CN113641011B

CN113641011B - Thin film electro-optic modulator and preparation method thereof

Info

Publication number: CN113641011B
Application number: CN202110961560.3A
Authority: CN
Inventors: 尹志军; 倪荣萍; 吴剑波; 叶志霖; 李胜雨; 张虞; 许志城
Original assignee: Nanjing Nanzhi Institute Of Advanced Optoelectronic Integration
Current assignee: Nanjing Nanzhi Institute Of Advanced Optoelectronic Integration
Priority date: 2021-08-20
Filing date: 2021-08-20
Publication date: 2023-08-25
Anticipated expiration: 2041-08-20
Also published as: CN113641011A

Abstract

The application discloses a thin film electro-optic modulator, which comprises a substrate layer (1), a piezoelectric thin film layer (3) and a grid electrode layer (4), wherein a ridge waveguide (6) is formed on one side of the piezoelectric thin film layer (3), and the ridge waveguide (6) and the grid electrode layer (4) are separated at two sides of the piezoelectric thin film layer (3), so that secondary etching can be performed on the piezoelectric thin film layer (3), and the ridge waveguide (6) has stronger binding capacity on optical waves, thereby reducing signal loss. The application also provides a method for preparing the thin film electro-optic modulator, which is prepared based on a low-cost substrate-free piezoelectric wafer, and uses a glaze material with silicon dioxide as a main component as an adhesive to connect the piezoelectric thin film layer (3) and the substrate layer (1), thereby breaking through the limitations of the traditional process and cost.

Description

Thin film electro-optic modulator and preparation method thereof

Technical Field

The application belongs to the field of semiconductor electro-optical devices, and particularly relates to a thin film electro-optical modulator and a preparation method thereof.

Background

Electro-optic modulators using electro-optic materials, e.g. lithium niobate crystals (LiNbO) ₃ ) Gallium arsenide crystals (GaAs) or lithium tantalate crystals (LiTaO) ₃ ) A modulator made of an electro-optic effect, wherein the electro-optic effect is the electro-opticWhen a voltage is applied to a material, the refractive index of the material changes, which causes the effect of changing the characteristics of light waves passing through the material, and the electro-optical modulator can be used for modulating the phase, the amplitude, the intensity and the polarization state of an optical signal.

Fig. 1 is a schematic cross-sectional structure of a conventional electro-optic modulator, as shown in fig. 1, a core component of the conventional electro-optic modulator is a waveguide made of electro-optic material, wherein the waveguide and a metal electrode are disposed on the same side of a piezoelectric thin film layer, and a loss rate of the signal in the waveguide is mainly affected by factors such as a height and a width of the waveguide, and a thickness of the piezoelectric thin film layer.

However, the conventional thin film waveguide electro-optic modulator requires ion implantation and bonding processes due to the process limitations of the conventional thin film waveguide electro-optic modulator, for example, the ion implanter and the bonding machine are expensive, which limits the preparation of the thin film of lithium niobate for many enterprises; in addition, the single bonding machine can only operate on a single sheet, so that the preparation of a large number of lithium niobate thin films becomes difficult, and the large-scale preparation is difficult; moreover, conventional thin-film electro-optic modulators are produced on the basis of piezoelectric thin films with substrates, which are correspondingly expensive due to the high price of the piezoelectric thin films.

Disclosure of Invention

In order to solve the above problems, the present application provides a thin film electro-optical modulator comprising a substrate layer 1, a piezoelectric thin film layer 3 and a grid electrode layer 4, wherein a ridge waveguide 6 is formed on one side of the piezoelectric thin film layer 3, and the ridge waveguide 6 and the grid electrode layer 4 are separated on both sides of the piezoelectric thin film layer 3, so that secondary etching can be performed on the piezoelectric thin film layer 3, so that the ridge waveguide 6 has a stronger binding capability for optical waves, thereby reducing signal loss. The application also provides a method for preparing the thin film electro-optic modulator, which is prepared based on a low-cost substrate-free piezoelectric wafer, and uses a glaze material with silicon dioxide as a main component as an adhesive to connect the piezoelectric thin film layer 3 and the substrate layer 1, thereby breaking through the limitations of the traditional process and cost.

The application aims to provide the following two aspects:

in a first aspect, the present application provides a thin film electro-optical modulator, which sequentially includes a substrate layer 1, a frit fusion layer 2, a piezoelectric thin film layer 3, a grid electrode layer 4, and an encapsulation layer 5, wherein the piezoelectric thin film layer 3 is formed with a ridge waveguide 6 on a side adjacent to the frit fusion layer 2, and the ridge waveguide 6 and the grid electrode layer 4 are separated on two sides of the piezoelectric thin film layer 3.

In one possible embodiment, a silicon dioxide layer 7 is also provided between the frit-sealing layer 2 and the piezoelectric film layer 3.

In one implementation manner, a waveguide groove 8 corresponding to the ridge waveguide 6 may be further formed on a side surface of the piezoelectric film layer 3 adjacent to the grid electrode layer 4, and the width of the waveguide groove 8 is not greater than the width of the ridge waveguide 6, so that the cross section of the ridge waveguide 6 forms a similar "concave" structure.

