WO2019180979A1 - Composite substrate for electro-optical device - Google Patents

Composite substrate for electro-optical device Download PDF

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Publication number
WO2019180979A1
WO2019180979A1 PCT/JP2018/019658 JP2018019658W WO2019180979A1 WO 2019180979 A1 WO2019180979 A1 WO 2019180979A1 JP 2018019658 W JP2018019658 W JP 2018019658W WO 2019180979 A1 WO2019180979 A1 WO 2019180979A1
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WIPO (PCT)
Prior art keywords
electro
substrate
optic crystal
crystal substrate
refractive index
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PCT/JP2018/019658
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French (fr)
Japanese (ja)
Inventor
近藤　順悟
哲也 江尻
山口　省一郎
知義 多井
Original Assignee
日本碍子株式会社
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Application filed by 日本碍子株式会社 filed Critical 日本碍子株式会社
Priority to JP2020507295A priority Critical patent/JP6736795B2/en
Publication of WO2019180979A1 publication Critical patent/WO2019180979A1/en

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    • 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
    • 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
    • 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

Definitions

  • the technology disclosed in this specification relates to a composite substrate for an electro-optical element (for example, an optical modulator) that uses an electro-optical effect.
  • an electro-optical element for example, an optical modulator
  • an electro-optical element such as an optical modulator
  • the electro-optic element can convert an electrical signal into an optical signal by utilizing an electro-optic effect.
  • the electro-optic element is employed in, for example, optical wave fusion communication, and its development is being promoted in order to realize high-speed and large-capacity communication.
  • Japanese Patent Application Laid-Open No. 2010-85789 discloses an optical modulator.
  • This optical modulator includes an electro-optic crystal substrate having an electro-optic effect, and an optical waveguide is formed therein.
  • a reinforcing substrate having a dielectric constant lower than that of the electro-optic crystal substrate is bonded to the electro-optic crystal substrate.
  • This reinforcing substrate not only mechanically reinforces the electro-optic crystal substrate, but also reduces the dielectric loss, thereby facilitating high-speed operation of the optical modulator and driving at a low voltage.
  • a composite substrate in which such an electro-optic crystal substrate and a low dielectric constant substrate are combined can be suitably used not only for an optical modulator but also for various electro-optic elements.
  • the electro-optic crystal substrate and the low dielectric constant substrate are bonded by an adhesive.
  • the adhesive deteriorates with time, so that the composite substrate may be peeled off, and further, the peeling may cause damage such as cracks.
  • an amorphous material composed of the elements of the electro-optic crystal substrate and the elements of the low dielectric constant substrate is interposed between the electro-optic crystal substrate and the low dielectric substrate. A layer is formed.
  • This amorphous layer has no crystallinity, optical properties are different from those of both substrates, and the interface between the electro-optic crystal substrate and the amorphous layer is not flat.
  • Such a non-flat interface may scatter (for example, irregular reflection or leakage) and absorb light transmitted through the electro-optic crystal substrate.
  • the present specification provides a composite substrate that can avoid or reduce the above-described problems and a method for manufacturing the same.
  • the composite substrate includes an electro-optic crystal substrate having an electro-optic effect, a low-dielectric substrate having a dielectric constant lower than that of the electro-optic crystal substrate, a low dielectric constant substrate, and an electro-optic substrate.
  • a low refractive index layer having a lower refractive index than that of the electro-optic crystal substrate, and a low dielectric constant substrate and the low refractive index layer. It comprises an amorphous layer composed of the constituent elements and the elements constituting the low refractive index layer.
  • the above-described composite substrate can be manufactured by the following manufacturing method.
  • a step of forming a low refractive index layer having a refractive index lower than that of the electro-optical crystal substrate and a low refractive index layer are formed on the main surface of the electro-optical crystal substrate having an electro-optical effect.
  • the direct bonding here means a bonding in which atoms diffuse between two members to be bonded and a covalent bond is formed between the atoms.
  • a composite substrate in which an electro-optic crystal substrate and a low dielectric constant substrate are laminated can be manufactured without requiring an adhesive.
  • an amorphous layer resulting from direct bonding is formed between the low dielectric constant substrate and the low refractive index layer. That is, a low refractive index layer is interposed between the amorphous layer and the electro-optic crystal substrate, and the amorphous layer does not contact the electro-optic crystal substrate. Therefore, light traveling through the electro-optic crystal substrate is not scattered or absorbed by the amorphous layer or the non-flat interface between the amorphous layer and the electro-optic crystal substrate.
  • the low refractive index layer in contact with the electro-optic crystal substrate has a lower refractive index than the electro-optic crystal substrate, it can suppress leakage of light transmitted through the electro-optic crystal substrate, such as a clad in an optical fiber. it can.
  • an electro-optical element that can be driven at high speed and driven at a low voltage can be manufactured.
  • a modification of the composite substrate 10 is shown, and electrodes 32 and 34 for forming an electric field on the electro-optic crystal substrate 12 and an optical waveguide region 36 provided in the electro-optic crystal substrate 12 are added.
  • a modification of the composite substrate 10 is shown, and a second low refractive index layer 20 is added between the low dielectric constant substrate 14 and the amorphous layer 18.
  • a modification of the composite substrate 10 is shown, and a ridge portion 13 is formed on the upper surface 12 a of the electro-optic crystal substrate 12.
  • a modification of the composite substrate 10 is shown, and a first electrode 42 and a second electrode 44 are added as compared with the modification shown in FIG.
  • the c-axis (c-axis) of the electro-optic crystal substrate 12 is parallel to the electro-optic crystal substrate 12.
  • a modification of the composite substrate 10 is shown, and a conductive layer 22 is added along the lower surface 14b of the low dielectric constant substrate 14 as compared with the modification shown in FIG.
  • a modification of the composite substrate 10 is shown, and a support substrate 24 bonded to the conductive layer 22 is added as compared with the modification shown in FIG.
  • a modification of the composite substrate 10 is shown, and a first electrode 52 and a second electrode 54 are added as compared with the modification shown in FIG.
  • the c-axis of the electro-optic crystal substrate 12 is perpendicular to the electro-optic crystal substrate 12.
  • a modification of the composite substrate 10 is shown, and a conductive layer 22 is added along the lower surface 14b of the low dielectric constant substrate 14 as compared with the modification shown in FIG.
  • a modification of the composite substrate 10 is shown, and a support substrate 24 bonded to the conductive layer 22 is added as compared with the modification shown in FIG.
  • a modification of the composite substrate 10 is shown, and an optical waveguide region 56 is added in the ridge portion 13 as compared with the modification shown in FIG.
  • a modification of the composite substrate 10 is shown, and an optical waveguide region 56 is added in the ridge portion 13 as compared with the modification shown in FIG.
  • a modification of the composite substrate 10 is shown, and an optical waveguide region 56 is added in the ridge portion 13 as compared with the modification shown in FIG.
  • a modification of the composite substrate 10 is shown, and an optical waveguide region 56 is added in the ridge portion 13 as compared with the modification shown in FIG.
  • the low refractive index layer 16 has a multilayer structure including a main layer 16a and a surface layer 16b.
  • the second low refractive index layer 20 has a multilayer structure including a main layer 20a and a surface layer 20b.
  • the low refractive index layer may have a dielectric constant lower than that of the electro-optic crystal substrate. According to such a configuration, dielectric loss in the low refractive index layer can be reduced, and high-speed operation of the electro-optical element and driving at a low voltage can be further facilitated.
  • the low refractive index layer can be composed of at least one of silicon oxide, tantalum oxide, aluminum oxide, glass, magnesium fluoride, and calcium fluoride.
  • the composite substrate may further include a second low refractive index layer that is located between the low dielectric constant substrate and the amorphous layer and has a refractive index lower than that of the electro-optic crystal substrate.
  • the amorphous layer may be composed of an element constituting the low refractive index layer and an element constituting the second low refractive index layer instead of the element constituting the low dielectric constant substrate.
  • Such a composite substrate can be manufactured by directly bonding a low dielectric constant substrate on which a second low refractive index layer is formed to an electro-optic crystal substrate on which a low refractive index layer is formed. At this time, if the materials of the low refractive index layer and the second low refractive index layer are the same or have similar structures, high-quality direct bonding can be performed relatively easily.
  • a ridge portion may be formed on the surface of the electro-optic crystal substrate.
  • an electro-optic element that requires a ridge-type optical waveguide can be easily manufactured.
  • an optical waveguide region doped with impurities for example, titanium or zinc
  • the optical waveguide region doped with impurities has a small refractive index step due to impurity doping and a small light confinement effect, the near-field image (near field diameter) of light becomes relatively large.
  • the electro-optic element manufactured from the composite substrate As a result, in the electro-optic element manufactured from the composite substrate, the electric field efficiency is lowered, so that the required driving voltage is increased. This increases the element size.
  • the ridge type optical waveguide is preferable from the viewpoint of reducing the driving voltage and size of the electro-optic element.
  • the c-axis (that is, the crystal main axis) of the electro-optic crystal substrate may be parallel to the electro-optic crystal substrate. That is, the electro-optic crystal substrate may be an x-cut substrate.
  • the composite substrate includes a first electrode provided on one side surface of the ridge portion, and a second electrode provided on the other side surface of the ridge portion and facing the first electrode across the ridge portion. May be further provided. These first and second electrodes can be used as electrodes for applying an electric signal (that is, an electric field) to the ridge-type optical waveguide when an electro-optical element is manufactured from the composite substrate.
  • the c-axis (that is, the crystal main axis) of the electro-optic crystal substrate may be perpendicular to the electro-optic crystal substrate. That is, the electro-optic crystal substrate may be a z-cut substrate.
  • the composite substrate further includes a first electrode provided on the top surface of the ridge portion and a second electrode provided in a range excluding the ridge portion of the surface of the electro-optic crystal substrate. You may prepare. These first and second electrodes can be used as electrodes for applying an electric signal (that is, an electric field) to the ridge-type optical waveguide when an electro-optical element is manufactured from the composite substrate.
  • the composite substrate has a first electrode and a second electrode
  • a low refractive index film having a refractive index lower than that of the electro-optic crystal substrate may be formed. According to such a configuration, at the interface between the electro-optic crystal substrate and the first electrode (or second electrode), the light transmitted through the electro-optic crystal substrate is suppressed from being absorbed or scattered by the electrode. Can do.
  • an optical waveguide region containing impurities may be formed along the longitudinal direction of the ridge portion. According to such a configuration, a desired optical waveguide can be easily formed by changing the impurity doping region without changing the ridge portion.
  • the composite substrate may further include a conductive layer positioned on the opposite side of the electro-optic crystal substrate with respect to the low dielectric constant substrate.
  • a conductive layer can suppress leakage of an electric field from the low dielectric constant substrate in an electro-optic element manufactured from the composite substrate.
  • the composite substrate may further include a support substrate bonded to the conductive layer.
  • the thickness of the electro-optic crystal substrate and the low dielectric constant substrate can be reduced while maintaining the mechanical strength of the composite substrate by the support substrate.
  • the frequency at which an electric signal resonates in the composite substrate (resonance frequency) can be shifted to the high frequency side as the thickness of the electro-optic crystal substrate and the low dielectric constant substrate decreases.
  • the resonance frequency is 300 gigahertz or more.
  • the electro-optic element can avoid the problem that an electric signal of a high frequency (so-called millimeter wave band) such as 100 GHz is attenuated by substrate resonance.
  • the composite substrate 10 of the present embodiment can be employed in various electro-optic 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 electro-optic element manufacturer.
  • the diameter of the composite substrate 10 is approximately 10 cm (4 inches).
  • a plurality of electro-optic elements are manufactured from one composite substrate 10.
  • the composite substrate 10 is not limited to the form of a wafer, and may be manufactured and provided in various forms.
  • the composite substrate 10 includes an electro-optic crystal substrate 12.
  • the electro-optic crystal substrate 12 has an upper surface 12 a exposed to the outside and a lower surface 12 b located in the composite substrate 10. Part or all of the electro-optic crystal substrate 12 is 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. Specifically, 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 greatly.
  • the c-axis of the electro-optic crystal substrate 12 may be parallel to the electro-optic crystal substrate 12. That is, the electro-optic crystal substrate 12 may be an x-cut or y-cut substrate, for example. 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 a z-cut substrate, for example.
  • the thickness T2 of the electro-optic crystal substrate 12 is not particularly limited, but may be, for example, 1 micrometer or more and 50 micrometers or less.
  • the material composing the electro-optic crystal substrate 12 is not particularly limited, but lithium niobate (LiNbO 3 : LN), lithium tantalate (LiTaO 3 : LT), potassium titanate phosphate (KTiOPO 4 : KTP), niobic acid Potassium / lithium (K x Li (1-x) NbO 2 : KLN), potassium niobate (KNbO 3 : KN), tantalate / potassium niobate (KNb x Ta (1-x) O 3 : KTN), niobium It may be either a solid solution of lithium acid lithium and lithium tantalate.
  • the electro-optic crystal substrate 12 may have an electro-optic effect that changes other optical constants in addition to or instead of the refractive index.
  • the composite substrate 10 further includes a low dielectric constant substrate 14.
  • the low dielectric constant substrate 14 has an upper surface 14a located in the composite substrate 10 and a lower surface 14b exposed to the outside.
  • the electro-optic crystal substrate 12 described above is laminated on the upper surface 14 a side.
  • the low dielectric constant substrate 14 is made of a material having a dielectric constant lower than that of the electro-optic crystal substrate 12.
  • the dielectric constant (relative dielectric constant) of the low dielectric constant substrate 14 is not particularly limited, but is preferably 5 or less.
  • examples of the material constituting the low dielectric constant substrate 14 include quartz and glass.
  • the thickness T4 of the low dielectric constant substrate 14 is not particularly limited, but may be larger than the thickness T2 of the electro-optic crystal substrate 12.
