Abstract:
A fingerprint-sensing device of thin film transistor type that is capable of minimizing an insulation breakage between thin film transistor lines includes a sensor for sensing contact of a fingerprint to the sensor array and for generating a sensing signal when said fingerprint is in contact with the sensor array. In the device, a sensor array converts a light reflected from a fingerprint into a current quantity upon contact of the fingerprint. A driving voltage supply applies a driving voltage to the sensor array. A controller responds to the sensing signal from the sensor to generate control signals for controlling the driving voltage supply.

Description:
[0001]    This application claims the benefit of Korean Patent Application No. P00-34776, filed on Jun. 23, 2000, the entirety of which is hereby incorporated by reference for all purposes as if fully set forth herein.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates to a fingerprint sensor, and more particularly to a thin film transistor type fingerprint sensor that is capable of minimizing an insulation breakage between thin film transistor lines.  
           [0004]    2. Description of the Related Art  
           [0005]    Various types of electronic equipment has been developed which uses thin film transistors (TFTs) in a variety of applications. For example, recently, TFTs have used for active matrix liquid crystal displays as well as security devices, such as fingerprint recognition devices.  
           [0006]    Referring to FIG. 1, a conventional fingerprint sensor array using TFTs includes a sensor TFT  2 , a capacitor  3 , a switch TFT  4 , and a backlight  8 .  
           [0007]    The backlight  8  applies light to a fingerprint (not shown in FIG. 1). The sensor TFT  2  applies a current corresponding to a quantity of light reflected from the fingerprint to a capacitor  3 . The capacitor  3  temporarily stores the current supplied from the sensor TFT  2  and applies the stored current to the switch TFT  4 . The switch TFT  4  applies the current supplied from the capacitor  3  to a discriminator (not shown). The discriminator judges an identification of the fingerprint depending on a quantity of the current received from the switch TFT  4 .  
           [0008]    A method of fabricating the sensor TFT  2  and the switch TFT  4  will be described below. First, gate electrodes  20  made from Al, Mo or Cr, etc. are formed on a substrate  18 . After formation of the gate electrodes  20 , a capacitor electrode  10  made from a transparent conductive material such as indium-tin-oxide (ITO) is formed on the gate electrode  20  of the sensor TFT  2  and on the substrate  18 . The capacitor electrode  10  is not formed on the gate electrode  20  of the switch TFT  4 .  
           [0009]    After formation of the capacitor electrode  10 , a gate insulating film  22  made from an inorganic material such as SiN x , etc. is formed to cover the substrate  18 , the gate electrode  20  and the capacitor electrode  10 . On the gate insulating film  22 , a semiconductor layer  24  made from amorphous silicon (a-Si), and an ohmic contact layer  26  made from a-Si doped with n +  ions, are continuously deposited.  
           [0010]    After the continuous deposition of the semiconductor layer  24  and the ohmic contact layer  26 , the sensor TFT  2  is provided with a source electrode  28  and a drain electrode  30  which are made from a transparent conductive material such as ITO. At this time, the drain electrode  30  of the sensor TFT  2  is electrically connected to the source electrode  28  of the switch TFT  4 .  
           [0011]    The ohmic contact layer  26  between the source electrode  28  and the drain electrode  30  is removed by dry etching or wet etching. Then, a first protective film  32  made from a transparent material is entirely deposited onto the substrate  18 . After the entire deposition of the first protective film  32 , a light shield  36  made from a metal is deposited on the first protective film  32  of the switch TFT  4 . Thereafter, a second protective film  34  made from a transparent film is entirely deposited onto the first protective film  32 .  
           [0012]    The drain electrode  30  of the sensor TFT  2  and the capacitor electrode  10  function as a capacitor. In other words, the capacitor  3  consists of the drain electrode  30  of the sensor TFT  2  and the capacitor electrode  10 . The capacitor  3  stores a current from the sensor TFT  2  and applies the stored current to the switch TFT  4 . The source electrode  28 , the drain electrode  30  and the light shield  36  of the switch TFT  4 , which are made from a metal, block off light input from the exterior thereof to prevent the semiconductor layer  24  of the switch TFT  4  from being activated.  
           [0013]    [0013]FIG. 2 is an equivalent circuit diagram of the conventional fingerprint array using TFTs.  
           [0014]    Referring to FIG. 2, a voltage of 10V is applied to the source electrode  28  of the sensor TFT  2 . A voltage of −5V is applied to the gate electrodes  20  of the sensor TFT  2  and the switch TFT  4 . The light shield  36  of the switch TFT  4  is connected to a ground voltage source GND. The drain electrode  30  of the sensor TFT  2  is electrically connected to the source electrode  28  of the switch TFT  4 . A capacitor  3  is arranged between the drain electrode  30  and the gate electrode  20  of the sensor TFT  2 .  
