JP4748847B2 - EL display device and electric appliance - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an EL (electroluminescence) display device formed by forming a semiconductor element (an element using a semiconductor thin film, typically a thin film transistor) on a substrate, and an electric appliance having the EL display device as a display portion.
[0002]
[Prior art]
In recent years, a technique for forming a thin film transistor (hereinafter referred to as TFT) on a substrate has greatly advanced, and application development to an active matrix display device has been advanced. In particular, a TFT using a polysilicon film has higher field-effect mobility than a TFT using a conventional amorphous silicon film, and thus can operate at high speed. For this reason, it is possible to control a pixel, which has been conventionally performed by a drive circuit outside the substrate, with a drive circuit formed on the same substrate as the pixel.
[0003]
Such an active matrix display device has various advantages such as a reduction in manufacturing cost, a reduction in size of the display device, an increase in yield, and a reduction in throughput by forming various circuits and elements on the same substrate. It is attracting attention as.
[0004]
In an active matrix EL display device, each pixel is provided with a switching element (hereinafter referred to as a switching TFT) made of a TFT, and a driving element (hereinafter referred to as a current control TFT) that controls current is operated by the switching TFT. The EL layer (strictly, the light emitting layer) emits light. For example, there is an EL display device described in JP-A-10-189252.
[0005]
The EL element includes a layer containing an organic compound (hereinafter referred to as an EL layer) from which luminescence (Electro Luminescence) generated by applying an electric field is obtained, an anode layer, and a cathode layer. Luminescence in an organic compound includes light emission (fluorescence) when returning from the singlet excited state to the ground state and light emission (phosphorescence) when returning from the triplet excited state to the ground state. The present invention can also be applied when light emission is used.
[0006]
In this specification, all layers provided between the anode and the cathode are defined as EL layers. Specifically, the EL layer includes a light emitting layer, a hole injection layer, an electron injection layer, a hole transport layer, an electron transport layer, and the like. Basically, the EL element has a structure in which an anode / light emitting layer / cathode is laminated in order, and in addition to this structure, an anode / hole injection layer / light emitting layer / cathode and an anode / hole injection layer. In some cases, the light emitting layer / the electron transporting layer / the cathode are laminated in this order.
[0007]
[Problems to be solved by the invention]
In the EL display device, when the film resistance of the anode in the element composed of the cathode, the EL layer, and the anode (hereinafter referred to as EL element) increases, the in-plane potential distribution of the anode becomes non-uniform due to the voltage drop, and the brightness of the EL element is increased. Inconveniences such as variations occur. Accordingly, an object of the present invention is to provide an EL display device having a structure in which the film resistance of an anode in an EL element is lowered or has an effect equivalent thereto. Then, it is an object to provide an electric appliance having a stable display unit by using such an EL display device as a display unit.
[0008]
[Means for Solving the Problems]
The present invention will be described with reference to FIG. In FIG. 1, reference numeral 101 denotes a substrate having an insulating surface, and an insulating substrate such as a quartz substrate or a glass substrate, a ceramic substrate, a crystallized glass substrate, a metal substrate, or a plastic substrate provided with an insulating film on the surface can be used.
[0009]
Pixels 102 are formed on the substrate 101. Although three pixels are shown in FIG. 1, actually, a plurality of pixels are further formed in a matrix. Although one of the three pixels will be described here, the other pixels have the same structure.
[0010]
Each pixel 102 is formed with two TFTs, a switching TFT 103 and a current control TFT 104. At this time, the drain of the switching TFT 103 is electrically connected to the gate of the current control TFT 104. Further, a pixel electrode (in this case, also serving as a cathode of the EL element) 105 is electrically connected to the drain of the current control TFT 104. Thus, the pixel 102 is formed.
[0011]
Each wiring and pixel electrode of the TFT may be formed using a metal with low resistivity. Here, an aluminum alloy is preferably used.
[0012]
When the pixel electrodes 105 are formed, an insulating compound (hereinafter referred to as an alkali compound) 106 containing an alkali metal or an alkaline earth metal is formed on all the pixel electrodes. Note that the outline of the alkali compound 106 is indicated by a dotted line because it is not clear whether it is formed in a layer shape or is scattered in an island shape because the film thickness is as thin as several nm.
[0013]
Examples of the alkali compound include lithium fluoride (LiF) and lithium oxide (Li ₂ O), barium fluoride (BaF) ₂ ), Barium oxide (BaO), calcium fluoride (CaF) ₂ ), Calcium oxide (CaO), strontium oxide (SrO) or cesium oxide (Cs) ₂ O) can be used. Since these are insulating, even if they are formed in layers, there is no possibility of causing a short circuit between the pixel electrodes.
[0014]
Of course, a known conductive material such as an MgAg electrode can be used as the cathode, but it is necessary to selectively provide the cathode itself or perform patterning so that the pixel electrodes are not short-circuited.
[0015]
When the alkali compound 106 is formed, an EL layer (electroluminescence layer) 107 is formed thereon. A known material and structure can be used for the EL layer 107. That is, only the light emitting layer that provides a recombination field may be used as an EL layer, and an electron injection layer, an electron transport layer, a hole transport layer, an electron blocking layer, a hole element layer, or a hole injection layer as necessary. May be laminated. In this specification, all layers into which carriers are injected, transported, or recombined are referred to as an EL layer.
[0016]
The organic material used for the EL layer 107 may be a low molecular weight organic material or a polymer (high molecular weight) organic material. However, it is desirable to use a polymer organic material that can be formed by an easy film formation method such as a spin coating method or a printing method.
[0017]
Moreover, the structure of FIG. 1 is an example in the case of using a monochromatic light emission method. That is, in this example, a monotone image is displayed by using an EL layer that emits monochromatic light such as red, blue, green, white, yellow, orange, and purple. What is necessary is just to form the EL layer which emits each of these monochromatic light with a well-known material.
[0018]
A transparent conductive film is formed as the anode 108 on the EL layer 107. As the transparent conductive film, a compound of indium oxide and tin oxide (called ITO), a compound of indium oxide and zinc oxide, tin oxide, zinc oxide, or the like can be used.
[0019]
Further, in this specification, the film resistance of the entire anode obtained by averaging the film resistance of the portion where the metal film 109 and the anode 108 are laminated and the film resistance of only the anode, that is, the entire portion electrically connected to the anode. If the film resistance is called the average film resistance of the anode, the average film resistance at the anode can be lowered by providing the metal film 109 on the anode. Furthermore, the metal film 109 also serves as a light shielding film.
[0020]
As a method for forming the metal film 109, a vapor deposition method is desirable in consideration of damage during film formation on the anode.
[0021]
Further, when providing the metal film 109, the metal film 109 is provided so as to hide the gap 111 between the pixel electrodes when viewed from the viewing direction of the observer (the normal direction of the counter substrate). This is because that portion is a non-light emitting portion, and an electric field is complicated at the end of the pixel electrode, and light cannot be emitted with a desired luminance or chromaticity.
[0022]
When the metal film 109 is formed as described above, an insulating film is provided as the second passivation film 112. As the passivation film 112, it is desirable to use a silicon nitride film or a silicon nitride oxide film (represented by SiOxNy). Although a silicon oxide film can be used, an insulating film with as little oxygen content as possible is preferable.
[0023]
The substrate thus completed is referred to as an active matrix substrate in this specification. That is, a TFT and a pixel electrode electrically connected to the TFT are used as a cathode, and a substrate on which an EL element composed of an EL layer, an anode, and a metal film is formed is called an active matrix substrate.
[0024]
Further, the counter substrate 110 is attached to the active matrix substrate so as to enclose the EL element. Although not shown here, the counter substrate 110 is affixed to the active matrix substrate with a sealant, and the space indicated by 113 is a sealed space.
[0025]
As the counter substrate 110, it is necessary to use a light-transmitting substrate so as not to hinder the progress of light. For example, a glass substrate, a quartz substrate, or a plastic substrate is preferable.
[0026]
The sealed space 113 may be filled with an inert gas (rare gas or nitrogen gas), or may be filled with an inert liquid. Alternatively, a light-transmitting adhesive or resin may be filled to bond the entire substrate. Furthermore, it is preferable to provide a desiccant such as barium oxide in the sealed space 113. Since the EL layer 107 is extremely vulnerable to moisture, it is desirable to prevent moisture from entering the sealed space 113 as much as possible.
