Thin film transistor and its manufacturing method

Abstract

The present invention relates to a thin film transistor and a method for manufacturing the same, and more particularly to a thin film transistor having improved characteristics and a method for manufacturing the same. A thin film transistor according to an embodiment of the present invention includes a gate electrode, an active layer disposed vertically spaced apart from the gate electrode, source and drain electrodes disposed spaced apart from each other on the active layer, and a contact layer formed between the active layer and the source and drain electrodes.

Description

[Technical field]

[0001] The present invention relates to a thin film transistor and a method for manufacturing the same, and more particularly to a thin film transistor having improved characteristics and a method for manufacturing the same. [Background technology]

[0002] Thin film transistors (TFTs) are used as circuits for independently driving each pixel in semiconductor devices, liquid crystal displays (LCDs), organic electroluminescence (EL) displays, and the like.

[0003] Such a thin film transistor is formed together with a gate line and a data line on a lower substrate of a display device, that is, the thin film transistor includes a gate electrode which is a part of the gate line, an active layer used as a channel, a source electrode and a drain electrode which are parts of the data line, and a gate insulating film.

[0004] In the manufacturing process of a thin film transistor, the active layer is exposed to an etching gas for patterning. When the active layer is exposed to the etching gas, the exposed surface of the active layer is damaged by the etching gas and loses oxygen. In addition, the active layer is connected to a source electrode and a drain electrode, which are part of a data line, and oxygen moves from the active layer to the source electrode and the drain electrode when the thin film transistor is operated, resulting in the active layer losing oxygen. When oxygen deficiency occurs in the active layer, the electrical conductivity of the active layer unintentionally increases and the active layer becomes a conductor. This causes a short circuit in the device, which makes it difficult to stably operate the thin film transistor. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Korean Patent Publication No. 10-2004-0013273 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention provides a thin film transistor capable of preventing oxygen deficiency in an active layer and improving stability, and a method for manufacturing the same. [Means for solving the problem]

[0007] A thin film transistor according to an embodiment of the present invention comprises a gate electrode, an active layer containing an oxide of a first metal element and arranged vertically spaced apart from the gate electrode, source and drain electrodes arranged spaced apart from each other on the active layer, and a contact layer containing a second metal element and formed between the active layer and the source and drain electrodes.

[0008] The contact layer may include a metal or an alloy having the second metallic element.

[0009] The second metal element may include ruthenium (Ru).

[0010] The contact layer may include an oxide of a second metallic element.

[0011] The oxide of the first metal element and the oxide of the second metal element may have compositions different from each other.

[0012] The oxide of the first metal element and the oxide of the second metal element each include zinc oxide doped with an impurity, and the oxide of the first metal element and the oxide of the second metal element may have a different impurity content from each other.

[0013] The oxide of the second metal element may have a higher impurity content than the oxide of the first metal element.

[0014] The impurities include indium (In), gallium (Ga), tungsten (W), lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), manganese (Mg), tantalum (Ta), chromium (Cr), molybdenum (Mo), and manganese (Mg). The metal oxide may include at least one of manganese (Mn), technetium (Tc), rhenium (Re), iron (Fe), ruthenium (Ru), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), platinum (Pt), copper (Cu), silver (Ag), gold (Au), boron (B), thallium (Tl), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), phosphorus (P), and arsenic (As).

[0015] The oxide of the first metal element may contain impurities in an amount of 20 at% or more and less than 40 at% relative to the entire oxide of the first metal element, and the oxide of the second metal element may contain impurities in an amount of 40 at% or more and less than 60 at% relative to the entire oxide of the second metal element.

[0016] The oxide of the second metal element may have a lower oxygen (O) content than the oxide of the first metal element.

[0017] The contact layer may be formed to a thickness of 30 to 100 Å.

[0018] The semiconductor device may further include an insulating film disposed on the active layer and having a contact hole exposing a portion of a surface of the active layer, the contact layer being formed on the portion of the surface of the active layer exposed by the contact hole, and the source and drain electrodes extending onto the insulating film in contact with the contact layer.

[0019] A method for manufacturing a thin film transistor according to an embodiment of the present invention includes the steps of: preparing a substrate on which a gate electrode and an active layer spaced apart from the gate electrode in the vertical direction are formed; and forming a contact layer on the active layer for connecting the active layer to source and drain electrodes.

[0020] In the step of preparing the substrate, a substrate is prepared on which an insulating film having a contact hole exposing a portion of a surface of the active layer is formed, and in the step of forming the contact layer, the contact layer may be formed on the portion of the surface of the active layer exposed by the contact hole.

[0021] In the step of forming the contact layer, the contact layer may be formed on a portion of a surface of the active layer to a thickness of 30 to 100 Å.

[0022] The step of forming the contact layer may be performed by an atomic layer deposition process in which a process cycle including a step of supplying a source gas containing a metal element onto the active layer and a step of supplying a reaction gas containing oxygen onto the active layer is repeated multiple times.

[0023] In the step of supplying the source gas, a first source gas containing zinc (Zn) and a second source gas containing indium (In), gallium (Ga), tungsten (W), lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), ), manganese (Mn), technetium (Tc), rhenium (Re), iron (Fe), ruthenium (Ru), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), platinum (Pt), copper (Cu), silver (Ag), gold (Au), boron (B), thallium (Tl), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), phosphorus (P), and arsenic (As) may be supplied simultaneously with a second source gas containing at least one of these.

[0024] In the step of supplying the source gases, a supply amount of the second source gas may be controlled to be greater than a supply amount of the first source gas.

[0025] The method for manufacturing the thin film transistor may further include forming source and drain electrodes on the contact layer.

