Thin-film transistor and electronic device

Abstract

To provide an electronic device using a thin-film transistor with which false operation can be prevented.SOLUTION: Provided is a thin-film transistor disposed on one side of a substrate 11, the thin-film transistor comprising: a gate electrode 13; a first insulating film 14 covering the gate electrode; a source electrode 15a and a drain electrode 15b arranged so that a gap between the two overlaps the gate electrode in a plan view; a second insulating film 16 having an opening for exposing a section of each of the source and drain electrodes; a semiconductor layer 18 provided in the opening; an individual electrode 17 having a through-hole overlapping the opening in a plan view and having a section in contact with the drain electrode via a contact hole of the second insulting film, and located so as to overlap the source and drain electrodes in a plan view; and a columnar insulator 21 provided via the opening and the through-hole so as to hide the semiconductor film.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to thin film transistors, electronic devices. [Background technology]

[0002] Japanese Patent Laid-Open Publication No. 2006-58730 (Patent Document 1) describes a display device that includes a drive circuit substrate, a counter substrate, and a liquid crystal layer, and the drive circuit substrate is provided with organic TFTs and storage capacitors corresponding to each pixel, and the source electrodes, drain electrodes, and gate electrodes of the organic TFTs and the storage capacitor electrodes of the storage capacitors are formed of transparent conductive materials to improve the aperture ratio. The organic TFTs in this display device are, for example, bottom-gate TFTs in which the source electrodes, drain electrodes, and organic semiconductor layer are arranged on the outermost surface of the drive circuit substrate. The source electrodes and other elements are covered with an interlayer insulating film and a liquid crystal alignment film.

[0003] However, when the source electrode, drain electrode, and organic semiconductor layer are present on the outermost surface of the substrate as described above, even if an interlayer insulating film or the like is interposed between them and the liquid crystal layer, the voltage of the source electrode or the like is applied to the liquid crystal layer, which can cause unnecessary alignment changes in the liquid crystal layer. Such unnecessary alignment changes are undesirable because they can lead to malfunctions such as false lighting. Note that such malfunctions can occur not only in liquid crystal display devices but also in various electronic devices configured using thin film transistors. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-58730 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of a specific embodiment of the present disclosure is to provide a technique capable of preventing malfunctions in electronic devices that use thin film transistors. [Means for solving the problem]

[0006] [1] A thin film transistor according to one embodiment of the present disclosure includes: A thin film transistor provided on one surface of a substrate, a gate electrode provided on one surface of the substrate; a first insulating film provided on one surface of the substrate and covering the gate electrode; a source electrode and a drain electrode provided on one surface of the first insulating film and arranged so that a gap between them overlaps with the gate electrode in a plan view; a second insulating film provided on one surface of the first insulating film and having openings that expose portions of the source electrode and the drain electrode; a semiconductor layer provided in the opening so as to fill the gap and to contact one end of each of the source electrode and the drain electrode; an individual electrode provided on one surface of the second insulating film, the individual electrode having a through hole overlapping with the opening in a plan view, the individual electrode having a portion in contact with the drain electrode via a contact hole in the second insulating film, and the individual electrode being arranged to overlap with the source electrode and the drain electrode in a plan view; a columnar insulator provided so as to cover the semiconductor film through the opening and the through-hole; The thin film transistor includes: [2] An electronic device according to one aspect of the present disclosure is an electronic device including the thin film transistor according to [1]. The electronic device may be, for example, a liquid crystal display device, an electrophoretic display device, an electrochromic display device, a dye-sensitized solar cell, or a photodetector.

[0007] According to the above configuration, it is possible to provide a technique that can prevent malfunctions in electronic devices that use thin film transistors. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic cross-sectional view showing the configuration of a thin film transistor according to one embodiment and a liquid crystal display device including the thin film transistor. [Figure 2] FIG. 2 is a schematic plan view for explaining the structures of a gate electrode, a source electrode, a drain electrode, and the like provided on the first substrate. [Figure 3] FIG. 3 is a schematic plan view for explaining the structure of pixel electrodes and the like provided on the first substrate. [Figure 4] 4(A) to 4(D) are diagrams illustrating a method for manufacturing a liquid crystal display device according to one embodiment. [Figure 5] 5(A) to 5(C) are diagrams illustrating a method for manufacturing a liquid crystal display device according to one embodiment. [Figure 6] 6(A) to 6(D) are diagrams illustrating a method for manufacturing a liquid crystal display device according to another embodiment. [Figure 7] 7(A) to 7(C) are diagrams illustrating a method for manufacturing a liquid crystal display device according to another embodiment. [Figure 8] FIG. 8 is a photograph showing the appearance of a liquid crystal display device for explaining the effect of spacers in each pixel. [Figure 9] Fig. 9(A) is a schematic cross-sectional view showing an example of the configuration of an electrophoretic display device as an example of an electronic device, and Fig. 9(B) is a schematic cross-sectional view showing an example of the configuration of an electrochromic device as an example of an electronic device. [Figure 10] Fig. 10(A) is a schematic cross-sectional view showing a configuration example of a dye-sensitized solar cell as an example of an electronic device, and Fig. 10(B) is a schematic cross-sectional view showing a configuration example of a photodetector as an example of an electronic device. DETAILED DESCRIPTION OF THE INVENTION

[0009] FIG. 1 is a schematic cross-sectional view showing the configuration of a thin-film transistor according to one embodiment and a liquid crystal display device including the same. The liquid crystal display device shown in FIG. 1 generally includes a first substrate 11 and a second substrate 12 disposed opposite each other, a liquid crystal layer 19 disposed therebetween, a first polarizing plate 31 disposed on the outer side of the first substrate 11 (the side farther from the liquid crystal layer 19), and a second polarizing plate 32 disposed on the outer side of the second substrate 12 (the side farther from the liquid crystal layer 19). When the liquid crystal display device of this embodiment is used as a transmissive liquid crystal display device, it is preferable to arrange a backlight (not shown) so that light is incident from the first substrate 11 side. Although FIG. 1 shows the configuration of one pixel, in reality, a plurality of pixels having similar configurations are arranged in a matrix in a plan view.

