(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2010/0026664 A1
`
`
`(43) Pub. Date:GEAGHAN Feb. 4, 2010
`
`US 20100026664A1
`
`(54) TOUCH SENSITIVE DEVICES WITH
`COMPOSITE ELECTRODES
`
`(76)
`
`Inventor:
`
`Bernard 0. GEAGHAN, Salem,
`NH (US)
`
`Corresmndence Addressz
`3M INNOVATIVE PROPERTIES COMPANY
`PO BOX 33427
`ST. PAUL, MN 55133-3427 (US)
`
`(21) Appl. No.:
`
`12/511,487
`
`(22)
`
`Filed:
`
`Jul. 29, 2009
`.
`.
`Related US Application Data
`(60) Provisional application No. 61/085,693, filed on Aug.
`l, 2008.
`
`Publication Classification
`
`(51)
`
`Int. C1.
`G06F 3/044
`
`(2006.01)
`
`(52) US. Cl. ........................................................ 345/174
`
`(57)
`
`ABSTRACT
`
`A matrix touch panel having upper and lower electrodes, the
`upper electrodes being composite electrodes made of a plu-
`rality of spaced micro-wires, and allowing, for example, an
`electric field from lower electrodes to pass between the
`micro-wires and thereby capacitively couple with a touching
`object, such as a finger.
`
`800
`
`\ .
`
`PETITIONERS
`
`Exhibit 1018, Page 1
`
`PETITIONERS
`Exhibit 1018, Page 1
`
`

`

`Patent Application Publication
`
`Feb. 4, 2010 Sheet 1 0f 12
`
`US 2010/0026664 A1
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`PETITIONERS
`
`Exhibit 1018, Page 2
`
`PETITIONERS
`Exhibit 1018, Page 2
`
`

`

`Patent Application Publication
`
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`PETITIONERS
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`Exhibit 1018, Page 3
`
`PETITIONERS
`Exhibit 1018, Page 3
`
`

`

`Patent Application Publication
`
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`PETITIONERS
`
`Exhibit 1018, Page 4
`
`PETITIONERS
`Exhibit 1018, Page 4
`
`

`

`Patent Application Publication
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`
`PETITIONERS
`Exhibit 1018, Page 5
`
`

`

`Patent Application Publication
`
`Feb. 4, 2010 Sheet 5 0f 12
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`US 2010/0026664 A1
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`PETITIONERS
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`Exhibit 1018, Page 6
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`PETITIONERS
`Exhibit 1018, Page 6
`
`

`

`Patent Application Publication
`
`Feb. 4, 2010 Sheet 6 0f 12
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`US 2010/0026664 A1
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`
`
`PETITIONERS
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`Exhibit 1018, Page 7
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`PETITIONERS
`Exhibit 1018, Page 7
`
`

`

`Patent Application Publication
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`Feb. 4, 2010 Sheet 7 0f 12
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`US 2010/0026664 A1
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`PETITIONERS
`
`Exhibit 1018, Page 8
`
`PETITIONERS
`Exhibit 1018, Page 8
`
`

`

`Patent Application Publication
`
`Feb. 4, 2010 Sheet 8 of 12
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`US 2010/0026664 A1
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`
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`
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`
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`
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`
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`
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`
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`
`Figs, §b
`
`PETITIONERS
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`Exhibit 1018, Page 9
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`PETITIONERS
`Exhibit 1018, Page 9
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`

`

`Patent Application Publication
`
`Feb. 4, 2010 Sheet 9 0f 12
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`US 2010/0026664 A1
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`
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`
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`
`PETITIONERS
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`Exhibit 1018, Page 10
`
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`
`PETITIONERS
`Exhibit 1018, Page 10
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`

`

`Patent Application Publication
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`Feb. 4, 2010 Sheet 10 0f 12
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`US 2010/0026664 Al
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`
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`
`PETITIONERS
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`Exhibit 1018, Page 11
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`PETITIONERS
`Exhibit 1018, Page 11
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`

`

`Patent Application Publication
`
`Feb. 4, 2010 Sheet 11 0f 12
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`US 2010/0026664 A1
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`
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`PETITIONERS
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`Exhibit 1018, Page 12
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`PETITIONERS
`Exhibit 1018, Page 12
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`

