JP3299017B2 - Polyimide optical waveguide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide in which the refractive index of polyimide is easily changed and used for a polyimide optical waveguide.

[0002]

2. Description of the Related Art Polyimide is widely used as an electronic material for insulating films of electronic parts and flexible printed wiring boards because of its excellent heat resistance, electrical properties, and mechanical properties. On the other hand, with the development of optical communication systems, development of various optical components having high performance and high functionality is expected, and optical materials having performances suitable for each optical component are required. So far, as an optical material for optical communication, quartz, which is also a material of an optical fiber, has been mainly studied, and various optical components have been developed. However, the production of an optical component using a quartz-based optical material requires a high temperature of 1000 ° C. or higher, which limits the substrate that can be produced, and has drawbacks such as lack of flexibility, and is not a universal optical material. Plastic optical materials excellent in flexibility and manufacturability with respect to inorganic optical materials typified by quartz, especially plastic optical materials excellent in heat resistance from the viewpoint of reliability and process compatibility are expected. Quartz has a very good light transmittance as demonstrated in an optical fiber. Therefore, even when used as a waveguide, a low optical loss of 0.1 dB / cm or less is achieved at a wavelength of 1.3 μm. However, there are manufacturing problems such as a long time required for manufacturing the optical waveguide, a high temperature required for manufacturing, and difficulty in increasing the area. On the other hand, a plastic optical waveguide such as polymethyl methacrylate (PMMA) can be molded at a low temperature and has advantages such as low cost, but has a drawback of poor heat resistance. Therefore, a plastic optical waveguide excellent in heat resistance has been expected. On the other hand, polyimide having excellent heat resistance is widely used as an electronic material for an insulating film of an electronic component, a flexible printed wiring board, and the like, but there has been almost no record of application to an optical component such as an optical waveguide.

[0003] From such a viewpoint, the present inventors are conducting research and development on polyimide optical materials. When polyimide is used as an optical material, it is particularly important to have excellent light transmittance and to be able to freely control the refractive index. The present inventors have disclosed in JP-A-3-72528 that copolymerization of fluorinated polyimide makes it possible to control the refractive index necessary for forming an optical waveguide, for example. The optical waveguide using the fluorinated polyimide is disclosed in JP-A-4-9807 and JP-A-4-9807.
No. 235505 and 4-235506. In these optical waveguides, the refractive index difference between the core having the role of transmitting light and the cladding having the role of confining light is controlled by adjusting the content of fluorine contained in the polyimide. That is, two types of fluorinated polyimides having different refractive indexes for the core and the clad are used. For this reason, a problem may occur in certain types of optical waveguides, such as different thermal characteristics between the core and the clad and different birefringence. If the refractive index can be freely controlled by using the same polyimide, it is possible to form an unprecedented polyimide optical waveguide. In addition, the conventional method of manufacturing a polyimide optical waveguide mainly employs a method using reactive ion etching (RIE) used in a semiconductor manufacturing process, and has a drawback that the manufacturing process is many and requires a long time for manufacturing. . There is a demand for a method of fabricating an optical waveguide which can be fabricated in a short time with a small number of fabrication steps in place of the method for fabricating these polyimide optical waveguides.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for easily changing the refractive index of a polyimide film, and to provide a novel polyimide light guide which is free from the problem of thermal property difference between core and clad and birefringence difference. To provide a wave path.

[0005]

If it outlined present invention According to an aspect of the present <br/> onset Ming is the invention relates to polyimide optical waveguide, using the polyimide having a controlled refractive index by synchrotron radiation as the core It is characterized by.

In view of the above-mentioned situation, the present inventors have made intensive studies and as a result have found that the refractive index of the polyimide can be changed by irradiating the polyimide with radiation, thereby completing the present invention.

The polyimide used in the present invention can be produced, for example, from the following tetracarboxylic acid or a derivative thereof and a diamine. A polyimide alone, a polyimide copolymer, a polyimide mixture and, if necessary, additives such as an additive. There are those added.

