Non-cladding optical waveguide modulation structure based on piezoelectric driving and manufacturing method

Abstract

The invention discloses a cladding-free optical waveguide modulation structure based on piezoelectric driving and a manufacturing method thereof, and mainly solves the problems of poor effect of stress and strain transmitted to an optical waveguide structure and difficulty in device size reduction caused by relatively thick cladding in an existing piezoelectric driving tunable device. According to the scheme, a substrate, a sacrificial layer and a waveguide modulation area are arranged from bottom to top, and the sacrificial layer is subjected to cavity digging treatment; wherein the waveguide modulation area comprises a piezoelectric structure and an optical waveguide structure, the piezoelectric structure is a single piezoelectric structure formed by a bottom electrode, a piezoelectric layer and a top electrode, or a dual-voltage structure formed by two single piezoelectric structures; the optical waveguide structure is a strip-shaped waveguide or a ridge-shaped waveguide, and the waveguide is not wrapped by a wrapping layer; and the optical waveguide structure in the waveguide modulation area is in close contact with the piezoelectric layer. According to the invention, the thickness of the device can be reduced, the distance between the optical waveguide and the piezoelectric structure is shortened, the tuning efficiency of phase modulation when an optical signal is propagated in the waveguide is remarkably improved, and the device cost is reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photonic integrated devices, further relates to composite modulation technology, and in particular to a cladding-free optical waveguide modulation structure based on piezoelectric driving and a manufacturing method thereof, which can be used in the fields of optical communication, piezoelectric actuators and optical signal processing. BACKGROUND

[0002] Optical communication optical interconnection technology uses photons as a transmission carrier, can realize wideband, low delay and long distance information transmission, has strong anti-interference ability and no interconnection heat production, and has attracted widespread attention. Electronic integrated circuits are currently limited by problems such as large crosstalk and difficult thermal management caused by high integration and high interconnection density, and more and more people focus on the field of optical communication. In an optical communication link, the high-speed propagation of an optical signal in an optical fiber is used to transmit a target signal from one end to the other end, so it is very important to modulate and demodulate the target signal onto the optical signal. The performance of the modulator largely determines the transmission effect of the target signal on the photonic link. At present, the optoelectronic integrated chip based on a silicon-on-insulator platform, the silicon device mainly modulates the optical signal through thermal energy, which has a large energy consumption and faces natural disadvantages in the design and preparation of low-power tuning devices, high-speed modulator devices and nonlinear devices. The piezoelectric effect driven optical waveguide material can improve the above problems and become the development direction of the next generation of optoelectronic integrated chips.

[0003] The piezoelectric effect is that when an external mechanical force or pressure is applied, some crystal materials will generate positive and negative charges, forming an electric field inside, and after the external force is removed, the crystal returns to the original state. When an external electric field is applied to these crystal materials, the crystal materials deform and the refractive index changes. Due to the progress and maturity of thin film deposition and growth technology, many low-loss and high piezoelectric coefficient piezoelectric thin films have been successfully prepared, such as aluminum nitride (AlN), lithium niobate (LiNbO3), hafnium dioxide (HfO2), lead zirconate titanate (PZT), etc. Integrated photon technology based on piezoelectric effect has developed rapidly. Piezoelectric driving optoelectronic integrated devices can realize low-power tuning, and compared with thermal-optical tuning in silicon materials, the power consumption of piezoelectric driving can be reduced by 3-5 orders of magnitude, which has great significance for realizing low-power driving and large-scale optoelectronic integrated chips in kHz to GHz response frequency application scenarios.

[0004] The inverse piezoelectric effect is that the piezoelectric body deforms under the action of an external electric field, and the deformation is proportional to the intensity of the external electric field. In the field of optoelectronic integrated devices, piezoelectric-driven tunable devices are designed and prepared based on this effect. When an external electric field is applied to the piezoelectric material, stress and deformation will be generated in the piezoelectric material due to the inverse piezoelectric effect. On the one hand, under the action of stress, the refractive index of the waveguide material will change due to the elasto-optic effect. On the other hand, the displacement of the optical waveguide boundary occurs under the action of deformation, the optical path changes, and the effective refractive index changes, ultimately leading to the phase change of the optical signal in the waveguide, realizing optical tuning.

[0005] In existing piezoelectric tunable optoelectronic devices, silicon dioxide is usually used as the cladding material of the optical waveguide, and its refractive index is about 1.46, which is much smaller than the refractive index of common optical waveguide materials, so it can well confine the optical signal in the optical waveguide; in addition, silicon dioxide is an excellent insulating material, which can well isolate the piezoelectric structure from the optical waveguide, avoiding the contact between the metal electrodes in the piezoelectric structure and the optical waveguide, which leads to the absorption of the optical signal. However, the silicon dioxide cladding needs a relatively thick size to achieve the above functions, which leads to a thicker device, which is not conducive to the miniaturization of the device size; moreover, part of the stress and strain generated by the piezoelectric structure through the inverse piezoelectric effect is distributed in the cladding material, and the effect of transmission to the optical waveguide is poor, resulting in low piezoelectric tuning efficiency. If the optical waveguide is not protected by the silicon dioxide cladding, the piezoelectric assembly is in close contact with the optical waveguide, and the absorption of the optical signal in the optical waveguide by the metal electrode cannot be solved. SUMMARY

