WO2020095421A1 - 電気光学素子のための複合基板とその製造方法 - Google Patents

電気光学素子のための複合基板とその製造方法 Download PDF

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Publication number
WO2020095421A1
WO2020095421A1 PCT/JP2018/041548 JP2018041548W WO2020095421A1 WO 2020095421 A1 WO2020095421 A1 WO 2020095421A1 JP 2018041548 W JP2018041548 W JP 2018041548W WO 2020095421 A1 WO2020095421 A1 WO 2020095421A1
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WIPO (PCT)
Prior art keywords
electro
refractive index
substrate
interface
low refractive
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Ceased
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PCT/JP2018/041548
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English (en)
French (fr)
Japanese (ja)
Inventor
雄大 鵜野
近藤　順悟
知義 多井
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NGK Insulators Ltd
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NGK Insulators Ltd
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Priority to PCT/JP2018/041548 priority Critical patent/WO2020095421A1/ja
Priority to EP19881111.9A priority patent/EP3879336B1/en
Priority to PCT/JP2019/027570 priority patent/WO2020095478A1/ja
Priority to CN202210482598.7A priority patent/CN114815329B/zh
Priority to JP2019549494A priority patent/JP6646187B1/ja
Priority to CN201980061122.2A priority patent/CN112955811B/zh
Priority to JP2020002430A priority patent/JP7337713B2/ja
Publication of WO2020095421A1 publication Critical patent/WO2020095421A1/ja
Priority to US17/217,360 priority patent/US11150497B2/en
Anticipated expiration legal-status Critical
Priority to US17/480,870 priority patent/US12025864B2/en
Ceased legal-status Critical Current

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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
    • G02F1/0305—Constructional arrangements
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
    • G02F1/035—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect in an optical waveguide structure
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B2006/12083—Constructional arrangements
    • G02B2006/12097—Ridge, rib or the like
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B2006/12083—Constructional arrangements
    • G02B2006/121—Channel; buried or the like
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B2006/12133—Functions
    • G02B2006/12142—Modulator

Definitions

  • the technology disclosed in the present specification relates to a composite substrate for an electro-optical element (for example, an optical modulator) that utilizes an electro-optical effect.
  • an electro-optical element for example, an optical modulator
  • Electro-optical elements such as optical modulators are known.
  • the electro-optical element can convert an electric signal into an optical signal by utilizing the electro-optical effect.
  • the electro-optical element is an essential element for, for example, optical radio wave fusion communication, and further development is underway in order to realize high-speed and large-capacity communication.
  • An optical modulator is disclosed in Japanese Patent Laid-Open No. 2010-85789.
  • This optical modulator is a type of electro-optical element, and is configured using a composite substrate.
  • the composite substrate includes an electro-optic crystal substrate and a support substrate bonded to the electro-optic crystal substrate via a bonding layer.
  • a material having a lower refractive index than that of the electro-optic crystal substrate is used for the supporting substrate and the bonding layer.
  • the mechanical strength of the composite substrate (that is, the mechanical strength of the electro-optical element) can be increased as the thickness of the supporting substrate is increased.
  • the thickness of the support substrate is increased, electromagnetic waves are more likely to resonate in the composite substrate when the electro-optical element is used in a high frequency band (for example, 10 GHz or higher).
  • a high frequency band for example, 10 GHz or higher.
  • the present specification provides a technique capable of suppressing resonance of electromagnetic waves in a composite substrate.
  • the electromagnetic waves caused by it are repeatedly propagated in the composite substrate along the thickness direction while being reflected on the surface or interface of the composite substrate. Then, such electromagnetic waves overlap each other in the same phase, so that the resonance occurs in the composite substrate. Therefore, in the technique disclosed in this specification, at least one of the plurality of interfaces existing in the composite substrate is an interface having a high degree of roughness. With such a configuration, the electromagnetic waves propagating in the thickness direction of the composite substrate are variously refracted or reflected at the interface having a large degree of roughness, and an infinite number of variations occur in the paths along which the electromagnetic waves propagate. This makes it possible to prevent electromagnetic waves propagating in the composite substrate along the thickness direction from overlapping each other in the same phase.
  • the position of the interface having a large degree of roughness described above is not particularly limited. However, if the interface having a high degree of roughness is the interface in contact with the electro-optical crystal substrate, light transmitted through the electro-optical crystal substrate may be scattered or absorbed by the interface having a high degree of roughness. Therefore, in the present technology, the low-refractive index layer that is in contact with the electro-optical crystal substrate is provided, and the interface between the electro-optical crystal substrate and the low-refractive index layer is a smooth interface. Thereby, the scattering and absorption of the light transmitted through the electro-optic crystal substrate is suppressed, and the light can be confined in the electro-optic crystal substrate.
