(12) United States Patent
`Geaghan
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 8,279,187 B2
`Oct. 2, 2012
`
`US008279187B2
`
`(54) TOUCH SENSITIVE DEVICES WITH
`COMPOSITE ELECTRODES
`
`_
`(75) Inventor. Bernard 0. Geaghan, Salem, NH (US)
`_
`(73) Ass1gnee: 3M Innovative Properties Company,
`Saint Paul, MN (Us)
`
`1/2006 Sanelle et a1.
`2006/0001800 A1
`1/2006 Knapp et a1.
`2006/0012575 A1
`5/2006 Hotelling et al.
`2006/0097991 A1
`2006/0274055 A1 12/2006 Reynolds et al.
`2007/0030254 A1
`2/2007 Robrecht et a1‘
`2007/0062739 A1* 3/2007 Philipp et a1. ............ .. 178/1806
`2007/0074914 A1
`4/2007 Geaghan et a1.
`2007/0128905 A1
`6/2007 Speakman
`2007/0236618 A1 10/2007 Maag et al.
`2008/0095988 A1* 4/2008 Frey et al. ................... .. 428/173
`2008/0143683 A1
`6/2008 Hotelling
`2008/0158172 A1
`7/2008 Hotelling et a1.
`2008/0158183 A1
`7/2008 Hotelling et a1.
`2008/0252608 A1 10/2008 Geaghan
`2009/0165296 A1
`7/2009 Carmi
`2009/0218310 A1
`9/2009 Zu et a1.
`2009/0219257 A1
`9/2009 Frey et al.
`(Continued)
`
`FOREIGN PATENT DOCUMENTS
`EP
`0 911 906 A2
`4/1999
`JP
`2003-256136
`9/2003
`W0 W0 2007/1150” A2 100007
`OTHER PUBLICATIONS
`
`U.S. Appl. No. 61/182,366, ?led May 29, 2009, Titled: “High Speed
`Multi-Touch Device and Controller Therefor”.
`_
`(Commued)
`_
`_
`.
`_
`Pr’rfmry Exam?” 7 Grafm Sm? _
`ASSlSZLlI’lZ Examiner * Sa1ful A S1dd1qu1
`(74) A210" "6% Agent! or Firm * Steven A Bern
`
`ABSTRACT
`(57)
`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 ?eld from loWer electrodes to pass between the
`micro-Wires and thereby capacitively couple With a touching
`ObJeCt’ Such as a ?ngen
`
`20 Claims, 12 Drawing Sheets
`
`‘E169
`V420
`
`i
`
`128
`
`11455
`
`*
`
`(
`
`~
`
`,
`
`) Nome‘
`
`~
`
`~
`
`~
`
`-
`
`Sublect_t° any (3531mm? the germgftglg
`Pawnt 1S exten e or a Juste un er
`U.S.C. 154(b) by 411 days.
`
`(21) Appl. No.: 12/511,487
`
`(22) Filed.
`
`.
`
`Jul 29 2009
`
`.
`
`,
`
`(65)
`
`Prior Publication Data
`
`US 2010/0026664 A1
`
`Feb. 4, 2010
`
`.
`.
`Related US. Application Data
`(60) l1’ro2\(/)i3i8onal application No. 61/085,693, ?led on Aug.
`
`(51) Illt- Cl-
`(2006.01)
`G06F 3/044
`(52) us. Cl. ................... .. 345/173; 345/156; 178/1801;
`178/ 1 8.06
`(58) Field of Classi?cation Search ........ .. 345/156479;
`178/1801i18'05
`See application ?le for complete search history.
`
`(56)
`
`References Cited
`
`us PATENT DOCUMENTS
`5,512,131 A
`4/ 1996 Kumar et a1.
`6,137,427 A : 10/2000 Blnstea?‘ ~~~~~~~~~~~~~~~~~~~~~~~ ~~ 341/33
`*
`gf?glglde et a1‘
`" 341/33
`731293935 B2 10/2006 Mackey
`7,160,583 B2
`1/2007 Frey et al.
`2005/0083307 A1
`4/2005 Aufderheide et a1.
`
`131 130
`112\116a 1160 1160 116d
`
`1
`
`118a
`
`“$1813
`
`1181;:
`“1222
`118d
`
`TPK 2006
`Wintek v. TPK Touch Solutions
`IPR2013-00568
`
`

