Abstract:
An OLED device comprised of: an OLED means for generating light, two or more conductive elements adapted for conducting current, a first substrate for mounting the OLED means and the two or more conductive elements, wherein the substrate has a first surface and a second surface, wherein the OLED means is in contact with the first surface and the two or more conductive elements are mounted to the second surface.

Description:
FIELD OF THE INVENTION 
     This invention relates to organic light emitting diodes, and in particular to the integration of organic light emitting diodes and near field imaging touch sensors. 
     BACKGROUND OF THE INVENTION 
     Organic Light Emitting diodes (OLED) devices are comprised of two electrodes and an organic light emitting layer. The organic layer is disposed between the two electrodes. One electrode is the anode and the other electrode is the cathode. The organic layer is structured such that when the anode has a voltage bias that is sufficiently positive relative to the cathode, holes are injected from the anode and electrons are injected from the cathode. The necessary voltage bias depends upon the materials used for the organic layers. The holes and electrons recombine within the organic layer to induce an exited state in a molecule comprising the organic layer. Light is emitted during the process of excited molecules relaxing to their ground state. The anode is typically manufactured from a high work function material such as a Transparent Conducting Oxide (TCO), and the cathode is typically manufactured from a highly reflecting material such as aluminum or silver. However, there exist many different electrode designs which allow light to exit the cathode, the anode, or through both the cathode and the anode. The organic layer can be comprised of a single organic film, or it can be comprised of a stack of multiple organic films. OLED devices are useful as indicators and displays can be constructed from patterned arrays of OLED devices. 
     In conventional capacitive touch sensors, a touch is detected by detecting the change in capacitance between an electrode and ground. The change in the capacitance necessary to trigger a touch response needs to be determined in advance. However, environmental conditions (e.g. the humidity) can affect the capacitance of the electrode to ground and make it difficult to determine the proper change in capacitance that will work for all conditions. 
     A more sophisticated type of capacitive touch sensor is the Near Field Imaging (NFI) or gradient touch sensor. NFI sensors are typically constructed from a minimum of three layers. There is a bottom dielectric substrate, there is a layer of conductive elements mounted on the dielectric substrate, and there is another dielectric layer mounted on the conductive elements which serve to protect the conductive elements. Each of the conductive elements is adapted to conduct current, and are supplied with a Radio-Frequency (RF) voltage. The current flowing through each element is detected. As an object approaches the NFI sensor the capacitance of the individual conductive elements changes and causes a change in the measured currents. 
     The change in capacitance can be due to an increase or decrease in the capacitance of the individual conductive elements to ground or they can be due to changes in the electric field caused by the approaching object. Both conductive objects and dielectric objects will cause a change in the capacitance between individual elements. Some elements have their capacitance and hence the measured current change more than others. These localized changes in the current allow the location of the touch to be inferred. The elements which are affected less by the approaching object can be used as a reference compare against when determining the threshold for when a touch has occurred. 
     PCT Patent WO 2004/010369 discloses a combined Liquid Crystal Display (LCD) screen and NFI touch screen. 
     SUMMARY OF THE INVENTION 
     The invention provides for an electronic circuit, an OLED device, an OLED apparatus and an OLED kit. Embodiments of the invention are given in the dependent claims. 
     Embodiments of the invention provide touch sensors that are very robust and their driving is independent of the environmental conditions such that no adjustment is required. This is accomplished by the lamination of a Near Field Imaging (NFI) sensor foil onto an OLED device. A NFI sensor allows the detection of gradient field changes and is inherently more robust than standard capacitive sensors. Embodiments of the invention are useful for implementing backlight switches and sliders. 
     Embodiments of the invention provide for an electronic circuit that is adapted for interfacing with an OLED device. The OLED device is comprised of an OLED means which generates light, two or more conductive elements adapted for conducting current, and a substrate for mounting the OLED means in the two or more conductive elements. 
     Embodiments of the circuit are comprised of a voltage bias means which is able to provide a voltage bias to the OLED means. The voltage bias is a benefit, because the OLED means needs a voltage bias in order to produce light. Electronic circuits are also comprised of an RF voltage means which provides the one or more conductive elements with an RF voltage. The voltage means are an advantage because they provide a constant voltage RF source used in conjunction with the conductive elements of the OLED device to form an NFI touch sensor. 