In one realisation, the waveguide grooves 8 have a depth of 0nm to 1 μm, preferably 10nm to 100nm.

In one implementation, the ridge waveguides 6 have two, and the two ridge waveguides 6 form a mach-zehnder structure.

Alternatively, the two ridge waveguides 6 in the Mach-Zehnder structure are partially parallel and have a pitch of 5 μm to 30 μm, preferably 10 μm to 20 μm.

In one realisation, the ridge waveguide 6 has a ridge height of 100nm to 5 μm, preferably 300nm to 1 μm.

In one implementation manner, the grid electrode layer 4 includes a plurality of electrode strips 41, optionally, the electrodes located at two sides of the mach-zehnder structure are ground electrodes, and the shape and the size of the electrodes are the same, and the electrodes located at the middle of the mach-zehnder structure are ground signal electrodes, and the shape and the size of the electrodes and the shape and the size of the ground electrodes may be different.

Alternatively, the electrode strip 41 is spaced from the linear portion of the ridge waveguide by a distance of 100nm to 5. Mu.m, preferably 300nm to 1. Mu.m.

In a second aspect, the present application also provides a method of making a thin film electro-optic modulator according to the first aspect, the method comprising:

preparing a waveguide structure on one side surface of a piezoelectric wafer;

preparing a glaze layer on the surface of a substrate material;

fusing the surface of the waveguide structure with a layer of frit;

thinning the piezoelectric wafer to obtain a piezoelectric film layer;

preparing a grid electrode layer on the surface of the piezoelectric film layer;

and preparing an encapsulation layer on the grid electrode layer.

In one implementation, the preparing the waveguide structure on the piezoelectric wafer surface includes photoresist and focused ion beam etching.

In one implementation, after the preparation of the waveguide structure is completed and before fusing the surface of the waveguide structure with the frit layer, it may further include: deposition of SiO on the surface of the prepared waveguide structure ₂ And performing planarization processing.

It will be appreciated that if the waveguide surface is deposited with SiO ₂ Fusing the surface of the waveguide structure with the glaze layer is to fuse SiO ₂ The layer is fused with the glaze layer.

In one implementation, the preparing the glaze layer on the surface of the substrate material may include:

coating glaze on the surface of the piezoelectric wafer;

and carrying out flattening treatment and shaping on the glaze.

Optionally, the main component of the glaze is silicon dioxide, and the auxiliary materials comprise: alumina, zinc oxide, ethylcellulose, solvents including: at least two of esters, ethers, alcohols and hydrocarbon compounds, generally, lipid and other types of compounds are mixed, the lipid can enable the slurry to have good lubricating performance, namely the slurry can be heated to be smoother, other materials are gasified in the heating process due to low boiling point, so that pores are relatively few after heating, the content of silicon dioxide is 50-200 g/mL based on the total volume of the glaze, the viscosity of the glaze is 50-400 Pa.s, the main component is high-purity silicon dioxide, the melting point of the glaze is lower than the melting point of a piezoelectric wafer, preferably, the glaze can be glass slurry, wherein the sintering temperature of the glass slurry is 470-550 ℃, the fineness is less than 8 mu m, the viscosity is 100-200 Pa.s, so that only the glaze is in a molten state in the process of preparing a composite piezoelectric substrate, the piezoelectric wafer is in a solid state, and the lattice structure of the piezoelectric wafer can be kept unchanged, so that the piezoelectric performance of the composite piezoelectric substrate is ensured.

Alternatively, the method of applying the glaze to the surface of the piezoelectric wafer includes brushing, suspension coating and spraying.

Further, the brushing includes:

paving a layer of silk screen on the piezoelectric wafer, wherein the thickness of the silk screen is 100-500 mu m, the grid of the silk screen can be square, the mesh size is 1-20 mm, and the material can be copper or stainless steel;

uniformly brushing a layer of glaze on the surface of the piezoelectric wafer through the silk screen, wherein the thickness of the glaze is smaller than or equal to that of the silk screen;

and removing the silk screen.

In the application, the suspension coating can be any suspension coating method which takes a wafer as an object in the prior art; the spraying can be any suspension coating method which can take a wafer as an object in the prior art.

In one possible implementation, planarizing and shaping the glaze includes:

heating the piezoelectric wafer coated with the glaze to the volatilization temperature of the glaze solvent, and preserving heat;

continuously heating to the melting point of the glaze, preserving heat and cooling.

Optionally, the glaze layer may be subjected to a surface treatment after the glaze cools and solidifies, the surface treatment including grinding and polishing. In the application, after surface treatment, the roughness of the surface of the glaze layer is less than 10nm, so that the upper and lower surfaces are parallel after the fusion of the substrate and the upper film is facilitated.

In one possible implementation, the frit layer has a thickness of 0.1 to 1000 μm to provide sufficient support for the piezoelectric wafer.

In one implementation manner, after the preparation of the glaze fusion layer is completed, the piezoelectric wafer may be thinned, and any method in the prior art for thinning the piezoelectric wafer may be adopted, for example, an ion implantation method, a grinding polishing method, and the like.

