JP2008134634A - Display element driving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an element driving method capable of reducing the cost of a display device such as portable display device, for example, non-contact IC card. <P>SOLUTION: Upon the driving of a planar state of cholesteric liquid crystal cell, a pulse voltage is applied to the liquid crystal cell, thereafter, a driving impedance on the power source side is set to be a value lower than the impedance of the liquid crystal cell and, at the same time, an applied voltage is made to be zero. Further, on the driving to a focal conic state, a pulse voltage is applied and, thereafter, the driving impedance is set to be a value higher than the impedance of the liquid crystal cell. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid crystal display, a driving method thereof, and a non-contact type IC card as a portable display device. More specifically, the display continues even when the power is turned off, for example, a display element using a cholesteric liquid crystal. The present invention relates to a driving method thereof, and an IC card having an antenna structure using a multilayer wiring board while greatly improving mechanical strength.

  In recent years, non-contact IC cards, RF (radio frequency) tags, etc., which are durable and convenient, have begun to spread in applications such as logistics where contact IC cards and barcodes are used. . In the future, new application fields such as electronic money will be developed, and cards and tags that perform wireless communication with external devices are expected to become increasingly popular. Although an IC card is excellent in information recording, there is a problem in that it cannot be confirmed until the recorded contents are read by a dedicated device. In point cards and transportation coupon cards, it is desired that the recorded contents can be visually confirmed.

FIG. 1 shows a conventional example of a contact type IC card. In contact with the IC card reader / writer includes a terminal C1~C8 for exchanging data and power, for example, to the terminal C1 is supplied V _CC used as a power supply voltage of the circuit.

  In the conventional contact type IC card, a display medium using magnetic flakes or a medium that can be visually recognized by thermal writing using a leuco dye has been proposed. Since it is a contact type, there is a dedicated device for inserting an IC card, and a display writing device for a magnetic head or a thermal head is built in the device. A non-contact type IC card or RF tag, which is expected to spread in the future, cannot be equipped with a conventional write head. Since the display must be performed with an electric signal supplied wirelessly, a liquid crystal system or an electrophoretic system that can be electrically driven is required.

The following documents are available for IC cards equipped with display elements. Patent Document 1 discloses an IC card provided with a display element, and proposes the use of a non-contact type or a liquid crystal display. Patent Document 2 discloses a wireless tag that can directly read and display tag information, and the use of electronic paper is also proposed.
No. 7-30384 “IC Card” Japanese Patent Laid-Open No. 2002-236891 “Wireless Tag with Data Display Function”

  FIG. 2 is an explanatory diagram of a configuration example of a non-contact type IC card. In the figure, for example, a close contact IC card 50 exchanges data with a card reader / writer 51 in a non-contact manner. As shown in the cross-sectional view at the top of the figure, the contact IC card includes an antenna unit for communication.

  The close contact IC card 50 includes a microcomputer unit 52, an RF interface 53, and a non-contact interface 54. The microcomputer unit 52 includes a CPU 55, a memory 56, an I / O port 57, and the like.

  The card reader / writer 51 includes a non-contact interface 60 as an interface for communication with the contact IC card 50 and an interface circuit 61 as an interface with a host computer.

  In order to actually use an IC card or an RF tag as a display element, there is a big problem and it has not been realized. The problem is physical durability. For example, in order to use it for an IC card, it is necessary to clear the bending resistance and the environmental test standardized by JIS. A general liquid crystal cannot be tolerated. For example, in the case of an IC card, it is required that the operation of bending the center by 2 cm with respect to the long side of 85 mm is repeated 500 times or more and there is no damage. Conventional liquid crystals cannot withstand problems such as substrate breakage, disorder of alignment, and peeling of the sealing material. In a contact type or hybrid type (both contact and non-contact functions) card, a strong roller pressure is applied to the card surface by a conveying roller in order to insert the card into the reader. In the conventional liquid crystal, the liquid crystal is brought to one side by the roller pressure, the seal is broken at the edge portion, the liquid crystal leaks out, and the function as the liquid crystal display element is lost.

  FIG. 3 shows a conventional example of the structure of a liquid crystal cell using columnar spacers. A columnar spacer 102 is inserted between the two substrates 101 to support the substrate. The use of such spacers and the proposal of pillars with adhesive properties are disclosed in the following documents, but such a structure is also insufficient in durability for application to an IC card. There was a point.

Patent Document 3
Japanese Utility Model Publication No. 58-13515 "Liquid Crystal Display"
Patent Document 4
Japanese Patent Application Laid-Open No. 7-318912 “Liquid Crystal Panel Frame, Liquid Crystal Panel Body, and Liquid Crystal Display”
Patent Document 5
Japanese Patent No. 3196744 “Liquid Crystal Display Element and Method for Producing the Same”
Since the liquid crystal cell structures in Patent Document 3, Patent Document 4, and Patent Document 5 use a matrix structure, the aperture ratio, that is, the ratio of the area occupied by the liquid crystal effective for display in the cell surface area is designed to be large. However, there is no idea that the area of the columnar spacer is 20% or more, and there is a problem in terms of durability of the liquid crystal cell.

  In addition, in the display part of a commonly used liquid crystal calculator, liquid crystal is injected into the entire cell, and only one part is driven, so that expensive liquid crystal is wasted. It was.

