Display device and method for manufacturing the display device

A display device and a method for manufacturing the same, for discharging static electricity generated in the manufacturing process of a display device using a mechanical shutter and thus preventing the mechanical shutter from being deformed by the static electricity are provided. The display device includes a TFT substrate having thin film transistors thereon respectively provided with a plurality of mechanical shutters located in a matrix and also having terminals thereon for supplying a signal to the thin film transistors from outside; and a counter substrate joined with the TFT substrate. Along at least one of an edge of the TFT substrate and an edge of the counter substrate, an injection opening for injecting an insulating liquid into an area between the TFT substrate and the counter substrate and a ground electrode for covering at least a part of an inner surface of the injection opening are provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2011-278731, filed on 20 Dec. 2011, the entire contents of which are incorporated herein by reference.

FIELD

The present invention relates to a display device and a method for manufacturing the same, and specifically to a display device using a mechanical shutter and a method for manufacturing the same.

BACKGROUND

Recently, a display device using a mechanical shutter to which a MEMS (Micro Electro Mechanical Systems) technology is applied (hereinafter, such a shutter will be referred to as a “MEMS shutter”) is a target of attention. A display device using a MEMS shutter (hereinafter, referred to as a “MEMS display device”) opens or closes a MEMS shutter provided in correspondence with each of pixels, at a high speed by use of a thin film transistor (TFT), to control the amount of light to be transmitted through the shutter, and thus adjusts the brightness of an image (see, for example, Japanese Laid-Open Patent Publication No. 2008-197668). A mainstream gray scale system of such MEMS display devices is a time-ratio gray scale system of displaying an image by sequentially switching light provided from one of red, green and blue LEDs of an LED backlight unit to light provided from another LED of the LED backlight unit. Accordingly, the MEMS display devices have features that polarizing films or color filters used for a display device are not required; and as compared with a display device, the utilization factor of backlight is about 10 times higher, the power consumption is no more than half, and the color reproducibility is superior.

A MEMS display device is formed as follows. A TFT including switching elements for driving MEMS shutters, and gate and data drivers for driving the switching elements is formed on a substrate. Terminals for supplying signals from an external device to the TFT are also formed on the substrate. Usually for forming a MEMS display device, on the TFT substrate having the TFTs and the terminals formed thereon, a passivation film (insulating film) for covering the TFTs and the terminals is formed, and MEMS shutters are formed on the passivation film. An insulating film is formed to cover the MEMS shutters except for a part of each MEMS shutter which is to be electrically connected to a terminal. A movable section of the MEMS shutter has a hollow structure. Therefore, the insulating film is formed by CVD (Chemical Vapor Deposition) or the like on the entirety of a surface of the TFT substrate having the MEMS shutters formed thereon, so that a side surface and a bottom surface of the movable section is covered with the insulating film. Then, a counter substrate is joined to the TFT substrate. The terminals formed on the TFT substrate need to be supplied with signals from an external device. Therefore, the TFT substrate and the counter substrate are joined together such that the counter substrate does not cover a top surface of each terminal.

FIG. 10is a schematic view of a pixel of a conventional MEMS display device. Elements of a display panel including a MEMS shutter on a TFT substrate adheres to the substrate or is deformed by static electricity. A spring structure formed of springs8bconnected to move the MEMS shutter is expanded or contracted by an electrical signal and thus moves a blocking section8aof the MEMS shutter. A manufacturing process of the panel including a MEMS shutter on a power supply section (or wiring section)1bof the TFT substrate includes a step of enclosing an insulating liquid such as silicone oil or the like to an area between the substrate having the MEMS shutter thereon and a counter substrate having a window. This step is carried out for the purpose of preventing the springs8bconnected to move the MEMS shutter from adhering to the TFT substrate having the MEMS shutter thereon or to the counter substrate having the window.

However, at the time of enclosure of the insulating liquid, static electricity is generated by friction of the liquid. Therefore, the MEMS shutter cannot be kept at a proper position or cannot be kept in a state of floating in the insulating liquid, and thus adheres to the substrate.

The present invention made in light of the above-described problem has an object of providing a display device and a method for manufacturing the same, for removing static electricity generated by friction at the time of enclosure of the insulating liquid and thus preventing a blocking section and springs of a MEMS shutter from adhering to the substrate or from being deformed.

