KR102468860B1 - Thin film transistor and display device having thereof - Google Patents

Abstract

In the thin film transistor of the present invention, leakage current due to the photoelectric effect of the semiconductor layer is prevented and the aperture ratio of the display device is improved by providing a transmittance adjusting layer at the bottom of the semiconductor layer to block low-wavelength light and transmit high-wavelength light. The transmittance control layer is composed of a transparent conductive layer, a SiNx layer, and a SiO ₂ layer. The transparent conductive layer is at least one material selected from the group consisting of ITO (Indium Tin Oixde), IZO (Indium Zinc Oixde), and IGZO (Indium Gallium Zinc Oxide). In this case, the thickness of the transparent conductive layer is 160-780 Å, the thickness of the SiNx layer is 160-600 Å, and the thickness of the SiO ₂ layer is 800-1200 Å.

Description

Thin film transistor and display device having the same {THIN FILM TRANSISTOR AND DISPLAY DEVICE HAVING THEREOF}

The present invention relates to a thin film transistor, and more particularly, to a thin film transistor capable of improving an aperture ratio by forming a light blocking layer of a transparent material to prevent light from being irradiated onto a semiconductor layer, and a display device having the same.

Recently, interest in information display has increased and the demand for using portable information media has increased. Research and commercialization are being focused on. Such a flat panel display includes a liquid crystal display, an organic light emitting display, and an electrophoretic display, and these display devices are currently being applied to various fields.

The flat panel display implements an image by driving a plurality of pixels arranged in a matrix shape. Each pixel displays an image by driving a thin film transistor, which is a switching element, in response to an external signal being applied.

1 is a cross-sectional view showing the structure of a conventional thin film transistor.

As shown in FIG. 1, a conventional thin film transistor includes a light blocking layer 16 disposed on a substrate 10, a buffer layer 21 formed over the entire substrate 10 on which the light blocking layer 16 is formed, and the buffer layer. (21) a semiconductor layer 12 disposed on, an insulating layer 22 stacked over the entire substrate 10 on which the semiconductor layer 12 is formed, and a gate electrode 11 disposed on the insulating layer 22 ), a gate insulating layer 23 disposed on the second buffer layer 21 and covering the gate electrode 11, and a second buffer layer 22 disposed on the second buffer layer 22 and the gate insulating layer 23 and a source electrode 14 and a drain electrode 15 making ohmic contact with the semiconductor layer 12 through the contact hole 26 formed in the gate insulating layer 23 .

A protective layer 24 is stacked on the substrate 10 on which the source electrode 14 and the drain electrode 15 are formed, and an electrode (eg, a pixel electrode) is disposed on the protective layer 24 to form a protective layer ( The electrode 30 is electrically connected to the drain electrode 15 of the thin film transistor through the contact hole 27 formed in 24).

When a scan signal is applied to the gate electrode 11 from the outside through a wiring such as a gate line in the thin film transistor having the above structure, the semiconductor layer 12 is activated, which is a signal passage to the semiconductor layer 12. A channel is formed. In this state, when a signal is applied to the source electrode 14 through a wiring such as a data line, an image signal is transferred to the drain electrode 15 through a channel formed in the semiconductor layer 12, and the transmitted image signal is displayed. It is applied to the electrode 30 of the device and an image is implemented.

However, the thin film transistor having the above structure has the following problems.

When the thin film transistor having the above structure is applied to a display device, when the semiconductor layer of the thin film transistor is made of crystalline silicon, when light is incident on the semiconductor layer 12 from an external light source such as a backlight, a photoelectric effect occurs in the semiconductor layer. In the layer 12, electrons protrude and move inside the semiconductor layer 12, and the movement of these electrons causes leakage current in the thin film transistor. Since this leakage current is an important factor in degrading the electrical characteristics of the thin film transistor, a light blocking layer 16 is disposed below the semiconductor layer 12 to block light incident on the semiconductor layer 12 .

The light blocking layer 16 is an opaque metal layer formed of a Cr-based metal, and prevents leakage current by effectively blocking light incident on the semiconductor layer 12 from an external light source such as a backlight.

However, in order to completely block light incident on the semiconductor layer 12, the area of the light blocking layer 16 is larger than the area of the semiconductor layer 12, so that the light blocking layer 16 completely covers the semiconductor layer 12. There must be. Therefore, an opaque light blocking layer 16 extends from the lower region of the semiconductor layer 12 to the inside of a pixel where an image is displayed. The aperture ratio of the device is lowered.

The present invention has been made in view of the above, a thin film capable of improving the aperture ratio transparently without generating leakage current in the semiconductor layer by blocking light of the low wavelength band and transmitting light of the high wavelength band to the lower portion of the semiconductor layer. It is an object of the present invention to provide a transistor and a display device having the same.

The present invention is to achieve the above object, by providing a transmittance control layer that blocks low-wavelength light and transmits high-wavelength light at the bottom of the semiconductor layer, thereby preventing leakage current due to the photoelectric effect of the semiconductor layer and display device It is possible to improve the aperture ratio of

The transmittance control layer is composed of a transparent conductive layer, a SiNx layer, and a SiO ₂ layer. The transparent conductive layer is at least one selected from the group consisting of indium tin oxide (ITO), indium zinc oxide (IZO), and indium gallium zinc oxide (IGZO). may be made of matter.

