JP2813713B2 - Polyimide optical waveguide - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide, and more particularly to a plastic optical waveguide excellent in heat resistance.

[Conventional technology]

With the practical use of optical communication systems by the development of low-loss optical fibers, development of various optical communication components has been desired.
It is also desired to establish an optical wiring technology for mounting these optical components at a high density, particularly an optical waveguide technology.

In general, optical waveguides are required to have conditions such as low optical loss, easy manufacture, control of the refractive index difference between the core and clad, and excellent heat resistance.

As a low-loss optical waveguide, a silica-based optical waveguide is mainly studied. As demonstrated in optical fibers, quartz has extremely good light transmittance, so even when used as a waveguide, a 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, plastic optical waveguides such as polymethyl methacrylate (PMMA) can be molded at low temperatures, and can be expected to be low in price, but have poor heat resistance.
There are drawbacks such as insufficient loss reduction at long wavelengths.

[Problems to be Solved by the Invention] As shown in the prior art, there are problems with both silica-based optical waveguides and plastic-based optical waveguides, and at present, optical waveguides satisfying the above four conditions required for optical waveguides. The wave path has not been obtained.

SUMMARY OF THE INVENTION An object of the present invention is to provide a low-loss optical waveguide that can easily control the difference in refractive index, is easy to manufacture, and has good heat resistance.

[Means for solving the problem]

To summarize the present invention, the present invention relates to a polyimide-based optical waveguide, and in a polyimide-based optical waveguide comprising a polyimide obtained from tetracarboxylic dianhydride and a diamine, the polyimide has the following structure: Formula I: Or a polyimide from a diamine containing the same, or a mixture thereof.

The present invention is characterized in that polyimide having the highest heat resistance among plastics is used for one or both of the core layer and the cladding layer of the optical waveguide. Polyimide has a heat resistance temperature of 300 ° C. or higher, and sufficiently retains solder heat resistance, which is an important property as an electronic material. Further, the spin coating method has an advantage that a large area waveguide can be easily manufactured, and the cost of the waveguide can be reduced.
Further, since the production temperature of the polyimide waveguide is usually 400 ° C. or less, there is an advantage that it can be produced on a general-purpose substrate already used as an electric wiring substrate such as polyimide in addition to quartz and silicone. On the other hand, the polyimides already on the market have high hygroscopicity and have disadvantages such as a change in the refractive index during use and a large light loss due to material absorption. The present inventors have synthesized various polyimides with the aim of applying optical waveguides and studied the applicability. As a result, they have found that good optical waveguides can be formed in the following fluorinated polyimide group. That is, in the polyimide obtained from the tetracarboxylic dianhydride and the diamine, it is necessary to use a polyimide from the diamine represented by the above structural formula I or a diamine containing the same or a mixture thereof as a component of the optical waveguide. .

As the tetracarboxylic dianhydride used in the present invention,
For example, pyromellitic dianhydride, 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride, 3,3', 4,4'-biphenyltetracarboxylic dianhydride, 2,2-bis ( 3,4-
Dicarboxyphenyl) -hexafluoropropane dianhydride, trifluoromethylpyromellitic dianhydride, 1,
4-di (trifluoromethyl) pyromellitic dianhydride, 1,4-di (pentafluoromethyl) pyromellitic dianhydride, heptafluoropropylpyromellitic dianhydride and the like. Among them, trifluoromethyl pyromellitic dianhydride, which is a fluorinated dianhydride having a fluoroalkyl group introduced into the benzene ring of pyromellitic acid,
A method for producing 1,4-di (trifluoromethyl) pyromellitic dianhydride, 1,4-di (pentafluoroethyl) pyromellitic dianhydride, heptafluoropropyl pyromellitic dianhydride, etc. is a patent application. It is described in the specification of Sho 63-165056.

Further, as the diamine other than the diamine represented by the formula I, 3,3'-dimethyl-4,4'-diaminobiphenyl, 4,4
4'-diamino-p-terphenyl and the like. 2,2 '-(bistrifluoromethyl) -4 of the formula I
The method for producing 4'-diaminobiphenyl is described, for example, in The Chemical Society of Japan, Vol. 1972, No. 3, pp. 675-676 (1972).

The method for producing the polyamic acid which is a precursor of the polyimide used in the present invention may be the same as the production conditions for ordinary polyamic acid, and is generally N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N The reaction is carried out in a polar organic solvent such as N-dimethylformamide. In the present invention, not only a diamine or tetracarboxylic dianhydride co-single compound may be used, but also a plurality of diamines and tetracarboxylic dianhydrides may be mixed and used. In that case, the sum of the number of moles of a plurality or a single diamine and the sum of the number of moles of a plurality or a single tetracarboxylic dianhydride are equal or almost equal.

Next, a polyimide is synthesized by imidization of the obtained polyamic acid, and an ordinary polyimide synthesis method can be used. In the present invention, in addition to imidation of a single polyamic acid, imidation in a state in which a plurality of polyamic acids are mixed is performed to obtain a polyimide mixture.