SUMMARY

An embodiment of the present invention provides a display device comprising a TFT substrate having thin film transistors thereon respectively provided with a plurality of MEMS shutters located in a matrix and also having terminals thereon for supplying a signal to the thin film transistors from outside; and a counter substrate joined with the TFT substrate. Along at least one of an edge of the TFT substrate and an edge of the counter substrate, an injection opening for injecting an insulating liquid into an area between the TFT substrate and the counter substrate and a ground electrode for covering at least a part of an inner surface of the injection opening are provided.

An embodiment of the present invention provides a method for manufacturing a display device, comprising forming, on a TFT substrate, thin film transistor and terminals for supplying a signal to the thin film transistors from outside; forming, on the TFT substrate having the thin film transistors and the terminals formed thereon, a passivation film for covering the thin film transistors and the terminals; forming, on the passivation film, a plurality of MEMS shutters located in a matrix and provided respectively in correspondence with the thin film transistors; joining together the counter substrate to the TFT substrate; and forming a ground electrode for covering at least a part of an injection opening for injecting an insulating liquid into an area between the TFT substrate and a counter substrate, the ground electrode being formed along at least one of an edge of the TFT substrate and an edge of the counter substrate.

DESCRIPTION OF EMBODIMENTS

As described above, a display device according to the present invention has a feature that static electricity, generated in a step of injecting an insulating liquid into an area where a MEMS shutter is to be located, is removed by a ground electrode which is formed at an injection opening for the insulating liquid and at least a part of an inner surface of the injection opening.

The ground electrode needs to have at least a shape and a structure which allow the ground electrode to be conductive to an external ground electrode. In order to improve the function of removing the static electricity, it is preferable that the ground electrode has a shape covering the entirety of an area from the injection opening to an injection path, not only an area in the vicinity of the edge of the injection opening. For example, as shown inFIG. 1andFIG. 6throughFIG. 8referred to later, it is preferable that a ground electrode7is located on at least a surface of a TFT substrate1or a surface of a counter substrate2so as to face the counter substrate2or the TFT substrate1, from an area including an injection opening4and an injection path4aalong an edge of the TFT substrate1and the counter substrate2.

It is preferable that the ground electrode formed on at least one of the TFT substrate and the counter substrate is structured to have conductivity to a metal part or a ground electrode part which forms a section used in the step of injecting the insulating liquid. For example, as shown inFIG. 3referred to later, it is preferable that a part of the ground electrode7is exposed outside from the area where the TFT substrate1and the counter substrate2are joined together, so that this part is used as a conductive part7a. The conductive part7ais connected to a part of an injection section9used for the injection step, or to a part of securing sections (jigs20A and20B shown inFIG. 3) for securing the TFT substrate1and the counter substrate2, the part being grounded or being kept at a ground potential.

The ground electrode formed on the TFT substrate and/or the counter substrate may be formed of a metal material such as copper, aluminum or the like, a conductive paste, a carbon nanotube film, an oxide material such as an ITO film or the like, or any other material, as long as the material has conductivity. Preferably, the ground electrode to be formed on the TFT substrate and/or the counter substrate is produced at the same time as an ITO film used for a wiring line in the case where the ground electrode is formed on the TFT substrate, and at the same time as an aluminum film used for a wiring line in the case where the ground electrode is formed on the counter substrate.

Now, with reference toFIG. 9, a structure of the MEMS shutter usable for the present invention will be described.FIG. 9shows a structure of the MEMS shutter130ausable for the display device100in an embodiment according to the present invention.FIG. 9shows one MEMS shutter130afor the convenience of description, but the display device100in an embodiment according to the present invention includes a plurality of MEMS shutters130ashown inFIG. 9arranged in a matrix on a substrate110.

