JPS61232299A - Substrate for optical device - Google Patents

Abstract

PURPOSE:A substrate for optical devices, obtained by forming a dielectric layer consisting of potassium tantalate niobate (KTN) through an insulator film on a silicon single crystal substrate, and capable of giving optical switches, optical modulators, etc., having low driving voltage and improved stability of characteristics. CONSTITUTION:An insulator film 2, e.g. epitaxial film of magnesium aluminate spinel, on a silicon single crystal substrate 1 by the epitaxial growth method, etc. A dielectric layer 3 having a composition expressed by the formula (0<=x<=1) is formed thereon by the epitaxial growth method to give the aimed substrate for optical devices. As a specific method for forming the dielectric layer 3 to be cited, raw materials, e.g. K2CO3, Ta2O5 and Nb2O5, are weighed to give K2CO3 in a molar amount of about 10mol% excess of the theoretical amount and mixed, and the resultant mixture is calcined to afford a powdery target, which is used to carry out sputtering in a mixed gas of Ar and O2, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical device substrate comprising a semiconductor layer and an insulating layer and used for optical devices such as optical switches and optical modulators.

(Prior Art) Optical devices such as optical switches and optical modulators are extremely important in optical communication or optical information processing equipment. These devices generally use materials having an electro-optic effect (hereinafter referred to as electro-optic materials) from the viewpoint of high speed and the like. The electro-optic effect is classified into the Pockels effect, in which the change in birefringence is proportional to the electric field intensity, and the Kerr effect, in which the change in birefringence is proportional to the square of the electric field intensity. Lithium niobate (LIN), which has the Pockels effect, is currently commonly used.
b0) S: y Tani acid lithium A (LiTaO,)
However, in order to reduce the driving voltage, it is more advantageous to use an electro-optic material having the Kerr effect.

A typical material exhibiting a large Kerr effect is one represented by the general formula KTa xNb, -xO.

Since this material is generally abbreviated as KTN, it will be referred to hereinafter as KTN. Especially when X=0.65 ChiKT a
It is known that a material having a composition of O,65N b O,350s exhibits a much larger Kerr effect than other materials. For example, Journal of Applied Physics (J, KPPL, Phys) Volume 37, No. 1, 196
6, pages 388-398 [LightModu
Jation and Beam Defl
ecttonWith Potassium Tant
In a paper published entitled Alate-NiobateCrystalsJ, an optical modulator that can be driven at low voltage by using a KTN single crystal,
It is stated that an optical deflector can be constructed.

(Problems with the Prior Art) As described above, the single crystal of KTN is an extremely useful electro-optic material, but it has not been put to practical use because it is difficult to produce a uniform single crystal.

A single crystal of KTN is generally produced by a pulling method from a raw material melt, but since KTN is a completely solid solution crystal, when a crystal is grown from a certain amount of melt, the X of the solidified crystal is This is because it gradually changes in a smaller direction and becomes non-uniform.

Furthermore, in order to achieve lower voltage and higher integration, a waveguide-type optical device in which a thin film of electro-optic material is formed on a suitable substrate is preferable to a bulk single crystal.

(Objective of the Invention) The present invention improves the drawbacks of the above-mentioned prior art, and aims to provide a substrate for an optical device that is capable of low-voltage driving and integration, and has excellent uniformity of characteristics. .

(Structure of the Invention) That is, in the present invention, an insulating film is formed on a silicon single crystal substrate, and a chemical formula of KTaxNb, , x
This is an optical device substrate characterized by forming a dielectric layer represented by Ol. It must be. To form an epitaxial film, a substrate suitable for the symmetry and lattice constant of KTN is required, and magnesia spinel (M
gA'204) and magnesia (MgO) are considered. Although it is difficult to manufacture these single crystals with a large diameter at low cost, it is possible to epitaxially grow a single crystal thin film on a silicon single crystal substrate. Since silicon single crystal substrates with very large diameters are easily available today, as claimed in the present invention, MgA1. An optical device substrate in which an epitaxial thin film of O, MgO, or the like is formed, and a KTN thin film is formed thereon is of great practical significance.

In this case, MgO was proposed by the present applicant (Japanese Patent Application No. 57-22
9033) L, a single crystal film of better quality can be formed by forming it on a silicon substrate via MgAl, q, than by directly growing it on a silicon single crystal substrate. Therefore, the insulating single crystal film may have a two-layer structure. In addition, the applicant has also discovered that the MgAl, 04 epitaxial film formed on a silicon substrate is MgAl! O, MgA 1.0. by thermally oxidizing the silicon substrate through the film. /
8 io, /S i structure has already been proposed (Japanese Patent Application No. 103967/1983). Therefore, an amorphous 8i0. It is also possible to have a structure such as through.

Magnesia, subine/l/ (MgAlt Oa)
, the refractive index of magnesia (MgO) is approximately 1.758i0.
The refractive index of KTN is approximately 1.5, and both of them are
(approximately 2.2), therefore MgO18i0. It is possible to guide light through a KTN thin film formed on an insulator layer made of, etc., and various waveguide devices can be fabricated.

The KTN epitaxial thin film can be formed using physical vapor deposition such as sputtering or ion blating, or chemical vapor deposition such as CVD. When growing thin films using these methods, crystal growth is not from a melt or liquid phase as in conventional bulk single crystal growth, but from a gas phase, so as mentioned above, There is no problem of non-uniformity due to compositional changes due to the fact that it is a complete solid solution, which was a problem in bulk single crystals.

