Abstract:
A photo sensor that is capable of generating a photo sensing signal corresponding only to ambient light by comprehending changes in electrical current depending on the change of temperature and compensating for the electrical current according the change of temperature and a flat panel display device using the photo sensor, and the photo sensor including a photo sensing unit generating a first current corresponding to an ambient light and a second current corresponding to an ambient temperature; a temperature compensating unit including a dark diode generating a third current having a same magnitude as the second current, corresponding to the ambient temperature due to block of light to be incident; and a buffer unit outputting a light sensing signal corresponding to current having the same magnitude as the first current by subtracting the third current generated in the temperature compensating unit from the second current generated in the photo sensing unit.

Description:
CLAIM OF PRIORITY 
       [0001]    This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application for PHOT SENSOR AND FLAT PANEL DISPLAY USING THEREOF earlier filed in the Korean Intellectual Property Office on 13 Feb. 2008 and there duly assigned Serial No. 10-2008-0013032. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a photo sensor, a flat panel display device using the photo sensor and a process of fabricating a dark diode, and more particularly, to a photo sensor and a flat panel display device using the photo sensor outputting a signal responding to only light. 
         [0004]    2. Description of the Related Art 
         [0005]    Recently, various flat panel display (FPD) devices having reduced weight and volume, which are unfavorable in a cathode ray tube (CRT), have been developed. As flat panel display devices, there are liquid crystal display devices, field emission display devices, plasma display panels, organic light emitting display devices and other related display devices. 
         [0006]    The organic light emitting display device displays an image using an organic light emitting diode (OLED) generating light by recombination of an electron and a hole. 
         [0007]    The organic light emitting display device has various advantages such as an excellent color representation, a thin thickness, and other related advantages, so that the organic light emitting display device is widely used in a variety of applications such as PDAs (personal digital assistants), MP3 devices, and other related electronic devices, in addition to a cellular phone. 
         [0008]    Visibility of the displayed image on such a flat panel display device may vary with the brightness of ambient light. In other words, even though an image is displayed with the same brightness, when the brightness of the ambient light is relatively high, the displayed image may appear darker to users&#39; bare eyes, and when the brightness of the ambient light is relatively low, the displayed image may appear brighter to users&#39; bare eyes. 
         [0009]    Therefore, in order to enhance visibility of the displayed image to users&#39; bare eyes, the brightness of the ambient light is sensed, wherein when the brightness of the ambient light is relatively high, the brightness of the displayed image may be raised, and when the brightness of the ambient light is relatively low, the brightness of the displayed image may be lowered. Also, when the brightness of an image is controlled according to the brightness of the ambient light, the brightness of the displayed image will not be unnecessarily raised, and thus possibly reducing the power consumption of the display device. 
         [0010]    Based on the reasons mentioned above, there has been contrived a method to control the brightness of the displayed image corresponding to the ambient light by attaching a photo sensor sensing the ambient light to a flat panel display device. 
         [0011]    The photo sensor includes a photodiode, which is sensitive to the temperature. Therefore, when the ambient temperature rises to a predetermined degree, an electrical current generated by temperature becomes significantly larger than an electrical current generated by light in the photodiode so that the electrical currents generated by light may be ignored. Therefore, in order to complement brightness corresponding to the ambient light for the display device, the electrical current generated from the photodiode should be compensated by temperature. 
       SUMMARY OF THE INVENTION 
       [0012]    It is therefore an object of the present invention to provide a photo sensor, a flat panel display device using the photo sensor and a process of fabricating a dark diode in order to solve the problems as stated above. 
         [0013]    It is another object of the present invention to provide a photo sensor and a flat panel display device using the photo sensor that is capable of generating a photo sensing signal corresponding only to ambient light by comprehending changes in an electrical current induced by a temperature change and compensating for the electrical current according the temperature change. 
