HK1160962B - Touch sensitive computing system, capacitive touch sensor panel and related shielding method - Google Patents

Description

Touch sensitive computing system, capacitive touch sensor panel and related shielding method

The application is a divisional application of a patent application with the application number of 200810125849.6, the application date of 2008, 1/3 and the invention name of 'double-sided touch sensitive panel with protective layer and combined driving layer'.

Technical Field

The present invention relates to a touch sensor panel (touch sensor panel), and more particularly, to a capacitive multi-touch sensor panel in which rows and columns are formed on both sides of the same substrate.

Background

In computer systems, a variety of input devices are now available that perform various operations, such as buttons or keys, mice, trackballs, touch pads, joysticks, touch screens, and the like. Touch screens, in particular, have become increasingly popular due to their simplicity and versatility of operation and reduced price. The touch screen may include a touch pad, which may be a clear pad having a touch-sensitive surface. The touch pad may be placed in front of the display screen such that the touch-sensitive surface covers the viewable area of the display screen. Touch screens can allow a user to make selections and move a cursor by simply touching the display screen with a finger or stylus. In general, a touch screen is capable of recognizing a touch and the location of the touch on a display screen, and a computing system is capable of interpreting the touch and then performing an action based on the touch event.

A touchpad may include an array of touch sensors capable of detecting touch events (touches on a touch-sensitive surface using a finger or other object). Future touchpads are capable of detecting multiple touches (touches at different locations on the touch-sensitive surface at approximately the same time using a finger or other object) as well as near touches (near areas of a finger or other object within the detection capabilities of the touch sensor) and identifying and tracking their locations. An example of a multi-touch panel is described in applicant's co-pending U.S. application No.10/842,862 entitled "multi-touch screen," filed on 6/5/2004 and published as U.S. published application No.2006/0097991 on 11/5/2006, the contents of which are incorporated herein by reference.

Capacitive touch sensor panels are constructed of row and column traces on opposite sides of an insulator. At the "intersections" where the traces cross over and under each other (but they are not in direct electrical contact with each other), the traces actually constitute two electrodes. Conventional touch panels used on display devices typically have a top layer of glass on which transparent column traces of Indium Tin Oxide (ITO) or Antimony Tin Oxide (ATO) are etched, and a bottom layer of glass on which row traces of ITO are etched. However, if the conductive material is sufficiently thin (on the order of 30 microns), transparent traces need not be used. Also, if a transparent touch panel is not required (e.g., a touch panel is not used on a display device), an opaque material such as copper may be used to make the conductive material. The upper and lower glassy layers are separated by a spacer layer of transparent polymer which acts as an insulating material between the row and column traces. The traces of the upper and lower vitreous layers may have a pitch of about 5 mm.

To scan the sensor panel, an excitation is applied to one row while the other rows maintain a DC voltage level. When a row is activated, a modulated output signal is capacitively coupled to the columns of the sensor plate. The columns would be connected to analog channels (also referred to herein as event detection and demodulation circuits). For each row that is stimulated, each analog channel associated with a column generates an output value that represents the amount of change in the modulated output signal due to a touch or hover event occurring at the sensor located at the intersection of the stimulated row and the column associated therewith. After the analog channel output values for each column of the sensor panel are obtained, a new row is activated (the other rows are again held at the DC voltage level) and additional analog channel output values are obtained. When all rows are activated and analog channel output values are obtained, the panel is said to be "scanned" and a complete "image" of touch or dwell across the panel is obtained. The image of touches or dwells may contain analog channel output values for each pixel (row and column) on the panel, each output value representing the number of touches or dwells detected at a particular location.

Since the rows must either be excited by an AC signal or maintained at a DC voltage level and since the columns must be connected to analog channels so that the modulated output signals can be detected, demodulated and converted to output values, electrical connections must be made to the rows and columns on both sides of the sensing plate dielectric. Since the rows and columns are perpendicular to each other, the most straightforward way to connect these rows and columns is to bond a flex circuit at one edge of the sensor board (e.g., the short side of the quadrilateral plate) to provide connections to the columns, and bond another flex circuit at an adjacent edge of the sensor board (e.g., the long side of the quadrilateral plate) to provide connections to the rows. However, since these flex circuit connection areas are not on the same side of the sensor board and they are not directly opposite sides of the insulating material, the sensor board must be made larger to accommodate these two non-overlapping connection areas.

