Light-emitting device

Abstract

To provide a light-emitting device in which the variation in luminance among pixels owing to the variation in threshold voltage can be reduced even when a transistor is normally on.SOLUTION: In a light-emitting device, the supply of current to a light-emitting element is controlled by use of a transistor having a normal gate electrode (first gate electrode) and a second gate electrode for controlling a threshold voltage. Further, the light-emitting device has one or more switches for selecting conduction or non-conduction between the first gate electrode of the transistor and a drain terminal. When the threshold voltage of the transistor is acquired, the first gate electrode of the transistor and the drain terminal are brought into conduction with the switch, and the threshold voltage of the transistor is shifted by controlling the potential of the second gate electrode.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a light-emitting device in which a transistor is provided in each pixel. [Background technology]

[0002] An active matrix light emitting device using a light emitting element usually includes at least a light emitting element and A transistor (switching transistor) that controls the input of image signals to pixels, and A transistor (driving transistor) that controls the current value supplied to the light emitting element according to the image signal. In the light-emitting device having the above configuration, the driver transistor Since the drain current is supplied to the light emitting element, the threshold voltage of the driving transistor between the pixels If variations occur in the light emitting element, the variations are reflected in the luminance of the light emitting element.

[0003] In order to prevent the variation in threshold voltage from affecting the brightness of the light-emitting element, the following Patent Document 1 The following describes a display device that corrects the threshold voltage of the TFT6, which is a driver element. are. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-280059 Summary of the Invention [Problem to be solved by the invention]

[0005] In the display device described in Patent Document 1, when detecting the threshold voltage, the TF Since the gate electrode and drain electrode of TFT6 are shorted, TFT6 operates in the saturation region. Therefore, in TFT6, the current flowing from the drain electrode to the source electrode becomes 0. When the potential difference between the gate electrode and the source electrode converges, it becomes equal to the threshold voltage, and the threshold voltage is obtained. It is possible.

[0006] However, in the display device described in Patent Document 1, when detecting the threshold voltage, the gate electrode and the drain Since the input electrode is short-circuited, the potential of the source electrode of TFT6 is higher than the potential of the gate electrode. In other words, the potential difference between the gate electrode and the source electrode does not have a negative value. Therefore, if TFT6 is normally off and its threshold voltage is 0V or higher, The potential difference between the gate electrode and the source electrode can be made equal to the threshold voltage. When the threshold voltage is negative, the potential difference between the gate electrode and the source electrode is large. Therefore, if TFT6 is normally on, , the threshold voltage cannot be obtained, and the brightness unevenness of the light-emitting element due to the variation in the threshold voltage is It is not possible to prevent the occurrence of

[0007] Based on the above-mentioned technical background, the present invention provides a method for manufacturing a normally-on transistor. The goal is to provide a light-emitting device that can suppress variations in brightness between pixels due to variations in threshold voltage. It shall be one of the following. [Means for solving the problem]

[0008] The light emitting device according to one aspect of the present invention includes a gate electrode (first gate electrode) and a threshold voltage A transistor having a second gate electrode for controlling the voltage is used to supply a voltage to the light emitting element. Furthermore, the light emitting device has a configuration for controlling the supply of a current. The gate electrode and the drain terminal are connected to a switch for selecting whether or not the gate electrode and the drain terminal are electrically connected to each other. When obtaining the threshold voltage of the transistor, the first gate of the transistor is connected to the switch. By controlling the potential of the second gate electrode and the drain terminal, The threshold voltage of the transistor is shifted.

[0009] The transistor that controls the supply of current to the light-emitting element is an insulated gate field effect transistor. Specifically, a first gate electrode, a second gate electrode, and a first gate electrode and a second gate electrode are a semiconductor film located between the second gate electrode and a first gate electrode located between the first gate electrode and the semiconductor film; and a second insulating film located between the second gate electrode and the semiconductor film. Furthermore, a source terminal and a drain terminal in contact with the semiconductor film may be added to the components. .

[0010] With the above configuration, the transistor that controls the supply of current to the light-emitting element is normally on. Even if the threshold voltage is obtained, the transistor can be normally off. The first gate electrode and the drain terminal of the transistor are electrically connected by the switch. That is, in the connected state, the potential difference between the first gate electrode and the source terminal is set equal to the threshold voltage. It can be done more efficiently. [Effects of the Invention]

[0011] In the light-emitting device according to one embodiment of the present invention, a transistor for controlling current supply to a light-emitting element is Even in the normally on state, the threshold voltage can be acquired. Therefore, the threshold voltage can be corrected. This reduces the luminance variation between pixels. [Brief explanation of the drawings]

[0012] [Figure 1] 1A and 1B are diagrams showing the structure of a pixel included in a light-emitting device. [Figure 2] An enlarged view of the circuit 12. [Figure 3] FIG. 2 is a diagram showing the configuration of a pixel portion. [Figure 4] 1A and 1B are diagrams showing the structure of a pixel included in a light-emitting device. [Figure 5] 4 is a timing chart showing the operation of a pixel. [Figure 6] FIG. 2 is a diagram schematically illustrating the operation of a pixel. [Figure 7] FIG. 2 is a diagram schematically illustrating the operation of a pixel. [Figure 8] FIG. 1 is a diagram schematically showing a state in which a capacitor element and a light-emitting element are connected in series. [Figure 9] 1A and 1B are diagrams showing the structure of a pixel included in a light-emitting device. [Figure 10] 1A and 1B are diagrams showing the structure of a pixel included in a light-emitting device. [Figure 11] Top view of a pixel. [Figure 12] FIG. [Figure 13] FIG. [Figure 14] FIG. [Figure 15] FIG. [Figure 16] Electronic equipment illustration. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention is not limited to the following description, and the embodiments and aspects thereof may be modified without departing from the spirit and scope of the present invention. It will be readily apparent to those skilled in the art that various modifications may be made to the details. However, the present invention should not be construed as being limited to the description of the following embodiments.

[0014] In this specification, a light-emitting device refers to a panel in which a light-emitting element is formed in each pixel, and This category includes modules in which ICs, including controllers, are mounted on the board.

[0015] (Embodiment 1) 1 shows a pixel configuration of a light-emitting device according to one embodiment of the present invention. The pixel 10 shown in FIG. A switch 11, a circuit 12 for controlling the amount of current according to an image signal, a switch 13, and The light emitting element 14 is supplied with the current from the circuit 12.

[0016] Specifically, the switch 11 determines whether the image signal applied to the terminal 18 is applied to the circuit 12 or not. For example, the switch 11 may be configured using one or more transistors. Alternatively, the switch 11 may be a capacitor in addition to one or more transistors. You may also use a child.

[0017] The circuit 12 includes a transistor 15 whose drain current is applied to a light emitting element 14, and a switch The switch 16 has a gate electrode ( Select the conduction or non-conduction between the drain terminal (shown as G) and the drain terminal (shown as D). The switch 16 can be configured using one or more transistors. The capacitance element 17 is a potential difference between the gate electrode and the source terminal (denoted by S) of the transistor 15. That is, the gate voltage Vgs is maintained. However, the capacitance element 17 is, for example, a transistor In cases where the gate capacitance formed between the gate electrode 15 and the active layer is sufficiently large, It is not necessary to provide the circuit 12 with either.

[0018] In one embodiment of the present invention, the transistor 15 has a normal gate electrode (first gate electrode). In addition, it has a back gate electrode (second gate electrode) for controlling the threshold voltage. The potential of the gate electrode of the transistor 15 is applied to the circuit 12 via the switch 11. The switch 13 is controlled in accordance with a signal. The switch 13 controls the supply of the potential at the terminal 21. For example, the switch 13 controls the supply of the potential at the terminal 21. Alternatively, the switch 13 may be configured using one or more transistors. In addition to the resistor, a capacitive element may be used.

[0019] The source terminal and the drain terminal of the transistor are determined by the channel type and The name changes depending on the level of the potential applied to each electrode. In a transistor with a low potential, the electrode to which the low potential is applied is called the source terminal, and the electrode to which the high potential is applied is called the The electrode to which the current is applied is called the drain terminal. The electrode to which a potential is applied is called the drain terminal, and the electrode to which a higher potential is applied is called the source terminal. For convenience, the source and drain terminals are referred to as fixed terminals in this specification. The connection relationship of the transistors may be explained on the assumption that The names of the source terminal and the drain terminal are interchanged according to the

[0020] The source terminal of a transistor is a source region that is part of the active layer, or a region that is connected to the active layer. Similarly, the drain terminal of a transistor is a part of the active layer. It means a drain region or a drain electrode connected to the active layer.

[0021] In this specification, connection means electrical connection, and a current, a voltage, or a potential is This corresponds to a state where the signal can be supplied or transmitted. Therefore, the connected state is a direct connection. does not necessarily refer to the state in which a current, voltage, or potential is available or transferable. To enable transmission, the signal is transmitted through elements such as wiring, conductive films, resistors, diodes, and transistors. This also includes situations where the connection is indirectly made via a direct connection.

[0022] Also, even if components that are independent on the circuit diagram are connected, For example, when a part of a wiring functions as an electrode, one conductive film is used for connecting a plurality of components. In this specification, the term "connection" refers to such a single conductive film. However, if a product combines the functions of multiple components, it is also included in this category.

[0023] In FIG. 1, the transistor 15 is an n-channel type. The source terminal of the transistor 15 is connected to the anode of the light-emitting element 14. The drain terminal of the transistor 15 is connected to the terminal 19, and the cathode of the light-emitting element 14 is , and is connected to the terminal 20. The potential of the terminal 19 is connected to the potential of the terminal 20. the threshold voltage Vthe of the transistor 11 and the threshold voltage Vth of the transistor 15. Therefore, according to the image signal given to the circuit 12 through the switch 11, When the value of the drain current of the transistor 15 is determined, the drain current is supplied to the light emitting element 14. As a result, the light emitting element 14 is brought into a light emitting state.

[0024] If the transistor 15 is a p-channel type, the source terminal of the transistor 15 is connected to the light emitting diode. The cathode of element 14 is connected to terminal 19. The drain terminal of transistor 15 is connected to terminal 19. The anode of the light emitting element 14 is connected to the terminal 20. The potential of the terminal 19 is the threshold voltage Vthe of the light emitting element 14 and the threshold voltage Vth of the transistor 15. The potential is higher than the sum of the voltage Vth and the n-th voltage Vth. As in the case of the p-channel type, the switching The drain current of the transistor 15 is controlled in accordance with the image signal given to the circuit 12 via the transistor 11. When the value of is determined, the drain current is supplied to the light emitting element 14, and the light emitting element 14 It becomes luminous.

[0025] In one embodiment of the present invention, the value of the drain current of the transistor 15 is determined in accordance with an image signal. Before the start of the operation, the switch 16 is used to connect the gate electrode and drain terminal of the transistor 15. In the conductive state, the threshold voltage of the transistor 15 is obtained. By determining the value of the drain current of the transistor 15 in accordance with the image signal, This prevents the variations in threshold voltage caused by the above-mentioned MOSFETs from affecting the value of the drain current. Cut.

