U.S. patent application number 09/772410 was filed with the patent office on 2002-08-01 for fluid-jet printhead and method of fabricating a fluid-jet printhead.
Invention is credited to Kumpf, Susanne L., Miller, Richard Todd.
Application Number | 20020101484 09/772410 |
Document ID | / |
Family ID | 25094976 |
Filed Date | 2002-08-01 |
United States Patent
Application |
20020101484 |
Kind Code |
A1 |
Miller, Richard Todd ; et
al. |
August 1, 2002 |
Fluid-jet printhead and method of fabricating a fluid-jet
printhead
Abstract
A fluid-jet printhead has a substrate on which at least one
layer defining a fluid chamber for ejecting fluid is applied. The
printhead includes an elevation layer disposed on the substrate and
aligned with the fluid chamber. The printhead also includes a
resistive layer disposed between the elevation layer and the
substrate wherein the resistive layer has a smooth planer surface
interfacing with the resistive layer.
Inventors: |
Miller, Richard Todd;
(Corvallis, OR) ; Kumpf, Susanne L.; (Corvallis,
OR) |
Correspondence
Address: |
HEWLETT-PACKARD COMPANY
Intellectual Property Administration
P.O. Box 272400
Fort Collins
CO
80527-2400
US
|
Family ID: |
25094976 |
Appl. No.: |
09/772410 |
Filed: |
January 29, 2001 |
Current U.S.
Class: |
347/63 |
Current CPC
Class: |
B41J 2/1408 20130101;
B41J 2/14129 20130101; B41J 2202/03 20130101 |
Class at
Publication: |
347/63 |
International
Class: |
B41J 002/05 |
Claims
What is claimed is:
1. An fluid-jet printhead having a substrate, comprising: at least
one layer defining a fluid chamber for ejecting fluid; a elevation
layer disposed on the substrate and aligned with the fluid chamber;
and a resistive layer having a smooth planar surface between the
elevation layer and the fluid chamber.
2. The fluid-jet printhead of claim 1, further comprising a
conductive layer disposed between said resistive layer and said
substrate wherein a portion of said conductive layer is elevated by
said elevation layer whereby said resistive layer and the elevated
conductive layer are in direct contact.
3. The fluid-jet printhead of claim 1 wherein the elevation layer
is comprised of polysilicon.
4. The fluid-jet printhead of claim 1 wherein the elevation layer
is comprised of a dielectric material.
5. A fluid-jet cartridge, comprising: the fluid-jet printhead of
claim 1; a body for containing fluid; and a fluid delivery system
in fluidic connection with the fluid-jet printhead and the
body.
6. A recording device, comprising: the fluid-jet cartridge of claim
5; and a transport mechanism for moving a medium in a first and
second direction across the fluid-jet printhead of the fluid-jet
cartridge.
7. A fluid-jet printhead including a substrate, comprising: an
elevation layer disposed on the substrate; a dielectric layer
disposed on said elevated layer and substrate; a conductive layer
disposed on said dielectric layer wherein a portion of the
conductive layer is elevated with respect to the elevation layer;
an insulation layer disposed on and filling voids within the
elevated conductive layer; and a resistive layer disposed on the
elevated conductive layer to form a planar resistor.
8. The fluid-jet printhead of claim 7, further comprising a
passivation layer disposed on said planar resistor to form a planar
passivation layer.
9. The fluid-jet printhead of claim 8, further comprising a
cavitation layer disposed on said planar passivation layer to form
a planar cavitation layer.
10. The fluid-jet printhead of claim 9, further comprising: at
least one layer defining a fluid chamber for ejecting fluid, the
fluid chamber disposed on said planar cavitation layer.
11. The fluid-jet printhead of claim 10 wherein said planar
resistor has a planar surface interfacing with said fluid
chamber.
12. The fluid-jet printhead of claim 8 wherein electro-migration of
the patterned conductive layer onto the planar passivation layer is
minimized due to the resistive layer cladding the conductive layer
by contacting the elevated conductive layer.
13. The fluid-jet printhead of claim 7, wherein said planar
resistor is electrically attached to said patterned conductive
layer without vias thru a dielectric material using the cladding
surface contact.
14. A fluid-jet cartridge, comprising: the fluid-jet printhead of
claim 7; a body for containing fluid; and a fluid delivery system
in fluidic connection with the fluid-jet printhead and the
body.
