Thin film transistor, method of manufacturing thin film transistor, and display device including thin film transistor

Abstract

A thin film transistor, a method of manufacturing a thin film transistor, and a display device including the thin film transistor are provided, in which the thin film transistor includes a first gate electrode, an active layer spaced apart from the first gate electrode and including a channel portion, and a second gate electrode spaced apart from the active layer and disposed on an opposite side of the first gate electrode based on the active layer, in which at least a portion of the first gate electrode does not overlap the second gate electrode, and at least a portion of the second gate electrode does not overlap the first gate electrode, the channel portion overlaps at least one of the first and second gate electrodes, a portion of the channel portion overlaps only one of the first and second gate electrodes, and another portion of the channel portion overlaps only the other of the first and second gate electrodes, the active layer includes a first active layer and a second active layer disposed on the first active layer, and any one of the first and second active layers has a higher hydrogen concentration and a lower oxygen concentration than the other of the first and second active layers.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2020-0186700, filed on December 29, 2020, and Korean Patent Application No. 10-2021-0175278, filed on December 9, 2021, which are incorporated herein by reference as if they were set forth in their entirety herein. Technical Field

[0003] This disclosure relates to thin-film transistors, methods for manufacturing thin-film transistors, and display devices including thin-film transistors. Background Technology

[0004] Thin-film transistors (TFTs) have been widely used as switching or driving elements in display devices such as liquid crystal displays (LCDs) or organic light-emitting diodes (OLEDs) because they can be fabricated on glass or plastic substrates.

[0005] Thin-film transistors can be classified based on the material constituting the active layer as amorphous silicon thin-film transistors in which amorphous silicon is used as the active layer, polycrystalline silicon thin-film transistors in which polycrystalline silicon is used as the active layer, and oxide semiconductor thin-film transistors in which oxide semiconductor is used as the active layer.

[0006] Amorphous silicon thin-film transistors (a-Si TFTs) offer advantages such as short manufacturing time and low production cost because amorphous silicon can be deposited to form the active layer in a short time. On the other hand, amorphous silicon TFTs have the disadvantage of being limited to active-matrix organic light-emitting diodes (AMOLEDs) due to poor current driving capability and threshold voltage variation caused by low mobility.

[0007] Polycrystalline silicon thin-film transistors (poly-Si TFTs) are fabricated by depositing amorphous silicon and then crystallizing the deposited amorphous silicon. The advantages of polycrystalline silicon TFTs include high electron mobility, excellent stability, the ability to achieve thin profiles and high resolution, and high power efficiency. An example of a polycrystalline silicon TFT is the low-temperature polycrystalline silicon (LTPS) TFT. However, the manufacturing process of polycrystalline silicon TFTs requires a crystallization step of the amorphous silicon, which increases the number of process steps and the need for high-temperature crystallization, thus increasing manufacturing costs. Therefore, it is difficult to apply polycrystalline silicon TFTs to large-scale (large-size) display devices. Furthermore, due to the polycrystalline nature, it is difficult to ensure the uniformity of polycrystalline silicon TFTs.

[0008] Oxide-semiconductor thin-film transistors (TFTs), with their high mobility and large resistance variation depending on oxygen content, offer the advantage of readily obtainable desired characteristics. Furthermore, the manufacturing cost of TFTs is reduced because the oxide constituting the active layer can be grown at relatively low temperatures during the fabrication process. Considering the properties of oxides, their transparency facilitates the realization of transparent displays. However, compared to polycrystalline silicon TFTs, TFTs suffer from stability and reduced electron mobility.

[0009] When an oxide semiconductor thin-film transistor (TFT) is driven in the ON state for an extended period, its threshold voltage tends to change continuously. This variation in the TFT's driving characteristics can shorten device lifespan, degrade image quality, and potentially require expensive compensation techniques and additional circuitry. Therefore, there is a need to improve the driving stability of oxide semiconductor thin-film transistors. Summary of the Invention

[0010] This disclosure is made in view of the above problems, and the purpose of this disclosure is to provide a thin-film transistor having the characteristics of a top-gate structure and a bottom-gate structure to minimize the amount (or rate of change) of the threshold voltage.

[0011] Another object of this disclosure is to provide a thin-film transistor that has improved drive stability due to the presence of portions affected by the top gate and portions affected by the bottom gate in a channel portion.

[0012] Another object of this disclosure is to provide a thin-film transistor that has improved drive stability because portions that move the threshold voltage in the positive (+) direction and portions that move the threshold voltage in the negative (-) direction are connected in series with each other in a channel portion.

[0013] Another object of this disclosure is to provide a thin-film transistor comprising a channel portion having an excess oxygen region and an excess hydrogen region.

[0014] Another object of this disclosure is to provide a thin-film transistor that minimizes the change in threshold voltage by causing a positive (+) shift in the threshold voltage in an excess oxygen region and a negative (-) shift in the threshold voltage by causing a hole trap in an excess hydrogen region.

[0015] Another object of the present invention is to provide a method for manufacturing the thin-film transistor.

[0016] Another object of the present invention is to provide a display device including the thin-film transistor.

[0017] In addition to the purposes of this disclosure described above, those skilled in the art will clearly understand from the following description of this disclosure additional purposes and features.

[0018] According to one aspect of this disclosure, the above and other objectives can be achieved by providing a thin-film transistor comprising a first gate electrode; an active layer spaced apart from the first gate electrode, comprising a channel portion; and a second gate electrode spaced apart from the active layer and disposed on the opposite side of the first gate electrode based on (in other words, relative to) the active layer. At least a portion of the first gate electrode does not overlap with the second gate electrode, and at least a portion of the second gate electrode does not overlap with the first gate electrode. The channel portion overlaps with at least one of the first and second gate electrodes, a portion of the channel portion overlaps only with one of the first and second gate electrodes, and another portion of the channel portion overlaps only with the other of the first and second gate electrodes. The active layer comprises a first active layer (the first active layer comprising an oxide semiconductor material) and a second active layer disposed on the first active layer, the second active layer comprising an oxide semiconductor material, and either the first active layer or the second active layer has a higher hydrogen concentration and a lower oxygen concentration than the other of the first and second active layers.

[0019] The channel portion may include a first channel region that overlaps with the first gate electrode but does not overlap with the second gate electrode, and a second channel region that overlaps with the second gate electrode but does not overlap with the first gate electrode.

[0020] The first channel region is located at one end of the channel section, and the second channel region is located at the other end of the channel section.

[0021] The active layer includes a first connection portion and a second connection portion that are separate from each other and connected to the channel portion respectively.

[0022] The first connecting portion contacts the first channel region, and the second connecting portion contacts the second channel region.

[0023] The first connection portion may not overlap with the second gate electrode, and the second connection portion may not overlap with the first gate electrode.

[0024] At least a portion of the first connection portion may overlap with the first gate electrode.

[0025] A portion of the first gate electrode and a portion of the second gate electrode may overlap each other.

[0026] A portion of the channel may overlap with both the first gate electrode and the second gate electrode.

[0027] The thin-film transistor may further include a hydrogen supply layer disposed between the first gate electrode and the active layer.

[0028] The thin-film transistor may further include an oxygen supply layer disposed between the active layer and the second gate electrode.

[0029] The first active layer and the second active layer can have the same metallic composition.

[0030] The first active layer can have a higher hydrogen concentration than the second active layer, and the second active layer can have a higher oxygen concentration than the first active layer.

[0031] Thin-film transistors may further include a hydrogen-donating layer on the active layer.

[0032] The first active layer can have a higher oxygen concentration than the second active layer, and the second active layer can have a higher hydrogen concentration than the first active layer.

[0033] The first active layer may have a first region overlapping with the first gate electrode, and the first region may have a higher hydrogen concentration than other regions of the first active layer.

[0034] The second active layer may have a second region overlapping with the second gate electrode, and the second region may have a higher oxygen concentration than other regions of the second active layer.

[0035] According to another aspect of this disclosure, the above and other objectives can be achieved by providing a display device including the aforementioned thin-film transistors.

[0036] According to another aspect of this disclosure, the above and other objectives can be achieved by providing a method for manufacturing a thin-film transistor, the method comprising: forming a first gate electrode on a substrate, forming a first gate insulating layer on the first gate electrode, forming an active layer on the first gate insulating layer, and forming a second gate electrode on the active layer, wherein at least a portion of the first gate electrode does not overlap with the second gate electrode and at least a portion of the second gate electrode does not overlap with the first gate electrode, the active layer has a channel portion and the channel portion overlaps with at least one of the first gate electrode and the second gate electrode, the active layer comprises a first active layer and a second active layer on the first active layer, and either the first active layer or the second active layer has a higher hydrogen concentration and a lower oxygen concentration than the other of the first active layer and the second active layer.

[0037] According to the method of manufacturing a thin-film transistor, the first gate electrode and the second gate electrode can be formed such that a portion of the first gate electrode and a portion of the second gate electrode overlap each other.

[0038] The method of manufacturing a thin-film transistor may further include forming a hydrogen supply layer on the first gate electrode before forming a first gate insulating layer on the first gate electrode.

[0039] The method for manufacturing a thin-film transistor may further include oxygen treatment of the surface of the active layer before forming a second gate electrode on the active layer.

[0040] The oxygen treatment may include treating the surface of the active layer with N2O gas.

[0041] Forming a second gate electrode on the active layer may include forming a second gate electrode pattern on the active layer.

[0042] The method for manufacturing thin-film transistors may further include conductiveing ​​the active layer by using a second gate electrode pattern as a mask (making the active layer conductive). Attached Figure Description

[0043] The above and other objects, features and advantages of this disclosure will become clearer from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0044] Figure 1 This figure shows a cross-sectional view of a thin-film transistor according to an embodiment of the present disclosure;

[0045] Figure 2 It is shown in the figure. Figure 1 A partial cross-sectional view of the channel portion of the thin-film transistor shown.

