JPH04324836A - Active device and manufacture thereof - Google Patents

Abstract

PURPOSE:To produce an active device with small secular change in the element output. CONSTITUTION:No.1 electrode 2. No.1 dielectric layer 3 consisting of acrylic material, a ferro-dielectric layer 4 consisting of copolymeride of VDF and TrFE, No.2 dielectric layer 5 consisting of acrylic material, and No.2 electrode 6 are provided one over another on an insulative base board 1, and thus an active device is produced. The No.1 and No.2 electrodes 2, 6 will be exfoliated from the ferro-dielectric substance layer 4 by its piezo-basis vibrations, which should result in secular change. Therefore, the No.1 and No.2 dielectric layers 3, 5 are interposed between the two in order to prevent their exfoliation.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active device used in a liquid crystal device and a method for manufacturing an active device.

0002

2. Description of the Related Art Conventionally, an active device as shown in FIG. 2 has been known. Figure 2(a) is a top view, Figure 2(b)
is a sectional view taken along line A-A in FIG. A first electrode 2 made of ITO provided on an insulating substrate 1 made of a glass substrate, and a combination of VDF (vinylidene fluoride) and TrFE (trifluoroethylene) provided on the first electrode 2 and the insulating substrate 1. Ferroelectric layer 4 made of copolymer
, is an active device in which a second electrode 6 made of Al is provided on a ferroelectric layer 4.

0003

[Problems to be Solved by the Invention] However, conventional active devices have had the problem of deterioration over time, in which the element output decreases over time. The present invention is intended to solve these problems, and an object thereof is to provide an active device whose element output changes little over time.

0004

[Means for Solving the Problems] The active device of the present invention includes a first electrode provided on an insulating substrate, a first dielectric layer provided on the first electrode, and a first dielectric layer provided on the first electrode. a ferroelectric layer provided on the ferroelectric layer, a second dielectric layer provided on the ferroelectric layer, the ferroelectric layer and the first and second dielectric layers on the second dielectric layer; It is characterized by comprising a second electrode provided so as to partially overlap the first electrode through the body layer. The method for manufacturing an active device of the present invention includes: (1) forming a first electrode on an insulating substrate; (2) forming a first dielectric layer on the first electrode; (2) forming the first dielectric layer on the first electrode; a step of providing a ferroelectric layer thereon and heating the ferroelectric layer to a temperature above its Curie point and below its melting point, followed by slow cooling;
The method includes at least the following steps: forming a second dielectric layer on the ferroelectric layer at a temperature below the melting point of the ferroelectric layer; and forming a second electrode on the dielectric layer. shall be. The active device manufacturing method of the present invention includes forming a first electrode on an insulating substrate, forming a first dielectric layer on the first electrode, and forming a ferroelectric layer on the first dielectric layer. ferroelectric layer, a second dielectric layer on the ferroelectric layer, and a second electrode on the second dielectric layer. The method is characterized in that it includes at least a step of heating the ferroelectric layer to a temperature above the Curie point and below the melting point and slowly cooling the ferroelectric layer after forming the body layer.

[0005]

Embodiments Below, embodiments of the present invention will be explained based on the drawings. 1(a) and (b) show the configuration of a first active device according to the present invention, (b) is a top view, and (a)
) is a sectional view taken along line A-A in (b). A first electrode 2 made of ITO provided on an insulating substrate 1 made of a glass substrate; a first dielectric layer 3 made of acrylic provided on the first electrode 2; and a first dielectric layer 3 made of acrylic provided on the insulated substrate 1; body layer 3
VDF (vinylidene fluoride) and TrFE provided on top
A ferroelectric layer 4 made of a copolymer with (trifluoroethylene), a second dielectric layer 5 made of acrylic provided on the ferroelectric layer 4, and a second dielectric layer 5 provided on the second dielectric layer 5. A
A second electrode 6 consisting of 1 is provided. The second electrode 6 is provided so as to partially overlap the first electrode 2 via the ferroelectric layer 4 and the first and second dielectric layers 3 and 5. The active layer of the active device comprises first and second electrodes 2, 4.
The ferroelectric layer 4 is sandwiched between the ferroelectric layers 4 and 4.