  • the interface having a high degree of roughness can be provided between the low refractive index layer and the supporting substrate to suppress the above resonance of electromagnetic waves.
  • One aspect of the present technology discloses a composite substrate for an electro-optical element.
  • This composite substrate has an electro-optic crystal substrate having an electro-optic effect, a low-refractive index layer that is in contact with the electro-optic crystal substrate and has a lower refractive index than the electro-optic crystal substrate, and at least a bonding layer in the low-refractive index layer And a support substrate bonded via the.
  • At least one of the plurality of interfaces existing between the low-refractive index layer and the support substrate is an interface having a higher degree of roughness than the interface between the electro-optic crystal substrate and the low-refractive index layer.
  • the existence of the interface having a high degree of roughness in the composite substrate can prevent the electromagnetic waves from resonating in the composite substrate.
  • the interface between the electro-optic crystal substrate and the low refractive index layer is relatively smooth, the scattering and absorption of the light propagating through the electro-optic crystal substrate is suppressed, and the light inside the electro-optic crystal substrate is suppressed. Can be trapped.
  • a method for manufacturing a composite substrate for an electro-optical element comprises a step of forming a low refractive index layer having a lower refractive index than the electro-optical crystal substrate on the surface of the electro-optical crystal substrate having an electro-optical effect, and a low refractive index provided on the electro-optical crystal substrate.
  • the method includes a step of forming a bonding layer on the surface of the layer, and a step of bonding a support substrate to the surface of the bonding layer formed on the low refractive index layer.
  • the surface of the low refractive index layer before the formation of the bonding layer has a higher degree of roughness than the surface of the electro-optic crystal substrate before the formation of the low refractive index layer.
  • the interface between the low refractive index layer and the bonding layer may be an interface having a higher degree of roughness than the interface between the electro-optical crystal substrate and the low refractive index layer. it can.
  • FIG. 1 is a perspective view schematically showing a composite substrate 10 of Example 1.
  • FIG. 1 is a perspective view schematically showing a composite substrate 10 of Example 1.
  • FIG. 3 is a diagram schematically showing a cross-sectional structure of the composite substrate 10 of Example 1.
  • FIG. 3 is a diagram showing a step of the method of manufacturing the composite substrate 10 of Example 1.
  • FIG. 3 is a diagram showing a step of the method of manufacturing the composite substrate 10 of Example 1.
  • FIG. 3 is a diagram showing a step of the method of manufacturing the composite substrate 10 of Example 1.
  • FIG. 3 is a diagram showing a step of the method of manufacturing the composite substrate 10 of Example 1.
  • FIG. 3 is a diagram showing a step of the method of manufacturing the composite substrate 10 of Example 1.
  • FIG. 7 shows a modified example of the composite substrate 10, in which electrodes 32 and 34 for applying an electric signal to the electro-optical crystal substrate 12 and an optical waveguide region 36 provided in the electro-optical crystal substrate 12 are added.
  • FIG 9 shows a modified example of the composite substrate 10, in which a ridge portion 13 is formed on the upper surface 12 a of the electro-optic crystal substrate 12.
  • FIG 9 shows a modified example of the composite substrate 10, in which electrodes 42 and 44 for applying an electric signal are added to the ridge portion 13.
  • the c-axis of the electro-optic crystal substrate 12 is parallel to the electro-optic crystal substrate 12.
  • FIG 9 shows a modified example of the composite substrate 10, in which electrodes 52 and 54 for applying an electric signal are added to the ridge portion 13.
  • the c-axis of the electro-optic crystal substrate 12 is perpendicular to the electro-optic crystal substrate 12.
  • FIG. 5 is a diagram schematically showing a cross-sectional structure of a composite substrate 10a of Example 2.
  • 6A and 6B are views for explaining the method for manufacturing the composite substrate 10a according to the second embodiment.
  • FIG. 9 is a diagram schematically showing a cross-sectional structure of a composite substrate 10b of Example 3.
  • 6A and 6B are diagrams illustrating a method of manufacturing the composite substrate 10b according to the third embodiment.
  • FIG. 9 is a diagram schematically showing a cross-sectional structure of a composite substrate 10c of Example 4.
  • 6A and 6B are diagrams illustrating a method of manufacturing the composite substrate 10c according to the fourth embodiment.
  • the roughness of the interface having a large roughness may be 3 times or more the roughness of the interface between the electro-optic crystal substrate and the low refractive index layer, or 5 It may be two times or more or ten times or more.
  • the effect of the present technology can be enhanced by increasing the difference in roughness between the two interfaces.
