PATENT DOCUMENT

Publication Number: US-8400408-B2
Application Number: US-81831107-A
Country: US
Kind Code: B2

Title: Touch screens with transparent conductive material resistors

Abstract:
Systems and methods for touch screens with integrated transparent conductive material resistors are provided. Metal traces on the surface of a touch screen may be subject to radio-frequency interference (RFI) that can adversely affect the performance of the touch screen. Transparent conductive material resistors inserted within the metal trace paths can be used to form low-pass filters which can reduce the affect of the RFI.

Claims:
1. A touch panel having integrated transparent conductive material resistors, comprising:
 a pattern of transparent conductive material traces formed from a deposition of a transparent conductive material on a first surface of the touch panel, the pattern of transparent conductive material traces deposited in a display area of the touch panel and the same deposition of the transparent conductive material also forming a plurality of transparent conductive material resistors in a non-display area of the touch panel; and 
 a plurality of metal traces connected to the pattern set of transparent conductive material traces; 
 wherein the plurality of transparent conductive material resistors are connected to the metal traces and configured to form a portion of a low pass filter for blocking electromagnetic interference on the connected metal traces. 
 
     
     
       2. The touch panel of  claim 1 , wherein the transparent conductive material resistors are connected between the metal traces and capacitive sensing circuitry. 
     
     
       3. The touch panel of  claim 1 , wherein the transparent conductive material resistors have a resistance of approximately 400 Ohms. 
     
     
       4. The touch panel of  claim 1 , the low-pass filters having a cut-off frequency of approximately 10 MHz. 
     
     
       5. The touch panel of  claim 4 , wherein the low-pass filters block signals having frequencies greater than approximately 1 GHz. 
     
     
       6. The touch panel of  claim 2 , wherein the transparent conductive material resistors increase the sensitivity of the capacitive sensing circuitry. 
     
     
       7. The touch panel of  claim 1 , further comprising flex circuitry connected directly to the transparent conductive material resistors. 
     
     
       8. The touch panel of  claim 1 , further comprising connecting the transparent conductive material resistors adjacent to an end of the metal traces. 
     
     
       9. The touch panel of  claim 1 , the deposition of transparent conductive material having portions removed to form the transparent conductive material traces and resistors. 
     
     
       10. The touch panel of  claim 1 , wherein the transparent conductive material comprises at least one of indium tin oxide (ITO), conductive clear polymer, and antimony tin oxide (ATO). 
     
     
       11. A computer system having a touch panel with integrated transparent conductive material resistors, comprising:
 a processor configured to execute instructions and to carry out operations associated with the computer system; 
 a display device that is operatively coupled to the processor; 
 a touch panel that is operatively coupled to the processor, the touch panel being a substantially transparent panel that is positioned in front of the display, the touch panel including
 a pattern of transparent conductive material traces formed from a deposition of a transparent conductive material on a first surface of the touch panel, the pattern of transparent conductive material traces deposited in a display area of the touch panel and the same deposition of the transparent conductive material also forming a plurality of transparent conductive material resistors in a non-display area of the touch panel; and 
 a plurality of metal traces connected to the pattern set of transparent conductive material traces; 
 wherein the plurality of transparent conductive material resistors are connected to the metal traces and configured to form a portion of a low pass filter for blocking electromagnetic interference on the connected metal traces. 
 
 
     
     
       12. The computer system of  claim 11 , wherein the transparent conductive material resistors are connected between the metal traces and capacitive sensing circuitry. 
     
     
       13. The computer system of  claim 11 , wherein the transparent conductive material resistors have a resistance of approximately 400 Ohms. 
     
     
       14. The computer system of  claim 11 , the low-pass filters having a cut-off frequency of approximately 10 MHz. 
     
     
       15. The computer system of  claim 14 , wherein the low-pass filters block signals having frequencies greater than approximately 1 GHz. 
     
     
       16. The computer system of  claim 12 , wherein the transparent conductive material resistors increase the sensitivity of the capacitive sensing circuitry. 
     
     
       17. The computer system of  claim 11 , further comprising flex circuitry connected directly to the transparent conductive material resistors. 
     
     
       18. The computer system of  claim 11 , further comprising connecting the transparent conductive material resistors adjacent to an end of the metal traces. 
     
