Heater chip configuration for an inkjet printhead and printer

A heater chip has a plurality of heaters each having a length, width and thickness. The length multiplied by the width (heater area) is in a range from about 50 to about 500 micrometers squared while the thickness is in a range from about 500 to about 5000 or 6000 angstroms. The energy required to jet or emit a single drop of ink from the heater during use is in a range from about 0.007 to about 0.99 or 1.19 microjoules. The heater chip is formed as a plurality of thin film layers on a substrate. Energy ranges are taught for all heaters having an area from about 50 to about 4000 micrometers squared and thicknesses ranging from about 500 to about 16,000 angstroms. Printheads containing the heater chip and printers containing the printheads are also disclosed.

FIELD OF THE INVENTION

The present invention relates to inkjet printheads. In particular, it relates to a thin film configuration of a heater chip of the printhead optimized to attain a particular energy range for stable ink jetting performance.

BACKGROUND OF THE INVENTION

The art of printing images with inkjet technology is relatively well known. In general, an image is produced by emitting ink drops from an inkjet printhead at precise moments such that they impact a print medium, such as a sheet of paper, at a desired location. The printhead is supported by a movable print carriage within a device, such as an inkjet printer, and is caused to reciprocate relative to an advancing print medium and emit ink drops at such times pursuant to commands of a microprocessor or other controller. The timing of the ink drop emissions corresponds to a pattern of pixels of the image being printed. Other than printers, familiar devices incorporating inkjet technology include fax machines, all-in-ones, photo printers, and graphics plotters, to name a few.

A conventional thermal inkjet printhead includes access to a local or remote supply of color or mono ink, a heater chip, a nozzle or orifice plate attached to the heater chip, and an input/output connector, such as a tape automated bond (TAB) circuit, for electrically connecting the heater chip to the printer during use. The heater chip, in turn, typically includes a plurality of thin film resistors or heaters fabricated by deposition, masking and etching techniques on a substrate such as silicon.

To print or emit a single drop of ink, an individual heater is uniquely addressed with a small amount of current to rapidly heat a small volume of ink. This causes the ink to vaporize in a local ink chamber (between the heater and nozzle plate) and be ejected through and projected by the nozzle plate towards the print medium.

As demands for higher resolution and increased printing speed continue, however, heater chips are made smaller with more and denser heater configurations. Thus, heater chip size, fragility, life, and heat dissipation becomes implicated with all future designs. In addition, printheads accrue fewer costs when heater chips use as little energy as possible when firing each heater.

Accordingly, the inkjet printhead arts desire optimum heater configurations requiring little firing energy that support relatively long life, small size, high density, chip stability and good heat dissipation properties.

SUMMARY OF THE INVENTION

The above-mentioned and other problems become solved by applying the apparatus and method principles and teachings associated with the hereinafter described heater chip configuration for an inkjet printhead and printer.

In one embodiment, the heater chip includes a heater having a length, width and thickness. The length multiplied by the width (heater area) is in a range from about 50 to about 500 micrometers squared while the thickness is in a range from about 500 to about 5000 or 6000 angstroms. In another embodiment, the heater area is less than about 400 micrometers squared while the thickness is less than about 4000 angstroms. The heater chip is formed as a plurality of thin film layers on a substrate. In particular, a thermal barrier layer is on the substrate, a resistor layer is on the thermal barrier layer, a conductor layer is on the resistor layer and an overcoat layer is on the resistor layer. The overcoat layer may include both a passivation and a cavitation layer. The conductor layer includes an anode and a cathode.

In other embodiments, the energy required to jet or emit a single drop of ink from the heater during use is in a range from about 0.007 to about 0.99 or about 1.19 microjoules. Energy ranges for heater chips are disclosed in tabular form for all heaters having an area ranging from about 50 to about 4000 micrometers squared and for thicknesses ranging from about 500 to about 16,000 angstroms.

Printheads containing the heater chip and printers containing the printheads are also taught.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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 inventions may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that process, electrical or mechanical changes may be made without departing from the scope of the present invention. The terms wafer and substrate used in this specification include any base semiconductor structure such as silicon-on-sapphire (SOS) technology, silicon-on-insulator (SOI) technology, thin film transistor (TFT) technology, doped and undoped semiconductors, epitaxial layers of a silicon supported by a base semiconductor structure, as well as other semiconductor structures well known to one skilled in the art. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims and their equivalents.