[0027]
In the EL display device of the present invention configured as described above, light emitted from the EL element is emitted through the counter substrate and enters the observer's eyes. Therefore, the observer can recognize the image from the counter substrate side. At this time, the EL display device of the present invention is characterized in that a metal film 109 having a low resistivity is provided on the anode 108 which is a part of the EL element, and the metal film 109 hides the gap 111 between the pixel electrodes 105. It is a point provided. As a result, not only the average film resistance of the anode in the EL element can be lowered, but also light leakage in the gap 111 of the pixel electrode 105 can be prevented, and an image display with clear contours between pixels can be achieved.
[0028]
As described above, by implementing the present invention, the average film resistance of the anode of the EL element portion is reduced, and an EL display device that displays an image with clear outlines between pixels, and such an EL display device are displayed. An electric appliance used as a part can be obtained.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to FIGS. 2 is a cross-sectional view of a pixel portion of an EL display device according to the present invention, FIG. 3A is a top view thereof, and FIG. 3B is a circuit configuration thereof. Actually, a plurality of pixels are arranged in a matrix to form a pixel portion (image display portion). Note that a cross-sectional view taken along line AA ′ in FIG. 3A corresponds to FIG. Accordingly, since the same reference numerals are used in FIG. 2 and FIG. 3, both drawings should be referred to as appropriate. Further, in the top view of FIG. 3, two pixels are illustrated, but both have the same structure.
[0030]
In FIG. 2, 11 is a substrate, and 12 is an insulating film (hereinafter referred to as a base film) serving as a base. As the substrate 11, a glass substrate, a glass ceramic substrate, a quartz substrate, a silicon substrate, a ceramic substrate, a metal substrate, or a plastic substrate (including a plastic film) can be used.
[0031]
The base film 12 is particularly effective when a substrate containing mobile ions or a conductive substrate is used, but it need not be provided on the quartz substrate. As the base film 12, an insulating film containing silicon may be used. Note that in this specification, the “insulating film containing silicon” specifically includes silicon, oxygen, or nitrogen such as a silicon oxide film, a silicon nitride film, or a silicon nitride oxide film (indicated by SiOxNy) at a predetermined ratio. An insulating film.
[0032]
Here, two TFTs are formed in the pixel. Reference numeral 201 denotes a TFT that functions as a switching element (hereinafter referred to as a switching TFT), and 202 denotes a TFT that functions as a current control element that controls the amount of current flowing to the EL element (hereinafter referred to as a current control TFT). Is also formed of an n-channel TFT.
[0033]
Since the field effect mobility of the n-channel TFT is larger than that of the p-channel TFT, the operation speed is high and a large current is likely to flow. Even when the same amount of current flows, the n-channel TFT can be made smaller in TFT size. Therefore, it is preferable to use an n-channel TFT as a current control TFT because the effective area of the display portion is widened.
[0034]
The p-channel TFT has the advantage that hot carrier injection is hardly a problem and has a low off-current value, and examples of using it as a switching TFT and an example of using it as a current control TFT have already been reported. However, the present invention solves the problem of hot carrier injection and the problem of off-current value even in the n-channel TFT by adopting a structure where the positions of the LDD regions are different, and all the TFTs in all the pixels are n-channel type. Another characteristic is that it is a TFT.
[0035]
However, in the present invention, the switching TFT and the current control TFT need not be limited to n-channel TFTs, and p-channel TFTs can be used for both or one of them.
[0036]
The switching TFT 201 includes a source region 13, a drain region 14, LDD regions 15a to 15d, an active layer including a high concentration impurity region 16 and channel forming regions 17a and 17b, a gate insulating film 18, gate electrodes 19a and 19b, and a first interlayer. An insulating film 20, a source wiring 21, and a drain wiring 22 are formed.
[0037]
As shown in FIG. 3, the gate electrodes 19a and 19b have a double gate structure in which the gate electrodes 19a and 19b are electrically connected by a gate wiring 211 formed of another material having a lower resistance than the gate electrodes 19a and 19b. . Needless to say, not only a double gate structure but also a so-called multi-gate structure (a structure including an active layer having two or more channel formation regions connected in series) such as a triple gate structure may be used. The multi-gate structure is extremely effective in reducing the off-current value. In the present invention, the switching element 201 of the pixel has a multi-gate structure to realize a switching element with a low off-current value.
[0038]
The active layer is formed of a semiconductor film including a crystal structure. That is, a single crystal semiconductor film, a polycrystalline semiconductor film, or a microcrystalline semiconductor film may be used. The gate insulating film 18 may be formed of an insulating film containing silicon. Any conductive film can be used for the gate electrode, the source wiring, or the drain wiring.
[0039]
Further, in the switching TFT 201, the LDD regions 15a to 15d are provided so as not to overlap the gate electrodes 19a and 19b with the gate insulating film 18 interposed therebetween. Such a structure is very effective in reducing the off-current value.
[0040]
In the case of a multi-gate structure having two or more gate electrodes, a high-concentration impurity region provided between channel formation regions is effective in reducing the off-current value.
[0041]
As described above, a switching element having a sufficiently low off-state current value can be realized by using a TFT having a multi-gate structure as the switching element 201 of the pixel. Therefore, the gate voltage of the current control TFT can be maintained for a sufficient time (between the selection and the next selection) without providing a capacitor as shown in FIG. 2 of JP-A-10-189252.
[0042]
Next, the current control TFT 202 includes an active layer including a source region 31, a drain region 32, an LDD region 33, and a channel formation region 34, a gate insulating film 18, a gate electrode 35, a first interlayer insulating film 20, a source wiring 36, and A drain wiring 37 is formed. The gate electrode 35 has a single gate structure, but may have a multi-gate structure.
[0043]
As shown in FIG. 2, the drain of the switching TFT 201 is connected to the gate of the current control TFT 202. Specifically, the gate electrode 35 of the current control TFT 202 is electrically connected to the drain region 14 of the switching TFT 201 via the drain wiring (also referred to as connection wiring) 22. The source wiring 36 is connected to the current supply line 212 (FIG. 3A).
[0044]
The current control TFT 202 is an element for controlling the amount of current injected into the EL element 203, but it is not preferable to flow a large amount of current in consideration of deterioration of the EL element. Therefore, it is preferable to design the channel length (L) to be long so that an excessive current does not flow through the current control TFT 202. Desirably, it is set to 0.5 to 2 μm (preferably 1 to 1.5 μm) per pixel.
[0045]
Based on the above, as shown in FIG. 9, the channel length of the switching TFT is L1 (where L1 = L1a + L1b), the channel width is W1, the channel length of the current control TFT is L2, and the channel width is W2. In this case, W1 is preferably 0.1 to 5 μm (typically 0.5 to 2 μm), and W2 is preferably 0.5 to 10 μm (typically 2 to 5 μm). L1 is preferably 0.2 to 18 μm (typically 2 to 15 μm), and L2 is preferably 1 to 50 μm (typically 10 to 30 μm). However, the present invention is not limited to the above numerical values.
[0046]
The length (width) of the LDD region formed in the switching TFT 201 may be 0.5 to 3.5 μm, typically 2.0 to 2.5 μm.
[0047]
In the EL display device shown in FIG. 2, the LDD region 33 is provided between the drain region 32 and the channel formation region 34 in the current control TFT 202. Here, a structure is shown in which the LDD region 33 has a region that overlaps the gate electrode 35 with the gate insulating film 18 interposed therebetween and a region that does not overlap the gate electrode 35, but overlaps the gate electrode 35 with the gate insulating film 18 interposed therebetween. A structure in which only the region is the LDD region 33 may be used.
[0048]
The current control TFT 202 supplies a current for causing the EL element 203 to emit light, and at the same time controls the supply amount to enable gradation display. Therefore, it is necessary to take measures against deterioration by hot carrier injection so that it does not deteriorate even when current is passed.
[0049]
Regarding deterioration due to hot carrier injection, it is known that a structure in which an LDD region overlaps a gate electrode is very effective. For this reason, a structure in which an LDD region is provided in a region overlapping the gate electrode 35 with the gate insulating film 18 interposed therebetween is appropriate, but in this embodiment, a structure in which an LDD region that does not overlap with the gate electrode is also provided as a countermeasure against off-current. Indicated. However, the LDD region that does not overlap with the gate electrode is not necessarily provided.
[0050]
On the other hand, if the length of the LDD region overlapped with the gate electrode is too long, the on-current is lowered, whereas if it is too short, the effect of preventing hot carriers is weakened.
Therefore, in this embodiment, as shown in FIG. 2, an LDD region that overlaps the gate electrode is provided in a length that takes these into consideration, and a capacitance generated by providing the LDD region that overlaps the gate electrode is used as a storage capacitor. Yes.