The thickness of the transparent conductive layer is 160-780 Å, the thickness of the SiNx layer is 160-600 Å, the thickness of the SiO ₂ layer is 800-1200 Å, preferably the thickness of the transparent conductive layer is 200-650 Å, the thickness of the SiNx layer is 200-500 Å, SiO The thickness of the _second layer may be 1000 Å. The semiconductor layer is a crystalline semiconductor layer.

The thin film transistor according to the present invention can be applied to various display devices. When applied to a liquid crystal display device, the liquid crystal display device is formed on a first substrate and a second substrate including a plurality of pixels and each pixel of the first substrate. a transmittance control layer disposed on the first substrate to block low-wavelength light and transmit high-wavelength light, a semiconductor layer disposed on the transmittance control layer, an insulating layer disposed on the semiconductor layer, and an insulating layer disposed on the insulating layer. A thin film transistor including an disposed gate electrode, a gate insulating layer disposed on the gate electrode, a source electrode and a drain electrode disposed on the semiconductor layer, a common electrode and a pixel electrode disposed on the pixel, and formed on the second substrate It consists of a black matrix and color filter layer, and a liquid crystal layer disposed between the first and second substrates.

In addition, when applied to an organic light emitting display device, the organic light emitting display device is formed on a substrate including a plurality of pixels and each pixel of the substrate, and is disposed on the substrate to block low wavelength light and high A transmittance control layer through which light in the wavelength range is transmitted, a semiconductor layer disposed on the transmittance control layer, a first insulating layer disposed on the semiconductor layer, a gate electrode disposed on the insulating layer, and a gate insulating layer disposed on the gate electrode. , a thin film transistor including a source electrode and a drain electrode disposed on the semiconductor layer, a second insulating layer disposed on the substrate on which the thin film transistor is formed, a pixel electrode in each pixel on the insulating layer, and formed on the pixel electrode It is composed of an organic light emitting unit that emits light and a common electrode formed on the organic light emitting unit.

In the present invention, the transmittance of light in the low wavelength band is low and the transmittance of light in the high wavelength band is high by providing a transmittance control layer under the crystalline semiconductor layer, so that leakage due to the photoelectric effect occurs when light is incident on the semiconductor layer due to the low transmittance in the low wavelength band. It is possible to improve the aperture ratio of the display device by not generating current and having high transmittance in the high wavelength range.

According to the present invention, compared to conventional liquid crystal display devices in which the light blocking layer is formed of an opaque Cr-based metal, the liquid crystal display device according to the present invention having a transmittance control layer composed of an ITO light blocking layer/SiNx buffer layer/SiO2 buffer layer has a light blocking layer of about 2.5 % of the aperture ratio is improved.

1 is a view showing the structure of a conventional thin film transistor.
2a and 2b are views showing the structure of a thin film transistor according to the present invention.
3 is a graph showing the relationship between wavelength band transmittance in a laminated structure of ITO and ITO/SiNx/SiO ₂ .
Figure 4a is SiO ₂ for the SiNx buffer layer A graph showing the thickness ratio of the buffer layer.
Figure 4b is a graph showing the thickness ratio of the ITO light-shielding layer to the SiNx buffer layer.
5A and 5B are diagrams illustrating a display device to which a thin film transistor according to the present invention is applied.
6 is a view showing another display device to which a thin film transistor according to the present invention is applied.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

In the present invention, in order to prevent leakage current due to light incident on the semiconductor layer of the thin film transistor, the light blocking layer disposed below the semiconductor layer to block light incident on the semiconductor layer is not formed of an opaque material but is transparent. It is formed of a material to prevent leakage current due to the photoelectric effect of the semiconductor layer and improve transmittance of the display device.

In particular, in the present invention, the light-blocking layer does not transmit all components of light, but blocks relatively high-energy short-wavelength light and transmits only low-energy long-wavelength light, thereby suppressing the occurrence of the photoelectric effect in the semiconductor layer while being transparent. be able to

In this way, since the light blocking layer blocks only some components of light and transmits other components, not only can the generation of leakage current due to the photoelectric effect of the semiconductor layer be suppressed, but also the light blocking layer is transparent to the human eye by long wavelength light. it becomes visible Therefore, when the area of the light-blocking layer is larger than that of the semiconductor layer, the aperture ratio is increased by the difference between the area of the light-blocking layer and the area of the semiconductor layer because the light-blocking layer extending to the pixels of the display device is transparent.

In the present invention, a first buffer layer made of SiNx and a second buffer layer made of SiO ₂ are provided on top of a light-shielding layer made of a transparent metal oxide, and transmittance of a specific wavelength range is obtained by a difference in refractive index between the light-shielding layer and the first and second buffer layers. It is possible to obtain the effect of improving the aperture ratio and preventing leakage current by adjusting.

2a and 2b are views showing the structure of a thin film transistor according to the present invention. At this time, the thin film transistor of the present invention is a crystalline thin film transistor.

