(57) Disclosed is a thermal print head (1) in which heating resistance elements (14) are
arranged with high density. The thermal print head comprises a head substrate (10),
formed of a single-crystal silicon wafer, and a print driver circuit element (3, 4).
The print driver circuit element (3, 4), which is formed by doping the head substrate
(10) directly with an impurity, is composed of an MOS-FET. A FET used to form the
single-crystal silicon substrate (10) has high electrical mobility, and serves to
improve the operating speed of the thermal print head (1). Each heating resistance
element (14), whose base material is polycrystalline silicon, is adjusted to a predetermined
resistance value by being subjected to diffusion of an impurity. The resistance elements
(14) are formed on a protuberance (12) which is formed on the head substrate (10).
Thus, the portion of an insulating protective film (15) which corresponds to the protuberance
(12) projects outward from the rest, thereby ensuring contact with a printing sheet.
An earthing diode (16, 17) or laminate structure is used for an earth line of each
heating resistance elements (14) so that the resistance element (14) is situated close
to a side edge portion of the head substrate (10).
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