JPH049807A - Polyimide optical waveguide - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an optical waveguide, and particularly to a plastic optical waveguide with excellent heat resistance.

[Conventional technology]

BACKGROUND OF THE INVENTION With the development of low-loss optical fibers and the practical use of optical communication systems, the development of various optical communication components is desired. Furthermore, it is desired to establish optical wiring technology, especially optical waveguide technology, for mounting these optical components at high density.

Generally, optical waveguides are required to meet the following conditions: (1) low optical loss, (2) easy manufacturing, (2) controllable refractive index difference between the core and cladding, and (2) excellent heat resistance.

Quartz-based optical waveguides are mainly being considered as low-loss optical waveguides. As has already been demonstrated in optical fibers, quartz has extremely good optical transparency, and even when used as a waveguide, a loss of 0.16 B/cm or less has been achieved at a wavelength of 1.3 μm. However, there are manufacturing problems, such as the long time it takes to fabricate the optical waveguide, the need for high temperatures during fabrication, and the 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 inexpensive, but they have poor heat resistance and have not achieved sufficiently low loss at long wavelengths. There are drawbacks such as.

[Problem to be solved by the invention]

As shown in the prior art, both quartz-based optical waveguides and plastic-based optical waveguides have problems, and at present no optical waveguide has been obtained that satisfies the above four conditions required for an optical waveguide.

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

[Means to solve the problem]

To summarize the present invention, the present invention relates to a polyimide optical waveguide having a polyimide obtained from a tetracarboxylic dianhydride and a diamine as a constituent element, wherein the polyimide has the following structure. It is characterized by being a polyimide made from a diamine represented by the formula (2): F, or a diamine containing the same, or a mixture thereof.

The present invention is characterized in that polyimide, which has the highest heat resistance among plastics, is used for either or both of the core layer and cladding layer of the leading waveguide. The heat resistance temperature of polyimide is 300° C. or higher, and it sufficiently maintains solder heat resistance, which is an important property for electronic materials. Furthermore, the spin code method has the advantage that a large-area waveguide can be easily produced, and the cost of the waveguide can be reduced.

Furthermore, since the manufacturing temperature of polyimide waveguides is usually 400° C. or lower, they have the advantage that they can be manufactured on general-purpose substrates that are already used as electrical wiring boards, such as polyimide in addition to quartz and silicone. - The polyimide coated on the blade has high hygroscopicity, which has drawbacks such as a change in refractive index during use and large light loss due to material absorption. The present inventors synthesized various polyimides and examined their applicability with the aim of applying them to optical waveguides, and as a result, they found that a good optical waveguide could be formed using the fluorinated polyimide group shown below. That is, in polyimide obtained from tetracarboxylic dianhydride and diamine,
It is necessary to use the diamine represented by the above structural formula I or a polyimide made from a diamine containing the same, or a mixture thereof as a constituent element of the optical waveguide.

Examples of the tetracarboxylic dianhydride used in the present invention include pyromellitic dianhydride, 3°3', 4.4'
-benzophenone tetracarboxylic dianhydride, 3.3'
, 4.4'-biphenyltetracarboxylic dianhydride, 2.2-bis(3,4-dicarboxyphenyl)-hexafluorobrovannianhydride, trifluoromethylpyromellitic dianhydride, 1.4- Examples include di(trifluoromethyl)pyromellitic dianhydride, 1°4-di(pentafluoroethyl)pyromellitic dianhydride, heptafluoropropylpyromellitic dianhydride, and the like. Among them, trifluoromethylpyromellitic dianhydride, which is a fluorine-containing dianhydride with a fluoroalkyl group introduced into the benzene ring of pyromellitic acid, and 1,4-di(trifluoromethyl)pyromellitic dianhydride. Methods for producing 1,4-di(pentafluoroethyl)pyromellitic dianhydride, heptafluoropropylpyromellitic dianhydride, etc. are described in Japanese Patent Application No. 165056/1983.

Further, as diamines other than the diamine represented by formula I,
Examples thereof include 3.3'-dimethyl-4,4'-diaminobiphenyl and 4.4'-diamino-p-terphenyl. The method for producing 2,2'-(bistrifluoromethyl)-4°4'-diaminobiphenyl represented by the formula (■) is described, for example, in Journal of the Chemical Society of Japan, Vol. 1972, No. 3,
No. 675-676 (1972).

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

Next, polyimide is synthesized by imidizing the obtained polyamic acid, and a conventional polyimide synthesis method can be used. In the present invention, in addition to imidization of a single polyamic acid, a mixture of a plurality of polyamic acids is imidized to obtain a polyimide mixture.

