Abstract:
The panel is composed of a touch sensing structure and a touch pressure sensing structure, which separately include functional layers. The touch sensing structure can determine the location of a touch by a change in capacitance on the surface when touching the panel. The touch pressure sensing structure has a strain isolation layer with a property of elastic deformation between electrodes for detecting pressure applied onto the panel by a change in capacitance resulting from relative displacement between two electrodes.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Technical Field 
         [0002]    The invention relates to input devices for portable computers, particularly to touchscreens. 
         [0003]    2. Related Art 
         [0004]    For inputting texts, touchscreen modules have been extensively applied in smartphones, tablets and laptop computers. Conventional touchscreens can detect a coordinate of the position which is being touched, so they can cooperate with the screen picture to input texts or make an operation. In some cases, such an operating mode may meet a difficulty, for example, a virtual key shown on a touchscreen may be unexpectedly activated because it merely needs a very light force or even does not need a force to apply thereon. In order to avoid such a problem, how to correctly detect a touching operation to a virtual key is the core. A currently known solution is to add a pressure sensor under the touchscreen, by which a force exerted on the touchscreen can be detected. As a result, a touching operation can be correctly determined. 
         [0005]    U.S. Pat. No. 8,988,384 discloses a force sensor interface in a touch controller of a touch sensitive device, which includes one or more touch sensors and one or more force sensors. The touch controller can correctly determine a touch operation by associating a touch signal with a force signal. The touch sensitive device includes a rigid cover, under which the touch sensors and force sensors are arranged. The rigid cover will not be bent or deformed to trigger the force sensor. Such a force sensor is a strain gauge based upon a resistor bridge a shown in  FIG. 4B . The strain gauge is a force sensitive variable resistor which varies in resistance depending on a force applied thereon. As a result, the force sensor can detect the force from a touching operation. In this solution, the touch sensors and the force sensors are independent elements and the force sensors are disposed near or under the touch sensors. It is a serious challenge in assembling accuracy. And the force sensors will also increase an overall thickness of a touch sensitive device. This is not advantageous to portable devices. Additionally, the rigid cover must be movable to deliver the applied force to the force sensors, so such a movable mechanism may reduce or damage a sealing effect of the product. 
       SUMMARY OF THE INVENTION 
       [0006]    An object of the invention is to provide a touch and pressure sensitive panel, which is easy to be manufactured. Thus its manufacturing cost can be effectively reduced. 
         [0007]    Another object of the invention is to provide a touch and pressure sensitive panel, which is a flexible thin plate without any movable mechanism. Thus it will not reduce or damage a sealing effect of a product using it. 
         [0008]    To accomplish the above objects, the touch and pressure sensitive panel of the invention includes: 
         [0009]    a surface layer, being a flexible transparent sheet; 
         [0010]    an insulative layer, being a flexible transparent sheet; 
         [0011]    a first electrode layer, being a flexible transparent conductive film, sandwiched between the surface layer and the insulative layer, and having sensing electrodes covered by the surface layer; 
         [0012]    a second electrode layer, being a flexible transparent conductive film, disposed under the insulative layer, and having driving electrodes, wherein the insulative layer is sandwiched between the first electrode layer and the second electrode layer to form a touch sensing structure; 
         [0013]    a strain isolation layer, disposed under the second electrode layer, and having a property of elastic deformation 
         [0014]    a third electrode layer, disposed under the strain isolation layer, and having sensing electrodes; and 
         [0015]    a base layer, being a rigid transparent sheet, disposed under the third electrode layer; 
         [0016]    wherein the sensing electrodes on the third electrode layer and the driving electrodes on the second electrode layer face each other and keep a gap therebetween, the strain isolation layer completely fill the gap, and the second and third electrode layers and the strain isolation layer constitute a touch pressure sensing structure. 
     
    
     
       BRIEF DESCRIPTION OF THE INVENTION 
         [0017]      FIG. 1  is an exploded view of the invention; 
           [0018]      FIG. 2  is a cross-sectional view of the invention; 
           [0019]      FIG. 3  is another cross-sectional view of the invention when being pressed; 
           [0020]      FIG. 4  is a schematic view of patterns of the second and third electrode layers; and 
           [0021]      FIG. 5  is a cross-sectional view of another embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    Please refer to  FIGS. 1 and 2 . As shown, the touch and pressure sensitive panel of the invention includes a surface layer  10 , a first electrode layer  20 , an insulative layer  30 , a second electrode layer  40 , a strain isolation layer  50 , a third electrode layer  60  and a base layer  70 . 
         [0023]    The surface layer  10  is made of a transparent sheet material, such as an optical glass sheet. To make the surface layer  10  flexible, its thickness is about 0.4 mm. Also, the surface layer  10  may be further reinforced by a chemical or tempering process. Additionally, each of four corners of the surface layer  10  is formed with a chamfering  11  to prevent the surface layer  10  from peeling off. 
         [0024]    The first electrode layer  20  is a flexible transparent conductive film, such as an ITO (indium tin oxide) conductive film, and is sandwiched between the surface layer  10  and the insulative layer  30 . There are sensing electrodes  21  at regular intervals on the first electrode layer  20 . 
         [0025]    The insulative layer  30  is a flexible transparent sheet, for example, an optical glass plate or PMMA (polymethylmethacrylate) or COP (cyclo olefin polymers) thin plate with a thickness of about 0.1 mm. Alternately, the insulative layer  30  may select a dielectric material to improve a gain of touch signal. 