  • the arithmetic mean roughness (Ra) of the interface between the electro-optic crystal substrate and the low refractive index layer is in the range of 0.03 nm (nanometer) to 0.5 nm.
  • the arithmetic mean roughness (Ra) of the interface having a large roughness may be in the range of 0.5 nm to 500 nm.
  • the interface having a high degree of roughness may be the interface between the low refractive index layer and the bonding layer.
  • the arithmetic mean roughness (Ra) of the interface between the low refractive index layer and the bonding layer may be 1/1000 or more of the thickness of the low refractive index layer.
  • the arithmetic mean roughness (Ra) of the interface between the low refractive index layer and the bonding layer may be 0.5 nm or more, and the thickness of the low refractive index layer is 0.5 ⁇ m ( Micrometer) or more.
  • the interface having a large roughness may be the interface between the bonding layer and the supporting substrate. Even with such a structure, the resonance of the electromagnetic wave in the composite substrate can be suppressed by the existence of the interface having a large roughness in the composite substrate.
  • the composite substrate may further include an intermediate layer located between the low refractive index layer and the bonding layer.
  • the interface having high roughness may be the interface between the intermediate layer and the bonding layer. Even with such a structure, the resonance of the electromagnetic wave in the composite substrate can be suppressed by the existence of the interface having a large roughness in the composite substrate.
  • the material forming the intermediate layer may be a material that can be used for the low refractive index layer or the bonding layer, and is a material different from the material actually used for the low refractive index layer and the bonding layer. Good.
  • the composite substrate may further include an intermediate layer located between the bonding layer and the supporting substrate.
  • the interface having high roughness may be the interface between the intermediate layer and the supporting substrate. Even with such a structure, the resonance of the electromagnetic wave in the composite substrate can be suppressed by the existence of the interface having a large roughness in the composite substrate.
  • the composite substrate may further include a conductive layer made of a conductor.
  • the interface having a large degree of roughness may be located in the range between the electro-optic crystal substrate and the conductive layer.
  • the electromagnetic waves propagating through the composite substrate are shielded without passing through the conductive layer, so that they mainly propagate in the range between the electro-optic crystal substrate 12 and the conductive layer.
  • the interface having a large roughness is located in the range between the electro-optic crystal substrate and the conductive layer where electromagnetic waves mainly propagate.
  • the conductive layer may be at least a part of the bonding layer or the intermediate layer.
  • some or all of the bonding layer and / or the intermediate layer are made of metal. It may be made of a conductor.
  • the electro-optic crystal substrate is lithium niobate (LiNbO 3 : LN), lithium tantalate (LiTaO 3 : LT), potassium titanate phosphate (KTiOPO 4 : KTP), potassium niobate.
  • the substrate may be any one of a solid solution of lithium oxide and lithium tantalate.
  • the low refractive index layer includes silicon oxide (SiO 2 ), tantalum oxide (Ta 2 O 5 ), aluminum oxide (Al 2 O 3 ), magnesium fluoride (MgF 2 ), and fluorine. It may be composed of at least one of calcium fluoride (MgF 2 ).
  • the bonding layer is tantalum oxide (Ta 2 O 5 ), niobium oxide (Nb 2 O 5 ), silicon (Si), aluminum oxide (Al 2 O 3 ), titanium oxide (TiO 2 ). , Gold (Au), silver (Ag), copper (Cu), aluminum (Al), platinum (Pt), and an alloy containing at least two of these metals. May be.
  • the support substrate is lithium niobate (LiNbO 3 : LN), lithium tantalate (LiTaO 3 : LT), silicon (Si), glass, sialon (Si 3 N 4 —Al 2 O 3). ), Mullite (3Al 2 O 3 ⁇ 2SiO 2 , 2Al 2 O 3 ⁇ SiO 2 ), aluminum nitride (AlN), silicon nitride (Si 3 N 4 ), magnesium oxide (MgO), sapphire, quartz, crystal, gallium nitride
  • the substrate may be any one of (GaN), silicon carbide (SiC), and gallium oxide (Ga 2 O 3 ).
  • the supporting substrate may have conductivity or semiconductivity from the viewpoint of suppressing resonance of electromagnetic waves.
  • lithium niobate and lithium tantalate are usually insulating materials, but they can acquire conductivity when they are in an oxygen-deficient state.
  • black LN or black LT is an example of such a material, and a black LN or black LT substrate can be adopted as a supporting substrate.
  • the present technology is embodied in a method for manufacturing a composite substrate.
  • the bonding layer is formed on the surface of the low refractive index layer having a large roughness. Therefore, the surface roughness of the bonding layer can be relatively large.
