Semiconductor device, display device having the same and electronic appliance

The present invention provides a semiconductor device and its driving method in which amplitude of a data line is decreased to reduce power consumption. In a reset period, a reset transistor and a switch transistor are turned on. In the reset period, an input of a potential from the reset transistor is dominant in a node D, and a selection transistor is turned off when a potential of the node D gets higher than a gate potential of the selection transistor. Thus, even though a potential of the data line changes, a potential of the node G does not change. Since the potential of the data line is not directly written in a gate of a driver transistor, it is possible to separately set an on/off potential to be applied to the gate of the driver transistor and the amplitude of the data line.

This Application is a National Phase Application filed under 35 U.S.C. 371 claiming the benefit of priority of PCT/JP2006/307990 filed Apr. 10, 2006, having a priority benefit of a Japanese application No. 2005-119676 filed Apr. 18, 2005.

TECHNICAL FIELD

The present invention relates to a semiconductor device. In particular, the present invention relates to a structure of a pixel in an active matrix display which includes a light-emitting element and which is manufactured using a semiconductor device. Moreover, the present invention relates to a display device equipped with the semiconductor device, and an electronic appliance equipped with the display device.

A semiconductor device herein described indicates any device which can function by using a semiconductor characteristic.

BACKGROUND ART

In recent years, demand for thin displays mainly applied to TVs, PC monitors, mobile terminals, and the like have increased rapidly and further development has been promoted. The thin displays include a liquid crystal display device (LCD) and a display device equipped with a light-emitting element. In particular, an active matrix display using a light-emitting element is expected as a next-generation display for its features of high response speed, wide viewing angle, and the like in addition to advantages of a conventional LCD such as thinness, lightness in weight, and high image quality.

In an active matrix display using a light-emitting element, a structure shown inFIG. 17Ais given as the most basic pixel structure (see Non-Patent Document 1: M. Mizukami, K. Inukai, H. Yamagata, et al., SID '00 Digest, vol. 31, pp. 912-915). InFIG. 17A, each pixel has a driver transistor202for controlling current supply to a light-emitting element204, a switch transistor201for taking a potential of a data line206into a gate node G of the driver transistor202by a scan line205, and a holding capacitor203for holding the potential of the node G.

DISCLOSURE OF INVENTION

InFIG. 17A, the light-emitting element204can be driven by an analog driving method or a digital driving method. In the analog driving method, an analog value is supplied to the gate node G of the driver transistor202and the analog value is changed continuously, thereby expressing grayscale. In the digital driving method, a digital value is supplied to the node G, thereby expressing grayscale. The expression of grayscale is performed by a digital time grayscale method in which a light-emission period is changed continuously. The digital driving is advantageous in point of high image quality as compared with the analog driving, because the digital driving is hard to be affected by variation in TFTs.

A specific example of a potential relation and operation timing when driving the pixel inFIG. 17Ais shown inFIG. 17B, and the operation is described. At this time, the light-emitting element204is driven by the digital driving method.

InFIG. 17A, a potential of a counter electrode of the light-emitting element204is set to be GND (hereinafter 0 V), a potential of a current supply line207is set to be 7 V, a High potential of the data line206is set to be 7 V and a Low potential thereof is set to be 0 V, and a High potential of a scan line205is set to be 10 V and a Low potential thereof is set to be 0 V.

In a period while the scan line205has a potential of 10 V, the switch transistor201is turned on, whereby the potential of the data line206is applied to the node G. The potential of the data line206at the moment when the potential of the scan line205is switched from 10 V to 0 V is held at the node G. If the held potential is the High potential 7 V, the driver transistor202is turned off and the light-emitting element204is in a non-light-emission state. If the held potential is the Low potential 0 V, the driver transistor202is turned on and the light-emitting element204is in a light-emission state. At this time, since the driver transistor202operates in a linear region, Vds (source-drain voltage) is extremely low and a potential difference of about 7 V is generated between opposite electrodes of the light-emitting element204, whereby current flows in the light-emitting element204.

In the pixel structure described here, the potential of the data line206is written in the node G. Since the driver transistor202is turned on or off depending on the potential of the node G, it is necessary that at least the High potential of the data line206is the same as or higher than the potential of the current supply line207and that, in the case of digital driving, the Low potential is the potential to turn on the driver transistor202in a linear region.

Selection pulses are sequentially outputted from a scan line driver circuit to the respective rows of the scan line205, and data signals are outputted from a data line driver circuit to the respective columns of the data line206in accordance with the selection pulses.

Electric power in a buffer portion in the data line driver circuit for charging/discharging the data line206is dominant in the power consumption of the driver circuits. The power consumption P is generally calculated from the following formula (I), where F is frequency, C is capacitance, and V is voltage.
P=FCV2(1)

Therefore, it is understood from the formula (1) that decreasing the amplitude of the data line206is effective to reduce the power consumption.

However, in consideration of variation in threshold and fluctuation in threshold due to temperature between the driver transistors202, noise in a holding period, off-leak of the switch transistor201, and the like, it is not easy to decrease the amplitude of the data line206. Moreover, in the time grayscale method, one frame period is divided into a plurality of sub-frames to control a light-emission period; therefore, the number of times of charging/discharging the data line206increases, which further affects the power consumption of the data line driver circuit.

In view of the above problem, the present invention provides a semiconductor device and its driving method, in which the amplitude of the data line is made small to reduce the power consumption by not writing the potential of the data line in the driver transistor.

A semiconductor device of the present invention includes a light-emitting element, a scan line, a data line, a current supply line, a node, a first transistor of which a gate is connected to the node and one of a source and a drain is connected to the current supply line and the other is connected to one electrode of the light-emitting element, a second transistor which is turned on or off depending on potentials of the data line and the scan line and which determines a potential of the node, and a means for setting the potential of the node so as to be a potential for turning off the first transistor without depending on the potential of the data line.

A semiconductor device of the present invention includes a light-emitting element, a scan line, a data line, a current supply line, first and second nodes, a first transistor of which a gate is connected to the first node and one of a source and a drain is connected to the current supply line and the other is connected to one electrode of the light-emitting element, a second transistor which is turned on or off depending on potentials of the data line and the scan line and which determines a potential of the second node, a means for setting the potential of the second node so as to be a potential for turning off the first transistor without depending on fluctuation of the potential of the data line, and a switch for controlling electrical connection or disconnection between the first node and the second node.

In these semiconductor devices of the present invention, the potential of the current supply line is higher than the potential of the other electrode of the light-emitting element. Moreover, the first transistor is a P-channel transistor and the second transistor is an N-channel transistor.

A semiconductor device of the present invention includes a first transistor of which one of a source and a drain is connected to a current supply line, a light-emitting element of which one electrode is connected to the other of the source and the drain of the first transistor, and a second transistor of which one of a source and a drain is connected to a scan line, wherein a gate of the second transistor is connected to a data line, and wherein the other of the source and the drain of the second transistor is connected to a gate of the first transistor.

A semiconductor device of the present invention includes a first transistor of which one of a source and a drain is connected to a current supply line, a light-emitting element of which one electrode is connected to the other of the source and a drain of the first transistor, a second transistor of which one of a source and a drain is connected to a first scan line, and a third transistor of which a gate is connected to a second scan line, wherein a gate of the second transistor is connected to a data line, and wherein the other of the source and the drain of the second transistor is connected to a gate of the first transistor through the third transistor.

A semiconductor device of the present invention includes a first transistor of which one of a source and a drain is connected to a current supply line, a light-emitting element of which one electrode is connected to the other of the source and the drain of the first transistor, a second transistor of which one of a source and a drain is connected to a first scan line, a third transistor of which a gate and one of a source and a drain are connected to the first scan line, and a fourth transistor of which a gate is connected to a second scan line, wherein a gate of the second transistor is connected to the data line, wherein the other of the source and the drain of the second transistor is connected to a gate of the first transistor through the fourth transistor, and wherein the other of the source and the drain of the second transistor is connected to the other of the source and the drain of the third transistor.

