JP2003043522A - Reflection type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a contact characteristic between one main electrode 63 of a thin film transistor Tr and a pixel electrode 75 having a function of a reflecting film, with respect to a reflection type liquid crystal display device. SOLUTION: The pixel electrode 75 having a function of a reflecting film is connected with one main electrode 83 of the thin film transistor, and the pixel electrode 75 is formed of two or more kinds of material layers 76, 77 having a material layer 76 for reducing electrical resistance of the part in contact with the main electrode 63.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflective liquid crystal display device. More specifically, the present invention relates to a pixel electrode having a function of a reflective film that forms a good contact with a main electrode of a thin film transistor.

[0002]

2. Description of the Related Art An active matrix type liquid crystal display device (so-called TFT drive type liquid crystal display) in which a pixel electrode is driven by a thin film transistor (TFT) is promisingly developed as a display driven with low power consumption. The reason is that it is not a self-luminous type such as a cathode ray tube but has a function as a light switch, so that it can be used as a reflective type and can see the display on the display by using external light. . Therefore, since the liquid crystal display essentially requires no power other than driving the thin film transistor, it is suitable for a portable mobile display.

FIG. 3 shows a schematic structure of a reflective liquid crystal display. The reflective liquid crystal display 1 includes a reflective liquid crystal panel 2, an optical element 3 having a polarizing plate and a phase plate, a front light 4, and a touch panel 5. The reflective liquid crystal panel 2 includes a thin film transistor (not shown) that is a switching element, a reflective film 7 that serves as a pixel electrode for diffuse reflection, and an alignment film (not shown) on one substrate 6A.
And the color filter 8 is formed on the other transparent substrate 6B.
A counter electrode and an alignment film (not shown) are formed, and the spacer 1
A liquid crystal 10 is enclosed between both substrates 6A and 6B whose distance is regulated by 1. It should be noted that the front light 4 is currently used for a dark place because it cannot sufficiently recognize an image in a dark place. In the reflective liquid crystal display 1, the light incident from the substrate 6B side passes through the liquid crystal 10, is reflected by the pixel electrode 7, passes through the liquid crystal 10 again, and is emitted from the substrate 6B to perform a desired display.

FIG. 4 is an example of a cross-sectional structure of a main part showing a thin film transistor and a pixel electrode of a reflective liquid crystal panel. In this reflective liquid crystal panel 11, for example, a gate electrode 13 integrated with a gate line (so-called scanning line) and a lower electrode 14 of a capacitive element (Cs) are formed of, for example, a Mo film on a glass substrate 12. The lower electrode 14 is formed integrally with the Cs line. A gate insulating film 24 is formed on the substrate 12.
And the SiN _x film 15 and the SiO ₂ film 1 which will be the dielectric film 25.
An insulating film 17 of 5 is formed, and a polycrystalline silicon thin film 18 is formed on the insulating film 17. The polycrystalline silicon thin film 18 is formed commonly in the thin film transistor formation region and the capacitive element formation region. The polycrystalline silicon thin film 18 is impurity-doped except for the channel region 19C on the gate electrode 13, and has a source region 19S and a drain region 1
9D is formed, and at the same time, the upper electrode 20 of the capacitive element is formed. Reference numeral 21 is a stopper film made of, for example, SiO ₂ which serves as a stopper when impurities are doped. In this example, the stopper film 21 is also formed on the upper electrode 20 of the capacitive element.

Next, an interlayer insulating film 24 made of a laminated film of, for example, the SiN _x film 22 and the SiO ₂ film 23 is formed on the entire surface, and the source region 19S is formed through the contact hole.
A signal line 26 connected to the drain region 19D is formed, and a drain electrode 27 connected to the drain region 19D is formed. The signal line 26 and the drain electrode 27 are formed of an Al film 28 connected to the polycrystalline silicon thin film 18 and a Ti film 29 thereon. The gate electrode 13, the gate insulating film 24, and the polycrystalline silicon film 18 (source region 19S, drain region 19
D, the channel region 19C) forms, for example, an n-channel bottom type thin film transistor Tr, and the lower electrode 1
4, the upper electrode 20 formed of the dielectric film 25 and the polycrystalline silicon film 18 provides the additional capacitance element Cs for holding the voltage.
Is formed.

Further, a diffusion layer 31 (made of resin, for example) having an uneven surface is formed on the entire surface, and a planar layer 32 made of acrylic resin, for example, having an uneven surface is formed following the surface of the diffusion layer 31. A pixel electrode 34 connected to the drain electrode 27 through the contact hole 33 and extending on the planar layer 32 is formed. The pixel electrode 34 functions as a reflective film that reflects light.
Etc.

