Shielded JFET Structure for Lower Miller Capacitance
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Solution Overview
Problem
Semiconductor devices with junction-type field effect transistors face challenges in reducing switching loss due to high Miller capacitance ratios, which can lead to increased surge current concentration and threshold voltage magnitude.
Innovation Solution
Incorporating a shield layer between the gate and drift layers, maintained at a potential different from the gate layer, with a depth ratio of the gate layer to the body layer equal to or smaller than 0.45, reduces the Miller capacitance ratio and suppresses the increase in threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a junction-type field effect transistor is used with conventional structure, then the device can operate with basic functionality, but the Miller capacitance ratio is high leading to increased switching loss
Solution Approach 1:
The device is segmented into multiple functional layers including drift layer, channel layer, source layer, gate layer, body layer, and shield layer. This segmentation allows each layer to perform its specific function optimally, with the shield layer specifically designed to reduce Miller capacitance and the body layer to control surge current, thereby reducing overall switching loss without excessive complexity increase
Solution Approach 2:
A shield layer is introduced as an intermediary element between the gate layer and drift layer. This shield layer acts as a mediator to reduce the Miller capacitance ratio by controlling the electric field distribution, thereby reducing switching loss while maintaining manageable device structure
2Ease of operation
If the gate layer is positioned deeper in the channel layer, then the control over channel is improved, but the threshold voltage magnitude increases
Solution Approach 1:
The depth ratio of the gate layer to the body layer is optimized to be equal to or smaller than 0.45. This parameter change allows the gate layer to be positioned deep enough to provide good channel control while preventing the threshold voltage magnitude from becoming excessively large, achieving a balanced operating point
3Power
If surge current is allowed to flow freely, then the device can handle high current demands, but the surge current concentrates on the gate layer causing damage
Solution Approach 1:
A body layer is introduced as an intermediary structure to intercept and divert surge current away from the gate layer. This body layer acts as a protective mediator that handles the surge current, preventing it from concentrating on the gate layer and causing damage, while still allowing the device to handle high current demands through the drain layer
Data Source
AI summary
A semiconductor device includes a drift layer, a channel layer, a source layer being the first conductivity type, a gate layer, a body layer, a shield layer and a drain layer. The channel is disposed on the drift layer. The source layer is disposed on a surface layer portion of the channel layer. The gate layer is arranged to be deeper than the source layer. The body layer is arranged to be deeper than the source layer. The shield layer is disposed at a portion of the channel layer between the gate layer and the drift layer. The shield layer is maintained at a potential different from a potential of the gate layer. The drain layer is disposed at a side opposite to the channel layer. A depth ratio of a depth of the gate layer to a depth of the body layer is equal to or larger than 0.45.