     The electronic circuit also has a current measuring means, which is a benefit because it is able to measure the current flow through each of the one or more conductive elements. By supplying the one or more conductive elements with a constant voltage, the current measuring means are able to detect when the current flow through an individual conductive element is able to be detected. The current or the change in the current can be used to detect an object touching the OLED device. Having multiple conductive elements is a benefit, because the current through many different elements can be used to determine if the touch sensor has been touched. 
     With single element capacitive sensors, the device needs to be adjusted in advance to determine the threshold change in capacitance for which a touch is detected. However, environmental conditions can cause the capacitance that is measured and therefore the current to vary. Embodiment of the invention use the current from several different strips to determine if a touch has been registered by normalizing the result. 
     The electronic circuit is also comprised of a means for generating a signal which depends upon the current which is flowing through the one or more conductive elements. This could be integrated into an electronic circuit or it could be sent as a control signal to another electronic circuit. This has the advantage that a complex analysis of the change in the currents can be used to generate a signal. For example, the currents can be normalized to the average capacitance. This eliminates any environmental changes. A microcontroller or computer can be used to implement this. 
     In another embodiment, the electronic circuit is further comprised of a decoupling amplifier which is able to eliminate the effects of the capacitive coupling between the OLED means and the one or more conductive elements. This is an advantage, because the capacitance between the one or more conductive elements and one or more electrodes of the OLED can be larger than the capacitance change induced by a touch. This means that there could be a substantial leakage current flowing from the connective elements to the OLED means. The decoupling amplifier is used to add the same RF bias that is applied to the one or more conductive elements to the OLED means. Since both the OLED means and the conductive elements are changing by the same voltage the capacitance is effectively eliminated between the two. This allows the relative change in the current as measured by the current measuring means to be much larger when an operator&#39;s finger or other conductive element is brought near to the touch sensor. 
     In another embodiment the decoupling amplifier is a unity gain amplifier. Using a unity gain amplifier is a benefit, because this adds exactly the same voltage as was applied to the conductive elements. In this embodiment the electrical connection means are attached to the cathode of an OLED means and the output of that unity gain amplifier is connected to the anode of the OLED means. This is an advantage, because a large number of OLED devices are designed so that the light is transmitted through the anode and through a clear substrate. The OLED means is mounted on one side of the substrate and the NFI touch sensor is mounted on the other side. The anode is then the closest electrode of the OLED means to the NFI sensor. 
     In another embodiment the capacitance coefficients are calculated using the current flow and the voltage. This has the advantage that a subset of the capacitance coefficients can be determined and can be compared to other capacitance coefficients or subsets of capacitance coefficients. This allows the detection of the small changes of the capacitance between different conductive elements. A dielectric object approaching the touch sensor will alter the electric fields and cause a change in the capacitance between different conductive elements. This change can therefore be used to detect the approach of dielectric objects. A microcontroller or computer can be used to implement this. 
     In another aspect, embodiments of the invention provide for an OLED device which is comprised of an OLED means for generating light, two or more conductive elements adapted for conducting current, and a first substrate for mounting the OLED means and the two or more conductive elements. The OLED means are mounted on one side of the substrate, and the two more conductive elements are mounted on the other side of the substrate. This has the advantage that the OLED means is capable of being integrated with an NFI touch sensor. The conductive elements are typically protected with a dielectric layer. The conductive elements can be mounted to the first substrate in a variety of ways: they can be deposited or formed directly on the substrate, they can be laminated to the substrate, or they can be glued to the substrate. The conductive elements can also be mounted to or incorporated into the structure of a second substrate. This second substrate can then be mounted or attached to the first substrate. 
     In another embodiment, the OLED device is further comprised of a second substrate adapted for lamination to the OLED means. The second substrate is fabricated from a transparent material, and is laminated to the first substrate. The two or more conductive elements are mounted to the second substrate. This has the advantage that the OLED means and the conductive elements that are used for the touch sensor can be fabricated separately. The two components can be laminated together. 
