Patent Publication Number: US-7594708-B2

Title: Methods and apparatuses for sensing temperature of multi-via heater chips

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is related to U.S. patent application Ser. No. 11/324,167, filed contemporaneously herewith, and entitled “Methods and Apparatuses for Regulating the Temperature of Multi-Via Heater Chips.” 
   FIELD OF THE INVENTION 
   The present invention relates generally to printing devices, and more particularly to methods and apparatuses for sensing temperature of multi-via heater chips. 
   BACKGROUND OF THE INVENTION 
   A number of printers, copiers, and multi-function products utilize heater chips in their printing heads for discharging ink drops. The ink is supplied through one or more ink vias in the chip. These heater chips typically provide only one heater array for each ink via that is disposed along one side of the ink via. In particular, as shown in  FIG. 1 , a traditional heater chip  100  may include three ink vias—a cyan ink via  102 , a magenta ink via  104 , and a yellow ink via  106 . The cyan ink via  102  operates with the cyan heater array  108 ; the magenta ink via  104  operates with the magenta heater array  110 ; and the yellow ink via  106  operates with the yellow heater array  112 . 
   Similarly,  FIG. 2  shows a heater chip which includes three ink vias, each connected to a single heater array. The cyan ink via  202  operates with the cyan heater array  208 ; the magenta ink via  204  operates with the magenta heater array  210 ; and the yellow ink via  206  operates with the yellow heater array  212 . However, the traditional use of single heater array on a single side of an ink via limits the achievable printing resolution, including the vertical resolution. The configurations shown in  FIG. 1  and  FIG. 2  may have significant difficulty providing ink drop sizes of less than 4 pL (picoliters) while achieving a vertical resolution of about 1200 dpi (dots per inch) or better. Therefore, it is desirable to position heater arrays on both sides of the ink vias, which allow the ink vias to provide smaller ink drops in order to achieve higher printing resolutions. 
   Additionally, for proper functionality, inkjet heater chips need to monitor and maintain the silicon substrate of the heater chip at an acceptable temperature for printing. If the temperature is too low, the ink drops formed will be smaller and have a lower drop-weight than that required for good image quality. As the temperature rises, the drop-weight of the ink drop will rise. Variations in drop-weight will cause visible hue shifts in the printed image. 
   A thermal sense resistor (TSR) is typically used to sense the temperature of the silicon substrate. The temperature of the heater chip shown in  FIG. 1  is measured by way of a metal serpentine temperature sense resistor  120 . The serpentine temperature sense resistor  120  is routed around the periphery of the heater chip and provides an average temperature of the entire die. This average measurement provides no discrimination between individual colors and does not provide any feedback on temperature differences between one area of the heater chip versus another. Thus, the metal serpentine temperature sense resistor  120  lacks the ability to control temperature on a per color or area basis. 
   The heater chip shown in  FIG. 2  improves on that of  FIG. 1  by providing for temperature sensing on a per color basis. Three temperature sense resistors  220 ,  222 , and  224  are placed in close proximity to each of the heater arrays, each situated on the same side of their respective ink vias. As shown, a first TSR  220  is situated on the left side of the cyan ink via  202  and cyan heater array  208 ; a second TSR  222  is situated on the left side of the magenta ink via  204  and magenta heater array  210 ; and a third TSR  224  is situated on the left side of the yellow ink via  206  and the yellow heater array  212 . The ink vias  202 ,  204 , and  206  act as a thermal barrier between the colors. All the thermal heater arrays  208 ,  210 , and  212  are situated on only one side of their respective ink vias, ensuring that there is only a small amount of thermal crosstalk between the temperature sense resistors. 
   Once the temperature within the heater chip is measured, the temperature can be maintained and regulated at an acceptable temperature for printing. Some traditional heater chips use substrate heating elements to heat the silicon substrate to an acceptable temperature. Other heater chips apply fire pulses to selected heater arrays of a short duration to maintain desired temperature. The duration of the fire pulses is too short to cause the nucleation and subsequent ejection of an ink drop, but the pulses are sufficient to ensure that the heater chip operates within an acceptable temperature range. 
