A suspension modulator based on stress optical effect and its preparation method

Abstract

The present invention provides a suspended air modulator based on stress optical effect and a preparation method thereof, which belongs to the technical field of modulators. The suspended air modulator includes an SOI waveguide, a covering layer covering the SOI waveguide, a lower electrode deposited on the upper surface of the covering layer, a piezoelectric layer arranged on the upper surface of the lower electrode, an upper electrode deposited in the middle of the upper surface of the piezoelectric layer, and a protective layer covering the upper surface of the upper electrode; the SOI waveguide includes a silicon substrate, a buried oxide layer and a waveguide layer from bottom to top. At least one air groove is provided on the side of the silicon substrate away from the buried oxide layer. The present invention regulates the refractive index change of the SOI waveguide and the material of the surface covering layer through the inverse piezoelectric effect of the piezoelectric material, and optimizes the internal stress distribution of the SOI waveguide in combination with the structure of the suspended air groove, thereby achieving the effect of efficiently regulating the phase of light.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon-based optoelectronic integration, in particular to the technical field of modulators, and specifically to a suspended air modulator based on stress optical effect and a preparation method thereof. Background Art

[0002] At present, silicon-based electro-optic modulators are generally divided into two types according to their structures: one is based on the MachβZehnder interferometer (MZI) type modulator, and the other is based on the ring resonator type micro-ring modulator. For the MZI type modulator, its size is generally in the millimeter order, which is not conducive to high-density, large-scale optical chip integration; in addition, it has high modulation power consumption, which is not conducive to the preparation of low-power devices. The size of the modulator based on the ring resonator is much more compact, generally in the micron order, and the modulation power consumption is low. At the same time, there are two main modulation modes of silicon-based modulators, namely thermo-optic modulation and plasma dispersion modulation. Thermo-optic modulation is based on the thermo-optic effect of silicon materials, which is difficult to achieve high-speed modulation. At present, the modulation function of most high-speed silicon-based modulators at home and abroad is based on the plasma dispersion effect of silicon materials. The principle is that the change of free carrier concentration will affect the real and imaginary parts of its refractive index and change its absorptivity. Therefore, the free carrier dispersion effect will increase the modulation rate while also causing huge energy consumption.

[0003] Lead zirconate titanate (PZT) is a high piezoelectric coefficient (e 31 Reach -15C / m 2 , d 33 300pC / N,d 31 200pC / N) of piezoelectric materials, the application of stress optical effect in various optical devices has been widely studied in recent years. At present, there is a technology that uses the stress optical effect of lead zirconate titanate to tune optical waveguides. Compared with thermo-optical modulators, the power consumption of stress optical effect can reach the nanowatt (nW) level, and it provides wide optical bandwidth and medium electrical bandwidth. However, in the actual design and preparation process, how to more effectively transmit the stress of the piezoelectric layer to the waveguide to achieve a more efficient modulation effect while avoiding excessive absorption loss of the electrode is a more worthy problem to study.

[0004] Prior art 1, "Bistability in silicon microring resonator based on straininduced by a piezoelectric lead zirconate titanate thin film" (DOI: http: / / dx.doi.org / 10.1063 / 1.3701587), discloses a stress-optical phase modulator based on SOI (Silicon-on-insulator, silicon on insulating substrate) waveguide and using PZT piezoelectric material. The device structure is as follows: Figure 1 As shown. Since the stress distribution induces strong birefringence through anisotropy, an electric field is applied to the piezoelectric layer. The piezoelectric layer deposited on the top of the optical waveguide is used to control the phase of light propagating in the structure. The nonlinear response of the piezoelectric material is converted into the effective refractive index of the optical waveguide through the stress optical effect. The efficiency of this stress optical effect modulator depends on the design of the device geometry. Figure 2 As shown in the figure, by applying a voltage of 6V (converted to an electric field of 12V / μm), the effective refractive index of the optical waveguide changes by 1.8×10 -4 In this scheme, a piezoelectric layer is integrated on the SOI waveguide structure to utilize the stress-optical effect. In this way, it has lower power consumption and higher modulation speed without affecting the optical insertion loss; however, the formation of this ridge structure does not fully transmit the stress to the waveguide core, resulting in low modulation efficiency.

