Printing structure with insulator layer

Details Printing structure with insulator layer Printing structure with insulator layer

2000-09-05

2002-06-04

Barlow, John (Department: 2853)

Incremental printing of symbolic information

Ink jet

Ejector mechanism

C347S065000

Reexamination Certificate

active

06398348

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to inkjet printers and, more particularly, to a monolithic printhead for an inkjet printer.
BACKGROUND
The various fully integrated thermal inkjet printheads described in the above-identified applications by Naoto Kawamura et al. include thin film layers containing heater resistors, conductors, and other layers over a silicon substrate. The backside of the substrate is etched completely through (forming a trench), and holes are formed through the thin film layers to allow ink to flow from the backside of the substrate, through the substrate, and into vaporization chambers formed on the top surface of the substrate. Energizing a heater resistor vaporizes a portion of the ink within a vaporization chamber, creating a bubble, which causes a droplet of ink to be ejected out of an associated nozzle in an orifice member formed over the thin film layers. Multiple embodiments were shown in the previous applications.
FIGS. 1-3
herein are reproduced from the previous applications to place into context the present improvement over the printheads disclosed in the previous application.
FIG. 1
is a perspective view of one type of inkjet print cartridge
10
which may incorporate the printhead structures described herein. The print cartridge
10
of
FIG. 1
is the type that contains a substantial quantity of ink within its body
12
, but another suitable print cartridge may be the type that receives ink from an external ink supply either mounted on the printhead or connected to the printhead via a tube.
The ink is supplied to a printhead
14
. Printhead
14
channels the ink into ink ejection chambers, each chamber containing an ink ejection element. Electrical signals are provided to contacts
16
to individually energize the ink ejection elements to eject a droplet of ink through an associated nozzle
18
. The structure and operation of conventional print cartridges are very well known.
FIG. 2
is a cross-sectional view of a portion of the printhead of
FIG. 1
taken along line
2
—
2
in FIG.
1
. Although a printhead may have
300
or more nozzles and associated ink ejection chambers, detail of only a single ink ejection chamber need be described in order to understand the invention. It should also be understood by those skilled in the art that many printheads are formed on a single silicon wafer and then separated from one another using conventional techniques.
In
FIG. 2
, a silicon substrate
20
has formed on it various thin film layers
22
. The thin film layers
22
include a resistive layer for forming resistors
24
. Other thin film layers perform various functions, such as providing electrical insulation from the substrate
20
, providing a thermally conductive path from the heater resistor elements to the substrate
20
, and providing electrical conductors to the resistor elements. One electrical conductor
25
is shown leading to one end of a resistor
24
. A similar conductor leads to the other end of the resistor
24
. In an actual embodiment, the resistors and conductors in a chamber would be obscured by overlying layers.
Ink feed holes
26
are formed completely through the thin film layers
22
.
An orifice layer
28
is deposited over the surface of the thin film layers
22
and developed to form ink ejection chambers
30
, one chamber per resistor
24
. A manifold
32
is also formed in the orifice layer
28
for providing a common ink channel for a row of ink ejection chambers
30
. The inside edge of the manifold
32
is shown by a dashed line
33
. Nozzles
34
may be formed by laser ablation using a mask and conventional photolithography techniques. Chemical etching may also be used to form the orifice layer.
The silicon substrate
20
is etched to form a trench
36
extending along the length of the row of ink feed holes
26
so that ink
38
from an ink reservoir may enter the ink feed holes
26
for supplying ink to the ink ejection chambers
30
.
In one embodiment, each printhead is approximately one-half inch long and contains two offset rows of nozzles, each row containing 150 nozzles for a total of
300
nozzles per printhead. The printhead can thus print at a single pass resolution of 600 dots per inch (dpi) along the direction of the nozzle rows or print at a greater resolution in multiple passes. Greater resolutions (e.g., 1200 dpi) may also be printed along the scan direction of the printhead.
In operation, an electrical signal is provided to heater resistor
24
, which vaporizes a portion of the ink to form a bubble within an ink ejection chamber
30
. The bubble propels an ink droplet through an associated nozzle
34
onto a medium. The ink ejection chamber is then refilled by capillary action.
FIG. 3
is a cross-sectional perspective view along line
2
—
2
in
FIG. 1
illustrating a single ink ejection chamber
40
in another embodiment of a monolithic printhead described in the prior applications.
In
FIG. 3
, a silicon substrate
50
has formed on it a plurality of thin film layers
52
, including a resistive layer and an AlCu layer that are etched to form the heater resistors
42
. AlCu conductors
43
are shown leading to the resistors
42
.
Ink feed holes
47
are formed through the thin film layers
52
to extend to the surface of the silicon substrate
50
. An orifice layer
54
is then formed over the thin film layers
52
to define ink ejection chambers
40
and nozzles
44
. The silicon substrate
50
is etched to form a trench
56
extending the length of the row of ink ejection chambers. The trench
56
may be formed prior to the orifice layer. Ink
58
from an ink reservoir is shown flowing into trench
56
, through ink feed hole
47
, and into chamber
40
.
The applications incorporated by reference describe in detail the manufacturing processes for forming the embodiments of
FIGS. 2 and 3
and need not be repeated herein. Such processes may use conventional techniques for forming printhead thin film layers.
The thin film layers formed over the substrate in
FIGS. 2 and 3
are only on the order of
4
microns thick and, thus, when the underlying silicon is etched away, the thin film (or membrane) is prone to buckling when the trench widths are greater than about 70 microns. Such buckling of unsupported membrane widths greater than 70 microns cause ink drop trajectory errors. Cracks may also be a problem within the membrane shelf and are catastrophic, leading to resistor “opens” and gross topology changes. These are serious issues needed to be resolved to increase the longevity of these devices.
An additional issue regarding
FIGS. 2 and 3
is that there is not satisfactory heat transfer between the heater resistors and the bulk silicon via the membrane at high firing frequencies. This leads to overheating of the membrane. Such overheating of the membrane, and particularly the membrane backside, may heat the ink contacting the backside of the membrane to the point where the ink is vaporized, and bubbles are formed in unwanted areas. These bubbles can cause vapor lock, preventing refill of the firing chambers. One attempted solution was to deposit a layer of metal on the backside of the membrane, but this approach has various drawbacks and is thus not a viable long-term solution.
Accordingly, what is needed is a technique for accurately controlling the width of the backside substrate etching to limit the width of any unsupported membrane to a desired width. It would be further desirable to avoid unsupported membrane widths altogether. What is also desirable is a technique for increasing the heat transfer between the heater resistors and the bulk substrate to prevent the above-described problems from occurring.
SUMMARY
We have overcome the above-described problems by using a silicon-on-insulator (SOI) wafer as the starting substrate. In one embodiment, the substrate consists of a relatively thick layer of silicon (e.g., 660 microns) on which is formed a layer of thermal oxide approximately 5,000 Angstroms, on top of which is a thin layer of silicon (e.g., 10 microns). Thin film layers, incl

Affiliated with

Also associated with

Rating

Printing structure with insulator layer does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Printing structure with insulator layer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Printing structure with insulator layer will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2901451