  • the surface of the bonding layer is preferably smooth. Therefore, in one embodiment of the present technology, the manufacturing method may further include a step of smoothing the surface of the bonding layer between the step of forming the bonding layer and the step of bonding the supporting substrate. With such a configuration, the electro-optic crystal substrate and the supporting substrate can be bonded well.
  • the low refractive index layer may be formed by sputtering in the step of forming the low refractive index layer.
  • the surface roughness of the low refractive index layer naturally increases. Therefore, by forming the low refractive index layer by sputtering, it is possible to easily form the low refractive index layer having a surface with a large degree of roughness.
  • the roughness of the surface of the low refractive index layer increases as the thickness of the low refractive index layer increases.
  • a treatment for roughening the surface of the low refractive index layer for example, lapping, sandblasting, etching, etc.
  • the manufacturing method may further include a step of forming a bonding layer on the surface of the supporting substrate before the step of bonding the supporting substrate.
  • the bonding layer formed on the supporting substrate may be made of the same material as the bonding layer formed on the low refractive index layer.
  • the composite substrate 10 of the present embodiment can be applied to various electro-optical elements such as an optical modulator.
  • the composite substrate 10 of the present embodiment is manufactured in the form of a so-called wafer and provided to the manufacturer of the electro-optical element.
  • composite substrate 10 has a diameter of approximately 10 centimeters (4 inches).
  • a plurality of electro-optical elements are manufactured from one composite substrate 10.
  • the composite substrate 10 is not limited to the wafer form, and may be manufactured and provided in various forms.
  • the composite substrate 10 includes an electro-optic crystal substrate 12, a low refractive index layer 14, a bonding layer 16, and a support substrate 18.
  • the electro-optic crystal substrate 12 is bonded to the support substrate 18 via the low refractive index layer 14 and the bonding layer 16.
  • These substrates 12, 18 and layers 14, 16 extend parallel to each other throughout the composite substrate 10.
  • the electro-optic crystal substrate 12 is located in the uppermost layer of the composite substrate 10, and its upper surface 12a is exposed to the outside. Part or all of the electro-optic crystal substrate 12 serves as an optical waveguide that transmits light in the electro-optic element manufactured from the composite substrate 10.
  • the electro-optic crystal substrate 12 is made of a crystal of a material having an electro-optic effect. Therefore, when an electric field is applied to the electro-optic crystal substrate 12, the refractive index of the electro-optic crystal substrate 12 changes. In particular, when an electric field is applied along the c-axis of the electro-optic crystal substrate 12, the refractive index of the electro-optic crystal substrate 12 changes significantly.
  • the c-axis of the electro-optical crystal substrate 12 may be parallel to the electro-optical crystal substrate 12. That is, the electro-optic crystal substrate 12 may be, for example, an x-cut or y-cut substrate. Alternatively, the c-axis of the electro-optic crystal substrate 12 may be perpendicular to the electro-optic crystal substrate 12. That is, the electro-optic crystal substrate 12 may be, for example, a z-cut substrate.
  • the thickness T12 of the electro-optic crystal substrate 12 is not particularly limited, but may be, for example, 0.1 ⁇ m or more and 10 ⁇ m or less.
  • the material constituting the electro-optic crystal substrate 12 is not particularly limited, but lithium niobate, lithium tantalate, potassium titanate phosphate, potassium niobate / lithium niobate, potassium niobate, tantalate / potassium niobate, lithium niobate. And a solid solution of lithium tantalate.
  • the electro-optic crystal substrate 12 may have an electro-optic effect of changing other optical constants in addition to or instead of the refractive index.
  • the low refractive index layer 14 is in contact with the electro-optic crystal substrate 12 below the electro-optic crystal substrate 12.
  • the low refractive index layer 14 has a lower refractive index than the electro-optic crystal substrate 12.
  • the material forming the low refractive index layer 14 is not particularly limited, but may be at least one of silicon oxide, tantalum oxide, aluminum oxide, magnesium fluoride, and calcium fluoride.
  • the thickness T14 of the low refractive index layer 14 is not particularly limited, but may be, for example, 0.1 ⁇ m or more and 10 ⁇ m or less.
  • the low refractive index layer 14 has a lower dielectric constant than the electro-optic crystal substrate 12. Therefore, when the composite substrate 10 includes the low refractive index layer 14, it becomes easy to satisfy the velocity matching condition and adjust the characteristic impedance in the electro-optical element manufactured from the composite substrate 10. Further, since the stray capacitance and the dielectric loss can be reduced, the electro-optical element can operate at high speed and the voltage can be lowered.
  • the bonding layer 16 is located between the low refractive index layer 14 and the supporting substrate 18.