15. A recording device, comprising: the fluid-jet cartridge of
claim 14; and a transport mechanism for moving a medium in a first
and second direction across the fluid-jet printhead of the
fluid-jet cartridge.
16. A method for creating a planar resistor on a substrate surface,
comprising the steps of: depositing a insulator layer on the
substrate surface; depositing an elevated layer on the insulator
surface; depositing a first dielectric layer on the insulator
layer; depositing a conductor layer on the first dielectric layer
wherein a portion of the conductor layer is elevated over the
elevated layer; patterning the conductor layer to define a resistor
area within a portion of the elevated conductor layer; etching the
patterned conductor layer to form a resistor area, having a
resistor length dimension; applying a second dielectric layer to
fill the resistor area and cover the patterned conductor layer;
planarizing the second dielectric layer to expose the elevated
conductor layer to form a planar resistor area; depositing a
resistive layer on the planar resistor area; patterning the
resistive layer to define a resistor width dimension; and etching
the resistive layer to form the resistor width.
17. A method for creating a printhead, comprising the steps of:
creating a planar resistor of claim 16; and applying at least one
layer defining a fluid chamber on the planar resistor.
18. The method of claim 17, further comprising the step of
depositing a planar passivation layer between the planar resistor
and the fluid chamber.
19. The method of claim 18, further comprising the step of
depositing a planar cavitation layer between the planar passivation
layer and the fluid chamber.
20. A resistor for a fluid-jet printhead made with the method of
claim 16.
21. A printhead made with the method of claim 17.
22. A method for using the planar resistor created by the method of
claim 16, comprising the steps of: combining at least one layer
defining a fluid chamber for ejecting fluid on the planar resistor;
supplying fluid into the fluid chamber; and wherein the planar
resistor is capable of being activated to thereby heat the fluid
and cause it to be ejected from the fluid chamber.
23. A method of using the printhead of claim 21, comprising the
steps of attaching the printhead to a fluid container having a
fluid conduction path that makes fluidic contact with the fluid
chamber.
24. The method using the printhead of claim 23, further comprising
the step of combining the attached printhead and fluid cartridge
with a printing mechanism.
25. A fluid-jet print cartridge, comprising: a body; a fluid
delivery system contained in the body; and a printhead mounted to
the body and in fluid communication with the fluid delivery system,
the printhead having a substrate including, at least one layer
defining a fluid chamber for ejecting fluid, a elevation layer
disposed on the substrate and aligned with the fluid chamber, and a
resistive layer having a smooth planar surface between the
elevation layer and the fluid chamber.
Description
THE FIELD OF THE INVENTION
[0001] This invention relates to the manufacturer of printheads
used in fluid-jet printers, and more specifically to a fluid-jet
printhead used in a fluid-jet print cartridge having improved
dimensional control and improved step coverage.
BACKGROUND OF THE INVENTION
[0002] One type of fluid-jet printing system uses a piezoelectric
transducer to produce a pressure pulse that expels a droplet of
fluid from a nozzle. A second type of fluid-jet printing system
uses thermal energy to produce a vapor bubble in a fluid-filled
chamber that expels a droplet of fluid. The second type is referred
to as thermal fluid-jet or bubble jet printing systems.
[0003] Conventional thermal fluid-jet printers include a print
cartridge in which small droplets of fluid are formed and ejected
towards a printing medium. Such print cartridges include fluid-jet
printheads with orifice structures having very small nozzles
through which the fluid droplets are ejected. Adjacent to the
nozzles inside the fluid-jet printhead are fluid chambers, where
fluid is stored prior to ejection. Fluid is delivered to fluid
chambers through fluid channels that are in fluid communication
with a fluid supply. The fluid supply may be, for example,
contained in a reservoir part of the print cartridge.
[0004] Ejection of a fluid droplet, such as ink, through a nozzle
may be accomplished by quickly heating a volume of fluid within the
adjacent fluid chamber. The rapid expansion of fluid vapor forces a
drop of fluid through the nozzle in the orifice structure. This
process is commonly known as "firing." The fluid in the chamber may
be heated with a transducer, such as a resistor, that is disposed
and aligned adjacent to the nozzle.
