Patent Application
20140327662
1. Field of the Invention
Field of the invention relates to a method of driving a display device, a display device, and an electronic appliance, and the like.
2. Description of the Related Art
Various types of pixel circuit of a display device have been proposed in, for example, Patent Documents 1 and 2.
[Patent Document 1] Japanese Published Patent Application No. 2006-317923
[Patent Document 2] Japanese Published Patent Application No. 2009-122657
However, the threshold voltage of a transistor electrically connected to a display element in each pixel circuit of a display device varies among the pixel circuits in some cases.
In view of this, an object of the present invention is to reduce the influence of such variations in the threshold voltage of the transistor.
A display device and the method of driving the display device which solve the above problem will be described below.
One embodiment of the present invention is a display device including a display element, a transistor, and a capacitor.
One embodiment of the present invention is the method of driving a display device in which a display element is electrically connected to a first terminal of a transistor, and a capacitor is electrically connected between a gate of the transistor and a second terminal of the transistor.
One embodiment of the present invention is a method of driving a display device including a transistor, a capacitor one electrode of which is electrically connected to a first terminal of the transistor and the other electrode of which is electrically connected to a gate of the transistor, and a display element a first electrode of which is electrically connected to a second terminal of the transistor, including the steps of: electrically connecting the gate of the transistor, the first terminal of the transistor, and both electrodes of the capacitor to a first line in a first period; electrically connecting the gate of the transistor and the other electrode of the capacitor to a second line in a second period; and electrically connecting the first terminal of the transistor and one electrode of the capacitor to a third line in a third period.
One embodiment of the present invention is a method of driving a display device including a transistor, a capacitor one electrode of which is electrically connected to a first terminal of the transistor and the other electrode of which is electrically connected to a gate of the transistor, and a display element a first electrode of which is electrically connected to a second terminal of the transistor, including the steps of electrically connecting the gate of the transistor, the first terminal of the transistor, and both electrodes of the capacitor to a second line in a first period; electrically connecting the gate of the transistor and the other electrode of the capacitor to the second line in a second period; and electrically connecting the first terminal of the transistor and one electrode of the capacitor to a third line in a third period.
One embodiment of the present invention is a method of driving a display device including a transistor, a capacitor one electrode of which is electrically connected to a first terminal of the transistor and the other electrode of which is electrically connected to a gate of the transistor, and a display element a first electrode of which is electrically connected to a second terminal of the transistor, including the steps of: electrically connecting the gate of the transistor, the first terminal of the transistor, and both electrodes of the capacitor to a third line in a first period; electrically connecting the gate of the transistor and the other electrode of the capacitor to a second line in a second period; and electrically connecting the first terminal of the transistor and one electrode of the capacitor to the third line in a third period.
One embodiment of the present invention is a method of driving a display device including a transistor, a capacitor one electrode of which is electrically connected to a first terminal of the transistor and the other electrode of which is electrically connected to a gate of the transistor, a display element a first electrode of which is electrically connected to a second terminal of the transistor, a first switch electrically connected between the gate of the transistor and a second line, a second switch electrically connected between the gate of the transistor and the first terminal of the transistor, a third switch electrically connected to the first terminal of the transistor and a first line, and a fourth switch electrically connected to the first terminal of the transistor and a third line, including the steps of: bringing the first switch into an off, the second switch into an on state, the third switch into the on state, and the fourth switch into the off state in a first period; bringing the first switch into the on state, the second switch into the off state, the third switch into the off state, and the fourth switch into the off state in a second period; and bringing the first switch into the off state, the second switch into the off state, the third switch into the off state, and the fourth switch into the on state in a third period.
One embodiment of the present invention is a method of driving a display device including a transistor, a capacitor one electrode of which is electrically connected to a first terminal of the transistor and the other electrode of which is electrically connected to a gate of the transistor, a display element a first electrode of which is electrically connected to a second terminal of the transistor, a first switch electrically connected between the gate of the transistor and a second line, a second switch electrically connected between the gate of the transistor and the first terminal of the transistor, a third switch electrically connected to the first terminal of the transistor and the second line, and a fourth switch electrically connected to the first terminal of the transistor and a third line, including the steps of: bringing the first switch into an off, the second switch into an on state, the third switch into the on state, and the fourth switch into the off state in a first period; bringing the first switch into the on state, the second switch into the off state, the third switch into the off state, and the fourth switch into the off state in a second period; and bringing the first switch into the off state, the second switch into the off state, the third switch into the off state, and the fourth switch into the on state in a third period.