[0008] Examples of the tetracarboxylic acid and its derivatives such as acid anhydrides, acid chlorides, and esterified compounds include the following. Here, an example of tetracarboxylic acid will be given. (Trifluoromethyl) pyromellitic acid, di (trifluoromethyl) pyromellitic acid, di (heptafluoropropyl) pyromellitic acid, pentafluoroethylpyromellitic acid, bis {3,5-di (trifluoromethyl) phenoxy} Pyromellitic acid, 2,3
3 ′, 4′-biphenyltetracarboxylic acid, 3,3 ′,
4,4′-tetracarboxydiphenyl ether, 2,
3,3 ′, 4′-tetracarboxydiphenyl ether, 3,3 ′, 4,4′-benzophenonetetracarboxylic acid, 2,3,6,7-tetracarboxynaphthalene,
1,4,5,7-tetracarboxynaphthalene, 1,
4,5,6-tetracarboxynaphthalene, 3,3 ′,
4,4′-tetracarboxydiphenylmethane, 3,
3 ', 4,4'-tetracarboxydiphenyl sulfone, 2,2-bis (3,4-dicarboxyphenyl) propane, 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane, 5,5 '-Bis (trifluoromethyl) -3,3', 4,4'-tetracarboxybiphenyl, 2,2 ', 5,5'-tetrakis (trifluoromethyl) -3,3', 4,4'- Tetracarboxybiphenyl, 5,5'-bis (trifluoromethyl) -3,3 ', 4,4'-tetracarboxydiphenyl ether, 5,5'-bis (trifluoromethyl)-
3,3 ′, 4,4′-tetracarboxybenzophenone, bis {(trifluoromethyl) dicarboxyphenoxy} benzene, bis {(trifluoromethyl) dicarboxyphenoxy} (trifluoromethyl) benzene,
Bis (dicarboxyphenoxy) (trifluoromethyl) benzene, bis (dicarboxyphenoxy) bis (trifluoromethyl) benzene, bis (dicarboxyphenoxy) tetrakis (trifluoromethyl) benzene, 3,4,9,10-tetra Carboxyperylene,
2,2-bis {4- (3,4-dicarboxyphenoxy) phenyl} propane, butanetetracarboxylic acid, cyclopentanetetracarboxylic acid, 2,2-bis {4-
(3,4-dicarboxyphenoxy) phenyl {hexafluoropropane, bis (trifluoromethyl) dicarboxyphenoxy} biphenyl, bis {(trifluoromethyl) dicarboxyphenoxy} bis (trifluoromethyl) biphenyl, bis} ( Trifluoromethyl)
Dicarboxyphenoxy diphenyl ether, bis (dicarboxyphenoxy) bis (trifluoromethyl) biphenyl, bis (3,4-dicarboxyphenyl) dimethylsilane, 1,3-bis (3,4-dicarboxyphenyl) tetramethyldi Siloxane, difluoropyromellitic acid, 1,4-bis (3,4-dicarboxytrifluorophenoxy) tetrafluorobenzene,
1,4-bis (3,4-dicarboxytrifluorophenoxy) octafluorobiphenyl and the like.