[0010] The first substrate 11 is made of a transparent substrate such as a glass substrate or a resin substrate, and is disposed so that one surface thereof faces the second substrate 12. Similarly, the second substrate 12 is made of a transparent substrate such as a glass substrate or a resin substrate, and is disposed so that one surface thereof faces the first substrate 11.

[0011] The gate electrode 13 is a transparent electrode that functions as the gate of the thin film transistor and is provided on one surface of the first substrate. The gate electrode 13 of this embodiment can be formed using a transparent conductive film such as an ITO (indium tin oxide) film.

[0012] The first insulating film 14 is a transparent insulating film configured to cover the gate electrode 13, and is provided on one surface of the first substrate 11. The first insulating film 14 can be formed using, for example, an acrylic photosensitive resin. The portion of the first insulating film 14 that overlaps with the gate electrode 13 functions as a gate insulating film.

[0013] The source electrode 15a and the drain electrode 15b are transparent electrodes that function as the source and drain of the thin film transistor, respectively, and are provided on one surface of the first insulating film 14 that is closer to the liquid crystal layer 19. The source electrode 15a is provided so that one end thereof contacts the semiconductor layer 18. The drain electrode 15b is provided so that one end thereof contacts the semiconductor layer 18. The source electrode 15a and the drain electrode 15b of this embodiment can each be formed using a transparent conductive film such as an ITO (indium tin oxide) film.

[0014] The gate electrode 13, the first insulating film 14, the source electrode 15a, and the drain electrode 15b constitute a thin film transistor. In this embodiment, one thin film transistor is provided for each pixel (see FIG. 2, which will be described later).

[0015] The second insulating film 16 is a transparent insulating film configured to cover the source electrode 15a and the drain electrode 15b, and is provided on one side of the first insulating film 14 closer to the liquid crystal layer 19. The second insulating film 16 can be formed using, for example, an acrylic photosensitive resin. The second insulating film 16 has the function of isolating and insulating the source electrode 15a and the drain electrode 15b from the pixel electrode 17. The second insulating film 16 is provided at a position overlapping the gate electrode 13 in a plan view, and has openings 16a (see FIG. 4(C) and the like described below) that expose one end of each of the source electrode 15a and the drain electrode 15b.

[0016] The pixel electrode 17 is a transparent electrode that functions as an individual electrode for configuring each pixel of the liquid crystal display device, and is provided on one surface of the second insulating film 16 that is closer to the liquid crystal layer 19. The pixel electrode 17 is provided in contact with a part of the drain electrode 15b via a contact hole so as to be electrically connected to the drain electrode 15b. The pixel electrode 17 also has a through-hole 17a (see FIG. 3, described later) in a portion facing the opening 16a. The pixel electrode 17 of this embodiment can be formed using a transparent conductive film such as an ITO (indium tin oxide) film.

[0017] The semiconductor layer 18 is provided inside the opening 16a of the second insulating film 16 so as to contact a portion of each of the source electrode 15a and the drain electrode 15b. The semiconductor layer 18 is disposed opposite the gate electrode 13 via the first insulating film 14, and is disposed so as to overlap at least a portion of the gate electrode 13 in a plan view. The semiconductor layer 18 of this embodiment is made of an organic semiconductor material. Preferred examples of the organic semiconductor material include acene-based materials such as pentacene, and heterocyclic conjugated polymers such as polythiophene. The semiconductor layer 18 may also be a single layer or a laminate structure made of the same material, or a laminate structure made of different materials.

[0018] The liquid crystal layer 19 is provided between one surface of the first substrate 11 (the surface closer to the second substrate 12) and one surface of the second substrate 12 (the surface closer to the first substrate 11). The liquid crystal layer 19 of this embodiment is made of a nematic liquid crystal material. The liquid crystal layer 19 is configured to have a layer thickness of, for example, several μm. The alignment mode of the liquid crystal layer 19 can be selected as appropriate; for example, in this embodiment, the liquid crystal layer 19 is in a vertical alignment mode in which the liquid crystal molecules are aligned perpendicular to each surface of the first substrate 11 and the second substrate 12 when no voltage is applied.

[0019] The counter electrode 20 functions as a common electrode for constituting each pixel of the liquid crystal display device, and is provided on one surface of the second substrate 12 so as to face the pixel electrode 17. The counter electrode 20 of this embodiment can be formed using a transparent conductive film such as an ITO (indium tin oxide) film. A pixel is defined in the region where the pixel electrode 17 and the counter electrode 20 overlap in a plan view.

[0020] The columnar insulators 21 are used as spacers that function to separate the first substrate 11 and the second substrate 12 from each other, and are provided between one surface of the first substrate 11 (the surface closer to the second substrate 12) and one surface of the second substrate 12 (the surface closer to the first substrate 11) at positions that overlap with the gate electrode 13 and the semiconductor layer 18 in a planar view. The columnar insulators 21 are arranged so as to overlap with approximately the centers of the pixel electrodes 17 in a planar view. The columnar insulators 21 can be formed using, for example, an acrylic photosensitive resin. In this embodiment, the columnar insulators 21 are provided on one surface of the common electrode 20 of the second substrate 12 (the surface closer to the liquid crystal layer 19).

[0021] The columnar insulators 21 of this embodiment also have the function of preventing the liquid crystal layer 19 from performing unintended operations due to the voltage generated between the semiconductor layer 18 and the common electrode 20. Furthermore, the columnar insulators 21 of this embodiment also have the function of stabilizing the alignment of the liquid crystal layer 19 and the function of forming the liquid crystal layer 19 into multi-domains within the pixel. These functions will be described in detail later.

