JPH0634925A - Optical waveguide circuit device - Google Patents

Abstract

PURPOSE:To provide long-term reliability and to enable the simple adjustment of a resistance value to be conducted by specifying the material of a thin-film heater as a phase shifter which is disposed on the clad layer of an optical waveguide and finely adjusts the optical path length of an optical waveguide. CONSTITUTION:This optical waveguide circuit device has a substrate 1, a core part 2 which is provided on this substrate, the clad layer 3 which covers this core part 2 and the thin-film heater 4 which is disposed on the clad layer 3 of this optical waveguide and finely adjusts the optical path length of a part of the optical waveguide. A Ta2N film is used as the thin-film heater 4 serving as the phase shifter. This thin-film heater is preferably coated with a protective film 6 which is at least one layer among SiO2 films, Si3N4 and Ta2O5 films. Further, the resistance value of this thin-film heater 4 is preferably regulated to a desired value by heating by means of an electric oven, etc., or by energization to the thin-film heater itself after the film formation. As a result, the long-term stability of the resistance value of the thin-film heater is obtd. and the service life thereof is prolonged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide circuit device in which an optical waveguide is arranged on a substrate, and more specifically, an optical waveguide circuit having a thin film heater as a phase shifter capable of adjusting the optical path length of the optical waveguide. It relates to the device.

[0002]

2. Description of the Related Art Conventionally, a single-mode optical waveguide manufactured on a substrate, particularly a silica-based glass single-mode optical waveguide manufactured on a silicon substrate, is a waveguide type optical component excellent in compatibility with an optical fiber. It is expected as a means to realize, and there are research examples of various parts. For example, Masao Kawauchi: “Applications to silica-based optical waveguides and integrated optical components”, Optics, 18 (1989) 68.
1-686. Can be mentioned.

Among the above optical circuit parts, a waveguide type optical interferometer composed of a silica glass single mode optical waveguide is particularly expected as a part of an optical demultiplexer, an optical switch and the like. The configuration of this waveguide type optical interferometer requires a phase shifter having a function of adjusting the phase of the propagating light in the waveguide. Usually, a thin film heater for utilizing the thermo-optic effect is used as the phase shifter. The structure of this phase shifter and its operating principle are described below.

FIG. 1 shows a schematic configuration example of a general silica glass waveguide having a phase shifter. FIG. 1 (a) shows
It is a top view of the said optical waveguide, and FIG.1 (b) is an expanded sectional view which followed the AA 'line of FIG. Reference numeral 1 is a silicon substrate, 2 is a core portion made of silica glass, 3 is a cladding layer made of silica glass covering the core portion 4, and 4 is a phase shifter formed on the upper surface of the cladding layer 3 above the core portion 2. The thin film heaters 5a and 5b made of a Cr film are electrode pad portions for supplying power to the thin film heater 4, and 6 is a heater thin film protective film. The electrode pad portions 5a and 5
Illustration of an electric wiring wire and a power supply for b is omitted.

In the above structure, the thin film heater 4
When the core portion 2 is heated through the clad layer 3 due to the thermo-optical effect, the refractive index of the heated core portion 2 increases, and the effective refractive index of the lower portion of the thin film heater 4 changes. , The phase of propagating light can be changed. More specifically, the temperature change of the refractive index n of the silica-based glass (Δ
n / ΔT) is 10 ⁻⁵ 1 / ° C., so 5 mm, for example
Temperature rise (ΔT) of optical waveguide over the length (ΔL)
At 15 ° C., the change in optical path length (Δn × ΔL) is 0.
It becomes 75 μm, which corresponds to a half-wave phase shift of the propagating light having a wavelength of 1.5 μm. Since the phase shifter using such a thin film heater can control the optical path length externally, it is applied to various waveguide type optical circuit components.

Although the thin film heater is required to have long-term reliability in practical use, the Cr film which has been conventionally used is not stable for a long-time energization of at least one year or more, and the probability of occurrence of disconnection cannot be ignored. There was a problem that it was high.

Even if the wire is not broken, the resistance of the thin-film heater changes and the amount of the phase shifter changes with time when the material is deteriorated such as oxidation. Therefore, it may not be used depending on the usage of the part. It will be possible. In this respect as well, the Cr film has a problem that a long-term resistance change cannot be ignored.

Still another problem is as follows.