[0007]

By the way, in the reflection type liquid crystal display, as shown in FIG. 3, external light must be efficiently reflected by the reflection film 7 which is the pixel electrode. It is necessary to devise the material and shape of the reflective film 7. As a material, silver (Ag) has the best reflection property. This silver is a material that is easily discolored and difficult to use in mass production, but since it requires its reflective characteristics, it is used intentionally in a manufacturing process with a small margin.

An electrical contact resistance has the smallest margin in this manufacturing process. The reflective film 7 that is a pixel electrode is supplied with an electric signal from an electrode that forms the underlying thin film transistor. Therefore, if the contact resistance between the electrode of the thin film transistor and the reflective film 7 is large, an accurate image voltage cannot be obtained. become. Therefore, if the contact resistance is large, defects such as point defects and unevenness occur in the image.

Since this contact resistance is a fundamental problem in thin film transistors, various measures have been taken. For example, as a device when the step is large, a configuration using a plating method to cover the depth of the contact hole has been proposed (see Japanese Patent Laid-Open No. 11-233783). To return to the basics, it is desirable to select a metal with a small work function difference as the metal to be contacted or to use a material that does not easily form an oxide. However, we have not yet been satisfied.

On the other hand, as shown in FIG. 4, the drain electrode 27 connected to the drain region 19D of the thin film transistor Tr and the signal line 26 for transmitting a signal connected to the source region 19S are made of the same metal material. . Signal line 26
As it is better to reduce the resistance as much as possible,
1 film 28 is used. The Al film 28 also has good contact with the underlying polycrystalline silicon thin film 18, which is also a factor in its use. However, in the reflective liquid crystal panel, the signal line 26
Since we want to reduce the reflection from the
It is necessary to form it on the I film 28. Here, the Ti film 29 is formed.

The Ti film 29 may be easily oxidized by oxygen (O ₂ ) ashing or water washing used in the thin film transistor manufacturing process. This makes it difficult to make contact. On the other hand, the Ag film 28 is formed by a sputtering method, but since Ag does not react with oxygen, if an oxide film is present, an electrical barrier remains and contact cannot be established. That is, whether or not an oxide film is formed on the Ti film 29 determines the contact performance,
It was unstable in the manufacturing process.

In view of the above points, the present invention provides a reflective liquid crystal display device having excellent contact characteristics between a main electrode of a thin film transistor and a pixel electrode serving as a reflective film.

[0013]

In a reflective display device according to the present invention, a pixel electrode having a function of a reflective film is formed on one main electrode of a thin film transistor, and the pixel electrode is electrically connected to a main electrode. The structure is formed by two or more kinds of material layers each having a material layer for reducing resistance.

In the reflection type display device of the present invention, since the pixel electrode is formed of two or more kinds of material layers having a material layer that reduces the electric resistance of the connection portion with the main electrode of the thin film transistor, Since the contact characteristics with the electrodes are improved and a material layer having good reflection characteristics can be formed on the upper layer, the reflection characteristics are not deteriorated.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

1 and 2 show an embodiment of a reflective liquid crystal display device according to the present invention. The figure shows a planar structure and a sectional structure of a main part corresponding to one pixel of the reflective liquid crystal panel, that is, a part of a thin film transistor and a pixel electrode. In the reflective liquid crystal panel 41 according to this embodiment, a gate electrode 44 integrated with a gate line (so-called scanning line) 43 and a lower electrode 45 of a capacitive element (Cs) are formed on a substrate, for example, a glass substrate 42. . The lower electrode 45 is formed integrally with the Cs line 46. In this example, the gate electrode 44, the lower electrode 45, and the Cs line 46 are formed of a Mo layer. An insulating film 49 serving as a gate insulating film 47 and a dielectric film 48 is formed on the substrate 42 so as to cover the gate electrode 44, the upper electrode 45, and the Cs line 46.
The semiconductor thin film 50 is formed on the insulating film 49. The insulating film 49 is formed of, for example, a laminated film of a SiN _x film 52 and a SiO ₂ film 53. The semiconductor thin film 50 is formed of, for example, a polycrystalline silicon film formed by laser crystallization.

