JP2545701B2 - Method for manufacturing waveguide optical device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a waveguide optical device such as an optical switching element which is constructed by using an optical waveguide formed on a substrate having a pyroelectric effect.

[0002]

2. Description of the Related Art A waveguide optical device has a low driving voltage,
It is capable of high-speed operation and is promising in terms of miniaturization and integration. However, in the case where a crystal having a pyroelectric effect, that is, spontaneous polarization, such as LiNbO ₃ (lithium niobate) is used as a substrate and a diffusion layer such as Ti (titanium) is formed on the substrate to form a waveguide, ,
Due to the temperature change, charges due to the pyroelectric effect are generated on the surface of the substrate, and the charge distribution is not uniform, which causes a problem that the operating characteristics (for example, switching characteristics) as a waveguide optical device fluctuate. .

FIG. 4 is a perspective view of a conventional waveguide optical device (here, an optical switching element is shown as an example), and FIG. 5A is a sectional view taken along line AA. This waveguide optical device comprises a substrate 1 made of a Z plate LiNbO ₃ and a Ti substrate.
A diffusion layer 2 is formed as an optical waveguide, a buffer layer 3 made of SiO ₂ which is a transparent insulating film having a refractive index lower than that of the optical waveguide is formed on the upper surface thereof, and a plurality of Al (aluminum) layers are formed on the upper surface thereof. The electrodes 4 are appropriately arranged at appropriate intervals. When the temperature of the waveguide optical device having such a configuration is raised, as shown in FIG. 5B, the Z-plate LiNbO ₃ substrate 1 changes its polarization state due to its pyroelectric effect. The reverse charge (−charge in the figure) corresponding to the charge (+ charge in the figure) generated on the surface of 1 is supplied to the bottom surface of the electrode 4 from the outside. Then, in the substrate 1, from the interelectrode portion where there is no electrode 4 to the electrode 4
A useless electric field 5 is generated toward the electrode portion having a gap as shown in the figure. The waveguide optical device changes the refractive index of the optical waveguide formed of the Ti diffusion layer 2 by applying an electric field between the electrodes to perform, for example, a switching operation of the optical path. When the electric field 5 is generated, the refractive index changes due to an unnecessary electro-optical effect based on the electric field, and the operating point of the waveguide optical device fluctuates, which has a great adverse effect on the operating characteristics (for example, switching characteristics). Will give.

Therefore, conventionally, in order to prevent the characteristic fluctuation due to the temperature change, the structure of the optical waveguide and the electrode are often made insensitive to the temperature change.

[0005]

However, the structure which is insensitive to the temperature change as described above has a problem that the device structure is limited and the change of the operating characteristics due to the temperature change cannot be sufficiently prevented. was there.

It is an object of the present invention to provide a method of manufacturing a waveguide optical device capable of sufficiently preventing the polarization charge generated on the substrate surface due to the pyroelectric effect from adversely affecting the operating characteristics.

[0007]

According to a first aspect of the present invention, after an optical waveguide is formed on a substrate having a pyroelectric effect,
A transparent buffer layer having a refractive index lower than that of the optical waveguide is formed on the upper surface of the substrate including the optical waveguide, and then a plurality of electrodes are formed on the buffer layer, and further, a charge due to polarization generated on the substrate is dealt with. Then, a film body having a resistance value capable of supplying reverse charges and preventing substantial conduction between electrodes is coated so as to cover the entire surface of the substrate from the upper surface of the electrode.

According to a second aspect of the present invention, after forming an optical waveguide on a substrate having a pyroelectric effect, a transparent buffer layer having a refractive index lower than that of the optical waveguide is formed on an upper surface of the substrate including the optical waveguide. Then, on the transparent buffer layer, a resistance value capable of supplying a reverse charge corresponding to a charge due to polarization generated in the substrate with a resistance value that substantially prevents conduction between electrodes of a plurality of electrodes to be formed later. The film body is coated, and the plurality of electrodes are further formed on the film body.

[0009]

According to the manufacturing method of the present invention, an original film body (this film body is formed on the substrate, at least between the electrodes and where the electrodes are not provided) is in contact with the electrodes.
It is possible to supply a reverse charge corresponding to the charge due to the polarization generated in the substrate and to have a resistance value that prevents substantial conduction between the electrodes). With such a configuration, even if polarization charges are generated on the substrate surface due to the pyroelectric effect, the film body is present between the electrodes without electrodes, and therefore the electrode portion with electrodes and the electrode without electrodes are The opposite charge corresponding to the polarization charge is uniformly supplied to both of the parts (here, the film body), and as a result, the influence of the polarization charge is homogenized between the electrode part and the inter-electrode part. Such an unnecessary electric field is not generated, and thus a device having extremely stable operation characteristics with respect to temperature changes can be obtained.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A is a sectional view of a waveguide optical device obtained by the manufacturing method according to the first embodiment of the present invention. This waveguide optical device has the same basic structure as the optical switching element shown in FIG. 4, except for the characteristic points of this embodiment described later.