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`Patent Application Publication
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`Feb. 4, 2010 Sheet 12 0f 12
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`US 2010/0026664 A1
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`
`Fig. 3.35
`
`PETITIONERS
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`Exhibit 1018, Page 13
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`PETITIONERS
`Exhibit 1018, Page 13
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`

`

`US 2010/0026664 A1
`
`Feb. 4, 2010
`
`TOUCH SENSITIVE DEVICES WITH
`COMPOSITE ELECTRODES
`
`CROSS REFERENCE TO RELATED
`APPLICATION
`
`[0001] This patent document claims the benefit, under 35
`U.S.C. §l 19(e), of US. Provisional Patent Application Ser.
`No. 61/085,693 filed on Aug. 1, 2008, and entitled “Electric
`Field Pervious Electrodes” the disclosure of which is incor-
`
`porated by reference in its entirety.
`
`FIELD OF INVENTION
`
`[0002] This invention relates generally to touch sensitive
`devices, particularly those that rely on capacitive coupling
`between a user’s finger or other touch implement and the
`touch device to identify an occurrence or location of a touch.
`
`BACKGROUND
`
`[0003] Touch sensitive devices allow a user to conveniently
`interface with electronic systems and displays by reducing or
`eliminating the need for mechanical buttons, keypads, key-
`boards, and pointing devices. For example, a user can carry
`out a complicated sequence of instructions by simply touch-
`ing an on-display touch screen at a location identified by an
`icon.
`
`[0004] There are several types of technologies for imple-
`menting a touch sensitive device including, for example,
`resistive, infrared, capacitive, surface acoustic wave, electro-
`magnetic, near field imaging, etc. Capacitive touch sensing
`devices have been found to work well in a number of appli-
`cations. In many touch sensitive devices, the input is sensed
`when a conductive object in the sensor is capacitively coupled
`to a conductive touch implement such as a user’s finger.
`Generally, whenever two electrically conductive members
`come into proximity with one another without actually touch-
`ing, a capacitance is formed between them. In the case of a
`capacitive touch sensitive device, as an object such as a finger
`approaches the touch sensing surface, a tiny capacitance
`forms between the object and the sensing points in close
`proximity to the object. By detecting changes in capacitance
`at each of the sensing points and noting the position of the
`sensing points, the sensing circuit can recognize multiple
`objects and determine the characteristics of the object as it is
`moved across the touch surface.
`
`[0005] There are two known techniques used to capaci-
`tively measure touch. The first is to measure capacitance-to-
`ground, whereby a signal is applied to an electrode. A touch in
`proximity to the electrode causes signal current to flow from
`the electrode, through an object such as a finger, to electrical
`ground.
`[0006] The second technique used to capacitively measure
`touch is through mutual capacitance. Mutual capacitance
`touch screens apply a signal to a driven electrode, which is
`capacitively coupled to a receiver electrode by an electric
`field. Signal coupling between the two electrodes is reduced
`by an object in proximity, which reduces the capacitive cou-
`pling.
`[0007] Capacitive touch sensing devices often include two
`arrays of long, narrow electrodes in the form of a matrix. The
`arrays can be on two parallel planes and separated by an
`inter-electrode dielectric. Electrical parameters influenced by
`sensor construction, such as electrode resistance, inter-elec-
`trode (mutual) capacitance, and electrode capacitance to
`
`ground must be balanced with performance considerations.
`For example, high levels of parasitic mutual capacitance
`among electrodes may interfere with the measurement of
`small changes to mutual capacitance that occur due to a touch.
`While a reduction in parasitic mutual capacitance may be
`achieved by increasing inter-electrode dielectric thickness,
`this increases the thickness and weight of the touch sensor,
`and also decreases the capacitance-changing effect ofa touch.
`[0008] There are numerous other performance and con-
`struction considerations present when designing a touch sen-
`sor. For example, it can be desirable to shield touch signals
`from electromagnetic interference emitted from nearby elec-
`trical components. Capacitive coupling between a touching
`implement or finger and the lower electrodes can be equalized
`relative to the top electrodes. There also exists a desire for
`greater flexibility in the design of electrically conductive
`elements and a method for an improved manufacturing pro-
`cess for touch systems with customized sensors and unique
`electrode configurations.
`
`BRIEF SUMMARY
`
`[0009] The present application discloses, inter alia, touch
`sensitive devices capable, with appropriate electronics, of
`detecting either a single touch or multiple touches applied to
`different portions of a touch sensitive device at the same or at
`overlapping times. Touch sensitive devices consistent with
`the present disclosure include a first set of composite elec-
`trodes that are pervious to an electric field generated by a
`signal from a second set of electrodes such that the electric
`field permeates through the electrodes to capacitively couple
`with a touching object (e.g., a finger). The first and second
`sets ofelectrodes are on different planes, and may be arranged
`to form a matrix-type touch sensor. Such devices measure
`capacitive coupling between the two sets of electrodes or
`between one set of electrodes and ground to determine the
`occurrence and location of a touch event.
`
`In one embodiment, a multi-layer touch panel is
`[0010]
`described, the touch panel comprising a first layer comprising
`a transparent touch surface; an upper electrode layer compris-
`ing a plurality of composite electrodes comprised of a plural-
`ity of micro-wire conductors; a lower electrode layer com-
`prising a plurality of electrodes, the upper electrodes and
`lower electrodes defining an electrode matrix having nodes
`where the upper and lower electrodes intersect, and wherein
`the upper electrode layer is disposed between the first layer
`and the lower electrode layer; and, a dielectric layer disposed
`between the upper electrode layer and the lower electrode
`layer. The micro-wires can have varying widths, from 1 to 100
`microns, and be made of metals or metal alloys.
`[0011]
`In another embodiment, a method for identifying
`locations of touches or near-touches on a touch sensitive
`
`apparatus is described, the method comprising sensing, with
`an electronic controller, a value indicative of the change of
`mutual capacitance between an overlapping upper electrode
`and a lower electrode disposed in a matrix-type touch sensor,
`the change in mutual capacitance induced by the presence of
`an object proximate to the touch sensor, wherein the upper
`electrode is a composite electrode comprised of a plurality of
`micro-wire conductors.
`
`In some embodiments, the composite electrodes
`[0012]
`described herein may allow for greater mutual capacitance
`changes between a touch and non-touch event, thus meaning,
`PETITIONERS
`
`Exhibit 1018, Page 14
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`PETITIONERS
`Exhibit 1018, Page 14
`
`