[0026] In one embodiment of the present invention, as described above, the transistor 15 is connected to a normal gate electrode. In addition, the transistor 15 has a back gate electrode for controlling the threshold voltage. The threshold voltage Vth is controlled according to the potential applied to the gate electrode. Now, when the transistor 15 is normally on and the threshold voltage is obtained, By controlling the potential of the back gate electrode, the transistor 15 is normally off. The threshold voltage Vth of the transistor 15 is shifted. The amount of charge is the height of the potential of the back gate electrode, more specifically, the difference between the source terminal and the back gate It is controlled by the potential difference between the electrodes.

[0027] Specifically, when the transistor 15 is an n-channel type, its threshold voltage Vth is a negative value. Therefore, when the transistor 15 is an n-channel type, In this case, the potential of the back gate electrode is set to a value lower than the potential of the source terminal, thereby The voltage Vth is shifted in the positive direction to make the transistor 15 normally off. In the case of a diode type, if its threshold voltage Vth has a positive value, it is normally on. Therefore, when the transistor 15 is a p-channel type, the potential of the back gate electrode is By setting the value higher than the potential of the transistor, the threshold voltage Vth is shifted in the negative direction. Normally off.

[0028] It is difficult to obtain the threshold voltage when the transistor 15 is in a normally-on state. The reason for this will be explained by taking the case where the transistor 15 is an n-channel type as an example. .

[0029] FIG. 2 shows an enlarged view of the circuit 12. As shown in FIG. 2(A), the transistor 15 is an n-channel transistor. In the case of a transistor of the type, the potential of the terminal 19 is set to the transistor before the threshold voltage is obtained. Specifically, the potential of the source terminal of the transistor 15 is kept higher than the potential of the source terminal of the transistor 15. The threshold voltage Vth of the transistor 15 is added to the potential of the transistor 15. A potential difference Von is provided between the source terminal of the transistor 15 and the terminal 19. By turning on 16, the gate electrode and drain of transistor 15 Leave the terminals connected.

[0030] Therefore, as shown in FIG. 2A, the gate voltage Vgs of the transistor 15 is Therefore, the transistor 15 is turned on and a drain current flows. The gate electrode of the transistor 15 is connected to one electrode of the capacitor element 17. The source terminal of the transistor 15 is connected to the other electrode of the capacitance element 17. The on-state current flows only through the capacitance element 17.

[0031] With the above configuration, the charge stored in the capacitor 17 is released, and the solenoid of the transistor 15 is turned off. The potential of the source terminal of the transistor 15 rises. When the current starts to flow, it has a value equal to the potential difference Von, but when the potential of the source terminal rises, As it rises, it gradually becomes smaller.

[0032] When the transistor 15 is normally off, the gate voltage Vgs is equal to the threshold voltage Vt As the drain current approaches h, the threshold voltage Vth of the capacitance element 17 becomes 0 A. However, the transistor 15 is normally on. Therefore, in order to obtain the threshold voltage Vth, At this time, the potential of the gate electrode becomes lower than the potential of the source terminal, and the gate voltage Vgs has a negative value. However, as mentioned above, the potential at terminal 19 is The potential of the gate electrode is kept higher than the potential of the source terminal, so the potential of the gate electrode is Therefore, when the transistor 15 is normally on, the As shown, the gate voltage Vgs approaches 0V, and the source and drain terminals of transistor 15 When the potential difference between the terminals approaches 0V, the drain current of transistor 15 becomes 0A. Therefore, the capacitive element 17 does not hold the threshold voltage Vth.

[0033] In one embodiment of the present invention, the threshold voltage is obtained even if the transistor 15 is normally on. At this time, the threshold voltage Vth is shifted to make the transistor 15 normally off. By obtaining the threshold voltage, the voltage between the pixels can be obtained. It is possible to correct the existing variations in threshold voltage and reduce the variations in brightness between pixels. This can be done.

[0034] As described above, in one embodiment of the present invention, the gate of the transistor 15 is turned on by the switch 16. Any configuration is possible as long as the connection between the source electrode and the drain terminal can be controlled. , or if there is no capacitance element 17, the gate capacitance of the transistor 15 The gate voltage Vgs of the transistor 15 can be maintained. The drain current discharges the charge stored in the capacitor 17, and as a result, the transistor The circuit 12 has only to be configured so that the threshold voltage of the transistor 15 is held in the capacitor 17. In addition to the transistor 15, the switch 16, and the capacitance element 17, The circuit may further include other circuit elements such as resistors and inductors. As shown, other circuit elements include a transistor 15, a switch 16, a capacitor 17, and a terminal 19. It may be provided between them.

[0035] FIG. 3 illustrates an example of a structure of a pixel portion of a light-emitting device according to one embodiment of the present invention. The pixel section 40 has a plurality of pixels 10 arranged in a matrix. 0, a scanning line GL for selecting a plurality of pixels 10 for each row, and an image for the selected pixels 10 The pixels 10 have at least a few scanning lines GL and signal lines SL for transmitting signals. The signal lines SL are connected to at least one of the signal lines SL.

[0036] The type and number of the wirings are determined depending on the configuration, number and arrangement of the pixels 10. Specifically, in the case of the pixel section 40 shown in FIG. 3, the pixels 10 are arranged in a matrix of x columns and y rows. The signal lines SL1 to SLx and the scanning lines GL1 to GLy are connected to the pixel section 40. This shows an example where the

[0037] In one embodiment of the present invention, a pixel 10 in which the transistor 15 is normally on and a transistor Even if pixels 10 in which the normal state is 15 and pixels 10 in which the normal state is 15 are mixed in the pixel section 40, all The transistor 15 in all pixels 10 is normally off, and the threshold voltage is acquired. can be done.

[0038] Specifically, in the pixel section 40 shown in FIG. 3, the barrier of the transistor 15 is A potential for correcting the threshold voltage may be applied to the gate electrode of the same row. In the pixels, that is, in the pixels connected to the same scanning line GL, the transistor A potential for correcting the threshold voltage may be applied to the back gate electrode of the transistor 15. is expressed as follows for pixels in the same column, i.e., for a plurality of pixels connected to the same signal line SL: Even if a potential for correcting the threshold voltage is applied to the back gate electrode of the transistor 15, With the above configuration, the transistors 15 in all the pixels 10 of the pixel section 40 are normal. Even if the transistor 15 is normally on, the pixel 10 has a normally on transistor. Even when pixels 10 that are normally off and pixels 5 that are normally off are mixed in the pixel section 40, the threshold Voltage can be acquired.

[0039] (Embodiment 2) FIG. 4 illustrates an example of a specific structure of a pixel in a light-emitting device according to one embodiment of the present invention.

[0040] The pixel 10 shown in FIG. 4 includes a switch 11, a circuit 12, a switch 13, and 4, the pixel 10 has a switch 11 and a light-emitting element 14. The circuit 12 is composed of a transistor 15, a capacitor 17, and a transistor 30. The transistor 3 includes transistors 31 to 36 and a capacitor 38. 1 corresponds to the switch 16 shown in FIG. 1. The switch 13 is a transistor 37. It is composed of:

[0041] Note that FIG. 4 illustrates an example in which the transistor 15 is an n-channel transistor.

[0042] Specifically, in the pixel 10 shown in FIG. 4, the gate electrode of the transistor 30 is connected to the scanning line GLa. In addition, one of the source terminal and the drain terminal of the transistor 30 is connected to the signal line SL, and the other is connected to the gate electrode of transistor 15. The gate electrode of the transistor 31 is connected to the scanning line GLa. One of the terminal and drain terminal is connected to the gate electrode of the transistor 15, and the other is connected to the The gate electrode of transistor 32 is connected to the drain terminal of the scan line Also, one of the source terminal and drain terminal of the transistor 32 is connected to The transistor is connected to one electrode of the capacitance element 17, and the other electrode is connected to the wiring VLa. The gate electrode of the transistor 33 is connected to the scanning line GLb. One of the source and drain terminals is connected to the drain terminal of the transistor 15, and the other is The gate electrode of the transistor 34 is connected to the scanning line GLb. In addition, one of the source terminal and the drain terminal of the transistor 34 is connected to the transistor The other end is connected to one electrode of the capacitance element 17. The gate electrode of the transistor 35 is connected to the scanning line GLb. One of the source terminal and drain terminal of the transistor 15 and the capacitor 17 The other electrode is connected to the anode of the light-emitting element 14. The gate electrode of the transistor 36 is connected to the scanning line GLc. One of the source terminal and the drain terminal of the capacitor 17 is connected to the other electrode of the capacitor 17 and the source terminal of the transistor 15. One of the potentials of the capacitance element 38 is connected to the line VLb, and the other is connected to the line VLb. The electrode is connected to the back gate electrode of the transistor 15, and the other electrode is connected to the back gate electrode of the transistor 15. The gate electrode of the transistor 37 is connected to the source terminal of the scan line GLc. In addition, one of the source terminal and the drain terminal of the transistor 37 is connected to the transistor The other end is connected to the back gate electrode of the capacitor 15, and the other end is connected to the wiring VLc.

[0043] In the pixel 10 shown in FIG. 4, one of the source terminal and the drain terminal of the transistor 31 is connected to the other of the source terminal and drain terminal of transistor 30, The other of the source and drain terminals of transistor 1 is connected to the source and drain terminals of transistor 33. However, transistor 31 is connected to one of the terminals of transistor 15. It is sufficient if the connection between the electrode and the drain terminal can be controlled. As in pixel 10, one of the source and drain terminals of transistor 31 is connected to the transistor The other of the source and drain terminals of transistor 30 and the source and drain terminals of transistor 33 the other of the source and drain terminals of the transistor 31. may be connected to one of the source and drain terminals of transistor 34.

[0044] Next, the operation of the pixel 10 shown in FIG. 4 will be described.

[0045] 5 shows the potential Vdata applied to the signal line SL and the potentials of the scanning lines GLa, GLb, and GLc. The timing chart of the potentials applied to the lines GLc is shown as an example. The timing chart shown in FIG. 5 is based on the transistors 15, 30, and 1 shows an example in which all the transistors 37 are of the n-channel type.

[0046] As shown in FIG. 5, the operation of the pixel 10 is explained by dividing it into four periods, period t1 to period t4. The operation of the pixel 10 in each period is shown schematically in FIGS. 6 and 7, the transistors 30 to 35 functioning as switching elements are The resistor 37 is illustrated by a switch symbol.

[0047] Throughout the period t1 to the period t4, the potential Vano is applied to the wiring VLa, and the potential VLb is applied to the wiring VLb. A potential V0 is applied to the wiring VLc, a potential V1 is applied to the cathode of the light emitting element 14, The potential Vcat is given to the potential Vano and the potential Vcat. The difference in the potential Vcat is assumed to be greater than the threshold voltage Vthe of the light emitting element 14. Hereinafter, it is assumed that the threshold voltage Vthe of the light emitting element 14 is 0V.

[0048] First, as shown in FIG. 5, during a period t1, a low level signal is applied to the scanning lines GLa and GLb. A high-level potential is applied to the scanning line GLc. 36 and transistor 37 are turned on, and transistors 30 to 35 are turned off. This becomes:

[0049] FIG. 6A shows a schematic diagram of the operation of the pixel 10 during the period t1. The transistors 30 to 37 perform the switching described above. A potential V1 is applied to the back gate electrode of the transistor 15, and a potential V2 is applied to the source terminal of the transistor 15. Therefore, the potential difference between the back gate electrode and the source terminal is V1-V0. The potential difference is held in the capacitance element 38 .

