TWI526910B - Sensor structure of touch panel and method for fabricating the same - Google Patents

Description

Touch panel touch structure and manufacturing method thereof

The present invention relates to a touch panel and a method of fabricating the same, and more particularly to a capacitive touch panel and a method of fabricating the same.

With the advancement of technology and the demand for human-computer interaction, touch panels have been widely used in various electronic products, such as smart phones, satellite navigation systems, tablet computers, personal digital assistants and notebook computers. At present, according to differences in technical principles, touch panels can be classified into resistive, capacitive, ultrasonic, and optical touch panels; among them, capacitive touch panels are touched by fingers or other electrical conductors. Capacitive sensing occurs, so it has quite good sensing performance, so it is widely used in a variety of high-priced consumer electronics.

The first figure is a schematic flow diagram illustrating a simplified process for a known capacitive touch panel. As shown in the first figure, first, in step S101, a substrate (for example, a glass substrate) is provided; in step S102, a conductive layer (for example, an indium tin oxide layer) is coated (or plated) on the glass substrate, and Step S103, patterning the conductive layer by lithography and etching process to form longitudinal sensing of the touch panel; forming an insulating layer, such as a dielectric layer, on the longitudinal sensing in step S104; and insulating in step S105 Coating (or plating) another conductive layer (for example, an indium tin oxide layer) on the layer; in step S106, patterning the another conductive layer by a lithography and etching process to form a lateral sensing of the touch panel; In step S107, a metal layer is coated (or plated) on the formed structure, and The metal layer is patterned to form metal traces, as by step S108. Finally, in step S109, an overcoat is applied on the structure to form a touch structure of the touch panel. After the metal trace is exposed, a touch panel is formed. The touch panel is formed by longitudinal sensing of ITO (Indium Tin Oxide), lateral sensing of the insulating layer and ITO to form a capacitive sensing structure, which can be generated by touching an external electrical conductor (such as a finger). The current changes to accurately calculate the touch position.

The double-layer sensing structure (ie, longitudinal sensing and lateral sensing) of the touch panel is formed in the above manner, which can improve the ITO utilization rate in the touch panel process and reduce the occurrence of process anomalies. However, in the formation process of the foregoing double-layer sensing structure, the edge of the electrode pattern is often displaced due to poor alignment between the first conductive layer and the second conductive layer, resulting in wave pattern on the appearance of the panel, resulting in The overall optical performance of the sensing structure is poor and visible to the outside, affecting the perception

Therefore, an improved manufacturing method is needed to improve the alignment accuracy of the double-layer sensing structure in the capacitive touch panel process, and to further improve the appearance visibility of the sensing structure.

In view of the foregoing description, the present invention provides a method for manufacturing a touch structure of a touch panel, which can improve alignment accuracy when forming a touch structure by stacking double-layer sensing structures, and avoid appearance due to poor alignment. The effect of the wavy lines is exhibited, which affects the visual visibility of the sensing structure.

A first method of the present invention is to provide a method for manufacturing a touch structure of a touch panel, the method comprising the steps of: providing a substrate; forming a first conductive layer on the substrate; partially patterning the first conductive layer to Forming a first electrode pattern, the first electrode pattern including a plurality of first sensing units and a first insulating portion, wherein the plurality of first sensing units are connected to a first direction; forming an insulating layer on the first conductive layer; forming a first layer on the insulating layer a second conductive layer; and simultaneously patterning the first conductive layer and the second conductive layer to form a second electrode pattern, the second electrode pattern comprising a plurality of second sensing units and a second insulating portion, wherein the plurality The second sensing unit is connected to a second direction, and the second direction is different from the first direction; wherein the simultaneously patterning the first conductive layer and the second conductive layer such that the first insulation The portion has substantially the same width and corresponding position as the second insulating portion, and the first sensing units and the second sensing units have substantially the same size and corresponding positions.

A second method of the present invention is to provide a method for manufacturing a touch panel, comprising: providing a substrate; forming a first conductive layer on the substrate; partially patterning the first conductive layer to form a plurality of holes; Forming an insulating layer on the first conductive layer; forming a second conductive layer on the insulating layer; and simultaneously patterning the first conductive layer and the second conductive layer to form a two-layer electrode pattern, the double layer The electrode pattern includes a plurality of first sensing units and a first insulating portion formed by the first conductive layer, and a plurality of second sensing units and second insulating portions formed by the second conductive layer, wherein the The plurality of first sensing units are connected to a first direction, the plurality of second sensing units are connected to a second direction, and the second direction is different from the first direction; wherein the simultaneous patterning The first conductive layer and the second conductive layer are such that the first insulating portion has substantially the same width and corresponding position as the second insulating portion, and the first sensing unit and the second sensing portion Units are essentially identical The size of the corresponding position.

