JPH0715527B2 - Optical / electrical integrated circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical / electrical integrated circuit in which an electric circuit and an optical waveguide can be easily formed and the optical propagation loss of the optical waveguide is small.

[Conventional technology]

As a substrate for an optical integrated circuit and an optical waveguide, conventionally,
Glass, lithium niobate (LiNbO ₃ ) crystals, gallium arsenide (GaAs) crystals, etc. have been used. Of these,
Lithium niobate and gallium arsenide are expensive because they have high raw materials and mass production technology for producing high quality crystals has not been established. In addition, many problems remain in making the circuit three-dimensional in order to further increase the density of the electric circuit. Moreover, in the current technology, the optical loss of the optical waveguide is several dB.
It is as large as / cm.

On the other hand, although glass is relatively inexpensive, when it is used as a substrate, it has low thermal conductivity, so that in a normal optical / electrical integrated circuit including a light emitting source, the substrate temperature and the element temperature are The rise is unavoidable, which causes unstable operation of the light source.
This causes instability in the light propagation characteristics of the optical waveguide.

On the other hand, methods of forming an optical waveguide with glass on an inexpensive ceramic substrate have been proposed in Japanese Patent Laid-Open Nos. 53-50464 and 59-127005.

However, in these methods, no consideration is given to the reduction of loss of the optical waveguide in terms of structure and material composition. Further, although it is related to the thermal conductivity of the substrate and the reduction of the loss of the optical waveguide, which is required in a circuit including a light emitting source, no consideration is given to the linear expansion coefficient of the substrate and the waveguide.

[Problems to be solved by the invention]

Since the above-mentioned conventional technique does not take into consideration the reduction of the loss of light propagation in the optical waveguide, there is a problem that the light is greatly attenuated during the light propagation.

Further, in the conventional technique, since the thermal conductivity of the substrate is not taken into consideration, there is a problem that the optical waveguide characteristic of the optical circuit becomes unstable.

An object of the present invention is to solve the above problems, and to provide an optical / electrical integrated circuit in which an electric circuit and an optical circuit can be easily formed, the optical propagation loss of the optical waveguide is small, and the operation characteristics are stable.

[Means for solving problems]

The above objects, inexpensive compared with the single crystal of GaAs and LiNbO ₃ as a light condenser static circuit board, printed and electrical circuit formed easily by photolithography or the like, the thermal conductivity of 10W · m ^-1 · K ^{- 1} or more, linear expansion coefficient of 3.5 × 10 ^-6 K ^-1 to 9.0 × 10 ^-6 K ^-1 and a part of electrical wiring provided on the surface, the content of glass component is 10% by weight or less A crystalline substrate, or an amorphous substrate having the above-mentioned two attributes and provided with a part of electric wiring on its surface, and a linear expansion coefficient on this substrate which is not larger than that of this substrate A glass layer whose surface is an optically polished borosilicate as a main component, and further, on the surface of this glass layer, as compared with this glass layer, has a low softening point,
The linear expansion coefficient is not more than the same, and it is achieved by an optical / electrical integrated circuit that is composed of an optical waveguide layer containing silicic acid, boron oxide, barium oxide, niobium oxide, tantalum oxide, lanthanum oxide, zinc oxide, etc. as main components. To be done.

In addition, the substrate has a linear expansion coefficient of 3.5 × 10 ⁻⁶ K ⁻¹ to 9.0 × 10 ⁻⁶ K ⁻¹ and a thermal conductivity of 10 W · m ⁻¹ · K ⁻¹ or more, and one of its surface is The above object can also be achieved by using a polycrystalline or alumophous substrate in which an insulating film is formed on a portion and a part of electric wiring is provided on the insulating film.

[Action]

Since the substrate has a high thermal conductivity of 10 W · m ⁻¹ · K ⁻¹ or more, it is possible to easily dissipate the heat generated by the light emitting diode or semiconductor laser, which is the light source, to the surroundings. Less temperature rise. This stabilizes the operation of these light emitting sources and the light propagation characteristics of the optical waveguide.

As a substrate material, a polycrystalline or amorphous material is used because the manufacturing cost is lower than that of a single crystal such as GaAs or LiNbO ₃ because the cost of the integrated circuit is low, and the multilayered and tertiary circuits are used. The original circuit can be easily made, and this makes it possible to supply small-sized and low-cost integrated circuits.

The linear expansion coefficient of the substrate is set to 3.5 × 10 ^-6 K ^-1 to 9.0 × 10 ^-6 K ^-1 below or above that for the light receiving element, light emitting element, IC, optical device mounted or wired on the substrate. Due to the difference in the linear expansion coefficient between the lens / prism and the wiring conductor, a change in the ambient temperature causes a partial peeling of these from the substrate, which makes operation unstable and it becomes impossible to provide an integrated circuit with stable operation characteristics.