  Next, selective reflection of cholesteric liquid crystal, which has semi-permanent memory properties and is expected to be applied to display portions of IC cards and electronic paper, has been historically old, and was discovered from a cholesterol derivative in 1888. The following Patent Document 6 discloses a display element that utilizes two stability states of a selective reflection state and a transmission state by mixing a polymer network and a chiral nematic liquid crystal. Chiral nematic liquid crystal is a kind of cholesteric liquid crystal and has the same basic properties. Chiral nematic liquid crystals are obtained by adding a chiral substance (chiral agent) to nematic liquid crystals to form a cholesteric phase.

  A cholesteric liquid crystal (chiral nematic liquid crystal) undergoes a state transition between a planar state that is a reflection state and a focal conic state that is a transmission state by electrical control. The planar state and the focal conic state are maintained semipermanently unless any external force is applied, and the cholesteric liquid crystal has a semipermanent memory property.

Patent Document 6
Japanese Patent Publication No. 6-507505 “Liquid Crystal Light Modulation Device and Liquid Crystal Material”
FIG. 4 is an explanatory diagram of the driving waveform of such a cholesteric liquid crystal. The properties of the cholesteric liquid crystal will be described in more detail later. Basically, it is a liquid crystal having two stable states, a planar state and a focal conic state. In the planar state, light in a certain range of frequencies is selectively reflected, whereas in the focal conic state, all light is transmitted, that is, a transparent state.

  In order to obtain a planar state, that is, to perform planar driving, as shown on the left side of FIG. 4, for example, a method of applying a pulse of about ± 40V is used. For focal conic driving, about ± 18V is applied as shown on the right side. The method of applying the pulse is used. The reason why the positive and negative pulses are applied here is to prevent afterimages due to ion deviation in the liquid crystal and display unevenness.

  Thus, a display element using cholesteric liquid crystal has a semi-permanent memory property and is suitable for use in an IC card or the like. However, as described in FIG. 4, the peak value differs depending on the planar drive and the focal conic drive. Since it is necessary to use two types of pulses properly and the peak value is as high as about +40 V, the power supply circuit is complicated in the non-powered IC card having no battery.

  Next, problems of the conventional antenna structure in the non-contact IC card will be described. FIG. 5 is an explanatory diagram of antenna wiring in a conventional general non-contact IC card. As shown in the figure, the antenna wiring is arranged on the outermost side of the film substrate, and data transmitted from the IC card reader / writer is received by the antenna.

  For example, an IC card with a display function using a cholesteric liquid crystal requires a relatively high voltage as described above, and in order to generate such a voltage, a high frequency is applied to the antenna wiring in addition to the conventional antenna wiring. When a current flows, it is necessary to add a coil pattern in which a voltage is induced by electromagnetic induction, and to supply power to the display driver using the voltage induced in the coil pattern.

  FIG. 6 is an explanatory diagram of the structure of an IC card in which such a coil pattern is arranged near the outer periphery of the film substrate in the vicinity of the antenna wiring. In the figure, for example, an LCD driver is operated using a voltage induced in a coil pattern. However, in many actual use cases of IC cards, such as bank cash cards, embossing is performed to generate character information such as numbers and alphabets as protrusions on the IC card. 7 and 8 are explanatory views of problems associated with the embossing.

  In FIG. 7, in the embossed area, extrusion is performed in the thickness direction of the card by embossing. Therefore, when an antenna wiring or a coil pattern is applied to the embossed area, the wiring is cut.

  A conventional improved method for this problem is shown in FIG. FIG. 8 is a conventional example of an IC card in which the width of the wiring is widened only for the portion of the wiring related to the embossed characters and the wiring portion is not cut even when embossing is performed. In the figure, only the antenna wiring is formed near the outer periphery of the film substrate, and the coil pattern wiring as shown in FIG. 6 is not performed.

  Therefore, when the antenna wiring and the coil pattern are arranged near the outer periphery of the film substrate as shown in FIG. 6 and a plurality of different voltage values as described in FIG. 4 are required, a plurality of corresponding voltage values are required. Although it is necessary to provide the coil pattern close to the antenna wiring and to increase the width of each, it has been a problem that such a structure is not possible with the conventional substrate structure.

A first object of the present invention is to improve the mechanical durability of a display device such as a portable display device such as a non-contact IC card. The second object is to provide an element driving method for reducing the cost for driving the element in such a portable display device, and the third object is to supply voltage to the antenna wiring and the display unit. An object of the present invention is to provide a portable display device that efficiently arranges a coil pattern for the purpose.

  The display element driving method of the present invention is to drive a display element using, for example, a cholesteric liquid crystal. When driving the liquid crystal cell in the planar state, after applying a pulse voltage to the liquid crystal cell, the method of setting the drive impedance on the power source side to a value lower than the impedance of the liquid crystal cell and setting the applied voltage to 0 is also in the focal conic state. At the time of driving, a method of setting the driving impedance to a value higher than the impedance of the liquid crystal cell after applying a pulse voltage is used.

  As described above, according to the present invention, the mechanical durability of the display element is greatly increased by providing the wall surface structure that holds the substrate at a portion other than the display portion between the two substrates facing the display element. To improve.

  FIG. 9 is a diagram illustrating the principle of the structure for improving the durability of a liquid crystal display element according to the present invention. In the figure, a display unit 2 using liquid crystal is sandwiched between two substrates 1, but the display unit 2 is surrounded by a wall material 3 and the liquid crystal is connected by an injection path.