[0046] Figure 3 This figure shows a cross-sectional view of a thin-film transistor according to another embodiment of the present disclosure;

[0047] Figure 4A and 4B This figure shows a cross-sectional view of a thin-film transistor according to yet another embodiment of the present disclosure;

[0048] Figure 5A and 5B These are cross-sectional views illustrating a thin-film transistor according to another embodiment of the present disclosure;

[0049] Figure 6 This figure shows a cross-sectional view of a thin-film transistor according to another embodiment of the present disclosure;

[0050] Figure 7 and 8 This is a cross-sectional view of a thin-film transistor according to a comparative example;

[0051] Figure 9 It is a graph showing the change in the threshold voltage;

[0052] Figure 10A , 10B The graphs for 10C and 10C show the change of the threshold voltage over time.

[0053] Figures 11A to 11M This is a process view illustrating a method for manufacturing a thin-film transistor according to an embodiment of the present disclosure;

[0054] Figure 12 This is a schematic view illustrating a display device according to an embodiment of the present disclosure;

[0055] Figure 13 It is shown in the figure. Figure 12 The circuit (view) diagram of any pixel;

[0056] Figure 14 This is a circuit diagram illustrating any pixel of a display device according to another embodiment of the present disclosure;

[0057] Figure 15 This is a circuit diagram illustrating any pixel of a display device according to yet another embodiment of the present disclosure;

[0058] Figure 16 This is a circuit diagram illustrating any pixel of a display device according to another embodiment of the present disclosure. Detailed Implementation

[0059] The advantages and features of this disclosure and its implementation methods will be illustrated by the embodiments described below with reference to the accompanying drawings. However, this disclosure may be embodied (or implemented) in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of this disclosure to those skilled in the art. Furthermore, this disclosure is limited only by the scope of the claims.

[0060] The shapes, sizes (dimensions), ratios, angles, and quantities disclosed in the accompanying drawings used to describe embodiments of this disclosure are merely examples, and therefore, this disclosure is not limited to the details illustrated. Throughout the specification, the same (similar) reference numerals refer to the same (similar) elements. In the following description, detailed descriptions of relevant known functions or configurations will be omitted where they are determined to unnecessarily obscure the essential points of this disclosure.

[0061] When using the terms “comprising,” “having,” and “including” as described in this specification, an additional part may be added unless “only” is used. Unless otherwise stated, singular terms may include plural forms.

[0062] When interpreting a component, even without an explicit description, the component is interpreted as including a range of errors.

[0063] When describing positional relationships, for example, when the positional relationship is described as "~above", "~above", "~below" and "~near", one or more parts may be arranged between two other parts unless "only" or "directly" is used.

[0064] Spatially relative terms such as “below,” “below,” “down,” “above,” and “above” may be used herein to readily describe the relationship between one or more elements shown in the figures and another one or more elements. It should be understood that these terms are intended to cover different orientations of the device beyond those depicted in the figures. For example, if the device shown in the figure is inverted, a device described as being arranged “below” or “below” another device may be arranged “above” another device. Thus, the exemplary term “below or below” can include both orientations of “below or below” and “above.” Similarly, the exemplary terms “above” or “above” can include both orientations of “above” and “below or below.”

[0065] When describing temporal relationships, such as when time sequence is described as “after,” “following,” “immediately following,” and “before,” discontinuous cases may be included unless “only” or “directly” is used.

[0066] It should be understood that although the terms “first,” “second,” etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used only to distinguish one element from another. For example, without departing from the scope of this disclosure, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element.

[0067] The term "at least one" should be understood as any and all combinations that include one or more of the associated listed items. For example, "at least one of the first, second, and third items" means a combination of two or more of the first, second, and third items, as well as all items selected or proposed from the first, second, or third items.

[0068] As will be fully understood by those skilled in the art, the features of the various embodiments of this disclosure may be joined (coupled) or combined with each other in part or in whole, and may interoperate with each other and be technically driven in various ways. Embodiments of this disclosure may be implemented independently of each other or together in an interdependent relationship.

[0069] In the accompanying drawings, the same or similar elements are indicated by the same reference numerals, even if they are depicted in different drawings. Throughout the drawings, the same reference numerals will be used as much as possible to refer to the same or similar parts.

[0070] In the embodiments of this disclosure, the source electrode and drain electrode are distinguished from each other for ease of description. However, the source electrode and drain electrode can be used interchangeably. A source electrode can be a drain electrode, and a drain electrode can be a source electrode. Furthermore, a source electrode in any embodiment of this disclosure can be a drain electrode in another embodiment of this disclosure, and a drain electrode in any embodiment of this disclosure can be a source electrode in another embodiment of this disclosure.

[0071] In some embodiments of this disclosure, for ease of description, the source region is distinguished from the source electrode, and the drain region is distinguished from the drain electrode. However, embodiments of this disclosure are not limited to this structure. For example, the source region may be the source electrode, and the drain region may be the drain electrode. Furthermore, the source region may be the drain electrode, and the drain region may be the source electrode.

[0072] Figure 1 This is a cross-sectional view illustrating a thin-film transistor 100 according to an embodiment of the present disclosure.

[0073] A thin-film transistor 100 according to an embodiment of the present disclosure includes (or comprises) a first gate electrode 121, an active layer 140, and a second gate electrode 122.

[0074] The active layer 140 is configured to be spaced apart from the first gate electrode 121. At least a portion of the active layer 140 overlaps with the first gate electrode 121.

[0075] The second gate electrode 122 is spaced apart from the active layer 140 and is disposed opposite to the first gate electrode 121 based on the active layer 140. In other words, the second gate electrode 122 is disposed on the opposite side of the first gate electrode 121 based on the active layer 140. That is, the first gate electrode 121 is disposed on one side of the active layer 140, while the second gate electrode 122 is disposed on the other side of the active layer 140.

[0076] The active layer 140 includes a channel portion 140a. The channel portion 140a overlaps with at least one of a first gate electrode 121 and a second gate electrode 122. Moreover, the first gate electrode 121 may be wider than the second gate electrode 122, and the first gate electrode 121 may overlap with a larger portion of the channel portion 140a compared to the second gate electrode 122.

[0077] Figure 2 It is shown in the figure. Figure 1 A partial cross-sectional view of the channel portion 140a of the thin-film transistor 100 shown.

[0078] Reference Figure 1 and 2 A thin-film transistor 100 according to an embodiment of the present disclosure will be described in more detail.

[0079] refer to Figure 1 and 2 The first gate electrode 121 is disposed on the substrate 110.

[0080] Glass or plastic can be used as the material for substrate 110. Transparent plastics with flexible properties (e.g., polyimide) can be used as the plastic. When polyimide is used as the material for substrate 110, heat-resistant polyimide that can withstand high temperatures can be used, taking into account the high-temperature deposition process performed on substrate 110.

[0081] The first gate electrode 121 may comprise at least one of aluminum-based metals such as aluminum (Al) or aluminum alloys, silver-based metals such as silver (Ag) or silver alloys, copper-based metals such as copper (Cu) or copper alloys, molybdenum-based metals such as molybdenum (Mo) or molybdenum alloys, chromium (Cr), tantalum (Ta), neodymium (Nd), or titanium (Ti). The first gate electrode 121 may have a multilayer structure comprising at least two conductive layers having different physical properties from each other.

[0082] A first gate insulating layer 131 is disposed on the first gate electrode 121. The first gate insulating layer 131 may have insulating properties and may contain at least one of silicon oxide, silicon nitride, or metal-based oxides. According to one embodiment of the present disclosure, the first gate insulating layer 131 may contain silicon nitride. Silicon nitride contains a relatively higher concentration of hydrogen compared to silicon oxide and metal-based oxides.

[0083] The first gate insulating layer 131 may have a single-layer structure or a multi-layer structure.

[0084] The active layer 140 is disposed on the first gate insulating layer 131.

[0085] According to one embodiment of this disclosure, the active layer 140 comprises an oxide semiconductor material. The active layer 140 may be made of an oxide semiconductor layer.

[0086] The active layer 140 may, for example, comprise at least one of IZO (InZnO)-based, IGO (InGaO)-based, ITO (InSnO)-based, IGZO (InGaZnO)-based, IGZTO (InGaZnSnO)-based, ITZO (InSnZnO)-based, IGTO (InGaSnO)-based, GO (GaO)-based, GZTO (GaZnSnO)-based, and GZO (GaZnO)-based oxide semiconductor materials. However, one embodiment of this disclosure is not limited to this example, and the active layer 140 may be made of other oxide semiconductor materials known in the art.

[0087] The active layer 140 includes a channel portion 140a and a first connecting portion 140b and a second connecting portion 140c respectively disposed on both sides of the channel portion 140a. The first connecting portion 140b and the second connecting portion 140c are spaced apart from each other and are respectively connected to the channel portion 140a.

[0088] The second gate insulating layer 132 is disposed on the active layer 140. The second gate insulating layer 132 may have insulating properties and may contain at least one of silicon oxide, silicon nitride, or metal-based oxide. The second gate insulating layer 132 may have a single-layer structure or a multi-layer structure.

[0089] According to one embodiment of this disclosure, the second gate insulating layer 132 may comprise silicon oxide. The silicon oxide may contain a relatively higher concentration of oxygen compared to silicon nitride.

[0090] The second gate insulating layer 132 may be patterned or may not be patterned. A patterned second gate insulating layer 132 may at least cover the channel portion 140a of the active layer 140, but one embodiment of this disclosure is not limited thereto. The second gate insulating layer 132 may cover the entire upper surface of the active layer 140.