The following are examples of the diamine. m-phenylenediamine, 2,4-diaminotoluene, 2,4-diaminoxylene, 2,4-diaminodulene, 4- (1H, 1H, 11H-eicosafluoroundecanooxy) -1,3-diaminobenzene, 4-
(1H, 1H-perfluoro-1-butanoxy) -1,
3-diaminobenzene, 4- (1H, 1H-perfluoro-1-heptanoxy) -1,3-diaminobenzene,
4- (1H, 1H-perfluoro-1-octanoxy)
-1,3-diaminobenzene, 4-pentafluorophenoxy-1,3-diaminobenzene, 4- (2,3
5,6-tetrafluorophenoxy) -1,3-diaminobenzene, 4- (4-fluorophenoxy) -1,3
-Diaminobenzene, 4- (1H, 1H, 2H, 2H-
Perfluoro-1-hexanoxy) -1,3-diaminobenzene, 4- (1H, 1H, 2H, 2H-perfluoro-1-dodecanoxy) -1,3-diaminobenzene,
p-phenylenediamine, 2,5-diaminotoluene,
2,3,5,6-tetramethyl-p-phenylenediamine, 2,5-diaminobenzotrifluoride, bis (trifluoromethyl) phenylenediamine, diaminotetra (trifluoromethyl) benzene, diamino (pentafluoroethyl) benzene , 2,5-diamino (perfluorohexyl) benzene, 2,5-diamino (perfluorobutyl) benzene, benzidine, 2,2'-
Dimethylbenzidine, 3,3′-dimethylbenzidine,
3,3′-dimethoxybenzidine, 2,2′-dimethoxybenzidine, 3,3 ′, 5,5′-tetramethylbenzidine, 3,3′-diacetylbenzidine, 2,2′-
Bis (trifluoromethyl) -4,4′-diaminobiphenyl, octafluorobenzidine, 3,3′-bis (trifluoromethyl) -4,4′-diaminobiphenyl, 4,4′-diaminodiphenyl ether, 4,4 '
-Diaminodiphenylmethane, 4,4'-diaminodiphenylsulfone, 2,2-bis (p-aminophenyl)
Propane, 3,3'-dimethyl-4,4'-diaminodiphenyl ether, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 1,2-bis (anilino) ethane, 2,2-bis (p- Aminophenyl) hexafluoropropane, 1,3-bis (anilino) hexafluoropropane, 1,4-bis (anilino) octafluorobutane, 1,5-bis (anilino) decafluoropentane, 1,7-bis (anilino ) Tetradecafluoroheptane, 2,2′-bis (trifluoromethyl) -4,
4'-diaminodiphenyl ether, 3,3'-bis (trifluoromethyl) -4,4'-diaminodiphenyl ether, 3,3 ', 5,5'-tetrakis (trifluoromethyl) -4,4'-diaminodiphenyl ether , 3,3'-bis (trifluoromethyl) -4,4 '
-Diaminobenzophenone, 4,4 ''-diamino-p
-Terphenyl, 1,4-bis (p-aminophenyl)
Benzene, p-bis (4-amino-2-trifluoromethylphenoxy) benzene, bis (aminophenoxy)
Bis (trifluoromethyl) benzene, bis (aminophenoxy) tetrakis (trifluoromethyl) benzene, 4,4 ′ ″-diamino-p-quarterphenyl, 4,4′-bis (p-aminophenoxy) biphenyl, , 2-bis {4- (p-aminophenoxy) phenyl} propane, 4,4'-bis (3-aminophenoxyphenyl) diphenylsulfone, 2,2-bis {4-
(4-aminophenoxy) phenyl} hexafluoropropane, 2,2-bis {4- (3-aminophenoxy)
Phenyl {hexafluoropropane, 2,2-bis} 4
-(2-aminophenoxy) phenyl} hexafluoropropane, 2,2-bis {4- (4-aminophenoxy) -3,5-dimethylphenyl} hexafluoropropane, 2,2-bis {4- (4- Aminophenoxy)-
3,5-ditrifluoromethylphenyl @ hexafluoropropane, 4,4'-bis (4-amino-2-trifluoromethylphenoxy) biphenyl, 4,4'-bis (4-amino-3-trifluoromethylphenoxy) ) Biphenyl, 4,4′-bis (4-amino-2-trifluoromethylphenoxy) diphenylsulfone, 4,4 ′
-Bis (3-amino-5-trifluoromethylphenoxy) diphenylsulfone, 2,2-bis {4- (4-amino-3-trifluoromethylphenoxy) phenyl}
Hexafluoropropane, bis {(trifluoromethyl) aminophenoxy} biphenyl, bis [{(trifluoromethyl) aminophenoxy} phenyl] hexafluoropropane, diaminoanthraquinone, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, Bis {2-[(aminophenoxy) phenyl] hexafluoroisopropyl} benzene, bis (2,3,5,6-tetrafluoro-4-aminophenyl) ether, bis (2,3,5,6-tetrafluoro- 4-aminophenyl) sulfide, 1,3-bis (3-aminopropyl)
Tetramethyldisiloxane, 1,4-bis (3-aminopropyldimethylsilyl) benzene, bis (4-aminophenyl) diethylsilane, 1,3-diaminotetrafluorobenzene, 1,4-diaminotetrafluorobenzene, 4, 4'-bis (tetrafluoroaminophenoxy) octafluorobiphenyl and the like.

[0010] It is particularly preferable to use a fluorinated polyimide obtained by bonding a fluorine atom to one or both of an acid dianhydride and a diamine.

By irradiating the polyimide film formed on a substrate such as a silicon wafer with radiated light, a polyimide film having a changed refractive index can be obtained.
The linear absorption coefficient of the radiation absorbed by the polyimide film in the radiation irradiation direction is determined by the composition of the polyimide and the energy of the radiation, and the refractive index also changes according to the composition of the polyimide, the energy of the radiation, and the intensity of the radiation. However, the degree of change in the refractive index depends on the chemical structure of the polyimide.