A semiconductor device of the present invention includes a first transistor of which one of a source and a drain is connected to a current supply line, a light-emitting element of which one electrode is connected to the other of the source and the drain of the first transistor, a second transistor of which one of a source and a drain is connected to a first scan line, a third transistor of which a gate is connected to the first scan line and one of a source and a drain is connected to a wire, and a fourth transistor of which a gate is connected to a second scan line, wherein a gate of the second transistor is connected to a data line, wherein the other of the source and the drain of the second transistor is connected to a gate of the first transistor through the fourth transistor, and wherein the other of the source and the drain of the second transistor is connected to the other of the source and the drain of the third transistor. Further, the current supply line can be used as the wire.

The third transistor in the present invention can be a diode of which one electrode is connected to the first scan line and the other electrode is connected to the source or the drain of the second transistor.

Moreover, the semiconductor device may have a means for inputting a signal for turning off the first transistor to the gate of the first transistor, in addition to a signal for controlling light-emission or non-light-emission of the light-emitting element to be inputted to the gate of the second transistor from the data line.

Further, the semiconductor device may have a means for inputting a signal for turning off the first transistor into the gate of the first transistor before inputting the signal for controlling light-emission or non-light-emission of the light-emitting element to be inputted to the gate of the second transistor from the data line.

The first transistor of the present invention can be a P-channel transistor and the second transistor can be an N-channel transistor.

The potential of the current supply line of the present invention is higher than the potential of a counter electrode of the light-emitting element.

A light-emitting element included in the semiconductor device of the present invention is an EL element having a light-emitting layer exhibiting electroluminescence (hereinafter referred to as EL) between a pair of electrodes.

Electroluminescence from an EL element of which a light-emitting layer is formed with an organic compound includes light emission generated when returning from a singlet excited state to a ground state (fluorescence) and light emission generated when returning from a triplet excited state to the ground state (phosphorescence). A light-emitting element of the present invention can employ either light emission.

An EL element of which a light-emitting layer is formed with an inorganic material emits light in such a way that an electron taken out from an interface between an insulating layer and the light-emitting layer is accelerated at a high electric field and is excited by colliding with a localized light-emission center. As the inorganic material, ZnS, SrS, BaAl2S4, or the like is given. Further, Mn, Th, Tm, Eu, or the like is given as a light-emission center to be added to the inorganic material.

By using a pixel structure of a semiconductor device of the present invention, it is possible to separately set an on/off potential to be applied to a gate of a driver transistor and an amplitude of a data line. Therefore, a potential to be applied to a gate electrode of a driver transistor of a semiconductor device of the present invention can have enough margin in consideration of switching noise, threshold, off-leak in a light-emission period, and the like.

Further, by using the pixel structure of the semiconductor device of the present invention, the amplitude of the data line can be set to be small. Therefore, the power consumption can be reduced drastically.

BEST MODE FOR CARRYING OUT THE INVENTION

In a basic structure of a semiconductor device of the present invention, a data line is connected to a gate electrode of a selection transistor and one of a source electrode and a drain electrode of the selection transistor is electrically connected to a gate electrode of a driver transistor.

Specific pixel structure and drive timing are described in detail with reference toFIG. 1. Here, although only one pixel is shown, a pixel portion of the semiconductor device actually has a plurality of pixels arranged in matrix in a row direction and a column direction.

Each pixel of the present invention has a selection transistor101(also referred to as a second transistor) and a reset transistor102(also referred to as a third transistor) which determine a potential of a node D by a first scan line107and a data line109, a switch transistor103(also referred to as a fourth transistor) for electrically connecting the node D and a node G by a second scan line108, a driver transistor104(also referred to as a first transistor) for controlling current supply to a light-emitting element106from a current supply line110(also referred to as a power source line) by the potential of the node G, and a holding capacitor105for holding the potential of the node G. The first transistor104is a P-channel transistor while the second transistor101, the third transistor102, and the fourth transistor103are N-channel transistors. However, the polarity of each transistor is not limited as long as the potentials of wires connected to terminals of the transistors are changed appropriately so that the transistors operate in the same manner as the transistors of the present invention. Moreover, the node G is also referred to as a first node while the node D is also referred to as a second node in this specification.

One of a source and a drain of the first transistor104is connected to the current supply line110. Moreover, the other of the source and the drain of the first transistor104is connected to one electrode of the light-emitting element106. The other electrode of the light-emitting element106serves as a counter electrode111. One of a source and a drain of the second transistor101is connected to the first scan line107. A gate of the second transistor101is connected to the data line109. The other of the source and the drain of the second transistor101is connected to one of a source and a drain of the fourth transistor103. A gate of the fourth transistor103is connected to the second scan line108. The other of the source and the drain of the fourth transistor103is connected to a gate of the first transistor104. Moreover, one electrode of the holding capacitor105is connected to the gate of the first transistor104while the other electrode is connected to the current supply line110. A gate and one of a source and a drain of the third transistor102are connected to the first scan line107. The other of the source and the drain of the third transistor102is connected to the other of the source and the drain of the second transistor101.

In this embodiment mode, gate capacitance of the driver transistor104may be used to form a capacitor. In this case, the holding capacitor105is not necessarily provided.

In this embodiment mode, a diode can be provided instead of the third transistor (reset transistor)102as can be clearly seen from the fact that the third transistor102is connected so as to serve as a diode.

The counter electrode111of the light-emitting element106has a lower potential (Vss) than the current supply line110. Vss satisfies Vss<Vdd where Vdd, which is the potential of the current supply line110in a light-emission period of the pixel, is a reference. For example, Vss may be equal to GND (ground potential).

Next, the pixel structure ofFIG. 1is described with reference toFIGS. 2A and 2BandFIGS. 3A and 3B.

FIG. 2Ais a timing chart of potentials of the first scan line107, the second scan line108, the data line109, the node D, and the node G in the pixel structure of the present invention. In the pixel structure of the present invention, whether each pixel emits light or not is selected by a reset period, a selection period, or a sustain period (also referred to as a light-emission period or a non-light-emission period).

In the pixel structure of the present invention, the potential for turning on or off the first transistor (driver transistor) is not inputted from the data line. A potential for turning off the driver transistor is inputted in advance to a gate of the driver transistor in the pixel (the first node), i.e., the holding capacitor. A period in which the signal for turning off the driver transistor is inputted in advance to the gate (the first node) of the driver transistor in the pixel is referred to as a reset period in this specification.

FIG. 2Bshows potentials of the wires and turning on or off of the transistors in the reset period in the pixel structure ofFIG. 1. In order to describe the driving, specific potentials of the current supply lines are set as follows: a High potential of the data line109is 3 V and a Low potential thereof is 0 V, High potentials of the first scan line107and the second scan line108are 10 V and Low potentials thereof are 0 V, a potential of the current supply line110is 8 V, and a potential of the counter electrode111of the light-emitting element106is 0 V. The specific potentials of the wires shown here are just examples, and the present invention is not limited to these as long as the potentials are those required for turning on or off the transistors.

First, in the reset period, selection pulses are outputted to the first scan line107and the second scan line108to provide a potential of 10 V, thereby turning on the reset transistor102and the switch transistor103. At this time, if an absolute value of the threshold is 1 V in each transistor, the potentials of the node D and the node G decrease to 9 V, because the potential decreases from the potential of the first scan line107by the threshold of the reset transistor102. Since the current supply line110has a potential of 8 V, the driver transistor104is turned off.

