Low topography thermal inkjet drop ejector structure

Details Low topography thermal inkjet drop ejector structure Low topography thermal inkjet drop ejector structure

2000-06-19

2001-05-08

Barlow, John (Department: 2853)

Incremental printing of symbolic information

Ink jet

Ejector mechanism

C347S063000

Reexamination Certificate

active

06227657

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates generally to the mechanical and electrical structure of the thermal inkjet drop ejectors.
2. Description of Related Art
A conventional thermal inkjet transducer array is essentially a large bank of thin-film resistive heaters electrically connected in parallel. In particular, a thermal inkjet printer comprises an array of drop ejectors. Each drop ejector has an ink channel having an inlet end and a nozzle end and contains a resistive heater. The nozzle end of each resistive heater in the array of drop ejectors is connected to a common electrical bus, which in turn is connected to an electrical power supply providing a printer operating voltage. Each individual drop ejector is driven to eject a droplet of ink by grounding an inlet end of the resistive heater through an individually-addressable driver transistor.
The common electrical bus should be narrow, so that the length of the ink nozzle can be kept as short as possible. This tends to increase drop ejection energy efficiency. To reduce the electrical series resistance of the common bus, it is desirable to make the common bus relatively thick. Often, the common bus will have two or more layers of metal and/or polysilicon.
SUMMARY OF THE INVENTION
However, this thick bus structure presents a “bump”-shaped obstacle in the nozzle that misdirects the ejected main drop and/or associated satellite droplets that are ejected with the main drop. The misdirected satellite drops tend to limit the print quality achievable with drop ejectors having this bump-shaped obstacle. Unfortunately, no reasonable alternative to these drop ejectors was previously available.
This invention provides an electrical contact structure that connects the resistive heaters of the drop ejectors to the common bus that avoid the bump-shaped mechanical structure of the conventional electrical contact structure.
This invention separately provides a mechanical structure for the electrical contact structure between the common bus and the resistive heater that avoids placing relatively thick electrical contact layers in an ink drop ejection path between the resistive heater of the drop ejector and the nozzle of that drop ejector.
This invention separately provides a low-topography inkjet printhead drop ejector array that avoids a large common bus structure in the front of the drop ejectors.
This invention separately provides a low-topography inkjet printhead drop ejector array that locates individual electrical feed-through lines between each drop ejector in the array.
This invention separately provides an inkjet printhead drop ejector array that reduces visible defects due to misdirected satellite drops.
This invention separately provides inkjet printhead drop ejector arrays that relocates the thick electrical contact lines from the ink drop ejection path between the drop ejector resistive heater and the corresponding nozzle.
In various exemplary embodiments of a thermal inkjet printhead according to this invention, the high-current common bus does not extend in front of the row of resistive heaters in the array of drop ejectors. Instead, a flat layer of highly-doped polysilicon forms the common bus. This flat, highly-doped polysilicon layer runs between the resistive heaters and is routed to interconnection pads for each ink drop ejector without placing a bump in the path of an exiting ink droplet.
In various exemplary embodiments, a floor of the ink channel is left more or less flat at the level of the resistive heater. A layer of passivation material, such as, for example, silicon nitride, can be added to the nozzle region of the ink channel to reduce any residual topography. By making the floor of the ink channel more or less coplanar from an inlet end of the resistive heater through the nozzle and out to the front face of the printhead, the topographic features that contribute to misdirecting main drops and/or creating satellite drops are reduced.
These and other features and advantages of this invention are described in, or are apparent from, the following detailed description of various exemplary embodiments of the low-topography inkjet printhead drop ejectors according to this invention.


REFERENCES:
patent: 4445266 (1984-05-01), Mai et al.
patent: 4742019 (1988-05-01), Bechade
patent: 4887098 (1989-12-01), Hawkins et al.
patent: 5257042 (1993-10-01), Buhler
patent: 5534901 (1996-07-01), Drake
patent: 5988797 (1999-11-01), Itoh

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