FIG. 3 shows the first active device manufacturing method of the present invention. I on an insulating substrate 1 made of a glass substrate.
TO is provided by a vapor deposition method, and ITO is patterned using a photolithography method to form the first electrode 2. Figure 3(a). Next, a first dielectric layer 3 made of acrylic
is formed by a spin coating method. Figure 3(b). VDF and T
A ferroelectric layer 4 made of a copolymer with rFE is placed on an insulating substrate 1.
The ferroelectric layer 4 is heated at a temperature above its Curie point and below its melting point for 10 hours, and slowly cooled to near room temperature (preferably below 80 to 60° C.) over about 4 hours. Figure 3(c). Next, a second dielectric layer 5 is provided using a spin coating method, and is fired and formed by annealing. Figure 3 (d
). Finally, a second electrode 6 made of Al is provided on the second dielectric layer 5 by vapor deposition, and patterned using photolithography to form the second electrode 6. Figure 3 (e
).

An active device using the ferroelectric layer 4 as an active layer transfers spontaneous polarization in the active layer to the first and second electrodes 2,
It operates by being inverted by the voltage applied between 6 and 6. At this time, since the ferroelectric material also has piezoelectricity, the ferroelectric layer vibrates. This vibration causes peeling between the ferroelectric layer 4 and the first and second electrodes 2 and 6. This separation creates a layer of air that causes a voltage drop. Therefore, a sufficient voltage is not applied to the active layer. Therefore, the spontaneous polarization is not sufficiently reversed, and the element output of the active device (the voltage applied to the capacitive component connected to the second electrode 5) decreases.

[0008] For these reasons, the element output of the active device has a tendency to decrease over time.

The ferroelectric layer made of a copolymer of VDF and TrFE is made of ethers such as dioxane, ketones,
It is known that it can be formed into a film by spin coating or casting because it is soluble in highly polar organic solvents such as amines. Furthermore, it is also known that large ferroelectricity (large remanent polarization or saturated remanent polarization) can be exhibited only by heating the film at a temperature above the Curie point and below the melting point and slowly cooling it.

The reason why the ferroelectric layer 4 was heated at a temperature above the Curie point and below the melting point and then slowly cooled was for the reason described above. The ferroelectric layer 4 has high ferroelectricity.

[0011] The first electrode 2 and the first dielectric layer 3, and the first dielectric layer 3 and the ferroelectric layer 4 each have strong adhesion and are firmly adhered to each other. When the first dielectric layer 3 was not used, the first electrode 2 and the ferroelectric layer 4 were easily peeled off in a tape peel test, but when the first dielectric layer 3 was used, the
Even after a 0% moisture resistance test, no peeling occurred in the same test. Furthermore, the first dielectric layer 3 is a ferroelectric layer 4
It is used as a buffer layer to absorb vibrations between layers. Therefore, the adhesion between the first electrode 2 and the ferroelectric layer 4 becomes substantially stronger. These prevent the first electrode 2 and the ferroelectric layer 4 from peeling off during operation of the active device.

