Printhead apparatus

Details Printhead apparatus Printhead apparatus

1998-04-22

2001-09-25

Barlow, John (Department: 2853)

Incremental printing of symbolic information

Ink jet

Ejector mechanism

Reexamination Certificate

active

06293654

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to ink jet printers and, more specifically, to reducing the volume of ink drops expelled from an inkjet print head.
BACKGROUND OF THE INVENTION
Several types of ink jet printers are known in the art and they include those made by Epson, Canon and Hewlett-Packard, amongst others. To improve image quality, ink jet makers have continually tried to increase the number of ink dots that are ejected by the print head per unit area (usually square inch), for example, moving from 300 to 600 dots per square inch (dpi). This is achieved in part by reducing the size of each individual dot which in turn is achieved by reducing the volume of ink used to form each dot. An ink jet print head generally includes a firing chamber or well (hereinafter referred to as “well”) that is fed by capillary action and bordered by a cover plate having an ejection orifice therein. An ink drop expulsion mechanism such as a heating element in a thermal ink jet printer or a piezo-electronic actuator in a mechanical ink jet printer is located adjacent the well. When it is desired to expel an ink drop from the well, the expulsion mechanism is excited causing an ink drop to be expelled through the ejection orifice.
Prior art attempts to reduce drop volume have included reducing well volume. If the well volume is reduced and the cover plate thickness remains the same, then the relative distance an ink drop must travel before being expelled is increased. This increased distance necessitates additional energy (increased heat or mechanical pressure, etc.), thus creating print heads that are disadvantageously energy consumptive and suffer reduced reliability because of stresses associated with increased operating temperature or additional mechanical pressure, etc. Higher operating temperatures may also affect print quality.
To reduce the distance an ink drop must travel before expulsion (and to reduce the requisite energy associated therewith) attempts have been made to reduce the thickness of the cover plate. Ths thickness, however, cannot be reduced in scale with other components due to physical limitations of the cover plate thickness. For example, in some commercially available units cover plate thickness has already been reduced to 45 &mgr;m which is approximately ⅓ the thickness of a human hair. It is difficult to reduce the cover plate thickness using conventional techniques substantially more than this and maintain structural integrity.
A need thus exists for a reduced well volume (drop volume) ink jet print head that does not require significantly increased expulsion energy and achieves this result in a manner substantially independent of cover plate thickness.
SUMMARY OF THE INVENTION
In the present invention, an ink jet print head apparatus includes a barrier layer formed on a substrate that defines an ink well. The apparatus further include an ink expulsion mechanism formed between said substrate and said ink. well, and an electrical passivation layer formed between said ink well and said expulsion mechanism that has a thickness of less than 7000 angstroms and that includes at least a nitride layer and a SiC layer.
The attainment of the foregoing and related advantages and features of the invention should be more readily apparent to those skilled in the art, after review of the following more detailed description of the invention taken together with the drawings.


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