Further, when a transparent capacitive touch sensor panel is bonded to a Liquid Crystal Display (LCD), the modulated Vcom layer on the LCD couples to the columns of the sensor panel, thus causing noise on the columns.

Disclosure of Invention

A multi-touch sensor panel is created using a substrate with row and column traces formed on both sides of the substrate using a novel fabrication process. Flex circuits can be used to connect the row and column traces on both sides of the sensor board to its associated sensor board circuitry. The traces, which are made of copper or other highly conductive metal, which extend along the edges of the substrate, can be used to bring the row traces to the same edge of the substrate as the column traces, so that the flex circuit can be connected to the same edge on directly opposite sides of the substrate, minimizing the area required for connection and reducing the overall size of the sensor board. A single flex circuit can be made to connect to the rows and columns on directly opposite sides at the same edge of the substrate. Further, the row traces can be widened to shield the column traces from the modulated Vcom layer.

Column and row ITO traces can be formed on both sides of a DITO substrate using a variety of fabrication methods. In one embodiment, the substrate is placed on the rollers of a manufacturing machine and the ITO layer is sputtered onto the first side of the DITO substrate, followed by etching (e.g., using a photolithographic process) to form the column traces. A protective coating of photoresist (e.g., two layers of photoresist) is then applied over the column traces, and the DITO substrate is flipped over so that the rollers only contact the photoresist applied on the first side and not the formed column traces. Another layer of ITO is then sputtered onto the now exposed back side of the DITO substrate and etched to form row traces 508.

If no metal traces are needed, the photoresist on the first side can be stripped to end the fabrication process. However, if metal traces are required at the edges to connect to the row traces and bring them to a particular edge of the substrate, a protective coating of photoresist (e.g., two layers of photoresist) can be applied over the row traces, with the edge exposed. A metal layer is then sputtered over the photoresist and exposed edges and then etched to form metal traces on the edges. Finally, all remaining photoresist layers are stripped.

Flex circuit portions are formed on a single flex circuit to connect to the row and column traces, respectively, on both sides of the DITO substrate and to a host processor. The flex circuit can also include a circuit area on which a multi-touch subsystem, multi-touch panel processor, high voltage driver and decoder circuitry, EEPROM and some important small circuit elements such as bypass capacitors, etc. can be mounted and connected to save space.

Rows on a DITO substrate can also be widened for shielding purposes and to provide a uniform appearance according to embodiments of the present invention. To avoid capacitive coupling of the modulated Vcom layer to the columns of the substrate, the rows can be widened. The number of rows does not vary, but can be much wider, leaving only about 30 microns spacing between them. Since these wider rows are not insulated, but instead are held at a DC voltage or stimulated with a stimulating voltage, these wider rows act as shields to avoid capacitive coupling of the modulated Vcom layer onto the columns. In addition, the wider rows provide a uniform appearance due to the narrow spacing between them. Thus, the single ITO layer provides shielding, modulation, and a uniform appearance.

Drawings

FIG. 1 illustrates an exemplary computing system that can operate using a capacitive multi-touch sensor panel according to one embodiment of this invention.

FIG. 2a illustrates an exemplary capacitive multi-touch sensor panel according to one embodiment of this invention.

FIG. 2b is a side view of an exemplary pixel in a steady state (no touch) condition in accordance with one embodiment of the present invention.

FIG. 2c is a side view of an exemplary pixel in a dynamic (touch) condition, according to one embodiment of this invention.

FIG. 3 is an exploded perspective view of an exemplary capacitive touch sensor panel comprised of a top layer of glass etched to form transparent ITO column traces and a bottom layer of glass etched to form ITO row traces.

FIG. 4 shows an exemplary capacitive touch sensor panel fabricated using a double-sided ITO (DITO) substrate with column and row ITO traces formed on both sides of the substrate and bonded between the cover layer and the LCD using a transparent adhesive, according to one embodiment of this invention.

FIG. 5 is an exploded perspective view of an exemplary DITO substrate (with its thickness exaggerated for purposes of illustration only) with rows and columns formed on each side, according to one embodiment of this invention.

FIG. 6 shows an exemplary flex circuit according to one embodiment of this invention, including flex circuit portions for connecting to row and column traces, respectively, on both sides of a DITO substrate, and a flex circuit portion for connecting to a host processor.