Furthermore, a second electrode 6 and a second dielectric layer 5
, and the second dielectric layer 5 and the ferroelectric layer 4 each have strong adhesion and are tightly adhered to each other. When the second dielectric layer 5 was not used, the second electrode 6 and the ferroelectric layer 4 were easily peeled off in a tape peeling test, but when the second dielectric layer 5 was used, the ferroelectric layer 4 was easily peeled off.
Even after a 0°C, 90% humidity storage test, no peeling occurred in the same test. Furthermore, the second dielectric layer 5 is used as a buffer layer that absorbs vibrations between the ferroelectric layers 4. Therefore, the adhesion between the second electrode 6 and the ferroelectric layer 4 becomes substantially stronger. These prevent the second electrode 6 and the ferroelectric layer 4 from peeling off during operation of the active device. As a result, the change over time in the output of the active device is reduced, and the device life is significantly improved. When the first and second dielectric layers 3 and 5 were not formed, it took 10 hours for the device output to be half of the initial value, but when the first and second dielectric layers 3 and 5 were formed, Therefore, the time was 50,000 hours. Therefore, the lifespan of a liquid crystal element using an active device, which will be described later, ranges from 10 hours to 5 hours.
It was extended to 0000 hours.

The melting point of the ferroelectric layer 4 varies depending on the VDF content and crystal type of the VDF/TrFE copolymer and its volume percentage. To determine the melting point, differential thermal analysis such as the DSC method may be used, or if the ferroelectric layer 4 is heated above the melting point and then cooled rapidly by leaving it in the air to room temperature, the film will become rough, so it can be determined by the presence or absence of film roughness. It's okay. Film roughness can be easily observed with a metallurgical microscope (magnification of 1000 or less).

In FIGS. 3A and 3E, the method for providing the first and second electrodes 2 and 6 is not limited to vapor deposition, and sputtering or the like may also be used. Moreover, the method for patterning them is not limited to the photolithography method, and a printing method or the like may be used, or patterning may be omitted by using a mask vapor deposition method or a sputtering method. In FIG. 3(c), heating the ferroelectric layer 4 to a temperature above the Curie point and below the melting point is 10
There is no need to limit the time; it can be longer or shorter. Further, the slow cooling time after heating is not necessarily limited to 4 hours, and may be longer or shorter than that. Heating and slow cooling are preferably carried out in nitrogen or inert gas. However, it may also be carried out in a gas containing oxygen. In FIGS. 3(b), (c), and (d), the ferroelectric layer 4 and the first and second dielectric layers 3 and 5 are not limited to spin coating, but may be formed by casting, coating, etc.
A printing method may also be used. Annealing may not be performed in FIG. 3(d). Drying such as vacuum drying may be performed instead of annealing. When performing annealing, the annealing time is preferably 5 minutes or more, and the cooling method may be slow cooling or rapid cooling. Alternatively, a coupling agent such as a silane coupling agent or a primer may be mixed into the first and second dielectric layers 3 and 5. The coupling agent and primer are desirably those that can obtain good adhesion to at least one of the first and second electrodes 2 and 6 and the ferroelectric layer 4. Furthermore, before forming the second dielectric layer 5, the surface of the ferroelectric layer 4 may be subjected to metal sodium treatment or plasma treatment. The plasma treatment preferably includes oxygen, but an inert gas such as nitrogen or argon may also be used. Further, the first and second dielectric layers 3 and 5 may be formed using a vapor deposition method or a sputtering method instead of a coating method.

In order to obtain a large (good) element output (proportional to residual polarization) of the active device, it is necessary to make the ferroelectric layer 4 as thick as possible and apply a large electric field to it. In order not to reduce the element output of the active device, the thickness of the ferroelectric layer 4 is the first priority.
It needs to be thicker than the total thickness of the second dielectric layers 3 and 5. Preferably, the total thickness of the first and second dielectric layers 3 and 5 is 20% or less of that of the ferroelectric layer 4, preferably 1.
It is 0% or less, more preferably 5% or less. The initial output of the active device was reduced by 5-10% when the thickness of the ferroelectric layer 4 was 10-20% compared to the case where the two dielectric layers 3 and 5 were not used. However, because the change in element output over time is reduced, the reliability (life) of the final element is greatly improved. When the film thickness of the two dielectric layers 3 and 5 was 5-10%, the initial output of the active device decreased by 2-3%, but this was hardly a problem in practice. When the total thickness of the two dielectric layers 3 and 5 was 5% or less, almost no decrease in the initial output was observed. Of course, even if the total film thickness is less than 10%, the effect of reducing changes over time is 1.
Same as 0-20%.