   In  FIG. 2 , fire pulses may be applied on a per color basis from the respective heater arrays  208 ,  210 , and  212 . As previously mentioned, the ink vias  202 ,  204 , and  206  function as thermal barriers between the colors. For example, heat generated by the magenta heater array  210  will not readily couple to the cyan heater array  208  and yellow heater array  212  on either side across the intervening ink vias  202  and  204 . Thus, an adequate operating temperature can be maintained for each color of the heater chip. 
   When a heater array is positioned on both sides of an ink vias, the temperature sensing and regulating devices utilized in the prior art do not provide adequate thermal control. A serpentine temperature sense resistor  120 , as depicted in  FIG. 1  is not capable of discriminating between the individual colors of the heater arrays and does not provide any feedback on temperature difference between various areas of the heater chip. Further, monitoring and regulating the operating temperature on a per color basis by situating a temperature sense resistor on the same side of each respective ink via, as shown in  FIG. 2 , is insufficient due to the fact that heater arrays of more than one color now occupy the silicon region between ink vias. Without accurate temperature readings, the method of providing fire pulses to regulate thermal conditions on a per color basis would also be subject to error. 
   Accordingly, there is a need in the industry for heater chips that can provide for monitoring and regulating the various regions of a heater chip at a desired temperature when heater arrays are placed on both sides of the ink vias. 
   BRIEF SUMMARY OF THE INVENTION 
   According to one embodiment of the present invention, there is disclosed a chip for use with a printing device. The chip includes a first heater array, positioned substantially adjacent a first via, and a second heater array, positioned substantially adjacent a second via. The chip also includes a region, positioned between the first heater array and the second heater array, and a temperature sensing element operable to sense the temperature of the region, where the temperature sensing element is substantially centrally disposed with respect to the region. 
   According to one embodiment, the temperature sensing element may include a temperature sensing resistor. The temperature sensing element may also include a thermal sense resistor, such as an n-type implant donor thermal sensing resistor. According to another embodiment of the invention, the temperature sensing element may be positioned several hundred microns, such as at least 300 microns, from both the first heater array and the second heater array. According to yet another embodiment of the invention, the temperature sensing element is positioned substantially planar to each of the first heater array and the second heater array such that the temperature sensing element is not positioned directly above the first or second heater arrays. 
   According to another embodiment of the invention, the chip may include at least one control element operable to receive a temperature measured by the temperature sensing element. Additionally, the chip may include a third heater array, positioned substantially adjacent the second via, and a fourth heater array, positioned substantially adjacent a third via. The chip may also include a second region, positioned between the third heater array and the fourth heater array, and a second temperature sensing element operable to sense the temperature of the second region, where the temperature sensing element is substantially centrally disposed with respect to the second region. Furthermore, the temperature sensing element positioned between the first heater array and the second heater array may be different than the second temperature sensing element positioned between the third heater array and the fourth heater array. 
   According to another embodiment of the invention, there is disclosed a method of fabricating chips for use with a printing device. The method includes providing a first heater array, positioned substantially adjacent a first via, and providing a second heater array, positioned substantially adjacent a second via. The method also includes positioning a temperature sensing element in a region between the first heater array and the second heater array, where the temperature sensing element is operable to sense the temperature of the region. 
   According to one embodiment, positioning a temperature sensing element in the region includes positioning a temperature sensing element in substantially the center of the region. According to another embodiment of the invention, positioning a temperature sensing element in the region includes positioning a temperature sensing resistor in the region. Positioning a temperature sensing element in the region may also include positioning a thermal sense resistor in the region. Additionally, positioning a temperature sensing element in the region may also include positioning an n-type implant donor thermal sensing resistor in the region. 
   According to yet another embodiment of the invention, positioning a temperature sensing element in the region between the first heater array and the second heater array includes positioning the temperature sensing element several hundred microns, such as at least 300 microns, from each of the first heater array and the second heater array. Additionally, positioning a temperature sensing element in the region between the first heater array and the second heater array may include positioning the temperature sensing element substantially planar to each of the first heater array and the second heater array such that the temperature sensing element is not positioned directly above the first or second heater arrays. 