Based on the concept of the present invention, the proposed method further includes forming a protective layer on the patterned second conductive layer.

In accordance with the teachings of the present invention, in the proposed method, the first conductive layer and the The second conductive layer is an Indium Tin Oxide (ITO) layer.

In accordance with the teachings of the present invention, in the proposed method, the formation temperature of the first conductive layer is lower than the formation temperature of the second conductive layer.

In accordance with the teachings of the present invention, in the proposed method, the thickness of the first conductive layer is greater than the thickness of the second conductive layer.

In accordance with the teachings of the present invention, in the proposed method, the crystallization density of the first conductive layer is less than the crystallization density of the second conductive layer.

A third aspect of the present invention is to provide a touch structure of a touch panel having improved appearance visibility. The touch structure includes: a substrate; a first transparent conductive layer patterned to include a plurality of first sensing units and a first insulating portion, wherein the plurality of first sensing units are connected to one a first insulating layer disposed on the first sensing layer; and a second transparent conductive layer patterned to include a plurality of second sensing units and a second insulating portion, wherein the plurality of The second sensing unit is connected to a second direction, and the second direction is different from the first direction; wherein the width of the first insulating portion is smaller than the width of the second insulating portion, and the first transparent conductive layer And a thickness of at least one of the second transparent conductive layers is less than 250 Å.

As described above, the present invention mainly utilizes the difference in film quality and etching rate between two conductive layers, and removes the residual structure of the first conductive layer in the second patterning process, and simultaneously completes the first layer and the second layer. The electrode pattern of the layer; thereby, the alignment problem of the double-layer sensing structure can be solved simply and effectively, and the alignment precision of the double-layer sensing structure can be improved without increasing the complexity and cost of the process.

The foregoing and other features, embodiments, and aspects of the present invention will be further understood from the following detailed description, Advantage.

S101-S109‧‧‧Steps

200, 300, 400, 500‧‧‧ touch structure

210, 310, 410, 510‧‧‧ substrates

220, 320, 420, 520‧‧‧ first conductive layer

222, 322, 422, 522‧‧ ‧ sensing unit

224, 324, 424, 524‧‧ ‧ sensing unit

226, 326, 526‧‧ ‧Insulation

228, 328, 428, 528‧‧ ‧ neck

230, 330, 430, 530‧‧ ‧ insulation structure

240, 340, 440, 540‧‧‧ second conductive layer

242, 342, 442, 542‧‧ ‧ sensing unit

244, 344, 444, 544‧‧ ‧ sensing unit

246, 346, 546‧‧ ‧Insulation

248, 348, 448, 548‧‧ neck

426‧‧‧ring area

446‧‧‧Insulation

D1, D2, d1, d2‧‧‧ width of the insulation

The first figure is a schematic flow diagram illustrating a simplified process of a known capacitive touch panel.

2A through 2D are top plan views showing a partial structure formed in various stages of the manufacturing method of the present invention in accordance with a first embodiment of the present invention.

3A through 3D are top plan views showing a partial structure formed in various stages of the manufacturing method of the present invention in accordance with a second embodiment of the present invention.

4A through 4D are schematic top plan views showing a partial structure formed in various stages of the manufacturing method of the present invention in accordance with a third embodiment of the present invention.

5A to 5C are schematic plan views showing a partial structure formed in each stage of the manufacturing method of the present invention in accordance with a fourth embodiment of the present invention.

The specific embodiments of the present invention are described by way of illustration It is to be understood that the following description and drawings are for the purpose of illustration and description The scope of the present invention is interpreted and limited by the relationship between the shape and the configuration. The enclosure is defined by the scope of the patent application.

As used herein, the term "patterning" refers to a process for forming a particular pattern of a particular material layer during the manufacture of a touch panel, preferably a process for patterning a particular layer of material using lithography and etching processes.

