Back Ballasted NPN Transistor for Uniform ESD Conduction
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Solution Overview
Problem
Vertical NPN bipolar transistors used for ESD protection in integrated circuits face issues with non-uniform current conduction due to competing lateral and vertical p-n junction breakdowns, leading to uneven ESD stress and increased circuit board area requirements.
Innovation Solution
The implementation of back ballasted NPN bipolar transistors with a silicide blocked collector portion and deep N doped region for lateral breakdown control, along with dual ballasting for improved lateral and vertical conduction, facilitating uniform operation and space savings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If vertical NPN bipolar transistors are used for ESD protection, then ESD protection function is provided, but non-uniform current conduction occurs due to competing lateral and vertical p-n junction breakdown
Solution Approach 1:
The patent applies local quality by creating different doping concentrations in specific regions of the transistor. The base region has a first doping concentration while the collector region has a second doping concentration that is lower than the first. This non-uniform doping distribution creates different breakdown characteristics in different regions, allowing the lateral p-n junction to break down at a higher voltage than the vertical junction, thereby eliminating the competing breakdown behavior and achieving uniform current conduction.
2Manufacturing precision
If islanded internally stacked NPN ESD protection devices are used, then enhanced control of breakdown voltage characteristics is achieved, but significant circuit board area is occupied
Solution Approach 1:
The patent applies segmentation by dividing the transistor into distinct regions with different doping concentrations - a base region with a first doping concentration and a collector region with a second doping concentration. This segmentation allows independent control of the breakdown characteristics of the lateral and vertical p-n junctions, enabling enhanced control of breakdown voltage characteristics while maintaining a compact single-transistor structure that occupies less circuit board area than stacked devices.
3Ease of manufacture
If conventional vertical NPN transistor structure is used, then fabrication is simplified, but lateral and vertical p-n junction breakdown compete leading to non-uniform operation
Solution Approach 1:
The patent applies parameter changes by modifying the doping concentration parameter in different regions of the transistor. The base region is doped with a first concentration while the collector region is doped with a second concentration that is lower. This parameter change creates different breakdown voltages for the lateral and vertical junctions, ensuring that the lateral junction breaks down at a higher voltage and eliminates the competing breakdown behavior, thereby achieving uniform operation while maintaining fabrication simplicity.
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
This design provides harmonized control of breakdown voltage and snap-back voltage, ensuring consistent operation with reduced circuit board area usage compared to internally stacked NPN devices, while maintaining effective ESD protection.
Implementation Method 1
The silicide blocked second collector portion provides back side ballasting for lateral breakdown and low current conduction via a deep N doped region
Implementation Method 2
vertical NPN transistors suffer from competing lateral and vertical p-n junction breakdown behavior
Data Source
AI summary
An integrated circuit includes a bipolar transistor, e.g. a back-ballasted NPN, that can conduct laterally and vertically. At a low voltage breakdown and low current conduction occur laterally near a substrate surface, while at a higher voltage vertical conduction occurs in a more highly-doped channel below the surface. A relatively high-resistance region at the surface has a low doping level to guide the conduction deeper into the collector.