         [0014]    In order to accomplish the above object, in accordance with a first aspect of the present invention, a photo sensor may be constructed with a photo sensing unit generating a first electrical current corresponding to ambient light and a second electrical current corresponding to ambient temperature; a temperature compensating unit including a dark diode generating a third electrical current having the same magnitude as the second electrical current, corresponding to ambient temperature due to block of light to be incident; and a buffer unit outputting a light sensing signal corresponding to electrical current having the same magnitude as the first electrical current by subtracting the third electrical current generated in the temperature compensating unit from the second electrical current generated in the photo sensing unit. 
         [0015]    In order to accomplish the above object, in accordance with a second aspect of the present invention, a flat panel display device may be constructed with a pixel unit displaying an image by corresponding to a data signal and a scan signal; a photo sensor generating a light sensing signal by sensing ambient light; a data driver generating the data signal corresponding to the light sensing signal; and a scan driver generating the scan signal, wherein the photo sensor includes: a photo sensing unit generating a first electrical current corresponding to ambient light and a second electrical current corresponding to an ambient temperature; a temperature compensating unit including a dark diode generating a third electrical current having the same magnitude as the second electrical current, corresponding to the ambient temperature due to block of light to be incident; and a buffer unit outputting a light sensing signal corresponding to an electrical current having the same magnitude as the first electrical current by subtracting the third electrical current generated in the temperature compensating unit from the second electrical current generated in the photo sensing unit. 
         [0016]    In order to accomplish the above object, in accordance with a second aspect of the present invention, a dark diode may be constructed with a transparent substrate; a buffer layer formed on the transparent substrate; a semiconductor layer formed on the buffer layer; a first insulating film formed on the semiconductor layer; a second insulating film on the first insulating film; first and second metal electrodes formed on the second insulating film and contacted to both ends of the semiconductor layer, respectively; a third insulating film formed on the first and second metal electrodes; a planarization film formed on the third insulating film; and an anode electrode formed on the planarization film and opposed to the semiconductor layer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicated the same or similar components, wherein: 
           [0018]      FIG. 1  is a schematic view illustrating a structure of an organic light emitting display device, which is one example of a flat panel display device constructed as the present invention; 
           [0019]      FIG. 2  is a schematic diagram illustrating a circuit constructed as a first embodiment of a photo sensor adopted to the organic light emitting display device of  FIG. 1 ; 
           [0020]      FIG. 3  is a group of waveforms illustrating an operation of the photo sensor of  FIG. 2 ; 
           [0021]      FIG. 4  is a cross-sectional view showing a first embodiment of a dark diode adopted to the photo sensor of  FIG. 2 ; 
           [0022]      FIG. 5  is a cross-sectional view showing a second embodiment of the dark diode adopted to the photo sensor of  FIG. 2 ; and 
           [0023]      FIG. 6  is a cross-sectional view showing a third embodiment of the dark diode adopted to the photo sensor of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    In the following detailed description, only certain exemplary embodiments of the present invention have been shown and described, simply by way of illustration. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. In addition, when an element is referred to as being “on” another element, it can be directly on the element or be indirectly on the element with one or more intervening elements interposed therebetween. When a first element is described as being coupled to a second element, the first element may be not only directly coupled to the second element but may also be indirectly coupled to the second element via a third element. Also, when an element is referred to as being “connected to” another element, it can be directly connected to the element or be indirectly connected to the element with one or more intervening elements interposed therebetween. Hereinafter, like reference numerals refer to like element. 
         [0025]    Hereinafter, exemplary embodiments in accordance with the present invention will be described with reference to the accompanying drawings. 
         [0026]      FIG. 1  illustrates a structure of an organic light emitting display device, which is one example of a flat panel display device constructed as the present invention. Referring to  FIG. 1 , the organic light emitting display device includes a pixel unit  100 , a photo sensor  200 , a data driver  300 , and a scan driver  400 . 
         [0027]    Pixel unit  100  is arranged with a plurality of pixels  101 , wherein each pixel  101  includes an organic light emitting diode (not shown) emitting light corresponding to flow of current. Also, pixel unit  100  is arranged with a number of n scan lines S 1 , S 2 , . . . , Sn- 1  and Sn formed in a row direction and transferring scan signals, and a number of m data lines D 1 , D 2 , . . . , Dm- 1  and Dm formed in a column direction and transferring data signals. 