  • the thickness T16 of the bonding layer 16 is not particularly limited, but may be 0.01 ⁇ m or more and 1 ⁇ m or less.
  • the low refractive index layer 14 and the bonding layer 16 are formed on the electro-optic crystal substrate 12, and the support substrate 18 is bonded to the bonding layer 16 by direct bonding.
  • the bonding layer 16 is a film provided for this direct bonding, and can be made of a material suitable for direct bonding.
  • the material forming the bonding layer 16 may be at least one of tantalum oxide, niobium oxide, silicon, aluminum oxide, and titanium oxide.
  • the material forming the bonding layer 16 may be at least one of gold, silver, copper, aluminum, platinum, and an alloy containing at least two of these metals.
  • the support substrate 18 is located at the lowermost layer of the composite substrate 10, and the lower surface 18b thereof is exposed to the outside.
  • the support substrate 18 is provided to increase the strength of the composite substrate 10, and thus the thickness of the electro-optic crystal substrate 12 can be reduced.
  • the thickness T18 of the support substrate 18 is not particularly limited, but may be, for example, 100 ⁇ m or more and 1000 ⁇ m or less.
  • the support substrate 18 is not particularly limited, but includes lithium niobate, lithium tantalate, silicon, glass, sialon, mullite, aluminum nitride, silicon nitride, magnesium oxide, sapphire, quartz, quartz, gallium nitride, silicon carbide, and oxide. It may be any of the substrates of gallium.
  • the linear expansion coefficient of the support substrate 18 is preferably close to the linear expansion coefficient of the electro-optic crystal substrate 12.
  • the material forming the support substrate 18 may be the same as the material forming the electro-optic crystal substrate 12.
  • the mechanical strength of the composite substrate 10 (that is, the mechanical strength of the electro-optical element) can be increased.
  • the electromagnetic waves are more likely to resonate in the composite substrate 10 when the electro-optical element is used in a high frequency band (for example, 10 GHz or higher). When such resonance occurs, an unintended ripple (fluctuation) may occur in the output signal of the electro-optical element, which may hinder the normal operation of the electro-optical element.
  • the interface F2 between the low refractive index layer 14 and the bonding layer 16 is more than the interface F1 between the electro-optic crystal substrate 12 and the low refractive index layer 14.
  • the interface has a high degree of roughness.
  • the roughness of the interface F2 between the low refractive index layer 14 and the bonding layer 16 is the roughness of the interface F1 between the electro-optic crystal substrate 12 and the low refractive index layer 14. It may be more than three times the degree. Alternatively, the roughness of the interface F2 may be 5 times or more or 10 times or more that of the interface F1. The greater the difference in roughness between the two interfaces F1 and F2, the more the effect of the present technology can be enhanced.
  • the arithmetic mean roughness (Ra) of the interface F1 between the electro-optic crystal substrate 12 and the low refractive index layer 14 is in the range of 0.03 nm to 0.5 nm. Good.
  • the arithmetic mean roughness (Ra) of the interface F2 between the low refractive index layer 14 and the bonding layer 16 may be in the range of 0.5 nm to 500 nm.
  • the arithmetic mean roughness (Ra) of the interface F2 between the low refractive index layer 14 and the bonding layer 16 is 1/1000 or more of the thickness T14 of the low refractive index layer 14. You may. Additionally or alternatively, the arithmetic mean roughness (Ra) of the interface F2 between the low refractive index layer 14 and the bonding layer 16 may be 0.5 nm or more, and the thickness of the low refractive index layer 14 is It may be 0.5 ⁇ m or more. When the composite substrate 10 satisfies these numerical requirements, the composite substrate 10 having the effect of the present technology can be manufactured by a relatively simple procedure.
  • a first sample was prepared in which the electro-optic crystal substrate 12 was a lithium niobate substrate and the thickness T12 was 1.5 ⁇ m.
  • the low refractive index layer 14 was made of silicon oxide
  • its thickness T14 was set to 0.7 ⁇ m
  • the bonding layer 16 was made of tantalum oxide
  • its thickness T16 was set to 0.05 nm.
  • the supporting substrate 18 is a lithium niobate substrate, and its thickness T18 is 1000 ⁇ m.
  • the arithmetic mean roughness (Ra) of the interface F1 between the electro-optical crystal substrate 12 and the low refractive index layer 14 is 0.2 nm, and the interface F2 between the low refractive index layer 14 and the bonding layer 16 is obtained.
  • the arithmetic mean roughness (Ra) of was 0.7 nm.
  • a second sample was prepared by changing the thickness T14 of the low refractive index layer 14 to 2.5 ⁇ m in the first sample described above.