   According to yet another embodiment of the invention, the method may include providing at least one control element operable to receive a temperature measured by the temperature sensing element. The method may also include providing a third heater array substantially adjacent the second via, providing a fourth heater array substantially adjacent a third via, and positioning a second temperature sensing element in a second region located between the third heater array and the fourth heater array, where the temperature sensing element is operable to sense the temperature of the second region, and where the temperature sensing element is substantially centrally disposed with respect to the second region. Additionally, the temperature sensing element positioned between the first heater array and the second heater array may be different than the second temperature sensing element positioned between the third heater array and the fourth heater array. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
     Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein: 
       FIG. 1  illustrates a traditional heater chip utilizing a serpentine temperature sense resistor for providing an average temperature of the entire die. 
       FIG. 2  illustrates a traditional heater chip utilizing temperature sense resistors and heater arrays to monitor and regulate temperature on a by color basis. 
       FIG. 3  illustrates an exemplary configuration for a heater chip having a heater array positioned on both sides of each ink via, according to an illustrative embodiment of the present invention. 
       FIG. 4  illustrates an exemplary configuration for a heater chip having regions defined between the ink vias, according to an illustrative embodiment of the present invention. 
       FIG. 5  illustrates an exemplary configuration for a heater chip in accordance with an illustrative embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION 
   The present inventions now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the inventions are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout. 
   According to an exemplary embodiment of the present invention, heater arrays may be positioned on both sides of at least a portion of the ink vias, which can allow higher printing resolutions. Each of these heater arrays may include a plurality of individual heaters fabricated as resistors in the heater chips. For example, these resistors may be thin-film resistors in accordance with an exemplary embodiment of the invention. These thin-film resistors may be formed of a variety of materials, including platinum, aluminum, alloys, and other materials. The heaters may also be formed of other technologies besides thin-film resistors, as are known to those of ordinary skill in the art. When the heaters in the heater arrays are activated, they provide thermal energy to the nozzle chamber, and the ink is discharged through the nozzle. 
     FIG. 3  shows an illustrative heater chip  300  according to an embodiment of the present invention. The heater chip  300  illustrates the placement of a single via in between two corresponding heater arrays. With the heater arrays positioned on both sides of at least a portion of the ink vias, higher printing resolutions can be achieved. As shown in  FIG. 3 , the illustrative heater chip  300  is a CMYK (cyan-magenta-yellow-monochrome) heater chip that includes four ink vias each disposed between two heater arrays. In particular, a cyan ink via  302  is positioned between a first heater array  308  and a second heater array  314 ; a magenta ink via  304  is positioned between a first heater array  310  and a second heater array  316 ; a yellow ink via  306  is positioned between a first heater array  312  and a second heater array  318 ; and a monochrome (K) ink via  307  is positioned between a first heater array  313  and a second heater array  319 . 
   Although the heater chip  300  illustrated in  FIG. 3  shows only four ink vias, it will be appreciated by one of ordinary skill in the art that a greater number of vias and corresponding heater arrays may be utilized. As an example, an additional monochrome (K) ink via may be disposed between two additional heater arrays to form a CMYKK heater chip. Additionally, there may be numerous vias for a particular color within a heater chip. According to another embodiment of the invention, only some of the ink vias may be disposed between two heater arrays. For example, the monochrome ink via  307  may include only one monochrome heater array along a single side of the monochrome ink via  307 . 
   The heater arrays  308 ,  310 ,  312 ,  313 ,  314 ,  316 ,  318 ,  319  shown in  FIG. 3  may include one or more individual heaters fabricated as resistors in the heater chip. These resistors may be thin-film resistors in accordance with an exemplary embodiment of the invention. Thin-film resistors may be formed of one or more materials, including platinum (Pt), gold (Au), silver (Ag), copper (Cu), aluminum (Al), tantalum (Ta), titanium tungsten (TiW), silicon-nitrogen (SiN), silicon carbide (SiC), diamond-like carbon (DLC) coating, etc. Other metals, alloys, or materials appreciable by one of ordinary skill in the art may also be used. The heater arrays may also be formed of other technologies besides thin-film resistors, as is known to those of ordinary skill in the art. 
   It will be appreciated that the placement of a single via in between two heater arrays presents a challenge in attempting to sense the temperature of individual colors. If there is a single TSR associated with each heater array in the illustrative embodiment of  FIG. 2 , then two TSRs will be placed next to each other between adjacent ink vias. For instance, if one TSR is associated with the left yellow heater array and another TSR is associated with the right magenta heater array, the region between the magenta and yellow vias would include two TSRs. If a print job is heavy in yellow and light in magenta, the thermal energy generated by the yellow heaters would rapidly couple through the common silicon to the magenta TSR positioned in between the yellow and magenta ink vias, providing a false high reading for magenta. Rather than try to sense temperature on a per color basis with TSR&#39;s in close proximity to heaters, the present invention senses temperature by silicon region. 