The structure of the optical waveguide of the present invention may be the same as all commonly manufactured optical waveguides, such as fiber type, planar type, ridge type, lens type, and buried type. The core material and cladding material of the optical waveguide may be selected so that the difference in refractive index is appropriate for the wavelength of light and the intended use.

A method for manufacturing the ridge type will be explained with reference to FIG. That is, FIG. 1 is a process diagram showing an example of a method for manufacturing a ridge type optical waveguide according to the present invention, in which reference numeral 1 indicates a substrate;
2 means a lower cladding layer, 3 means a core layer, 4 means an aluminum layer, and 5 means a resist layer. A lower cladding layer 2 is obtained by coating a polyamic acid capable of forming polyimide, which is a component of the present invention, to a predetermined thickness on a substrate 1 made of silicon or the like and heating it. Next, a polyamic acid capable of forming polyimide, which is a component of the present invention having a higher refractive index than the lower cladding layer, is coated on the lower cladding layer 2 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-beta, exposure, development, and after-beta are performed.
A patterned resist layer 5 is obtained. 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 guided waveguide is obtained in which the lower cladding layer and the core layer are made of polyimide, which is a component of the present invention, and the upper cladding layer is an air layer.

Also, as shown in FIG. By forming the upper cladding layer 6 made of polyimide, which is a component of the present invention and has a lower refractive index than the core layer, on the ridge-type optical waveguide of J, the lower cladding layer, the core layer, and the upper cladding layer can be combined with the present invention. A buried optical waveguide made of polyimide is obtained. That is, FIG. 2 is a cross-sectional view of an example of a buried optical waveguide, where symbols 1 to 3 have the same meanings as in FIG. 1, and 6 means an upper cladding layer.

〔Example〕

The present invention will be explained in more detail below using some examples. Note that it is clear that an infinite number of polyimide optical waveguides of the present invention can be obtained by combining various polyimides and by changing the guiding waveguide structure, and the present invention is not limited to these examples.

Table 1 shows the thermal decomposition temperature and refractive index of the polyimide and its mixture used in this example. The thermal decomposition temperature was expressed as the 10 wt% weight loss temperature when the temperature was raised at a rate of 10° C./min under a nitrogen stream. The refractive index was measured using an Atsube refractometer.
It is shown as a refractive index at a wavelength of 589 nm at 20°C. In Table 1, numbers 1 to 6 are polyimide alone, and numbers 7 to 6 are polyimide alone.
15 is a polyimide copolymer, and numbers 16 to 20 are polyimide mixtures.

Table 1-1 Characteristics 3 of polyimide used in this example!
l-2 Characteristics of the polyimide mixture used in this example As described above, the polyimide and its composition used in this example have a fine refractive index between 1.49 and 1.65. The refractive index difference between the core and cladding can be freely controlled. In addition, the thermal decomposition temperature is as high as 500°C or higher for all of them, and they have sufficient heat resistance to withstand solder.

Examples of optical waveguides fabricated using polyimides and mixtures thereof shown in Table 1 are shown below. Note that the optical propagation loss was measured at wavelengths of 0.63 μm, 0.85 μm, and 1.3 μm in the fabricated leading waveguide.
It was measured by streak light scattering method or cutback method through μm light.

Example 1 A 10 wt % dimethylacetamide solution of polyamic acid, which is a precursor of polyimide No. 1 in Table 1, was spun on a silicon wafer with a diameter of 3 inches with a silicon oxide layer on the surface so that the film thickness after heating was 10 μm. After coating by the cord method, it was heat-treated at a maximum temperature of 350°C. In this way, the simplest planar optical waveguide was obtained, in which the lower cladding layer was a silicon oxide layer, the core layer was made of polyimide number 1 in Table 1, and the upper cladding layer was an air layer. When light with a wavelength of 0.63 μm was passed through this optical waveguide and the optical propagation loss was measured by a streak light scattering method, it was found to be 0.85 dB/cm.

Examples 2 to 20 Dimethylacetamide 1 of polyamic acid, which is a precursor of polyimide number 1 in Table 1 used in Example 1
The lower cladding layer was formed in the same manner as in Example 1 using a 10 wt % dimethylacetamide solution of polyamic acid, which is a precursor of a polyimide selected from numbers 2 to 20 in Table 1 and a mixture thereof, instead of the 0 wt % solution. The simplest planar optical waveguide was obtained, in which the silicon oxide layer, the core layer was made of polyimide selected from numbers 2 to 20 in Table 1, and the upper cladding layer was an air layer. Light with a wavelength of 0.63 μm was passed through this optical waveguide, and the optical propagation loss was measured by IJ-reflection light scattering method. The results are shown in Table 2.