     
       19. The computer system of  claim 11 , the deposition of transparent conductive material having portions removed to form the transparent conductive material traces and the transparent conductive material resistors. 
     
     
       20. The computer system of  claim 11 , wherein the transparent conductive material comprises at least one of indium tin oxide (ITO), conductive clear polymer, and antimony tin oxide (ATO). 
     
     
       21. A method for fabricating a touch panel having transparent conductive material resistors, comprising:
 forming a plurality of metal traces on the touch panel, the metal traces including one or more breaks; and 
 forming a pattern of material traces from a deposition of a-transparent conductive material on a first surface of the touch panel, the pattern of material traces deposited in a display area of the touch panel and the same deposition of the transparent conductive material also forming a plurality of transparent conductive material resistors in a non-display area of the touch panel, the resistors formed within the breaks of the metal traces and configured to form a portion of a low pass filter for blocking electromagnetic interference on the connected metal traces. 
 
     
     
       22. The method of  claim 21 , wherein the transparent conductive material comprises at least one of indium tin oxide (ITO), conductive clear polymer, and antimony tin oxide (ATO).

Description:
BACKGROUND OF THE INVENTION 
     This relates to touch screen systems and methods having integrated transparent conductive material resistors. The transparent conductive material resistors can be make from indium tin oxide (ITO), conductive clear polymer, antimony tin oxide (ATO), or other suitable materials. 
     There exist many styles of input devices for performing operations in a computer system. The operations generally correspond to moving a cursor and/or making selections on a display screen. By way of example, the input devices may include buttons or keys, mice, trackballs, touch pads, joy sticks, touch screens and the like. Touch screens, in particular, are becoming increasingly popular because of their ease and versatility of operation as well as to their declining price. Touch screens allow a user to make selections and move a cursor by simply touching the display screen via a finger or stylus. In general, the touch screen recognizes the touch and position of the touch on the display screen and the computer system interprets the touch and thereafter performs an action based on the touch event. 
     Touch screens typically include a touch panel, a controller and a software driver. The touch panel is a clear panel with a touch sensitive surface. The touch panel is positioned in front of a display screen so that the touch sensitive surface covers the viewable area of the display screen. The touch panel registers touch events (the touching of fingers or other objects upon a touch sensitive surface) and sends these signals to the controller. The controller processes these signals and sends the data to the computer system. The software driver translates the touch events into computer events. 
     Touch panels can include an array of touch sensors capable of detecting touch events. Some touch panels can detect multiple touches (the touching of fingers or other objects upon a touch-sensitive surface at distinct locations at about the same time) and near touches (fingers or other objects within the near-field detection capabilities of their touch sensors), and identify and track their locations. Those touch panels capable of detecting multiple touches may be referred to as multi-touch panels. 
     Mutual capacitive touch panels can be formed from rows and columns of traces on opposite sides of a dielectric. At the “intersections” of the traces, where the traces pass above and below each other (but do not make direct electrical contact with each other), the traces essentially form two electrodes with a mutual capacitance therebetween. To scan a sensor panel, a stimulus can be applied to one row with all other rows held at DC voltage levels. When a row is stimulated, a modulated output signal can be capacitively coupled onto the columns of the sensor panel. The columns can be connected to analog channels (also referred to herein as event detection and demodulation circuits). When the panel is touched or nearly-touched, a small amount of charge is drawn to the point of contact. For every row that is stimulated, each analog channel connected to a column generates an output value representative of an amount of change in the modulated output signal due to a touch or hover event occurring at the sensor located at the intersection of the stimulated row and the connected column. After analog channel output values are obtained for every column in the sensor panel, a new row is stimulated (with all other rows once again held at DC voltage levels), and additional analog channel output values are obtained. When all rows have been stimulated and analog channel output values have been obtained, the sensor panel is said to have been “scanned,” and a complete “image” of touch or hover can be obtained over the entire sensor panel. This image of touch or hover can include an analog channel output value for every pixel (row and column) in the panel, each output value representative of the amount of touch or hover that was detected at that particular location. 