[0050] In this embodiment, V1-V0 has a negative value. When the potential difference between the back gate electrode and the source terminal becomes V1-V0, the The threshold voltage Vth shifts in the positive direction. Even if the transistor 15 is normally on when the potential difference is 0, the threshold voltage Vth The voltage can be shifted in the direction of the reference voltage and set to 0 V or higher to make the device normally off.

[0051] Next, as shown in FIG. 5, during a period t2, a high-level potential is applied to the scanning line GLa. A low level potential is applied to the scanning lines GLb and GLc. Transistors 30 to 32 are turned on, and transistors 33 to 37 are turned off. Further, the signal line SL is supplied with the potential Vdata of the image signal.

[0052] FIG. 6B shows a schematic diagram of the operation of the pixel 10 during the period t2. The transistors 30 to 37 perform the switching as described above, and the signal When the potential Vdata of the image signal is applied to the line SL, the source terminal of the transistor 15 The potential of the other electrode of the capacitor 17 (potential of node A) becomes potential V0. The potential of one electrode of the capacitance element 17 (the potential of node B) becomes the potential Vano. The potential difference applied to the capacitance element 17 is Vano-V0.

[0053] The potential difference V1-V0 between the back gate electrode and the source terminal of the transistor 15 is The threshold voltage Vth of the transistor 15 is 0. V or more, and transistor 15 remains normally off.

[0054] In addition, the potential of the gate electrode of the transistor 15 (potential of node C) is equal to the potential Vdata. Therefore, the gate voltage Vgs of the transistor 15 becomes Vdata-V0. The potential Vdata of the image signal naturally varies depending on the image information contained in the image signal. However, the potential is higher than the potential V0 plus the threshold voltage Vth of the transistor 15. Therefore, the transistor 15 is turned on, and the capacitance The charge stored in element 17 is released.

[0055] Then, when the charge is released from the capacitance element 17, the voltage at the source terminal of the transistor 15 is The potential rises, and the gate voltage Vgs, which was the potential difference Vdata-V0 at the beginning of the period t2, As time passes, the capacitance element approaches the threshold voltage Vth. The potential difference applied to 17 is Vano-V0, but the charge is released from the capacitance element 17. As a result, the potential difference held in the capacitance element 17 becomes Vano-Vdata +Vth, and eventually transistor 15 turns off.

[0056] Therefore, in one embodiment of the present invention, even if the transistor 15 is normally on, The threshold voltage Vth of the transistor 15 is shifted to make the transistor 15 normally off. During the period t2, the threshold voltage Vth of the transistor 15 can be obtained.

[0057] In one embodiment of the present invention, the gate voltage Vgs of the transistor 15 is set to the threshold voltage Vth. For example, the gate voltage of the transistor 15 Vgs is smaller than the potential difference Vdata-V0 and larger than the threshold voltage Vth. At some point, the period t2 may be terminated.

[0058] Next, as shown in FIG. 5, during a period t3, the scanning lines GLa, GLb, and GL Therefore, the transistors 30 to 37 are It will be turned off.

[0059] 7A is a schematic diagram illustrating the operation of the pixel 10 during the period t3. The transistor 37 performs the switching as described above, and a potential difference V The back gate electrode of the transistor 15 is held at Vdata-Vth. The potential difference V1-V0 between the source terminal and the drain terminal is maintained in the capacitance element 38.

[0060] Next, as shown in FIG. 5, during a period t4, a high-level potential is applied to the scanning line GLb. A low level potential is applied to the scanning lines GLa and GLc. Transistors 33 to 35 are turned on, and transistors 30 to 32 and Transistor 36 and transistor 37 are turned off.

[0061] FIG. 7B shows a schematic diagram of the operation of the pixel 10 during the period t4. The transistors 30 to 37 perform the switching described above. The potential difference V1-V0 between the back gate electrode and the source terminal of the capacitor 38 is Therefore, the threshold voltage Vth of the transistor 15 is maintained at 0 V or higher. , the transistor 15 remains in a normally-off state.

[0062] Ideally, the potential difference Vano-Vdata+Vth held by the capacitance element 17 is , the gate voltage Vgs of the transistor 15, the gate electrode and source is given between the terminals.

[0063] In reality, the gate voltage Vgs of the transistor 15 is determined by the capacitance value of the capacitor 17. and the capacitance value of the light emitting element 14, it is not necessarily an ideal value, In other words, the potential difference is not necessarily Vano-Vdata+Vth. The potential VA of node A will be described in detail.

[0064] 8A shows a circuit diagram of the capacitance element 17. The capacitance element 17 has a capacitance value C1. As shown in FIG. 8A, at the end of the period t3, one electrode (n The electrode (corresponding to nodeB) is at potential Vano, and the other electrode (corresponding to nodeA) is Therefore, the potential difference Vano-Vdat a+Vth is maintained.

[0065] During the period t4, the capacitor 17 and the light emitting element 14 are connected in series via the transistor 35. 8B, the capacitance element 17 and the light emitting element 14 are connected in series. In FIG. 8B, the light emitting element 14 is assumed to be one of the capacitive elements. , the light emitting element 14 has a capacitance value C2. As shown in FIG. 8(B), during At the end of t4, node B is at a potential Vano, and the cathode of the light-emitting element 14 is at a potential V The other electrode of the capacitance element 17 and the anode (node) of the light-emitting element 14 are connected to each other. eA) is the potential VA.

[0066] The potential VA of the node A is determined by the capacitance C1 of the capacitor 17 and the capacitance C2 of the light-emitting element 14. Specifically, at the end of the period t4, the node A is at a potential VA Then, the gate voltage Vgs of the transistor 15 during the period t4 is expressed by the following equation 1. In addition, in the formula 1, the node A is at the potential Vdata-Vth during the period t3. This example illustrates a case where

[0067] Vgs=Vano-VA=C2(Vano-Vdata) / (C1+C2)+Vth (Formula 1)

[0068] At the end of the period t4, the ideal gate voltage Vgs is Vgs=Vano-Vda If the gate voltage Vgs has the above value, the threshold voltage of the transistor 15 is Even if there is a variation in the value voltage Vth, the influence of the variation is limited to the drain of the transistor 15. To make the gate voltage Vgs closer to the ideal value, from Equation 1, C2 / It is clear that it is desirable to make (C1+C2) close to 1. If the capacitance value C2 is sufficiently larger than the capacitance value C1 of the capacitance element 17, the gate voltage Vgs is can be made closer to the ideal value.

[0069] During the period t4, the gate voltage Vgs has a value close to Vano-Vdata+Vth. If so, the gate voltage Vgs of the transistor 15 is a value that takes into account the threshold voltage Vth. With the above configuration, the variation in the threshold voltage Vth of the transistor 15 is This can prevent the drain current supplied to the element 14 from being affected. Even if the transistor 15 deteriorates and the threshold voltage Vth changes, the change is not applied to the light emitting element 14. This prevents the drain current from being affected, thereby reducing brightness unevenness. This makes it possible to provide a light emitting device that displays high quality images.

[0070] It is not necessary to provide period t3, and it is also possible to transition directly from period t2 to period t4. However, by providing the period t3, the potential applied to the scanning line GLa is set to a high level. After the potential applied to the scanning line GLb is changed from low to high, With the above configuration, the potential held in the capacitance element 17 can be switched to a low level. The difference Vano - Vdata + Vth varies depending on the potential applied to the scan line GLb. This can prevent this from happening.

[0071] The above operation is performed for each row of pixels 10. Image signals are written to each row of pixels. An image is displayed by writing an image signal to all the pixels 10 of the pixel section row by row. do.

[0072] In the light-emitting device according to one embodiment of the present invention, for example, the semiconductor film of the transistor 15 is made of amorphous silicon. When a silicon or oxide semiconductor is used, even if the transistor 15 is normally on, the brightness This reduces unevenness in the image quality, enabling high-quality display.

[0073] It should be noted that the gate voltage Vgs at the end of the period t2 is not the threshold voltage Vth but the above-mentioned Thus, the potential difference Vdata is smaller than Vdata-V0 and is larger than the threshold voltage Vth. In this case, not only the variation in the threshold voltage of the transistor 15 but also the variation in the mobility of the light emitting element This will prevent the brightness of the image from being reflected in the brightness of the image. .

[0074] The drain current Id flowing through the light emitting element 14 is Id=kμ(Vgs−Vth) 2 / 2 where μ is the mobility of the transistor 15, k is the channel length of the transistor 15, It is a constant determined by the channel width and gate capacitance. When the mobility μ increases, the drain current Id flowing through the light emitting element 14 also increases. When the drain current Id flowing through the light emitting element 14 decreases, the drain current Id also decreases.

[0075] For example, if the potential of node A at the end of period t2 is smaller than Vdata-Vth, In this case, the gate voltage Vgs of the transistor 15 is set to a voltage Va. The voltage Va is the threshold voltage Vt The offset voltage Vb is added to h. In this case, at the end of the period t2, The capacitance element 17 holds a potential difference Vano-Vdata+Vb+Vth.

[0076] During the period t4, the potential difference held in the capacitance element 17 is directly transferred to the transistor. The gate voltage Vgs of the transistor 15 is the drain current Id during the period t4. d=kμ(Vano-Vdata+Vb) 2 / 2. Therefore, at the end of period t2 Even if the potential of node A at It can be seen that the fluctuations in the drain current value caused by variations in th are cancelled out.

[0077] On the other hand, if the transistor 15 is an n-channel type, the offset voltage Vb has a positive value. Therefore, the smaller the mobility μ, the larger the absolute value of the drain current Id. The larger the mobility μ, the smaller the absolute value of the drain current Id. is a correction term for correcting the variation of the drain current Id due to the mobility μ during the period t4. Even if the mobility μ becomes smaller, the drain current Id is prevented from decreasing. Even if the mobility μ increases, the drain current Id is prevented from increasing.

[0078] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0079] (Embodiment 3) FIG. 10 illustrates an example of a specific structure of a pixel in a light-emitting device according to one embodiment of the present invention.

[0080] The pixel 10 shown in FIG. 10 includes a switch 11, a circuit 12, a switch 13, and a 10, the pixel 10 has a switch 11 and a light-emitting element 14. The circuit 12 is composed of a transistor 15, a capacitor 17, and , transistors 52 to 55, capacitors 57 and 58. The transistor 52 corresponds to the switch 16 shown in FIG. is composed of transistor 56.

[0081] Note that FIG. 10 illustrates an example in which the transistor 15 is an n-channel type.