[0005] In conventional thermal fluid-jet printhead devices, such as
ink-jet cartridges, thin film resistors are used as heating
elements. In such thin film devices, the resistive heating material
is typically deposited on a thermally and electrically insulating
substrate. A conductive layer is then deposited over the resistive
material. The individual heater element (i.e., resistor) is
dimensionally defined by conductive trace patterns that are
lithographically formed through numerous steps including
conventionally masking, ultraviolet exposure, and etching
techniques on the conductive and resistive layers. More
specifically, the critical width dimension of an individual
resistor is controlled by a dry etch process. For example, an ion
assisted plasma etch process is used to etch portions of the
conductive and resistive layers not protected by a photoresist
mask. The width of the remaining conductive thin film stack (of
conductive and resistive layers) defines the final width of the
resistor. The resistive width is defined as the width of the
exposed resistive layer between the vertical walls of the
conductive layer. Conversely, the critical length dimension of an
individual resistor is controlled by a subsequent wet etch process.
A wet etch process is used to produce a resistor having sloped
walls on the conductive layer defining the resistor length. The
sloped walls of the conductive layer permit step coverage of later
fabricated layers.
[0006] As discussed above, conventional thermal fluid-jet printhead
devices require both dry etch and wet etch processes. The dry etch
process determines the width dimension of an individual resistor,
while the wet etch process defines both the length dimension and
the necessary sloped walls commencing from the individual resistor.
As is well known in the art, each process requires numerous steps,
thereby increasing both the time to manufacture a printhead device
and the cost of manufacturing a printhead device.
[0007] One or more passivation and cavitation layers are fabricated
in a stepped fashion over the conductive and resistive layers and
then selectively removed to create a via for electrical connection
of a second conductive layer to the conductive traces. The second
conductive layer is pattered to define a discrete conductive path
from each trace to an exposed bonding pad remote from the resistor.
The bonding pad facilitates connection with electrical contacts on
the print cartridge. Activation signals are provided from the
printer to the resistor via the electrical contacts.
[0008] Further, the wet etching process for defining the resistor
length suffers from uniformity issues and can be highly dependent
upon the chemistries used. The first conductive layer may be
vulnerable to corrosion through pinholes and cracks in the
passivation layers during subsequent wet etches.
[0009] The printhead substructure is overlaid with at least one
orifice layer. Preferably, the at least one orifice layer is etched
to define the shape of the desired firing fluid chamber within the
at least one orifice layer. The fluid chamber is situated above,
and aligned with, the resistor. The at least one orifice layer is
preferably formed with a polymer coating or optionally made of an
fluid barrier layer and an orifice plate. Other methods of forming
the orifice layer(s) are know to those skilled in the art.
[0010] In direct drive thermal fluid-jet printer designs, the thin
film device is selectively driven by electronics preferably
integrated within the thermal electric integrated circuit part of
the printhead substructure. The integrated circuit conducts
electrical signals directly from the printer microprocessor to the
resistor through conductive layers. The resistor increases in
temperature and creates super-heated fluid bubbles for ejection of
the fluid from the chamber through the nozzle. However,
conventional thermal fluid-jet printhead devices can suffer from
inconsistent and unreliable fluid drop sizes and inconsistent turn
on energy required to fire a fluid droplet, if the resistor
dimensions are not tightly controlled. Further, the stepped regions
within the fluid chamber can affect drop trajectory and device
reliability. The device reliability is affected by the bubble
collapsing after the drop ejection thereby wearing down the stepped
regions.
[0011] It is desirous to fabricate a fluid-jet printhead capable of
producing fluid droplets having consistent and reliable fluid drop
sizes and less susceptible to corrosion. In addition, it is
desirous to fabricate a fluid-jet printhead having a consistent
turn on energy (TOE) required to fire a fluid droplet, thereby
providing greater control of the size of the fluid drops.
SUMMARY OF THE INVENTION
[0012] A fluid-jet printhead has a substrate on which at least one
layer defining a fluid chamber for ejecting fluid is applied. The
printhead includes an elevation layer disposed on the substrate and
aligned with the fluid chamber. The printhead also includes a
resistive layer disposed between the elevation layer and the
substrate wherein the resistive layer has a smooth planer surface
interfacing with the resistive layer.
