Patent Application
20050253901
The disclosure relates to micro-fluid ejection devices and in particular to improved protective layers and methods for making the improved protective layers for heater resistor used in micro-fluid ejection devices.
In the production of thermal micro-fluid ejection devices such as ink jet printheads, a cavitation layer is typically provided as an ink contact layer for a heater resistor. The cavitation layer prevents damage to the underlying dielectric and resistive layers during ink ejection. Between the cavitation layer and heater resistor there are typically one or more layers of a passivation material to reduce ink corrosion of the heater resistor. As ink is heated in an ink chamber by the heater resistor, a bubble forms and forces ink out of the ink chamber and through an ink ejection orifice. After the ink is ejected, the bubble collapses causing mechanical shock to the thin metal layers comprising the ink ejection device. In a typical printhead, tantalum (Ta) is used as a cavitation layer. The Ta layer is deposited on a dielectric layer such as silicon carbide (SiC) or a composite layer of SiC and silicon nitride (SiN). In the composite layer, SiC is adjacent to the Ta layer.
One disadvantage of the multilayer thin film heater construction is that the cavitation and protective layers are less heat conductive than the underlying resistive layer. Accordingly, such construction increases the energy requirements for a printhead constructed using such protective layers. Increased energy input to the heater resistors not only increases the overall printhead temperature, but also reduces the frequency of drop ejection thereby decreasing the printing speed of the printer. Hence, there continues to be a need for printheads having lower energy consumption and methods for producing such printheads without affecting the life of the printheads.
With regard to the above, one embodiment of the disclosure provides a heater chip for a micro-fluid ejection device having enhanced adhesion between a resistor layer and a protective layer. The heater chip includes a semiconductor substrate, a resistive layer deposited on the substrate, and a substantially non-conductive protective layer on the resistive layer. The protective layer is selected from a titanium-doped diamond-like carbon thin film layer, and a single thin film diamond-like carbon layer having at least a first surface comprised of more than about 30 atom % titanium.
In another embodiment, the disclosure provides a method for making a heater chip for a micro-fluid ejection device, wherein the heater chip exhibits enhanced adhesion between a resistive layer and a protective layer therefor. The method includes the steps of providing a semiconductor substrate, and depositing an insulating layer on the substrate. The insulating layer having a thickness ranging from about 8,000 to about 30,000 Angstroms. A resistive layer is deposited on the insulating layer. The resistive layer has a thickness ranging from about 500 to about 1,500 Angstroms and is selected from the group consisting of TaAl, Ta2N, TaAl(O,N), TaAlSi, TaSiC, Ti(N,O), WSi(O,N), TaAlN, and TaAl/Ta. A first metal layer is deposited on the resistive layer and is etched to define ground and address electrodes and a heater resistor therebetween. A substantially non-conductive protective layer is deposited on the heater resistor. The protective layer has a thickness ranging from about 1000 to about 5000 Angstroms and is selected from a titanium-doped diamond-like carbon thin film layer, and a single thin film diamond-like carbon layer having at least a first surface comprised of more than about 30 atom % titanium.
In yet another embodiment, the disclosure provides an ink jet printhead for an ink jet printer having an improved heater chip. The printhead includes a nozzle plate attached to a heater chip. The heater chip is provided by a semiconductor substrate, a resistive layer deposited on the substrate, and a substantially non-conductive protective layer on the resistive layer. The protective layer is selected from a titanium-doped diamond-like carbon thin film layer, and a single thin film diamond-like carbon layer having at least a first surface comprised of more than about 30 atom % titanium.
An advantage of the embodiments disclosed herein is the provision of enhanced adhesion between a diamond-like carbon protective layer and a heater resistor layer thereby prolonging the life of a micro-fluid ejection device made with the heater chip. Another advantage is that a total thickness of protection layers on the heater resistor may be reduced thereby reducing power requirements for ejecting fluid from the micro-fluid ejecting device. A further advantage is a reduction in the process steps required to make a micro-fluid ejection device thereby reducing manufacturing costs therefor.
Further advantages of the invention will become apparent by reference to the detailed description of preferred embodiments when considered in conjunction with the following drawings, in which like reference numbers denote like elements throughout the several views, and wherein:
Embodiments as described herein are particularly suitable for micro-fluid ejection devices such as are used in ink jet printers. An ink jet printer 10 is illustrated in
An exemplary ink jet printer cartridge 12 is illustrated in
A cross-sectional view of a portion of a micro-fluid ejection assembly 14 is illustrated in
In the prior art device 14 shown in
Overlying the conductive layer 44 is another insulating layer or dielectric layer 52 typically composed of epoxy photoresist materials, polyimide materials, silicon nitride, silicon carbide, silicon dioxide, spun-on-glass (SOG), laminated polymer and the like. The insulating layer 52 provides insulation between a second metal conductive layer 54 and the underlying first metal conductive layer 44.
In some prior art printheads, a thick polymer film layer is deposited on the second metal conductive layer 54 to define an ink chamber and ink channel therein. In other ink jet printheads, the thick film layer may be eliminated and the ink channel 36 and ink chamber 38 are formed integral with the nozzle plate 18 in the nozzle plate material as shown in
One disadvantage of the prior art printhead 14 described above is that multiple protective layers 46, 48, and 50 are deposited and etched to provide suitable protection for the heater resistor 34 from erosion and corrosion. Also, difficulties have been encountered when using tantalum as a cavitation layer 50 with underlying layers 46 and 48 other than silicon carbide and silicon nitride. Tantalum adheres well to silicon carbide, however, when the passivation layers 46/48 are comprised of other materials, such as diamond-like carbon (DLC), adhesion of the tantalum layer 50 is not as reliable. Furthermore, costly capital equipment is required to separately deposit the tantalum layer 50 on the chip 32. Finally, multiple layers having suitable thicknesses required to protect the heater resistor 34 also tend to increase the power requirements required to eject a drop of fluid from the nozzle holes 20.