[0082] Specifically, in the pixel 10 shown in FIG. 10, the gate electrode of the transistor 51 is connected to the scanning line GLa In addition, one of the source terminal and the drain terminal of the transistor 51 is connected to the signal The other is connected to the gate electrode of the transistor 15 and one electrode of the capacitance element 17. The gate electrode of the transistor 52 is connected to the scanning line GLb. Also, one of the source terminal and drain terminal of transistor 52 is connected to the gate of transistor 15. The other terminal is connected to the drain terminal of the transistor 15. The gate electrode of the transistor 53 is connected to the scanning line GLb. In addition, one of the source terminal and the drain terminal of the transistor 53 is connected to the wiring VLb. , and the other is connected to the drain terminal of transistor 15. The gate of transistor 54 The electrode is connected to the scanning line GLc. One of the IN terminals is connected to the drain terminal of the transistor 15, and the other is connected to the wiring VLa. The gate electrode of the transistor 55 is connected to the scanning line GLd. One of the source terminal and the drain terminal of the transistor 55 is connected to the anode of the light-emitting element 14. The gate electrode of the transistor 56 is connected to the scanning line G One of the source terminal and the drain terminal of the transistor 56 is connected to One end is connected to the back gate electrode of the transistor 15, and the other end is connected to the wiring VLc. One electrode of the capacitor 57 is connected to the source terminal of the transistor 15 and the other electrode of the capacitor 17. One electrode of the light emitting element 14 is connected to the anode of the light emitting element 14, and the other electrode is connected to the wiring VLd. One electrode of the capacitor 58 is connected to the back gate electrode of the transistor 15. The other electrode is connected to the source terminal of transistor 15.

[0083] Next, the operation of the pixel 10 shown in FIG. 10 will be described.

[0084] The operation of the pixel 10 shown in FIG. 10 will be explained by dividing it into five periods, period t1 to period t5. It is possible.

[0085] Throughout the periods t1 to t5, the potential Vano is applied to the wiring VLa, and the potential VLb is applied to the wiring VLb. A potential V2 is applied to the wiring VLc, a potential V3 is applied to the wiring VLd, and a potential V4 is applied to the wiring VLc. A potential Vcat is applied to the cathode of the light emitting element 14. The difference between the potential Vano and the potential Vcat when the potential Vano is used as a reference is the threshold voltage Vth of the light emitting element 14. It is assumed that the threshold voltage Vthe of the light emitting element 14 is 0 V. Also, the potential V2 is higher than the potential Vcat and lower than the potential Vano. The potential V3 is lower than the potential Vcat and the potential V4. Also, the potential V4 is assumed to be lower than the potential Vcat.

[0086] First, in a period t1, the transistors 55 and 56 are turned on. Therefore, in the period t1, the transistors 51 to 54 are turned off. A potential V3 is applied to the back gate electrode, and a potential V4 is applied to the source terminal of the transistor 15. Therefore, the potential difference between the back gate electrode and the source terminal is V3-V4, and The potential difference is held in the capacitance element 58 .

[0087] The potential difference V3-V4 between the back gate electrode and the source terminal of the transistor 15 has a negative value. Therefore, the threshold voltage Vth of the transistor 15 shifts in the positive direction. When the potential difference between the gate electrode and the source terminal is 0V, the transistor 15 is normally on. However, the threshold voltage Vth is shifted in the positive direction, and the value is set to 0V or more, and the transistor is normally off. It is possible.

[0088] Next, in a period t2, the transistors 52, 53, and 55 transistor 51, transistor 54, and transistor 56 are turned off. The potential difference V3-V4 between the back gate electrode and the source terminal of the transistor 15 is Therefore, the threshold voltage Vth of the transistor 15 is kept below 0V. In the period t2, the signal line t1 is kept on, and the transistor 15 is kept in a normally-off state. The gate voltage Vgs of the transistor 15 has a potential difference V2-V4. The transistor 15 is turned on, and a drain current flows through the transistor 15.

[0089] Next, in a period t3, the transistors 52 and 53 are turned on. Transistor 51, transistors 54 to 56 are turned off. The potential difference V3-V4 between the gate electrode and the source terminal is maintained in the capacitor element 58. Therefore, the threshold voltage Vth of the transistor 15 is maintained at 0 V or higher. The transistor 15 remains in a normally-off state. The charge stored in element 17 is released, and the voltage at the source terminal of transistor 15 is The gate voltage Vgs, which was the potential difference V2-V4 at the beginning of the period t3, rises. However, as time passes, the voltage approaches the threshold voltage Vth, and the transistor 15 eventually turns off. becomes.

[0090] Therefore, in one embodiment of the present invention, even if the transistor 15 is normally on, The threshold voltage Vth of the transistor 15 is shifted to make the transistor 15 normally off. During the period t3, the threshold voltage Vth of the transistor 15 can be obtained.

[0091] In one embodiment of the present invention, the gate voltage Vgs of the transistor 15 is set to the threshold voltage Vth. For example, the gate voltage of the transistor 15 is When Vgs is smaller than the potential difference V2-V4 and larger than the threshold voltage Vth, With the above configuration, in the case of the pixel 10 shown in FIG. As in the case of the above, not only the variation in the threshold voltage Vth but also the variation in the mobility of the transistor 15 occurs. It is also possible to correct the

[0092] Next, in a period t4, the transistor 51 is turned on, and the transistors 52 to 54 are turned on. The signal line SL is supplied with the potential Vdata of the image signal. The potential difference V3-V4 between the back gate electrode and the source terminal of the transistor 15 is Therefore, the threshold voltage Vth of the transistor 15 is 0 V or more. The transistor 15 is maintained in a normally-off state. When a potential Vdata is applied to the gate electrode of the transistor 15, the gate voltage Vg Ideally, s is the potential difference Vdata-Vcat+Vth.

[0093] In reality, the gate voltage Vgs of the transistor 15 is determined by the capacitance value of the capacitor 17. and the capacitance value of the capacitor 57 and the light emitting element 14. The potential difference is not necessarily the ideal value, i.e., Vdata-Vcat+Vth. 4, the composite pixel 10 is composed of the capacitance element 57 and the light emitting element 14. If the capacitance value of the capacitor is sufficiently larger than the capacitance value of the capacitive element 17, the gate voltage Vgs is increased. This can approach the ideal value described above.

[0094] Next, in a period t5, the transistor 54 is turned on, and the transistors 51 to 54 are turned on. Transistor 53, transistor 55, and transistor 56 are turned off. The potential difference V3-V4 between the back gate electrode and the source terminal is held in the capacitance element 58. Therefore, the threshold voltage Vth of the transistor 15 is maintained at 0 V or higher. Sta 15 remains in a normally off state.

[0095] The transistor 15 also generates a drain current whose value is determined according to its gate voltage Vgs. is supplied to the light emitting element 14. The light emitting element 14 controls its light emitting power in accordance with the value of the drain current. The larger the drain current, the higher the brightness of the light emitting element 14. The smaller the current, the lower the luminance of the light emitting element 14 becomes.

[0096] During the period t4, the gate voltage Vgs has a value close to Vdata-Vcat+Vth. If so, the gate voltage Vgs of the transistor 15 is a value that takes into account the threshold voltage Vth. With the above configuration, during the period t5, the threshold voltage Vth It is possible to prevent the variation in the drain current supplied to the light emitting element 14 from affecting the drain current. Alternatively, even if the transistor 15 deteriorates and the threshold voltage Vth changes, the above change can be prevented. This can prevent the influence of the voltage Vcc on the drain current supplied to the light emitting element 14. As a result, it is possible to provide a light emitting device that can reduce unevenness in brightness and display high quality images.

[0097] The above operation is performed for each row of the pixels 10. The image signal is sent to all the pixels 10 in the pixel section for each row. By writing the number, the image is displayed.

[0098] In the light-emitting device according to one embodiment of the present invention, for example, the semiconductor film of the transistor 15 is made of amorphous silicon. When a silicon or oxide semiconductor is used, even if the transistor 15 is normally on, the brightness This reduces unevenness in the image quality, enabling high-quality display.

[0099] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0100] (Fourth embodiment) Taking the pixel 10 shown in FIG. 4 as an example, the pixel layout of the light-emitting device according to one embodiment of the present invention will be described. The above-described structure will be described with reference to FIGS. 11 and 12. FIG. 11 is an example of a top view of a pixel. 12 is a diagram showing the top view of FIG. 11 along the dashed lines A1-A2 and A3-A4. This corresponds to an example of a cross-sectional view. However, in order to clearly show the pixel layout, The top view of the pixel is shown with various insulating films omitted. To clearly show the layout of the conductive elements, the EL layer and the cathode are omitted. A plan view is shown.

[0101] In the pixel shown in FIGS. 11 and 12, the transistor 30 is connected to a substrate 80 having an insulating surface. A conductive film 801 functioning as a gate electrode and a gate insulating film 801 are formed on the conductive film 801. 2, and a semiconductor film 80 located on the gate insulating film 802 at a position where the semiconductor film 80 is overlapped with the conductive film 801. 3, and a conductive film that functions as a source terminal or a drain terminal and is located on the semiconductor film 803. The conductive film 801 also functions as a scan line GLa. The conductive film 804 also functions as a signal line SL.

[0102] The transistor 34 has a gate electrode formed on a substrate 800 having an insulating surface. a conductive film 806, a gate insulating film 802 on the conductive film 806, and a position where the conductive film 806 overlaps the gate insulating film 802. In the figure, a semiconductor film 807 located on a gate insulating film 802 and a source terminal or a drain terminal The conductive film 805 and the conductive film 808 function as terminals and are located over the semiconductor film 807. The conductive film 806 also functions as the scanning line GLb.

[0103] The transistor 33 has a gate electrode formed on a substrate 800 having an insulating surface. a conductive film 806, a gate insulating film 802 on the conductive film 806, and a position where the conductive film 806 overlaps the gate insulating film 802. In the figure, a semiconductor film 809 located on a gate insulating film 802 and a source terminal or a drain terminal The conductive film 810 and the conductive film 811 function as terminals and are located over the semiconductor film 809. The conductive film 811 also functions as the wiring VLa.

[0104] The transistor 32 has a gate electrode formed on a substrate 800 having an insulating surface. A conductive film 801, a gate insulating film 802 on the conductive film 801, and a position where the conductive film 801 overlaps the gate insulating film 802 8, a semiconductor film 812 located on the gate insulating film 802 and a source terminal or a drain terminal The conductive film 811 and the conductive film 808 function as terminals and are located over the semiconductor film 812. do.

[0105] The transistor 31 has a gate electrode formed on a substrate 800 having an insulating surface. A conductive film 801, a gate insulating film 802 on the conductive film 801, and a position where the conductive film 801 overlaps the gate insulating film 802 In the figure, a semiconductor film 813 located on the gate insulating film 802 and a source terminal or a drain terminal The conductive film 810 and the conductive film 814 function as terminals and are located over the semiconductor film 813. The conductive film 814 is connected to the conductive film 805 via a conductive film 815.

[0106] The transistor 35 has a gate electrode formed on a substrate 800 having an insulating surface. a conductive film 806, a gate insulating film 802 on the conductive film 806, and a position where the conductive film 806 overlaps the gate insulating film 802. 8, a semiconductor film 816 located on the gate insulating film 802 and a source terminal or a drain terminal The conductive film 817 and the conductive film 818 function as terminals and are located over the semiconductor film 816. do.

[0107] The transistor 36 has a gate electrode formed on a substrate 800 having an insulating surface. a conductive film 823, a gate insulating film 802 on the conductive film 823, and a position overlapping with the conductive film 823 8, a semiconductor film 824 located on the gate insulating film 802 and a source terminal or a drain terminal The conductive film 818 and the conductive film 825 function as terminals and are located over the semiconductor film 824. The conductive film 823 also functions as the scanning line GLc. The conductive film 830 functions as b.

