Compact Dual Direction BJT Clamps with Shared Sub-Collector

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Solution Overview

Problem

Dual direction ESD protection devices face challenges in achieving a small footprint while maintaining a low turn-on voltage, as existing solutions either have high turn-on voltage or result in large footprint devices due to stacking BJTs back to back.

Innovation Solution

A dual direction BJT clamp is designed with a plurality of emitter and base regions sharing a common sub-collector region, implemented as a BiCMOS or SiGe/GaN device, where the emitter and base regions are alternatingly connected to achieve bi-directionality without the need for collector regions, utilizing a floating NBL and n-sinker to manage ESD events efficiently.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If isolated BJT cells are stacked back to back to achieve low turn-on voltage, then the turn-on voltage is reduced, but the device footprint increases

Engineering Contradiction:

Improveturn-on voltageVSAvoiddevice footprint

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

Multiple emitter and base regions are merged to share a common sub-collector region, allowing the device to achieve low turn-on voltage through multiple BJT cells while maintaining a compact footprint by eliminating redundant collector regions

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The common sub-collector region serves multiple emitter-base pairs simultaneously, enabling the device to provide bidirectional ESD protection with low turn-on voltage without requiring separate collector regions for each BJT cell

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Area of stationary object

If non-self aligned BJT junctions are used to achieve small footprint, then the device size is reduced, but the turn-on voltage increases

Engineering Contradiction:

Improvedevice footprintVSAvoidturn-on voltage

Core Design Contradiction:

Area of stationary objectVSReliability

Solution Approach 1:

Multiple emitter and base regions share a common sub-collector, achieving compact integration while maintaining proper BJT alignment characteristics through the shared collector structure

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent uses a multi-finger configuration where emitters and bases are arranged in alternating fingers sharing a common sub-collector, achieving compact layout in planar dimension while maintaining vertical BJT structure for proper alignment

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Data Source

PatentUS7932582B2Compact dual direction BJT clamps

Publication Date: 2011.04.26 NAT SEMICON CORP

AI summary

In a dual direction BJT clamp, multiple emitter and base fingers are alternatingly connected to ground and pad and share a common sub-collector.