One embodiment of the present invention is a method of driving a display device including a transistor, a capacitor one electrode of which is electrically connected to a first terminal of the transistor and the other electrode of which is electrically connected to a gate of the transistor, a display element a first electrode of which is electrically connected to a second terminal of the transistor, a first switch electrically connected between the gate of the transistor and a second line, a second switch electrically connected between the gate of the transistor and the first terminal of the transistor, and a fourth switch electrically connected to the first terminal of the transistor and a third line, including the steps of: bringing the first switch into an off, the second switch into an on state, and the fourth switch into the on state in a first period; bringing the first switch into the on state, the second switch into the off state, and the fourth switch into the off state in a second period; and bringing the first switch into the off state, the second switch into the off state, and the fourth switch into the on state in a third period.
In the method of driving a display device which is one embodiment of the present invention, the switches are transistors.
In the method of driving a display device which is one embodiment of the present invention, the switches are diodes.
In the method of driving a display device which is one embodiment of the present invention, the display elements are EL elements.
In the method of driving a display device which is one embodiment of the present invention, the display devices are liquid crystal elements.
In the method of driving a display device which is one embodiment of the present invention, an electrode of the display element is larger than an electrode of the capacitor, and capacitance of the display element is larger than capacitance of the capacitor.
In the method of driving a display device which is one embodiment of the present invention, the transistors are p-channel transistors.
One embodiment of the present invention is a display device using the above method of driving a display device.
One embodiment of the present invention is an electronic appliance including the above display device.
One embodiment of the present invention is a display device including: a transistor; a capacitor one electrode of which is electrically connected to a first terminal of the transistor and the other electrode of which is electrically connected to a gate of the transistor; a display element a first electrode of which is electrically connected to a second terminal of the transistor; a first switch electrically connected between the gate of the transistor and a second line; a second switch electrically connected between the gate of the transistor and the first terminal of the transistor; a third switch electrically connected to the first terminal of the transistor and a first line; and a fourth switch electrically connected to the first terminal of the transistor and a third line.
One embodiment of the present invention is a display device including: a transistor; a capacitor one electrode of which is electrically connected to a first terminal of the transistor and the other electrode of which is electrically connected to a gate of the transistor; a display element a first electrode of which is electrically connected to a second terminal of the transistor; a first switch electrically connected between the gate of the transistor and a second line; a second switch electrically connected between the gate of the transistor and the first terminal of the transistor; a third switch electrically connected to the first terminal of the transistor and the second line; and a fourth switch electrically connected to the first terminal of the transistor and a third line.
One embodiment of the present invention is a display device including: a transistor; a capacitor one electrode of which is electrically connected to a first terminal of the transistor and the other electrode of which is electrically connected to a gate of the transistor; a display element a first electrode of which is electrically connected to a second terminal of the transistor; a first switch electrically connected between the gate of the transistor and a second line; a second switch electrically connected between the gate of the transistor and the first terminal of the transistor; and a fourth switch electrically connected to the first terminal of the transistor and a third line.
In the display device which is one embodiment of the present invention, the switches are transistors.
In the display device which is one embodiment of the present invention, the switches are diodes.
In the display device which is one embodiment of the present invention, the display elements are EL elements.
In the display device which is one embodiment of the present invention, the display devices are liquid crystal elements.
In the display device which is one embodiment of the present invention, an electrode of the display element is larger than an electrode of the capacitor, and capacitance of the display element is larger than capacitance of the capacitor.
In the display device which is one embodiment of the present invention, the transistors are p-channel transistors.
One embodiment of the present invention is an electronic appliance using the above display device.
The above display device and the method of driving the display device makes it possible to reduce variations among pixel circuits in threshold voltage of a transistor electrically connected to a display element which is in each pixel circuit of a display device.