     In another embodiment, the OLED device is further comprised of an NFI touch sensor foil. The NFI touch sensor foil is comprised of the second substrate and the two or more conductive elements. This has the advantage that an NFI touch sensor foil can be laminated to an existing OLED device. 
     In another embodiment, the second substrate is constructed from a flexible material. This had the advantage that a touch sensor constructed out of a flexible material such as plastic can be mounted to the OLED means. 
     In another embodiment, embodiments of the invention provide for an OLED device where the thickness of the second substrate is chosen so that the capacitance between the OLED means and the two or more conductive elements is minimized. This is an advantage, because the change in capacitance when a finger is brought near to the NFI sensor is small in comparison to the capacitance between the two or more conductive elements and the OLED means. Increasing the thickness of the substrate reduces the capacitance and therefore makes it easier to detect the change in capacitance when someone touches the NFI screen. 
     In another embodiment the invention provides for an OLED device where the thickness of the first substrate is chosen so that the capacitance between the OLED means and the two or more conductive elements is minimized. This is an advantage, because the change in capacitance when a finger is brought near to the NFI sensor is small in comparison to the capacitance between the two or more conductive elements and the OLED means. Increasing the thickness of the substrate reduces the capacitance and therefore makes it easier to detect the change in capacitance when someone touches the NFI screen. 
     In another embodiment the two or more conductive elements are adapted for transmitting light. This is an advantage because the two or more conductive elements are positioned on the substrate where the light comes through the OLED means. If they are not adapted for transmitting light, it will reduce the amount of visible light which an operator or user is able to see. By making them transparent the device is more efficient. Conductive oxides such as ITO can be used to implement this. The conductive elements can also be adapted to transmit light by positioning the conductive elements so that they do not obstruct the light coming from the OLED means. Another alternative is to pattern the conductive elements such that the eye does not detect a regular pattern. This has the advantage of being less distracting to a user and making it less noticeable that there are conductive elements. 
     In another aspect the invention provides for an OLED apparatus comprised of the OLED device and an electronic circuit for powering and operating the OLED device. The electronic circuit is operable to calculate two or more capacitive coefficients of the capacitance formed by the two or more conductive elements for detecting a user input action. An advantage is that the calculation of these capacitances can be used to implement an NFI sensor, the advantages of which have already been discussed. Examples of user input actions are a user touching the surface to activate a switch, a user sliding his or her finger along the surface of the OLED device, or moving a finger in a circular motion on the surface of the OLED device. NFI sensors are able to detect the proximity of both conductive and dielectric objects. As a result a user input action can also be caused by moving an object into the proximity of the OLED device, or moving the object while it is in the proximity of the OLED device. This apparatus has the advantage that the OLED device is interfaced with the electronic circuit so that the OLED means is able to generate light, and the two or more conductive elements are connected to the electronic circuit which is able to detect if a touch has occurred and send a signal to another electronic circuit. This is useful because OLED apparatus is able to generate light and also to detect when an operator has touched it. This can be used for displays and control panels. 
     In another embodiment the electronic circuit is comprised of a means for providing the OLED means with a voltage bias, and a current generating means for generating a current flow in each of the two or more conductive elements. Providing the OLED means with a voltage bias is advantageous, because the OLED means requires a voltage bias to generate light. Generating a current flow in the two or more conductive elements is advantageous, because objects in proximity to the conductive elements change the conductive elements capacitance. This can be sensed and used to implement a capacitive proximity sensor. It is further comprised of a means for calculating two or more capacitive coefficients by either measuring the current flow through each of the conductive elements or by measuring the voltage drop across each of the conductive elements. If a known RF current is flowing through a conductive element, then a measurement of the RF voltage can be used to calculate the capacitance. If a known RF voltage is applied to a conductive element, then a measurement of the RF current can be used to calculate the capacitance. This is advantageous, because the two or more conductive elements can be used to implement an NFI type sensor. The advantages of which have already been explained. The circuit is also comprised of a signal generating means for generating a signal, were the signal depends upon the value of the two or more capacitive coefficients. One implementation is that the electronic circuit is incorporated into or interfaced with a second electronic circuit. This signal can also be implemented by the transmission of an analog or digital signal to another electronic circuit. This has the advantage that the OLED apparatus can be incorporated into a wide variety of control circuits. 