Generally, the resistance value of the heater thin film is not completely constant due to variations in the manufacturing process. It is time consuming, costly and difficult to redo the manufacturing process to obtain a thin film heater having a desired constant resistance value. For this reason, there is a need for a method capable of easily adjusting the resistance value after film formation, but there is also a problem in that the resistance value is always adversely affected by adjusting the resistance value of the Cr film.

[0010]

SUMMARY OF THE INVENTION Therefore, the object of the present invention is to solve the above problems and to provide long-term reliability.
Another object of the present invention is to provide an optical waveguide circuit device including a thin film heater capable of easily adjusting the resistance value.

[0011]

In order to achieve the above object, the optical waveguide device of the present invention is characterized by using a Ta ₂ N film as a thin film heater as a phase shifter.

Further, the thin film heater has a protective film made of SiO ₂ , S.
It may be covered with at least one layer of i ₃ N ₄ and Ta ₂ O ₅ films.

Further, the thin film heater may be one whose resistance value is adjusted to a desired constant value by heating by an electric furnace or the like, or heating by energizing the thin film heater itself after film formation.

[0014]

According to the present invention, by using the Ta ₂ N film as the thin film heater as the phase shifter, long-term resistance value stability of the thin film heater can be obtained for one year or more, and the life until the thin film heater is broken. Since the length becomes longer, the reliability of the optical waveguide circuit device provided with the thin film heater is greatly improved. Also,
By using a Ta ₂ N film covered with a protective film such as SiO ₂ , Si ₃ N ₄ or Ta ₂ O ₅ , the life of the thin film heater can be further extended.

According to the present invention, by performing the heat treatment after the Ta ₂ N film formation, it is possible to adjust the resistance value of the thin film heater to a predetermined constant value without adversely affecting the life. This is possible, and the manufacturing yield of the optical waveguide circuit device is significantly improved. Further, when the heat treatment to the thin film heater is performed by energization, only the thin film heater portion can be locally heated, so that it is not necessary to heat the entire optical waveguide circuit device.

[0016]

Embodiments of the present invention will now be described in detail with reference to the drawings.

(Embodiment 1) The construction of an embodiment of the present invention will be described with reference to FIG. As the thin film heater 4 of FIG.
An a ₂ N film was used. The specifications of the structure of the optical waveguide having the configuration of FIG. 1 can be variously determined, but here, they are determined as follows. That is, the thickness of the silicon substrate 1 is 0.7.
mm, the thickness of the cladding layer 3 was 50 μm, the cross-sectional dimension of the core portion 2 was 8 μm × 8 μm, and the relative refractive index difference between the core portion and the cladding layer was 0.25%.

The Ta ₂ N film was formed by using a known reactive sputtering method. Typical manufacturing conditions at this time are described below. That is, the partial pressure of nitrogen gas is 1 × 10 ⁻⁴ Tor.
r, mixed gas of nitrogen and argon gas Total gas pressure is 2 × 10 ^-2 To
rr, RF power 50 W, substrate temperature 300 ° C. At this time, the film formation rate is 10 nm / min, and is usually 300 nm.
The film was formed to a thickness of nm. The patterning of the Ta ₂ N film was carried out by a reactive ion etching method using SF ₆ gas, using a resist pattern manufactured by photolithography as a mask. The RF power during etching was 100 W, and the SF ₆ gas flow rate was 20 sccm. The processing dimensions of the Ta ₂ N film here are 50 μm width and 4 mm length.
Is. An Au film having a thickness of 300 nm was used for the electrodes 5a and 5b in FIG. In order to improve the adhesion between the Au film and the Ta ₂ N film, a 20 nm thick Cr film was formed between the Au film and the Ta ₂ N film.

The resistivity ρ of the Ta ₂ N film is 200 to 25.
0 μΩm, temperature change of resistivity TCR is -40 to -150
It was ppm / ° C. The Cr film of the same pattern manufactured for comparison (conventional example) has ρ = 80 μΩm and TCR = 1.
It was 00 ppm / ° C.

With the protective film 6 of FIG. 1 not formed, Cr
The results of examining the resistance stability of the film and the Ta ₂ N film are shown in FIG. FIG. 2 compares changes with time of the resistance value of the thin film heater 4 when a power of 6 W is continuously applied between the electrodes 5a and 5b of FIG. 1 for each of the Cr film and the Ta ₂ N film. As is clear from FIG. 2, the Ta ₂ N film has a disconnection life about 10 times that of the Cr film.