In this reset period, the selection transistor101is turned on depending on the change of the potential of the data line109. For example, in the case where the node D has a potential of 0 V before the reset period, when the data line109has a potential of 3 V, the selection transistor101is turned on. However, in the reset period, the input of the potential from the reset transistor102is dominant in the node D and the selection transistor101is turned off when the potential of the node D gets higher than the gate potential of the selection transistor101. Therefore, even though the potential of the data line109changes, the potential of a gate terminal of the driver transistor104does not change.

FIGS. 3A and 3Bshow potentials of the wires and turning on or off of the transistors in the case where a light-emission state or a non-light-emission state of the light-emitting element is selected in the selection period in the pixel structure ofFIG. 1. In the selection period, the first scan line107has a potential of 0 V.

At this time, when a potential of 3 V as a light-emission signal is inputted to the data line109, the selection transistor101is turned on, the potentials of the node D and the node G become the potential of 0 V of the first scan line107, the driver transistor104is turned on, and current flows from the current supply line110to the counter electrode111of the light-emitting element106, whereby the light-emitting element106emits light as shown inFIG. 3A.

Moreover, when a potential of 0 V as a non-light-emission signal is inputted to the data line109, the selection transistor101remains off and the potentials of the node D and the node G also remain 9 V and the driver transistor104also remains off as shown inFIG. 3B.

Subsequently, the light-emission period starts, the second scan line108has a potential of 0 V, and the switch transistor103is turned off. Then, the potential of the node G determined in the selection period is held by the holding capacitor105.

As thus described, by using the pixel structure of the semiconductor device of the present invention, it is possible to separately set the on/off potential to be applied to the gate electrode of the first transistor (driver transistor) and the amplitude of the data line. Therefore, the amplitude of the data line can be set to be small, whereby the power consumption can be reduced drastically.

This embodiment mode can be freely combined with other embodiment modes and embodiments.

Embodiment Mode 2 will show an example in which the connection of the reset transistor102in the pixel structure shown inFIG. 1has been changed.FIG. 4shows a specific structure based on which the description is made. Here, although only one pixel is shown, a pixel portion of a semiconductor device actually has a plurality of pixels arranged in matrix in a row direction and a column direction.

Each pixel of the present invention has a selection transistor (also referred to as a second transistor)301and a reset transistor302(also referred to as a third transistor) which determine a potential of a node D by a first scan line307and a data line309, a switch transistor303(also referred to as a fourth transistor) for electrically connecting the node D and a node G by a second scan line308, a driver transistor304(also referred to as a first transistor) which controls current supply to a light-emitting element306from a current supply line310by the potential of the node G, and a holding capacitor305for holding the potential of the node G.

In this embodiment mode, gate capacitance of the driver transistor304may be used to form a capacitor. In this case, the holding capacitor305is not necessarily formed.

One of a source and a drain of the first transistor304is connected to the current supply line310while the other of the source and the drain of the first transistor304is connected to one electrode of the light-emitting element306. The other electrode of the light-emitting element306serves as a counter electrode311. One of a source and a drain of the second transistor301is connected to the first scan line307, a gate of the second transistor301is connected to the data line309, and the other of the source and the drain of the second transistor301is connected to one of a source and a drain of the fourth transistor303. A gate of the fourth transistor303is connected to the second scan line while the other of the source and the drain of the fourth transistor303is connected to a gate of the first transistor304. One electrode of the holding capacitor305is connected to the gate of the first transistor304while the other electrode thereof is connected to the current supply line310. A gate of the third transistor302is connected to the first scan line307. One of a source and a drain of the third transistor302is connected to the current supply line310. The other of the source and the drain of the third transistor302is connected to the other of the source and the drain of the second transistor301.

Similarly to the reset transistor102inFIG. 1, the reset transistor302sets a potential of the node D at a High potential of 10V in the reset period, thereby turning off the driver transistor304. A driving method, timing, and the like in the reset period, the selection period, and the light-emission period are similar to those inFIGS. 2A and 2BandFIGS. 3A and 3B.

In this embodiment mode, one of a source and a drain of the reset transistor302is connected to the current supply line310; however, a current supply line may be additionally provided to be connected to the one of the source and the drain of the reset transistor302.

This embodiment mode can be freely combined with other embodiment modes and embodiments.

Embodiment Mode 3 will show an example of a pixel structure, which is different from that shown inFIG. 1. A specific structure is shown inFIG. 5based on which the description is made. Here, although only one pixel is shown, a pixel portion of a semiconductor device actually has a plurality of pixels arranged in matrix in a row direction and a column direction.

As shown inFIG. 5, each pixel in this embodiment mode has a selection transistor401(also referred to as a second transistor) and a reset transistor402(also referred to as a third transistor) which determine a potential of a node G by a scan line408and a data line409, a driver transistor404(also referred to as a first transistor) which controls current supply from a current supply line410to a light-emitting element406based on the potential of the node G, and a holding capacitor405which holds the potential of the node G. It is to be noted that the first transistor404is a P-channel transistor and the second transistor401and the third transistor402are N-channel transistors. However, the polarity of each transistor is not limited in particular as long as the potentials of wires connected to terminals of the transistors are changed appropriately so that the transistors operate in the same manner as the transistors of the present invention.

In this embodiment mode, gate capacitance of the driver transistor404may be used to provide a capacitor. In this case, the holding capacitor405is not always necessary.

Further, in this embodiment mode, a diode can be provided instead of the third transistor (reset transistor)402. This is obvious from the fact that the third transistor402is connected so that the third transistor402serves as a diode.

A counter electrode411of the light-emitting element406is set to have a potential Vss which is lower than that of the current supply line410. Vss satisfies Vss<Vdd, where Vdd, which is a potential of the current supply line410in a light-emission period, is a reference. For example, Vss may be equal to GND (ground potential).

Moreover, a High potential of the scan line408is set to be higher than the potential of the current supply line410, a potential thereof in a selection period (this potential is hereinafter referred to as a Low potential1) is set to be the same as a Low potential of the data line409, and a potential thereof in a light-emission period (this potential is hereinafter referred to as a Low potential2) is set to be the same as a High potential of the data line409.

Next, an operation method with a pixel structure ofFIG. 5is described with reference toFIGS. 6A and 6B, andFIGS. 7A and 7B.

FIG. 6Ais a timing chart showing potentials of the scan line408, the data line409, and the node G in the pixel structure of the present invention. In the pixel structure of the present invention, a light-emission state or a non-light-emission state of each pixel is selected in accordance with a reset period, a selection period, and a sustain period (also referred to as a light-emission period or a non-light-emission period).

In the pixel structure of the present invention, a potential for turning on or off the first transistor (driver transistor) is not inputted from the data line. The potential for turning off the driver transistor is inputted in advance to a gate (a first node) of the driver transistor in a pixel, i.e., a holding capacitor. A period in which a signal for turning off the driver transistor is inputted in advance to the gate of the driver transistor in the pixel is referred to as a reset period in this specification.

FIG. 6Bshows potentials of wires and turning on or off of the transistors in the reset period in the pixel structure shown inFIG. 5. In order to explain the driving, a High potential of the data line409is set to be 0 V, a Low potential thereof is set to be −3 V, a High potential of the scan line408is set to be 10 V, a Low potential1thereof is set to be 0 V, a Low potential2thereof is set to be −3 V, a potential of the current supply line410is set to be 8 V, and a potential of the counter electrode411of the light-emitting element406is set to be 0 V. These specific potentials of the respective wires are just examples and the present invention is not limited to these as long as the transistors can be turned on or off by the potentials of these wires.

First, in the reset period, a selection pulse is outputted to the scan line408so that the potential of the scan line408changes from 0 V to 10 V, whereby the reset transistor402is turned on. If the absolute values of the thresholds of the transistors at this time are both 1 V, the node G has a potential of 9 V because the potential decreases from the potential of the scan line408by the threshold of the reset transistor402. Since the current supply line410has a potential of 10 V, the driver transistor404is turned off.