As described above, the present invention aims to improve the alignment accuracy of the double-layer sensing structure in the touch panel, avoiding the appearance of the sensing structure in the appearance due to poor stack alignment accuracy, and avoiding the alignment accuracy due to the stack. Good affects the optical performance of the sensing structure. According to the method of the present invention, the film quality and the etching rate of the two conductive layers are different by using the change of the process conditions (for example, temperature), and the sensing layer conforming to the concept of the present invention is realized by matching different thickness and pattern design of the conductive layer. structure. Various specific embodiments of the touch panel manufacturing method of the present invention will be described below in conjunction with the structures formed in the various stages of the method of the present invention.

Referring to the top plan view of the second to fourth figures, a partial structure formed in each stage of the manufacturing method of the present invention is schematically illustrated in accordance with a first embodiment of the present invention.

First, as shown in FIG. 2A, a substrate (for example, a glass substrate) 210 is provided, and a first conductive layer 220 is formed on the substrate 210. The first conductive layer 220 is patterned to form an insulation of a partial region; that is, in this step, the first conductive layer 220 is etched to form a plurality of sensing units 222, 224, an insulating portion 226 and The electrode pattern of the neck 228, wherein the sensing unit 222 is connected by the neck 228 to a first direction (eg, parallel to the X-axis). The insulating portion 226 is formed such that the sensing units 224 are not connected to each other, and the width D1 of the insulating portion 226 formed by this step is smaller than the width of the designed touch structure insulating portion (to be further explained later).

Next, as shown in FIG. 2B, an insulating layer is formed on the structure shown in FIG. A, and the insulating layer is patterned to form an insulating structure 230 on the neck 228 connecting the two sensing units 222. .

Next, as shown in FIG. C, a second conductive layer 240 is formed on the structure shown in FIG. The second conductive layer 240 is patterned to form an electrode pattern having a plurality of sensing units 242, 244, an insulating portion 246 and a neck portion 248, wherein the sensing unit 244 is connected by a neck 248 to a second direction (eg, Parallel to the direction of the Y axis). The insulating portion 246 is formed such that the sensing units 242 are not connected to each other, and the width D2 of the insulating portion 246 formed by the step is greater than the width D1 of the insulating portion 226; that is, the size ratio of the sensing units 242, 244 The sensing units 222, 224 in the first conductive layer 220 are small.

Finally, the first conductive layer 220 and the second conductive layer 240 are simultaneously patterned (eg, etched) such that the insulating portion 246 has substantially the same width and corresponding position as the insulating portion 226, and after the etching step, the sensing unit The 222, 224 and the sensing units 242, 244 also have substantially the same size and corresponding positions, respectively, forming the touch structure 200 as shown in the second D. More specifically, in the embodiment of the present invention, a preliminary electrode pattern of small area insulation is formed in the first conductive layer 220. Subsequently, the first conductive layer 220 and the second conductive layer 240 are simultaneously etched, and in the etching step, the electrode patterns and structures of the upper and lower sensing layers are simultaneously completed, so that the upper and lower sensing layers respectively have each other The correspondingly sized, equal-sized sensing units 222, 224 and sensing units 242, 244, and the insulating portion having the desired design width (in this example, D2) are shown in Figure 2D.

In the embodiment of the present invention, the film quality is adjusted by using different plating temperature of the conductive layer, thereby causing a difference in etching rate thereof. For example, when indium tin oxide is formed by direct crystallization When the (Indium Tin Oxide, ITO) layer is used as the conductive layer (sensing layer), the plating temperature can be used to adjust the etching rate, and the plating film deposited at a lower temperature has a loose film quality and higher after film formation. Etching rate. In other words, in the embodiment of the present invention, the plating temperature of the first conductive layer (ITO layer) is lower than that of the second conductive layer, so that the film quality (crystal) is looser than the second conductive layer, and the etching rate thereof is lower than that of the second conductive layer. The layer is fast. Therefore, in the process of etching together with the second conductive layer, it is possible to prevent the dense second conductive layer from being etched for a long time to cause lateral etching.

In addition, in the embodiment of the present invention, since the thickness of the second conductive layer is smaller than the thickness of the first conductive layer (ITO) layer, if the thickness of the conductive layer is required to reduce the resistance value of the conductive layer, The second conductive layer above the insulating layer is prevented from wrinkling during high temperature coating. For example, in an embodiment of the invention, the thickness of the second conductive layer can be designed to be less than 450 Å (eg, 300 Å), and the thickness of the first conductive layer is increased to a suitable thickness as needed.