FIG. 7 is an exploded perspective view of an exemplary DITO substrate (with its thickness exaggerated for purposes of illustration only) with rows and columns formed on both sides and with die insulating squares between the rows and columns to provide a uniform appearance.

FIG. 8 illustrates a stacked structure of an exemplary double-sided touch panel along with an overlay and a Liquid Crystal Display (LCD), according to one embodiment of the invention.

FIG. 9 is a perspective view of an exemplary DITO substrate (with its thickness exaggerated for purposes of illustration only) showing widened rows for shielding purposes and for providing a uniform appearance, according to one embodiment of the present invention.

FIG. 10a shows an exemplary mobile telephone that can include a capacitive touch sensor panel and a flex circuit that can be connected to both sides of a substrate according to one embodiment of the invention.

FIG. 10b shows an exemplary digital audio player that can include a capacitive touch sensor panel and a flex circuit that can be connected to both sides of the substrate according to embodiments of the invention.

Detailed Description

In the following description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the preferred embodiments of the present invention.

The multi-touch sensor panel and its associated sensor panel circuitry are capable of detecting multiple touches (touch events or touch points) that occur at approximately the same time and identifying and tracking their locations. FIG. 1 shows an exemplary computing system 100 that can operate using a capacitive multi-touch sensor panel 124, according to embodiments of this invention. Multi-touch sensor panel 124 is created using a substrate with column and row traces formed on both sides of the substrate using a novel fabrication process. Flex circuits are used to connect the row and column traces on either side of the sensor board to its associated sensor board circuitry. The traces, which are made of copper or other highly conductive metal, extending along the edges of the substrate, can be used to bring the row traces to the same edge of the substrate as the column traces, so that the flex circuit is connected to the same edge on directly opposite sides of the substrate, minimizing the area required for connection and reducing the overall size of the sensor board. A single flex circuit can be made to connect to the rows and columns on directly opposite sides of the same edge of the substrate. Further, the row traces can be widened to shield the column traces from the modulated Vcom layer.

Computing system 100 can include one or more board processors 102 and peripherals 104, and a board subsystem (panel subsystem) 106. The one or more board processors 102 may include, for example, an ARM968 processor or other processor with similar functionality and capabilities. However, in other embodiments, the board processor functionality may instead be implemented by dedicated logic, such as a state machine. The peripherals 104 can include, but are not limited to, Random Access Memory (RAM) or other types of storage and memory devices, watchdog timers and the like.

Board subsystem 106 may include, but is not limited to, one or more analog channels 108, channel scan logic 110, and drive logic 114. Channel scan logic 110 can access RAM112, autonomously read data from the analog channels and provide control for the analog channels. The control may include multiplexing columns of multi-touch pad 124 to analog channels 108. In addition, channel scan logic 110 is capable of controlling the drive logic and the stimulation signals selectively applied to the rows of multi-touch panel 124. In some embodiments, board subsystem 106, board processor 102, and peripherals 104 can be integrated into a single Application Specific Integrated Circuit (ASIC).

The driver logic 114 may provide a plurality of board subsystem outputs 116 and may be capable of providing a proprietary interface to drive high voltage drivers, including a decoder 120 and subsequent level shifters (level shifters) and driver stages 118, although the level shifting function may be implemented prior to the decoding function. Level shifter and driver 118 provides level shifting from a low voltage level (e.g., CMOS level) to a higher voltage level, providing better signal-to-noise ratio (S/N) for noise reduction. Decoder 120 may decode the drive interface signal into one of N outputs, where N is the maximum number of rows on the board. Decoder 120 can be used to reduce the number of drive lines required between the high voltage driver and plate 124. The row input 122 of each panel can drive one or more rows on the panel 124. In some embodiments, the driver 118 and decoder 120 may be integrated into a single ASIC. However, in other embodiments, driver 118 and decoder 120 may be integrated into drive logic 114, and in other embodiments, driver 118 and decoder 120 may be omitted entirely.

Computing system 100 may also include a host processor 128 for receiving output from board processor 102 and performing actions based on the output, which actions may include, but are not limited to, moving an object such as a cursor or pointer, scrolling or panning, adjusting control settings, opening a file or document, viewing a menu, making a selection, executing instructions, operating a peripheral device connected to the host device, answering a call, making a call, ending a call, changing volume or audio settings, storing information related to telephone communications such as an address, a frequently dialed number, answered calls, missed calls, logging onto a computer or computer network, allowing authorized individuals access to restricted areas of the computer or computer network, loading user profiles associated with a user's favorite computer desktop profile, allowing access to network content, running a particular program, encrypting or decoding a message, and so on. The host computer 128 may also perform other functions unrelated to board processing and may be coupled to a program memory 132 and a display device 130, such as a Liquid Crystal Display (LCD), to provide a UI for a user of the device.