The semiconductor thin film 50 serves as an active layer of the thin film transistor and an upper electrode of the capacitive element, and is commonly formed in the thin film transistor forming region and the capacitive element forming region.
In the semiconductor thin film 50, the source region 50S and the drain region 50D are formed by impurity doping except the channel region 50C on the gate electrode 44, and the upper electrode 54 of the capacitive element is formed. Here, the channel region 50
For example, Si for preventing the above impurity doping is provided on C.
A stopper film 55 made of an O ₂ film is formed. Further, the semiconductor thin film portion to be the upper electrode 54 of the capacitor may or may not be impurity-doped. In this example, the stopper film 55 does not dope impurities.

Then, an interlayer insulating film 57 is formed on the entire surface. The interlayer insulating film 57 is formed of, for example, a laminated film of a SiN _x film 58 and a SiO ₂ film 59. Contact holes 60 and 61 are formed in the interlayer insulating film 57, and the source region 5 is formed through the contact holes 60 and 61.
The signal line 62 connected to 0S is formed, and the drain electrode 63 connected to the drain region 50D is formed. 67 indicates a contact portion between the signal line 62 and the source region 50S, and 68 indicates a contact portion between the drain region 50D and the drain electrode 63. Signal line 62 and drain electrode 6
In the present example, when a polycrystalline silicon film is used as the semiconductor thin film 50 in the present example, 3 has a two-layer structure of an Al film 64 having a good contact property with the polycrystalline silicon film and a Ti film 65 for suppressing light reflection thereon. Gate electrode 44, gate insulating film 47
The semiconductor thin film 50 (source region 50S, drain region 50D, channel region 50C) forms, for example, an n-channel bottom type thin film transistor Tr, and the lower electrode 45, the dielectric film 48, and the upper electrode 54 including the semiconductor thin film 50 Additional capacitance element Cs for holding voltage
Is formed. Although one thin film transistor Tr is provided in the above example, two thin film transistors may be connected in series to form a switching element.

Further, a diffusion layer 7 having an uneven surface on the entire surface
1. A planar layer 72 having an uneven surface is formed following the surface of the diffusion layer 71. The diffusion layer 71 is made of, for example, a resin, and the planar layer 72 is also made of, for example, an acrylic resin. A contact hole 73 reaching the drain electrode 63 is formed in the diffusion layer 71 and the planar layer 72, and the pixel electrode 7 connected to the drain electrode 63 through the contact hole 73 and extending on the planar layer 72 having an uneven surface is formed.
5 is formed. The surface of the pixel electrode 75 is formed in an uneven shape following the unevenness of the surface of the planar layer 72, and is formed of a material having a good reflection characteristic and has a function as a reflection film.

In the present embodiment, especially the pixel electrode 7
5 is formed of two or more kinds of material layers so as to have excellent reflection characteristics and to reduce the electric resistance of the connection portion with the drain electrode 63, that is, the connection with the drain electrode 63 with a small contact resistance. In this example, the side in contact with the drain electrode 63 is I
The TO (indium tin oxide) film 76 is formed in a two-layer film structure in which an after-mentioned liquid crystal side is an Ag film 77 (so-called Ag / ITO laminated structure) having good reflection characteristics. In other words,
Ag film 77 to be a reflection film and Ti film 6 of drain electrode 63
An ITO film 76 is previously formed between the first and second electrodes.

Even if the ITO film 77 is an oxide film, it takes oxygen into itself and becomes a conductor. Drain electrode 6
Even if the surface of the Ti film 65 of No. 3 is oxidized, the ITO film 63
However, since this oxygen is taken in, the contact between the drain electrode 63 and the pixel electrode 75 becomes good as a result. Since the ITO film 63 is generally used as a transparent electrode of a transmissive liquid crystal display, it has a good track record of conductivity.

The ITO film 76 and the Ag film 77 can be formed as follows. Since the ITO film 76 is formed by a sputtering method, the Ag film 77 may be formed in a different chamber of the same device or may be formed in a different device before sputtering. Further, in the case of forming only the conventional Ag film as the pattern formation of the pixel electrode, after patterning the resist layer of the Ag film by the photoresist process, the Ag film is etched by wet etching through the resist mask to separate each pixel. ing. In the case of the two-layer film structure of the present embodiment, the resist layer is patterned in the photoresist process, etching is continuously performed through the resist mask, and the Ag film and the ITO film are separated for each pixel in the same pattern. . Alternatively, first, an ITO film is formed and pixels are separated by a shift photo etching method, and then A
A g film is applied and the pixels are separated by a photoetching method. That is, the patterning of the ITO film and the patterning of the Ag film can be separately performed. By doing so, it is possible to further improve the reflection characteristics.