  • the low dielectric constant substrate 14 adjacent to the electro-optic crystal substrate 12 can reduce dielectric loss when an electric field is applied to the electro-optic crystal substrate 12. Therefore, by using the composite substrate 10, an electro-optic element that can be driven at high speed and driven at a low voltage can be manufactured.
  • the composite substrate 10 further includes a low refractive index layer 16.
  • the low refractive index layer 16 is provided along the lower surface 12 b of the electro-optic crystal substrate 12 and is located between the low dielectric constant substrate 14 and the electro-optic crystal substrate 12.
  • the low refractive index layer 16 has a lower refractive index than the electro-optic crystal substrate 12.
  • the material which comprises the low-refractive-index layer 16 is not specifically limited, For example, it may be one or more of silicon oxide, tantalum oxide, aluminum oxide, glass, magnesium fluoride, and calcium fluoride.
  • the thickness T6 of the low refractive index layer 16 is not particularly limited, but may be, for example, 0.3 micrometers or more and 1 micrometers or less.
  • the low refractive index layer 16 in this embodiment has a dielectric loss (less than that of the electro-optic crystal substrate 12) so that the dielectric loss can be suppressed and the effective dielectric constant of the electric signal can be reduced and light can be efficiently modulated.
  • tan ⁇ or a material having a low dielectric constant.
  • the composite substrate 10 further includes an amorphous layer 18.
  • the amorphous layer 18 is located between the low dielectric constant substrate 14 and the low refractive index layer 16.
  • the amorphous layer 18 has an amorphous structure, and is composed of an element constituting the low dielectric constant substrate 14 and an element constituting the low refractive index layer 16.
  • the thickness T8 of the amorphous layer 18 is not particularly limited, but may be 0.5 nanometers or more and 100 nanometers or less.
  • the composite substrate 10 can be manufactured by directly bonding the low dielectric constant substrate 14 to the electro-optic crystal substrate 12 on which the low refractive index layer 16 is formed.
  • the amorphous layer 18 is a layer generated in this direct bonding, and is formed by diffusing atoms of the low refractive index layer 16 and the low dielectric constant substrate 14 respectively. Therefore, the upper surface 18a of the amorphous layer 18 (that is, the interface in contact with the low refractive index layer 16) and the lower surface 18b of the amorphous layer 18 (that is, the interface in contact with the low dielectric constant substrate 14) are not necessarily flat.
  • an amorphous layer resulting from direct bonding is composed of elements constituting the material located above and below it, has no crystallinity, and may incorporate different elements from the outside. Different. Further, the interface of the amorphous layer is not flat, and optical absorption and scattering may occur. For this reason, if the amorphous layer 18 is in direct contact with the electro-optic crystal substrate 12, light transmitted through the electro-optic crystal substrate 12 is attenuated by the amorphous layer 18. On the other hand, in the composite substrate 10 of the present embodiment, the low refractive index layer 16 having a thickness that is not affected is interposed between the amorphous layer 18 and the electro-optic crystal substrate 12, and the amorphous layer 18 is formed by the electro-optic crystal substrate.
  • the electro-optic crystal substrate 12 is not touching. Therefore, light transmitted through the electro-optic crystal substrate 12 is not scattered by the amorphous layer 18 or the upper surface 18a.
  • the low refractive index layer 16 in contact with the electro-optic crystal substrate 12 has a lower refractive index than the electro-optic crystal substrate 12, leakage of light transmitted through the electro-optic crystal substrate 12 is prevented like a clad in an optical fiber. It can be suppressed and propagated in the optical waveguide.
  • the low dielectric constant substrate 14 is provided adjacent to the electro-optic crystal substrate 12, so that when the electric field is applied to the electro-optic crystal substrate 12, the dielectric Loss can be reduced. Further, since the electro-optic crystal substrate 12 and the low dielectric constant substrate 14 are directly bonded without using an adhesive, there is no dielectric loss due to the adhesive, and there is no alteration or deformation, so that reliability can be ensured. . Since the amorphous layer 18 resulting from the direct bonding is separated from the electro-optic crystal substrate 12 by the low refractive index layer 16, the light transmitted through the electro-optic crystal substrate 12 can be propagated to the output side without loss. it can.
  • an electro-optic crystal substrate 12 is prepared.
  • the electro-optic crystal substrate 12 may be an x-cut or y-cut substrate (c-axis is parallel to the substrate), and when a polarization inversion portion is formed, the c-axis is an angle within 10 ° with the horizontal plane of the substrate. May be an offset substrate. Alternatively, it may be a z-cut substrate (c-axis is perpendicular to the substrate).
  • a low refractive index layer 16 is formed on the lower surface 12 b of the electro-optic crystal substrate 12.
  • the film formation of the low refractive index layer 16 is not particularly limited, but can be performed by vapor deposition (physical vapor deposition or chemical vapor deposition).
  • the lower surface 12 b of the electro-optic crystal substrate 12 is one main surface of the electro-optic crystal substrate 12.
  • a low dielectric constant substrate 14 is prepared, and the low dielectric constant substrate 14 is directly bonded to the lower surface 12b of the electro-optic crystal substrate 12 on which the low refractive index layer 16 is formed.
  • the above-described amorphous layer 18 is formed between the low dielectric constant substrate 14 and the low refractive index layer 16.
  • the composite substrate 10 shown in FIGS. 1 and 2 is manufactured.
  • Specific procedures and processing conditions for the direct bonding described above are not particularly limited. It can be determined as appropriate according to the materials of the layers or substrates to be bonded to each other.
  • a neutralized beam is irradiated to each bonding surface in a high vacuum chamber (for example, about 1 ⁇ 10 ⁇ 6 Pascal). Thereby, each joint surface is activated.
  • the activated bonding surfaces are brought into contact with each other in a vacuum atmosphere and bonded at room temperature.
  • the load at the time of joining can be, for example, 100 to 20000 Newton.
  • an inert gas is introduced into the chamber, and a high voltage is applied from a DC power source to the electrode disposed in the chamber.
  • a high voltage is applied from a DC power source to the electrode disposed in the chamber.
  • an electron moves by the electric field produced between an electrode (positive electrode) and a chamber (negative electrode), and the beam of atoms and ions by an inert gas is generated.
  • the ion beam is neutralized by the grid, so that a beam of neutral atoms is emitted from the fast atom beam source.
  • the atomic species constituting the beam is preferably an inert gas element (for example, argon (Ar), nitrogen (N), etc.).
  • the voltage upon activation by beam irradiation can be 0.5 to 2.0 kilovolts, and the current can be 50 to 200 milliamps.
  • the composite substrate 10 may be provided with electrodes 32 and 34 for forming an electric field on the electro-optic crystal substrate 12 on the upper surface 12 a of the electro-optic crystal substrate 12.
  • the material which comprises the electrodes 32 and 34 should just be a conductor, for example, may be metals, such as gold
  • the number, position, and shape 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-optic elements manufactured from the composite substrate 10 and the number of electrodes 32 and 34 required for each electro-optic element.
  • the 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 increased (that is, locally) by doping 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 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. If the optical waveguide region 36 is provided in advance on the composite substrate 10, the manufacturer of the electro-optical element can easily manufacture the electro-optical element from the composite substrate 10.
  • the composite substrate 10 may further include a second low refractive index layer 20.
  • the second low refractive index layer 20 is located between the low dielectric constant substrate 14 and the amorphous layer 18 and is made of a material having a refractive index lower than that of the electro-optic crystal substrate 12.
  • the second low refractive index layer 20 may be made of a material having a dielectric constant lower than that of the electro-optic crystal substrate 12 in order to suppress dielectric loss.
  • the second low refractive index layer 20 can be composed of, for example, at least one of silicon oxide, tantalum oxide, aluminum oxide, glass, magnesium fluoride, and calcium fluoride.
  • the second low refractive index layer 20 may be made of the same material as the low refractive index layer 16 or may be formed of a different material.
  • FIG. 8 shows a method for manufacturing the composite substrate 10 shown in FIG.
  • the second low refractive index layer 20 is formed on the lower surface 12b of the electro-optic crystal substrate 12 on which the low refractive index layer 16 is formed. It can be manufactured by directly bonding the filmed low dielectric constant substrate 14. According to this manufacturing method, the amorphous layer 18 shown in FIG. 7 is formed between the low refractive index layer 16 and the second low refractive index layer 20.
  • the materials of the low refractive index layer 16 and the second low refractive index layer 20 are the same or have similar structures, high-quality direct bonding can be performed relatively easily.
  • 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 along the upper surface 12a.
  • the ridge portion 13 constitutes a ridge type optical waveguide in the electro-optic 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 micrometer or more and 10 micrometers or less.
  • the height T1 of the ridge portion 13 is not particularly limited, but may be 10% or more and 95% or less of the thickness T2 of the electro-optic crystal substrate 12.
  • the number, position, and shape of the ridge portions 13 are not particularly limited.
  • the composite substrate 10 is used for manufacturing a Mach-Zehnder type electro-optic modulator, it is preferable to form two ridge portions 13 at least partially extending in parallel.
  • 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 may be provided on one side surface 13 a of the ridge portion 13.
  • the second electrode 44 is preferably provided on the other side surface 13 b of the ridge portion 13 and is opposed to the first electrode 42 with the ridge portion 13 interposed therebetween. According to such a configuration, the first electrode 42 and the second electrode 44 can apply an electric field in parallel to the c-axis to the ridge portion 13 serving as an optical waveguide in the electro-optic element.
  • the material which comprises the 1st electrode 42 and the 2nd electrode 44 should just be a conductor, for example, may be metal materials, such as gold
  • a low refractive index film having a refractive index lower than that of the electro-optic crystal substrate 12 is provided between the first electrode 42 and the electro-optic crystal substrate 12 and between the second electrode 44 and the electro-optic crystal substrate 12. May be. Such a low refractive index film functions as a cladding layer and can suppress loss of light transmitted through the ridge portion 13.
  • a conductive layer 22 may be provided on the composite substrate 10 along the lower surface 14 b of the low dielectric constant substrate 14.
  • a conductive layer 22 can be used as a ground electrode in the electro-optic element manufactured from the composite substrate 10.
  • the conductive layer 22 can suppress the leakage of the electric field applied by the first electrode 42 and the second electrode 44 from the lower surface 14 b of the low dielectric constant substrate 14.
  • the material constituting the conductive layer 22 may be a conductor, such as gold (Au), silver (Ag), copper (Cu), aluminum (Al), platinum (Pt), or at least two of them. You may have a layer of an alloy containing two.
  • the conductive layer 22 may have a single layer structure or a multilayer structure.
  • the conductive layer 22 is a base layer in contact with the low dielectric constant substrate 14, and in order to prevent peeling or migration of the conductive layer 22, titanium (Ti), chromium (Cr), nickel (Ni), platinum (Pt), etc. You may have a layer of. Note that the conductive layer 22 shown in FIG. 11 can be similarly provided on the other composite substrate 10 described above.
  • the composite substrate 10 may further include a support substrate 24 bonded to the conductive layer 22.
  • the thickness of the electro-optic crystal substrate 12 and the low dielectric constant substrate 14 can be reduced while maintaining the mechanical strength of the composite substrate 10 by the support substrate 24.
  • the resonance frequency for the electrical signal increases as the thickness of the electro-optic crystal substrate 12 and the low dielectric constant substrate 14 decreases.
  • the resonance frequency is 300 gigahertz or more.
  • the electro-optical element can process a high-frequency (so-called millimeter wave band) electric signal such as 100 GHz without any problem.
  • the material constituting the support substrate 24 is not particularly limited.
  • the support substrate 24 is made of 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 (GaN), silicon carbide (SiC), gallium oxide (Ga 2 O 3 ) It may be.
  • the linear expansion coefficient of the material forming the support substrate 24 is preferably as close as possible to the linear expansion coefficient of the material forming the electro-optic crystal substrate 12.
  • the linear expansion coefficient of the material constituting the support substrate 24 may be within ⁇ 50 percent of the linear expansion coefficient of the material constituting the electro-optic crystal substrate 12.
  • the material constituting the support substrate 24 may be the same as the material constituting the electro-optic crystal substrate 12.
  • the support substrate 24 shown in FIG. 12 can be similarly provided on the above-described other composite substrate 10 together with the conductive layer 22.
  • the conductive layer 22 and the support substrate 24 may be joined by direct joining.
  • the surface layer of the conductive layer 22 may be made of platinum. Platinum is a material suitable for direct bonding. Therefore, when the surface layer of the conductive layer 22 is made of platinum, the electro-optic crystal substrate 12 on which the conductive layer 22 is formed can be directly and well bonded to the support substrate 24.
  • an amorphous layer resulting from direct bonding is formed between the conductive layer 22 and the support substrate 24. This amorphous layer is composed of an element (mainly platinum) constituting the conductive layer 22 and an element constituting the support substrate 24.
  • the 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.
  • a first electrode 52 and a second electrode 54 may be provided on the upper surface 12 a of the electro-optic crystal substrate 12.
  • the first electrode 52 is preferably provided on the top surface 13 c of the ridge portion 13
  • the second electrode 54 is in a range excluding the portion of the ridge portion 13 of the upper surface 12 a of the electro-optic crystal substrate 12. It is good to be provided. According to such a configuration, the first electrode 52 and the second electrode 54 can apply an electric field in parallel to the c-axis to the ridge portion 13 serving as an optical waveguide in the electro-optic element.
  • the composite substrate 10 shown in FIG. 13 may also be provided with a conductive layer 22 along the lower surface 14b of the low dielectric constant substrate.
  • the conductive layer 22 can be used as a ground electrode in the electro-optic element manufactured from the composite substrate 10.
  • a support substrate 24 may be bonded to the conductive layer 22 in the same manner as the composite substrate 10 shown in FIG. 12. Thereby, the thickness of the electro-optic crystal substrate 12 and the low dielectric constant substrate 14 can be reduced while maintaining the mechanical strength of the composite substrate 10.