The MEMS shutter130aincludes a shutter131, first springs136a,136b,136cand136d, second springs137a,137b,137cand137d, and anchor sections138a,138b,138c,138d,139aand139b. The shutter131has openings134, and a main body of the shutter131acts as a light blocking section. Although not shown, a counter substrate140(seeFIG. 4) has a light-transmissive section for transmitting light. The counter substrate140is joined to the substrate110via a sealing material or the like such that the openings134of the shutter131and the light-transmissive section of the counter substrate140generally overlap each other in a planar direction. The display device100is structured such that light supplied from behind the counter substrate140and transmitted through the light-transmissive section of the counter substrate140is transmitted through the openings134of the shutter131and thus is visually recognized by the human eye. The MEMS shutter130ain this embodiment is merely an example of MEMS shutter usable for the display device100according to the present invention. The MEMS shutter usable for a display device according to the present invention is not limited to having the structure shown inFIG. 9, but may be any MEMS shutter which can be driven by a switching element.

One side of the shutter131is connected to the anchor sections138aand138bvia the first springs136aand136b. The anchor sections138aand138bhave a function of supporting the shutter131such that shutter131floats above a surface of the substrate110together with the first springs136aand136b. The anchor section138ais electrically connected to the first spring136a, and the anchor section138bis electrically connected to the first spring136b. The anchor section138aand138bare each supplied with a bias potential from a switching element104(seeFIG. 5) and thus the first springs136aand136bare each supplied with the bias potential. The second springs137aand137bare electrically connected to the anchor section139a. The anchor section139ahas a function of supporting the second springs137aand137bsuch that the second springs137aand137bfloat above the surface of the substrate110. The anchor section139ais supplied with a ground potential, and thus the second springs137aand137bare each supplied with the ground potential. The anchor section139amay be supplied with a predetermined potential instead of the ground potential. This is also applicable to the following description regarding the ground potential.

The other side of the shutter131is connected to the anchor sections138cand138dvia the first springs136cand136d. The anchor sections138cand138dhave a function of supporting the shutter131such that shutter131floats above the surface of the substrate110together with the first springs136cand136d. The anchor section138cis electrically connected to the first spring136c, and the anchor section138dis electrically connected to the first spring136d. The anchor section138cand183dare each supplied with a bias potential from the switching element104, and thus the first springs136cand136dare each supplied with the bias potential. The second springs137cand137dare electrically connected to the anchor section139b. The anchor section139bhas a function of supporting the second springs137cand137dsuch that the second springs137cand137dfloat above the surface of the substrate110. The anchor section139bis electrically connected to the second springs137cand137d. The anchor section139bis supplied with a ground potential, and thus the second springs137cand137dare each supplied with the ground potential.

As described above, in this embodiment, the anchor sections138aand138bare each supplied with a bias potential from the switching element104, and thus the first springs136aand136bare each supplied with the bias potential. Also, the anchor section139ais supplied with a ground potential, and thus the second springs137aand137bare each supplied with the ground potential. By a potential difference of the first springs136aand136bfrom the second springs137aand137b, the first spring136aand the second spring137aare electrostatically driven and moved to be attracted to each other, and the first spring136band the second spring137bare electrostatically driven and moved to be attracted to each other. Thus, the shutter131is moved.

Similarly, the anchor sections138cand138dare each supplied with a bias potential from the switching element104, and thus the first springs136cand136dare each supplied with the bias potential. Also, the anchor section139bis supplied with a ground potential, and thus the second springs137cand137dare each supplied with the ground potential. By a potential difference of the first springs136cand136dfrom the second springs137cand137d, the first spring136cand the second spring137care electrostatically driven and moved to be attracted to each other, and the first spring136dand the second spring137dare electrostatically driven and moved to be attracted to each other. Thus, the shutter131is moved.

In this embodiment, the first springs, the second springs and the anchor sections are provided on both sides of the shutter131, but the display device100according to the present invention is not limited to such a structure. For example, the first springs, the second springs and the anchor sections may be provided on one side of the shutter131, and only the first springs and the anchor sections may be provided on the other side of the shutter131. The first springs and the anchor sections provided on the other side of the shutter131may have a function of supporting the shutter131such that the shutter131floats above the substrate110, and the first springs and the second springs on the one side of the shutter131may be electrostatically driven to move the shutter131.

Hereinafter, preferable embodiments of a display device according to the present invention will be described with reference to the drawings. The display device according to the present invention is not limited to the following embodiments, and the present invention can be carried out in various modifications.