The value of the linear absorption coefficient of the polyimide film varies greatly depending on the energy of the emitted light.
When the energy is about V, the energy is about 1 μm ⁻¹ , and the area of the change in the refractive index is also about 1 μm. When the energy becomes higher, the value of the linear absorption coefficient decreases, and the refractive index changes to a deep region. Also, when the irradiation amount is increased, the change in the refractive index increases accordingly. However, if the irradiation amount is too large, material destruction may occur depending on the chemical structure of the polyimide. Thus, the chemical structure of polyimide,
By controlling the energy of the emitted light and the irradiation amount, the refractive index can be changed so that the region where the refractive index changes has various profiles.

There are several methods for manufacturing an optical waveguide. Most simply, the core can be formed by using an X-ray mask. That is, first, a polyamic acid solution is spin-coated on a substrate such as silicon and then cured by heating to obtain a polyimide film. Next, this is irradiated with radiation light so as to have a predetermined refractive index and a predetermined size through an X-ray mask. After spin-coating the same polyamic acid solution on this film, it is cured by heating,
The polyimide film is peeled off from the silicon substrate and has a two-layer structure in which a core layer is formed. This polyimide film is adhered to the silicon substrate with the radiation irradiation film side facing upward. Finally, the same polyamic acid solution as the upper clad is spin-coated and cured by heating to obtain a buried optical waveguide. The buried waveguide can also be formed by sandwiching a polyimide film serving as a clad from above and below the core layer film and bonding the polyimide film via a very thin adhesive layer. As the optical waveguide structure, a slab type, a ridge type, and various other types of optical waveguide structures generally manufactured can be manufactured. In addition, both the single mode type and the multi mode type as the light propagation mode can be manufactured by controlling the refractive index difference between the core and the clad.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to several embodiments. Note that the present invention is not limited to only these examples.

EXAMPLE 1 88.8 g of 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride was placed in an Erlenmeyer flask.
(0.2 mol) and 64.0 g of 2,2'-bis (trifluoromethyl) -4,4'-diaminobiphenyl (0.
2 mol) and N, N-dimethylacetamide 1000
g was added. This mixture was stirred under a nitrogen atmosphere at room temperature for 3 days to obtain a polyamic acid solution having a concentration of about 15 wt%. This polyamic acid solution is spin-coated on a silicon wafer and then heated in an oven at 70 ° C. for 2 hours, 160 ° C. for 1 hour, 250 ° C. for 30 minutes, and 350 ° C. for 1 hour,
By imidation, a polyimide film having a thickness of 10 μm was obtained. This polyimide film on the silicon substrate has 27
Irradiation light of 200 eV to 1000 eV having a peak at 5 eV was applied for 5 minutes. As a result of measuring the change in the refractive index of this polyimide film, it was 0.3% on average in the film thickness direction.

Example 2 88.8 g of 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride was placed in an Erlenmeyer flask.
(0.2 mol) and 64.0 g of 2,2'-bis (trifluoromethyl) -4,4'-diaminobiphenyl (0.
2 mol) and N, N-dimethylacetamide 1000
g was added. This mixture was stirred under a nitrogen atmosphere at room temperature for 3 days to obtain a polyamic acid solution having a concentration of about 15 wt%. This polyamic acid solution is spin-coated on a silicon wafer provided with an oxide film, and then heated in an oven at 70 ° C. for 2 hours.
Heating was performed at 60 ° C. for 1 hour, at 250 ° C. for 30 minutes, and at 380 ° C. for 1 hour to perform imidization to obtain a polyimide film having a thickness of 10 μm. The polyimide film on the silicon substrate was irradiated with radiation of 200 to 1000 eV having a peak at 275 eV for 5 minutes through an X-ray mask, and the core (1
(0 .mu.m square) was obtained by irradiating radiation light to obtain one layer of polyimide optical waveguide. The manufacturing process is shown in FIG. The change in the refractive index of this core was 0.3%. In addition, light having a wavelength of 1320 nm was passed through this waveguide, and the light was confined when observed with a microscope equipped with an infrared camera from the emission end face. This polyimide optical waveguide was manufactured in two steps. FIG. 3 shows the light energy of the emitted light (horizontal axis, e
V) and luminance (vertical axis, photons / s / mrad ² / mA / 0.
1% -bw) is shown as a graph.

Example 3 A polyimide film produced in the same manner as in Example 1 was irradiated for 5 minutes through an X-ray mask under the same conditions as in Example 1 as shown in FIG. As a result of measuring the refractive index change of the refractive index change portion of this polyimide film, it was 0.8% on average in the film thickness direction.

Example 4 A polyimide film produced in the same manner as in Example 1 was irradiated for 15 minutes under the same conditions as in Example 1. As a result of measuring the refractive index change of this polyimide film, it was 0.8% on average in the film thickness direction.