`

`US 2010/0026664 A1
`
`Feb. 4, 2010
`
`for example, greater sensitivity to touch and less susceptibil-
`ity to noise and parasitic capacitance.
`
`BRIEF DESCRIPTION OF DRAWINGS
`
`[0013] The present disclosure may be more completely
`understood and appreciated in consideration of the following
`detailed description of various embodiments in connection
`with the accompanying drawings, in which:
`[0014]
`FIG. 1 is a schematic view of a touch device;
`[0015]
`FIG. 2 shows a cross sectional view ofan exemplary
`sensor with a finger touching the touch surface, wherein some
`ofthe top electrodes are capacitively coupled to the finger and
`an electric field is generated between the finger and the top
`electrodes;
`[0016]
`FIG. 3 shows a cross sectional view ofan exemplary
`sensor with a finger touching the touch surface, wherein some
`of the lower electrodes are capacitively coupled to the finger
`and an electric field is generated between the finger and the
`lower electrodes;
`[0017]
`FIG. 4 is a schematic view of a touch sensor includ-
`ing various embodiments of composite electrodes;
`[0018]
`FIG. 4a shows an expanded view of parallel con-
`ductors with bridging conductors;
`[0019]
`FIG. 5a shows a segment of sensor substrate with
`parallel conductors on the substrate;
`[0020]
`FIG. 5b shows a segment of sensor substrate with
`end conductors electrically connecting parallel conductors to
`form composite electrodes;
`[0021]
`FIG. Sc shows a segment of sensor substrate with
`end conductors electrically connecting parallel conductors to
`form composite electrodes;
`[0022]
`FIG. 5d shows a segment of sensor substrate with
`end conductors electrically connecting parallel conductors to
`form composite electrodes;
`[0023]
`FIG. Se shows a segment of sensor substrate with
`end conductors electrically connecting parallel conductors to
`form composite electrodes, wherein some ofthe parallel con-
`ductors are interleaved;
`[0024]
`FIG. 5f shows a segment of sensor substrate with
`end conductors electrically connecting parallel network con-
`ductors to form composite electrodes;
`[0025]
`FIG. 6 shows an exploded view of an exemplary
`matrix sensor with an array of parallel conductors arranged
`above a second array of ITO electrodes;
`[0026]
`FIG. 7a shows a cross sectional view of an exem-
`plary matrix sensor with composite electrodes;
`[0027]
`FIG. 7b shows a cross sectional view of an exem-
`plary matrix sensor with an alternative construction com-
`pared with that shown in FIG. 7a;
`[0028]
`FIG. 8a shows a cross section of a touch sensor with
`composite upper electrodes;
`[0029]
`FIG. 8b shows a cross section of a touch sensor with
`a solid upper electrode;
`[0030]
`FIG. 9a is a graph that compares the capacitive
`coupling ofa composite top electrode to a finger to the capaci-
`tive coupling of a solid top electrode to a finger;
`[0031]
`FIG. 9b is a graph that compares capacitive coupling
`from a lower electrode to a finger using capacitance-to-
`ground measurements when the top electrode is composite
`(i.e., pervious to an electrical field) to when the top electrode
`is solid;
`FIG. 90 is a graph that shows the relationship
`[0032]
`between inter-conductor spacing (in the top electrode) and
`coupling from a finger to the top and lower electrodes;