     In another aspect, the invention provides for an OLED kit comprised of the OLED device and an electronic circuit for powering and operating the OLED device. The electronic circuit is operable to calculate two or more capacitive coefficients of the capacitance formed by the two or more conductive elements for detecting a user input action. This has the same advantages as the OLED apparatus, but in this case the two components are separate and they can be assembled by a user or operator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following preferred embodiments of the invention will be described, by way of example only, and with reference to the drawings in which: 
         FIG. 1  shows a perspective cross sectional view of an embodiment of an OLED device with an integrated NFI touch sensor, 
         FIG. 2  shows a cross sectional view of the same embodiment shown in  FIG. 1  with a simplified equivalent circuit superimposed, 
         FIG. 3  shows an embodiment of a circuit used for driving a combined OLED and NFI device, 
         FIG. 4  shows a simulation of an embodiment of an OLED apparatus when the capacitance between the conductive elements and the OLED means is 1 pF, 
         FIG. 5  shows a simulation of an embodiment of an OLED apparatus when the capacitance between the conductive elements and the OLED means is 100 pF, 
         FIG. 6  shows a simulation of an embodiment of an OLED apparatus when the capacitance between the conductive elements and the OLED means is 100 pF. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Like numbered elements in these figures are either identical elements or perform the same function. Elements which have been discussed previously will not necessarily be discussed in later figures if the function is identical. 
       FIG. 1  shows an OLED device  100  comprised of an OLED means  102  with a laminated NFI sensor foil  104 . There is a substrate  112  which is part of the OLED means  102 . The substrate  112  has two sides. The OLED means  102  is located on the first side and the NFI sensor  104  is located on the other side. The anode  110  is located directly against the substrate  112 . Located next to the anode is the organic layer  108  and on the organic layer  108  is mounted the cathode  106 . When a sufficient voltage bias is applied to the anode  110  and cathode  106 , light is generated in the organic layer  108 . Light then travels through the anode  110  and the substrate  112 . On the second side of the substrate, is the NFI sensor foil  104 . Located directly immediate to the substrate  112  are conductive elements  114 . In this embodiment there are long strips. Above the conductive elements is a protective dielectric layer  116 . The conductive elements  114  can be made of a conductive oxide like Indium Tin Oxide (ITO). The conductive elements  114  could also be made out of an opaque electrode and then arranged in a way so that they minimize the amount of obstructed light. The conductive elements  114  function as the electrodes of an NFI touch sensor. 
       FIG. 2  shows a simplified electrical model of the OLED device superimposed upon a OLED device  200 . Visible is a finger  126  which is a approaching the OLED device  200 . This figure shows a model of the different capacitances and their relationship with the components in the OLED device. The same OLED means  102  and NFI sensor foil  104  of  FIG. 1  are shown in this figure as a cross section. There are four conductive elements in this  FIGS. 118 ,  120 ,  122 , and  124 . There is a capacitance between each of these conductive elements  118 ,  120 ,  122 , and  124  and the anode  110 . The capacitance between the first conductive element  118  and the anode is  150 . The capacitance between the second conductive element  120  and the anode is capacitance  152 . The capacitance between the third conductive  122  element and the anode is capacitance  154 . The capacitance between the fourth conductive element  124  and the anode is  156 . The OLED device is modelled as a diode  160  and a capacitance  158  which represents the capacitance between the anode  110  and the cathode  106 . The conductive elements also have a stray capacitance between them. Capacitance  140  is the capacitance between the first  118  and the second  120  conductive elements. Capacitance  142  is the capacitance between the second conductive element  120  and the third conductive element  122 . Capacitance  144  is the capacitance between the third conductive element  122  and the fourth conductive element  124 . Visible in this figure is a finger  126 . There is a capacitance between the operator&#39;s finger  126  and each of the conductive elements. The capacitance between the finger  126  and the first conductive element  118  is capacitance  130 . The capacitance between the finger  126  and the second conductive element  120  is capacitance  132 . The capacitance between the finger  126  and the third conductive element  122  is capacitance  134 . The capacitance between the finger and the fourth conductive element  124  is capacitance  136 . In this figure it is seen that the finger or the operator&#39;s hand  126  is located closer to some of the conductive elements than to other conductive elements. The effect of this is that when the finger is in this position, the change in the capacitance of conductive elements  118 ,  120 ,  122 , and  124  will be different. The comparison of these different changes in capacitance is how the sensor is able to detect a touch under varied conditions. 