With reference toFIG. 1, a printhead of the present invention having a heater chip incorporating thermal inkjet technology is shown generally as10. The printhead10has a housing12formed of any suitable material, such as plastic, for holding ink. Its shape can be varied and is often dependent upon the external device that carries or contains the printhead. The housing has at least one compartment16internal thereto for holding an initial or refillable supply of ink. In one embodiment, the compartment is a singular chamber holding a supply of black ink, photo-ink, cyan ink, magenta ink or yellow ink. In another embodiment, the compartment is multi-chambered and contains three supplies of ink. Preferably, it includes cyan, magenta and yellow ink. In other embodiments, the compartment contains plural supplies of black, photo, cyan, magenta or yellow ink. A foam or lung insert, or other, may also accompany the supply of ink in the compartment16to provide a means for maintaining an appropriate level of compartment16backpressure during use. Such inserts are well known in the art. It will be appreciated that the compartment16, while shown as locally integral within the housing12, may alternatively be connected to a remote source of ink and fed from a supply tube, for example.

Adhered to one surface18of the housing12is a portion19of a tape automated bond (TAB) circuit20. The other portion21of the TAB circuit20is adhered to another surface22of the housing. In this embodiment, the two surfaces18,22are perpendicularly arranged to one another about an edge23of the housing.

The TAB circuit20has a plurality of input/output (I/O) connectors24fabricated thereon for electrically connecting the heater chip25to an external device, such as a printer, fax machine, copier, photo-printer, plotter, all-in-one, etc., during use. Pluralities of electrical conductors26exist on the TAB circuit20to electrically connect and short the I/O connectors24to the bond pads28of the heater chip25of the present invention. Various techniques are known for facilitating such connections. It will be appreciated that while eight I/O connectors24, eight electrical conductors26and eight bond pads28are shown, any number greater than one are equally embraced herein. It is also to be appreciated that such number of connectors, conductors and bond pads may not be equal to one another, but for simplicity, equal numbers are shown. Even further, the connectors, conductors and bond pads, may assume other geometries and locations on the housing12and the heater chip25.

The heater chip25is arranged on the surface22of the housing12as either a bottom, top or side of the printhead10. In accordance with such arrangement, the printhead becomes known as a top- or roof-shooter style printhead and all embodiments are embraced herein.

The heater chip25contains at least one ink via32that is in fluidic access with one of the ink supplies contained in compartment16. Each via is formed, preferably by any of the well known processes of grit blasting, deep reactive ion etching, ion etching, wet etching, laser cutting, or plunge cutting, in a substrate34of the heater chip. The heater chip25is preferably attached to the housing with any of a variety of adhesives, epoxies, etc. well known in the art. In another embodiment, the heater chip contains three ink vias having fluidic access to a cyan, yellow, magenta, and/or black ink supply in compartment16.

The heater chip25contains at least one row of a plurality of heaters. As shown, four rows, Rows A, B, C and D, are arranged with two rows of heaters per longitudinal side of the ink via32. Rows A and D are far rows of heaters while Rows B and C are near rows of heaters. Such rows of near and far heaters are a reference to a distance of the rows to the ink via. As implied by their names, the row of near heaters is closer in distance to the ink via than the row of far heaters. For simplicity in this crowded figure, the pluralities of heaters in rows A through D are shown as dots. It will be appreciated, however, that the rows of heaters may be further defined in staggered array groups, linear arrangements, stair-step profiles, or other relative relationships. In one embodiment, each row contains about 160 heaters.

With reference toFIG. 2, an external device, in the form of an inkjet printer, for containing the printhead10is shown generally as40. The printer40includes a carriage42having a plurality of slots44for containing one or more printheads10. The carriage42is caused to reciprocate (via an output59of a controller57) along a shaft48above a print zone46by a motive force supplied to a drive belt50as is well known in the art. The reciprocation of the carriage42is performed relative to a print medium, such as a sheet of paper52, that is advanced in the printer40along a paper path from an input tray54, through the print zone46, to an output tray56.

In the print zone, the carriage42reciprocates in the Reciprocating Direction generally perpendicularly to the paper52being advanced in the Advance Direction as shown by the arrows. Ink drops from compartments16(FIG. 1) are caused to be ejected from the heater chip25at such times pursuant to commands of a printer microprocessor or other controller57. The timing of the ink drop emissions corresponds to a pattern of pixels of the image being printed. Often times, such patterns are generated in devices electrically connected to the controller57(via Ext. input) that are external to the printer such as a computer, a scanner, a camera, a visual display unit, a personal data assistant, etc.