Although a display device according to the present invention includes a plurality of pixel circuits, a single pixel circuit of the display device will be described below.
In this embodiment, an example of the configuration of the pixel circuit of the display device and an example of the method of driving the display device is described.
Description will be made with reference to
The display device according to the present invention includes a transistor 101, a capacitor 102, and a display element 103, for example. An example of this embodiment, however, is not limited to this. For example, the display device of this embodiment can additionally include a switch, a transistor, a diode, and/or, a capacitor in order to achieve the behavior shown in
The transistor 101 has a function of supplying a current to the display element 103, for example. The value of such a current corresponds to, for example, a potential difference (Vgs) between the gate and source of the transistor 101 in many cases. Thus, the transistor 101 can function as a driver transistor or current source, for example. An example of this embodiment, however, is not limited to this. For example, the transistor 101 can function as a switch.
Note that the transistor 101 is a p-channel transistor, for example. A p-channel transistor is turned on when a potential difference (Vgs) between a gate and a source is smaller than threshold voltage (Vth 101). An example of this embodiment, however, is not limited to this. For example, the transistor 101 can be an n-channel transistor. An n-channel transistor is turned on when a potential difference (Vgs) between a gate and a source is larger than threshold voltage (Vth 101).
In other words, when an n-channel transistor is used, the display device can be operated by setting the polarity of the potential in reverse to a display device using a p-channel transistor. In this case, the circuit configuration is changed as appropriate in order to obtain the reverse polarity of the potential to that in a circuit using a p-channel transistor.
Note that for example, a plurality of pixels included in the display device according to the present invention, are categorized by a plurality of color groups (e.g. red, blue, green, white, yellow, magenta, cyan, or the like). In this case, it is recommended that the channel width (W) and channel length (L) of the transistor 101 or the W/L ratio (the ratio of channel width to channel length) of the transistor 101 are varied among the pixels according to the color group. For example, compared to a green emitting EL element, a red (or blue) emitting EL element has low luminous efficiency in some cases. In these cases, it is recommended that the W/L ratio of the transistor 101 in a pixel belonging to a green group is smaller than that of the transistor 101 in a pixel belonging to a red (or blue) group. Thus, the value of a video signal and/or the potential of a line 212 do not need to be varied among the pixels according to the color group. This simplifies the configuration of a circuit (e.g. a source driver circuit) which inputs a video signal to the pixels or reduces the number of power sources or signals required for a circuit (e.g. a source driver circuit) which inputs a video signal to the pixels. An example of the display device according to the present invention is not limited to this. For example, in all the pixels, the channel width (W) and channel length (L) of the transistor 101 or the W/L ratio of the transistor 101 can be approximately the same.
A capacitor 102 has a function of holding a potential difference (Vgs) between the gate of the transistor 101 and the first terminal of the transistor 101, for example. Thus, the capacitor 102 functions as a storage capacitor, for example. An example of the display device according to the present invention, however, is not limited to this.
The display element 103 is sandwiched between a first electrode 103A and a second electrode 103B, for example. Examples of the display element 103 are a light emitting element such as an EL element, a liquid crystal element, and an element containing electronic ink, and the like. An example of the display device according to the present invention, however, is not limited to this. For example, the display element 103 can include three electrodes.
Note that the display device according to the present invention includes a plurality of pixels, for example. In this case, the second electrodes 103B in pixels are electrically connected to each other in many cases. Thus, the second electrode 103B functions as a common electrode, a counter electrode, or a cathode, for example. An example of the display device according to the present invention is not limited to this. For example, the second electrodes 103B can be electrically separated by the type or area of the pixel.
Note that voltage (V1), for example, is applied to the second electrode 103B. The voltage (V1) serves as common voltage or cathode voltage, for example. An example of the display device according to the present invention is not limited to this. For example, a signal can be input to the display element 103. Thus, the display element 103 can be reverse-biased.
Note that the first electrode 103A functions as a pixel electrode, for example. An example of this embodiment, however, is not limited to this. For example, assuming that the first electrode 103A is electrically connected to a capacitor, the first electrode 103A can function as one electrode of the capacitor.
