JP2003313294A - Optical part using fluorinated polyimide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost optical part showing a heat resistance and an optical transparency at a wavelength of 0.85 μm band. <P>SOLUTION: By using a fluorinated polyimide wherein a fluorine-containing alicyclic diamine containing at least two cyclohexyl rings and two fluoroalkyl groups within its molecule is at least partially used as a monomer, the number of benzene rings containing C-H bonds within repeating units containing the benzene rings can be reduced, the optical transparency at the wavelength of 0.85 μm band can be improved, and the heat resistance sufficient for soldering can be improved. By manufacturing an optical waveguide using this fluorinated polyimide, the low-cost optical part which has the good optical transparency at the wavelength of 0.85 μm band, and a consistent refractive index with a quartz core can be manufactured. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical component using a heat-resistant fluorinated polyimide having a refractive index substantially equal to that of quartz glass and having a high light transmittance in a wavelength band of 0.85 μm. Is.

[0002]

2. Description of the Related Art As optical communication technology permeates as a basic technology of information communication systems, optical waveguides become more and more important as key devices for optical networks, and at the same time, applied to fields such as electronic circuit wiring boards. Is being developed for.

In particular, in recent years, along with the increase in the amount of data in the network, optical signal processing in the transmission device connected to the network and in the large computer has become essential, and the 0.85 μm band in the optical interconnection. The development of a system using the surface emitting laser (VCSEL) and the application of an optical waveguide to this system have been actively studied. On the other hand, as an optical waveguide, easiness of processing, cost reduction, mass production, and the like are demanded, and a resin optical waveguide has been developed as a promising candidate.

Resin materials for optical waveguides include polymethacrylate, polycarbonate, fluorinated epoxy,
Examples thereof include deuterated polysiloxane and benzene ring-containing fluorinated polyimide. For the resin material and the optical waveguide applied to the above optical interconnection, the light transmittance in the 0.85 μm band, and the soldering process for connecting devices such as PD (photodiode) and IC (280 for gold / tin solder) Heat resistance to (.degree. C.) and further low cost are required, and it is essential for practical application to satisfy these required characteristics.

However, none of the above-mentioned conventional resin materials for an optical waveguide satisfy all of these required characteristics. Polymethacrylate and polycarbonate have good light transmittance in the wavelength band of 0.85 μm, but have a low glass transition temperature of 100 ° C. or less and low heat resistance. Further, deuterated polysiloxane and benzene ring-containing fluorinated polyimide have a glass transition temperature of 300 ° C. or higher and high heat resistance, and have high light transmittance in the wavelength band of 1.3 and 1.5 μm, but have a wavelength of 0.85 μm. Light transmittance in the band is low. On the other hand, fluorinated epoxy has good light transmittance in the wavelength band of 0.85 μm, but has a glass transition temperature of 200 ° C. to 250 ° C., and has insufficient heat resistance from the viewpoint of reliability. The cost is high and it is difficult to put the device to practical use. Therefore, the development of a resin material for an optical waveguide, which has high light transmittance at a wavelength of 0.85 μm, has heat resistance, and is low in cost, and an optical component using the same have been awaited.

Further, a line switching operation (cross-connect system) is indispensable in an optical communication network, and a thermo-optical (TO) switch utilizing the temperature dependence of the refractive index is being studied as a key device. In a TO switch, high switching characteristics (extinction ratio, high switching speed (several milliseconds or less)), reliability, and low operating power are essential for practical use. From the viewpoint of switch characteristics and reliability, it is preferable to use a silica-based optical waveguide, but the silica-based optical waveguide has a problem that the temperature change of the refractive index (TO constant) is small and the operating power is large.

On the other hand, although the resin-based optical waveguide has a TO constant one order of magnitude larger than that of the silica-based optical waveguide and can achieve low operating power, there is a problem that the switch characteristics and reliability are inferior to those of the silica-based optical waveguide. On the other hand, by making the lower clad layer and core layer of the optical waveguide with a quartz system and the upper clad layer with a resin system, it has been attempted to achieve high switching characteristics and reliability as well as low operating power. There are few materials that have high heat resistance, and general resin materials have a higher refractive index than that of silica glass, which is unsuitable as an upper clad layer for a silica-based core. Therefore, the development of a heat-resistant resin material for optical waveguides, which has a refractive index matching property with quartz glass, and a TO switch using the same has been awaited.