In this reset period, the selection transistor401is turned on depending on the change of the potential of the data line409. For example, if the node D has a potential of 0 V before the reset period and the data line has a potential of 3 V, the selection transistor401is turned on. However, when the input of the potential from the reset transistor is dominant in the node D in the reset period, resulting in that the node D has a higher potential than the gate potential of the selection transistor401, the selection transistor401is turned off. Therefore, even if the potential of the data line409changes, the potential of a gate terminal of the driver transistor404does not change.

FIGS. 7A and 7Bshow potentials of the wires and turning on or off of the transistors in the case of selecting a light-emission state or a non-light-emission state of the light-emitting element in the selection period in the pixel structure ofFIG. 5. In the selection period, the scan line408has a potential of −3 V.

At this time, if a potential of 0 V as a light-emission signal is inputted to the data line409, the selection transistor401is turned on as shown inFIG. 7Aand the node G has a potential of −3 V, which is the same as the potential of the scan line408, so that the driver transistor404is turned on. Thus, current is fed from the current supply line410to the counter electrode411of the light-emitting element406, whereby the light-emitting element406emits light.

When a potential of −3 V as a non-light-emission signal is inputted to the data line409, the selection transistor401remains off as shown inFIG. 7B. Therefore, the potential of the node G remains 9 V and the driver transistor404also remains off.

Subsequently, the light-emission period starts, and the scan line408has a potential of 0 V. In the selection period, if the node G has a potential of 9 V, the selection transistor401remains off and the potential of the node G (9 V) is held in the holding capacitor405. In the case where the node G has a potential of −3 V in the selection period, if the data line409has a High potential of 0 V even only once in the light-emission period, the selection transistor401is turned on. At this time, if the threshold voltage of the selection transistor401is 1 V, the node G has a potential of −1 V because the potential decreases from the potential of the scan line408(0 V) by the threshold of the selection transistor401. However, the driver transistor404remains on.

At this time, Vgs (voltage between a gate electrode and a source electrode) in the case where the driver transistor404in each pixel is turned on is −7 V or −11 V depending on the potential of the data line409in the light-emission period. However, Vgs does not affect the luminance of the light-emitting element406that much because the light-emitting element406is driven in a linear region in either case.

This embodiment mode can be freely combined with other embodiment modes and embodiments.

Embodiment 1 will describe a cross-sectional structure of a light-emitting device equipped with a semiconductor device of the present invention with reference to the drawings. Here, a cross section of a multilayer structure of a light-emitting device including a selection transistor101, a driver transistor104, and a light-emitting element is described with reference toFIG. 8.

As a substrate1201(a first substrate) having an insulating surface, a glass substrate, a quartz substrate, a stainless steel substrate, or the like can be used. A substrate formed with a flexible synthetic resin such as acrylic or plastic typified by polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or the like can also be used as long as the substrate can resist treatment temperature in the manufacturing process.

Over the substrate1201, a base film1202is formed first. The base film1202can be formed by using an insulating film such as a silicon oxide film, a silicon nitride film, or a silicon nitride oxide film. Next, an amorphous semiconductor film is formed over the base film1202. The thickness of the amorphous semiconductor film ranges from 25 to 100 nm. Not only silicon but also silicon germanium can be used as the material of the amorphous semiconductor film. Subsequently, the amorphous semiconductor film is crystallized as necessary, thereby forming a crystalline semiconductor film. As the crystallization method, a heating furnace, laser irradiation, irradiation with light emitted from a lamp, or a combination thereof can be used. For example, a metal element is added to the amorphous semiconductor film and a heat treatment is conducted using a heating furnace to form the crystalline semiconductor film. Adding a metal element in this way is preferable because the crystallization can be carried out at low temperature.

Since a thin film transistor (TFT) formed with a crystalline semiconductor has higher electric field effect mobility and larger ON current than a TFT formed with an amorphous semiconductor, the TFT formed with a crystalline semiconductor is more suitable for a semiconductor device.

Next, etching is carried out to shape the crystalline semiconductor film into a predetermined form. Then, an insulating film serving as a gate insulating film is formed. The insulating film is formed in thickness from 10 to 150 nm so as to cover the semiconductor film. For example, a silicon oxynitride film, a silicon oxide film, or the like can be formed in a single layer or multilayer structure.

Next, a conductive film serving as a gate electrode is formed over the crystalline semiconductor film with the gate insulating film interposed therebetween. The gate electrode may have a single layer or multilayer structure, and here the gate electrode is formed by stacking plural conductive films. Conductive films1203A and1203B are formed with an element selected from Ta, W, Ti, Mo, Al, and Cu, or an alloy or compound material containing any one of the above elements as its main component. In this embodiment, the conductive film1203A is formed using a tantalum nitride film with a thickness of 10 to 50 nm and the conductive film1203B is formed using a tungsten film with a thickness of 200 to 400 nm.

Next, an impurity element is added to the crystalline semiconductor film by using the gate electrode as a mask, thereby forming an impurity region. At this time, a low-concentration impurity region may be formed in addition to a high-concentration impurity region. The low-concentration impurity region is referred to as an LDD (Lightly Doped Drain) region.

Next, insulating films1204and1205serving as an interlayer insulating film1206are formed. The insulating film1204is preferably formed by using an insulating film containing nitrogen, and here a 100-nm-thick silicon nitride film is formed by a plasma CVD method. The insulating film1205is preferably formed with an organic material or an inorganic material. As the organic material, polyimide, acrylic, polyamide, polyimide-amide, benzocyclobutene, or siloxane can be used. Siloxane has a skeletal structure with a bond of silicon (Si) and oxygen (O). As a substituent, an organic group containing at least hydrogen (such as an alkyl group or aromatic hydrocarbon) is used. As a substituent, a fluoro group or a fluoro group and an organic group containing at least hydrogen may be used. As the inorganic material, an insulating film containing oxygen or nitrogen, such as a silicon oxide (SiOx) film, a silicon nitride (SiNx) film, a silicon oxynitride (SiOxNy) (x>y, x and y are natural numbers) film, or a silicon nitride oxide (SiNxOy) (x<y, x and y are natural numbers) film can be used. It is noted that a film containing an organic material has favorable flatness whereas the organic material absorbs moisture and oxygen. In order to prevent the absorption of moisture and oxygen, an insulating film containing an inorganic material is preferably formed over the insulating film containing an organic material.

Next, after forming a contact hole in an interlayer insulating film1206, a conductive film1207serving as a source wire and a drain wire of a transistor is formed. The conductive film1207can be formed with an element selected from aluminum (Al), titanium (Ti), molybdenum (Mo), tungsten (W), and silicon (Si), or alloy containing any of these elements. In this embodiment, the conductive film1207is formed with a multilayer film including a titanium film, a titanium nitride film, a titanium-aluminum alloy film, and another titanium film.

Next, an insulating film1208is formed so as to cover the conductive film1207. The insulating film1208can be formed with the material mentioned as the material of the interlayer insulating film1206. Next, a pixel electrode (also referred to as a first electrode)1209is formed in an opening portion provided in the insulating film1208. In the opening portion, in order to improve step coverage of the pixel electrode1209, an edge surface of the opening portion preferably has a round shape so as to have a plurality of radii of curvature.

The pixel electrode1209is preferably formed with a conductive material such as metal, alloy, an electrically conductive compound, a mixture thereof, or the like, each having a high work function (a work function of 4.0 eV or higher). As a specific example of the conductive material, indium oxide containing tungsten oxide (IWO), indium zinc oxide containing tungsten oxide (IWZO), indium oxide containing titanium oxide (ITiO), indium tin oxide containing titanium oxide (ITTiO), or the like can be given. Needless to say, indium tin oxide (ITO), indium zinc oxide (IZO), indium tin oxide with silicon oxide added (ITSO), or the like can also be used.