           [0015]    If the sensor TFT  2  does not recognize a fingerprint, then a current as shown in FIG. 3A flows into the source electrode  28  and the drain electrode  30  of the sensor TFT  2  by the voltage of 10V applied to the source electrode  28  of the sensor TFT  2  and the voltage of −5V applied to the gate electrode  20  of the sensor TFT  2 . The current flowing in the source electrode  28  and the drain electrode  30  of the sensor TFT  2  is temporarily stored by the capacitor  3  and thereafter produces a desired voltage at the source electrode  28  of the switch TFT  4 . The switch TFT  4  is turned on by the voltage of −5V applied to the gate electrode  20  to apply the desired voltage from the source electrode  28  thereof to the drain electrode  30  thereof. The desired voltage applied to the drain electrode  30  of the switch TFT  4  is then sent to the discriminator. The discriminator checks a level of the voltage delivered from the switch TFT  4  to determine that a fingerprint has not been recognized.  
           [0016]    On the other hand, if the fingerprint sensor array recognizes a fingerprint  6  as shown in FIG. 4, then light inputted from the backlight  8  is reflected into the sensor TFT  2  by the fingerprint  6 . At this time, since a fingerprint pattern is shaped differently for every person, a quantity of a light reflected into the sensor TFT  2  becomes different due to the differently shaped fingerprint pattern. The light reflected into the switch TFT  4  is shut off by means of the light shield  36 .  
           [0017]    Light incident to the sensor TFT  2  activates the semiconductor layer  24  of the sensor TFT  2 . At this time, the extent of activation of the semiconductor layer  24  is determined by a quantity of a light received from the fingerprint  6 . When the semiconductor layer  24  is activated, a current as shown in FIG. 3B flows in the source electrode  28  and the drain electrode  30  of the sensor TFT  2 . In other words, a voltage applied to the source electrode  28  and the gate electrode  20  of the sensor TFT  2  is constant, but a current more than the current as shown in FIG. 3A, when the fingerprint  6  is not recognized, is caused to flow by virtue of the activation of the semiconductor layer  24 .  
           [0018]    The current flowing in the source electrode  28  and the drain electrode  30  of the sensor TFT  2  is temporarily stored by the capacitor  3 , producing a desired voltage which is then sent to the source electrode  28  of the switch TFT  4 . The switch TFT  4  delivers the desired voltage applied from the capacitor  3  to the source electrode  28  thereof into the discriminator (not shown). The discriminator checks the level of the voltage received from the switch TFT  4  to judge the identity of the fingerprint.  
           [0019]    Referring to FIG. 5, the conventional fingerprint-sensing device includes a sensor  60  and a controller  50 . The sensor  60  includes a sensor array  40  having the sensor TFT  2  and the switch TFT  4 . The controller  50  includes a power supply  42  for supplying an operating voltage to the sensor array  40 , and a control logic unit  44  for controlling operations of the power supply  42  and the sensor array  40 .  
           [0020]    A gate line  43 , a data line  45 , and a shield line  47  for applying desired voltages supplied from the power supply  42  are installed between the power supply  42  and the sensor array  40 . The gate line  43  delivers a voltage of −5V, received from the power supply  42 , to the gate electrodes  20  of the sensor TFT  2  and the switch TFT  4 . The data lines delivers a voltage of 10V, received from the power supply  42 , to the source electrode  28  of the sensor TFT  2 . The shield line  47  connects the light shield  36  of the switch TFT  4  to the ground voltage source GND. The shield line  47  protects the switch TFT  4  from external incident light to prevent a leakage current from flowing in the switch TFT  4 .  
           [0021]    In such a conventional fingerprint-sensing device, a direct current voltage having a different voltage level is applied to each of the gate line  43 , the data line  45  and the shield line  47 . However, an insulation breakage between the lines  43 ,  45  and  47  may occur due to static electricity produced upon contact of the fingerprint  6  with the sensor array  44 .  
         SUMMARY OF THE INVENTION  
         [0022]    Accordingly, it is an object of the present invention to provide a fingerprint sensor of thin film transistor type that is capable of minimizing an insulation breakage between thin film transistor lines.  
           [0023]    In order to achieve these and other objects of the invention, a fingerprint-sensing device of thin film transistor type according to the present invention includes a sensor array for converting a light reflected from a fingerprint into a current quantity upon contact of said fingerprint; driving voltage supply means for applying a driving voltage to the sensor array; a sensor for sensing a contact of said fingerprint to the sensor array to generate a sensing signal when said fingerprint is in contact with the sensor array; and a controller for responding to said sensing signal from the sensor to generate control signals for controlling the driving voltage supply means.  
