Abstract:
A touch-sensitive interface module that is able to provide 3-dimensional information about a touch by a user is disclosed. The touch-sensitive interface can detect the x-y position and the amount of the force applied on the interface. It comprises of a flexible display panel, an array of MEMS capacitive force sensors, each of which is electrically addressable and/or a circuit board of electrical connections. The force sensors comprise of a piston-tube electrode configuration that allows for easy to detect capacitive changes even when a small force is applied.

Description:
RELATED APPLICATIONS 
       [0001]    This application repeats a substantial portion of prior application Ser. No. 14/449,544 filed on Aug. 1, 2014 and U.S. Pat. No. 9,306,475 B1, issued Apr. 5, 2016, and adds and claims additional disclosure not presented in the prior application. Since this application names the inventor or at least one joint inventor named in the prior application, it may constitute a continuation-in-part of the prior application. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to the field of touch-sensitive electronic interfaces that are used in a variety of consumer electronic devices that receive an input from a user using a finger touch or an object. 
       BACKGROUND OF THE INVENTION 
       [0003]    Current electronic devices utilize touch-sensitive screens to receive an input from a user. Most of these screens have the ability to detect either the x-y position of the finger touched the screen or the amount of the force applied. Projected or surface capacitive touch screens are widely used in such electronic devices to sense the x-y position of the fingers. However, they are only responsive to capacitive objects such as human fingers or a stylus or any other object that is capacitive. But such screens do not have the capability to detect the amount of the force applied, limiting the user experience. Other capacitive touch screens are meant to provide 3-dimensional information such as the inventions disclosed in US20120013571 A1 and US8169416B2. However, these inventions are based on parallel plate capacitor configurations in which the stroke of the plate is limited to one third of the initial gap between the capacitor plates. To make such a configuration highly sensitive, the gap between the plate electrodes has to be small; which in turn limits the dynamic range of the sensor in terms of the range of the force applied. 
         [0004]    Piezoresistive touch screens offer the ability to detect the x-y position and the amount of the force applied. However, such technologies suffer from low sensitivity when the forces applied are limited to a small range, such as when a finger touch is applied. In addition, these piezoresistive touch sensors are sensitive to temperature changes. These type of touch screens are also complex in structure as they might contain liquid cells. An example of such screens is presented in US Provisional Patent Applications No. US20130096849 A1, 2014/0007705 A1, and US 20150138112 A1. 
         [0005]    The present invention of a touch-sensitive interface module, which is based on a MEMS piston-tube capacitive force sensor, is able to overcome the limitations of conventional capacitive touch screens. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention discloses a touch-sensitive interface based on MEMS capacitive force sensors that can detect an input force by utilizing the MEMS electrostatic piston-tube electrode configuration that was previously disclosed in U.S. patent application Ser. No. 15/091,259 and U.S. Pat. No. 9,306,475 B1 and PCT/IB2014/001498, which are incorporated by reference herein below. 
         [0007]    The main features of the present touch capacitive screen are related to the unique configuration of the piston-tube force sensor. These features include the high sensitivity of the sensor for force detection and its ability to measure a wide range of the input force. The high sensitivity of the piston-tube electrode configuration is due to the fact that any small displacements of the rotor corresponding to an applied mechanical force/pressure induce measurable changes in the capacitance of the structure which can be detected by the sensing readout circuit. The piston-tube electrode configuration is also able to detect a wide range (pN to mN) of input force as the high stiffness of the sensor structure (thick springs) and large stroke of the rotor of the sensor (in the ranges of 10&#39;s of μm) enables the sensor to measure large forces and over a wide range. 
         [0008]    Mechanical stoppers are also easily made during the fabrication of the touch-sensitive module so that it can withstand forces that are beyond the measurable range of the input force without causing the sensor to be damaged or short circuited. 