[0026] A thin film transistor according to an embodiment of the present invention may include a gate electrode, an active layer including an oxide of a first metal element and spaced apart from the gate electrode in a vertical direction, a first insulating film disposed on the active layer and having a first contact hole exposing a portion of a surface of the active layer, a second insulating film disposed on the first insulating film and exposing the first contact hole and a portion of a surface of the first insulating film extending from the first contact hole, a contact layer including a second metal element and formed on the portion of the surface of the active layer exposed by the first insulating film, and source and drain electrodes disposed on the contact layer and spaced apart from each other, and extending over the portion of the surface of the first insulating film exposed by the second insulating film.

[0027] The first insulating film may include silicon oxide, and the second insulating film may include silicon nitride.

[0028] The first metal element may include at least one of indium (In), gallium (Ga), and zinc (Zn), and the second metal element may include at least one of indium (In), gallium (Ga), zinc (Zn), and ruthenium (Ru).

[0029] A method for manufacturing a thin film transistor according to an embodiment of the present invention may include the steps of: preparing a substrate on which a gate electrode and an active layer are formed, the active layer being vertically spaced apart from the gate electrode and having a portion of its surface exposed by a contact hole formed in a first insulating film; and forming a second insulating film containing silicon nitride on the first insulating film.

[0030] A method for manufacturing a thin film transistor according to an embodiment of the present invention may include the steps of: preparing a substrate on which a gate electrode and an active layer are formed, the active layer being disposed vertically spaced apart from the gate electrode and having a portion of its surface exposed by contact holes formed in a first insulating film and a second insulating film that are stacked together; and forming a contact layer on the exposed portion of the surface of the active layer by a selective atomic layer deposition method to connect the active layer to source and drain electrodes.

[0031] The contact layer may include a metal oxide doped with an impurity.

[0032] The impurities include indium (In), gallium (Ga), tungsten (W), lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), manganese (M), and arsenic (A). n), technetium (Tc), rhenium (Re), iron (Fe), ruthenium (Ru), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), platinum (Pt), copper (Cu), silver (Ag), gold (Au), boron (B), thallium (Tl), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), phosphorus (P), and arsenic (As) may be included as at least one of them.

[0033] The method for manufacturing a thin film transistor may further include, after the step of forming the contact layer, a step of etching the impurity-doped metal oxide film formed on the second insulating film.

[0034] The impurity-doped metal oxide film may be etched with hydrogen bromide (HBr).

[0035] A method for manufacturing a thin film transistor according to an embodiment of the present invention may include the steps of: preparing a substrate on which a gate electrode and an active layer are formed, the active layer being disposed vertically apart from the gate electrode and having a portion of its surface exposed by a first contact hole formed in a first insulating film containing silicon oxide; forming a second insulating film on the first insulating film, the second contact hole exposing the first contact hole being formed therein, the second insulating film containing silicon nitride; and forming a contact layer on the exposed portion of the surface of the active layer by selective atomic layer deposition to connect the active layer to source and drain electrodes.

[0036] A thin film transistor according to an embodiment of the present invention may include a gate electrode, an active layer arranged vertically apart from the gate electrode and containing at least one of indium (In), gallium (Ga) and zinc (Zn), source and drain electrodes arranged on the active layer at a distance from each other, and a ruthenium oxide layer formed between the active layer and the source and drain electrodes.

[0037] A thin film transistor according to an embodiment of the present invention may include a gate electrode, an active layer disposed vertically apart from the gate electrode and containing at least one of indium (In), gallium (Ga) and zinc (Zn), source and drain electrodes disposed on the active layer and spaced apart from each other, a high-concentration metal oxide layer formed between the active layer and the source and drain electrodes and having a higher impurity content than the active layer, and a ruthenium oxide layer formed between the high-concentration metal oxide layer and the source and drain electrodes.

[0038] A method for manufacturing a thin film transistor according to an embodiment of the present invention may include the steps of: preparing a substrate on which a gate electrode and an active layer spaced apart from the gate electrode in a vertical direction are formed; and forming a ruthenium oxide layer on the active layer for connecting the active layer to source and drain electrodes.

[0039] A method for manufacturing a thin film transistor according to an embodiment of the present invention may include the steps of: preparing a substrate on which a gate electrode and an active layer is formed, the active layer being spaced apart from the gate electrode in a vertical direction; forming a high-concentration metal oxide layer on the active layer, the high-concentration metal oxide layer having a higher impurity content than the active layer; and forming a ruthenium oxide layer on the high-concentration metal oxide layer for connecting the active layer to source and drain electrodes.

[0040] The impurities include indium (In), gallium (Ga), tungsten (W), lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), manganese (M), and arsenic (A). n), technetium (Tc), rhenium (Re), iron (Fe), ruthenium (Ru), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), platinum (Pt), copper (Cu), silver (Ag), gold (Au), boron (B), thallium (Tl), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), phosphorus (P), and arsenic (As) may be included as at least one of them. Effect of the Invention

[0041] According to an embodiment of the present invention, by forming a contact layer between the active layer and the source and drain electrodes to prevent oxygen deficiency in the active layer, it is possible to prevent the active layer from becoming a conductor and improve switching characteristics.

[0042] In addition, the contact resistance between the active layer and the source and drain electrodes can be effectively reduced, improving the characteristics and reliability of the device. [Brief description of the drawings]

[0043] [Figure 1]1 is a diagram illustrating a thin film transistor according to a first embodiment of the present invention; [Diagram 2] FIG. 4 is a diagram illustrating a thin film transistor according to a second embodiment of the present invention. [Diagram 3] 1A to 1C are diagrams illustrating a method for manufacturing a thin film transistor according to a first embodiment of the present invention. [Figure 4] 5A to 5C are diagrams illustrating a method for manufacturing a thin film transistor according to a second embodiment of the present invention. [Diagram 5] FIG. 4 is a diagram illustrating a thin film transistor according to a third embodiment of the present invention. [Figure 6] FIG. 13 is a diagram illustrating a thin film transistor according to a fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] Hereinafter, the embodiments of the present invention will be described in more detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and can be embodied in various different forms. The following embodiments are provided for the purpose of making the disclosure of the present invention complete and fully conveying the scope of the invention to those skilled in the art.