`

`US 8,279,187 B2
`Page 2
`
`US. PATENT DOCUMENTS
`2009/0219258 A1
`9/2009 Geaghan et al.
`2011/0199333 A1* 8/2011 Philipp et al. ............... .. 345/174
`
`OTHER PUBLICATIONS
`
`U.S. Appl. No. 12/393,194, ?led Feb. 26, 2009, Titled: “Touch Screen
`Sensor Having Varying Sheet Resistance”.
`
`U.S. Appl. No. 61/076,731, ?led Jun. 30, 2008, Titled: “Method of
`Forming a Microstructure”.
`U.S. Appl. No. 61/076,736, ?led Jun. 30, 2008, Titled: “Method of
`Forming a Patterned Substrate”.
`International Search Report, PCT/US2009/052070, International
`Filing Date Jul. 2009, Form PCT/ISN210, 3 pages.
`
`* cited by examiner
`
`

`

`US. Patent
`
`0a. 2, 2012
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`US 8,279,187 B2
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`US. Patent
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`Oct. 2, 2012
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`US 8,279,187 B2
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`US. Patent
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`Oct. 2, 2012
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`US. Patent
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`Oct. 2, 2012
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`Sheet 10 0f 12
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`

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`US. Patent
`US. Patent
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`0a. 2, 2012
`Oct. 2, 2012
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`Sheet 11 0112
`Sheet 11 of 12
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`US 8,279,187 B2
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`

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`US. Patent
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`Oct. 2, 2012
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`Sheet 12 0112
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`US 8,279,187 B2
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`

`

`US 8,279,187 B2
`
`1
`TOUCH SENSITIVE DEVICES WITH
`COMPOSITE ELECTRODES
`
`CROSS REFERENCE TO RELATED
`APPLICATION
`
`This patent document claims the bene?t, under 35 U.S.C.
`§l 19(e), of US. Provisional Patent Application Ser. No.
`61/085,693 ?led onAug. 1,2008, and entitled “Electric Field
`Pervious Electrodes” the disclosure of Which is incorporated
`by reference in its entirety.
`
`FIELD OF INVENTION
`
`This invention relates generally to touch sensitive devices,
`particularly those that rely on capacitive coupling betWeen a
`user’ s ?nger or other touch implement and the touch device to
`identify an occurrence or location of a touch.
`
`BACKGROUND
`
`Touch sensitive devices alloW a user to conveniently inter
`face 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 identi?ed by an
`icon.
`There are several types of technologies for implementing a
`touch sensitive device including, for example, resistive, infra
`red, capacitive, surface acoustic Wave, electromagnetic, near
`?eld imaging, etc. Capacitive touch sensing devices have
`been found to Work Well in a number of applications. 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 ?nger. Generally, Whenever
`tWo electrically conductive members come into proximity
`With one another Without actually touching, a capacitance is
`formed betWeen them. In the case of a capacitive touch sen
`sitive device, as an object such as a ?nger 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 sens
`ing circuit can recogniZe multiple objects and determine the
`characteristics of the object as it is moved across the touch
`surface.
`There are tWo knoWn techniques used to capacitively mea
`sure touch. The ?rst is to measure capacitance-to-ground,
`Whereby a signal is applied to an electrode. A touch in prox
`imity to the electrode causes signal current to How from the
`electrode, through an object such as a ?nger, to electrical
`ground.
`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 capaci
`tively coupled to a receiver electrode by an electric ?eld.
`Signal coupling betWeen the tWo electrodes is reduced by an
`object in proximity, Which reduces the capacitive coupling.
`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 in?uenced by sen
`sor construction, such as electrode resistance, inter-electrode
`(mutual) capacitance, and electrode capacitance to ground
`must be balanced With performance considerations. For
`example, high levels of parasitic mutual capacitance among
`
`2
`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 of a touch.
`There are numerous other performance and construction
`considerations present When designing a touch sensor. For
`example, it can be desirable to shield touch signals from
`electromagnetic interference emitted from nearby electrical
`components. Capacitive coupling betWeen a touching imple
`ment or ?nger and the loWer electrodes can be equaliZed
`relative to the top electrodes. There also exists a desire for
`greater ?exibility 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 con?gurations.
`
`BRIEF SUMMARY
`
`20
`
`25
`
`30
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`35
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`40
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`
`50
`
`55
`
`60
`
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`
`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 overlap
`ping times. Touch sensitive devices consistent With the
`present disclosure include a ?rst set of composite electrodes
`that are pervious to an electric ?eld generated by a signal from
`a second set of electrodes such that the electric ?eld perme
`ates through the electrodes to capacitively couple With a
`touching object (e.g., a ?nger). The ?rst and second sets of
`electrodes 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 described,
`the touch panel comprising a ?rst layer comprising a trans
`parent touch surface; an upper electrode layer comprising a
`plurality of composite electrodes comprised of a plurality of
`micro-Wire conductors; a loWer electrode layer comprising a
`plurality of electrodes, the upper electrodes and loWer elec
`trodes de?ning an electrode matrix having nodes Where the
`upper and loWer electrodes intersect, and Wherein the upper
`electrode layer is disposed betWeen the ?rst 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.
`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 capaci
`tance 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 described
`herein may alloW for greater mutual capacitance changes
`betWeen a touch and non-touch event, thus meaning, for
`example, greater sensitivity to touch and less susceptibility to
`noise and parasitic capacitance.
`
`BRIEF DESCRIPTION OF DRAWINGS
`
`The present disclosure may be more completely under
`stood and appreciated in consideration of the folloWing
`
`

