Thermal printing head and method of making same

Abstract

A thermal printing head for printing alphanumeric characters on a thermally-responsive medium, the head being faced with a pattern of heat generating "dot" elements electrically insulated from one another and having conductive leads, with means for connecting the leads selectively to a source of electric current. The heat generating elements are formed of a film of boron phosphide. Preferably the leads are also formed of boron phosphide, integral with the elements, but "doped" to secure a high degree of conductivity. The printing head is formed by applying a boron phosphide compound on a substrate, covering the same with a passivation film, removing the passivation film to expose a background area of the compound film defining a central "island" of unexposed area, doping the exposed background area to increase the conductivity thereof, removing the passivation film from the island, and forming grooves in the compound film dividing the island into separate heat generating elements, with the grooves extended into the background area to form pairs of integral conductive leads for the elements.

Dependencies are inferred from the claim text.