[0045] Throughout the specification, when a component, such as a film, region, or substrate, is referred to as being "on" another component, it can be interpreted that the component may be in direct contact with the other component, or there may be additional components interposed therebetween.

[0046] Also, relative terms such as "upper" or "lower" can be used herein to describe the relative relationship of one component to another component as shown in the figures. It can be understood that the relative terms are intended to include other orientations of the elements in addition to the orientation depicted in the figures. Here, the figures may be exaggerated to illustrate the invention in detail, and the same reference numerals in the figures refer to the same components.

[0047] FIG. 1 is a diagram illustrating a thin film transistor according to a first embodiment of the present invention, and FIG. 2 is a diagram illustrating a thin film transistor according to a second embodiment of the present invention.

[0048] 1 and 2, a thin film transistor according to an embodiment of the present invention includes a gate electrode 150, an active layer 130 disposed vertically spaced apart from the gate electrode 150, source and drain electrodes 180a, 180b disposed spaced apart from each other on the active layer 130, and a contact layer 170 formed between the active layer 130 and the source and drain electrodes 180a, 180b.

[0049] As shown in FIG. 1, the thin film transistor according to the first embodiment of the present invention may be a top-gate type thin film transistor including an active layer 130 formed on a substrate 110, a gate insulating film 140 formed on the active layer 130, a gate electrode 150 formed on the gate insulating film 140, a source electrode 180a and a drain electrode 180b spaced apart from each other on the active layer 130 with the gate insulating film 140 and the gate electrode 150 sandwiched therebetween, and contact layers 170 formed between the active layer 130 and the source electrode 180a and between the active layer 130 and the drain electrode 180b, respectively.

[0050] The substrate 110 may be a transparent substrate, such as a silicon substrate, a glass substrate, or a plastic substrate in the case of implementing a flexible display. The substrate 110 may be a reflective substrate, such as a metal substrate. The metal substrate may be made of stainless steel (SUS), titanium (Ti), molybdenum (Mo), or an alloy thereof. A buffer layer 120 may be formed on the substrate 110, and the buffer layer 120 may be made of an insulating material including silicon oxide (SiO2).

[0051] An active layer 130 can be formed on the buffer layer 120. The active layer 130 can be formed in a predetermined region on the buffer layer 120, and a gate electrode 110, which will be described later, can be formed above the active layer 130 and spaced therefrom so as to overlap a portion of the active layer 130.

[0052] Here, the active layer 130 can be formed from a metal oxide. That is, the active layer 130 can be formed from a metal oxide thin film, and can be formed from a plurality of metal oxide thin films having different compositions. For example, the active layer 130 may include an oxide containing at least one of indium (In), gallium (Ga), and zinc (Zn).

[0053] Conventionally, active layers have been formed using amorphous silicon or crystalline silicon. However, since a glass substrate must be used as a substrate for a thin film transistor using silicon, it is not only heavy but also has the disadvantage of being unable to be used as a flexible display device because it is not flexible. Therefore, in order to realize a high-speed element, i.e., to improve mobility, a metal oxide thin film with high carrier concentration and excellent electrical conductivity can be used as the active layer.

[0054] The active layer 130 may be formed of a material including zinc oxide doped with impurities. The impurities may be indium (In), gallium (Ga), tungsten (W), lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), manganese (Mn), technetium (Tc), rhenium (Rb), or tantalum (Ta). At least one of the following substances may be included: Re, iron (Fe), ruthenium (Ru), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), platinum (Pt), copper (Cu), silver (Ag), gold (Au), cadmium (Cd), mercury (Hg), boron (B), thallium (Tl), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi).

[0055] For example, indium (In) is a metal with a relatively small bandgap and a relatively high standard electrode potential, and is characterized by increasing the carrier concentration and improving mobility. In contrast, gallium (Ga) is a metal with a relatively large bandgap and a relatively high standard electrode potential, and is characterized by decreasing the carrier concentration and improving stability. Therefore, the content of impurities contained in the metal oxide thin film can be controlled to adjust the electrical conductivity of the active layer 130. In this way, the active layer 130 made of a metal oxide has a characteristic that the electrical conductivity decreases as the oxygen ratio increases, and increases as the oxygen ratio decreases.

[0056] The active layer 130 may contain magnesium (Mg) as an impurity to form a p-type active layer, or silicon (Si) as an impurity to form an n-type active layer. In addition, the active layer 130 may contain a wide variety of noble metals such as ruthenium (Ru), platinum (Pt), gold (Au), silver (Ag), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), yttrium (Yi), tungsten (W), and molybdenum (Mo).

[0057] A gate insulating film 140 can be formed on the active layer 130. The gate insulating film 140 can be formed in a portion of the active layer 130, and can be formed using one or more insulating materials selected from inorganic insulating materials including silicon oxide (SiO2), silicon nitride (SiN), alumina (Al2O3), and zirconia (ZrO2), which have excellent adhesion to metal materials and excellent dielectric strength.

[0058] The gate electrode 150 can be formed on the gate insulating film 140. The gate electrode 150 can be formed using a conductive material, for example, at least one of aluminum (Al), neodymium (Nd), silver (Ag), chromium (Cr), titanium (Ti), tantalum (Ta), molybdenum (Mo), and copper (Cu), or an alloy containing these metals. The gate electrode 150 can be formed not only as a single layer, but also as a multilayer consisting of multiple metal layers. That is, the gate electrode 150 can be formed as a double layer including a metal layer such as chromium (Cr), titanium (Ti), tantalum (Ta), or molybdenum (Mo) having excellent physicochemical properties and an aluminum (Al), silver (Ag), or copper (Cu) metal layer having low resistivity.