FIG. 1shows a display device100according to Embodiment 1 of the present invention.FIG. 1(A)is a front view of the display device100showing the interior thereof, andFIG. 1(B)is a cross-sectional view taken along line B-B inFIG. 1(A). As shown inFIG. 1, the TFT substrate1has a pixel area6thereon. A MEMS shutter8is provided for each of pixels included in the pixel area6, and thus a plurality of MEMS shutters8are located in a matrix. On the rear side of the TFT substrate1, a LED backlight unit including red, green and blue LEDs (not shown) is provided.

FIG. 2is an enlarged view showing a structure of one pixel on the TFT substrate1. The MEMS shutter8provided for each pixel includes a hollow blocking section8afor blocking light from the LED backlight unit, and springs8bsecured to a wiring section (power supply section)1bof the TFT substrate1. The springs8bof the MEMS shutter are secured to the wiring section1bvia anchoring sections8c, and the spring structure formed of the springs8bis expanded and contracted by an electrical signal supplied from the wiring section1b. The expansion and contraction operation of the springs8bsequentially switches the color of light transmitted through slits8dof the blocking section8a, and thus an image is displayed on the display device. As represented by A-A line, the springs8bof each MEMS shutter are guaranteed as being conductive with the electrode7via the wiring section1band the anchoring sections8c.

At the time when the TFT substrate1and the counter substrate2are joined together, an area to be filled with an insulating liquid such as silicone oil or the like is formed in the pixel area6between the substrates1and2. Reference sign10inFIG. 2represents a support for providing a clearance with certainty between the TFT substrate1and the counter substrate2. The clearance is required to form the area to be filled with an insulating liquid at the time when the TFT substrate1and the counter substrate2are joined together. Between the TFT substrate1and the counter substrate2, a sealing member3is sandwiched for preventing the injected insulating liquid from leaking.

At least one of the TFT substrate1and the counter substrate2has an injection opening4for injecting the insulating liquid. In at least a partial area of the injection opening4, an electrode conductive with an external electrode is formed.

As shown inFIG. 3, in the state where the TFT substrate1and the counter substrate2are joined together and left and right edges thereof are held by jigs20A and20B, the insulating liquid is injected through the injection opening4after passing the injection section9. As represented by reference sign R, the insulating liquid flows into the pixel area6. The flow R of the insulating liquid contacts the injection opening4, the injection path4a, the MEMS shutter8, the TFT substrate1and the like, and thus generates static electricity.

In the display device according to this embodiment, the electrode7having a predetermined width is formed along an area where the TFT substrate1and the counter substrate2are joined together, namely, an area where the pixel area6is not formed. More specifically, the electrode7is formed along an edge of such an area, which is the edge at which the injection opening4and the injection path4aare formed; and extends to the left and to the right from the area where the injection opening4and the injection path4aare formed. A part of the electrode7is exposed outside beyond the area where the TFT substrate1and the counter substrate2are joined together. The exposed part acts as the conductive part7a. In the step of injecting the insulating liquid, the conductive part7ais kept at a ground potential via a contact part T thereof contacting the jig20A. Therefore, the static electricity flows from the jig20A to a ground section12via the conductive part7a. Thus, even in the step of injecting the insulating liquid, the MEMS shutter8in the pixel area6can be prevented from adhering to the TFT substrate1or the counter substrate2.

After the pixel area6is filled with the insulating liquid sufficiently, the injection opening4is closed by use of an end seal5, and thus the injection step is finished. The electrode7shown inFIG. 3includes the exposed conductive part7aonly at one of two ends thereof, and is not exposed at the end close to the jig20B. Alternatively, the electrode7may have a length with which the electrode7can also contact the jig20B.

FIG. 4(A)andFIG. 4(B)show a detailed structure of the display device100according to Embodiment 1.FIG. 4(A)is an isometric view of the display device100, andFIG. 4(B)is a plan view thereof. The display device100in this embodiment includes a substrate110and a counter substrate140. The substrate110includes a display section101a, driving circuits101b,101cand101d, and a terminal section101e. The substrate110and the counter substrate140are joined together by use of a sealing material or the like.