         [0009]    An example of the present touch-sensitive interface based on the MEMS piston-tube capacitive force sensor consists of a flexible display panel, an array of MEMS piston-tube capacitive sensors and/or Flexible Circuit Board (FCB)/Printed Circuit Board (PCB). The display panel could be an LCD (in which the force sensitive interface is attached to the back-light layer of the LCD) or an LED screen that is flexible enough to transmit the force from the finger or any object applied to the screen. The array of the MEMS piston-tube force sensors could have two forms. In one form, all of the rotors (moving electrodes) of the sensors are electrically connected forming a single common electrode, and the stators (fixed electrodes of the force sensors) are electrically isolated. In this case, a flexible circuit board, or a printed circuit board, is used to achieve the electrical routing between the stators of all sensors and the capacitive read-out circuit. In the other form, all of the stators of the sensors are electrically connected forming a single common electrode, and the rotors (moving electrodes) are electrically isolated by utilizing an insulating layer at the bonding interface between the rotor plate and stator plate. Capacitive read-out circuits are used to detect the changes in capacitance in each individual sensor, and algorithms are used to identify the activated sensor and the amount of the force applied; hence, 3-dimensional information is provided about the user touch. 
         [0010]    Each piston-tube capacitive force sensor comprises a lower structure which forms the stator, an upper structure which forms the rotor that is attached to the substrate through springs, and the force contact platform that is placed on the moving rotor of each sensor and beneath the flexible display panel of the touch screen. When an input force is applied to flexible display, the force contact platform transmits the mechanical force, and the rotor of the sensor moves downward leading to a change in the capacitance between the sensing piston and tube electrodes. 
         [0011]    The sensing electrodes (pistons) in the stator of each sensor could be electrically connected (having a single polarity) to measure only the magnitude of the force, or could be divided into a number of piston arrays electrically isolated from each other to sense the magnitude and the position of a concentrated force relative the rotor of each sensor. Different structures of the piston-tube electrode configuration designs that are disclosed in the U.S. Pat. No. 9,306,475 B1 and PCT/IB2014/001498 could be used to sense the force. 
         [0012]    It will be readily apparent to the one with ordinary skills in the art that this invention could be altered in many ways, used in many applications for force measurement without departure from the soul of the invention. It will also be readily apparent to the one with ordinary skills in the art that this force sensor could be used as displacement sensor as the applied force is proportional to the springs&#39; stiffness and the displacement; once the force is known, the displacement is determined. 
         [0013]    One object of the present invention is to provide a touch-sensitive screen that is able to detect a small acting force, in the range of hundreds of micro-Newtons, and also a large input force, in the range of 10&#39;s of milli-Newtons. The present device can achieve this due to the high sensitivity of the piston-tube electrode configuration of each of its force sensors in its array, and to the large stroke that the rotor can travel, and to the high stiffness of the flexure mechanism of the rotor for each of these sensors. 
         [0014]    Another object of the present invention is to provide a screen that is able to detect the touch force of any object (finger, stylus, pen, etc.) as they do not require a capacitive object to operate. 
         [0015]    Another object of the present invention is to provide a touch sensitive screen that the capacitance changes linearly with respect to the applied force. Therefore, more information can be transferred by the amount of the force applied. 
         [0016]    Another object of the present invention is to provide sensors that can withstand the application of an input force that far exceeds their range. This is achieved by the use of mechanical stoppers in the sensor structure. 
