Sensor pixel and fingerprint sensor including the same

A sensor pixel includes a sensor electrode, a first transistor including a gate electrode connected to the sensor electrode and which controls a current output provided to an output line, a second transistor connected to a first voltage line and a first transistor, a third transistor connected to the first transistor and the output line, and a compensator unit which compensates a threshold voltage of the first transistor.

This application claims priority to Korean Patent Application No. 10-2017-0016863, filed on Feb. 7, 2017, and all the benefits accruing therefrom under 35 U.S.C. § 119, the content of which in its entirety is herein incorporated by reference.

BACKGROUND

Exemplary embodiments of the invention relate to a sensor pixel for fingerprint recognition and a fingerprint sensor including the same.

2. Description of the Related Art

Interest in information displays has been on the rise, and demand for portable information media has increased. Accordingly, there has been an increasing demand for display devices, and increased emphasis on the research and commercialization thereof.

A variety of functions utilizing personal information, such as banking services and security, as well as communications functions including phone calls and a text messaging service, have been provided by display devices. Therefore, a fingerprint sensor may be widely used in such display devices in order to prevent other people from accessing the display devices.

Fingerprint sensors may be implemented using various recognition methods. For example, optical fingerprint sensors, thermal fingerprint sensors, and capacitive fingerprint sensors are known in the art.

Among them, a capacitive fingerprint sensor may obtain a shape of a fingerprint (e.g., fingerprint pattern) by detecting changes in capacitance caused by the ridges and valleys of the fingerprint when the human finger approaches a conductive sensing electrode.

SUMMARY

Exemplary embodiments of the invention are directed to a sensor pixel capable of improving fingerprint sensing sensitivity by compensating for a difference in threshold voltage between sensor pixels, and a fingerprint sensor including the same.

A sensor pixel according to an exemplary embodiment of the invention includes a sensor electrode, a first transistor including a gate electrode connected to the sensor electrode and which controls a current output provided to an output line, a second transistor connected to a first voltage line and the first transistor, a third transistor connected to the first transistor and the output line, and a compensator unit which compensates a threshold voltage of the first transistor.

In an exemplary embodiment, the sensor pixel may further include a capacitor electrode which is included in a first capacitor with the sensor electrode.

In an exemplary embodiment, a gate electrode of the second transistor and a gate electrode of the third transistor may be connected to a third scan line.

In an exemplary embodiment, the capacitor electrode may be connected to the third scan line.

In an exemplary embodiment, the compensator unit may include a fourth transistor connected to a second voltage line and a common node between the first and second transistors, and a fifth transistor connected to the sensor electrode and a common node between the first and third transistors.

In an exemplary embodiment, a gate electrode of the fourth transistor and a gate electrode of the fifth transistor may be connected to a second scan line.

In an exemplary embodiment, the sensor pixel may further include a sixth transistor connected to a third voltage line and the sensor electrode.

In an exemplary embodiment, a gate electrode of the sixth transistor may be connected to a first scan line.

A sensor pixel according to an exemplary embodiment includes a first transistor including a gate electrode connected to a first node and which is connected to a second node and a third node in other electrodes, a second transistor including a gate electrode connected to a third scan line and which is connected to a first voltage line and the second node in other electrodes, a third transistor including a gate electrode connected to the third scan line and which is connected to the third node and an output line in other electrodes, a fourth transistor including a gate electrode connected to a second scan line and which is connected to the second node and a second voltage line in other electrodes, a fifth transistor including a gate electrode connected to the second scan line and which is connected to the third node and the first node in other electrodes, a sixth transistor including a gate electrode connected to a first scan line and which is connected to a third voltage line and the first node in other electrodes, and a capacitor connected to the third scan line and the first node.

A fingerprint sensor according to an exemplary embodiment includes sensor pixels, and a scan driver which supplies a scan signal to the sensor pixels, wherein each of the sensor pixels may include a sensor electrode, a first transistor including a gate electrode connected to the sensor electrode and which controls a current output provided to an output line, a second transistor connected to a first voltage line and the first transistor, a third transistor connected to the first transistor and the output line, and a compensator unit which compensates for a threshold voltage of the first transistor.

In an exemplary embodiment, each of the sensor pixels may further include a capacitor electrode which is included in a first capacitor with the sensor electrode.

In an exemplary embodiment, a gate electrode of the second transistor and a gate electrode of the third transistor may be connected to a third scan line.

In an exemplary embodiment, the capacitor electrode may be connected to the third scan line.

In an exemplary embodiment, the compensator unit may include a fourth transistor connected to a second voltage line and a common node between the first and second transistors, and a fifth transistor connected to the sensor electrode and a common node between the first and third transistors.

In an exemplary embodiment, a gate electrode of the fourth transistor and a gate electrode of the fifth transistor may be connected to the second scan line.

In an exemplary embodiment, each of the sensor pixels may further include a sixth transistor connected to a third voltage line and the sensor electrode.

