Abstract:
A capacitive electrode has a flat electrode with a geometric shape, wherein at least one central portion of the electrode is removed to provide for a frame-like form of the electrode.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates in general to human interface devices and in particular to capacitive sensor electrodes. 
       BACKGROUND 
       [0002]    Capacitive sensing electrodes are used for many different purposes, for example, to provide for a human interface device. Many different types of keyboard like interfaces, touchscreen interfaces or pen tablet devices have been developed and are in existence. For these type of devices and interfaces, capacitive sensors as shown in  FIGS. 1 and 2  are used. These capacitive sensor electrodes as shown, however can only provide for a limited sensitivity. There are a number of different electrode patterns that have been developed and used in the marketplace for Projected Capacitive Touch Sensors. However, there still exists a need exists for an improved capacitive sensor electrode that can provide increased sensitive and also reliability. 
       SUMMARY 
       [0003]    According to an embodiment, a capacitive electrode may have a flat electrode having a geometric shape, wherein at least one central portion of the electrode is removed to provide for a frame-like form of the electrode. 
         [0004]    According to a further embodiment, a thickness of the frame may define a capacitive parameter of the electrode. According to a further embodiment, the electrode may comprise a base frame and a plurality of finger frames arranged perpendicular to the base frame and overlapping the base frame. According to a further embodiment, the electrode can be formed by a layer of Indium Tin Oxide (ITO) on plastic film or glass. According to a further embodiment, the electrode can be formed by a layer of electrically conductive material on a substrate. 
         [0005]    According to another embodiment, a capacitive sensor structure may comprise a first layer with a plurality of capacitive electrodes arranged in parallel, wherein each electrode comprises a flat electrode having a geometric shape, wherein at least one central portion of the electrode is removed to provide for a frame-like form of the electrode. 
         [0006]    According to a further embodiment of the above capacitive sensor, the capacitive sensor structure may further comprise a second layer of electrodes arranged perpendicular to said electrodes of the first layer, wherein first and second layer are insulated by a substrate. According to a further embodiment of the above capacitive sensor, a thickness of the frame may define a capacitive parameter of the electrode. According to a further embodiment of the above capacitive sensor, the electrode may comprise a base frame and a plurality of finger frames arranged perpendicular to the base frame and overlapping the base frame. According to a further embodiment of the above capacitive sensor, the first layer further may comprise connection lines for electrically connecting the electrode. According to a further embodiment of the above capacitive sensor, the base frame and the finger frames can each be rectangular frames. According to a further embodiment of the above capacitive sensor, the base frame and the finger frames may each be rectangular frames. According to a further embodiment of the above capacitive sensor, the connection line may extend through a length of the base frame thereby providing for at least two central portions of the electrode being removed. According to a further embodiment of the above capacitive sensor, the finger frames can overlap the base frame symmetrically. According to a further embodiment of the above capacitive sensor, the finger frames of the most right and the most left electrodes of the first layer may overlap the respective base frame asymmetrically. According to a further embodiment of the above capacitive sensor, finger frames of an electrode can be offset and arranged in inter-digit fashion with respect to finger frames of an adjacent electrode. According to a further embodiment of the above capacitive sensor, finger frames of adjacent electrodes may provide for a mutual capacitances between adjacent electrodes. According to a further embodiment of the above capacitive sensor, the electrode can be formed by a layer of Indium Tin Oxide (ITO) on plastic film or glass. According to a further embodiment of the above capacitive sensor, the electrode can be formed by a layer of electrically conductive material on a substrate. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  shows a conventional grid for providing capacitive sensing in a touchscreen pen tablet device. 
           [0008]      FIG. 2  shows typical variants of capacitive sensor electrodes as used, for example, in a conventional grid. 
           [0009]      FIG. 3  shows first and second embodiments of an improved capacitive sensor electrode. 
           [0010]      FIG. 4  shows further embodiments of capacitive sensor electrode. 
           [0011]      FIG. 5  shows the effect of manufacture defects in a conventional electrode and an electrode according to various embodiments. 
           [0012]      FIG. 6  illustrates the improved sensing properties of a capacitive sensor electrode according to various embodiments. 
           [0013]      FIG. 7  shows an embodiment of a top sensor structure for use in a touchscreen or tablet device. 
           [0014]      FIG. 8  shows an enlarged section of the structure according to  FIG. 7 . 
           [0015]      FIG. 9  shows an embodiment of a bottom sensor structure associated with the top sensor structure shown in  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    A projected capacitive touch sensor often consists of, but is not limited to two layers, each having a plurality of conductive electrodes arranged parallel to each other as shown in  FIG. 1 . The layers are fixed in close proximity to each other and electrically insulated from each other. Transparent materials are used for touchscreen devices whereas pen tablets or track pads do not require such material as they are not necessarily combined with a display. The layers are generally oriented with their electrodes orthogonal to each other. The example in  FIG. 1  has the top layer electrodes labeled Y01-Y09 and bottom layer electrodes labeled X01-X12. These electrodes therefore form a grid wherein the primary capacitive couplings are provided at each intersection. As mentioned above, the electrodes are often constructed of, for example, Indium Tin Oxide (ITO) on plastic film or glass for use with display devices. 
         [0017]      FIG. 2  shows specific structures as commonly used in such matrix sensor arrangements. Structure  210  is the most basic form similar to the electrodes shown in  FIG. 1 . Structure  220  differs in providing a plurality of side arms thereby forming a ladder shaped sensor electrode. 