     Metal traces that are etched into the touch panels can be used to transmit charges from the panel surface to the event detection and demodulation circuits connected to the panel. As the size of a touch screen increases, the length of the metal traces etched into the touch panel also increases. These longer metal traces can act as antennas and cause radio-frequency interference (RFI) signals to be brought into the touch panel circuits and controller. RFI is any undesirable RF signal that interferes with the integrity of electronics and electrical systems. These RFI signals may adversely affect the operation of the touch screen. 
     Accordingly, what is needed are systems and methods for reducing the affect of RFI signals in touch screens. 
     SUMMARY OF THE INVENTION 
     Systems and methods for touch screens with transparent conductive material resistors are provided. 
     Transparent conductive material resistors can be inserted into the metal traces that are etched into the touch panels which are used to transmit charges from the panel surface to the capacitance detection circuitry connected to the panel. For example, the metal traces can be broken and transparent conductive material resistors can be formed inside these breaks. The resistance of these transparent conductive material resistors in combination with the inherent capacitance values of the circuitry and connectors that are connected to the touch panel can form a low-pass filter that is capable of blocking the RFI signals. 
     Inserting the transparent conductive material resistors within the metal traces in this manner can be accomplished with little or no incremental cost because the transparent conductive material may already be patterned on the surface of the touch panel to create the electrode rows and columns used to form the touch sensors. These electrode rows and columns are generally formed by depositing a transparent conductive material layer over the substrate surface, and then by etching away portions of the transparent conductive material layer in order to form the traces. Therefore, the transparent conductive material resistors can be formed as part of the process of creating the transparent conductive material electrode rows and columns. Instead of etching away all of the extra portions of the transparent conductive material layer, some of the transparent conductive material portions may be kept to serve as transparent conductive material resistors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features of the present invention, its nature and various advantages will become more apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which: 
         FIG. 1  shows an exemplary touch screen computing system operable with a capacitive touch panel in accordance with an embodiment of the present invention. 
         FIG. 2  shows an exploded perspective view of an illustrative touch screen computing system in accordance with an embodiment of the present invention. 
         FIG. 3  shows a detailed cross-sectional view of an illustrative touch screen in accordance with an embodiment of the present invention. 
         FIG. 4  shows an illustrative capacitive touch panel with integrated transparent conductive material resistors in accordance with an embodiment of the present invention. 
         FIG. 5  shows an illustrative touch panel with integrated transparent conductive material resistors in which the flex circuits are bonded to the same edge, on directly opposite sides of the panel in accordance with an embodiment of the present invention. 
         FIG. 6  shows an illustrative touch panel with integrated transparent conductive material resistors in which the flex circuits are bonded to the same edge, on the same side of the panel in accordance with an embodiment of the present invention. 
         FIG. 7  shows a single illustrative indium tin oxide (ITO) electrode column that is connected to a capacitive sensing circuit via a metal trace, an ITO resistor and a flex circuit in accordance with an embodiment of the present invention. 
         FIG. 8  shows a schematic illustration of the elements of  FIG. 7  in accordance with an embodiment of the present invention. 
         FIGS. 9 and 10  show two exemplary configurations for connecting a flex circuits to metal traces having integrated transparent conductive material resistors in accordance with an embodiment of the present invention. 
         FIG. 11  shows a flowchart of an illustrative process for fabricating a touch panel with integrated transparent conductive material resistors in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Commonly assigned Steve Hotelling et al. U.S. patent application Ser. No. 10/840,862, filed May 6, 2004, entitled “MULTIPOINT TOUCHSCREEN” is hereby incorporated by reference in its entirety. 
     Commonly assigned Steve Hotelling et al. U.S. patent application Ser. No. 11/650,182, filed Jan. 3, 2007, entitled “DOUBLE-SIDED TOUCH-SENSITIVE PANEL WITH SHIELD AND DRIVE COMBINED LAYER” is hereby incorporated by reference in its entirety. 
     Commonly assigned Steve Hotelling U.S. patent application Ser. No. 11/818,394, filed Jun. 13, 2007, entitled “PET-BASED TOUCHPAD” is hereby incorporated by reference in its entirety. 