Further, the thickness of the piezoelectric wafer after the thinning process may be specifically set according to the needs of use.

In one implementation, the fusing the surface of the waveguide structure with the frit layer may include:

preparing a silicon dioxide layer on the waveguide structure;

heating the glaze layer to a molten state;

attaching the glaze layer to the silicon dioxide layer;

and (3) cooling the system.

In one implementation, the thinning the piezoelectric wafer to obtain the piezoelectric thin film layer may include ion implantation delamination method and grinding.

In one implementation, the preparation of the grid electrode layer on the surface of the piezoelectric film layer may include an electron beam evaporation coating method, magnetron sputtering, ion sputtering, and the like.

In one implementation, the encapsulation layer may be made of silicon dioxide.

Alternatively, the preparing the encapsulation layer on the grid electrode layer may include a thermal deposition method, magnetron sputtering, vacuum evaporation ion sputtering, and the like.

Compared with the prior art, the thin film electro-optical modulator is prepared based on the piezoelectric wafer with relatively low price, and the waveguide with the Mach-Zehnder structure and the metal electrode are respectively arranged on two sides of the piezoelectric thin film layer, so that the piezoelectric thin film layer can be further etched to form a relatively closed signal transmission space, and signals are completely bound in the waveguide structure in the transmission process, so that loss is reduced; the method for preparing the lithium acid film electro-optic modulator provided by the application is prepared based on a piezoelectric wafer with relatively low price, and the easily obtained glaze is used as an adhesive to connect the piezoelectric film layer and the substrate material, so that the production cost is greatly reduced, the structure of the personalized piezoelectric film layer can be conveniently prepared, the limitation and the cost restriction on the preparation process of the electro-optic modulator based on the piezoelectric film with the substrate are broken, and the glaze welding layer has no negative effect on the performance of the electro-optic modulator.

In addition, compared with the welding layer using organic compounds such as polymers and the like as the substrate layer and the lithium niobate layer, the application uses the inorganic glaze to prepare the welding layer, and the inorganic glaze has low production cost, can be purchased in China at present and has mature market; in addition, the inorganic glaze has stable performance, high temperature resistance and difficult aging after sintering; further, the dielectric constant and the resistivity of the fusion layer which can be prepared by the inorganic glaze with different proportions of the components can be different, so that the formulation of the inorganic glaze can be prepared according to the requirements.

Compared with the structure of the existing film photoelectric modulator, the film photoelectric modulator provided by the application is provided with the etchable waveguide groove position (8), so that the waveguide can be better restrained.

Experiments prove that the performance of the thin film electro-optic modulator provided by the application is equivalent to and even better than that of the traditional thin film electro-optic modulator.

Drawings

FIG. 1 is a schematic diagram showing a cross-sectional structure of a conventional electro-optic modulator;

FIG. 2 is a schematic diagram showing a cross-sectional structure of a thin film electro-optic modulator according to the present application;

FIG. 3 shows a perspective exploded view of the thin film electro-optic modulator of FIG. 2;

FIG. 4 is a schematic cross-sectional view showing another preferred thin film electro-optic modulator of this example;

fig. 5 shows a flow chart of a preferred method of making the lithium niobate thin film electro-optic modulator.

Description of the reference numerals

1-substrate layer, 2-frit fusion layer, 3-piezoelectric film layer, 4-grid electrode layer, 41-electrode strip, 5-packaging layer, 6-ridge waveguide, 7-silicon dioxide layer and 8-waveguide groove.

Detailed Description

Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, the same numbers in different drawings refer to the same or similar elements, unless otherwise indicated. The implementations described in the following exemplary examples do not represent all implementations consistent with the application. Rather, they are merely examples of methods consistent with aspects of the application as detailed in the accompanying claims.

The thin film electro-optic modulator and the preparation method thereof provided by the application are described in detail below by specific examples.

First, a brief description will be given of a usage scenario of the present solution.

With the increasing number of multimedia services, wireless access, internet access devices and mobile users, it is increasingly difficult for network broadband to meet the increasing network demands of people. One of the factors affecting the network bandwidth is the bandwidth of the optical modulator, and in order to obtain a larger network bandwidth, it is imperative to pursue an electro-optical modulator with higher quality in order to increase the data conversion speed and reduce the cost.

Fig. 2 shows a schematic cross-sectional structure of a thin film electro-optical modulator according to the present application, fig. 3 shows a perspective exploded view of the thin film electro-optical modulator shown in fig. 2, and as shown in fig. 2 and 3, the lithium niobate thin film electro-optical modulator sequentially includes a substrate layer 1, a frit fusion layer 2, a silicon dioxide layer 7, a piezoelectric thin film layer 3, a grid electrode layer 4, and a packaging layer 5, wherein the piezoelectric thin film layer 3 is formed with a ridge waveguide 6 on a side adjacent to the frit fusion layer 2, and the ridge waveguide 6 and the grid electrode layer 4 are separated on two sides of the piezoelectric thin film layer 3.

The material for preparing the substrate layer 1 is not particularly limited in this example, and any material that can be used as a piezoelectric thin film substrate in the prior art, for example, silicon dioxide, single crystal silicon, aluminum oxide, lithium tantalate, lithium niobate, or other semiconductor material, etc. may be used.