         [0018]      FIG. 3  shows embodiments of improved capacitive sensor electrodes according to various embodiments. The concept according to various embodiments is to change from a conventional solid conductor electrode for the sensor&#39;s top layer “receivers” to be frame or outline conductors as shown in  FIGS. 3 and 4 . As shown in  FIGS. 3 and 4 , these improved capacitive sensor electrodes  310 - 340  can also be applied to electrodes of different patterns. The frame conductor electrodes according to various embodiments have a number of advantages with respect to manufacturability and yield, electrode capacitance control, improved touch sensitivity. 
       Manufacturability and Yield 
       [0019]    It may sometimes be desirable for the electrode width to be near the minimal capability of manufacturing methods. If this is the case, then variations in the manufacturing process may result in some of the electrodes being electrically broken as shown in  FIG. 5  with electrode  210  and breaking point  510 . The broken electrodes  210  as shown in  FIG. 5  cause a functionality problem with an integrated touch product and would therefore normally be scrapped in manufacturing. This decreases the manufacturing yield, which increases the product cost of manufacturing. The frame conductor electrodes  310  according to various embodiments can suffer from a single break  520  and still remain functional as shown in  FIG. 5 . This presents a manufacturing advantage when the desired electrodes are close to the manufacturing capabilities. The advantage provided by the various embodiments of capacitive sensor electrodes is that it may reduce the manufacturing cost, depending on the desired electrode dimensions and the manufacturing process limitations. 
       Electrode Capacitance Control 
       [0020]    The capacitance of an electrode is partially dependent on the surface area of the conductor. The frame conductor according to various embodiments allows additional design control over the capacitance of the electrodes as shown in  FIG. 4  with different frame sizes in electrodes  330 ,  340  and  340 . This is important because certain projected capacitive controllers might realize performance benefits by the receiver electrodes being either lower or higher in capacitance. For a given desired conductor footprint, as shown with electrode embodiments  330 ,  340 , and  350 , the width of the loop conductor can be varied by design to alter the capacitance of the overall electrode. The advantage provided by the various embodiments is that it enables some design control over the capacitance of a given electrode footprint. 
       Improved Touch Sensitivity 
       [0021]    The loop conductor electrode according to various embodiments as shown for example in  FIGS. 3 and 4  alters the shape of the electric field. The frame, for example as shown in the top embodiment of  FIG. 3 , essentially creates dual electrically common capacitor plates  315 ,  317  on the sensor&#39;s top layer “receivers”.  FIG. 6  shows the effect provided by the dual capacitor plates resulting in improved touch sensitivity and electric field shaping. 
         [0022]    It is desired for a touch to alter the electric field. The effect of the dual plates  315  and  317  as shown in  FIG. 6  is to change the electric field characteristics. The standard “filled” electrode  210  shown on the left side of  FIG. 6  has two strong regions of fringe field over the two sides of the electrode, which a touch, for example by a finger  600  could alter. The frame electrode  315 ,  317  provides in contrast for four strong regions of fringe field over the four sided of the dual plates electrode  315 ,  317 , which a touch by a finger  600  could alter. Thus, according to various embodiments, more pronounced top side fringe electric fields are created, which can increase the sensitivity to a touch from above. 
         [0023]      FIG. 7  shows an embodiment of a plurality of frame sensor electrodes arranged in vertically parallel for use in a touch sensor device, for example, a top layer electrode structure in a touchscreen or a touch pad device. The structure  700  provides for a plurality of frame sensor electrodes  710  according to various embodiments wherein the most left and right electrodes may be shaped slightly different as shown in  FIG. 700 . According to an embodiment as shown in more detail in  FIG. 8 , each frame sensor electrode  710  of the top layer provides for a rectangular framed sensor electrode base  810  and a plurality of rectangular framed side arm or finger electrodes  820  overlapping the base. A connecting line  830  connects an evaluation circuit with the electrode  710 . As shown in  FIG. 8 , the connection line may be extended through the frame of the base  810 , thus providing for even more capacitor plates. The framed side arms  820  of each electrode may be slightly offset to the framed side arms of an adjacent electrode and neighboring electrodes may be arranged in an inter-digit fashion as shown in  FIGS. 7 and 8 . The center electrodes comprise fingers section  820  arranged symmetrically whereas the most left and most right electrodes are shaped asymmetrical with respect to the finger sections  820 . The offset arrangement of the frame fingers  820   a  of one electrode with respect to frame fingers  820   b  of an adjacent electrode further provides for a mutual capacitance between the neighboring electrodes which also can be alters by a touch. 
         [0024]      FIG. 9  shows a corresponding bottom electrode structure of the bottom electrodes which here use a conventional electrode formatted and provide for a plurality of horizontally parallel arranged counter electrodes. The top and bottom layer may be separated by glass or a printed circuit board or any other suitable substrate. According to some embodiments, the electrodes of the bottom layer can also be formed similarly to those of the top layer. 
         [0025]    Even though the embodiment shown in  FIGS. 7-9  can be used for touchscreen sensors or track pad sensors, the electrodes according to various embodiments can be used for other purposes, such as simple touch sensors, sliders or other operating elements. The geometric shapes are not limited to the shown examples. Rather these shapes are mere suggestions for an electrode. Other shapes and forms for electrodes may be used.