[0022] 2 is a schematic plan view for explaining the structures of gate electrodes, source electrodes, drain electrodes, etc. provided on the first substrate. Here, a plan view of gate electrodes, etc. for 12 pixels arranged in 3 rows and 4 columns is shown, but in reality, gate electrodes 13, etc. corresponding to any number of pixels are provided. Note that the cross-sectional view shown in FIG. 1 corresponds to the cross section in the direction of line aa shown in FIG. 2.

[0023] As shown in the figure, the source electrode 15a and the drain electrode 15b are arranged with a gap between them. This gap is located at a position where it overlaps with the gate electrode 13. In the following description, the portion of the semiconductor layer 18 that is located in this gap will be referred to as the channel portion 13a. The length of the channel portion 13a, i.e., the channel length between the source electrode 15a and the drain electrode 15b, can be set to, for example, 10 μm. The width of the channel portion 13a can be set to, for example, 50 μm.

[0024] The gate electrodes 13 are configured such that adjacent ones in the left-right direction in the figure share one gate wiring 113. In the example shown, four gate wirings 13 aligned in the left-right direction are configured as one gate wiring 113. Each gate wiring 113 functions as a signal line that supplies a gate voltage to each gate electrode 13.

[0025] Each source electrode 15a is separated for each pixel, and a source wiring 115a is integrally provided on the left side of each electrode in the drawing. In this embodiment, each source wiring 115a is separated from the others for each pixel. Each source wiring 115a has a shape in a plan view that resembles a T rotated 90 degrees counterclockwise. Each source wiring 115a is disposed between two drain wirings 115b that are adjacent to each other in the vertical direction in the drawing.

[0026] Lower-layer source wirings 113a are intermittently provided below the source wirings 115a, which in this embodiment is in the same layer as the gate electrodes 13. Each source wiring 115a is electrically and physically connected to the two lower-layer source wirings 113a provided below it via contact holes 120 and 121.

[0027] Each lower-layer source wiring 113a is electrically and physically connected to two adjacent source wirings 115a in the vertical direction in the figure via contact holes 120, 121. This allows each source wiring 115a and each lower-layer source wiring 113a to be continuously connected. These continuously connected source wirings 115a and each lower-layer source wiring 113a collectively function as a data line that supplies a voltage to each source electrode 15a.

[0028] Each drain electrode 15b is separated for each pixel and is integrally provided with a drain wiring 115b that is arranged across the right and upper sides in the figure. Each drain wiring 115b has a shape like a reversed F in plan view, with a part of its left end in the figure overlapping one lower-layer source wiring 113a in plan view, and a part of its bottom end in the figure overlapping one gate wiring 113 in plan view.

[0029] 3 is a schematic plan view illustrating the structure of pixel electrodes and the like provided on the first substrate. Here, a plan view of pixel electrodes and the like for 12 pixels arranged in three rows and four columns is shown. Portions of source electrodes 15a, drain electrodes 15b, and the like below each pixel electrode 17 that overlap with each pixel electrode 17 in plan view are indicated by dotted lines, and portions that do not overlap with each pixel electrode 17 are indicated by solid lines.

[0030] Each pixel electrode 17 has a substantially rectangular shape (substantially square shape in this example) in plan view, and is arranged in a matrix. While Fig. 3 shows a plan view of gate electrodes etc. for 12 pixels arranged in 3 rows and 4 columns, in reality, pixel electrodes 17 etc. corresponding to any number of pixels are provided.

[0031] Each pixel electrode 17 has a substantially circular through-hole 17a at its approximate center in plan view. As described above, each through-hole 17a is provided so as to overlap with an opening 16a (see FIG. 1) provided in the second insulating film 16. Each pixel electrode 17 is electrically and physically connected to the underlying drain wiring 115b via a contact hole 122. This allows a voltage to be supplied from each drain electrode 15b to each pixel electrode 17 via each drain wiring 115b.

[0032] Each through hole 17a is arranged so as to overlap, in plan view, with each thin film transistor T, which is composed of the gate electrode 13, the source electrode 15a, the drain electrode 15b, etc. By providing the through hole 17a and the opening 16a, at least a portion of each thin film transistor T, including the channel portion 13a, is exposed without being covered by the pixel electrode 17. Furthermore, each through hole 17a is arranged so as to overlap, in plan view, with each of the columnar insulators 21 described above.

[0033] Each drain wiring 115b is arranged so that its upper portion in the figure overlaps with the gap between adjacent pixel electrodes 17 in the vertical direction in the figure. Also, each drain wiring 115b is arranged so that its right portion in the figure overlaps with the gap between adjacent pixel electrodes 17 in the horizontal direction in the figure. The portions of each drain wiring 115b that overlap with the gap between each pixel electrode 17 have the same potential as the pixel electrode 17 connected to the respective drain wiring 115b. Therefore, these portions can function as inter-pixel electrodes for applying voltage to the liquid crystal layer 19 from the gaps between each pixel electrode 17 on the upper and right sides in the figure.

[0034] That is, when a voltage is applied from pixel electrode 17 to liquid crystal layer 19, the same voltage can be applied to liquid crystal layer 19 on the upper and right sides thereof. This makes it possible to expand the area of ​​the portion to which a voltage can be applied to liquid crystal layer 19, thereby increasing the area of ​​the portion that essentially functions as a pixel and improving the aperture ratio.

[0035] Figures 4(A) to 4(D) and 5(A) to 5(C) are diagrams for explaining a method for manufacturing a liquid crystal display device according to one embodiment. Figures 4(A), 4(C), and 5(A) to 5(C) show cross sections taken along line aa in Figure 2, and Figures 4(B) and 4(D) show cross sections taken along line bb in Figure 2. The order of the steps can be arbitrarily changed as long as no contradictions arise, and other steps can also be added (the same applies to other embodiments described below).

[0036] A gate electrode 13 is formed on one surface of the first substrate 11 (FIG. 4(A)). At this time, a gate wiring 113 and a lower-layer source wiring 113a are also formed (FIG. 4(B)). As an example, an ITO film is formed on one surface of the first substrate 11, and this ITO film is patterned to form the gate electrode 13, the gate wiring 113, and the lower-layer source wiring 113a all at once.