As shown in FIG. 2A, the thin film transistor according to the present invention has a light blocking layer 116 disposed on a substrate 110 such as transparent glass or plastic, and laminated on the substrate 110 to form the light blocking layer 116. The covering first buffer layer 121a and the second buffer layer 121b, the semiconductor layer 112 disposed on the second buffer layer 121b, the insulating layer 122 disposed on the semiconductor layer 112, and the A gate electrode 111 disposed on the insulating layer 122, a gate insulating layer 123 stacked on the insulating layer 122 and covering the gate electrode 111, and disposed on the gate insulating layer 123 It is composed of a source electrode 114 and a drain electrode 115 that make ohmic contact with the semiconductor layer 112 through the contact hole 126 formed in the gate insulating layer 123 and the insulating layer 122 .

A passivation layer 124 is stacked over the entire substrate 110 on the top of the thin film transistor of the above configuration, and a pixel electrode 130 for applying a signal to an image display device of a display device is formed on the passivation layer 124. Thus, the pixel electrode 130 is electrically connected to the drain electrode 115 of the thin film transistor through the contact hole 127 formed in the protective layer 124.

At this time, the protective layer 124 may be formed of an inorganic material such as Si0 ₂ or SiNx, but is preferably formed of an organic insulating material such as photoacrylic to flatten the upper portion of the protective layer 124. In addition, the protective layer 124 may be formed of a plurality of layers of inorganic insulating layer/organic insulating layer/inorganic insulating layer. The image implementing element is for realizing an image, and is an organic light emitting layer in the case of an organic light emitting display device, a liquid crystal layer in the case of a liquid crystal display device, and an electrophoretic layer in the case of an electrophoretic display device.

The gate electrode 111 may be formed of a metal such as Cr, Mo, Ta, Cu, Ti, Al or an Al alloy, and the gate insulating layer 122 is a single material made of an inorganic insulating material such as SiO ₂ or SiNx. layer or a double layer of SiO ₂ and SiNx.

The semiconductor layer 112 is formed of a crystalline semiconductor material such as single crystal silicon or polysilicon. At this time, the crystalline semiconductor layer may be formed by directly stacking crystalline semiconductors, or may be formed by stacking amorphous semiconductors and then crystallizing the amorphous material by various crystallization methods such as laser crystallization. Doping layers are formed on both sides of the crystalline silicon layer by doping n ⁺ or p ⁺ type impurities.

The insulating layer 123 may be composed of a single layer made of an inorganic insulating material such as SiO ₂ or SiNx or a double layer made of SiO ₂ and SiNx, and the source electrode 114 and the drain electrode 115 are Cr, It may be composed of metals such as Mo, Ta, Cu, Ti, Al, and Al alloys.

The light blocking layer 116 is made of a transparent metal oxide such as indium tin oxide (ITO), indium tin oxide (IZO), or indium gallium tin oxide (IGZO), the first buffer layer 121a is made of SiNx, and the second buffer layer is made of SiNx. (121b) is composed of SiO ₂ . In general, ITO is a transparent material, and when the light-blocking layer 116 is formed with ITO, light in the full wave spectrum is transmitted as it is. However, as the first buffer layer 121a made of SiNx and the second buffer layer 121b made of SiO ₂ are disposed on the ITO light blocking layer 116, the transmittance for each wavelength band is changed.

FIG. 3 is a diagram showing transmittance for each wavelength of ITO/SiNx/SiO ₂ , which is a stacked structure of ITO and the light blocking layer 116/first buffer layer 121a/second buffer layer 121b.

The number of electrons emitted by the photoelectric effect by light irradiation of the crystalline semiconductor layer 112 such as polysilicon is proportional to the intensity of the irradiated light, and the wavelength of the light determines the maximum kinetic energy of the electrons. That is, the maximum kinetic energy of electrons in the semiconductor layer 112 generated by the photoelectric effect is independent of the intensity of light and is determined by the frequency (frequency) of light.

As a result of experiments by repeatedly irradiating light of various wavelengths to the crystalline semiconductor layer 112 such as crystalline silicon, the present applicant derived that the photoelectric effect mainly occurred below a specific wavelength (Wc), and this critical wavelength (Wc) It is about 500 nm.

As shown in FIG. 3, ITO has almost similar transmittance in all wavelength bands. That is, it can be seen that the transmittance of the wavelength range below the critical wavelength (Wc) is 80% or more, and at this level of transmittance, most of the light components below the critical wavelength (Wc) incident on the light blocking layer 116 pass through the semiconductor layer 112. means entering into Therefore, when only the light-blocking layer 116 made of ITO is disposed below the semiconductor layer 112 to block light, most of the light components having a high energy below the critical wavelength Wc are incident on the semiconductor layer 112, A photoelectric effect occurs at 112, and leakage current is generated in the thin film transistor.

On the other hand, in the ITO/SiNx/SiO ₂ laminated structure, the transmittance of light in the wavelength range above the critical wavelength (Wc) is about 80% or more, whereas the transmittance of light in the wavelength range below the critical wavelength (Wc) is about 70% or less. Moreover, in the wavelength range below the critical wavelength Wc, the transmittance decreases as the wavelength decreases, and the transmittance is about 70% at a wavelength of 530 nm, whereas the transmittance is about 40% at a wavelength of 400 nm. This means that the transmitted light amount decreases as the wavelength of the incident light decreases, that is, as the energy of the incident light increases. Therefore, in the stacked structure of ITO/SiNx/SiO ₂ , the transmittance of light in the low wavelength band having high energy is low, and the light in the high wavelength band having high energy is high in transmittance.