[0051]
Further, in the above structure, a parasitic capacitance is formed in a region where the gate electrode and the LDD region overlap with each other. Therefore, it is preferable not to provide between the source region 31 and the channel formation region 34. Since the current control TFT always has the same direction of carrier (electrons) flow, it is sufficient to provide an LDD region only on the drain region side.
[0052]
Further, from the viewpoint of increasing the amount of current that can be passed, the thickness of the active layer (especially the channel formation region) of the current control TFT 202 may be increased (preferably 50 to 100 nm, more preferably 60 to 80 nm). It is valid. Conversely, in the case of the switching TFT 201, from the viewpoint of reducing the off-current value, the thickness of the active layer (especially the channel formation region) should be reduced (preferably 20 to 50 nm, more preferably 25 to 40 nm). Is also effective.
[0053]
Next, reference numeral 41 denotes a first passivation film, and the film thickness may be 10 nm to 1 μm (preferably 200 to 500 nm). As a material, an insulating film containing silicon (in particular, a silicon nitride oxide film or a silicon nitride film is preferable) can be used.
[0054]
On the first passivation film 41, a second interlayer insulating film (also referred to as a flattening film) 42 is formed so as to cover each TFT, and a step formed by the TFT is flattened. As the second interlayer insulating film 42, an organic resin film is preferable, and polyimide, polyamide, acrylic, BCB (benzocyclobutene), or the like may be used. Of course, an inorganic film may be used if sufficient planarization is possible.
[0055]
It is very important to flatten the step due to the TFT by the second interlayer insulating film 42. Since an EL layer to be formed later is very thin, a light emission defect may occur due to the presence of a step. Therefore, it is desirable to planarize the pixel electrode before forming the pixel electrode so that the EL layer can be formed as flat as possible.
[0056]
Reference numeral 43 denotes a pixel electrode (corresponding to a cathode of the EL element) made of a light-shielding conductive film, and after opening a contact hole (opening) in the second interlayer insulating film 42 and the first passivation film 41, The opening is formed so as to be connected to the drain wiring 37 of the current control TFT 202.
[0057]
On the pixel electrode 43, a lithium fluoride film having a thickness of 5 to 10 nm is formed as an alkali compound 44 by a vapor deposition method. Since the lithium fluoride film is an insulating film, if the film thickness is too thick, current cannot flow through the EL layer. Moreover, there is no problem even if it is formed so as to be scattered in islands rather than in layers.
[0058]
Next, the EL layer 45 is formed. In this embodiment, the polymer organic material is formed by a spin coating method. Any known material can be used as the polymer organic material. In the present embodiment, a light emitting layer is used as the EL layer 45 as a single layer, but a layered structure combined with a hole transport layer or an electron transport layer has a higher light emission efficiency. However, when laminating polymer organic substances, it is desirable to combine them with low molecular organic substances formed by vapor deposition. In the spin coating method, an organic material that becomes an EL layer is mixed and applied in an organic solvent, and therefore, if there is an organic material on the base, it may be dissolved again.
[0059]
Typical polymer organic materials that can be used in the present embodiment include polymer materials such as polyparaphenylene vinylene (PPV), polyvinyl carbazole (PVK), and polyfluorene. In order to form an electron transport layer, a light emitting layer, a hole transport layer, or a hole injection layer with these polymer organic materials, it is applied in the state of a polymer precursor and heated (baked) in a vacuum. It may be converted into a polymer organic material.
[0060]
Specifically, the light emitting layer may be cyanopolyphenylene vinylene for the red light emitting layer, polyphenylene vinylene for the green light emitting layer, and polyphenylene vinylene or polyalkylphenylene for the blue light emitting layer. The film thickness may be 30 to 150 nm (preferably 40 to 100 nm). As the hole transport layer, polytetrahydrothiophenylphenylene which is a polymer precursor is used, and polyphenylene vinylene is obtained by heating. The film thickness may be 30 to 100 nm (preferably 40 to 80 nm).
[0061]
It is also possible to emit white light using a polymer organic material. For that purpose, the techniques described in JP-A-8-96959, JP-A-7-220871, JP-A-9-63770, etc. may be cited. The polymer-based organic substance is particularly effective when emitting white light because the color can be easily adjusted by adding a fluorescent dye to a solution in which the host material is dissolved.
[0062]
The above examples are examples of organic substances that can be used as the EL layer of the present invention, and do not limit the present invention.
[0063]
Although an example in which an EL element is formed using a polymer organic material is shown here, a low molecular organic material may be used. Further, an inorganic substance may be used for the EL layer.
[0064]
Further, when forming the EL layer 45, it is desirable that the treatment atmosphere is a dry atmosphere with as little moisture as possible, and is performed in an inert gas. Since the EL layer easily deteriorates due to the presence of moisture and oxygen, it is necessary to eliminate such factors as much as possible when forming the EL layer. For example, a dry nitrogen atmosphere or a dry argon atmosphere is preferable. For this purpose, it is desirable to install the coating processing chamber and the baking processing chamber in a clean booth filled with an inert gas and perform the processing in the atmosphere.
[0065]
After the EL layer 45 is formed as described above, an anode 46 made of a transparent conductive film is formed next. In this embodiment, a conductive film made of a compound of indium oxide and tin oxide is used as the anode 46. A small amount of gallium may be added thereto.
[0066]
Next, a light-shielding metal film 47 (47a, 47b) is formed on the anode 46. In the present embodiment, the metal film 47 is disposed so as to hide the gap between the pixel electrode 43 and the adjacent pixel electrode, and also has an effect as a light shielding film. In the present embodiment, the metal film 47 has a lower film resistance than that of the anode 46 (also referred to as sheet resistance).
Also, adhesion with the anode material is important. Although it is important to use a metal material suitable for improving adhesion, the film formation conditions of the anode (in this embodiment, a conductive film made of a compound of indium oxide and tin oxide) and after film formation It is also effective to optimize the heat treatment conditions.
[0067]
Further, as the metal film 47, it is desirable to use a metal material having a low resistivity (also referred to as a specific resistance). As the metal material with low resistivity, titanium (Ti), aluminum (Al), tantalum (Ta), tungsten (W), chromium (Cr), copper (Cu), silver (Ag), or the like can be used. is there.
[0068]
In the present embodiment, since the metal film 47 is directly formed on the anode 46, it is desirable to form it by a vapor deposition method. The film thickness may be 30 to 100 nm (preferably 40 to 80 nm).
[0069]
When the metal film 47 is formed as described above, the second passivation film 48 is formed. In the present embodiment, a silicon nitride film having a thickness of 10 nm to 1 μm (preferably 200 to 500 nm) is used as the second passivation film 48.
[0070]
A counter substrate 49 is provided to face the thus completed active matrix substrate. In this embodiment, a glass substrate is used as the counter substrate 49.
[0071]
Further, the active matrix substrate and the counter substrate 49 are bonded with a sealant (not shown) to form the sealed space 50. In the present embodiment, the sealed space 50 is filled with argon gas. Of course, the desiccant may be disposed in the sealed space 50.
[0072]
The EL display device of this embodiment has a pixel portion composed of pixels having a structure as shown in FIG. 2, and TFTs having different structures are arranged in the pixels according to functions. In other words, by forming a switching TFT with a sufficiently low off-current value and a current control TFT resistant to hot carrier injection in the same pixel, it has high reliability and low resistance of the EL element. An enabled EL display device is obtained.
[0073]
【Example】
[Example 1]
An embodiment of the present invention will be described with reference to FIGS. Here, a method for simultaneously manufacturing a TFT of a pixel portion and a driver circuit portion provided around the pixel portion will be described. However, in order to simplify the description, a CMOS circuit, which is a basic circuit, is illustrated with respect to the drive circuit.
[0074]
First, as shown in FIG. 4A, a base film 301 is formed to a thickness of 300 nm over a glass substrate 300. In this embodiment, a silicon nitride oxide film is stacked as the base film 301. At this time, the nitrogen concentration in contact with the glass substrate 300 is preferably set to 10 to 25 wt%.
[0075]
In addition, it is effective to provide an insulating film made of the same material as the first passivation film 41 shown in FIG. Since the current control TFT flows a large current, it easily generates heat, and it is effective to provide an insulating film having a heat dissipation effect as close as possible.
