Pseudo-Schottky Diode Trench Bottom Junction
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Solution Overview
Problem
Conventional semiconductor diodes in motor vehicle alternators experience high conduction losses due to forward voltage, leading to inefficiency and increased cooling costs, and pseudo-Schottky diodes based on trench MOS concepts face issues with avalanche breakdown and hot hole injection damaging the gate oxide.
Innovation Solution
A pseudo-Schottky diode design featuring a highly n+-doped silicon substrate with trenches, a thin dielectric layer, and p-doped polysilicon filling, where the breakdown voltage is managed by a pn junction at the trench bottom, preventing hot hole injection and maintaining stable threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional pn diodes are used for rectification, then the generator can deliver current, but conduction losses are high (around 200 W for 100 A generator) due to forward voltage, reducing efficiency and requiring complex cooling measures
Solution Approach 1:
The patent changes the fundamental parameter of the diode structure from conventional pn junction to trench MOSFET-based pseudo-Schottky design, achieving forward voltage drop reduction from typical pn diode levels (around 1V) to 0.5-0.7V range, thereby reducing conduction losses and cooling requirements
2Loss of energy
If high-efficiency Schottky diodes are used to reduce conduction losses, then efficiency increases and cooling costs decrease, but manufacturing becomes expensive and technically very demanding requiring fine trench structures with mesa widths below 500 nm and special silicide processes
Solution Approach 1:
The patent replaces expensive high-efficiency Schottky diodes requiring special silicide processes with pseudo-Schottky diodes based on standard MOSFET technology, achieving similar electrical performance (forward voltage 0.5-0.7V) through a more economical manufacturing approach that uses readily available MOSFET fabrication processes
Solution Approach 2:
The patent changes the device architecture from Schottky contact-based to MOSFET-based pseudo-Schottky structure, maintaining low forward voltage characteristics while eliminating the need for complex silicide formation processes and fine trench structures with sub-500 nm dimensions
3Loss of energy
If pseudo-Schottky diodes based on trench MOS concepts are used, then low forward voltage is achieved, but avalanche breakdown generates hot charge carriers that are injected into the gate oxide, damaging the device
Solution Approach 1:
The patent converts the harmful avalanche breakdown effect into a beneficial voltage clamping mechanism by designing the trench MOSFET body diode to break down at a controlled voltage (20-40V), limiting generator voltage overshoot during load changes while the generated hot carriers are safely dissipated through the body region rather than injected into the gate oxide
Solution Approach 2:
The patent introduces the body diode as an intermediary element that safely handles the avalanche breakdown process, acting as a controlled breakdown path that limits voltage overshoot while protecting the main MOSFET channel from damage by confining hot carrier generation to the body region
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 design achieves low forward voltage and stable operation during reverse voltage breakdown, comparable to high-efficiency Schottky diodes, while preventing voltage overshoot and maintaining device integrity.
Implementation Method 1
the breakdown voltage of the pn junction 12-2 is lower than the breakdown voltage of the remaining trench structure formed from the layers 5, 4 and 2, and also lower is than the breakdown voltage of the body diode (pn junction 6-2)
Implementation Method 2
Hot charge carriers (electrons and holes) are generated during avalanche or reverse voltage breakdown. The electrons flow to the cathode, the holes directly to the anode via the body region.
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention relates to a pseudo-Schottky diode, comprising an n-channel trench field effect transistor, which comprises a cathode (K), an anode (A) and between the cathode and the anode a highly n+ doted silicon substrate (1), an n-doted epitaxial layer (2), trenches (3) extending in the n-doted epitaxial layer (2), p-doted body regions (6) provided between the trenches (3), as well as highly n+ doted regions (8) and highly p+ doted regions (7) provided on the surface of the body regions (6), wherein the gate, the body regions and the source region are monolithically and electrically connected to each other, and in which the drain region serves as a cathode, wherein on the lateral edges of the trenches (3) dielectric layers (4) are provided, the trenches (3) are filled with a p-doted polysilicon layer (5), the bottoms of some or all trenches (3) are formed from a further p-doted layer (12) contacted with the p-doted polysilicon layer (5), wherein the further p-doted layers (12) determine the breakdown voltage of the pseudo-Schottky diode.