The method for manufacturing the second active device of the present invention is almost the same as the first method. To explain using FIG. 3, a first electrode 2 is formed on an insulating substrate 1. Figure 3 (
a). A first dielectric layer 3 is formed on the first electrode 2 . Figure 3(b). A ferroelectric layer 4 is formed on the first dielectric layer 3. Figure 3(c). A second dielectric layer 5 on the ferroelectric layer 4
form. Figure 3(d). A second electrode 6 is formed on the second dielectric layer 5. Figure 3(e). The difference from the first active device manufacturing method of the present invention is that after forming the second dielectric layer 5, the ferroelectric layer 4 is heated to a temperature above the Curie point and below the melting point and then slowly cooled. Of course, this is the second electrode 6
It may be performed after formation. The detailed steps other than the above-mentioned differences are the same as the first active device manufacturing method.

FIGS. 4A and 4B show a liquid crystal element using the active device shown in FIG. FIG. 4(b) is a top view, and FIG. 4(a) is a cross-sectional view taken along line A-A in FIG. 4(b). An active substrate consisting of a first electrode 2, a first dielectric layer 3, a ferroelectric layer 4, a second dielectric layer 5, and a second electrode 6 on an insulating substrate 1 consisting of a glass substrate and a glass substrate. This is an element in which a liquid crystal is held between an insulating substrate 7 and a counter substrate consisting of a counter electrode 8 made of ITO. FIG. 5 shows a second active device according to the invention. FIG. 5(b) is a top view, and FIG. 5(a) is a cross-sectional view taken along line A-A in FIG. 5(b). A first electrode 2 made of ITO provided on an insulating substrate 1 made of a glass substrate, a first dielectric layer 3 made of acrylic provided on the first electrode 2 and an insulated substrate 1, a first dielectric VDF and Tr provided on body layer 3
Ferroelectric layer 4 made of copolymer with FE, ferroelectric layer 4
A second dielectric layer 5 made of acrylic is provided thereon, and a second electrode 6 made of Al is provided on the second dielectric layer 5. The second electrode 6 is provided so as to partially overlap the first electrode 2 via the first and second dielectric layers 3 and 5 and the ferroelectric layer 4. The active layer of the active device is a ferroelectric layer 4 sandwiched between first and second electrodes 2, 6. In the second active device, the first and second dielectric layers 3 and 5 and the ferroelectric layer 4 are etched after the second electrode 6 is formed using the second electrode 6 as a mask. , the second dielectric layers 3 and 5 and the ferroelectric layer 4 have the same shape as the second electrode 6 in a top view.

The second active device of the present invention can also be manufactured using the first and second active device manufacturing methods of the present invention, and a liquid crystal element as shown in FIG. 4 can be formed. The difference is that, as described above, after the second electrode 6 is formed, the first and second dielectric layers 3 and 5 and the ferroelectric layer 4 are etched using the second electrode as a mask. In that case, the first and second dielectric layers 3 and 5 and the ferroelectric layer 4 may be etched with the resist used for etching the second electrode 6, or the resist may be removed. Etching may be performed in this state. It is desirable to use plasma containing oxygen for etching. Alternatively, only the second dielectric layer 5 may be etched and the ferroelectric layer 4 may be left unetched. In that case, a part of the ferroelectric layer 4 may be etched. Alternatively, only a portion of the second dielectric layer 5 may be etched. In addition, the first dielectric layer 3
It is also possible to etch a part of it.

FIGS. 1 and 5 show only one example of the configuration of an active device according to the present invention. Even in other configurations, an active device composed of a first electrode 2, a first dielectric layer 3, a ferroelectric layer 4, a second dielectric layer 5, and a second electrode 6 is a part of the present invention. Considered as an example. Furthermore, they are manufactured using the active device manufacturing method described above.