The surface perpendicular to the wall surface of the wall material 3 is bonded to the substrate 1, and the bonded area can be made larger than the area of the surface of the liquid crystal serving as the display unit 2 on the substrate 1 side.
The display unit using the liquid crystal 2 is a segment display unit, and the liquid crystal can be injected into each segment of the segment display unit through a liquid crystal injection path.
Further, a light shielding layer that shields light other than the opening smaller than the width of the liquid crystal injected into each segment may be provided between the liquid crystal serving as the display unit 2 and the substrate 1. A light absorption layer can also be provided between the substrate different from the substrate provided with the display portion and the wall surface material 3.
The display unit 2 can also be a display unit using cholesteric liquid crystal.

  The display unit 2 has a structure in which a plurality of numbers or character characters are arranged, and the wall surface material 3 can form blocks for each character, and the blocks can be connected by a liquid crystal injection path. A liquid crystal inlet and an outlet are provided corresponding to the block, and the liquid crystal injection path in the block can be branched at the inlet and merged at the outlet.

  Next, the display element driving method of the present invention is used for driving a display element using cholesteric liquid crystal, and when driving to the planar state, after applying a pulse voltage to the liquid crystal cell, the driving impedance on the power source side is set to the liquid crystal cell. A method of making the applied voltage lower than the impedance and making the applied voltage 0 is a method of making the driving impedance higher than the impedance of the liquid crystal cell after applying the pulse voltage when driving to the focal conic state.

In this method, the polarity of the pulse voltage can be reversed at least once during application of the pulse voltage to the liquid crystal cell, and the peak value of the pulse voltage is set to be equal to or higher than the voltage value at which the liquid crystal cell surely transitions to the planar state. You can also.
The driving impedance value after applying the pulse voltage during driving to the planar state is such that the discharge time of the charge accumulated in the liquid crystal cell is less than the maximum time required for the liquid crystal cell to transition to the planar state. It can also be set to such a value.

Further, a portable display device including a display element using this driving method and an antenna portion for receiving supply of data and power from the outside can be used.
Furthermore, the portable display device of the present invention uses a multilayer wiring board, and is provided with an antenna pattern for receiving data and power from the outside, and is provided close to the antenna pattern, and current flows through the antenna pattern. A coil pattern for using a voltage generated by electromagnetic induction as a power supply voltage for display is provided on different layers of the multilayer wiring board. On the multilayer wiring board, the portion where the antenna pattern and the coil pattern are arranged may be two or more layers, and the portion where other components are arranged may be one or more layers.

Next, embodiments of the present invention will be described in more detail, including the structure of the liquid crystal display element described in FIG.
In general, when a liquid crystal element is used for an IC card or an RF (Radio Frequency) tag, a number of numbers, numbers such as numbers and symbols, or alphabets, that is, character characters are used. If it is a number, the method of expressing one number by 7 segments is generally used.

  The area used for display inside the liquid crystal element is limited, and it is not necessary to inject liquid crystal outside the numerical display area. Therefore, as shown in FIG. 9, by adopting a wall surface structure other than the display (segment) portion, it becomes possible to give overwhelming durability to the IC card. A super durable structure is realized by providing a wall surface structure of 50% or more with respect to at least the dimensions of the display element, that is, the size on the front side.

  The element structure of the present invention can be applied to matrix display at the expense of the aperture ratio, but is more suitable for segment type liquid crystal display such as numerical display and character display. In a display unit of a liquid crystal calculator that is generally used, liquid crystal is injected into the entire cell, and only one part is driven. Expensive liquid crystal is used wastefully, and cost reduction can be realized by using the structure shown in FIG.

  As the wall material 3, a resist as described in Patent Document 5 described above can be used, and an adhesive force can be given by heat treatment. Depending on the type of resist, the thickness setting value, for example, about 5 μm, may be deteriorated due to softening associated with the heat treatment. In such a case, the thickness can be stably controlled by using a spherical or fiber spacer together. A columnar spacer (such as a UV curable resin) having no adhesive force but good thickness stability may be used in combination. Spherical or fiber-like spacers may be mixed with the wall material 3 or dispersed on the substrate 1.

  FIG. 10 shows an example of using a segment light shielding mask. For application to an IC card or the like, a liquid crystal with memory characteristics (display holding after power-off) is required. A cholesteric liquid crystal having a selective reflection function and having bistability is a candidate. It is a bistable liquid crystal that is in a reflective state when a high voltage pulse is applied and in a transparent state when a low voltage pulse is applied. However, it is known that the state of this liquid crystal changes depending on changes in pressure and heat.

  In a region where there is no segment electrode (near the injection port or an injection path between segments), there is no opposing electrode, and if the liquid crystal changes to the reflective state, it cannot be electrically initialized. Noise is displayed and the visibility of numbers is reduced. Therefore, the segment light-shielding mask 4 shields the area unnecessary for the segment display, so that a good display is obtained. By providing the segment-shaped light-shielding mask 4 on the wall surface material 3 in FIG. 9, it is possible to hide the injection path which is necessary for liquid crystal injection but is excessive for display, and the display visibility is improved. It becomes possible to improve.

  As shown in FIG. 11, the light shielding mask 4 is desirably provided inside the cell. Although it can be provided outside the substrate 1, the thickness of the substrate 1 causes a sense of depth, which is inconvenient for visibility. In order to ensure the wide viewing angle range, it is desirable to form the light shielding mask 4 inside the cell. The width of the light transmission part of the light shielding mask 4 is made smaller than the width of the liquid crystal formed by the wall surface material 3. At the same size, there is no margin for alignment, and if it is too large, an unnecessary place can be seen and visibility is lowered.