[0108] The transistor 37 has a gate electrode formed on a substrate 800 having an insulating surface. a conductive film 823, a gate insulating film 802 on the conductive film 823, and a position overlapping with the conductive film 823 8, a semiconductor film 826 located on the gate insulating film 802 and a source terminal or a drain terminal The conductive film 827 and the conductive film 828 function as terminals and are located over the semiconductor film 826. The conductive film 828 is connected to a conductive film 829 that functions as the wiring VLc.

[0109] The transistor 15 has a gate electrode formed on a substrate 800 having an insulating surface. a conductive film 831, a gate insulating film 802 on the conductive film 831, and a position where the conductive film 831 overlaps the gate insulating film 802. 8, a semiconductor film 832 located on the gate insulating film 802 and a source terminal or a drain terminal The conductive film 810 and the conductive film 818 function as terminals and are located over the semiconductor film 832. Furthermore, the transistor 15 includes an insulating film stacked in this order on the conductive film 810 and the conductive film 818. The insulating film 820 and the insulating film 821 are formed on the insulating film 820 and the insulating film 821. A conductive film 833 functioning as a back gate electrode is provided in a position overlapping with the conductive film 32. The conductive film 833 is connected to the conductive film 827. The conductive film 831 is connected to the conductive film 814. It has been done.

[0110] The capacitor 17 is formed on a substrate 800 having an insulating surface, and includes a conductive film 834 and a conductive film 834. The gate insulating film 802 and the conductive film 834 are overlapped with each other. The conductive film 834 is connected to the conductive film 808.

[0111] The capacitor 38 is formed on a substrate 800 having an insulating surface, a conductive film 835, and a The gate insulating film 802 and the conductive film 835 are located on the gate insulating film 802 at positions where the conductive film 835 overlaps the gate insulating film 802. The conductive film 835 is connected to the conductive film 827.

[0112] A conductive film 819 functioning as an anode is provided over the insulating film 821. The conductive film 819 is electrically connected to the insulating film 820 through an opening 822 formed in the insulating film 821. It is connected to the membrane 817.

[0113] In addition, an insulating film 836 having an opening through which a part of the conductive film 819 is exposed is formed on the conductive film 81 9 and the insulating film 821. In this example, an EL layer 837 and a conductive film 838 functioning as a cathode are stacked in this order. The area where the conductive film 819, the EL layer 837, and the conductive film 838 overlap is , corresponds to the light emitting element 14.

[0114] In one embodiment of the present invention, the semiconductor film 803, the semiconductor film 807, the semiconductor film 809, and the semiconductor film 812, semiconductor film 813, semiconductor film 816, semiconductor film 824, semiconductor film 826, or The semiconductor film 832 is amorphous, microcrystalline, polycrystalline, or single crystalline silicon or germanium. The semiconductor may include a semiconductor such as a silicon semiconductor, or may include a wide-gap semiconductor such as an oxide semiconductor. It's okay to be.

[0115] Light-emitting devices made up of transistors containing amorphous silicon or oxide semiconductors are considered to be fifth-generation It can handle glass substrates of 1200mm wide x 1300mm long or larger, resulting in high productivity. However, the cost of the transistors containing amorphous silicon and oxide semiconductors is low. Transistors are generally unipolar and tend to be normally on. In one embodiment of the present invention, the transistor 15 that controls the supply of current to the light-emitting element 14 is Even if the transistor is normally on, it can be made normally off by shifting its threshold voltage. Therefore, a transistor having amorphous silicon or an oxide semiconductor can be obtained. Even in a light-emitting device configured with a photodiode, it is possible to reduce uneven brightness and ensure high-quality display. This can be done.

[0116] The semiconductor film 803, the semiconductor film 807, the semiconductor film 809, the semiconductor film 812, and the semiconductor film 8 13, the semiconductor film 816, the semiconductor film 824, the semiconductor film 826, or the semiconductor film 832 is non semiconductors such as silicon or germanium, which may be amorphous, microcrystalline, polycrystalline or monocrystalline. In this case, an impurity element that imparts one conductivity is added to the semiconductor film to form a source region or For example, phosphorus or arsenic is added to the above semiconductor to form an impurity region that functions as a drain region. By adding it to a conductive film, an impurity region with n-type conductivity can be formed. In addition, for example, by adding boron to the semiconductor film, an impurity region having p-type conductivity is formed. can be formed.

[0117] Semiconductor film 803, semiconductor film 807, semiconductor film 809, semiconductor film 812, semiconductor film 813, The semiconductor film 816, the semiconductor film 824, the semiconductor film 826, or the semiconductor film 832 is an oxide semiconductor. If a conductor is included, dopants may be added to the semiconductor film to form source or drain regions. An impurity region that functions as an insulating region may be formed. The dopant is added by ion implantation. The dopant can be a rare gas such as helium, argon, or xenon. Group 15 atoms such as arsenic, antimony, and nitrogen, phosphorus, arsenic, and antimony can be used. For example, when nitrogen is used as a dopant, the concentration of nitrogen atoms in the impurity region is 5×10 1 9 / cm 3 More than 1×10 22 / cm 3 It is desirable that the following:

[0118] Silicon semiconductors are grown by vapor deposition methods such as plasma CVD or sputtering. Amorphous silicon produced by the laser annealing method, and amorphous silicon The surface layer is formed by implanting hydrogen ions into polycrystalline silicon and single crystal silicon wafers. For example, single crystal silicon from which a portion has been peeled off can be used.

[0119] The oxide semiconductor contains at least indium (In) or zinc (Zn). It is preferable that the oxide semiconductor contains In and Zn. As a stabilizer to reduce the variation in the electrical characteristics of the transistors In addition, it is preferable to contain gallium (Ga). Also, tin (S) is used as a stabilizer. It is preferable that the stabilizer contains hafnium (Hf). It is also preferable that the stabilizer contains aluminum (Al). It's nice.

[0120] Other stabilizers include lanthanides such as lanthanum (La) and cerium ( Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), hol Mium (Ho), Erbium (Er), Thulium (Tm), Ytterbium (Yb), Ru It may contain one or more of tetraethion (Tetrium) (Lu).

[0121] For example, oxide semiconductors include indium oxide, tin oxide, zinc oxide, and oxides of binary metals. In-Zn oxides, Sn-Zn oxides, Al-Zn oxides, Zn-Mg oxides Oxides, Sn-Mg oxides, In-Mg oxides, In-Ga oxides, ternary metal oxides In-Ga-Zn oxide (also written as IGZO), In-Al-Zn oxide Oxides, In-Sn-Zn oxides, Sn-Ga-Zn oxides, Al-Ga-Zn oxides oxides, Sn-Al-Zn oxides, In-Hf-Zn oxides, In-La-Zn oxides In-Ce-Zn oxides, In-Pr-Zn oxides, In-Nd-Zn oxides , In-Sm-Zn oxide, In-Eu-Zn oxide, In-Gd-Zn oxide, In-Tb-Zn oxide, In-Dy-Zn oxide, In-Ho-Zn oxide, I n-Er-Zn oxide, In-Tm-Zn oxide, In-Yb-Zn oxide, In -Lu-Zn ​​oxides, In-Sn-Ga-Zn oxides, which are oxides of quaternary metals, I n-Hf-Ga-Zn oxide, In-Al-Ga-Zn oxide, In-Sn-Al- Zn-based oxide, In-Sn-Hf-Zn-based oxide, In-Hf-Al-Zn-based oxide are used. The oxide semiconductor may contain silicon.

[0122] For example, an In-Ga-Zn oxide means an oxide containing In, Ga, and Zn. The ratio of In, Ga, and Zn is not important. In-Ga-Zn oxides have a sufficiently high resistance in the absence of an electric field, and It is possible to sufficiently reduce the current and the mobility is high, so it is suitable for use in semiconductor devices. It is suitable as a semiconductor material.

[0123] For example, In:Ga:Zn=1:1:1 (=1 / 3:1 / 3:1 / 3) or In:G In-Ga-Zn oxide with an atomic ratio of a:Zn=2:2:1 (=2 / 5:2 / 5:1 / 5) Alternatively, In:Sn:Zn=1: 1:1(=1 / 3:1 / 3:1 / 3), In:Sn:Zn=2:1:3(=1 / 3:1 / 6:1 / 2) or In:Sn:Zn=2:1:5(=1 / 4:1 / 8:5 / 8) It is preferable to use an In-Sn-Zn oxide with a molecular ratio or an oxide with a composition close to that.

[0124] For example, high mobility can be obtained relatively easily with In-Sn-Zn oxides. Therefore, even in In-Ga-Zn oxides, the mobility can be increased by reducing the defect density in the bulk. It can be done.

[0125] In addition, impurities such as water or hydrogen, which act as electron donors (donors), are reduced, and the acid The oxide semiconductor (purified Oxide) is highly purified by reducing the electron vacancies. An i-type semiconductor is an intrinsic semiconductor or is very close to an i-type semiconductor. Therefore, the transistor including the oxide semiconductor has a characteristic of having an extremely low off-state current. The band gap of the oxide semiconductor is 2 eV or more, preferably 2.5 eV or more. The concentration of impurities such as moisture and hydrogen is sufficiently reduced. and a highly purified oxide semiconductor film having reduced oxygen vacancies is used. This allows the off-state current of the transistor to be reduced.

[0126] Specifically, the off-state current of a transistor using a highly purified oxide semiconductor for a semiconductor film is low. For example, when the channel width is 1×10 6 μm Even with a device with a channel length of 10 μm, the voltage between the source and drain terminals (drain voltage When the voltage is in the range of 1V to 10V, the off-state current is measured by a semiconductor parameter analyzer. Below the limit, i.e., 1×10 -13 In this case, the characteristics of the The off-state current normalized by the channel width of the transistor was found to be 100 zA / μm or less. In addition, by connecting the capacitance element and the transistor, the current flowing into or out of the capacitance element can be reduced. The off-state current was measured using a circuit that controls the outflow of charge using the transistor. In the measurement, a highly purified oxide semiconductor film was used for the channel formation region of the transistor. The off-state current of the transistor is measured from the change in the amount of charge per unit time of the capacitor. As a result, when the voltage between the source terminal and the drain terminal of the transistor is 3V, several tens of It was found that an even lower off-state current of 0.5A / μm could be obtained. In a transistor using an oxide semiconductor film having a crystallinity of 0.1 μm or less for a channel formation region, the off-state current is This is significantly lower than that of a silicon-based transistor.

[0127] Unless otherwise specified, the off-state current in this specification refers to the off-state current in an n-channel transistor. In this case, when the drain terminal is at a higher potential than the source terminal and gate electrode, When the potential of the gate electrode is 0 V or less with respect to the potential of the source terminal, The off-state current in this specification means a current that flows between the gate and drain terminals. In a p-channel transistor, the drain terminal is lower than the source terminal and gate electrode. When the potential of the gate electrode is 0 V, the potential of the gate electrode is 0 V. This refers to the current that flows between the source and drain terminals when V is equal to or greater than V.