In the present embodiment, first, as an example of a substrate having a pyroelectric effect, a substrate 1 made of a Z plate LiNbO ₃ is provided with T
The i diffusion layer 2 is formed in a predetermined pattern, and this Ti diffusion layer 2 is used as an optical waveguide having a higher refractive index than its surroundings. In the example of FIG. 4, two linear waveguides intersect each other. After that, a buffer layer 3 made of SiO ₂ which is a transparent insulating film having a refractive index lower than that of the Ti diffusion layer (optical waveguide) 2 is uniformly formed on the upper surface thereof to a thickness of, for example, about 2000 Å, and For example, a thickness of 3000Å on the upper surface
A plurality of electrodes 4 made of Al having a certain degree are formed in a predetermined pattern. In the example of FIG. 4, two Ti diffusion layers (optical waveguide)
One electrode 4 is arranged directly above the intersection of two, and the other electrode 4 is arranged with a predetermined distance so that the electrode 4 is sandwiched from both sides, and the central electrode 4 and the electrodes 4 on both sides thereof are arranged. A predetermined voltage can be applied between the two.

Further, in this embodiment, a predetermined film body 6 made of, for example, an ITO film having a thickness of about 1000Å is coated by sputtering or the like so as to cover the entire surface of the substrate 1 from the upper surface of the electrode 4 through the upper surface of the buffer layer 3. To do. This film body 6
Has a resistance value within a range capable of supplying a reverse charge corresponding to the charge due to the polarization generated on the substrate 1, and the electrodes 4, 4
It is set within a range that can prevent substantial conduction between them. For example, the gap between the adjacent electrodes 4 and 4 is 5 μm.
m, the length of the electrode 4 (length in the direction perpendicular to the paper surface of FIG. 1) is 10 mm, and the thickness of the film body 6 is 1000Å as described above.
Then, the resistance of the film body 6 existing between the electrodes 4 and 4 is set to, for example, 10 to 10 ¹⁰ Ω.

The waveguide optical device of FIG. 1 thus manufactured according to the present embodiment is provided on the buffer layer 3 between the electrodes 4 and 4 in a portion where the electrode 4 is not provided (interelectrode portion). The film body 6 having a predetermined resistance value is provided so as to come into contact with the electrodes 4 and 4 together. According to the device having such a configuration, the resistance between the adjacent electrodes 4 and 4 can be reduced from the conventional value of 10 ¹³ Ω or more to 10 to 10 ¹⁰ Ω as described above. As a result, as shown in FIG. 1B, even if the device temperature rises and polarization charge (+ charge in the figure) is generated on the surface of the substrate 1 by the pyroelectric effect, Since the film body 6 is present, the reverse charge (− in the figure −) corresponding to the polarization charge generated on the substrate 1 is applied to both the electrodes 4 and the film body 6 between the electrodes 4 and 4.
Electric charge) is uniformly supplied. Therefore, the influence of the polarization charge is homogenized in the electrode portion and the inter-electrode portion, and it is possible to prevent the useless electric field (electric field 5 shown in FIG. 5B) from occurring as in the conventional case, and as a result, the temperature change. In contrast, a waveguide optical device having extremely stable operation characteristics can be realized.

FIG. 2 is a sectional view of a waveguide optical device obtained by the manufacturing method of the second embodiment of the present invention. This waveguide optical device is also the same except for the features of this embodiment described later.
It has the same basic structure as the optical switching element shown in FIG.

In this embodiment, first, similarly to the first embodiment, a Ti diffusion layer 2 as an optical waveguide is formed on a substrate 1 made of Z plate LiNbO ₃ , and a buffer layer 3 made of SiO ₂ is formed on the upper surface thereof. Are formed uniformly. After that, before forming the electrodes, a thickness of 10 is formed so as to cover the entire surface of the buffer layer 3.
A predetermined film body 7 made of an ITO film of about 00Å is coated by sputtering or the like. Similarly to the film body 6 used in the first embodiment, the resistance value of the film body 7 is also within a range in which the reverse charge can be supplied corresponding to the charge due to the polarization generated in the substrate 1, and the electrode 4, It is set within a range that can prevent substantial conduction between the four. And finally, the film body 7
A plurality of electrodes 4 made of Al are formed on the upper surface of the same as in the first embodiment.

In the waveguide optical device of FIG. 2 thus manufactured according to this embodiment, only the portion between the electrodes 4 and 4 on the buffer layer 3 where the electrode 4 is not provided (interelectrode portion). Instead, the film body 7 having a predetermined resistance value is provided directly below each electrode 4 so as to come into contact with the electrodes 4 and 4. According to the device having such a configuration, even if the temperature of the device rises and polarization charge is generated on the surface of the substrate 1 by the pyroelectric effect,
Since the film body 7 is uniformly present between the four portions, the reverse charge corresponding to the polarization charge generated on the substrate 1 is supplied to the film body 7 more uniformly than in the case of the first embodiment. To be done.
Therefore, the influence of the polarization charge is further homogenized in the electrode part and the part between the electrodes, and it is possible to more effectively prevent the generation of an unnecessary electric field, and as a result, the waveguide light having a remarkably stable operation characteristic against temperature changes. Device can be realized.