[0013] The present invention provides numerous advantages over
conventional thin film printheads. First, the present invention
provides a structure capable of Firing a fluid droplet in a
direction substantially perpendicular (normal or orthogonal) to a
plane defined by the formed resistive element and ejection surface
of the printhead. Second, the dimensions and planarity of the
resistive material layer are more precisely controlled, which
reduces the variation in the turn on energy required to fire a
fluid droplet. Third, the size of a fluid droplet is better
controlled due to less variation in resistor size. Fourth, the
corrosion resistance and electro-migration resistance of the
conductive layers are improved inherently by the design.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is an enlarged, cross-sectional, partial view
illustrating an exemplary conventional thin film printhead
substructure.
[0015] FIG. 2 is a flow chart of an exemplary process used to
implement the conventional thin film printhead structure.
[0016] FIG. 3A is a cross-sectional, partial view illustrating a
first embodiment of the invention's thin film printhead structure
showing the resistor length dimension.
[0017] FIG. 3B is a cross-sectional, partial view illustrating the
first embodiment of the invention's thin film printhead structure
showing the resistor width dimension.
[0018] FIG. 3C is a cross-sectional, partial view illustrating a
second embodiment of the invention's thin film printhead structure
showing the resistor length dimension.
[0019] FIG. 4 is a flowchart of an exemplary process and optional
steps used to implement several embodiments of the invention's
thin-film printhead structure.
[0020] FIG. 5 is a perspective view of a printhead fabricated with
the invention.
[0021] FIG. 6 is an exemplary print cartridge that integrates and
uses the printhead of FIG. 5.
[0022] FIG. 7 is an exemplary recoding device, a printer, which
uses the print cartridge of FIG. 6.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] In the following detailed description of the preferred
embodiments, reference is made to the accompanying drawings that
form a part hereof, and in which is shown by way of illustration
specific embodiments in which the invention may be practiced. It is
to be understood that other embodiments may be utilized and
structural or logical changes may be made without departing from
the scope of the present invention. The following detailed
description, therefore, is not to be taken in a limiting sense, and
the scope of the present invention is defined only by the appended
claims.
[0024] The present invention is a fluid-jet printhead, a method of
fabricating the fluid-jet printhead, and use of a fluid-jet
printhead. The present invention provides numerous advantages over
the conventional fluid-jet or ink-jet printheads. First, the
present invention provides a structure capable of firing a fluid
droplet in a direction substantially perpendicular (normal or
orthogonal) to a plane defined by the formed resistive element and
ejection surface of the printhead. Second, the dimensions and
planarity of the resistive layer are more precisely controlled,
which reduces the variation in the turn on energy required to fire
a fluid droplet. Third, the size of a fluid droplet is better
controlled due to less variation in resistor size. Fourth, the
design inherently provides for improved corrosion resistance and
improved electro-migration resistance of the conductive layers.
[0025] FIG. 1 is an enlarged, cross-sectional, partial view
illustrating a conventional thin film printhead 190. The
thicknesses of the individual thin film layers are not drawn to
scale and are drawn for illustrative purposes only. As shown in
FIG. 1, thin film printhead 190 has affixed to it a fluid barrier
layer 70, which is shaped along with orifice plate 80 to define
fluid chamber 100 to create an orifice layer 82 (see FIG. 5).
Optionally, the orifice layer 82 and fluid barrier layers 70 may be
made of one or more layers of polymer material. Additionally, other
methods of forming a fluid chamber and orifice opening are known to
those skilled in the art and can be substituted without departing
from the scope and spirit of the invention. A fluid droplet within
a fluid chamber 100 is rapidly heated and fired through nozzle 90
when the printhead is used.
[0026] Thin film printhead substructure 190 includes a substrate
10, an insulating insulator layer 20, a resistive layer 30, a
conductive layer 40 (including conductors 42A and 42B), a
passivation layer 50, a cavitation layer 60, and a fluid barrier
structure 70 defining fluid chamber 100 with orifice plate 80.
[0027] As diagrammed in FIG. 2, an insulator layer 20 (also
referred to as an insulative dielectric) is applied to substrate 10
in step 110 preferably by deposition. Silicon dioxides are examples
of materials that are used to fabricate insulator layer 20. In one
embodiment, insulator layer 20 is formed from
tetraethylorthosilicate (TEOS) oxide having a 14,000 Angstrom
thickness. In an alternative embodiment, insulative layer 20 is
fabricated from silicon dioxide. In another alternative embodiment,
it is formed of silicon nitride.
