Transistor device having an edge trench

A transistor device, comprising:

• a semiconductor substrate comprising a first major surface;
• a plurality of elongate trenches extending from the first major surface into the semiconductor substrate and positioned substantially parallel to one another such that one or more inner elongate trenches are arranged between two outermost elongate trenches;
• an elongate mesa between neighbouring ones of the elongate trenches;
• and
• an edge trench extending from the first major surface into the semiconductor substrate and laterally surrounding the plurality of elongate trenches,
• wherein the edge trench comprises longitudinal trench portions and transverse trench portions that extend between the longitudinal trench portions such that an inner trench corner is formed at each intersection between an inner side wall of the longitudinal trench portion and an inner side wall of the transverse trench portion, and
• wherein the inner trench corner of the edge trench has a radius of curvature that is greater than a width of the closest elongate mesa.

A transistor device, comprising:

• a semiconductor substrate comprising a first major surface;
• a plurality of elongate trenches extending from the first major surface into the semiconductor substrate and positioned substantially parallel to one another such that one or more inner elongate trenches are arranged between two outermost elongate trenches;
• an elongate mesas between neighbouring ones of the elongate trenches;
• and
• an edge trench extending from the first major surface into the semiconductor substrate and laterally surrounding the plurality of elongate trenches,
• wherein the edge trench comprises longitudinal trench portions and transverse trench portions that extend between the longitudinal trench portions such that an inner trench corner is formed at each intersection between an inner side wall of the longitudinal trench portion and an inner side wall of the transverse trench portion,
• wherein each inner trench corner of the edge trench has a radius of curvature,
• wherein one or both of the two outermost elongate trenches has an outer corner facing towards the edge trench,
• wherein for each inner corner of the edge trench, a difference between a width measured between the inner corner of the edge trench and the outer corner of the closest outermost elongate trench and a width measured between the longitudinal trench portion at the intersection that forms the inner trench corner and a longitudinal side wall of the closest outermost elongate trench is less than 10%.