  • the resonance frequency for the electric signal can be made sufficiently higher than a high frequency band such as a millimeter wave band.
  • the conductive layer 22 and the support substrate 24 can be bonded by direct bonding. In this case, as described above, when the surface layer of the conductive layer 22 is made of platinum, the direct bonding between the conductive layer 22 and the support substrate 24 can be favorably performed.
  • the optical waveguide region 56 containing impurities extends along the longitudinal direction of the ridge portion 13 inside the ridge portion 13. It may be formed.
  • the composite substrate 10 shown in FIG. 16 is obtained by adding an optical waveguide region 56 in the ridge portion 13 to the composite substrate 10 shown in FIG.
  • the composite substrate 10 shown in FIG. 17 is obtained by adding an optical waveguide region 56 in the ridge portion 13 to the composite substrate 10 shown in FIG.
  • the composite substrate 10 shown in FIG. 18 is obtained by adding an optical waveguide region 56 in the ridge portion 13 to the composite substrate 10 shown in FIG.
  • a composite substrate 10 shown in FIG. 19 is obtained by adding an optical waveguide region 56 in the ridge portion 13 to the composite substrate 10 shown in FIG.
  • an optical waveguide region containing impurities is formed in the ridge portion 13 along the longitudinal direction of the ridge portion 13. May be.
  • the low refractive index layer 16 of the composite substrate 10 may have a multilayer structure including a main layer 16a and a bonding layer 16b.
  • the bonding layer 16 b is a layer located between the main layer 16 a and the amorphous layer 18 and in contact with the amorphous layer 18.
  • the material constituting the main layer 16a may be one or more of silicon oxide, tantalum oxide, aluminum oxide, glass, magnesium fluoride, and calcium fluoride.
  • the material constituting the bonding layer 16b is a direct bonding such as tantalum oxide (Ta 2 O 5 ), niobium oxide (Nb 2 O 5 ), aluminum oxide (Al 2 O 3 ), titanium oxide (TiO 2 ).
  • the low refractive index layer 16 having the bonding layer 16 b can be bonded directly and favorably to the low dielectric constant substrate 14. Note that the low refractive index layer 16 having a multilayer structure can be employed in all the embodiments disclosed in this specification.
  • the second low refractive index layer 20 when the composite substrate 10 further includes the second low refractive index layer 20, the second low refractive index layer 20 also has a multilayer structure including the main layer 20a and the bonding layer 20b. Also good.
  • the bonding layer 20 b is located between the main layer 20 a and the amorphous layer 18 and is in contact with the amorphous layer 18.
  • the material constituting the bonding layer 20b is preferably a material suitable for direct bonding, such as tantalum oxide, niobium oxide, aluminum oxide, and titanium oxide. According to such a configuration, as shown in FIG.
  • the low-refractive index layer 16 on the electro-optic crystal substrate 12 side can be favorably directly bonded to the second low-refractive index layer 16 having the bonding layer 20b. it can.
  • the low refractive index layer 16 on the electro-optic crystal substrate 12 side may have a single-layer structure or may not have the bonding layer 16b.
  • the low refractive index layer 20 having a multilayer structure can be employed in all embodiments disclosed in this specification.

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Abstract

Disclosed is a composite substrate for an electro-optical device. This composite substrate is equipped with: an electro-optical crystal substrate having an electro-optical effect; a low-dielectric-constant substrate which has a lower dielectric constant than does the electro-optical crystal substrate and on which the electro-optical crystal substrate is layered; a low-refractive-index layer which has a lower refractive index than does the electro-optical crystal substrate, and is positioned between the low-dielectric-constant substrate and the electro-optical crystal substrate; and an amorphous layer which is positioned between the low-dielectric-constant substrate and the low-refractive-index layer, and is configured from the elements constituting the low-dielectric-constant substrate and the elements constituting the low-refractive-index layer. It is possible to produce this composite substrate by directly joining an electro-optical crystal substrate, on which a low-refractive-index layer is formed as a film, to a low-dielectric-constant substrate.

Description

電気光学素子のための複合基板Composite substrate for electro-optic elements
　本明細書で開示する技術は、電気光学効果を利用する電気光学素子（例えば、光変調器）のための複合基板に関する。 The technology disclosed in this specification relates to a composite substrate for an electro-optical element (for example, an optical modulator) that uses an electro-optical effect.
　例えば光変調器といった電気光学素子が知られている。電気光学素子は、電気光学効果を利用して、電気信号を光信号に変換することができる。電気光学素子は、例えば光電波融合通信に採用されており、高速かつ大容量な通信を実現するために、その開発が進められている。 For example, an electro-optical element such as an optical modulator is known. The electro-optic element can convert an electrical signal into an optical signal by utilizing an electro-optic effect. The electro-optic element is employed in, for example, optical wave fusion communication, and its development is being promoted in order to realize high-speed and large-capacity communication.
　例えば、特開２０１０－８５７８９号公報に、光変調器が開示されている。この光変調器は、電気光学効果を有する電気光学結晶基板を備えており、その内部に光導波路が形成されている。電気光学結晶基板には、電気光学結晶基板よりも誘電率の低い補強基板が接合されている。この補強基板は、電気光学結晶基板を機械的に補強するだけでなく、誘電損失を低減することによって、光変調器の高速動作や低電圧での駆動を容易とする。このような電気光学結晶基板と低誘電率基板とを組み合わせた複合基板は、光変調器だけでなく、様々な電気光学素子にも好適に採用することができる。 For example, Japanese Patent Application Laid-Open No. 2010-85789 discloses an optical modulator. This optical modulator includes an electro-optic crystal substrate having an electro-optic effect, and an optical waveguide is formed therein. A reinforcing substrate having a dielectric constant lower than that of the electro-optic crystal substrate is bonded to the electro-optic crystal substrate. This reinforcing substrate not only mechanically reinforces the electro-optic crystal substrate, but also reduces the dielectric loss, thereby facilitating high-speed operation of the optical modulator and driving at a low voltage. A composite substrate in which such an electro-optic crystal substrate and a low dielectric constant substrate are combined can be suitably used not only for an optical modulator but also for various electro-optic elements.
　従来の複合基板では、電気光学結晶基板と低誘電率基板との間が、接着剤によって接合されている。このような構成であると、接着剤が経時的に劣化することによって、複合基板に剥離が生じることや、さらにこの剥離が原因でクラックといった損傷が生じることがある。このような問題を避けるために、接着剤を用いることなく、電気光学結晶基板と低誘電率基板とを直接接合することが考えられる。しかしながら、電気光学結晶基板と低誘電率基板とを直接接合すると、電気光学結晶基板と低誘電率基板との間には、電気光学結晶基板の元素と低誘電率基板の元素から構成されるアモルファス層が形成される。このアモルファス層は結晶性がなく、光学物性も双方の基板とは異なり、電気光学結晶基板とアモルファス層との間の界面も平坦ではない。このような平坦でない界面は、電気光学結晶基板を伝わる光を、散乱（例えば、乱反射や漏出）、吸収させるおそれがある。 In the conventional composite substrate, the electro-optic crystal substrate and the low dielectric constant substrate are bonded by an adhesive. With such a configuration, the adhesive deteriorates with time, so that the composite substrate may be peeled off, and further, the peeling may cause damage such as cracks. In order to avoid such a problem, it is conceivable to directly bond the electro-optic crystal substrate and the low dielectric constant substrate without using an adhesive. However, when the electro-optic crystal substrate and the low dielectric constant substrate are directly joined, an amorphous material composed of the elements of the electro-optic crystal substrate and the elements of the low dielectric constant substrate is interposed between the electro-optic crystal substrate and the low dielectric substrate. A layer is formed. This amorphous layer has no crystallinity, optical properties are different from those of both substrates, and the interface between the electro-optic crystal substrate and the amorphous layer is not flat. Such a non-flat interface may scatter (for example, irregular reflection or leakage) and absorb light transmitted through the electro-optic crystal substrate.
　従って、本明細書は、上述した問題を回避又は低減し得る複合基板及びその製造方法を提供する。 Therefore, the present specification provides a composite substrate that can avoid or reduce the above-described problems and a method for manufacturing the same.
　本明細書は、電気光学素子のための複合基板を開示する。この複合基板は、電気光学効果を有する電気光学結晶基板と、電気光学結晶基板が積層されているとともに、電気光学結晶基板よりも誘電率の低い低誘電率基板と、低誘電率基板と電気光学結晶基板との間に位置しており、電気光学結晶基板よりも屈折率の低い低屈折率層と、低誘電率基板と低屈折率層との間に位置しており、低誘電率基板を構成する元素と低屈折率層を構成する元素とで構成されたアモルファス層とを備える。 This specification discloses a composite substrate for an electro-optic element. The composite substrate includes an electro-optic crystal substrate having an electro-optic effect, a low-dielectric substrate having a dielectric constant lower than that of the electro-optic crystal substrate, a low dielectric constant substrate, and an electro-optic substrate. A low refractive index layer having a lower refractive index than that of the electro-optic crystal substrate, and a low dielectric constant substrate and the low refractive index layer. It comprises an amorphous layer composed of the constituent elements and the elements constituting the low refractive index layer.
　上記した複合基板は、次の製造方法によって製造することができる。この製造方法は、電気光学効果を有する電気光学結晶基板の主表面上に、電気光学結晶基板よりも屈折率の低い低屈折率層を成膜する工程と、低屈折率層が成膜された電気光学結晶基板の主表面に、電気光学結晶基板よりも誘電率の低い低誘電率基板を直接接合する工程とを備える。ここでいう直接接合とは、接合される二つの部材の間で原子が拡散し合い、それらの原子間で共有結合が形成される接合を意味する。 The above-described composite substrate can be manufactured by the following manufacturing method. In this manufacturing method, a step of forming a low refractive index layer having a refractive index lower than that of the electro-optical crystal substrate and a low refractive index layer are formed on the main surface of the electro-optical crystal substrate having an electro-optical effect. Directly bonding a low dielectric constant substrate having a dielectric constant lower than that of the electro-optic crystal substrate to the main surface of the electro-optic crystal substrate. The direct bonding here means a bonding in which atoms diffuse between two members to be bonded and a covalent bond is formed between the atoms.
　上記した製造方法によると、接着剤を必要とすることなく、電気光学結晶基板と低誘電率基板とが積層された複合基板を製造することができる。製造された複合基板では、直接接合に起因するアモルファス層が、低誘電率基板と低屈折率層との間に形成される。即ち、アモルファス層と電気光学結晶基板との間には低屈折率層が介在し、アモルファス層が電気光学結晶基板に接しない。従って、電気光学結晶基板を伝わる光が、アモルファス層やこのアアモルファス層と電気光学結晶基板との間の平坦でない界面で、散乱又は吸収されることがない。加えて、電気光学結晶基板に接する低屈折率層は、電気光学結晶基板よりも屈折率が低いことから、光ファイバにおけるクラッドのように、電気光学結晶基板を伝わる光の漏出を抑制することができる。この複合基板を用いることで、高速動作や低電圧での駆動を可能とする電気光学素子を製造することができる。 According to the manufacturing method described above, a composite substrate in which an electro-optic crystal substrate and a low dielectric constant substrate are laminated can be manufactured without requiring an adhesive. In the manufactured composite substrate, an amorphous layer resulting from direct bonding is formed between the low dielectric constant substrate and the low refractive index layer. That is, a low refractive index layer is interposed between the amorphous layer and the electro-optic crystal substrate, and the amorphous layer does not contact the electro-optic crystal substrate. Therefore, light traveling through the electro-optic crystal substrate is not scattered or absorbed by the amorphous layer or the non-flat interface between the amorphous layer and the electro-optic crystal substrate. In addition, since the low refractive index layer in contact with the electro-optic crystal substrate has a lower refractive index than the electro-optic crystal substrate, it can suppress leakage of light transmitted through the electro-optic crystal substrate, such as a clad in an optical fiber. it can. By using this composite substrate, an electro-optical element that can be driven at high speed and driven at a low voltage can be manufactured.
実施例の複合基板１０を模式的に示す斜視図。The perspective view which shows the composite substrate 10 of an Example typically.
実施例の複合基板１０の断面構造を模式的に示す図。The figure which shows typically the cross-section of the composite substrate 10 of an Example.
実施例の複合基板１０の製造方法の一工程を示す図。The figure which shows 1 process of the manufacturing method of the composite substrate 10 of an Example.
実施例の複合基板１０の製造方法の一工程を示す図。The figure which shows 1 process of the manufacturing method of the composite substrate 10 of an Example.
実施例の複合基板１０の製造方法の一工程を示す図。The figure which shows 1 process of the manufacturing method of the composite substrate 10 of an Example.
複合基板１０の一変形例を示しており、電気光学結晶基板１２に電界を形成する電極３２、３４と、電気光学結晶基板１２内に設けられた光導波路領域３６が付加されている。A modification of the composite substrate 10 is shown, and electrodes 32 and 34 for forming an electric field on the electro-optic crystal substrate 12 and an optical waveguide region 36 provided in the electro-optic crystal substrate 12 are added.
複合基板１０の一変形例を示しており、低誘電率基板１４とアモルファス層１８との間に第２低屈折率層２０が付加されている。A modification of the composite substrate 10 is shown, and a second low refractive index layer 20 is added between the low dielectric constant substrate 14 and the amorphous layer 18.
図７に示す変形例の複合基板１０の製造方法を示す図。The figure which shows the manufacturing method of the composite substrate 10 of the modification shown in FIG.
複合基板１０の一変形例を示しており、電気光学結晶基板１２の上面１２ａにリッジ部１３が形成されている。A modification of the composite substrate 10 is shown, and a ridge portion 13 is formed on the upper surface 12 a of the electro-optic crystal substrate 12.