Referring to the top plan view of the third to third figures, a partial structure formed in each stage of the manufacturing method of the present invention is schematically illustrated in accordance with a second embodiment of the present invention. The principle and mechanism of this embodiment are the same as those of the first embodiment shown in FIG. 2A to FIG. 2D, except that the electrode patterns of the first conductive layer and the second conductive layer are adjusted, as follows: Description.

First, as shown in FIG. 3A, a substrate (for example, a glass substrate) 310 is provided, and a first conductive layer 320 is formed on the substrate 310. The first conductive layer 320 is patterned to form a plurality of holes as an insulating portion; that is, in this step, the first conductive layer 320 is etched to form an electrode having a plurality of insulating portions 326 in the conductive layer. pattern.

Next, as shown in FIG. B, an insulating layer is formed on the structure shown in FIG. A, and the insulating layer is patterned to form an insulating structure 330 that shields a portion of the hole.

Next, as shown in FIG. 3C, a second conductive layer 340 is entirely formed on the structure shown in FIG.

Finally, the first conductive layer 320 and the second conductive layer 340 are simultaneously patterned to form a two-layer electrode pattern, and the two-layer electrode pattern includes a plurality of first sensing units 322 formed by the first conductive layer 320, 324 and an insulating portion formed by the insulating portion 326, and a plurality of second sensing units 342, 344 and an insulating portion 346 formed by the second conductive layer 340, wherein the plurality of first sensing units 322 are from the neck 328 is coupled to a first direction (eg, parallel to the X-axis), and the plurality of second sensing units 344 are coupled by a neck 348 to a second direction (eg, parallel to the Y-axis).

In the embodiment of the present invention, the first conductive layer 320 and the second conductive layer 320 are simultaneously patterned in an etching process to form an insulating portion having substantially the same width and corresponding position, and have substantially the same size and corresponding The sensing unit 322, 324 and the sensing unit 342, 344 are configured to form a double-layer sensing touch structure 300 as shown in FIG. More specifically, in the embodiment of the present invention, the holes are formed in the first conductive layer 320, and the first conductive layer 320 and the second conductive layer 340 are simultaneously etched, and in the etching step, Simultaneously completing the electrode patterns and structures of the upper and lower sensing layers, so that the upper and lower sensing layers respectively have sensing units 322, 324 and sensing units 342, 344 corresponding to each other and having the same size, and have the required design width. The insulating portion (in this example, D2) is as shown in the third D diagram.

Similarly, in the embodiment of the present invention, the ITO film quality is adjusted by using the difference in the plating temperature of the conductive layer, thereby causing a difference in etching rate. Compared with the first embodiment shown in the second A to the second D, in the specific embodiments shown in the third A to the third D, the first conductive layer 320 and the second conductive are simultaneously etched. Layer 340, which can remove the first ITO layer and the second ITO The overlapping portions of the layers prevent ITO from remaining in the spacer regions, so that a better visual appearance can be achieved. Similarly, in the specific embodiments shown in the third A to the third D, since the thickness of the second conductive layer is smaller than the thickness of the first conductive layer (ITO) layer, if the resistance value of the conductive layer is lowered When the thickness of the conductive layer needs to be increased, the second conductive layer above the insulating layer can also be prevented from being bucked during the high temperature coating process.

Referring to the top plan view of the fourth to fourth D drawings, a partial structure formed in each stage of the manufacturing method of the present invention is schematically illustrated in accordance with a third embodiment of the present invention. The principle and mechanism of this embodiment are the same as the second embodiment shown in the second embodiment to the second embodiment, and the second embodiment shown in the third to third embodiments. The difference is that the first The electrode patterns of the conductive layer and the second conductive layer are adjusted as described below.

First, as shown in FIG. 4A, a substrate (for example, a glass substrate) 410 is provided, and a first conductive layer 420 is formed on the substrate 410. The first conductive layer 420 is patterned to form an insulating portion. In this particular embodiment, the first conductive layer 420 is patterned (eg, etched) to remove conductive material from at least one of the annular regions 426.

Next, as shown in FIG. 4B, an insulating layer is formed on the structure shown in FIG. A, and the insulating layer is patterned to form an insulating structure 430 which shields the annular portion 426.

Next, as shown in FIG. 4C, a second conductive layer 440 is entirely formed on the structure shown in FIG.