       FIG. 1  shows an exemplary touch screen computing system  100  operable with capacitive touch panel  124  according to embodiments of this invention. Touch panel  124  can be connected to other components in computing system  100  through connectors integrally formed on the sensor panel, or using flex circuits. Computing system  100  can include one or more panel processors  102  and peripherals  104 , and panel subsystem  106 . The one or more processors  102  can include, for example, ARM968 processors or other processors with similar functionality and capabilities. However, in other embodiments, the panel processor functionality can be implemented instead by dedicated logic such as a state machine. Peripherals  104  can include, but are not limited to, random access memory (RAM) or other types of memory or storage, watchdog timers and the like. 
     Panel subsystem  106  can include, but is not limited to, one or more analog channels  108 , channel scan logic  110  and driver logic  114 . Channel scan logic  110  can access RAM  112 , autonomously read data from the analog channels and provide control for the analog channels. This control can include multiplexing columns of multi-touch panel  124  to analog channels  108 . In addition, channel scan logic  110  can control the driver logic and stimulation signals being selectively applied to rows of multi-touch panel  124 . In some embodiments, panel subsystem  106 , panel processor  102  and peripherals  104  can be integrated into a single application specific integrated circuit (ASIC). 
     Driver logic  114  can provide multiple panel subsystem outputs  116  and can present a proprietary interface that drives high voltage driver  118 . High voltage driver  118  can provide level shifting from a low voltage level (e.g. complementary metal oxide semiconductor (CMOS) levels) to a higher voltage level, providing a better signal-to-noise (S/N) ratio for noise reduction purposes. The high voltage driver outputs can be sent to decoder  120 , which can selectively connect one or more high voltage driver outputs to one or more panel row inputs  122  through a proprietary interface and enable the use of fewer high voltage driver circuits in the high voltage driver  118 . Each panel row input  122  can drive one or more rows in a multi-touch panel  124 . In some embodiments, high voltage driver  118  and decoder  120  can be integrated into a single ASIC. However, in other embodiments high voltage driver  118  and decoder  120  can be integrated into driver logic  114 , and in still other embodiments high voltage driver  118  and decoder  120  can be eliminated entirely. 
     Computing system  100  can also include host processor  128  for receiving outputs from panel processor  102  and performing actions based on the outputs that can include, but are not limited to, moving an object such as a cursor or pointer, scrolling or panning, adjusting control settings, opening a file or document, viewing a menu, making a selection, executing instructions, operating a peripheral device connected to the host device, answering a telephone call, placing a telephone call, terminating a telephone call, changing the volume or audio settings, storing information related to telephone communications such as addresses, frequently dialed numbers, received calls, missed calls, logging onto a computer or a computer network, permitting authorized individuals access to restricted areas of the computer or computer network, loading a user profile associated with a user&#39;s preferred arrangement of the computer desktop, permitting access to web content, launching a particular program, encrypting or decoding a message, and/or the like. Host processor  128  can also perform additional functions that may not be related to panel processing, and can be coupled to program storage  132  and display device  130  such as a liquid crystal display (LCD) for providing a UI to a user of the device. 
     As mentioned above, multi-touch panel  124  can in some embodiments include a capacitive sensing medium having a plurality of row traces or driving lines and a plurality of column traces or sensing lines separated by a dielectric. In some embodiments, the dielectric material can be transparent, such as polyethylene terephthalate (PET), glass, or another material such as Mylar. The row and column traces can be formed from a transparent conductive material such as indium tin oxide (ITO), conductive clear polymer, or antimony tin oxide (ATO), although other non-transparent materials such as copper can also be used. In some embodiments, the row and column traces can be perpendicular to each other, although in other embodiments other non-orthogonal orientations are possible. For example, in a polar coordinate system, the sensing lines can be concentric circles and the driving lines can be radially extending lines (or vice versa). It should be understood, therefore, that the terms “row” and “column,” “first dimension” and “second dimension,” or “first axis” and “second axis” as may be used herein are intended to encompass not only orthogonal grids, but the intersecting traces of other geometric configurations having first and second dimensions (e.g. the concentric and radial lines of a polar-coordinate arrangement). 