[0091] The second gate electrode 122 is disposed on the second gate insulating layer 132.

[0092] The second gate electrode 122 may be made of the same material as the first gate electrode 121, or it may be made of a different material. The second gate electrode 122 is disposed on the opposite side of the first gate electrode 121 based on the active layer 140. For example, the active layer 140 is located between the first gate electrode 121 and the second gate electrode 122.

[0093] According to one embodiment of this disclosure, at least a portion of the first gate electrode 121 does not overlap with the second gate electrode 122, and at least a portion of the second gate electrode 122 does not overlap with the first gate electrode 121. A portion of the first gate electrode 121 and a portion of the second gate electrode 122 may overlap each other. For example, the first gate electrode 121, the channel portion 140a, and the second gate electrode 122 may be vertically stacked in an alternating configuration, wherein the first gate electrode 121 may primarily overlap approximately half of the channel portion 140a, and the second gate electrode 122 may primarily overlap the other half of the channel portion 140a.

[0094] refer to Figure 1 An interlayer dielectric layer 150 is disposed on the second gate electrode 122. The interlayer dielectric layer 150 may be made of an insulating material.

[0095] Source electrode 161 and drain electrode 162 are disposed on interlayer dielectric layer 150. Source electrode 161 and drain electrode 162 are spaced apart from each other and connected to active layer 140.

[0096] refer to Figure 1 The source electrode 161 is connected to the first connection portion 140b through a contact hole formed in the interlayer dielectric layer 150, and the drain electrode 162 is connected to the second connection portion 140c through another contact hole formed in the interlayer dielectric layer 150. The first connection portion 140b connected to the source electrode 161 can be referred to as the source connection portion, and the second connection portion 140c connected to the drain electrode 162 can be referred to as the drain connection portion.

[0097] According to one embodiment of this disclosure, the first connection portion 140b and the second connection portion 140c can be formed by selectively conductiveizing the active layer 140. For example, the active layer 140 can be selectively conductive by doping with a dopant, thereby forming the first connection portion 140b and the second connection portion 140c.

[0098] For doping, at least one of boron (B) ions, phosphorus (P) ions, or fluorine (F) ions can be used.

[0099] According to one embodiment of this disclosure, the first connection portion 140b may be a drain connection portion, and the second connection portion 140c may be a source connection portion. Furthermore, either the first connection portion 140b or the second connection portion 140c may be a source electrode, while the other of the first connection portion 140b and the second connection portion 140c may be a drain electrode.

[0100] The first connecting part 140b and the second connecting part 140c can be used as a line.

[0101] In the following text, reference will be made to Figure 2 The channel portion 140a of the active layer 140 is described in more detail.

[0102] According to one embodiment of this disclosure, the channel portion 140a overlaps with at least one of the first gate electrode 121 and the second gate electrode 122. When all regions of the channel portion 140a overlap with at least one of the first gate electrode 121 and the second gate electrode 122, the continuity of the channel portion 140a can be ensured, for example, from one end of the channel portion 140a, for example... Figure 2 The left side of the channel portion 140a shown to the other end of the channel portion 140a, for example Figure 2 The right side of the channel portion 140a shown (for example, all portions of the channel portion 140a may overlap with at least one of the first gate electrode 121 or the second gate electrode 122, thereby allowing full coverage of the channel).

[0103] refer to Figure 1 and 2At least a portion of the first gate electrode 121 does not overlap with the second gate electrode 122, and at least a portion of the second gate electrode 122 does not overlap with the first gate electrode 121.

[0104] Due to the configuration (arrangement) of the first gate electrode 121 and the second gate electrode 122, a portion of the channel portion 140a overlaps only with one of the first gate electrode 121 and the second gate electrode 122, while another portion of the channel portion 140a overlaps only with the other of the first gate electrode 121 and the second gate electrode 122. Furthermore, the channel portion 140a may include an intermediate portion that overlaps with both the first gate electrode 121 and the second gate electrode 122.

[0105] For more details, see the reference. Figure 2 According to an embodiment of the present disclosure, the channel portion 140a of the active layer 140 includes a first channel region a1 that overlaps with the first gate electrode 121 but not with the second gate electrode 122, and a second channel region a2 that overlaps with the second gate electrode 122 but not with the first gate electrode 121.

[0106] As a result, the first channel region a1 of the channel portion 140a is driven by the first gate electrode 121, while the second channel region a2 of the channel portion 140a is driven by the second gate electrode 122. The first channel region a1 of the channel portion 140a is the region affected by the first gate electrode 121, while the second channel region a2 of the channel portion 140a is affected by the second gate electrode 122.

[0107] refer to Figure 2 The first channel region a1 is located at one end of the channel portion 140a, and the second channel region a2 is located at the other end of the channel portion 140a. According to one embodiment of this disclosure, as... Figure 2 As shown, the first connecting portion 140b can contact the first channel region a1, and the second connecting portion 140c can contact the second channel region a2.

[0108] refer to Figure 1 and 2The first connection portion 140b does not overlap with the second gate electrode 122, and the second connection portion 140c does not overlap with the first gate electrode 121. According to one embodiment of this disclosure, at least a portion of the first connection portion 140b may overlap with the first gate electrode 121. To ensure that the first gate electrode 121 sufficiently covers the first channel region a1, the first gate electrode 121 may have a larger area than the first channel region a1. As a result, a portion of the first connection portion 140b may overlap with the first gate electrode 121. Although a portion of the first connection portion 140b overlaps with the first gate electrode 121, the first connection portion 140b is conductive and therefore not used as a channel. Therefore, even if there is an overlapping area between the first connection portion 140b and the first gate electrode 121, the driving of the thin-film transistor 100 is not affected by the overlapping area.

[0109] On the other hand, according to one embodiment of this disclosure, the first connection portion 140b may not overlap with the second gate electrode 122. The second gate electrode 122 is part of a pattern used as a mask during the selective conductivity process of the active layer 140. Therefore, the second gate electrode 122 may not overlap with the first connection portion 140b and the second connection portion 140c.

[0110] According to one embodiment of this disclosure, a portion of the first gate electrode 121 and a portion of the second gate electrode 122 may overlap each other. Therefore, a portion of the channel portion 140a may overlap with both the first gate electrode 121 and the second gate electrode 122.

[0111] According to one embodiment of this disclosure, the channel portion 140a may include a third channel region a3 that overlaps with both the first gate electrode 121 and the second gate electrode 122. The third channel region a3 is the region affected by both the first gate electrode 121 and the second gate electrode 122.

[0112] To ensure the continuity of the channel portion 140a, the channel portion 140a needs to overlap with at least one of the first gate electrode 121 and the second gate electrode 122. Taking into account process errors in the manufacturing of the first gate electrode 121 and the second gate electrode 122, the first gate electrode 121 and the second gate electrode 122 can be designed to partially overlap each other. According to one embodiment of this disclosure, the length of the third channel region a3 can be designed to be as small as possible.

[0113] When the third channel region a3 exists in the channel portion 140a, the continuity of the channel portion 140a from one end to the other end can be ensured.

[0114] According to one embodiment of this disclosure, the active layer 140 includes a first active layer 141 and a second active layer 142 on the first active layer 141. (See also...) Figure 1 and 2 A first active layer 141 is disposed on a first gate insulating layer 131, and a second active layer 142 is disposed on the first active layer 141. The first active layer 141 and the second active layer 142 are respectively oxide semiconductor material layers. The oxide semiconductor material constituting the first active layer 141 and the second active layer 142 may contain metal and oxygen. According to one embodiment of this disclosure, the first active layer 141 and the second active layer 142 may have the same metal composition. According to one embodiment of this disclosure, the first active layer 141 and the second active layer 142 have the same metal composition and can be distinguished from each other by the difference in the content of at least one of oxygen and hydrogen.

[0115] According to one embodiment of this disclosure, either the first active layer 141 or the second active layer 142 has a higher hydrogen concentration and a lower oxygen concentration than the other of the first active layer 141 and the second active layer 142.

[0116] For example, the first active layer 141 may have a hydrogen concentration higher than that of the second active layer 142, and an oxygen concentration lower than that of the second active layer 142. The second active layer 142 may have a hydrogen concentration lower than that of the first active layer 141, and an oxygen concentration higher than that of the first active layer 141.

[0117] According to one embodiment of this disclosure, the first active layer 141 contains an excess of hydrogen (H) compared to the second active layer 142. The first active layer 141 may be an excess hydrogen layer having a higher hydrogen concentration than a conventional oxide semiconductor material layer used as a channel for a thin-film transistor.

[0118] When the first active layer 141 contains excess hydrogen, a hole trapping effect occurs due to the ionization effect of hydrogen (H), thereby shifting the threshold voltage of the thin-film transistor 100 in the negative (-) direction. Therefore, the threshold voltage Vth can be shifted (displaced) in the negative (-) direction.

[0119] According to one embodiment of this disclosure, the second active layer 142 contains an excess of oxygen (O) compared to the first active layer 141. The second active layer 142 may be an excess oxygen layer having a higher oxygen concentration than conventional oxide semiconductor materials used as channels in thin-film transistors.

[0120] When the second active layer 142 contains excess oxygen, an electron trapping effect occurs, thereby shifting the threshold voltage of the thin-film transistor 100 in the positive (+) direction. Therefore, the threshold voltage Vth can be shifted in the positive (+) direction.

[0121] According to an embodiment of the present disclosure, the thin-film transistor 100 can simultaneously have a negative (-) offset effect of the threshold voltage Vth due to the layer containing excess hydrogen and a positive (+) offset effect of the threshold voltage Vth due to the layer containing excess oxygen, so that the change of the threshold voltage Vth of the thin-film transistor 100 can be suppressed even over time.