         [0017]    Another object of the present invention is to provide a high resolution by scaling down the size of each of the MEMS piston-tube capacitive force sensors in the sensor array without significantly compromising the sensitivity of each of these sensors. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0018]    Embodiments herein will hereinafter be described in conjunction with the appended drawings provided to illustrate and not to limit the scope of the claims, wherein like designations denote like elements, and in which: 
           [0019]      FIG. 1A  shows a perspective view of a touch-sensitive interface based on the MEMS capacitive piston-tube force sensor, according to an example embodiment of the present invention; 
           [0020]      FIG. 1B  shows an exploded perspective view of the touch-sensitive interface based on the MEMS capacitive piston-tube force sensor shown in  FIG. 1A ; 
           [0021]      FIG. 1C  shows a top, cross-section, a detailed, and perspective view of the touch-sensitive interface module using the common rotor and electrically insulated stators configuration based on the MEMS capacitive piston-tube force sensor, according to an example embodiment of the present invention; 
           [0022]      FIG. 1D  is a cross-sectional view of the touch-sensitive interface module using the common stator and electrically insulated rotors configuration based on the MEMS capacitive piston-tube force sensor, according to an example embodiment of the present invention; 
           [0023]      FIG. 1E  shows an exploded perspective view of the touch-sensitive interface module based on the MEMS capacitive piston-tube force sensor shown in  FIG. 1C ; 
           [0024]      FIG. 1F  shows a perspective view of a MEMS capacitive piston-tube force sensor; 
           [0025]      FIG. 1G  shows an exploded perspective view of the MEMS capacitive piston-tube force sensor shown in  FIG. 1F ; 
           [0026]      FIG. 2  is a perspective view illustrating the upper structure (the rotor, springs, and outer periphery) of the piston-tube capacitive force sensor; 
           [0027]      FIG. 3A  is a perspective view illustrating the lower structure (stator) of the piston-tube capacitive force sensor; 
           [0028]      FIG. 3B  is a perspective view illustrating the small thickness routing layer that connects the pistons in each sub-array in the lower structure (stator) of the piston-tube capacitive force sensor; 
           [0029]      FIG. 4  is a perspective view illustrating the force contact platform that forms the foundation on which the input force is applied; 
           [0030]      FIG. 5  shows a cross-sectional view illustrating the piston-tube capacitive force sensor at rest, no input force is applied; 
           [0031]      FIG. 6  shows a cross-sectional view illustrating the piston-tube capacitive force sensor during the application of an input force, concentrated at the center of the rotor or distributed over the entire rotor, on the force contact platform; and 
           [0032]      FIG. 7  shows a cross-sectional view illustrating the piston-tube capacitive force sensor during the application of an eccentric concentrated force on the rotor. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0033]    The preferred embodiment of the touch-sensitive interface module  120  based on the MEMS capacitive piston-tube force sensor is illustrated in  FIG. 1-7 . The touch-sensitive interface module consists of a flexible display panel  121 , a touch-sensitive interface  110 , and/or signal routing circuit that could be printed or a flexible circuit board  122  ( FIG. 1E ). 
         [0034]    
       7 
     
         [0035]      FIG. 1A-B  illustrate the touch-sensitive interface  110  containing an array of MEMS capacitive piston-tube force sensors  100 , and it comprises a stator (fixed electrodes) plate  114 , electrical insulation layer  113 , rotor (moving electrodes) plate  112 , and/or force contact platforms  111 . The stator plate contains the fixed electrodes of the sensors that are electrically insulated from each other by means of etching such as Deep Reactive Ion Etching (DRIE) through the whole stator plate or any other etching method. The insulating layer  113  provides the electrical isolation between the stator and rotor plates of the interface. The rotor plate is a common electrode between all of the sensors in the interface. The force contact platforms are used to transmit the force from the flexible display to the rotors (moving electrodes) of the sensors. 
         [0036]    The touch-sensitive interface module  120  is further illustrated in  FIG. 1C-E . It consists of the flexible display  121  that could be an LCD or LED screen. This flexible display transmits the user inputs from the user to the force contact platforms. An FCB or PCB  122  is used to provide electrical connections to the individual stators (fixed electrodes) of the sensors. 
         [0037]    There are two configurations of the electrical insulation and connection between the moving electrodes and the fixed sensing electrodes. The first, shown in the cross sectional view in  FIG. 1C , is the common rotor and electrically insulated stators configuration. In such configuration, the stators (fixed electrodes) of all of the force sensors are electrical insulating form each other and the rotors (moving electrodes) are all electrically connected forming a single electrode. The electrical insulation between the fixed sensing electrodes is achieved by means of etching such as Deep Reactive Ion Etching (DRIE) through the whole stator plate or any other etching method. The insulating layer  113  provides the electrical isolation between the stator and rotor plates of the interface, and also between the individual stators (fixed sensing electrodes). In this case (common rotor and electrical insulated stators), a flexible board circuit or PCB  122  is needed to be attached to the backside of the stator plate to provide the electrical routing to the separated stators (fixed electrodes). 
