Double IO Pad Cell Layout for Low-Resistance ESD and Latch-Up Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional analog input-output (IO) pad cells for electrostatic discharge (ESD) protection in CMOS technologies 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 rail clamps.
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 conventional tall ESD diodes are used for protection, then ESD protection coverage is improved, but cell area is significantly increased and series resistance is increased
Solution Approach 1:
The patent transitions from vertical stacking (tall diodes extending upward) to horizontal arrangement (diodes laid out side-by-side), effectively changing the spatial dimension of diode placement. This allows the ESD diodes to maintain their protective function while reducing the vertical height requirement and optimizing the overall cell area utilization.
Solution Approach 2:
The patent embeds the ESD diodes within the cell structure in a nested configuration, where the diodes are positioned to overlap with supply buses and integrate with the cell layout. This nesting approach allows the ESD protection elements to occupy space efficiently without adding significant area overhead, as they are incorporated into the existing cell architecture rather than being added as separate external components.
2Reliability
If conventional tall ESD diodes are used for protection, then ESD protection coverage is improved, but series resistance is increased
Solution Approach 1:
By arranging diodes horizontally rather than vertically, the current path length through the diode structure is reduced. The horizontal layout shortens the vertical metal straps required for connecting the diodes to supply buses, thereby reducing the series resistance in the ESD discharge path while maintaining adequate protection coverage.
Solution Approach 2:
The patent optimizes the geometric parameters of the ESD diode structure, specifically the length and width of metal straps and the spacing between diodes. By adjusting these parameters in the horizontal layout, the series resistance is minimized while maintaining the diodes' protective function, achieving a balance between protection effectiveness and energy loss.
3Ease of manufacture
If N+ active region is formed within P-type well close to boundary, then diode functionality is achieved, but latch-up is induced in nearby victim structures
Solution Approach 1:
The patent extracts or removes the harmful effect by positioning the N+ active regions away from cell boundaries and introducing guard rings at strategic locations. This separation isolates the electron injection sources from nearby victim structures, preventing latch-up while maintaining the essential diode functionality formed by the P+/N- and N+/P structures.
Solution Approach 2:
The patent introduces guard rings as intermediary structures between the ESD diodes and nearby victim circuits. These guard rings act as protective barriers that intercept or redirect charge carriers, preventing the injected electrons from reaching and triggering latch-up in adjacent MOSFETs and parasitic SCRs, thus mediating between the diode operation and victim structure protection.
4Reliability
If vertical guard rings are added along cell boundaries, then latch-up protection is improved, but cell area is wasted
Solution Approach 1:
The patent applies guard rings selectively at specific locations where they are most needed for latch-up protection, rather than uniformly around the entire cell perimeter. By concentrating protection measures at critical interfaces between ESD diodes and victim structures, the design achieves adequate latch-up protection with minimal area overhead, avoiding the waste associated with comprehensive boundary guard rings.
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 ESD path performance.
Implementation Method 1
One of the ESD diodes has an N+ active region formed within a P-type well (PW), which represents a strong electron injector (n-Emitter) located relatively close to the top boundary of the conventional IO pad cell. The injected electrons can induce latch-up in nearby victim structures
Implementation Method 2
the diodes are positioned so that N-wells of P+/NW diodes act as collector guard bands for the corresponding N+/PW diodes
Data Source
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.