FIG. 5is a circuit block diagram of the display device100in Embodiment 1. The display device100in Embodiment 1 according to the present invention shown inFIG. 5is supplied with an image signal and a control signal from a controller103. The display device100in Embodiment 1 according to the present invention shown inFIG. 5is also supplied with light from a backlight unit150controlled by the controller103. The display device100according to the present invention may be structured to include the controller103and the backlight unit150.

As shown inFIG. 5, the display section101aincludes a plurality of pixels106arranged in a matrix and respectively provided in correspondence with intersections of gate lines (G1, G2, . . . , Gn) and data lines (D1, D2, . . . , Dm). Each of the pixels106includes a mechanical shutter (MEMS shutter)130a, a switching element104, and a storage capacitance105. The driving circuits101band101care data drivers, and supply data signals to the switching elements104via the data lines (D1, D2, . . . , Dm). The driving circuit101dis a gate driver and supplies gate signals to the switching elements104via the gate lines (G1, G2, . . . , Gn). In this embodiment, as shown inFIG. 4, the driving circuits101band101cas the data drivers are provided to have the display section101atherebetween, but the arrangement of the driving circuits101band101cis not limited to this. Each switching element104drives the corresponding MEMS shutter130abased on the data signal supplied from the corresponding data line among the data lines (D1, D2, . . . , Dm).

FIG. 6shows a display device100according to Embodiment 2 of the present invention.FIG. 6(A)is a front view of the display device100showing the interior thereof, andFIG. 6(B)is a cross-sectional view taken along line B-B inFIG. 6(A).

This embodiment is different from Embodiment 1 on the structure of the electrode7. Specifically, the electrode7in Embodiment 1 is formed to extend to the left and to the right from the area where the injection opening4and the injection path4aare formed. Meanwhile, the electrode7in Embodiment 2 extends in one direction from the area where the injection opening4and the injection path4aare formed.

The electrode7in this embodiment is shorter than the electrode7in Embodiment 1, but such a structure can sufficiently exert a function of removing static electricity generated in the injection step. In addition, since the electrode7is shorter, the production yield of the display device100can be improved.

FIG. 7shows a display device100according to Embodiment 3 of the present invention.FIG. 7(A)is a front view of the display device100showing the interior thereof, andFIG. 7(B)is a cross-sectional view taken along line B-B inFIG. 7(A).

This embodiment is different from Embodiment 1 and also Embodiment 2 on the structure of the electrode7. Specifically, the injection opening4and the electrode7are formed only in the vicinity of one end among two ends of the TFT substrate1and the counter substrate2held by the jigs20A and20B.

This embodiment is preferably applicable for changing the position of the injection opening4when the structure of the display device is changed. The electrode7in this embodiment is shorter than the electrode7in Embodiment 1 and also the electrode in Embodiment 2, but such a structure can sufficiently exert a function of removing static electricity generated in the injection step. In addition, since the electrode7is shorter, the production yield of the display device100can be improved.

FIG. 8shows a display device100according to Embodiment 4 of the present invention.FIG. 8(A)is a front view of the display device100showing the interior thereof, andFIG. 8(B)is a cross-sectional view taken along line B-B inFIG. 8(A).

In this embodiment, the electrode7is formed on the TFT substrate1and also on the counter substrate2joined with the TFT substrate1, such that the electrodes7face each other. The electrode7facing each other are electrically connected to each other via a solder bump7b. Alternatively, the two electrodes7facing each other may be connected to each other via a metal wiring line formed of copper (Cu), aluminum (Al) or the like instead of the solder bump.

In this embodiment, the electrodes7are provided both on the TFT substrate1and the counter substrate2. Such a structure has a splendid function of discharging static electricity outside, and provides a superior effect of removing static electricity generated by friction at the time of enclosure of the insulating injection.

A display device and a method for manufacturing the same according to the present invention can effectively remove static electricity from generated by friction at the time of enclosure of the insulating liquid, although by a simple method, and thus can effectively prevent the MEMS shutter from adhering to the substrate or from being deformed.

According to a display device and a method for manufacturing the same of the present invention, the static electricity generated at the time of enclosure of the insulating liquid, and also the static electricity already generated, can be removed. Thus, the MEMS shutter can be returned to a proper position.

The invention made by the present inventor has been described by way of embodiments. The present invention is not limited to the above-described embodiments and may be modified variously without departing from the gist of the invention, needless to say.