10% by weight of the glass component contained in the polycrystalline substrate
Below, the thermal conductivity is usually 0 if more than this.
This is because glass as low as 5 to 2 W · m ⁻¹ · K ⁻¹ penetrates into the grain boundaries of the polycrystalline substance, and the thermal conductivity of the substrate is greatly reduced.

As a substrate satisfying the above-mentioned characteristics, there are alumina, spinel, AlN, SiC, Fe, Ni, Co alloys (e.g. Kovar) in a polycrystalline body, and amorphous germanium in an amorphous body. Kovar, which has a low insulating property as a substrate, can be used as such a substrate by previously providing an insulating film at the portion where the electrical wiring is provided.

These substrates are generally hard and difficult to polish, but the substrate surface in the present invention does not need to be optically polished.

However, the surface of the glass layer adhered on the substrate needs to be optically polished. This is because it serves as the reference surface of the optical waveguide formed on the glass layer, and the surface of the glass layer is optically smooth, and the interface between the glass layer side of the optical waveguide formed on it and the opposite side However, since it becomes optically smooth, light is not scattered at the waveguide interface during light propagation, and the light propagation loss in the optical waveguide is greatly reduced. The surface polishing of this glass layer is easier to process with glass than polishing the substrate, and the polishing time is short. The linear expansion coefficient of this glass layer is equal to or less than that of the substrate
This is because tensile strain occurs in the glass layer and microcracks are likely to occur in the glass layer. The composition of the glass layer is such that the sum of silicic acid and boron oxide is 60% by weight or more of the total composition because these compositions have the following advantages.

The low index of refraction needed to confine light in the optical waveguide layer can be achieved.

Good compatibility with the substrate (wetting, no chemical reaction during formation, etc.).

In order to efficiently return the exudation of light from the optical waveguide to the optical waveguide again, it is required that the glass layer have high optical uniformity and light transmittance, but at that point a crystal that interferes with optical uniformity. Is less likely to occur and light loss is small.

The softening point of the optical waveguide layer is lower than that of the glass layer because it is heated when the optical waveguide is formed, but at that time, the glass layer flows to deform the optically polished surface and increase the optical waveguide loss. This is to prevent The linear expansion coefficient of the optical waveguide layer is smaller than that of the glass layer because the optical waveguide layer is subjected to compressive stress and tensile stress to the glass layer after formation of the optical waveguide.
This is because the photoelastic effect increases the refractive index of the optical waveguide layer and decreases the refractive index of the glass layer, thereby increasing the light confinement effect in the optical waveguide. The composition of the optical waveguide layer contains two or more components of silicic acid, boron oxide, barium oxide, niobium oxide, tantalum oxide, lanthanum oxide, and zinc oxide, and the sum of them is 60% by weight or more. This is because these compositions have the following advantages in addition to the reason that the softening point and the linear expansion coefficient are easily achieved.

Good compatibility with the glass layer (wetting, no chemical reaction during formation, etc.).

The high refractive index required to confine light in the optical waveguide can be realized.

In order to reduce the light propagation loss in the optical waveguide, the light transmittance is high, and crystallization that hinders the optical uniformity is unlikely to occur.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. FIG. 1 shows a part of an optical / electrical integrated circuit prepared for wavelength division multiplexing. Short wavelength (wavelength: 0.85μm) entered from optical five
Light enters the optical waveguide 3 and remains as low loss as SiO ₂ and TiO ₂
The light is reflected by the long-wavelength-passing filter 4 made up of the multilayer film, and enters the photodiode 8. Light having a long wavelength (wavelength: 1.3 μm) is emitted from the semiconductor laser 6, and the light entering the optical waveguide passes through the filter 4 for passing a long wavelength as it is and enters the optical fiber 7 with low loss.

In FIG. 1, 1 is a substrate, 2 is a cladding layer, 5
Is solder and 9 is an electrode.

This optical / electrical circuit was prepared by the following four methods.