The display device according to the present invention is electrically connected, for example, to a line 211, the line 212, and a line 213. An example of the display device according to the present invention is not limited to this. For example, the display device according to the present invention can be electrically connected, for example, to other lines (e.g. a power supply line, a scan line, or the like). For another example, any of the lines 211 to 213 can be omitted.
A signal (Vdata), for example, is input to the line 211. The signal (Vdata) serves as a video signal. Thus, the line 211 functions as a signal line, a video signal line, or a source signal line, for example. An example of the display device according to the present invention is not limited to this. For example, constant voltage can be applied to the line 211. Thus, the line 211 can function as a power supply line.
Note that the signal (Vdata) is an analog signal, for example. An example of this embodiment, however, is not limited to this. For example, the signal (Vdata) can be a digital signal. Thus, digital time grayscale can be achieved.
The voltage (Vref), for example, is applied to the line 212. The voltage (Vref) serves as a reference voltage, for example. Therefore, the line 212 functions as a power supply line or an initialization line, for example. An example of this embodiment, however, is not limited to this. For example, a signal can be input to the line 212. Therefore, the line 212 can serve as a signal line, for example.
Note that a voltage (Vref) is a value lower than a voltage (V1) (Vref<V1), for example. An example of the display device according to the present invention is not limited to this. For example, the voltage (Vref) is approximately the same value as the voltage (V1). This reduces the number of the types of voltage needed to drive the pixels of the display device according to the present invention.
A voltage (V2), for example, is applied to the line 213. The voltage (V2) serves as anode voltage, for example. Therefore, the line 213 functions as a power supply line or anode line, for example. An example of the display device according to the present invention is not limited to this. For example, a signal can be input to the line 213. Thus, the line 213 functions as a signal line, for example.
Note that the voltage (V2) is a value higher than the voltage (V1) (V2>V1), for example. An example of this embodiment, however, is not limited to this. For example, when the anode and cathode of the display element 103 are interchanged, the voltage (V2) can be a value lower than the voltage (V1).
Note that for example, the display device includes a plurality of pixels, and the plurality of pixels is categorized by a plurality of color groups (e.g. red, blue, green, white, yellow, magenta, cyan, or the like). In this case, it is recommended that the value of a voltage applied to the line 213 is varied among the pixels according to the color group. For example, compared to a green emitting EL element, a red (or blue) emitting EL element has low luminous efficiency in some cases. In these cases, it is recommended that a voltage applied to the line 211 that is electrically connected to a pixel belonging to the green group is lower than a voltage applied to the line 211 that is electrically connected to a pixel belonging to the red (or blue) group. Thus, the value of a video signal and/or the W/L ratio of the transistor do not need to be varied among the pixels according to the color group. This simplifies the configuration of a circuit (e.g. a source driver circuit) which inputs a video signal to the pixels. An example of the display device according to the present invention is not limited to this. For example, in all the pixels, the potential of the line 213 can be approximately the same.
An example of the behavior of the display device according to the present invention will be described with reference to
The timing chart shown in
First, in the first period (T1), the display device of this embodiment behaves as shown in
In
Then, the transistor 101 is turned on, so that the potential of the second terminal of the transistor 101 (V13) starts to decrease from Vel (a potential that depends on a current flowing through the display element 103 in the third period (T3) described later). The transistor 101 is turned off when the potential of the second terminal of the transistor 101 (V13) decreases to Vref−Vth101. Thus, the second terminal of the transistor 101 becomes floating, and the potential of the second terminal of the transistor 101 (V13) is held at Vref−Vth101. At that time, Vref−Vth101 is lower than the potential of the second electrode 103B of the display element 103, for example. Thus, the display element 103 functions as a capacitor, and thus holds a potential difference between the first electrode 103A and the second electrode 103B, i.e. a potential difference between the second terminal of the transistor 101 and the second electrode 103B (Vref−Vth101−V1). Consequently, the potential of the second terminal of the transistor 101 (V13) is held at Vref−Vth101. Note that Vth101 is the threshold voltage of the transistor 101.