As described above, multi-touch panel 124 in some embodiments includes a capacitive sensing medium having a plurality of row traces or driving lines and a plurality of column traces or sensing lines separated by insulating material (although other sensing media may also be used). In some embodiments, the insulating material may be transparent, such as glass, or may be made of other materials, such as mylar. The row and column traces can be made of a transparent conductive medium such as ITO or ATO, but other transparent or opaque materials such as copper can also be used. In some embodiments, the row and column traces are perpendicular to each other, while in other embodiments other angles other than right angles and non-Cartesian directions may occur. For example, in a polar coordinate system, the sense lines may be concentric circles and the drive lines may be radially diverging lines (or vice versa). It should be understood, therefore, that the terms "rows" and "columns," "first dimension" and "second dimension," or "first axis" and "second axis" as used herein are intended to encompass not only orthogonal grids, but also intersecting traces of other geometries having first and second dimensions (e.g., concentric and radial lines in a polar coordinate arrangement).

At the "intersections" of the traces, where the traces pass above or below each other (but do not make direct electrical contact with each other), the traces actually form two electrodes (although intersections of more than two traces may also occur). The intersection of each row and column trace represents a capacitive sensing node and can be viewed as a picture element (pixel) 126, which is useful when multi-touch sensor panel 124 is viewed as capturing an "image" of touch. (that is, after multi-touch subsystem 106 determines whether a touch event has been detected on each touch sensor of the multi-touch panel, the pattern of touch sensors on the multi-touch panel on which the touch event occurred (pattern) is treated as an "image" of the touch (e.g., a pattern of a finger touching the touch panel.) when a given row is held at DC, the capacitance between the row and column electrodes can be treated as a parasitic capacitance on all columns and as a mutual capacitance Csig when the given row is stimulated by an AC signal). The proximity or touching of a finger or other object on the multi-touch panel can be detected by measuring changes to Csig. The columns of multi-touch panel 124 can drive one or more analog channels 108 (also referred to herein as event detection and demodulation circuitry) in multi-touch subsystem 106. In some embodiments, each column is coupled to one dedicated analog channel 108. However, in other embodiments, the columns are coupled to at least several analog channels 108 through analog switches.

Fig. 2a shows an exemplary capacitive multi-touch panel 200. FIG. 2a shows the presence of a stray capacitance Cstray at each pixel 202 located at the intersection of a row 204 and column 206 trace (Cstray is shown for only one column in FIG. 2a for simplicity of illustration). Note that although FIG. 2a shows rows 204 and columns 206 as being substantially vertical, they need not be so arranged, as described above. In the example of FIG. 2a, AC excitation signal Vstim 214 is applied to one row, while all other rows are connected to DC. The excitation signal injects charge onto the column electrode through the mutual capacitance of the crossing points. The charge is Qsig × Vstim. Each column 206 is selectively coupled to one or more analog channels (see analog channels 108 in fig. 1).

Fig. 2b is a side view of exemplary pixel 202 in a steady state (no touch) condition. The electric field of the electric field lines 208 of the mutual capacitance between the column 206 and row 204 traces or electrodes separated by the insulating material 210 is shown in fig. 2 b.

Fig. 2c is a side view of exemplary pixel 202 in a dynamic (touch) condition. In fig. 2c, finger 212 is placed adjacent to pixel 202. Finger 212 is a low impedance object at signal frequencies and has an AC capacitance Cfinger from column trace 204 to the body. The body has a self-capacitance to ground Cbody of about 200pF, where Cbody is much larger than Cfinger. If finger 212 blocks some of the electric field lines 208 between the row and column electrodes (those fringing fields that exit the insulating material and pass through the air above the row electrode), then these electric field lines are shunted to ground through the capacitance path inherent in the finger and the body, and as a result, the steady state signal capacitance Csig is reduced by Δ Csig. That is, the capacitance of the connected body and finger subtracts Csig by a value of Δ Csig (which may also be referred to herein as Csig _ sense), and can act as a shunt or dynamic loop to ground, blocking some of the electric field resulting in a reduced net signal capacitance. The signal capacitance at the pixel becomes Csig- Δ Csig, where Csig represents the steady (no touch) component and Δ Csig represents the dynamic (touch) component. Note that Csig- Δ Csig is always non-zero because a finger, palm or other object cannot block all electric fields, especially those that remain entirely in the dielectric material. In addition, it should be appreciated that as the finger presses harder or more fully contacts the multi-touch pad, the finger may become flatter, blocking more and more of the electric field, and Δ Csig is variable and represents the degree to which the finger presses on the pad (e.g., ranging from "no touch" to "full touch").

