Trenched MOSFET with Integrated Schottky Diode
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Solution Overview
Problem
Conventional power MOSFETs with P-N junction diodes suffer from high forward conduction loss, excessive stored minority charges, voltage overshoots, and radio frequency interference, while Schottky diodes, although preferable, occupy significant surface area on semiconductor substrates, increasing production costs and device size.
Innovation Solution
The integration of a trenched gate MOSFET and ACCUFET or Depleted Body FET on a heavily doped semiconductor substrate, featuring gate trenches, contact trenches, and heavily doped source regions, with a conductive material filling the gate trenches and a barrier metal ohmic contact, allows for efficient 3rd quadrant conduction with reduced Schottky diode surface area utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If P-N junction diodes are used in power MOSFETs, then the device can operate in forward bias, but it results in high forward conduction loss and excessive stored minority charges
Solution Approach 1:
The patent merges the MOSFET and Schottky diode into a single integrated structure where the Schottky diode anode is formed by the same heavily doped region that serves as the MOSFET source. This integration eliminates the need for separate P-N junction diodes, reducing forward conduction losses while avoiding minority charge storage issues through the Schottky junction's majority carrier conduction mechanism.
Solution Approach 2:
The patent changes the diode junction type from P-N junction to Schottky junction, fundamentally altering the conduction mechanism from minority carrier diffusion to majority carrier drift. This parameter change reduces forward conduction loss and eliminates stored minority charge effects that cause voltage overshoots and recovery currents.
2Loss of energy
If Schottky diodes are integrated with power MOSFETs, then forward conduction loss is reduced, but the surface area occupied increases production costs
Solution Approach 1:
The Schottky diode and MOSFET share common regions: the heavily doped source region serves as both the MOSFET source and the Schottky diode anode, while the body region serves as the Schottky cathode. This merging eliminates the need for separate diode structures, significantly reducing the surface area required compared to discrete Schottky diode integrations.
Solution Approach 2:
The patent makes the MOSFET structure multi-functional by enabling it to operate both as a switching device and as a rectifier through the integrated Schottky diode. The same physical structure performs multiple functions, eliminating the need for additional dedicated diode area and reducing overall device footprint.
3Device complexity
If conventional MOSFETs with body diodes are used, then the device structure is simple, but the body diode has slow reverse recovery characteristic affecting converter efficiency
Solution Approach 1:
The patent changes the diode type from P-N junction to Schottky junction, which fundamentally alters the reverse recovery characteristic. The Schottky diode's majority carrier conduction mechanism eliminates minority charge storage, resulting in extremely fast reverse recovery that does not affect converter efficiency, while maintaining a relatively simple integrated structure.
4Reliability
If P-N junction diodes are used, then the device can block reverse voltage, but it generates radio frequency interference during fast switching
Solution Approach 1:
The patent changes the junction type from P-N to Schottky, which eliminates minority carrier storage effects. This parameter change prevents the generation of radio frequency interference during fast switching while maintaining the ability to block reverse voltage through the Schottky barrier, as the Schottky diode inherently blocks reverse voltage until breakdown occurs.
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 reduces conduction losses, minimizes stored charge effects, and enhances efficiency by enabling low threshold voltage operation, allowing for more compact and cost-effective power MOSFET designs with improved performance.
Implementation Method 1
An ohmic contact comprising a barrier metal, metal plug is formed inside each contact trench
Implementation Method 2
Each gate trench is substantially filled with a conductive material that is separated from trench walls of a layer of dielectric material to form a gate region
Implementation Method 3
Each of the high side and low side MOSFETs with a normal source-body short contains an intrinsic body diode at the junction between its drain and body regions
Data Source
AI summary
A plurality of gate trenches is formed into an epitaxial region of a first conductivity type over a semiconductor substrate. One or more contact trenches are formed into the epitaxial region, each between two adjacent gate trenches. One or more source regions of the first conductivity type are formed in a top portion of the epitaxial region between a contact trench and a gate trench. A barrier metal is formed inside each contact trench.Each gate trench is substantially filled with a conductive material separated from trench walls by a layer of dielectric material to form a gate . A heavily doped well region of a conductivity opposite the first type is provided in the epitaxial region proximate a bottom portion of each of the contact trenches. A horizontal width of a gap between the well region and the gate trench is about 0.05 μm to 0.2 μm.