[0122] In one embodiment of this disclosure, the presence of “excess oxygen” in the oxide semiconductor material layer means that the oxygen ratio is higher than the oxygen ratio when the metals constituting the oxide semiconductor and oxygen form stable chemical bonds in a stoichiometric manner.

[0123] The case of In, Ga, and Zn being contained in an IGZO (InGaZnO)-based oxide semiconductor in a 1:1:1 ratio will be described by way of example.

[0124] Indium (In) can combine with oxygen in the state of In₂O₃. Gallium (Ga) can combine with oxygen in the state of Ga₂O₃. Additionally, zinc (Zn) can combine with oxygen in the state of ZnO. Therefore, when the stoichiometric ratio of In, Ga, and Zn is 1:1:1, the corresponding stoichiometric ratio of oxygen is 1.5:1.5:1. As a result, when In, Ga, and Zn are used in a 1:1:1 ratio, the stoichiometric ratio of oxygen becomes 4. In this case, the stoichiometric ratio of In, Ga, Zn, and O is 1:1:1:4 (In:Ga:Zn:O = 1:1:1:4), and the stoichiometric ratio of oxygen can be 4. Therefore, the case of "excess oxygen" in an oxide semiconductor material layer means that when the stoichiometric ratio of In, Ga, and Zn is 1:1:1, the stoichiometric ratio of oxygen exceeds 4. This can be represented by the following Equation 1.

[0125] [Equation 1]

[0126] InGaZnO 4+x (where x>0)

[0127] Generally, excess hydrogen can be described as an oxygen-deficient portion. For example, in an oxide semiconductor layer in which the stoichiometric ratio of In, Ga, and Zn is 1:1:1, an oxygen-deficient state can be described when the stoichiometric content of oxygen is less than 4. For example, the oxygen-deficient state can be described by Equation 2.

[0128] [Equation 2]

[0129] InGaZnO 4-y (where y>0)

[0130] Generally, gaps in an oxide semiconductor layer caused by oxygen deficiency can be filled with hydrogen (H). An oxide semiconductor layer having "excess hydrogen" means that the oxide semiconductor contains more hydrogen than in a stable oxygen-deficient state. According to one embodiment of this disclosure, an oxide semiconductor layer can be described as having a hydrogen excess state when the hydrogen content is at least twice that of an oxygen-deficient state. More specifically, in Equation 2, an oxide semiconductor layer can be described as having a hydrogen excess state when the stoichiometric content of hydrogen is 2y or higher.

[0131] refer to Figure 2 The first channel region a1 of the channel portion 140a is driven by the first gate electrode 121, and the first active layer 141 in the first channel region a1 is positioned closer to the first gate electrode 121 than the second active layer 142. Therefore, the driving of the first channel region a1 of the channel portion 140a is primarily influenced by (or affected by) the first active layer 141. As a result, when the first active layer 141 has a higher hydrogen concentration and a lower oxygen concentration than the second active layer 142, the first channel region a1 can be used to shift the threshold voltage of the thin-film transistor 100 in the negative (-) direction.

[0132] The second channel region a2 of the channel portion 140a is driven by the second gate electrode 122, and the second active layer 142 in the second channel region a2 is positioned closer to the second gate electrode 122 than the first active layer 141. Therefore, the driving of the second channel region a2 of the channel portion 140a is primarily influenced by (or affected by) the second active layer 142. As a result, when the second active layer 142 has a higher oxygen concentration and a lower hydrogen concentration than the first active layer 141, the second channel region a2 can be used to shift the threshold voltage of the thin-film transistor 100 in the positive (+) direction.

[0133] As described above, the channel portion 140a of a thin-film transistor 100 according to an embodiment of the present disclosure includes a first channel region a1 for offsetting the threshold voltage in the negative (-) direction and a second channel region a2 for offsetting the threshold voltage Vth in the positive (+) direction. Therefore, in the thin-film transistor 100 according to an embodiment of the present disclosure, the offset effect of the threshold voltage Vth in the negative (-) direction and the offset effect of the threshold voltage Vth in the positive (+) direction are canceled out, thereby suppressing changes in the threshold voltage Vth. Therefore, the thin-film transistor 100 according to an embodiment of the present disclosure can be stably driven without significant changes in the threshold voltage Vth. In particular, even when the thin-film transistor is driven in the ON state for a long time, the thin-film transistor can be stably driven without changes in the threshold voltage. For example, due to this unique design, even after the device has been used for a long time, the implemented invention can effectively set (or fix) the threshold voltage Vth to a specific value and maintain it there.

[0134] However, one embodiment of this disclosure is not limited to the above example, and the first active layer 141 may have a lower hydrogen concentration and a higher oxygen concentration than the second active layer 142, while the second active layer 142 may have a higher hydrogen concentration and a lower oxygen concentration than the first active layer 141 (see reference). Figure 4B and 5B ).

[0135] refer to Figure 2 The first channel region a1 of the channel portion 140a is driven by the first gate electrode 121, and the first active layer 141 contained in the first channel region a1 is positioned closer to the first gate electrode 121 than the second active layer 142. Therefore, the driving of the first channel region a1 of the channel portion 140a is primarily influenced by the first active layer 141. As a result, when the first active layer 141 has a lower hydrogen concentration and a higher oxygen concentration than the second active layer 142, the first channel region a1 can be used to shift the threshold voltage of the thin-film transistor 301 or 401 in the positive (+) direction.

[0136] The second channel region a2 of the channel portion 140a is driven by the second gate electrode 122, and the second active layer 142 contained in the second channel region a2 is positioned closer to the second gate electrode 122 than the first active layer 141. Therefore, the second channel region a2 of the channel portion 140a is primarily affected by the second active layer 142. As a result, when the second active layer 142 has a higher hydrogen concentration and a lower oxygen concentration than the first active layer 141, the second channel region a2 can be used to shift the threshold voltage of the thin-film transistor 301 or 401 in the negative (-) direction.

[0137] As described above, the channel portion 140a of a thin-film transistor 301 or 401 according to an embodiment of the present disclosure includes a first channel region a1 for shifting the threshold voltage Vth in a positive (+) direction and a second channel region a2 for shifting the threshold voltage Vth in a negative (-) direction (see reference). Figure 4B and 5B Therefore, in the thin-film transistor 301 or 401 according to an embodiment of the present disclosure, the offset effect of the threshold voltage Vth along the positive (+) direction and the offset effect of the threshold voltage Vth along the negative (-) direction are canceled out, thereby suppressing the change of the threshold voltage Vth. Therefore, the thin-film transistor 301 or 401 according to an embodiment of the present disclosure can be stably driven without a large change in the threshold voltage Vth.

[0138] As described above, according to one embodiment of this disclosure, the first active layer 141 may have a higher hydrogen concentration and a lower oxygen concentration than the second active layer 142, and the first active layer 141 may have a lower hydrogen concentration and a higher oxygen concentration than the second active layer 142. Due to the difference in hydrogen and oxygen concentrations between the first active layer 141 and the second active layer 142, and the configuration characteristics of the first gate electrode 121 and the second gate electrode 122, the thin-film transistor 100 according to one embodiment of this disclosure can exhibit excellent stability when the threshold voltage Vth remains unchanged.

[0139] The hydrogen and oxygen concentrations of the first active layer 141 and the second active layer 142 can be adjusted in various ways.

[0140] For example, the materials used in the manufacturing process of the first active layer 141 and the second active layer 142 can be appropriately selected so that the hydrogen concentration and oxygen concentration of the first active layer 141 and the second active layer 142 can be adjusted.

[0141] According to one embodiment of this disclosure, the first active layer 141 and the second active layer 142 can be formed by a metal-organic chemical vapor deposition (MOCVD) method. In this case, the hydrogen concentration and oxygen concentration of the first active layer 141 and the second active layer 142 can be adjusted by adjusting the content of hydrogen (H2) or ozone (O3) used in the MOCVD method.

[0142] The hydrogen and oxygen concentrations of the first active layer 141 and the second active layer 142 can be adjusted by providing a hydrogen supply layer near the first active layer 141 or the second active layer 142, or by treating the first active layer 141 or the second active layer 142 with oxygen (e.g., with N2O gas).

[0143] Figure 3This figure shows a cross-sectional view of a thin-film transistor 200 according to another embodiment of the present disclosure. In the following, to avoid redundancy, descriptions of the already described elements will be omitted.

[0144] refer to Figure 3 The second gate insulating layer 132 can cover the entire upper surface of the active layer 140. Figure 3 In this embodiment, the surface of the active layer 140 facing the second gate electrode 122 is referred to as the upper surface. According to another embodiment of this disclosure, the second gate insulating layer 132 may not be patterned.

[0145] refer to Figure 3 Contact holes can be formed in the second gate insulating layer 132.

[0146] According to another embodiment of this disclosure, the source electrode 161 can be connected to the first connection portion 140b of the active layer 140 through a contact hole formed in the interlayer dielectric layer 150 and the second gate insulating layer 132. The drain electrode 162 can be connected to the second connection portion 140c of the active layer 140 through another contact hole formed in the interlayer dielectric layer 150 and the second gate insulating layer 132.

[0147] Figure 4A This figure shows a cross-sectional view of a thin-film transistor 300 according to another embodiment of the present disclosure. The thin-film transistor 300 according to another embodiment of the present disclosure includes a hydrogen supply layer 135 disposed between a first gate electrode 121 and an active layer 140.

[0148] refer to Figure 4A A buffer layer 118 may be disposed on the substrate 110. The buffer layer 118 may contain at least one of silicon oxide and silicon nitride. The buffer layer 118 may protect the active layer 140 and may have planarization characteristics to planarize the upper part of the substrate 110.