[0037] Next, a first insulating film 14 is formed on one surface of the first substrate 11 so as to cover the gate electrode 13, the gate wiring 113, and the lower-layer source wiring 113a (FIGS. 4(A) and 4(B)). As an example, a photosensitive resin film (e.g., an acrylic resin film) is formed on one surface of the first substrate 11. Then, by patterning the photosensitive resin film, contact holes 120 and 121 are formed to expose a portion of the lower-layer source wiring 113a (FIG. 4(B)).

[0038] Next, a source electrode 15a and a drain electrode 15b are formed on one surface of the first insulating film 14 (FIG. 4(A)). At this time, a source wiring 115a and a drain wiring 115b are also formed (FIG. 4(B)). The source wiring 115a is formed so as to contact a part of the lower-layer source wiring 113a through each of the contact holes 120 and 121. As an example, an ITO film is formed on one surface of the first insulating film 14, and this ITO film is patterned to form the source electrode 15a, the drain electrode 15b, and the source wiring 113a all at once.

[0039] Next, a second insulating film 16 is formed on one surface of the first insulating film 14 so as to cover the source electrode 15a, the drain electrode 15b, etc. (FIGS. 4(C) and 4(D)). As an example, a photosensitive resin film (e.g., an acrylic resin film) is formed on one surface of the first insulating film 14. Then, by patterning the photosensitive resin film, openings 16a are formed at positions overlapping the gate electrode 13 in a plan view, for exposing one end of each of the source electrode 15a and the drain electrode 15b (FIG. 4(C)).

[0040] Next, a pixel electrode 17 having a through-hole 17a is formed on one surface of the second insulating film 16 (FIGS. 4(C) and 4(D)). As an example, an ITO film is formed on one surface of the second insulating film 16, and this ITO film is patterned to form the pixel electrode 17 and the through-hole 17a all at once. The planar shape of the through-hole 17a is not limited to the circular shape exemplified in FIG. 3 above, and can be any shape. The planar shape of the through-hole 17a can be determined during patterning in this process.

[0041] Here, preferred examples of ITO films for each process are described. Polycrystalline ITO films are preferably used as ITO films for forming the source electrode 15a, drain electrode 15b, etc. In contrast, amorphous ITO films are preferably used as ITO films for forming the pixel electrode 17, etc. This is because amorphous ITO films can be etched with weak acids such as oxalic acid, whereas polycrystalline ITO films are almost resistant to etching. Therefore, by adopting the above combination, damage to the source electrode 15a, drain electrode 15b, etc. due to etching can be prevented during patterning of the pixel electrode 17 and through-hole 17a. Note that either polycrystalline ITO films or amorphous ITO films may be used for the gate electrode 13, etc.

[0042] Next, a semiconductor layer 18 is formed in the opening 16a of the second insulating film 16 (FIG. 5A). As an example, the semiconductor layer 18 can be formed by dropping an appropriate amount of organic semiconductor material into the opening 16a using a precision dispenser or inkjet device. It is also preferable to form a passivation film 22 in the opening 16a of the second insulating film 16 so as to overlap the semiconductor layer 18 (FIG. 5A). As an example, the passivation film 22 can be formed by dropping an appropriate amount of passivation material into the opening 16a using a precision dispenser or inkjet device. As the passivation material, for example, a fluororesin known as "Cytop" by AGC Inc. can be used. Alternatively, other materials such as parylene may be used as the passivation material.

[0043] In addition to the above-described method, the semiconductor layer 18 and the passivation film 22 can also be formed by the following method, for example.

[0044] Specifically, first, a semiconductor layer made of an organic semiconductor material is formed on the entire one surface side of the second insulating film 16, and then a passivation film is formed on the entire one surface side of the second insulating film 16 so as to cover the semiconductor layer.

[0045] Next, a thin metal film (e.g., an aluminum film) is formed on one side of the passivation film using a vacuum deposition machine or the like, and then a resist film material is applied to one side of the metal film, and the resist film is patterned by photolithography. The resist film is patterned so that a portion overlapping with the portion that will become the passivation film 22 remains.

[0046] Next, the metal film is removed by wet etching using the patterned resist film as an etching mask, and then the passivation film is removed by dry etching. After that, the resist film and the metal film in the portion overlapping with the resist film are removed. As a result, the portion of the passivation film formed over the entire second insulating film 16 that will become the passivation film 22 remains. In other words, the passivation film 22 is formed.

[0047] Next, dry etching (for example, oxygen plasma) is performed using the passivation film 22 as an etching mask, thereby leaving a portion of the semiconductor layer formed over the entire second insulating film 16 that will become the semiconductor layer 18. That is, the semiconductor layer 18 is formed.

[0048] On the other hand, a counter electrode 20 is formed on one surface of the second substrate 12 (FIG. 5(B)). As an example, an ITO film is formed on one surface of the second substrate 12, and the ITO film is patterned to form the counter electrode 20. One counter electrode 20 may be provided so as to face all the pixel electrodes 17, or multiple counter electrodes 20 may be provided so as to face each of the pixel electrodes 17.

[0049] Next, columnar insulators 21 are formed on one surface of the counter electrode 20 (FIG. 5(B)). As an example, an insulating film material such as a photosensitive acrylic resin is formed to a predetermined thickness (for example, several μm) over the entire one surface of the counter electrode 20, and then exposed and developed using a photomask so that a resin film of a predetermined size and in a predetermined position remains, followed by heat treatment, thereby forming the columnar insulators 21. The columnar insulators 21 may have a diameter of, for example, about 8 μm to 50 μm, but are not limited to this. They may have any size as long as they can block the channel portion 13a and prevent contact with the liquid crystal layer 19.

[0050] Next, if necessary, an alignment film (not shown) is formed on each of the first substrate 11 and the second substrate 12. For example, an alignment film material is applied to one surface of the first substrate 11 and one surface of the second substrate 12 by flexographic printing or inkjet printing, and then heat treatment is performed to form the alignment film. It is preferable that the alignment film is formed only inside a sealant (not shown) for sealing the liquid crystal layer 19.