In an exemplary embodiment, a gate electrode of the sixth transistor may be connected to a first scan line.

In an exemplary embodiment, the first voltage line and the second voltage line may be the same voltage line.

In an exemplary embodiment, the first voltage line and the third voltage line may be the same voltage line.

In an exemplary embodiment, the sixth transistor may maintain an ON state during a first period, each of the fourth and fifth transistors may maintain an ON state during a second period, and each of the second and third transistors may maintain an ON state during a third period.

DETAILED DESCRIPTION

Hereinafter, a sensor pixel and a fingerprint sensor according to exemplary embodiments of the invention are described below with reference to the drawings associated with the exemplary embodiments of the invention.

FIG. 1is a diagram illustrating an exemplary embodiment of a sensor pixel SP.

Referring toFIG. 1, the sensor pixel SP may include a sensor electrode210, a capacitor electrode220, and a sensor circuit250.

The sensor electrode210and the capacitor electrode220may be included in a first capacitor C1. In addition, when a user's finger approaches the sensor pixel SP for the purpose of finger recognition, a second capacitor C2may be formed between the sensor electrode210and the user's finger as shown inFIGS. 2A and 2B.

In an exemplary embodiment, the sensor electrode210may be connected to the sensor circuit250and include a conductive material. Examples of the conductive material may include metals, an alloy thereof, a conductive polymer, and a transparent conductive material.

In an exemplary embodiment, examples of the conductive polymer may include polythiophene compounds, polypyrrole compounds, polyaniline compounds, polyacetylene compounds, polyphenylene compounds, and a mixture thereof. Among the polythiophene compounds, a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (“PEDOT/PSS”) compound may be used, for example.

In an exemplary embodiment, examples of the transparent conductive material may include silver nanowires (“AgNW”), Indium Tin Oxide (“ITO”), Indium Zinc Oxide (“IZO”), Antimony Zinc Oxide (“AZO”), Indium Tin Zinc Oxide (“ITZO”), Zinc Oxide (“ZnO”), and Tin Oxide (“SnO2”), carbon nanotubes, and graphene.

The capacitor electrode220may overlap with the sensor electrode210. The sensor electrode210and the capacitor electrode220may be included in the first capacitor C1.

In an exemplary embodiment, the capacitor electrode220may be coupled to a third scan line SL3. For example, the capacitor electrode220may include the same material as the third scan line SL3.

The sensor circuit250may be connected to the first capacitor C1, the first scan line SL1, a second scan line SL2, the third scan line SL3, an output line O, and voltage lines180.

The sensor circuit250may operate in response to signals supplied through the first scan line SL1, the second scan line SL2, and the third scan line SL3, and control an output current Io which is output to the output line O.

The voltage lines180may include a first voltage line181, a second voltage line182, and a third voltage line183.

In an exemplary embodiment, for example, the first voltage line181may supply a first voltage Vcom to the sensor circuit250, the second voltage line182may supply a second voltage Vcp to the sensor circuit250, and the third voltage line183may supply a third voltage Vint to the sensor circuit250.

A voltage supply unit (not illustrated) may supply the first voltage Vcom, the second voltage Vcp, and the third voltage Vint to the first voltage line181, the second voltage line182, and the third voltage line183, respectively.

FIGS. 2A and 2Bare diagrams illustrating that a capacitance of a second capacitor formed between a sensor electrode and a finger changes depending on whether a point of the finger located over a sensor pixel is a ridge or a valley of a fingerprint. More specifically,FIG. 2Aillustrates a case that a ridge310of a finger300is located over the sensor pixel SP, andFIG. 2Billustrates a case that a valley320of the finger300is located over the sensor pixel SP.

Referring toFIGS. 2A and 2B, the sensor electrode210and the capacitor electrode220may be included in the first capacitor C1. The sensor electrode210and the capacitor electrode220may be separated from each other, and an insulating layer (not illustrated) may be interposed therebetween.

In an exemplary embodiment, when the user's finger300is located over the sensor pixel SP for the purpose of fingerprint recognition, the second capacitor C2between the sensor electrode210and the finger300may occur.

The second capacitor C2may be a variable capacitor. The capacitance of the second capacitor C2may vary depending on whether the ridge310or the valley320is located over the sensor electrode210.

In other words, the distance between the ridge310and the sensor electrode210may be shorter than the distance between the valley320and the sensor electrode210. Therefore, the capacitance of the second capacitor C2when the ridge310is located over the sensor electrode210as shown inFIG. 2Amay be different from the capacitance of the second capacitor C2when the valley320is located over the sensor electrode210as shown inFIG. 2B.

The change in capacitance of the second capacitor C2may affect the output current Io of the sensor pixel SP. Therefore, a read-out circuit (not illustrated) may recognize the user's fingerprint by detecting a variation in the output current Io.

FIG. 3is a detailed circuit diagram of an exemplary embodiment of the sensor pixel SP shown inFIG. 1.

Referring toFIG. 3, according to an exemplary embodiment, the sensor pixel SP may include the first capacitor C1and the sensor circuit250.