Example 1. Alumina having a purity of 96% was used as a substrate. The thermal conductivity of this substrate is 21 W ・ m ^-1・ K ^-1 , and the linear expansion coefficient is 7.8 × 10 ^-6 K ^-1.
Met. On the surface of this substrate excluding the left and right, the composition SiO ₂ = 7
Glass of 0, B ₂ O ₃ = 12, Al ₂ O ₃ = 10, ZnO = 3, Na ₂ O = 5 (unit:% by weight) was formed by the thick film printing method. This was baked in an electric furnace at 1100 ° C. for 20 minutes. The glass layer after firing had a layer thickness of 55 μm, and the surface thereof was optically polished using grains having a grain size of 0.08 μm to finally make the layer thickness 45 μm. As for the physical properties of this glass layer, the softening point was 820 ° C., the linear expansion coefficient was 7.5 × 10 ⁻⁶ K ⁻¹ , and the refractive index was 1.49. A glass waveguide was formed in a T-shaped pattern on the surface of the glass layer. The composition of the glass is SiO ₂ = 20, B ₂ O ₃ = 16, Al ₂ O ₃ =
4, La ₂ O ₃ = 35, BaO = 16, Na ₂ O = 9 (unit: wt%). This was formed into a film by the ion plating method using the electron beam heating method. The substrate temperature was kept at 500 ° C. and ion plating was performed for 30 minutes to obtain an optical waveguide having a film thickness of 10 μm. As a result of the measurement, the physical properties of this glass for a waveguide were a softening point of 760 ° C and a linear expansion coefficient of 6.9 × 10 ^-6 K ^-1 . The prepared optical waveguide had a refractive index of 1.81 and a light propagation loss of 0.1 dB / cm or less, which was less than the measurement accuracy.

The substrate with the T-shaped optical waveguide was etched with a hydrofluoric acid-based etching solution to form glass grooves on the left and right sides of the substrate and the end faces of the optical waveguide, and diagonal grooves with a width of 15 μm at the intersection of the optical waveguide T-shaped, Etching was performed so that it was vertical to the substrate. Further, electrode patterns for semiconductor lasers and pads for fixing an optical fiber were formed on the left and right sides of this substrate by a sputtering method.

An optical fiber with a metallized clad surface, a long-wavelength pass filter, a semiconductor laser, and a photodiode were mounted on this to complete an optical / electrical integrated circuit for wavelength multiplexing.

Example 2. Spinel porcelain was used as the substrate. The thermal conductivity of this substrate was 14 W · m ⁻¹ · K ⁻¹ , and the linear expansion coefficient was 8.8 × 10 ⁻⁶ K ⁻¹ . A Pd-Ag paste was formed on this substrate by a thick film printing method to form a laser semiconductor electrode and an optical fiber fixing pad, and then firing at 1000 ° C. for 10 minutes. Further on this Au
The paste was used for thick film printing, and baked at 950 ° C. for 10 minutes.

The composition SiO ₂ = 60, B ₂ O ₃ = 2, A
A glass layer of l ₂ O ₃ = 3, K ₂ O = 20, PbO = 10, Na ₂ O = 5 (unit: wt%) was formed by a thick film printing method. The layer thickness of the glass layer after firing was 50 μm, and this surface was optically polished by using particles having a grain size of 0.08 μm to give a final layer thickness of 40 μm. As a result of the measurement, the physical properties of this glass layer are 710
C, linear expansion coefficient was 8.6 × 10 ^-6 K ^-1 , and refractive index was 1.50.

A T-shaped glass waveguide was formed on the surface of the glass layer. The composition of this glass is SiO ₂ = 61, B ₂ O ₃ = 15.Al ₂ O ₃ =
3, BaO = 13, Na ₂ O = 8 (unit: wt%). As the method for forming the optical waveguide, the same thick film printing method as described above was used. Firing is 85
It was carried out in a vacuum baking furnace at 0 ° C for 30 minutes. After firing, the film thickness is 50
It became an optical waveguide of μm. As for the physical properties of this glass for a waveguide, the softening point was 650 ° C and the linear expansion coefficient was 5.7 × 10 ^-6 K.
It was ^-1 . The prepared optical waveguide had a refractive index of 1.70 and an optical propagation loss of 0.1 dB / cm or less, which was less than the measurement accuracy.

The method for forming an integrated circuit by processing a substrate having a T-shaped optical waveguide with a hydrofluoric acid-based etching solution and further mounting components is the same as in the first embodiment.

Example 3. As a substrate, alumina having a purity of 96% was used. The thermal conductivity of this substrate is 27 W ・ m ^-1・ K ^-1 , and the linear expansion coefficient is 5.3 × 10 ^-6 K ^-1.
Met. On the surface of this substrate excluding left and right, the composition SiO ₂ = 6
Glass of 8, B ₂ O ₃ = 19, Al ₂ O ₃ , K ₂ O = 8, Li ₂ O = 1, Na ₂ O = 1 (unit: wt%) was formed using a thick film printing method. . This was baked in an electric furnace at 1000 ° C. for 20 minutes. The layer thickness of the glass layer after firing was 55 μm, and this surface was optically polished using grains having a grain size of 0.08 μm, and finally the layer thickness was set to 45 μm. The physical properties of this glass layer were measured and the softening point was 720.
The linear expansion coefficient was 5.1 × 10 ^-6 K ^-1 , and the refractive index was 1.49.
A glass waveguide furnace was formed in a T-shaped pattern on the surface of the glass layer. The glass composition is SiO ₂ = 20, B ₂ O ₃ = 15, Al ₂ O
₃ = 4, Nb ₂ O ₃ = 18, BaO = 22, ZnO = 7, Ta ₂ O ₅ = 4, Na ₂ O = 10
(Unit: weight%). This was formed into a film by the ion plating method using the electron beam heating method. Keep the above substrate temperature at 500 ° C and ion-plat for 30 minutes to obtain a film thickness of 1
It became an optical waveguide of 0 μm. The physical properties of this glass for a waveguide were measured, and it was found that the softening point was 690 ° C and the linear expansion coefficient was 4.8 × 10 ^-6 K.
It was ^-1 . The refractive index of the fabricated optical waveguide was 1.75, and the optical propagation loss was 0.1 dB / cm or less, which was less than the measurement accuracy.