       FIG. 3  shows an embodiment of an OLED apparatus. This is an electrical schematic and the OLED device is represented by several features in the schematic. The OLED means is represented by the diode  160  and the capacitance  158 . These are not individual components, the diode represents the current voltage characteristic caused by the OLED means  102  and the capacitance is formed by the electrodes  106 ,  110  of the OLED means  102 . In this embodiment there are four conductive elements  118 ,  120 ,  122  and  124 . As in  FIG. 2 , there is a stray capacitance between each of the conductive elements. These are represented by capacitances  140 ,  142  and  144 . These are not components which are part of an electric circuit, but they are capacitances which exist because of the physical location of the conductive elements next to each other. Also in this figure is shown a capacitance between the conductive elements  118 ,  120 ,  122  and  124  and the anode  110  of the OLED means  102 . These are represented by the capacitances  150 ,  152 ,  154  and  156 . Again these are not capacitors which are added as electrical components, but they are formed by the proximity of the conductive elements  118 ,  120 ,  122 , and  124  to the OLED means  102 . The OLED means  102  is driven by a DC power source  174 . The positive output is connected to the anode  110  of the OLED means  102  and the negative output is connected to the cathode  106  of the OLED means  102 . There is an RF source  176 , a unity gain amplifier  178  and four current measurements or sensors  180 ,  182 ,  184  and  186 . The output of the unity gain amplifier  178  is connected to the anode  110  of the OLED means  102 . The input of the unity gain amplifier  178  is connected to the output of the RF generator  176 . The negative of the DC power supply  174  is connected to the cathode  106  of the OLED means  102  and the ground of the RF generator  176  is connected to the negative of the DC supply  174 . There is a capacitance  170  which represents the capacitance between the ground of the apparatus and earth. In an alternative embodiment the ground of the device and earth are identical. 
     There is a current sensor for each conducting element. The output of the RF generator is connected not only to the unity gain amplifier  178  but also to the inputs of each of the current sensors  180 ,  182 ,  184  and  186 . The current sensor  186  is connected to the first conductive element  118 . The second current sensor  184  is connected to the second conductive element  120 . The third current sensor  182  is connected to the third conductive element  122 . The fourth current sensor  180  is connected to the fourth conductive element  124 . Each of the conductive elements is adapted for conducting current. 
     In  FIG. 3  there are several different paths for conducting current. The first is through the capacitive coupling to the OLED means  102  and the second is through a capacitive coupling to ground  172 . There are four capacitances corresponding to each of the conductive elements  162 ,  164 ,  166  and  168 . These represent the capacitance of each of the conductive elements. Capacitance  162  corresponds to conductive element  118 , capacitance  164  corresponds to the second conductive element  120 , capacitance  166  corresponds to the third conductive element  122 , and the fourth capacitance  168  corresponds to the fourth conductive element  124 . These four capacitances represent the capacitance of each of these elements and these capacitances change as an object is brought near to the conductive elements  118 ,  120 ,  122 , and  124 . 
     As an object such as a finger  126  approaches the conductive elements it has a different proximity to each of the conductive elements and the current flowing through each element changes. A control device such as a microcontroller would compare the currents measured by the four current sensors  180 ,  182 ,  184 , and  186  and use this to determine if a touch has occurred and in which location. A difficulty is that the capacitances  150 ,  152 ,  154  and  156  between the conductive elements  118 ,  120 ,  122  and  124  and the OLED means  102  can be quite large. The unity gain amplifier  178  is able to eliminate this capacitance. It puts an RF voltage bias on the anode  110  which is equivalent to the RF bias that is applied to the conductive elements. This forces the voltage across  150 ,  152 ,  154  and  156  to be zero. This effectively eliminates this capacitance. This is very advantageous because it allows a larger signal to be observed. The capacitances are measured and normally the large capacitance between the conductive elements  118 ,  120 ,  122 ,  124  and the anode  110  obscures the signal but this unity gain amplifier  178  eliminates this effect and makes the device more sensitive. 