[0008]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems in a resin material for an optical waveguide, heat resistance, light transmission in a wavelength band of 0.85 μm, refractive index matching with quartz glass, An object is to provide an optical component using an optical material having low cost.

[0009]

[Means for Solving the Problems] The inventors of the present invention have made extensive studies to solve the above-mentioned problems. As a result, a fluorinated polyimide having two or more cyclohexyl rings and two or more cyclohexyl rings in the molecule. Polyimide using a diamine containing a fluoroalkyl group as a part of the monomer has high heat resistance and light transmittance in the wavelength 0.85 μm band, and its refractive index is almost equal to that of quartz glass. Furthermore, they have found that an optical component such as an optical waveguide can be manufactured at low cost, and have reached the present invention.

That is, fluorine containing at least one of the repeating units represented by the general formulas (1) and (2) in at least one of the lower clad layer, core layer and upper clad layer of the optical waveguide constituting the optical component. The polyimide is used. Further, the optical component is a thermo-optical switch, and at least the upper clad layer of the optical waveguide is made of fluorinated polyimide.

[0011]

[Chemical 2]

(In the formula, R is one or more tetravalent groups selected from straight chain, branched chain, alicyclic ring, aromatic ring and hetero ring, and may partially contain fluorine oxygen nitrogen).

[0013]

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have paid attention to polyimide, and examined various existing polyimides and polyimide optical materials with respect to heat resistance, light transmittance in a wavelength band of 0.85 μm, and refractive index. The cause was thoroughly studied. As a result, even in polyimides that are said to have high heat resistance among plastics, sufficient heat resistance is obtained with a diamine, which is a component, and / or a polyimide structure using an acyclic aliphatic compound as an acid anhydride. I knew I couldn't. In addition, the first cause of the decrease in light transmittance in the wavelength 0.85 μm band is that it has a benzene ring structure having a C—H bond as a polyimide structure. There is almost a correlation between the number and the light absorption, and when both the diamine and the acid dianhydride constituting the polyimide have a benzene ring structure having a C—H bond, the light absorption is remarkable. It became clear. Further, it was found that the refractive index was lowered by the introduction of the cycloaliphatic structure and could be precisely controlled by the fluorine content.

The optical component of the present invention is characterized by being manufactured by using a specific fluorinated polyimide for the optical waveguide. That is, a diamine containing two or more cyclohexyl rings and two or more fluoroalkyl groups is used as a diamine component which is a raw material of a fluorinated polyimide, and C is contained in a repeating unit.
By reducing the number of benzene rings containing a -H bond, the light absorption based on the benzene ring containing a C-H bond, which is the cause of the decrease in light transmittance in the wavelength 0.85 µm band, is reduced, and the fluorine atom The light transmittance can be improved by introducing Further, by containing an alicyclic structure in the main chain, sufficient heat resistance against soldering can be imparted. Furthermore, the introduction of the cyclic aliphatic structure lowers the refractive index, and the refractive index can be precisely controlled by the fluorine content.

Examples of the diamine which is a raw material of the fluorinated polyimide used for manufacturing the optical component of the present invention include, for example, 2,2
-Bis (4-aminocyclohexyl) -hexafluoropropane (hereinafter referred to as 6FBACP), 2,2'-bis (trifluoromethyl) -4,4'-diaminobicyclohexyl (hereinafter referred to as TFDBCH) and the like. .
This can be synthesized by the reduction reaction of the corresponding aromatic diamine, and has the advantage that the raw material cost of the diamine and the polyimide obtained by polymerization are low cost. Further, as long as these diamines are contained, a polyimide which is a copolymer containing diamines other than the above may be used. Other diamines that can be used in combination within the range that does not impair the characteristics of the fluorinated polyimide used for producing the optical component of the present invention include 2,2′-bis (trifluoromethyl) -4,4′-diaminobiphenyl (hereinafter referred to as TFDB. ), 2,2-bis (p-aminophenyl) hexafluoropropane, 2,2′-dimethylbenzidine, 3,3′-dimethylbenzidine, 4,4′-oxydianiline and the like.

