Thin film transistor and thin film transistor substrate including a polycrystalline semiconductor thin film having a large heat capacity part and a small heat capacity part

A thin film transistor comprising:

• a polycrystalline semiconductor thin film including a large heat capacity part having a large heat capacity and a small heat capacity part having a small heat capacity, in which the small heat capacity part is used at least as a channel part,
• wherein the polycrystalline semiconductor thin film is formed of a crystal grain film by laser annealing of an energy density with which the small heat capacity part melts completely but the large heat capacity part does not melt completely, the small heat capacity part is so formed as to be interposed between two adjacent large heat capacity parts,
• wherein distances between said two adjacent large heat capacity parts facing each other across the small heat capacity part varies so that a distance across said small heat capacity part is not constant, the polycrystalline semiconductor thin film includes a short distance region and a long distance region corresponding to the distances between the large heat capacity parts,
• wherein, in the short distance region, the polycrystalline semiconductor thin film includes a grain boundary formed by collision, at a point where the small heat capacity part is divided in two parts, of the large crystal grains which are crystal-grown toward different directions from the large heat capacity parts facing each other, and
• wherein the polycrystalline semiconductor thin film includes said grain boundary formed at the crystal growth edge by growth and collision of the large crystal grains in the long distance region.

A thin film transistor comprising:

• a substrate;
• a polycrystalline semiconductor thin film including a large heat capacity part having a first heat capacity and a small heat capacity part having a smaller heat capacity, in which the small heat capacity part is used at least as a channel part;
• and
• a metal film between said large heat capacity part and said substrate, said metal film being absent between said small heat capacity part and said substrate,
• the polycrystalline semiconductor thin film is formed of a crystal grain film by laser annealing of an energy density with which the small heat capacity part melts completely to form a microcrystalline structure, but the large heat capacity part does not melt completely so that there is an absence of any microcrystalline structure in said large heat capacity part,
• wherein the small heat capacity part is interposed between two large heat capacity parts, and crystal grain films in two aligned rows are provided, which are grown from boundaries between the large heat capacity parts and the small heat capacity parts to the small heat capacity part side to thereby contact each other,
• wherein distances between the large heat capacity parts facing each other across the small heat capacity part are different, and the polycrystalline semiconductor thin film includes a short distance region and a long distance region corresponding to the distances between the large heat capacity parts,
• wherein, in the short distance region, the polycrystalline semiconductor thin film includes a grain boundary formed by collision, at a point where the small heat capacity part is divided in two parts, of the large crystal grains which are crystal-grown toward different directions from the large heat capacity parts facing each other, and
• wherein the polycrystalline semiconductor thin film includes said grain boundary formed at the crystal growth edge by growth and collision of the large crystal grains in the long distance region.