`
`FIG. 9d is a graph that shows changes in mutual
`[0033]
`capacitance between the top and lower electrodes for glass
`and poly(methyl methacrylate) (PMMA) top substrates as top
`substrate thickness increases;
`[0034]
`FIG. 96 is a graph that shows percent change in
`mutual capacitance between the top and lower electrodes for
`glass and PMMA top substrates as top substrate thickness
`increases;
`shows a two-dimensional electrode
`1011
`[0035]
`FIG.
`arrangement with two composite
`electrodes oriented
`orthogonally to each other;
`[0036]
`FIG. 10b shows a two-dimensional electrode
`arrangement with a composite upper electrode oriented
`orthogonally to a solid bottom electrode;
`[0037]
`FIG. 100 shows a two-dimensional electrode
`arrangement with a solid upper electrode oriented orthogo-
`nally to a bottom solid electrode;
`[0038]
`FIG. 11a is a graph that shows change in mutual
`capacitance due to touch as top substrate thickness varies; and
`[0039]
`FIG. 11b is a graph that shows the percent change in
`mutual capacitance due to touch as top substrate thickness
`varies.
`
`In the following description of the illustrated
`[0040]
`embodiments, reference is made to the accompanying draw-
`ings,
`in which is shown by way of illustration, various
`embodiments in which the invention may be practiced. It is to
`be understood that the embodiments may be utilized and
`structural changes may be made without departing from the
`scope of the present invention. Drawings and graphs are for
`illustration of the disclosure and are not to scale, and in some
`drawings, dimensions are exaggerated for purposes of illus-
`tration.
`
`DETAILED DESCRIPTION
`
`[0041] The present invention now will be described more
`fully hereinafter with reference to the accompanying draw-
`ings, in which embodiments of the invention are shown. This
`invention may, however, be embodied in many different
`forms and should not be construed as limited to the embodi-
`
`ments set forth herein; rather, these embodiments are pro-
`vided so that this disclosure will be thorough and complete,
`and will fully convey the scope of the invention to those
`skilled in the art. Like numbers refer to like elements through-
`out.
`
`In the following description, the following defini-
`[0042]
`tions clarify terms used within this disclosure:
`[0043] Ground (Gnd) refers to a common electrical refer-
`ence point which may be at the voltage of earth ground, or
`may be a local common voltage.
`is
`[0044] Mutual
`capacitance
`(Cm)
`between two electrodes in a touch sensor.
`
`capacitance
`
`the
`
`[0045] Capacitance to ground is the capacitance between a
`sensor electrode and ground.
`[0046]
`Parasitic capacitance is the level of capacitance
`without the presence of a touch.
`[0047] A touch sensor includes one or more electrodes
`configured to make capacitive contact with a conductive
`object for the purpose of detection and/or location of the
`object.
`Printed circuit board (PCB) refers to a circuit pat-
`[0048]
`terned onto a substrate. As used herein, PCB may refer to a
`rigid PCB made of fiberglass reinforced plastic, or a flexible
`PCB, commonly referred to as flexprint, or any other type of
`PCB known in the art.
`
`PETITIONERS
`
`Exhibit 1018, Page 15
`
`PETITIONERS
`Exhibit 1018, Page 15
`
`