         [0038]    The second is the common stator and electrically insulated rotors configuration. Such configuration is shown in  FIG. 1D  and is achieved by electrically insulating the rotors (moving electrodes) of each force sensor from each other by means of DRIE. The fixed sensing electrodes are all connected form a single electrode. In such configuration, there is no need of the FCB or PCB to be attached to the back of the touch interface as the rotor plate is utilized to provide electrical routings to the individual rotors (moving electrodes) by means of DRIE of the rotor plate. 
         [0039]    The preferred embodiment of the individual MEMS capacitive piston-tube force sensors  100  is illustrated in  FIG. 1-7 . Each sensor unit comprises a lower structure  300  that forms the stator, an upper structure  200  that houses the rotor  230  and mechanical springs  220 ,  221 ,  222 ,  223 , and a force contact platform  400 . The lower structure  300  is shown in  FIG. 3 , and it forms a plurality of rectangular-shaped pistons (teeth)  310 ,  311 ,  312 ,  313 , and the upper structure  200  is shown in  FIG. 2 , and it houses the rotor which consists of a plurality of rectangular-shaped tubes (openings)  230 , that correspond to the pistons in the lower structure. 
         [0040]    The pistons could form one or multiple sensing electrodes (preferably four), and they protrude vertically towards the upper structure and extend horizontally along the two in-plane axes (x and y). Each sensing electrode, within a single sensor, is electrically isolated from other sensing electrodes by utilizing the Buried Oxide (BOX) layer  314  of an SOI wafer or any other dielectric (i.e. insulation) layer. The division of the pistons into multiple arrays enables the detection of the force magnitude as well as force position with respect to the rotor when the force is concentrated. When the applied force is distributed and the magnitude of the force is only required to be sensed, all pistons are electrically connected and there is no need for the insulation layer  314  beneath the pistons, and the insulation layer  113 , refer to  FIG. 1B , between the stator plate and rotor plate will be utilized to provide the electrical separation between the stator and rotor of each sensor. The pistons within each single group (sensing electrode) are electrically connected to each other via a small thickness (height) layer  320  forming a single capacitor with the moving (common) electrode in the upper structure. It will be readily clear to the one with ordinary skills in the art that this layer  320 , shown in  FIG. 3B , is connected to the outer fixed periphery of the sensor  330  which is divided into different electrical pads by means of DRIE etching up to the insulating layer. 
         [0041]    Another way of achieving the electrical insulation between the groups of pistons within the stator of each force sensor is by a back DRIE etching step through the whole stator plate up to the insulating layer  113  located in the bonding interface between the stator and rotor plates. 
         [0042]    The tubes  230  form the moving electrode, which is a common electrode that in conjunction with the lower sensing electrodes  310 ,  311 ,  312 ,  313  make up the capacitors. The tubes are rectangular through holes, and they are vertically aligned with the pistons (sensing electrodes). The cross-section of the tubes is larger than that of the pistons so that the pistons penetrate along the tubes during the application of the force. The tubes usually have height (thickness) less that the pistons such that they fully engage without causing short circuit during the engagement of the pistons and the tubes while sensing. The moving structure containing the tubes is attached to the outer fixed periphery  201  of the sensor by multiple supporting springs  220 ,  221 ,  222 ,  223 . 
         [0043]    The force contact platform  400  is placed on the rotor of the sensor and could be made of any solid materials; light weight materials such as glass or plastic is preferable. A glass force contact platform could be attached to the rotor by means of ionic bonding during the fabrication of the sensor or by an adhesive. The force contact platform provides a means for the force transmission form the display panel to the rotor and also works as a mechanical stopper for the rotor during the application of an input force that exceeds the range of the sensor or severe shocks. 
