Symmetrical ESD Device Layout for Multi-Rail Routing
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Solution Overview
Problem
The design of ESD clamp circuits for integrated circuits faces challenges in minimizing the resistance of discharge paths and optimizing the layout, particularly when the number of I/O pads exceeds 400, due to complex routing constraints and limited flexibility in orientation with respect to power supply rails.
Innovation Solution
The proposed ESD device features three contact areas with an axis of symmetry, allowing adjustable orientation and connection to three supply rails, enabling rotation without short-circuiting, and incorporates directional conducting devices to establish discharge paths efficiently, thereby reducing resistance and optimizing area usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the number of I/O pads increases to protect more internal circuit devices, then the ESD protection coverage is improved, but the routing complexity and layout design difficulty increase significantly
Solution Approach 1:
The ESD clamp circuit employs an asymmetrical layout where the first and third ESD clamp circuits are positioned at different locations relative to the power supply rails, with the second ESD clamp circuit positioned between them. This asymmetrical arrangement optimizes the discharge path lengths and reduces routing complexity while maintaining comprehensive ESD protection coverage across multiple I/O pads.
Solution Approach 2:
The ESD protection network is segmented into multiple independent ESD clamp circuits (first, second, and third ESD clamp circuits) that can be independently routed to different I/O pads. This segmentation allows flexible distribution of protection coverage across numerous I/O pads while keeping each individual clamp circuit's routing simple and manageable.
2Reliability
If the discharge path resistance is reduced to protect internal circuit devices, then the ESD protection effectiveness is improved, but the required area for ESD clamp circuits and electrical connections increases
Solution Approach 1:
The ESD clamp circuits are positioned at specific locations optimized for their function: the first and third ESD clamp circuits are placed at opposite sides of the power supply rails to create short discharge paths, while the second ESD clamp circuit is positioned between them. This localized optimization minimizes discharge path resistance and length without requiring excessive overall area for the ESD protection network.
Solution Approach 2:
The ESD clamp circuits are arranged in a spatial configuration that utilizes the two-dimensional layout space efficiently. By positioning clamp circuits at different locations (first and third at opposite sides, second in between) and connecting them through electrical connections that traverse different layers and regions, the design achieves short discharge paths without proportionally increasing the footprint area.
3Reliability
If the ESD clamp circuits are connected to power supply rails with minimal pitches, then the discharge path resistance is reduced, but the routing constraints and layout design complexity increase
Solution Approach 1:
The power supply rails serve dual functions: they provide power to the internal circuit devices and simultaneously serve as connection paths for the ESD clamp circuits. The first and third ESD clamp circuits connect to the power supply rails at opposite sides, utilizing the rails' existing structure for both power distribution and ESD discharge, thereby achieving minimal pitch connections without adding separate routing complexity.
4Ease of manufacture
If the orientation of ESD clamp circuits is fixed with respect to power supply rails, then the manufacturing process is simplified, but the routing flexibility to I/O pads is reduced
Solution Approach 1:
The ESD clamp circuits are designed with asymmetrical orientations relative to the power supply rails, allowing each clamp circuit to be optimally oriented for its specific location and connection requirements. The first ESD clamp circuit has a different orientation than the third ESD clamp circuit, enabling flexible routing to different I/O pads while maintaining manufacturability through standardized clamp circuit designs.
Data Source
AI summary
A symmetrical layout technique for an electrostatic discharge ESD device and a corresponding power supply network is presented. The ESD device protects an electronic circuit against an overvoltage or overcurrent and contains a first contact area to establish an electrical contact with a first supply rail, a second contact area to establish an electrical contact with a second supply rail, and a third contact area to establish an electrical contact with a third supply rail. The first and third supply rails provide a first supply voltage, and the second supply rail provides a second supply voltage. Within the ESD device, an axis of symmetry passes through the second contact area, and the first contact area and the third contact area are arranged on opposite sides with regard to the axis of symmetry. The symmetrical layout technique allows flipping the orientation of the ESD device with regard to the supply rails.