MOSFET Termination Region for Extended ESOA

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Solution Overview

Problem

High-voltage metal oxide semiconductor field effect transistors (MOSFETs) face limitations in electrically safe operating area (ESOA) and unsatisfactory drain-source conductance characteristics, particularly at high gate-source and drain-source voltages, which worsen as device sizes shrink, limiting device scaling.

Innovation Solution

The semiconductor device incorporates a source region with a first dopant type, a well with a second dopant type, and a termination region with a higher dopant concentration of the second type, along with a polysilicon gate extension that serves as a mask for implantations, reducing electric fields and suppressing impact ionization to extend the ESOA and maintain conductivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If device sizes are shrunk to enable scaling, then device density and integration are improved, but electrically safe operating area (ESOA) limitations and unsatisfactory drain-source conductance characteristics worsen

Engineering Contradiction:

Improvedevice scalingVSAvoidESOA limitations

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent applies local quality by creating a termination region with a different dopant concentration profile than the bulk device. Specifically, the termination region has a higher concentration of second dopant type (opposite polarity to source) near the drain end, which locally modifies the electric field distribution to reduce impact ionization and extend ESOA without affecting the overall device scaling

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent changes the dopant concentration parameter in the termination region to resolve the contradiction. By increasing the concentration of the second dopant type in the termination region compared to the well, the patent modifies the electrical characteristics to reduce electric fields and suppress impact ionization, thereby extending ESOA while maintaining device scaling

Inventive Principle:

Principle #35Parameter changes

2Productivity

If device sizes are shrunk to enable scaling, then device density is improved, but drain-source conductance characteristics deteriorate at high voltages

Engineering Contradiction:

Improvedevice scalingVSAvoiddrain-source conductance characteristics

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The termination region with modified dopant concentration locally improves the electric field distribution near the drain, reducing impact ionization and maintaining satisfactory drain-source conductance characteristics even as device dimensions are reduced for scaling

Inventive Principle:

Principle #3Local quality

3Adaptability or versatility

If higher voltages are applied to expand operating range, then application versatility is improved, but impact ionization and electric field effects increase

Engineering Contradiction:

Improveoperating voltage rangeVSAvoidimpact ionization

Core Design Contradiction:

Adaptability or versatilityVSObject-generated harmful factors

Solution Approach 1:

By changing the dopant concentration parameter in the termination region (higher concentration of second dopant type), the patent reduces the electric field strength at high voltages, thereby suppressing impact ionization and enabling expanded voltage operating ranges without harmful effects

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the potentially harmful high electric fields into a beneficial configuration by using the termination region's dopant profile to shape the electric field distribution, reducing peak fields and suppressing impact ionization while maintaining high-voltage operation capability

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 enables MOSFETs to operate safely over a wider range of voltages without degraded conductance, supporting applications like switched-mode DC-DC converters with high-side switches by reducing electric fields and impact ionization.

Implementation Method 1

The termination region comprises a semiconducting material having the second dopant type. A preselected concentration value of the dopant in the termination region is greater than a concentration value of the second dopant type in the well.

Methodology Applied

Scientific EffectField screening: Electric Field

Implementation Method 2

The source region comprises a first dopant type, and the well comprises a second dopant type opposite the first dopant type.

Methodology Applied

Scientific EffectElectrostatic control of conductivity: Electric Field

Data Source

PatentUS20190214471A1Semiconductor device with extended electrically-safe operating area

Publication Date: 2019.07.11 TEXAS INSTRUMENTS INC

AI summary

In at least some embodiments, a semiconductor device comprises a source region is formed within a well. The source region comprises a first dopant type, and the well comprises a second dopant type opposite the first dopant type. A termination region is formed within the well, the termination region being aligned with the source region and having an end adjacent to and spaced apart from an end of the source region. The termination region comprises a semiconducting material having the second dopant type. A preselected concentration value of the dopant in the termination region is greater than a concentration value of the second dopant type in the well.