Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1997-01-21
2001-02-06
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S063000
Reexamination Certificate
active
06183067
ABSTRACT:
TECHNICAL FIELD
The invention relates generally to inkjet printheads and more particularly to forming a mechanism for projecting fluid ink from a printhead.
BACKGROUND ART
Thermal inkjet printheads include an array of ink firing chambers having openings from which ink is projected onto a sheet of paper or other medium. Each ink firing chamber is aligned with a thermal actuator, i.e., a resistive heater. Current flow through the actuator causes a portion of the ink within the firing chamber to vaporize and eject an ink drop through the opening. The openings are arranged in linear arrays along a surface of the printhead.
With reference to
FIG. 1
, a prior art thermal inkjet printhead is schematically shown as including a silicon substrate
10
and a polymer barrier layer
12
. Formed on the silicon substrate is a resistor layer
14
and a metallization layer
16
. The resistor layer is patterned to define dimensions and locations of ink firing actuators
18
. While not shown in
FIG. 1
, the metallization layer extends beyond the actuator and provides an electrical path for control signals to the actuator. A passivation layer
20
is disposed over the metallization layer, and the polymer barrier layer
12
is attached to the passivation layer. The polymer barrier layer is patterned to include an ink firing chamber that exposes the thermal actuator
18
. The barrier layer
12
includes an open side
22
that is in fluid communication with an ink supply channel.
Referring now to
FIGS. 1 and 2
, atop the barrier layer
12
is an orifice substrate
24
having an opening
26
. In practice, the barrier layer
12
is often formed in conjunction with the orifice substrate
24
. The opening
26
defines the geometry for firing ink from the inkjet mechanism in response to activation of the thermal actuator
18
. The actuator is individually addressed by means of a switching transistor
28
connected to the actuator by a conductive trace
30
.
In operation, current flow through the thermal actuator
18
is initiated by the electronic circuitry
28
. As the actuator heats, a vapor bubble is formed in the firing chamber and a pressure field is generated. As a result, ink is projected from the firing chamber toward a medium, such as a sheet of paper. The firing chamber is replenished with ink by flow from a supply channel
32
of the silicon substrate
10
. The ink enters the firing chamber through the open side
22
of the barrier layer
12
.
As explained in U.S. Pat. No. 5,450,109 to Hock, which is assigned to the assignee of the present invention, the conventional method of fabricating inkjet printheads is to utilize photolithographic techniques to form the thermal actuators
18
on the silicon substrate
10
. Separately, the ink firing chambers are photolithographically defined within the polymer barrier layer
12
that is formed on the orifice substrate
24
. The orifice substrate may be formed of a gold-plated nickel material. The orifice substrate and barrier layer are then attached to the actuator substrate
10
with the firing chambers in precise alignment with the actuators.
Utilizing conventional fabrication techniques, the inkjet printhead includes three structures, i.e., the silicon substrate with the thermal actuators, the barrier layer in which the ink supply channels and firing chambers are formed, and the orifice plate having the openings for the projection of ink. Often, the manufacturing process includes adhering two substrates together to provide the final product. Adhering the substrates in order to provide the desired architecture raises concerns with respect to reliability, cost, manufacturability and print quality. Improved print quality requires smaller ink drop volumes and, therefore, smaller ink firing chambers and openings. As ink firing chambers and thermal actuators are reduced in size, it becomes increasingly difficult to properly align the array of ink firing chambers on one substrate with the array of thermal actuators on another substrate. Limits imposed by the ability to repeatedly and reliably align the two substrates are factors in dictating the throughput, cost and print quality available using inkjet technology. Another limitation of the bonded structure stems from the fact that adhesives tend to fail due to long-term exposure to aggressive inks and thermal cycling. Repeated heating and cooling, as well as contact with chemically aggressive inks, often cause degradation of the polymer barrier layer and loss of adhesive properties. Partial or total delamination of the orifice substrate from the actuator substrate may result.
U.S. Pat. No. 5,412,412 to Drake et al. describes the procedure for bonding the substrates as being paramount to maintaining the efficiency, consistency and reliability of an inkjet printhead. The alignment and bonding process described in Drake et al. includes introducing elements into the fabrication sequence to compensate for any topographical formations that are developed in a thick film insulating layer during fabrication. The insulating layer is formed to intentionally include a non-functional heater pit and a non-functional bypass recess. The non-functional features are on opposite sides of arrays of functional heater pits and bypass recesses. In like manner, a silicon substrate is formed to include non-functional grooves that are positioned to straddle topographical formations formed proximate to the non-functional heater pits and bypass recesses formed in the insulating layer. Therefore, the topographical formations do not cause the silicon substrate to stand off from the thick film insulating layer.
Another patent that addresses the process of connecting two substrates in forming an inkjet printhead is U.S. Pat. No. 5,388,326 to Beeson et al., which is assigned to the assignee of the present invention. The first substrate includes inkjet nozzles and an array of conductive traces that are formed in a preselected pattern. The second substrate is a “die layout” having a barrier material, an array of resistors formed in wells within the barrier material, and an array of channels formed in the barrier material. The positions of the resistors and the channels of the die layout match the positions of the inkjet nozzles and the conductive traces, respectively. By interlocking the conductive traces with the channels, the resistors are aligned with the inkjet nozzles. The first substrate and the barrier material are then laminated so as to bond the two together.
While the prior art techniques for bonding substrates of an inkjet printhead provide acceptable results, further improvements are desired in order to accommodate advancements with respect to print quality, printhead reliability, manufacturing throughput, and cost reduction. Moreover, a major source of printhead failures continues to be delamination of the orifice substrate from the actuator substrate. As previously noted, the substrate-to-substrate bonds tend to fail due to the long-term exposure to thermal cycling. U.S. Pat. No. 5,016,024 to Lam et al. provided a degree of improvement by forming heaters adjacent to the orifices on an orifice plate. An ink reservoir wall is connected in parallel with the orifice plate. An ink heating zone for a particular orifice is provided by a gap between the ink reservoir wall and the orifice plate. Electrical current through a heater rapidly heats the volume of ink in the adjacent ink heating zone, forming a bubble for projecting ink through the orifice. While the Lam et al. printhead reduces substrate-to-substrate alignment requirements, substrate delamination remains a concern, since the ink heating zone still includes the zone between the orifice plate and the bonded substrate. Another concern relates to the spatial relationship between a heater and an associated orifice. The thermal transfer is at a 90 degree angle to the direction of ink projection. This relationship may adversely affect either or both of the efficiency and the reliability of a firing operation. Furthermore, if the electronic circuitry for controlling ink firing i
Agilent Technologies
Barlow John
Mahoney Helen
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