Abstract:
A method for manufacturing a touch screen sensor assembly that includes providing a first transparent substrate, depositing a first non-metallic conductive layer onto the first substrate, removing the first conductive layer from a viewing portion of the first substrate, depositing a second non-metallic conductive layer onto the viewing portion, and removing portions of the second and first conductive layers to respectively form a first electrode pattern and a plurality of traces. The disclosed method also includes providing a second transparent substrate, depositing a third non-metallic conductive layer onto a viewing portion of the second substrate, removing portions of the third conductive layer to form a second electrode pattern, and bonding the first substrate to the second substrate using an optically clear adhesive. Each trace on the first substrate formed from the first conductive layer is electrically coupled to at least one electrode of either the first or second electrode patterns.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. 119 to U.S. Provisional Application No. 61/120,254, entitled: “CAPACITIVE TOUCH PANEL HAVING DUAL RESISTIVE LAYER,” filed on Dec. 5, 2008, the contents of which are incorporated herein as if set forth in full. 
    
    
     BACKGROUND 
     As computers and other electronic devices become more popular, touch-sensing systems are becoming more prevalent as a means for inputting data. For example, touch-sensing systems can be found in automatic teller machines, personal digital assistants, casino game machines, mobile phones, and numerous other applications. 
     Capacitive touch sensing is one of the most widely used techniques in touch screen industries. Capacitive touch sensors are mainly divided in two groups, namely, continuous capacitive sensors and discontinuous (patterned) capacitive sensors. In a continuous capacitive sensor, the sensor includes a sheet of conducting thin film that is electrically excited from four corners of the touch screen. The signals induced by a user&#39;s touch are transmitted from the four corners to a controller, where they are decoded and translated into coordinates. In a typical patterned capacitive touch screen, the sensor may include one or more series of parallel conductive bars that are driven from one or both ends with excitation signals from a controller coupled to the conductive bars by lead lines. The signals induced by a user&#39;s touch may be transmitted to the controller with the same lead lines that excite the sensor bars. These signals may then be decoded in the controller and the touch coordinates may be reported to a computer. 
     Touch sensors utilizing more than one patterned sensing layer are often used to determine the coordinates of a touch with high accuracy, provided that the sensing layers have a suitable pattern geometry. One example of a touch screen assembly  10  that includes two patterned conductive layers  12  and  14  is shown in  FIG. 1A  and  FIG. 1B . The patterned conductive layers  12  and  14  may be made from a transparent conductive material, such as indium tin oxide (ITO), and each layer is generally disposed on a transparent substrate (not shown here). Each row of conductive elements of each of the sensor layers  12  and  14  includes a series of diamond-shaped electrodes that are connected to each other with short strips of relatively narrow rectangles. A dielectric layer  16  separates the two conductive layers  12  and  14 , and serves to prevent them from coming into direct contact with each other. As an example the dielectric layer  16  may include an adhesive manufactured from any non-conductive, transparent material. 
     As shown, the end of each row of the two patterned conductive layers  12  and  14  is coupled to one of a set of traces  18  (e.g., silver traces) that are in turn coupled to a controller  20 . Generally, the traces  18  are used to couple the electrodes to the controller  20  because the resistance of the ITO conductive layer is relatively high. The resistance of the ITO conductive layer is relatively high because the amount of conductive material used in the ITO compound is kept relatively low so that the layer is substantially transparent. The traces  18  may generally be deposited on to the substrate using any suitable process. One method includes vacuum sputtering a metal layer (e.g., aluminum or Mo—Al—Mo) onto the substrate, then etching the traces  18  using a photo etching process. Another method includes silk-screen printing silver conductive ink to form the traces  18 . 
     The controller  20  may include circuitry for providing excitation currents to the capacitive sensors  12  and  14  and for detecting signals generated by the sensors. Further, the controller  20  may include logic for processing the signals and conveying touch information to another part of an electronic device, such as a processor. 
