Hewlett-packard Company

Frank Ura

C S Chan

Robert R Hay

Conrad L Wright

James G Bearrs

A passivation layer in a thermal ink jet printhead is formed or 'grown' by a reaction between the materials of the ink jet structure to be protected and an element which will form a chemically inert, electrically insulating, thermally conductive compound. The resistor structure may be of tantalum or tantalum nitride and the electrical conductors therefor may be of aluminum. By subjecting this resistor-conductor structure to a reactive oxide atmosphere, the exposed surfaces of both are anodized so that a surface film of aluminum oxide is formed on the aluminum conductor and a surface film of tantalum pentoxide or tantalum oxynitride is formed on the resistor structure.

Thermal ink jet printhead with self-passivating elements

The thermal print head disclosed herein comprises resistive heating elements deposited on mesas of glass glaze over an aluminum oxide substrate for more efficient marking of thermally sensitive recording material. After the mesas are formed in the glass glaze by etching, resistive and conductive materials are deposited over the mesas by thin film techniques. Thereafter, the raised heater elements and conductors are delineated chemically, then heat-treated to upwardly adjust the resistance of and to grow a protective oxide over the individual heater elements. Since the resistance value of the heater elements can be controllably increased as a function of the temperature and time of heat treatment, external trimming resistors are eliminated. The protective oxide which forms over the resistors during heat treatment provides better adhesion to wear-resistant materials and an effective barrier to migration of ions from the recording material into the heater elements causing degration of performance and shortened element life.

Thin film thermal print head

After the mesas are formed in the glass glaze over an aluminum oxide substrate by etching, and before resistive and conductive materials are deposited over the mesas by thin film techniques, an aluminum oxide underlayer is applied. The aluminum oxide underlayer provides controlled etching of the raised heater elements and conductors to prevent undesirable additional erosion of the glass glaze mesas.

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Palo Alto, CA, United States of America

Frank Ura