  • the arithmetic mean roughness (Ra) of the interface F1 between the electro-optic crystal substrate 12 and the low refractive index layer 14 is 0.2 nm
  • the interface F1 between the low refractive index layer 14 and the bonding layer 16 is The arithmetic mean roughness (Ra) of the interface F2 was 2.5 nm.
  • the electro-optic crystal substrate 12 is prepared, and the low refractive index layer 14 is formed on the lower surface 12 b of the electro-optic crystal substrate 12.
  • the roughness of the lower surface 14b of the low refractive index layer 14 is made larger than the roughness of the lower surface 12b of the electro-optic crystal substrate 12.
  • the arithmetic average roughness (Ra) of the lower surface 12b of the electro-optic crystal substrate 12 may be in the range of 0.03 nm to 0.5 nm.
  • the arithmetic average roughness (Ra) of the lower surface 14b of the low refractive index layer 14 is preferably in the range of 0.5 nm to 500 nm.
  • the formation of the low refractive index layer 14 is not particularly limited, but can be performed by sputtering.
  • the low refractive index layer 14 is formed by sputtering, the roughness of the lower surface 14b of the low refractive index layer 14 naturally becomes larger than the roughness of the lower surface 12b of the electro-optic crystal substrate 12.
  • the low refractive index layer 14 is made of silicon oxide, the tendency becomes more remarkable. Therefore, when the low-refractive index layer 14 is formed by sputtering, the treatment for roughening the lower surface 14b of the low-refractive index layer 14 can be omitted or simplified.
  • the method of forming the low refractive index layer 14 is not limited to sputtering, and may be vapor deposition (physical vapor deposition or chemical vapor deposition), for example. Further, after the formation of the low refractive index layer 14, a treatment for roughening the lower surface 14b of the low refractive index layer 14 (for example, lapping, sandblasting, etching, etc.) may be performed, if necessary.
  • the electro-optic crystal substrate 12 may be an x-cut or y-cut substrate (c-axis is parallel to the substrate) or a z-cut substrate (c-axis is perpendicular to the substrate).
  • the electro-optic crystal substrate 12 may be an offset substrate whose c-axis forms an angle within 10 ° with the horizontal plane of the substrate.
  • the bonding layer 16 is formed on the lower surface 14 b of the low refractive index layer 14.
  • the bonding layer 16 can be formed by sputtering similarly to the low refractive index layer 14.
  • the step of forming the low refractive index layer 14 is not limited to sputtering, and may be vapor deposition (physical vapor deposition or chemical vapor deposition), for example.
  • the lower surface 16b of the bonding layer 16 is smoothed by, for example, polishing. Since the bonding layer 16 is formed on the lower surface 14b of the low refractive index layer 14 having a large roughness, the lower surface 16b of the bonding layer 16 can also have a relatively large roughness. Therefore, the lower surface 16b of the bonding layer 16 may be smoothed, if necessary, before the step of bonding the support substrate 18 described below.
  • the support substrate 18 is prepared, and the support substrate 18 is bonded to the lower surface 16b of the bonding layer 16. Although the bonding of the support substrate 18 is not particularly limited, direct bonding can be performed. Finally, as shown in FIG. 7, the upper surface 12a of the electro-optic crystal substrate 12 is polished to process the electro-optic crystal substrate 12 to a desired thickness.
  • the composite substrate 10 may be further provided with electrodes 32 and 34.
  • These electrodes 32 and 34 are provided on the upper surface 12 a of the electro-optic crystal substrate 12 in order to apply an electric signal to the electro-optic crystal substrate 12.
  • the material forming the electrodes 32 and 34 may be a conductor, and may be a metal such as gold, silver, copper, aluminum or platinum.
  • the electrodes 32, 44 are titanium (Ti), chromium (Cr), nickel (Ni) as a base layer (bottom layer) in contact with the electro-optic crystal substrate 12 in order to prevent peeling and migration of the electrodes 32, 34. , Platinum or the like.
  • the numbers, positions, and shapes of the electrodes 32 and 34 are not particularly limited.
  • the number of electrodes 32 and 34 can be appropriately determined according to the number of electro-optical elements manufactured from the composite substrate 10 and the number of electrodes 32 and 34 required for each electro-optical element. If the electrodes 32 and 34 are provided in advance on the composite substrate 10, a manufacturer of the electro-optical element can easily manufacture the electro-optical element from the composite substrate 10.
  • the optical waveguide region 36 may be provided in the electro-optic crystal substrate 12 by doping impurities.
  • the refractive index can be selectively (that is, locally) increased by doping with a specific impurity such as titanium or zinc, whereby the optical waveguide region 36 can be formed. ..
  • the number, position, and shape of the optical waveguide regions 36 are also not particularly limited.