       FIG. 2  illustrates the various layers that may be included in a touch screen sensor assembly  40 . The assembly  40  includes a top substrate  42   a  and a bottom substrate  42   b  that are each coated with patterned ITO layers  44   a  and  44   b , respectively, that include a plurality of electrodes. The substrates  42   a  and  42   b  may be configured from any suitable transparent material, including glass, plastic (e.g., PET), or the like. Further, the top ITO layer  44   a  may be separated from the bottom ITO layer  44   b  by a suitable dielectric spacer  48  that is adhered by optically clear adhesive layers  46   a  and  46   b.    
     As discussed above, the ITO layers  44   a  and  44   b  may be coupled to one or more controllers that are operable to excite and sense electrical signals on the electrodes of the ITO layers  44   a  and  44   b . To electrically connect the controller to the ITO layers  44   a  and  44   b , a flexible printed circuit (FPC)  56  may be coupled to the assembly  40 . The FPC  56  may include an FPC substrate  55 , top copper traces  54   a , and bottom copper traces  54   b  that are used to couple the top and bottom ITO layers  44   a  and  44   b  to a controller. To make the connection between the copper traces  54   a  and  54   b  and the ITO layers  44   a  and  44   b , traces  50   a  and  50   b  may be disposed in contact with portions of the ITO layers. Further, the traces  50   a  and  50   b  may be coupled to the copper traces  54   a  and  54   b  using electrically conducive adhesive layers  52   a  and  52   b , which may, for example, include an anisotropic conductive adhesive (ACA). 
     SUMMARY 
     The following embodiments and aspects of thereof are described and illustrated in conjunction with systems, tools, and methods which are meant to be exemplary and illustrative, and not limiting in scope. In various embodiments, one or more of the above-described problems have been reduced or eliminated, while other embodiments are directed to other improvements. 
     According to a first aspect, a patterned substrate for use in a touch screen sensor assembly is provided. The patterned substrate includes a substrate and a first non-metallic conductive layer disposed on the substrate, the first non-metallic conductive layer forming a pattern of electrodes. The patterned substrate also includes a second non-metallic conductive layer disposed on the substrate, the second non-metallic conductive layer forming a pattern of traces that are each electrically coupled to at least one of the electrodes. In addition, the second non-metallic conductive layer has a surface resistivity that is less than the first non-metallic conductive layer. 
     According to a second aspect, a method for manufacturing a patterned substrate for a touch screen sensor assembly is provided. The method includes providing a substrate, and depositing a first non-metallic conductive layer onto the substrate, wherein the first non-metallic conductive layer has a surface resistivity. The method also includes removing the first non-metallic conductive layer from the substrate in a viewing portion of the substrate, wherein the viewing portion corresponds to an area of the substrate that is to be aligned with a display when the patterned substrate is configured as part of a touch screen sensor assembly. The method further includes depositing a second non-metallic conductive layer onto the viewing portion of the substrate, wherein the second non-metallic conductive layer has a surface resistivity that is higher than that of the first non-metallic conductive layer. Additionally, the method includes removing portions of the second non-metallic conductive layer to form a pattern of electrodes, and removing portions of the first non-metallic conductive layer to form a plurality of traces, wherein each trace is electrically coupled to at least one electrode. 
     According to a third aspect, a touch screen sensor assembly is provided that includes first and second substrates disposed in parallel with each other with a space therebetween. Each of the first and second substrates includes a first non-metallic conductive layer disposed on the substrate, the first non-metallic conductive layer forming a pattern of electrodes. Each of the first and second substrates also includes a second non-metallic conductive layer disposed on the substrate, the second non-metallic conductive layer forming a pattern of traces that are each electrically coupled to at least one of the electrodes. Further, the second non-metallic conductive layer has a surface resistivity that is less than the first non-metallic conductive layer. 
     According to a fourth aspect, a patterned substrate for use in a touch screen sensor assembly is provided. The patterned substrate includes a substrate and a first ITO layer disposed on the substrate, the first ITO layer forming a pattern of electrodes. The patterned substrate also includes a second ITO layer disposed on the substrate, the second ITO layer forming a pattern of traces that are each electrically coupled to at least one of the electrodes. Additionally, the second ITO layer has a surface resistivity that is less than that of the first ITO layer. 