`

`US 8,279,187 B2
`
`3
`detailed description of various embodiments in connection
`With the accompanying drawings, in Which:
`FIG. 1 is a schematic vieW of a touch device;
`FIG. 2 shoWs a cross sectional vieW of an exemplary sensor
`With a ?nger touching the touch surface, Wherein some of the
`top electrodes are capacitively coupled to the ?nger and an
`electric ?eld is generated betWeen the ?nger and the top
`electrodes;
`FIG. 3 shoWs a cross sectional vieW of an exemplary sensor
`With a ?nger touching the touch surface, Wherein some of the
`loWer electrodes are capacitively coupled to the ?nger and an
`electric ?eld is generated betWeen the ?nger and the loWer
`electrodes;
`FIG. 4 is a schematic vieW of a touch sensor including
`various embodiments of composite electrodes;
`FIG. 4a shoWs an expanded vieW of parallel conductors
`With bridging conductors;
`FIG. 5a shoWs a segment of sensor substrate With parallel
`conductors on the substrate;
`FIG. 5b shoWs a segment of sensor substrate With end
`conductors electrically connecting parallel conductors to
`form composite electrodes;
`FIG. 5c shows a segment of sensor substrate With end
`conductors electrically connecting parallel conductors to
`form composite electrodes;
`FIG. 5d shoWs a segment of sensor substrate With end
`conductors electrically connecting parallel conductors to
`form composite electrodes;
`FIG. 5e shoWs a segment of sensor substrate With end
`conductors electrically connecting parallel conductors to
`form composite electrodes, Wherein some of the parallel con
`ductors are interleaved;
`FIG. 5f shoWs a segment of sensor substrate With end
`conductors electrically connecting parallel netWork conduc
`tors to form composite electrodes;
`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;
`FIG. 7a shoWs a cross sectional vieW of an exemplary
`matrix sensor With composite electrodes;
`FIG. 7b shoWs a cross sectional vieW of an exemplary
`matrix sensor With an alternative construction compared With
`that shoWn in FIG. 7a;
`FIG. 8a shoWs a cross section of a touch sensor With com
`posite upper electrodes;
`FIG. 8b shoWs a cross section of a touch sensor With a solid
`upper electrode;
`FIG. 9a is a graph that compares the capacitive coupling of
`a composite top electrode to a ?nger to the capacitive cou
`pling of a solid top electrode to a ?nger;
`FIG. 9b is a graph that compares capacitive coupling from
`a loWer electrode to a ?nger using capacitance-to-ground
`measurements When the top electrode is composite (i.e., per
`vious to an electrical ?eld) to When the top electrode is solid;
`FIG. 90 is a graph that shoWs the relationship betWeen
`inter-conductor spacing (in the top electrode) and coupling
`from a ?nger to the top and loWer electrodes;
`FIG. 9d is a graph that shoWs changes in mutual capaci
`tance betWeen the top and loWer electrodes for glass and
`poly(methyl methacrylate) (PMMA) top substrates as top
`substrate thickness increases;
`FIG. 9e 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;
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`FIG. 1011 shows a tWo-dimensional electrode arrangement
`With tWo composite electrodes oriented orthogonally to each
`other;
`FIG. 10b shoWs a tWo-dimensional electrode arrangement
`With a composite upper electrode oriented orthogonally to a
`solid bottom electrode;
`FIG. 100 shows a tWo-dimensional electrode arrangement
`With a solid upper electrode oriented orthogonally to a bottom
`solid electrode;
`FIG. 11a is a graph that shoWs change in mutual capaci
`tance due to touch as top substrate thickness varies; and
`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 embodi
`ments, reference is made to the accompanying draWings, 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, dimen
`sions are exaggerated for purposes of illustration.
`
`DETAILED DESCRIPTION
`
`The present invention noW Will be described more fully
`hereinafter With reference to the accompanying draWings, in
`Which embodiments of the invention are shoWn. This inven
`tion may, hoWever, be embodied in many different forms and
`should not be construed as limited to the embodiments set
`forth herein; rather, these embodiments are provided 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 throughout.
`In the folloWing description, the folloWing de?nitions
`clarify terms used Within this disclosure:
`Ground (Gnd) refers to a common electrical reference
`point Which may be at the voltage of earth ground, or may be
`a local common voltage.
`Mutual capacitance (Cm) is the capacitance betWeen tWo
`electrodes in a touch sensor.
`Capacitance to ground is the capacitance betWeen a sensor
`electrode and ground.
`Parasitic capacitance is the level of capacitance Without the
`presence of a touch.
`A touch sensor includes one or more electrodes con?gured
`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 patterned
`onto a substrate. As used herein, PCB may refer to a rigid PCB
`made of ?berglass reinforced plastic, or a ?exible PCB, com
`monly referred to as ?exprint, or any other type of PCB
`knoWn in the art.
`PMMA refers to poly(methyl methacrylate), a thermoplas
`tic and transparent plastic that is a synthetic polymer of
`methyl methacrylate. PMMA is also commonly referred to as
`acrylic glass.
`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 num
`bers of electrodes, matrix siZes and electrode con?gurations
`can also be used. Touch panel 112 can be substantially trans
`parent so that the user is able to vieW an object, such as a
`pixilated display of a computer, hand-held device, mobile
`
`