In this way, the difference in transmittance for each wavelength band in the stacked structure of ITO/SiNx/SiO ₂ is caused by the difference in refractive index between ITO, SiNx, and SiO ₂ . That is, for light in the low wavelength band, reflection occurs more than refraction at the interface between ITO, SiNx, and SiO ₂ , and for light in the high wavelength band, refraction occurs more than reflection at the interface between ITO, SiNx, and SiO ₂ . Silver has low transmittance and high wavelength light has high transmittance.

When such a structure is applied to a thin film transistor, the semiconductor layer 112 is mainly irradiated with light of a wavelength range having low energy, so that the photoelectric effect is affected by the semiconductor layer 112 while maintaining the transmittance of the light blocking layer 116 at a certain level. leakage current can be prevented. Of course, even in this structure, light of the critical wavelength (Wc) or less is irradiated to the semiconductor layer 112, but light in this wavelength range has low transmittance, so the light energy applied to the semiconductor layer 112 Since it is smaller than the work function, the photoelectric effect does not occur.

As described above, in the present invention, the light blocking layer 116 is made of ITO, which is a transparent material, and the first buffer layer 121a and the second buffer layer 121b are provided thereon to reduce transmittance in the low frequency band. As described above, in the present invention, although the ITO film is referred to as the light blocking layer 116 that prevents light from entering the semiconductor layer 112, the light blocking layer 116 itself does not block light, but the first buffer layer 121a and the first buffer layer 121a. Since part of the light component is blocked together with the second buffer layer 121b, the laminated structure of the light blocking layer 116/first buffer layer 121a/second buffer layer 121b is called a light blocking layer, and the light blocking layer 116, Each of the first buffer layer 121a and the second buffer layer 121b may be regarded as a first light blocking layer, a second light blocking layer, and a third light blocking layer. In addition, strictly speaking, since the light-blocking layer 116/first buffer layer 121a/second buffer layer 121b stack structure does not block the transmission of light but adjusts the light transmittance according to the wavelength range, these stacked structures have transmittance. You could also call it a control layer.

4a is a graph showing the thickness ratio of the second buffer layer 121b made of SiO ₂ to the first buffer layer 121a made of SiNx, and FIG. 4b is a light blocking layer made of ITO with respect to the first buffer layer 121a made of SiNx ( 116) is a graph showing the thickness ratio.

As shown in FIG. 4A, each curve shown in the graph has a thickness ratio of the second buffer layer 121b to the first buffer layer 121a of 1:10, 1:5, 1:3.3, 1:2, represents the case of 1:1. In all thickness ratio curves, the transmittance below the critical wavelength Wc is lower than the transmittance below the critical wavelength Wc. According to the present invention, when light having a wavelength of about 400 nm or less, in particular light having a wavelength of about 400 nm, transmits and is irradiated to the semiconductor layer 112, if the transmittance is 70% or more, the light energy applied to the semiconductor layer 112 It is higher than the work function of crystalline silicon, and leakage current due to the photoelectric effect occurs, and leakage current due to the photoelectric effect does not occur when it is 70% or less.

Therefore, in the present invention, when the thickness ratio of the second buffer layer 121b to the first buffer layer 121a is 1:5, 1:3.3, or 1:2, leakage current due to the photoelectric effect does not occur and the first buffer layer 121a When the thickness ratio of the second buffer layer 121b to ) is 1:10 or 1:1, leakage current is generated due to the photoelectric effect.

Accordingly, in the present invention, the thickness of the second buffer layer 121b may be formed to be about 800-1200 Å, preferably 1000 Å, and at this time, the thickness of the first buffer layer 121a may be about 160-600 Å, preferably 200-1200 Å. 500 Å.

As shown in FIG. 4B, each of the curves shown in the graph indicates that the thickness ratio of the light blocking layer 116 to the first buffer layer 121a is 1:2, 1:1.4, 1:1.3, 1:1.2, and 1, respectively. :1.1, indicates the case of 1:1. In all thickness ratio curves except for the thickness of 1:2, the transmittance below the critical wavelength (Wc) is lower than the transmittance above.

If the transmittance of light below the critical wavelength (Wc), in particular, light with a wavelength of about 400 nm is 70% or less, leakage current due to the photoelectric effect does not occur. When the thickness ratio is 1:1.3, 1:1.2, 1:1.1, or 1:1, leakage current due to the photoelectric effect does not occur, and the thickness ratio of the light blocking layer 116 to the first buffer layer 121a is 1:2, 1 : In the case of 1.4, leakage current occurs due to the photoelectric effect.

Accordingly, in the present invention, when the thickness of the first buffer layer 121a is about 160-600 Å, preferably 200-500 Å, the thickness of the light blocking layer 116 is 160-780 Å, preferably 200-650 Å.