[0006] The present application aims at the deficiencies of the prior art, and proposes a cladding-free optical waveguide modulation structure based on piezoelectric driving and a manufacturing method, which is used to solve the problem of large size and low tuning efficiency of the optical waveguide modulator caused by the oxide cladding material in the prior art. By placing the optical waveguide in the center of the piezoelectric layer, designing a modulation structure in which the piezoelectric structure is in close contact with the waveguide structure, and isolating the optical waveguide from the metal electrode by the piezoelectric layer, or by removing the cladding material of the optical waveguide and exposing the optical waveguide to air, the optical signal is confined in the waveguide by air; thereby reducing the thickness of the device and enhancing the effect of the piezoelectric structure on the optical waveguide; in addition, a large cavity is provided below the piezoelectric structure to make the piezoelectric structure suspended, thereby enhancing the vibration effect of the device under an external voltage, and the stress and strain generated by the inverse piezoelectric effect of the piezoelectric material are transmitted to the waveguide, thereby enhancing the piezoelectric tuning efficiency. The present application can effectively reduce the size of the device, and significantly improve the tuning efficiency of the phase modulation of the optical signal propagating in the waveguide.

[0007] In order to solve the above problems, the technical scheme adopted by the present application comprises:

[0008] A piezoelectric driving uncladded optical waveguide modulation structure, from bottom to top, sequentially comprises a substrate 1, a sacrificial layer 2 and a waveguide modulation region 3;

[0009] The sacrificial layer 2 is a hollow silica layer processed by cavity hollowing;

[0010] The waveguide modulation region 3 comprises a piezoelectric structure and an optical waveguide structure 32; wherein the piezoelectric structure is a single piezoelectric structure 31 or a double piezoelectric structure; the single piezoelectric structure 31 is composed of a bottom electrode 311, a piezoelectric layer 312 and a top electrode 313; the double piezoelectric structure is composed of two single piezoelectric structures 31;

[0011] The optical waveguide structure 32 is a strip waveguide 321 or a slab waveguide 322, or a ridge waveguide composed of the two; the waveguide is not wrapped by a cladding layer;

[0012] In the waveguide modulation region 3, the optical waveguide structure 32 is in close contact with the piezoelectric layer 312 in the piezoelectric structure 31.

[0013] Further, the substrate 1 is made of silicon or sapphire; the optical waveguide structure 32 is made of any one of silicon, silicon nitride, lithium niobate and aluminum nitride; the bottom electrode 311 is made of any one of platinum, molybdenum and titanium; the top electrode 313 is made of any one of indium tin oxide, aluminum, gold and rubidium oxide; the piezoelectric layer 312 is made of any one of lead zirconate titanate, lithium niobate, doped hafnium oxide and doped aluminum nitride.

[0014] Further, the piezoelectric layer 312 is made of doped hafnium oxide or doped aluminum nitride; when the doped hafnium oxide is used, the doping element is any one of zirconium Zr, yttrium Y and silicon Si, and the doping mode is substitutional doping or interstitial doping; specifically, the doping element zirconium Zr or yttrium Y is doped in hafnium oxide by substitutional doping, and the doping ratio is 33-67% and 1-5%, respectively; the doping element silicon Si is doped in hafnium oxide by interstitial doping, and the doping ratio is 3-7%; when the doped aluminum nitride is used, the doping element is scandium Sc or boron B, and specifically, the doping element is doped in aluminum nitride by substitutional doping, and the doping ratio is 0-40%.

[0015] Further, the thickness of the optical waveguide structure 32 and the piezoelectric layer (312) is greater than 100 nm, and the thickness of the optical waveguide structure 32 is less than the thickness of the piezoelectric layer 312; the thickness of the bottom electrode 311 and the top electrode 313 is greater than 50 nm and less than 100 nm.

[0016] Further, the positional relationship between the optical waveguide structure 32 and the piezoelectric structure includes that the optical waveguide structure (32) is located at the center of the piezoelectric structure, the optical waveguide structure 32 is located above the piezoelectric structure, and the optical waveguide structure 32 is located below the piezoelectric structure.

[0017] Meanwhile, the application further provides a preparation method of the piezoelectric driving uncladded optical waveguide modulation structure, comprising the following steps:

[0018] S1. selecting a substrate material and pre-treating the same to obtain a pre-treated substrate;

[0019] S2. growing a sacrifice layer on the pre-treated substrate by plasma enhanced chemical vapor deposition (PECVD);

[0020] S3. depositing a metal electrode on the sacrifice layer by electron beam evaporation or magnetron sputtering process, as a bottom electrode of the device;

[0021] S4. depositing and growing a piezoelectric layer on the bottom electrode layer by magnetron sputtering process;

[0022] S5. coating a positive photoresist on the piezoelectric layer for photoetching and developing, and then washing away the photoresist in the middle part after developing, and then depositing and growing an optical waveguide film by magnetron sputtering process, to obtain an optical waveguide layer in the middle part after removing the photoresist;

[0023] S6. depositing and growing a piezoelectric layer covering the optical waveguide layer on the structure obtained in step S5 by magnetron sputtering process, and then polishing the same by chemical mechanical polishing (CMP);

[0024] S7. depositing a metal electrode on the polished piezoelectric layer by electron beam evaporation or magnetron sputtering process, as a top electrode of the device;

[0025] S8. continuously coating a positive photoresist for photoetching, and then etching the top electrode-piezoelectric layer-bottom electrode in sequence by inductively coupled plasma-reactive ion etching (ICP-RIE) technology until the sacrifice layer, to obtain a release groove structure;

[0026] S9. placing the structure in a hot phosphoric acid solution, and then removing the sacrifice layer below the waveguide modulation region through the release groove structure, so that the piezoelectric structure is suspended;

[0027] S10. completing the preparation process to obtain the piezoelectric driving uncladded optical waveguide modulation structure.