         [0028]    Such a pixel unit  100  is driven by receiving a first power and a second power from the external. In other words, pixel unit  100  generates light by means of driving current flowing on the organic light emitting diode by means of the scan signals, the data signals, the first power and the second power, to display an image. 
         [0029]    Photo sensor  200  generates a light sensing signal is sensing ambient light and controlling brightness of an image displayed on pixel unit  100  corresponding to the brightness of the ambient light which may have high brightness or low brightness. The light sensing signal  1   s  is transferred to data driver  300 . Data driver  300  then generates a data signal corresponding to the light sensing signal  1   s.    
         [0030]    Data driver  300 , which is a means for generating a data signal, receives video signals R, G and B data having red, blue, and green components, and the light sensing signal Is to generate a data signal. Data driver  300  connected to the data lines D 1 , D 2 , . . . , Dm- 1 , and Dm applies the data signals to pixel unit  100 . 
         [0031]    Scan driver  400 , which is a means for generating a scan signal, is connected to the scan signals S 1 , S 2 , . . . , Sn- 1 , and Sn to transfer scan signals to a specific row of pixel unit  100 . Pixel  101  transferred with the scan signals is transferred with the data signals output from data driver  300  so that a driving electrical current is generated. The generated driving electrical current is flown on organic light emitting diodes. 
         [0032]      FIG. 2  is a schematic view illustrating a circuit constructed as a first embodiment of a photo sensor adopted to the organic light emitting display device of  FIG. 1 . Referring to  FIG. 2 , photo sensor  20  includes a photo sensing unit  210 , a temperature compensating unit  220 , and a buffer unit  230 . 
         [0033]    Photo sensing unit  210  includes aphotodiode PD. The photodiode PD generates electrical current corresponding to the brightness of the ambient light. In other words, if the ambient light are incident to the photodiode PD, the electrical current corresponding thereto flows in a direction from a cathode electrode to an anode electrode, the flowing electrical current intensity corresponding to the brightness of the ambient light. Here, the photodiode is also sensitive to the temperature so that the electrical current generated from the photodiode PD may vary according to the temperature change. 
         [0034]    More specifically, photo sensing unit  210  includes the photodiode PD, a first transistor M 1 , a second transistor M 2 , a first capacitor Cst 1 , and a second capacitor Cboost 1 . 
         [0035]    A cathode electrode of the photodiode PD is electrically connected to a driving power supply, and an anode electrode thereof is electrically connected to a drain electrode of the first transistor M 1  and a source electrode of the second transistor M 2 . 
         [0036]    A source electrode of the first transistor M 1  is electrically connected to a first node N 1 , a drain electrode of the first transistor M 1  is connected to the anode electrode of the photodiode PD, and a gate electrode thereof is electrically connected to a first control line HOLD. 
         [0037]    A source electrode of the second transistor M 2  is electrically connected to the anode electrode of the photodiode D, a drain electrode of the second transistor M 2  is electrically connected to a initialization signal line Vint, and a gate electrode thereof is electrically connected to a reset signal line RESET. 
         [0038]    A first electrode of the first capacitor Cst 1  is electrically connected to a driving power supply VDD, and a second electrode of the first capacitor Cst 1  is electrically connected to the first node N 1 . A first electrode of the second capacitor Cboost 1  is electrically connected to the first node N 1  and a second electrode of the second capacitor Cboost 1  is electrically connected to a second node N 2 . 