[0051] The type of alignment film is selected depending on the alignment mode of the liquid crystal layer 19, and for example, a vertical alignment film is used. If necessary, the alignment film may be subjected to alignment treatment (rubbing treatment, photo-alignment treatment, etc.).

[0052] It should be noted that the formation of an alignment film is not essential. If an alignment film is not used, it is preferable to use a so-called self-alignment (SA) liquid crystal material in which the liquid crystal material itself used to form the liquid crystal layer 19 is vertically aligned.

[0053] Next, a sealing material (not shown) is applied in advance to the outer edge portions of both the first substrate 11 and the second substrate 12. Then, the first substrate 11 and the second substrate 12 are superimposed on each other with one surface of each substrate facing each other (FIG. 5(C)). At this time, the first substrate 11 and the second substrate 12 are aligned so that the columnar insulators 21 cover the semiconductor layer 18.

[0054] After the first substrate 11 and the second substrate 12 are stacked together, a sealing seal is formed by hardening the material through heat treatment (or light irradiation treatment). The sealing seal is formed so that it has an opening in one part. A liquid crystal material is vacuum-injected through this opening to form a liquid crystal layer 19 (FIG. 5(C)). For example, a fluorine-based liquid crystal material with a negative dielectric constant can be used as the liquid crystal material. A higher alcohol (SA material) may be added to the liquid crystal material.

[0055] The ODF method (drop injection method) may be used to form the liquid crystal layer 19. In this case, before the first substrate 11 and the second substrate 12 are superimposed, an appropriate amount of liquid crystal material is dropped inside the sealing seal.

[0056] In this way, a liquid crystal display device equipped with thin film transistors is completed.

[0057] 6(A) to 6(D) and 7(A) to 7(C) are diagrams for explaining a manufacturing method of a liquid crystal display device according to another embodiment. Each diagram shows a cross section along line aa in FIG. 2. Note that the steps up to forming pixel electrodes 17 and the like on one surface of the first substrate 11 and the steps up to forming columnar insulators 21 on one surface of the second substrate 12 are the same as those in the manufacturing method of the above-described embodiment, and therefore only the differences will be described below.

[0058] An alignment film 23 is formed on one surface of the first substrate 11 so as to cover the second insulating film 16, the pixel electrode 17, etc. (FIG. 6(A)). Similarly, an alignment film 24 is formed on one surface of the second substrate 12 so as to cover the counter electrode 20 (FIG. 7(A)). For example, an alignment film material is applied to each of one surface of the first substrate 11 and one surface of the second substrate 12 by flexographic printing, inkjet printing, or the like. It is preferable that the alignment film is formed only inside a sealant (not shown) for sealing the liquid crystal layer 19. The type of alignment film is selected depending on the alignment mode of the liquid crystal layer 19, and for example, a vertical alignment film is used. Furthermore, the alignment film may be subjected to alignment treatment (rubbing treatment, photo-alignment treatment, etc.) as needed.

[0059] Next, an etchant 25 for dissolving the alignment film 23 is dropped from one surface of the first substrate 11 through the through-hole 17a of the pixel electrode 17 and the opening 16a of the second insulating film 16 onto the bottom of the opening 16a (FIG. 6(B)). This partially dissolves the alignment film 23, exposing one end of each of the source electrode 15a and the drain electrode 15b and one surface of the first insulating film 14 at the bottom of the opening 16a (FIG. 6(C)). Thereafter, the dropped etchant 25 is washed away using pure water or the like. Thereafter, the alignment film 23 is subjected to a heat treatment. For example, the alignment film can be hardened by baking at 200°C for 1.5 hours. Note that this baking may be performed before patterning using droplets of the etchant 25. Furthermore, an alignment treatment is performed as necessary.

[0060] The etchant 25 can be dispensed using, for example, a precision dispenser or an inkjet device. The etchant 25 can be, for example, NMP (N-methyl-2-pyrrolidone), other polar solvents, alkaline solutions (e.g., KOH, NaOH), or gelled solutions thereof. Gelded solutions are compatible with precision dispensers, allowing for small droplet sizes. Because the inner walls of the openings 16a are tapered, dispensing an appropriate amount of etchant 25 prevents the etchant 25 from spreading beyond the openings 16a. This allows for control of the extent to which the alignment film 23 is etched. Using an inkjet device allows for the droplet size of the etchant 25 to be controlled to a few picoliters. This is also preferable because it allows for high-speed dispensing of the etchant 25 at multiple locations arranged in a matrix. This method allows for precise patterning of the alignment film 23 without using photolithography techniques such as photomasks.

[0061] Next, the semiconductor layer 18 is formed in the opening 16a of the second insulating film 16 (FIG. 6(D)). As in the above-described embodiment, the semiconductor layer 18 can be formed by, for example, dropping an appropriate amount of organic semiconductor material into the opening 16a using a precision dispenser or inkjet device. Note that, although the example shown here is one in which the passivation film 22 is not formed, the passivation film 22 may be formed so as to overlap the semiconductor layer 18, as in the above-described embodiment.

[0062] If the alignment film 23 were formed after the semiconductor layer 18, there is a high possibility that the semiconductor layer 18 would be damaged by the organic solvent contained in the alignment film material, the heat during baking, the alignment treatment (particularly the rubbing treatment), and the like. This is particularly noticeable when the passivation film 22 is not formed. In contrast, in the above-described manufacturing method, the semiconductor layer 18 is formed after the alignment film 23 is formed, so the semiconductor layer 18 is not damaged as described above. As a result, a thin-film transistor using the semiconductor layer 18 can achieve good characteristics.

[0063] Next, a sealing material (not shown) is applied in advance to the outer edge portions of both the first substrate 11 and the second substrate 12. Then, the first substrate 11 and the second substrate 12 are superimposed on each other with one surface of each substrate facing each other (FIG. 7(B)). At this time, the first substrate 11 and the second substrate 12 are aligned so that the columnar insulators 21 cover the semiconductor layer 18.