[0028] Compared with the prior art, the application has the following advantages:

[0029] First, because this invention exposes the optical waveguide to the air or encapsulates it with a piezoelectric layer material, without using an oxide cladding material to encapsulate the optical waveguide, it effectively reduces the device size and thickness, which is beneficial for device miniaturization, increases on-chip device density, and reduces costs. At the same time, not using a cladding material reduces the distance between the optical waveguide and the piezoelectric structure, avoiding the dispersion of stress generated by the cladding, making the stress and strain transmitted to the optical waveguide more concentrated, and significantly increasing the deformation of the optical waveguide.

[0030] Secondly, the modulation region designed in this invention has a suspended structure below it. The cavity between the piezoelectric layer and the substrate can effectively reduce the downward leakage of energy, thereby enhancing the vibration effect of the piezoelectric structure, generating greater stress and strain, and improving the modulation efficiency of the optical waveguide phase. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0032] Figure 2 The embodiments of the present invention provide a basis for... Figure 1 The simulation results of the stress distribution of the structure shown are displayed under an applied voltage of 1V.

[0033] Figure 3 for Figure 1 Schematic diagram of the waveguide region in the structure;

[0034] Figure 4 for Figure 1 Schematic diagrams of piezoelectric and waveguide structures; where (a) is the piezoelectric structure and (b) is the waveguide structure;

[0035] Figure 5 This is a schematic diagram of the modulation structure of the strip waveguide located at the center of the single piezoelectric structure in an embodiment of the present invention;

[0036] Figure 6 This is a schematic diagram of the modulation structure of the strip waveguide located at the center of the upper and lower double piezoelectric structures provided in an embodiment of the present invention;

[0037] Figure 7 This is a schematic diagram of the modulation structure of the strip waveguide located at the center of the left and right double piezoelectric structures provided in an embodiment of the present invention;

[0038] Figure 8 This is a schematic diagram of the modulation structure provided in an embodiment of the present invention, in which a strip waveguide is located below a single piezoelectric structure.

[0039] Figure 9 This is a schematic diagram of a modulation structure where a strip waveguide is located above a single piezoelectric structure, as provided in an embodiment of the present invention.

[0040] Figure 10Modulation structure schematic diagram of the ridge waveguide provided in the embodiment of the present application is located below the double piezoelectric structure;

[0041] Figure 11 Modulation structure schematic diagram of the ridge waveguide provided in the embodiment of the present application is located above the double piezoelectric structure;

[0042] Figure 12 One-dimensional photonic crystal nanobeam resonator modulator schematic diagram constructed based on the structure of the present application;

[0043] Figure 13 MZ modulator schematic diagram constructed based on the structure of the present application;

[0044] Figure 14 Micro-ring modulator schematic diagram constructed based on the structure of the present application;

[0045] Figure 15 Realization process schematic diagram of the optical waveguide modulation structure of the present application;

[0046] Figure 16 Modulation structure schematic diagram of the slab waveguide provided in the embodiment of the present application is located in the center of the single piezoelectric structure;

[0047] Figure 17 Modulation structure schematic diagram of the slab waveguide provided in the embodiment of the present application is located in the center of the double piezoelectric structure from top to bottom;

[0048] Figure 18 Modulation structure schematic diagram of the slab waveguide provided in the embodiment of the present application is located in the center of the double piezoelectric structure from left to right. DETAILED DESCRIPTION

[0049] The application will be further described in detail below with reference to the accompanying drawings.

[0050] Embodiment one: refer to Figures 1-11 The present application provides a piezoelectric driven unclad optical waveguide modulation structure, which comprises, from bottom to top, a substrate 1, a sacrificial layer 2 and a waveguide modulation region 3; the sacrificial layer 2 is a hollow silica layer processed by cavity hollowing; the waveguide modulation region 3 comprises a piezoelectric structure and an optical waveguide structure 32; the piezoelectric structure is a single piezoelectric structure 31 or a double piezoelectric structure; the single piezoelectric structure 31 is composed of a bottom electrode 311, a piezoelectric layer 312 and a top electrode 313; the double piezoelectric structure is composed of two single piezoelectric structures 31; the optical waveguide structure 32 is a strip waveguide 321 or a slab waveguide 322, or a ridge waveguide composed of the two; the waveguide is not wrapped by a cladding layer; in the waveguide modulation region 3, the optical waveguide structure 32 is in close contact with the piezoelectric layer 312 in the piezoelectric structure 31.

[0051] In this embodiment, the substrate 1 is made of silicon or sapphire; the optical waveguide structure 32 is made of any one of silicon, silicon nitride, lithium niobate, or aluminum nitride; the bottom electrode 311 is made of any one of platinum, molybdenum, or titanium; the top electrode 313 is made of any one of indium tin oxide, aluminum, gold, or rubidium oxide; and the piezoelectric layer 312 is made of any one of lead zirconate titanate, lithium niobate, hafnium oxide, or aluminum nitride. The piezoelectric layer 312 described above uses hafnium oxide or aluminum nitride doped material. When hafnium oxide is used, the doping element is any one of zirconium (Zr), yttrium (Y), or silicon (Si), and the doping method is substitutional doping or interstitial doping. Specifically, substitutional doping is used to dop the doping element zirconium (Zr) or yttrium (Y) into hafnium oxide, with doping ratios of 33-67% and 1-5%, respectively; interstitial doping is used to dop the doping element silicon (Si) into hafnium oxide, with a doping ratio of 3-7%. When aluminum nitride is used, the doping element is scandium (Sc) or boron (B), specifically, substitutional doping is used to dop the doping element into aluminum nitride, with a doping ratio of 0-40%. The optical waveguide structure 32 and the piezoelectric layer (312) mentioned above both have a thickness greater than 100 nm, and the thickness of the optical waveguide structure 32 is less than the thickness of the piezoelectric layer 312; the thickness of the bottom electrode 311 and the top electrode 313 are both greater than 50 nm and less than 100 nm.