[0076]
Next, an amorphous silicon film (not shown) having a thickness of 50 nm is formed on the base film 301 by a known film formation method. Note that the semiconductor film is not limited to an amorphous silicon film, and any semiconductor film including an amorphous structure (including a microcrystalline semiconductor film) may be used. Further, a compound semiconductor film including an amorphous structure such as an amorphous silicon germanium film may be used. The film thickness may be 20 to 100 nm.
[0077]
Then, the amorphous silicon film is crystallized by a known technique to form a crystalline silicon film (also referred to as a polycrystalline silicon film or a polysilicon film) 302. Known crystallization methods include a thermal crystallization method using an electric furnace, a laser annealing crystallization method using laser light, and a lamp annealing crystallization method using infrared light. In this embodiment, crystallization is performed using excimer laser light using XeCl gas.
[0078]
In this embodiment, a pulse oscillation type excimer laser beam processed into a linear shape is used. However, a rectangular shape, a continuous oscillation type argon laser beam, or a continuous oscillation type excimer laser beam may be used. .
[0079]
In this embodiment, a crystalline silicon film is used as an active layer of a TFT, but an amorphous silicon film can also be used. It is also possible to form the active layer of the switching TFT that needs to reduce the off-current with an amorphous silicon film and form the active layer of the current control TFT with a crystalline silicon film. Since the amorphous silicon film has low carrier mobility, it is difficult for an electric current to flow and an off current is difficult to flow. That is, the advantages of both an amorphous silicon film that hardly allows current to flow and a crystalline silicon film that easily allows current to flow can be utilized.
[0080]
Next, as shown in FIG. 4B, a protective film 303 made of a silicon oxide film is formed on the crystalline silicon film 302 to a thickness of 130 nm. This thickness may be selected in the range of 100 to 200 nm (preferably 130 to 170 nm). Any other film may be used as long as it is an insulating film containing silicon. This protective film 303 is provided in order to prevent the crystalline silicon film from being directly exposed to plasma when an impurity is added and to enable fine concentration control.
[0081]
Then, resist masks 304 a and 304 b are formed thereon, and an impurity element imparting n-type (hereinafter referred to as an n-type impurity element) is added through the protective film 303. Note that as the n-type impurity element, an element typically belonging to Group 15, typically phosphorus or arsenic can be used. In this example, phosphine (PH _Three ) Using a plasma doping method in which plasma is excited without mass separation, and phosphorus is 1 × 10 ¹⁸ atoms / cm ^Three Add at a concentration of Of course, an ion implantation method for performing mass separation may be used.
[0082]
In the n-type impurity regions 305 and 306 formed by this step, an n-type impurity element is 2 × 10 6. ¹⁶ ~ 5x10 ¹⁹ atoms / cm ^Three (Typically 5 × 10 ¹⁷ ~ 5x10 ¹⁸ atoms / cm ^Three ) Adjust the dose so that it is included at the concentration of
[0083]
Next, as shown in FIG. 4C, the protective film 303 and the resists 304a and 304b are removed, and the added elements belonging to Group 15 are activated. As the activation means, a known technique may be used. In this embodiment, activation is performed by irradiation with excimer laser light. Of course, the pulse oscillation type or the continuous oscillation type may be used, and it is not necessary to limit to the excimer laser beam. However, since the purpose is to activate the added impurity element, it is preferable to irradiate with energy that does not melt the crystalline silicon film. Note that laser light may be irradiated with the protective film 303 attached.
[0084]
Note that activation by heat treatment may be used in combination with the activation of the impurity element by the laser beam. When activation by heat treatment is performed, heat treatment at about 450 to 550 ° C. may be performed in consideration of the heat resistance of the substrate.
[0085]
By this step, the end portion of the n-type impurity regions 305 and 306, that is, the boundary portion (junction portion) with the region to which the n-type impurity element existing around the n-type impurity regions 305 and 306 is not added becomes clear. . This means that when the TFT is later completed, the LDD region and the channel formation region can form a very good junction.
[0086]
Next, as shown in FIG. 4D, unnecessary portions of the crystalline silicon film are removed, and island-shaped semiconductor films (hereinafter referred to as active layers) 307 to 310 are formed.
[0087]
Next, as illustrated in FIG. 4E, a gate insulating film 311 is formed so as to cover the active layers 307 to 310. As the gate insulating film 311, an insulating film containing silicon with a thickness of 10 to 200 nm, preferably 50 to 150 nm may be used. This may be a single layer structure or a laminated structure. In this embodiment, a silicon nitride oxide film having a thickness of 110 nm is used.
[0088]
Next, a conductive film having a thickness of 200 to 400 nm is formed and patterned to form gate electrodes 312 to 316. The ends of the gate electrodes 312 to 316 can be tapered. Note that in this embodiment, the gate electrode and a wiring (hereinafter referred to as a gate wiring) electrically connected to the gate electrode are formed using different materials. Specifically, a material having a resistance lower than that of the gate electrode is used for the gate wiring. This is because a material that can be finely processed is used for the gate electrode, and a material that has a low wiring resistance is used for the gate wiring even though it cannot be finely processed. Of course, the gate electrode and the gate wiring may be formed of the same material.
[0089]
The gate electrode may be formed of a single-layer conductive film, but it is preferable to form a stacked film of two layers or three layers as necessary. Any known conductive film can be used as the material of the gate electrode. However, a material that can be finely processed as described above, specifically, that can be patterned to a line width of 2 μm or less is preferable.
[0090]
Typically, a film made of an element selected from tantalum (Ta), titanium (Ti), molybdenum (Mo), tungsten (W), chromium (Cr), and silicon (Si), or a nitride film of the element (Typically a tantalum nitride film, a tungsten nitride film, a titanium nitride film), an alloy film (typically, a Mo—W alloy, a Mo—Ta alloy), or a silicide film of the above elements (typical) Specifically, a tungsten silicide film or a titanium silicide film) can be used. Of course, it may be used as a single layer or may be laminated.
[0091]
In this embodiment, a stacked film including a tungsten nitride (WN) film having a thickness of 50 nm and a tungsten (W) film having a thickness of 350 nm is used. This may be formed by sputtering. Further, when an inert gas such as Xe or Ne is added as a sputtering gas, peeling of the film due to stress can be prevented.
[0092]
At this time, the gate electrodes 313 and 316 are formed so as to overlap a part of the n-type impurity regions 305 and 306 with the gate insulating film 311 interposed therebetween. This overlapped portion later becomes an LDD region overlapping with the gate electrode.
[0093]
Next, as shown in FIG. 5A, an n-type impurity element (phosphorus in this embodiment) is added in a self-aligning manner using the gate electrodes 312 to 316 as masks. The impurity regions 317 to 323 thus formed are adjusted so that phosphorus is added at a concentration of 1/2 to 1/10 (typically 1/3 to 1/4) of the n-type impurity regions 305 and 306. To do. Specifically, 1 × 10 ¹⁶ ~ 5x10 ¹⁸ atoms / cm ^Three (Typically 3x10 ¹⁷ ~ 3x10 ¹⁸ atoms / cm ^Three ) Is preferred.
[0094]
Next, as shown in FIG. 5B, resist masks 324a to 324d are formed so as to cover the gate electrodes and the like, and an n-type impurity element (phosphorus in this embodiment) is added to contain phosphorus at a high concentration. Impurity regions 325 to 331 are formed. Again, phosphine (PH _Three The concentration of phosphorus in this region is 1 × 10 ²⁰ ~ 1x10 ^{twenty one} atoms / cm ^Three (Typically 2 × 10 ²⁰ ~ 5x10 ²⁰ atoms / cm ^Three ).
[0095]
Although the source region or the drain region of the n-channel TFT is formed by this step, the switching TFT leaves a part of the n-type impurity regions 320 to 322 formed in the step of FIG. This remaining region corresponds to the LDD regions 15a to 15d of the switching TFT in FIG.
[0096]
Next, as shown in FIG. 5C, the resist masks 324a to 324d are removed, and a new resist mask 332 is formed. Then, a p-type impurity element (boron in this embodiment) is added to form impurity regions 333 and 334 containing boron at a high concentration. Here, diborane (B ₂ H ₆ 3 × 10 by ion doping method using ²⁰ ~ 3x10 ^{twenty one} atoms / cm ^Three (Typically 5 × 10 ²⁰ ~ 1x10 ^{twenty one} atoms / cm ^Three Boron is added so that the concentration of
[0097]
Note that the impurity regions 333 and 334 already have 1 × 10 6. ²⁰ ~ 1x10 ^{twenty one} atoms / cm ^Three However, the boron added here is added at a concentration at least three times that of phosphorus. Therefore, the n-type impurity region formed in advance is completely inverted to the p-type and functions as a p-type impurity region.