[0064] After the first substrate 11 and the second substrate 12 are stacked together, a sealing seal is formed by hardening the material through heat treatment (or light irradiation treatment). The sealing seal is formed so that it has an opening in one part. A liquid crystal material is vacuum-injected through this opening to form a liquid crystal layer 19 (FIG. 7(C)). For example, a fluorine-based liquid crystal material with a negative dielectric constant can be used as the liquid crystal material. A higher alcohol (SA material) may be added to the liquid crystal material.

[0065] In this way, a liquid crystal display device equipped with thin film transistors is completed.

[0066] Next, we will explain in detail the effects of providing the columnar insulators 21 corresponding to each pixel electrode 17 in the liquid crystal display device of this embodiment. The main effects are to prevent the liquid crystal layer 19 from performing unintended operations due to the potential difference generated between the semiconductor layer 18 and the common electrode 20, and to stabilize the orientation of the liquid crystal layer 19 in each pixel and to form a multi-domain liquid crystal layer 19 within the pixel.

[0067] First, the former effect will be explained. In a liquid crystal display device having a general thin film transistor, the thin film transistor is formed near the edge of the pixel (i.e., outside the pixel). In a reflective liquid crystal display device, the thin film transistor may be formed below the pixel electrode (metal reflective electrode). In this case, the pixel electrode is formed so as to cover the thin film transistor, particularly the channel portion.

[0068] Furthermore, in liquid crystal display devices equipped with general thin film transistors, a light-shielding film is generally formed in the area of ​​the thin film transistor due to the influence of light-induced malfunction. In contrast, in the liquid crystal display device of this embodiment, the semiconductor layer 18 must be formed after the patterning process required for forming the pixel electrodes 17. This is because organic semiconductor materials cannot withstand the patterning process. Therefore, the semiconductor layer 18 is exposed on one side of the first substrate 11. In this embodiment, the semiconductor layer 18 is formed using a material capable of forming a transparent semiconductor layer, making it possible to realize a fully transparent liquid crystal display device.

[0069] On the other hand, if the semiconductor layer 18 of the thin-film transistor is present within a pixel, the liquid crystal layer 19 may malfunction, i.e., light may be turned on or off in unintended areas (changes in the alignment of the liquid crystal layer 19). This is due to the voltages generated in the various components of the thin-film transistor. Specifically, an off voltage is applied to the semiconductor layer 18 except when a pixel voltage is written, and the same voltage as the pixel electrode 17 is applied when writing. Furthermore, a different pixel voltage is applied to the source electrode 15a except when a pixel voltage is written, and the same voltage as the pixel electrode 17 is applied when writing. The same voltage as the pixel electrode 17 is always applied to the drain electrode 15b. Therefore, in the channel portion 13a where the semiconductor layer 18 and the source electrode 15a are the outermost surfaces, a voltage different from the normal voltage is applied to the liquid crystal layer 19, causing the malfunction described above.

[0070] To address this problem, columnar insulators 21 made of a resin film (insulating film) are provided to cover the channel portion 13a including the semiconductor layer 18, etc., thereby preventing the voltage generated in the channel portion 13a from being applied to the liquid crystal layer 19. Furthermore, by making the size (size in a plan view) of the columnar insulators 21 slightly larger than the minimum area required to cover the channel portion 13a, it is possible to ensure that no liquid crystal layer 19 is present in the area overlapping with the channel portion 13a. This prevents unintended alignment changes in the liquid crystal layer 19 and prevents malfunctions.

[0071] Next, the latter effect will be explained. Here, we will consider a liquid crystal display device having a vertically aligned liquid crystal layer 19. If no alignment treatment is performed or no alignment control structure (protrusions, slits, etc.) is provided, the direction in which the liquid crystal molecules in the liquid crystal layer 19 tilt when a voltage is applied will be random. If the tilt direction of the liquid crystal molecules in a pixel is misaligned with the polarization axis of the polarizers 31 and 32, birefringence occurs in the light passing through the liquid crystal layer 19, resulting in a bright appearance. On the other hand, if the tilt direction of the liquid crystal molecules in a pixel is parallel to or perpendicular to the polarization axis of the polarizers 31 and 32, no birefringence occurs in the light passing through the liquid crystal layer 19, resulting in a dark appearance.

[0072] In the liquid crystal display device of this embodiment, the columnar insulator 21 is provided approximately at the center of the pixel electrode 17, so that the liquid crystal molecules tilt around the columnar insulator 21. As a result, as shown in the external appearance photograph of the pixel in the upper part of FIG. 8, the position where a dark state occurs and its shape in plan view can be made uniform in each pixel. That is, the alignment of the liquid crystal layer 19 can be stabilized. Furthermore, when a voltage is applied to the liquid crystal layer 19, the liquid crystal molecules tilt in multiple directions around the columnar insulator 21, so that each pixel can be uniformly formed into a multi-domain. That is, the action of the columnar insulator 21 can generate multiple alignment domains with mutually different alignment directions.

[0073] In contrast, when the columnar insulators 21 are not provided, the positions where dark states occur and the planar shapes thereof become non-uniform in each pixel, as shown in the external appearance photograph of the pixel in the lower part of Fig. 8. In other words, the alignment of the liquid crystal layer 19 becomes unstable. Furthermore, the multi-domain structure of each pixel becomes non-uniform.

[0074] The above effect can be obtained even if the diameter of the columnar insulators 21 is several micrometers. When the first polarizer 13 and the second polarizer 32 are arranged in a crossed Nicol configuration, the area where the columnar insulators 21 are located always appears dark. However, since the diameter of the columnar insulators 21 is approximately the same as that of a typical spherical spacer, there is virtually no decrease in transmittance. Since the size of the columnar insulators 21 is smaller than that of conventional alignment control structures (protrusions, slits, etc.), a multi-domain wide-viewing-angle liquid crystal display device with little transmittance loss can be obtained.

