JPH02196213A - Formation of buffer layer of waveguide type element - Google Patents

Abstract

PURPOSE:To suppress the generation of an operating point drift and hysteresis to a low level by executing the heat treatment of the thin oxide film on a waveguide at >=750 deg.C and <=850 deg.C, thereby forming a buffer layer. CONSTITUTION:The buffer layer 12 is formed on an LiNbO3 or LiTaO3 substrate 10 and after the thin film 14 of the oxide is deposited thereon, the thin film 14 is heat-treated to form the buffer layer 16 and an electrode 18 is provided thereon. The characteristics of the buffer layer 16 are improved and the generation of the so-called DC drift (operating point drift) with which the operating voltage of the element changes with time and the generation of hysteresis are suppressed to a lower level if the heat treatment of the thin oxide film 14 is executed at >=700 deg.C and <=850 deg.C at this time. The waveguide type optical element having the excellent characteristics is thus formed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for forming a buffer layer included in the structure of a waveguide optical device formed using a LiNbO3 or LiTaO3 substrate.

(Prior Art) A waveguide type optical element is a functional device that uses a thin film optical waveguide to electrically control the propagation of light. It is formed and used as a coupler, optical switch, etc.

First, in order to facilitate understanding of the present invention, the manufacturing process of a typical conventional waveguide type optical device will be briefly explained.

Figures 2 (A) to (D) are explanatory diagrams of the main manufacturing process of a waveguide type optical device using a LiNb○3 substrate, and each figure is a cross section of a portion along the extending direction of the waveguide. This is schematically shown.

A L i N b 03 substrate 10 is prepared, and this substrate 10
Ti is then diffused under appropriate conditions to form an optical waveguide 12 (FIG. 2(A)).

Next, t: On the waveguide 12, S i 02 , A n
A thin film 14 of 203 or other suitable oxide is formed by a suitable method (FIG. 2(8)).

Next, this oxide thin film 14 is heat-treated, and this heat-treated oxide thin film becomes the buffer layer 16 (FIG. 2(C)).

Next, apply appropriate adhesives 18 to the required locations on this buffer layer 16.
was deposited and patterned to form an electrode (second
Figure (D)).

If the electrode 18 is formed directly on the waveguide 12, the buffer layer 16 is provided to separate the electrode 18 and the waveguide 12 from each other, since there is a risk that the safe of the electrode 18 may absorb light from the waveguide. ．． : It is a layer. Conventionally, in this buffer layer 16, oxygen vacancies are generated when an oxide such as Sin or Al2O2 is formed, so that the resistance value of the thin oxide film itself is small.

Therefore, if an electrode is provided directly on this oxide thin film and a DC voltage is applied (), the operating voltage of the device will change over time because the charge moves in the direction of canceling the electric field. DC) drift (operating point drift).

Therefore, in the past, after forming a thin film of this oxide, f(t) was deposited in an oxygen-containing atmosphere, for example, an oxygen atmosphere containing water vapor (wet atmosphere), or an oxygen atmosphere containing water vapor (wet atmosphere). Atmosphere containing only oxygen (dry atmosphere)
Heat treatment was carried out inside. This heat treatment was performed by leaving the sample to be heat treated in an atmosphere heated to 500-600 DEG C. for an appropriate period of time, for example, within a range of about 2 to 8 hours. (For example, literature: rFL
EcTORONics LETTER3J (Electronics Letters) VOJ2. .

22, No, 5. (1986), PP, 262-263.
9).

(Problem to be Solved by the Invention) However, in a waveguide type optical device including a buffer layer formed by this conventional method, LiNbO3 and LiTa0:
No matter which i-substrate is used for formation, there are the following problems.

(2) When this was operated by applying a DC bias voltage for a long period of time, a large operating point 1-noise still occurred. For example, a 5.5 mm long inverted ΔB electrode type optical switch (however, a 5.5 mm long inverted ΔB electrode type optical switch (however, a bar For samples with a voltage of 40 V), 5
This resulted in an operating point drift of about v.

■Also, when the waveguide type optical element is configured as an optical switch, when the voltage applied to the electrode is increased and when it is decreased,
Large hysteresis occurred in the switching characteristics.

The inventors of this application conducted various studies and experiments in order to investigate the causes of these problems, and found that, as mentioned above, the heat treatment temperature! We found that the buffer layer formed at 500 to 600°C was a contributing factor, and we conducted experiments to form the buffer layer under various heat treatment temperature conditions, and found that the buffer layer had sufficient properties within a certain temperature range. I discovered that it can be obtained.

Therefore, an object of the present invention is to provide a method for forming a buffer layer that can suppress operating point drift and hysteresis to a minimum and obtain a waveguide optical device with excellent characteristics.

(Means for Solving the Problems) In order to achieve this object, according to the method for forming a buffer layer according to the present invention, the oxide thin film is heat-treated at a temperature within the range of 700°C or higher and 850°C or lower. Subtle things.

(Function) When the oxide thin film is heat-treated at an appropriate temperature within the temperature range of 700 to 850°C, the characteristics of the buffer layer become better, although the reason is not clear.
It is possible to obtain a waveguide type optical device with smaller operating point drift and smaller hysteresis than conventional ones.

(Example) Hereinafter, with reference to the drawings, an example of a method for forming a buffer layer of a waveguide type optical device of the present invention will be described.