Referring back to FIG. 2a, as described above, Vstim signal 214 can be applied to a row of multi-touch panel 200 such that a change in signal capacitance can be detected when a finger, palm or other object is present. Vstim signal 214 can be generated as one or more pulse trains 216 at a particular frequency, each pulse train including a plurality of pulses. Although pulse train 216 is illustrated as a square wave, other waveforms, such as a sine wave, may also be used. Multiple pulse trains 216 at different frequencies may be transmitted for noise reduction purposes to detect and avoid noisy frequencies. Vstim signal 214 essentially injects a charge into a row, and can be applied to multi-touch pad 200 one row at a time with the other rows held at a DC level. However, in other embodiments, the multi-touch panel may be divided into two or more zones, with Vstim signal 214 being applied synchronously on one row of each zone while the DC voltage is maintained on all other rows of the zone.

Each analog channel coupled to a column measures the mutual capacitance formed between the column and the row. The mutual capacitance includes the signal capacitance Csig and any change Csig _ sense in the signal capacitance caused by the presence of a finger, palm or other body part or object. The column values provided by the analog channels may be provided in parallel when a single row is fired, or may be provided in series. If all values representing the signal capacitances for the columns are obtained, another row on multi-touch panel 200 is stimulated while the other rows are held at a DC voltage, and the column signal capacitance measurements may be repeated. Finally, if Vstim is applied to all rows and the signal capacitance values for all columns on all rows are captured (e.g., "scanning" the entire multi-touch panel 200), then a "snapshot" of all pixel values is taken for the entire multi-touch panel 200. These snapshot data may first be stored in the multi-touch subsystem and then output for interpretation by other devices in the computing system, such as the host processor. Since multiple snapshots are taken, saved and interpreted by the computing system, it is possible to detect, track, and perform other functions with multiple touches.

As described above, since the rows can be excited by an AC signal or held at a DC voltage level, and since the columns need to be connected to analog channels so that the modulated output signals can be detected, demodulated and converted to output values, electrical connections must be made to the rows and columns on each side of the sensing plate dielectric.

FIG. 3 is an exploded perspective view of an exemplary capacitive touch sensor panel 300 comprised of a glassy upper layer 302 and a glassy lower layer 306, the glassy upper layer 302 having transparent ITO column traces 304 etched thereon and the glassy lower layer 306 having ITO row traces 308 etched thereon. The upper and lower vitreous layers 302 and 306 are separated by a transparent polymeric spacer layer 310, the polymeric spacer layer 310 serving as an insulating material between the row and column traces. Since the rows and columns are perpendicular to each other, the most straightforward way to connect these rows and columns is to bond a flex circuit 312 at one edge of the sensor board and another flex circuit 314 at the adjacent edge of the sensor board. However, the connection areas of flex circuit 312 and flex circuit 314 are not on the same edge of sensor board 300 and are not on directly opposite sides of insulating material 310, so the sensor board must be made larger to accommodate these two non-overlapping connection areas.

Since it has not been practical to form column and row traces on both sides of a single substrate, capacitive touch sensor panels typically form the row and column traces on two pieces of glass as shown in FIG. 3. Conventional methods of forming ITO traces on one side of a substrate require that the substrate be placed on rollers during the manufacturing process. However, if the substrate is then reversed to make ITO traces on the second side, the rollers will damage any traces that have already been made on the first side of the substrate. In addition, when an etching process is used to etch away a portion of the ITO to make traces on one side of the substrate, the entire substrate is conventionally placed in an etch bath, and any traces previously made on the other side of the substrate are etched away.

