SiC MOSFET Sense Region Layout for Accurate Current Sensing
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Solution Overview
Problem
Silicon carbide semiconductor devices face reliability issues due to stacking faults caused by forward current flow, leading to increased forward voltage and reduced current flow, particularly in MOSFETs with built-in Schottky barrier diodes, which also result in inaccurate current sensing and potential ammeter damage.
Innovation Solution
A silicon carbide semiconductor device design with a dummy sense region between active and active sense regions, using Schottky connections to prevent forward current flow in the dummy sense region, allowing accurate current sensing without ammeter damage and maintaining power conduction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the whole lower part of the current sense pad serves as an active current sense region, then current sensing function is achieved, but invalid sense current increases causing increased loss
Solution Approach 1:
The current sense pad is segmented into multiple regions: an active current sense region for sensing MOSFET current, a dummy sense region for preventing forward current, and a source region. This segmentation allows the device to achieve current sensing function while preventing invalid current flow through the dummy sense region, thereby reducing energy loss.
2Reliability
If a p-type well region of the dummy sense region is connected to the current sense pad, then forward current is prevented, but large reflux current flows causing difficulty in ammeter selection
Solution Approach 1:
The dummy sense region is configured with specific local properties: a p-type well region that is NOT connected to the current sense pad, while only the active current sense region connects to the sense pad. This local quality differentiation allows the dummy sense region to prevent forward current without creating a low-impedance path for large reflux current, enabling the use of ammeters with appropriate current capacity for accurate sensing.
3Quantity of substance
If a well region of the dummy sense region is connected to the source pad, then large reflux current is prevented, but forward current flows in the pn diode causing deterioration in power conduction
Solution Approach 1:
The dummy sense region's p-type well region is extracted from connection to both the current sense pad and source pad. Instead, only the active current sense region connects to the sense pad through Schottky connection, while the dummy sense region remains electrically isolated. This extraction prevents forward current flow in the pn diode between the p-type well region and n-type drift layer, maintaining power conduction efficiency while still preventing large reflux current through the sense pad.
4Area of stationary object
If the current sense pad area is reduced, then device size is minimized, but current sensing accuracy decreases
Solution Approach 1:
The sense pad structure uses local quality differentiation where only the active current sense region (not the entire sense pad area) contributes to current sensing. The dummy sense region occupies space on the sense pad but is electrically isolated to prevent forward current. This allows the device to maintain adequate sensing accuracy through the active region while minimizing the total sense pad area by eliminating the need for large dummy regions connected to the pad.
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 enables accurate current sensing with high reliability by preventing forward current flow in the dummy sense region, reducing power conduction deterioration, and allowing the use of smaller ammeters for precise current measurement.
Implementation Method 1
a source electrode provided to have contact with the first separation regions in Schottky connection
Data Source
AI summary
A silicon carbide semiconductor device includes: a dummy sense region; and a drift layer of a first conductivity type, wherein a MOSFET with a built-in SBD including a first well region of a second conductivity type connected to a source electrode is formed in an active region, a MOSFET with a built-in SBD including a second well region of a second conductivity type connected to a sense pad is formed in an active sense region, and a third well region of a second conductivity type which is not ohmic-connected to any of the source electrode and the sense pad is formed on an upper layer part of the n-type drift layer in the dummy sense region. A gate electrode of the MOSFET with the built-in SBD in the active region and the MOSFET with the built-in SBD in the active sense region is connected to a gate pad.