In this example, the thickness of the substrate layer 1 may be specifically set according to the requirements of the thin film electro-optical modulator, for example, the thickness of the substrate layer 1 is 5 μm to 20 μm.

In this example, the frit fusion layer 2 is void-free, and the inventors have found that the frit can eliminate voids therein during the fusion process, and finally a void-free frit fusion layer is obtained.

Further, the inventors have found that frit fusion layers prepared from different formulations of frit have slightly different properties, in particular slightly different parameters such as dielectric constant and conductivity. In this example, a dielectric constant of 3.4 to 6 and a conductivity of 3X 10 can be selected ^-2 ～3×10 ^-14 Ω ^-1 〃cm ^-1 To meet the performance requirements of the electro-optic modulator.

In this example, the thickness of the frit fusion layer 2 may be 20nm to 1 μm, so that the total volume of the thin film electro-optical modulator is substantially unchanged, thereby ensuring that the application range of the thin film electro-optical modulator at least meets the application range of the conventional thin film electro-optical modulator. Further, the thickness of the frit weld can be used to adjust the performance of the electro-optic modulator, i.e., a higher speed modulator can be obtained by adjusting the thickness of the frit weld, and in particular, impedance matching and wave speed matching can be obtained by adjusting the thickness of the frit weld 2.

In this example, the substrate layer 1 and the piezoelectric film layer 3 are fused together through the glaze fusion layer 2, and the inventor finds that a silicon dioxide layer 7 can be arranged between the glaze fusion layer 2 and the piezoelectric film layer 3, and the silicon dioxide layer 7 can serve as a transition layer to enable the bonding strength between the glaze fusion layer 2 and the piezoelectric film layer 3 to be larger, so that the structural stability of the final product film electro-optic modulator is improved.

In this example, the frit fusion layer 2 is prepared from a frit whose main component is silica, preferably high purity silica, and is supplemented with adjuvants and solvents, wherein the adjuvants include: alumina, zinc oxide, ethylcellulose, the solvent comprising: at least two of esters, ethers, alcohols and hydrocarbon compounds.

Alternatively, the solvent is a composition formed by a lipid compound and other compounds, and the inventor finds that the lipid compound can enable the glaze to have good lubricating performance, so that the glaze is smoother at a high temperature, and can be gasified during the temperature rising treatment of the glaze due to the lower boiling point of the lipid compound, namely, the lipid compound can be gasified before the glaze is completely solidified, so that pores in a welded layer of the obtained glaze are less, and the porosity of the welded layer 2 of the glaze is reduced.

In this example, the silica content is 50g/mL to 200g/mL, the viscosity of the glaze is 50pa·s to 400pa·s, preferably the glaze may be glass paste, doped glass paste or other binder with a melting point lower than that of the piezoelectric wafer, wherein the glass paste may have a sintering temperature of 470 ℃ -550 ℃, the fineness may be less than 8 μm, the viscosity may be 100pa·s to 200pa·s, and the melting point of the glaze is lower than that of the piezoelectric wafer, so that only the glaze is in a molten state during the preparation of the composite piezoelectric substrate, and the piezoelectric wafer is in a solid state, and the lattice structure of the piezoelectric wafer can be kept unchanged, so as to ensure the piezoelectric performance of the composite piezoelectric substrate.

The present inventors found that a frit-welded layer was produced using the above frit, the frit was treated to remove volatile components such as solvent, and finally a frit-welded layer 2 was formed on the substrate layer, and the frit-welded layer 2 was mainly composed of silica.

In this example, the thickness of the silica layer 7 is 20nm to 50nm, preferably 30nm to 40nm, and the inventors have found that the silica layer 7 of the above thickness is easy to prepare and can provide a sufficient transitional coupling effect for the frit fusion layer 2 and the piezoelectric thin film layer 3.

In this example, the piezoelectric film layer 3 may be any piezoelectric material film in the prior art, for example, a homogeneous lithium niobate film, a near stoichiometric lithium niobate film, a doped lithium niobate film, etc., and it is understood that other piezoelectric films in the prior art may be used.

The inventor finds that the lithium niobate crystal is an artificially synthesized negative uniaxial crystal and has higher piezoelectric coefficient, ferroelectric coefficient and acousto-optic coefficient, in particular, the lithium niobate crystal has higher electro-optic coefficient and lower half-wave voltage required by unit length, so that a device prepared by using the lithium niobate has long service life and stable working performance; the optical waveguide manufactured by the lithium niobate crystal can be directly coupled with the optical fiber, and the coupling loss is low; in theory, the optical waveguide prepared by using lithium niobate can realize zero chirp signal modulation, is hardly limited by optical fiber dispersion, is suitable for signal transmission of high-speed long-distance single-mode optical fibers, and is especially suitable for the optical fiber communication field with the working wavelength of about 1550 nm; since the traveling wave electrode structure is provided in the optical waveguide, the operation speed of the optical waveguide made of lithium niobate can be made very high, and therefore, the present application preferably uses lithium niobate as the piezoelectric material of the piezoelectric thin film electro-optical modulator.