To print or emit a single drop of ink, the heaters (the dots of rows A-D,FIG. 1) are uniquely addressed in a particular order with a small amount of current to rapidly heat a small volume of ink. This causes the ink to vaporize in a local ink chamber140(FIG. 3A) and be ejected through, and projected by, a nozzle plate (not shown) towards the print medium. The fire pulse required to emit such an ink drop is typically in the form of a single or split firing pulse well known in the art.

A control panel58having user selection interface60may also be provided as an input62to the controller57to provide additional printer capabilities and robustness.

With reference toFIGS. 3A and 3B, a more detailed embodiment of a portion of the heater chip25of the printhead10is shown. In particular, an individual heater of the pluralities of heaters in one of the near and/or far rows of heaters is shown generally as100. It will be appreciated that what is depicted in this figure is the result of a substrate having been processed through a series of growth layers, deposition, masking, photolithography, and/or etching or other processing steps. Some of the preferred deposition techniques for the hereinafter described layers include, but are not limited to, any variety of chemical vapor depositions (CVD), physical vapor depositions (PVD), epitaxy, evaporation, sputtering or other similarly known techniques. Preferred CVD techniques include low pressure (LP) ones, but could also be atmospheric pressure (AP), plasma enhanced (PE), high density plasma (HDP) or other. Preferred etching techniques include, but are not limited to, any variety of wet or dry etches, reactive ion etches, deep reactive ion etches, etc. Preferred photolithography steps include, but are not limited to, exposure to ultraviolet or x-ray light sources, or other, and photomasking includes photomasking islands and/or photomasking holes. The particular embodiment, island or hole, depends upon whether the configuration of the mask is a clear-field or dark-field mask as those terms as well understood in the art.

The resulting heater100is a series of thin film layers. In particular, it is a substrate102that provides the base layer upon which all other layers will be formed. In one embodiment, the substrate is a silicon wafer of p-type,100orientation, having a resistivity of 5-20 ohm/cm. Its beginning thickness is preferably, but is not required to be, any one of 525+/−20 microns, 625+/−20 microns, or 625+/−15 microns with a respective wafer diameter of 100+/−0.50 mm, 125+/−0.50 mm, and 150+/−0.50 mm.

The next layer, which is on the substrate, is a thermal barrier layer104. Some embodiments of the layer include a silicon oxide layer mixed with a glass, such as BPSG, PSG or PSOG, with an exemplary thickness of at least about 1 micron.

Subsequent to the thermal barrier layer, and disposed thereon, is a resistor layer 106. Preferably, the resistor layer is about a 50-50 atomic % tantalum-aluminum composition layer. In other embodiments, the resistor layer includes essentially pure or composition layers of any of the following: hafnium, Hf, tantalum, Ta, titanium, Ti, tungsten, W, hafnium-diboride, HfB2, Tantalum-nitride, Ta2N, TaAl(N,O), TaAlSi, TaSiC, Ta/TaAl layered resistor, Ti(N,O) and WSi(O).

A conductor layer112overlies a portion of the resistor layer106and includes an anode114and cathode116. On a surface of the resistor layer106between the anode and cathode (as between points118and120) is a distance that defines a heater length, LH, as shown inFIG. 3Bof the present invention. In an area107generally beneath the heater length, the resistor layer106has a thickness ranging from a surface108to a surface110that defines a resistor thickness. A width of the resistor layer106also defines a heater width, WH, as shown inFIG. 3A.

In one embodiment, the conductor layer is about a 99.5-0.5% aluminum-copper composition of about 5000+/−10% angstroms thick. In other embodiments, the conductor layer includes pure or compositions of aluminum with 2% copper and aluminum with 4% copper.

An overcoat layer124generally overlies the resistor layer between points118and120and, outside of points118and120, it overlies the conductor layer112. The overcoat layer has a thickness generally from a top131of the conductor layer112to a top133of the overcoat layer124. This overcoat thickness, when in an area generally above the surface of the resistor layer106between points118and120, when combined with the resistor thickness, defines a thickness of the heater, TH. Preferably, but by no means a requirement, the overcoat layer124includes both a passivation layer126and a cavitation layer128. In one embodiment, the passivation layer126is a dual layer of dielectrics. In another, it is two layers comprised of silicon-carbide (SiC) and silicon-nitride (Si3N4). The cavitation layer128is processed subsequent to the passivation layer and in one embodiment is a tantalum (Ta) layer. In another embodiment, the overcoat layer is merely a layer of dielectric material without a cavitation layer. In such an embodiment, however, the heater, having heater width, WH, length, LH, and thickness, TH, is caused to wear out faster because of corrosive effects from ink.