[0059] An insulating film 160 may be formed on the active layer 130, covering the gate electrode 150 and having contact holes that expose a portion of the surface of the active layer 130 on both sides of the gate electrode 150. That is, the insulating film 160 has contact holes formed therein so that the source electrode 180a and the drain electrode 180b can be electrically connected to the active layer 130 via the contact layer 170. Such an insulating film 160 may be formed from an insulating material including silicon oxide (SiO2).

[0060] A contact layer 170 is formed on a portion of the surface of the active layer 130 exposed by the contact hole. Such a contact layer 170 includes a metal element. That is, the contact layer 170 can be formed of a metal or an alloy, and in this case, the contact layer 170 can be formed of ruthenium (Ru) or a ruthenium (Ru) alloy. Also, the contact layer 170 can be formed of a metal oxide. That is, the contact layer 170 may include a metal oxide thin film, and in this case, the contact layer 170 may be formed of a single metal oxide thin film like the active layer 130, or may be formed of a plurality of metal oxide thin films having different compositions. For example, the active layer may include ruthenium oxide. Also, the contact layer 170 can be formed of a material including zinc oxide doped with an impurity. Here, the impurities are indium (In), gallium (Ga), tungsten (W), lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), manganese (Mn), technetium (Tc), rhenium ( At least one of the following substances may be included: Re, iron (Fe), ruthenium (Ru), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), platinum (Pt), copper (Cu), silver (Ag), gold (Au), cadmium (Cd), mercury (Hg), boron (B), thallium (Tl), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi).

[0061] The contact layer 170 can be formed from a metal oxide having a different composition than the metal oxide forming the active layer 130. That is, when the metal oxide contained in the active layer 130 is referred to as an oxide of a first metal element and the metal oxide contained in the contact layer 170 is referred to as an oxide of a second metal element, the oxide of the first metal element can have a different composition than the oxide of the second metal element. In this case, when the oxide of the first metal element and the oxide of the second metal element each contain zinc oxide doped with an impurity, the oxide of the second metal element has a content of indium (In), gallium (Ga), tungsten (W), lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), or the like, greater than the content of the oxide of the first metal element. The content of impurities may be even greater, including at least one of the following: Mo, manganese (Mn), technetium (Tc), rhenium (Re), iron (Fe), ruthenium (Ru), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), platinum (Pt), copper (Cu), silver (Ag), gold (Au), cadmium (Cd), mercury (Hg), boron (B), thallium (Tl), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi). For example, when the oxide of the first metal element forming the active layer 130 contains 20 at% or more and less than 40 at% of impurities relative to the entire oxide of the first metal element, the oxide of the second metal element may contain 40 at% or more and less than 60 at% of impurities relative to the entire oxide of the second metal element. In this way, the oxide of the second metal element having a high impurity content may have an even lower oxygen (O) content than the oxide of the first metal element.

[0062] If the contact layer 170 is not formed and the source electrode 180a and the drain electrode 180b are formed on the active layer 140, the active layer 130 is exposed to the etching gas in the process of forming contact holes in the insulating film 160 to form the source electrode 180a and the drain electrode 180b. If the active layer 130 is exposed to the etching gas, the active layer 130 is damaged by the etching gas from the upper surface to a certain depth, losing oxygen and becoming in an oxygen-deficient state. Also, if the source electrode 180a and the drain electrode 180b are formed directly on the surface of the active layer 130 damaged by the etching gas in this way, oxygen will move from the active layer 130 to the source electrode 180a and the drain electrode 180b when the thin film transistor is driven. If oxygen deficiency occurs in the active layer in this way, the electrical conductivity of the active layer will unintentionally increase and the active layer will become a conductor, causing a short circuit of the element and making it impossible to stably drive the thin film transistor.

[0063] In contrast, if the contact layer 170 made of a metal, alloy, or metal oxide is formed between the active layer 140 and the source electrode 180a and drain electrode 180b as in the embodiment of the present invention, the oxygen or metal material contained in the contact layer 170 can fill the area where oxygen has escaped from the active layer 130. That is, the metal element or oxygen contained in the contact layer 170 spreads to the area where oxygen has escaped from the active layer 130, preventing oxygen from moving from the active layer 130 to the source electrode 180a and drain electrode 180b, and preventing the active layer 130 from becoming a conductor.

[0064] At this time, the contact layer 170 can be formed to a layer thickness D of 30 to 100 Å. At this time, if the contact layer 170 is formed to a layer thickness of less than 30 Å, sufficient oxygen migration prevention effect cannot be obtained, and if the contact layer 170 is formed to a layer thickness of more than 100 Å, there is a problem that the process time is excessively long, which hinders miniaturization of the thin film transistor. Therefore, the contact layer 170 is preferably formed to a layer thickness of 30 to 100 Å.

[0065] The source electrode 180a and the drain electrode 180b are formed on the contact layer 170. That is, the source electrode 180a and the drain electrode 180b are formed on the contact layer 170 formed in the contact hole so as to be in contact with each other, and the source electrode 180a and the drain electrode 180b can be formed separately from each other with the gate electrode 110 sandwiched therebetween. At this time, the source electrode 180a and the drain electrode 180b can be formed so as to be in contact with the contact layer 170 and extend on the insulating film 160. The source electrode 180a and the drain electrode 180b can be formed by the same process using the same material, and can be formed using a conductive material, for example, at least one metal selected from aluminum (Al), neodymium (Nd), silver (Ag), chromium (Cr), titanium (Ti), tantalum (Ta), and molybdenum (Mo), or an alloy containing these. That is, the source electrode 180a and the drain electrode 180b can be formed from the same material as the gate electrode 150, but can also be formed from a different material. In addition, the source electrode 180a and the drain electrode 180b may be formed as a single layer or multiple layers, and in this case, each layer may contain a different metal or alloy.