The tetracarboxylic acid and its derivative components, which are the raw materials for the fluorinated polyimide used in the production of the optical component of the present invention, are not particularly limited, but specific examples are as follows. is there. Here, an example of tetracarboxylic acid will be given. 2,2-bis (3,4-
Dicarboxyphenyl) hexafluoropropane, 1,
2,3,4-tetracarboxycyclobutane, 1,2,
4,5-tetracarboxycyclohexane, 3,3 ',
4,4'-tetracarboxydiphenyl ether, 3,
3 ', 4,4'-benzophenone tetracarboxylic acid,
3,3 ', 4,4'-tetracarboxydiphenyl sulfone, pyromellitic acid and the like can be mentioned. These tetracarboxylic acids and their derivatives may be used alone,
You may mix and use it. In order to obtain high heat resistance and high light transmittance, it is preferable to use one having a cyclobutane ring or a cyclohexane ring structure.

For the production of the fluorinated polyimide, a usual method for producing a polyimide can be applied. That is, diamine and acid dianhydride are polymerized in a polar solvent such as N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide to prepare a polyamic acid solution, and then heat imidization or It is chemically imidized to obtain polyimide. At this time, a method of reacting a disilylated diamine and an acid dianhydride to synthesize a silyl ester of a polyamic acid can also be adopted. In the production of the fluorinated polyimide in the present invention, the mixing ratio of the diamine component and the tetracarboxylic acid component is such that the total number of moles of each component is equal or almost equal. Alternatively, a vacuum vapor deposition polymerization method without using a solvent may be used.

The fluorinated polyimide used for producing the optical component of the present invention is characterized by containing the structures represented by the following general formulas (1) and (2) in the repeating unit, and has a high heat resistance. It is suitable for exhibiting the properties, high light transmittance in the wavelength band of 0.85 μm, and refractive index matching with quartz glass.

[0020]

[Chemical 3]

The above-mentioned polyamic acid solution or polyimide solution is applied onto an optical substrate such as silicon, polyimide, quartz, or glass by a spin coating method or a printing method, and dried and cured by a heating device to form a polyimide film. It is possible. If necessary, these films can be patterned by a known method using photolithography and reactive ion etching, and by forming them into a predetermined shape, they become optical parts.

Examples of the optical component in the present invention include an optical waveguide, an optical switching device, an optical branching device, an optical multiplexer, an optical filter, an optical modulator and an optical splitter.

[0023]

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Pyrolysis temperature (temperature at which weight is reduced by 10%),
The glass transition temperature was measured under a nitrogen stream at a temperature rising rate of 10 ° C./min. The refractive index and the light transmission loss of the film are the prism coupling type refractometer (2010 type manufactured by Metricon).
Was measured using. Refractive index 22 ° C, wavelength 0.83μ
m, measured in TE mode. The light transmission loss is measured by measuring the intensity of the scattered light generated at this time through a polyimide prism through a coupler prism with a wavelength of 0.83 μm, and measuring the intensity of the scattered light from the direction perpendicular to the film surface. The light transmission loss was calculated and determined. The optical propagation loss of the ridge-type linear optical waveguide was determined by the cutback method at multimode and wavelength of 0.85 μm.

Example 1 6FBAC was added to a three-necked flask.
P6.92 g (0.02 mol) and 2,2-bis (3,3
4-Dicarboxyphenyl) hexafluoropropane dianhydride (hereinafter referred to as 6FDA) 8.88 g (0.02 m
ol) and N, N-dimethylacetamide 89, 5 g were added. This mixture was stirred at room temperature under a nitrogen atmosphere for 3 days to obtain a polyamide solution having a concentration of about 15 wt% (hereinafter 6FBA).
CP / 6 FDA polyamic acid solution) was obtained. This solution is cast on a silicon wafer and 70 in an oven
℃ 1 hour, 160 ℃ 1 hour, 250 ℃ 1 hour, 350 ℃
Heat imidization was performed for 1 hour to obtain a polyimide film. The thermal decomposition temperature of this polyimide film is 510 ° C,
The glass transition temperature was 290 ° C., the refractive index was 1.495, and the light transmission loss was 0.4 dB / cm. It has heat resistance,
A suitable optical material having a high light transmittance in the 0.85 μm band was obtained.