[0149] The first gate electrode 121 is disposed on the buffer layer 118, and the first passivation layer 133 is disposed on the first gate electrode 121. The first passivation layer 133 can serve to insulate and protect the first gate electrode 121. The first passivation layer 133 can be made of the same material as the first gate insulating layer 131.

[0150] A hydrogen supply layer 135 is disposed on the first passivation layer 133. The hydrogen supply layer 135 supplies hydrogen to the active layer 140. As a result, a first active layer 141 containing a higher concentration of hydrogen than the second active layer 142 can be formed. The first active layer 141 contains hydrogen at a concentration higher than the typical hydrogen concentration of an oxide semiconductor layer. According to another embodiment of the present disclosure, the first active layer 141 is an excess hydrogen layer containing excess hydrogen.

[0151] The hydrogen-donating layer 135 may be formed, for example, from silicon nitride (SiNx). The silicon nitride (SiNx) layer used as the hydrogen-donating layer 135 may contain a high concentration of hydrogen.

[0152] A first gate insulating layer 131 is disposed on the hydrogen supply layer 135. The first gate insulating layer 131 may have insulating properties and may contain at least one of silicon oxide, silicon nitride, and metal-based oxides. The first gate insulating layer 131 may be formed of the same material as the first passivation layer 133. The first gate insulating layer 131 and the first passivation layer 133 may be collectively referred to as the first gate insulating layer or the lower gate insulating layer.

[0153] An active layer 140 is disposed on a first gate insulating layer 131, and a second gate insulating layer 132 is disposed on an active layer 140.

[0154] The second gate electrode 122 is disposed on the second gate insulating layer 132, and the interlayer dielectric layer 150 is disposed on the second gate electrode 122. The source electrode 161 and the drain electrode 162 are disposed on the interlayer dielectric layer 150.

[0155] However, another embodiment of this disclosure is not limited to... Figure 4A The configuration (or arrangement) shown is illustrated. According to another embodiment of this disclosure, the hydrogen supply layer 135 may be disposed above the active layer 140. For example, the hydrogen supply layer 135 may be disposed in the second gate insulating layer 132, or it may be disposed in the interlayer dielectric layer 150.

[0156] Figure 4B This figure shows a cross-sectional view of a thin-film transistor 301 according to yet another embodiment of the present disclosure. Reference Figure 4B The hydrogen supply layer 135 can be disposed on the second gate insulating layer 132. For example... Figure 4B As depicted, when the hydrogen supply layer 135 is disposed above the active layer 140, the second active layer 142 may contain an excess of hydrogen.

[0157] Figure 5A This figure illustrates a cross-sectional view of a thin-film transistor according to another embodiment of the present disclosure. Figure 4A Compared to the thin-film transistor 300, Figure 5A The thin-film transistor 400 further includes an oxygen-supplying layer 136.

[0158] In detail, according to another embodiment of the present disclosure, a thin-film transistor 400 includes an oxygen supply layer 136 disposed between an active layer 140 and a second gate electrode 122. The oxygen supply layer 136 supplies oxygen to the active layer 140. As a result, a second active layer 142 containing oxygen at a higher concentration than that of the first active layer 141 can be formed. The second active layer 142 may contain oxygen at a higher concentration than that of a typical oxide semiconductor layer. According to another embodiment of the present disclosure, the second active layer 142 is an excess oxygen layer containing excess oxygen.

[0159] Figure 5B This figure shows a cross-sectional view of a thin-film transistor according to another embodiment of the present disclosure. Figure 5B The thin-film transistor 401 includes a hydrogen-donating layer 135 and an oxygen-donating layer 136.

[0160] refer to Figure 5B An oxygen supply layer 136 can be disposed on the first passivation layer 133. The oxygen supply layer 136 can supply oxygen to the lower part of the active layer 140. As a result, the first active layer 141 can have a higher oxygen concentration than the second active layer 142.

[0161] A first gate insulating layer 131 is disposed on the oxygen supply layer 136, and an active layer 140 is disposed on the first gate insulating layer 131. A second gate insulating layer 132 is disposed on the active layer 140, and a second gate electrode 122 is disposed on the second gate insulating layer 132.

[0162] refer to Figure 5B A hydrogen supply layer 135 may be disposed within the second gate insulating layer 132. The hydrogen supply layer 135 can supply hydrogen to the upper portion of the active layer 140. As a result, the second active layer 142 can have a higher hydrogen concentration than the first active layer 141. The second gate insulating layer 132 may be divided into a lower layer 132a and an upper layer 132b based on the hydrogen supply layer 135. For example, the hydrogen supply layer 135 may be disposed between the lower layer 132a and the upper layer 132b of the second gate insulating layer 132.

[0163] In yet another embodiment of the present disclosure Figure 5B In the thin-film transistor 401 shown, the first active layer 141 may have a higher oxygen concentration than the second active layer 142, and the second active layer 142 may have a higher hydrogen concentration than the first active layer 141.

[0164] Figure 6 This figure shows a cross-sectional view of a thin-film transistor 500 according to another embodiment of the present disclosure.

[0165] refer to Figure 6A hydrogen supply layer 135 is disposed on the first gate electrode 121. The hydrogen supply layer 135 supplies hydrogen to a predetermined region of the active layer 140. As a result, the first region 141a1 located above the hydrogen supply layer 135 of the first active layer 141 can have a higher hydrogen concentration than other regions of the first active layer 141.

[0166] More specifically, the first active layer 141 has a first region 141a1 that overlaps with the first gate electrode 121, wherein the first region 141a1 has a higher hydrogen concentration than other regions of the first active layer 141.

[0167] refer to Figure 6 The second active layer 142 may have a second region 142a2. The second region 142a2 of the second active layer 142 overlaps with the second gate electrode 122. The second region 142a2 may have an oxygen concentration higher than that of other regions of the second active layer 142.

[0168] For example, according to another embodiment of the present disclosure, the second active layer 142 may be selectively oxygenated to form a second region 142a2 in the second active layer 142.

[0169] refer to Figure 6 According to another embodiment of the present disclosure, the thin-film transistor 500 has an oxygen supply layer 136 disposed between the second gate insulating layer 132 and the second gate electrode 122. The oxygen supply layer 136 can supply oxygen to the second active layer 142 to form a second region 142a2 in the second active layer 142. For example, oxygen and hydrogen can be concentrated at opposite corners / sides of the channel portion 140a of the thin-film transistor.

[0170] Figure 7 and 8 This is a cross-sectional view of a thin-film transistor according to a comparative example. In the following text, Figure 7 The thin-film transistor shown will be referred to as Comparative Example 1. Figure 8 The thin-film transistor shown will be referred to as Comparative Example 2.

[0171] like Figure 7 As shown, the thin-film transistor according to Comparative Example 1 does not include a first gate electrode 121, but only a second gate electrode 122. Figure 7 The thin-film transistor shown is also known as a top-gate thin-film transistor.

[0172] Figure 7 The channel portion 140a of the thin-film transistor shown overlaps with only one gate electrode. Therefore, Figure 7The thin-film transistor shown does not include a configuration in which a portion of the channel portion 140a overlaps only with one of the first gate electrode 121 and the second gate electrode 122, and another portion of the channel portion 140a overlaps only with the other of the first gate electrode 121 and the second gate electrode 122.

[0173] according to Figure 8 The thin-film transistor shown in Comparative Example 2 includes both a first gate electrode 121 and a second gate electrode 122. Figure 8 The thin-film transistor shown is also known as a dual-gate thin-film transistor.

[0174] exist Figure 8 In the thin-film transistor shown, the entire region of the channel portion 140a overlaps with the first gate electrode 121 and the second gate electrode 122. Therefore, Figure 8 The thin-film transistor shown does not include a configuration in which a portion of the channel portion 140a overlaps only with one of the first gate electrode 121 and the second gate electrode 122, and another portion of the channel portion 140a overlaps only with the other of the first gate electrode 121 and the second gate electrode 122.

[0175] have Figure 7 The thin-film transistor constructed as shown in Figure 8 has a threshold voltage Vth variation that is greater than the variation of each of the thin-film transistors 100, 200, 300, 301, 400, 401 and 500 according to embodiments of the present disclosure.

[0176] Figure 9 This is a graph showing the change in the threshold voltage Vth.

[0177] exist Figure 9 In the curve at the center of the graph shown, the threshold voltage Vth is close to 0V. On the other hand, in Figure 9 In the curve on the left side of the graph shown, the threshold voltage shifts along the negative (-) voltage direction. For example, in... Figure 9 As shown in the curve on the left side of the graph, the threshold voltage Vth shifts in the negative (-) direction when the threshold voltage shifts in the negative (-) voltage direction.

[0178] exist Figure 9 In the curve on the right side of the graph shown, the threshold voltage shifts along the positive (+) voltage direction. For example, in... Figure 9 As shown in the curve on the right side of the graph, when the threshold voltage shifts in the positive (+) voltage direction, the threshold voltage Vth shifts in the positive (+) direction.

[0179] Figure 10A , 10B The graphs for 10C and 10C show the change of the threshold voltage over time. In detail, Figure 10A , 10B10C indicates the result of the positive bias temperature stress (PBTS) test.

[0180] PBTS refers to the stress under conditions of applied positive (+) bias voltage and constant temperature. As PBTS increases, the stress in the oxide semiconductor layer 120 or thin-film transistor 100 increases, which may increase the amount of change in threshold voltage ΔVth (or the rate of change).

[0181] exist Figure 10A In the process of applying PBTS to according to Figure 7 In the state of the thin-film transistor shown in Comparative Example 1, the change ΔVth of the threshold voltage Vth over time was measured. (Reference) Figure 10A It should be noted that when PBTS is applied to Figure 7 In the thin-film transistor shown (Comparative Example 1), the change in threshold voltage Vth increases over time. Figure 7 In the thin-film transistor shown (Comparative Example 1), it should be noted that when PBTS is applied, the threshold voltage Vth increases continuously without converging to a specific value, and after 40,000 seconds, the change in threshold voltage ΔVth is approximately 0.254V.