[0066] Meanwhile, the thin film transistor according to the second embodiment of the present invention may be a bottom gate type thin film transistor including a gate electrode 150 formed on a substrate 110, a gate insulating film 140 formed on the gate electrode, an active layer 130 formed on the gate insulating film, a source electrode 180a and a drain electrode 180b spaced apart from each other on the active layer 130, and contact layers 170 formed between the active layer 130 and the source electrode 180a and between the active layer 130 and the drain electrode 180b, respectively, as shown in FIG. 2.

[0067] 1 can be applied as it is to such a bottom gate type thin film transistor. That is, even in the case of the thin film transistor according to the second embodiment of the present invention, the contact layer 170 can be formed between the active layer 130 and the source electrode 180a and between the active layer 130 and the drain electrode 180b. As described above, even in the case of the thin film transistor according to the second embodiment of the present invention, only the stacking order of the gate insulating film 140 and the gate electrode 150 is different, and the contents described in the section of the thin film transistor according to the first embodiment of the present invention can be applied as it is, so that the overlapping description will be omitted.

[0068] FIG. 3 is a diagram illustrating a method for manufacturing a thin film transistor according to a first embodiment of the present invention.

[0069] Referring to FIG. 3, the method for manufacturing a thin film transistor according to the first embodiment of the present invention includes the steps of preparing a substrate 110 on which a gate electrode 150 and an active layer 130 spaced apart from the gate electrode 150 in the vertical direction are formed, and forming a contact layer 170 on the active layer 130 to connect the active layer 130 to a source electrode 180a and a drain electrode 180b, respectively.

[0070] First, in the step of preparing the substrate 110, as shown in FIG. 3(a), the substrate 110 is prepared on which the gate electrode 150 and the active layer 130 disposed vertically apart from the gate electrode 150 are formed. In this case, in the step of preparing the substrate 110, the substrate 110 may be prepared on which the active layer 130 is formed, the gate insulating film 140 is formed on the active layer 130, and the gate electrode 150 is formed on the gate insulating film 140 in order to manufacture a top-gate type thin film transistor. In addition, a buffer layer 120 may be further formed between the substrate 110 and the active layer 130, and an insulating film 160 having contact holes exposing a part of the surface of the active layer 130 to form a source electrode 180a and a drain electrode 180b may be further formed on the active layer 130.

[0071] 3(b), in the step of forming the contact layer 170, the contact layer 170 for connecting the active layer 130 to the source electrode 180a and the drain electrode 180b is formed on the active layer 130. Here, the contact layer 170 can be formed on a part of the surface of the active layer 130 exposed by the contact holes in the insulating film 160.

[0072] Such a contact layer 170 can be formed from a metal, an alloy, or a metal oxide. The contact layer 170 can be formed by various thin film formation processes. For example, in order to form the contact layer 170 from a metal oxide, the step of forming the contact layer 170 can be performed by an atomic layer deposition (ALD) process in which a process cycle including a step of supplying a source gas containing a metal element onto the active layer 130 and a step of supplying a reactive gas containing oxygen onto the active layer 130 is repeated multiple times. In such an atomic layer deposition process, a process cycle including a step of supplying a source gas containing a metal element, a step of purging the source gas, a step of supplying a reactive gas containing oxygen, and a step of purging the reactive gas can be repeated multiple times in this order.

[0073] In this case, in the step of supplying the raw material gas, a first raw material gas containing zinc (Zn), indium (In), gallium (Ga), tungsten (W), lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), manganese (Mn), technetium A second source gas containing at least one of tungsten (Tc), rhenium (Re), iron (Fe), ruthenium (Ru), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), platinum (Pt), copper (Cu), silver (Ag), gold (Au), cadmium (Cd), mercury (Hg), boron (B), thallium (Tl), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), phosphorus (P), arsenic (As), antimony (Sb) and bismuth (Bi) can be supplied at the same time. In this manner, by simultaneously supplying a first source gas containing zinc (Zn) and a second source gas containing impurities such as indium (In), gallium (Ga), or tungsten (W), the contact layer 170 can be formed from a material containing zinc oxide doped with impurities such as indium (In), gallium (Ga), or tungsten (W).

[0074] On the other hand, in the step of supplying the source gases, the source gases can be supplied by controlling the supply amount of the first source gas to be greater than the supply amount of the second source gas, so that the metal oxide forming the contact layer 170 can be formed to contain impurities of 40 at % or more and less than 60 at % with respect to the whole.

[0075] After the step of forming the contact layer 170, a step of forming a source electrode 180a and a drain electrode 180b on the contact layer 170 may be performed, as shown in FIG. 3(c).

[0076] FIG. 4 is a diagram illustrating a method for manufacturing a thin film transistor according to a second embodiment of the present invention.

[0077] In the method for manufacturing a thin film transistor according to the second embodiment of the present invention, in the step of preparing a substrate 110, in order to manufacture a bottom-gate type thin film transistor, the substrate 110 may be prepared on which a gate electrode 150 is formed, a gate insulating film 140 is formed on the gate electrode 150, and an active layer 130 is formed on the gate insulating film 140. It goes without saying that a buffer layer 120 may be further formed between the substrate 110 and the gate electrode 150.

[0078] 4 shows that the contact layer 170 is formed in separate regions on the active layer 130, it goes without saying that in the method for manufacturing a thin film transistor according to another embodiment of the present invention, the contact layer 170 can be formed from one layer that covers both the top and side surfaces of the active layer 130. Other than this, the contents described in the section on the method for manufacturing a thin film transistor according to the first embodiment of the present invention can be applied as is, and therefore repeated description will be omitted.

[0079] FIG. 5 is a diagram illustrating a thin film transistor according to a third embodiment of the present invention.