[0098]
Next, after removing the resist mask 332, the n-type or p-type impurity element added at each concentration is activated. As the activation means, furnace annealing, laser annealing, or lamp annealing can be used. In this embodiment, heat treatment is performed in an electric furnace in a nitrogen atmosphere at 550 ° C. for 4 hours.
[0099]
At this time, it is important to eliminate oxygen in the atmosphere as much as possible. This is because the presence of even a small amount of oxygen oxidizes the exposed surface of the gate electrode, which increases resistance and makes it difficult to make ohmic contact later. Therefore, the oxygen concentration in the treatment atmosphere in the activation step is 1 ppm or less, preferably 0.1 ppm or less.
[0100]
Next, when the activation process is completed, a gate wiring 335 having a thickness of 300 nm is formed as shown in FIG. As a material of the gate wiring 335, a metal containing aluminum (Al) or copper (Cu) as a main component (occupying 50 to 100% as a composition) may be used. As shown in FIG. 3, the gate wiring 211 and the switching TFT gate electrodes 19a and 19b (314 and 315 in FIG. 4E) are electrically connected as shown in FIG.
[0101]
With such a structure, the wiring resistance of the gate wiring can be extremely reduced, so that an image display region (pixel portion) having a large area can be formed. That is, the pixel structure of this embodiment is extremely effective in realizing an EL display device having a screen size of 10 inches or more (or 30 inches or more) diagonally.
[0102]
Next, as shown in FIG. 6A, a first interlayer insulating film 336 is formed. As the first interlayer insulating film 336, an insulating film containing silicon may be used as a single layer, or a stacked film in which insulating films containing two or more types of silicon are combined may be used. The film thickness may be 400 nm to 1.5 μm. In this embodiment, a structure is formed in which a silicon oxide film having a thickness of 800 nm is stacked on a silicon nitride oxide film having a thickness of 200 nm.
[0103]
Further, a hydrogenation treatment is performed by performing a heat treatment at 300 to 450 ° C. for 1 to 12 hours in an atmosphere containing 3 to 100% hydrogen. This step is a step in which the dangling bonds of the semiconductor film are terminated with hydrogen by thermally excited hydrogen. As another means of hydrogenation, plasma hydrogenation (using hydrogen excited by plasma) may be performed.
[0104]
Note that the hydrogenation treatment may be performed before the first interlayer insulating film 336 is formed. That is, a hydrogenation treatment may be performed as described above after a 200 nm thick silicon nitride oxide film is formed, and then the remaining 800 nm thick silicon oxide film may be formed.
[0105]
Next, contact holes are formed in the first interlayer insulating film 336 and the gate insulating film 311, and source wirings 337 to 340 and drain wirings 341 to 343 are formed. In this embodiment, this electrode is a laminated film having a three-layer structure in which a Ti film is 100 nm, an aluminum film containing Ti is 300 nm, and a Ti film 150 nm is continuously formed by sputtering. Of course, other conductive films may be used.
[0106]
Next, a first passivation film 344 is formed with a thickness of 50 to 500 nm (typically 200 to 300 nm). In this embodiment, a silicon nitride oxide film having a thickness of 300 nm is used as the first passivation film 344. This may be replaced by a silicon nitride film. Of course, the same material as that of the first passivation film 41 in FIG. 2 can be used.
[0107]
Prior to the formation of the silicon nitride oxide film, H ₂ , NH _Three It is effective to perform plasma treatment using a gas containing isohydrogen. Hydrogen excited by this pretreatment is supplied to the first interlayer insulating film 336 and heat treatment is performed, whereby the film quality of the first passivation film 344 is improved. At the same time, since hydrogen added to the first interlayer insulating film 336 diffuses to the lower layer side, the active layer can be effectively hydrogenated.
[0108]
Next, as shown in FIG. 6B, a second interlayer insulating film 345 made of an organic resin is formed. As the organic resin, polyimide, polyamide, acrylic, BCB (benzocyclobutene), or the like can be used. In particular, since the second interlayer insulating film 345 has a strong meaning of flattening, acrylic having excellent flatness is preferable. In this embodiment, the acrylic film is formed with a film thickness that can sufficiently flatten the step formed by the TFT. The thickness is preferably 1 to 5 μm (more preferably 2 to 4 μm).
[0109]
Next, contact holes are formed in the second interlayer insulating film 345 and the first passivation film 344, and a pixel electrode 346 that is electrically connected to the drain wiring 343 is formed. In this embodiment, an aluminum alloy film (aluminum film containing 1 wt% titanium) having a thickness of 300 nm is formed as the pixel electrode 346. Reference numeral 347 denotes an end portion of an adjacent pixel electrode.
[0110]
Next, as shown in FIG. 6C, an alkali compound 348 is formed. In this embodiment, a lithium fluoride film is formed by vapor deposition aiming at a thickness of 5 nm. Then, an EL layer 349 having a thickness of 100 nm is formed thereon by a spin coating method.
[0111]
In this example, the material described in JP-A-8-96959 or JP-A-9-63770 is used as the polymer organic substance that emits white light. For example, 1,2-dichloromethane, PVK (polyvinylcarbazole), Bu-PBD (2- (4′-tert-butylphenyl) -5- (4 ″ -biphenyl) -1,3,4-oxadiazole ), Coumarin 6, DCM1 (4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran), TPB (tetraphenylbutadiene), and Nile Red may be used.
[0112]
Note that although the EL layer 349 has a single-layer structure including only the light-emitting layer in this embodiment, an electron injection layer, an electron transport layer, a hole transport layer, a hole injection layer, an electron blocking layer, or a hole is used as necessary. An element layer may be provided.
[0113]
Next, an anode 350 made of a transparent conductive film having a thickness of 200 nm is formed so as to cover the EL layer 349. In this embodiment, a film made of a compound of indium oxide and tin oxide is formed by a vapor deposition method to serve as an anode.
[0114]
Next, a metal film 351 made of a metal having low resistivity is formed on the anode 350. Note that a metal material whose film resistance is lower than that of the anode 350 is preferably used for the film thickness of the metal film 351.
[0115]
Further, since the metal film 351 is provided so as to hide the gap 111 between the pixel electrodes when viewed from the observer's line-of-sight direction (the normal direction of the counter substrate), the metal film 351 is etched after the metal film 351 is formed. . At this time, it is important not to etch the anode 350 at the same time. In this embodiment, a dry etching method is used as an etching method, and the anode 350 is made of a compound of indium oxide and tin oxide, so that a chlorine-based gas is used as an etching gas.
[0116]
In this embodiment, a laminated structure in which titanium and aluminum are deposited by vapor deposition is used, and a metal film 351 is formed by depositing 50 nm of titanium on the anode 350 and 250 nm of aluminum on the titanium.
[0117]
By employing a structure in which titanium is sandwiched between the anode 350 and aluminum, electrolytic corrosion (also referred to as electrochemical corrosion) generated between the anode 350 and aluminum can be prevented. Note that titanium nitride (TiN) may be used instead of titanium used here. Titanium nitride has the advantage that it is easy to make electrical contact with the anode.
[0118]
In this embodiment, the vapor deposition method is used in consideration of damage to the anode, but a sputtering method may be used.
[0119]
The metal film 351 in the present invention has a laminated structure, but may have a single layer structure.
[0120]
Finally, a second passivation film 352 made of a silicon nitride film is formed to a thickness of 100 nm by plasma CVD. The second passivation film 352 protects the EL layer 349 from moisture and the like. In addition, it plays a role of releasing heat generated in the EL layer 349. In order to further enhance the heat dissipation effect, a silicon nitride film and a carbon film (preferably a diamond-like carbon film) may be laminated to form a second passivation film.
[0121]
Thus, an active matrix EL display device having a structure as shown in FIG. 6C is completed. By the way, the active matrix EL display device of this embodiment can provide extremely high reliability and improve the operating characteristics by arranging TFTs having an optimal structure not only in the pixel portion but also in the drive circuit portion.
[0122]
First, a TFT having a structure that reduces hot carrier injection so as not to reduce the operating speed as much as possible is used as an n-channel TFT 205 of a CMOS circuit that forms a driving circuit. Note that the drive circuit here includes a shift register, a buffer, a level shifter, a sampling circuit (sample and hold circuit), and the like. In the case of performing digital driving, a signal conversion circuit such as a D / A converter may be included.