Example 5 A polyimide film produced in the same manner as in Example 1 was irradiated for 30 minutes under the same conditions as in Example 1. As a result of measuring the change in the refractive index of this polyimide film, it was 1.3% on average in the film thickness direction.

Example 6 A polyimide film produced in the same manner as in Example 1 was irradiated with radiated light through an X-ray stencil mask having a substrate of a predetermined shape. When the X-ray stencil mask was in soft contact with the polyimide film and irradiated with radiation for 5 minutes under the same conditions as in Example 1, only the refractive index of the X-ray transmission portion changed, and the shape of the transmission portion of the stencil mask was changed. Was obtained.

Example 7 A reflective X-ray mask having an X-ray reflecting portion and an absorbing portion was used on a polyimide film produced in the same manner as in Example 1, and a pattern image on the X-ray mask was formed on the polyimide surface. Irradiation was performed so that As a result of irradiating the emitted light for 5 minutes under the same conditions as in Example 1, it was possible to selectively change the refractive index only in the portion corresponding to the X-ray reflection portion.

Example 8 The same polyamic acid solution as in Example 2 was spin-coated on the top of the one-layer optical waveguide of Example 2 and then heated to 70 ° C. in an oven.
For 2 hours, 160 ° C. for 1 hour, 250 ° C. for 30 minutes, 38
Heating was performed at 0 ° C. for 1 hour to perform imidization, thereby obtaining an embedded waveguide in which the lower clad was SiO ₂ and the upper clad was polyimide. Let light of wavelength 1320 nm pass through this waveguide,
Observation with a microscope equipped with an infrared camera from the emission end face confirmed that the light was confined.

Example 9 The waveguide fabricated in Example 8 was peeled off from a Si wafer.
The radiation-irradiated film surface is turned to the upper surface, and the same polyamic acid solution is spin-coated on the film surface, and then placed in an oven at 70 ° C. for 2 hours, 160 ° C. for 1 hour, 250 ° C. for 30 minutes, 350
C. for 1 hour to perform imidization to form an upper clad. In this way, a buried waveguide in which the core, the upper clad, and the lower clad were made of the same polyimide was obtained. When light having a wavelength of 1320 nm was passed through this waveguide and observed from a light-emitting end face with a microscope equipped with an infrared camera, it was confirmed that the light was confined.

Comparative Example 1 FIG. 4 shows a manufacturing process of a conventional ridge type polyimide optical waveguide using RIE. A total of 5 steps are required.

[0025]

As described above, it is possible to change the refractive index of the polyimide by irradiating the emitted light, and it is possible to change the amount of change in the refractive index by changing the irradiation amount of the emitted light. Therefore, if the refractive index is changed to a predetermined shape using an X-ray mask, an optical waveguide or the like can be freely formed. Also, by selecting the energy of the emitted light, it is possible to provide a refractive index distribution, and it is possible to expect effects such as the ability to form a graded index optical waveguide and a planar lens. In addition, an optical waveguide using a polyimide whose core has a refractive index controlled by irradiation of radiation, the core and the clad are formed of the same material, and can solve the problems of a difference in thermal characteristics and a difference in birefringence caused by a difference in the material. effective. In the present invention, the polyimide optical waveguide has the effects of reducing the manufacturing process, shortening the manufacturing time, and easily forming the polyimide optical waveguide.

[Brief description of the drawings]

FIG. 1 is a process diagram showing a manufacturing process of a ridge-type polyimide optical waveguide using radiation light irradiation according to the present invention.

FIG. 2 is a process chart showing a process of a method for irradiating a polyimide with radiation light in the present invention.

FIG. 3 is a graph showing a relationship between photon energy of emitted light and luminance.

FIG. 4 is a process chart showing a manufacturing process of a conventional ridge type polyimide optical waveguide using RIE.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshiyuki Horiuchi 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Tsuneyuki Haga 1-16-1 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Hiroo Kinoshita 1-6-1, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-1-161718 (JP, A) JP-A-4 -9807 (JP, A) JP-A-4-235505 (JP, A) JP-A-4-235506 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08J ^7/ 00- 7/18 G02B 6/12

Claims (2)

(57) [Claims] 1. A polyimide optical waveguide comprising a polyimide and a core and a clad, wherein the core is made of polyimide irradiated with radiation light. 2. A polyimide optical waveguide having a core and a clad made of polyimide, wherein the core is a fluorinated polyimide irradiated with radiation light.