複合基板１０の一変形例を示しており、図９に示す変形例と比較して、第１の電極４２及び第２の電極４４が付加されている。なお、この変形例では、電気光学結晶基板１２のｃ軸（ｃ－ａｘｉｓ）が、電気光学結晶基板１２に対して平行である。A modification of the composite substrate 10 is shown, and a first electrode 42 and a second electrode 44 are added as compared with the modification shown in FIG. In this modification, the c-axis (c-axis) of the electro-optic crystal substrate 12 is parallel to the electro-optic crystal substrate 12.
複合基板１０の一変形例を示しており、図１０に示す変形例と比較して、低誘電率基板１４の下面１４ｂに沿って導電層２２が付加されている。A modification of the composite substrate 10 is shown, and a conductive layer 22 is added along the lower surface 14b of the low dielectric constant substrate 14 as compared with the modification shown in FIG.
複合基板１０の一変形例を示しており、図１１に示す変形例と比較して、導電層２２に接合された支持基板２４が付加されている。A modification of the composite substrate 10 is shown, and a support substrate 24 bonded to the conductive layer 22 is added as compared with the modification shown in FIG.
複合基板１０の一変形例を示しており、図９に示す変形例と比較して、第１の電極５２及び第２の電極５４が付加されている。なお、この変形例では、電気光学結晶基板１２のｃ軸（ｃ－ａｘｉｓ）が、電気光学結晶基板１２に対して垂直である。A modification of the composite substrate 10 is shown, and a first electrode 52 and a second electrode 54 are added as compared with the modification shown in FIG. In this modification, the c-axis of the electro-optic crystal substrate 12 is perpendicular to the electro-optic crystal substrate 12.
複合基板１０の一変形例を示しており、図１３に示す変形例と比較して、低誘電率基板１４の下面１４ｂに沿って導電層２２が付加されている。A modification of the composite substrate 10 is shown, and a conductive layer 22 is added along the lower surface 14b of the low dielectric constant substrate 14 as compared with the modification shown in FIG.
複合基板１０の一変形例を示しており、図１４に示す変形例と比較して、導電層２２に接合された支持基板２４が付加されている。A modification of the composite substrate 10 is shown, and a support substrate 24 bonded to the conductive layer 22 is added as compared with the modification shown in FIG.
複合基板１０の一変形例を示しており、図９に示す変形例と比較して、リッジ部１３内に光導波路領域５６が付加されている。A modification of the composite substrate 10 is shown, and an optical waveguide region 56 is added in the ridge portion 13 as compared with the modification shown in FIG.
複合基板１０の一変形例を示しており、図１３に示す変形例と比較して、リッジ部１３内に光導波路領域５６が付加されている。A modification of the composite substrate 10 is shown, and an optical waveguide region 56 is added in the ridge portion 13 as compared with the modification shown in FIG.
複合基板１０の一変形例を示しており、図１４に示す変形例と比較して、リッジ部１３内に光導波路領域５６が付加されている。A modification of the composite substrate 10 is shown, and an optical waveguide region 56 is added in the ridge portion 13 as compared with the modification shown in FIG.
複合基板１０の一変形例を示しており、図１５に示す変形例と比較して、リッジ部１３内に光導波路領域５６が付加されている。A modification of the composite substrate 10 is shown, and an optical waveguide region 56 is added in the ridge portion 13 as compared with the modification shown in FIG.
複合基板１０の一変形例を示しており、低屈折率層１６が主体層１６ａと表面層１６ｂとを含む多層構造を有する。A modification of the composite substrate 10 is shown, and the low refractive index layer 16 has a multilayer structure including a main layer 16a and a surface layer 16b.
図２０に示す複合基板１０の製造方法の一工程（直接接合）を説明する図。The figure explaining 1 process (direct joining) of the manufacturing method of the composite substrate 10 shown in FIG.
複合基板１０の一変形例を示しており、第２低屈折率層２０が主体層２０ａと表面層２０ｂとを含む多層構造を有する。A modification of the composite substrate 10 is shown, and the second low refractive index layer 20 has a multilayer structure including a main layer 20a and a surface layer 20b.
図２２に示す複合基板１０の製造方法の一工程（直接接合）を説明する図。The figure explaining 1 process (direct bonding) of the manufacturing method of the composite substrate 10 shown in FIG.
　本技術の一実施形態において、低屈折率層は、電気光学結晶基板よりも誘電率が低くてもよい。このような構成によると、低屈折率層における誘電損失を低減することができ、電気光学素子の高速動作や低電圧での駆動をさらに容易とすることができる。特に限定されないが、低屈折率層は、酸化シリコン、酸化タンタル、酸化アルミニウム、ガラス、フッ化マグネシウム及びフッ化カルシウムのうちの少なくとも一つで構成されることができる。 In one embodiment of the present technology, the low refractive index layer may have a dielectric constant lower than that of the electro-optic crystal substrate. According to such a configuration, dielectric loss in the low refractive index layer can be reduced, and high-speed operation of the electro-optical element and driving at a low voltage can be further facilitated. Although not particularly limited, the low refractive index layer can be composed of at least one of silicon oxide, tantalum oxide, aluminum oxide, glass, magnesium fluoride, and calcium fluoride.
　本技術の一実施形態において、複合基板は、低誘電率基板とアモルファス層との間に位置しており、電気光学結晶基板よりも屈折率の低い第２低屈折率層をさらに備えてもよい。この場合、アモルファス層は、低誘電率基板を構成する元素に代えて、低屈折率層を構成する元素と第２低屈折率層を構成する元素とで構成されているとよい。このような複合基板は、低屈折率層が成膜された電気光学結晶基板に、第２低屈折層が成膜された低誘電率基板を、直接接合して製造することができる。このとき、低屈折率層と第２低屈折率層との各材料が同一、又は構造が類似していると、高品質の直接接合を比較的に容易に行うことができる。 In an embodiment of the present technology, the composite substrate may further include a second low refractive index layer that is located between the low dielectric constant substrate and the amorphous layer and has a refractive index lower than that of the electro-optic crystal substrate. . In this case, the amorphous layer may be composed of an element constituting the low refractive index layer and an element constituting the second low refractive index layer instead of the element constituting the low dielectric constant substrate. Such a composite substrate can be manufactured by directly bonding a low dielectric constant substrate on which a second low refractive index layer is formed to an electro-optic crystal substrate on which a low refractive index layer is formed. At this time, if the materials of the low refractive index layer and the second low refractive index layer are the same or have similar structures, high-quality direct bonding can be performed relatively easily.
　本技術の一実施形態において、電気光学結晶基板の表面には、リッジ部が形成されていてもよい。複合基板にリッジ部が予め形成されていると、リッジ型光導波路を必要とする電気光学素子の製造を、容易に行うことができる。なお、リッジ部に加えて、又は代えて、電気光学結晶基板には、不純物（例えばチタン又は亜鉛）がドーピングされた光導波路領域が形成されていてもよい。但し、不純物がドーピングされた光導波路領域は、不純物のドーピングによる屈折率の段差が小さく、光の閉じ込め効果が小さいので、光の近視野像（ニアフィールド径）は比較的に大きくなる。その結果、複合基板から製造される電気光学素子では、電界効率が低下することから、必要とされる駆動電圧が大きくなる。このため素子サイズも大きくなる。電気光学素子の低駆動電圧化や小型化の観点では、リッジ型光導波路の方が好ましい。 In one embodiment of the present technology, a ridge portion may be formed on the surface of the electro-optic crystal substrate. When the ridge portion is formed in advance on the composite substrate, an electro-optic element that requires a ridge-type optical waveguide can be easily manufactured. In addition to or instead of the ridge portion, an optical waveguide region doped with impurities (for example, titanium or zinc) may be formed on the electro-optic crystal substrate. However, since the optical waveguide region doped with impurities has a small refractive index step due to impurity doping and a small light confinement effect, the near-field image (near field diameter) of light becomes relatively large. As a result, in the electro-optic element manufactured from the composite substrate, the electric field efficiency is lowered, so that the required driving voltage is increased. This increases the element size. The ridge type optical waveguide is preferable from the viewpoint of reducing the driving voltage and size of the electro-optic element.
　上記した実施形態において、電気光学結晶基板のｃ軸（即ち、結晶主軸）が、電気光学結晶基板に対して平行であってもよい。即ち、電気光学結晶基板は、ｘカットの基板であってもよい。この場合、複合基板は、リッジ部の一方の側面に設けられた第１の電極と、リッジ部の他方の側面に設けられ、リッジ部を挟んで第１の電極に対向する第２の電極とをさらに備えてもよい。これらの第１及び第２の電極は、複合基板から電気光学素子を製造するときに、リッジ型光導波路へ電気信号（即ち、電界）を加える電極として利用することができる。 In the above-described embodiment, the c-axis (that is, the crystal main axis) of the electro-optic crystal substrate may be parallel to the electro-optic crystal substrate. That is, the electro-optic crystal substrate may be an x-cut substrate. In this case, the composite substrate includes a first electrode provided on one side surface of the ridge portion, and a second electrode provided on the other side surface of the ridge portion and facing the first electrode across the ridge portion. May be further provided. These first and second electrodes can be used as electrodes for applying an electric signal (that is, an electric field) to the ridge-type optical waveguide when an electro-optical element is manufactured from the composite substrate.
　あるいは、電気光学結晶基板のｃ軸（即ち、結晶主軸）が、電気光学結晶基板に対して垂直であってもよい。即ち、電気光学結晶基板は、ｚカットの基板であってもよい。この場合、複合基板は、リッジ部の頂上面に設けられた第１の電極と、電気光学結晶基板の表面のうちのリッジ部の部分を除いた範囲に設けられた第２の電極とをさらに備えてもよい。これらの第１及び第２の電極は、複合基板から電気光学素子を製造するときに、リッジ型光導波路へ電気信号（即ち、電界）を加える電極として利用することができる。 Alternatively, the c-axis (that is, the crystal main axis) of the electro-optic crystal substrate may be perpendicular to the electro-optic crystal substrate. That is, the electro-optic crystal substrate may be a z-cut substrate. In this case, the composite substrate further includes a first electrode provided on the top surface of the ridge portion and a second electrode provided in a range excluding the ridge portion of the surface of the electro-optic crystal substrate. You may prepare. These first and second electrodes can be used as electrodes for applying an electric signal (that is, an electric field) to the ridge-type optical waveguide when an electro-optical element is manufactured from the composite substrate.
　複合基板が第１の電極と第２の電極を有する実施形態では、第１の電極と電気光学結晶基板との間と、第２の電極と前記電気光学結晶基板との間との少なくとも一方に、電気光学結晶基板よりも屈折率の低い低屈折率膜が形成されていてもよい。このような構成によると、電気光学結晶基板と第１の電極（又は第２の電極）との間の界面において、電気光学結晶基板を伝わる光が電極で吸収や散乱されることを抑制することができる。 In an embodiment in which the composite substrate has a first electrode and a second electrode, at least one of between the first electrode and the electro-optic crystal substrate and between the second electrode and the electro-optic crystal substrate. A low refractive index film having a refractive index lower than that of the electro-optic crystal substrate may be formed. According to such a configuration, at the interface between the electro-optic crystal substrate and the first electrode (or second electrode), the light transmitted through the electro-optic crystal substrate is suppressed from being absorbed or scattered by the electrode. Can do.
　電気光学結晶基板がリッジ部を有する実施形態では、不純物を含有する光導波路領域が、リッジ部の長手方向に沿って形成されていてもよい。このような構成によると、リッジ部を変更することなく、不純物をドーピングする領域を変更することによって、所望の光導波路を容易に形成することができる。 In an embodiment in which the electro-optic crystal substrate has a ridge portion, an optical waveguide region containing impurities may be formed along the longitudinal direction of the ridge portion. According to such a configuration, a desired optical waveguide can be easily formed by changing the impurity doping region without changing the ridge portion.
　本技術の一実施形態において、複合基板は、低誘電率基板に対して電気光学結晶基板とは反対側に位置する導電層をさらに備えてもよい。このような導電層は、複合基板から製造された電気光学素子において、低誘電率基板から電界が漏れ出ることを抑制することができる。 In one embodiment of the present technology, the composite substrate may further include a conductive layer positioned on the opposite side of the electro-optic crystal substrate with respect to the low dielectric constant substrate. Such a conductive layer can suppress leakage of an electric field from the low dielectric constant substrate in an electro-optic element manufactured from the composite substrate.
　上記した実施形態において、複合基板は、導電層に接合された支持基板をさらに備えてもよい。このような構成によると、支持基板によって複合基板の機械的な強度を維持しながら、電気光学結晶基板及び低誘電率基板の厚みを小さくすることができる。複合基板から製造された電気光学素子では、電気光学結晶基板及び低誘電率基板の厚みが小さくなるほど、電気信号が複合基板内で共振する周波数（共振周波数）を高周波側にシフトすることができる。例えば、電気光学結晶基板及び低誘電率基板の合計の厚みが６０マイクロメートル以下であれば、共振周波数は３００ギガヘルツ以上となる。この場合、電気光学素子は、１００ギガヘルツといった高周波（いわゆるミリ波帯）の電気信号が基板共振によって減衰する問題を回避することができる。 In the above-described embodiment, the composite substrate may further include a support substrate bonded to the conductive layer. According to such a configuration, the thickness of the electro-optic crystal substrate and the low dielectric constant substrate can be reduced while maintaining the mechanical strength of the composite substrate by the support substrate. In an electro-optic element manufactured from a composite substrate, the frequency at which an electric signal resonates in the composite substrate (resonance frequency) can be shifted to the high frequency side as the thickness of the electro-optic crystal substrate and the low dielectric constant substrate decreases. For example, if the total thickness of the electro-optic crystal substrate and the low dielectric constant substrate is 60 micrometers or less, the resonance frequency is 300 gigahertz or more. In this case, the electro-optic element can avoid the problem that an electric signal of a high frequency (so-called millimeter wave band) such as 100 GHz is attenuated by substrate resonance.