     At the “intersections” of the traces, where the traces pass above and below each other (but do not make direct electrical contact with each other), the traces essentially form two electrodes (although more than two traces can intersect as well). Each intersection of row and column traces can represent a capacitive sensing node and can be viewed as picture element (pixel)  126 , which can be particularly useful when multi-touch panel  124  is viewed as capturing an “image” of touch. (In other words, after panel subsystem  106  has determined whether a touch event has been detected at each touch sensor in multi-touch panel  124 , the pattern of touch sensors in the multi-touch panel at which a touch event occurred can be viewed as an “image” of touch (e.g. a pattern of fingers touching the panel).) When the two electrodes are at different potentials, each pixel can have an inherent self or mutual capacitance formed between the row and column electrodes of the pixel. If an AC signal is applied to one of the electrodes, such as by exciting the row electrode with an AC voltage at a particular frequency, an electric field and an AC or signal capacitance can be formed between the electrodes, referred to as Csig. The presence of a finger or other object near or on multi-touch panel  124  can be detected by measuring changes to Csig. The columns of multi-touch panel  124  can drive one or more analog channels  108  in panel subsystem  106 . In some embodiments, each column is coupled to one dedicated analog channel  108 . However, in other embodiments, the columns can be couplable via an analog switch to a fewer number of analog channels  108 . 
       FIG. 2  shows an exploded perspective view of an illustrative touch screen computing system  200 . Touch screen system  200  includes liquid crystal display (LCD)  230  and transparent touch screen  220  positioned in front of LCD  230 . LCD  230  can be configured to display a graphical user interface (GUI) including perhaps a pointer or cursor as well as other information to a user. Touch screen  220 , on the other hand, is an input device that is sensitive to a user&#39;s touch, allowing a user to interact with the graphical user interface on LCD  230 . By way of example, touch screen  220  may allow a user to move an input pointer or make selections on the graphical user interface by simply pointing at the GUI on LCD  230 . 
     Housing  210  encloses and protects touch screen  220 , LCD  230 , as well as circuitry  240 . Circuitry  240  can include controller circuitry for touch screen  220 , and LCD  230  as well as additional circuitry including processor circuitry, memory circuitry, and power circuitry. Touch screen system  200  may be a stand alone unit or it may integrated with other devices. When stand alone, touch screen system  200  (or each of its components) can act like a peripheral device that includes its own housing and that can be coupled to a host device through wired or wireless connections. When integrated, touch screen system  200  shares housing  210  and is hard wired into the host device thereby forming a single unit. By way of example, touch screen system  200  may be disposed inside a variety of host devices including but not limited to general purpose computers such as a desktop, laptop or tablet computers, handhelds such as PDAs and media players such as music players, peripheral devices such as cameras, printers and/or the like, or hybrid computer/phone devices. 
       FIG. 3  shows a detailed cross-sectional view of illustrative touch screen  300 . Touch screen  300  includes capacitive touch panel  330  which is sandwiched between protective cover  310  and LCD  340 . LCD  340  can correspond to any conventional LCD display known in the art. Although not shown, the LCD  340  typically includes various layers including a fluorescent panel, polarizing filters, a layer of liquid crystal cells, a color filter and the like. 
     Protective cover  310  serves to protect the under layers and provide a surface for allowing an object to slide thereon. Cover  310  can be suitably thin to allow for sufficient coupling to capacitive touch panel  330 . Cover  310  can be formed from any suitable clear material such as glass and plastic. In addition, cover  310  can be treated with coatings to reduce sticktion when touching and reduce glare when viewing the underlying LCD  310 . By way of example, a low sticktion/anti reflective coating can be applied over the cover sheet  310 . 
     Touch screen  300  also includes various bonding layers  320 . Bonding layers  320  bond capacitive touch panel to LCD  340  and cover  310  together to form the laminated structure and to provide rigidity and stiffness to the laminated structure. In essence, bonding layers  320  help to produce a monolithic sheet that is stronger than each of the individual layers taken alone. In some cases, the bonding agent includes an index matching material to improve the visual appearance of the touch screen  300 . In some embodiments, one or both bonding layers  320  can be eliminated without affecting the performance of the touch screen. 
       FIG. 4  shows an illustrative capacitive touch panel  400  with integrated transparent conductive material resistors. Touch panel  400  includes a plurality of capacitance sensing nodes  440 . The capacitive sensing nodes may be widely varied. For example, the capacitive sensing nodes may be based on self capacitance or mutual capacitance. In self capacitance, the “self” capacitance of a single electrode is measured as for example relative to ground. In mutual capacitance, the mutual capacitance between at least first and second electrodes is measured. In either case, each node  440  can work independent of the other nodes  440  so as to produce simultaneously occurring signals representative of different points on the touch panel  400 . 