           [0024]    The driving voltage supply means includes a common terminal for receiving a common voltage; a plurality of voltage terminals for receiving said driving voltage applied to the sensor array; and switching devices installed at each voltage terminal.  
           [0025]    The switching devices are connected to the plurality of voltage terminals when said sensing signal is received while being connected to the common terminal when said sensing signal is not received. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]    These and other objects of the invention will be apparent from the following detailed description of the embodiments of the present invention with reference to the accompanying drawings, in which:  
         [0027]    [0027]FIG. 1 is a section view showing a structure of a conventional sensor array;  
         [0028]    [0028]FIG. 2 is an equivalent circuit diagram of the sensor array shown in FIG. 1;  
         [0029]    [0029]FIG. 3A is a graph representing a current flowing when the sensor array of FIG. 1 does not recognize a fingerprint;  
         [0030]    [0030]FIG. 3B is a graph representing a current flowing when the sensor array of FIG. 1 recognizes a fingerprint;  
         [0031]    [0031]FIG. 4 is a view for explaining a process in which the sensor array of FIG. 1 recognizes a fingerprint;  
         [0032]    [0032]FIG. 5 is a block diagram showing a configuration of the conventional TFT-type fingerprint-sensing device including the sensor array of FIG. 1;  
         [0033]    [0033]FIG. 6 is a block diagram showing a configuration of a TFT-type fingerprint-sensing device according to an embodiment of the present invention;  
         [0034]    [0034]FIG. 7A and FIG. 7B are views for explaining an operational process of the switching device shown in FIG. 6;  
         [0035]    [0035]FIG. 8A and FIG. 8B are views for explaining a method of sensing a contact of the sensor array of FIG. 6 with a fingerprint; and  
         [0036]    [0036]FIG. 9 is a circuit diagram of the switching device shown in FIG. 6. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0037]    Referring to FIG. 6, there is shown a fingerprint-sensing device according to an embodiment of the present invention. The fingerprint-sensing device includes a sensor  70  and a controller  80 . The sensor  70  includes a sensor array  51  having a sensor TFT  2  and a switch TFT  4  as shown in FIG. 1. The controller  80  includes a driving voltage supply means such as the power supply  46  for supplying operating voltages to the sensor array  51 , a control logic unit  48  for controlling operations of the power supply  46  and the sensor array  51 , and a feedback unit  52  for monitoring a contact of a fingerprint to the sensor array  51 .  
         [0038]    The feedback unit  52  generates a first control signal when a fingerprint contacts the sensor array  51  and delivers it to the control logic unit  48 . The control logic unit  48  generates a second control signal when the first control signal is received from the feedback unit  52 , while generating a third control signal when the first control signal is not received therefrom. The second or third control signal from the control logic unit  48  is applied to a switching device  54  installed within the power supply  46 .  
         [0039]    When the second control signal is received from the control logic unit  48 , the switching device  54  connects the gate line  53 , the data line  55  and the shield line  57 , to a gate terminal  64 , a data terminal  66  and a shield terminal  68 , respectively. On the other hand, when the third control signal is received from the control logic unit  48 , the switching device  54  connects the gate line  53 , the data line  55  and the shield line  57  to a common terminal  62 . The common terminal  62  and the shield terminal  68  installed within the power supply  46  are each connected to the ground voltage source GND. The gate terminal  64  and the data terminal  66  installed within the power supply  46  are supplied with DC voltages of −5V and 10V, respectively.  
         [0040]    As shown in FIG. 7A and FIG. 7B, the switching device  54  consists of three switches  63 ,  65  and  67 . The switches  63 ,  65  and  67  are switched under control of the control logic unit  48 .  
         [0041]    An operation process upon recognition of a fingerprint will be described below. First, when a fingerprint contacts the sensor array  51 , a first control signal is generated from the feedback unit  52 . The first control signal from the feedback unit  52  is applied to the control logic unit  48 . The control logic unit  48  having receiving the first control signal from the feedback unit  52  generates a second control signal and applies it the switches  63 ,  65  and  67 . The switches  63 ,  65  and  67  having receiving the second control signal from the control logic unit  48  are switched to connect the gate line  53 , the data line  55 , and the shield line  57 , to the gate terminal  64 , the data terminal  66  and the shield terminal  68  respectively, as shown in FIG. 7B. Accordingly, driving, or operating, voltages are applied to the sensor array  51  having recognized the presence of a fingerprint.  