　以下では、本発明の代表的かつ非限定的な具体例について、図面を参照して詳細に説明する。この詳細な説明は、本発明の好ましい例を実施するための詳細を当業者に示すことを単純に意図しており、本発明の範囲を限定することを意図したものではない。また、以下に開示される追加的な特徴ならびに発明は、さらに改善された複合基板、並びにそれらの使用及び製造方法を提供するために、他の特徴や発明とは別に、又は共に用いることができる。 Hereinafter, representative and non-limiting specific examples of the present invention will be described in detail with reference to the drawings. This detailed description is intended merely to present those skilled in the art with the details for practicing the preferred embodiments of the present invention and is not intended to limit the scope of the invention. In addition, the additional features and inventions disclosed below can be used separately from or in conjunction with other features and inventions to provide further improved composite substrates and methods for their use and manufacture. .
　また、以下の詳細な説明で開示される特徴や工程の組み合わせは、最も広い意味において本発明を実施する際に必須のものではなく、特に本発明の代表的な具体例を説明するためにのみ記載されるものである。さらに、上記及び下記の代表的な具体例の様々な特徴、ならびに、独立及び従属クレームに記載されるものの様々な特徴は、本発明の追加的かつ有用な実施形態を提供するにあたって、ここに記載される具体例のとおりに、あるいは列挙された順番のとおりに組合せなければならないものではない。 Further, the combinations of features and steps disclosed in the following detailed description are not indispensable when practicing the present invention in the broadest sense, and are particularly only for explaining representative specific examples of the present invention. It is described. Moreover, various features of the representative embodiments described above and below, as well as those described in the independent and dependent claims, are described herein in providing additional and useful embodiments of the present invention. They do not have to be combined in the specific examples given or in the order listed.
　本明細書及び／又はクレームに記載された全ての特徴は、実施例及び／又はクレームに記載された特徴の構成とは別に、出願当初の開示ならびにクレームされた特定事項に対する限定として、個別に、かつ互いに独立して開示されることを意図するものである。さらに、全ての数値範囲及びグループ又は集団に関する記載は、出願当初の開示ならびにクレームされた特定事項に対する限定として、それらの中間の構成を開示する意図を持ってなされている。 All features described in this specification and / or claims, apart from the configuration of the features described in the examples and / or claims, are individually disclosed as limitations on the original disclosure and claimed specific matters. And are intended to be disclosed independently of each other. Further, all numerical ranges and group or group descriptions are intended to disclose intermediate configurations thereof as a limitation to the original disclosure and claimed subject matter.
　図面を参照して、実施例の複合基板１０とその製造方法について説明する。本実施例の複合基板１０は、例えば光変調器といった、各種の電気光学素子に採用することができる。図１に示すように、本実施例の複合基板１０は、いわゆるウエハの形態で製造され、電気光学素子の製造者へ提供される。一例ではあるが、複合基板１０の直径は、およそ１０センチ（４インチ）である。通常、一枚の複合基板１０から、複数の電気光学素子が製造される。なお、複合基板１０は、ウエハの形態に限定されず、様々な形態で製造され、提供されてもよい。 With reference to the drawings, a description will be given of a composite substrate 10 of the embodiment and a manufacturing method thereof. The composite substrate 10 of the present embodiment can be employed in various electro-optic elements such as an optical modulator. As shown in FIG. 1, the composite substrate 10 of the present embodiment is manufactured in the form of a so-called wafer and provided to the electro-optic element manufacturer. As an example, the diameter of the composite substrate 10 is approximately 10 cm (4 inches). Usually, a plurality of electro-optic elements are manufactured from one composite substrate 10. The composite substrate 10 is not limited to the form of a wafer, and may be manufactured and provided in various forms.
　図１、図２に示すように、複合基板１０は、電気光学結晶基板１２を備える。電気光学結晶基板１２は、外部に露出する上面１２ａと、複合基板１０内に位置する下面１２ｂとを有する。電気光学結晶基板１２の一部又は全部は、複合基板１０から製造される電気光学素子において、光を伝える光導波路となる。電気光学結晶基板１２は、電気光学効果を有する材料の結晶で構成されている。詳しくは、電気光学結晶基板１２に電界が印加されると、電気光学結晶基板１２の屈折率が変化する。特に、電気光学結晶基板１２のｃ軸に沿って電界が印加されると、電気光学結晶基板１２の屈折率は大きく変化する。ここで、電気光学結晶基板１２のｃ軸は、電気光学結晶基板１２に平行であってもよい。即ち、電気光学結晶基板１２は、例えばｘカット又はｙカットの基板であってもよい。あるいは、電気光学結晶基板１２のｃ軸は、電気光学結晶基板１２に垂直であってもよい。即ち、電気光学結晶基板１２は、例えばｚカットの基板であってもよい。電気光学結晶基板１２の厚みＴ２は、特に限定されないが、例えば１マイクロメートル以上であって、５０マイクロメートル以下であってよい。 As shown in FIGS. 1 and 2, the composite substrate 10 includes an electro-optic crystal substrate 12. The electro-optic crystal substrate 12 has an upper surface 12 a exposed to the outside and a lower surface 12 b located in the composite substrate 10. Part or all of the electro-optic crystal substrate 12 is 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. Specifically, 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 greatly. Here, the c-axis of the electro-optic crystal substrate 12 may be parallel to the electro-optic crystal substrate 12. That is, the electro-optic crystal substrate 12 may be an x-cut or y-cut substrate, for example. 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 a z-cut substrate, for example. The thickness T2 of the electro-optic crystal substrate 12 is not particularly limited, but may be, for example, 1 micrometer or more and 50 micrometers or less.
　電気光学結晶基板１２を構成する材料は、特に限定されないが、ニオブ酸リチウム（ＬｉＮｂＯ３：ＬＮ）、タンタル酸リチウム（ＬｉＴａＯ３：ＬＴ）、チタン酸リン酸カリウム（ＫＴｉＯＰＯ４：ＫＴＰ）、ニオブ酸カリウム・リチウム（ＫｘＬｉ（１－ｘ）ＮｂＯ２：ＫＬＮ）、ニオブ酸カリウム（ＫＮｂＯ３：ＫＮ）、タンタル酸・ニオブ酸カリウム（ＫＮｂｘＴａ（１－ｘ）Ｏ３：ＫＴＮ）、ニオブ酸リチウムとタンタル酸リチウムとの固溶体のいずれかであってよい。なお、電気光学結晶基板１２は、屈折率に加えて、又は代えて、他の光学定数を変化させる電気光学効果を有してもよい。 The material composing the electro-optic crystal substrate 12 is not particularly limited, but lithium niobate (LiNbO 3 : LN), lithium tantalate (LiTaO 3 : LT), potassium titanate phosphate (KTiOPO 4 : KTP), niobic acid Potassium / lithium (K x Li (1-x) NbO 2 : KLN), potassium niobate (KNbO 3 : KN), tantalate / potassium niobate (KNb x Ta (1-x) O 3 : KTN), niobium It may be either a solid solution of lithium acid lithium and lithium tantalate. The electro-optic crystal substrate 12 may have an electro-optic effect that changes other optical constants in addition to or instead of the refractive index.
　複合基板１０は、低誘電率基板１４をさらに備える。低誘電率基板１４は、複合基板１０内に位置する上面１４ａと、外部に露出する下面１４ｂとを有する。低誘電率基板１４には、その上面１４ａ側に、上述した電気光学結晶基板１２が積層されている。低誘電率基板１４は、電気光学結晶基板１２よりも誘電率の低い材料で構成されている。低誘電率基板１４の誘電率（比誘電率）は、特に限定されないが、５以下であるとよい。例として、低誘電率基板１４を構成する材料には、例えば石英やガラスが挙げられる。低誘電率基板１４の厚みＴ４も、特に限定されないが、電気光学結晶基板１２の厚みＴ２より大きくてもよい。電気光学結晶基板１２に隣接する低誘電率基板１４は、電気光学結晶基板１２へ電界が印加されたときに、誘電損失を低減することができる。従って、複合基板１０を用いることにより、高速動作や低電圧での駆動が可能な電気光学素子を製造することができる。 The composite substrate 10 further includes a low dielectric constant substrate 14. The low dielectric constant substrate 14 has an upper surface 14a located in the composite substrate 10 and a lower surface 14b exposed to the outside. On the low dielectric constant substrate 14, the electro-optic crystal substrate 12 described above is laminated on the upper surface 14 a side. The low dielectric constant substrate 14 is made of a material having a dielectric constant lower than that of the electro-optic crystal substrate 12. The dielectric constant (relative dielectric constant) of the low dielectric constant substrate 14 is not particularly limited, but is preferably 5 or less. As an example, examples of the material constituting the low dielectric constant substrate 14 include quartz and glass. The thickness T4 of the low dielectric constant substrate 14 is not particularly limited, but may be larger than the thickness T2 of the electro-optic crystal substrate 12. The low dielectric constant substrate 14 adjacent to the electro-optic crystal substrate 12 can reduce dielectric loss when an electric field is applied to the electro-optic crystal substrate 12. Therefore, by using the composite substrate 10, an electro-optic element that can be driven at high speed and driven at a low voltage can be manufactured.
　複合基板１０は、低屈折率層１６をさらに備える。低屈折率層１６は、電気光学結晶基板１２の下面１２ｂに沿って設けられており、低誘電率基板１４と電気光学結晶基板１２との間に位置している。低屈折率層１６は、電気光学結晶基板１２よりも低い屈折率を有する。これにより、電気光学結晶基板１２の下面１２ｂ（即ち、低屈折率層１６に接する界面）では、電気光学結晶基板１２を伝わる光が全反射されやすく、電気光学結晶基板１２から漏れ出すことが抑制される。低屈折率層１６を構成する材料は、特に限定されないが、例えば酸化シリコン、酸化タンタル、酸化アルミニウム、ガラス、フッ化マグネシウム及びフッ化カルシウムの一又は複数であってよい。低屈折率層１６の厚みＴ６も、特に限定されないが、例えば０．３マイクロメートル以上であって、１マイクロメートル以下であってもよい。一例ではあるが、本実施例における低屈折率層１６は、誘電損失の抑制や電気信号の実効誘電率を小さくし、効率よく光変調できるように、電気光学結晶基板１２よりも誘電体損（ｔａｎδ）又は誘電率が低い材料で構成されている。 The composite substrate 10 further includes a low refractive index layer 16. The low refractive index layer 16 is provided along the lower surface 12 b of the electro-optic crystal substrate 12 and is located between the low dielectric constant substrate 14 and the electro-optic crystal substrate 12. The low refractive index layer 16 has a lower refractive index than the electro-optic crystal substrate 12. Thereby, on the lower surface 12b of the electro-optic crystal substrate 12 (that is, the interface in contact with the low refractive index layer 16), light transmitted through the electro-optic crystal substrate 12 is easily totally reflected, and leakage from the electro-optic crystal substrate 12 is suppressed. Is done. Although the material which comprises the low-refractive-index layer 16 is not specifically limited, For example, it may be one or more of silicon oxide, tantalum oxide, aluminum oxide, glass, magnesium fluoride, and calcium fluoride. The thickness T6 of the low refractive index layer 16 is not particularly limited, but may be, for example, 0.3 micrometers or more and 1 micrometers or less. As an example, the low refractive index layer 16 in this embodiment has a dielectric loss (less than that of the electro-optic crystal substrate 12) so that the dielectric loss can be suppressed and the effective dielectric constant of the electric signal can be reduced and light can be efficiently modulated. tan δ) or a material having a low dielectric constant.
　複合基板１０は、アモルファス層１８をさらに備える。アモルファス層１８は、低誘電率基板１４と低屈折率層１６との間に位置している。アモルファス層１８は、アモルファス構造を有しており、低誘電率基板１４を構成する元素と、低屈折率層１６を構成する元素とで構成されている。アモルファス層１８の厚みＴ８は、特に限定されないが、０．５ナノメートル以上であって、１００ナノメートル以下であってよい。後述するように、複合基板１０は、低屈折率層１６が成膜された電気光学結晶基板１２に、低誘電率基板１４を直接接合することによって、製造することができる。アモルファス層１８は、この直接接合において生成される層であり、低屈折率層１６及び低誘電率基板１４の原子がそれぞれ拡散することによって形成される。従って、アモルファス層１８の上面１８ａ（即ち、低屈折率層１６に接する界面）、及び、アモルファス層１８の下面１８ｂ（即ち、低誘電率基板１４に接する界面）は、必ずしも平坦ではない。 The composite substrate 10 further includes an amorphous layer 18. The amorphous layer 18 is located between the low dielectric constant substrate 14 and the low refractive index layer 16. The amorphous layer 18 has an amorphous structure, and is composed of an element constituting the low dielectric constant substrate 14 and an element constituting the low refractive index layer 16. The thickness T8 of the amorphous layer 18 is not particularly limited, but may be 0.5 nanometers or more and 100 nanometers or less. As will be described later, the composite substrate 10 can be manufactured by directly bonding the low dielectric constant substrate 14 to the electro-optic crystal substrate 12 on which the low refractive index layer 16 is formed. The amorphous layer 18 is a layer generated in this direct bonding, and is formed by diffusing atoms of the low refractive index layer 16 and the low dielectric constant substrate 14 respectively. Therefore, the upper surface 18a of the amorphous layer 18 (that is, the interface in contact with the low refractive index layer 16) and the lower surface 18b of the amorphous layer 18 (that is, the interface in contact with the low dielectric constant substrate 14) are not necessarily flat.