[0182] exist Figure 10B In the process of applying PBTS to according to Figure 8 In the state of the thin-film transistor shown in Comparative Example 2, the change ΔVth of the threshold voltage Vth over time was measured. (Reference) Figure 10B It should be noted that when PBTS is applied to Figure 8 In the thin-film transistor shown (Comparative Example 2), the change in threshold voltage Vth increases over time. Figure 8 In the thin-film transistor shown (Comparative Example 2), it should be noted that when PBTS is applied, the threshold voltage Vth increases continuously without converging to a specific value, and after 40,000 seconds, the change in threshold voltage ΔVth is approximately 2.54V.

[0183] according to Figure 8 The thin-film transistor shown in Comparative Example 2 can have excellent on-current characteristics due to its dual-gate structure, but it has the problem that the change in threshold voltage Vth ΔVth increases over time.

[0184] Figure 10C The diagram illustrates the basis Figure 4A A graph showing the threshold voltage of a thin-film transistor 300 according to another embodiment of this disclosure. (See reference...) Figure 10CIt should be noted that even when PBTS is applied to the thin-film transistor 300 according to another embodiment of this disclosure, the threshold voltage Vth hardly changes. Therefore, compared with Figure 7 and Figure 8 Compared to the example constructions, the specific type of interleaved, dual-gate construction of the present invention provides a much more stable threshold voltage over time.

[0185] In the following text, reference will be made to Figure 11A-11M To describe a method of manufacturing a thin-film transistor 300 according to another embodiment of the present disclosure.

[0186] Figure 11A-11M This is a process view illustrating a method for manufacturing a thin-film transistor 300 according to another embodiment of the present disclosure.

[0187] refer to Figure 11A A buffer layer 118 is formed on the substrate 110, and a first gate electrode 121 is formed on the buffer layer 118.

[0188] refer to Figure 11B A first passivation layer 133 is formed on the first gate electrode 121, a hydrogen supply layer 135 is formed on the first passivation layer 133, and a first gate insulating layer 131 is formed on the hydrogen supply layer 135.

[0189] The first passivation layer 133 may be made of an insulating material. The hydrogen supply layer 135 is a layer for supplying hydrogen to the active layer 140, which will be described later. The hydrogen supply layer 135 may be formed, for example, of silicon nitride (SiNx). The silicon nitride (SiNx) layer applied to the hydrogen supply layer 135 may contain a high concentration of hydrogen. The first gate insulating layer 131 has insulating properties.

[0190] refer to Figure 11C An active layer 140 is formed on the first gate insulating layer 131. The active layer 140 comprises an oxide semiconductor material. The active layer 140 may be an oxide semiconductor layer. The active layer 140 may, for example, comprise at least one of the following oxide semiconductor materials: IZO (InZnO)-based, IGO (InGaO)-based, ITO (InSnO)-based, IGZO (InGaZnO)-based, IGZTO (InGaZnSnO)-based, ITZO (InSnZnO)-based, IGTO (InGaSnO)-based, GO (GaO)-based, GZTO (GaZnSnO)-based, and GZO (GaZnO)-based.

[0191] refer to Figure 11D The surface of the active layer 140 is treated with oxygen. Figure 11D The oxygen treatment shown may include treating the surface of the active layer 140 with N2O gas.

[0192] Hydrogen is supplied to the active layer 140 through the hydrogen supply layer 135, and oxygen (O) is supplied to the surface of the active layer 140 through oxygen treatment, thereby forming the first active layer 141 and the second active layer 142.

[0193] The result is, as Figure 11E As shown, an active layer 140 is formed comprising a first active layer 141 and a second active layer 142. The first active layer 141 may have a higher hydrogen concentration and a lower oxygen concentration than the second active layer 142. Furthermore, the second active layer 142 may have a lower hydrogen concentration and a higher oxygen concentration than the first active layer 141.

[0194] However, another embodiment of this disclosure is not limited to the above example, and the first active layer 141 may have a lower hydrogen concentration and a higher oxygen concentration than the second active layer 142, while the second active layer 142 may have a higher hydrogen concentration and a lower oxygen concentration than the first active layer 141.

[0195] For example, the first active layer 141 and the second active layer 142 can be formed by a metal-organic chemical vapor deposition (MOCVD) method. In this case, the hydrogen and oxygen concentrations of the first active layer 141 and the second active layer 142 can be adjusted by changing the content of hydrogen (H2) or ozone (O3) used in the MOCVD method. By increasing the amount of ozone (O3) used in forming the first active layer 141 and increasing the amount of hydrogen used in forming the second active layer 142, the first active layer 141 can have a lower hydrogen concentration and a higher oxygen concentration than the second active layer 142.

[0196] refer to Figure 11F A second gate insulating layer 132 is formed on the active layer 140, and a second gate electrode material layer 122a is formed on the second gate insulating layer 132. The second gate electrode material layer 122a may contain at least one of aluminum-based metals such as aluminum (Al) or aluminum alloys, silver-based metals such as silver (Ag) or silver alloys, copper-based metals such as copper (Cu) or copper alloys, molybdenum-based metals such as molybdenum (Mo) or molybdenum alloys, chromium (Cr), tantalum (Ta), neodymium (Nd), and titanium (Ti). The second gate electrode material layer 122a may have a multilayer structure, which includes at least two conductive layers having different physical properties from each other.

[0197] refer to Figure 11G A first photoresist pattern 190a is formed on the second gate electrode material layer 122a. The first photoresist pattern 190a can be formed by exposure and development of the photoresist.

[0198] refer to Figure 11HThe second gate electrode material layer 122a is etched using the first photoresist pattern 190a as a mask. As a result, the second gate electrode pattern 122b is formed.

[0199] refer to Figure 11I The second gate insulating layer 132 can be patterned by etching using the second gate electrode pattern 122b as a mask. At this time, a portion of the first photoresist pattern 190a is removed to form the second photoresist pattern 190b.

[0200] However, another embodiment of this disclosure is not limited to the above example, and the second gate insulating layer 132 may not be patterned.

[0201] refer to Figure 11J The active layer 140 is selectively made conductive (treated). For example, dopants can be selectively doped onto the active layer 140. Figure 11J An exemplary map illustrates the process of selectively making the active layer 140 conductive through doping.

[0202] refer to Figure 11J The active layer 140 can be selectively made conductive by using the second gate electrode pattern 122b as a mask for doping. Regions of the active layer 140 not protected by the second gate electrode pattern 122b are selectively made conductive.

[0203] The dopant may contain at least one of boron (B), phosphorus (P), and fluorine (F). The dopant may be in an ionic state. According to one embodiment of this disclosure, conductivity can be achieved by ion implantation.

[0204] refer to Figure 11K As a result of selectively conductiveing ​​the active layer 140 using the second gate electrode pattern 122b as a mask, a first connection portion 140b and a second connection portion 140c are formed. (See reference...) Figure 11K At least a portion of the second connection portion 140c may overlap with the first gate electrode 121. To ensure the first gate electrode 121 fully covers... Figure 2 The first gate electrode 121 can have a larger area than the first channel region a1 shown. As a result, a portion of the first connection portion 140b can overlap with the first gate electrode 121. Although a portion of the first connection portion 140b overlaps with the first gate electrode 121, the first connection portion 140b is conductive and therefore does not serve as a channel. Therefore, even if there is an overlapping area between the first connection portion 140b and the first gate electrode 121, the driving of the thin-film transistor 300 is not affected by the overlapping area.

[0205] According to one embodiment of this disclosure, the channel portion 140a of the active layer 140 is not conductive. The second gate electrode pattern 122b serves as a mask to protect the channel portion 140a during the conductivity process.

[0206] refer to Figure 11L The second gate electrode 122 is formed by etching the second gate electrode pattern 122b using the second photoresist pattern 190b as a mask. After the second gate electrode 122 is formed, the second photoresist pattern 190b is removed.

[0207] According to another embodiment of this disclosure, at least a portion of the first gate electrode 121 does not overlap with the second gate electrode 122, and at least a portion of the second gate electrode 122 is formed to not overlap with the first gate electrode 121. The first gate electrode 121 may overlap with a portion of the second gate electrode 122.

[0208] The channel portion 140a is formed to overlap with at least one of the first gate electrode 121 and the second gate electrode 122.

[0209] In addition, at least a portion of the first gate electrode 121 is formed not to overlap with the second gate electrode 122, and at least a portion of the second gate electrode 122 is formed not to overlap with the first gate electrode 121.

[0210] According to another embodiment of the present disclosure, the channel portion 140a is designed such that a portion of it overlaps only with one of the first gate electrode 121 and the second gate electrode 122, while another portion of it overlaps only with the other of the first gate electrode 121 and the second gate electrode 122.

[0211] refer to Figure 11M An interlayer dielectric layer 150 is formed on the second gate electrode 122, and a source electrode 161 and a drain electrode 162 are disposed on the interlayer dielectric layer 150. The source electrode 161 and the drain electrode 162 are spaced apart from each other and connected to the active layer 140.

[0212] refer to Figure 11M Before forming the source electrode 161 and the drain electrode 162, contact holes can be formed in the interlayer dielectric layer 150. The source electrode 161 is connected to the first connection portion 140b through the contact hole formed in the interlayer dielectric layer 150, and the drain electrode 162 is connected to the second connection portion 140c through another contact hole formed in the interlayer dielectric layer 150.