     According to a fifth aspect, a method for manufacturing a touch screen sensor assembly is provided. The method includes providing a first transparent substrate and depositing a first non-metallic conductive layer onto the first transparent substrate, wherein the first non-metallic conductive layer has a surface resistivity. The method also includes removing the first non-metallic conductive layer from the first transparent substrate in a viewing portion of the first transparent substrate, wherein the viewing portion corresponds to an area of the first transparent substrate that is to be aligned with a display. The method further includes depositing a second non-metallic conductive layer onto the viewing portion of the first transparent substrate, wherein the second non-metallic conductive layer has a surface resistivity that is higher than that of the first non-metallic conductive layer. The method also includes removing portions of the second non-metallic conductive layer from the first transparent substrate to form a first pattern of electrodes, and removing portions of the first non-metallic conductive layer from the first transparent substrate to form a plurality of traces. Additionally, the method includes providing a second transparent substrate, and depositing a third non-metallic conductive layer onto the viewing portion of the second transparent substrate, wherein the third non-metallic conductive layer has a surface resistivity that is substantially equal to that of the second non-metallic conductive layer. Further, the method includes removing portions of the third non-metallic conductive layer from the second transparent substrate to form a second pattern of electrodes, and bonding the first transparent substrate to the second transparent substrate using an optically clear adhesive. In addition, each trace on the first transparent substrate formed from the first non-metallic conductive layer is electrically coupled to at least one electrode of either the first pattern of electrodes or the second pattern of electrodes. 
     In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following descriptions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  illustrate a top view and cross-sectional view of a prior art capacitive touch sensor assembly. 
         FIG. 2  illustrates the configuration of various layers for a prior art touch screen sensor assembly. 
         FIG. 3  illustrates an automatic teller machine that incorporates an exemplary touch screen assembly. 
         FIG. 4  illustrates an electronic device that incorporates an exemplary touch screen sensor assembly. 
         FIGS. 5-8  illustrate process steps for manufacturing an exemplary touch screen sensor assembly. 
         FIG. 9  illustrates the configuration of various layers for an exemplary touch screen sensor assembly. 
         FIGS. 10A-H  illustrate an exemplary manufacturing process for a touch screen sensor assembly. 
     
    
    
     DETAILED DESCRIPTION 
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that it is not intended to limit the invention to the particular form disclosed, but rather, the invention is to cover all modifications, equivalents, and alternatives falling within the scope and spirit of the invention as defined by the claims. 
       FIGS. 3 and 4  illustrate an automatic teller machine (ATM)  60  that incorporates an exemplary touch screen sensor assembly  62 . Although the ATM  60  is illustrated, the embodiments described herein may be incorporated into any electronic device that includes a touch screen, such as a personal digital assistant (PDA), a casino game machine, a mobile phone, a computer, a voting machine, or any other electronic device. The touch screen sensor assembly  62  may include two layers of transparent patterned conductive material (may also be called “resistive” material), such as a non-metallic ceramic like ITO, that are disposed on two substrates positioned in a spaced, parallel relationship (see  FIG. 9 ). The touch screen sensor assembly  62  may also be coupled to control logic  66  (shown in  FIG. 3 ) that is operable to excite the conductive material and to sense touches on or near the touch screen sensor assembly  62 . As an example, the control logic  66  may include a commercial touch screen controller (e.g., a controller provided by Cypress Semiconductor, Analog Devices, Atmel, Synaptics, and others), an application specific integrated circuit (ASIC), or any other suitable controller. Further, the touch sensor assembly  62  may overlay a display  64  (shown in  FIG. 3 ), which may be any type of display, such as an LCD display. 
       FIGS. 5-8  illustrate top views of an ITO patterned substrate  70  in various sequential stages of an exemplary manufacturing process. The substrate  70  may be included in a touch screen sensor assembly (e.g., the touch screen sensor assembly  62  shown in  FIGS. 3-4 ). Throughout  FIGS. 5-8 , similar or identical elements are indicated by the same reference numerals. 
       FIG. 5  shows the substrate  70  after it has been coated with an ITO layer  72  that has a relatively low surface resistivity (e.g., less than 20 Ohms, less than 10 Ohms, or the like). The ITO layer  72  may be deposited onto the substrate  70  using any suitable process, such as vacuum sputtering. Although the ITO layer  72  is shown to be opaque, this is generally for illustrative purposes and it should be appreciated that the layer  72  may be somewhat transparent. The substrate may be formed from any suitable material, including glass, plastic (e.g., PET), or other material. 