[Example 2] 6FBAC was added to a three-necked flask.
P 6.92 g (0.02 mol) and 1,2,3,4-tetracarboxycyclobutane dianhydride 3.92 g (0.
02 mol) and N, N-dimethylacetamide 61,
4 g was added. This mixture was stirred at room temperature for 3 days under a nitrogen atmosphere, and a polyamide solution having a concentration of about 15 wt% (hereinafter referred to as 6
FBACP / CB polyamic acid solution) was obtained. This solution is cast on a silicon wafer and placed in an oven.
0 ° C 1 hour, 160 ° C 1 hour, 250 ° C 1 hour, 350
The polyimide film was obtained by heating and imidizing at 1 ° C. for 1 hour. The thermal decomposition temperature of this polyimide film is 480.
℃, glass transition temperature 300 ℃, refractive index 1.481,
The light transmission loss was 0.3 dB / cm. A suitable optical material having heat resistance and high light transmittance in the 0.85 μm band was obtained.

Example 3 TFDBC was placed in a three-necked flask.
H 6.64 g (0.02 mol) and 6FDA 8.88 g
(0.02 mol) and N, N-dimethylacetamide 87, 9 g were added. This mixture was stirred under a nitrogen atmosphere at room temperature for 3 days to obtain a polyamide solution having a concentration of about 15 wt% (hereinafter referred to as TFDBCH / 6FDA polyamic acid solution). Cast this solution on a silicon wafer,
70 ° C for 1 hour, 160 ° C for 1 hour, 250 ° C in the oven
Heat imidization was performed for 1 hour at 350 ° C. for 1 hour to obtain a polyimide film. The polyimide film had a thermal decomposition temperature of 520 ° C., a glass transition temperature of 295 ° C., a refractive index of 1.502, and a light transmission loss of 0.4 dB / cm.
A suitable optical material having heat resistance and high light transmittance in the 0.85 μm band was obtained.

Example 4 A ridge type linear optical waveguide was manufactured. 6FBACP / CB polyamic acid solution was cast on a 4-inch silicon wafer, and heat imidization was performed in an oven at 70 ° C for 1 hour, 160 ° C for 1 hour, 250 ° C for 1 hour, and 350 ° C for 1 hour, and the lower clad layer was 40 microns. A film was formed. On this lower clad layer, 6FBACP / 6
An FDA polyamic acid solution was applied and baked in the same manner as the lower clad layer to form a core layer of 30 μm. The relative refractive index difference between the core and the clad was set to 1.0%. Silicon was formed as a mask layer on the core layer to a thickness of 1.2 μm by magnetron sputtering. A resist layer was further formed on this mask layer, and the optical waveguide pattern was exposed using an aligner to form a patterned resist layer.
Next, the silicon of the mask layer not protected by the resist layer was etched by using a RIE apparatus while flowing CF ₄ gas. Subsequently, O ₂ gas was introduced to remove the core layer portion of the mask layer which was not protected by silicon by etching to form a linear core pattern having a length of 70 mm, a width of 30 μm and a height of 30 μm. Next, the substrate was immersed in dilute hydrofluoric acid to remove the mask layer. Further, similarly to the lower clad, an upper clad layer having a thickness of 40 μm was formed using a 6FBACP / CB polyamic acid solution. When 0.85 μm light was passed through the fabricated straight waveguide and the optical propagation loss was measured by the cutback method, it was 0.4 dB /
Thus, a suitable optical waveguide having a low loss and heat resistance was obtained as an optical waveguide for the 0.85 μm band.