     As shown, the touch panel  400  includes a two layer grid of spatially separated non-overlapping lines. In the illustrated embodiment touch panel  400  includes transparent conductive material column traces  410  on the top surface and transparent conductive material row traces  420  on the bottom surface. In most cases, the lines on each surface are parallel one another. Furthermore, although in different planes, the lines on the different surfaces are configured to intersect or cross in order to produce capacitive sensing nodes  440 , which each represent different coordinates in the plane of the touch panel  400 . The nodes  440  are configured to receive capacitive input from an object touching the touch panel  400  in the vicinity of the node  440 . When an object is proximate to a node  440 , the object steals charge thereby affecting the capacitance at the node  440 . 
     As previously described, row traces  420  are individually stimulated with an AC signal while column traces  410  are connected to capacitive sensing circuitry (not shown) that may continuously sense all of column traces  410 . The capacitive sensing circuitry typically includes one or more sensor ICs that measure the capacitance in each of column traces  410  and reports its findings to a host controller. The sensor ICs may, for example, convert the analog capacitive signals to digital data and thereafter transmit the digital data over a serial bus to a host controller. Any number of sensor ICs may be used. For example, a sensor IC may be used for all column traces  410 , or multiple sensor ICs may be used for a single or group of column traces  410 . In most cases, the sensor ICs report tracking signals, which are a function of both the position of the node  440  and the intensity of the capacitance at the node  440 . 
     Column traces  410  and row traces  420  can be placed on the surfaces of dielectric member  401  using any suitable patterning technique including for example, deposition, etching, printing and the like. Because row traces  420  may be either stimulated with an AC signal or held at a DC voltage level, and because column traces  410  need to be connected to analog channels so that modulated output signals can be detected, demodulated and converted to output values, electrical connections must be formed with row traces  420  and column traces  410 . 
     Flex circuits can be electrically connected directly to row traces  420  and column traces  410 . However, as the size of touch panel  400  increases, the size of the flex circuits required to couple directly to row traces  420  and column traces  410  also increases. In order to reduce the size of the flex circuits and to allow for greater variation in the placement of flex circuits, metal traces  415  and  425  can be used to connect row traces  420  and column traces  410  to the flex circuits. 
     Metal traces  415  and  425  can be beneficial for this arrangement because they allow the use of compact flex circuits  430  and  460 . Flex circuits  430  and  460  only occupy a small portion of the edges of touch panel. These flex circuits can be significantly smaller than the size of flex circuits that would be required to directly couple to row traces  420  and column traces  410 . For example, coupling flex circuitry directly to the row and column traces may require the flex circuits to span nearly the entire edge of the touch panel.  FIGS. 5 and 6  show two other exemplary arrangements that can be made by using metal traces to couple electrode rows and electrode columns to their respective flex circuits. 
       FIG. 5  shows an illustrative touch panel  500  in which the flex circuits are bonded to the same edge, on directly opposite sides of dielectric  501 . This arrangement can be made by running metal traces  525  along the edge of dielectric  501 . Connecting the flex circuits in this arrangement can minimize the area of touch panel  500  needed for connectivity and can reduce the overall size of touch panel  500 . Further, a single flex circuit can be fabricated to connect to rows  520  and columns  510  on directly opposing sides of the same edge of the substrate. Connecting the flex circuits in this arrangement can minimize the area of touch panel  500  needed for connectivity and can reduce the overall size of touch panel  500 . 
       FIG. 6  shows an illustrative touch panel  600  in which the flex circuits are bonded to the same edge, on the same side of dielectric  601 . This arrangement can be made by running metal traces through dielectric  601  in order to connect rows  620  to the top surface of dielectric  601  and then running metal traces  625  along the edge of the top surface of dielectric  601 . Connecting the flex circuits in this arrangement can minimize the area of touch panel  600  needed for connectivity and can reduce the overall size of touch panel  600 . Further, a single flex circuit can be fabricated to connect to rows  620  and columns  610 . 