[0213] The thin-film transistors 100, 200, 300, 301, 400, 401, and 500 according to embodiments of the present disclosure can be effectively (usefully) applied to display devices. In particular, the thin-film transistors 100, 200, 300, 301, 400, 401, and 500 according to embodiments of the present disclosure can be effectively applied to outdoor display devices that are driven in an on-state for extended periods or to display devices using micro-LEDs.

[0214] Figure 12 This is a schematic view illustrating a display device 600 according to another embodiment of the present disclosure.

[0215] like Figure 12 As shown, a display device 600 according to another embodiment of the present disclosure includes a display panel 310, a gate driver 320, a data driver 330, and a controller 340.

[0216] Display panel 310 includes gate line GL, data line DL, and pixel P disposed in the intersection area between gate line GL and data line DL. Pixel P includes display element 710 and pixel driving circuit PDC for driving display element 710. Images are displayed on display panel 310 by driving pixel P.

[0217] The controller 340 controls the gate driver 320 and the data driver 330.

[0218] The controller 340 outputs a gate control signal GCS for controlling the gate driver 320 and a data control signal DCS for controlling the data driver 330 by using a synchronization signal and a clock signal provided from an external system (not shown). Furthermore, the controller 340 samples input image data from the external system, rearranges the sampled data, and provides the rearranged digital image data (RGB) to the data driver 330.

[0219] The gate control signal GCS includes the gate start pulse GSP, the gate shift clock GSC, the gate output enable signal GOE, the start signal Vst, and the gate clock GCLK. Additionally, the gate control signal GCS may include control signals for controlling the shift register 350.

[0220] The data control signal DCS includes the source start pulse SSP, the source shift clock signal SSC, the source output enable signal SOE, and the polarity control signal POL.

[0221] The data driver 330 provides a data voltage to the data line DL of the display panel 310. Specifically, the data driver 330 converts the image data RGB input from the controller 340 into an analog data voltage, and provides a horizontal line of data voltage to the data line DL each first horizontal cycle (where a gate pulse is provided to the gate line GL).

[0222] The gate driver 320 may include a shift register 350.

[0223] The shift register 350 sequentially supplies gate pulses to the gate line GL within a frame using a start signal and a gate clock transmitted from the controller 340. In this case, a frame means a time period during which an image is output through the display panel 310. The gate pulses have a turn-on voltage that can turn on the switching elements (thin-film transistors) disposed in the pixel P.

[0224] In addition, shift register 350 provides a gate turn-off signal to gate line GL during a separate period of a frame in which no gate pulse is provided, enabling the switching element to turn off. Hereinafter, the gate pulse and the gate turn-off signal will be collectively referred to as the scan signal SS or Scan.

[0225] According to one embodiment of this disclosure, the gate driver 320 can be packaged on the substrate 310. Thus, the structure in which the gate driver 320 is directly packaged on the substrate 310 is referred to as a gate-in-panel (GIP) structure. The gate driver 320 may include... Figure 1 and 3 At least one of the thin-film transistors 100, 200, 300, 301, 400, 401 and 500 shown in -6.

[0226] Figure 13 It is shown in the figure. Figure 12 The circuit diagram of any pixel.

[0227] Figure 13 The circuit diagram is an equivalent circuit diagram of pixel P of a display device 600 that includes an organic light-emitting diode (OLED) as a display element 710. Pixel P includes the display element 710 and a pixel driving circuit PDC for driving the display element 710.

[0228] Figure 13 The pixel driving circuit PDC includes a first thin-film transistor TR1 as a switching transistor and a second thin-film transistor TR2 as a driving transistor. Figure 1 and 3 Each of the thin-film transistors 100, 200, 300, 301, 400, 401 and 500 shown in -6 can be used as a first thin-film transistor TR1 or a second thin-film transistor TR2.

[0229] The first thin-film transistor TR1 is connected to the gate line GL and the data line DL, and is turned on or off by the scan signal SS provided through the gate line GL.

[0230] The data line DL provides the data voltage Vdata to the pixel driving circuit PDC, and the first thin-film transistor TR1 controls the application of the data voltage Vdata.

[0231] The driving power line PL provides a driving voltage Vdd to the display element 710, and the second thin-film transistor TR2 controls the driving voltage Vdd. The driving voltage Vdd is the pixel driving voltage used to drive the organic light-emitting diode (OLED) that serves as the display element 710.

[0232] When the first thin-film transistor TR1 is turned on by the scan signal SS applied from the gate driver 320 through the gate line GL, a data voltage Vdata is supplied to the gate electrode of the second thin-film transistor TR2, which is connected to the display element 710, through the data line DL. The data voltage Vdata is charged in a first capacitor C1 formed between the gate electrode and the source electrode of the second thin-film transistor TR2. The first capacitor C1 is a storage capacitor Cst.

[0233] The amount of current supplied to the organic light-emitting diode (OLED) 710 via the second thin-film transistor TR2 is controlled based on the data voltage Vdata, thereby controlling the grayscale of the light emitted from the display element 710.

[0234] Figure 14 This is a circuit diagram illustrating a pixel P of a display device 700 according to another embodiment of the present disclosure.

[0235] Figure 14 The pixel P of the display device 700 shown includes an organic light-emitting diode (OLED) as a display element 710 and a pixel driving circuit PDC for driving the display element 710. The display element 710 is connected to the pixel driving circuit PDC.

[0236] In pixel P, signal lines DL, GL, PL, RL, and SCL are set to provide signals to the pixel driving circuit PDC.

[0237] The data voltage Vdata is provided to the data line DL, the scan signal SS is provided to the gate line GL, the driving voltage Vdd for driving the pixel is provided to the driving power line PL, the reference voltage Vref is provided to the reference line RL, and the sensing control signal SCS is provided to the sensing control line SCL.

[0238] refer to Figure 14 Assume the gate line of the nth pixel P is "GL". nThe gate line of the (n-1)th pixel P adjacent to the nth pixel P is "GL". n-1 ", and the gate line "GL" of the (n-1)th pixel P n-1 "Used as the sensing control line SCL for the nth pixel P."

[0239] The pixel driving circuit PDC includes, for example, a first thin-film transistor TR1 (switching transistor) connected to the gate line GL and the data line DL, a second thin-film transistor TR2 (driving transistor) for controlling the amount of current output to the display element 710 according to the data voltage Vdata transmitted through the first thin-film transistor TR1, and a third thin-film transistor TR3 (reference transistor) for sensing the characteristics of the second thin-film transistor TR2.

[0240] The first capacitor C1 is disposed between the gate electrode of the second thin-film transistor TR2 and the display element 710. The first capacitor C1 is referred to as the storage capacitor Cst.

[0241] The first thin-film transistor TR1 is turned on by the scan signal SS provided to the gate line GL, so as to transmit the data voltage Vdata provided to the data line DL to the gate electrode G2 of the second thin-film transistor TR2.

[0242] The third thin-film transistor TR3 is connected to the first node n1 and reference line RL between the second thin-film transistor TR2 and the display element 710, and is thus turned on or off by sensing the control signal SCS, and senses the characteristics of the second thin-film transistor TR2 as a driving transistor during the sensing period.

[0243] A second node n2, connected to the gate of the second thin-film transistor TR2, is connected to the first thin-film transistor TR1. A first capacitor C1 is formed between the second node n2 and the first node n1.

[0244] When the first thin-film transistor TR1 is turned on, the data voltage Vdata supplied through the data line DL is provided to the gate electrode of the second thin-film transistor TR2. The data voltage Vdata charges in the first capacitor C1 formed between the gate electrode and the source electrode of the second thin-film transistor TR2.

[0245] When the second thin-film transistor TR2 is turned on, current is supplied to the display element 710 through the second thin-film transistor TR2 according to the driving voltage Vdd used to drive the pixel, thereby outputting light from the display element 710.

[0246] Figure 14 At least one of the first thin-film transistor TR1, the second thin-film transistor TR2, and the third thin-film transistor TR3 may have the following characteristics: Figure 1 and 3The thin-film transistors shown in Figure 6 have the same structure as any of the thin-film transistors 100, 200, 300, 301, 400, 401 and 500.

[0247] Figure 15 This is a circuit diagram illustrating any pixel P of a display device 800 according to another embodiment of the present disclosure.

[0248] Figure 15 The pixel P of the display device 800 shown includes an organic light-emitting diode (OLED) as a display element 710 and a pixel driving circuit PDC for driving the display element 710. The display element 710 is connected to the pixel driving circuit PDC.

[0249] The pixel drive circuit PDC includes thin-film transistors TR1, TR2, TR3, and TR4.

[0250] In pixel P, signal lines DL, EL, GL, PL, SCL and RL are set to provide drive signals to the pixel drive circuit PDC.

[0251] and Figure 14 Compared to the pixel P, Figure 15 Pixel P further includes a transmission control line EL. A transmission control signal EM is provided to the transmission control line EL.

[0252] In addition, with Figure 14 Compared to the pixel drive circuit PDC, Figure 15 The pixel driving circuit PDC further includes a fourth thin-film transistor TR4, which is an emission control transistor used to control the light emission timing of the second thin-film transistor TR2.

[0253] refer to Figure 15 Assume the gate line of the nth pixel P is "GL". n The gate line of the (n-1)th pixel P adjacent to the nth pixel P is "GL". n-1 ", and the gate line "GL" of the (n-1)th pixel P n-1 "Used as the sensing control line SCL for the nth pixel P."

[0254] The first capacitor C1 is positioned between the gate electrode of the second thin-film transistor TR2 and the display element 710. The second capacitor C2 is positioned between one terminal of the fourth thin-film transistor TR4, which provides the drive voltage Vdd to it, and one electrode of the display element 710.