[0128] For example, the oxide semiconductor film may contain In (indium), Ga (gallium), and Zn ( It can be formed by sputtering using a target containing In-Ga- When the Zn-based oxide semiconductor film is formed by sputtering, it is preferable that the atomic ratio of In :Ga:Zn=1:1:1, 4:2:3, 3:1:2, 1:1:2, 2:1:3, or An In-Ga-Zn oxide target with an atomic ratio of 3:1:4 is used. an oxide semiconductor film is formed using an In-Ga-Zn oxide target having In addition, polycrystals or CAAC-OS, which will be described later, are easily formed. The filling rate of the target containing Zn is 90% or more and 100% or less, preferably 95% or more and 100% or less. The oxide semiconductor film formed by using a target with a high filling rate is less than 0%. becomes a dense film.

[0129] When an In-Zn oxide material is used as the oxide semiconductor, The atomic ratio of the metal elements is In:Zn=50:1 to 1:2 (converted to molar ratio, In2 O3:ZnO=25:1 to 1:4), preferably In:Zn=20:1 to 1:1 (molar number In terms of ratio, In2O3:ZnO=10:1 to 1:2), more preferably In:Zn = 1.5:1 to 15:1 (converted to mole ratio In2O3:ZnO = 3:4 to 15:2 For example, a target used to form an oxide semiconductor film made of an In-Zn oxide is When the atomic ratio is In:Zn:O=X:Y:Z, Z>1.5X+Y. The ratio of Zn By keeping the ratio within the above range, it is possible to achieve an improvement in mobility.

[0130] Specifically, the oxide semiconductor film is formed by holding the substrate in a treatment chamber maintained in a reduced pressure state. The remaining moisture in the processing chamber is removed, and the sputtering gas from which hydrogen and moisture have been removed is introduced. During film formation, the substrate temperature is preferably 100°C or higher and 600°C or lower. Preferably, the temperature may be 200° C. or higher and 400° C. or lower. This allows the concentration of impurities contained in the formed oxide semiconductor film to be reduced. Damage caused by tarring is reduced. To remove residual moisture in the processing chamber, an adsorption type It is preferable to use a vacuum pump. For example, a cryopump, an ion pump, a titanium sa It is preferable to use a displacement pump. Also, a turbo pump is used as the exhaust means. A cold trap may be added to the process chamber. Then, for example, hydrogen atoms, compounds containing hydrogen atoms such as water (H2O) (more preferably carbon Since the exhaust gas contains oxygen (including compounds containing hydrogen atoms), the oxide semiconductor film formed in the treatment chamber is The concentration of impurities contained in the material can be reduced.

[0131] Note that the oxide semiconductor film formed by sputtering or the like contains moisture or hydrogen ( The water or hydrogen atoms form donor levels. Therefore, in one embodiment of the present invention, To reduce impurities such as water or hydrogen in semiconductor films (dehydration or dehydrogenation) , an oxide semiconductor film is heated under a reduced pressure atmosphere, an inert gas atmosphere such as nitrogen or a rare gas, or an acid atmosphere. under nitrogen gas atmosphere or ultra-dry air (CRDS (cavity ring-down laser spectroscopy) When measured using a dew point meter, the moisture content is 20 ppm (-55°C in dew point equivalent) or less. The heat treatment is carried out in an atmosphere of air, preferably 1 ppm or less, preferably 10 ppb or less. To administer.

[0132] By performing heat treatment on the oxide semiconductor film, moisture or hydrogen in the oxide semiconductor film is released. Specifically, the substrate temperature is 250° C. or higher and 750° C. or lower, preferably 400° C. or higher. For example, the heat treatment may be performed at 500°C for 3 to 6 minutes. If the RTA method is used for the heat treatment, dehydration or dehydrogenation can be carried out in a short time. Therefore, processing can be performed at temperatures exceeding the strain point of the glass substrate.

[0133] Note that the heat treatment causes oxygen to be released from the oxide semiconductor film and oxygen to be left in the oxide semiconductor film. Therefore, in one embodiment of the present invention, a gate electrode in contact with the oxide semiconductor film is An insulating film containing oxygen is used as an insulating film such as a gate insulating film. After the insulating film is formed, heat treatment is performed, whereby oxygen is supplied from the insulating film to the oxide semiconductor film. With the above structure, oxygen vacancies that serve as donors are reduced, and oxygen atoms contained in the oxide semiconductor film are The stoichiometric composition of the oxide semiconductor can be satisfied. As a result, the oxide semiconductor film is made i-type. This reduces variations in the electrical characteristics of transistors due to oxygen vacancies, Therefore, it is possible to realize improved electrical properties.

[0134] Note that the heat treatment for supplying oxygen to the oxide semiconductor film is performed using nitrogen, ultra-dry air, or dilute In a gas (argon, helium, etc.) atmosphere, preferably at 200°C to 400°C The temperature is, for example, 250°C or higher and 350°C or lower. It is desirable that the concentration is not more than 1 ppm, and more preferably not more than 10 ppb.

[0135] The oxide semiconductor may be amorphous (non-crystalline) or crystalline. In the latter case, it may be a single crystal, a polycrystal, or a structure having a partial crystallinity. It may be composed of an amorphous material, or may have a structure containing a crystalline portion in an amorphous material, or may be a non-amorphous material. An example of a structure having partial crystallinity is a structure having a c-axis orientation and an ab-plane, It has a triangular or hexagonal atomic arrangement when viewed from the direction perpendicular to the plane or interface, and the atoms perpendicular to the c axis When viewed from the perpendicular direction, metal atoms are arranged in layers or metal atoms and oxygen atoms are arranged in layers, and In the b-plane, the oxide crystals contain crystals with different a-axis or b-axis orientations (rotated around the c-axis). Physical semiconductor (CAAC-OS:C Axis Aligned Crystalline Oxide Semiconductor.) may also be used.

[0136] In a broad sense, CAAC-OS is a non-single crystal that has three crystals perpendicular to the ab plane. The atomic arrangement is a square, hexagonal, equilateral triangle, or regular hexagonal, and the direction is perpendicular to the c-axis direction. From this perspective, oxides containing a phase in which metal atoms are arranged in layers, or metal atoms and oxygen atoms are arranged in layers, are called say.

[0137] The CAAC-OS is not a single crystal, but it is not formed solely from amorphous material. Although CAAC-OS contains crystalline parts, the boundary between one crystalline part and another crystalline part cannot be clearly determined. Sometimes it's impossible to distinguish.

[0138] A part of oxygen atoms constituting the CAAC-OS may be substituted with nitrogen atoms. The c-axes of the individual crystals constituting the CAAC-OS are aligned in a certain direction (e.g., the substrate The CAAC-OS surface may be aligned perpendicular to the surface of the CAAC-OS. The normal of the ab plane of each crystal part constituting the OS is in a certain direction (for example, CAAC-OS). The direction may be perpendicular to the substrate surface on which the CAAC-OS is formed, or perpendicular to the surface of the CAAC-OS.

[0139] Depending on the composition, CAAC-OS may or may not be transparent to visible light. It may not be there.

[0140] An example of such a CAAC-OS is a film-like CAAC-OS. When observed from a direction perpendicular to the substrate surface, a triangular or hexagonal atomic arrangement is observed. When the cross section of the film is observed, metal atoms or metal atoms and oxygen atoms (or nitrogen atoms) Also included are crystals in which the layered arrangement of the following is observed.

[0141] The CAAC-OS film can be formed by sputtering a polycrystalline oxide semiconductor target. The sputtering target is used to form a film by sputtering. Upon impact, the crystalline regions contained in the sputtering target cleave from the ab plane, forming a -b Peels off as flat or pellet-shaped sputtered particles with surfaces parallel to the plane In this case, the plate-like sputtered particles may be transferred to the substrate while maintaining their crystalline state. By reaching the plate, a CAAC-OS film can be formed.

[0142] In addition, the following conditions are preferably applied to form the CAAC-OS film.

[0143] By reducing the amount of impurities mixed in during film formation, it is possible to prevent the crystal state from being destroyed by impurities. For example, the concentration of impurities (hydrogen, water, carbon dioxide, nitrogen, etc.) present in the processing chamber can be In addition, the impurity concentration in the deposition gas can be reduced. A deposition gas at a temperature of -80°C or lower, preferably -100°C or lower, is used.

[0144] In addition, by increasing the substrate heating temperature during film formation, the migration of sputtered particles after they reach the substrate is reduced. Specifically, the substrate heating temperature is set to 100°C or higher and 740°C or lower, preferably The film is formed at a temperature between 200°C and 500°C. When a plate-shaped sputtering particle reaches the substrate, migration occurs on the substrate, The flat surface of the sputtered particle adheres to the substrate.

[0145] In addition, increasing the oxygen ratio in the deposition gas and optimizing the power reduces plasma damage during deposition. The oxygen ratio in the deposition gas is preferably 30% by volume or more, and more preferably 100% by volume or more. The product is %.

[0146] As an example of a sputtering target, an In-Ga-Zn-O compound target is The following are the results:

[0147] InO X powder, GaO Y Powder and ZnO Z The powders are mixed in a specified number of moles and then pressurized. By heat treatment at a temperature between 1000℃ and 1500℃, polycrystalline In-Ga -Zn-O compound target, where X, Y, and Z are any positive numbers. , the predetermined molar ratio is, for example, InO X powder, GaO Y Powder and ZnO Z Powder, 2 :2:1, 8:4:3, 3:1:1, 1:1:1, 4:2:3 or 3:1:2. The type of powder and the molar ratio of the powder to be mixed depend on the sputtering target to be prepared. This can be changed as appropriate depending on the kit.

[0148] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0149] (Embodiment 5) In the light-emitting device according to one embodiment of the present invention, a light-emitting element that emits monochromatic light such as white light and a color light It uses a color filter system that displays full color images by combining a color filter. Alternatively, a plurality of light emitting elements that emit light of different hues can be used to form a flashlight. In this method, the light emitting element has The EL layer between the pair of electrodes is painted to correspond to each color, so it is called a color-coded method. Called.

[0150] In the case of the separate coating method, the EL layer is usually coated using a mask such as a metal mask. This is done by vapor deposition. Therefore, the size of the pixel depends on the accuracy of the EL layer coating by vapor deposition. On the other hand, in the case of the color filter method, unlike the separate coloring method, the EL layer is separated into separate colors. Therefore, it is easier to reduce the pixel size than in the case of the color-by-color method. This makes it possible to realize a high-definition pixel portion.

[0151] In addition, the light emitting device includes a substrate on which a transistor is formed, that is, a device substrate, on which light from a light emitting element is emitted. The bottom emission structure extracts the light from the light emitting element from the opposite side of the element substrate. In the case of a top emission structure, the light emitted from the light emitting element is The light that is transmitted is not blocked by various elements such as wiring, transistors, and capacitors. Therefore, the light extraction efficiency from the pixel can be improved compared to the bottom emission structure. Therefore, the top emission structure can provide a high current even if the current value supplied to the light emitting element is kept low. Since high brightness can be obtained, this is advantageous for extending the life of the light-emitting element.

[0152] In addition, in the light-emitting device according to one embodiment of the present invention, light emitted from the EL layer is resonated within the light-emitting element. The light source may have a microcavity (micro optical resonator) structure. The Tee structure can increase the extraction efficiency of light of a specific wavelength from the light emitting element. Therefore, the brightness and color purity of the pixel portion can be improved.

[0153] An example of a cross-sectional view of a pixel is shown in FIG. 13. Note that FIG. 13 shows a cross-section of a pixel corresponding to red. A part of the surface, a part of the cross section of the pixel corresponding to blue, and a part of the cross section of the pixel corresponding to green are shown. There are.