[0052] The positional relationship between the optical waveguide structure 32 and the piezoelectric structure proposed in this embodiment includes: the optical waveguide structure (32) is located at the center of the piezoelectric structure, the optical waveguide structure 32 is located above the piezoelectric structure, and the optical waveguide structure 32 is located below the piezoelectric structure. Regarding the positional relationship between the piezoelectric structure and the waveguide, in Figure 1 Based on the structure shown, various structural evolutions can be made. The waveguide can be a strip waveguide, a planar waveguide, or a ridge waveguide composed of both. The piezoelectric structure can be a single piezoelectric structure or a double piezoelectric structure.

[0053] Example 2: The optical waveguide modulation structure proposed in this example is the same as in Example 1, and will now be referred to... Figures 5-7 A specific example is given when the optical waveguide structure 32 is located at the center of the piezoelectric structure:

[0054] When the optical waveguide structure 32 is located at the center of the piezoelectric structure, a strip waveguide 321 is preferably used, and the piezoelectric structure is a single piezoelectric structure 31 or a double piezoelectric structure.

[0055] a) When the piezoelectric structure is a single piezoelectric structure 31, such as Figure 5As shown, the structure is located above the sacrificial layer 2, wherein the bottom electrode 311 is in close contact with the sacrificial layers 2 on both sides below, and there is a cavity between the middle of the bottom electrode 311 and the substrate 1 below, and the two do not contact each other; the piezoelectric layer 312 is located above the bottom electrode 311 and wraps the strip waveguide 321 in its center; the top electrode 313 is located above the piezoelectric layer 312.

[0056] b) When the piezoelectric structure is a double piezoelectric structure, such as Figure 6 and Figure 7 As shown, the structure consists of two single piezoelectric structures 31 placed vertically or horizontally on the strip waveguide 321; when the dual piezoelectric structure consists of two single piezoelectric structures 31 placed vertically on the strip waveguide 321, as shown... Figure 6 As shown, the strip waveguide 321 is located at the center of the upper and lower single piezoelectric structures, and its upper and lower interfaces are in close contact with the piezoelectric layers of the upper and lower single piezoelectric structures 31, respectively; when the dual piezoelectric structure is composed of two single piezoelectric structures 31 placed at the left and right positions of the strip waveguide 321, as shown... Figure 7 As shown, the strip waveguide 321 is located in the middle of the two single piezoelectric structures on the left and right, and its sidewalls are in close contact with the piezoelectric layers of the single piezoelectric structures on the left and right sides, respectively. Specifically: when the dual piezoelectric structure is composed of two single piezoelectric structures 31 placed above and below the strip waveguide 321, the strip waveguide 321 is located at the center of the two single piezoelectric structures, and its upper and lower interfaces are in close contact with the piezoelectric layers of the two single piezoelectric structures 31, respectively; the lower single piezoelectric structure includes a first bottom electrode, a first piezoelectric layer, and a first top electrode, wherein the two ends of the lower surface of the first bottom electrode are in close contact with the sacrificial layer 2, and a cavity that does not contact the substrate 1 is formed in the middle; the first piezoelectric layer is located on the upper surface of the first bottom electrode, and is in close contact with the substrate 1. The strip waveguide 321 directly above it is in close contact; the first top electrode is located on the upper surface of the first piezoelectric layer and is distributed on both sides of the strip waveguide 321 and in close contact with its sidewalls; the single piezoelectric structure above includes a second bottom electrode, a second piezoelectric layer and a second top electrode, wherein the second top electrode is located on the upper surface of the second piezoelectric layer and is in close contact with it; the second piezoelectric layer is in close contact with the strip waveguide 321 directly below it, and the second bottom electrode is located on the lower surface of the second piezoelectric layer and is distributed on both sides of the strip waveguide 321 and in close contact with its sidewalls. When the dual piezoelectric structure is composed of two single piezoelectric structures 31 placed on the left and right sides of the strip waveguide 321, the strip waveguide 321 is located in the middle of the two single piezoelectric structures, and its sidewalls are in close contact with the piezoelectric layers of the two structures, and form a cavity that does not contact each other with the substrate 1 directly below. The bottom electrodes of the two single piezoelectric structures are in close contact with the sacrificial layers 2 on the left and right sides below, respectively, and the middle part near the strip waveguide 321 forms a cavity with the substrate 1 below. The piezoelectric layers are all located above the bottom electrodes and are in close contact with the left and right sidewalls of the strip waveguide 321, respectively, and the top electrodes are all located on the upper surface of the piezoelectric layers.

[0057] This embodiment uses a strip waveguide 321 as an example. When the optical waveguide structure 32 is located at the center of the piezoelectric structure, a planar waveguide can also be used to replace the strip waveguide to form the waveguide modulation region. Its placement is similar to that of the strip waveguide structure, such as... Figures 16-18 As shown, it will not be elaborated upon here.