Finally, the first conductive layer 420 and the second conductive layer 440 are simultaneously patterned to form a two-layer electrode pattern, and the two-layer electrode pattern includes a plurality of first sensing units 422 formed by the first conductive layer 420, 424 and the insulating portion formed by the annular region 426, and the plurality of second sensing units 442, 444 and the insulating portion 446 formed by the second conductive layer 440, wherein the plurality of A sensing unit 422 is connected by a neck 428 in a first direction (eg, parallel to the X-axis), and a plurality of second sensing units 444 are connected by a neck 448 to a second direction (eg, parallel to Y) The direction of the axis).

In the embodiment of the present invention, the first conductive layer 420 and the second conductive layer 420 are simultaneously patterned in an etching process to form an insulating portion having substantially the same width and corresponding position, and have substantially the same size and corresponding The position sensing units 422, 424 and the sensing units 442, 444 form a double-layer sensing touch structure 400 as shown in FIG. More specifically, in the embodiment of the present invention, the conductive material in the annular region is removed from the first conductive layer 420, and the first conductive layer 420 and the second conductive layer 440 are simultaneously etched. In the sub-etching step, the electrode patterns and structures of the upper and lower sensing layers are simultaneously completed, so that the upper and lower sensing layers respectively have sensing units 422, 424 and sensing units 442, 444 corresponding to each other and equal in size, and An insulating portion having a desired design width (in this example, D2), as shown in the fourth D.

Similarly, in the embodiment of the present invention, the ITO film quality is adjusted by using the difference in the plating temperature of the conductive layer, thereby causing a difference in etching rate. Compared with the first embodiment shown in the second A to the second D, in the specific embodiments shown in the fourth A to the fourth D, the first conductive layer 420 and the second conductive are simultaneously etched. The layer 440 can remove the portion of the first ITO layer that is not overlapped with the second ITO layer, thereby preventing the ITO from remaining in the spacer region, so that a better visual appearance can be achieved. Similarly, in the specific embodiments shown in FIGS. 4A to 4D, for example, in the embodiment of the present invention, the thickness of the first conductive layer is 700 Å, and the thickness of the second conductive layer is less than 450Å (eg 300Å).

Please refer to the top view of the structure shown in Figures 5A to C, which are rooted. According to a fourth embodiment of the present invention, a partial structure formed in each stage of the manufacturing method of the present invention is schematically illustrated. Compared with the foregoing specific embodiments, the specific embodiments shown in FIGS. 5A to 5C are applicable to a thinner transparent conductive layer touch structure, as described in detail below.

First, as shown in FIG. 5A, a substrate 510 is provided, and a first transparent conductive layer 520, such as an ITO layer, is formed on the substrate 510. The first transparent conductive layer 420 is patterned to form a first electrode pattern composed of a plurality of first sensing units 522, 524 and an insulating portion 526 and a neck portion 528; wherein the sensing unit 522 is connected by the neck 528 In a first direction (eg, parallel to the X-axis), and the formation of the insulating portion 526 causes the sensing units 524 to fail to connect to each other. The insulating portion 526 formed by this step has a width d1.

Next, as shown in FIG. 5B, an insulating layer is formed on the structure shown in FIG. A, and the insulating layer is patterned to form an insulating structure 530 on the neck 528 connecting the two sensing units 522. .

Next, as shown in FIG. 5C, a second transparent conductive layer 540 (eg, an ITO layer) is formed and patterned on the structure shown in FIG. 5B to form a double layer of the touch panel according to the present invention. Sensing structure. The second transparent conductive layer 540 is patterned to form an electrode pattern having a plurality of sensing units 542, 544, an insulating portion 546 and a neck portion 548, wherein the sensing unit 544 is connected to the second direction by the neck portion 548 ( For example, parallel to the direction of the Y axis). The insulating portion 546 is formed such that the sensing units 542 are not connected to each other, and the width d2 of the insulating portion 546 formed by the step is smaller than the width d1 of the insulating portion 526; in other words, in the embodiment of the present invention, the sensing unit The size of 542, 544 is larger than the sensing units 522, 524 in the first transparent conductive layer 520, and can completely cover the sensing units 522, 524 below it.

