Double IO Pad Cell ESD Layout With Guard-Band Diode Integration
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Solution Overview
Problem
Conventional analog input-output (IO) pad cells for electrostatic discharge (ESD) protection in integrated circuits suffer from significant area wastage due to tall ESD diodes, which increase series resistance and induce latch-up in nearby victim structures, reducing the effectiveness of ESD protection.
Innovation Solution
A compact double IO pad cell with a dual-diode ESD protection scheme, where N-wells of P+/NW diodes act as collector guard bands for N+/PW diodes, optimizing aspect ratios to minimize cell area and ESD diode strapping resistance, and positioning diodes to reduce latch-up risk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If tall ESD diodes are used for protection, then ESD protection coverage is improved, but cell area increases and series resistance increases
Solution Approach 1:
The patent transitions from vertical stacking (tall diodes extending upward) to horizontal arrangement (diodes positioned side-by-side), effectively changing the spatial dimension of ESD protection structure. This allows adequate protection coverage while reducing the vertical height requirement and optimizing cell area utilization.
Solution Approach 2:
The patent combines multiple ESD protection elements (diodes, guard rings, clamps) into a compact integrated structure where functions are merged spatially. The N-well of one diode serves dual purposes: as the active region for ESD protection and as a guard ring for adjacent structures, reducing overall cell area while maintaining protection effectiveness.
2Reliability
If tall ESD diodes are used for protection, then ESD protection coverage is improved, but series resistance increases
Solution Approach 1:
The patent reduces the vertical height of diodes by arranging them horizontally, which directly reduces the length of vertical metal straps required for connection. This dimensional change decreases the series resistance in the ESD path while maintaining adequate protection coverage through optimized horizontal positioning.
Solution Approach 2:
The patent optimizes the geometric parameters of the ESD structure, specifically reducing the height of diodes and adjusting the aspect ratios of active regions. These parameter changes minimize the length of current paths and reduce series resistance, improving ESD protection effectiveness.
3Area of stationary object
If N+ active region is positioned close to cell boundary for compact layout, then cell area is reduced, but latch-up risk increases
Solution Approach 1:
The patent introduces an N-well structure as an intermediary element between the N+ active region and the P-type substrate. This N-well acts as a protective barrier that prevents direct interaction between injected electrons and the substrate, thereby eliminating latch-up risk while allowing compact positioning of the active region near cell boundaries.
Solution Approach 2:
The patent implements preliminary protective measures by positioning N-wells adjacent to N+ active regions before ESD events occur. These N-wells pre-establish electron collection paths that intercept and neutralize injected electrons before they can trigger latch-up in nearby victim structures, proactively preventing the harmful effect.
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 solution effectively reduces latch-up risk and improves the effectiveness of ESD protection by minimizing series resistance and optimizing the layout of ESD diodes, leading to a more efficient use of cell area and enhanced protection for nearby victim structures.
Implementation Method 1
the N-well of the P+/NW diode acts as a collector guard band
Implementation Method 2
electrostatic discharge (ESD) protection
Data Source
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AI summary
A double IO pad cell including a busing frame formed on a busing metal layer aligned with a same-sized component frame integrated on a component layer of an IC. The busing frame includes first and second IO pads, a supply voltage rail, and a ground voltage rail. The component frame includes first and second primary ESD circuitry each including a first diode coupled between a respective one of the first and second IO pads and the supply voltage rail and a second diode coupled between the respective IO pad and the ground voltage rail. The second diodes of each primary ESD circuitry are integrated adjacent each other sandwiched between the first diodes which act as collector guard bands for the second diodes. The diodes of each primary ESD circuitry of the component frame are aligned with a corresponding one of the first and second IO pads of the busing frame.