[0075] According to the above-described embodiment, a technique is provided that can prevent malfunctions in a liquid crystal display device, which is an example of an electronic device that uses thin film transistors.

[0076] The present disclosure is not limited to the above-described embodiment, and various modifications can be made within the scope of the present disclosure. For example, in the above-described embodiment, the passivation film 22 is patterned to selectively cover the semiconductor layer 18. However, the passivation film may be provided over the entire one surface of the second insulating film 16 so as to cover the semiconductor layer 18, pixel electrodes 17, etc. When an alignment film is provided on the first substrate 11, the passivation film may be provided over the entire one surface of the second insulating film 16 as long as the passivation film does not repel the alignment film. On the other hand, in the case of a passivation film that repels the alignment film, the passivation film 22 is preferably selectively patterned relative to the position of the semiconductor layer 18, as in the above-described embodiment.

[0077] Furthermore, in the above-described embodiment, a liquid crystal display device has been described as an example of an electronic device having a thin film transistor according to the present disclosure, but the thin film transistor according to the present disclosure can also be applied to other electronic devices.

[0078] 9(A) is a schematic cross-sectional view showing an example of the configuration of an electrophoretic display device as an example of an electronic device. The electrophoretic display device shown in the figure basically has the same configuration as the liquid crystal display device shown in FIG. 1 etc., except that the liquid crystal layer 19 is replaced with an electrophoretic layer 29. The same reference numerals are used for components common to both, and detailed descriptions of these components will be omitted.

[0079] The electrophoretic layer 29 is formed by mixing, for example, white and black pigment particles in a transparent dispersion medium, and the white and black pigment particles are electrically charged with different polarities (positive and negative). Although not shown, the electrophoretic layer 29 may be formed by arranging a large number of microcapsules containing a transparent dispersion medium containing pigment particles. By applying a voltage using the pixel electrodes 17, the white and black pigment particles can be caused to migrate in the transparent dispersion medium. A pixel in which white pigment particles have migrated on the front side (e.g., the second substrate 12 side) displays white, and a pixel in which black pigment particles have migrated displays black. Note that the color of the pigment particles is not limited to white or black, and any color can be used to display that color.

[0080] The columnar insulators 21 may be formed, for example, in a lattice shape in a plan view so as to surround each pixel electrode 17. In this case, too, the columnar insulators 21 are arranged corresponding to the positions of each semiconductor layer 18. Note that the columnar insulators 21 do not necessarily have to be formed in a lattice shape, and may be columnar in shape similar to that of the liquid crystal display device of the above-described embodiment.

[0081] In such an electrophoretic display device, the columnar insulators 21 cover and conceal the semiconductor layers 18, thereby preventing malfunction of the electrophoretic layer 29.

[0082] 9(B) is a schematic cross-sectional view showing an example of the configuration of an electrochromic device as an example of an electronic device. The illustrated electrochromic device basically has the same configuration as the liquid crystal display device shown in FIG. 1 and the like, except that the liquid crystal layer 19 is replaced with an electrolyte layer 39. The same reference numerals are used for components common to both devices, and detailed descriptions of these components will be omitted. The electrochromic device described here may be used for display purposes, or may be used for other purposes, such as a light-control window (so-called light-control glass).

[0083] The electrolyte layer 39 is a layer that has the property of undergoing an electrochemical oxidation-reduction reaction when a voltage is applied between the pixel electrode 17 and the counter electrode 20, resulting in a reversible change in color. Although the illustrated example shows a bulk-type electrolyte layer 39, an interface-type electrolyte layer may also be used.

[0084] In such an electrochromic device, the columnar insulators 21 cover and conceal the semiconductor layers 18, thereby preventing malfunction in the electrolyte layer 39.

[0085] 10(A) is a schematic cross-sectional view showing an example of the configuration of a dye-sensitized solar cell as an example of an electronic device. The illustrated dye-sensitized solar cell basically has the same configuration as the liquid crystal display device shown in FIG. 1 etc., except that the liquid crystal layer 19 is replaced with an electrolyte layer 49 and that the individual electrodes 17 are coated with titanium oxide particles 50. The same reference numerals are used for components common to both, and detailed description of these components will be omitted.

[0086] A dye is adsorbed onto the titanium oxide particles 50. When light strikes this dye, the dye becomes excited and releases electrons. The released electrons are injected into the titanium oxide particles 50 and move to the individual electrodes 17. The extraction of the current generated by these electrons can be controlled by a thin-film transistor. The electrons move from the thin-film transistor to the counter electrode 20 via an external circuit (not shown), and are passed on to iodine contained in the electrolyte layer 49. This generates iodide ions. These iodide ions absorb light and transfer electrons to the oxidized dye. This regenerates the dye, and the iodide ions become iodine again. This cycle is repeated, converting light energy into electrical energy.

[0087] In such a dye-sensitized solar cell, the columnar insulators 21 cover and conceal the semiconductor layers 18, thereby preventing malfunction in the electrolyte layer 49.

[0088] 10(B) is a schematic cross-sectional view showing an example of the configuration of a photodetector as an example of an electronic device. The photodetector shown in the figure has a configuration basically similar to that of the liquid crystal display device shown in FIG. 1 etc., except that a photodiode 59 and a conductor 60 are provided in the space where the liquid crystal layer 19 was provided. The same reference numerals are used for components common to both, and detailed description of these components will be omitted.

[0089] Each photodiode 59 is configured to have an active layer sandwiched between electrodes. In the illustrated example, each photodiode 59 shares a counter electrode 20 as one of its electrodes, and the other electrode is configured individually. The active layer is a layer for generating an electromotive force by light incident from outside. Although not shown here, functional layers such as a carrier injection layer, a carrier blocking layer, and a transport layer may be provided between the active layer and each electrode.

[0090] Each conductor 60 electrically and physically connects each photodiode 59 to each individual electrode 17, and is disposed between each photodiode 59 and each individual electrode 17. For example, a resin containing gold-coated microspheres can be used as the conductor 60. The conductor 60 may also be an anisotropic conductive film.

