Deep Trench MOSFET Gate Structure for High Voltage Rectifiers
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Solution Overview
Problem
High voltage Schottky rectifiers face limitations in breakdown voltage and leakage current, making them unsuitable for applications above 300 V, as increasing breakdown voltage leads to higher forward voltage and reduced switching speed.
Innovation Solution
A high switching speed and high voltage rectifier device is designed with two n-type semiconductor layers and a p-type semiconductor layer, featuring deep trenches with oxide coating and polysilicon filling, along with N+ source regions, to enhance breakdown voltage and reduce leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If techniques are used to increase breakdown voltage (guard ring structure, high-resistivity silicon epitaxial layer, high Schottky barrier height), then breakdown voltage is improved, but forward voltage increases and reverse leakage current increases, reducing switching speed
Solution Approach 1:
The device is divided into multiple functional regions including deep trenches segmented into different depth zones, with first deep trenches extending to the interface between N- epitaxial layer and N+ substrate, and second deep trenches extending only into the N- epitaxial layer. This segmentation allows different regions to perform specialized functions for voltage blocking and current management without compromising switching speed
Solution Approach 2:
Oxide layers are introduced as intermediary materials coating the sidewalls of deep trenches, and polysilicon layers are deposited as intermediary conductive elements filling the trenches. These intermediary materials enable high breakdown voltage through oxide insulation while maintaining low forward voltage and low leakage current through controlled polysilicon conduction paths
2Reliability
If thick epitaxial layer is used to increase breakdown voltage, then breakdown voltage is improved, but current density decreases, losing the advantage of high switching speed and low forward-voltage drop
Solution Approach 1:
Different regions of the device are assigned different doping concentrations and structural properties. The N- epitaxial layer has lightly doped regions for voltage blocking, while N+ source regions have heavy doping for high current density. The deep trenches create localized fields that concentrate voltage stress in specific areas, allowing the bulk epitaxial layer to remain thin while achieving high breakdown voltage
3Ease of manufacture
If conventional Schottky rectifier structure is used, then manufacturing is simple, but leakage current is high and breakdown voltage is limited to below 300 V
Solution Approach 1:
The invention transitions from a planar Schottky structure to a three-dimensional deep trench structure. Deep trenches extend vertically into the epitaxial layer and substrate, creating additional dimensional space for field management. This vertical dimension allows electric fields to be controlled through the depth of trenches rather than only through lateral doping profiles, enabling breakdown voltages exceeding 300 V while maintaining manufacturing feasibility through standard semiconductor processing techniques
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 device achieves high reverse bias voltage up to 2,000 V with low leakage current, maintaining high switching speed and reducing body resistivity, thus overcoming the limitations of traditional Schottky rectifiers.
Implementation Method 1
Both deep trenches have oxide coating on their sidewalls and bottom surfaces
Implementation Method 2
a polysilicon layer filling their centers and connected to the metal layer for operation
Implementation Method 3
At least two enclosed deep trenches in concentric continuous ring circles acting as operating (or active) trenches are etched from the top of the p-type semiconductor layer down to the interface of the N+ substrate and the N− epitaxial layer
Data Source
AI summary
Apparatus and other embodiments associated with high speed and high breakdown voltage MOS rectifier are disclosed. A Junction All Around structure, where a deep trench structure surrounds and encloses a P-N junction or a MOS structure, is created and applied in various rectifiers. In one embodiment, multiple deep trenches in concentric ring circles enclosed several horizontal P-N junctions in concentric ring circles. In another embodiment, an enclosed deep trench in ring circle surrounds a horizontal P-N junction, which results in a planar N-channel MOS during forward bias. This structure can be extended to multiple deep trenches with associated horizontal P-N junctions.