  • the number of optical waveguide regions 36 can be appropriately determined according to the number of electro-optical elements manufactured from the composite substrate 10 and the number of optical waveguide regions 36 required by each electro-optical element.
  • the manufacturer of the electro-optical element can easily manufacture the electro-optical element from the composite substrate 10.
  • a ridge portion 13 may be formed on the upper surface 12 a of the electro-optic crystal substrate 12.
  • the ridge portion 13 is a protruding portion that extends in an elongated shape along the upper surface 12a.
  • the ridge portion 13 constitutes a ridge type optical waveguide in the electro-optical element in which the composite substrate 10 is manufactured.
  • the width W of the ridge portion 13 is not particularly limited, but may be 1 ⁇ m or more and 10 ⁇ m or less.
  • the height TR of the ridge portion 13 is also not particularly limited, but may be 10% or more and 95% or less of the thickness T12 of the electro-optic crystal substrate 12.
  • the number, position, and shape of the ridge portions 13 are not particularly limited. As an example, when the composite substrate 10 is used for manufacturing a Mach-Zehnder type electro-optical modulator, it is preferable that at least two ridge portions 13 extending in parallel be formed.
  • the composite substrate 10 having the ridge portion 13 may be further provided with a first electrode 42 and a second electrode 44.
  • the first electrode 42 is preferably provided on the one side surface 13 a of the ridge portion 13. .
  • the second electrode 44 is preferably provided on the other side surface 13b of the ridge portion 13 and faces the first electrode 42 with the ridge portion 13 interposed therebetween.
  • the first electrode 42 and the second electrode 44 can apply an electric field parallel to the c-axis to the ridge portion 13 that serves as an optical waveguide in the electro-optical element.
  • the c-axis (c-axis) of the electro-optic crystal substrate 12 may be perpendicular to the electro-optic crystal substrate 12. Even in this case, the ridge portion 13 may be formed on the upper surface 12 a of the electro-optic crystal substrate 12. Further, the first electrode 52 and the second electrode 54 may be provided on the upper surface 12 a of the electro-optic crystal substrate 12. However, it is preferable that the first electrode 52 is provided on the top surface 13c of the ridge portion 13, and the second electrode 54 is within the range of the upper surface 12a of the electro-optic crystal substrate 12 excluding the portion of the ridge portion 13. It should be provided. With such a configuration, the first electrode 52 and the second electrode 54 can apply an electric field parallel to the c-axis to the ridge portion 13 that serves as an optical waveguide in the electro-optical element.
  • the composite substrate 10a of the second embodiment further includes an intermediate layer 20 located between the low refractive index layer 14 and the bonding layer 16, and in this respect, the composite substrate 10 of the first embodiment. Is different from. Then, instead of the interface F2 between the low refractive index layer 14 and the bonding layer 16, an interface F5 between the intermediate layer 20 and the bonding layer 16 is formed between the electro-optic crystal substrate 12 and the low refractive index layer 14. The interface has a higher degree of roughness than the interface F1.
  • the resonance of the electromagnetic wave in the composite substrate 10a can be suppressed by the existence of the interface F5 having a large roughness in the composite substrate 10a.
  • the interface F4 between the low refractive index layer 14 and the intermediate layer 20 is the electro-optical crystal substrate 12 and the low refractive index layer. It may be an interface having a higher degree of roughness than the interface F1 with the interface 14. Due to the presence of a plurality of interfaces having a high degree of roughness, the electromagnetic waves propagating in the composite substrate 10a along the thickness direction may overlap each other in the same phase as in the case where only one interface having a degree of roughness is present. Property is further reduced, and resonance of electromagnetic waves can be further suppressed.
  • the composite substrate 10a of this embodiment can also be manufactured by bonding the electro-optic crystal substrate 12 to the supporting substrate 18.
  • the intermediate layer 20 may be formed in advance on the electro-optic crystal substrate 12 between the low refractive index layer 14 and the bonding layer 16.
  • the interface F5 between the intermediate layer 20 and the bonding layer 16 has a larger degree of roughness than the interface F1 between the electro-optic crystal substrate 12 and the low refractive index layer 14. It can be an interface.
  • the material forming the intermediate layer 20 may be a material that can be used for the low refractive index layer 14 or the bonding layer 16, and It may be a material different from the material actually adopted for the low refractive index layer 14 and the bonding layer 16. However, since the intermediate layer 20 is located between the electro-optic crystal substrate 12 and the interface F4 having a high degree of roughness, the material forming the intermediate layer 20 is a metal so that electromagnetic waves are not shielded by the intermediate layer 20. It is advisable to avoid using such conductors.
  • a composite substrate 10b according to a third embodiment will be described with reference to FIGS.