         [0039]    Temperature compensating unit  220  has the same structure as photo sensing unit  210 , and blocks the ambient light from being incident to the photodiode to generate the electrical current corresponding to temperature. Dark diode DPD has one or more reflective layers between, for example, the protective layer  1009  and transparent substrate  1000  (for example, anode electrode  1008  which is a highly reflective layer because that layer is made from metal as shown in  FIG. 4 ) that prevent incident ambient light  1500  from being impingent on dark diode DPD, therefore dark diode DPD only generates an electrical current corresponding to the ambient temperature. As light is not impingent on the dark diode DPD included in temperature compensating unit  220 , only the electrical current having an amplitude that varies according to the ambient temperature surrounding the DPD diode, flows on the dark diode DPD. Therefore, when the electrical current generated in temperature compensating unit  220  is subtracted from the electrical current generated in photo sensing unit  210 , the resulting electrical current is the electrical current generated corresponding to the ambient light. 
         [0040]    More specifically, temperature compensating unit  220  includes the dark diode DPD, a third transistor M 3 , a fourth transistor M 4 , a third capacitor Cst 2 , and a fourth capacitor Cboost 2 . 
         [0041]    An anode electrode of the dark diode DPD is electrically connected to an initialization power supply Vint, a cathode electrode of the dark diode DPD is electrically connected to a drain electrode of the third transistor M 3  and a source electrode of the fourth transistor M 4 . 
         [0042]    A source electrode of the third transistor M 3  is electrically connected to a third node N 3 , a drain electrode the third transistor M 3  is connected to a cathode electrode of the dark diode DPD, and a gate electrode the third transistor M 3  is electrically connected to a first control line HOLD. 
         [0043]    A source electrode of the fourth transistor M 4  is electrically connected to a cathode electrode of the dark diode DPD, a drain electrode of the fourth transistor M 4  is electrically connected to a driving power supply VDD, and a gate electrode of the fourth transistor M 4  is electrically connected to a reset signal line RESET. 
         [0044]    A first electrode of the third capacitor Cst 2  is electrically connected to an initialization power supply Vint, and a second electrode of the third capacitor Cst 2  is electrically connected to a third node N 3 . 
         [0045]    A first electrode of the fourth capacitor Cboost 2  is electrically connected to a third node is N 3 , and a second electrode thereof is electrically connected to a second node N 2 . 
         [0046]    Buffer unit  230  subtracts the electrical current generated in temperature compensating unit  220  from the electrical current generated in photo sensing unit  210 . Buffer  230  subtracts the electrical current generated by temperature from the electrical current generated by the ambient light and the electrical current generated by temperature in photo sensing unit  210  to generate the electrical current corresponding only to the ambient light regardless of temperature. Also, buffer unit  230  may improve the property of the generated electrical current. 
         [0047]    More specifically, buffer unit  230  includes a fifth transistor M 5 , a sixth transistor M 6 , a seventh transistor M 7 , and an eighth transistor M 8 . 
         [0048]    A source electrode of the fifth transistor M 5  is electrically connected to a driving power supply VDD, a drain electrode of the fifth transistor M 5  is electrically connected to a fourth node N 4 , and a gate electrode of the fifth transistor M 5  is electrically connected to a second node N 2 . 
         [0049]    A source electrode of the sixth transistor M 6  is electrically connected to the second node N 2 , a drain electrode of the sixth transistor M 6  is electrically connected to the fourth node N 4 , and a gate electrode of the sixth transistor M 6  is electrically connected to a reset signal line RESET. 
         [0050]    A source electrode of the seventh transistor M 7  is electrically connected to the fourth node N 4 , a drain electrode of the seventh transistor M 7  is electrically connected to a first output line Iref, and a gate electrode of the seventh transistor M 7  is electrically connected to the reset signal line RESET. 
         [0051]    A source electrode of the eighth transistor M 8  is electrically connected to the fourth node N 4 , a drain electrode of the eighth transistor M 8  is connected to a second output line lout, and a gate electrode of the eighth transistor M 8  is electrically connected to a second control line TX. 
         [0052]      FIG. 3  is a group of waveforms illustrating an operation of the photo sensor of  FIG. 2 . 
         [0053]    Referring to  FIG. 3 , photo sensor  200  operates by a reset period T 1 , an integration period T 2 , and a sampling period T 3 . 