As described above, the first capacitor C1may include the sensor electrode210and the capacitor electrode220.

The sensor circuit250may include a first transistor T1, a second transistor T2, a third transistor T3, and a compensator unit270.

The first transistor T1may include a gate electrode connected to the sensor electrode210and control the output current Io, which is output to the output line O.

In an exemplary embodiment, for example, the first transistor T1may include the gate electrode coupled to a first node N1and be connected between a second node N2and a third node N3in other electrodes.

More specifically, the first transistor T1may include the gate electrode connected to the first node N1, a first electrode connected to the second node N2, and a second electrode connected to the third node N3.

Therefore, the output current Io may change in response to a gate voltage of the first transistor T1(e.g., a voltage of the first node N1).

The second transistor T2may be connected between the first voltage line181and the first transistor T1.

In an exemplary embodiment, for example, the second transistor T2may include a gate electrode connected to the third scan line SL3and be connected between the first voltage line181and the second node N2in other electrodes.

More specifically, the second transistor T2may include the gate electrode connected to the third scan line SL3, a first electrode connected to the first voltage line181, and a second electrode coupled to the second node N2.

Therefore, when a scan signal is supplied to the third scan line SL3, the second transistor T2may be turned on.

The third transistor T3may be connected between the first transistor T1and the output line O.

In an exemplary embodiment, for example, the third transistor T3may include a gate electrode connected to the third scan line SL3and be connected between the third node N3and the output line O in other electrodes.

More specifically, the third transistor T3may include a gate electrode connected to the third scan line SL3, a first electrode connected to the third node N3, and a second electrode connected to the output line O.

Therefore, when a scan signal is supplied to the third scan line SL3, the third transistor T3may be turned on.

The compensator unit270may compensate for a threshold voltage of the first transistor T1.

In an exemplary embodiment, the compensator unit270may include a fourth transistor T4and a fifth transistor T5.

The fourth transistor T4may be connected between the second voltage line182and the common node N2between the first and second transistors T1and T2.

In an exemplary embodiment, for example, the fourth transistor T4may include a gate electrode connected to the second scan line SL2and be connected between the second node N2and the second voltage line182in other electrodes.

More specifically, the fourth transistor T4may include the gate electrode connected to the second scan line SL2, a first electrode connected to the second voltage line182, and a second electrode connected to the second node N2.

Therefore, when a scan signal is supplied to the second scan line SL2, the fourth transistor T4may be turned on.

The fifth transistor T5may be connected between the sensor electrode210and the common node N3between the first transistor T1and the third transistor T3.

In an exemplary embodiment, for example, the fifth transistor T5may include a gate electrode coupled to the second scan line SL2and be connected between the third node N3and the first node N1in other electrodes.

More specifically, the fifth transistor T5may include a gate electrode connected to the second scan line SL2, a first electrode connected to the first node N1, and a second electrode connected to the third node N3.

Therefore, when a scan signal is supplied to the second scan line SL2, the fifth transistor T5may be turned on.

The first capacitor C1may be connected between the first node N1and the third scan line SL3.

In an exemplary embodiment, for example, the sensor electrode210may be connected to the first node N1, and the capacitor electrode220may be connected to the third scan line SL3.

The second capacitor C2may be formed when the user's finger300approaches the sensor pixel SP. The second capacitor C2may function as a variable capacitor. The second capacitor C2may be regarded as being connected in series with the first capacitor C1at the first node N1in an equivalent circuit.

In an exemplary embodiment, the sensor circuit250may further include a sixth transistor T6to initialize the sensor pixel SP.

The sixth transistor T6may be connected between the third voltage line183and the sensor electrode210.

In an exemplary embodiment, for example, the sixth transistor T6may include a gate electrode coupled to the first scan line SL1and be connected between the third voltage line183and the first node N1in other electrodes.

More specifically, the sixth transistor T6may include the gate electrode connected to the first scan line SL1, a first electrode connected to the third voltage line183, and a second electrode connected to the first node N1.

Therefore, when a scan signal is supplied to the first scan line SL1, the sixth transistor T6may be turned on.

When the sixth transistor T6is turned on, a voltage of the sensor electrode210which amounts to a voltage of the first node N1may be changed to the third voltage Vint.

The first electrode of each of the transistors T1, T2, T3, T4, T5, and T6may be set to one of a source electrode and a drain electrode. The second electrode of each of the transistors T1, T2, T3, T4, T5, and T6may be set to the other electrode of the source electrode and the drain electrode, which is different from the first electrode. In an exemplary embodiment, for example, when the first electrode is set to a source electrode, the second electrode may be set to a drain electrode.

FIG. 4is a timing diagram of scan signals illustrating exemplary operations of the sensor pixel SP as shown inFIG. 3.FIG. 4illustrates the timing diagrams of a scan signal supplied to the first scan line SL1, a scan signal supplied to the second scan line SL2, and a scan signal supplied to the third scan line SL3.