[0123]
In this embodiment, as shown in FIG. 6C, the active layer of the n-channel type 205 includes a source region 355, a drain region 356, an LDD region 357, and a channel formation region 358, and the LDD region 357 has gate insulation. It overlaps with the gate electrode 313 with the film 311 interposed therebetween.
[0124]
The reason why the LDD region is formed only on the drain region side is to prevent the operation speed from being lowered. In addition, the n-channel TFT 205 does not need to care about the off-current value, and it is better to focus on the operation speed than that. Therefore, it is desirable that the LDD region 357 is completely overlapped with the gate electrode and the resistance component is reduced as much as possible. That is, it is better to eliminate the so-called offset.
[0125]
In addition, since the p-channel TFT 206 of the CMOS circuit is hardly concerned about deterioration due to hot carrier injection, it is not particularly necessary to provide an LDD region. Needless to say, it is possible to provide an LDD region as in the case of the n-channel TFT 205 and take measures against hot carriers.
[0126]
Note that the sampling circuit in the driver circuit is a little special compared to other circuits, and a large current flows in both directions in the channel formation region. That is, the roles of the source region and the drain region are interchanged. Furthermore, it is necessary to keep the off-current value as low as possible, and in that sense, it is desirable to dispose a TFT having an intermediate function between the switching TFT and the current control TFT.
[0127]
Therefore, it is desirable to dispose a TFT having a structure as shown in FIG. 10 as the n-channel TFT forming the sampling circuit. As shown in FIG. 10, part of the LDD regions 901a and 901b overlaps with the gate electrode 903 with the gate insulating film 902 interposed therebetween. This effect is as described in the description of the current control TFT 202, and is different in that the sampling circuit is provided so as to sandwich the channel formation region 904.
[0128]
Actually, when the process up to FIG. 6C is completed, the active matrix substrate and the counter substrate are bonded with a sealant as described in FIGS. At that time, if the inside of the sealed space sandwiched between the active matrix substrate and the counter substrate is made an inert atmosphere, or if a hygroscopic material (for example, barium oxide) is disposed inside, the reliability (life) of the EL layer contained therein is increased. Can be improved.
[0129]
In addition, after the process of bonding the active matrix substrate and the counter substrate is completed, a connector (flexible printed circuit: FPC) for connecting a terminal routed from an element or circuit formed on the substrate and an external signal terminal is provided. Install and complete as a product.
[0130]
Here, the configuration of the active matrix EL display device of this embodiment will be described with reference to the perspective view of FIG. The active matrix EL display device of this embodiment includes a pixel portion 602, a gate side driver circuit 603, and a source side driver circuit 604 formed on a glass substrate 601. The switching TFT 605 in the pixel portion is an n-channel TFT, and is arranged at the intersection of the gate wiring 606 connected to the gate side driving circuit 603 and the source wiring 607 connected to the source side driving circuit 604. The drain of the switching TFT 605 is connected to the gate of the current control TFT 608.
[0131]
Further, the source side of the current control TFT 608 is connected to the current supply line 609. In the structure as in this embodiment, a predetermined voltage is applied to the current supply line 609. An EL element 610 is connected to the drain of the current control TFT 608.
[0132]
The FPC 611 serving as an external input / output terminal is provided with connection wirings (connection wirings) 612 and 613 for transmitting signals to the drive circuit and a connection wiring 614 connected to the current supply line 609.
[0133]
An example of a circuit configuration of the EL display device illustrated in FIG. 7 is illustrated in FIG. The EL display device of this embodiment includes a source side driver circuit 701, a gate side driver circuit (A) 707, a gate side driver circuit (B) 711, and a pixel portion 706. Note that in this specification, the drive circuit is a generic name including a source side processing circuit and a gate side drive circuit.
[0134]
The source side driver circuit 701 includes a shift register 702, a level shifter 703, a buffer 704, and a sampling circuit (sample and hold circuit) 705. The gate side driver circuit (A) 707 includes a shift register 708, a level shifter 709, and a buffer 710. The gate side driver circuit (B) 711 has a similar structure.
[0135]
Here, the driving voltages of the shift registers 702 and 708 are 5 to 16 V (typically 10 V), and an n-channel TFT used in a CMOS circuit forming the circuit has a structure indicated by 205 in FIG. Is suitable.
[0136]
As the level shifters 703 and 709 and the buffers 704 and 710, a CMOS circuit including the n-channel TFT 205 in FIG. In addition, it is effective in improving the reliability of each circuit that the gate wiring has a multi-gate structure such as a double gate structure or a triple gate structure.
[0137]
In addition, since the sampling circuit 705 needs to reduce the off current value in addition to the inversion of the source region and the drain region, a CMOS circuit including the n-channel TFT 208 in FIG. 10 is suitable.
[0138]
For the pixel portion 706, the pixel having the structure shown in FIG.
[0139]
In addition, the said structure can be easily implement | achieved by manufacturing TFT according to the manufacturing process shown to FIGS. In addition, in this embodiment, only the configuration of the pixel portion and the drive circuit is shown. However, according to the manufacturing process of this embodiment, other driving such as a signal dividing circuit, a D / A converter circuit, an operational amplifier circuit, and a γ correction circuit is performed. It is considered that logic circuits other than circuits can be formed on the same substrate, and further, a memory portion, a microprocessor, and the like can be formed.
[0140]
Further, the EL display device of this embodiment will be described with reference to FIGS. Note that the reference numerals used in FIGS. 7 and 8 are cited as necessary.
[0141]
A substrate (including a base film under a TFT) 1000 is an active matrix substrate, and a pixel portion 1001, a source side driver circuit 1002, and a gate side driver circuit 1003 are formed over the substrate. Various wirings from the respective driving circuits reach the FPC 611 through connection wirings 612 to 614 and are connected to an external device.
[0142]
At this time, the counter substrate 1004 is provided so as to surround at least the pixel portion, preferably the driver circuit and the pixel portion. Note that an adhesive (sealant) 1005 is bonded to form a sealed space 1006 between the counter substrate 1004 and the active matrix substrate 1000. At this time, the EL element is completely enclosed in the sealed space 1006 and is shielded from the outside air.
[0143]
In this embodiment, a photo-curable epoxy resin is used as the adhesive 1005, but an adhesive such as an acrylate resin can also be used. A thermosetting resin can also be used if the heat resistance of the EL layer permits. However, it is necessary to use a material that does not transmit oxygen and moisture as much as possible. The adhesive 1005 may be formed using a coating apparatus such as a dispenser.
[0144]
Further, in this embodiment, the sealed space 1006 between the counter substrate 1004 and the active matrix substrate 1000 is filled with nitrogen gas. Further, a black-colored portion 1007 in FIG. 11A shows a metal film, but actually, it is provided on the anode 1008 so as to fill in the gaps between all the pixel electrodes. In this embodiment, a metal film having a laminated structure in which titanium and aluminum are deposited is used as the metal film 1007.
[0145]
As shown in FIG. 11B, a plurality of pixels each having an isolated EL element are provided in the pixel portion, and all of them have the anode 1008 as a common electrode. At this time, the EL layer only needs to be provided on the pixel portion and does not have to be provided on the driver circuit.
In order to selectively provide the EL layer, an evaporation method using a shadow mask, a lift-off method, a dry etching method, or a laser scribing method may be used.
[0146]
The anode 1008 is electrically connected to the connection wiring 1009. The connection wiring 1009 is a current supply line for applying a predetermined voltage to the anode 1008, and is electrically connected to the FPC 611 through the anisotropic conductive film 1010. Although the connection wiring 1009 has been described here, the other connection wirings 612 to 614 are also electrically connected to the FPC 611 in the same manner.
[0147]
In the state shown in FIG. 11 as described above, an image can be displayed on the pixel portion by connecting the FPC 611 to a terminal of an external device. In this specification, an article capable of displaying an image by attaching an FPC, that is, an active matrix substrate and a counter substrate are bonded together, and a module to which the FPC is attached is defined as an EL display device. .
[0148]
[Example 2]
In the first embodiment, the case of the top gate type TFT has been described. However, since the present invention is not limited to the TFT structure, the bottom gate type TFT (typically an inverted stagger type TFT) may be used. I do not care. Further, the reverse stagger type TFT may be formed by any means.
[0149]
Since the inverted stagger type TFT has a structure in which the number of steps can be easily reduced as compared with the top gate type TFT, it is very advantageous for reducing the manufacturing cost which is the subject of the present invention. Note that the configuration of the present embodiment can be combined with the configuration of the first embodiment.