[0091] In this photodetector, the photodiodes 59 are arranged in a matrix in plan view, so that the photocurrent generated by the incident light can be detected in a matrix. The photocurrent generated in each photodiode 59 can be output to the outside via each thin film transistor.

[0092] In such a photodetector, each semiconductor layer 18 is covered with the columnar insulator 21, thereby preventing the thin film transistor from malfunctioning due to incident light.

[0093] The present disclosure has the following features. (Appendix 1) A thin film transistor provided on one surface of a substrate, a gate electrode provided on one surface of the substrate; a first insulating film provided on one surface of the substrate and covering the gate electrode; a source electrode and a drain electrode provided on one surface of the first insulating film and arranged so that a gap between them overlaps with the gate electrode in a plan view; a second insulating film provided on one surface of the first insulating film and having openings that expose portions of the source electrode and the drain electrode; a semiconductor layer provided in the opening so as to fill the gap and to contact one end of each of the source electrode and the drain electrode; an individual electrode provided on one surface of the second insulating film, the individual electrode having a through hole overlapping with the opening in a plan view, the individual electrode having a portion in contact with the drain electrode via a contact hole in the second insulating film, and the individual electrode being arranged to overlap with the source electrode and the drain electrode in a plan view; a columnar insulator provided so as to cover the semiconductor film through the opening and the through-hole; a thin film transistor comprising: (Appendix 2) The semiconductor layer is made of an organic semiconductor material. 2. The thin film transistor of claim 1. (Appendix 3) The semiconductor device further includes a transparent passivation film provided between the semiconductor layer and the pillar-shaped insulator and covering the semiconductor layer. 3. The thin film transistor according to claim 1 or 2. (Appendix 4) the source electrode and the drain electrode are made of a polycrystalline ITO film, The individual electrodes are formed using an amorphous ITO film. 4. A thin film transistor according to any one of claims 1 to 3. (Appendix 5) The individual electrodes are generally rectangular in plan view, the through hole is disposed at approximately the center of the individual electrode in a plan view; 5. A thin film transistor according to any one of claims 1 to 4. (Appendix 6) A liquid crystal display device comprising the thin film transistor according to any one of claims 1 to 5, a transparent first substrate on which the thin film transistor is provided; a transparent second substrate having a counter electrode and disposed so that the counter electrode faces the first substrate; a liquid crystal layer disposed between the individual electrodes of the first substrate and the counter electrode of the second substrate; A liquid crystal display device comprising: (Appendix 7) the columnar insulators are used as spacers for separating the first substrate and the second substrate; 7. A liquid crystal display device according to claim 6. (Appendix 8) the columnar insulator is provided at a position that overlaps substantially the center of the individual electrode in a plan view; 8. The liquid crystal display device according to claim 6 or 7. (Appendix 9) the liquid crystal layer is vertically aligned when no voltage is applied, and when a voltage is applied, a plurality of alignment domains having mutually different alignment directions are generated by the action of the columnar insulators; 9. A liquid crystal display device according to claim 8. (Appendix 10) An electronic device comprising the thin film transistor according to any one of claims 1 to 5. [Explanation of symbols]

[0094] 11: first substrate, 12: second substrate, 13: gate electrode, 13a: channel portion, 14: first insulating film, 15a: source electrode, 15b: drain electrode, 16: second insulating film, 17: pixel electrode (individual electrode), 18: semiconductor layer, 19: liquid crystal layer, 20: counter electrode, 21: columnar insulator, 22: passivation film, 31: first polarizer, 32: second polarizer

Claims

1. A thin film transistor provided on one surface of a substrate, a gate electrode provided on one surface of the substrate; a first insulating film provided on one surface of the substrate and covering the gate electrode; a source electrode and a drain electrode provided on one surface of the first insulating film and arranged such that a gap between them overlaps with the gate electrode in a plan view; a second insulating film provided on one surface of the first insulating film and having openings exposing portions of the source electrode and the drain electrode; a semiconductor layer provided in the opening so as to fill the gap and to contact one end of each of the source electrode and the drain electrode; an individual electrode provided on one surface of the second insulating film, the individual electrode having a through hole overlapping with the opening in a plan view, the individual electrode having a portion contacting the drain electrode via a contact hole in the second insulating film, and the individual electrode being arranged to overlap with the source electrode and the drain electrode in a plan view; a columnar insulator provided so as to cover the semiconductor film through the opening and the through-hole; a thin film transistor comprising:

2. The semiconductor layer is made of an organic semiconductor material. The thin film transistor of claim 1 .

3. The semiconductor device further includes a transparent passivation film provided between the semiconductor layer and the pillar-shaped insulator and covering the semiconductor layer. The thin film transistor of claim 1 .

4. the source electrode and the drain electrode are made of a polycrystalline ITO film, The individual electrodes are formed using an amorphous ITO film. The thin film transistor of claim 1 .

5. The individual electrodes are generally rectangular in plan view, the through hole is disposed at approximately the center of the individual electrode in a plan view; The thin film transistor of claim 1 .

6. A liquid crystal display device comprising the thin film transistor according to claim 1, a transparent first substrate on which the thin film transistor is provided; a transparent second substrate having a counter electrode and disposed so that the counter electrode faces the first substrate; a liquid crystal layer disposed between the individual electrodes of the first substrate and the counter electrode of the second substrate; A liquid crystal display device comprising:

7. the columnar insulator is used as a spacer for separating the first substrate and the second substrate; The liquid crystal display device according to claim 6 .

8. the columnar insulator is provided at a position that overlaps substantially the center of the individual electrode in a plan view; The liquid crystal display device according to claim 6 .

9. the liquid crystal layer is vertically aligned when no voltage is applied, and when a voltage is applied, a plurality of alignment domains having mutually different alignment directions are generated by the action of the columnar insulators; The liquid crystal display device according to claim 8 .

10. An electronic device comprising the thin film transistor of claim 1.

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