[0058] Example 3: The optical waveguide modulation structure proposed in this example is the same as in Example 1, and will now be referred to... Figures 8-11 Specific examples are given when the optical waveguide structure 32 is located above or below the piezoelectric structure:

[0059] When the optical waveguide structure 32 is located above or below the piezoelectric structure, the optical waveguide structure 32 adopts a strip waveguide 321 or a ridge waveguide, wherein the ridge waveguide is composed of a strip waveguide 321 and a planar waveguide 322; if a strip waveguide 321 is used, the piezoelectric structure is a single piezoelectric structure, such as... Figure 8 and Figure 9 As shown; if a ridge waveguide is used, the piezoelectric structure is a double piezoelectric structure, such as... Figure 10 and Figure 11 As shown. Specifically includes:

[0060] When the optical waveguide structure 32 is a strip waveguide 321 and is located directly above the single piezoelectric structure 31, as shown... Figure 8 As shown, the strip waveguide 321 is in close contact with the piezoelectric layer 312 below; the piezoelectric structure 31 is a single piezoelectric structure 31, located above the sacrificial layer 2, wherein the bottom electrode 311 is in close contact with the sacrificial layers 2 on both sides below, and there is a cavity between the middle part and the substrate 1 below, and the two do not contact each other, but are in close contact with the piezoelectric layer 312 above. The piezoelectric layer 312 is located above the bottom electrode 311 and in close contact with the strip waveguide 321 directly above. The top electrode 313 is located to the upper left and upper right of the piezoelectric layer 312 and does not contact the sidewall of the strip waveguide 321.

[0061] When the optical waveguide structure 32 is a strip waveguide 321 and is located directly below the single piezoelectric structure 31, as shown... Figure 9 As shown, the strip waveguide 321 is in close contact with the upper piezoelectric layer 312, and there is a cavity between it and the lower substrate 1, so the two do not contact each other; the piezoelectric structure 31 is a single piezoelectric structure 31, located above the sacrificial layer 2, wherein the bottom electrode 311 is in close contact with the sacrificial layers 2 on both sides below, and there is a cavity between the middle part near the strip waveguide 321 and the lower substrate 1, so the two do not contact each other, and is in close contact with both sides of the upper piezoelectric layer 312, located at the lower left and lower right of the piezoelectric layer 312. The piezoelectric layer 312 is located above the bottom electrode 311 and in close contact with the strip waveguide 321 directly below it. The top electrode 313 is located on the upper surface of the piezoelectric layer 312.

[0062] When the optical waveguide structure 32 is a ridge waveguide and is located below a double piezoelectric structure composed of two single piezoelectric structures (31), as Figure 10 As shown, the waveguide is located above the sacrificial layer 2, wherein the planar waveguide 322 is in close contact with the sacrificial layers 2 on both sides below, and there is a cavity between the middle of the planar waveguide 322 and the substrate 1 below, and the two are not in contact, but are in close contact with the single piezoelectric structure 31 on the upper left and upper right, and the strip waveguide 321 is located directly above the planar waveguide 322; the two single piezoelectric structures 31 are located on the upper left and upper right of the planar waveguide 322 respectively, wherein the bottom electrode 311 is in close contact with the planar waveguide 322 below, the piezoelectric layer 312 is located above the bottom electrode 311, and the top electrode 313 is located above the piezoelectric layer (312).

[0063] When the optical waveguide structure 32 is a ridge waveguide and is located above a double piezoelectric structure composed of two single piezoelectric structures 31, as shown in the image... Figure 11 As shown, the planar waveguide 322 is in close contact with the two single piezoelectric structures 31 at the lower left and lower right, and the strip waveguide 321 is located directly above the planar waveguide 322; the two single piezoelectric structures 31 are located at the upper left and upper right of the sacrificial layer 2, the bottom electrode 311 is in close contact with the sacrificial layers 2 on the lower left and right sides respectively, and there is a cavity between the middle part near the center of the planar waveguide 322 and the substrate 1 below, and the two do not contact each other. The piezoelectric layer 312 is located above the bottom electrode 311, and the top electrode 313 is located above the piezoelectric layer 312 and is in close contact with the planar waveguide 322 above it.

[0064] Example 4: The structure proposed in this example is the same as in Example 1, and will now be referred to... Figures 1-4 , as Figure 1 The working principle of the present invention will be further explained using the typical structure shown as an example:

[0065] The overall structure proposed in this embodiment is as follows: Figure 1 As shown, the structure includes a substrate 1, a sacrificial layer 2, and a waveguide modulation region 3. The waveguide modulation region 3 is located above the sacrificial layer 2 and serves to generate stress and strain, confine the transmitted optical field, and simultaneously transfer stress and strain to the optical waveguide structure. This achieves phase modulation of the optical signal. The structure of the waveguide modulation region in this embodiment is as follows... Figure 3 and Figure 4 As shown, it includes a bottom electrode 311, a piezoelectric layer 312, a top electrode 313, and a strip waveguide 321. The bottom electrode 311 is in close contact with the sacrificial layers 2 on both sides below. There is a cavity between the middle of the bottom electrode 311 and the substrate 1 below, and the two do not contact each other. The piezoelectric layer 312 is located above the bottom electrode 311, wrapping the optical waveguide structure 321 in the center. The top electrode (313) is located above the piezoelectric layer 312.