The composition ratio of the conductive material is as follows. The composition ratio of indium oxide containing tungsten oxide may be tungsten oxide:indium oxide=1.0 wt %:99.0 wt %. The composition ratio of indium zinc oxide containing tungsten oxide may be tungsten oxide:zinc oxide:indium oxide=1.0 wt %:0.5 wt %:98.5 wt %. The composition ratio of indium oxide containing titanium oxide may be titanium oxide:indium oxide=1.0 to 5.0 wt %:99.0 to 95.0 wt %. The composition ratio of indium tin oxide (ITO) may be tin oxide: indium oxide=10.0 wt %:90.0 wt %. The composition ratio of indium zinc oxide (IZO) may be zinc oxide:indium oxide=10.7 wt %:89.3 wt %. The composition ratio of indium tin oxide containing titanium oxide may be titanium oxide:tin oxide:indium oxide=5.0 wt %:10.0 wt %:85.0 wt %. These composition ratios are just examples, and the composition ratio may be appropriately determined.

Next, an electroluminescent layer1210is formed by an evaporation method or an ink jet method. The electroluminescent layer1210is formed with an organic material or an inorganic material by appropriately combining an electron-injecting layer (EIL), an electron-transporting layer (ETL), a light-emitting layer (EML), a hole-transporting layer (HTL), a hole-injecting layer (HIL), and the like. It is not always necessary that the boundary between the respective layers is clear. In some cases, the materials of the layers are partially mixed, resulting in that the interface is unclear.

The electroluminescent layer is preferably formed with plural layers having different functions, such as a hole-injecting/transporting layer, a light-emitting layer, an electron-injecting/transporting layer, and the like.

The hole-injecting/transporting layer is preferably formed with an organic compound material having a hole-transporting property and an inorganic compound material having an electron-receiving property with respect to the organic compound material. This structure generates a large number of hole carriers in an organic compound, which originally has almost no inherent carriers, to provide an excellent hole-injecting/transporting property. Accordingly, the driving voltage can be lower than conventional driving voltage. Further, since the hole-injecting/transporting layer can be made thick without raising the driving voltage, short circuit of the light-emitting element due to dust and the like can be reduced.

As an organic compound having a hole-transporting property, for example, copper phthalocyanine (abbreviated to CuPc), vanadyl phthalocyanine (abbreviated to VOPc), 4,4′,4″-tris(N,N-diphenylamino)triphenylamine (abbreviated to TDATA), 4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine (abbreviated to MTDATA), 1,3,5-tris[N,N-di(m-tolyl)amino]benzene (abbreviated to m-MTDAB), N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (abbreviated to TPD), 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviated to NPB), 4,4′-bis{N-[4-di(m-tolyl)amino]phenyl-N-phenylamino}biphenyl (abbreviated to DNTPD), 4,4′,4″-tris(N-carbazolyl)triphenylamine (abbreviated to TCTA), or the like is given as an example. However, the organic compound is not limited to these.

As the inorganic compound material having an electron-receiving property, titanium oxide, zirconium oxide, vanadium oxide, molybdenum oxide, tungsten oxide, rhenium oxide, ruthenium oxide, zinc oxide, or the like is given. In particular, vanadium oxide, molybdenum oxide, tungsten oxide, and rhenium oxide are preferable because these can be formed by vacuum evaporation and easily treated.

The light-emitting layer may use a singlet excited light-emitting material and a triplet excited material including a metal complex. For example, among a red light-emitting pixel, a green light-emitting pixel, and a blue light-emitting pixel, the red light-emitting pixel whose luminance half-reduced period is relatively short is formed with a triplet-excited light-emitting material and the others are formed with singlet-excited light-emitting materials. Because of high luminous efficiency, the power consumption of a triplet-excited light-emitting material is less than that of a singlet-excited light-emitting material to obtain the same luminance. In other words, if the red light-emitting pixel is formed with a triplet-excited light-emitting material, the reliability thereof can be improved because the amount of current to be fed to the light-emitting element of the red light-emitting pixel is small. In order to reduce the power consumption, the red light-emitting pixel and the green light-emitting pixel may be formed with triplet-excited light-emitting materials and the blue light-emitting pixel may be formed with a singlet-excited light-emitting material. By forming the green light-emitting element, which has high visibility to human eyes, with a triplet-excited light-emitting material, further reduction in the power consumption can be achieved.

The light-emitting layer may have a structure for displaying in colors by forming a light-emitting layer with a different light emission wavelength band for each pixel. Typically, light-emitting layers each corresponding to each color of R (red), G (green), and B (blue) are formed. Even in this case, by having a structure in which a filter for passing light with the light emission wavelength band is provided on a light emission side of the pixel, color purity can be increased and reflection (glare) of the pixel portion can be prevented. By providing the filter, it is possible to omit a circular polarizing plate and the like which have been conventionally required and to avoid the loss of light emitted from the light-emitting layer. Moreover, the change of color tone which occurs when the pixel portion (display screen) is viewed obliquely can be decreased.

In addition, as an electroluminescent material applicable to the light-emitting layer a high molecular weight material such as a polyparaphenylenevinylene-based material, a polyparaphenylene-based material, a polythiophene-based material, a polyfluorene-based material, or the like is given.

In any way, the layer structure of the electroluminescent layer can be modified. Within the scope for achieving the function as the light-emitting element, such modification is allowable that predetermined hole or electron injecting/transporting layer and light-emitting layer are replaced by electrode layers having the same purposes or a light-emitting material is provided by being diffused.

Moreover, a color filter (colored layer) may be formed over a sealing substrate. The color filter (colored layer) can be formed by an evaporation method or a droplet discharging method. By using the color filter (colored layer), high-definition display can be carried out because the color filter (colored layer) can compensate a broad peak so as to be a sharp peak in a light-emission spectrum in each color of RGB.

Further, full-color display can be achieved by forming a material expressing light emission of a single color and combining the material with a color filter or a color conversion layer. The color filter (colored layer) or the color conversion layer may be formed over, for example, a second substrate (sealing substrate) and pasted to the substrate1201.

Then, a counter electrode (also referred to as a second electrode)1211is formed by a sputtering method or an evaporation method. One of the pixel electrode1209and the counter electrode1211serves as an anode while the other serves as a cathode.

As a cathode material, it is preferable to use metal, alloy, an electrically conductive compound, a mixture thereof, or the like each having a low work function (a work function of 3.8 eV or lower). As a specific example of the cathode material, an element belonging to Group 1 or 2 in the periodic table, i.e., alkali metal such as Li or Cs, alkaline earth metal such as Mg, Ca, or Sr, alloy containing these metal such as Mg:Ag or Al:Li, a compound containing these metal such as LiF, CsF, or CaF2, or transition metal containing rare-earth metal can be used. However, since the cathode needs to have a light-transmitting property, these metal or alloy containing the metal is formed extremely thin and another metal such as ITO (including alloy) is stacked thereover.

After that, a protective film including a silicon nitride film or a DLC (Diamond-like Carbon) film may be provided so as to cover the counter electrode1211. Through the above steps, a light-emitting device of the present invention is completed.

This embodiment can be freely combined with the above Embodiment Modes and another Embodiment.

Embodiment 2 will describe an example of an active matrix display using a pixel structure of the present invention, with reference toFIG. 9.

The active matrix display includes a substrate501over which a transistor and a wire are formed, an FPC508for connecting the wire with the outside, a light-emitting element, and a counter substrate502for sealing the light-emitting element.

A display portion506including a plurality of pixels arranged in matrix, a data line driver circuit503, a scan line driver circuit A504, a scan line driver circuit B505, and an FPC connection portion507to be connected to the FPC508for which various power sources and signals are inputted are provided over the substrate501.