In the embodiment of the present invention, the first transparent conductive layer 520 and the second transparent conductive layer The thickness of one of the 540 layers is less than 250 Å. For example, the thickness of the first transparent conductive layer 520 may be less than 250 Å, and the thickness of the second transparent conductive layer 540 may be less than 450 Å; or the thickness of the second transparent conductive layer 540 may be less than 250 Å, and the first The thickness of the transparent conductive layer 520 is not particularly limited. According to the embodiment of the present invention, although the electrode patterns of the upper and lower ITO layers are formed separately, the thickness of the insulating layer formed by appropriately selecting the thickness of the insulating layer (d1, d2) is selected because the thickness of the selected single layer of ITO is relatively thin. The sensing unit in the electrode pattern of the upper ITO layer can completely cover the sensing unit of the lower layer, so that the appearance of the texture due to the alignment offset between the two sensing structures can be improved, so that the texture is not easily perceived externally. .

As described above, the present invention provides a touch panel and a method of fabricating the same, which can improve the alignment accuracy of the two-layer sensing structure in the process of the capacitive touch panel and further improve the visibility of the sensing structure. The invention utilizes the difference in film quality and etching rate between the two conductive layers, and removes the residual edge structure of the first conductive layer in the second patterning process, and simultaneously completes the electrode patterns of the first layer and the second layer; Therefore, the alignment problem of the double-layer sensing structure can be solved simply and effectively, and the alignment precision of the double-layer sensing structure can be improved without increasing the complexity and cost of the process, and the cause of the two-layer sensing structure can be improved. The appearance of the texture due to the offset of the position makes the texture difficult to detect externally.

210‧‧‧Substrate

220‧‧‧First conductive layer

222, 224‧‧‧ Sensing unit

226, 246‧‧‧Insulation

228, 248 ‧ ‧ neck

230‧‧‧Insulation structure

240‧‧‧Second conductive layer

242, 244‧‧‧ Sensing unit

D1, D2‧‧‧ width of the insulation

Claims (9)

A method for manufacturing a touch structure of a capacitive touch panel, comprising: providing a substrate; forming a first conductive layer on the substrate; partially patterning the first conductive layer to form a first electrode pattern, The first electrode pattern includes a plurality of first sensing units and a first insulating portion, wherein the plurality of first sensing units are connected to a first direction; an insulating layer is formed on the first conductive layer; Forming a second conductive layer on the layer, the second conductive layer having a thickness smaller than a thickness of the first conductive layer; and simultaneously patterning the first conductive layer and the second conductive layer to form a second electrode pattern, The second electrode pattern includes a plurality of second sensing units and a second insulating portion, wherein the plurality of second sensing units are coupled to a second direction, and the second direction is different from the first direction; Simultaneously patterning the first conductive layer and the second conductive layer such that the first insulating portion has substantially the same width and corresponding position as the second insulating portion, and the first sensing unit and the first sensing unit Second sensing unit Substantially the same size as the corresponding position. The method of claim 1, further comprising: forming a protective layer on the patterned second conductive layer. The method of claim 1, wherein the first conductive layer is formed at a lower temperature than the first The formation temperature of the two conductive layers. The method of claim 1, wherein the first conductive layer has a crystal density which is less than a crystal density of the second conductive layer. A method for manufacturing a touch structure of a capacitive touch panel, comprising: providing a substrate; forming a first conductive layer on the substrate; partially patterning the first conductive layer to form a plurality of holes; Forming an insulating layer on a conductive layer; forming a second conductive layer on the insulating layer; and simultaneously patterning the first conductive layer and the second conductive layer to form a two-layer electrode pattern, the double-layer electrode pattern The plurality of first sensing units and the first insulating portion formed by the first conductive layer, and the plurality of second sensing units and second insulating portions formed by the second conductive layer, wherein the plurality of The first sensing unit is connected to a first direction, the plurality of second sensing units are connected to a second direction, and the second direction is different from the first direction; wherein the The first conductive portion has substantially the same width and corresponding position as the second insulating portion, and the first sensing unit and the second sensing unit have Substantially the same size and It should position. The method of claim 5, further comprising: forming a protective layer on the patterned second conductive layer. The method of claim 5, wherein the first conductive layer is formed at a lower temperature than the first The formation temperature of the two conductive layers. The method of claim 5, wherein the thickness of the second conductive layer is less than the thickness of the first conductive layer. The method of claim 5, wherein the first conductive layer has a crystal density which is less than a crystal density of the second conductive layer.