Instead of the ITO film 76, another metal may be used.
For example, Al, Mo, W film or the like can be used. Instead of the Ag film 77, an Ag alloy film can be used. The drain electrode 63 may have a Ti / Ag alloy laminated structure instead of the Ti / Al laminated structure described above. Further, the pixel electrode is not limited to the two-layer film structure, and may have a multi-layer film structure including two or more kinds of films. For example, an ITO film (having a film thickness of, for example, about 50 nm), an Al film (having a film thickness of, for example, about 50 nm), and an Ag film (having a film thickness of, for example, about 100 nm) ITO from the drain electrode side.
The pixel electrode can also be formed of a / Al / Ag three-layer structure film.

A specific example of the film thickness of each layer is shown below. The thickness of the gate electrode 44 and the lower electrode 45 formed of the Mo layer is about 90 nm, and the gate insulating film 47 and the dielectric film 48 are formed.
The film thickness of the SiN _x film 52 forming the
The thickness of the O ₂ film 53 can be about 120 nm. The semiconductor film thickness 50 of the polycrystalline silicon film is 4
About 2 nm, SiO ₂ film of thickness 200nm about which serves as a stopper film 55, SiN _X constituting the interlayer insulating film 57
The film 58 can have a thickness of about 300 nm, and the SiO ₂ film 59 can have a thickness of about 150 nm. The film thickness of the Al film 64 forming the signal line 62 and the drain electrode 63 is 500.
The thickness of the Ti film 65 may be about 100 nm. The thickness of the diffusion layer 71 can be about 1.5 μm, and the thickness of the planar layer 72 can be about 0.6 μm. The film thickness of the ITO film 76 forming the pixel electrode 75 is 10
The film thickness of the Al film 77 may be about 0 nm and the film thickness of the Al film 77 may be about 400 nm.

After forming the components on the glass substrate 42 shown in FIG. 2, an alignment layer is formed on the entire surface including each pixel electrode 75 (not shown). On the other hand, as shown in FIG.
Transparent substrate, for example a color filter on the inner surface of the glass substrate,
A counter electrode and an alignment layer common to each pixel are formed. Liquid crystal is sealed between these two substrates to form a target reflective liquid crystal panel 41. A reflective liquid crystal display device is configured by including the liquid crystal panel 41. For example, as in the case of FIG. 3 described above, a reflective liquid crystal display device can be configured by including the liquid crystal panel 41, the optical element 3 having a polarizing plate and a retardation plate, the front light 4, the touch panel 4, and the like.
The front light 4 can be omitted.

According to the present embodiment described above, the pixel electrode 7
For example, when the pixel electrode 75 is connected to the drain electrode 63 of the thin film transistor Tr which is a switching element, the drain electrode 63 of Ti film 6
Even if the surface of 5 is oxidized, the ITO film 76 takes in the oxygen, so that the contact between the pixel electrode 75 and the drain electrode 63 can be improved. That is, contact resistance can be reduced and stable contact can be made, and contact defects can be reduced. Therefore, it is possible to provide a highly reliable reflective liquid crystal display device. In addition, the manufacturing yield can be improved. Ag film 77 and I
When the Ag film 77 and the ITO film 76 are formed in the same pattern when forming the pixel electrode 75 having the two-layer structure of the TO film 76, the process of forming the pixel electrode 75 can be simplified. Further, when the Ag film 77 and the ITO film 76 are formed in different patterns, the reflection characteristic can be further improved. That is, since the ITO film 76 is inferior in shape followability to the uneven surface of the base as compared with Ag, this IT
When the Ag film 77 is deposited on the O film 76, the characteristics as a reflection plate deteriorate. Therefore, the ITO film 76 and the Ag film 77 are separately patterned, and the ITO film 76 serves as the drain electrode 63.
Formed only in the contact area with
The film 77 is formed over the entire pixel portion including the ITO film 76. As a result, the Ag film 77 can follow the uneven surface of the base layer well, and the reflection characteristics can be further improved. This pixel electrode structure can be applied to other laminated film structures. Even when an Al, Mo, W film is formed instead of the ITO film 76, the contact performance between the pixel electrode 75 and the drain electrode 63 can be improved. That is, Al, Mo
Alternatively, since the W film is formed by sputtering in a non-oxidizing atmosphere, the Ti film 65 of the underlying drain electrode 63 is not oxidized, and at the same time, even if there is an oxide film on the surface of the Ti film 65, the oxide film is not formed. It is reverse-sputtered and removed (substantially Al, Mo, or W atoms penetrate through the oxide film to enter), and as a result, the contact between the drain electrode 63 and the pixel electrode 75 is improved.