The data line driver circuit503has circuits such as a shift register, a latch, a level shifter, and a buffer, and data signal are outputted to a data line of each column. Each of the scan line driver circuit A504and the scan line driver circuit B505has circuits such as a shift register, a level shifter, and a buffer. The scan line driver circuit A504outputs a sequential selection pulse to a second scan line of each row while the scan line driver circuit B505outputs a sequential selection pulse to a first scan line of each row.

Whether the light-emitting element emits light or not is controlled in accordance with a data signal written in each pixel at such timing that selection pulses are outputted from the scan line driver circuit A504and the scan line driver circuit B505.

In addition to the above driver circuit, circuits such as a CPU and a controller may be integrally formed over the substrate501. This makes it possible to decrease the number of external circuits (ICs) to be connected and further reduce the weight and thickness, which is particularly effective for mobile terminals and the like.

In this specification, as shown inFIG. 9, a panel to which the steps up to attaching the FPC have been carried out and which uses an EL element for the light-emitting element is referred to as an EL module.

This embodiment can be freely combined with the above embodiment Modes and embodiments.

Embodiment 3 will describe an example in which the potential of a current supply line is compensated to suppress an effect due to fluctuation of a current value of a light-emitting element caused by change in ambient temperature and change over time.

A light-emitting element using an organic compound in a light-emitting layer has such a property that its resistance value (internal resistance value) is easier to change than a light-emitting element using an inorganic material, depending on the ambient temperature. Specifically, when the room temperature is set at a normal temperature, if the temperature is higher than normal, the resistance value decreases, while if the temperature is lower than normal, the resistance value increases. Therefore, if the temperature increases, in the case of applying the same voltage, the current value increases, causing the luminance to exceed the desired luminance. If the temperature decreases, in the case of applying the same voltage, the current value decreases, causing the luminance to fall below the desired luminance. The light-emitting element has such a property that the current value decreases over time. Specifically, when a light-emission period and a non-light-emission period are accumulated, the resistance value increases with the deterioration of the light-emitting element. Thus, if the light-emission period and the non-light-emission period are accumulated, in the case of applying the same voltage, the current value decreases, causing the luminance to fall below the desired luminance.

Because of the above-mentioned property of the light-emitting element, the luminance varies because of the change in the ambient temperature or the change over time. In this embodiment, by using the potential of the current supply line of the present invention for compensation, it is possible to suppress an effect due to fluctuation in the current value of the light-emitting element caused by the change in the ambient temperature and the change over time. This embodiment is particularly effective when the light-emitting element is an organic EL element whose resistance value easily fluctuates by the change in the ambient temperature and the change over time.

FIG. 10shows a circuit structure. In a pixel, a semiconductor device shown inFIG. 1is provided. The description on the same portion as that inFIG. 1is omitted. InFIG. 10, a current supply line1401and a counter electrode1402are connected to each other through a driver transistor1403and a light-emitting element1404as shown inFIG. 1. Then, current flows from the current supply line1401to the counter electrode1402. The light-emitting element1404emits light in accordance with the amount of current flowing from the current supply line1401to the counter electrode1402. A reference numeral1405denotes a data line driver circuit.

In the case of such a pixel structure, if the potentials of the current supply line1401and the counter electrode1402are fixed and current keeps flowing to the light-emitting element1404, the characteristic of the light-emitting element1404deteriorates. Moreover, the characteristic of the light-emitting element1404changes according to the ambient temperature.

Specifically, if current keeps flowing to the light-emitting element1404, the voltage-current characteristic begins to shift. In other words, the resistance value of the light-emitting element1404increases, so that the amount of flowing current gets smaller even though the same amount of voltage is applied. Moreover, although the same amount of current is fed, the luminous efficiency decreases to lower the luminance. As for the temperature characteristic, if the temperature decreases, the voltage-current characteristic shifts, which raises the resistance value of the light-emitting element1404.

Therefore, the above-mentioned deterioration and effect by the fluctuation are compensated by using a monitor circuit. In this embodiment, by adjusting the potential of the current supply line1401, the deterioration and the fluctuation by the temperature of the light-emitting element1404are compensated.

Here, a structure of a monitor circuit is described. A first monitor power source line1406and a second monitor power source line1407are connected to each other through a monitor current source1408and a monitor light-emitting element1409. To a connection point of the monitor light-emitting element1409and the monitor current source1408, an input terminal of a sampling circuit1410for outputting the potential of the monitor light-emitting element1409is connected. To an output terminal of the sampling circuit1410, the current supply line1401is connected. Therefore, the potential of the current supply line1401is controlled by the output of the sampling circuit1410.

Next, operation of the monitor circuit is described. First, the monitor current source1408feeds current with the amount required to make the light-emitting element1404emit light with the largest number of grayscales. The current value at this time is Imax.

Then, at opposite ends of the monitor light-emitting element1409, the voltage with the level necessary to feed current with the amount of Imax is applied. If the current-voltage characteristic of the monitor light-emitting element1409changes in accordance with the deterioration, the temperature, or the like, the voltage to be applied at the opposite ends of the monitor light-emitting element1409also changes to be optimum. Therefore, the effect of the fluctuation in the monitor light-emitting element1409(such as deterioration or the temperature change) can be compensated.

To an input terminal of the sampling circuit1410, the voltage to be applied to the monitor light-emitting element1409is inputted. Therefore, the potential of the output terminal of the sampling circuit1410, i.e., the potential of the current supply line1410is compensated by the monitor circuit, whereby the fluctuation of the light-emitting element1404by the deterioration or the temperature can be compensated.

The sampling circuit1410may be any kind of circuit as long as the voltage in accordance with the inputted current can be outputted. For example, a voltage follower circuit is also a kind of an amplifier circuit; however, the circuit is not limited to this. The circuit may be formed using any one of an operational amplifier, a bipolar transistor, and a MOS transistor or a combination of these.

The monitor light-emitting element1409is desirably formed over the same substrate, at the same time, and by the same manufacturing method as the light-emitting element1404of the pixel, because the compensation would be misaligned if the characteristic were different in the light-emitting element for the monitor and the light-emitting element to be arranged in the pixel.

Since the light-emitting element1404arranged in the pixel often has a period in which current does not flow, if current keeps flowing to the monitor light-emitting element1409, the deterioration progresses in the monitor light-emitting element1409rather than in the light-emitting element1404. Therefore, the potential to be outputted from the sampling circuit1410becomes an excessively compensated potential. Accordingly, the potential outputted from the sampling circuit1410may follow the actual degree of deterioration of the pixel. For example, if the lighting ratio of the whole screen is 30% on average, current may be fed to the monitor light-emitting element1409for the period corresponding to a luminance of 30%. At that time, the monitor light-emitting element1409has a period in which current does not flow; however, it is necessary to supply voltage constantly from the output terminal of the sampling circuit1410. In order to achieve this, the input terminal of the sampling circuit1410may be provided with a capacitor element where the potential generated when current is fed to the monitor light-emitting element1409is held.

If the monitor circuit is operated in accordance with the largest number of grayscales, the excessively compensated potential is outputted. However, since burning-in at the pixel (variation in luminance due to the fluctuation in the degree of deterioration per pixel) becomes unnoticeable, it is desirable that the monitor circuit be operated in accordance with the largest number of grayscales.

In this embodiment, it is more preferable that the driver transistor1403be operated in a linear region. The driver transistor1403is operated approximately as a switch by being operated in a linear region. Therefore, it is possible to suppress the effect of the fluctuation in the characteristic by the deterioration, temperature, and the like of the driver transistor1403. In the case of operating the driver transistor1403only in a linear region, whether current is fed to the light-emitting element1404or not is often controlled in a digital manner In this case, in order to increase the number of grayscales, it is preferable to combine a time grayscale method, an area grayscale method, and the like.