`

`US 2010/0026664 A1
`
`Feb. 4, 2010
`
`PMMA refers to poly(methyl methacrylate), a ther-
`[0049]
`moplastic and transparent plastic that is a synthetic polymer
`ofmethyl methacrylate. PMMA is also commonly referred to
`as acrylic glass.
`[0050]
`FIG. 1 shows exemplary touch device 110. Device
`110 includes touch panel 112 connected to controller 114,
`which includes electronic circuitry for sensing touches and
`possibly near touches occurring in proximity to touch panel
`112. Touch panel 112 is shown as having a 5x5 matrix of
`column electrodes 116a-e and row electrodes 118a-e, but
`other numbers of electrodes, matrix sizes and electrode con-
`figurations can also be used. Touch panel 112 can be substan-
`tially transparent so that the user is able to view an object,
`such as a pixilated display of a computer, hand-held device,
`mobile phone, or other peripheral device, through the touch
`panel 112. The boundary 120 represents the viewing area of
`touch panel 112 and also preferably the viewing area of such
`a display, if used. In one embodiment, electrodes 116a-e,
`118a-e are spatially distributed, from a plan view perspective,
`over the viewing area 120.
`[0051]
`For illustrative purposes, the electrodes in FIG. 1 are
`shown to be wide and obtrusive, but in practice they may be
`relatively narrow and inconspicuous to a user. Each electrode
`can be designed to have variable widths, e.g., an increased
`width in the form of a diamond- or other-shaped pad in the
`vicinity of the nodes of the matrix in order to increase the
`inter-electrode fringe field and thereby increase the effect of a
`touch on electrode-to-electrode capacitive coupling. In an
`exemplary embodiment ofthe present disclosure, one or more
`electrodes can be made of an array of electrodes (or conduc-
`tors), for example, thin wires or micro-wires, printed conduc-
`tive traces or networks of conductors, as discussed in further
`detail below. An electrode made up of a plurality of conduc-
`tors, as further described herein, is referred to as a composite
`electrode.
`
`In exemplary embodiments the electrodes may be
`[0052]
`composed of indium tin oxide (ITO), wires, micro-wires or
`other suitable electrically conductive materials. Wires or
`micro-wires forming conductors may be made of,
`for
`example, copper, silver, gold.
`[0053] Column electrodes 116a-e may be in a different
`plane than the row electrodes 118a-e (e.g., column electrodes
`116a-e may be underneath row electrodes 118a-e) such that
`no physical contact is made between respective column and
`row. The matrix of electrodes typically lies beneath a cover
`glass, plastic film, or the like (not shown in FIG. 1), so that the
`electrodes are protected from direct physical contact with a
`user’s finger or other touch-related implement. An exposed
`surface of such a cover glass, film, or the like may be referred
`to as the touch surface of touch panel 112.
`[0054] The capacitive coupling between a given row and
`column electrode is primarily a function of the geometry of
`the electrodes in the region where the electrodes are closest
`together. Such regions correspond to the “nodes” of the elec-
`trode matrix, some of which are labeled in FIG. 1. For
`example, capacitive coupling between column electrode
`116a and row electrode 118d occurs primarily at node 122,
`and capacitive coupling between column electrode 116!) and
`row electrode 118e occurs primarily at node 124. The 5x5
`matrix of FIG. 1 has 25 such nodes, any one of which can be
`addressed by controller 114 via appropriate selection of one
`ofthe control lines 126, which individually couple the respec-
`tive column electrodes 116a-e to the controller, and appro-
`
`priate selection of one of the control lines 128, which indi-
`vidually couple the respective row electrodes 118a-e to the