In this example, the thickness of the piezoelectric thin film layer 3 may be 1 μm to 100 μm, and the present inventors have found that the thickness of the piezoelectric thin film layer 3 is within the above range, and the performance and size of the obtained thin film electro-optical modulator can meet the requirements.

The inventors have found that a thin film electro-optic modulator made of lithium niobate has a smaller volume than a thin film modulator made of other materials because of the relatively high electro-optic coefficient of lithium niobate.

In this example, the ridge waveguide 6 is disposed between the piezoelectric thin film layer 3 and the silicon dioxide layer 7, and the ridge waveguide 6 is integrally formed with the piezoelectric thin film layer 3, so that an acoustic-optical signal can propagate along the ridge waveguide.

In this example, the shape of the ridge waveguide 6 may be any shape of a thin film waveguide in the prior art, for example, may be a waveguide with a mach-zehnder structure, specifically, two ridge waveguides 6, and two ridge waveguides 6 form a mach-zehnder structure, and specifically, a mach-zehnder modulator structure includes two 1×2 optical splitters and two optical waveguides for transmitting light beams. The light beam is split into two light beams by a 1X 2 optical beam splitter, the phases of the two light waveguides are modulated differently by a grid electrode layer 4 which is sleeved on the surface of the piezoelectric film layer 3, and then the two light waveguides are combined into one beam to be output by the 1X 2 optical beam splitter.

In this example, the ridge waveguide 6 has a ridge height of 100nm to 5. Mu.m, preferably 300nm to 1. Mu.m.

In this example, the ridge waveguide has a width of 0nm to 1 μm, preferably 0nm to 100nm.

The inventor finds that the ridge waveguide with the specification can efficiently perform photoelectric conversion and optical information transmission, and has small occupied volume, thereby being convenient for the integration of devices.

In this example, the metal for preparing the grid electrode layer 4 may be gold, silver, aluminum, titanium, etc., since the above metals have a material resistivity ρ unit at 20 °: nΩ "m is respectively: silver 15.86, copper 16.78, gold 24, aluminum 26.548, bonding cost and difficulty in preparation process, gold is preferably used as the electrode material in the present application.

In this example, the grid electrode layer 4 includes a plurality of electrode bars 41, each of the electrode bars 41 being rectangular, each electrode bar 41 being parallel to a straight portion of the ridge waveguide 6 for use in a thin film electro-optic modulator.

Optionally, the electrodes at two sides of the mach-zehnder structure are ground electrodes, the shapes and the sizes of the ground electrodes are the same, the middle electrode of the mach-zehnder structure is a ground signal electrode, and the shapes and the sizes of the ground electrodes can be different from those of the ground electrodes.

Alternatively, the electrode strip 41 is spaced from the linear portion of the ridge waveguide by a distance of 100nm to 5. Mu.m, preferably 300nm to 1. Mu.m. The inventors have found that in the above-described position, the grid electrode layer 4 is able to obtain an electric field distribution modulated light field.

In this example, the grid electrode layer 4 is disposed between the piezoelectric thin film layer 3 and the encapsulation layer 5, that is, the ridge waveguide 6 and the grid electrode layer 4 are disposed on two sides of the piezoelectric thin film layer 3, so that the piezoelectric thin film layer 3, that is, the "back surface" of the ridge waveguide 6 is disposed between the adjacent electrode strips 41, so that secondary processing is performed on the ridge waveguide, that is, the "back surface" of the ridge waveguide 6 is removed from the corresponding portion of the piezoelectric thin film layer 3, thereby forming a similar "concave" structure, that is, providing a foundation for forming the waveguide groove 8.

Fig. 4 shows a schematic cross-sectional structure of another preferred thin film electro-optical modulator of this example, and as shown in fig. 4, the width of the waveguide groove 8 is not greater than the width of the ridge waveguide 6, and alternatively, the depth of the waveguide groove 8 is 0nm to 1 μm, preferably 10nm to 100nm. The inventors have found that the waveguide grooves 8 form the ridge waveguide 6 into a "concave" structure which is more conducive to confining the optical signal by the waveguide, thereby reducing signal loss and improving the performance of the thin film electro-optic modulator. Furthermore, the waveguide groove 8 with the specification can better restrict light in the waveguide, obtain a better optical waveguide mode and reduce the transmission loss of the light.

In this example, the encapsulation layer 5 may be made of silicon dioxide.

In this example, on the encapsulation layer 5, structures matching the electrode bars 41 and the piezoelectric thin film layer 3 are formed on the side adjacent to the grid electrode layer 4, so that the encapsulation layer 5 is closely attached to the grid electrode layer 4 and the piezoelectric thin film layer 3, thereby forming a thin film electro-optical modulator.

Fig. 5 shows a flowchart of a preferred method for preparing the lithium niobate thin film electro-optic modulator, as shown in fig. 5, the method includes the following steps S101 to S106:

in step S101, a waveguide structure is prepared on one side surface of the piezoelectric wafer.