This embodiment can be freely combined with the above embodiment modes and embodiments.

As electronic appliances equipped with semiconductor devices of the present invention, a television receiving appliance, a camera such as a video camera or a digital camera, a goggle type display, a navigation system, a sound reproducing device (such as a car audio component), a computer, a game machine, a mobile information terminal (such as a mobile computer, a mobile phone, a mobile game machine, or an electronic book), an image reproducing device equipped with a recording medium (specifically, a device for reproducing a recording medium such as a digital versatile disk (DVD), which is equipped with a display for displaying the reproduced image), and the like are given. Specific examples of these electronic appliances are shown inFIG. 11,FIG. 12,FIGS. 13A and 13B,FIGS. 14A and 14B,FIG. 15, andFIGS. 16A to 16E.

FIG. 11shows an EL module in which a display panel5001and a circuit substrate5011are combined. Over the circuit substrate5011, a control circuit5012, a signal dividing circuit5013, and the like are formed, and the display panel5001and the circuit substrate5011are connected to each other with a connection wire5014.

This display panel5001is equipped with a pixel portion5002in which a plurality of pixels are provided, a scan line driver circuit5003, and a data line driver circuit5004for supplying a video signal to the selected pixel. In the case of manufacturing an EL module, semiconductor devices constituting the pixels in the pixel portion5002may be manufactured by using the above embodiments. Further, control driver circuit portions such as the scan line driver circuit5003and the data line driver circuit5004can be manufactured by using TFTs formed by the above embodiments. Thus, an EL module television shown inFIG. 11can be completed.

FIG. 12is a block diagram showing a main constitution of an EL television receiving machine. A video signal and an audio signal are received with a tuner5101. The video signal is processed by an image signal amplifying circuit5102, an image signal processing circuit5103for converting a signal outputted from the image signal amplifying circuit5102into a color signal corresponding to red, green, or blue, and a control circuit5012for converting the image signal in accordance with an input specification of a driver IC. The control circuit5012outputs signals to a scan line side and a data line side, respectively. In the case of digital driving, a signal dividing circuit5013may be provided on the data line side, so that the inputted digital signal may be divided into m number of signals and supplied.

Among the signals received with the tuner5101, an audio signal is sent to an audio signal amplifying circuit5105and outputted to a speaker5107through an audio signal processing circuit5106. A control circuit5108receives control information such as a receiving station (receiving frequency) or volume from the input portion5109and sends a signal to the tuner5101or the audio signal processing circuit5106.

As shown inFIG. 13A, a television receiving machine can be completed by incorporating an EL module in a housing5201. With the EL module, a display screen5202is formed. Further, speakers5203, an operation switch5204, and the like are appropriately provided.

FIG. 13Bshows a television receiving appliance of which only a display can be wirelessly carried. A housing5212incorporates a battery and a signal receiver, and a display portion5213and a speaker portion5217are driven with the battery. The battery can be repeatedly charged with a battery charger5210. The battery charger5210can send and receive a video signal and can send the video signal to the signal receiver in the display. The housing5212is controlled by an operation key5216. Since the appliance shown inFIG. 13Bcan send a signal from the housing5212to the battery charger5210by operating the operation key5216, the appliance can also be referred to as a two-way video/audio communication device. Moreover, by operating the operation key5216, a signal can be sent from the housing5212to the battery charger5210and the signal can be further sent from the battery charger5210to another electronic appliance, so that communication control of another electronic appliance is also possible. Therefore, it is also referred to as a general-purpose remote control device. The present invention can be applied to the display portion5213.

By using the semiconductor device of the present invention in the television receiving appliance shown inFIG. 11,FIG. 12, andFIGS. 13A and 13B, it is possible to separately set the on/off potential to be applied to a gate electrode of a first transistor (driver transistor) and the potential of the amplitude of a data line in a pixel of a display portion. Therefore, the amplitude of the data line can be set to be small, whereby a semiconductor device consuming much less electric power can be provided. Accordingly, a product with the drastically suppressed power consumption can be provided to customers.

Needless to say, the present invention is not limited to the television receiving machine, and the present invention can be applied to various purposes, such as monitors for personal computers, large display media like information displaying boards at railway stations or airports, or advertisement display boards on streets.

FIG. 14Ashows a module in which a display panel5301and a printed wiring substrate5302are combined. The display panel5301is equipped with a pixel portion5303in which a plurality of pixels are provided, a first scan line driver circuit5304, a second scan line driver circuit5305, and a data line driver circuit5306for supplying a video signal to the selected pixel.

The printed wiring substrate5302is equipped with a controller5307, a central processing unit (CPU)5308, a memory5309, a power source circuit5310, an audio processing circuit5311, a sending/receiving circuit5312, and the like. The printed wiring substrate5302and the display panel5301are connected to each other by a flexible wiring substrate (FPC)5313. The printed wiring substrate5302may be provided with a capacitor element, a buffer circuit, and the like so that noise on power source voltage and a signal, and a delay of the signal rise time can be prevented. Moreover, the controller5307, the audio processing circuit5311, the memory5309, the CPU5308, the power source circuit5310, and the like can be mounted to the display panel5301by a COG (Chip On Glass) method. By the COG method, the scale of the printed wiring substrate5302can be reduced.

Various control signals are inputted/outputted through an interface (I/F) portion5314provided to the printed wiring substrate5302. Moreover, an antenna port5315for sending/receiving a signal between the antenna and the printed wiring substrate5302is provided to the printed wiring substrate5302.

FIG. 14Bis a block diagram showing a module shown inFIG. 14A. This module has a VRAM5316, a DRAM5317, a flash memory5318, and the like as the memory5309. The VRAM5316stores image data to be displayed on the panel, the DRAM5317stores image data or audio data, and the flash memory5318stores various programs.

The power source circuit5310supplies electric power for operating the display panel5301, the controller5307, the CPU5308, the audio processing circuit5311, the memory5309, and the sending/receiving circuit5312. The power source circuit5310is sometimes equipped with a current source depending on the specification of the panel.

The CPU5308has a control signal generating circuit5320, a decoder5321, a register5322, an arithmetic circuit5323, a RAM5324, an interface (I/F) portion5319for the CPU5308, and the like. Various signals inputted to the CPU5308through the interface portion5319are inputted to the arithmetic circuit5323, the decoder5321, and the like after being held in the register5322once. The arithmetic circuit5323performs calculation based on the inputted signal and specifies an address to send various instructions to. Meanwhile, the signal inputted to the decoder5321is decoded and the decoded signal is inputted to the control signal generating circuit5320. The control signal generating circuit5320generates a signal including various instructions based on the inputted signal and sends the signal to the address specified by the arithmetic circuit5323, specifically to the memory5309, the sending/receiving circuit5312, the audio processing circuit5311, the controller5307, and the like.

The memory5309, the sending/receiving circuit5312, the audio processing circuit5311, and the controller5307operate in accordance with the received instructions. Hereinafter the operation is briefly described.

A signal inputted from an inputting means5325is sent to the CPU5308mounted on the printed wiring substrate5302through the I/F portion5314. The control signal generating circuit5320converts image data stored in the VRAM5316into a predetermined format in accordance with the signal sent from the inputting means5325such as a pointing device or a keyboard and sends the converted image data to the controller5307.

The controller5307processes the signal including the image data which has been sent from the CPU5308in accordance with the specification of the panel and supplies the signal to the display panel5301. The controller5307generates a Hsync signal, a Vsync signal, a clock signal CLK, alternating voltage (AC Cont), and a switching signal L/R based on various signals inputted from the CPU5308and power source voltage inputted from the power source circuit5310, and supplies these signals to the display panel5301.

