second gates with first and second voltages, respectively, in response to an electrostatic discharge (ESD) event. The trigger circuit includes a biasing circuit for generating the first voltage as a function of the supply voltage, a PMOS transistor coupled between the first conductor and the second gate, wherein the PMOS transistors includes a third gate. The trigger circuit also includes a resistive element coupled between the first conductor and the third gate, and a capacitive element coupled between the third gate and the first gate. In one configuration a voltage at the third gate should decrease in response to activation of the second MOS transistor.