In this example, the piezoelectric wafer is a raw material for preparing a piezoelectric thin film layer, and the diameter of the piezoelectric thin film layer is the same as that of the piezoelectric wafer, specifically, the piezoelectric wafer may be a homogeneous component lithium niobate thin film, a near stoichiometric ratio lithium niobate thin film, a doped lithium niobate thin film, or the like.

In this example, before the waveguide structure is manufactured, the piezoelectric wafer may be subjected to pretreatment such as cleaning and polishing, so that the surface of the piezoelectric wafer meets the requirement for manufacturing the piezoelectric film.

In this example, the preparation of the waveguide structure on the piezoelectric wafer surface includes a photoresist process and a focused ion beam etching process.

The present example illustrates a process of preparing a waveguide structure by using a photoresist method, and specifically, may include the following steps S111 to S116:

and S111, preparing a photoresist structure with a structure complementary with the ridge waveguide on the surface of the piezoelectric wafer.

In this example, the ridge waveguide is a mach-zehnder structure, and therefore, the photoresist is complementary to the mach-zehnder structure. The mach-zehnder structure is as described above and will not be described in detail herein.

Step S112, plating a metal mask on the surface of the piezoelectric wafer with the photoresist by using an electron beam coating method.

In this example, the metal for preparing the mask is not particularly limited, and may be any metal used in the prior art for lithography of piezoelectric material, for example, chromium (Cr) metal, or other metals available in the prior art.

Further, the thickness of the metal mask may be 50nm to 1 μm, and the specific thickness may be specifically set according to the kind of metal used to prepare the mask, the position and width of the metal, and the like.

And S113, removing the photoresist, and leaving a metal mask structure on the surface of the piezoelectric wafer.

The method for removing the photoresist in this example is not particularly limited, and any method of removing the photoresist on the surface of the piezoelectric wafer in the prior art, for example, a method of dissolving the photoresist using NMP solution (1-methyl-2 pyrrolidone solution) or acetone or the like, may be employed.

In this example, the width of the metal mask left on the surface of the piezoelectric wafer is the width of the ridge waveguide.

Step S114, etching the piezoelectric wafer, and transferring the metal mask structure to the surface of the piezoelectric wafer.

In this example, the method for etching the piezoelectric wafer is not particularly limited, and any method of etching the piezoelectric wafer according to a metal mask in the related art, for example, a method of reactive ion etching (ICP), may be employed.

In this example, the depth of the etch may be 100nm-5 μm, i.e., the ridge waveguide ridge height is about 100nm-5 μm.

In step S115, the remaining metal mask is removed.

The method for removing the residual metal mask in this embodiment is not particularly limited, and any method in the prior art for removing the metal mask on the piezoelectric wafer may be used.

And step S116, polishing the surface of the ridge waveguide.

In this example, the surface roughness of the ridge waveguide after polishing can be as low as 2nm or less, so that the loss of signals in the ridge waveguide can be reduced.

In this example, after step S116, the method may further include: deposition of SiO on the surface of the prepared waveguide structure ₂ And performing planarization processing.

The specific implementation of this step is not particularly limited, and any of the prior art techniques may be used to deposit SiO on the waveguide surface ₂ And performing planarization processing.

Step S102, preparing a glaze layer on the surface of the substrate material.

In this example, the present step may specifically include the following step S121 and step S122:

step S121, coating glaze on the surface of the piezoelectric wafer.

Further, the brushing includes:

and removing the silk screen.

Step S122, flattening the glaze and shaping.

In this example, the present step may include the following steps S1221 and S1222:

and S1221, heating the piezoelectric wafer coated with the glaze to the volatilization temperature of the glaze solvent, and preserving heat.

Step S1222, continuously heating to the melting point of the glaze, preserving heat and cooling.

In this example, after the temperature is raised to the melting point of the glaze, the glaze is uniformly formed into a film.

In this example, the frit layer has a thickness of 0.1 to 1000 μm, preferably 1 to 100 μm, for example, 20 to 60 μm after melting to provide sufficient support for the piezoelectric wafer.

And step S103, fusing the surface of the waveguide structure with the glaze layer.

In this example, the present step may include the following steps S131 to S134:

step S131, preparing a silicon dioxide layer on the waveguide structure.

In this example, the present step may include step S1311 and step S1312:

step S1311, preparing a silica coating on the waveguide structure, where the silica coating has the same structure as the waveguide.

In this example, the method of preparing the silica plating layer on the waveguide structure is not particularly limited, and any method of preparing the silica layer on the piezoelectric material in the prior art, for example, vapor deposition or the like, may be employed.

And step S1312, carrying out planarization processing on the silicon dioxide coating so that the surface of the silicon dioxide coating is planar, namely removing the waveguide structure on the surface of the silicon dioxide coating to form a silicon dioxide layer.

In this example, the thickness of the silicon oxide coating is slightly greater than the height of the waveguide structure, so that the waveguide structure can be completely buried in the silicon oxide layer after the silicon oxide coating is planarized, thereby enabling the glaze layer and the piezoelectric thin film layer to be stably bonded.

Step S132, heating the glaze layer to a molten state.

And step S133, attaching the glaze layer and the silicon dioxide layer.