[0066] In this invention, a piezoelectric structure and an optical waveguide form a modulation region, suspended above the substrate without contact. The piezoelectric structure, from bottom to top, consists of electrodes, a piezoelectric layer, and another electrode, with the waveguide located in the center of the piezoelectric layer. Applying an external voltage to the piezoelectric structure causes deformation and stress, which is transmitted to the optical waveguide, changing its refractive index and thus altering the phase of the optical signal. The structure is modeled and simulated using finite element method software, with the piezoelectric layer having a thickness of 1µm, the waveguide thickness of 0.4µm, a waveguide width of 2µm, and the electrode thickness of 0.1µm. Figure 2 As shown, Figure 1 The stress distribution of the structure shown is as follows under an applied voltage of 1V. The stress distribution on the waveguide is relatively concentrated, indicating that the stress and strain generated by the piezoelectric structure are well transferred to the waveguide, realizing piezoelectric-driven optical tuning. The specific technical principle is as follows:

[0067] In this invention, the terminal of the external power supply and the ground terminal are respectively connected to the two electrodes of the piezoelectric structure. An electric field is applied to the piezoelectric layer, and stress and deformation are generated in the piezoelectric layer through the inverse piezoelectric effect. This stress is transmitted to the optical waveguide, causing a change in the effective refractive index, which in turn leads to a change in the phase of the optical signal, thereby achieving optical modulation.

[0068] As the core structure of this invention, the optical waveguide is not clad with silicon dioxide; instead, air or piezoelectric material is chosen for its cladding protection. The piezoelectric structure and the optical waveguide form the modulation region, suspended above the substrate with a large cavity between them. This enhances the stress and deformation transmitted from the piezoelectric structure to the waveguide structure, improving the tuning efficiency of the optical signal within the waveguide. Firstly, the absence of a cladding reduces the device thickness and the distance between the optical waveguide and the piezoelectric structure, allowing the stress and strain generated by the piezoelectric structure to be effectively transmitted to the optical waveguide. Secondly, the large cavity below the modulation region prevents the stress and strain generated by the piezoelectric structure from leaking downwards. Thirdly, the large cavity below the modulation region enhances the vibration effect of the piezoelectric structure under applied voltage, generating greater stress and strain.

[0069] Example 5: The structure proposed in this example is the same as in Example 4. By changing the geometry of the optical waveguide, this structure is applied commercially in piezoelectrically driven tunable devices. It has significant development potential primarily in nanobeam resonant cavity modulators, Mach-Zehnder (MZ) modulators, and microring modulators. (See below for further details.) Figures 12-14The figures show cross-sectional and top views of a nanobeam resonant cavity modulator, a Mach-Zehnder (MZ) modulator, and a microring modulator, respectively. For the Mach-Zehnder (MZ) modulator, by setting the modulation structure of this embodiment on one waveguide arm, the stress affects the refractive index of the waveguide arm, thereby affecting the phase of the optical signal. This enables the conversion between "0" and "1" in the output optical signal, thus changing the intensity of the output optical mode. For the nanobeam resonant cavity modulator and the microring modulator, the stress generated by the deformation of the piezoelectric structure changes the refractive index of the waveguide structure, achieving modulation of the optical mode phase. The modulation structure of this embodiment can effectively confine the stress within the optical waveguide, achieving better piezoelectric tuning effects. The nanobeam microcavity modulator has a more compact structure and is easier to integrate on a chip.

[0070] Example 6: Refer to Figure 15 The present invention proposes a method for fabricating a piezoelectrically driven, cladding-less optical waveguide modulation structure, which specifically includes the following steps:

[0071] Step S1. Select a substrate material and pretreat it to obtain a pretreated substrate;

[0072] Step S2. A sacrificial layer is grown on the pretreated substrate by plasma-enhanced chemical vapor deposition (PECVD);

[0073] Step S3. Deposit a metal electrode on the sacrificial layer using electron beam evaporation or magnetron sputtering as the bottom electrode of the device;

[0074] Step S4. Deposit and grow a piezoelectric layer on the bottom electrode layer using a magnetron sputtering process;

[0075] Step S5. Coat the piezoelectric layer with positive photoresist for photolithography and development, and wash away the photoresist in the middle part after development. Then, deposit and grow an optical waveguide thin film by magnetron sputtering. After removing the photoresist, the optical waveguide layer in the middle part is obtained.

[0076] Step S6. On the structure obtained in step S5, a piezoelectric layer covering the optical waveguide layer is deposited and grown by magnetron sputtering, and then smoothed by chemical mechanical polishing (CMP).

[0077] Step S7. Deposit a metal electrode on the smoothed piezoelectric layer using electron beam evaporation or magnetron sputtering as the top electrode of the device;

[0078] Step S8. Continue to coat positive photoresist for photolithography. Using inductively coupled plasma-reactive ion etching (ICP-RIE) technology, etch the top electrode, piezoelectric layer, bottom electrode, and sacrificial layer in sequence to obtain the release trench structure.

[0079] Step S9. Place the structure in a hot phosphoric acid solution and remove the sacrificial layer below the waveguide modulation region by releasing the groove structure, thereby suspending the piezoelectric structure.

[0080] Step S10. Complete the fabrication process to obtain a piezoelectrically driven, cladding-less optical waveguide modulation structure.

[0081] Example 7: The fabrication method of the optical waveguide modulation structure proposed in this example is implemented in the same way as in Example 6. Now, combined with... Figure 1 The specific materials and parameters are given, and the process of fabricating the piezoelectrically driven claddingless optical waveguide modulation structure containing a silicon nitride sacrificial layer in the cavity region is further described in this invention:

[0082] In this embodiment, a silicon Si substrate, a lithium niobate LiNbO3 piezoelectric layer, an aluminum nitride AlN waveguide layer, and a silicon nitride Si3N4 sacrificial layer are used as examples. Of course, when other materials in Embodiment 1 are used to prepare the structure, the modulation structure of the present invention can also be realized by following the corresponding process steps.