Referring toFIG. 4, in association with operations of the sensor pixel SP, a first period P1, which is an initializing period, a second period P2, which is a threshold voltage compensating period, and a third period P3, which is a sensing period, may be in sequential order.

A scan signal may be supplied to the first scan line SL1during the first period P1.

Therefore, during the first period P1, the sixth transistor T6may maintain an ON state, and a voltage of the first node N1may correspond to the third voltage Vint applied from the third voltage line183.

In an exemplary embodiment, for example, the third voltage Vint may have a voltage level enough to turn on the first transistor T1.

Subsequently, a scan signal may be supplied to the second scan line SL2during the second period P2.

Therefore, each of the fourth transistor T4and the fifth transistor T5included in the compensator unit270may maintain an ON state during the second period P2.

When the fourth transistor T4is turned on, the second voltage Vcp may be applied to the second node N2. When the fifth transistor T5is turned on, the first transistor T1may function as a diode.

Therefore, a voltage VN1of the first node N1during the second period P2may be set to a value obtained by subtracting a threshold voltage Vth1of the first transistor T1from the second voltage Vcp according to the following Equation:
VN1=Vcp−Vth1.

Subsequently, a scan signal may be supplied to the third scan line SL3during the third period P3.

Therefore, during the third period P3, each of the second transistor T2and the third transistor T3may maintain an ON state. Therefore, the output current Io may flow from the first voltage line181to the output line O.

The first transistor T1may control the amount of the output current Io in response to the gate voltage which is the voltage VN1of the first node N1.

In an exemplary embodiment, for example, the output current Io may change in response to the voltage VN1of the first node N1, and the voltage VN1of the first node N1during the third period P3may be determined by the following Equation:
VN1=Vcp−Vth1+(Cc1/(Cc1+Cc2))*Vs.

In this Equation, Cc1is a capacitance of the first capacitor C1, Cc2is a capacitance of the second capacitor C2, and Vs is a voltage variation of the scan signal supplied to the third scan line SL3.

In an exemplary embodiment, the output current Io may be determined by the following Equation:
Io=K*(Vsg−Vth1)2.

In this Equation, K is a constant, and Vsg is a voltage difference between the first electrode and the gate electrode of the first transistor T1.

Since the first electrode of the first transistor T1has the first voltage Vcom during the third period P3, the output current Io during the third period P3may be expressed by the following Equation:

As a result, the output current Io which is output from the first transistor T1may be determined regardless of the threshold voltage Vth1, such that non-uniformity in sensitivity caused by the difference in threshold voltage between the sensor pixels may be eliminated.

A read-out circuit (not illustrated) may recognize the ridge310and the valley320of the fingerprint by using the output current Io.

In other words, a capacitance Cc2of the second capacitor C2may vary depending on whether the ridge310or the valley320is located over the sensor electrode210. A variation of the capacitance Cc2of the second capacitor C2may affect the output current Io of the sensor pixel SP. Thus, the read-out circuit (not shown) may recognize the ridge310and the valley320of the fingerprint by sensing the variation of the output current Io.

FIG. 5is a diagram illustrating exemplary embodiment of a fingerprint sensor100.

Referring toFIG. 5, the fingerprint sensor100may include sensor pixels SP, a scan driver150, and a read-out circuit160.

The sensor pixels SP may be disposed on a substrate110. In an exemplary embodiment, the sensor pixels SP may be arranged in an n×m matrix form, where n and m are natural numbers. In addition, the sensor pixels SP may be connected to scan lines SL1to SL2n+1 and output lines O1to Om.

Each of the sensor pixels SP may receive a scan signal through one of the scan lines SL1to SL2n+1 and output a predetermined current corresponding to a valley or ridge of a fingerprint to one of the output lines O1to Om.

The scan lines SL1to SL2n+1 may be disposed on the substrate110and extend in a first direction (e.g., X-axis direction), and each of the scan lines SL1to SL2n+1 may be connected to corresponding sensor pixels SP arranged in the first direction.

The output lines O1to Om may be disposed on the substrate110and extend in a second direction (e.g., Y-axis direction), and each of the output lines O1to Om may be connected to corresponding sensor pixels SP arranged in the second direction.

However, the directions in which the scan lines SL1to SLn and the output lines O1to Om are arranged are not limited thereto and may be changed.

In an exemplary embodiment, the sensor pixels SP may be connected to the voltage line180and receive a driving voltage from the voltage supply unit170.

The scan driver150may supply scan signals to the sensor pixels SP through the scan lines SL1to SL2n+1.

In an exemplary embodiment, for example, the scan driver150may sequentially output the scan signals to the scan lines SL1to SL2n+1.

A scan signal may have a voltage level enough for a transistor receiving the scan signal to be turned on.

The scan driver150may be directly mounted on the substrate110, or may be connected to the substrate110through a separate component such as a flexible printed circuit board to be connected to the scan lines SL1to SL2n+1.