In conclusion, in the present invention, the thickness of the light blocking layer 116 may be 160-780 Å, the thickness of the first buffer layer 121a may be 160-600 Å, and the thickness of the second buffer layer 121b may be 800-1200 Å, preferably. The thickness of the light blocking layer 116 may be 200-650 Å, the thickness of the first buffer layer 121a may be 200-500 Å, and the thickness of the second buffer layer 121b may be 1000 Å.

FIG. 2B is a plan view schematically illustrating a thin film transistor according to the present invention. In the drawing, only the semiconductor layer 112, the light blocking layer 116, the source electrode 114, and the drain electrode 115 are shown for convenience of description.

As shown in FIG. 2B, the semiconductor layer 112 is disposed with a length of ℓ1 and a width of d1, and a contact hole 126 is formed on top of the semiconductor layer 112 to form a source electrode 114 and a drain electrode ( 115 is in ohmic contact with the semiconductor layer 112 through the contact hole 126 . The light blocking layer 116 is disposed below the semiconductor layer 112 . At this time, the light blocking layer 116 has a length of ℓ2 and a width of d2. At this time, since the length ℓ2 and width d2 of the light blocking layer 116 are greater than the length ℓ1 and width d1 of the semiconductor layer 112 (ℓ2>ℓ1, d2>d1), the light blocking layer 116 ) is formed extending to the outside of the semiconductor layer 112 . That is, an area of 2Δℓ×2Δd out of the total area of the light blocking layer 116 is exposed to the outside of the semiconductor layer 112 without overlapping with the semiconductor layer 112 .

When the light blocking layer 116 is formed of an opaque metal such as a Cr-based metal, light is not incident to the semiconductor layer 112 by the light blocking layer 116 and an area of 2Δℓ×2Δd is reduced. The light is not irradiated even in the area with the light.

However, when the light blocking layer 116 is formed of a transparent metal oxide such as ITO or IGZO and the transmittance control layer is disposed on the semiconductor layer by stacking the first buffer layer 121a and the second buffer layer 121b thereon, the critical wavelength Since light of (Wc) or higher transmits through the light blocking layer 116 with a high transmittance, in the case of the opaque metal light blocking layer 116, light is irradiated even to areas where light is not irradiated. That is, as the transparent light blocking layer 116 and the first and second buffer layers 121a and 121b of the present invention are provided, the light transmission area is increased by 2Δℓ×2Δd compared to the case where the opaque light blocking layer 116 is used. this will increase

5A and 5B are a plan view and a cross-sectional view showing an example of a display device having a thin film transistor according to the present invention, wherein the display device is a liquid crystal display device. In particular, the illustrated liquid crystal display device is a fringe field switching (FFS) mode liquid crystal display device, but the present invention is not limited to such an FFS mode liquid crystal display device, but an in plane switching (IPS) mode liquid crystal display device and a twisted nematic (TN) It can be applied to liquid crystal display devices of various modes, such as mode liquid crystal display devices and VA (vertical alignment) mode liquid crystal display devices.

As shown in FIG. 5A, the liquid crystal display device according to the present invention is composed of gate lines 203 and data lines 205 defining a plurality of pixels, and thin film transistors T formed in each pixel. In general, a plurality of pixels including R, G, and B pixels are formed in an FFS mode liquid crystal display, but only one pixel is shown in the drawings for convenience of description.

The thin film transistor T includes a semiconductor layer 212, a gate electrode 211 disposed on the semiconductor layer 212 and connected to a gate line 203, and a contact hole 126 disposed on the gate electrode 211. It is composed of a source electrode 214 and a drain electrode 215 that make ohmic contact with the semiconductor layer 212 and are connected to the data line 205.

A light blocking layer 216 is disposed below the thin film transistor T, and the area of the light blocking layer 216 is larger than that of the semiconductor layer 212 of the thin film transistor T. In addition, the light blocking layer 216 is composed of a transparent metal oxide such as ITO or IGZO, and a buffer layer such as a SiNx layer and a SiO ₂ layer is stacked thereon to block low wavelength light and transmit high wavelength light.

A pixel electrode 230 having a box-shaped common electrode 225 and a slit 230s is formed in each pixel. The pixel electrode 230 is electrically connected to the drain electrode 115 of the thin film transistor T through the contact hole 227 to receive an image signal, and the common electrode 225 is parallel to the gate line 203. It is electrically connected to the common line 228 arranged in such a way that a common voltage is applied.

A plurality of slits 230s are formed in the pixel electrode 230 . The slits 230s are arranged substantially parallel to the data lines 205, and a fringe field is generated by two long sides of the slits 230s and the common electrode 225.

In the FFS mode liquid crystal display having such a structure, as a scanning signal is input to the gate electrode 211 of the thin film transistor T through the gate line 203, the semiconductor layer 212 of the thin film transistor T is activated and channel At the same time, the image signal input to the data line 205 is input to the pixel electrode 230 through the source electrode 214 and the drain electrode 215 of the thin film transistor (T), and the pixel electrode 230 and An image is implemented by forming an electric field between the common electrodes 125 .

The structure of the liquid crystal display having the above configuration will be described in more detail with reference to FIG. 5B.

