Triple Stack NMOS ESD Clamp for Latch-Up Immunity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Traditional ESD clamps face issues with transient latch-up and false triggering during electrical fast-transient testing due to RC elements, leading to high noise damping and increased chip area, necessitating a solution for a compact and noise-immune ESD clamp.
Innovation Solution
A triple stack NMOS integrated circuit structure is employed, where three NMOS elements are connected in series with separate active regions, eliminating RC time constants and allowing for a higher holding voltage, thus preventing snapback and latch-up events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If traditional RC-NMOS ESD clamp is used, then fast turn-on speed is achieved, but large chip area is allocated to R and C elements
Solution Approach 1:
The patent removes the RC elements (resistors and capacitors) from the ESD clamp circuit entirely, extracting the problematic components that caused both the area occupation and the transient latch-up issues. The triple-stack NMOS structure replaces the RC-based triggering mechanism with a direct voltage-based triggering approach.
Solution Approach 2:
The patent changes the fundamental operating parameters of the ESD clamp by using a triple-stack NMOS configuration with specific threshold voltage relationships. The holding voltage is designed to be between the trigger voltage and the supply voltage, creating a new operational regime that eliminates transient latch-up while maintaining fast response.
2Reliability
If RC elements are used in ESD clamp, then transient detection is enabled, but transient latch-up and false triggering occur during electrical fast-transient testing
Solution Approach 1:
The patent converts the harmful RC time constant effect into a beneficial direct voltage response. By removing the RC elements, the circuit responds directly to voltage transients without the delayed response characteristic of RC circuits, thereby eliminating false triggering while maintaining ESD detection capability.
Solution Approach 2:
The patent changes the triggering mechanism from RC-time-constant-based to direct voltage-threshold-based. The triple-stack NMOS structure is designed with specific threshold voltage relationships where the holding voltage is maintained between the trigger voltage and supply voltage, preventing transient latch-up while enabling reliable ESD detection.
3Reliability
If clamp device size is increased to improve ESD performance, then ESD protection capability is enhanced, but chip area increases significantly
Solution Approach 1:
The patent applies local quality by using three NMOS transistors with different threshold voltages in series. Each transistor is optimized for its specific function: the first for triggering, the second for holding, and the third for clamping. This localized optimization allows compact sizing while maintaining high ESD protection capability.
Solution Approach 2:
The patent uses a composite structure of three different NMOS transistors with distinct threshold voltage characteristics. This composite transistor stack creates a device with superior ESD performance that is more area-efficient than a single large clamp device, as each transistor contributes a specific function to the overall protection mechanism.
Data Source
AI summary
A triple stack NMOS integrated circuit structure protection circuit for a plurality of terminals operative at respective voltage levels is coupled between the plurality of terminals. First and second NMOS elements of the triple stack NMOS share a common active region. A third NMOS element, vertically positioned with respect to the first and second NMOS elements, has an active region separate from the active region of the first and second NMOS elements. The first, second and third NMOS elements are connected in series between two terminals of the plurality of terminals.