Normally, the wavelength of 1.
The applied power to the heater thin film for shifting the optical path length of 3 μm light by half a wavelength is about 0.5 W, and the value of 6 W applied power in FIG. 2 is compared to the heater power when used for applications such as optical switching. Very big. That is, the characteristics of FIG. 2 are the results of the accelerated life test of the heater thin film.

Next, when a 2 μm thick SiO ₂ film is formed as the protective film 6 in FIG. 1, the disconnection life between the Cr film and the Ta ₂ N film has a larger difference than that in the case without the protective film. That is, as shown in FIG. 3, it is 1000 times or more when 10 W is applied. In the comparison with the power of 6 W, as shown in FIG. 4, the change with time of the resistance value of the Ta ₂ N film is extremely smaller than that of the Cr film. In FIG. 4, for example, comparing the time until the resistance value changes by 5%, the Ta ₂ N film is more C
It is 100 times longer than that of the r film. That is, it was found that the Ta ₂ N film was more stable than the Cr film even when the same power was applied, with less material deterioration.

As the protective film 6 shown in FIG. 1, Si _{3 having a} thickness of 2 μm is used.
When the N ₄ film or the Ta ₂ O ₅ film having a thickness of ₂ μm was used, the same characteristics as those in FIGS. 3 and 4 were obtained.

As described above, as a thin film heater, Ta ₂
It was found that the N film has a much longer life of disconnection than the Cr film, the change in resistance value over time is small, and the long-term reliability is excellent.

(Embodiment 2) As a second embodiment of the present invention, a 2 × 2 thermo-optical switch circuit device was manufactured. FIG. 5A shows a plan view and FIG. 5B shows a sectional view. In FIG. 5, 7a and 7b are directional couplers, 8 is a first optical input port, 9 is a second optical input port, 10 is a first optical output port, and 11 is a second optical output port. A Ta ₂ N film was used as the thin film heaters 4a and 4b in FIG. Ta ₂ N
The manufacturing conditions of the film and the heater shape were the same as in Example 1.

When the electric power applied to the thin film heater 4 in FIG. 5 is changed and the optical switching characteristics are examined, it is found that the optical switching characteristics shown in FIG.
The basic characteristics of × 2 optical switching were obtained. Figure 6
Is a change in optical power output from the second output port 11 when light is input from the first input port 8 in FIG. The optical output of is indicated by the ratio with the optical power from the first output port 10. As shown in FIG.
It has been found that when the ₂ N film is used as a thin film heater, sufficient optical switching characteristics can be obtained as a 2 × 2 thermo-optical switch circuit.

Example 3 An optical waveguide circuit device having a heat-treated thin film heater was manufactured as a third example of the present invention. That, Ta ₂ as a thin film heater shown in FIG. 1
After forming the N film, heat treatment was performed under the following conditions. The optical waveguide circuit device shown in FIG.
It was taken out after being kept at a constant temperature of 00 ° C. or lower for 30 minutes. At this time, the manufacturing conditions of the Ta ₂ N film, the heater shape, and the like were the same as in Example 1. As shown in FIG. 7, when the heat treatment temperature is increased, Ta ₂ N after heat treatment is increased.
The resistivity of the film increases. At this time, the heat treatment temperature is 50
If the temperature was 0 ° C. or lower, there was no change in the breaking life of the Ta ₂ N film. If the heat treatment temperature exceeds 500 ° C, Ta
Oxidation of the heater caused the resistance of the heater to rise rapidly, and at the same time, the life of the wire breakage was greatly shortened. Therefore, heat treatment temperature 500 ℃
If the following, without reducing the reliability of the heater,
It was found that the resistance value can be adjusted.

When 100 thin film heater patterns shown in FIG. 1 were formed and the thin film heater resistance values were examined, there was a variation in the range of ± 7%. Therefore, the thin film heater pattern was formed considering the resistance value to be 10% lower than the desired value on average, and the resistance value was measured. If they differ from each other as described above, the heat treatment was performed at a heat treatment temperature at which a desired resistance value was obtained according to the characteristics of FIG. As a result, the variation in the heater resistance value was ± 2% or less.