[0154] Specifically, in FIG. 13, a pixel 140r corresponding to red, a pixel 140g corresponding to green, and a pixel 140g corresponding to blue Pixel 140r, pixel 140g, pixel 140b corresponding to the pixel 140r are shown. The anodes 715r, 715g, and 715b are respectively included. The node 715r, the anode 715g, and the anode 715b are connected to the pixel 140r and the pixel 140g. In each of the pixels 140b, a dielectric film 750 is provided on the substrate 740. It is being done.

[0155] An insulating film is provided on the anode 715r, the anode 715g, and the anode 715b. The partition wall 730 has an opening, and the opening is The node 715r, the anode 715g, and the anode 715b are each partially exposed. In addition, an EL layer 731 and a visible light emitting layer 732 are formed on the partition wall 730 so as to cover the exposed region. A cathode 732 that is transparent to light is laminated in this order.

[0156] The overlapping portion of the anode 715r, the EL layer 731, and the cathode 732 corresponds to red. It corresponds to the light-emitting element 741r. The anode 715g, the EL layer 731, and the cathode 732 The overlapping portion corresponds to the light-emitting element 741g corresponding to green. The overlapping portion of the layer 731 and the cathode 732 corresponds to the light emitting element 741b corresponding to blue. do.

[0157] The substrate 742 also has a structure in which the light emitting elements 741r, 741g, and 741b are spaced apart. The substrate 742 faces the substrate 740, sandwiching the pixel 140r. A colored layer 743r, a colored layer 743g corresponding to the pixel 140g, a colored layer corresponding to the pixel 140b The colored layer 743r has a transmittance of 100% for light in the wavelength region corresponding to red. The colored layer 743g has a higher transmittance for light in the wavelength region corresponding to green. The colored layer 743b is a layer having a higher transmittance for light in the blue wavelength region than for light in other wavelength regions. The transmittance of light in the wavelength region corresponding to the wavelength of the light source is higher than the transmittance of light in other wavelength regions.

[0158] Furthermore, on the substrate 742, a colored layer 743r, a colored layer 743g, and a colored layer 743b are provided so as to cover the colored layer 743r, the colored layer 743g, and the colored layer 743b. The overcoat 744 is provided on the colored layer 743. r, a transparent layer having visible light transparency for protecting the colored layer 743g and the colored layer 743b; It is preferable to use a resin material with high flatness. The colored layer 743g, the colored layer 743b, and the overcoat 744 are collectively regarded as a color filter. Alternatively, the colored layers 743r, 743g, and 743b may be colored. It may be considered as a filter.

[0159] In FIG. 13, the anode 715r is provided with a conductive film 745r having a high reflectance for visible light and a A conductive film 746r having a visible light transmittance higher than that of the conductive film 745r is laminated in this order. In addition, the anode 715g has a conductive film 745g with high reflectivity for visible light and a transparent conductive film 745g with high transmittance for visible light. The conductive film 74 is used by stacking a conductive film 746g having a thickness higher than that of the conductive film 745g in this order. The thickness of the conductive film 746r is smaller than that of the anode 715b. A conductive film 745b having high reflectance for visible light is used for the insulating film 745b.

[0160] Therefore, in the light-emitting device shown in FIG. 13, the light emitted from the EL layer 731 in the light-emitting element 741r The optical path length of the incident light can be adjusted by the distance between the conductive film 745r and the cathode 732. In the light emitting element 741g, the optical path length of the light emitted from the EL layer 731 is This can be adjusted by adjusting the distance between the film 745g and the cathode 732. In the example shown in FIG. 7b, the optical path length of the light emitted from the EL layer 731 is the distance between the conductive film 745b and the cathode 73 The distance between the two can be adjusted.

[0161] In one embodiment of the present invention, the light emitting element 741r, the light emitting element 741g, and the light emitting element 741b are By adjusting the optical path length in accordance with the wavelength of the light corresponding to each of the light beams, the light emitted from the EL layer 731 can be The light emitted from the light emitting element may be resonated in the light emitting element, thereby forming a microcavity structure. stomach.

[0162] By employing the above-described microcavity structure in a light-emitting device according to one aspect of the present invention, light emission In the light emitted from the element 741r, the intensity of the light having a wavelength corresponding to red is Therefore, the color purity and brightness of the red light obtained through the colored layer 743r are improved. In addition, in the light emitted from the light emitting element 741g, the intensity of light having a wavelength corresponding to green is Therefore, the color purity and In addition, the light emitted from the light emitting element 741b has a wavelength corresponding to blue. The intensity of the light having the blue wavelength is increased by the resonance. The color purity and brightness of the

[0163] In addition, although FIG. 13 shows a configuration using pixels corresponding to three colors, red, green, and blue, In one embodiment of the present invention, the color combination used is not limited to this configuration. For example, using four colors: red, green, blue, and yellow, or three colors: cyan, magenta, and yellow. Alternatively, the color combination may be light red, green, and blue, and dark red, Alternatively, the color combination may be red, green, blue, silver, or silver-based. Alternatively, six colors of blue, magenta, and yellow may be used.

[0164] For example, colors that can be expressed using red, green, and blue pixels are expressed by the respective colors on the chromaticity diagram. The colors are limited to those shown inside the triangle formed by the three points corresponding to the light colors. A light-emitting element whose emission color is outside the triangle on the chromaticity diagram, such as when a yellow pixel is used By adding a separate color gamut, the color gamut that can be expressed by the light-emitting device can be expanded, and color reproducibility can be enriched. It is possible.

[0165] In addition, in FIG. 13, among the light emitting element 741r, the light emitting element 741g, and the light emitting element 741b, In the light-emitting element 741b having the shortest wavelength λ, a conductive film 745b having a high reflectance of visible light is provided. The other light emitting element 741r and the light emitting element 741g are used as anodes, and the film thicknesses of the other light emitting elements 741r and 741g are The optical path length is adjusted by using different conductive films 746r and 746g. In one embodiment of the present invention, even in the light-emitting element 741b having the shortest wavelength λ, the reflectance of visible light is On the conductive film 745b having a high transmittance of visible light, such as the conductive film 746r and the conductive film 746g, However, as shown in FIG. 13, the wavelength λ is the shortest. In the case where the anode of the optical element 741b is made of a conductive film 745b having a high reflectance for visible light, In this case, in all light-emitting elements, the anode is made of a conductive film having a high transmittance for visible light. This is also preferable because it simplifies the process of producing the anode.

[0166] The conductive film 745b having a high reflectance of visible light is made of a conductive film 746r having a high transmittance of visible light. The work function is often smaller than that of the conductive film 746g. In the light-emitting element 741b, the anode 71 is smaller than the light-emitting element 741r and the light-emitting element 741g. Since holes are not easily injected from 5b to the EL layer 731, the luminous efficiency tends to be low. In one embodiment of the present invention, the EL layer 741b of the light-emitting element 741b having the shortest wavelength λ of light has a 31, a layer in contact with the conductive film 745b having a high reflectance of visible light has a high hole transport property. A substance that exhibits acceptor properties (electron accepting properties) for the substance with high hole transport properties. It is preferable to use a composite material containing the above-mentioned compound. By forming the anode 715b in this manner, holes are easily injected from the anode 715b to the EL layer 731. This increases the luminous efficiency of the light-emitting element 741b.

[0167] As a substance that exhibits acceptor properties, 7,7,8,8-tetracyano-2,3,5,6- Examples include tetrafluoroquinodimethane (abbreviation: F4-TCNQ), chloranil, etc. Further, transition metal oxides can be mentioned. Examples of oxides of metals belonging to Groups 1 to 8 include vanadium oxide, vanadium oxide, Niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide Molybdenum oxide and rhenium oxide are preferred because they have high acceptor properties. It is preferred because it is stable in the air, has low hygroscopicity, and is easy to handle.

[0168] As a material with high hole transporting properties used in the composite material, aromatic amine compounds, carbazole derivatives, Conductors, aromatic hydrocarbons, polymer compounds (oligomers, dendrimers, polymers, etc.), etc. Various compounds can be used. It is preferable that the organic compound has high transportability. -6 cm 2 / Vs or more However, it is preferable that the material has a hole mobility higher than that of the material having a hole transporting property. Any substance other than these may be used.

[0169] The conductive films 745r, 745g, and 745b having high reflectance for visible light are For example, aluminum, silver, or an alloy containing these metal materials may be used as a single layer or The conductive film 745r, the conductive film 745g, and the conductive film 745r can be formed by laminating them. The conductive film 745b is made of a conductive film having a high reflectivity for visible light and a thin conductive film (preferably 20n For example, a visible light emitting layer may be formed by laminating a visible light emitting layer (e.g., a layer of 100 nm or less, more preferably a layer of 100 nm or less). A thin titanium film or molybdenum film is laminated on a conductive film with high light reflectivity to form a conductive film 745b. By forming a conductive film (aluminum, aluminum-containing film) with high reflectivity for visible light, This can prevent the formation of an oxide film on the surface of a metal (such as an alloy containing zinc or silver).

[0170] The conductive films 746r and 746g, which have high transmittance for visible light, are made of, for example, indium oxide. Indium, tin oxide, zinc oxide, indium tin oxide, indium zinc oxide, etc. It is possible.

[0171] The cathode 732 is, for example, a thin conductive film (preferably 20 nm thick) that is thin enough to transmit light. 10 nm or less, and more preferably 10 nm or less) and a conductive film made of a conductive metal oxide. A thin conductive film that is thin enough to transmit light can be made of silver, magnesium, The material can be formed as a single layer or a laminated layer of aluminum or an alloy containing these metal materials. Conductive metal oxides include indium oxide, tin oxide, zinc oxide, and indium Indium tin oxide, indium zinc oxide, or these metal oxide materials containing silicon oxide The mixture can be used.

[0172] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0173] (Sixth embodiment) In this embodiment, a top emission structure, a bottom emission structure, a dual emission structure, The dual emission structure is a structure in which the light from the light emitting element is This means a structure in which the signal is extracted from the plate side and from the side opposite the element substrate.

[0174] In FIG. 14(A), light emitted from a light emitting element 6033 is extracted from the anode 6034 side. The transistor 6031 is covered with an insulating film 6037. A partition wall 6038 having an opening is formed on the insulating film 6037. The anode 6034 is partially exposed at the opening. , an EL layer 6035, and a cathode 6036 are laminated in this order.

[0175] The anode 6034 is formed of a material or film thickness that easily transmits light, and the cathode 6036 is formed of The anode 6034 is formed of a material or with a film thickness that is difficult for light to transmit. A bottom emission structure can be obtained, in which light is extracted as indicated by the white arrow.

[0176] In FIG. 14(B), light emitted from the light emitting element 6043 is extracted from the cathode 6046 side. The transistor 6041 is covered with an insulating film 6047. A partition wall 6048 having an opening is formed on the insulating film 6047. The anode 6044 is partially exposed at the opening. , an EL layer 6045, and a cathode 6046 are laminated in this order.

[0177] The anode 6044 is formed of a material or film thickness that is difficult to transmit light, and the cathode 6046 is formed of The cathode 6046 is formed of a material or with a film thickness that allows light to pass through easily. A top-emission structure can be obtained, extracting light as indicated by the white arrow.