Note that in the first period (T1), the potential of the second terminal of the transistor 101 (V13) is lower than the potential of the other electrode 103B of the display element 103 (V1). Hence, the display element 103 is reverse-biased. This suppresses degradation of the display element 103 and reduces defects, for example. An example of the display device according to the present invention is not limited to this. For example, the potential of the second terminal of the transistor 101 (V13) can be a value lower than the sum of the potential of the second electrode 103B of the display element 103 and the threshold voltage of the transistor 101.
Note that the transistor 101 is a normally-off transistor, for example. Hence, the threshold voltage of the transistor 101 (Vth101), which is a p-channel transistor, is a negative value. Note that an example of the display device according to the present invention is not limited to this. For example, the transistor 101 can be a normally-on transistor. In this case, in the first period (T1), the potential of the second terminal of the transistor 101 (V13) is approximately Vref.
Next, in the second period (T2), the display device according to the present invention behaves as shown in
In
The potential of the line 211 is a value lower than the potential of the line 212 (Vref) by Vdata (Vref−Vdata), for example. Hence, the potential of the gate of the transistor 101 (V11) becomes approximately the same value as the potential of the line 211 (Vref−Vdata). When an expression Vdata>0 is satisfied, the transistor 101 is turned on.
Consequently, electrical continuity between the first terminal of the transistor 101 and the second terminal of the transistor 101 is established, so that the potential of the first terminal of the transistor 101 (V12) becomes approximately the same value as the potential of the second terminal of the transistor 101 (V13). This value is determined by the capacitance of the capacitor 102 (C102) and the capacitance of the display element 103 (C103). Here, assuming that C102<C103, the potential of the first terminal of the transistor 101 (V12), and the potential of the second terminal of the transistor 101 (V13) each become approximately Vref−Vth101. Consequently, a potential difference between the gate and first terminal of the transistor 101 (Vth101−Vdata) is stored in the capacitor 102.
Note that at least an expression C102<C103 is satisfied, and preferably an expression C102<<C103 is satisfied. In other words, an approximation of the sum of C103 and C102 preferably is approximately C103.
In addition, the area of the electrode of the display element is larger than that of the electrode of the capacitor. Such a composition easily satisfies the expression C102<C103. Note that the area of each electrode of the display element and the capacitor refers to an area where a first electrode overlaps with a second electrode.
In addition, a combination of the first period (T1) and the second period (T2) is an address period.
Next, in the third period (T3), the display device according to the present invention behaves as shown in
In
Consequently, the potential of the first terminal of the transistor 101 (V12) becomes approximately the same value as the potential of the line 213 (V2). At that time, the gate of the transistor 101 becomes floating, so that the potential of the gate of the transistor 101 (V11) increases to V2−Vdata+Vth101 because of capacitive coupling in the capacitor 102. This is because the capacitor 102 holds a potential difference between the gate of the transistor 101 and the first terminal of the transistor 101 in the second period (T2) (Vth101−Vdata). In other words, a potential difference between the gate and source of the transistor 101 (Vgs) remains Vth101−Vdata. Thus, when the transistor 101 operates in the saturation region, a drain current of the transistor 101 (a current that flows through the display element 103) is independent of the threshold voltage of the transistor 101. The threshold voltage of the transistor 101 can thus be canceled or compensated.
In the first period (T1) which is an initialization period, the potential of the electrodes of the capacitor 102, and the first terminal and gate of the transistor 101 is Vref. In addition, a potential difference that equals to the threshold voltage of the transistor 101 is given between the node 11 and the node 13. The first terminal (node 12) and gate (node 11) of the transistor 101 each have a potential (Vref), and the transistor 101 is thus turned off. Consequently, the second terminal (node 13) of the transistor 101 becomes floating, and the potential of the second terminal of the transistor 101 becomes Vref−Vth101. Therefore, a potential difference that equals to the threshold voltage of the transistor 101 (Vth101) is given between the node 11 and the node 13.
In other words, in the first period (T1), the potential of the electrodes of the capacitor 102 and the first terminal and gate of the transistor 101 is initialized to Vref, and a potential difference that equals to the threshold voltage of the transistor 101 (Vth101) is given between the node 11 and the node 13.