  • the interface F3 between the bonding layer 16 and the support substrate 18 is larger than the interface F1 between the electro-optic crystal substrate 12 and the low refractive index layer 14.
  • the interface has a high degree of roughness. Even with such a configuration, resonance of electromagnetic waves in the composite substrate 10b can be suppressed by the presence of the interface F3 having a large degree of roughness in the composite substrate 10b.
  • the other interface F2 has a larger surface roughness than the interface F1 between the electro-optic crystal substrate 12 and the low refractive index layer 14. It may be an interface.
  • the composite substrate 10a of this embodiment can also be manufactured by bonding the electro-optic crystal substrate 12 to the support substrate 18.
  • the upper surface 18a of the support substrate 18 is roughened and then the bonding layer 16 'is formed on the upper surface 18a in advance.
  • the interface F3 between the bonding layer 16 and the supporting substrate 18 has a higher surface roughness than the interface F1 between the electro-optic crystal substrate 12 and the low refractive index layer 14. It can be a large interface.
  • the bonding layers 16 and 16 ′ are formed on the electro-optic crystal substrate 12 and the supporting substrate 18, respectively, the substrates 12 and 18 can be easily bonded.
  • the composite substrate 10c of the fourth embodiment further includes an intermediate layer 22 located between the bonding layer 16 and the support substrate 18, and in this respect, the composite substrate 10c differs from the composite substrate 10 of the third embodiment. To do. Further, instead of the interface F3 between the bonding layer 16 and the support substrate 18, an interface F6 between the intermediate layer 20 and the bonding layer 16 is an interface between the electro-optic crystal substrate 12 and the low refractive index layer 14. The interface has a higher surface roughness than F1.
  • the interface F6 having a large degree of roughness in the composite substrate 10c.
  • the other interfaces F2 and F7 are further rougher than the interface F1 between the electro-optic crystal substrate 12 and the low refractive index layer 14.
  • the interface may be large.
  • the composite substrate 10c of this embodiment can also be manufactured by bonding the electro-optic crystal substrate 12 to the support substrate 18.
  • the intermediate layer 22 and the bonding layer 16 ′ may be formed on the support substrate 18 in advance.
  • the interface F6 between the bonding layer 16 and the intermediate layer 22 has a higher surface roughness than the interface F1 between the electro-optic crystal substrate 12 and the low refractive index layer 14. It can be a large interface.
  • the bonding layer 16 and the intermediate layers 20, 22 may be made of a conductor such as metal.
  • a conductor such as metal.
  • electromagnetic waves propagating through the composite substrate 10, 10a-10c are shielded without passing through the conductive layer, so that the electro-optic crystal substrate 12 and the conductive layer are mainly used. Propagate the range between. Therefore, the interface having a large degree of roughness may be located in the range between the electro-optic crystal substrate 12 and the conductive layer, where electromagnetic waves mainly propagate.

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
PCT/JP2018/041548 2018-11-08 2018-11-08 電気光学素子のための複合基板とその製造方法 Ceased WO2020095421A1 (ja)

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PCT/JP2018/041548 WO2020095421A1 (ja) 2018-11-08 2018-11-08 電気光学素子のための複合基板とその製造方法
CN201980061122.2A CN112955811B (zh) 2018-11-08 2019-07-11 电光元件用的复合基板及其制造方法
PCT/JP2019/027570 WO2020095478A1 (ja) 2018-11-08 2019-07-11 電気光学素子のための複合基板とその製造方法
CN202210482598.7A CN114815329B (zh) 2018-11-08 2019-07-11 电光元件用的复合基板及其制造方法
JP2019549494A JP6646187B1 (ja) 2018-11-08 2019-07-11 電気光学素子のための複合基板とその製造方法
EP19881111.9A EP3879336B1 (en) 2018-11-08 2019-07-11 Composite substrate for electro-optical element and production method therefor
JP2020002430A JP7337713B2 (ja) 2018-11-08 2020-01-09 電気光学素子のための複合基板とその製造方法
US17/217,360 US11150497B2 (en) 2018-11-08 2021-03-30 Composite substrate for electro-optic element and method for manufacturing the same
US17/480,870 US12025864B2 (en) 2018-11-08 2021-09-21 Composite substrate for electro-optic element and method for manufacturing the same

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WO2020194763A1 (ja) * 2019-03-28 2020-10-01 日本碍子株式会社 半導体膜
TWI884167B (zh) 2020-05-20 2025-05-21 日商日本碍子股份有限公司 電光元件用複合基板

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EP3879336B1 (en) 2026-04-29
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JP7337713B2 (ja) 2023-09-04
US11150497B2 (en) 2021-10-19

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