FIG. 3 shows a similar relationship (indicated by A in the figure) between the temperature change and the operating point variation in the device obtained by the embodiment of the present invention (indicated by B in the figure). Shown) in comparison with the above. IT
In the conventional device without the O film bodies 6 and 7, the characteristic A
As shown by, it can be seen that the operating point fluctuates greatly according to the temperature change. On the other hand, in the device provided with the ITO film bodies 6 and 7, as shown by the characteristic B, it can be seen that the operating point hardly changes even if the temperature changes. As described above, according to the present invention, it is possible to significantly improve the temperature characteristics of the waveguide optical device.

In the above embodiment, the film bodies 6 and 7 are I
Although the TO film is used, the present invention is not limited to this, as long as it can supply the reverse charge corresponding to the polarization charge generated on the substrate and has a resistance value that prevents substantial conduction between the electrodes. Various other materials can be used. For example, a SnO ₂ film or a Si film may be used within the range of the above resistance value, or a material obtained by doping a SiO ₂ film with a metal may be used, and an antistatic material may be used. Is also possible.

The substrate is not limited to the Z-plate LiNbO ₃ substrate, and any other substrate can be used as long as it is a substrate made of a crystal having a pyroelectric effect. As the material of the buffer layer, various materials can be used as long as they are transparent insulating films having a refractive index lower than that of the optical waveguide. The electrode material is also Al
Various other conductive materials can be used, and the diffusing material used to form the optical waveguide is not limited to Ti.

[0020]

According to the present invention, a waveguide optical device having a unique film body having a predetermined resistance value between at least electrodes on a substrate can be obtained. Even if occurs, it is possible to supply the opposite charge corresponding to the polarization charge to both the electrode portion and the inter-electrode portion, and as a result, the influence of the polarization charge is entirely homogenized, Therefore, it is possible to realize a waveguide optical device having extremely stable operation characteristics even with temperature changes.

[Brief description of drawings]

FIG. 1 (a) is a cross-sectional view of a waveguide optical device obtained by a manufacturing method according to a first embodiment of the present invention, and FIG. 1 (b) shows a uniform charge distribution generated in the device as the temperature rises. FIG.

FIG. 2 is a sectional view of a waveguide optical device obtained by a manufacturing method according to a second embodiment of the present invention.

FIG. 3 is a characteristic diagram showing a relationship between a temperature change and an operating point fluctuation in a device obtained according to an example of the present invention in comparison with a similar relationship in a conventional device.

FIG. 4 is a perspective view of a conventional waveguide optical device (here, an optical switching element is shown as an example).

5A is a cross-sectional view taken along the line AA of the conventional waveguide optical device shown in FIG. 4, and FIG. 5B is a diagram showing a non-uniform charge distribution generated in the device as the temperature rises. is there.

[Explanation of symbols]

 1 substrate 2 diffusion layer (optical waveguide) 3 buffer layer 4 electrode 5 electric field 6 and 7 film body

Continuation of the front page (56) Reference JP-A-55-69122 (JP, A) JP-A-56-165122 (JP, A) JP-A 61-240227 (JP, A) JP-A-55-35476 (JP , A)

Claims (8)

(57) [Claims] 1. A transparent buffer layer (3) having a refractive index lower than that of the optical waveguide after the optical waveguide (2) is formed on the substrate (1) having a pyroelectric effect. And then a plurality of electrodes (4) on the buffer layer
And a film body (6) having a resistance value capable of supplying a reverse charge corresponding to a charge due to polarization generated on the substrate and blocking a substantial conduction between electrodes from the upper surface of the electrode to the substrate. A method for manufacturing a waveguide optical device, characterized by coating the entire upper surface. 2. After forming an optical waveguide (2) on a substrate (1) having a pyroelectric effect, a transparent buffer layer (3) having a refractive index lower than that of the optical waveguide on the upper surface of the substrate including the optical waveguide. Then, a reverse electric charge can be supplied to the transparent buffer layer corresponding to the electric charge due to polarization generated in the substrate with a resistance value that prevents substantial conduction between the plurality of electrodes to be formed later. A structure in which a film body having a resistance value covers the entire upper surface of the substrate.
And a plurality of electrodes (4) are formed on the film body, which is a method for manufacturing a waveguide optical device. 3. The method of manufacturing a waveguide optical device according to claim 1, wherein the film body is a transparent conductive film made of ITO. 4. The method of manufacturing a waveguide optical device according to claim 1, wherein the film body is made of a transparent conductive film of SnO ₂ . 5. The method of manufacturing a waveguide optical device according to claim 1, wherein the film body is made of Si. 6. The method of manufacturing a waveguide optical device according to claim 1, wherein the film body is made of a material obtained by doping SiO ₂ with a metal. 7. The method of manufacturing a waveguide optical device according to claim 1, wherein the film body is made of an antistatic material. 8. The method of manufacturing a waveguide optical device according to claim 1, wherein the substrate is made of LiNbO ₃ .