In the second period (T2) which is a write period, an input of the video signal (Vdata) is done. Consequently, the potential of the node 11 becomes Vref−Vdata, and a potential difference between the node 11 and the node 13 becomes Vth101−Vdata. Thus, the transistor 101 is turned on. This is because when the transistor 101 is turned on, the potential of the node 12 and the potential of the node 13 become approximately the same and charge enough to produce a potential difference that corresponds to Vth101−Vdata is stored in the capacitor 102. In other words, in the second period (T2), charge enough to turn on the transistor 101 during a display period without respect to the threshold voltage of the transistor 101 is stored in the capacitor 102.
In the third period (T3) which is a display period, current is fed into the display element. This is achieved because a potential difference (Vth101−Vdata) is given between the node 11 and the node 12 by the capacitor 102 and a potential difference that can turn on the transistor 101 without respect to the threshold voltage of the transistor 101 is given between the node 11 and the node 12. In other words, in the third period (T3), the transistor 101 is turned on without respect to the threshold voltage of the transistor 101, and thus supplied with current by the display element.
As described above, the display device according to the present invention can display an image without being influenced by variations in the threshold voltage of the transistor 101 or degradation of the transistor 101.
This embodiment can be combined with any of all the other embodiments.
Here, in each period, the display device according to the present invention can perform various behavior in addition to the behavior shown in
Note that the behavior in the second period (T2) and third period (T3) shown in
Note that when the display device according to the present invention performs the behavior shown in
This embodiment can be combined with any of all the other embodiments.
Here, a display device according to the present invention can include a switch in order to achieve the above behavior of the display device. An example of the display device according to the present invention including a switch in order to achieve the above behavior of the display device will be described below.
An example of the behavior of the display device shown in
An example the behavior of the display device shown in
Note that the behavior in the first to third periods (T1) to (T3) described with reference to
In this case, in the first period (T1), the switch 301 is turned off, the switch 302 is turned on, the switch 303 is turned on, and the switch 304 is turned off. In addition, the potential of the line 211 is preferably Vref in the first period (T1). In the second period (T2), the switch 301 is turned on, the switch 302 is turned off, the switch 303 is turned off, and the switch 304 is turned off. In the third period (T3), the switch 301 is turned off, the switch 302 is turned off, the switch 303 is turned off, and the switch 304 is turned on. An example of this embodiment, however, is not limited to this.
Alternatively, in the first period (T1), the switch 301 is turned off, the switch 302 is turned on, the switch 303 is turned off, and the switch 304 is turned on. In addition, the potential of the line 213 is preferably Vref in the first period (T1). In the second period (T2), the switch 301 is turned on, the switch 302 is turned off, the switch 303 is turned off, and the switch 304 is turned off. In the third period (T3), the switch 301 is turned off, the switch 302 is turned off, the switch 303 is turned off, and the switch 304 is turned on. An example of this embodiment, however, is not limited to this.
In this case, in the first period (T1), the switch 301 is turned off, the switch 302 is turned on, the switch 303 is turned on, and the switch 304 is turned off. Note that the switch 301 is not necessarily turned off at that time. In addition, the potential of the line 211 is preferably Vref in the first period (T1). In the second period (T2), the switch 301 is turned on, the switch 302 is turned off, the switch 303 is turned off, and the switch 304 is turned off. Note that the switch 303 is not necessarily turned off at that time. In the third period (T3), the switch 301 is turned off, the switch 302 is turned off, the switch 303 is turned off, and the switch 304 is turned on. An example of this embodiment, however, is not limited to this.
Alternatively, in the first period (T1), the switch 301 is turned off, the switch 302 is turned on, the switch 303 is turned off, and the switch 304 is turned on. In addition, the potential of the line 213 is preferably Vref in the first period (T1). In the second period (T2), the switch 301 is turned on, the switch 302 is turned off, the switch 303 is turned off, and the switch 304 is turned off. Note that the switch 303 is not necessarily turned off at that time. In the third period (T3), the switch 301 is turned off, the switch 302 is turned off, the switch 303 is turned off, and the switch 304 is turned on. An example of this embodiment, however, is not limited to this.