The read-out circuit160may receive signals (e.g., current) from the sensor pixels SP through the output lines O1to Om.

In an exemplary embodiment, for example, when the scan driver150sequentially supplies scan signals to the scan lines in an order from the scan line SL1to the scan line SL2n+1, the sensor pixels SP corresponding to respective scan lines may be selected sequentially, and the read-out circuit160may sequentially receive the current outputs in an order from the sensor pixels SP corresponding to the scan line SL1to the sensor pixels SP corresponding to the scan line SL2n+1.

The read-out circuit160may recognize fingerprint information by sensing variations in current.

The read-out circuit160may be directly mounted on the substrate110, or may be connected to the substrate110through a separate component such as a flexible printed circuit board, to be connected to the output lines O1to Om.

The voltage supply unit170may supply a predetermined voltage to the sensor pixels SP through the voltage line180.

The voltage supply unit170may be directly mounted on the substrate110, or may be connected to the substrate110through a separate component such as a flexible printed circuit board, to be connected to the voltage line180.

InFIG. 5, the scan driver150, the read-out circuit160, and the voltage supply unit170are illustrated as separate components. However, at least some of the components may be integrated in alternative exemplary embodiment.

In addition, the scan driver150, the read-out circuit160, and the voltage supply unit170may be provided using various methods such as a chip on glass method, a chip on plastic method, a tape carrier package method, and a chip on film method.

FIG. 6is a detailed circuit diagram illustrating an exemplary embodiment of a sensor pixel SP shown inFIG. 5.FIG. 7is a timing diagram of scan signals illustrating exemplary operations of the sensor pixel SP shown inFIG. 6.

For convenience of explanation,FIG. 6illustrates the sensor pixel SP connected to an i−1-th scan line SLi−1, an i-th scan line SLi, an i+1-th scan line SLi+1, and a j-th output line Oj, where i is an integer of 2 or more and j is a natural number. In addition,FIG. 7illustrates a scan signal supplied to the i−1-th scan line SLi−1, a scan signal supplied to the i-th scan line SLi, and a scan signal supplied to an i+1-th scan line SLi+1.

Referring toFIG. 6, the sensor pixel SP may include the first capacitor C1and the sensor circuit250.

The sensor circuit250may include the first transistor T1, the second transistor T2, the third transistor T3, and the compensator unit270.

The first transistor T1may include a gate electrode connected to the sensor electrode210and control the output current Io which is output to the j-th output line Oj.

In an exemplary embodiment, for example, the first transistor T1may include the gate electrode connected to the first node N1and be connected between the second node N2and the third node N3in other electrodes.

More specifically, the first transistor T1may include the gate electrode connected to the first node N1, a first electrode connected to the second node N2, and a second electrode connected to the third node N3.

Therefore, the output current Io may vary in response to a gate voltage of the first transistor T1(e.g., a voltage of the first node N1).

The second transistor T2may be connected between the first voltage line181and the first transistor T1.

In an exemplary embodiment, for example, the second transistor T2may include a gate electrode connected to the i+1-th scan line SLi+1 and be connected between the first voltage line181and the second node N2in other electrodes.

More specifically, the second transistor T2may include the gate electrode connected to the i+1-th scan line SLi+1, a first electrode connected to the first voltage line181, and a second electrode connected to the second node N2.

Therefore, when a scan signal is supplied to the i+1-th scan line SLi+1, the second transistor T2may be turned on.

The third transistor T3may be connected between the first transistor T1and the j-th output line Oj.

In an exemplary embodiment, for example, the third transistor T3may include the gate electrode coupled to the i+1-th scan line SLi+1 and be connected between the third node N3and the j-th output line Oj in other electrodes.

More specifically, the third transistor T3may include the gate electrode coupled to the i+1-th scan line SLi+1, a first electrode coupled to the third node N3, and a second electrode coupled to the j-th output line Oj.

Therefore, when a scan signal is supplied to the i+1-th scan line SLi+1, the third transistor T3may be turned on.

The compensator unit270may compensate for a threshold voltage of the first transistor T1.

The compensator unit270may include the fourth transistor T4and the fifth transistor T5.

The fourth transistor T4may be connected between the second voltage line182and the common node N2of the first and second transistors T1and T2.

In an exemplary embodiment, for example, the fourth transistor T4may include a gate electrode coupled to the i-th scan line SLi and be connected between the second node N2and the second voltage line182in other electrodes.

More specifically, the fourth transistor T4may include the gate electrode coupled to the i-th scan line SLi, a first electrode connected to the second voltage line182, and a second electrode connected to the second node N2.

Therefore, when a scan signal is supplied to the i-th scan line SLi, the fourth transistor T4may be turned on.

The fifth transistor T5may be connected between the sensor electrode210and the common node N3of the first and third transistors T1and T3.

In an exemplary embodiment, for example, the fifth transistor T5may include a gate electrode connected to the i-th scan line SLi and be connected between the third node N3and the first node N1in other electrodes.