   According to an exemplary embodiment of the present invention, an adequate operating temperature is monitored and regulated for various thermal regions separated by insulating ink vias on the heater chip.  FIG. 4  illustrates an exemplary configuration for a heater chip  400  having thermal regions defined between the ink vias, according to one embodiment of the present invention. In particular, a first region  430  is defined as the area between the left edge of the heater chip  400  and the cyan ink via  402 ; a second region  432  is defined as the area between the cyan ink via  402  and the magenta ink via  404 ; a third region  434  is defined as the area between the magenta ink via  404  and the yellow ink via  406 ; a fourth region  436  is defined as the area between the yellow ink via  406  and the mono ink via  407 ; and a fifth region  438  is defined as the area between the mono ink via  407  and the right edge of the heater chip  400 . It will be understood by those of ordinary skill in the art that any number of thermal regions may be defined for monitoring and regulating temperature on the heater chip. 
   The heater chip  400  includes components, such as the ink vias  402 ,  404 ,  406 ,  407  and heater arrays  408 ,  414 ,  410 ,  416 ,  412 ,  418 ,  413 ,  419  connected to a substrate (not shown) made up of a semiconductor material. According to an exemplary embodiment of the present invention, the substrate may be a silicon substrate. It will be appreciated by those skilled in the art, however, that the substrate can be formed from a variety of solid crystalline substances used as a base material for electronic devices, such as germanium (Ge), having electrical conductivity greater than insulators but less than good conductors. The thermal regions  430 ,  432 ,  434 ,  436 , and  438  are defined regions of the silicon substrate of the heater chip  400  situated around and between the ink vias  402 ,  404 ,  406 , and  407 . The minimum width of the thermal regions  430 ,  432 ,  434 ,  436 , and  438  is generally limited by the heater chip  400  circuitry. 
   According to an exemplary embodiment of the present invention, temperature of the heater chip  400  is measured on a per thermal region basis. A temperature sensing element is placed in each of the thermal regions, and each is operable to measure the temperature of the silicon substrate in a corresponding thermal region. According to an exemplary embodiment of the present invention, the temperature sensing elements are n-type implant donor thermal sensing resistors (NSD sense resistors), as will be understood by those skilled in the art. As the substrate temperature of the heater chip  400  increases, the resistance of the TSRs increases, allowing a temperature measurement to be taken. It will also be appreciated by those of ordinary skill in the art that many other temperature sensing elements can be used, including but not limited to metal resistors and p-type implant donors. 
   With particular reference to  FIG. 5 , a TSR is positioned within each of the thermal regions  430 ,  432 ,  434 ,  436 ,  438 . Thus, a first TSR  540  is situated in the first region  430 ; a second TSR  542  is situated in the second region  432 ; a third TSR  544  is situated in the third region  434 ; a fourth TSR  546  is situated in the fourth region  436 ; and a fifth TSR  548  is situated in the fifth region  438 . The TSRs  540 ,  542 ,  544 ,  546 , and  548  are placed well away from the heater arrays  408 ,  410 ,  412 ,  413 ,  414 ,  416 ,  418 ,  419 , at a distance  550  of several hundred microns, rather than in close proximity to the heater arrays. For the first region  430  the first TSR  440  is centered between the left edge (i.e., the left edge of the substrate) of the heater chip  400  and the cyan ink via  402 . Similarly, for the fifth region  438  the fifth TSR  448  is centered between the right edge of the heater chip  400  and the mono ink via  402 . The remaining TSRs  542 ,  544 ,  546  are centered between heater arrays from adjacent ink vias corresponding to different colors (i.e., heater arrays  414  and  410 ,  416  and  412 , and  418  and  413 , respectively). It will be understood by those skilled in the art that the TSRs  540 ,  542 ,  544 ,  546 , and  548  need not be centered within their respective thermal regions  430 ,  432 ,  434 ,  436 , and  438 , but rather, they can be positioned at any point within their respective thermal regions. 