  Cholesteric liquid crystals are bistable and have two modes, a reflective state and a transmissive state. In order to obtain a display element, a bright part and a dark part are necessary, and by absorbing light rays in the transmissive state, the reflective state is bright and the transmissive state is dark. Therefore, the light absorption layer 5 as shown in FIG. 11 is provided. The light absorption layer 5 is desirably formed inside the cell on the common electrode 7. Although it is possible to provide the light absorption layer 5 on the outside of the substrate 1, even if the electrode is a transparent electrode such as ITO, there is light reflection, which causes a decrease in contrast. The stacked structure shown in FIG. 11 makes it possible to realize a display with high contrast and good visibility.

FIG. 12 shows the stacking process. The segment light-shielding mask 4 is formed on the segment electrode substrate of FIG. 12 in which the transparent electrode segment pattern is formed on the substrate, and the wall surface material 3 is formed. The light shielding mask 4 and the wall material 3 are formed by a photolithography technique or a printing technique. On the common substrate, the light absorption layer 5 is formed on the solid electrode solid pattern. As a forming method, a photolithography technique or a printing technique is used. You may use the electrode which consists of a black absorber. Each layer is formed on both substrates and bonded. The bonded substrates are bonded by heat treatment. (Here, the description of other process sealing materials, transfer coating, and spherical spacer spraying steps is omitted.)
Here, since the segment substrate, the light shielding mask, and the wall surface structure form a display original pattern, a highly accurate alignment technique is required. Since the counter substrate, which is a common substrate, is a solid light absorption layer 5 and a common electrode, high-precision alignment is not required. In order to create the post-bonding structure 10 in FIG. 12, it is a process technique that does not require a highly accurate alignment bonding process.

  In order to realize the bending durability necessary for IC card application, a plastic substrate or a film substrate is used instead of a glass substrate. In such a base material, highly accurate bonding is difficult, and the process process in this invention is needed. As the structure of the element, a structure in which a light absorption layer is provided on the segment pattern and the display is viewed from the common electrode substrate side is also assumed, but if the display is not viewed from the segment substrate side, in the bonding process shown above Relaxation of alignment accuracy cannot be realized. That is, by making the segment electrode side the display surface, the manufacturing process can be facilitated, and an improvement in yield and cost reduction can be expected.

  FIG. 13 shows a cross-sectional view of the element viewed from the side. The segment substrate 11 side is a display surface. In order to give a signal from the segment electrode 6 of the segment substrate 11, the segment substrate 11 has a larger substrate size than the common substrate 12. A voltage is applied from the segment electrode 6 by bonding a flexi cable or the like. The common electrode 7 of the counter substrate is electrically connected to predetermined wiring on the segment substrate 11 by conductive particles or conductive paste, and voltage is applied from the predetermined wiring of the segment substrate. The common electrode 7 is a solid electrode, but an electrode removal portion 14 is provided on a part of the common substrate 12.

The common electrode removal portion 14 is outside the sealing material 15 described with reference to FIG. In a glass substrate, there is little bending property and it is hard to become an obstacle, but in the case of a film substrate, a common electrode and a segment display extraction wiring may be short-circuited due to the bending. Since it is difficult to control the spread of the sealing material, this portion is previously structured to remove the electrode. With this structure, even in the case of a film substrate, avoidance of a short circuit is realized, and the yield can be improved. There is no need to remove the common electrode except for the portion facing the segment display lead-out wiring. Instead of removing the common electrode, a non-conductive substance can be applied.

  FIG. 14 shows the arrangement structure of the sealing material and the transfer. If the wall surface material 3 has a sufficiently strong adhesive force, the sealing material 15 can be omitted, but the sealing material 15 is used together in order to provide sufficient durability. The wall material secures an injection path for liquid crystal, and a sealing material 15 is formed around the passage. Since the sealing material 15 and the liquid crystal are not in contact with each other and are different from the conventional liquid crystal structure, it is not necessary to use a special adhesive that does not impede the liquid crystal. Conventionally, large problems such as a change in display characteristics due to the dissolution of impurities from the sealing material into the liquid crystal have occurred. With this structure in which the sealing material and the liquid crystal are not in contact with each other, the yield is greatly improved. Further, since the transfer material 16 does not come into contact with the liquid crystal, a material having good conductivity can be arbitrarily selected. The transfer is required to have high durability for display driving.

  In general liquid crystal elements, a transfer is disposed outside a sealing material in order to avoid influences such as impurities on liquid crystal and disorder of alignment. However, the substrate is peeled off by the force such as bending from the outer peripheral portion, and the transfer is preferably formed inside the sealing material. As shown in FIG. 14, the liquid crystal is surrounded by the wall material, the transfer is arranged outside the wall material, and the seal material is arranged outside the wall material, whereby the durability can be greatly improved. Although one transfer may be used, reliability is further improved by arranging a plurality of transfers. Arrangement of display elements at symmetrical positions is also effective in improving display uniformity and durability.

  FIG. 15 and FIG. 16 show an example in which multiple chamfering is performed from one substrate. As shown in FIG. 15, a plurality of elements are formed on one substrate. The sealing material is formed continuously with the adjacent element. The sealing material is generally formed by application from a syringe needle using a robot dispenser or the like. Although there is a printing method as a method for forming the sealing material, it is not appropriate because of the three-dimensional structure of the wall surface material. When a sealing material is formed on the counter substrate, the alignment accuracy at the time of bonding becomes a problem. As shown in FIG. 15, the sealing material is applied by a dispenser to the substrate on which the wall surface material is formed. It is known that application by a dispenser is excessively applied at a writing point and a writing end point. Therefore, as shown in FIG. 15, the writing position and the writing end position are outside the element, and a sealing material is formed continuously with the adjacent element. Therefore, since there is no excessive sealing in any element, the yield such as uniformity of cell thickness is improved.