In this example, after bonding the glaze in a molten state to the silica layer, 20g/cm was applied to the bonded body ² ～20000g/cm ² And maintaining the pressure at that temperature for 0.5 to 10 hours to allow the two to bond sufficiently.

Step S134, cooling the system.

In this example, the cooling rate may be 1-3 ℃/h to allow the bond to cool slowly, leaving the microstructure of the layers intact, avoiding chipping due to quenching.

And after the system is cooled, the glaze layer is welded with the silicon dioxide layer to form a glaze welding layer.

And step S104, thinning the piezoelectric wafer to obtain a piezoelectric film layer.

In this example, the thinning of the piezoelectric wafer to obtain the piezoelectric thin film layer may include ion implantation delamination method and grinding.

In order to facilitate the operation and reduce the production cost, the application preferably adopts a grinding method for thinning treatment.

Step S105, preparing a grid electrode layer on the surface of the piezoelectric film layer.

In this example, the present step may specifically include an electron beam evaporation plating method, magnetron sputtering, ion sputtering, and the like.

The present example is described taking an electron beam evaporation coating method as an example, and specifically includes the following steps S151 to S153:

step S151, preparing a photoresist structure on the surface of the piezoelectric film in step S104.

In this example, the photoresist structure is a structure complementary to the electrode grid structure.

In this example, the method of preparing the photoresist structure is not particularly limited, and any method of preparing the photoresist structure on the piezoelectric film in the prior art, for example, ultraviolet lithography or electron beam exposure may be employed.

And step S152, plating metal on the photoresist.

In this example, the metal is a metal electrode, e.g., gold.

Alternatively, the thickness of the metal is 100nm to 10 μm.

The width of each metal electrode bar and the spacing between adjacent electrode bars are as described above, and will not be described in detail herein.

Step S153, removing the photoresist.

And removing the photoresist to obtain a metal mask, namely the metal electrode strip.

The method for removing the photoresist is not particularly limited in this example, and may be a method of dissolving with a solvent such as NMP solution or acetone.

Optionally, after step S105, a waveguide groove may also be prepared on the piezoelectric thin film layer, and specifically, the following steps S151 'to S155' may be included:

and S151', preparing photoresist on the piezoelectric element.

And S152', preparing a metal film on the photoresist.

And S153', removing the photoresist, and leaving a metal mask structure on the voltage film layer.

And S154', etching the piezoelectric film layer, and transferring the metal mask structure onto the piezoelectric film layer.

And S155', removing the metal mask.

Thereby obtaining a waveguide groove, the depth of which can be specifically set as required.

And step S106, preparing an encapsulation layer on the grid electrode layer.

In this example, the encapsulation layer may be a silicon dioxide layer, and optionally, the encapsulation is to prepare a layer of silicon dioxide on the grid electrode layer.

In this example, the encapsulation layer is deposited on the surface of the grid electrode by PECVD with a silicon dioxide layer having a thickness of 1-20 μm.

Examples

Example 1

Taking a 4-inch lithium niobate piezoelectric wafer, polishing and cleaning the technological surface of the wafer, and preparing a waveguide structure on the technological surface;

preparing a silicon dioxide coating on the waveguide structure, and carrying out planarization treatment on the silicon dioxide coating to obtain a silicon dioxide layer, wherein the surface flatness of the silicon dioxide layer is less than 20nm;

coating a layer of glaze on the surface of a substrate material by adopting a grid method, and flattening the glaze;

fusing the surface of the waveguide structure with a layer of frit;

thinning the lithium niobate wafer in a grinding and polishing mode to obtain a lithium niobate thin film layer on the substrate material;

preparing a grid electrode layer on the surface of the lithium niobate thin film layer in an evaporation mode;

and preparing a silicon dioxide packaging layer on the grid electrode layer.

The electro-optical modulator prepared by the method of the embodiment does not need to use lithium niobate thin film raw materials (about 6000 yuan in market price), and the total cost price of the thin film sheet prepared by the method is about 2500 yuan, so that the production cost is greatly reduced.

Comparative example

Comparative example 1

At present, the lithium niobate thin film electro-optic modulator is in a monopoly stage abroad, and cannot be commercially available in China at present, and the cross-section structures of a lithium niobate waveguide and an electrode of the foreign hypersight thin film electro-optic modulator can be shown by referring to fig. 1.

The inventor finds that in the traditional scheme, the piezoelectric film (taking 4 inches as an example, the price of the lithium niobate film is about 15000 yuan) is used as the basis for etching to obtain the ridge waveguide, however, in the etching process of the ridge waveguide, the poor mouth rate of the film electro-optic modulator is higher because of the insufficient smoothness of the side wall of the ridge waveguide caused by the inherent error existing in the process, and the cost of the piezoelectric film is higher, so that the cost of the film electro-optic modulator is limited to be a key factor of the cost of the film electro-optic modulator, and therefore, the cost of the film electro-optic modulator prepared by adopting the traditional scheme is high; the method provided by the application adjusts the preparation procedure, and adopts the scheme that the ridge waveguide is etched on the piezoelectric wafer (the price of a single lithium niobate wafer is lower than 1000 yuan) with relatively low cost (still taking 4 inches as an example), and then the piezoelectric wafer with the ridge waveguide is used for preparing the film, so that the shape of the ridge waveguide can be screened in the first step of product preparation, unqualified products are removed, if the shape of the ridge waveguide is unqualified, the ridge waveguide can be removed by polishing and other methods, and the piezoelectric wafer is continuously used for preparing the ridge waveguide again, thereby further saving the production cost.