   Due to the relative high thermal conductivity of the silicon substrate, each of the thermal regions  430 ,  432 ,  434 ,  436 ,  438  have a very uniform temperature across the width of that region. Because of this conductivity, the TSRs  540 ,  542 ,  544 ,  546 ,  548  can be placed in the center of their respective thermal regions  430 ,  432 ,  434 ,  436 , and  438  and still provide an accurate temperature measurement for the region. The ink vias  402 ,  404 ,  406 ,  407 , on the other hand, act as thermal insulators between the thermal regions  430 ,  432 ,  434 ,  436 ,  438 . As an example, if the right cyan heater array  414  fires, then the adjacent left magenta heater array  410  will quickly be at the same temperature as the right cyan heater array  414 . A temperature reading from the second region  432  represents the temperature of both the magenta and cyan heater arrays  414  and  410  in the second region. As previously mentioned, the minimum width of the thermal regions  430 ,  432 ,  434 ,  436 , and  438  is generally limited by the heater chip  400  circuitry. It will be appreciated by those of ordinary skill in the art that the maximum practical width for temperature sensing accuracy depends on a combination of the printing rate and the frequency at which the temperature is read from a thermal region. For instance, if the right cyan heater array  414  is firing at a high frequency, then the width of the second region  432  would need to be small enough to ensure uniform temperature across the second region  432  for a given temperature sampling rate of the second TSR  542 . 
   According to one embodiment of the invention, each TSR  540 ,  542 ,  544 ,  546 ,  548  makes up half of a wheatstone bridge circuit, as is known to those of ordinary skill in the art for use in measuring small changes in resistance. The other half of the bridge circuit feeds into a differential op-amp, the output of which is provided as input to an A/D converter. The A/D converter may be included in an Application Specific Integrated Circuit (ASIC) that controls the functioning of the printhead. Firmware running on the system, in conjunction with the ASIC may monitor the measured temperature from each TSR. According to one embodiment of the invention, the temperature may be monitored continuously prior to the beginning of printing. As described in detail below, this information can allow the heater arrays to be fired at a high frequency to maintain a desired temperature in each region. According to another embodiment of the invention, the monitoring of temperature in each region may not be monitored during printing. 
   According to yet another embodiment of the present invention, the temperature of the heater chip  400  is regulated on a per region basis. The heater chip  400  may use non-nucleating heating (NNH) to maintain an adequate substrate temperature for the heater chip  400  in each region in order to ensure the best print quality. NNH includes applying fire pulses to selected heater arrays  408 ,  410 ,  412 ,  413 ,  414 ,  416 ,  418  of a duration too short to cause nucleation and the subsequent ejection of an ink drop from an ink via  402 ,  404 ,  406 , and  407 . NNH is applied on a per thermal region basis rather than on a per color basis. According to one embodiment of the invention, NNH pulses are applied to heaters within each region. Additionally, the heaters used in each region may vary, and the firing of pulses in two or more heaters may be asynchronous to minimize the current and power required for maintaining a desired temperature in each region. Instructions for firing heaters may be provided via one or more data streams used to control heater address data, the printhead, and like elements. Those skilled in the art will recognize that other methods for heating the various thermal areas can be used, including but not limited to substrate heating elements. 
   As shown in  FIG. 5 , the first region  430  is heated by the left cyan heater array  408 ; the second region  432  is heated by the right cyan heater array  414  and the left magenta heater array  410 ; the third region  434  is heated by the right magenta heater array  416  and the left yellow heater array  412 ; the fourth region  436  is heated by the left yellow heater array  418  and the mono heater array  413 ; and the fifth region  438  is heated by the right mono heater array  419 . According to one embodiment of the invention, one or more of the regions may not be heated by both adjacent heater arrays due to hardware constraints. For instance, the fourth region  436  may be heated only by the left mono heater array  413  rather than by both the left mono heater array  413  and the right yellow heater array  418 . As described above, the firing of pulses in two or more heaters may be asynchronous to minimize the current and power required for maintaining a desired temperature in each region. Based on the average thermal region temperature measurements provided by the TSRs  540 ,  542 ,  544 ,  546 ,  548 , if heating is required in a particular thermal region, NNH is applied to each heater array situated in that thermal region. Thus, each thermal region can be regulated at its optimal operating temperature. 
   Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.