       FIG. 6  illustrates the next step in the manufacturing process, which is to remove (e.g., by photo etching) the lower resistance ITO layer  72  off the portion of the substrate  70  that will overlay a display (indicated by the arrow  74 ). A section of the ITO layer  72  is retained along one or more edges of the substrate  70  that will not overlay the display, and is used in a later step to form traces that function to couple the ITO electrodes to a controller. Although only a strip of the ITO layer  72  is retained in  FIG. 6 , it should be appreciated that the ITO layer  72  may be retained wherever it may be desirable to form conductive traces on the substrate  70 . Further, the low resistance ITO layer  72  may not be used in the viewing area because its transparency may be too low, such that the layer  72  would obstruct the view of an underlying display. 
       FIG. 7  illustrates the next step in the manufacturing process, which is to deposit (e.g., by vacuum sputtering) a relatively higher resistance ITO layer  76  onto the viewing portion of the substrate  70 . As a non-limiting example, the ITO layer  76  may have a surface resistivity of about 50 Ohms, 100 Ohms, 200 Ohms, or the like. The ITO layer  76  may be relatively transparent, so that the view of a display associated with an assembled touch screen that includes the substrate  70  will not be obstructed. 
       FIG. 8  shows the substrate  70  after the next step in the manufacturing process, wherein a pattern of electrodes has been formed by etching (e.g., photo etching) the higher resistivity ITO layer  76 , and traces have been formed by etching the lower resistivity ITO layer  72 . In this regard, the electrodes formed by the ITO layer  76  may be coupled to a controller by the traces formed by the ITO layer  72 , which advantageously eliminates the need for metal traces. It should be appreciated that  FIG. 8  illustrates one example of a pattern of electrodes and traces, and that the manufacturing process described herein may be used to produce a substrate with any suitable pattern of electrodes and traces. 
       FIG. 9  illustrates the various layers that may be included in an exemplary touch screen sensor assembly  80 . The assembly  80  includes a top substrate  82   a  and a bottom substrate  82   b  that are each coated with relatively high resistance ITO layers  84   a  and  84   b  (labeled ITO 1 ), respectively, that include a plurality of electrodes. The substrates  82   a  and  82   b  may be configured from any suitable transparent material, including glass, plastic (e.g., PET), or the like. Further, the top ITO layer  84   a  may be separated from the bottom ITO layer  84   b  by a suitable dielectric spacer  88  that is adhered by optically clear adhesive layers  86   a  and  86   b.    
     As discussed above, the ITO layers  84   a  and  84   b  may be coupled to one or more controllers that are operable to excite and sense electrical signals on the electrodes of the ITO layers  84   a  and  84   b . To electrically connect the controller to the ITO layers  84   a  and  84   b , a flexible printed circuit (FPC)  96  may be coupled to the assembly  80 . The FPC  96  may include an FPC substrate  95 , top copper traces  94   a , and bottom copper traces  94   b , that are used to couple the top and bottom ITO layers  84   a  and  84   b , respectively, to a controller. To make the connection between the copper traces  94   a  and  94   b  and the ITO layers  84   a  and  84   b , lower resistance ITO layers  90   a  and  90   b  (labeled ITO 2 ) may be disposed in contact with portions of the ITO layers  84   a  and  84   b . Further, the lower resistance ITO layers  90   a  and  90   b  may be coupled to the copper traces  94   a  and  94   b  using electrically conductive adhesive layers  92   a  and  92   b , which may, for example, include an anisotropic conductive adhesive (ACA). It is noted that one reason the lower resistance ITO layers  90   a - b  are used for connection to the copper traces  94   a - b , as opposed to the higher resistance ITO layers  84   a - b , is that it may be desirable that the trace widths be relatively narrow, as narrow trace widths reduce the area required for the traces, and may also reduce the undesirable capacitance present in the traces. At the desirable trace widths, the relatively transparent ITO layer  84  may have a high resistance, which would greatly reduce the performance of the touch screen sensor. 