[0080] 5, a thin film transistor according to a third embodiment of the present invention includes a gate electrode 150, an active layer 130 disposed vertically apart from the gate electrode 150, a first insulating film 160 disposed on the active layer 130 and having a first contact hole (not shown) exposing a portion of a surface of the active layer 130, a second insulating film 165 disposed on the first insulating film 160 and exposing the first contact hole and a portion of the surface of the first insulating film 160 extending from the first contact hole, a contact layer 170 formed on the portion of the surface of the active layer 130 exposed by the first insulating film 160, and source and drain electrodes 180a, 180b disposed on the contact layer 170 and spaced apart from each other, and extending on the portion of the surface of the first insulating film 160 exposed by the second insulating film 165.

[0081] The thin film transistor according to the third embodiment of the present invention is different from the thin film transistor according to the first embodiment in that a second insulating film 165 is further disposed therein, and the contents described for the thin film transistor according to the first embodiment are applicable to the other configurations as they are. In this case, the first insulating film 160 and the first contact hole of the thin film transistor according to the third embodiment of the present invention have the same configuration as the insulating film 160 and the contact hole of the thin film transistor according to the first embodiment of the present invention, and therefore the same reference numerals are used.

[0082] More specifically, the thin film transistor according to the third embodiment of the present invention may include a gate electrode 150, an active layer 130 including an oxide of a first metal element and spaced apart from the gate electrode 150 in the vertical direction, a first insulating film 160 disposed on the active layer 130 and having a first contact hole exposing a portion of the surface of the active layer 130, a second insulating film 165 disposed on the first insulating film 160 and exposing the first contact hole and a portion of the surface of the first insulating film 160 extending from the first contact hole, a contact layer 170 including a second metal element and formed on the portion of the surface of the active layer 130 exposed by the first insulating film 160, and source and drain electrodes 180a, 180b disposed on the contact layer 170 and spaced apart from each other and extending over the portion of the surface of the first insulating film 160 exposed by the second insulating film 165.

[0083] Here, the first insulating film 160 and the second insulating film 165 may have different compositions. That is, the first insulating film 160 may contain silicon oxide (SiO), and the second insulating film 165 may contain silicon nitride (SiN). Here, the second insulating film 165 is formed on the first insulating film 160, and has a second contact hole larger than the first contact hole at a position overlapping the first contact hole formed in the first insulating film 160. Therefore, when the second insulating film 165 is disposed on the first insulating film 160, the first contact hole and a part of the surface of the first insulating film extending from the first contact hole can be exposed. As described above, the active layer 130 can be formed from an oxide of a first metal element including at least one of indium (In), gallium (Ga), and zinc (Zn), and the contact layer 170 may include a second metal element including at least one of indium (In), gallium (Ga), zinc (Zn), and ruthenium (Ru).

[0084] In this manner, when the second insulating film 165 is further formed on the first insulating film 160, the contact layer 170 can be formed by an area selective-atomic layer deposition (AS-ALD) method. Here, the selective atomic layer deposition method refers to a method of selectively depositing a thin film only on the surface of a specific region by an atomic layer deposition method, and a wide variety of known selective atomic layer deposition methods can be applied to form the contact layer 170. In addition, it goes without saying that the contact layer 170 can also be selectively formed on a portion of the surface of the exposed active layer 130 by a deposition method using a mask.

[0085] That is, the method for manufacturing a thin film transistor according to the third embodiment of the present invention may include a step of preparing a substrate 110 on which a gate electrode 150 and an active layer 130, which is disposed vertically apart from the gate electrode 150 and has a part of its surface exposed by a first contact hole formed in a first insulating film 160, are formed, and a step of forming a second insulating film 165 including silicon nitride on the first insulating film 160. In this case, a part of the surface of the active layer 130 is exposed by the first contact hole and the second contact hole formed in the stacked first insulating film 160 and second insulating film 165, respectively, and a contact layer 170 for connecting the active layer 130 to the source and drain electrodes 180a and 180b may be formed on the exposed part of the surface of the active layer 130 by a selective atomic layer deposition method.

[0086] Thus, even if the contact layer 170 is selectively formed on a portion of the surface of the exposed active layer 130, a residual film formed during the process of forming the contact layer 170 may be formed on the second insulating film 165. For example, when the contact layer 170 includes a metal oxide doped with impurities, the metal oxide film doped with impurities may remain on the second insulating film 165. For this reason, in the embodiment of the present invention, after the step of forming the contact layer 170, a step of etching the metal oxide film doped with impurities formed on the second insulating film 165 may be further included. At this time, the metal oxide film doped with impurities may be etched by hydrogen bromide (HBr).

[0087] FIG. 6 is a diagram illustrating a thin film transistor according to a fourth embodiment of the present invention.

[0088] Referring to FIG. 6, the thin film transistor according to the fourth embodiment of the present invention includes a gate electrode 150, an active layer 130 disposed vertically spaced apart from the gate electrode 150, source and drain electrodes 180a, 180b disposed spaced apart from each other on the active layer 130, a ruthenium oxide layer 172 formed between the active layer 130 and the source and drain electrodes 180a, 180b, and a high-concentration metal oxide layer 174.

[0089] The thin film transistor according to the fourth embodiment of the present invention is different from the thin film transistor according to the third embodiment described above in that the contact layer 170 is composed of a ruthenium oxide layer 172 and a high-concentration metal oxide layer 174 disposed on the ruthenium oxide layer 172. With respect to the other components, the same description as given in relation to the thin film transistor according to the third embodiment described above can be applied as is.

[0090] That is, the thin film transistor according to the fourth embodiment of the present invention may include a gate electrode 150, an active layer 130 disposed vertically apart from the gate electrode 150 and containing at least one of indium (In), gallium (Ga) and zinc (Zn), source and drain electrodes 180a, 180b disposed on the active layer 130 and spaced apart from each other, a high-concentration metal oxide layer 174 formed between the active layer 130 and the source and drain electrodes 180a, 180b and having a higher impurity content than the active layer 130, and a ruthenium oxide layer 172 formed between the high-concentration metal oxide layer 174 and the source and drain electrodes 180a, 180b.