Example 5 A Mach-Zehnder type thermo-optical switch was manufactured. Using SiO2-GeO2-based glass, glass particles were deposited on the lower clad layer and the core layer on the silicon substrate by the flame deposition method. Then 1300
It was heated to ℃ and melted into glass (refractive index of about 1.50,
Relative refractive index difference 0.75%). A Mach-Zehnder interferometer pattern was formed using photolithography technology and reactive ion etching (waveguide width and height were 8 μm,
The straight part of the branch is 7 mm). TF for the upper clad material
Using a DBCH / 6FDA polyamic acid solution, heating imidization was performed in an oven to form an upper clad layer (refractive index was 1.50, which is the same as that of the lower clad layer). A Cr metal film serving as a heating electrode was formed on the upper cladding of the Mach-Zehnder interferometer by vacuum evaporation. After spin coating a photoresist on the Cr metal film, the mask pattern of the electrode was transferred to the resist by photolithography. Cr was etched using the photoresist as a mask to prepare an electrode. TE mode light with a wavelength of 850 nm was introduced from the light incident end of the manufactured optical waveguide, and the characteristics of the Mach-Zehnder type thermo-optical switch were evaluated. As a result, the switching time was 4 milliseconds and the operating power was 10 m.
It was found that W, extinction ratio was 40 dB, insertion loss was 0.6 dB, and that the device operates as a low power, high speed optical switch.

[Comparative Example 1] TFDB was added to a three-necked flask.
6.40 g (0.02 mol) and 6FDA 8.88 g
(0.02 mol) and N, N-dimethylacetamide 86, 6 g were added. This mixture was stirred at room temperature for 3 days under a nitrogen atmosphere to obtain a polyamide solution having a concentration of about 15 wt% (hereinafter referred to as TFDB / 6FDA polyamic acid solution). This solution was cast on a silicon wafer and heated and imidized in an oven at 70 ° C. for 1 hour, 160 ° C. for 1 hour, 250 ° C. for 1 hour, and 350 ° C. for 1 hour to obtain a benzene ring-containing polyimide film. The thermal decomposition temperature of this polyimide film is 535 ° C, the glass transition temperature is 330 ° C,
Since the refractive index was 1.531 and the light transmission loss was 1.0 dB / cm, the light transmission loss was large and it was unsuitable as an optical material for the 0.85 μm band.

Comparative Example 2 A Mach-Zehnder type thermo-optical switch was manufactured by the same method as in Example 5, except that the upper clad material was changed to SiO2-GeO2-based glass. The characteristics of the fabricated Mach-Zehnder type thermo-optic optical switch were evaluated. As a result, the switching time was 3 milliseconds, the operating power was 400 mW, the extinction ratio was 35 dB, and the insertion loss was 0.5 dB. It was unsuitable.

[0031]

According to the method of the present invention, an optical component having heat resistance, light transmission in the wavelength band of 0.85 μm, and low cost can be manufactured.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kazuhiko Maeda             3-7-1 cent Kandanishikicho, Chiyoda-ku, Tokyo             Inside Ral Glass Co., Ltd. (72) Inventor Shigeki Sakaguchi             3-7-1 cent Kandanishikicho, Chiyoda-ku, Tokyo             Inside Ral Glass Co., Ltd. F-term (reference) 2H047 NA01 PA02 QA05 RA08                 4J043 PA01 PB08 PB15 QB31 RA35                       SA06 SA46 SA54 SB01 SB03                       TA13 TA14 TA22 TA70 TA71                       TA74 TB01 UA02 UA03 UA04                       UB01 UB05 UB12 XA19 YA06                       ZA51 ZA52

Claims (4)

[Claims] 1. A fluorinated polyimide comprising a fluorine-containing alicyclic diamine containing at least two cyclohexyl rings and two fluoroalkyl groups in a molecule, which is used as at least a part of a monomer. Optical parts to do. 2. A fluorinated polyimide containing any of the repeating units represented by the general formulas (1) and (2) in at least one of a lower clad layer, a core layer and an upper clad layer constituting an optical waveguide. Optical parts characterized by being used. [Chemical 1] (In the formula, R is one or more tetravalent organic groups selected from straight chain, branched chain, alicyclic ring, aromatic ring, and hetero ring, and may partially contain fluorine, oxygen, or nitrogen.) 3. The optical component according to claim 1, which is used in a wavelength band of 0.85 μm. 4. An optical component used as a thermo-optical switch, characterized in that at least an upper clad layer of an optical waveguide is composed of the fluorinated polyimide according to claim 1.