[0255] The first thin-film transistor TR1 is turned on by the scan signal SS provided to the gate line GL, so as to transmit the data voltage Vdata provided to the data line DL to the gate electrode of the second thin-film transistor TR2.

[0256] The third thin-film transistor TR3 is connected to the reference line RL and is thus turned on or off by sensing the control signal SCS, and senses the characteristics of the second thin-film transistor TR2, which is the driving transistor, during the sensing period.

[0257] The fourth thin-film transistor TR4 transmits the driving voltage Vdd to the second thin-film transistor TR2 according to the emission control signal EM, or shields the driving voltage Vdd. When the fourth thin-film transistor is turned on, current is supplied to the second thin-film transistor TR2, thereby outputting light from the display element 710.

[0258] Figure 15 At least one of the first thin-film transistor TR1, the second thin-film transistor TR2, the third thin-film transistor TR3, and the fourth thin-film transistor TR4 may have the following characteristics: Figure 1 and 3 The thin-film transistors shown in Figure 6 have the same structure as any of the thin-film transistors 100, 200, 300, 301, 400, 401 and 500.

[0259] In addition to the structure described above, the pixel driving circuit PDC according to another embodiment of the present disclosure can be formed in various structures. For example, the pixel driving circuit PDC may include five or more thin-film transistors.

[0260] Figure 16 This is a circuit diagram illustrating a pixel P of a display device 900 according to another embodiment of the present disclosure.

[0261] Figure 16 The display device 900 is a liquid crystal display device.

[0262] Figure 16 The pixel P of the display device 900 shown includes a pixel driving circuit PDC and a liquid crystal capacitor Clc connected to the pixel driving circuit PDC. The liquid crystal capacitor Clc corresponds to the display element.

[0263] The pixel driving circuit PDC includes a thin-film transistor TR connected to the gate line GL and the data line DL, and a storage capacitor Cst connected between the thin-film transistor TR and the common electrode 372. A liquid crystal capacitor Clc and the storage capacitor Cst are connected in parallel between the pixel electrode 371 and the common electrode 372 connected to the thin-film transistor TR.

[0264] The liquid crystal capacitor Clc charges the differential voltage between the data signal supplied to the pixel electrode via the thin-film transistor TR and the common voltage Vcom supplied to the common electrode 372, and controls the amount of light transmission by driving the liquid crystal according to the charging voltage. The storage capacitor Cst stably maintains the charging voltage in the liquid crystal capacitor Clc.

[0265] In another embodiment of this disclosure, the display device 900 may include Figure 1 and 3 At least one of the thin-film transistors 100, 200, 300, 301, 400, 401 and 500 shown in Figure 6.

[0266] The following advantages can be obtained according to this disclosure.

[0267] Since the thin-film transistor according to one embodiment of the present disclosure includes portions affected by the top gate and portions affected by the bottom gate in a channel portion, the amount (or rate of change) of the threshold voltage is small, thereby achieving driving stability.

[0268] A thin-film transistor according to an embodiment of the present disclosure includes a channel portion comprising an excess oxygen region and an excess hydrogen region. In the excess oxygen region, electron trapping causes a shift in the threshold voltage in the positive (+) direction, while in the excess hydrogen region, hole trapping causes a shift in the threshold voltage in the negative (-) direction. In the thin-film transistor according to an embodiment of the present disclosure, the excess oxygen region for shifting the threshold voltage in the positive (+) direction and the excess hydrogen region for shifting the threshold voltage in the negative (-) direction are connected in series, thereby reducing the amount of threshold voltage variation of the thin-film transistor and improving driving stability. In particular, even when the thin-film transistor is driven in the ON state for a long time, the thin-film transistor according to an embodiment of the present disclosure can operate stably without a change in the threshold voltage.

[0269] A thin-film transistor according to an embodiment of the present disclosure can be disposed in various electronic devices, and when a thin-film transistor according to an embodiment of the present disclosure is used, the driving stability of the electronic device can be improved. A thin-film transistor according to an embodiment of the present disclosure can be effectively applied to display devices, and in particular, to outdoor display devices that are driven in an on-state for extended periods and to display devices using micro-LEDs.

[0270] It will be apparent to those skilled in the art that this disclosure is not limited to the embodiments and drawings described above, and that various substitutions, modifications, and variations can be made in this disclosure without departing from its spirit or scope. Therefore, the scope of this disclosure is defined by the appended claims, and all variations or modifications derived from the meaning, scope, and equivalent concepts of the claims fall within the scope of this disclosure.

Claims

1. A thin-film transistor, comprising: First gate electrode; An active layer separated from the first gate electrode includes a channel portion; as well as A second gate electrode, which is spaced apart from the active layer and disposed on the opposite side of the first gate electrode based on the active layer, Wherein, at least a portion of the first gate electrode does not overlap with the second gate electrode, and at least a portion of the second gate electrode does not overlap with the first gate electrode. The channel portion overlaps with at least one of the first gate electrode and the second gate electrode. A portion of the channel overlaps only with one of the first gate electrode and the second gate electrode, and another portion of the channel overlaps only with the other of the first gate electrode and the second gate electrode. The active layer includes: A first active layer comprising an oxide semiconductor material; and A second active layer disposed on the first active layer comprises an oxide semiconductor material, and Either the first active layer or the second active layer has a higher hydrogen concentration and a lower oxygen concentration than the other of the first active layer and the second active layer.

2. The thin-film transistor according to claim 1, wherein, The channel portion includes: A first channel region that overlaps with the first gate electrode but does not overlap with the second gate electrode; and A second channel region that overlaps with the second gate electrode but does not overlap with the first gate electrode.

3. The thin-film transistor according to claim 2, wherein, The first channel region is located at one end of the channel portion, and the second channel region is located at the other end of the channel portion.

4. The thin-film transistor according to claim 2, wherein, The active layer includes a first connection portion and a second connection portion that are separate from each other and respectively connected to the channel portion.

5. The thin-film transistor according to claim 4, wherein, The first connecting portion contacts the first channel region, and the second connecting portion contacts the second channel region.

6. The thin-film transistor according to claim 5, wherein, The first connection portion does not overlap with the second gate electrode, and the second connection portion does not overlap with the first gate electrode.

7. The thin-film transistor according to claim 5, wherein, At least a portion of the first connection portion overlaps with the first gate electrode.

8. The thin-film transistor according to claim 1, wherein, A portion of the first gate electrode and a portion of the second gate electrode overlap each other.

9. The thin-film transistor according to claim 1, wherein, A portion of the channel overlaps with both the first gate electrode and the second gate electrode.

10. The thin-film transistor of claim 1, further comprising a hydrogen supply layer disposed between the first gate electrode and the active layer or on the active layer.

11. The thin-film transistor of claim 1, further comprising an oxygen supply layer disposed between the active layer and the second gate electrode.

12. The thin-film transistor according to claim 1, wherein, The first active layer and the second active layer have the same metal composition.

13. The thin-film transistor according to claim 1, wherein, The first active layer has a higher hydrogen concentration than the second active layer, and the second active layer has a higher oxygen concentration than the first active layer, or The first active layer has a higher oxygen concentration than the second active layer, and the second active layer has a higher hydrogen concentration than the first active layer.

14. The thin-film transistor according to claim 1, wherein, The first active layer has a first region that overlaps with the first gate electrode, and the first region has a higher hydrogen concentration than other regions of the first active layer.

15. The thin-film transistor according to claim 1, wherein, The second active layer has a second region that overlaps with the second gate electrode, and the second region has a higher oxygen concentration than other regions of the second active layer.

16. A display device comprising a thin-film transistor according to any one of claims 1-15.

17. A method for manufacturing a thin-film transistor, the method comprising: A first gate electrode is formed on the substrate; A first gate insulating layer is formed on the first gate electrode; An active layer is formed on the first gate insulating layer; as well as A second gate electrode is formed on the active layer. Wherein, at least a portion of the first gate electrode does not overlap with the second gate electrode, and at least a portion of the second gate electrode does not overlap with the first gate electrode. The active layer has a channel portion, and the channel portion overlaps with at least one of the first gate electrode and the second gate electrode. The active layer includes a first active layer and a second active layer on the first active layer, and Either the first active layer or the second active layer has a higher hydrogen concentration and a lower oxygen concentration than the other of the first active layer and the second active layer.

18. The method according to claim 17, wherein, The first gate electrode and the second gate electrode are formed such that a portion of the first gate electrode and a portion of the second gate electrode overlap each other.

19. The method of claim 17, further comprising forming a hydrogen supply layer on the first gate electrode before forming the first gate insulating layer on the first gate electrode.

20. The method of claim 17, further comprising oxygen treatment of the surface of the active layer prior to forming a gate electrode on the active layer.

21. The method according to claim 20, wherein, The oxygen treatment includes treating the surface of the active layer with N2O gas.

22. The method according to claim 17, wherein, Forming the second gate electrode on the active layer includes forming a second gate electrode pattern on the active layer.

23. The method of claim 22, further comprising conducting the active layer to conductivity by using the second gate electrode pattern as a mask.

24. A thin-film transistor, comprising: First gate electrode; The active layer, including the channel portion; as well as Second gate electrode, The channel portion of the active layer is disposed between the first gate electrode and the second gate electrode. The first portion of the channel overlaps only with the first gate electrode and not with the second gate electrode, and The second portion of the channel overlaps only with the second gate electrode and not with the first gate electrode. The active layer includes: A first active layer comprising an oxide semiconductor material; and A second active layer disposed on the first active layer comprises an oxide semiconductor material, and Either the first active layer or the second active layer has a higher hydrogen concentration and a lower oxygen concentration than the other of the first active layer and the second active layer.

25. The thin-film transistor of claim 24, wherein, The first gate electrode is wider than the second gate electrode, and overlaps with more of the channel portion compared to the second gate electrode.

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