[0028] There are numerous ways to fabricate insulation layer 20,
such as through a plasma enhanced chemical vapor deposition (PECVD)
or a thermal oxide process. Insulator layer 20 serves as both a
thermal and electrical insulator for the resistive circuit that
will be built on its surface. The thickness of the insulator layer
can be adjusted to vary the heat transferring or isolating
capabilities of the layer depending on a desired turn-on energy and
firing frequency.
[0029] Next in step 112, the resistive layer 30 is applied to
uniformly cover the surface of insulation layer 20. Preferably, the
resistive layer is tantalum silicon nitride or tungsten silicon
nitride of a 1200 Angstrom thickness although tantalum aluminum can
also be used. Next in step 114, conductive layer 40 is applied over
the surface of resistive layer 30. In conventional structures,
conductive layer 40 is formed with preferably aluminum copper or
alternatively with tantalum aluminum or aluminum gold.
Additionally, a metal used to form conductive layer 40 may also be
doped or combined with materials such as copper, gold, or silicon
or combinations thereof. A preferable thickness for the conductive
layer 40 is 5000 Angstroms. Resistive layer 30 and conductive layer
40 can be fabricated though various techniques, such as through a
physical vapor deposition (PVD).
[0030] In step 116, the conductive layer 40 is patterned with a
photoresist mask to define the resistor's width dimension. Then in
step 118, conductive layer 40 is etched to define conductors 42A
and 42B. Fabrication of conductors 42A and 42B define the critical
length and width dimensions of the active region of resistive layer
30. More specifically, the critical width dimension of the active
region of resistive layer 30 is controlled by a dry etch process.
For example, an ion assisted plasma etch process is used to
vertically etch portions of conductive layer 40 and resistive layer
30 which are not protected by a photoresist mask, thereby defining
a maximum resistor width as being equal to the width of conductors
42A and 42B. In step 120, the conductor layer is patterned with
photoresist to define the resistor's length dimension defined as
the distance between conductors 42A and 42B. In step 122, the
critical length dimension of the active region of resistive layer
30 is controlled by a wet etch process. A wet etch process is used
since it is desirable to produce conductors 42A and 42B having
sloped walls, thereby defining the resistor length. The wet etch
process used is chosen such that the etch is highly reactive to the
conductive layer but minimally reactive to the resistive layer.
Sloped walls of conductive layer 42A enables step coverage of later
fabricated layers such as a passivation layer that is applied in
step 124.
[0031] Conductors 42A and 42B serve as the conductive traces that
deliver a signal to the active region of resistive layer 30 for
firing a fluid droplet. Thus, the conductive trace or path for an
electrical signal impulse that heats the active region of resistive
layer 30 is from conductor 42A through the active region of
resistive layer 30 to conductor 42B.
[0032] In step 124, passivation layer 50 is then applied uniformly
over the device. There are numerous passivation layer designs
incorporating various compositions. In one conventional embodiment,
two passivation layers, rather than a single passivation layer are
applied. In the conventional printhead example of FIG. 1, the two
passivation layers comprise a layer of silicon nitride followed by
a layer of silicon carbide. More specifically, the silicon nitride
layer is deposited on conductive layer 40 and resistive layer 30
and then a silicon carbide is preferably deposited.
[0033] After passivation layer 50 is deposited, cavitation barrier
60 is applied. In the conventional example, the cavitation barrier
comprises tantalum. A sputtering process, such as a physical vapor
deposition (PVD) or other techniques known in the art deposits the
tantalum. Fluid barrier layer 70 and orifice layer 80 are then
applied to the structure, thereby defining fluid chamber 100. In
one embodiment, fluid barrier layer 70 is fabricated from a
photosensitive polymer and orifice layer 80 is fabricated from
plated metal or organic polymers. Fluid chamber 100 is shown as a
substantially rectangular or square configuration in FIG. 1.
However, it is understood that fluid chamber 100 may include other
geometric configurations without varying from the present
invention.
[0034] Thin film printhead 190, shown in FIG. 1, illustrates one
example of a typical conventional printhead. However, printhead 190
requires both a wet and a dry etch process in order to define the
functional length and width of the active region of resistive layer
30, as chamber as to create the sloped walls of conductive layer 40
necessary for adequate step coverage of the later fabricated
layers, such as the passivation 50 and cavitation 60 layers.
