Power MOS Transistor with Parallel Avalanche Diode for UIS Robustness
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Solution Overview
Problem
Transistor power switch devices face avalanche breakdown due to unclamped inductive switching, leading to excessive current flow and potential device destruction, especially when subjected to repetitive voltage transients, which existing technologies struggle to withstand without failure.
Innovation Solution
Incorporating a reverse biased vertical avalanche diode in parallel with the array of transistors to conduct breakdown current, minimizing heat generation and increasing the device's ability to handle repetitive avalanche currents by providing a dedicated path for avalanche current and enhancing thermal management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a transistor power switch device operates with fast switching speeds, then productivity is improved, but reliability deteriorates due to unclamped inductive switching causing avalanche breakdown
Solution Approach 1:
A dedicated avalanche diode is introduced as an intermediary component connected in parallel with the MOSFET array. This diode provides a separate, controlled path for avalanche current, preventing it from damaging the MOSFETs while allowing the fast switching operation to continue. The diode acts as a mediator that absorbs the harmful avalanche effects without interfering with the normal switching function.
Solution Approach 2:
The current path is segmented into two separate channels: one for normal switching current through the MOSFETs and another for avalanche current through the dedicated avalanche diode. This segmentation allows the device to handle both fast switching operations and avalanche events simultaneously without compromising either function, effectively resolving the contradiction between switching speed and avalanche resistance.
2Loss of energy
If avalanche current is conducted through the transistor array, then power dissipation increases, but device destruction is avoided
Solution Approach 1:
The avalanche diode serves as a specialized intermediary designed specifically to handle avalanche current with lower power dissipation. By routing avalanche current through this dedicated diode rather than the MOSFET array, the system achieves both goals: the avalanche events are survived (reliability improved) while heat generation is minimized (energy loss reduced) due to the diode's optimized structure for this specific function.
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 solution significantly enhances the robustness of the transistor power switch device to repetitive unclamped inductive switching current pulses, improving its ability to withstand avalanche events by distributing current density and facilitating effective heat dissipation, resulting in a ten-fold improvement in UIS robustness compared to devices without this feature.
Implementation Method 1
A reverse biased vertical avalanche diode in the semiconductor body electrically in parallel with the array of transistors for conducting breakdown current
Data Source
AI summary
A transistor power switch device comprising an array of vertical transistor elements for carrying current between the first and second faces of a semiconductor body and a vertical avalanche diode electrically in parallel with the array of vertical transistors. The array of transistor elements includes at the first face an array of source regions of a first semiconductor type, at least one p region of a second semiconductor type opposite to the first type interposed between the source regions and the second face, at least one control electrode for switchably controlling flow of the current through the p region, and a conductive layer contacting the source regions and insulated from the control electrode. The vertical avalanche diode is configured to conduct breakdown current between the first and second faces in the off state of the device and having a first current carrying diode region of the second semiconductor type in contact with the first face and with the conductive layer and a second semiconductor region of the first semiconductor type electrically connected with the second face.