(Embodiment 4) As a fourth embodiment of the present invention, an optical waveguide circuit device having a thin film heater which has been subjected to an electric current heat treatment was manufactured. That is, after forming a Ta ₂ N film as the thin film heater 4 shown in FIG. 1, an energization heat treatment was performed under the following conditions. That is, the electrode 5 of the optical waveguide circuit device shown in FIG.
A constant power was applied between a and 5b for 10 minutes, and the temperature of the Ta ₂ N film heater 4 was raised by this heater power. At this time, the Ta ₂ N film manufacturing conditions and heater shape were the same as in Example 1. When the heater temperature was measured when the heater was energized, it was 500 ° C. when 8 W was applied. When the change in the heater resistance after energization with respect to this heater temperature was examined, it was the same as in FIG. 7. If the heater temperature was 500 ° C. or lower, the heater burnout life did not change. Therefore, as in Example 3, if the energization heat treatment was performed at a heater power of not more than 500 ° C., the heater resistance value could be adjusted without shortening the life of the heater. Unlike the case of Example 3, according to the method of this example, each heater film on the same substrate can be heat-treated under different conditions, and the resistance value of each thin film heater in the same substrate can be adjusted.

By performing the same method as in Example 3,
Even in the case of electric heat treatment, the variation in the heater resistance value is ± 2
Could be within%.

[0031]

As described above, in the present invention, Ta _{2 is used} as the thin film heater for adjusting the optical path length of the optical waveguide.
By using the N film, the life can be significantly extended and the resistance value can be less changed with time as compared with the Cr film which has been conventionally used, and thus the reliability of the optical waveguide circuit device having the thin film heater can be greatly improved. Can be improved. This T
Characteristics of the phase shifter of the optical waveguide by a ₂ N film was also sufficient.

Further, by using a Ta ₂ N film as the thin film heater, it is possible to adjust the resistance value of the thin film heater without shortening the life, by heat treatment in an electric furnace or by heat treatment for directly energizing the heater film. It is possible to reduce variations in the resistance value of each heater.

[Brief description of drawings]

1A and 1B show a configuration of a first embodiment of the present invention, in which FIG. 1A is a plan configuration diagram, and FIG. 1B is a line AA ′ in FIG. FIG.

FIG. 2 is a characteristic diagram comparing a change in heater resistance when a heater power of 6 W is applied between a Cr film without a protective film and a Ta ₂ N film in FIG.

FIG. 3 shows a change in heater resistance when a heater power of 10 W is applied,
FIG. 3 is a characteristic diagram comparing a Cr film and a Ta ₂ N film using the protective film of FIG. 1 as a 2 μm thick SiO ₂ film.

[4] The heater resistance change at the time the heater power 6W applied, Cr film and T using the protective film of Figure 1 as a 2μm thick SiO ₂
It is a characteristic diagram comparing with a ₂ N film.

5A and 5B show a configuration of a 2 × 2 thermo-optical switch as a second embodiment of the present invention, in which FIG. 5A is a plan view and FIG. 5B is a sectional view taken along line BB ′ in FIG. It is a figure.

FIG. 6 is a characteristic diagram showing characteristics of the 2 × 2 thermo-optical switch shown in FIG.

FIG. 7 is a characteristic diagram showing a change in heater resistance value after heat treatment depending on a heat treatment temperature of a thin film heater.

[Explanation of symbols]

 1 Silicon Substrate 2 Optical Waveguide Core Part 2a, 2b Optical Waveguide Core Part 3 Cladding Layer 4 Thin Film Heater 4a, 4b Thin Film Heater 5a, 5b Electrode Pad 6 Heater Thin Film Protective Film 7a, 7b Directional Coupler 8 First Optical Input Port 9 Second optical input port 10 First optical output port 11 Second optical output port

Claims (4)

[Claims] 1. A substrate, an optical waveguide having a core portion provided on the substrate and a cladding layer covering the core portion, and a portion of the optical waveguide disposed on the cladding layer of the optical waveguide. An optical waveguide circuit device including a thin film heater for finely adjusting an optical path length, wherein the thin film heater is a Ta ₂ N film. 2. A protective film of at least one of a SiO ₂ film, a Ta ₂ O ₅ film and a Si ₃ N ₄ film which covers the thin film heater is formed on the thin film heater. 1. The optical waveguide circuit device according to 1. 3. The optical waveguide circuit according to claim 1, wherein the thin film heater disposed on the optical waveguide is heat-treated after being disposed at a temperature of 500 ° C. or less. apparatus. 4. The optical waveguide according to claim 1, wherein the thin film heater provided on the optical waveguide is heat-treated after being provided by energizing the thin film heater. Circuit device.