As shown in FIG. 5B, a light blocking layer 216 made of ITO, IZO or IGZO is disposed on a first substrate 210 made of a transparent material such as glass, and a first buffer layer 221a made of SiNx and SiO2 are disposed thereon. The second buffer layer 221b made of is sequentially stacked.

At this time, the thickness of the light blocking layer 216 may be 160-780 Å, the thickness of the first buffer layer 221a may be 160-600 Å, and the thickness of the second buffer layer 221b may be 800-1200 Å. ) may have a thickness of 200-650 Å, the thickness of the first buffer layer 221a may be 200-500 Å, and the thickness of the second buffer layer 221b may be 1000 Å.

A semiconductor layer 212 is disposed on the second buffer layer 221b. The semiconductor layer 212 is a single crystal or polycrystalline semiconductor, and is formed by laminating and etching crystalline silicon or by crystallizing a semiconductor material such as amorphous silicon (a-Si) by a low-temperature crystallization process using a laser and then etching it. .

An insulating layer 222 is stacked on the semiconductor layer 212 and a gate electrode 211 is disposed thereon. The insulating layer 222 is formed by laminating an inorganic insulating material such as SiOx or SiNx by a Chemical Vapor Deposition (CVD) method, and the gate electrode 211 is made of Cr, Mo, Ta, Cu, Ti, Al or an Al alloy. It is formed by laminating an opaque metal having good conductivity by a sputtering process and then etching it by a photolithography process.

A gate insulating layer 223 is disposed on the gate electrode 211 , and a source electrode 214 and a drain electrode 215 are disposed on the gate insulating layer 223 . The gate insulating layer 223 is formed by laminating an inorganic insulating material such as SiOx or SiNx by a CVD method, and the source electrode 214 and the drain electrode 215 are Cr, Mo, Ta, Cu, Ti, Al or Al. It is formed by laminating opaque metals with good conductivity, such as alloys, by sputtering and then etching them.

The source electrode 214 and the drain electrode 215 are connected to the semiconductor layer 212 through contact holes 226 formed in the insulating layer 222 and the gate insulating layer 223 . Although not shown in the drawing, a semiconductor material to which impurities are added is formed between the semiconductor layer 212, the source electrode 214, and the drain electrode 215 to form the semiconductor layer 212 between the source electrode 214 and the drain electrode ( 215) and an ohmic contact layer for ohmic contact are formed.

In addition, a common electrode 225 is formed on the gate insulating layer 223 in the pixel. The common electrode 225 is formed by laminating and etching a transparent conductive material such as ITO or IZO. In this case, the common electrode 225 may be disposed on the first substrate 210 or the insulating layer 222 .

As described above, the passivation layer 224 is formed over the entire first substrate 210 on which the source electrode 214 and the drain electrode 215 are formed, and the pixel electrode 230 on which a plurality of slits 230s are formed. is formed

The protective layer 224 is formed by laminating an organic insulating material such as BCB (Benzo Cyclo Butene) or photo acryl, and the pixel electrode 230 is formed by laminating a transparent conductive material with good conductivity such as ITO or IZO. and formed by etching. In addition, an inorganic insulating material such as SiOx or SiNx may be used as the protective layer 224 . A contact hole 227 is formed in the passivation layer 224 to electrically connect the pixel electrode 225 to the drain electrode 215 .

In the drawing, the slit 230s is formed in the pixel electrode 230 and the common electrode 215 is formed integrally, but the slit may be formed in the common electrode 225 and the pixel electrode 230 may be integrally formed. Also, in the drawing, the pixel electrode 230 is disposed on the upper portion and the common electrode 225 is disposed on the lower portion with the protective layer 224 interposed therebetween, but the pixel electrode 230 is disposed on the lower portion and the common electrode 225 is disposed on the lower portion. It can also be placed on top.

A black matrix 252 and a color filter layer 254 are formed on the second substrate 250 made of a transparent material such as glass. The black matrix 252 is made of an opaque metal such as Ar or ArOx or a black resin, and prevents image quality from deteriorating due to light passing through a thin film transistor formation area, a gate line, and a data line formation area. In the color filter layer 254, R (Red), G (Green), and B (Blue) color filters are formed to implement actual colors. Although not shown in the drawings, a planarization layer may be formed on the color filter layer 254 .

As described above, the first substrate 210 on which the thin film transistor is formed and the second substrate 250 on which the color filter 254 is formed are bonded, and the liquid crystal layer 260 is formed therebetween to complete the liquid crystal display device.

As described above, in the liquid crystal display device according to the present invention, the transmittance of low wavelength light is low and the transmittance of high wavelength light is high under the crystalline semiconductor layer 212 (that is, the light blocking layer 216 / the first buffer layer). 221a/second buffer layer 221b is provided so that the transmittance control layer is transparent and leakage current does not occur due to the photoelectric effect of light incident on the semiconductor layer 212. Therefore, conventionally opaque light blocking While light supplied to a partial region of the pixel is blocked by the layer, in the present invention, since light incident into the pixel is not blocked by the transmittance control layer (or light blocking layer), the aperture ratio is improved compared to the prior art. According to the present invention, compared to a conventional liquid crystal display in which the light blocking layer is formed of an opaque Cr-based metal, the liquid crystal display according to the present invention having a transmittance adjusting layer composed of an ITO light blocking layer/SiNx buffer layer/SiO2 buffer layer has about 2.5% The aperture ratio of is improved.