More specifically, the fifth transistor T5may include the gate electrode connected to the i-th scan line SLi, a first electrode connected to the first node N1, and a second electrode connected to the third node N3.

Therefore, when a scan signal is supplied to the i-th scan line SLi, the fifth transistor T5may be turned on.

The first capacitor C1may be connected between the first node N1and the i+1-th scan line SLi+1.

In an exemplary embodiment, for example, the sensor electrode210may be connected to the first node N1and the capacitor electrode220may be connected to the i+1-th scan line SLi+1.

The second capacitor C2may be formed when the user's finger300approaches the sensor pixel SP and function as a variable capacitor. The second capacitor C2may be regarded as being connected in series with the first capacitor C1at the first node N1in an equivalent circuit.

In an exemplary embodiment, the sensor circuit250may additionally include the sixth transistor T6to initialize the sensor pixel SP.

The sixth transistor T6may be connected between the third voltage line183and the sensor electrode210.

In an exemplary embodiment, for example, the sixth transistor T6may include a gate electrode connected to the i−1-th scan line SLi−1 and be connected between the third voltage line183and the first node N1in other electrodes.

More specifically, the sixth transistor T6may include the gate electrode connected to the i−1-th scan line SLi−1, a first electrode connected to the third voltage line183, and a second electrode connected to the first node N1.

Therefore, when a scan signal is supplied to the i−1-th scan line SLi−1, the sixth transistor T6may be turned on.

When the sixth transistor T6is turned on, a voltage of the sensor electrode210which amounts to a voltage of the first node N1may be changed to the third voltage Vint.

The first electrode of each of the transistors T1, T2, T3, T4, T5, and T6may be set to one of a source electrode and a drain electrode, and the second electrode of each of the transistors T1, T2, T3, T4, T5, and T6may be set to the other electrode of the source electrode and the drain electrode, which is different from the first electrode. In an exemplary embodiment, for example, when the first electrode is set to the source electrode, the second electrode may be set to the drain electrode.

Referring toFIG. 7, a scan signal may be supplied to the i−1-th scan line SLi−1 during the first period P1, a scan signal may be supplied to the i-th scan line SLi during the second period P2, and a scan signal may be supplied to the i+1-th scan line SLi+1 during the third period P3.

In other words, the i−1-th scan line SLi−1, the i-th scan line SLi, and the i+1-th scan line SLi+1 may correspond to the first scan line SL1, the second scan line SL2, and the third scan line SL3described above with reference toFIG. 4, respectively.

Therefore, the sensor pixel SP shown inFIG. 6may operate in the same manner as the sensor pixel SP shown inFIG. 3. A description of the operations of the sensor pixel SP described above with reference toFIG. 6is omitted.

FIG. 8is a diagram illustrating an exemplary embodiment of a fingerprint sensor100′.

Referring toFIG. 8, the fingerprint sensor100′ may include the sensor pixels SP, the first scan driver151, the second scan driver152, and the read-out circuit160.

The sensor pixels SP may be disposed on the substrate110. In an exemplary embodiment, the sensor pixels SP may be arranged in an n×m matrix form, where n and m are natural numbers. In addition, the sensor pixels SP may be connected to first scan lines S10to S1n, second scan lines S21to S2nand the output lines O1to Om.

The sensor pixels SP may receive scan signals through the first scan lines S10to S1nand the second scan lines S21to S2n. In addition, the sensor pixels SP may output a predetermined current corresponding to valleys and ridges of a fingerprint to the output lines O1to Om.

The first scan lines S10to S1nmay be disposed on the substrate110and extend in a first direction (e.g., X-axis direction), and each of the scan lines S11to S1nmay be connected to corresponding sensor pixels SP arranged in the first direction.

In addition, the second scan lines S21to S2nmay be disposed on the substrate110and extend in the first direction (e.g., X-axis direction), and each of the scan lines S21to S2nmay be connected to corresponding sensor pixels SP arranged in the first direction.

The output lines O1to Om may be disposed on the substrate110and extend in a second direction (e.g., Y-axis direction), and each of the output lines O1to Om may to be connected to corresponding sensor pixels SP arranged in the second direction.

However, the directions in which the first scan lines S10to S1n, the second scan lines S21to S2n, and the output lines O1to Om are arranged are not limited thereto, and may be changed.

In an exemplary embodiment, the sensor pixels SP may be connected to the voltage line180and receive a driving voltage from the voltage supply unit170.

The first scan driver151may supply scan signals to the sensor pixels SP through the first scan lines S10to S1n.

In an exemplary embodiment, for example, the first scan driver151may sequentially output scan signals to the first scan lines S10to S1n.

The scan signal may have a voltage level enough for a transistor receiving the scan signal to be turned on.

The first scan driver151may be directly mounted on the substrate110, or may be connected to the substrate110through a separate component such as a flexible printed circuit board, to be connected to the first scan lines S10to S1n.

The second scan driver152may supply scan signals to the sensor pixels SP through the second scan lines S21to S2n.