Secondly, the solution provided by the application is to first deposit a layer of silicon dioxide on the piezoelectric wafer and fuse the frit to the substrate material, which are fused together by the silicon dioxide layer and frit and form a stable bond. Since the piezoelectric film and the deposited silicon dioxide layer directly affect the performance of the device, the selected glaze, namely the glaze fusion layer, has little influence on the performance of the film electro-optic modulator, namely the method provided by the application can increase the selectable range of the substrate material and increase the process flexibility.

In addition, the traditional thin film electro-optical modulator is prepared based on the piezoelectric film, so that the relative position relation between the metal electrode and the ridge waveguide can only be shown in fig. 1, namely, the metal electrode and the ridge waveguide are positioned on the same side of the piezoelectric film, so that the traditional thin film electro-optical modulator is not provided with waveguide grooves, and the relative position relation between the grid electrode and the ridge waveguide in the thin film electro-optical modulator prepared by the method provided by the application can be shown in fig. 2, namely, the grid electrode and the ridge waveguide are separated on two sides of the piezoelectric film, so that the ridge waveguide can be further etched to obtain the waveguide grooves, the waveguide has stronger constraint capability on an electro-optical signal, and therefore, the loss of the signal is reduced, and in addition, the grid electrode has larger parameter change space to obtain wave speed matching and impedance matching.

The application has been described in detail in connection with the specific embodiments and exemplary examples thereof, but such description is not to be construed as limiting the application. It will be understood by those skilled in the art that various equivalent substitutions, modifications or improvements may be made to the technical solution of the present application and its embodiments without departing from the spirit and scope of the present application, and these fall within the scope of the present application. The scope of the application is defined by the appended claims.

Claims

1. The utility model provides a film electro-optic modulator, its characterized in that, electro-optic modulator includes substrate layer (1), frit butt fusion layer (2), piezoelectricity thin film layer (3), grid electrode layer (4) and encapsulation layer (5) in proper order, wherein, piezoelectricity thin film layer (3) are formed with ridge waveguide (6) in the one side adjacent with frit butt fusion layer (2), ridge waveguide (6) with grid electrode layer (4) divide and living in the both sides of piezoelectricity thin film layer (3), wherein, frit butt fusion layer (2) are prepared by the frit, the principal component of frit is silica to assist auxiliary material and solvent, wherein, the auxiliary material includes: alumina, zinc oxide, ethylcellulose, the solvent comprising: at least two of esters, ethers, alcohols and hydrocarbons.

2. A thin film electro-optical modulator according to claim 1, characterized in that a silicon dioxide layer (7) is further provided between the frit fusion layer (2) and the piezoelectric thin film layer (3).

3. A thin film electro-optical modulator according to claim 1 or 2, characterized in that waveguide grooves (8) corresponding to the ridge waveguides (6) are provided on the sides of the piezoelectric thin film layer (3) adjacent to the grid electrode layer (4), the width of the waveguide grooves (8) being not greater than the width of the ridge waveguides (6).

4. A thin film electro-optic modulator according to claim 1 or 2, characterized in that the ridge waveguide (6) has a ridge height of 100nm to 5 μm.

5. A thin film electro-optic modulator according to claim 1 or 2, characterized in that the ridge waveguide (6) has a ridge height of 300nm to 1 μm.

6. A method of making the thin film electro-optic modulator of any one of claims 1 to 5, the method comprising:

preparing a waveguide structure on one side surface of a piezoelectric wafer;

preparing a glaze layer on the surface of a substrate material;

fusing the surface of the waveguide structure with a layer of frit;

thinning the piezoelectric wafer to obtain a piezoelectric film layer;

and preparing an encapsulation layer on the grid electrode layer.

7. The method of claim 6, wherein preparing the frit layer on the surface of the substrate material comprises:

coating glaze on the surface of the piezoelectric wafer;

and carrying out flattening treatment and shaping on the glaze.

8. The method of claim 6, wherein the method of applying the glaze to the surface of the piezoelectric wafer comprises brushing, suspension coating, and spraying.

9. The method of claim 8, wherein the brushing comprises:

paving a layer of silk screen on the piezoelectric wafer;

uniformly brushing a layer of glaze on the surface of the piezoelectric wafer through the silk screen;

and removing the silk screen.

10. The method of claim 6, wherein the thinning the piezoelectric wafer to obtain the piezoelectric thin film layer comprises ion implantation delamination method and lapping polishing.

11. The method of claim 6, wherein preparing a grid electrode layer on the surface of the piezoelectric thin film layer comprises an electron beam evaporation coating method and magnetron sputtering.

12. The method of claim 6, wherein said preparing an encapsulation layer on said grid electrode layer comprises thermal deposition, magnetron sputtering and vacuum evaporation ion sputtering.