       FIGS. 10A-H  illustrate an exemplary manufacturing process for a touch screen sensor assembly including ITO layers having two different resistivities. For example, the process may be used to manufacture the touch screen sensor assembly  62  shown in  FIGS. 3 and 4 . As shown in  FIG. 10A , the touch screen sensor assembly may include a bottom substrate  100  constructed from a suitable transparent material (e.g., glass, PET, or the like). The bottom substrate  100  may be coated with a layer  102  of ITO (or other suitable material) having a relatively low resistivity (e.g., 50 Ohms/square, or the like) using a deposition process such as vacuum sputtering. 
     Next, as shown in  FIG. 10B , the low resistivity ITO layer  102  may be etched away from a viewing portion  104  of the bottom substrate  100 . The etching may be performed by any suitable layer removal process, such as photo etching, or the like. 
     Once the low resistivity ITO layer  102  has been etched away from the viewing portion  104  of the bottom substrate  100 , a high resistivity ITO layer  106  may be deposited onto the viewing portion  104  of the bottom substrate  100 , as shown in  FIG. 10C . In a similar step shown in  FIG. 10D , a high resistivity ITO layer  122  may be deposited onto a top substrate  120 . As can be appreciated, the high resistivity ITO layers  106  and  122  may be more transparent than the low resistivity ITO layer  102 , such that a user may view a display that resides behind the viewing portion  104  of the assembled touch screen sensor assembly. 
       FIG. 10E  illustrates the result after an etching process, wherein the high resistivity ITO layer  106  has been etched into a pattern of electrodes. Further, the low resistivity ITO layer  102  has been etched into a pattern of traces outside of the viewing portion  104  of the bottom substrate  100 . The pattern of traces etched from the low resistivity ITO layer  102  includes a plurality of traces  103  and connection points  108  that are coupleable to electrodes formed by the high resistivity ITO layer  122  of the top substrate  120  when the touch screen sensor is assembled. Further, the traces etched from the ITO layer  102  include a portion  110  that operates to couple a connector to the traces (see  FIG. 10H ) so that the touch screen sensor may be connected to a controller and/or a computer system. Similarly,  FIG. 10F  illustrates the result after the high resistivity ITO layer  122  has been etched into a pattern of electrodes on the top substrate  120 . 
       FIG. 10G  illustrates the result after the bottom substrate  100  and the top substrate  120  have been laminated together using a suitable optically clear adhesive (OCA). As shown, the “rows” of electrodes formed from the ITO layer  106  and the “columns” of electrodes formed from the ITO layer  122  are aligned with each other to form a diamond pattern of electrodes that substantially covers the viewing portion of the touch screen sensor assembly. Further, as noted above, the electrodes formed from the ITO layer  122  of the top substrate  120  are coupled to the traces  103  via the connection points  108 , such that the traces formed from the low resistivity ITO layer  102  may operate to couple the electrodes from both the top substrate  120  and the bottom substrate  100  to a controller and/or a computer system. 
       FIG. 10H  illustrates the touch screen sensor assembly after a connector  130  (e.g., a flexible printed circuit connector) has been bonded to the bottom substrate  100  such that the traces formed from the ITO layer  102  are coupled to contacts of the connector  130 . The connector  130  may be bonded to the bottom substrate  100  using any suitable adhesive, such as an anisotropic conductive film (ACF) or adhesive. 
     The features described herein offer several advantages over previous designs. For example, in the case where metal traces are used, the manufacturing costs and complexity are high and environmental pollution may be a considerable problem. As another example, when silver conductive ink is printed for the traces, the trace height may be relatively large (e.g., greater than 10 um), the trace width must be relatively wide (e.g., greater than about 40 mm), and printing tolerances may be relatively large. Generally, a large trace height can cause unwanted bubbles to be formed when the top and bottom substrates are assembled together. By using a relatively low resistance ITO layer for the traces, the above-noted shortcomings are reduced or eliminated. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description is to be considered as exemplary and not restrictive in character. For example, certain embodiments described hereinabove may be combinable with other described embodiments and/or arranged in other ways (e.g., process elements may be performed in other sequences). Accordingly, it should be understood that only the preferred embodiment and variants thereof have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.