GaN Trench MOS Schottky Diode With P-Type Corner Junction
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Solution Overview
Problem
GaN-based trench metal oxide Schottky barrier diodes face issues with high electric fields in dielectric layers at trench corners leading to fatigue and unreliability, as well as poor anti-surge current ability due to unipolar device characteristics, which can result in device failure under high current density conditions.
Innovation Solution
The solution involves epitaxially forming a p-type high-concentration GaN region at the bottom of the trench and creating a contact window in the dielectric layer to connect the anode metal with the p-type GaN region, forming a pn junction that allows for additional current discharge paths and conductivity modulation, thereby reducing the electric field and enhancing anti-surge capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a trench structure is formed in GaN-based Schottky barrier diode to reduce surface electric field, then breakdown voltage is improved, but electric field concentration at trench corner causes dielectric layer fatigue and reliability degradation
Solution Approach 1:
The patent introduces a p-type GaN layer specifically at the trench bottom corner region where electric field concentration occurs. This local modification creates a pn junction precisely where needed to address the electric field problem, while leaving other regions unchanged. The p-type layer has different doping characteristics than the surrounding n-type material, providing localized electric field management without affecting overall device structure.
Solution Approach 2:
The p-type GaN layer acts as an intermediary element between the n-type drift region and the metal contact. It mediates the electric field distribution by forming a pn junction that provides an alternative current path, thereby reducing the stress on the dielectric layer at the trench corner while maintaining the beneficial trench structure for voltage blocking.
2Reliability
If TMBS structure is used to reduce reverse leakage current, then breakdown voltage is improved, but anti-surge current ability deteriorates due to unipolar device characteristics
Solution Approach 1:
The patent locally introduces p-type doping at the trench bottom corner to create a pn junction, while the rest of the device maintains its unipolar n-type structure. This localized bipolar region provides surge protection capability without significantly altering the overall unipolar characteristics that enable low reverse leakage current. The p-type region is confined to where it is most needed for surge protection.
Solution Approach 2:
The device structure becomes composite in nature, combining both unipolar (n-type GaN) and bipolar (pn junction) characteristics. The majority of the device operates as a unipolar Schottky barrier diode with low leakage, while the localized pn junction region provides bipolar surge protection. This composite structure allows the device to benefit from both operating modes.
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 improves the anti-surge current ability and reliability of the diode by reducing the electric field in the dielectric layer, making the device more stable under reverse bias and preventing burnout from short-time voltage or current pulses, while also increasing the breakdown voltage through uniform electric field distribution.
Implementation Method 1
forming a pn junction that allows for additional current discharge paths and conductivity modulation
Implementation Method 2
This is due to the mirror barrier reduction effect of Schottky junction and tunnel leakage under strong reverse bias
Implementation Method 3
the MOS structure deplete the n-type epitaxial layer, between the trench, and reduces the surface electric field, thus reducing the leakage current
Data Source
AI summary
The invention relates to a GaN-based trench metal oxide Schottky barrier diode and a preparation method therefor. The device structure from bottom to top includes: an ohmic contact metal layer covering a substrate i.e., cathode; a GaN self-supporting substrate; an n-type lightly doped epitaxial layer; a p-type high-concentration GaN layer arranged in parallel; a dielectric layer in the trench; a metal layer convering the upper surface of the device i.e., the anode. The p-type high-concentration GaN layer with high carrier concentration can be obtained by using a selective area epitaxial method to form the p-type high-concentration GaN layer. Then the dielectric layer is deposited, and a contact hole is provided on the dielectric layer, subsequently the anode metal is connected to the p-type high-concentration GaN layer through the contact hole, forming the ohmic contact.