JP-2026074604-A - Dielectric thin film substrate and method for manufacturing the same, optical waveguide element and optical modulation element

Abstract

[Problem] To provide a dielectric thin film substrate having a dielectric thin film made of lithium niobate film, which can form an optical waveguide for an optical modulation element with low optical loss, and a method for manufacturing the same. [Solution] The dielectric thin film-attached substrate 1 comprises a single crystal substrate 2 oriented along the c axis in the in-plane direction and a dielectric thin film 3 formed in contact with the single crystal substrate 2, wherein the dielectric thin film 3 is a lithium niobate film whose c axis is aligned in one direction of the in-plane direction. Preferably, the angle between the c-axis direction of the single crystal substrate 2 and the c-axis direction of the lithium niobate film is 0.4° to 5°. [Selection Diagram] Figure 1

Inventors

• 佐々木 権治
• 菊川 隆
• 川崎 克己

Assignees

• ＴＤＫ株式会社

Dates

Publication Date

20260507

Application Date

20241021

Claims (9)

1. The system comprises a single crystal substrate oriented along the c-axis in the in-plane direction, and a dielectric thin film formed in contact with the single crystal substrate. A substrate with a dielectric thin film, wherein the dielectric thin film is a lithium niobate film in which the c-axis is aligned in one direction of the in-plane direction.
2. The dielectric thin film substrate according to claim 1, wherein the angle between the c-axis direction of the single crystal substrate and the c-axis direction of the lithium niobate film is 0.4° to 5°.
3. The dielectric thin-film substrate according to claim 1, wherein the single-crystal substrate is a sapphire single-crystal substrate.
4. The dielectric thin film substrate according to claim 1, wherein the lithium niobate film is grown by vapor phase growth.
5. The dielectric thin film substrate according to claim 1, wherein the lithium niobate film is grown by sputtering.
6. A substrate with a dielectric thin film according to any one of claims 1 to 5 is provided, An optical waveguide element having an optical waveguide made of the dielectric thin film.
7. A substrate with a dielectric thin film according to any one of claims 1 to 5 is provided, An optical waveguide made of the dielectric thin film, The device has a first electrode and a second electrode provided on the dielectric thin film and arranged opposite to each other with spaced apart in the in-plane direction, An optical modulation element in which the optical waveguide is positioned between the first electrode and the second electrode.
8. A manufacturing method for producing a dielectric thin film substrate according to any one of claims 1 to 5, A method for manufacturing a substrate with a dielectric thin film, comprising a dielectric thin film deposition step of growing a lithium niobate film on a single crystal substrate in which the c-axis is oriented in the in-plane direction, by vapor phase growth, wherein the c-axis is aligned in one direction in the in-plane direction.
9. The method for manufacturing a dielectric thin film substrate according to claim 8, wherein the vapor phase growth method is sputtering.

Description

This invention relates to a dielectric thin film-coated substrate, a method for manufacturing a dielectric thin film-coated substrate, an optical waveguide element, and an optical modulation element. Conventionally, some optical modulation elements have used lithium niobate films epitaxially grown on a substrate. For example, Patent Document 1 describes an optical modulation element using a substrate with a dielectric thin film. Patent Document 1 describes a substrate with a dielectric thin film comprising a single crystal substrate and a dielectric thin film made of c-axis oriented lithium niobate epitaxially formed on the main surface of the single crystal substrate. Furthermore, Patent Document 2 describes a laminated structure comprising a single-crystal substrate, a dielectric layer made of lithium niobate, and a buffer layer provided between the single-crystal substrate and the dielectric layer. Patent Document 2 also describes that the c-axis of the crystals constituting the dielectric layer of the laminated structure is substantially parallel to the main surface of the single-crystal substrate, and the c-axis of the crystals constituting the buffer layer is substantially parallel to the main surface of the single-crystal substrate. International Publication No. 2018/016428Japanese Patent Publication No. 2016-109856 Figure 1(a) is a schematic cross-sectional view showing a substrate with a dielectric thin film according to one embodiment of the present invention. Figure 1(b) is a plan view showing a single crystal substrate on which the dielectric thin film substrate shown in Figure 1(a) is formed. Figure 1(c) is a plan view showing the dielectric thin film on which the dielectric thin film substrate shown in Figure 1(a) is formed.Figures 2(a) and 2(b) illustrate the arrangement of Al atoms in a sapphire single crystal substrate; Figure 2(a) is a schematic diagram showing the arrangement as viewed from the c-axis direction, and Figure 2(b) is a schematic diagram showing the arrangement on the a-plane (1100). Figures 2(c) and 2(d) illustrate the arrangement of Nb and Li atoms in a lithium niobate film; Figure 2(c) is a schematic diagram showing the arrangement as viewed from the c-axis direction, and Figure 2(d) is a schematic diagram showing the arrangement on the a-plane (1100).Figure 3 is a plan view showing an example of an optical waveguide element 100 equipped with the dielectric thin film substrate 1 shown in Figure 1.Figure 4 is a cross-sectional view of the optical waveguide element 100 shown in Figure 3, along the line A-A'.Figure 5 is a plan view showing an example of a Mach-Zehnder type optical modulation element 200 equipped with the dielectric thin film substrate 1 shown in Figure 1.Figure 6 is a cross-sectional view of the optical modulation element 200 shown in Figure 5, along the line B-B'.Figure 7 shows the X-ray diffraction intensity profile obtained by measuring (φ scan) the in-plane X-ray diffraction intensity of the lithium niobate film forming the dielectric thin film 3 on the dielectric thin film substrate of Example 1.Figure 8 is a diagram showing the measurement results of the X-ray diffraction poles of the lithium niobate film forming the dielectric thin film 3 on the dielectric thin film substrate of Example 1.Figure 9 shows the X-ray diffraction intensity profiles obtained by measuring (φ scan) the in-plane X-ray diffraction intensity of the sapphire single crystal substrate 2 forming the dielectric thin film substrate of Example 1, and the lithium niobate film forming the dielectric thin film 3.Figure 10(a) shows an enlarged portion of Figure 9, illustrating the X-ray diffraction intensity profile around a φ-axis angle of 85°. Figure 10(b) shows an enlarged portion of Figure 9, illustrating the X-ray diffraction intensity profile around a φ-axis angle of 265°. To solve the above problems and to create a dielectric thin film substrate that can form an optical modulation element with low driving voltage and low optical loss when used as a material for an optical waveguide made of a lithium niobate film into which TE mode light emitted from a laser light source or the like is incident, the inventors focused on the c-axis direction of the lithium niobate film and conducted diligent studies as described below. In other words, the inventors considered that when TE-mode light is incident on an optical waveguide made of a lithium niobate film in an optical modulation element, in order to align the polarization direction of the light with the direction of the c-axis of the lithium niobate film, it would be sufficient to use an optical waveguide made of a lithium niobate film in which the c-axis is aligned in one direction in the in-plane direction of the substrate. However, conventional techniques have not made it possible to grow a lithium niobate film on a single crystal substrate in contact with it, with its c-axis aligned in one direction within the substrate's plane. One poss