[0178] In FIG. 14(C), light emitted from the light emitting element 6053 is directed to the anode 6054 side and the cathode The cross-sectional view of the pixel when taken out from the 6056 side is shown. The insulating film 6057 is covered with a partition wall 6058 having an opening. The anode 6054 is partially exposed at the opening of the partition wall 6058. In the device, an anode 6054, an EL layer 6055, and a cathode 6056 are laminated in this order.

[0179] The anode 6054 and the cathode 6056 are formed of a material or with a film thickness that easily transmits light. With the above configuration, as shown by the white arrows from the anode 6054 and cathode 6056 side, This results in a dual emission structure that extracts light in the same way.

[0180] The anode or cathode electrode may be made of a metal, an alloy, an electrically conductive compound, or A mixture of these can be used. Specifically, indium oxide-tin oxide (I TO: Indium Tin Oxide, an oxide indium containing silicon or silicon oxide Indium-Tin Oxide, Indium Zinc Oxide , indium oxide containing tungsten oxide and zinc oxide, gold (Au), platinum (Pt) , Nickel (Ni), Tungsten (W), Chromium (Cr), Molybdenum (Mo), Iron ( Fe), cobalt (Co), copper (Cu), palladium (Pd), titanium (Ti), and other elements Elements belonging to Group 1 or 2 of the periodic table, such as lithium (Li) and cesium (C Alkali metals such as calcium (Ca) and strontium (Sr) Alkali-earth metals, magnesium (Mg) and alloys containing these (MgAg, AlLi), Rare earth metals such as uropium (Eu) and ytterbium (Yb) and alloys containing these metals; Other materials that can be used include graphene. The above materials are appropriately selected, and the thickness of the material is By setting the value to the optimum value, it is possible to select a top emission structure, a bottom emission structure, or This makes it possible to create dual emission structures.

[0181] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0182] (Embodiment 7) FIG. 15 is an example of a perspective view of a light-emitting device according to one embodiment of the present invention.

[0183] The light emitting device shown in FIG. 15 comprises a panel 1601, a circuit board 1602, and a connection portion 1603. The panel 1601 has a pixel portion 1604 in which a plurality of pixels are provided, and a A scanning line driver circuit 1605 for selecting each row and inputting image signals to pixels in the selected row. Specifically, the scanning line driver circuit 1605 , generate signals to be input to various scanning lines.

[0184] Various signals and power supply potentials are transmitted from the circuit board 1602 to the panel via the connection part 1603. The connection part 1603 is connected to an FPC (Flexible Printed Circuit) d Circuit) can be used. Also, COF tape can be used for the connection part 1603. When using a scanning line of a part of the circuit in the circuit board 1602 or the panel 1601, The driver circuit 1605 and a part of the signal line driver circuit 1606 are formed on a separately prepared chip. Then, the chip is connected to the COF tape using the COF (Chip On Film) method. It's fine to leave it as it is.

[0185] This embodiment can be implemented in combination with other embodiments.

[0186] (Embodiment 8) A light emitting device according to one aspect of the present invention includes a display device, a personal computer, and a recording medium. Image playback devices (typically DVD: Digital Versatile Disc, etc.) (a device having a display that can play back the recording medium and display the image) Other examples of electronic devices that can use the light-emitting device according to one embodiment of the present invention include: , mobile phones, handheld game consoles, personal digital assistants, e-books, video cameras, digital Cameras such as still cameras, goggle-type displays (head-mounted displays), Navigation systems, audio playback devices (car audio, digital audio players) - etc.), copiers, fax machines, printers, printer-combined machines, automated teller machines Examples of such electronic devices include ATMs, vending machines, etc. Specific examples of these electronic devices are shown in Figure 16.

[0187] FIG. 16A shows a portable game machine, which includes a housing 5001, a housing 5002, a display unit 5003, Display unit 5004, microphone 5005, speaker 5006, operation keys 5007, The display portion 5003 or the display portion 5004 has a display 5008 or the like. By using a light-emitting device that can provide a portable game machine with high image quality and minimal unevenness in brightness, The portable game machine shown in FIG. 16A has two display units 5003 and 5004, but the number of display units that the portable game machine has is not limited to this. .

[0188] FIG. 16B shows a display device, which includes a housing 5201, a display portion 5202, a support base 5203, and the like. By using the light-emitting device according to one embodiment of the present invention for the display portion 5202, luminance unevenness can be reduced. It is possible to provide a display device with high image quality. This includes all display devices for displaying information, such as for data, TV broadcast reception, and advertising displays.

[0189] FIG. 16C shows a notebook personal computer, which includes a housing 5401 and a display portion 5402. The display unit 5402 includes a keyboard 5403, a pointing device 5404, and the like. By using the light-emitting device according to one embodiment of the present invention, a notebook PC with high image quality and little luminance unevenness can be manufactured. A personal computer can be provided.

[0190] FIG. 16D shows a portable information terminal, which includes a first housing 5601, a second housing 5602, a first display unit, and a 5603, a second display unit 5604, a connection unit 5605, operation keys 5606, etc. Table 1 The display unit 5603 is provided in the first housing 5601, and the second display unit 5604 is provided in the second housing 5602. The first housing 5601 and the second housing 5602 are connected by a connection portion 56 5605, and the angle between the first housing 5601 and the second housing 5602 is The video on the first display unit 5603 can be changed by the connection unit 56 5. The structure for switching the angle between the first housing 5601 and the second housing 5602 in FIG. The first display portion 5603 or the second display portion 5604 may be configured as a display device according to one embodiment of the present invention. By using a light-emitting device that can provide a high-quality portable information terminal with little uneven brightness, In addition, a position can be input to at least one of the first display section 5603 and the second display section 5604. It is also possible to use a light emitting device with additional functions as a position input device. The function as a touch panel can be added to the light-emitting device. The function of the position input device is to use a photoelectric conversion element, also called a photosensor, to illuminate the image of a light-emitting device. It can also be added by providing it in the element portion.

[0191] FIG. 16(E) shows a mobile phone, which includes a housing 5801, a display portion 5802, an audio input portion 5803, It has an audio output unit 5804, operation keys 5805, a light receiving unit 5806, etc. By converting the received light into an electrical signal, an external image can be captured. By using the light-emitting device according to one embodiment of the present invention for the display portion 5802, high image quality with little luminance unevenness can be achieved. Mobile phones can be provided.

[0192] This embodiment mode can be implemented in appropriate combination with other embodiment modes. [Explanation of symbols]

[0193] 10 pixels 11 Switch 12 circuits 13 Switch 14 Light-emitting element 15 transistors 16 Switch 17 Capacitor element 18 terminals 19 terminals 20 terminals 21 terminals 30 transistors 31 Transistor 32 transistors 33 Transistor 34 transistors 35 transistors 36 transistors 37 Transistor 38 Capacitor element 40 pixel section 51 Transistor 52 transistors 53 Transistor 54 transistors 55 transistors 56 transistors 57 Capacitor element 58 Capacitor element 140b pixels 140g pixel 140r pixels 715b Anode 715g anode 715r anode 730 Bulkhead 731 EL layer 732 cathode 740 board 741b Light-emitting element 741g Light emitting element 741r Light-emitting element 742 PCB 743b Colored layer 743g colored layer 743r colored layer 744 Overcoat 745b Conductive film 745g conductive film 745r conductive film 746g conductive film 746r conductive film 750 insulating film 800 boards 801 Conductive film 802 Gate insulating film 803 Semiconductor film 804 Conductive film 805 Conductive film 806 Conductive film 807 Semiconductor film 808 Conductive film 809 Semiconductor film 810 Conductive film 811 Conductive film 812 Semiconductor film 813 Semiconductor film 814 Conductive film 815 Conductive film 816 Semiconductor film 817 Conductive film 818 Conductive film 819 Conductive film 820 insulating film 821 insulating film 822 Opening 823 Conductive film 824 Semiconductor film 825 Conductive film 826 Semiconductor Film 827 Conductive film 828 Conductive film 829 Conductive film 830 Conductive film 831 Conductive film 832 Semiconductor film 833 Conductive film 834 Conductive film 835 Conductive film 836 Insulating film 837 EL layer 838 Conductive film 1601 Panel 1602 Circuit Board 1603 Connection 1604 pixel section 1605 Scanning line driver circuit 1606 Signal line driver circuit 5001 Case 5002 Case 5003 Display section 5004 Display section 5005 Microphone 5006 Speaker 5007 Operation key 5008 Stylus 5201 Case 5202 Display section 5203 Support stand 5401 Housing 5402 Display section 5403 Keyboard 5404 Pointing Device 5601 Housing 5602 Housing 5603 Display section 5604 Display section 5605 Connection 5606 Operation Key 5801 Housing 5802 Display section 5803 Audio input unit 5804 Audio output unit 5805 Operation key 5806 Light receiving section 6031 Transistor 6033 Light-emitting element 6034 Anode 6035 EL layer 6036 cathode 6037 Insulating film 6038 Bulkhead 6041 Transistor 6043 Light-emitting element 6044 anode 6045 EL layer 6046 cathode 6047 Insulating film 6048 Bulkhead 6051 transistor 6053 Light-emitting element 6054 Anode 6055 EL layer 6056 cathode 6057 Insulating film 6058 Bulkhead

Claims

1. a pixel including first to third transistors and a light-emitting element; the first transistor has a function of controlling supply of current to the light-emitting element in accordance with an image signal; the second transistor has a function of controlling supply of the image signal to the pixel, the third transistor has a function of controlling supply of a first potential to a gate electrode of the first transistor, a first conductive film functioning as a gate electrode of the first transistor has a region overlapping with a second conductive film functioning as a second gate electrode of the first transistor through a channel formation region of the first transistor; a channel formation region of the second transistor has a region overlapping with a third conductive film having a function as a first pixel electrode of the light-emitting element, a channel formation region of the third transistor has a region overlapping with a fourth conductive film having a function as a second pixel electrode of a second light-emitting element located adjacent to the light-emitting element, each of the third conductive film and the fourth conductive film has a region in contact with an upper surface of one insulating film; the second conductive film has a region overlapping with the third conductive film, a channel formation region of the first transistor is disposed at a position spaced apart from the third conductive film and the fourth conductive film in a plan view; Light-emitting device.

2. a pixel including first to third transistors and a light-emitting element; the first transistor has a function of controlling supply of current to the light-emitting element in accordance with an image signal; the second transistor has a function of controlling supply of the image signal to the pixel, the third transistor has a function of controlling supply of a first potential to a gate electrode of the first transistor, a first conductive film functioning as a gate electrode of the first transistor has a region overlapping with a second conductive film functioning as a second gate electrode of the first transistor through a channel formation region of the first transistor; a channel formation region of the second transistor has a region overlapping with a third conductive film having a function as a first pixel electrode of the light-emitting element, a channel formation region of the third transistor has a region overlapping with a fourth conductive film having a function as a second pixel electrode of a second light-emitting element located adjacent to the light-emitting element, each of the third conductive film and the fourth conductive film functions as an anode; the second conductive film has a region overlapping with the third conductive film, a channel formation region of the first transistor is disposed at a position spaced apart from the third conductive film and the fourth conductive film in a plan view; Light-emitting device.

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