Semiconductor Device Floating Electrode Avalanche Protection
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Solution Overview
Problem
MOSFETs used in high current and high breakdown voltage applications are prone to avalanche breakdown when surge voltages exceed their breakdown voltage, leading to potential diode breakdown in active clamp circuits, which can increase gate voltage and form a channel, compromising device performance.
Innovation Solution
A semiconductor device design incorporating a floating electrode and specific capacitance and voltage relationships to manage voltage and prevent avalanche breakdown, with a structure including a first semiconductor layer, a second semiconductor layer, a third semiconductor layer, insulating films, and electrodes, where the voltage between the drain and source electrodes is controlled to be below the avalanche breakdown voltage, and the floating electrode's threshold voltage is used to form a channel without increasing the gate voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If MOSFETs are designed for high breakdown voltage to handle surge voltages, then the device can withstand higher voltages, but the on-resistance increases leading to higher power loss
Solution Approach 1:
The patent divides the single MOSFET structure into multiple semiconductor layers (first conductivity type and second conductivity type layers alternating) with multiple electrodes. This segmentation allows the device to achieve high breakdown voltage through the stacked structure while maintaining lower on-resistance by providing multiple parallel conduction paths through the alternating layers.
Solution Approach 2:
The patent transitions from a planar single-layer MOSFET structure to a three-dimensional stacked multi-layer structure. By adding the vertical dimension with alternating conductivity type layers and multiple electrodes, the device achieves both high breakdown voltage (through the stacked configuration) and low on-resistance (through parallel conduction paths in multiple layers).
2Reliability
If an active clamp circuit with diode is used to protect against avalanche breakdown, then the MOSFET is protected from surge voltage, but the diode may break down and increase gate voltage forming a channel
Solution Approach 1:
The patent introduces a third electrode that acts as an intermediary between the first and second electrodes. This third electrode, connected to the third semiconductor layer, serves as a mediator that can absorb or divert surge voltages before they cause avalanche breakdown in the main MOSFET structure, preventing the harmful effects of gate voltage increase and unintended channel formation.
Solution Approach 2:
The patent structures the device with alternating conductivity type layers and multiple electrodes in advance, creating a built-in protection mechanism before surge voltages occur. The third electrode and alternating layers are pre-configured to handle voltage spikes, preventing avalanche breakdown before it can affect the gate structure and cause harmful channel formation.
3Ease of manufacture
If the MOSFET structure is simplified for easier manufacture, then manufacturing cost decreases, but the breakdown voltage capability and performance are compromised
Solution Approach 1:
The patent merges multiple functions into the alternating conductivity type layer structure. The same stacked layers that provide the multi-path conduction for low on-resistance also provide the high breakdown voltage capability through their alternating configuration. This merging allows enhanced performance without proportionally increasing manufacturing complexity, as the layers are formed in an alternating sequence during fabrication.
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 effectively prevents avalanche breakdown by controlling the voltage between the drain and source electrodes, ensuring the semiconductor device operates safely within its breakdown limits, reducing the risk of channel formation and maintaining high breakdown voltage while minimizing on-resistance.
Implementation Method 1
a voltage BV0 between the first electrode and the second electrode is lower than an avalanche breakdown voltage BV1 of the semiconductor device without the floating electrode and the third semiconductor layer and the voltage BV0 is given by the following formulas: BV0=((Cfd+Cfs)/Cfd)×Vth
Implementation Method 2
Avalanche breakdown may occur in the MOSFETs, when a surge voltage generated by an induced electromotive force exceeds the breakdown voltage of the MOSFETs during switch-off
Data Source
AI summary
According to one embodiment, a semiconductor device includes a first semiconductor layer of a first conductivity type; a first electrode electrically connected to the first semiconductor layer; a second semiconductor layer of a second conductivity type provided on the first semiconductor layer; a third semiconductor layer of the first conductivity type selectively provided on the second semiconductor layer; a second electrode electrically connected to the second semiconductor layer and the third semiconductor layer; a third electrode and a floating electrode provided from an upper surface side of the third semiconductor layer through the third semiconductor layer and the second semiconductor layer to the first semiconductor layer via a first insulating film; a second insulating film provided between the second electrode and the third electrode, the second electrode and the floating electrode.