[0091] As described above, the contact layer 170 can be formed of a plurality of metal oxide thin films having different compositions including metal elements. In this case, in the fourth embodiment of the present invention, the contact layer 170 can be formed of a plurality of thin films including a ruthenium oxide layer 172 including an oxide of ruthenium (Ru) and a high-concentration metal oxide layer 174 including a metal oxide having a high impurity concentration. Here, the metal oxide may be at least one oxide of indium (In), gallium (Ga) and zinc (Zn), and the metal oxide layer 174 formed on the ruthenium oxide layer 172 may have a higher impurity content than the active layer 130. That is, when both the active layer 130 and the high-concentration metal oxide layer 174 include a metal oxide doped with an impurity, the high-concentration metal oxide layer 174 may have a higher impurity content than the active layer 130. It goes without saying that the ruthenium oxide layer 172 and the high concentration metal oxide layer 174 can both be formed by selective atomic layer deposition, or alternatively, can be formed sequentially on the exposed surface of the active layer 130 by evaporation using a mask.

[0092] Thus, according to the embodiment of the present invention, by forming a contact layer between the active layer and the source and drain electrodes to prevent oxygen deficiency in the active layer, it is possible to prevent the active layer from becoming a conductor and improve switching characteristics.

[0093] In addition, the contact resistance between the active layer and the source and drain electrodes can be effectively reduced, improving the characteristics and reliability of the device.

[0094] Although the preferred embodiment of the present invention has been described and illustrated using specific terms, these terms are merely for the purpose of clearly describing the present invention, and it is clear that the embodiments of the present invention and the described terms can be modified and changed in various ways without departing from the technical spirit and scope of the claims. Thus, these modified embodiments should not be understood separately from the spirit and scope of the present invention, but should be considered to belong to the scope of the claims of the present invention.

Claims

1. a gate electrode; an active layer including an oxide of a first metal element and spaced apart from the gate electrode in the vertical direction; source and drain electrodes spaced apart from each other and disposed on the active layer; a contact layer including an oxide of a second metal element and formed between the active layer and the source and drain electrodes; Equipped with the oxide of the second metal element includes a metal oxide doped with an impurity, the impurities include at least one of potassium (K), rubidium (Rb), cesium (Cs), calcium (Ca), strontium (Sr), barium (Ba), niobium (Nb), manganese (Mn), technetium (Tc), rhenium (Re), iron (Fe), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), palladium (Pd), platinum (Pt), gold (Au), thallium (Tl), lead (Pb), and arsenic (As).

2. The thin film transistor according to claim 1 , wherein the oxide of the first metal element and the oxide of the second metal element have different compositions.

3. the oxide of the first metal element and the oxide of the second metal element each contain zinc oxide doped with an impurity, The thin film transistor of claim 1 , wherein the oxide of the first metal element and the oxide of the second metal element have different impurity contents.

4. The thin film transistor according to claim 3 , wherein the oxide of the second metal element has a higher impurity content than the oxide of the first metal element.

5. the oxide of the first metal element contains impurities in an amount of 20 at % or more and less than 40 at % based on the entire oxide of the first metal element; 4. The thin film transistor according to claim 3, wherein the oxide of the second metal element contains impurities in an amount of 40 at % or more and less than 60 at % based on the entire oxide of the second metal element.

6. The thin film transistor according to claim 3 , wherein the oxide of the second metal element has a lower oxygen (O) content than the oxide of the first metal element.

7. 2. The thin film transistor according to claim 1, wherein the contact layer is formed to a thickness of 30 to 100 Å.

8. an insulating film disposed on the active layer and having a contact hole exposing a part of the surface of the active layer; the contact layer is formed on a portion of the surface of the active layer exposed by the contact hole; The thin film transistor of claim 1 , wherein the source and drain electrodes contact the contact layer and extend over the insulating film.

9. preparing a substrate on which a gate electrode and an active layer disposed vertically apart from the gate electrode are formed; forming a contact layer on the active layer for connecting the active layer to source and drain electrodes; Including, the contact layer includes a metal oxide doped with an impurity; the impurity includes at least one of potassium (K), rubidium (Rb), cesium (Cs), calcium (Ca), strontium (Sr), barium (Ba), niobium (Nb), manganese (Mn), technetium (Tc), rhenium (Re), iron (Fe), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), palladium (Pd), platinum (Pt), gold (Au), thallium (Tl), lead (Pb), and arsenic (As).

10. In the step of preparing the substrate, preparing a substrate on which an insulating film having a contact hole exposing a part of the surface of the active layer is formed on the active layer; In the step of forming the contact layer, The method for manufacturing a thin film transistor according to claim 9 , wherein the contact layer is formed on a portion of the surface of the active layer exposed by the contact hole.

11. In the step of forming the contact layer, 11. The method for manufacturing a thin film transistor according to claim 10, wherein the contact layer is formed on a part of the surface of the active layer to a thickness of 30 to 100 Å.

12. The step of forming the contact layer includes:

10. The method for manufacturing a thin film transistor according to claim 9, wherein the method is performed by an atomic layer deposition process in which a process cycle including a step of supplying a source gas containing a metal element onto the active layer and a step of supplying a reaction gas containing oxygen onto the active layer is repeated a plurality of times.

13. In the step of supplying the source gas, 13. The method for manufacturing a thin-film transistor according to claim 12, wherein a first source gas containing zinc (Zn) and a second source gas containing at least one of potassium (K), rubidium (Rb), cesium (Cs), calcium (Ca), strontium (Sr), barium (Ba), niobium (Nb), manganese (Mn), technetium (Tc), rhenium (Re), iron (Fe), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), palladium (Pd), platinum (Pt), gold (Au), thallium (Tl), lead (Pb), and arsenic (As) are simultaneously supplied.