Note that the behavior in the second period (T2) and third period (T3) shown in
In this case, in the first period (T1), the switch 301 is turned off, the switch 302 is turned on, and the switch 304 is turned on. In addition, the potential of the line 213 is preferably Vref in the first period (T1). In the second period (T2), the switch 301 is turned on, the switch 302 is turned off, and the switch 304 is turned off. In the third period (T3), the switch 301 is turned off, the switch 302 is turned off, and the switch 304 is turned on. An example of this embodiment, however, is not limited to this.
Alternatively, in the first period (T1), the switch 301 is turned on, the switch 302 is turned on, and the switch 304 is turned off. In addition, the potential of the line 211 is preferably Vref in the first period (T1). In the second period (T2), the switch 301 is turned on, the switch 302 is turned off, and the switch 304 is turned off. In the third period (T3), the switch 301 is turned off, the switch 302 is turned off, and the switch 304 is turned on. An example of this embodiment, however, is not limited to this. For example, the switch 303 can be electrically connected between the first terminal of the transistor 101 and the line 213, or between the gate of the transistor 101 and the line 213.
Note that the behavior in the second period (T2) and third period (T3) shown in
Note that, as shown in
The configurations which are shown in
In addition, a transistor or a diode, for example, is applicable to a switch of this embodiment. An example of this embodiment, however, is not limited to this. Any components having a switching function are applicable to a switch of this embodiment.
In addition, line sharing is possible as shown in
The transistors 401 to 404 can be either n-channel transistors or p-channel transistors. In addition, the conductivity type of the transistors 401 to 404 can be different from that shown in
The configuration shown in
Note that a transistor electrically connected to the line 211 and 212 the potential of which is lower than the potential of the second electrode 103B exhibits favorable switching when being an n-channel transistor. In addition, a transistor electrically connected to the line 213 the potential of which is higher than the potential of the second electrode 103B exhibits favorable switching when being a p-channel transistor.
Although
Although not shown, the switches 301 to 304 in
In other words, as for the configuration of the transistor, each of the switches 301, 302, and 304 can be replaced with a transistor. Alternatively, the switches 301, 302, and 304 can be a CMOS circuit which is a combination of a p-channel transistor and an n-channel transistor. One embodiment of the present invention is not limited to this.
When each of the switches 301 to 304 is replaced with a transistor, the conductivity type of the transistors is as follows: the transistors 401 and 403 are n-channel transistors, the transistors 402 and 404 are p-channel transistors; alternatively, the transistors 401 to 404 are all n-channel transistors. One embodiment of the present invention is not limited to this.
This embodiment can be combined with any of all the other embodiments.
The configuration of a transistor used for the above display device will be described.
Note that various types of transistor can be used as a transistor included in the above display device. In other words, there is no limitation on the type of a transistor which can be used. Therefore, a thin film transistor including a semiconductor layer typified by silicon, a transistor formed using a semiconductor substrate or an SOI substrate, a MOS transistor, a junction transistor, a bipolar transistor, a transistor including a compound semiconductor such as ZnO or InGaZnO, a transistor including an organic semiconductor or carbon nanotube, or other transistors can be used. Note that the semiconductor layer may contain hydrogen or halogen.
In the case where a transistor included in the above display device is a thin film transistor, various types of thin film transistors can be used. For example, a top-gate TFT, e.g. a planar TFT, or a bottom-gate TFT (a typical example of which is an inverted staggered TFT) can be used. One embodiment of the present invention is not limited to this.
Various types of semiconductor layers can be used for the above display device. For example, a non-single-crystal silicon layer typically using amorphous silicon, polycrystalline silicon, microcrystalline (also referred to as micro crystal or semi-amorphous) silicon; single crystalline silicon layer; or an oxide semiconductor layer can be used.
As an oxide semiconductor layer, a thin film of a material expressed by InMO3(ZnO)m (m>0) is formed, and a thin layer transistor having the thin film as an oxide semiconductor layer is fabricated. Note that M denotes a single metal element or a plurality of metal elements selected from Ga, Fe, Ni, Mn, and Co. For example, M might be Ga. In addition, M might be a plurality of elements: Ga and Ni or a plurality of elements: Ga and Fe, for example. Thus, M might include any of the above listed metal elements except Ga. Moreover, in some cases, the above oxide semiconductor contains a transition metal element such as Fe or Ni or an oxide of the transition metal as an impurity element in addition to a metal element M.