`

`US 8,279,187 B2
`
`5
`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.
`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 ?eld and thereby increase the effect of a touch on
`electrode-to-electrode capacitive coupling. In an exemplary
`embodiment of the present disclosure, one or more electrodes
`can be made of an array of electrodes (or conductors), for
`example, thin Wires or micro -Wires, printed conductive traces
`or netWorks of conductors, as discussed in further detail
`beloW. An electrode made up of a plurality of conductors, as
`further described herein, is referred to as a composite elec
`trode.
`In exemplary embodiments the electrodes may be com
`posed 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.
`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 physi
`cal contact is made betWeen respective column and roW. The
`matrix of electrodes typically lies beneath a cover glass, plas
`tic ?lm, or the like (not shoWn in FIG. 1), so that the electrodes
`are protected from direct physical contact With a user’ s ?nger
`or other touch-related implement. An exposed surface of such
`a cover glass, ?lm, or the like may be referred to as the touch
`surface of touch panel 112.
`The capacitive coupling betWeen a given roW and column
`electrode is primarily a function of the geometry of the elec
`trodes in the region Where the electrodes are closest together.
`Such regions correspond to the “nodes” of the electrode
`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 5><5 matrix of FIG. 1
`has 25 such nodes, any one of Which can be addressed by
`controller 114 via appropriate selection of one of the control
`lines 126, Which individually couple the respective column
`electrodes 116a-e to the controller, and appropriate selection
`of one of the control lines 128, Which individually couple the
`respective roW electrodes 118a-e to the controller.
`When ?nger 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 ?nger capaci
`tively couples to the electrode matrix. Finger 130 draWs
`charge from the matrix, particularly from those electrodes
`lying closest to the touch location, and in doing so it changes
`the coupling capacitance betWeen the electrodes correspond
`ing 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 1160 and 11819.
`This change in coupling capacitance can be detected by con
`troller 114 and interpreted as a touch at or near the 116a/118b
`node. The controller can be con?gured 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 capacitance
`changes for neighboring nodes so as to accurately determine
`
`20
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`25
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`30
`
`35
`
`40
`
`45
`
`50
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`55
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`60
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`65
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`6
`a touch location lying betWeen nodes by interpolation. Fur
`thermore, controller 114 can be designed to detect multiple
`distinct touches applied to different portions of the touch
`device at the same time, or at overlapping times. Thus, for
`example, if another ?nger 132 touches the touch surface of the
`device 110 at touch location 133 simultaneously With the
`touch of ?nger 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. U.S. 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.
`Controller 114 can employ a variety of circuit modules and
`components that enable it to rapidly determine the coupling