The main manufacturing process of the waveguide type optical device used to explain this invention is substantially the same as the conventional process except for the heat treatment conditions for forming the buffer layer, so it will be explained using FIG. 2. do.

First, a waveguide 12 is formed on a LiNbO3 or 1Ta03 substrate 1O using Ti diffusion, which is a technique similar to the conventional technique (FIG. 2(A)).

A thin film 16 of an oxide, e.g. Figure 2 (B)), a thin layer of this oxide
The thickness of the l116 film varies depending on the material and the wavelength of the light to be guided, but it is usually suitable for manufacturing and characteristics to have a value within the range of 2000A to 3500A.

After forming this oxide thin film 14, the oxide thin film is heat-treated in an atmosphere containing oxygen to further accelerate the oxidation treatment and form a buffer layer 16 (FIG. 2(C)).
In this case, as in the past, the process may be carried out in either a dry atmosphere or a wet atmosphere, but
This example is carried out in an oxygen atmosphere containing water vapor.

Next, the temperature conditions for this heat treatment will be explained.

FIG. 1 is a curve diagram showing the oxidation temperature-oxidation time characteristics of Si when Si is heat-treated in a wet oxygen atmosphere and a dry oxygen atmosphere. In the figure, the solid line is the characteristic curve when the oxidation treatment is performed in a wet atmosphere, and the broken line is the characteristic curve in the dry atmosphere. This is a characteristic curve when oxidation treatment is performed. Note that although these characteristic curves are second to that of Si, a similar tendency holds true for Aβ as well.
Since this is substantially the same as in the case of , illustration of the characteristic curve of Aβ is omitted.

As can be understood from the characteristic curve in Figure 1, the time required for oxidation treatment in a wet atmosphere to oxidize a Si film to 100 OA is approximately 100 hours at 600°C;
At 0°C, it takes about 8 hours, at 800°C, it takes about 1 hour and 30 minutes, and at 900'C, it takes about 1 hour and 30 minutes or less.

On the other hand, in a dry atmosphere it is 100V at 700℃! About 20vf at 800℃, 900℃
In addition, the oxidation treatment at a temperature higher than 600°C causes the movement of Li in the substrate, resulting in S
Although there is a concern that iO2 metamorphosis may occur and the properties of the buffer layer deteriorate, experiments have confirmed that there is no problem in terms of properties. However, when the temperature is higher than 850℃,
The heat treatment at a temperature of 850° C. or lower is preferable because Li moves and metamorphosis occurs in the LiNbO3 of the substrate.

Therefore, in this invention, the heat treatment of the oxide thin film I! 70
It is preferable to carry out the process at a temperature within the range of 0°C or higher and 850°C or lower, particularly preferably at a temperature of about 800°C.

In this example, a thin oxide film (indicated by 14 in FIG. 2(8)) was heated to 900° C., which is the metamorphic temperature of LiNbO3, for 2 to 5 hours in an oxygen atmosphere containing water vapor (wet atmosphere). A buffer layer 1618 is obtained by performing heat treatment at a temperature of about 800° C., which is just below the oxidation temperature (see Fig. 2).
C)).

Next (FIG. C82 (D) in which the electrode 18 is formed on this buffer layer 16 in the same manner as in the conventional method).

The waveguide type optical device including the buffer layer 16 formed as described above was constructed as a 5.5 mm long inverted ΔB electrode type optical switch (bar voltage was set to 840 V), and the operating point drift of this optical device was (DC drift) and the hysteresis of switching characteristics when increasing and decreasing the voltage applied to the electrodes were tested. the result,
It was found that the DC drift was 1.5V or less for 5 to 6 hours, which was considerably lower than the conventional 5V for 4 to 8 hours. It was also found that the hysteresis was significantly smaller than in the past, and was so large that it did not cause any problems.

This invention is not limited to the above-mentioned embodiment 1, and it is obvious that many modifications and variations can be made.
20,,j (), but even with other oxides, it is preferable that the oxidation temperature range is between 700℃ and 850℃ and the oxidation time at 1000A is between 100℃ and 100℃. It is fine as long as it is shorter than 20＠.

(Effects of the Invention) As is clear from the above description, the method for forming the Balanor layer of the waveguide optical device according to the present invention (accordingly, both the operating point drift [- and the hysteresis of the switching characteristics]) Therefore, by providing such a buffer layer in a waveguide type optical device, it is possible to provide a waveguide type optical device with excellent characteristics. , Sj oxidation temperature and oxidation time characteristic curves, and FIGS. 2(A) to 2(D) are main manufacturing process diagrams for explaining the method of forming the buffer layer of the present invention and the conventional waveguide type optical device. be.

10-1-iNbO3 (or 1Taos) substrate 12...waveguide, 14...-oxide thin film 16...buffer layer, +8-...electrode.

Claims (1)

[Claims] (1) Forming a waveguide on a LiNbO_3 or LiTaO_3 substrate; After depositing and forming an oxide thin film on the waveguide, heat treating the oxide thin film in an oxygen-containing atmosphere to form a buffer layer. A method for forming a buffer layer of a waveguide type optical device, which comprises a step of forming a buffer layer, and a step of forming an electrode on the buffer layer, includes heat-treating the oxide thin film at a temperature of 700°C or higher and 850°C or lower. A method for forming a buffer layer of a waveguide type optical device, characterized in that the process is performed at a temperature.