In an exemplary embodiment, for example, the second scan driver152may sequentially output scan signals to the second scan lines S21to S2n.

The second scan driver152may be directly mounted on the substrate110, or may be connected to the substrate110through a separate component such as a flexible printed circuit board, to be connected to the second scan driver152.

The read-out circuit160may receive signals (e.g., current) which is output from the sensor pixels SP through the output lines O1to Om.

In an exemplary embodiment, for example, when the sensor pixels SP sequentially receive scan signals, the sensor pixels SP may be selected in units of lines, and the read-out circuit160may sequentially receive currents output from the sensor pixels SP in units of lines.

The read-out circuit160may recognize fingerprint information by sensing current variations.

The read-out circuit160may be directly mounted on the substrate110, or may be connected to the substrate110through a separate component such as a flexible printed circuit board, to be output lines O1to Om.

The voltage supply unit170may supply a predetermined voltage to the sensor pixels SP through the voltage line180.

The voltage supply unit170may be directly mounted on the substrate110, or may be connected to the substrate110through a separate component such as a flexible printed circuit board, to be connected to the voltage line180.

As illustrated inFIG. 8, the first scan driver151, the second scan driver152, the read-out circuit160, and the voltage supply unit170may be separate components. However, at least some of the components may be integrated in alternative exemplary embodiment.

In addition, the first scan driver151, the second scan driver152, the read-out circuit160, and the voltage supply unit170may be provided using various methods such as a chip on glass method, a chip on plastic method, a tape carrier package method, and a chip on film method.

FIG. 9is a detailed diagram of a sensor pixel SP shown inFIG. 8. FIG.10is a timing diagram of scan signals illustrating exemplary operations of the sensor pixel SP shown inFIG. 9.

For convenience of explanation,FIG. 9illustrates the sensor pixel SP connected to an i−1-th first scan line S1i−1, an i-th first scan line S1i, an i-th second scan line S2i, and the j-th output line Oj, where i is an integer of 2 or more and j is a natural number. In addition,FIG. 10illustrates scan signals supplied to the i−1-th first scan line S1i−1, a scan signal supplied to the i-th second scan line S2i, and a scan signal supplied to the i-th first scan line S1i.

Referring toFIG. 9, the sensor pixel SP may include the first capacitor C1and the sensor circuit250.

The sensor circuit250may include the first transistor T1, the second transistor T2, the third transistor T3, and the compensator unit270.

The first transistor T1may include a gate electrode connected to the sensor electrode210and control the output current Io which is output to the j-th output line Oj.

In an exemplary embodiment, for example, the first transistor T1may include the gate electrode connected to the first node N1and be connected between the second node N2and the third node N3in other electrodes.

More specifically, the first transistor T1may include the gate electrode connected to the first node N1, a first electrode connected to the second node N2, and a second electrode connected to the third node N3.

The output current Io may change in response to a gate voltage of the first transistor T1(e.g., a voltage of the first node N1).

The second transistor T2may be connected between the first voltage line181and the first transistor T1.

In an exemplary embodiment, for example, the second transistor T2may be connected to a gate electrode connected to the i-th first scan line S1iand connected between the first voltage line181and the second node N2in other electrodes.

More specifically, the second transistor T2may include the gate electrode connected to the i-th first scan line S1i, a first electrode connected to the first voltage line181, and a second electrode connected to the second node N2.

When a scan signal is supplied to the i-th first scan line S1i, the second transistor T2may be turned on.

The third transistor T3may be connected between the first transistor T1and the j-th output line Oj.

In an exemplary embodiment, for example, the third transistor T3may include a gate electrode connected to the i-th first scan line S1iand be connected between the third node N3and the j-th output line Oj in other electrodes.

More specifically, the third transistor T3may include the gate electrode connected to the i-th first scan line S1i, a first electrode connected to the third node N3, and a second electrode connected to the j-th output line Oj.

Therefore, when a scan signal is supplied to the i-th first scan line S1i, the third transistor T3may be turned on.

The compensator unit270may compensate for a threshold voltage of the first transistor T1.

The compensator unit270may include the fourth transistor T4and the fifth transistor T5.

The fourth transistor T4may be connected between the second voltage line182and the common node N2of the first and second transistors T1and T2.

In an exemplary embodiment, for example, the fourth transistor T4may include a gate electrode connected to the i-th second scan line S2iand be connected between the second node N2and the second voltage line182in other electrodes.

More specifically, the fourth transistor T4may include the gate electrode connected to the i-th second scan line S2i, a first electrode connected to the second voltage line182, and a second electrode connected to the second node N2.

Therefore, when a scan signal is supplied to the i-th second scan line S2i, the fourth transistor T4may be turned on.

The fifth transistor T5may be connected between the sensor electrode210and the common node N3of the first and third transistors T1and T3.

In an exemplary embodiment, for example, the fifth transistor T5may include a gate electrode connected to the i-th second scan line S2iand be connected between the third node N3and the first node N1in other electrodes.

