1. Field of the Invention
The present invention relates to a thermal head and a thermal printer, and more particularly to a thermal head and a thermal printer using a single crystalline silicon substrate.
2. Description of the Related Art
In recent years, thermal heads for performing thermosensitive recording by selective heat generation of a heat generating element have been used.
Japanese Patent Application Laid-Open Nos. H02-137943 and H06-320769 disclose a thermal head using a single crystalline silicon substrate.
The thermal head disclosed in Japanese Patent Application Laid-Open Nos. H02-137943 and H06-320769 includes: a heat generating element formed on a single crystalline silicon substrate via an insulating film; a driver circuit unit formed on the single crystalline silicon substrate; a wiring layer for connecting the driver circuit unit to the heat generating element; and a protecting film for protecting a thermal head surface.
A heat generating resistor protrudes toward a printing medium for increasing contact pressure with a printing medium such as thermal paper or an ink sheet to increase printing efficiency.
Proposed methods therefor include a method of partially etching a silicon substrate to form a protruding portion and forming a heat generating portion on the protruding portion, and a method of forming a silicon oxide film having a thickness of several μm on a silicon substrate, then forming a protruding shape on the silicon oxide film by patterning, and forming a heat generating portion on the protruding portion.
In the structure in which a heat generating resistor is disposed on the protruding portion formed by partially etching the silicon substrate of the conventional techniques described above, the heat generating resistor is located near the silicon substrate having a large thermal conductivity of 152 W/m·K. Thus, thermal energy generated by the heat generating resistor easily escapes toward the silicon substrate to increase heat loss and thus increase power consumption.
In the structure in which the silicon oxide film is formed into a protruding shape, the limit of a height of the protruding portion is several μm due to the limit of stress, and thus sufficient contact pressure with the printing medium cannot be obtained and clear image quality cannot be obtained in some cases.
The present invention has an object to provide a thermal head that increases contact pressure between a heat generating portion and a printing medium to increase printing quality with a low heat loss.