         [0042]    An operation process when a fingerprint is not recognized will be described below. When a fingerprint is not in contact with the sensor array  5   1 , the feedback unit  52  does not generate a first control signal. When the first control signal is not applied from the feedback unit  52 , the control logic unit  48  generates a third control signal and applies it to the switches  63 ,  65  and  67 . The switches  63 ,  65  and  67  having received the third control signal from the control logic unit  48  are switched are switched to connect the gate line  53 , the data line  55 , and the shield line  57 , to the common terminal  62  as shown in FIG. 7A. Accordingly, driving, or operating, voltages are not applied to the sensor array  51  in which a fingerprint is not recognized.  
         [0043]    A method of monitoring a fingerprint contact at the feedback unit  52  will be described in detail with reference to FIG. 8A.  
         [0044]    Referring to FIG. 8A, in order to monitor a contact of the fingerprint  6 , first and second sensing electrodes  82  and  84  made from a transparent conductive material, such as ITO, are formed on the second protective film  34  of the sensor array  51 . The first and second sensing electrodes  82  and  84  comprise a fingerprint contact detector, or sensor. Desired voltages are applied to the first and second sensing electrodes  82  and  84 . The feedback unit  52  monitors the first and second sensing electrodes  82  and  84 . When the fingerprint  6  is not in contact with the sensor array  44 , the first and second sensing electrodes  82  and  84  are not shorted to each other, and therefore a current is not applied to the feedback unit  52 . When a current is not applied to the feedback unit  52 , the feedback unit  52  does not generate the first control signal.  
         [0045]    On the other hand, when the fingerprint is present on the sensor array  51 , the first and second sensing electrodes  82  and  84  are shorted to each other by the finger generating the fingerprint. When the fist and second sensing electrodes  82  and  84  are shorted, a fingerprint detection signal comprising a current is applied to the feedback unit  52 . When the current is applied to the feedback unit  52 , the feedback unit  52  generates the first control signal and applies it the control logic unit  48  as described in detail above.  
         [0046]    [0046]FIG. 8B shows another example of a fingerprint contact detector, or sensor, for providing a fingerprint contact signal to the feedback unit  52 .  
         [0047]    Referring to FIG. 8B, a switch  88  is provided between the sensor array  44  and a protective cover  86 . The protective cover  86  protects the sensor array  44  from various alien materials and an impact. When the fingerprint  6  is in contact with the sensor array  44 , the protective cover  86  is open. When the protective cover  86  is open, the switch  88  is closed. When the switch  88  is closed, the feedback unit  52  generates a first control signal and applies it to the control logic unit  48 .  
         [0048]    [0048]FIG. 9 represents the switches installed within the switching device in detail. Referring to FIG. 9, the first switch  63  is formed from two complementary metal-oxide semiconductor (CMOS) devices. A source electrode of the first CMOS device CMOS 1  is connected to the common terminal  62  while a drain electrode thereof is connected to a drain electrode of a second CMOS device CMOS 2 . A source electrode of the second CMOS device CMOS 2  is connected to the gate terminal  64 . The drain electrodes of the first and second CMOS devices CMOS 1  and CMOS 2  are connected to the gate line  53 .  
         [0049]    In operation, when the presence of a fingerprint  6  has not been recognized, a third control signal CS 3  generated from the control logic unit  48  is applied to the gate electrode of the first CMOS device CMOS 1 . The first CMOS device CMOS 1  having received the third control signal CS 3  is turned on to apply a voltage from the common terminal  62  to the gate line  53 . At this time, the second CMOS device CMOS 2  maintains a turned-off state.  
         [0050]    On the other hand, when the presence of a fingerprint  6  has been recognized, a second control signal CS 2  generated from the control logic unit  48 , the second CMOS device CMOS 2  is applied to the gate electrode. The second CMOS device CMOS 2  having received the second control signal CS 2  is turned on to apply a voltage from the gate terminal  64  to the gate line  53 . At this time, the first CMOS device CMOS 1  maintains a turned-off state. The switches  63 ,  65  and  67  may consist of a transistor, or a metal-oxide semiconductor (MOS), etc.  
         [0051]    As described above, according to the present invention, when a finger producing a fingerprint is not in contact with the sensor array, the gate line, the data line and the shield line are connected to a ground voltage source or a DC voltage source having a desired voltage level. Accordingly, a constant voltage is applied to the gate line, the data line and the shield line, so that an insulation breakage caused by static electricity can be minimized.  
         [0052]    Although the present invention has been explained by the embodiments shown in the drawings described above, it should be understood to the ordinary skilled person in the art that the invention is not limited to the embodiments, but rather that various changes or modifications thereof are possible without departing from the spirit of the invention. Accordingly, the scope of the invention shall be determined only by the appended claims and their equivalents.