　一般に、直接接合に起因するアモルファス層は、その上下に位置する材料を構成する元素から構成され、結晶性がなく、外部から異なる元素が取り込まれることもあり、光学特性が上下に位置する材料と異なる。またアモルファス層の界面が平坦でなく、光学的に吸収や散乱が生じ得る。このため、仮に、アモルファス層１８が電気光学結晶基板１２へ直接接触していると、電気光学結晶基板１２を伝わる光が、アモルファス層１８によって減衰する。これに対して、本実施例の複合基板１０では、アモルファス層１８と電気光学結晶基板１２との間に影響されない厚みの低屈折率層１６が介在しており、アモルファス層１８が電気光学結晶基板１２に接していない。従って、電気光学結晶基板１２を伝わる光が、アモルファス層１８やこの上面１８ａで散乱されることがない。加えて、電気光学結晶基板１２に接する低屈折率層１６は、電気光学結晶基板１２よりも屈折率が低いことから、光ファイバにおけるクラッドのように、電気光学結晶基板１２を伝わる光の漏出を抑制し、光導波路伝搬することができる。 In general, an amorphous layer resulting from direct bonding is composed of elements constituting the material located above and below it, has no crystallinity, and may incorporate different elements from the outside. Different. Further, the interface of the amorphous layer is not flat, and optical absorption and scattering may occur. For this reason, if the amorphous layer 18 is in direct contact with the electro-optic crystal substrate 12, light transmitted through the electro-optic crystal substrate 12 is attenuated by the amorphous layer 18. On the other hand, in the composite substrate 10 of the present embodiment, the low refractive index layer 16 having a thickness that is not affected is interposed between the amorphous layer 18 and the electro-optic crystal substrate 12, and the amorphous layer 18 is formed by the electro-optic crystal substrate. 12 is not touching. Therefore, light transmitted through the electro-optic crystal substrate 12 is not scattered by the amorphous layer 18 or the upper surface 18a. In addition, since the low refractive index layer 16 in contact with the electro-optic crystal substrate 12 has a lower refractive index than the electro-optic crystal substrate 12, leakage of light transmitted through the electro-optic crystal substrate 12 is prevented like a clad in an optical fiber. It can be suppressed and propagated in the optical waveguide.
　以上のように、本実施例の複合基板１０では、電気光学結晶基板１２に隣接して低誘電率基板１４が設けられているので、電気光学結晶基板１２へ電界が印加されたときに、誘電損失を低減することができる。また、電気光学結晶基板１２と低誘電率基板１４との間は、接着剤を用いることなく直接接合されているので、接着剤による誘電損失がなく、変質及び変形もないので信頼性も確保できる。そして、直接接合に起因するアモルファス層１８は、低屈折率層１６によって電気光学結晶基板１２から隔てられているので、電気光学結晶基板１２を伝わる光は、損失なく出力側へ伝搬されることができる。 As described above, in the composite substrate 10 of this embodiment, the low dielectric constant substrate 14 is provided adjacent to the electro-optic crystal substrate 12, so that when the electric field is applied to the electro-optic crystal substrate 12, the dielectric Loss can be reduced. Further, since the electro-optic crystal substrate 12 and the low dielectric constant substrate 14 are directly bonded without using an adhesive, there is no dielectric loss due to the adhesive, and there is no alteration or deformation, so that reliability can be ensured. . Since the amorphous layer 18 resulting from the direct bonding is separated from the electro-optic crystal substrate 12 by the low refractive index layer 16, the light transmitted through the electro-optic crystal substrate 12 can be propagated to the output side without loss. it can.
　次に、図３－図５を参照して、複合基板１０の製造方法について説明する。先ず、図３に示すように、電気光学結晶基板１２を用意する。電気光学結晶基板１２は、ｘカット又はｙカットの基板（ｃ軸が基板に平行）であってもよいし、分極反転部が形成される場合はｃ軸が基板の水平面と１０°以内の角度を成すオフセット基板であってもよい。あるいは、ｚカットの基板（ｃ軸が基板に垂直）であってもよい。次に、図４に示すように、電気光学結晶基板１２の下面１２ｂに、低屈折率層１６を成膜する。低屈折率層１６の成膜は、特に限定されないが、蒸着（物理蒸着又は化学蒸着）によって行うことができる。なお、電気光学結晶基板１２の下面１２ｂは、電気光学結晶基板１２の一方の主表面である。次に、図５に示すように、低誘電率基板１４を用意し、低屈折率層１６が成膜された電気光学結晶基板１２の下面１２ｂに、低誘電率基板１４を直接接合する。このとき、低誘電率基板１４と低屈折率層１６との間に、前述したアモルファス層１８が形成される。これにより、図１、図２に示す複合基板１０が製造される。 Next, a method for manufacturing the composite substrate 10 will be described with reference to FIGS. First, as shown in FIG. 3, an electro-optic crystal substrate 12 is prepared. The electro-optic crystal substrate 12 may be an x-cut or y-cut substrate (c-axis is parallel to the substrate), and when a polarization inversion portion is formed, the c-axis is an angle within 10 ° with the horizontal plane of the substrate. May be an offset substrate. Alternatively, it may be a z-cut substrate (c-axis is perpendicular to the substrate). Next, as shown in FIG. 4, a low refractive index layer 16 is formed on the lower surface 12 b of the electro-optic crystal substrate 12. The film formation of the low refractive index layer 16 is not particularly limited, but can be performed by vapor deposition (physical vapor deposition or chemical vapor deposition). Note that the lower surface 12 b of the electro-optic crystal substrate 12 is one main surface of the electro-optic crystal substrate 12. Next, as shown in FIG. 5, a low dielectric constant substrate 14 is prepared, and the low dielectric constant substrate 14 is directly bonded to the lower surface 12b of the electro-optic crystal substrate 12 on which the low refractive index layer 16 is formed. At this time, the above-described amorphous layer 18 is formed between the low dielectric constant substrate 14 and the low refractive index layer 16. Thereby, the composite substrate 10 shown in FIGS. 1 and 2 is manufactured.
　上記した直接接合について、具体的な手順や加工条件は特に限定されない。互いに接合される層又は基板の各材料に応じて、適宜定めることができる。一例ではあるが、本実施例の製造方法では、先ず、高真空チャンバー内（例えば、１×１０－６パスカル程度）において、各接合面に中性化ビームを照射する。これより、各接合面が活性化される。次いで、真空雰囲気で、活性化された接合面同士を接触させ、常温で接合する。この接合時の荷重は、例えば、１００～２００００ニュートンとすることができる。この製造方法において、中性化ビームによる表面活性化を行う際には、チャンバーに不活性ガスを導入し、チャンバー内に配置した電極へ、直流電源から高電圧を印加する。これにより、電極（正極）とチャンバー（負極）との間に生じる電界により、電子が運動して、不活性ガスによる原子とイオンのビームが生成される。グリッドに達したビームのうち、イオンビームはグリッドで中和されるので、中性原子のビームが高速原子ビーム源から出射される。ビームを構成する原子種は、不活性ガス元素（例えば、アルゴン（Ａｒ）、窒素（Ｎ）等）が好ましい。ビーム照射による活性化時の電圧は０．５～２．０キロボルト、電流は５０～２００ミリアンペアとすることができる。 Specific procedures and processing conditions for the direct bonding described above are not particularly limited. It can be determined as appropriate according to the materials of the layers or substrates to be bonded to each other. As an example, in the manufacturing method of the present embodiment, first, a neutralized beam is irradiated to each bonding surface in a high vacuum chamber (for example, about 1 × 10 −6 Pascal). Thereby, each joint surface is activated. Next, the activated bonding surfaces are brought into contact with each other in a vacuum atmosphere and bonded at room temperature. The load at the time of joining can be, for example, 100 to 20000 Newton. In this manufacturing method, when performing surface activation by a neutral beam, an inert gas is introduced into the chamber, and a high voltage is applied from a DC power source to the electrode disposed in the chamber. Thereby, an electron moves by the electric field produced between an electrode (positive electrode) and a chamber (negative electrode), and the beam of atoms and ions by an inert gas is generated. Of the beams that reach the grid, the ion beam is neutralized by the grid, so that a beam of neutral atoms is emitted from the fast atom beam source. The atomic species constituting the beam is preferably an inert gas element (for example, argon (Ar), nitrogen (N), etc.). The voltage upon activation by beam irradiation can be 0.5 to 2.0 kilovolts, and the current can be 50 to 200 milliamps.
　図６に示すように、複合基板１０には、電気光学結晶基板１２に電界を形成するための電極３２、３４が、電気光学結晶基板１２の上面１２ａに設けられてもよい。電極３２、３４を構成する材料は、導電体であればよく、例えば金といった金属であってよい。電極３２、３４と電気光学結晶基板１２との間には、電極３２、３４のはがれ防止やマイグレーションを防止するために、チタン（Ｔｉ）、クロム（Ｃｒ）、ニッケル（Ｎｉ）、白金（Ｐｔ）等の層が介在してもよい。電極３２、３４の数、位置、形状については、特に限定されない。例えば、電極３２、３４の数については、複合基板１０から製造される電気光学素子の数や、各々の電気光学素子が必要とする電極３２、３４の数に応じて、適宜定めることができる。複合基板１０に電極３２、３４が予め設けられていると、電気光学素子の製造者は、複合基板１０から電気光学素子を容易に製造することができる。 As shown in FIG. 6, the composite substrate 10 may be provided with electrodes 32 and 34 for forming an electric field on the electro-optic crystal substrate 12 on the upper surface 12 a of the electro-optic crystal substrate 12. The material which comprises the electrodes 32 and 34 should just be a conductor, for example, may be metals, such as gold | metal | money. Titanium (Ti), chromium (Cr), nickel (Ni), platinum (Pt) is used between the electrodes 32 and 34 and the electro-optic crystal substrate 12 to prevent the electrodes 32 and 34 from peeling off or migrating. Such layers may be interposed. The number, position, and shape of the electrodes 32 and 34 are not particularly limited. For example, the number of electrodes 32 and 34 can be appropriately determined according to the number of electro-optic elements manufactured from the composite substrate 10 and the number of electrodes 32 and 34 required for each electro-optic element. When the electrodes 32 and 34 are provided in advance on the composite substrate 10, the manufacturer of the electro-optical element can easily manufacture the electro-optical element from the composite substrate 10.
　加えて、又は代えて、電気光学結晶基板１２内には、不純物をドーピングすることによって、光導波路領域３６が設けられてもよい。電気光学結晶基板１２では、チタン又は亜鉛といった特定の不純物をドーピングすることで、屈折率を選択的に（即ち、局所的に）高めることができ、これによって光導波路領域３６を形成することができる。光導波路領域３６の数、位置、形状についても、特に限定されない。例えば、光導波路領域３６の数については、複合基板１０から製造される電気光学素子の数や、各々の電気光学素子が必要とする光導波路領域３６の数に応じて、適宜定めることができる。複合基板１０に光導波路領域３６が予め設けられていると、電気光学素子の製造者は、複合基板１０から電気光学素子を容易に製造することができる。 In addition or alternatively, the optical waveguide region 36 may be provided in the electro-optic crystal substrate 12 by doping impurities. In the electro-optic crystal substrate 12, the refractive index can be selectively increased (that is, locally) by doping 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 not particularly limited. For example, 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. If the optical waveguide region 36 is provided in advance on the composite substrate 10, the manufacturer of the electro-optical element can easily manufacture the electro-optical element from the composite substrate 10.
　図７に示すように、複合基板１０には、第２低屈折率層２０がさらに設けられてもよい。第２低屈折率層２０は、低誘電率基板１４とアモルファス層１８との間に位置しており、電気光学結晶基板１２よりも屈折率の低い材料で構成されている。また、第２低屈折率層２０は、誘電損失を抑制するために、電気光学結晶基板１２よりも誘電率の低い材料で構成されてもよい。第２低屈折率層２０は、例えば、酸化シリコン、酸化タンタル、酸化アルミニウム、ガラス、フッ化マグネシウム及びフッ化カルシウムのうちの少なくとも一つで構成されることができる。第２低屈折率層２０は、低屈折率層１６と同じ材料で構成されてもよいし、異なる材料で形成されてもよい。 As shown in FIG. 7, the composite substrate 10 may further include a second low refractive index layer 20. The second low refractive index layer 20 is located between the low dielectric constant substrate 14 and the amorphous layer 18 and is made of a material having a refractive index lower than that of the electro-optic crystal substrate 12. The second low refractive index layer 20 may be made of a material having a dielectric constant lower than that of the electro-optic crystal substrate 12 in order to suppress dielectric loss. The second low refractive index layer 20 can be composed of, for example, at least one of silicon oxide, tantalum oxide, aluminum oxide, glass, magnesium fluoride, and calcium fluoride. The second low refractive index layer 20 may be made of the same material as the low refractive index layer 16 or may be formed of a different material.
　図８は、図７に示す複合基板１０の製造方法を示す。図８に示すように、第２低屈折率層２０を有する複合基板１０は、低屈折率層１６が成膜された電気光学結晶基板１２の下面１２ｂに、第２低屈折率層２０が成膜された低誘電率基板１４を直接接合すことによって、製造することができる。この製造方法によると、低屈折率層１６と第２低屈折率層２０との間に、図７に示すアモルファス層１８が形成される。ここで、低屈折率層１６と第２低屈折率層２０との材料が同一、又は構造が類似していると、高品質の直接接合を比較的に容易に行うことができる。 FIG. 8 shows a method for manufacturing the composite substrate 10 shown in FIG. As shown in FIG. 8, in the composite substrate 10 having the second low refractive index layer 20, the second low refractive index layer 20 is formed on the lower surface 12b of the electro-optic crystal substrate 12 on which the low refractive index layer 16 is formed. It can be manufactured by directly bonding the filmed low dielectric constant substrate 14. According to this manufacturing method, the amorphous layer 18 shown in FIG. 7 is formed between the low refractive index layer 16 and the second low refractive index layer 20. Here, if the materials of the low refractive index layer 16 and the second low refractive index layer 20 are the same or have similar structures, high-quality direct bonding can be performed relatively easily.