For example, in the case of sputtering, since the sputtering rate and adsorption rate of each component element are different, the composition of the target and the composition of the thin film formed are generally slightly different, but the composition of the target is selected so that the thin film has the desired composition. If this is done, a thin film with a stable and uniform composition can be formed.

Also, if we pay attention to the Kerr effect in 'l'a, -5CNbx01, it is desirable that X = 0.65, but any other range of 0 x 1.0 has useful uses and can constitute an excellent substrate.

This will be explained in detail below using examples.

(Example 1) A film with a thickness of 1 μm was deposited on a silicon single crystal substrate with a plane orientation of (100).
Mg of magnesia and spinel (MgAl* 04 ) were epitaxially grown, and a 2 μm thick KTN thin film was formed thereon by sputtering. FIG. 1 is an explanatory diagram of this example, in which 1 is a (100)8i single crystal substrate 2 is MgA1,0. The epitaxial film 3 is a KTN single crystal film formed by sputtering. MgA1. O,
The present applicant has already proposed the vapor phase growth of
36051) L, grown using the `` method. That is, MgC1 as a reactive gas! , using AlCl, , co, , H, gas produced by reacting AI with HCI gas,
N gas was used as a carrier gas. MgA1. O,
The production reaction is MgC1, +2AICI, +4CO□+
4 → MgA1.04 + 4CO + 8HC1. It was grown at a growth temperature of 950°C, and X-ray diffraction and electron diffraction revealed MgA110. with (l OO) orientation. was confirmed to be growing epitaxially. The KTN epitaxial film was formed by RF magnetron sputtering. KtC
OsSatQNb, O, raw material KTaO, 65N
Bo, 1θ mol% of Co is higher than the composition ratio of 3s03.
Using a powder target that has been weighed, mixed, and calcined so that the excess is Ar and 0. The substrate temperature is 600℃ in a mixed gas of
Sputtering was performed at °C to 8000C.

The composition of the formed film is KT a O,65N b O,3
50s, and by X-ray diffraction and electron diffraction (100
) It was confirmed that it was an epitaxial film oriented in the direction.

(Example 2) (Zoo) An 8i substrate was thermally oxidized through a 0.2 μm thick MgAl, O, film epitaxially grown on a Si single crystal substrate. O, film thickness 0 between film and 8i substrate
．． After forming 8 μm of 8 io, MgAl, O,
A KTN film having a thickness of 2 μm was epitaxially grown on the x-pitaxial film. FIG. 2 is a process diagram of this example.

4 is an 8i substrate, 5 is MgA1. O, epitaxial film 6 is SiO, 7 is KTN epitaxial film 0
FIG. 2(a) shows the epitaxial growth process of MgA1.04 Φ) of 8i0. (C1 indicates the KTN epitaxial growth process. The formation of MgA1.04 was carried out in exactly the same manner as in Example 1, and the formation of 8i0. was carried out by steam oxidation at 1100 ° C. Thermal oxidation by MgAl
The crystallinity of ,O, was not impaired, but rather the half width of the X-ray rocking curve was reduced by 30% and the crystallinity was improved.

Sputtering was performed using the same target and sputtering conditions as in Example 1, and KTaQ, 65Nb0.35
An epitaxial film of No. 03 was obtained.

(Example 3) MgA film with a thickness of 0.2 μm on a (xoo)si single crystal substrate
ol, O, was epitaxially grown in the same manner as in Example 1, and Mg with a thickness of 0.8 μm was grown on top of it by vapor phase growth.
O was grown epitaxially. On top of that, a 2 μm thick film of KTaO and 65N was further applied by sputtering in the same manner as in Example 1.
A 0.350 g z-bitter+sha# film was grown. FIG. 3 is an explanatory diagram of the optical device substrate according to this embodiment. 8 is 8i single crystal substrate, 9 is MgAl, O, epitaxial film, 10 is MgO epitaxial film, 11 is KTN
It is an epitaxial film.

(Effects of the Invention) As described above, according to the present invention, an optical device substrate can be obtained in which an epitaxial thin film of KTa1xNbxO8 (KTN) is formed on an insulating film on a silicon single crystal substrate. The KTN thin film according to the present invention has excellent uniformity, and silicon single crystal substrates with large diameters and high quality are easily available, so the present invention can provide substrates for large diameter optical devices. be. According to the present invention, the low drive W
With EE, it is possible to mass produce devices such as optical switches and optical modulators with excellent characteristic stability, and its industrial value is great.

[Brief explanation of the drawing]

1 to 3 are explanatory diagrams showing embodiments of the substrate according to the present invention. 1, 4.8...8i single crystal substrate, 2.5.9...M
gA1,0. Epitaxial ill, 3.7.11...
・KTN Epitaxial Exhibition, Figure 1 Figure 2 (b) Figure 73

Claims (4)

[Claims] (1) An insulating film is formed on a silicon single crystal substrate, and the chemical formula KTa_xNb_1_-_xO_
1. A substrate for an optical device, characterized in that a dielectric layer represented by 3 (0≦x≦1.0) is formed. (2) The insulator film formed on the silicon single crystal substrate is magnesium aluminate spinel) (MgAl_2
O_4) The optical device substrate according to claim 1, which is an epitaxial film. (3) The insulator film formed on the silicon single crystal substrate is made of magnesium aluminate spinel (MgAl_2O
_4) The optical device substrate according to claim 1, which comprises an epitaxial film and a magnesia (MgO) epitaxial film formed thereon. (4) The insulator film formed on the silicon single crystal substrate is silicon dioxide (SiO2) formed on the surface of the silicon substrate.
_2) The substrate for an optical device according to claim 1, comprising a layer and an insulator epitaxial film formed thereon.