[0150]
Example 3
In FIG. 3B, the switching TFT in the pixel of the EL display device has a multi-gate structure, thereby reducing the off-current value of the switching TFT and eliminating the necessity of the storage capacitor. However, a structure in which a storage capacitor is provided as in the past may be used. In that case, as shown in FIG. 12, a storage capacitor 1301 is formed in parallel with the gate of the current control TFT 202 with respect to the drain of the switching TFT 201.
[0151]
In addition, the structure of a present Example can be freely combined with any structure of Example 1,2. That is, only a storage capacitor is provided in the pixel, and the TFT structure and the material of the EL layer are not limited.
[0152]
Example 4
In the first embodiment, laser crystallization is used as a means for forming the crystalline silicon film 302. In this embodiment, a case where a different crystallization means is used will be described.
[0153]
In this embodiment, after an amorphous silicon film is formed, crystallization is performed by using the technique described in Japanese Patent Application Laid-Open No. 7-130652. The technique described in this publication is a technique for obtaining a crystalline silicon film having high crystallinity by using an element such as nickel as a catalyst for promoting (promoting) crystallization.
[0154]
Further, after the crystallization step is completed, a step of removing the catalyst used for crystallization may be performed. In that case, the catalyst may be gettered by the technique described in JP-A-10-270363 or JP-A-8-330602.
[0155]
Further, a TFT may be formed using the technique described in the application specification of Japanese Patent Application No. 11-076967 by the present applicant.
[0156]
As described above, the manufacturing process shown in Embodiment 1 is one embodiment, and other manufacturing processes can be used as long as the structure of FIG. 2 or FIG. 6C of Embodiment 1 can be realized. No problem.
[0157]
In addition, the structure of a present Example can be freely combined with any structure of Examples 1-3.
[0158]
Example 5
In the first embodiment, a structure is shown in which the metal film 109 is provided on the anode 108 in the EL element so as to hide the gap 111 between the pixel electrodes. In this embodiment, as shown in FIG. A case in which a metal thin film 114 is provided on 108 and the metal thin film 114 is sandwiched between the anode 108 and the metal film 109 will be described.
[0159]
The thickness of the metal thin film 114 is set to a thickness that does not lose the light-transmitting property, and is set to about 10 to 50 nm (preferably 20 to 30 nm). Note that the metal film 109 may be provided on the metal thin film 114 as in the first embodiment.
[0160]
By laminating the metal thin film 114 and the metal film 109 on the anode 108 in the EL element, the average film resistance of the anode can be lowered.
[0161]
In addition, the structure of a present Example can be freely combined with any structure of Examples 1-4.
[0162]
Example 6
In the first embodiment, a structure is shown in which the metal film 109 is provided on the anode 108 in the EL element so as to hide the gap 111 between the pixel electrodes. In this embodiment, as shown in FIG. A case where a metal thin film 114 made of chromium is provided on 108 and the metal thin film 114 is sandwiched between the anode 108 and the metal film 109 will be described.
[0163]
The thickness of the metal thin film 114 is set to a thickness that does not lose the light-transmitting property, and is set to about 50 nm (preferably 30 nm). Note that the metal film 109 may be provided on the metal thin film 114 as in the first embodiment.
[0164]
By laminating the metal thin film 114 and the metal film 109 on the anode 108 in the EL element, the average film resistance of the anode 108 can be lowered.
[0165]
In this embodiment, when the anode 108 is made of a compound of indium oxide and tin oxide, and the metal film 109 is made of aluminum, the use of the metal thin film 114 made of chromium makes it possible to generate electric current generated between the anode 108 and the metal film 109. Plays a role in preventing food.
[0166]
In addition, the metal thin film 114 made of chromium and the metal film 109 made of aluminum used in this embodiment have a sufficient selection ratio when a chlorine-based etching gas is used. This is effective when performing dry etching.
[0167]
In addition, the structure of a present Example can be freely combined with any structure of Examples 1-5.
[0168]
Example 7
In driving the EL display device of the present invention, analog driving using an analog signal as an image signal can be performed, or digital driving using a digital signal can be performed.
[0169]
When analog driving is performed, an analog signal is sent to the source wiring of the switching TFT, and the analog signal including the gradation information becomes the gate voltage of the current control TFT. Then, the current control TFT controls the current flowing in the EL element, and the light emission intensity of the EL element is controlled to perform gradation display.
[0170]
On the other hand, when digital driving is performed, unlike analog gradation display, gradation display called a time-division gradation method is performed. That is, the color gradation is visually changed by adjusting the length of the light emission time.
[0171]
Since an EL element has a very high response speed compared to a liquid crystal element, it can be driven at a high speed. Therefore, it can be said that the device is suitable for the time-division gradation method in which gradation display is performed by dividing one frame into a plurality of subframes.
[0172]
As described above, since the present invention is a technique related to an element structure, any driving method may be used.
[0173]
In addition, the structure of a present Example can be freely combined with any structure of Examples 1-6.
[0174]
Example 8
Since the EL display device displays an image by self-light emission, it does not require a backlight. In addition, the reflective liquid crystal display device is characterized in that it can display an image by using outdoor light. However, in a dark place, the brightness is insufficient and a backlight is eventually required. In that respect, there is no problem because the EL display device is a self-luminous type even in a dark place.
[0175]
However, when an electronic device having an EL display device as a display unit is actually used outdoors, it may naturally be viewed in a dark place or a bright place. At this time, in a dark place, it can be recognized sufficiently even if the brightness is not so high, but in a bright place, it may not be recognized unless the brightness is high.
[0176]
Since the light emission of the EL layer changes depending on the amount of current that flows, the current that flows increases to increase the luminance, and the power consumption increases accordingly. However, if the light emission luminance is adjusted to such a high level, only the power consumption is large in a dark place, and the display becomes brighter than necessary.
[0177]
In such a case, it is desirable that the EL display device of the present invention has a function of sensing the external brightness with a sensor and changing the light emission luminance of the EL layer in accordance with the degree of brightness. That is, the light emission brightness is increased in a bright place and the light emission brightness is lowered in a dark place to prevent an increase in power consumption. As a result, the power consumption of the EL display device of the present invention can be reduced.
[0178]
Note that a CMOS sensor, a CCD, or the like can be used as a sensor for detecting external brightness. The CMOS sensor may be formed on the same substrate as the driving circuit and the pixel portion of the EL display device using a known technique. In addition, a semiconductor chip on which a CCD is formed may be attached to an EL display device, or a CCD or CMOS sensor may be provided in a part of an electronic device using the EL display device as a display portion.
[0179]
Thus, a circuit for changing the current flowing through the EL layer according to the signal obtained by the sensor that senses the external brightness can be provided, so that the light emission luminance of the EL layer can be adjusted according to the external brightness.
[0180]
In addition, the structure of a present Example can be implemented in combination freely with any structure of Example 1-7.
[0181]
Example 9
An EL display device formed by implementing the present invention is a self-luminous type, and thus has excellent visibility in a bright place as compared with a liquid crystal display device, and has a wide viewing angle. Therefore, it can be used as a display unit of various electric appliances. For example, in order to view TV broadcasts on a large screen, the EL of the present invention can be used as a display unit of an EL display (a display in which an EL display device is incorporated in a housing) having a diagonal size of 30 inches or more (typically 40 inches or more). A display device may be used.
[0182]
The EL display includes all information display displays such as a personal computer display, a TV broadcast receiving display, and an advertisement display. In addition, the EL display device of the present invention can be used as a display portion of various electric appliances.
[0183]
Such electrical appliances include video cameras, digital cameras, goggle type displays (head mounted displays), car navigation systems, car audio systems, notebook personal computers, game machines, personal digital assistants (mobile computers, mobile phones, portable types) A game machine or an electronic book), an image playback apparatus (specifically, a compact disc (CD), a laser disc (LD), or a digital video disc (DVD)) provided with a recording medium. A device having a display capable of displaying). In particular, since a portable information terminal that is often viewed from an oblique direction emphasizes the wide viewing angle, it is desirable to use an EL display device. Specific examples of these electric appliances are shown in FIG.
[0184]
FIG. 13A illustrates an EL display including a housing 2001, a support base 2002, a display portion 2003, and the like. The present invention can be used for the display portion 2003. Since the EL display is a self-luminous type, a backlight is not necessary, and a display portion thinner than a liquid crystal display can be obtained.