  FIG. 16 shows a counter substrate in the film substrate. A slit-shaped cut line is formed in advance. In the case of multi-sided cutting, the electrode lead-out line must be exposed after bonding, and it is necessary to cut only one substrate. In a general glass substrate, it is possible to easily cut only one substrate in a process (scribing process) of drawing a scratch line on the surface with a diamond blade and breaking the substrate. However, the scribing process cannot be performed on the film substrate. Attempting to cut with only one side with a cutter blade or the like will damage the opposing segment lead lines. Therefore, a single substrate is cut in advance as in the counter substrate (common substrate) of FIG. This method improves the yield without damaging the wiring.

FIG. 17 shows a structural example of a liquid crystal path in a highly durable liquid crystal element. As the liquid crystal, cholesteric liquid crystal is a candidate as described above. A cholesteric liquid crystal easily changes its display state due to an external force or distortion of bending or pressing force. If the distortion inside the display cell due to bending is reduced, the change can be suppressed. When the display change due to bending was experimentally observed in the liquid crystal injection path in the structure of FIG. 11, the change was significant in the central straight line. Since there is no wall structure that supports bending strain, it was found that large strain was added on the straight line. Short lines have little change. The longer the straight line length, the more distortion occurs. Therefore, as shown in FIGS. 17 and 18, it is possible to suppress the display change due to bending by changing the injection path and shortening the linear distance.

  In FIG. 17, in the second and subsequent characters, all the distances are the same in the three routes from the liquid crystal inlet to the outlet, and bubble entrainment during injection is reduced. In vacuum injection, if the degree of vacuum is high, air entrainment is reduced, but it is difficult to eliminate it completely. At the exit of the last 8 characters, a dummy road is created and an extra air buffer is provided.

  In FIG. 18, the three routes from the liquid crystal entrance to the exit in the figure 8 are not equidistant, but the liquid crystal path has the smallest linear distance, and the change in the liquid crystal display can be suppressed most. The end of the injection path is closed, but may be open. Although injection is possible depending on the surface tension, it is not possible to seal the opening part newly.

  In this embodiment, a non-contact IC card will be described as an example of a portable display device, but applications such as ferroelectric liquid crystal, guest-host liquid crystal, and electrophoresis are proposed as display methods in the non-contact IC card. However, the ferroelectric liquid crystal has a low contrast, basically cannot display a gradation, and is extremely vulnerable to impact. Since the guest-host liquid crystal also has a low contrast and the electrophoretic method has a problem in display memory properties, this embodiment will explain a display method using cholesteric liquid crystal.

  Cholesteric liquid crystals have the advantage of higher brightness and contrast than thermal and magnetic writing methods in terms of display quality, and are capable of colorization and halftone display, and display memory performance is almost semi-permanent. is there.

  Here, a mobile display device such as an IC card will be further described. A computer display device or a mobile display device is generally a CRT or a transmissive liquid crystal display with a backlight. All of these types are light-emitting displays. In recent years, it has been proposed that a non-light-emitting reflective display device is desirable for comfortable reading of text displays. Since the reflection type does not use the light source provided in the device, it is effective in reducing power consumption.

  Further, in order to further reduce power consumption, a display device having a memory property that does not disappear even when the power is turned off is desired. A typical medium with reflection and memory is paper, its history is very old, and it is one of the indispensable tools in modern times. A new display called “electronic paper” that combines the maximum features of paper, such as reflective and memory characteristics, with the features of displays that can be switched arbitrarily, that is, the fusion of paper and displays. Devices have attracted attention in recent years and are being developed by various companies with the aim of putting them into practical use. Although there are various application fields of electronic paper, the following description will be further made with an IC card with a display attracting attention as one of them.

  Today, many cards are used on a daily basis, as called the card society. It is used for various purposes such as credit cards, bank cash cards, prepaid cards such as telephone cards, company employee cards and school student cards. The appearance of IC cards was in 1970, and since the idea of embedding IC chips in the cards was born, IC cards have attracted a great deal of attention and are steadily spreading. In the 21st century, the environment surrounding IC cards has evolved greatly, including the establishment of the Internet and the expansion of electronic commerce.

An IC card is a card in which an IC chip is embedded in a plastic card such as a cash card or a credit card. An IC card has a calculation function, and the function of data handling is much larger than that of a magnetic card. The IC card can be classified as follows depending on whether the CPU is built in the IC chip or the difference in the interface. This classification is based on the following Non-Patent Document 1.