         [0044]    The force contact platform of each force sensor consists of two parts: the upper  410  and lower  420  as shown in  FIG. 4 . The bottom face  422  of the lower part is designed to fit the area of the moving rotor and has a height  421  which is equal to the maximum translation stroke of the moving rotor. The upper part  410  is larger in area than the lower part and could be set equal to the area of the whole force sensor unit to provide a large fill factor for the array of the sensors beneath the display panel. The upper part limits the motion of the rotor to the desired maximum translation or rotation stroke to avoid any short circuit between the pistons and tubes and also to prevent the sensor from being destroyed when forces that exceed the maximum force the sensor can handle are applied. 
         [0045]    When no input force is applied, the rotor is at rest as shown in  FIG. 5 . When an external mechanical force (concentrated  610  at the center of the rotor or distributed  620  over the entire rotor), please refer to  FIG. 6 , is applied towards the force contact platform via the flexible display, (i.e. the negative direction of the z-axis), the relative engagement of the moving structure (tubes) and the lower structure (pistons) increases. The change of capacitance between the moving electrode (tubes) and the sensing electrodes (pistons) is detected by the capacitive read-out circuit. Hence the force can be measured. 
         [0046]    The upper part  410  of the force contact platform works as a mechanical stopper when the rotor  230  of the sensor reaches the maximum stroke. The bottom surface  411  of this upper part hits the outer fixed periphery  201  of the sensor at the maximum stroke before the bottom surface of the rotor hits the lower structure. This is shown in  FIG. 6 . Such mechanism protects the actuator against large forces that exceed the capacity (i.e. range) of the sensor and prevents short circuits between the upper and lower structures. 
         [0047]    When an eccentric external concentered force  720 , refer to  FIG. 7 , or a distributed force that can be represented through an equivalent eccentric external concentrated force also as shown by  720  is applied, the relative motion of the moving electrode (tubes) with respect to the fixed electrodes (pistons) are rotations about the in-plane axes. The resulting change in the engagement of the tubes and the corresponding pistons is largely concentrated in one half of the force sensor structure leading to a change in the capacitance which can be detected by the read-out circuit. Thus, the quadrant to which the force is applied can be known. The upper part  410  of the force contact platform also works as a mechanical stopper as this part hits the outer fixed periphery before the inner walls of the tubes hits the outer walls of the pistons. It would be readily apparent to the one who is skilled in the art that the dimensions of the pistons and tubes in  FIG. 7  are not real as they are drawn only for illustration purposes. In a real design, a consideration is taken for the size of the horizontal gaps between the walls of the pistons and tubes such that the inner walls of the tubes do not touch the outer walls of the pistons when the maximum angle of rotation is reached. 
         [0048]    The eccentric external force could represented by the finger touch when the force sensor is relative large as opposed to the size of the finger print. In such case, one single force sensor could be used to provide four inputs from the user, i.e. position of the finger could be detected in each of the four corners of the sensor separately. The present device can be programmed to assign several functions to each MEMS sensor according to the penetration depth of the tubes and pistons, as well as location of the touch on each sensor. Since the height of the pistons and tubes are relatively large, more than two functional can be easily assigned for each sensor. 
         [0049]    The configuration of the springs holding the moving structure could be designed in many ways as it will be clearly apparent to one who is skilled in the art. One may use suspension springs that extend radially to support the tubes. Another preferred configuration of springs is that the springs extend along the periphery of the tubes&#39; plate which is the preferred configuration as it allows for a wider area for the application of the force, it enables the use of a wide area of the electrode capacitance, and it provides a high fill factor when a number of these sensors are connected in an array style. 
         [0050]    It also could be apparent that the disclosed force sensor can be used as a weight measurement sensor as the weight is a force. It also can be used as a displacement sensor by detecting the amount of force applied and having prior knowledge of the stiffness of the rotor springs.