[0185]
FIG. 13B illustrates a video camera, which includes a main body 2101, a display portion 2102, an audio input portion 2103, operation switches 2104, a battery 2105, an image receiving portion 2106, and the like. The EL display device of the present invention can be used for the display portion 2102.
[0186]
FIG. 13C shows a part (right side) of a head-mounted EL display, which includes a main body 2201, a signal cable 2202, a head fixing band 2203, a projection unit 2204, an optical system 2205, a display unit 2206, and the like. . The present invention can be used for the display portion 2206.
[0187]
FIG. 13D shows an image reproducing apparatus (specifically, a DVD reproducing apparatus) provided with a recording medium, which includes a main body 2301, a recording medium (CD, LD, DVD, etc.) 2302, an operation switch 2303, and a display unit (a). 2304, a display unit (b) 2305, and the like. The display unit (a) mainly displays image information, and the display unit (b) mainly displays character information. The EL display device of the present invention can be used for these display units (a) and (b). Note that the image reproducing device provided with the recording medium may include a CD reproducing device, a game machine, and the like.
[0188]
FIG. 13E shows a portable (mobile) computer, which includes a main body 2401, a camera portion 2402, an image receiving portion 2403, operation switches 2404, a display portion 2405, and the like. The EL display device of the present invention can be used for the display portion 2405.
[0189]
FIG. 13F illustrates a personal computer, which includes a main body 2501, a housing 2502, a display portion 2503, a keyboard 2504, and the like. The EL display device of the present invention can be used for the display portion 2503.
[0190]
If the light emission luminance of the EL material is increased in the future, the light including the output image information can be enlarged and projected by a lens or the like and used for a front type or rear type projector.
[0191]
In addition, the electric appliances often display information distributed through electronic communication lines such as the Internet or CATV (cable television), and in particular, opportunities to display moving image information are increasing. Since the response speed of the EL material is very high, the EL display device is preferable for moving image display. However, if the contour between pixels is blurred, the entire moving image is blurred. Therefore, it is extremely effective to use the EL display device of the present invention for clarifying the contour between pixels as a display unit of an electric appliance.
[0192]
In addition, since the EL display device consumes power in the light emitting portion, it is desirable to display information so that the light emitting portion is minimized. Therefore, when an EL display device is used for a display unit mainly including character information such as a portable information terminal, particularly a mobile phone or a car audio, it is driven so that the character information is formed by the light emitting part with the non-light emitting part as the background. It is desirable to do.
[0193]
Here, FIG. 14A illustrates a mobile phone, which includes a main body 2601, an audio output portion 2602, an audio input portion 2603, a display portion 2604, operation switches 2605, and an antenna 2606. The EL display device of the present invention can be used for the display portion 2604. Note that the display portion 2604 can suppress power consumption of the mobile phone by displaying white characters on a black background.
[0194]
FIG. 14B shows a car audio, which includes a main body 2701, a display portion 2702, and operation switches 2703 and 2704. The EL display device of the present invention can be used for the display portion 2702. Note that the display portion 2704 can suppress power consumption by displaying white characters on a black background.
[0195]
As described above, the application range of the present invention is extremely wide and can be used for electric appliances in various fields. Moreover, the electric appliance of a present Example can be obtained by using the EL display apparatus which combined the structure of Example 1- Example 8 freely.
[0196]
Example 10
Of the light emitted from the EL layer in the present invention, the light emitted toward the cathode side comes out from the anode side after being reflected by the cathode once.
[0197]
In this case, light with a wavelength corresponding to the material of the light-emitting layer can be visually recognized in the portion where the EL layer emits light, but in the portion where light is not emitted, the anode and the EL layer are transmitted and the back side of the cathode (light-emitting layer) The surface is visible. Therefore, there arises a problem that the back of the cathode acts like a mirror and the face of the observer moves. Therefore, in this embodiment, an example for avoiding this will be described.
[0198]
As the simplest method, a method of attaching a circularly polarizing film to an EL display device is possible. However, since a circularly polarizing film is expensive, there exists a problem that cost will become high. In addition, a method can be used in which undulations are provided on the reflective surface of the cathode (the surface in contact with the light emitting layer side) and the reflected light is scattered on the reflective surface of the cathode.
[0199]
Specifically, visible light (external light) incident from the anode side is irregularly reflected on the cathode reflection surface so that the observer does not see the cathode reflection surface.
[0200]
The undulating portion provided on the reflective surface of the cathode may be provided with a concave depression or may be provided with a convex protrusion. Moreover, it may be a corrugated surface in which irregularities are repeated. These undulations may be formed by photolithography, holography (for example, the uneven reflection structure described in “Sharp Technical Report, No. 74, pp16-19, August 1999”) or the like. Alternatively, it may be formed by surface treatment such as plasma treatment or etching treatment. Further, the undulating portion may be naturally generated on the surface under the film forming conditions of the cathode (or the electrode serving as the base).
[0201]
In other words, it may be provided regularly or irregularly, but it must be provided so that irregular reflection occurs on average within the plane of one pixel. In addition, undulations can be formed in other thin films in contact with the cathode. JP-A-9-69642 and JP-A-10-144927 can be cited as means for forming undulations in the aluminum film. That is, by forming an aluminum film based on the above publication and laminating the cathode on the aluminum film, a cathode having an undulating portion can be obtained.
[0202]
By using the above method in the present invention, reflection of the observer's face on the cathode back surface can be prevented. In addition, the structure of a present Example can be implemented in combination freely with the structure of Example 1- Example 9. FIG.
[0203]
【The invention's effect】
By carrying out the present invention, the average film resistance of the anode can be lowered by the metal film provided on the anode. Furthermore, since the metal film is light-shielding and is provided so as to hide the gap between the pixels, the outline between the pixels can be made clear in the pixel portion, and an EL display device for high-definition image display Can be obtained.
In addition, by using the EL display device of the present invention as a display portion, an electric appliance with high reliability and high visibility can be obtained.
[Brief description of the drawings]
FIG. 1 illustrates a pixel portion of an EL display device.
FIG. 2 illustrates a cross-sectional structure of a pixel of an EL display device.
FIG. 3 illustrates a top structure and a structure of a pixel portion of an EL display device.
FIGS. 4A and 4B illustrate a manufacturing process of an active matrix EL display device. FIGS.
FIGS. 5A and 5B illustrate a manufacturing process of an active matrix EL display device. FIGS.
6A and 6B illustrate a manufacturing process of an active matrix EL display device.
FIG. 7 is an external view of an EL module.
FIG. 8 is a diagram showing a circuit configuration of an EL display device.
FIG. 9 is an enlarged view of a pixel of an EL display device.
FIG. 10 shows a structure of a sampling circuit of an EL display device.
FIGS. 11A and 11B are diagrams illustrating an appearance and a cross-sectional structure of an EL module. FIGS.
FIG. 12 is a diagram showing a structure of a pixel of an EL display device.
FIG. 13 is a diagram showing a specific example of an electric appliance.
FIG. 14 is a diagram showing a specific example of an electric appliance.
FIG 15 illustrates a pixel portion of an EL display device.

Claims (8)

A plurality of pixels including a thin film transistor and an EL element;
The EL element has a pixel electrode electrically connected to the thin film transistor, a transparent conductive film, and an EL layer sandwiched between the pixel electrode and the transparent conductive film,
The EL layer and the transparent conductive film are provided so as to overlap an edge of the pixel electrode,
A plurality of the pixels, so as to overlap with the gap of the pixel electrode between the edge and the adjacent pixels of the pixel electrode, a metal film in contact with the transparent conductive film is provided,
The EL display device, wherein the metal film has a light shielding property. In claim 1,
The sheet resistance of the metal film is smaller than the sheet resistance of the transparent conductive film. In claim 1 or claim 2,
The EL display device, wherein the metal film is made of any one of Ti, Al, Ta, W, Cr, Cu, and Ag. In any one of Claim 1 thru | or 3,
The EL display device, wherein the transparent conductive film is a compound of indium oxide and tin oxide, a compound of indium oxide and zinc oxide, tin oxide, or zinc oxide.   5. The EL display device according to claim 1, further comprising an undulation portion on the EL layer side of the pixel electrode. In any one of Claims 1 thru | or 5,
In the thin film transistor, an active layer is formed using any one of a single crystal semiconductor film, a polycrystalline semiconductor film, and a microcrystalline semiconductor film. In any one of Claims 1 thru | or 6,
The EL display device, wherein the thin film transistor is an inverted stagger type.   An electric appliance using the EL display device according to any one of claims 1 to 7.

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