Non-patent document 1
Forefront of IC card business Industrial Research Committee (November 2000)
1. Classification based on the presence or absence of a CPU: Depending on whether or not a CPU is built in, it can be classified into a “memory card” and a “CPU card”.
Memory card: A ROM for storing data is built-in, and the amount of data stored is 500 to 16000 characters or more compared to 80 characters of the magnetic card. As the memory, PROM, EPROM, EEPROM or the like is used.
CPU card: Since the CPU is built in, the card itself has a calculation function. The CPU collates the input password number with the password number in the card and controls data access permission. For this reason, it has functions to prevent unauthorized access and tampering, and is extremely superior in terms of security.
2. Classification by interface: Can be classified into "contact card" and "contactless card" according to the external interface.
Contact type IC card: There is a metal terminal on the surface of the card. By inserting the IC card into the card reader / writer, power is supplied from the reader / writer to the terminal, and information is exchanged. Currently, it is prevailing and features heavy calculations and stable communication.
・ Non-contact type IC card: An antenna is built in the IC card and IC card reader / writer, and information is exchanged using electromagnetic waves. For this purpose, an antenna is provided around the card. The non-contact type is classified into four types, a contact type (2 mm), a proximity type (10 cm), a proximity type (1 m), and a remote type (several meters), depending on the communication distance between the IC card and the reader / writer. Because it is non-contact, there is also a hybrid type card that is excellent in operability and durability and has both a contact type and a non-contact type.
In order to view the information recorded in the IC card, a method of using a display unit such as a display provided in the reader / writer is still mainstream, and this method requires a connection between the IC card and the reader / writer. is there. However, in recent years, there are cases where a thermal writing method that erases printing using a thermosensitive coloring material or a magnetic writing method that erases printing using a magnetic material is applied to an IC card. It's being used. The following non-patent document 2 describes a rewritable recording medium using a leuco dye as a typical thermal coloring type system.

Non-Patent Document 2
Matsui, Torii, Furuya, Tsutsui: “Control of coloring and decoloring characteristics of leuco dye type rewritable recording medium”, Japan Hardcopy 2000 Proceedings, p. 69-72
However, the above display method has low display quality, low brightness, low contrast, and poor visibility. In any case, display is performed by directly contacting the recording unit with a thermal head, a magnetic head, or the like. To rewrite the display, the card must be inserted into a reader / writer equipped with a writing unit. The above display system is unsuitable for application to non-contact IC cards that can become the mainstream in the future, and a power-driven display system is promising for displaying information on non-contact IC cards. The use of the cholesteric liquid crystal described above is promising as such a display system driven by electric power. Therefore, the driving method of the cholesteric liquid crystal will be further described.

19 and 20 are explanatory diagrams of the planar state and the focal conic state of the cholesteric liquid crystal. In a display device using cholesteric liquid crystal, two states are controlled by switching the alignment state of liquid crystal molecules. FIG. 19 shows a planar state in which light in a specific wavelength region is selectively reflected. In this planar state, the helical pitch of the liquid crystal molecules and the circularly polarized light along the rotational direction of the spiral are selectively reflected. The wavelength λ at which the reflection is maximum can be considered by the following equation using the average refractive index n of the liquid crystal and the helical pitch p.

λ = n × p
The reflection band Δλ increases as the refractive index anisotropy Δn of the liquid crystal increases.
FIG. 20 shows the focal conic state. In this state, most of the incident light is transmitted and becomes transparent. Therefore, if a layer of an arbitrary color is provided under the liquid crystal layer, the color can be displayed in the focal conic state. Therefore, for example, by setting the wavelength band of the reflected light in the planar state to around 550 nm and providing a light absorption layer (black) under the liquid crystal layer, it is possible to perform a single color display of green on the background color black.

FIG. 21 summarizes the response characteristics of the cholesteric liquid crystal. The _{V F0} in figure is a voltage threshold transition to the focal conic state _starts, from _{V F100a} to _{V F100b} voltage range of the full focal conic _{state, V P0} is the threshold voltage transition to the planar state starts, V _P100 is a threshold voltage at which a completely planar state is achieved. When the initial state is the planar state (P), when the pulse voltage is increased, the drive band is set to the focal conic state up to a certain range, and when the pulse voltage is further increased, the drive band is set to the planar state again. When the initial state is the focal conic state (FC), the driving band gradually enters the planar state as the pulse voltage is increased.

  22 and 23 are explanatory diagrams of a general single polarity driving waveform for the cholesteric liquid crystal. The cholesteric liquid crystal is driven by applying a pulse voltage. When a strong electric field is applied, the helical structure of the liquid crystal molecules is unwound and all molecules become homeotropic according to the direction of the electric field.

  In FIG. 22, for example, by removing the electric field after applying a pulse of +40 V, a spiral structure in which the spiral axis of the liquid crystal molecules is perpendicular to the electrode is formed, and a planar state that selectively reflects light according to the spiral pitch Become.

  In FIG. 23, for example, when an electric field is removed after applying a pulse of +18 V, that is, when an electric field is removed after applying a weak electric field that does not completely unwind the liquid crystal molecules, the helical axis of the liquid crystal is applied to the electrodes. A focal conic state that is parallel and transmits incident light is obtained. On the other hand, when an electric field having an intermediate strength is applied and then the electric field is removed, a state in which the planar state and the focal conic state are mixed is obtained, and halftone display can be made possible.

  FIG. 24 is an explanatory diagram of an example of segment display using cholesteric liquid crystal. For example, in the last digit “3”, the parts (2) and (5) are in the focal conic state, and the other parts (1), (3), (4), (6) and (7) are planar. Display is performed by driving to the state.

  In order to drive such a cholesteric liquid crystal, generally, the two types of drive voltage waveforms described with reference to FIG. 4, FIG. 22, and FIG. 23 are used. For this reason, there is a problem that the driving circuit becomes expensive, and in this embodiment, a driving method capable of both planar driving and focal conic driving with one type of waveform is used.

FIG. 25 and FIG. 26 are examples of waveforms of bipolar pulses for planar driving and focal conic driving in this embodiment. FIG. 25 shows an example of a planar drive waveform, which is the same as the planar drive waveform in FIG.
On the other hand, in the waveform of the focal conic drive shown in FIG. 26, unlike FIG. 4, the power supply circuit is brought into a high impedance state after + and − pulses having a peak value of 40V. That is, when driving in the focal conic state, after applying the same pulse as the pulse driving in the planar state, the drive circuit is controlled to have high impedance in the state where -40 V is applied.