A nozzle plate, not shown, is eventually attached to the foregoing described heater100to direct and project ink drops, formed as bubbles in an ink chamber area140generally above the heater, onto a print medium during use.

As will be described in more detail hereinafter, it has been advantageously discovered, among other things, that the energy required to stably jet ink from an individual heater100is a function of heater area (heater width, WH, multiplied by heater length, LH) and thickness TH.FIGS. 10-12disclose particular preferred energy ranges for heater chips for all heaters having a heater area ranging from about 50 to about 4000 micrometers squared and for thicknesses ranging from about 500 to about 16,000 angstroms.

With reference toFIGS. 4A-4C, a first experimental setup leading to such discovery is shown generally as150. In particular, a printhead10having a single heater (100) of a heater chip25is energized or fired to emit a single drop of ink152along a trajectory153. The commands for firing the ink from the heater come from controller154along an appropriate signal path159and are shown graphically inFIG. 4B. The fire pulse has a period tcycleand ranges in voltage values corresponding to logic “0” or logic “1.” A camera156captures a picture of the ink drop152as it passes a reference line (Ref Line) that extends from the camera lens151generally perpendicular to the ink trajectory153. A light source158also receives commands from controller154. It flashes at appropriate times to assist the camera156in capturing a picture or image of the ink drop152as it passes Ref Line. The commands issued for the light source158are conveyed along signal path161by the controller154and are shown graphically inFIG. 4C. To facilitate inventor awareness, and so that a user can view the ink drop image captured by the camera, a visual display unit (VDU) (not shown) having the Ref Line superimposed on the screen is connected to the camera.

During use, a fire pulse, beginning at time to is sent from the controller to fire a first ink drop152from an individual heater (100) of the heater chip25of the printhead10. The camera captures the image, with assistance from a flash of light from the light source158, as it passes the Ref Line. The light source pulse for this first drop of ink is sent relative to the fire pulse at some time t1after time t0.

Thereafter, a second drop of ink is fired relative to the fire pulse and the light source pulse is delayed, after time t1, until time t2. Accordingly, the image captured by the camera156for the second ink drop160will be further along (ΔY) the trajectory153than the first ink drop152.

When plotting ink drop velocity, which is ΔY/(t2−t1), a graph165is discovered like that shown inFIG. 5A. Since meniscus induced variations in velocity can occur at times less than tm(meniscus time) because of the time it takes to refill the ink chamber, the velocity of the ink drop is examined when it is very stable at an isolation time, tiso, at frequencies much smaller than frequencies required to refill the ink chamber at time trefill. Thus, if at some time tiso, relatively far removed from the meniscus effects on velocity as shown by the X on curve167inFIG. 5B, variations in velocity are occurring, it can be deduced that instability is occurring with the way and manner in which the bubble or ink drop is being formed (bubble formation) in the ink chamber.

With reference toFIGS. 6 and 7, a second experimental setup was implemented to investigate bubble formation. In this setup, the camera156, connected to a VDU170so that a user can view the camera results, is positioned above and focused upon a single heater100of a heater chip25. The heater chip25is fashioned to a platform172capable of multi-dimensional adjustments. A controller154provides appropriate signals along signal path167to fire the single heater100. In a manner similar to that of the first experimental setup, a light source158receives inputs from the controller154along signal path169. A glass slide175is secured over the heater chip25. A minimal number of water droplets (i.e., one or two) or dye-less ink are placed between the glass slide and the heater chip so that bubble formation of a single heater100can be visually observed on the VDU170and recorded when the controller fires or energizes the single heater100. A microscope (not shown) may also be used if the camera156is incapable of detailed magnification.

During use, a current pulse, i (FIG. 6B), is sent from the controller to the single heater100. The current pulse is of some appropriate ampere magnitude having a time duration from between time zero, 0, to some time length of the pulse, tp. Depending upon the particular pulse parameters, what is observed on the VDU170is depicted inFIGS. 7A and 7B. In particular, a predictable, well rounded, generally symmetrically formed, continuously stable (from heater fire-to-fire) bubble180or an unpredictable, erratic, poorly shaped, bubble182. A bubble180is typical of a stably formed bubble having a velocity depiction like graph165shown inFIG. 5Awhile bubble182is typical of an unstably formed bubble having a velocity depiction like graph167inFIG. 5B.