More specifically, the fifth transistor T5may include the gate electrode connected to the i-th second scan line S2i, a first electrode connected to the first node N1, and a second electrode connected to the third node N3.

Therefore, when a scan signal is supplied to the i-th second scan line S2i, the fifth transistor T5may be turned on.

The first capacitor C1may be connected between the first node N1and the i-th first scan line S1i.

In an exemplary embodiment, for example, the sensor electrode210may be connected to the first node N1and the capacitor electrode220may be connected to the i-th first scan line S1i.

The second capacitor C2may be formed when the user's finger300approaches the sensor pixel SP and function as a variable capacitor. The second capacitor C2may be considered as being connected in series with the first capacitor C1at the first node N1in an equivalent circuit.

In addition, the sensor circuit250may additionally include the sixth transistor T6to initialize the sensor pixel SP.

The sixth transistor T6may be connected between the third voltage line183and the sensor electrode210.

In an exemplary embodiment, for example, the sixth transistor T6may include a gate electrode connected to the i−1-th first scan line S1i−1 and be connected between the third voltage line183and the first node N1in other electrodes.

More specifically, the sixth transistor T6may include the gate electrode connected to the i−1-th first scan line S1i−1, a first electrode connected to the third voltage line183, and a second electrode connected to the first node N1.

Therefore, when a scan signal is supplied to the i−1-th first scan line S1i−1, the sixth transistor T6may be turned on.

When the sixth transistor T6is turned on, a voltage of the sensor electrode210which amounts to a voltage of the first node N1may be changed to the third voltage Vint.

The first electrode of each of the transistors T1, T2, T3, T4, T5, and T6may be set to one of a source electrode and a drain electrode, and the second electrode of each of the transistors T1, T2, T3, T4, T5, and T6may be set to the other electrode of the source electrode and the drain electrode, which is different from the first electrode. In an exemplary embodiment, for example, when the first electrode is set to the source electrode, the second electrode may be set to the drain electrode.

Referring toFIG. 10, a scan signal may be supplied to the i−1-th first scan line S1i−1 during the first period P1, a scan signal may be supplied to the i-th second scan line S2iduring the second period P2, and a scan signal is supplied to the i-th first scan line S1iduring the third period P3.

In other words, the i−1-th first scan line S1i−1, the i-th second scan line S2i, and the i-th first scan line S1imay correspond to the first scan line SL1, the second scan line SL2, and the third scan line SL3described with reference toFIG. 4, respectively.

Therefore, the sensor pixel SP shown inFIG. 9may also operate in the same manner as the sensor pixel SP shown inFIG. 3. Thus, operations of the sensor pixel SP shown inFIG. 9will be omitted.

FIGS. 11A to 11Dare detailed circuit diagrams illustrating various embodiments of voltage lines. A description will be made on the basis of the sensor pixel SP shown inFIG. 9. The same may apply to the other embodiments the sensor pixels SP described above.

Referring toFIG. 11A, in the case that the second voltage Vcp has the same value as the first voltage Vcom, one voltage line may be used as both the second voltage line182and the first voltage line181.

Therefore, the first voltage line181and the second voltage line182may refer to the same voltage line. In comparison with the above exemplary embodiments, the number of voltage lines may be reduced.

Referring toFIG. 11B, in the case that the third voltage Vint has the same value as first voltage Vcom, one voltage line may be used as both the third voltage line183and the first voltage line181.

Therefore, the first voltage line181and the third voltage line183may refer to the same voltage line. In comparison with the above exemplary embodiments, the number of voltage lines may be reduced.

Referring toFIG. 11C, in the case that the third voltage Vint has the same value as the second voltage Vcp, one voltage line may be used as both the third voltage line183and the second voltage line182.

Therefore, the second voltage line182and the third voltage line183may refer to the same voltage line. In comparison with the above exemplary embodiments, the number of voltage lines may be reduced.

Referring toFIG. 11D, in the case that the second voltage Vcp and the third voltage Vint have the same value as the first voltage Vcom, one voltage line may be used as the second voltage line182, the third voltage line183, and the first voltage line181.

Therefore, the first voltage line181, the second voltage line182and the third voltage line183may refer to the same voltage line. In comparison with the above exemplary embodiments, the number of voltage lines may be reduced.

According to the exemplary embodiments of the invention, it is possible to provide a sensor pixel capable of improving fingerprint sensing sensitivity by compensating for the difference in threshold voltage between sensor pixels.

The technical spirit of the invention have been described through the above exemplary embodiments in detail, but the exemplary embodiments have been described herein for purposes of illustration and does not limit the invention. Further, those skilled in the art will appreciate that various modifications may be made without departing from the scope and spirit of the invention.

The detailed description of the invention includes the description of the particular exemplary embodiments, but various modification is available within the scope without departing from the scope and the technical spirit of the invention. Therefore, the scope of the invention is not limited to the exemplary embodiments described, but shall be defined by the claims to be described below and the equivalents to the claims.