The embodiments described herein improve upon the prior micro-fluid ejection device design by providing an improved protection layer that may be used with or without a separate cavitation layer. Features of the preferred embodiments will now be described with reference to
With reference to
Next the first metal layer 44 is deposited on the resistive layer 40 and is etched to define a heater resistor 34 and conductors 44A and 44B as described above. As before, the first metal layer 44 may be selected from conductive metals, including, but not limited to, gold, aluminum, silver, copper, and the like.
A protective layer 64 is then deposited over a portion of the resistive layer 40 defining the heater resistor 34. The protective layer 64 is preferably selected from a titanium-doped diamond-like carbon thin film layer, and a single thin film diamond-like carbon layer having at least a first surface comprised of more than about 30 atom % titanium. The protective layer 64 preferably has a thickness ranging from about 1000 to about 8000 Angstroms, more preferably about 5000 Angstroms.
In an alternative embodiment, shown in
In other alternative embodiments, shown in
In each of the embodiments described above with reference to
Alternatively, the DLC layer 64, 78 may have a step-wise increase in titanium from a first surface adjacent the heater resistor 34 to a second opposing surface. Regardless of the particular Ti-doped DLC material selected for layer 64, 78, it is preferred that there be sufficient titanium in the DLC layer 64, 78 to enhance adhesion between the DLC layer 64, 78 and the resistive layer 40, and optionally between the DLC layer 64, 78 and a separate cavitation layer 66, 84 of titanium or tantalum when used.
Without desiring to be bound by theory, it is believed a Ti-doped DLC layer 64, 78 as described above significantly improves adhesion between adjacent layers as compared to an undoped DLC layer or a SiN/SiC layer. For example, the adhesion between a cavitation layer 50 (
A method for making a heater chip 62, 68, 72, 80 for a micro-fluid ejection device 60, 70, 74, or 82 according to the embodiments disclosed herein is illustrated in
Next, the resistive layer 40 is deposited by conventional sputtering technology on the insulating layer 42 as shown in
The first metal conductive layer 44 is then deposited on the resistive layer 40 as shown in
In order to protect the heater resistor 34 from corrosion and erosion, the Ti-doped DLC layer 64 as described above is deposited on the heater resistor 34 as shown in
Second dielectric layer or insulating layer 52 is then deposited on exposed portions of the first metal layer 44 and preferably slightly overlaps the Ti-doped DLC layer and optional cavitation layer 66 as shown in
In order to provide a Ti-doped DLC layer 64 as described above, a plasma enhanced chemical vapor deposition (PE-CVD) reactor is supplied with a precursor gas providing a source of carbon such as methane, ethane, or other simple hydrocarbon gas and from a vapor derived from an organometallic compound. Such compounds include, but are not limited to, bis(cyclopentadienyl)bis(dimethyl-amino)titanium, tert-Butyltris(dimethylamino)titanium, tetrakis(diethylamino)titanium, tetrakis(dimethylamino)titanium, tetrakis(ethylmethylamino)titanium, tetrakis(isopropylmethylarnino)titanium, and the like. A preferred organometallic compound is tetrakis(dimethylamino)titanium.
During the deposition process for the DLC layer 64, the gasses in the reactor are disassociated to provide reactive ions that are incorporated into a growing film. During film growth, a radio frequency (RF) bias is applied to the substrate surface to promote retention of only strong DLC like bonds. By adjusting the ratio of the feed gases, the ratios of the titanium to DLC in the growing film can be adjusted from about 0 atom % to about 100 atom %.
A titanium-doped DLC layer, as described above, may be formed using a technique as follows:
A titanium-doped DLC layer is formed on a substrate in a conventional plama enhanced chemical vapor deposition (PECVD) chamber with about a 100 to about 1000 volt bias between the substrate and a gas plasma at an RF frequency of about 13.6 Khz. During deposition, the substrate is maintained at room temperature of about 25° C. Preferably, the gas plasma in the chambers includes vaporized methane and tetrakis(dimethylamino)titanium in helium gas (TDMAT/He). When a portion of the cavitation layer to be deposited is an undoped diamond-like carbon layer, the flow of TDMAT/He gas to the chamber is shut off thereby allowing a pure diamond-like carbon layer to plate out or build up on the substrate. When a portion of the cavitation layer is to be essentially pure titanium, the methane gas to the chamber is shut off thereby allowing pure titanium to plate or build up or plate out on the substrate. Various ranges of titanium concentration in the DLC layer as described herein may be made by adjusting the ratio of TDMAT/He to methane in the plasma gas during the deposition process. The titanium-doped DLC layer is deposited at a pressure of about 10 milliTorr to 1 Torr using a substrate power of about 100 to 1000 Watts with a methane flow rate ranging from about 10 to 100 standard cubic centimeters per minute (sccm) and a TDMAT flow rate ranging from about 1 to 100 sccm. During the deposition process, it may be desirable to provide a nitrogen carrier gas to the chamber with the TDMAT/He gas to control the gas pressure during deposition.
While specific embodiments of the invention have been described with particularity herein, it will be appreciated that the invention is applicable to modifications, and additions by those skilled in the art within the spirit and scope of the appended claims.
