LDMOS High-k Drain STI Dielectric for Breakdown Voltage

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Solution Overview

Problem

Current LDMOS transistors face a trade-off between low on-resistance and high breakdown voltage, as increasing drain side drift region doping to reduce on-resistance results in a decrease in breakdown voltage, necessitating a greater decoupling of these intrinsic limits.

Innovation Solution

The use of a high-k dielectric material in the drain shallow trench isolation (STI) of LDMOS transistors enhances accumulation under the field plate, reducing spread resistance and increasing breakdown voltage, allowing for increased doping or reduced drift region length without compromising breakdown voltage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If drain side drift region doping is increased to reduce on-resistance, then on-resistance decreases, but breakdown voltage decreases

Engineering Contradiction:

Improveon-resistanceVSAvoidbreakdown voltage

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The patent changes the dielectric constant parameter of the STI material from conventional silicon dioxide (k≈3.9) to high-k dielectric materials (k>25), which fundamentally alters the electrical field distribution and enables simultaneous achievement of low on-resistance and high breakdown voltage through modified charge accumulation characteristics

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs composite material structures combining high-k dielectric layers with specific doping profiles in the drift region, creating a multi-layered system where each material contributes specific properties: the high-k dielectric provides enhanced charge accumulation while the optimized doping profile maintains breakdown characteristics

Inventive Principle:

Principle #40Composite materials

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 approach effectively lowers on-resistance while maintaining or improving breakdown voltage, offering a more balanced performance in power field effect transistors.

Implementation Method 1

The high-k material in the STI provides for improved accumulation below the field plate, which lowers RON

Methodology Applied

Scientific EffectDielectric permittivity: Dielectric Permittivity

Implementation Method 2

The high-k material also reduces the electric field at the edge of the field plate and increases breakdown voltage for a given doping

Methodology Applied

Scientific EffectElectric field distribution: Electric Field

Data Source

PatentUS11081558B2LDMOS with high-k drain STI dielectric

Publication Date: 2021.08.03 TEXAS INSTRUMENTS INC

AI summary

A laterally diffused metal oxide silicon (LDMOS) transistor and a method of making the LDMOS transistor are disclosed. The LDMOS transistor includes a drain drift region formed in a substrate and containing a drain contact region. A gate structure overlies a channel region in the substrate and a first shallow-trench isolation (STI) structure located between the drain contact region and the channel region. The first STI structure contains a high-k dielectric and a second STI structure contains silicon oxide.