         [0026]    The second electrode layer  40  is a flexible transparent conductive film, such as an ITO conductive film, and is disposed under the insulative layer  30 . There are driving electrodes  41  at regular intervals on the second electrode layer  40 . Preferably, an ITO conductive layer may be directly formed on each side of the insulative layer  30  in advance, and then an etching process is applied to form an electrode pattern. 
         [0027]    The base layer  70  is a rigid transparent plate, such as an optical glass sheet with a thickness of about 0.2 mm. The rigid base layer  70  can provide support to the third electrode layer  60  to prevent from being bent by pressure. Usually, the invention is used for being disposed over a display (not shown), so the base layer  70  can be supported by the display on which the invention is placed. As a result, the base layer  70  will not be bent by normal pressure. 
         [0028]    The third electrode layer  60  is a transparent conductive film, such as an ITO conductive film. There are sensing electrodes  61  at regular intervals on the third electrode layer  60 . The third electrode layer  60  is disposed on the base layer  70  and under the second electrode layer  40  with a parallel gap D, which is about 150 μm. 
         [0029]    The strain isolation layer  50  is formed by filling the space formed by the gap D with a transparent insulative material with a property of elastic deformation. The strain isolation layer  50  isolates the second and third electrode layers  40 ,  60 . The strain isolation layer  50  will be deformed by pressure applied on the surface layer  10 , its property of elastic deformation allows the electrodes  41 ,  61  to change their relative positions, for example, shortening a vertical distance between two opposite electrodes or changing a horizontal interval between two adjacent electrodes. When the pressure removes, the strain isolation layer  50  resumes to its original shape and restores relative positions between two opposite layers of electrodes  41 ,  61 . The strain isolation layer  50  may select a material with a low index of refraction or an index of refraction near that of glass, such as an OCA (optical clear adhesive) or a dielectric material. When an OCA is adopted, it can further provide adhesion between the second and third electrode layers  40 ,  60 . When a dielectric material is used, it can gain a touch signal of a touching operation. 
         [0030]    The first electrode layer  20 , the second electrode layer  40  and the insulative layer  30  constitute a touch sensing structure  100 . Of course, the sensing electrodes  21  on the first electrode layer  20  and the driving electrodes  41  on the second electrode layer  40  can be separately electrically connected to a touch controller (not shown). 
         [0031]    As shown in  FIG. 2 , when a touching matter  80  such as a finger nears the surface layer  10 , the driving electrodes  41  near the touching matter  80  capacitively couple the touching matter  80 , and then charges will be grounded from the stimulated driving electrodes  41  through the touching matter  80 . This can reduce capacitance between the driving electrodes  41  and the sensing electrodes  21 . This change of capacitance can be interpreted as a touching position. 
         [0032]    The second electrode layer  40 , the third electrode layer  60  and the strain isolation layer  50  constitute a touch pressure sensing structure  200 . Of course, the driving electrodes  41  on the second electrode layer  40  and the sensing electrodes  61  on the third electrode layer  60  can be separately electrically connected to a touch controller (not shown). 
         [0033]    Please refer to  FIG. 3 . When a touching matter  80  applies pressure on the surface layer  10 , the surface layer  10 , the first electrode layer  20 , the insulative layer  30  and the second electrode layer  40  will be bent, and the strain isolation layer  50  generates elastic deformation to make the distances between the driving electrodes  41  on the second electrode layer  40  and the sensing electrodes  61  on the third electrode layer  60  shortened. As a result, capacitance between the two opposite electrodes  41 ,  61  will increase proportionally to the measurement of the pressure and the gap capacitance will also increase correspondingly. Besides, the elastic deformation of the strain isolation layer  50  also makes horizontally relative positions between the driving electrodes  41  and the sensing electrodes  61  shifted and a part of these electrodes  41 ,  61  will overlap with each other. This also causes increase of capacitance between two electrodes and the capacitance increases proportionally to the measurement of the pressure, i.e., overlapping capacitance increases correspondingly. As a result, this change of capacitance can be interpreted as pressure applied on the surface layer  10 . 
         [0034]    In order to increase sensible capacitance between the second and third electrode layers  40 ,  60 , the driving electrodes  41  and the sensing electrodes  61  can be formed into a grid shape with an interlacing arrangement as shown in  FIG. 4 . This can enhance accuracy of detection of pressure from the touching matter  80 . As a result, the touch pressure sensing structure  200  can obtain various levels of pressure measurement. 
         [0035]    In the above embodiment, the touch sensing structure  100  is the same as the touch pressure sensing structure  200  in fundamental framework. Accordingly, the invention can be applied without changing currently existing capacitive touchscreens, even can be compatible to currently existing controllers for capacitive touchscreens. This can effectively save costs of development of a new component. Furthermore, the touch sensing structure  100  and the touch pressure sensing structure  200  commonly share the driving electrodes  41  on the second electrode layer  40 . However, in another embodiment, a fourth electrode layer  90  can be further added between the second electrode layer  40  and the strain isolation layer  50  as shown in  FIG. 5 . The fourth electrode layer  90  is a flexible transparent conductive film and has driving electrodes  91 . The fourth electrode layer  90 , the third electrode layer  60  and the strain isolation layer  50  constitute a touch pressure sensing structure  200 . This creates an arrangement that each sensing electrode  61  associates with an exclusive driving electrode  91  to further improve sensing accuracy. 
         [0036]    It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims.