Vertical MOSFET Trench Schottky Layout for Lower Turn-On Loss
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Solution Overview
Problem
In silicon carbide semiconductor devices, the parasitic pn diode's high built-in potential and bipolar operation lead to increased on-resistance and degradation over time, resulting in forward voltage loss and turn-on loss, which are not effectively mitigated by conventional Schottky barrier diodes due to their structural limitations.
Innovation Solution
A semiconductor device structure featuring a striped pattern of trench gates with a surrounding trench Schottky barrier diode (SBD) that penetrates through the p-type base layer and n-type region, where the SBD operates as a parasitic Schottky diode to inhibit bipolar operation of the parasitic pn diode, reducing forward voltage degradation and turn-on loss by ensuring the SBD functions in both the active and connecting regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a parasitic pn diode is formed in a silicon carbide vertical MOSFET, then the device structure is simplified and cost is reduced, but the on-resistance increases and forward degradation occurs due to high built-in potential and bipolar operation
Solution Approach 1:
The patent extracts the harmful bipolar operation from the parasitic pn diode by introducing a separate Schottky barrier diode (SBD) structure. The SBD is formed with a Schottky barrier layer on the n-type drift layer, allowing the freewheeling function to be performed by the SBD instead of the parasitic pn diode, thereby eliminating the forward degradation caused by bipolar operation while maintaining the simplified device structure
Solution Approach 2:
The patent introduces a Schottky barrier layer as an intermediary element between the n-type drift layer and the p-type base layer. This Schottky barrier layer forms a Schottky barrier diode that mediates the freewheeling current path, preventing the parasitic pn diode from entering bipolar operation and thus eliminating forward degradation while maintaining structural simplicity
2Reliability
If a Schottky barrier diode is connected in parallel to the MOSFET, then forward degradation is suppressed, but the number of chips increases and cost increases
Solution Approach 1:
The patent merges the Schottky barrier diode structure with the MOSFET structure by forming the Schottky barrier layer on the n-type drift layer within the same device. This integration allows the SBD and MOSFET to share common structures such as the drift layer and substrate, eliminating the need for separate SBD chips while maintaining the suppression of forward degradation
Solution Approach 2:
The patent creates a multi-functional device structure where the Schottky barrier layer serves dual purposes: forming the Schottky barrier diode for freewheeling current and simultaneously suppressing forward degradation of the parasitic pn diode. This universal structure performs multiple functions within a single integrated device, reducing the total number of components required
3Reliability
If a contact trench penetrating through the p-type channel portion is formed, then the parasitic pn diode is eliminated, but manufacturing complexity increases
Solution Approach 1:
The patent applies local quality by forming the Schottky barrier layer selectively on specific regions of the n-type drift layer, particularly in the active region where the parasitic pn diode would form. This localized application of the Schottky barrier layer eliminates the parasitic pn diode in critical areas while avoiding the need for complex penetrating contact trenches throughout the entire device structure
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 configuration effectively suppresses bipolar operation and associated losses, reducing forward voltage degradation and turn-on loss by ensuring the SBD operates as intended across the device, enhancing the performance and reliability of silicon carbide semiconductor devices.
Implementation Method 1
a Schottky barrier diode (SBD) may be connected in parallel to the MOSFET on the circuit so that current flows to the SBD but not to the parasitic pn diode during freewheeling
Data Source
AI summary
One object is to provide a semiconductor device capable of reducing loss during turn-on and degradation of forward voltage. A vertical MOSFET includes a semiconductor substrate 2 of a first conductivity type, a first semiconductor layer 1 of the first conductivity type, a second semiconductor layer 16 of a second conductivity type, first semiconductor regions 17 of the first conductivity type, first trenches 31 and a second trench 32, gate electrodes 20 provided in the first trenches 31 via a gate insulating film 19, and a Schottky electrode 29 provided in the second trench 32. The first trenches 31 are provided in a striped pattern, in a plan view and the second trench 32 surrounds the first trenches 31.