     In an alternative embodiment the substrate  156  between the conductive elements  118 ,  120 ,  122 , and  124  and the anode  110  is made thicker. This reduces the capacitances  150 ,  152 ,  154 , and  156  and increases the sensitivity of the NFI sensor. In another embodiment, both the substrate thickness is increased and the unity gain amplifier  178  is used. 
       FIG. 4  shows the results of a simulation of the OLED apparatus. In this simulation the capacitance between the conductive elements and the OLED means is only 1 pF. The capacitance of the touch sensors  162 ,  164 ,  166  and  168  is considered to be around 10 pF. The capacitance  162  of the first element is increased by 1 pF. In this figure we see that the current through element  1  is larger than the current through the other three conductive elements. This shows that a small change in capacitance can be detected when the capacitance between the anode and the conductive elements is small. This shows that if the dielectric thickness of the substrate is increased, then a workable device can be constructed. 
       FIG. 5  shows an embodiment of a simulation which shows the effect of when the capacitance between the conductive elements and the anode is 100 pF. This is a value which represents a typical self capacitance. A simple estimation can be made using the formula for a parallel plate capacitor. Assuming a typical device thickness d of 100 nm, a relative permittivity of 1 the resulting self-capacitance is about 177 pF/mm 2 . 
     The self-capacitance can be used for the drive and sensing circuit of the touch sensor arrangement again the capacitance of conductive element  1 , capacitance  162  is increased by 1 pF. In this figure it can be seen that there is only a minimal change between the four different currents. 
       FIG. 6  shows the effect of using a decoupling amplifier. The same conditions as we used in  FIG. 5  are repeated here, except a unity gain amplifier is used to reduce the effect that capacitance between the conductive element and the OLED means has on the circuit. In this case the capacitance of conductive element  1  was increased from 10 pF to 11 pF. The other conductive elements have a capacitance of only 10 pF. However, it is very easy to see the difference in the current between conductive element  1  and through the other three conductive elements  2 ,  3  and  4 . This demonstrates the utility of using the unity gain amplifier. 
     LIST OF REFERENCE NUMERALS 
     
         
           100  OLED device 
           102  OLED means 
           104  NFI sensor foil 
           106  Cathode 
           108  Organic layer 
           110  Anode 
           112  Substrate 
           114  Conductive element 
           116  Dielectric 
           118  Conductive element  1   
           120  Conductive element  2   
           122  Conductive element  3   
           124  Conductive element  4   
           126  Finger 
           130  Capacitance between conductive element  1  and finger 
           132  Capacitance between conductive element  2  and finger 
           134  Capacitance between conductive element  3  and finger 
           136  Capacitance between conductive element  4  and finger 
           140  Capacitance between conductive element  1  and conductive element  2   
           142  Capacitance between conductive element  2  and conductive element  3   
           144  Capacitance between conductive element  3  and conductive element  4   
           150  Capacitance between conductive element  1  and the anode 
           152  Capacitance between conductive element  2  and the anode 
           154  Capacitance between conductive element  3  and the anode 
           156  Capacitance between conductive element  4  and the anode 
           158  Capacitance of OLED means 
           160  Diode representing current-voltage relations ship of OLED means 
           162  Capacitance of conducting element  1   
           164  Capacitance of conducting element  2   
           166  Capacitance of conducting element  3   
           168  Capacitance of conducting element  4   
           170  Capacitance to ground 
           172  Capacitance to ground 
           174  DC power supply 
           176  RF power supply 
           178  Decoupling amplifier 
           180  Current measurement of conducting element  4   
           182  Current measurement of conducting element  3   
           184  Current measurement of conducting element  2   
           186  Current measurement of conducting element  1   
           200  OLED device