`capacitance at some or all of the nodes of the electrode 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 electrodes 116a-e are
`used as drive electrodes (though it is possible 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 ?rst 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 With
`?nger 231 touching touch surface 239. The upper electrode
`array 212 is separated a distance D1 from the touch surface
`239 by a top substrate 238, Which can be made of polycar
`bonate, polyethylene terephthalate (PET), PMMA, glass,
`silica, or combinations of such (for example, silica coated on
`glass), PET hard coat material, or any other suitable material.
`In the case of non-transparent capacitive touch pads, top
`substrate 238 can be ?berglass 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 ?nger 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 ?nger. For example, 90% or more,
`95% or more, or 98% or more of the surface area of the loWer
`substrate 213 can be covered by loWer electrode array 214.
`
`

`

`US 8,279,187 B2
`
`7
`Upper electrodes are spaced to allow electric ?eld coupling
`from electrodes in loWer electrode array 214 betWeen elec
`trodes in upper electrode array 212, to a touching (or proxi
`mate) ?nger. Width of upper 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 resistance.
`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 con?guration and in any material
`consistent With the present disclosure.
`In FIG. 2, long-dashed electric ?eld lines 232 represent the
`electric ?eld (E-?eld) coupling betWeen electrodes in upper
`electrode array 212 and ?nger 231 When electrodes in upper
`electrode array 212 are activated With an electrical signal.
`This coupling takes place through spaces in the composite
`electrodes that comprise upper electrode array 212. Short
`dashed electric ?eld lines 234 represent electric ?eld coupling
`betWeen electrodes in the upper electrode array 212 and elec
`trodes in loWer electrode array 214. Some of short-dashed
`electric ?eld lines 234 couple from the bottom surface of
`electrodes in upper electrode array 212 to electrodes in loWer
`electrode array 214. Other electric ?eld short-dashed lines
`234 (particularly those not in proximity to ?nger 231) repre
`sent fringe ?elds, 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 ?nger 231, ?eld lines from the top surface of
`electrodes in array 212 couple to (are attracted to) ?nger 231,
`so feWer of them couple to electrodes in loWer electrode array
`214.
`When electrodes of upper electrode array 212 are activated
`With an electrical signal, ?nger 231 is connected to ground by
`relatively loW impedance body-to-ground capacitance, (for
`example, 400 pf) and electrodes of loWer electrode array 214
`are also connected to ground by parasitic capacitance (for
`example, 100 pf). Both of these have signi?cantly loWer
`impedance than the capacitance coupling ?nger 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 con?gu
`ration. 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 con
`?gurations of the upper electrode array 212 and loWer elec
`trode array 214. Similarly, activating an electrode of loWer
`electrode array 214 With an electrical signal generates an
`electric ?eld from the electrode in loWer electrode array 214,
`through electrodes in upper electrode array 212 to ?nger 231.
`NoW turning to FIG. 3, long-dashed electric ?eld lines 233
`represent the electric ?eld coupling betWeen electrodes in
`loWer electrode array 214 and ?nger 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 com
`posite electrodes as they Were in FIG. 2; they are instead
`traditional solid electrodes. Electric ?eld lines 2