[0083] Step 1. Pre-treat the Si wafer to obtain a pre-treated Si substrate;

[0084] Step 2. A Si3N4 sacrificial layer is grown on the pretreated Si substrate by plasma-enhanced chemical vapor deposition (PECVD);

[0085] Step 3. Deposit a metal electrode on the Si3N4 sacrificial layer obtained in Step 2 using electron beam evaporation or magnetron sputtering as the bottom electrode of the device;

[0086] Step 4. A LiNbO3 layer is deposited and grown on the bottom electrode layer obtained in step 3 by magnetron sputtering as the piezoelectric layer of the device;

[0087] Step 5. Coat the layer obtained in step 4 with positive photoresist for photolithography and development. The photoresist corresponding to the middle waveguide structure is washed away after development. Then, deposit and grow an AlN thin film by magnetron sputtering. Wash away the remaining photoresist to obtain the middle AlN waveguide core layer.

[0088] Step 6. On the structure obtained in step 5, a LiNbO3 layer is deposited and grown by magnetron sputtering to cover the AlN waveguide core layer. The LiNbO3 layer deposited on the AlN waveguide core layer is then smoothed by chemical mechanical polishing (CMP).

[0089] Step 7. Deposit a metal electrode on the LiNbO3 piezoelectric layer obtained in step 6 using electron beam evaporation or magnetron sputtering as the top electrode of the device;

[0090] Step 8. Continue to coat the layer obtained in step 7 with positive photoresist for photolithography. Then, using inductively coupled plasma-reactive ion etching (ICP-RIE) technology, etch the top electrode, piezoelectric layer, bottom electrode, and Si3N4 sacrificial layer in sequence to obtain the release groove structure.

[0091] Step 9. Place the structure obtained in steps 1-8 in a hot phosphoric acid solution and remove the Si3N4 sacrificial layer below the waveguide modulation region by using a release groove structure, thereby suspending the piezoelectric structure.

[0092] Step 10. Complete the fabrication process to obtain a piezoelectrically driven, cladding-less optical waveguide modulation structure.

[0093] The effects of the present invention will be further explained below with reference to simulation experiments.

[0094] 1. Simulation conditions:

[0095] The simulation of this invention uses finite element software. By selecting the solid mechanics (SEM) and electrostatic (ES) physics fields in the structural mechanics module, multi-physics coupling is performed to form a piezoelectric effect multi-physics field, which is used to simulate the geometric structure of this invention (e.g., Figure 1 Modeling and simulation are performed as shown in the figure.

[0096] 2. Simulation content:

[0097] This simulation sets up a suspended waveguide modulation region above a Si substrate. From bottom to top, the waveguide modulation region consists of a bottom electrode, a piezoelectric layer, and a top electrode, made of aluminum (Al), lead zirconate titanate (PZT), and aluminum (Al), with thicknesses of 0.1 μm, 1 μm, and 0.1 μm, respectively. The strip waveguide material is silicon (Si), with a width of 1 μm and a thickness of 0.4 μm, positioned at the center of the piezoelectric layer. A voltage is applied between the bottom and top electrodes, and the stress distribution in the waveguide modulation region is analyzed using a piezoelectric effect multiphysics approach.

[0098] 3. Simulation results:

[0099] Reference Figure 2 The stress is mainly distributed in the Si strip waveguide, indicating that the stress generated by the inverse piezoelectric effect of the PZT piezoelectric layer can act well on the optical waveguide at the center of the piezoelectric layer. In turn, the stress deformation of the Si strip waveguide changes its refractive index, affecting the phase of the optical signal propagation in it, thus achieving piezoelectric tuning of the optical signal.

[0100] Therefore, this invention places the optical waveguide at the center of the piezoelectric layer, and the stress generated by piezoelectric driving is concentrated and distributed on the optical waveguide, avoiding the dispersion of stress by the optical waveguide cladding material and enhancing the stress deformation effect of the waveguide. At the same time, the waveguide modulation region is suspended, which can minimize the downward transmission of stress, and the generated stress is distributed within the modulation region. In addition, eliminating the cladding of the optical waveguide helps to reduce the size of the device and the distance between the optical waveguide and the piezoelectric structure. While ensuring the functionality of the device, it can increase the device density, which is conducive to reducing the cost of piezoelectric driven tuning devices and improving their piezoelectric driving capability.

[0101] The above simulation analysis proves the correctness and effectiveness of the method proposed in this invention.

[0102] The parts of this invention not described in detail are common knowledge to those skilled in the art.

[0103] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Obviously, those skilled in the art, after understanding the content and principle of the present invention, may make various modifications and changes in form and detail without departing from the principle and structure of the present invention. However, these modifications and changes based on the concept of the present invention are still within the scope of protection of the claims of the present invention.

Claims

1. A piezoelectrically driven, cladding-less optical waveguide modulation structure, characterized in that, From bottom to top, it includes: substrate (1), sacrificial layer (2) and waveguide modulation region (3); The sacrificial layer (2) is a hollow silicon dioxide layer that has been hollowed out. The waveguide modulation region (3) includes a piezoelectric structure and an optical waveguide structure (32); wherein the piezoelectric structure is a single piezoelectric structure (31) or a double piezoelectric structure; the single piezoelectric structure (31) is composed of a bottom electrode (311), a piezoelectric layer (312) and a top electrode (313); the double piezoelectric structure is composed of two single piezoelectric structures (31); The optical waveguide structure (32) is a strip waveguide (321) or a planar waveguide (322), or a ridge waveguide composed of the two. The waveguide is not clad. In the waveguide modulation region (3), the optical waveguide structure (32) is in close contact with the piezoelectric layer (312) in the piezoelectric structure (31).