         [0054]    In the reset period T 1 , a reset signal reset transferred through a reset signal line RESET is low, a second control signal tx transferred through a second control line TX is high, and a first control signal hold transferred through a first control line HOLD is low. 
         [0055]    In the integration period T 2 , the reset signal reset is high, the second control signal tx is high, and the first control signal hold is low. 
         [0056]    In the sampling period T 3 , the reset signal reset is high, the second control signal tx is low, and the first control signal hold is high. 
         [0057]    First, in the reset period T 1 , the reset signal reset and the first control signal hold are low, and the second control signal tx is high so that the first transistor M 1 , the second transistor M 2 , the third transistor M 3 , the fourth transistor N 4 , the sixth transistor M 6 , and the seventh transistor M 7  turns on, and the eighth transistor M 8  turn off. Therefore, the first capacitor Cst 1  and the second capacitor Cboost 1  are initialized by means of initialization voltage, and a third capacitor Cst 2  and a fourth capacitor Cboost 2  are initialized by means of voltage of a driving voltage VDD. When reference electrical current iref flows through a first output terminal Iref electrically connected to a drain electrode of the seventh transistor M 7 , the second node N 2  has a predetermined voltage Vref corresponding to current amount of the reference current iref. Such a predetermined voltage Vref is maintained by means of the first capacitor Cst 1 , the second capacitor Cboost 1 , the third capacitor Cst 2 , and the fourth capacitor Cboost 2 . Here, the predetermined voltage is the voltage applied to a gate electrode of the fifth transistor M 5  so that the reference current iref flows. When the transistor M 8  is turned off, the transistor M 7  is turned on to allow an electric current Iref to flow through the drain of the transistor M 7 . When the electric current Iref flows through the drain of the transistor M 7 , the electric current Iref cones to flow through the drain of the transistor M 5  since the node N 4  is electrically connected to the source of the transistor M 7 . An electric current flowing through te drain of transistor being determined by a voltage between the sources and the gate of the transistor, if the electric current Iref flows through the drain of the transistor M 5 , a voltage to allow the current Iref to flow through the date of transistor M 5  is applied. Here, the voltage applied to the transistor M 5  is determined by the electric current Iref, regardless of the threshold voltage of transistor M 5 . 
         [0058]    In the integration period T 2 , the first control signal hold is low and the second control signal tx and the reset signal reset are high so that the first transistor M 1  and the third transistor M 3  maintain a turn-on state, and the second transistor M 2  and the fourth transistor M 4  maintain a turn-off state. Therefore, on the photodiode PD, current flows in a direction from a cathode electrode of the photodiode PD to an anode electrode of the photodiode PD by means of the incident light and the ambient temperature. On the dark diode DPD, current flows in a direction from a cathode electrode to an anode electrode by means of the ambient temperature. At this time, among the current flowing on the photodiode PD, the current flowing corresponding to the incident light is referred to a first current, and the current flowing corresponding to the ambient temperature is referred to a second current. Also, the current flowing on the dark diode DPD corresponding to ambient temperature is referred to a third current. 
         [0059]    The first current and the second current flown by means of the photodiode PD flow to the first node N 1 . The third current flown by means of the dark diode DPD flows from the third node N 3  to the initialization power line Vint through the dark diode DPD. At this time, the photodiode PD and the dark diode DPD are formed in the same process so that the second current and the third current generated by temperature have the same amount of current. 
         [0060]    Voltage of the first node N 1  is increased by means of the first current and the second current flowing in the photodiode PD, and voltage of the third node N 3  is decreased by means of the third current flowing in the dark diode DPD. Here, the second current and the third current are the same in view of the magnitude and opposite in view of the direction. Therefore, the extent where voltage of the first node N 1  is increased by means of the second current and the extent where voltage of the third node N 3  is decreased by means of the third current become the same. Therefore, voltage of the second node N 2  coupled with the first node N 1  and the third node N 3  through the first and second capacitors Cst 1  and Cboost 1  and the third and fourth capacitors Cst 2  and Cboost 2  is increased corresponding to the magnitude of the first current. 