6 is a view showing another example of a display device having a thin film transistor according to the present invention, and the display device at this time is an organic light emitting display device.

In general, an organic light emitting display device includes an R pixel outputting red light, a G pixel outputting green light, and a B pixel outputting blue light, but only one pixel is illustrated for convenience of description.

As shown in FIG. 6, a transmittance control layer is disposed on each of the R, G, and B pixels of the first substrate 310 made of a transparent material such as glass or plastic, and a driving thin film transistor is formed thereon.

The transmittance control layer is composed of a light blocking layer 316 made of ITO, IZO or IGZO, a first buffer layer 321a made of SiNx and a second buffer layer 321b made of SiO ₂ sequentially stacked thereon.

At this time, the thickness of the light blocking layer 316 may be 160-780 Å, the thickness of the first buffer layer 321a may be 160-600 Å, and the thickness of the second buffer layer 321b may be 800-1200 Å. ) may have a thickness of 200-650 Å, the thickness of the first buffer layer 321a may be 200-500 Å, and the thickness of the second buffer layer 321b may be 1000 Å.

The driving thin film transistor includes a semiconductor layer 312 disposed on the second buffer layer 321b, an insulating layer 322 stacked on the semiconductor layer 312, a gate electrode 311 disposed on the insulating layer 322, The semiconductor layer ( 312) and a source electrode 314 and a drain electrode 315 in ohmic contact.

A first insulating layer 324 is formed on the first substrate 310 on which the driving thin film transistor is formed. The first insulating layer 324 is made of an inorganic insulating material such as SiO ₂ . A color filter layer 317 having a corresponding color is disposed on each of the R, G, and B pixels on the first insulating layer 324 .

A second insulating layer 326 is formed on the color filter layer 317 . The second insulating layer 326 is an overcoat layer for planarizing the first substrate 310 and may be made of an organic insulating material such as photoacrylic.

A pixel electrode 230 is disposed on the second insulating layer 326 . At this time, a contact hole 327 is formed in the upper first insulating layer 324 and the second insulating layer 326 of the drain electrode 315 of the driving thin film transistor, so that the pixel electrode 330 covers the contact hole 327. Through this, it is electrically connected to the drain electrode 315 of the driving thin film transistor.

In addition, a bank layer 328 is formed on the second insulating layer 326 . The bank layer 328 is a kind of barrier rib, which divides each pixel and prevents light of a specific color emitted from adjacent pixels from being mixed and output. In addition, since the bank layer 328 fills a part of the contact hole, the level difference is reduced, and as a result, when the organic light emitting part 332 is formed, electric charges are concentrated in the step difference and the lifetime of the organic light emitting part 332 is prevented from deteriorating. You can do it. The pixel electrode 330 is made of a transparent metal oxide material such as ITO or IZO.

An organic light emitting unit 332 made of an organic light emitting material is disposed between the bank layer 328 on the pixel electrode 330 . The organic light emitting unit 332 includes a white organic light emitting layer that emits white light. The white organic light-emitting layer may be formed by mixing a plurality of organic materials emitting R, G, and B monochromatic lights, respectively, or by stacking a plurality of light-emitting layers emitting R, G, and B monochromatic lights, respectively. Although not shown in the drawings, the organic light emitting unit 332 includes not only the organic light emitting layer but also an electron injection layer and a hole injection layer respectively injecting electrons and holes into the organic light emitting layer and an electron transport layer respectively transporting the injected electrons and holes to the organic light emitting layer. And a hole transport layer may be formed.

A common electrode 325 is formed over the entire first substrate 310 on the organic light emitting portion 332 . The common electrode 325 is made of Ca, Ba, Mg, Al, Ag, or the like.

At this time, when the common electrode 325 is the cathode of the organic light emitting unit 332 and the pixel electrode 330 is the anode, and a voltage is applied to the common electrode 325 and the pixel electrode 330, the common electrode 325 Electrons are injected into the organic light emitting unit 332 from the pixel electrode 330 and holes are injected into the organic light emitting unit 332 from the pixel electrode 330, and excitons are generated in the organic light emitting layer, and the excitons decay. Accordingly, light corresponding to the energy difference between the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) of the light emitting layer is generated and emitted to the outside (towards the first substrate 310 in the drawing). At this time, the R, G, and B light emitting layers included in the organic light emitting layer emit red light, green light, and blue light, respectively, and these lights are mixed to emit white light. The emitted white light transmits through the R, G, and B-color filter layers 317, respectively, and outputs only light of a color corresponding to a corresponding pixel.

An adhesive is applied to the upper portion of the common electrode 325 to form an adhesive layer 342, and a second substrate 350 is disposed thereon. Attached to (310).