FIG. 4 shows an exemplary capacitive touch sensor panel 400 fabricated using a double-sided ITO (DITO) substrate 402 having column and row ITO traces 404 and 406, respectively, on each side of the substrate and bonded between a cover layer 408 and an LCD 410 using a transparent adhesive 412, according to embodiments of the invention. Substrate 402 may be fabricated using glass, plastic, glass/plastic hybrid materials, and the like. The cover layer 408 may be made of glass, acrylic, sapphire, or the like. To connect column and row traces 404 and 406, respectively, two flex circuit portions 414 are bonded to directly opposite sides of the same edge of DITO 402, although other bonding locations can be used.

FIG. 5 is an exploded perspective view of an exemplary DITO substrate 500 (with its thickness exaggerated for purposes of illustration only) with columns 502 and rows 508 formed on each side according to embodiments of the present invention. Some columns of ITO traces 502 on the top surface are connected to a small neck-end connector area 504, where they are distributed outside the touch sensor panel, guided by flex circuit portion 506, which flex circuit portion 506 is conductively connected to the top surface of DITO substrate 500. In some embodiments, row ITO traces 508 on the bottom surface can be connected to thinner metal traces 510 that extend along the edges of the bottom surface. Metal traces 510 lead to connector areas 512, which can be directly opposite connector areas 504 or at least on the same edge of DITO substrate 500 as connector areas 504. Providing connector areas 504 and 512 on the same edge of DITO substrate 500 allows the substrate, and thus the overall product, to be smaller. Another flex circuit portion 514 can be used to bring row ITO traces 508 out of the touch sensor panel.

Column and row ITO traces 502 and 508 can be formed on both sides of DITO substrate 500 using a variety of fabrication methods. In one embodiment, the substrate is placed on the rollers of a manufacturing machine and a layer of ITO is sputtered onto a first side of DITO substrate 500 and etched (e.g., using photolithographic techniques) to form column traces 502. A protective coating of photoresist (e.g., two layers of photoresist) is then applied over column traces 502, and DITO substrate 500 is flipped over so that the rollers only contact the applied photoresist on the first side and not the formed column traces. Another layer of ITO is then sputtered onto the now exposed back side of DITO substrate 500 and etched to create row traces 508.

If the metal traces 510 are not needed, the photoresist on the first side can be stripped to end the process. However, if metal traces 510 are needed on the edges to connect the row traces 508 and bring them to a particular edge of the substrate, a protective coating of photoresist (e.g., two layers of photoresist) can be applied over the row traces 508 leaving the edges exposed. A metal layer is then sputtered onto the photoresist and exposed edges, and the metal layer is then etched on the edges to form metal traces 510. Finally, all remaining photoresist layers are stripped.

Slight variations to the process described above are possible. The patterned second side of the DITO substrate can be formed, for example, by first patterning a photoresist using very simple geometric methods to cover only the interior region of the second side of the DITO substrate while leaving the edge region exposed. For this variation, the metal is sprayed first and then the photoresist with simple geometry is stripped so that only the metal in the edge of the region remains. The ITO is then sputtered over the entire second side of the DITO substrate. A second photoresist layer is then applied and patterned to form a mask for the electrode pattern. A series of etching steps are then performed on the topmost ITO layer and the underlying metal layer to form an electrode pattern. The first etching step etches only the ITO and the second etching step etches only the metal layer that produces the desired electrode geometry.

FIG. 6 shows an exemplary flex circuit 600 that includes flex circuit portions 606 and 614 for connection to row and column traces, respectively, on each side of a DITO substrate and flex circuit portion 608 for connection to a host processor, according to embodiments of the invention. Flex circuit 600 includes a circuit area 602 upon which a multi-touch subsystem, a multi-touch panel processor, high voltage driver and decoder circuitry (see fig. 1), EEPROM, and some important small circuit elements such as bypass capacitors, etc., can be located and connected to save space. Circuit area 602 may be shielded by an EMI can (not shown) that encloses circuit area 602 using upper and lower shielding portions. The lower shield portion may be connected to a structure of the device to protect the circuit area. From this circuit area 602, flex circuit 600 can be connected to the top surface of the DITO substrate through flex circuit portion 606, to the bottom surface of the DITO substrate through flex circuit portion 614, and to a host processor through flex circuit portion 608.