         [0061]    Therefore, voltage of Vref+ Δ V (extent of voltage change in the first node N 1  by means of the first current) is applied to the second node N 2 . At this time, the eighth transistor M 8  is a turn-off state, making it possible to prevent current from flowing through a second output terminal lout corresponding to the voltage applied to the second node N 2 . Therefore, no current is present at second output terminal lout at period T 2 . 
         [0062]    In the sampling period T 3 , the reset signal reset and the control signal hold are high and the second control signal tx is low so that the eighth transistor M 8  turns on. Therefore, the photodiode PD is disconnected with the first node N 1 , and the dark diode DPD is disconnected with the third node N 3 . Therefore, the voltage of the second node N 2  is not changed any further by means of the first capacitor Cst 1  and the second capacitor Cboost 1 , and the third capacitor Cst 2  and the fourth capacitor Cboost 2 . The second output terminal Iout is kept in connection with the drain electrode of the fifth transistor M 5  by means of the eighth transistor M 8 . Accordingly, current flows in a direction from the source electrode of the fifth transistor M 5  to the drain electrode thereof. Such current flows corresponding to the voltage at the second node N 2  passing through the second output terminal lout to the exterior of photo sensor  200  is used as a light sensing signal. 
         [0063]      FIG. 4  is a cross-sectional view showing a first embodiment of a dark diode adopted to the photo sensor of  FIG. 2 . Referring to  FIG. 4 , a buffer layer  1001  and a semiconductor layer including three regions, i.e., semiconductor regions  1002   a,    1002   b,  and  1002   c,  are sequentially formed on a transparent substrate  1000 . Then, a first insulating film  1003  is formed on buffer layer  1001  and the semiconductor layer. Here, semiconductor regions  1002   b  and  1002   c  are located at two end portions of the semiconductor layer respectively and semiconductor region  1002   a  is located at middle portions of the semiconductor layer. Semiconductor region  1002   a  may be covered by a mask or related tools, and an ion doping process may be then performed. One of semiconductor region  1002   b  and semiconductor region  1002   c  may become N-type, and the other one may become P-type after the doping process, and semiconductor region  1002   a  is not ion-doped to become an intrinsic semiconductor region. Subsequently, a second insulating film  1004  is formed on first insulating film  1003 , and contact holes  1100  penetrating first insulating film  1003  and second insulating film  1004  are formed. A metal layer is formed on second insulating film  1004  and then patterned to become first and second metal electrodes  1005   a  and  1005   b.  First and second metal electrodes  1005   a  and  1005   b  each electrically coupled with P-type semiconductor region  1002   b  and N-type semiconductor region  1002   c  of the semiconductor layers through contact holes  1100 . After first and second metal electrodes  1005   a  and  1005   b  are formed, a third insulating film  1006  is formed and a planarization layer  1007  is formed on third insulating film  1006 . An anode electrode  1008  of the organic light emitting display device is formed on planarization layer  1007 , and a protective film  1009  or the like is formed planarization layer  1007 . 
         [0064]    In the dark diode DPD formed as above, light is reflected by means of anode electrode  1008  so that light may not be incident to the dark diode DPD. Therefore, the dark diode DPD generates only current according to temperature change. 