　図９に示すように、電気光学結晶基板１２の上面１２ａには、リッジ部１３が形成されてもよい。リッジ部１３は、上面１２ａに沿って細長く延びる突出部である。リッジ部１３は、複合基板１０が製造される電気光学素子において、リッジ型光導波路を構成する。複合基板１０にリッジ部１３が予め形成されていると、リッジ型光導波路を必要とする電気光学素子の製造を、容易に行うことができる。リッジ部１３の幅Ｗは、特に限定されないが、１マイクロメートル以上であって、１０マイクロメートル以下であってよい。リッジ部１３の高さＴ１についても、特に限定されないが、電気光学結晶基板１２の厚みＴ２の１０パーセント以上であって、９５パーセント以下であってよい。リッジ部１３の数、位置、形状についても、特に限定されない。一例ではあるが、複合基板１０がマッハツェンダー型の電気光学変調器の製造に用いられるときは、少なくとも一部が平行に延びる二つのリッジ部１３が形成されるとよい。 As shown in FIG. 9, 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 along the upper surface 12a. The ridge portion 13 constitutes a ridge type optical waveguide in the electro-optic element in which the composite substrate 10 is manufactured. When the ridge portion 13 is formed in advance on the composite substrate 10, an electro-optic element that requires a ridge-type optical waveguide can be easily manufactured. The width W of the ridge portion 13 is not particularly limited, but may be 1 micrometer or more and 10 micrometers or less. The height T1 of the ridge portion 13 is not particularly limited, but may be 10% or more and 95% or less of the thickness T2 of the electro-optic crystal substrate 12. The number, position, and shape of the ridge portions 13 are not particularly limited. For example, when the composite substrate 10 is used for manufacturing a Mach-Zehnder type electro-optic modulator, it is preferable to form two ridge portions 13 at least partially extending in parallel.
　図１０に示すように、リッジ部１３を有する複合基板１０には、第１の電極４２及び第２の電極４４がさらに設けられてもよい。ここで、電気光学結晶基板１２のｃ軸（ｃ－ａｘｉｓ）が、電気光学結晶基板１２に対して平行である場合、第１の電極４２はリッジ部１３の一方の側面１３ａに設けられるとよい。そして、第２の電極４４は、リッジ部１３の他方の側面１３ｂに設けられ、リッジ部１３を挟んで第１の電極４２に対向するとよい。このような構成によると、電気光学素子において光導波路となるリッジ部１３に対して、第１の電極４２及び第２の電極４４はｃ軸と平行に電界を印加することができる。第１の電極４２及び第２の電極４４を構成する材料は、導電体であればよく、例えば金といった金属材料であってよい。また、第１の電極４２と電気光学結晶基板１２や、第２の電極４４と電気光学結晶基板１２との間には、電気光学結晶基板１２よりも屈折率の低い低屈折率膜が設けられてもよい。このような低屈折率膜は、クラッド層として機能し、リッジ部１３を伝わる光の損失を抑制することができる。 As shown in FIG. 10, the composite substrate 10 having the ridge portion 13 may be further provided with a first electrode 42 and a second electrode 44. Here, when the c-axis of the electro-optic crystal substrate 12 is parallel to the electro-optic crystal substrate 12, the first electrode 42 may be provided on one side surface 13 a of the ridge portion 13. . The second electrode 44 is preferably provided on the other side surface 13 b of the ridge portion 13 and is opposed to the first electrode 42 with the ridge portion 13 interposed therebetween. According to such a configuration, the first electrode 42 and the second electrode 44 can apply an electric field in parallel to the c-axis to the ridge portion 13 serving as an optical waveguide in the electro-optic element. The material which comprises the 1st electrode 42 and the 2nd electrode 44 should just be a conductor, for example, may be metal materials, such as gold | metal | money. Further, a low refractive index film having a refractive index lower than that of the electro-optic crystal substrate 12 is provided between the first electrode 42 and the electro-optic crystal substrate 12 and between the second electrode 44 and the electro-optic crystal substrate 12. May be. Such a low refractive index film functions as a cladding layer and can suppress loss of light transmitted through the ridge portion 13.
　図１１に示すように、複合基板１０には、低誘電率基板１４の下面１４ｂに沿って、導電層２２が設けられてもよい。このような導電層２２は、複合基板１０から製造された電気光学素子において、接地電極として使用されることができる。この場合、導電層２２は、第１の電極４２及び第２の電極４４によって印加された電界が、低誘電率基板１４の下面１４ｂから漏出することを抑制することができる。導電層２２を構成する材料は、導電体であればよく、例えば金（Ａｕ）、銀（Ａｇ）、銅（Ｃｕ）、アルミニウム（Ａｌ）、プラチナ（Ｐｔ）、又は、それらのうちの少なくとも二つを含む合金の層を有してもよい。導電層２２は、単層構造であってもよいし、多層構造を有してもよい。導電層２２は、低誘電率基板１４と接触する下地層として、導電層２２のはがれやマイグレーションを防止するために、チタン（Ｔｉ）、クロム（Ｃｒ）、ニッケル（Ｎｉ）、白金（Ｐｔ）等の層を有してもよい。なお、図１１に示す導電層２２は、上述した他の複合基板１０にも同様に設けることができる。 As shown in FIG. 11, a conductive layer 22 may be provided on the composite substrate 10 along the lower surface 14 b of the low dielectric constant substrate 14. Such a conductive layer 22 can be used as a ground electrode in the electro-optic element manufactured from the composite substrate 10. In this case, the conductive layer 22 can suppress the leakage of the electric field applied by the first electrode 42 and the second electrode 44 from the lower surface 14 b of the low dielectric constant substrate 14. The material constituting the conductive layer 22 may be a conductor, such as gold (Au), silver (Ag), copper (Cu), aluminum (Al), platinum (Pt), or at least two of them. You may have a layer of an alloy containing two. The conductive layer 22 may have a single layer structure or a multilayer structure. The conductive layer 22 is a base layer in contact with the low dielectric constant substrate 14, and in order to prevent peeling or migration of the conductive layer 22, titanium (Ti), chromium (Cr), nickel (Ni), platinum (Pt), etc. You may have a layer of. Note that the conductive layer 22 shown in FIG. 11 can be similarly provided on the other composite substrate 10 described above.
　加えて、図１２に示すように、複合基板１０には、導電層２２に接合された支持基板２４をさらに備えてもよい。このような構成によると、支持基板２４によって複合基板１０の機械的な強度を維持しながら、電気光学結晶基板１２及び低誘電率基板１４の厚みを小さくすることができる。複合基板１０から製造された電気光学素子では、電気光学結晶基板１２及び低誘電率基板１４の厚みが小さくなるほど、電気信号に対する共振周波数が高くなる。例えば、電気光学結晶基板１２及び低誘電率基板１４の合計の厚みが６０マイクロメートル以下であれば、共振周波数は３００ギガヘルツ以上となる。この場合、電気光学素子は、１００ギガヘルツといった高周波（いわゆるミリ波帯）の電気信号を問題なく処理することができる。 In addition, as shown in FIG. 12, the composite substrate 10 may further include a support substrate 24 bonded to the conductive layer 22. According to such a configuration, the thickness of the electro-optic crystal substrate 12 and the low dielectric constant substrate 14 can be reduced while maintaining the mechanical strength of the composite substrate 10 by the support substrate 24. In the electro-optic element manufactured from the composite substrate 10, the resonance frequency for the electrical signal increases as the thickness of the electro-optic crystal substrate 12 and the low dielectric constant substrate 14 decreases. For example, if the total thickness of the electro-optic crystal substrate 12 and the low dielectric constant substrate 14 is 60 micrometers or less, the resonance frequency is 300 gigahertz or more. In this case, the electro-optical element can process a high-frequency (so-called millimeter wave band) electric signal such as 100 GHz without any problem.
　支持基板２４を構成する材料は特に限定されない。例えば、支持基板２４は、シリコン（Ｓｉ）、ガラス、サイアロン（Ｓｉ３Ｎ４－Ａｌ２Ｏ３）、ムライト（３Ａｌ２Ｏ３・２ＳｉＯ２，２Ａｌ２Ｏ３・ＳｉＯ２）、窒化アルミニウム（ＡｌＮ）、窒化シリコン（Ｓｉ３Ｎ４）、酸化マグネシウム（ＭｇＯ）、サファイア、石英、水晶、窒化ガリウム（ＧａＮ）、炭化シリコン（ＳｉＣ）、酸化ガリウム（Ｇａ２Ｏ３）のうちのいずれかの基板であってよい。但し、複合基板１０の熱変形（特に反り）を抑制するために、支持基板２４を構成する材料の線膨張係数は、電気光学結晶基板１２を構成する材料の線膨張係数に近いほどよい。特に限定されないが、支持基板２４を構成する材料の線膨張係数は、電気光学結晶基板１２を構成する材料の線膨張係数の±５０パーセント以内であるとよい。一例ではあるが、支持基板２４を構成する材料は、電気光学結晶基板１２を構成する材料と同じであってもよい。なお、図１２に示す支持基板２４は、導電層２２と共に、上述した他の複合基板１０にも同様に設けることができる。 The material constituting the support substrate 24 is not particularly limited. For example, the support substrate 24 is made of 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 (GaN), silicon carbide (SiC), gallium oxide (Ga 2 O 3 ) It may be. However, in order to suppress thermal deformation (particularly warpage) of the composite substrate 10, the linear expansion coefficient of the material forming the support substrate 24 is preferably as close as possible to the linear expansion coefficient of the material forming the electro-optic crystal substrate 12. Although not particularly limited, the linear expansion coefficient of the material constituting the support substrate 24 may be within ± 50 percent of the linear expansion coefficient of the material constituting the electro-optic crystal substrate 12. As an example, the material constituting the support substrate 24 may be the same as the material constituting the electro-optic crystal substrate 12. In addition, the support substrate 24 shown in FIG. 12 can be similarly provided on the above-described other composite substrate 10 together with the conductive layer 22.
　図１２に示す複合基板１０の製造方法では、導電層２２と支持基板２４との間を、直接接合によって接合してもよい。この場合、導電層２２の表層は、白金で構成されていてもよい。白金は直接接合に適した材料である。そのことから、導電層２２の表層が白金で構成されていていると、導電層２２が成膜された電気光学結晶基板１２を、支持基板２４に対して良好に直接接合することができる。この場合、製造後の複合基板１０では、導電層２２と支持基板２４との間に、直接接合に起因するアモルファス層が形成される。このアモルファス層は、導電層２２を構成する元素（主に白金）と、支持基板２４を構成する元素とで構成される。 In the method for manufacturing the composite substrate 10 shown in FIG. 12, the conductive layer 22 and the support substrate 24 may be joined by direct joining. In this case, the surface layer of the conductive layer 22 may be made of platinum. Platinum is a material suitable for direct bonding. Therefore, when the surface layer of the conductive layer 22 is made of platinum, the electro-optic crystal substrate 12 on which the conductive layer 22 is formed can be directly and well bonded to the support substrate 24. In this case, in the composite substrate 10 after manufacture, an amorphous layer resulting from direct bonding is formed between the conductive layer 22 and the support substrate 24. This amorphous layer is composed of an element (mainly platinum) constituting the conductive layer 22 and an element constituting the support substrate 24.
　図１３に示すように、電気光学結晶基板１２のｃ軸（ｃ－ａｘｉｓ）は、電気光学結晶基板１２に対して垂直であってもよい。この場合でも、電気光学結晶基板１２の上面１２ａには、リッジ部１３が形成されてもよい。また、電気光学結晶基板１２の上面１２ａには、第１の電極５２及び第２の電極５４が設けられてもよい。但し、第１の電極５２は、リッジ部１３の頂上面１３ｃに設けられるとよく、第２の電極５４は、電気光学結晶基板１２の上面１２ａのうちのリッジ部１３の部分を除いた範囲に設けられるとよい。このような構成によると、電気光学素子において光導波路となるリッジ部１３に対して、第１の電極５２及び第２の電極５４はｃ軸と平行に電界を印加することができる。 As shown in FIG. 13, the 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. In addition, a first electrode 52 and a second electrode 54 may be provided on the upper surface 12 a of the electro-optic crystal substrate 12. However, the first electrode 52 is preferably provided on the top surface 13 c of the ridge portion 13, and the second electrode 54 is in a range excluding the portion of the ridge portion 13 of the upper surface 12 a of the electro-optic crystal substrate 12. It is good to be provided. According to such a configuration, the first electrode 52 and the second electrode 54 can apply an electric field in parallel to the c-axis to the ridge portion 13 serving as an optical waveguide in the electro-optic element.
　図１４に示すように、図１３に示した複合基板１０にも、低誘電率基板１４の下面１４ｂに沿って、導電層２２が設けられてもよい。前述したように、導電層２２は、複合基板１０から製造された電気光学素子において、接地電極として使用されることができる。また、図１５に示すように、その導電層２２には、図１２に示した複合基板１０と同様に、支持基板２４が接合されてもよい。これにより、複合基板１０の機械的な強度を維持しながら、電気光学結晶基板１２及び低誘電率基板１４の厚みを小さくすることができる。前述したように、電気光学結晶基板１２及び低誘電率基板１４の厚みを小さくすることで、電気信号に対する共振周波数を、例えばミリ波帯といった高周波帯域よりも十分に高くすることができる。図１５に示す複合基板１０の製造方法においても、導電層２２と支持基板２４との間は、直接接合によって接合することができる。この場合、前述したように、導電層２２の表層が白金で構成されていると、導電層２２と支持基板２４との直接接合を良好に行うことができる。 As shown in FIG. 14, the composite substrate 10 shown in FIG. 13 may also be provided with a conductive layer 22 along the lower surface 14b of the low dielectric constant substrate. As described above, the conductive layer 22 can be used as a ground electrode in the electro-optic element manufactured from the composite substrate 10. Further, as shown in FIG. 15, a support substrate 24 may be bonded to the conductive layer 22 in the same manner as the composite substrate 10 shown in FIG. 12. Thereby, the thickness of the electro-optic crystal substrate 12 and the low dielectric constant substrate 14 can be reduced while maintaining the mechanical strength of the composite substrate 10. As described above, by reducing the thickness of the electro-optic crystal substrate 12 and the low dielectric constant substrate 14, the resonance frequency for the electric signal can be made sufficiently higher than a high frequency band such as a millimeter wave band. Also in the method of manufacturing the composite substrate 10 shown in FIG. 15, the conductive layer 22 and the support substrate 24 can be bonded by direct bonding. In this case, as described above, when the surface layer of the conductive layer 22 is made of platinum, the direct bonding between the conductive layer 22 and the support substrate 24 can be favorably performed.