     Many other arrangements of flex circuits on the touch panels are possible through the use of metal traces in this manner. In some embodiments, both electrode rows and electrode columns can be coupled to their respective flex circuits using metal traces. In some other embodiments, only one set of electrodes are couples to their flex circuit using metal traces. For example, in the embodiment of  FIG. 5  rows  520  can be coupled to a flex circuit using metal traces, while columns  510  can be coupled directly to their flex circuit. 
     While the use of metal traces has many advantages, routing signals along metal traces  415  and  425  has one drawback. Metal traces  415  and  425  can act like antennas and may cause radio-frequency interference (RFI) signals to be coupled to the sensing circuits. These RFI signals may adversely affect the operation of the touch screen and the accuracy at which touch screen  400  is able to detect user input. As the size of touch screen  400  increases, the lengths of metal traces  415  and  425  also increase, thereby increasing the affect of the RFI signals. 
     In accordance with this invention, the metal traces can be broken and resistors  416  and  426  can be inserted into the signal paths in order to reduce the affect of the RFI signals. Resistors  416  and  426  can preferably be fabricated using the same transparent conductive material used to form traces  410  and  420 . For example, resistors  416  and  426  may be formed from ITO. 
       FIG. 7  shows a single illustrative ITO column trace  710  that is connected to a capacitive sensing circuit  750  via a metal trace  726 , an ITO resistor  726  and a flex circuit  730 . The ITO may have a sheet resistivity of approximately 200 Ohms per square unit, making the resistance of resistor  746  approximately equal to 400 Ohms. It should be understood that any other suitable transparent conductive material may be used to form column trace  710  and resistor  726 . 
       FIG. 8  shows a schematic illustration of the elements of  FIG. 7 . Sensing line  820  can be modeled as a continuously distributed capacitance. The resistivity of metal trace  825  and flex circuit  830  can be ignored as being negligible. Finally, ITO resistor  826  in conjunction with capacitor  840  forms a low-pass filter. Capacitor  840  represents the input capacitance of capacitive sensing circuit  850  as well as the capacitance of the flex circuitry that is used to couple metal trace  825  to capacitive sensing circuit  850 . In this embodiment the capacitance of capacitor  840  can be approximated as 40 pf. With the proper resistance values, this low-pass filter can preferably block or at least significantly attenuate the RFI signals picked up by the metal traces before they are detected at the capacitive sensing circuit. For example, a low-pass filter with a capacitance value of 40 pf and a resistance value of 400 Ohms has a calculated cut-off frequency of 10 MHz. In other words, the resistance and capacitance combination formed by inserting ITO resistors into the metal traces of a touch panel can block most signals with a frequency higher than 1 GHz. This cut-off frequency is suitable to block most of the RFI from entering the capacitive sensing circuitry. The size of ITO resistor  826  can be adjusted to obtain an appropriate resistance value in order to ensure an appropriate cut-off frequency value. 
     Inserting the transparent conductive material resistors within the metal traces in this manner can be accomplished with little or no incremental cost because the transparent conductive material may already be patterned on the surface of the touch panel to create the transparent conductive material electrode rows and columns. These electrode rows and columns are generally formed by depositing an transparent conductive material layer over the substrate surface, and then by etching away portions of the transparent conductive material layer in order to form the lines. Therefore the transparent conductive material resistors, in accordance with the invention, may be formed as part of the process of creating the electrode rows and columns. Then, instead of etching away all of the extra portions of the transparent conductive material layer, some of the portions transparent conductive material may be kept to serve as transparent conductive material resistors. In some other embodiments, multiple layers of transparent conductive material may be deposited over the substrate surface thereby allowing the transparent conductive material resistors to be formed separately from the electrode rows and columns. In some embodiments, the transparent conductive material used to form the resistors can be different than the transparent conductive material resistors used to form the electrode rows and columns. 
     