With reference toFIG. 8, it has been further discovered when plotting data from the two experimental setups regarding the timing of bubble formation (i.e., Onset of Bubble Nucleation (in microseconds) versus a heater's power per unit volume (in W/m3), where the volume dimensions of the heater are obtained from the heater geometry i.e., the heater width, WH, length, LW, and thickness, TH, and power is obtained from the current and voltage pulses supplied to the heater) that very stable bubbles are formed (stable ink jetting performance) with heater powers per volume being greater than about 1.5×1015(W/m3) at a relative position where line185intersects the curve187fit from the plotted experimental data. Even further, and somewhat arbitrary as a point, extremely stable ink jetting performance is obtained when heater powers per unit volume exceed about 2×1015(W/m3) at a position where line189intersects the curve187.

It should be appreciated that at heater powers per unit volume less than about 1.5×1015(W/m3) functional/working heater chips can be obtained but are susceptible to less stable ink jetting performance. Even further, at higher heater powers per unit volume, at point191, for example, very stable ink jetting occurs but at the expense of heater life because of the relatively large currents and/or voltages being applied to the heater during its lifetime.

With reference toFIG. 9, to understand how much energy to put into a fire pulse to keep a bubble stable, and provide continually stable and predictable ink jetting performance, numerous data points where obtained by varying heater energy. They were plotted against one another as a normalized velocity curve versus heater energy per volume (in GJ/m3). What was discovered was that stable performance, and thus an understanding of an appropriate heater energy per volume, occurred generally when the data points had higher heater energy per volume to the right of the “knee-bend” of the data points shown in the vicinity of data points195.

Advantageously, the relationship can now be understood between an individual heater's geometry (i.e., its width, WH, length, LH, and thickness, TH), regardless of the compositions of the layers, and the energy required to stably jet the heater. As a result, for a given heater area and thickness, an energy range can be consistently predicted that results in stable ink jetting performance.

Moreover, printhead costs can now be quantified because it is known that lower costs accrue when heater chips use as little energy as possible for firing heaters. Accordingly, the inkjet printhead arts can now optimize heater configurations to achieve minimal firing energy that support relatively long life, small size, high density, chip stability and good heat dissipation properties. Mathematically, the relationship between the heater geometry and energy per volume of a particular individual heater100can now advantageously be expressed as:

where LH, WH and TH (and i, and t and the integral) can all be measured and Rsheetis a known constant fixed by the thickness and bulk resistivity of resistor layer106expressed in ohms/square (square=LH/WH),

where PV is the desired power per unit volume condition fromFIG. 8(i.e., greater than about 1.5×1015(W/m3)).

Numerous data points are summarized in tabular form inFIGS. 10-12in preferred ranges for heater energy per volume (eqn. 1) for individual heaters on heater chips having a heater area (heater width, WH, multiplied by heater length, LH) ranging from about 50 to about 4000 micrometers squared and for heater thicknesses, TH, ranging from about 500 to about 16,000 angstroms.

As a working example, consider an individual heater100with a heater area (heater width, WH, multiplied by heater length, LH) of about 50 micrometers squared and a heater thickness of about 500 angstroms. The energy range in microjoules required to stably jet ink from such a heater would be in a range from about 0.007 to about 0.01 in accordance with table entry200inFIG. 12. Such range, about 0.007 to about 0.01, corresponds to heater energy per volume generally occurring with data points having higher energy per volume to the right of the “knee-bend” of the data points shown in the vicinity of data points195ofFIG. 9. Consider another individual heater100with a heater area (heater width, WH, multiplied by heater length, LH) of about 500 micrometers squared and a heater thickness of about 5000 angstroms. The energy range in microjoules required to stably jet ink from such a second heater would be in a range from about 0.74 to about 0.99 in accordance with the circle entry inFIG. 10. Thus, an individual heater100having a heater area (the heater length, LH, multiplied by the heater width WH) in a range from about 50 to about 500 micrometers squared and a heater thickness, TH, in a range from about 500 to about 5000 angstroms requires an energy per volume to emit an ink drop from the heater during use is in a range from about 0.007 to about 0.99 microjoules.

The present invention has been particularly shown and described with respect to certain preferred embodiment(s). However, it will be readily apparent to those skilled in the art that a wide variety of alternate embodiments, adaptations or variations of the preferred embodiment(s), and/or equivalent embodiments may be made without departing from the intended scope of the present invention as set forth in the appended claims. Accordingly, the present invention is not limited except as by the appended claims.