The method of processing a substrate having a T-shaped optical waveguide with a hydrofluoric acid-based etching solution, mounting components, and forming an integrated circuit is the same as in the first embodiment.

Example 4. Amorphous Ge was used as the substrate. The thermal conductivity of this substrate was 23 W · m ⁻¹ · K ⁻¹ , and the linear expansion coefficient was 6.0 × 10 ⁻⁶ K ⁻¹ . The method of forming the glass layer, the optical waveguide layer, and the integrated circuit using this substrate is the same as in the third embodiment.

〔The invention's effect〕

 The present invention has the following effects.

(1) Due to the limitation of the configuration and the material composition, it is possible to form an optical circuit in which the optical propagation loss is 0.1 dB / cm or less from the conventional dB / cm, and there is little change with time.

(2) Since the thermal conductivity of the substrate is as high as 10 W · m ⁻¹ · K ⁻¹ or higher, highly stable operation and high reliability can be obtained even in a circuit including a light emitting source.

Further, by considering the coefficient of linear expansion of the circuit structure, it is possible to obtain a highly stable operation and a high reliability over time even when the ambient temperature fluctuates and is repeated.

(3) The cost of the circuit can be reduced by using a polycrystalline body or an amorphous body, which has a low manufacturing cost, as the substrate. In addition, it is easy to form an electric circuit on those substrates, and it is possible to make an optical / electrical integrated circuit three-dimensional. From this point as well, a low-cost optical / electrical integrated circuit, and further miniaturization are achieved it can.

[Brief description of drawings]

1A is a plan view of an optical integrated circuit according to an embodiment of the present invention, and FIG. 1B is a front view thereof. 1 ... Substrate, 2 ... Cladding layer 3 ... Optical waveguide, 4 ... Dielectric multilayer filter, 5 ... Solder, 6 ... Semiconductor laser, 7 ... Optical fiber, 8 ... Photodiode, 9 ... electrode.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-59-127005 (JP, A) JP-A-53-50464 (JP, A) JP-A-59-146946 (JP, A) JP-A-57- 84189 (JP, A)

Claims (2)

[Claims] 1. An optical / electrical integrated circuit comprising at least the following three parts. (1) The coefficient of linear expansion is 3.5 × 10 ^-6 K ^-1 to 9.0 × 10 ^-6 K
^-1, with a thermal conductivity of 10 W · m ⁻¹ · K ⁻¹ or more and a glass substrate content of 10% by weight or less on the surface where a part of electric wiring is provided, or Amorphous substrate with two attributes and a part of electrical wiring on its surface. (2) The surface of the substrate of the above (1) is closely adhered and the surface opposite to the substrate side is optically polished, the coefficient of linear expansion is not larger than that of the substrate of the above (1), and silicon (SiO ₂ ) and oxidation A glass layer in which the total amount of boron (B ₂ O ₃ ) accounts for 60% by weight or more of the total. (3) It adheres to the glass layer surface of (2) above, has a lower softening point, a smaller linear expansion coefficient, and silicon (SiO ₂ ), boron oxide (B ₂ O ₃ ) than the glass layer of (2). , Barium oxide (BaO), niobium oxide (Nb ₂ O ₅ ), tantalum oxide (Ta ₂ O
₅ ), lanthanum oxide (La ₂ O ₃ ) and zinc oxide (ZnO) contain two or more components, the total of which is 60% by weight of the total.
The above is an optical waveguide layer. 2. The substrate (1) has a linear expansion coefficient of 3.
5 × 10 ^-6 K ^-1 to 9.0 × 10 ^-6 K ^-1 with thermal conductivity of 10 W.m ^-1
・ K ^-1 or more, and an insulating film is formed on a part of its surface,
The optical / electrical integrated circuit according to claim 1, wherein a polycrystalline or amorphous substrate provided with a part of electric wiring on the insulating film is used.