The sending/receiving circuit5312processes a signal which has been sent and received as an electric wave with an antenna5328and specifically includes a high-frequency circuit such as an isolator, a bandpass filter, a VCO (Voltage Controlled Oscillator), an LPF (Low Pass Filter), a coupler, or a balun. Among the signals sent to and received from the sending/receiving circuit5312, a signal including audio information is sent to the audio processing circuit5311in accordance with the instruction from the CPU5308.

The signal including audio information which has been sent in accordance with the instruction of the CPU5308is demodulated into an audio signal in the audio processing circuit5311and sent to the speaker5327. The audio signal which has been sent from a microphone5326is modulated in the audio processing circuit5311and sent to the sending/receiving circuit5312in accordance with an instruction from the CPU5308.

The controller5307, the CPU5308, the power source circuit5310, the audio processing circuit5311, and the memory5309can be mounted as a package in this embodiment. This embodiment can be applied to any circuit other than a high-frequency circuit such as an isolator, a bandpass filter, a VCO (Voltage Controlled Oscillator), an LPF (Low Pass Filter), a coupler, or a balun.

FIG. 15shows a mode of a mobile phone including the module shown inFIGS. 14A and 14B. The display panel5301is detachably incorporated in a housing5330. The housing5330can have any shape and size in accordance with the size of the display panel5301. The housing5330with the display panel5301fixed is fitted into a printed substrate5331and assembled as a module.

The display panel5301is connected to the printed substrate5331through the FPC5313. The printed substrate5331is provided with a speaker5332, a microphone5333, a sending/receiving circuit5334, and a signal processing circuit5335including a CPU, a controller, and the like. Such a module is combined with an inputting means5336, a battery5337, and an antenna5340and placed in a housing5339. A pixel portion of the display panel5301is provided so as to be observed from an opening window formed in the housing5339.

The mobile phone of this embodiment can be changed into various modes in accordance with the function and intended purpose. For example, a plurality of display panels may be provided, or the housing may be divided into plural housings appropriately and the housings may be connected to each other with a hinge so as to open and close.

The mobile phone shown inFIG. 15has a structure in which pixels included in a semiconductor device similar to those described in Embodiment Mode 1 are arranged in matrix in the display panel5301. In the semiconductor device, the on/off potential to be applied to a gate electrode of a driver transistor and the potential of the amplitude of a data line in the pixel can be separately set. Therefore, the amplitude of the data line can be set small and the power consumption of the semiconductor device can be drastically suppressed. Since the display panel5301including the semiconductor device has a similar characteristic, drastic reduction of power consumption is achieved in the mobile phone. This characteristic makes it possible to drastically decrease the number of power source circuits or reduce the size thereof; therefore, the housing5339can be lighter in weight. Since the mobile phone of the present invention consumes less electric power and is light in weight, products with improved portability can be provided to customers.

FIG. 16Ashows a television device including a housing6001, a supporter6002, a display portion6003, and the like. In this television device, pixels included in a semiconductor device similar to those described in Embodiment Mode 1 are arranged in matrix in the display portion6003. In the semiconductor device, the on/off potential to be applied to a gate electrode of a driver transistor and the potential of the amplitude of a data line in the pixel can be separately set. Therefore, the amplitude of the data line can be set small and the power consumption of the semiconductor device can be drastically suppressed. Since the display portion6003including the semiconductor device has a similar characteristic, drastic reduction of power consumption is achieved in the television device. Since this characteristic makes it possible to drastically decrease the number of power source circuits or reduce the size thereof, the housing6001can be lighter in weight. Since the television device of the present invention consumes less electric power and is lighter in weight, products suitable for dwelling environment can be provided to customers.

FIG. 16Bshows a computer including a main body6101, a housing6102, a display portion6103, a keyboard6104, an external connection port6105, a pointing mouse6106, and the like. In the computer, pixels included in a semiconductor device similar to those described in Embodiment Mode 1 are arranged in matrix in the display portion6103. In the semiconductor device, the on/off potential to be applied to a gate electrode of a driver transistor and the potential of the amplitude of a data line in the pixel can be separately set. Therefore, the amplitude of the data line can be set small and the power consumption of the semiconductor device can be drastically suppressed. Since the display portion6103including the semiconductor device has a similar characteristic, drastic reduction of power consumption is achieved in the computer. This characteristic makes it possible to drastically decrease the number of power source circuits or reduce the size thereof; therefore, the main body6101and the housing6102can be lighter in weight. Since the computer of the present invention consumes less electric power and is lighter in weight, products with high convenience can be provided to customers.

FIG. 16Cshows a mobile computer including a main body6201, a display portion6202, a switch6203, operation keys6204, an infrared port6205, and the like. In the mobile computer, pixels included in a semiconductor device similar to those described in Embodiment Mode 1 are arranged in matrix in the display portion6202. In the semiconductor device, the on/off potential to be applied to a gate electrode of a driver transistor and the potential of the amplitude of a data line in the pixel can be separately set. Therefore, the amplitude of the data line can be set small and the power consumption of the semiconductor device can be drastically suppressed. Since the display portion6202including the semiconductor device has a similar characteristic, drastic reduction of power consumption is achieved in the mobile computer. This characteristic makes it possible to drastically decrease the number of power source circuits or reduce the size thereof; therefore, the main body6201can be lighter in weight. Since the mobile computer of the present invention consumes less electric power and is lighter in weight, products with high convenience can be provided to customers.

FIG. 16Dshows a mobile game machine including a housing6301, a display portion6302, speaker portions6303, operation keys6304, a recording medium inserting portion6305, and the like. In the mobile game machine, pixels included in a semiconductor device similar to those described in Embodiment Mode 1 are arranged in matrix in the display portion6302. In the semiconductor device, the on/off potential to be applied to a gate electrode of a driver transistor and the potential of the amplitude of a data line in the pixel can be separately set. Therefore, the amplitude of the data line can be set small and the power consumption of the semiconductor device can be drastically suppressed. Since the display portion6302including the semiconductor device has a similar characteristic, drastic reduction of power consumption is achieved in the mobile game machine. This characteristic makes it possible to drastically decrease the number of power source circuits or reduce the size thereof; therefore, the housing6301can be lighter in weight. Since the mobile game machine of the present invention consumes less electric power and is lighter in weight, products with high convenience can be provided to customers.

FIG. 16Eshows a mobile image reproducing device equipped with a recording medium (specifically a DVD reproducing device), including a main body6401, a housing6402, a display portion A6403, a display portion B6404, a recording medium (such as a DVD) reading portion6405, an operation key6406, a speaker portion6407, and the like. The display portion A6403mainly displays image information while the display portion B6404mainly displays text information. In this image reproducing device, pixels included in a semiconductor device similar to those described in Embodiment Mode 1 are arranged in matrix in the display portions A6403and B6404. In the semiconductor device, the on/off potential to be applied to a gate electrode of a driver transistor and the potential of the amplitude of a data line in the pixel can be separately set. Therefore, the amplitude of the data line can be set small and the power consumption of the semiconductor device can be drastically suppressed. Since the display portions A6403and B6404including the semiconductor devices have similar characteristics, drastic reduction of power consumption is achieved in the image reproducing device. This characteristic makes it possible to drastically decrease the number of power source circuits or reduce the size thereof; therefore, the main body6401and the housing6402can be lighter in weight. Since the image reproducing device of the present invention consumes less electric power and is lighter in weight, products with high convenience can be provided to customers.

The display devices used in these electronic appliances can be formed using not only a glass substrate but also a heat-resistant plastic substrate depending on the size, strength, and intended purpose. Accordingly, further reduction in weight can be achieved.

The examples shown in this embodiment are just examples and the present invention is not limited to these.

This embodiment can be combined freely with any description of the above Embodiment Modes and Embodiments.

This application is based on Japanese Patent Application serial no. 2005-119676 filed in Japan Patent Office on Apr. 18, 2005, the entire contents of which are hereby incorporated by reference.