`controller.
`
`[0055] When finger 130 of a user or other touch implement
`comes into contact or near-contact with the touch surface of
`
`the device 110, as shown at touch location 131, the finger
`capacitively couples to the electrode matrix. Finger 130
`draws charge from the matrix, particularly from those elec-
`trodes lying closest to the touch location, and in doing so it
`changes the coupling capacitance between the electrodes cor-
`responding to the nearest node(s), as shown in more detail in
`FIGS. 2 and 3. For example, the touch at touch location 131
`lies nearest the node corresponding to electrodes 116c and
`11819. This change in coupling capacitance can be detected by
`controller 114 and interpreted as a touch at or near the 116a/
`1181) node. The controller can be configured to rapidly detect
`the change in capacitance, if any, of all of the nodes of the
`matrix, and is capable of analyzing the magnitudes of capaci-
`tance changes for neighboring nodes so as to accurately deter-
`mine a touch location lying between nodes by interpolation.
`Furthermore, controller 114 can be designed to detect mul-
`tiple distinct touches applied to different portions ofthe touch
`device at the same time, or at overlapping times. Thus, for
`example, ifanother finger 132 touches the touch surface ofthe
`device 110 at touch location 133 simultaneously with the
`touch of finger 130, or if the respective touches at least tem-
`porally overlap, the controller is capable of detecting the
`positions 131, 133 of both such touches and providing such
`locations on a touch output 11411. The number of distinct
`simultaneous or temporally overlapping touches capable of
`being detected by controller 114 is not necessarily limited to
`2, e.g., it may be 3, 4, or more, depending on the size of the
`electrode matrix. US. Patent Application No. 61/182,366,
`“High Speed Multi-Touch Device and Controller Therefor,”
`describes an exemplary drive scheme that can be used in a
`touch sensitive device to identify the location of multiple
`simultaneous touches.
`
`[0056] Controller 114 can employ a variety of circuit mod-
`ules and components that enable it to rapidly determine the
`coupling capacitance at some or all of the nodes of the elec-
`trode matrix. For example, the controller preferably includes
`at least one signal generator or drive unit. The drive unit
`delivers a drive signal to one set of electrodes, referred to as
`drive electrodes. In the embodiment of FIG. 1, column elec-
`trodes 116a-e are used as drive electrodes (though it is pos-
`sible to instead drive row electrodes 118a-e). The drive signal
`applied by controller 114 to the drive electrodes may be
`delivered to one drive electrode at a time, e.g., in a scanned
`sequence from a first to a last drive electrode. As each such
`electrode is driven, the controller monitors the other set of
`electrodes, referred to as receive electrodes (row electrodes
`118a-e). Controller 114 may include one or more sense units
`coupled to all of the receive electrodes. For each drive signal
`that is delivered to each drive electrode, the sense unit(s)
`generate a response signal for each of the plurality of receive
`electrodes. Changes in response signals may be indicative of
`a touch or near-touch event.
`
`FIG. 2 shows a cross sectional view of a sensor 210
`[0057]
`with finger 231 touching touch surface 239. The upper elec-
`trode array 212 is separated a distance D1 from the touch
`surface 239 by a top substrate 238, which can be made of
`polycarbonate, polyethylene terephthalate (PET), PMMA,
`glass, silica, or combinations of such (for example, silica
`coated on glass), PET hard coat material, or any other suitable
`PETITIONERS
`
`Exhibit 1018, Page 16
`
`PETITIONERS
`Exhibit 1018, Page 16
`
`