  The liquid crystal display cell is electrically a capacitor, and the charge accumulated in the display cell when -40 V is applied is slowly discharged in accordance with a time constant determined by the resistance of the liquid crystal cell itself and the capacitance of the capacitor. The cell is in a focal conic state. In FIGS. 25 and 26, the number of pulse polarity inversions is one, but the number may be plural. That is, if one cycle of the drive waveform is composed of positive and negative pulses, a waveform having a plurality of cycles may be applied.

  27 and 28 are explanatory diagrams of a planar driving waveform and a focal conic driving waveform by a single polarity pulse. The planar drive waveform in FIG. 27 is the same as the waveform described in FIG.

  In the focal conic drive waveform of FIG. 28, the voltage value of +40 V is maintained for 50 ms as in the planar drive waveform of FIG. 27, and then the power supply circuit is set to high impedance, and the charge accumulated in the display cell is as shown in FIG. In the same manner as described above, the battery is slowly discharged, and the display cell enters a focal conic state.

  FIG. 29 is a configuration example of the display unit driver circuit, and FIGS. 30 and 31 are operation time charts of the driver circuit. At the time of driving to the planar state, the logic output is maintained at the low level (L) for 50 ms after the power supply voltage Vcc is set to 40 V as shown in FIG. When the logic output becomes L, the transistor Tr in FIG. 29 is turned off, and the liquid crystal cell is charged to 40 V through the diode D and the resistor R2. Thereafter, when the logic output is set to H for at least 1 ms, the transistor Tr is turned on, and the charge accumulated in the liquid crystal cell is rapidly discharged through the Tr, so that the liquid crystal cell is in a planar state.

  At the time of driving to the focal conic state, as shown in FIG. 31, after Vcc is set to +40 V, the logic output is set to L for 50 ms, and thereafter, Vcc falls and the charge accumulated in the liquid crystal cell is discharged. By keeping the logic output at L, both the diode D and the transistor Tr are turned off, and the power supply side is in a high impedance state. Therefore, the charge accumulated in the liquid crystal cell is slowly discharged through the resistance of the liquid crystal cell itself, The liquid crystal cell is in a focal conic state.

  Next, for example, the configuration of an IC card having a display unit using chiral nematic liquid crystal as one kind of cholesteric liquid crystal will be described. FIG. 32 shows a configuration example of an IC card which can be used as a hybrid type, that is, a contact type or a non-contact type, and has a memory type display portion, that is, a display portion using chiral nematic liquid crystal.

  Nematic liquid crystal and chiral material are mixed with appropriate amounts of CB15 that induces twisting in the right direction, the reflection color in the planar state is green, and this liquid crystal is 100 μm thick ITO (Indium Tin Oxide) evaporated glass A glass cell was prepared by sandwiching the substrates. The thickness of the liquid crystal was 5 μm.

In FIG. 32, a display unit 20 as a segment drive element for numerical display using the chiral nematic liquid crystal is provided at the upper right of the IC card, and further, an element drive IC 21 is embedded thereon. This display unit is used for balance display in a cash card, for example. On the card, an IC 22 for receiving data and power without contact with an IC card reader / writer, an IC 23 for receiving power and data by contacting the reader / writer, and letters and numbers are punched. The embossed portion 24 is provided.

  FIG. 33 shows a configuration example of a non-contact IC card. In the figure, when the IC card 26 is brought close to the IC card reader / writer 27, the IC card 26 is supplied with electromagnetic waves by the antenna 28, supplied with data and power, and then starts to operate. Information is exchanged with the IC card reader / writer 27.

  The IC card 26 has a CPU 30 for overall control, a non-contact interface 31 for receiving data exchange and power supply with an IC card reader / writer 27, and a read-only memory 32 for storing data and programs. , A display unit driver 33 and a display unit 34.

Next, an arrangement method of the antenna pattern and the coil pattern on the IC card in this embodiment will be described. As described above, in a non-contact type IC card, for example, a radio wave transmitted from an antenna on an IC card, that is, an IC card reader / writer side, in order to supply power to a circuit that drives a display unit using cholesteric liquid crystal. A coil pattern is provided near the antenna pattern that receives the signal, and the electromagnetic induction action between the antenna pattern and the coil pattern is used to receive the voltage from the antenna pattern when receiving the radio wave from the antenna pattern. Use for.
However, as described above, a credit card or a cash card, which is a typical use example as an IC card, is mechanically embossed, that is, punched in numbers and letters. However, in this embodiment, by using a multilayer wiring board, by providing the coil pattern and the antenna pattern in different layers, it is difficult to place them close to each other. Solve this problem.

  34 and 35 show examples in which a multilayer wiring board is used and a coil pattern is formed on a layer different from the antenna pattern. FIG. 34 shows the surface of the IC card, and FIG. 35 shows a cross-sectional view of the dotted line portion of FIG. In FIG. 34, the portion to be embossed can be dealt with by widening the wiring as described in FIG.

  In FIG. 35, the antenna pattern for wireless IC, that is, the antenna pattern for receiving radio waves from the IC card reader / writer is one layer, while the coil pattern for supplying LCD driver power is three layers. This is because, for example, an existing LCD driver requires a power supply of several types of voltages, and a display unit using cholesteric liquid crystal needs a relatively high voltage such as 40 V as a driving voltage. For example, the number of turns of the coil pattern can be made many times without limiting the number of turns.