[0035] FIG. 3A is a cross-sectional, partial view illustrating the
layers for a fluid-jet printhead 200 incorporating the present
invention. The thicknesses of the individual thin film layers are
not drawn to scale and are drawn for illustrative purposes only.
FIG. 5 is an enlarged, plan view illustrating a fluid-jet printhead
200 incorporating the present invention. As shown in FIG. 4, in
step 110, insulative layer 20 is fabricated by being deposited
through any known means, such as a plasma enhanced chemical vapor
deposition (PECVD), a low pressure chemical vapor deposition
(LPCVD), an atmosphere pressure chemical vapor deposition (APCVD)
or a thermal oxide process onto substrate 10. Preferably, insulator
layer 20 is formed with field oxide or optionally from
tetraethylorthosilicate (TEOS) oxide. In one alternative
embodiment, insulative layer 20 is fabricated from silicon dioxide.
In another embodiment, it is formed of silicon nitride.
[0036] In step 126, a dielectric material 22 is deposited onto the
insulator layer. Preferably, the dielectric material 22 is formed
of phosphosilicate glass (PSG). In an alternative embodiment,
dielectric material 22 is formed from silicon nitride or TEOS. In
an alternative embodiment dielectric material 22 is fabricated from
silicon dioxide.
[0037] Alternatively, before step 126, a polysilicon layer 12 is
deposited on the insulator area in step 140. The purpose of the
polysilicon layer 12 is to provide a step in height to elevate the
subsequent conductive layer 40 in the area of the resistor to allow
the conductive layer 40 to make direct contact with the resistive
layer without the need for vias. In step 142, the polysilicon layer
12 patterned by an appropriate mask. In step 144, the polysilicon
layer 12 is etched and any photomask remaining striped to leave an
area of polysilicon between the substrate and the subsequent
formation of a fluid chamber.
[0038] Alternatively as shown in FIG. 3C, after step 126, in step
146 a capping layer 34 for the conductive layer is deposited on the
dielectric layer. In step 148, the capping layer 34 is patterned
preferably by photoresist. In step 150, the capping layer 34 is
etched to define an area between the resistor and the substrate.
The capping layer 34 is preferably formed of dielectric material,
such as TEOS or PSG, silicon nitride, or silicon dioxide, to name a
few. The capping layer 34 allows for maintaining the thin-film
interfaces of the conventional art printhead shown in FIG. 1. By
maintaining the conventional thin-film interfaces, potential
problems such as junction spiking and film interface reliability
issues are reduced. Optionally, the capping layer 34 can be used in
place of the polysilicon layer 12 to provide the step in height
elevation of a subsequently applied conductive layer 40.
[0039] In step 114, conductive layer 40 is then fabricated on top
of previously deposited layers. In one embodiment, conductive layer
40 is a layer formed through a physical vapor deposition (PVD) from
aluminum and copper. More specifically, in one embodiment,
conductive layer 40 includes up to approximately 2% percent copper
in aluminum, preferably approximately 0.5 percent copper in
aluminum. Utilizing a small percent of copper in aluminum limits
electro-migration. In another preferred embodiment, conductive
layer 40 is formed from titanium, copper, or tungsten.
[0040] In step 132, a photoimagable masking material such as a
photoresist is deposited on portions of conductive layer 40,
thereby exposing other portions of conductive layer 40. These
masking and patterning steps are used to define the resistor length
and conductive traces 42A and 42B that is determined by the mask
detail.
[0041] In step 154, the conductor layer is dry etched to create
conductive traces 42A and 42B and openings between the traces that
define the resistor length.
[0042] In step 156, a second insulating layer 44, such as TEOS or
spin-on-glass (SOG) is applied on the conductive layer 40, but
preferably SOG. The second insulating layer 44 is used to fill
between the conductor traces as well as the resistor length
gap.
[0043] In step 134, the second insulating layer 44 is planarized
preferably by using chemical mechanical polishing (CMP) to expose
the elevated surface of conductive layer 40. In an alternative
embodiment, the surface second insulating layer 44 is planarized
through use of a resist-etch-back (REB) process. By using the
optional polysilicon layer 12 to elevate conductive layer 40, the
amount of conductive layer 40 exposed during the planarization of
the Second insulating layer 44 is minimized. Further, only the
segments of conductive layer 40 necessary for contact with the
subsequently applied resistive layer 30 are exposed to the
planarization process if an additional cap is used.