In FIGS. 1, 4, and 5, the insulating substrates 1 and 7 are not limited to glass substrates, and may be made of organic insulating materials. The first electrode 2, the second electrode 6, and the counter electrode 8 are not limited to ITO or Al, and other transparent electrodes, metals, or superconducting materials may be used. The material used for the ferroelectric layer 4 is not limited to a copolymer of VDF and TrFE; an inorganic ferroelectric such as BaTiO3 or an organic ferroelectric such as a copolymer of vinylidene fluoride and tetrafluoroethylene may be used. It's okay. The material used for the first and second dielectric layers 3 and 5 is not limited to acrylic, but other materials such as ester resin, phenol resin, polyethylene resin, styrene resin, vinyl acetate resin, vinyl chloride resin, polyether can be used. resin, polyurethane resin, silicone resin, cyanoacrylate resin, chloroprene resin,
Chloroprene rubber, nitrile rubber, nitrile-prene resin, polyolefin resin, epoxy modified polyamide, polysulfide, synthetic rubber modified polyamide, silicone rubber, PMMA, epoxy resin, silicone resin,
Organic materials such as siloxane, polycarbonate, polyimide, polyamide, ferroelectric materials, or SiOx, SiO
Oxides and nitrides such as Nx, SiNx, and TaOx, or inorganic materials such as ferroelectrics and antiferroelectrics may be used. Furthermore, a stack of two or more layers or a mixture of them may be used. What is held between the active substrate and the counter substrate is not limited to liquid crystal, and other materials having an electro-optic effect or materials that can emit or non-emissive depending on the magnitude of applied voltage may be used.

In FIGS. 1, 4, 5(a) and (b), a second electrode 6, a first dielectric layer 3, a ferroelectric layer 4, and a second dielectric layer are disposed on an insulating substrate 1. 5. The first electrode 2 may be provided and used in this order.

[0022]

Effects of the Invention The active device of the present invention manufactured using the active device manufacturing method of the present invention has a small change in element output over time.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a first active device of the present invention.

FIG. 2 is a diagram showing a conventional active device.

FIG. 3 is a diagram showing a method for manufacturing an active device of the present invention.

FIG. 4 is a diagram showing a liquid crystal element using the first active device of the present invention.

FIG. 5 is a diagram showing a second active device of the present invention.

[Explanation of symbols]

1 Insulating substrate 2 First electrode 3 First dielectric layer 4 Ferroelectric layer 5 Second dielectric layer 6 Second electrode 7 Insulating substrate 8 Counter electrode

Claims (3)

[Claims] Claim 1: A first electrode provided on an insulating substrate;
A first dielectric layer provided on the first electrode, a ferroelectric layer provided on the first dielectric layer, and a second dielectric layer provided on the ferroelectric layer. , a second electrode provided on the second dielectric layer so as to partially overlap the first electrode via the ferroelectric layer and the first and second dielectric layers; Features an active device. 2. ■ Step of forming a first electrode on an insulating substrate; ■ Step of forming a first dielectric layer on the first electrode; ■ Step of forming a ferroelectric layer on the first dielectric layer. (1) forming a second dielectric layer on the ferroelectric layer at a temperature below the melting point of the ferroelectric layer; 1) forming a second electrode on the dielectric layer; 3. A first electrode is formed on an insulating substrate, a first dielectric layer is formed on the first electrode, and a ferroelectric layer is formed on the first dielectric layer. , a method for manufacturing an active device, comprising: forming a second dielectric layer on the ferroelectric layer; and forming a second electrode on the second dielectric layer; A method for manufacturing an active device, comprising at least the step of heating the ferroelectric layer to a temperature above the Curie point and below the melting point of the ferroelectric layer and slowly cooling the ferroelectric layer.