FIG. 7 is an exploded perspective view of an exemplary DITO substrate 700 (with its thickness exaggerated for purposes of illustration only) with columns 702 and rows 708 formed on each side. As shown in fig. 7, the column traces 702 may be about 1mm wide with a spacing of about 4mm between traces, and the row traces 708 may be about 2mm wide with a spacing of about 3mm between rows. To create a more uniform appearance, smaller blocks of insulating ITO 704 are formed between column traces 702 and row traces 708 on each side of DITO substrate 700 with a narrow spacing (e.g., about 30 microns) between the insulating blocks of ITO, so that each side of the DITO substrate can provide a uniform appearance similar to a solid sheet of ITO.

FIG. 8 illustrates a stacked configuration of an exemplary dual-sided touch panel 800, along with an overlay 802 and a Liquid Crystal Display (LCD)804, in accordance with embodiments of the present invention. From top to bottom, the LCD804 may include a polarizing layer 806, a glass top layer 808, a liquid crystal layer 810, a glass bottom layer 812, a polarizing layer 814, and a backlight layer 816.

From top to bottom, liquid crystal layer 810 can include RGB color filter layer 818, planarization layer 820, an unpatterned ITO conductive layer called Vcom layer 822, polyamide layer 824, liquid crystal layer 826, and polyamide layer 828. Below the polyamide layer 828 is a layer of ITO rectangles and TFTs (collectively referred to herein as TFT layer 830), one for each sub-pixel (where three sub-pixels make up a pixel).

The color filter layer 818 provides the three RGB colors that make up each pixel when illuminated, where the ratio of colors determines the color of the pixel. The planarization layer 820 is made of a transparent plastic to smooth the surface of the color filter layer 818. Vcom layer 822 represents a "common voltage" because it provides a common voltage for the ITO subpixel Vcom layer of TFT layer 830. Vcom layer 822 can be held at a constant voltage (LCDs using a constant Vcom voltage can be referred to as DC or constant Vcom LCDs), or modulated using an AC signal. Polyamide layers 824 and 828 serve as a pre-alignment of the orientation of the liquid crystals on liquid crystal layer 826. To generate color for a pixel, a voltage is applied across the ITO squares of each sub-pixel on TFT layer 830 relative to Vcom layer 822, which aligns the liquid crystals and allows light from backlight 816 to pass through liquid crystal layer 826 and the RGB color filters in color filter layer 818.

As described above, while Vcom layer 822 can be held constant, in some embodiments, the Vcom layer can also be driven by a modulated signal (e.g., a square wave from 1 volt to 4 volts). However, when Vcom layer 822 is driven by a modulated signal, the modulated signal can capacitively couple (see reference feature 834) through sparse conductor rows 836 on the bottom surface of dual-sided touch panel 800 to columns 838, causing noise on the columns. Note that even if multiple closely spaced ITO squares are included, row 836 is referred to as "sparse" because the squares are isolated and their effect can be ignored from a shielding standpoint. Note also that although modulated Vcom layer 822 is also capacitively coupled to rows 836, since the rows are driven by driver circuits with low impedance outputs, any capacitive coupling is shunted to the driver outputs and has negligible effect. However, columns 838 are designed to sense small changes in the AC capacitance on the touch panel, so the capacitance coupled from modulated Vcom layer 822 can be easily seen as noise at the analog channel receiving the column signal.

FIG. 9 is a perspective view of an exemplary DITO substrate 900 (with its thickness exaggerated for purposes of illustration only) showing rows 936 widened for shielding purposes and to provide a uniform appearance, according to embodiments of the present invention. To prevent capacitive coupling from the modulated Vcom layer to columns 938, rows 936 can be widened as shown in FIG. 9. The number of rows 936 does not change, but they are now wider (e.g., about 4.97mm), leaving only about 30 microns of space between them. Because the wider rows 936 are not insulated, but instead remain at a DC voltage or are stimulated by a stimulation voltage, these wider rows 936 serve to shield, prevent the modulated Vcom layer from capacitively coupling to the columns 938. In addition, rows 936 provide a uniform appearance due to the narrow space between them. Thus, shielding, modulation, and a uniform appearance can be obtained from a single ITO layer. Note that while FIG. 9 shows rows and columns formed on opposite sides of a single substrate, wide rows can also be used on the conventional touch sensor panel shown in FIG. 3. Another alternative to these wide rows is to add another layer of ITO as a shield between the LCD and DITO, but this would incur additional cost, additional thickness, light loss, and unwanted color shift.