　図１６－図１９に例示するように、本明細書が開示する各種の複合基板１０では、不純物を含有する光導波路領域５６が、リッジ部１３の内部において、リッジ部１３の長手方向に沿って形成されていてもよい。なお、図１６に示す複合基板１０は、図９に示す複合基板１０において、リッジ部１３内に光導波路領域５６が付加されたものである。図１７に示す複合基板１０は、図１３に示す複合基板１０において、リッジ部１３内に光導波路領域５６が付加されたものである。図１８に示す複合基板１０は、図１４に示す複合基板１０において、リッジ部１３内に光導波路領域５６が付加されたものである。そして、図１９に示す複合基板１０は、図１５に示す複合基板１０において、リッジ部１３内に光導波路領域５６が付加されたものである。図示省略するが、図１０－図１２に示す他の複合基板１０においても同様に、不純物を含有する光導波路領域が、リッジ部１３の内部において、リッジ部１３の長手方向に沿って形成されていてもよい。 As illustrated in FIG. 16 to FIG. 19, in various composite substrates 10 disclosed in this specification, the optical waveguide region 56 containing impurities extends along the longitudinal direction of the ridge portion 13 inside the ridge portion 13. It may be formed. The composite substrate 10 shown in FIG. 16 is obtained by adding an optical waveguide region 56 in the ridge portion 13 to the composite substrate 10 shown in FIG. The composite substrate 10 shown in FIG. 17 is obtained by adding an optical waveguide region 56 in the ridge portion 13 to the composite substrate 10 shown in FIG. The composite substrate 10 shown in FIG. 18 is obtained by adding an optical waveguide region 56 in the ridge portion 13 to the composite substrate 10 shown in FIG. A composite substrate 10 shown in FIG. 19 is obtained by adding an optical waveguide region 56 in the ridge portion 13 to the composite substrate 10 shown in FIG. Although not shown, in other composite substrates 10 shown in FIGS. 10 to 12, similarly, an optical waveguide region containing impurities is formed in the ridge portion 13 along the longitudinal direction of the ridge portion 13. May be.
　図２０に示すように、複合基板１０の低屈折率層１６は、主体層１６ａと接合層１６ｂとを含む多層構造を有してもよい。接合層１６ｂは、主体層１６ａとアモルファス層１８との間に位置し、アモルファス層１８に接する層である。主体層１６ａを構成する材料には、前述したように、酸化シリコン、酸化タンタル、酸化アルミニウム、ガラス、フッ化マグネシウム及びフッ化カルシウムの一又は複数であってよい。一方、接合層１６ｂを構成する材料については、例えば酸化タンタル（Ｔａ２Ｏ５）、酸化ニオブ（Ｎｂ２Ｏ５）、酸化アルミニウム（Ａｌ２Ｏ３）、酸化チタン（ＴｉＯ２）といった、直接接合に適した材料であるとよい。このような構成によると、図２１に示すように、接合層１６ｂを有する低屈折率層１６を、低誘電率基板１４に対して良好に直接接合することができる。なお、多層構造を有する低屈折率層１６は、本明細書で開示される全ての実施形態において採用することができる。 As shown in FIG. 20, the low refractive index layer 16 of the composite substrate 10 may have a multilayer structure including a main layer 16a and a bonding layer 16b. The bonding layer 16 b is a layer located between the main layer 16 a and the amorphous layer 18 and in contact with the amorphous layer 18. As described above, the material constituting the main layer 16a may be one or more of silicon oxide, tantalum oxide, aluminum oxide, glass, magnesium fluoride, and calcium fluoride. On the other hand, the material constituting the bonding layer 16b is a direct bonding such as tantalum oxide (Ta 2 O 5 ), niobium oxide (Nb 2 O 5 ), aluminum oxide (Al 2 O 3 ), titanium oxide (TiO 2 ). The material should be suitable for According to such a configuration, as shown in FIG. 21, the low refractive index layer 16 having the bonding layer 16 b can be bonded directly and favorably to the low dielectric constant substrate 14. Note that the low refractive index layer 16 having a multilayer structure can be employed in all the embodiments disclosed in this specification.
　図２２に示すように、複合基板１０が第２低屈折率層２０をさらに備える場合は、第２低屈折率層２０についても、主体層２０ａと接合層２０ｂとを含む多層構造を有してもよい。接合層２０ｂは、主体層２０ａとアモルファス層１８との間に位置し、アモルファス層１８に接する層である。上述したように、接合層２０ｂを構成する材料は、例えば酸化タンタル、酸化ニオブ、酸化アルミニウム、酸化チタンといった、直接接合に適した材料であるとよい。このような構成によると、図２３に示すように、電気光学結晶基板１２側の低屈折率層１６を、接合層２０ｂを有する第２低屈折率層１６に対して良好に直接接合することができる。なお、図２２、図２３に示す例において、電気光学結晶基板１２側の低屈折率層１６は、単層構造であってもよく、接合層１６ｂを有さなくてもよい。なお、多層構造を有する低屈折率層２０は、本明細書で開示される全ての実施形態において採用することができる。 As shown in FIG. 22, when the composite substrate 10 further includes the second low refractive index layer 20, the second low refractive index layer 20 also has a multilayer structure including the main layer 20a and the bonding layer 20b. Also good. The bonding layer 20 b is located between the main layer 20 a and the amorphous layer 18 and is in contact with the amorphous layer 18. As described above, the material constituting the bonding layer 20b is preferably a material suitable for direct bonding, such as tantalum oxide, niobium oxide, aluminum oxide, and titanium oxide. According to such a configuration, as shown in FIG. 23, the low-refractive index layer 16 on the electro-optic crystal substrate 12 side can be favorably directly bonded to the second low-refractive index layer 16 having the bonding layer 20b. it can. In the example shown in FIGS. 22 and 23, the low refractive index layer 16 on the electro-optic crystal substrate 12 side may have a single-layer structure or may not have the bonding layer 16b. The low refractive index layer 20 having a multilayer structure can be employed in all embodiments disclosed in this specification.
１０：複合基板
１２：電気光学結晶基板
１３：リッジ部
１３ａ、１３ｂ：リッジ部の側面
１３ｃ：リッジ部の頂上面
１４：低誘電率基板
１６：低屈折率層
１８：アモルファス層
２０：第２低屈折率層
２２：導電層
２４：支持基板
３２、３４、４２、４４、５２、５４：電極
３６、５６：光導波路領域 10: Composite substrate 12: Electro-optic crystal substrate 13: Ridge portion 13a, 13b: Side surface 13c of the ridge portion 14: Top surface of the ridge portion 14: Low dielectric constant substrate 16: Low refractive index layer 18: Amorphous layer 20: Second low Refractive index layer 22: conductive layer 24: support substrates 32, 34, 42, 44, 52, 54: electrodes 36, 56: optical waveguide region

Claims (12)

  1. 　電気光学素子のための複合基板であって、
    　電気光学効果を有する電気光学結晶基板と、
    　前記電気光学結晶基板が積層されているとともに、前記電気光学結晶基板よりも誘電率の低い低誘電率基板と、
    　前記低誘電率基板と前記電気光学結晶基板との間に位置しており、前記電気光学結晶基板よりも屈折率の低い低屈折率層と、
    　前記低誘電率基板と前記低屈折率層との間に位置しており、前記低誘電率基板を構成する元素と前記低屈折率層を構成する元素とで構成されたアモルファス層と、
    　を備える複合基板。     A composite substrate for an electro-optic element,
    An electro-optic crystal substrate having an electro-optic effect;
    The electro-optic crystal substrate is laminated, and a low dielectric constant substrate having a dielectric constant lower than that of the electro-optic crystal substrate,
    A low refractive index layer located between the low dielectric constant substrate and the electro-optic crystal substrate, having a lower refractive index than the electro-optic crystal substrate;
    An amorphous layer that is located between the low dielectric constant substrate and the low refractive index layer, and is composed of an element constituting the low dielectric constant substrate and an element constituting the low refractive index layer;
    A composite substrate comprising:
  2. 　前記低屈折率層は、前記電気光学結晶基板よりも誘電率が低い、請求項１に記載の複合基板。 The composite substrate according to claim 1, wherein the low refractive index layer has a dielectric constant lower than that of the electro-optic crystal substrate.
  3. 　前記低屈折率層は、酸化シリコン、酸化タンタル、酸化アルミニウム、ガラス、フッ化マグネシウム及びフッ化カルシウムのうちの少なくとも一つで構成されている、請求項２に記載の複合基板。 The composite substrate according to claim 2, wherein the low refractive index layer is made of at least one of silicon oxide, tantalum oxide, aluminum oxide, glass, magnesium fluoride, and calcium fluoride.
  4. 　前記低誘電率基板と前記アモルファス層との間に位置しており、前記電気光学結晶基板よりも屈折率の低い第２低屈折率層をさらに備え、
    　前記アモルファス層は、前記低誘電率基板を構成する元素に代えて、前記低屈折率層を構成する元素と前記第２低屈折率層を構成する元素とで構成されている、請求項１から３のいずれか一項に記載の複合基板。     A second low refractive index layer positioned between the low dielectric constant substrate and the amorphous layer and having a lower refractive index than the electro-optic crystal substrate;
    The amorphous layer is composed of an element constituting the low refractive index layer and an element constituting the second low refractive index layer instead of the element constituting the low dielectric constant substrate. 4. The composite substrate according to any one of 3 above.
  5. 　前記第２低屈折率層を構成する材料は、前記低屈折率層を構成する材料と同じである、請求項４に記載の複合基板。 The composite substrate according to claim 4, wherein a material constituting the second low refractive index layer is the same as a material constituting the low refractive index layer.
  6. 　前記電気光学結晶基板の表面には、リッジ部が形成されている、請求項１から５のいずれか一項に記載の複合基板。 The composite substrate according to any one of claims 1 to 5, wherein a ridge portion is formed on a surface of the electro-optic crystal substrate.
  7. 　前記電気光学結晶基板のｃ軸は、前記電気光学結晶基板に対して平行であり、
    　前記リッジ部の一方の側面に設けられた第１の電極と、前記リッジ部の他方の側面に設けられ、前記リッジ部を挟んで前記第１の電極に対向する第２の電極とをさらに備える、請求項６に記載の複合基板。     The c-axis of the electro-optic crystal substrate is parallel to the electro-optic crystal substrate,
    A first electrode provided on one side surface of the ridge portion; and a second electrode provided on the other side surface of the ridge portion and facing the first electrode across the ridge portion. The composite substrate according to claim 6.
  8. 　前記電気光学結晶基板のｃ軸は、前記電気光学結晶基板に対して垂直であり、
    　前記リッジ部の頂上面に設けられた第１の電極と、前記電気光学結晶基板の表面のうちの前記リッジ部の部分を除いた範囲に設けられた第２の電極とをさらに備える、請求項６に記載の複合基板。     The c-axis of the electro-optic crystal substrate is perpendicular to the electro-optic crystal substrate;
    The apparatus further comprises a first electrode provided on a top surface of the ridge portion and a second electrode provided in a range excluding a portion of the ridge portion on a surface of the electro-optic crystal substrate. 6. The composite substrate according to 6.
  9. 　前記リッジ部内には、不純物を含有する光導波路領域が、前記リッジ部の長手方向に沿って形成されている、請求項６から８のいずれか一項に記載の複合基板。 The composite substrate according to any one of claims 6 to 8, wherein an optical waveguide region containing impurities is formed in the ridge portion along a longitudinal direction of the ridge portion.
  10. 　前記低誘電率基板に対して前記電気光学結晶基板とは反対側に位置する導電層をさらに備える、請求項１から９のいずれか一項に記載の複合基板。 The composite substrate according to any one of claims 1 to 9, further comprising a conductive layer positioned on a side opposite to the electro-optic crystal substrate with respect to the low dielectric constant substrate.
  11. 　前記導電層に接合された支持基板をさらに備える、請求項１０に記載の複合基板。 The composite substrate according to claim 10, further comprising a support substrate bonded to the conductive layer.
  12. 　電気光学素子のための複合基板の製造方法であって、
    　電気光学効果を有する電気光学結晶基板の主表面に、前記電気光学結晶基板よりも屈折率の低い低屈折率層を成膜する工程と、
    　前記低屈折率層が成膜された前記電気光学結晶基板の前記主表面に、前記電気光学結晶基板よりも誘電率の低い低誘電率基板を直接接合する工程と、
    　を備える製造方法。     A method of manufacturing a composite substrate for an electro-optic element, comprising:
    Forming a low refractive index layer having a refractive index lower than that of the electro-optic crystal substrate on the main surface of the electro-optic crystal substrate having an electro-optic effect;
    Directly bonding a low dielectric constant substrate having a dielectric constant lower than that of the electro-optic crystal substrate to the main surface of the electro-optic crystal substrate on which the low refractive index layer is formed;
    A manufacturing method comprising:
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