HEMT Protection Device for DC-DC Converter Forward Voltage Reduction

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Solution Overview

Problem

High electron mobility transistors (HEMTs) face inefficiencies due to the forward voltage of body diodes in DC-DC converters, which results in significant power losses, and existing solutions like Schottky diodes have limitations in reducing these losses while maintaining reliability and low leakage currents.

Innovation Solution

A monolithically integrated protection device with a threshold voltage slightly higher than 0V is added to HEMTs, sharing the source and drain with the HEMT and having its gate electrically connected to the source, allowing for minimal forward voltage and suppressed dynamic restoring, enabling low switching power loss and reliable operation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If the threshold voltage of the HEMT is made small to reduce forward voltage, then the forward voltage is reduced, but the HEMT switches on again dynamically causing massive losses

Engineering Contradiction:

Improveforward voltageVSAvoiddynamic switching stability

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The device is segmented into two separate transistor regions: an HEMT region for main switching operations and a protection device region for reverse current handling. This segmentation allows each region to be independently optimized - the HEMT can have higher threshold voltage for stable switching while the protection device handles the reverse conduction path, eliminating the dynamic switching issue

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The protection device acts as an intermediary element between the HEMT and the body diode. It provides a controlled path for reverse current with a threshold voltage slightly higher than 0V, mediating the reverse conduction process and preventing the HEMT from experiencing dynamic switching instability while maintaining low forward voltage characteristics

Inventive Principle:

Principle #24Intermediary (Mediator)

2Loss of energy

If a Schottky diode is connected in parallel to reduce body diode forward voltage, then power loss is reduced, but reverse leakage currents increase at higher temperatures

Engineering Contradiction:

Improvepower lossVSAvoidtemperature stability

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The protection device uses a Schottky-like diode structure with specifically engineered parameters - a threshold voltage slightly higher than 0V (greater than 0V and less than 1.5V) - that optimizes the trade-off between forward voltage reduction and temperature stability. This parameter optimization reduces power loss while maintaining robustness against temperature and current stress

Inventive Principle:

Principle #35Parameter changes

3Loss of energy

If conventional Schottky diode structures are used with lateral HEMTs, then forward voltage is reduced, but the forward voltage is limited by material to about 1V

Engineering Contradiction:

Improveforward voltageVSAvoidforward voltage optimization range

Core Design Contradiction:

Loss of energyVSAdaptability or versatility

Solution Approach 1:

The protection device implements local quality optimization by creating a dedicated Schottky-like diode region with specific material properties and structural characteristics that differ from the main HEMT region. This localized structure achieves a threshold voltage slightly higher than 0V, providing forward voltage reduction while avoiding the 1V limitation of conventional Schottky diodes through optimized material composition and interface properties

Inventive Principle:

Principle #3Local quality

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 effectively reduces the forward voltage and threshold voltage of HEMTs, enhancing the efficiency and reliability of DC-DC converters by minimizing power losses and maintaining robustness against temperature and current stress.

Implementation Method 1

connect a Schottky diode in parallel with the body diode of the transistor. This additional diode has, depending on the metal contact, a lower forward voltage of about 0.4V

Methodology Applied

Scientific EffectSchottky barrier effect:

Implementation Method 2

the channel opens under the gate electrode of an HEMT in the off state in the reverse direction when the potential at the drain with respect to source a small negative voltage is applied

Methodology Applied

Scientific EffectField effect transistor operation:

Data Source

PatentUS9041066B2Protection device for normally-on and normally-off high electron mobility transistors

Publication Date: 2015.05.26 INFINEON TECH AUSTRIA AG

AI summary

A transistor device includes a compound semiconductor body, a normally-on high electron mobility field effect transistor (HEMT) formed in the compound semiconductor body and a protection device monolithically integrated in the same compound semiconductor body as the normally-on HEMT. The normally-on HEMT has a source, a drain, a gate, and a threshold voltage. The protection device has a source and a drain each shared with the normally-on HEMT, a gate and a positive threshold voltage that is less than a difference of the threshold voltage of the normally-on HEMT and a gate voltage used to turn off the normally-on HEMT. The protection device is operable to conduct current in a reverse direction when the normally-on HEMT is switched off. A transistor device including a normally-off HEMT and a monolithically integrated protection device is also provided.