Semiconductor device and inverter using same

A semiconductor device comprising:

• a semiconductor substrate of a first conductivity type, including a main region and a sense region;
• unit cells provided in the main region and in the sense region of the semiconductor substrate of the first conductivity type, each of the unit cells having a metal-insulator-semiconductor field effect transistor, the number of the unit cells in the sense region being smaller than the number of the unit cells in the main region, the metal-insulator-semiconductor field effect transistors being connected in parallel connection in each of the main region and the sense region;
• a gate pad on a principal face side of the semiconductor substrate;
• a first source pad and second source pad insulated from each other;
• and a drain pad on a back side of the semiconductor substrate, each metal-insulator-semiconductor field effect transistor including a first silicon carbide semiconductor layer of the first conductivity type located on the principal face of the semiconductor substrate,
• a body region of a second conductivity type in contact with the first silicon carbide semiconductor layer,
• a source region of the first conductivity type in contact with the body region, a second silicon carbide semiconductor layer on the first silicon carbide semiconductor layer and in contact with at least a portion of the body region and at least a portion of the source region,
• a gate insulating film on the second silicon carbide semiconductor layer, a gate electrode on the gate insulating film, a source electrode in contact with the source region, and a drain electrode on the back side of the semiconductor substrate, wherein:
• given that Vds is a potential of the drain electrode relative to a potential of the source electrode,
• Vgs is a potential of the gate electrode relative to the potential of the source electrode, and
• Vth is a gate threshold voltage of the metal-insulator-semiconductor field effect transistor,
• when Vds is positive, the metal-insulator-semiconductor field effect transistor allows a current to flow from the drain electrode to the source electrode if Vgs is equal to or greater than Vth,
• when Vds is negative, the metal-insulator-semiconductor field effect transistor functions as a diode to allow a current to flow from the source electrode to the drain electrode if Vas is less than Vth;
• an absolute value of an onset voltage of the diode is smaller than an absolute value of an onset voltage of a body diode which is constituted by the body region and the first silicon carbide semiconductor layer;
• the gate electrode of each of the unit cells in the main region and the gate electrode of each of the unit cells in the sense region are electrically connected to the gate pad;
• the drain electrode of each of the unit cells in the main region and the drain electrode of each of the unit cells in the sense region are electrically connected to the drain pad;
• the source electrode of each of the unit cells in the main region is electrically connected to the first source pad;
• the source electrode of each of the unit cells in the sense region is electrically connected to the second source pad;
• and
• at least a part of the second silicon carbide semiconductor layer comprises a first layer of the first conductivity type.