2. The structure according to claim 1, characterized in that: The substrate (1) is made of silicon or sapphire; the optical waveguide structure (32) is made of any one of silicon, silicon nitride, lithium niobate, or aluminum nitride; the bottom electrode (311) is made of any one of platinum, molybdenum, or titanium; the top electrode (313) is made of any one of indium tin oxide, aluminum, gold, or rubidium oxide; and the piezoelectric layer (312) is made of any one of lead zirconate titanate, lithium niobate, doped hafnium oxide, or doped aluminum nitride.

3. The structure according to claim 1, characterized in that: The piezoelectric layer (312) is made of hafnium oxide or aluminum nitride doped material; When using doped hafnium oxide materials, the doping element is any one of zirconium (Zr), yttrium (Y), or silicon (Si), and the doping method is substitutional doping or interstitial doping. Specifically: substitutional doping involves doping zirconium (Zr) or yttrium (Y) into hafnium oxide at doping ratios of 33-67% and 1-5%, respectively; interstitial doping involves doping silicon (Si) into hafnium oxide at doping ratios of 3-7%. When using doped aluminum nitride materials, the doping element is scandium (Sc) or boron (B). Specifically, the doping element is doped into aluminum nitride using a substitutional doping method, with a doping ratio of 0 to 40%.

4. The structure according to claim 1, characterized in that: The optical waveguide structure (32) and the piezoelectric layer (312) are both thicker than 100 nm, and the thickness of the optical waveguide structure (32) is less than the thickness of the piezoelectric layer (312); the thickness of the bottom electrode (311) and the top electrode (313) are both greater than 50 nm and less than 100 nm.

5. The structure according to claim 1, characterized in that: The positional relationship between the optical waveguide structure (32) and the piezoelectric structure includes: the optical waveguide structure (32) is located at the center of the piezoelectric structure, the optical waveguide structure (32) is located above the piezoelectric structure, and the optical waveguide structure (32) is located below the piezoelectric structure.

6. The structure according to claim 5, characterized in that: When the optical waveguide structure (32) is located at the center of the piezoelectric structure, the optical waveguide structure (32) adopts a strip waveguide (321), and the piezoelectric structure is a single piezoelectric structure (31) or a double piezoelectric structure.

7. The structure according to claim 6, characterized in that: When the piezoelectric structure is a single piezoelectric structure (31), the structure is located above the sacrificial layer (2), wherein the bottom electrode (311) is in close contact with the sacrificial layers (2) on both sides below, and there is a cavity between the middle of the bottom electrode (311) and the substrate (1) below, and the two do not contact each other; the piezoelectric layer (312) is located above the bottom electrode (311) and wraps the strip waveguide (321) in its center; the top electrode (313) is located above the piezoelectric layer (312).

8. The structure according to claim 6, characterized in that: When the piezoelectric structure is a dual piezoelectric structure, the structure consists of two single piezoelectric structures (31) placed above or below the strip waveguide (321) or to the left or right. When the dual piezoelectric structure consists of two single piezoelectric structures (31) placed above or below the strip waveguide (321), the strip waveguide (321) is located at the center of the two single piezoelectric structures, and its upper and lower interfaces are in close contact with the piezoelectric layers of the two single piezoelectric structures (31). When the dual piezoelectric structure consists of two single piezoelectric structures (31) placed to the left or right of the strip waveguide (321), the strip waveguide (321) is located in the middle of the two single piezoelectric structures, and its sidewalls are in close contact with the piezoelectric layers of the single piezoelectric structures on the left and right sides.

9. The structure according to claim 5, characterized in that: When the optical waveguide structure (32) is located above or below the piezoelectric structure, the optical waveguide structure (32) adopts a strip waveguide (321) or a ridge waveguide. The ridge waveguide is composed of a strip waveguide (321) and a planar waveguide (322). If a strip waveguide (321) is adopted, the piezoelectric structure is a single piezoelectric structure. If a ridge waveguide is adopted, the piezoelectric structure is a double piezoelectric structure.

10. A method for preparing the structure according to claim 1, characterized in that, Includes the following steps: S1. Select a substrate material and pretreat it to obtain a pretreated substrate; S2. A sacrificial layer is grown on the pretreated substrate by plasma-enhanced chemical vapor deposition (PECVD); S3. A metal electrode is deposited on the sacrificial layer using electron beam evaporation or magnetron sputtering as the bottom electrode of the device; S4. A piezoelectric layer is deposited and grown on the bottom electrode layer by magnetron sputtering. S5. Coat the piezoelectric layer with positive photoresist for photolithography and development, and wash away the photoresist in the middle part after development. Then, deposit and grow an optical waveguide thin film by magnetron sputtering. After removing the photoresist, the optical waveguide layer in the middle part is obtained. S6. A piezoelectric layer covering the optical waveguide layer is deposited and grown on the structure obtained in step S5 by magnetron sputtering, and then smoothed by chemical mechanical polishing (CMP). S7. Deposit a metal electrode on the smoothed piezoelectric layer using electron beam evaporation or magnetron sputtering as the top electrode of the device; S8. Continue to coat positive photoresist for photolithography. Using inductively coupled plasma-reactive ion etching (ICP-RIE) technology, etch the top electrode, piezoelectric layer, bottom electrode, and sacrificial layer in sequence to obtain the release groove structure. S9. The structure is placed in a hot phosphoric acid solution, and the sacrificial layer below the waveguide modulation region is removed by a release groove structure, thereby suspending the piezoelectric structure. S10. Complete the fabrication process to obtain a piezoelectrically driven, cladding-free optical waveguide modulation structure.

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