SiC MOSFET Terminal Well Isolation for Bipolar Current Suppression
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Solution Overview
Problem
In silicon carbide semiconductor devices, the passage of bipolar current through terminal well regions during reflux operations leads to reliability issues, including leakage currents and potential dielectric breakdowns, due to structural limitations and high resistance in the drift layer, which complicates electrical isolation and increases the risk of punch-through phenomena.
Innovation Solution
A silicon carbide semiconductor device design featuring a semiconductor substrate with a drift layer, well regions, and space regions structured to prevent ohmic connection between the source electrode and terminal well regions, utilizing a pnp slit structure and a conductive layer to manage voltage and current flow, thereby reducing bipolar current passage and preventing dielectric breakdowns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the source electrode is directly connected to terminal well regions, then electrical isolation is simplified, but bipolar current flows during reflux operations causing reliability deterioration
Solution Approach 1:
The terminal well region is divided into multiple segments: the main terminal well region and the isolated terminal well region. The isolated terminal well region is electrically separated from the source electrode through a high-resistance drift layer path, preventing bipolar current flow while maintaining electrical connection for potential utilization. This segmentation allows different parts of the terminal well to serve different functions - one for electrical isolation and another for current conduction.
Solution Approach 2:
The drift layer serves as an intermediary element between the terminal well region and the source electrode. By controlling the resistance of the drift layer in the isolated terminal well region, it acts as a mediator that blocks bipolar current during reflux operations while still allowing the terminal well to be electrically connected to the source electrode structure. This intermediary approach resolves the contradiction by using the drift layer's resistive properties to achieve both isolation and connection.
2Reliability
If the drift layer resistance is increased to block bipolar current, then reliability improves, but voltage-induced breakdowns increase
Solution Approach 1:
The drift layer is designed with non-uniform resistance characteristics - the region under the isolated terminal well has higher resistance to block bipolar current, while other regions maintain lower resistance to handle normal operating voltages. This local quality variation allows the drift layer to simultaneously prevent bipolar current flow and withstand operating voltages without dielectric breakdown.
Solution Approach 2:
The resistance parameter of the drift layer is dynamically optimized through structural design rather than uniform material property change. By adjusting the geometry, doping concentration, and thickness of the drift layer in specific regions, the resistance is tailored to block bipolar current during reflux operations while maintaining sufficient voltage breakdown strength during normal operation. This parameter optimization resolves the contradiction between blocking bipolar current and preventing dielectric breakdown.
3Reliability
If unipolar diodes are used in active regions, then bipolar current passage is suppressed, but terminal well regions still experience bipolar current due to structural limitations
Solution Approach 1:
The terminal well structure is segmented into isolated terminal well regions that are electrically separated from the source electrode. This segmentation prevents bipolar current from flowing through the terminal well during reflux operations, addressing the limitation of using unipolar diodes in active regions only. The isolated terminal well regions eliminate the need for complex additional structures while achieving bipolar current suppression.
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 proposed design effectively suppresses bipolar current flow during reflux operations, enhancing the reliability of silicon carbide semiconductor devices by reducing voltage-induced breakdowns and maintaining high switching performance, even under high-voltage conditions.
Implementation Method 1
the passage of bipolar current through terminal well regions during reflux operations leads to reliability issues
Implementation Method 2
structured to prevent ohmic connection between the source electrode and terminal well regions
Implementation Method 3
enhancing the reliability of silicon carbide semiconductor devices by reducing voltage-induced breakdowns
Implementation Method 4
which complicates electrical isolation and increases the risk of punch-through phenomena
Implementation Method 5
potential dielectric breakdowns, due to structural limitations and high resistance in the drift layer
Implementation Method 6
maintaining high switching performance, even under high-voltage conditions
Data Source
AI summary
An object of the present invention is to suppress the passage of bipolar current in a silicon carbide semiconductor device by reducing a voltage applied to a terminal well region during reflux operations. An SiC-MOSFET includes a plurality of first well regions, a second well region, a third well region in a surface layer of a drift layer, the first, second, and third well regions being of a second conductivity type. The third well region is provided on the side of the second well region opposite to the first well regions. A unit cell that includes the first well regions includes a unipolar diode. The SiC-MOSFET includes a source electrode connected to the unipolar diode and the ohmic electrode and not having ohmic connection with the second well region and the third well region.