Any material may be used as the adhesive as long as it has good adhesion and good heat resistance and water resistance, but in the present invention, a thermosetting resin such as an epoxy-based compound, an acrylate-based compound or an acrylic rubber is mainly used. At this time, the adhesive layer 342 is applied to a thickness of about 5-100 μm and cured at a temperature of about 80-170 degrees. The adhesive layer 342 not only bonds the first substrate 310 and the second substrate 350 together, but also serves as a sealant for preventing moisture from penetrating into the organic light emitting display device. Therefore, although the term of reference numeral 42 is expressed as an adhesive in the detailed description of the present invention, this is for convenience, and the adhesive layer may also be expressed as an encapsulant.

The second substrate 350 is an encapsulation cap for sealing the adhesive layer 342, such as a polystyrene (PS) film, a polyethylene (PE) film, a polyethylene naphthalate (PEN) film, or a polyimide (PI) film. It may be made of the same protective film. In addition, the second substrate 350 may be made of plastic or glass, and any material may be used as long as it can protect components formed on the first substrate 310 .

Although an organic light emitting display device having a specific structure is disclosed in the above description, the thin film transistor of the present invention is not applied only to the organic light emitting display device having this specific structure, but may be applied to organic light emitting display devices having various structures. . For example, in the above description, a bottom emission (or bottom emission type) organic light emitting display device in which light is output to the lower portion of the display device is disclosed, but the front surface in which light is output to the upper portion of the display device. It will also be applicable to light emitting type (or top emission type) organic light emitting display devices.

In the organic light emitting display device, a transmittance control layer having a low transmittance of light in a low wavelength band and a high transmittance of light in a high wavelength band is provided under the crystalline semiconductor layer 312 so that the transmittance control layer is transparent and at the same time covers the semiconductor layer 312. Even when incident, leakage current does not occur due to the photoelectric effect. Therefore, whereas in the prior art, light is not supplied to a partial region of a pixel by an opaque light-blocking layer, in the present invention, light supply into the pixel is not blocked by the transmittance adjusting layer (or light-blocking layer), compared to the prior art. The aperture ratio is improved.

Although many details are specifically described in the above description, this should be interpreted as an example of a preferred embodiment rather than limiting the scope of the invention. Therefore, the invention should not be defined by the described examples, but should be defined by what is equivalent to the claims and claims.

110: substrate 111: gate electrode
112: semiconductor layer 114: source electrode
115: drain electrode 116: light blocking layer
121a, 121b: buffer layer

Claims (9)

a first substrate and a second substrate including a plurality of pixels;
a transmittance control layer disposed on the first substrate to block low-wavelength light and transmit high-wavelength light;
Provided in each pixel of the first substrate, a semiconductor layer disposed on the transmittance control layer, an insulating layer disposed on the semiconductor layer, a gate electrode disposed on the insulating layer, a gate insulating layer disposed above the gate electrode, a thin film transistor including a source electrode and a drain electrode disposed on the semiconductor layer;
a common electrode and a pixel electrode disposed in the pixel;
a black matrix and color filter layer formed on the second substrate; and
Consisting of a liquid crystal layer disposed between the first substrate and the second substrate,
The transmittance control layer is composed of a transparent conductive layer, a SiNx layer and a SiO ₂ layer,
The thickness of the SiO ₂ layer is greater than the thickness of the SiNx layer,
The thickness of the transparent conductive layer is equal to or greater than the thickness of the SiNx layer. a substrate including a plurality of pixels;
a transmittance control layer disposed on the substrate to block low-wavelength light and transmit high-wavelength light;
Provided in each pixel of the substrate, a semiconductor layer disposed on the transmittance control layer, a first insulating layer disposed on the semiconductor layer, a gate electrode disposed on the first insulating layer, and a gate insulation disposed above the gate electrode a thin film transistor including a source electrode and a drain electrode disposed on the semiconductor layer;
a second insulating layer disposed on the substrate on which the thin film transistor is formed;
a pixel electrode at each pixel on the second insulating layer;
an organic light emitting unit formed on the pixel electrode to emit light; and
Consisting of a common electrode formed on the organic light emitting portion,
The transmittance control layer is composed of a transparent conductive layer, a SiNx layer and a SiO ₂ layer,
The thickness of the SiO ₂ layer is greater than the thickness of the SiNx layer,
The thickness of the transparent conductive layer is equal to or greater than the thickness of the SiNx layer. delete The display device of claim 1 or 2, wherein the transparent conductive layer is made of at least one material selected from a group consisting of indium tin oxide (ITO), indium zinc oxide (IZO), and indium gallium zinc oxide (IGZO). The method of claim 1 or 2, wherein the thickness ratio of the SiO ₂ layer to the SiNx layer is 1:5, 1:3.3, 1:2, and the thickness ratio of the transparent conductive layer to the SiNx layer is 1:1.3, 1:1.2 , 1:1.1, 1:1 display device. The display device of claim 5 , wherein the transparent conductive layer has a thickness of 160-780 Å, the SiNx layer has a thickness of 160-600 Å, and the SiO ₂ layer has a thickness of 800-1200 Å. The display device of claim 6 , wherein the transparent conductive layer has a thickness of 200-650 Å, the SiNx layer has a thickness of 200-500 Å, and the SiO ₂ layer has a thickness of 1000 Å. The display device according to claim 1 or 2, wherein the semiconductor layer is a crystalline semiconductor layer. According to claim 1 or 2,
The transparent conductive layer has a light transmittance of 80% or more.

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