[0044] Optionally, in step 152 the second insulating layer 44 is
baked out to remove moisture that might have an adverse affect on
the subsequently applied resistive layer 30.
[0045] Next in step 112, the resistive layer 30 is applied to
uniformly cover the surface of second insulating layer 44 and the
desired resistor area. Preferably, the resistive layer 30 is
tantalum aluminum although tungsten silicon nitride or tantalum
silicon nitride can also be used.
[0046] In step 116, a photoimagable masking material such as a
photoresist mask is deposited on resistive layer 30 to define the
resistor area, thereby exposing portions of resistive layer 30 for
removal.
[0047] In step 136, the exposed portion of resistive layer 30 is
removed through either a dry etch process several of which are
known to those skilled in the art such as described in step 118 of
FIG. 2 or a wet etch process that is reactive to the resistive
layer 30. This etching step 136 defines and forms the resistor
width. The photoresist mask is then removed, thereby exposing the
resistor element. The passivation 50, cavitation 60, barrier 70 and
orifice 80 layers are then applied as described for the
conventional printhead.
[0048] Conductors 42A and 42B provide an electrical connection/path
between external circuitry and the formed resistive element.
Therefore, conductors 42A and 42B transmit energy to the formed
resistor element to create heat capable of firing a fluid droplet
positioned on a top surface of the formed resistive element in a
direction perpendicular to the top surface of the formed resistive
element.
[0049] FIG. 3B is a cross-sectional, partial view illustrating the
first embodiment of the invention's thin film printhead structure
showing the resistor width dimension with respect to the thin-film
layers applied to substrate 10 using the process steps of FIG.
4.
[0050] As shown in FIGS. 3A and 3B, conductive traces 42A and 42B
define a resistor element between conductive traces 42A and 42B.
Preferably, the formed resistive element has a length L equal to
the distance between conductors 42A and 42B. Preferably, the formed
resistive element has a width W as shown in FIG. 3B equal to the
width of conductive traces 42A and 42B. However, it is understood
that the formed resistive element may be fabricated having any one
of a variety of configurations, shapes, or sizes, such as a thin
trace or a wide trace of conductive traces 42A and 42B. The only
requirement of the formed resistive element is that it contacts
conductive traces 42A and 42B to ensure a proper electrical
connection. While the actual length L of the formed resistive
element is equal to or greater than the distance between the edges
of conductor's 42A and 42B, the active portion of the formed
resistive element which conducts heat to a droplet of fluid
positioned above the formed resistive element corresponds to the
distance between the edges of conductors 42A and 42B.
[0051] FIG. 3C is a cross-sectional, partial view illustrating a
second embodiment of the invention in which the capping layer 34 is
used to elevate the conductor layer 30 instead of the polysilicon
layer 12 of FIG. 3A.
[0052] In FIG. 5, each orifice nozzle 90 is in fluid communication
with respective fluid chambers 100 (shown enlarged in FIG. 2)
defined in printhead 200. Each fluid chamber 100 is constructed in
orifice structure 82 adjacent to thin film structure 32 that
preferably includes a transistor coupled to the resistive
component. The resistive component is selectively driven (heated)
with sufficient electrical current to instantly vaporize some of
the fluid in fluid chamber 100, thereby forcing a fluid droplet
through nozzle 90.
[0053] Exemplary thermal fluid-jet print cartridge 220 is
illustrated in FIG. 6. The fluid-jet printhead device of the
present invention is a portion of thermal fluid-jet print cartridge
220. Thermal fluid-jet print cartridge 220 includes body 218,
flexible circuit 212 having circuit pads 214, and printhead 200
having orifice nozzles 90. Fluid is provided to fluid-jet print
cartridge 220 by the use of body 218 configured in fluid connection
using a fluid delivery system 216, shown as a sponge (preferably
closed-cell foam), within fluid-jet print cartridge 220 or by means
of a remote storage source in fluid connection with fluid-jet print
cartridge 220. While flexible circuit 212 is shown in FIG. 6, it is
understood that other electrical circuits known in the art may be
utilized in place of flexible circuit 212 without deviating from
the present invention. It is only necessary that electrical
contacts 214 be in electrical connection with the circuitry of
fluid-jet print cartridge 220. Printhead 200 having orifice nozzles
90 is attached to the body 218 and controlled for ejection of fluid
droplets, typically by a printer but other recording devices such
as plotters, and fax machines, to name a couple, can be used.