[0027]

According to the reflection type liquid crystal display device of the present invention,
The contact characteristics between the pixel electrode having the function of the reflective film and the main electrode of the thin film transistor can be improved, and the reliability of the reflective liquid crystal display device can be improved and the manufacturing yield can be improved. The main electrode of the thin film transistor is T
It has a laminated structure of i / Al or Ti / Ag alloy, and the pixel electrode has an ITO film on the side of contact with the main electrode and the upper layer is Ag or A.
When the g alloy is used, even if the Ti film of the main electrode is oxidized, the oxygen is taken in by the ITO film, so that the contact resistance is stable and contact defects can be reduced. The main electrode of the thin film transistor has a laminated structure of Ti / Al or Ti / Ag alloy, and the pixel electrode has Al, Mo or W on the contact side with the main electrode.
When the film or upper layer is made of Ag or Ag alloy, Al, Mo
Alternatively, since the W film is formed in a non-oxidizing atmosphere, the underlying contact portion is not oxidized, and even if an oxide film is formed on the surface, the oxide film is removed by reverse sputtering during film formation,
As a result, the contact characteristics are improved.

When the pixel electrode is formed in the same pattern in each layer, the process of forming the pixel electrode can be simplified. Further, when the pixel electrode has a two-layer structure and each layer is formed in a different pattern, the reflection characteristic can be further improved.

[Brief description of drawings]

FIG. 1 is a plan view of a main part corresponding to one pixel of a reflective liquid crystal display device according to the present invention.

2 is a cross-sectional view of a main part corresponding to one pixel of the reflective liquid crystal display device according to the present invention, which is a cross-sectional view taken along the line AA of FIG.

FIG. 3 is a schematic configuration diagram of a reflective liquid crystal display device.

FIG. 4 is a cross-sectional view of a main part corresponding to one pixel of a conventional reflective liquid crystal display device.

[Explanation of symbols]

41 ... Liquid crystal panel, 42 ... Substrate, 43 ... Gate line (scanning line), 44 ... Gate electrode, 45 ...
..Lower electrode, 46 ... Cs line, 47 ... Gate insulating film, 48 ... Dielectric film, 50 ... Semiconductor thin film, 50S ... Source region, 50D ... Drain region, 50C ... Channel region, 54 ... Upper electrode,
Tr: thin film transistor, Cs: additional capacitance, 6
2 ... Signal line, 63 ... Drain electrode, 64 ...
Al film, 65 ... Ti film, 71 ... Diffusion layer, 72 ...
..Planar layers, 75 ... Pixel electrodes, 76 ... IT
O film, 77 ... Ag film

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01L 21/28 301 H01L 21/28 301R 29/786 29/78 616U F term (reference) 2H092 GA17 GA19 GA28 JB07 NA28 4M104 AA09 BB14 BB16 CC01 DD20 GG20 5C094 AA31 AA32 AA42 AA53 BA03 BA43 CA19 EA04 EA06 EA07 EB04 EB05 FB14 5F110 AA03 BB01 CC08 DD02 NN NN NN NN NN25NN0323

Claims (5)

[Claims] 1. Two kinds of pixel electrodes having a function of a reflection film are connected to one main electrode of a thin film transistor, and the pixel electrode has a material layer for reducing electric resistance of a contact portion with the main electrode. A reflective liquid crystal display device comprising the above material layers. 2. The main electrode is formed of a Ti / Al laminated structure or a Ti / Ag alloy laminated structure, and the pixel electrode has an ITO film on the contact side with the main electrode and an upper layer of Ag or Ag alloy. The reflective liquid crystal display device according to claim 1, wherein the reflective liquid crystal display device is formed as a film. 3. The main electrode is formed of a Ti / Al laminated structure or a Ti / Ag alloy laminated structure, and the pixel electrode has Al and Mo on the contact side with the main electrode.
2. The reflection type liquid crystal display device according to claim 1, wherein the reflection type liquid crystal display device comprises a W film and an upper layer formed of Ag or an Ag alloy film. 4. The reflective display device according to claim 1, wherein each layer of the pixel electrode is formed in the same pattern. 5. The liquid crystal display device according to claim 1, wherein the pixel electrode has a two-layer structure, and each layer is formed in a different pattern.