Vertical Rectifier with Intermediate Region for Low Forward Voltage
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Solution Overview
Problem
Existing power semiconductor rectifiers face challenges in achieving a balance between low forward voltage drop and high reverse breakdown voltage, leading to significant power dissipation and inefficiency in motor control and power conversion circuits.
Innovation Solution
A semiconductor rectifier structure is developed by combining a MOS-transistor-like vertical structure with a JFET-like deeper structure, featuring an insulated trench to define a vertical channel and an additional p-type diffusion around the trench bottom, which creates a deep JFET-like device in series with the MOS channel, optimizing for low forward voltage and high reverse breakdown voltage in a compact area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional pn-junction diode is used, then high reverse breakdown voltage is achieved, but forward voltage drop is high causing significant power dissipation
Solution Approach 1:
The patent merges a Schottky barrier diode structure (for low forward voltage drop) with a pn-junction diode structure (for high reverse breakdown voltage) into a single integrated rectifier device. The Schottky barrier provides the low-voltage conduction path while the pn-junction provides the high-voltage blocking capability, allowing the device to achieve both low forward voltage drop and high reverse breakdown voltage simultaneously.
Solution Approach 2:
The patent employs composite material structures by combining different semiconductor regions with distinct properties - a metal-semiconductor Schottky barrier interface for low-voltage operation and a silicon pn-junction for high-voltage operation. This composite approach allows the single device to exhibit both low forward voltage characteristics and high reverse breakdown characteristics.
2Loss of energy
If a Schottky barrier diode is used, then low forward voltage is achieved, but reverse leakage is high and reverse breakdown is lower than junction diodes
Solution Approach 1:
The patent combines a Schottky barrier diode structure (providing low forward voltage) with a pn-junction diode structure (providing high reverse breakdown voltage and low reverse leakage) into a single integrated device. The Schottky barrier region handles low-voltage conduction while the pn-junction region provides high-voltage blocking, thereby achieving both low forward voltage and high reverse breakdown voltage with low reverse leakage.
3Loss of energy
If a larger area is used to reduce power dissipation, then current handling capacity increases, but device size and complexity increase
Solution Approach 1:
The patent transitions from a lateral planar structure to a vertical three-dimensional structure. The current flow path is arranged vertically through stacked Schottky and pn-junction regions, allowing high current handling capacity to be achieved in a compact footprint. This vertical integration reduces the device area required compared to lateral designs while maintaining low power dissipation through efficient current conduction paths.
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 results in reduced heat dissipation, increased current density, and improved efficiency in power semiconductor devices, enabling more efficient power conversion and motor driving circuits with enhanced ruggedness and lower on-resistance.
Implementation Method 1
through a portion of the body region which is inverted by capacitive coupling to the gate electrode
Implementation Method 2
depletion regions spread laterally from the intermediate region and from the body contact region
Implementation Method 3
to pinch off conduction between the body region and the second metallization
Implementation Method 4
a rectifier, i.e. an element which will pass DC current in only one direction
Data Source
AI summary
A new semiconductor rectifier structure. In general, a MOS-transistor-like structure is located above a JFET-like deeper structure. The present application teaches ways to combine and optimize these two structures in a merged device so that the resulting combined structure achieves both a low forward voltage and a high reverse breakdown voltage in a relatively small area. In one class of innovative implementations, an insulated (or partially insulated) trench is used to define a vertical channel in a body region along the sidewall of a trench, so that majority carriers from a “source” region (typically n+) can flow through the channel. An added “pocket” diffusion, of the same conductivity type as the body region (p-type in this example), provides an intermediate region around the bottom of the trench. This intermediate diffusion, and an additional deep region of the same conductivity type, define a deep JFET-like device which is in series with the MOS channel portion of the diode. This advantageously permits the MOS channel portion to be reasonably short, and to have a reasonably low threshold voltage, since the high-voltage withstand characteristics are defined by the deep JFET-like device.