In the present invention, among the oxide semiconductor layers whose composition formulae are represented by InMO3(ZnO)m (m>0), an oxide semiconductor whose composition formula includes at least Ga as M is referred to as an In—Ga—Zn—O-based oxide semiconductor, and a thin layer of the In—Ga—Zn—O-based oxide semiconductor is referred to as an In—Ga—Zn—O-based non-single-crystal layer. As a metal oxide used for the oxide semiconductor layer, any of the following metal oxides can be used in addition to the above: an In—Sn—O-based metal oxide; an In—Sn—Zn—O-based metal oxide; an In—Al—Zn—O-based metal oxide; a Sn—Ga—Zn—O-based metal oxide; an Al—Ga—Zn—O-based metal oxide; a Sn—Al—Zn—O-based metal oxide; an In—Zn—O-based metal oxide; a Sn—Zn—O-based metal oxide; an Al—Zn—O-based metal oxide; an In—O-based metal oxide; a Sn—O-based metal oxide; and a Zn—O-based metal oxide. Silicon oxide may be included in the oxide semiconductor layer formed using the above metal oxide.
In the case of the formation of a transistor included in the above display device, the transistor can be formed using a silicon wafer or an SOI substrate. One embodiment of the present invention, however, is not limited to this.
An SOI substrate can be made as follows. Halogen ions such as hydrogen ions and helium ions are implanted by ion implantation or the like in a single crystal silicon substrate, forming a brittle layer in the single crystal silicon substrate. An insulating substrate formed using glass or quartz glass, for example, is superimposed on a single crystal silicon substrate having the brittle layer. The superimposed substrates, i.e. the insulating substrate and the single crystal silicon substrate are heated, so that a part of the single crystal silicon substrate superimposed on the insulating substrate is separated along the brittle layer. Transistors in the display device can be made using such an SOI substrate. One embodiment of the present invention, however, is not limited to this.
In addition, when the above display device has a flexible substrate, it is also possible for a display device according to the present invention to be a flexible display device.
The flexible display device can be made as follows. A release layer is formed over a flexible substrate formed using plastic, resin, or the like. An element formation layer including a transistor and a display element is formed over the release layer. A flexible substrate or flexible film is formed over the element formation layer. The element formation layer is separated from the substrate and the release layer. The method of making the flexible display device is not limited to this.
This embodiment can be combined with any of all the other embodiments.
Examples of the electronic appliance using the display device according to the present invention include a video camera, a digital camera, a goggle type display (a head mounted display), a navigation system, an audio reproducing device (a car audio, an audio component and the like), a notebook personal computer, a game machine, a personal digital assistant (a mobile computer, a mobile phone, a portable game console, an electronic book, or the like), an image reproducing device provided with a recording medium (specifically, a device which reproduces a recording medium such as a Digital Versatile Disc (DVD) and which is provided with a display capable of displaying the image). Specific examples of such electronic appliances are shown in
As described above, various types of electronic appliances include a display portion on which image data etc. is displayed. The quality of displayed image data decreases when varies among pixel circuits the threshold voltage of a transistor electrically connected to a display element formed in each pixel circuit of a display device that the display portion has. It is therefore preferable to reduce variations in the threshold voltage of a transistor among pixel circuits. The display device according to the present invention can reduce variations in the threshold voltage of a transistor among pixel circuits.
Therefore, the scope of application of the present invention is extremely wide and the present invention is applicable to all types of electronic appliances. In addition, the electronic appliances of this embodiment can use any structures of the display devices of other embodiments.
This application is based on Japanese Patent Application serial no. 2009-241710 filed with Japan Patent Office on Oct. 20, 2009, the entire contents of which are hereby incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-241710 | Oct 2009 | JP | national |
This application is a continuation of copending U.S. application Ser. No. 12/906,539, filed on Oct. 18, 2010 which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12906539 | Oct 2010 | US |
| Child | 14335210 | US |
