Vertical TVS Diode Integration Reduces Lateral Area and Capacitance

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Solution Overview

Problem

Conventional transient voltage suppressor (TVS) circuits face challenges in miniaturization and capacitance reduction, particularly in integrating steering diodes with Zener diodes, which occupy significant area and hinder the development of low-cost, high-density TVS devices for portable electronics.

Innovation Solution

The integration of high-side and low-side steering diodes as vertical diodes within a semiconductor substrate, overlapping with a main Zener diode, reduces lateral area occupation and capacitance, utilizing a lightly doped epitaxial layer and N+ buried layer to enhance current spreading and suppress parasitic transistor action, thereby achieving lower series resistance and reduced power dissipation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of stationary object

If steering diodes are integrated with Zener diodes in conventional configurations, then protection function is achieved, but lateral area occupation increases and capacitance increases

Engineering Contradiction:

Improvelateral area occupationVSAvoidprotection function

Core Design Contradiction:

Area of stationary objectVSReliability

Solution Approach 1:

The patent transitions from lateral diode connections to vertical diode connections in the semiconductor substrate. The steering diodes and Zener diode are connected vertically through the substrate thickness, allowing current to flow in the vertical dimension rather than laterally. This dimensional change reduces the lateral footprint while maintaining protection functionality, as the vertical path utilizes the third dimension (substrate depth) to achieve the same electrical connection.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The patent implements nesting by placing the steering diodes within the vertical structure of the Zener diode. The steering diode anodes are connected to the Zener diode cathode region through vertical P-type regions that extend through the N-type drift layer, effectively nesting the steering function within the Zener diode structure. This nested configuration allows both diodes to share the same lateral footprint while maintaining distinct electrical pathways.

Inventive Principle:

Principle #7Nested doll (Nesting)

2Object-affected harmful factors

If steering diodes are designed with small size to reduce capacitance, then insertion loss is reduced, but forward biased voltage increases

Engineering Contradiction:

Improveinsertion lossVSAvoidforward biased voltage

Core Design Contradiction:

Object-affected harmful factorsVSUse of energy by moving object

Solution Approach 1:

The patent modifies the doping concentration parameters of the vertical P-type regions to optimize the trade-off between capacitance and forward voltage. By adjusting the doping levels in the steering diode P-regions and the Zener diode N-region, the invention achieves low junction capacitance (reducing insertion loss) while maintaining acceptable forward biased voltage characteristics. The parameter optimization includes controlling the doping concentration gradients in the vertical direction to balance these two competing requirements.

Inventive Principle:

Principle #35Parameter changes

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 configuration allows for further miniaturization of electronic devices, improves ruggedness, and reduces capacitance by approximately 70%, enabling efficient voltage clamping and protection against transient voltage events while maintaining low silicon die footprint.

Implementation Method 1

utilizing a lightly doped epitaxial layer and N+ buried layer to suppress parasitic transistor action

Methodology Applied

Scientific EffectField effect:

Implementation Method 2

enhance current spreading and suppress parasitic transistor action, thereby achieving lower series resistance

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Implementation Method 3

The Zener diode has a large size to function as an avalanche diode from the high voltage terminal

Methodology Applied

Scientific EffectAvalanche breakdown: Avalanche Breakdown

Data Source

PatentUS8981425B2Optimized configurations to integrate steering diodes in low capacitance transient voltage suppressor (TVS)

Publication Date: 2015.03.17 ALPHA & OMEGA SEMICONDUCTOR INC

AI summary

A transient-voltage suppressing (TVS) device disposed on a semiconductor substrate including a low-side steering diode, a high-side steering diode integrated with a main Zener diode for suppressing a transient voltage. The low-side steering diode and the high-side steering diode integrated with the Zener diode are disposed in the semiconductor substrate and each constituting a vertical PN junction as vertical diodes in the semiconductor substrate whereby reducing a lateral area occupied by the TVS device. In an exemplary embodiment, the high-side steering diode and the Zener diode are vertically overlapped with each other for further reducing lateral areas occupied by the TVS device.