Semiconductor device

A semiconductor device comprising:

• an insulating layer comprising a projection;
• a semiconductor layer on the projection;
• a source electrode layer and a drain electrode layer electrically connected to the semiconductor layer;
• a gate insulating film overlapping with the semiconductor layer;
• and
• a gate electrode layer overlapping with the semiconductor layer with the gate insulating film therebetween,
• wherein, in a portion of the semiconductor layer overlapping with the gate electrode layer between the source electrode layer and the drain electrode layer, a length D of a region where the semiconductor layer and the gate insulating film are in contact with each other as seen in a cross section of the semiconductor layer in a channel width direction is in a range expressed by the formula
• 2√{square root over ((a/2)2+b2)}≦D<a+2b,
• wherein a is a length of a side of the semiconductor layer in contact with the insulating layer as seen in the cross section of the semiconductor layer in the channel width direction,
• wherein b is a height of the semiconductor layer as seen in the cross section of the semiconductor layer in the channel width direction, and
• wherein b is equal to or greater than a.

A semiconductor device comprising:

• an insulating layer comprising a projection;
• a stack comprising a first semiconductor layer, a second semiconductor layer, and a third semiconductor layer formed in this order on the projection, the third semiconductor layer being in contact with the second semiconductor layer;
• a source electrode layer and a drain electrode layer electrically connected to the stack;
• a gate insulating film over the stack, the source electrode layer, and the drain electrode layer, the gate insulating film being in contact with the second semiconductor layer;
• and
• a gate electrode layer overlapping with the stack with the gate insulating film therebetween,
• wherein, in a portion of the stack overlapping with the gate electrode layer between the source electrode layer and the drain electrode layer, a length J of a region where the second semiconductor layer is in contact with the gate insulating film or the third semiconductor layer as seen in a cross section of the stack in a channel width direction is in a range expressed by the formula
• 2√{square root over ((f/2)2+g2)}<J<f+2g,
• wherein f is a length of a side of the second semiconductor layer in contact with the first semiconductor layer as seen in the cross section of the stack in the channel width direction,
• wherein g is a height of the second semiconductor layer as seen in the cross section of the stack in the channel width direction, and
• wherein g is equal to or greater than f.

A semiconductor device comprising:

• an insulating layer comprising a projection;
• a stack comprising a first semiconductor layer and a second semiconductor layer formed in this order on the projection;
• a source electrode layer and a drain electrode layer electrically connected to the stack;
• a third semiconductor layer over the stack, the source electrode layer, and the drain electrode layer, the third semiconductor layer being in contact with the second semiconductor layer;
• and
• a gate insulating film and a gate electrode layer each overlapping with the stack,
• wherein, in a portion of the stack overlapping with the gate electrode layer between the source electrode layer and the drain electrode layer, a length Q of a region where the second semiconductor layer and the third semiconductor layer are in contact with each other as seen in a cross section of the stack in a channel width direction is in a range expressed by the formula
• 2√{square root over ((m/2)2+n2)}≦Q<m+2n,
• wherein m is a length of a side of the second semiconductor layer in contact with the first semiconductor layer as seen in the cross section of the stack in the channel width direction,
• wherein n is a height of the second semiconductor layer as seen in the cross section of the stack in the channel width direction, and
• wherein n is equal to or greater than m.