The structure of the optical waveguide of the present invention may be the same as that of all optical waveguides generally manufactured, and examples thereof include a fiber type, a planar type, a ridge type, a lens type, and a buried type. The selection of the core material and the clad material of the optical waveguide may be made so that the difference in the refractive index suitable for the wavelength of light and the intended use is obtained.

A ridge type manufacturing method will be described with reference to FIG. That is, FIG. 1 is a process diagram showing an example of a method for producing a ridge-type optical waveguide according to the present invention, wherein reference numeral 1 denotes a substrate, 2 denotes a lower cladding layer, 3 denotes a core layer, 4 denotes an aluminum layer, and 5 denotes a resist layer. Means Substrate 1 of silicon etc.
The lower cladding layer 2 is obtained by applying a predetermined thickness of a polyamic acid capable of forming a polyimide, which is a constituent element of the present invention, and heating it. Next, the lower cladding layer 2
A polyamic acid capable of forming polyimide, which is a constituent element of the present invention having a higher refractive index than the lower cladding layer, is applied thereon to a predetermined thickness, and heated to obtain the core layer 3. Next, after applying an aluminum layer 4 by vapor deposition, resist coating, pre-baking, exposure, development, and after-baking are performed to obtain a patterned resist layer 5. After the aluminum is removed by wet etching, the polyimide is removed by dry etching. Finally, the remaining aluminum layer 4 is removed by wet etching to obtain an optical waveguide. In this way, a ridge type optical waveguide in which the lower clad layer and the core layer are polyimide, which is a component of the present invention, and the upper clad layer is an air layer, is obtained.

As shown in FIG. 2, an upper cladding layer 6 made of polyimide, which is a component of the present invention, having a lower refractive index than the core layer, is formed on the ridge-type optical waveguide of FIG. The embedded optical waveguide of polyimide, which is a component of the present invention, is obtained for all of the layers, the core layer, and the upper clad layer. That is, FIG. 2 is a cross-sectional view of an example of the embedded optical waveguide, and reference numerals 1 to 3 have the same meaning as in FIG.
Reference numeral 6 denotes an upper cladding layer.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to some examples. It is clear that an infinite number of polyimide-based optical waveguides of the present invention can be obtained by various combinations of polyimides and optical waveguide structures, and the present invention is not limited to only these examples.

Table 1 shows the thermal decomposition temperature and the refractive index of the polyimide and the mixture thereof used in this example. The thermal decomposition temperature was shown as the temperature at which the weight was reduced by 10 wt% when the temperature was increased at a rate of 10 ° C./min under a nitrogen stream. Refractive index is 20 ° C using Abbe refractometer
Indicates the refractive index at a wavelength of 589 nm. In Table 1, Nos. 1 to 6 are polyimides alone, Nos. 7 to 15 are polyimide copolymers, and Nos. 16 to 20 are polyimide mixtures.

As described above, the polyimide and the composition used in this example have a refractive index between 1.49 and 1.65, which is fine,
The refractive index difference between the core and the clad using these can be freely controlled. In addition, the thermal decomposition temperature is as high as 500 ° C or more, and it has heat resistance enough to withstand solder.

Examples of optical waveguides manufactured using the polyimides and their mixtures shown in Table 1 are shown. The light propagation loss was measured by passing light having wavelengths of 0.63 μm, 0.85 μm and 1.3 μm through the manufactured optical waveguide by a streak light scattering method or a cutback method.

Example 1 A 10 wt% solution of dimethylacetamide of polyamic acid, which is a precursor of the polyimide of No. 1 in Table 1, was spun onto a 3-inch diameter silicon wafer having a silicon oxide layer so that the film thickness after heating was 10 μm. After coating by a coating method, heat treatment was performed at a maximum temperature of 350 ° C. Thus, the simplest planar optical waveguide having the lower clad layer as the silicon oxide layer, the core layer as the polyimide of No. 1 in Table 1, and the upper clad layer as the air layer was obtained. This optical waveguide has a wavelength of 0.63
As a result of measuring a light propagation loss by a streak light scattering method through light of μm, it was 0.85 dB / cm.

Examples 2 to 20 Dimethylacetamide of polyamic acid which is a precursor of the polyimide of No. 1 in Table 1 used in Example 1
A lower cladding layer was formed in the same manner as in Example 1 by using a 10 wt% solution of dimethylacetamide of polyamic acid which is a precursor of a polyimide selected from Nos. 2 to 20 in Table 1 and a mixture thereof instead of the 10 wt% solution. The simplest planar optical waveguide in which the silicon oxide layer, the core layer was polyimide selected from Nos. 2 to 20 in Table 1, and the upper clad layer was an air layer was obtained. Light having a wavelength of 0.63 μm was passed through this optical waveguide, and the light propagation loss was measured by the streak light scattering method. Table 2 shows the results.