14. In the step of supplying the source gas, 14. The method for manufacturing a thin film transistor according to claim 13, wherein the supply amount of the second source gas is controlled to be greater than the supply amount of the first source gas.

15. 10. The method of claim 9, further comprising forming source and drain electrodes on the contact layer.

16. a gate electrode; an active layer including an oxide of a first metal element and spaced apart from the gate electrode in the vertical direction; a first insulating film disposed on the active layer and having a first contact hole having a second contact hole exposing a portion of the surface of the active layer; a second insulating film disposed on the first insulating film and exposing the first contact hole and a portion of the surface of the first insulating film extending from the first contact hole; a contact layer including an oxide of a second metal element and formed on a surface of a portion of the active layer exposed by the first contact hole; source and drain electrodes disposed on the contact layer and spaced apart from each other, and extending over a portion of the surface of the first insulating film exposed by the second contact hole; Equipped with the oxide of the second metal element includes a metal oxide doped with an impurity, the impurities include at least one of potassium (K), rubidium (Rb), cesium (Cs), calcium (Ca), strontium (Sr), barium (Ba), niobium (Nb), manganese (Mn), technetium (Tc), rhenium (Re), iron (Fe), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), palladium (Pd), platinum (Pt), gold (Au), thallium (Tl), lead (Pb), and arsenic (As).

17. the first insulating film contains silicon oxide; 17. The thin film transistor of claim 16, wherein the second insulating film comprises silicon nitride.

18. 17. The thin film transistor of claim 16, wherein the first metal element and the second metal element include at least one of indium (In), gallium (Ga), and zinc (Zn).

19. preparing a substrate on which a gate electrode and an active layer are formed, the active layer being disposed vertically apart from the gate electrode and having a surface partially exposed by a contact hole formed in a first insulating film; forming a second insulating film containing silicon nitride on the first insulating film, the second contact hole exposing the first contact hole; forming a contact layer on the exposed surface of the active layer to connect the active layer to source and drain electrodes; Including, the contact layer includes a metal oxide doped with an impurity; the impurity includes at least one of potassium (K), rubidium (Rb), cesium (Cs), calcium (Ca), strontium (Sr), barium (Ba), niobium (Nb), manganese (Mn), technetium (Tc), rhenium (Re), iron (Fe), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), palladium (Pd), platinum (Pt), gold (Au), thallium (Tl), lead (Pb), and arsenic (As).

20. preparing a substrate on which a gate electrode and an active layer are formed, the active layer being disposed vertically spaced apart from the gate electrode and having a surface partially exposed by contact holes formed in a first insulating film and a second insulating film that are stacked; forming a contact layer on the exposed surface of the active layer by selective atomic layer deposition to connect the active layer to source and drain electrodes; Including, the contact layer includes a metal oxide doped with an impurity; the impurity includes at least one of potassium (K), rubidium (Rb), cesium (Cs), calcium (Ca), strontium (Sr), barium (Ba), niobium (Nb), manganese (Mn), technetium (Tc), rhenium (Re), iron (Fe), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), palladium (Pd), platinum (Pt), gold (Au), thallium (Tl), lead (Pb), and arsenic (As).

21. After the step of forming the contact layer, 21. The method for manufacturing a thin film transistor according to claim 20, further comprising the step of etching the impurity-doped metal oxide film formed on the second insulating film.

22. 22. The method for manufacturing a thin film transistor according to claim 21, wherein the impurity-doped metal oxide film is etched by hydrogen bromide (HBr).

23. preparing a substrate on which a gate electrode and an active layer are formed, the active layer being disposed vertically apart from the gate electrode and having a surface partially exposed by a first contact hole formed in a first insulating film containing silicon oxide; forming a second insulating film containing silicon nitride on the first insulating film, the second contact hole exposing the first contact hole; forming a contact layer on the exposed surface of the active layer by selective atomic layer deposition to connect the active layer to source and drain electrodes; Including, the contact layer includes a metal oxide doped with an impurity; the impurity includes at least one of potassium (K), rubidium (Rb), cesium (Cs), calcium (Ca), strontium (Sr), barium (Ba), niobium (Nb), manganese (Mn), technetium (Tc), rhenium (Re), iron (Fe), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), palladium (Pd), platinum (Pt), gold (Au), thallium (Tl), lead (Pb), and arsenic (As).

24. a gate electrode; an active layer disposed vertically apart from the gate electrode and containing at least one of indium (In), gallium (Ga), and zinc (Zn); source and drain electrodes spaced apart from each other and disposed on the active layer; a high-concentration metal oxide layer formed between the active layer and the source and drain electrodes, the high-concentration metal oxide layer having a higher impurity content than the active layer; a ruthenium oxide layer formed between the high concentration metal oxide layer and the source and drain electrodes; Equipped with the impurities include at least one of potassium (K), rubidium (Rb), cesium (Cs), calcium (Ca), strontium (Sr), barium (Ba), niobium (Nb), manganese (Mn), technetium (Tc), rhenium (Re), iron (Fe), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), palladium (Pd), platinum (Pt), gold (Au), thallium (Tl), lead (Pb), and arsenic (As).

25. preparing a substrate on which a gate electrode and an active layer disposed vertically apart from the gate electrode are formed; forming a high-concentration metal oxide layer on the active layer, the high-concentration metal oxide layer having a higher impurity content than the active layer; forming a ruthenium oxide layer on the high-concentration metal oxide layer for connecting the active layer to source and drain electrodes; Including, the impurity includes at least one of potassium (K), rubidium (Rb), cesium (Cs), calcium (Ca), strontium (Sr), barium (Ba), niobium (Nb), manganese (Mn), technetium (Tc), rhenium (Re), iron (Fe), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), palladium (Pd), platinum (Pt), gold (Au), thallium (Tl), lead (Pb), and arsenic (As).

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