  However, when a multilayer wiring board is used and the antenna pattern and the coil pattern are wired in different layers, the total thickness T1 depends on the thickness of the IC card depending on the thickness of the substrate and the height of the components as shown in FIG. There is a possibility that it is not within a standard, for example, 0.8 mm.

  FIG. 37 and FIG. 38 are configuration examples of IC cards that solve this problem. Although the surface of the IC card is shown in FIG. 37, the component mounting part is provided in the two-layer part of the multilayer wiring board, and the antenna and coil pattern wiring part is provided in the four-layer part.

FIG. 38 shows a cross-sectional view of the IC card of FIG. The total thickness T2 including the two-layer portion as the component mounting portion and the four-layer portion as the wiring portion of the antenna pattern and the coil pattern is smaller than the thickness T1 shown in FIG. In FIG. 38, the four-layer wiring portion of the antenna pattern and the coil pattern naturally exists on the left side, but the portions are omitted.

  As described above, according to the present embodiment, the antenna pattern and the coil pattern are provided in different layers using the multilayer wiring board, so that a relatively high voltage is generated by the coil pattern or a plurality of types of voltage values are used. This is effective for expanding the range of use of a non-power source non-contact type IC card with a display function.

  The present invention can be used in all industries that use liquid crystal display elements, display element drivers, and portable display devices such as IC cards and electronic paper, as a matter of course. .

It is a figure which shows the prior art example of a contact type IC card. It is a figure which shows the structure of the prior art example of a non-contact-type IC card. It is a figure which shows the prior art example of the structure of the liquid crystal cell using a spacer. It is explanatory drawing of the prior art example of the drive system of a cholesteric liquid crystal. It is a figure which shows the prior art example of a non-contact-type IC card provided with antenna wiring. It is explanatory drawing of the prior art example of an IC card provided with the coil pattern for the power supply to a LCD driver. It is explanatory drawing of the problem of the prior art by embossing. It is explanatory drawing of the solution in the prior art of the problem of embossing. It is principle explanatory drawing of the durable improvement structure of the liquid crystal display element in this invention. It is an example of a structure of a liquid crystal display element provided with a segment light shielding mask. It is explanatory drawing of the structural example of a liquid crystal element provided with a light absorption layer. It is explanatory drawing of the bonding method of a liquid crystal element. It is explanatory drawing of the common electrode removal part in a liquid crystal element. It is explanatory drawing of the seal | sticker in a liquid crystal element, and a transfer format. It is explanatory drawing of multiple chamfering of an element. It is explanatory drawing of the cut line put in the opposing board | substrate for multi-surface drawing. It is a figure which shows the structural example (the 1) of the liquid-crystal injection path for durability improvement. It is a figure which shows the structural example (the 2) of the liquid-crystal injection path for durability improvement. It is explanatory drawing of the planar state of a cholesteric liquid crystal. It is explanatory drawing of the focal conic state of a cholesteric liquid crystal. It is a figure which shows the response characteristic of a cholesteric liquid crystal. It is explanatory drawing of the single polarity planar drive waveform with respect to a cholesteric liquid crystal. It is explanatory drawing of a single polarity focal conic drive waveform. It is explanatory drawing of the segment display using a cholesteric liquid crystal. It is explanatory drawing of the bipolar planar drive waveform in this embodiment. It is explanatory drawing of a bipolar focal conic drive waveform. It is explanatory drawing of the single polarity planar drive waveform in this embodiment. It is explanatory drawing of a single polarity focal conic drive waveform. It is a circuit block diagram of a display part driver. It is a time chart at the time of the drive to a planar state. It is a time chart at the time of the drive to a focal conic state. It is a figure which shows the structural example of an IC card with a hybrid type display. It is a block diagram which shows the structure of an IC card with a display. It is a figure which shows the structural example of the IC card using a multilayer wiring board. It is sectional drawing of the card | curd of FIG. It is sectional drawing of the IC card using a 4 layer board | substrate also with respect to components other than an antenna pattern and a coil pattern. This is a configuration example of an IC card in which an antenna and a coil pattern are mounted on a four-layer part and other components are mounted on a two-layer part. It is sectional drawing of the IC card of FIG.

Claims (5)

In a driving method of a display element using a cholesteric liquid crystal,
When driving the liquid crystal cell to the planar state, after applying a pulse voltage to the liquid crystal cell, the drive impedance on the power supply side is set to a value lower than the impedance of the liquid crystal cell, and the applied voltage is set to 0,
A display element driving method characterized in that, at the time of driving to a focal conic state, after applying a pulse voltage, the driving impedance is set to a value higher than the impedance of a liquid crystal cell.   2. The display element driving method according to claim 1, wherein the polarity of the pulse voltage is reversed at least once during application of the pulse voltage to the liquid crystal cell.   2. The display element driving method according to claim 1, wherein a peak value of the pulse voltage is equal to or higher than a voltage value at which the liquid crystal cell surely transitions to a planar state.   The value of the driving impedance on the power supply side after applying the pulse voltage when driving to the planar state is the maximum value of the discharge time of the charge accumulated in the liquid crystal cell and the time required for the liquid crystal cell to transition to the planar state 2. The display element driving method according to claim 1, wherein the value is as follows.   The display element driving method according to claim 1, wherein the driving method is used as a driving method of the display element in a portable display device including a display element and an antenna unit for receiving data and power from the outside. Method.

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