In some embodiments, the top surface of an exemplary DITO substrate can include isolated ITO squares between columns, while the bottom surface can include wide rows. The rows on the bottom surface may be guided into the flex connector area by metal traces extending along the long edges of the bottom surface. The flex connection regions on the top and bottom surfaces can be on the same edge of the DITO substrate, but the conductors themselves can be in non-overlapping areas to easily bond these flex circuits.

FIG. 10a shows an exemplary mobile phone 1136 that can include a capacitive touch sensor panel 1124 and a flex circuit 1134 that can be coupled to both sides of the substrate in accordance with embodiments of the present invention. The sensor plate 1124 can be made using a substrate that: column and row ITO traces are formed on each side of the substrate, and metal traces are formed along the edges of one side of the substrate, allowing flexible circuit connection areas to be placed on opposite sides of the same edge of the substrate. Further, sensor panel 1134 can be fabricated with wide rows to provide modulated Vcom layer shielding and a uniform appearance. FIG. 10b shows an exemplary digital audio/video player 1138 that can include a capacitive touch sensor panel 1124 and a flex circuit 1134 that can be connected to both sides of the substrate in accordance with embodiments of the present invention. The sensor plate 1124 can be made using a substrate that: column and row ITO traces are formed on each side of the substrate, and metal traces are formed along the edges of one side of the substrate, allowing flexible circuit connection areas to be placed on opposite sides of the same edge of the substrate. Further, sensor panel 1134 can be fabricated with wide rows to provide modulated Vcom layer shielding and a uniform appearance. The mobile phone and digital audio/video player of fig. 10a and 10b can benefit from sensor panel 1124 because a single, thin and small-sized sensor panel is used, and only one ITO layer is required to provide shielding and a uniform appearance. The overall effect is to reduce product size and production costs.

Although the present invention has been described in connection with the embodiments with reference to the accompanying drawings, it is to be noted that various modifications and changes will be apparent to those skilled in the art. Such modifications and variations are considered to be within the scope of the invention as set forth in the appended claims.

Claims (9)

1. A capacitive touch sensor panel, comprising:

a sensing trace formed on the first layer and arranged along a first dimension of a two-dimensional coordinate system; and

drive traces formed on a second layer spatially separated from the first layer by an insulator, the drive traces arranged along a second dimension of the two-dimensional coordinate system;

wherein the drive traces are widened compared to the sense traces to substantially cover the second layer except for a gap between adjacent drive traces to substantially electrically isolate the sense traces from a Liquid Crystal Display (LCD); and is

Wherein the sensor is formed at a position where the sensing trace crosses the driving trace while being separated by the insulator.

2. The capacitive touch sensitive panel of claim 1, wherein each drive trace has a substantially constant width.

3. A method for shielding a capacitive touch sensor panel from coupling of modulated signals, comprising:

forming a first set of sense traces on a first layer;

orienting the sensing trace along a first dimension of a two-dimensional coordinate system;

forming a second set of widened drive traces on a second layer spatially separated from the first layer, the drive traces being widened compared to the sense traces to substantially cover the second layer except for gaps between adjacent drive traces to substantially electrically isolate the first set of sense traces from a Liquid Crystal Display (LCD); and

the drive traces are oriented along a second dimension of the two-dimensional coordinate system to form a sensor where the sense traces intersect the drive traces.

4. The method of claim 3, wherein each drive trace has a substantially constant width.

5. A touch-sensitive computing system, comprising:

a touch processor;

a display;

a touch-sensing pad adjacent to the display and coupled to the touch processor, the touch-sensing pad comprising:

a sensing trace formed on the first layer, an

Drive traces formed on a second layer spaced apart from the first layer, the drive traces being widened compared to the sense traces to substantially cover the second layer except for gaps between adjacent drive traces to substantially electrically isolate the sense traces from a Liquid Crystal Display (LCD),

wherein the sensor is formed at a position where the sensing trace crosses the driving trace.

6. The touch sensitive computing system of claim 5, wherein each drive trace has a substantially constant width.

7. The touch sensitive computing system of claim 5, wherein the touch sensitive computing system is incorporated into a mobile phone.

8. The touch sensitive computing system of claim 5, wherein the touch sensitive computing system is incorporated into a media player.

9. The touch sensitive computing system of claim 5, wherein the touch sensitive computing system is incorporated into a personal computer.