Table 2 Optical propagation loss of planar optical waveguide (wavelength 0.63μ
l) Example 21 A 10 wt % dimethylacetamide solution of polyamic acid, which is a precursor of polyimide No. 15 in Table 1, was heated on a silicon wafer with a diameter of 3 inches and whose surface was a silicon oxide layer so that the film thickness after heating was 30 μm. It was applied using the spin code method. This coating film was heat-treated at a maximum temperature of 350°C to form a lower cladding layer. Subsequently, on this lower cladding layer, a 10 wt % solution of polyamic acid, which is a precursor of polyimide No. 1 in Table 1, in dimethylacetamide was applied by a spin cord method so that the film thickness after heating was 10 μm.

This coating film was heat-treated at a maximum temperature of 350 t to form a core layer. Next, aluminum was deposited to a thickness of 0.3 μm using an electron beam evaporator, and then resist processing was performed. First, a normal positive resist was applied by a spin code method, and then prebaked at about 95°C. Next, ultraviolet rays were irradiated using an ultra-high pressure mercury lamp through a pattern forming mask with a line width of 10 μm and a length of 60 mm, followed by development using a developer for positive resist. Thereafter, after-baking was performed at 135°C. Next, wet etching was performed on the aluminum that was not coated with resist. After washing and drying, polyimide was subjected to RIE processing using a dry etching device. Finally, the aluminum on the upper layer of polyimide is removed using the etching solution described above, and the lower cladding layer is made of polyimide number 15 in Table 1, the core layer is made of polyimide number 1 in Table 1, and the upper cladding layer is an air layer ridge type. A leading wavepath was obtained. The optical propagation loss was measured using the cutback method by passing light with a wavelength of 0.85 μm through this leading wavepath, and the result was 0.706B.
/cm. Further, the optical propagation loss at a wavelength of 1.3 μm was 0.36 B/cm.

Examples 22-40 Table 1 used as the lower cladding layer in Example 21
In place of the dimethylacetamide 1.0 wt% solution of polyamic acid, which is the precursor of polyimide number 15, Table 1
A 10 wt % solution of dimethylacetamide of polyamic acid, which is a precursor of polyimide selected from numbers 8 to 14 of Table 1, was used as a core layer. % solution instead of numbers l and 12~ in Table 1
Both the lower cladding layer and the core layer were prepared in the same manner as in Example 21 using a dimethylacetamide 1.0 wt% solution of polyamic acid, which is a precursor of polyimide having a higher refractive index than the lower cladding layer selected from Table 1. numbers 1 and 8
A ridge-type leading waveguide with an air layer in the upper cladding layer was obtained using polyimide selected from ~14. This optical waveguide has a wavelength of 0.
Light propagation loss was measured using a cutback method through light of 85 μm. The results are shown in Table 3.

Optical propagation loss of ridge type optical waveguide (wavelength 0.85 μs) Optical propagation loss of buried type optical waveguide (wavelength 0.85 μs +
) Examples 41 to 60 A 10 wt % dimethylacetamide solution of polyamic acid, which is a precursor of polyimide similar to that of the lower cladding layer, was heated on top of the edge-type optical waveguides produced in Examples 21 to 40, and the film thickness was as follows. Coating was performed by a spin code method to a thickness of 30 μm. This coating film was heat-treated at a maximum temperature of 350°C to form an upper cladding layer. In this way, a buried guide waveguide was obtained in which the lower cladding layer, the core layer, and the upper cladding layer were all made of polyimide, which is a component of the present invention. Light with a wavelength of 0.85 μm was passed through this optical waveguide and the optical propagation loss was measured using the cutback method. The results are shown in Table 4. Further, the optical propagation loss of the leading waveguide of Example 41 at a wavelength of 1.3 μm was 0.1 dB/cm.

〔Effect of the invention〕

According to the present invention, it is possible to freely control the refractive index difference that cannot be obtained with conventional silica-based optical waveguides and plastic-based optical waveguides, and it is possible to provide a low-loss optical waveguide that is easy to manufacture and has good heat resistance. .

[Brief explanation of the drawing]

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 sectional view of an example of a buried-type optical waveguide. 1: Substrate, 2: Lower cladding layer, 3: Core layer, 4 Ni aluminum layer, 5 Ni resist layer, 6: Upper cladding layer Patent applicant Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] 1. In a polyimide optical waveguide whose constituent elements are polyimide obtained from tetracarboxylic dianhydride and diamine, the polyimide has the following structural formula I: ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼... A polyimide-based optical waveguide characterized by being a polyimide made from a diamine represented by [I] or a diamine containing the same, or a mixture thereof.