Furthermore, there is an additional benefit to leaving additional transparent conductive material on the surface of a touch panel. As should be appreciated, the areas with transparent conductive material tend to have lower transparency than the areas without transparent conductive material. This is generally less desirable for the user as the user can distinguish the lines from the spaces therebetween, i.e., the patterned transparent conductive material can become quite visible thereby producing a touch screen with undesirable optical properties. In order to prevent the aforementioned problem, rather than simply etching away all of the transparent conductive material, the dead areas (the uncovered spaces) may be subdivided into unconnected electrically floating transparent conductive material pads, i.e., the dead areas may be patterned with spatially separated pads. The pads are typically separated with a minimum trace width. Furthermore, the pads are typically made small to reduce their impact on the capacitive measurements. This technique attempts to minimize the appearance of the transparent conductive material by creating a uniform optical retarder. That is, by seeking to create a uniform sheet of transparent conductive material, it is believed that the panel will function closer to a uniform optical retarder and therefore non-uniformities in the visual appearance will be minimized. Thus, in some embodiments, in addition to floating transparent conductive material pads, transparent conductive material resistor blocks can be patterned on the surface of the touch panel to provide RFI blocking as well as increasing the uniformity of the visual appearance of the touch panel. 
       FIGS. 9 and 10  show two exemplary configurations for connecting a flex circuits to metal traces having integrated transparent conductive material resistors. In  FIG. 9 , metal traces  910  are etched into the top surface of touch panel  900 . Near the edge of touch panel  900 , metal traces  910  are broken and transparent conductive material resistors  920  are inserted. After transparent conductive material resistors  920  metal traces portions  910   a  continue and are connected to the copper traces of flex circuit  930 . While metal trace portions  910   a  do not benefit from the RFI blocking of transparent conductive material resistors  920 , these portions can be made sufficiently short to minimize the affect of the RFI. 
       FIG. 10  shows another configuration for connecting flex circuits to metal traces having integrated transparent conductive material resistors. Metal traces  1010  are etched into the top surface of touch panel  1000  and near the edge of touch panel  1000 , metal traces  1010  are broken and transparent conductive material resistors  1020  are inserted. Transparent conductive material resistors  1020  are formed sufficiently close to the edge of touch panel  1000  so that flex circuit  1030  can be bonded directly to transparent conductive material resistors  1020 . Thus, in this configuration, transparent conductive material resistors  1020  are able to block the RFI for the entirety of metal traces  1010 . 
       FIG. 11  shows a flowchart of process  1100  for fabricating a touch panel with integrated transparent conductive material resistors in accordance with the present invention. At step  1110  transparent conductive material traces are formed on a surface of a touch panel. At step  1120  metal traces are formed to connect the transparent conductive material traces to a flex circuit connector. At step  1130  the metal traces are broken and at step  1140  transparent conductive material resistors are formed within the breaks of the metal traces. While this invention has been primarily described with reference to breaking metal traces to form the transparent conductive material resistors, it should be understood these steps may also be accomplished using any number of suitable techniques. For example, rather than breaking a metal trace, a metal trace may be formed having a gap that is sized to accommodate an transparent conductive material resistor. Furthermore, in some embodiments, the transparent conductive material layer may be fabricated before the metal trace layer. In these embodiments, the metal trace portions may actually be formed around the transparent conductive material resistors. 
     Thus it is seen that the systems and method for fabricating touch panels with integrated transparent conductive material resistors in accordance with the present invention are provided. Those skilled in the art will appreciate that the invention can be practiced by other than the described embodiments, which are presented for purposes of illustration rather than of limitation, and the invention is limited only by the claims which follow.

Metadata:
Filing Date: 20070613
Publication Date: 20130319
Grant Date: 20130319
Priority Date: 20070613
Inventors: HOTELLING STEVE PORTER
LAND BRIAN RICHARDS
Assignee: APPLE INC
CPC Classifications: [{"code": "A61P33/06", "inventive": true, "first": false, "tree": "[]"}, {"code": "C12N2710/10343", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61P37/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/045", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/044", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0416", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/04164", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/04166", "inventive": true, "first": false, "tree": "[]"}, {"code": "C12N15/86", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/0443", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/04164", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0446", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y02A50/30", "inventive": false, "first": false, "tree": "[]"}, {"code": "Y02A50/30", "inventive": false, "first": false, "tree": "[]"}, {"code": "C12N2710/10343", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0446", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/04166", "inventive": true, "first": false, "tree": "[]"}, {"code": "C12N15/86", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/0443", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 39571361