Example 21 A 10 wt% solution of dimethylacetamide of polyamic acid, which is a precursor of polyimide of No. 15 in Table 1, was spun on a 3-inch diameter silicon wafer having a silicon oxide layer so that the film thickness after heating was 30 μm. It was applied by a coating method. This coating film was heat-treated at a maximum temperature of 350 ° C. to form a lower cladding layer. Subsequently, a 10 wt% solution of dimethylacetamide of polyamic acid, which is a precursor of the polyimide of No. 1 in Table 1, was applied onto the lower clad layer by spin coating so that the film thickness after heating was 10 μm.
This coating film was heat-treated at a maximum temperature of 350 ° C. to form a core layer. Next, aluminum was removed by an electron beam evaporation machine.
After attaching 3 μm, resist processing was performed. First, a normal positive resist was applied by spin coating, and then prebaked at about 95 ° C. Next, ultraviolet rays were irradiated through a pattern forming mask having a line width of 10 μm and a length of 60 mm using an ultrahigh pressure mercury lamp, and then developed using a developing solution for a positive resist. Thereafter, after-baking was performed at 135 ° C. Next, wet etching of aluminum not coated with a resist was performed. After washing and drying, RIE processing of the polyimide was performed using a dry etching apparatus. Finally, the aluminum in the upper layer of the polyimide was removed with the above-mentioned etching solution, and the lower cladding layer was made of the polyimide of No. 15 in Table 1,
A ridge type optical waveguide was obtained in which the core layer was polyimide of No. 1 in Table 1 and the upper cladding layer was an air layer. The light having a wavelength of 0.85 μm was passed through this optical waveguide, and the light propagation loss was measured by the cutback method. The result was 0.70 dB / cm. In addition, wavelength 1.3μm
Was 0.3 dB / cm.

Examples 22 to 40 Table 1 used as a lower cladding layer in Example 21
No. 8 in Table 1 was used instead of a 10 wt% solution of polyamic acid, which is a precursor of the polyimide No. 15 in dimethylacetamide.
A 10 wt% solution of polyamic acid dimethylacetamide, a precursor of a polyimide selected from Nos. To 14, was used, and a 10 wt% solution of dimethylacetamide of polyamic acid, a precursor of the polyimide of No. 1 in Table 1 used as a core layer was used. Instead, using a 10 wt% solution of dimethylacetamide of polyamic acid, which is a precursor of polyimide having a higher refractive index than the lower cladding layer selected from Nos. 1 and 12 to 14 in Table 1, in the same manner as in Example 21, A ridge type optical waveguide having a clad layer and a polyimide selected from Nos. 1 and 8 to 14 in Table 1 for the core layer and an air layer in the upper clad layer was obtained. Light having a wavelength of 0.85 μm was passed through this optical waveguide, and the light propagation loss was measured by the cutback method. Table 3 shows the results.

Examples 41 to 60 A 10 wt% solution of dimethylacetamide of polyamic acid, which is a polyimide precursor similar to the lower clad layer, was heated on the ridge-type optical waveguide prepared in Examples 21 to 40, and the film thickness became 30 μm. Was applied by a spin coating method as described above. This coating film was heat-treated at a maximum temperature of 350 ° C. to form an upper clad layer. Thus, the lower cladding layer,
A buried optical waveguide using polyimide, which is a component of the present invention, for both the core layer and the upper cladding layer was obtained. Light having a wavelength of 0.85 μm was passed through this optical waveguide, and the light propagation loss was measured by the cutback method. Table 4 shows the results. Example 41
The light propagation loss of the optical waveguide at a wavelength of 1.3 μm was 0.1 dB / cm.

[Effects of the Invention] According to the present invention, a conventional silica-based optical waveguide, a low-loss optical waveguide that can easily control a refractive index difference not obtained by a plastic-based optical waveguide, is easy to manufacture, and has good heat resistance. Can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a process diagram showing an example of a method for manufacturing a ridge-type optical waveguide according to the present invention, and FIG. 2 is a cross-sectional view showing an example of a buried optical waveguide. 1: substrate, 2: lower cladding layer, 3: core layer, 4: aluminum layer, 5: resist layer, 6: upper cladding layer

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Fumio Yamamoto 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Shinji Ando 1-16-1 Uchisaiwaicho, Chiyoda-ku, Tokyo Japan Within Telegraph and Telephone Co., Ltd. (72) Inventor Shigekuni Sasaki 1-1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Co., Ltd. (58) Field surveyed (Int. Cl. ⁶ , DB name) G02B 6/12 C08F 73/10

Claims (1)

(57) [Claims] 1. A polyimide-based optical waveguide comprising a polyimide obtained from a tetracarboxylic dianhydride and a diamine as a component, wherein the polyimide has the following structural formula I: Or a polyimide from a diamine containing the same, or a mixture thereof.