Thermal fluid-jet print cartridge 220 includes orifice nozzles 90
through which fluid is expelled in a controlled pattern during
printing. Conductive drivelines for each resistor component are
carried upon flexible circuit 212 mounted to the exterior of print
cartridge body 218. Circuit contact pads 214 (shown enlarged in
FIG. 6 for illustration) at the ends of the resistor drive lines
engage similar pads carried on a matching circuit attached to a
printer (not shown). A signal for firing the transistor is
generated by a microprocessor and associated drivers on the printer
that apply the signal to the drivelines.
[0054] FIG. 7 is an exemplary recording device, a printer 240,
which uses the exemplary print cartridge 220 of FIG. 6. The print
cartridge 220 is placed in a carriage mechanism 254 to transport
the print cartridge 220 across a first direction of medium 256. A
medium feed mechanism 252 transports the medium 256 in a second
direction across printhead 220. An optional medium tray 250 is used
to hold multiple sets of medium 256. After the medium is recorded
by print cartridge 220 using printhead 200 to eject fluid onto
medium 256, the medium 256 is optionally placed on media tray
258.
[0055] In operation, a droplet of fluid is positioned within fluid
chamber 100. Electrical current is supplied to the formed resistive
element via conductors 42A and 42B such that the formed resistive
element rapidly generates energy in the form of heat. The heat from
the formed resistive element is transferred to a droplet of fluid
within fluid chamber 100 until the droplet of fluid is "fired"
through nozzle 90. This process is repeated several times in order
to produce a desired result. During this process, a single dye may
be used, producing a single color design, or multiple dyes may be
used, producing a multicolor design.
[0056] The present invention provides numerous advantages over the
conventional printhead. First, the resistor length of the present
invention is defined by the placement of dielectric material 44
that is fabricated during a combined photo process and dry etching
process. The accuracy of the present process is considerably more
controllable than conventional wet etch processes. More
particularly, the present process is more controllable in critical
dimension control of the resistor than a conventional process. With
the current generation of low drop weight, high-resolution
printheads, resistor lengths have decreased from approximately 35
micrometers to less than approximately 10 micrometers. Thus,
resistors size variations can significantly affect the performance
of a printhead. Resistor size variations translate into drop weight
and turn on energy variations across the resistor on a printhead.
Thus, the improved length control of the resistive material layer
yields a more consistent resistor size and resistance, which
thereby improves the consistency in the drop weight of a fluid
droplet and the turn on energy necessary to fire a fluid
droplet.
[0057] Second, the resistor structure of the present invention
includes a completely flat top surface and does not have the step
contour associated with conventional fabrication designs. A flat
structure provides consistent bubble nucleation, better scavenging
of the fluid chamber, and a flatter topology, thereby improving the
adhesion and lamination of the barrier structure to the thin
film.
[0058] Third, by introducing heat into the floor of the entire
fluid chamber, fluid droplet ejection efficiency is improved.
Additionally, the passivation and cavitation layers have reduced
stress points during thermal cycling.
[0059] Fourth, due to the encapsulation and cladding of conductive
layer 40 by resistive layer 30, electro-migration of the conductive
layer 40 is minimized in the resistor area as well as increasing
resistance to corrosion during thin-film processing.
[0060] Further, by attaching the printhead 200 to the fluid
cartridge 220, the combination forms a convenient module that can
be packaged for sale.
[0061] Although specific embodiments have been illustrated and
described herein for purposes of description of the preferred
embodiment, it will be appreciated by those of ordinary skill in
the art that a wide variety of alternate and/or equivalent
implementations calculated to achieve the same purposes may be
substituted for the specific embodiments shown and described
without departing from the scope of the present invention. Those
with skill in the chemical, mechanical, electromechanical,
electrical, and computer arts will readily appreciate that the
present invention may be implemented in a very wide variety of
embodiments. This application is intended to cover any adaptations
or variations of the preferred embodiments discussed herein.
Therefore, it is manifestly intended that this invention be limited
only by the claims and the equivalents thereof.
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