         [0065]      FIG. 5  is a cross-sectional view showing a second embodiment of a dark diode adopted to the photo sensor of  FIG. 2 . Referring to  FIG. 5 , a buffer layer  2001  and a semiconductor layer including three regions, i.e., semiconductor regions  2002   a,    2002   b,  and  2002   c,  are sequentially formed on a transparent substrate  2000 . Then, a first insulating film  2003  is formed on buffer layer  2001  and the semiconductor layer. Here, semiconductor regions  2002   b  and  2002   c  are located at two end portions of the semiconductor layer respectively and semiconductor region  2002   a  is located at middle portions of the semiconductor layer. Semiconductor region  2002   a  may be covered by a mask or related tools, and an ion doping process may be then performed. One of semiconductor region  2002   b  and semiconductor region  2002   c  may become N-type, and the other one may become P-type after the doping process, and semiconductor region  2002   a  is not ion-doped to become an intrinsic semiconductor region. A second insulating film  2004  is formed on first insulating film  2003 , and contact holes  2100  penetrating first insulating film  2003  and second insulating film  2004  are formed. Subsequently, a metal layer is formed thereon and then patterned to form first, second, and third metal electrodes  2005   a,    2005   b  and  2005   c.  The first and second metal electrodes  2005   a  and  2005   b  each electrically coupled to the P-type semiconductor region and N-type semiconductor region of the semiconductor layer through contact holes  2100 , and the third metal electrode  2005   c  is formed opposite to and spaced apart from intrinsic semiconductor region  2002   a  of the semiconductor layers. A third insulating film  2006  is formed on the first, second and third metal electrodes  2005   a,    2005   b,  and  2005   c,  and a planarization layer  2007  is formed on the third insulating film  2006 . An anode electrode  2008  of the organic light emitting display device is formed on planarization layer  2007 , and a protective film  2009  or the like is formed planarization layer  2007 . 
         [0066]    In the dark diode DPD of  FIG. 4 , even though light are reflected by means of anode electrode  1008 , a portion of light may still be incident to the dark diode DPD. Therefore, in order to solve this problem, in the dark diode of  FIG. 5 , the third metal electrode  2005   c  is formed between anode electrode  2008  and the semiconductor layer having semiconductor regions  2002   a,    2002   b,  and  2002   c.  Accordingly, a portion of light passing through anode electrode  2008  is blocked by means of metal electrode  2005   c  not to be incident to the semiconductor layer. Therefore, the dark diode DPD of  FIG. 5  may enhance the reduction of the effect by means of light compared to the dark diode of  FIG. 4 . 
         [0067]      FIG. 6  is a cross-sectional view showing a third embodiment of a dark diode adopted to the photo sensor of  FIG. 2 . Referring to  FIG. 6 , a buffer layer  3001  and a semiconductor layer having semiconductor regions  3002   a  and  3002   b  are sequentially formed on a substrate  3000 . Then, a first insulating film  3003  is formed on the semiconductor layer, and an ion doping process is performed. The semiconductor layer are divided into two portions  3002   a  and  3002   b  by means of the ion doping process. In other words, semiconductor region  3002   a  may become a P-type semiconductor region and semiconductor region  3002   b  may become an intrinsic semiconductor region. 
         [0068]    A metal layer is formed on first insulating film  3003  and is patterned to form a third metal electrode  3004  in a predetermined region. Third metal electrode  3004  is formed opposite to and spaced apart from the semiconductor layer, and is positioned to cover the middle portions of the semiconductor layer. 
         [0069]    A second insulating film  3005  is formed on third metal electrode  3004 . After second insulating film  3005  is formed, contact holes  3100  penetrating first insulating film  3003  and second insulating film  3005  is formed, and a metal layer is formed on second insulating film  3005 . The metal layer is patterned to form first and second metal electrodes  3006   a  and  3006   b.  At this time, the first and second metal electrodes  3006   a  and  3006   b  each electrically coupled with both end portions of semiconductor layers  3002   a  and  3002   b  by means of contact holes  3100 . Also, the first and second metal electrodes  3006   a  and  3006   b  are formed to be overlapped with the third metal electrode  3004 . Accordingly, the semiconductor layer is completely covered by means of the first, second and third metal electrodes  3006   a,    3006   b,  and  3006   c.  After the first and second metal electrodes  3006   a  and  3006   b  are formed, a third insulating film  3007  is formed and a planarization layer  3008  is formed on the third insulating film  3007 . An anode electrode  3009  of the organic light emitting display device is formed on the planarization layer, and a protective film  3010  or the like is formed thereon. 
         [0070]    With a photo sensor and a flat panel display device using the photo sensor constructed as the present invention as described above, electrical current according to temperature change maybe compensated so that the photo sensor may generate information only on the change of the ambient light. 
         [0071]    While the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, and equivalents thereof.