`

`US 2010/0026664 A1
`
`Feb. 4, 2010
`
`material. In the case ofnon-transparent capacitive touch pads,
`top substrate 238 can be fiberglass reinforced plastic (FRP) as
`used to make computer boards, or any other suitable material.
`In the sensor construction shown in FIG. 2, upper electrode
`array 212 is separated by a distance D2 from lower electrode
`array 214 by a lower substrate 213. The lower substrate 213
`can be made from any of the materials that can be used for top
`substrate 238, or any other appropriate material. The elec-
`trodes of the lower electrode array 214, only one member of
`which is shown, can be spaced, for example, at a distance
`from one another that allows three or more electrodes to make
`
`measurable capacitive contact with a touching finger 231. For
`example, lower electrode array 214 can have a center-to-
`center spacing of 5-6 mm or any other desired spacing. The
`width of electrodes in lower electrode array 214 is limited
`primarily by the desire in some embodiments to leave a mini-
`mal non-conductive space between them. Electrodes in lower
`electrode array 214 may be as wide as possible to maximize
`capacitive coupling with a finger. For example, 90% or more,
`95% or more, or 98% or more ofthe surface area of the lower
`substrate 213 can be covered by lower electrode array 214.
`[0058] Upper electrodes are spaced to allow electric field
`coupling from electrodes in lower electrode array 214
`between electrodes in upper electrode array 212, to a touching
`(or proximate) finger. Width ofupper electrodes (W in FIG. 2)
`can be, for example, 50% or less of center-to-center spacing
`S. When electrodes in upper electrode array 212 are made of
`ITO, their minimum width is often limited by electrode resis-
`tance. However, electrodes in upper electrode array 212 can
`be composite electrodes made of thin wires, micro-wires, an
`interconnected network of micro-conductors, printed micro-
`conductors or any other configuration and in any material
`consistent with the present disclosure.
`[0059]
`In FIG. 2, long-dashed electric field lines 232 rep-
`resent the electric field (E-field) coupling between electrodes
`in upper electrode array 212 and finger 231 when electrodes
`in upper electrode array 212 are activated with an electrical
`signal. This coupling takes place through spaces in the com-
`posite electrodes that comprise upper electrode array 212.
`Short-dashed electric field lines 234 represent electric field
`coupling between electrodes in the upper electrode array 212
`and electrodes in lower electrode array 214. Some of short-
`dashed electric field lines 234 couple from the bottom surface
`of electrodes in upper electrode array 212 to electrodes in
`lower electrode array 214. Other electric field short-dashed
`lines 234 (particularly those not in proximity to finger 231)
`represent fringe fields, coupling upward from the top surface
`of electrodes in upper electrode array 212, and curving down-
`ward to meet an electrode of the lower electrode array 214.
`Directly under finger 231, field lines from the top surface of
`electrodes in array 212 couple to (are attracted to) finger 231,
`so fewer ofthem couple to electrodes in lower electrode array
`214.
`
`[0060] When electrodes of upper electrode array 212 are
`activated with an electrical signal, finger 231 is connected to
`ground by relatively low impedance body-to-ground capaci-
`tance, (for example, 400 pf) and electrodes of lower electrode
`array 214 are also connected to ground by parasitic capaci-
`tance (for example, 100 pf). Both of these have significantly
`lower impedance than the capacitance coupling finger 231 to
`any of the electrodes in array 212 or array 214, which may be
`in the range of, for example, 1 pf to 5 pf in an exemplary
`configuration. These capacitance values depend on distances
`D1, D2, the materials used for substrates, and the distance
`
`from upper electrode array 212 and lower electrode array 214
`to grounded surfaces not shown in FIG. 2, along with the
`configurations of the upper electrode array 212 and lower
`electrode array 214. Similarly, activating an electrode of
`lower electrode array 214 with an electrical signal generates
`an electric field from the electrode in lower electrode array
`214, through electrodes in upper electrode array 212 to finger
`231.
`
`[0061] Now turning to FIG. 3, long-dashed electric field
`lines 233 represent the electric field coupling between elec-
`trodes in lower electrode array 214 and finger 231 electrodes
`in upper electrode array 222. FIG. 3 is similar to FIG. 2,
`except that in FIG. 3, electrodes in upper electrode array 222
`are not composite electrodes as they were in FIG. 2; they are
`instead traditional solid electrodes. Electric field lines 233
`
`couple predominantly from the electrodes of lower array 214,
`through spaces between the electrodes of upper electrode
`array 212, to finger 231. Short-dashed electric field lines 235
`represent coupling between electrodes of lower electrode
`array 214 and upper electrode array 222. Some of short-
`dashed lines 235 couple from the top surface of electrodes in
`lower electrode array 214 to the bottom surface of electrodes
`in upper electrode array 222. Other fringe short-dashed elec-
`tric field lines 235 (particularly those not in proximity to
`finger 231) couple upward from the top surface of electrodes
`in lower electrode array 214, and curve downward to meet the
`top surface of an electrode of upper electrode array 222.
`Long-dashed electric field lines 233 represent coupling ofthe
`top surface ofelectrodes in array 214 directly to finger 231, so
`fewer long-dashed electric field lines 233 bend and couple to
`the top of electrodes in upper electrode array 222.
`[0062] Note that when electrodes in the upper electrode
`array 222 are solid, they block the electric field from lower
`electrodes 214 so E-field 233 that couples to finger 231 is
`generated primarily in the spaces between upper electrodes
`222. However, when upper electrodes are pervious, such as
`composite electrodes 212 in FIG. 2, they allow the electric
`field to pass through the spaces between the electrode struc-
`tures.
`
`[0063] Electrodes ofupper electrode array (either electrode
`array 212 or 222) and/or lower electrode array 214 are not
`necessarily activated