[0005] Prior art 2 "Stress-optic modulator in TriPleX platform using apiezoelectric lead zirconate titanate (PZT) thin film" (DOI: 10.1364 / OE.23.014018) discloses a stress-optical phase modulator using PZT piezoelectric material on a passive TriPlex platform based on silicon nitride waveguide. The device structure is as follows Figure 3As shown, the piezoelectric layer deposited on the top of the optical waveguide is used to control the phase of light propagating in the structure by applying an electric field to the piezoelectric layer using the inverse piezoelectric effect of the piezoelectric material. This stress-induced low-power tuning mechanism is particularly suitable for low-loss silicon nitride waveguides. According to simulation and actual test results, smaller electrode sizes and thicker piezoelectric layers can improve device performance, and different piezoelectric materials require different sizes, and the device can be optimized by optimizing the stress distribution inside the waveguide. Compared with the latest thermo-optical modulation used in TriPleX, the stress-optical effect reduces the power consumption of the switch operation to 300nW, which is only one millionth of the thermo-optical power consumption, and increases the modulation speed to 200-300ns, an increase of about three orders of magnitude. This scheme proves that the optical switch made based on the stress-optical effect has many advantages such as low power consumption, fast response, and low mutual interference, and has broad development prospects.

[0006] Prior art 3 "Silicon nitride stress-optic microresonator modulator for optical control applications" (DOI: 10.1364 / OE.467721) discloses a stress optical microring modulator integrated with a piezoelectric PZT drive on a fully planar wafer-level silicon nitride platform. The device structure is as follows: Figure 4 As shown. By controlling the distance between the left and right piezoelectric layers, the device structure still maintains low loss (0.03dB / cm) at a 2μm interval, a bandwidth of 20MHz, an extinction ratio greater than 14dB, a quality factor of 7.1 million, and a power consumption of only 20nW. Two control applications are demonstrated in this document, one is to achieve laser stabilization in a PDH (Pound-Drever Hall) lock loop to reduce the laser frequency noise by 40dB, and the other is as a laser carrier tracking filter.

[0007] Although the prior art 2 and prior art 3 have made significant progress in the integrated piezoelectric-driven MZI and micro-ring modulators based on the silicon nitride platform, the following problems still exist: (1) The stress-optical effect modulator of the MZI structure requires a longer electrode length (millimeter level), resulting in a lower integration density. (2) The micro-ring structure requires a more complex process to form the piezoelectric drive layer on the left and right sides, and the micro-ring resonant cavity, waveguide, and piezoelectric layer design do not fully improve its bandwidth. (3) Since the vertical structure based on the silicon nitride waveguide needs to consider the optical waveguide absorption loss caused by the bottom electrode, it is necessary to prepare a thicker top oxide cladding to reduce the loss. The thicker oxide layer thickness prevents the stress from being fully concentrated in the waveguide, resulting in low tuning strength. Summary of the invention

[0008] In order to solve at least one of the above problems, the present invention provides a suspended air modulator based on stress optical effect. While achieving the purpose of low power consumption and low loss, the modulator can also achieve the purpose of more concentrated stress in the waveguide structure, thereby bringing higher tuning strength, and can meet the needs of high-speed, large bandwidth, low power consumption, and high integration modulators.

[0009] Specifically, in order to achieve the above purpose, the present invention adopts the following technical solutions:

[0010] A suspended air modulator based on stress optical effect, comprising an SOI waveguide, a covering layer covering the SOI waveguide, a lower electrode deposited on the upper surface of the covering layer, a piezoelectric layer arranged on the upper surface of the lower electrode, an upper electrode deposited in the middle of the upper surface of the piezoelectric layer, and a protective layer covering the upper surface of the upper electrode; the SOI waveguide comprises, from bottom to top, a silicon substrate, a buried oxide layer and a waveguide layer; the waveguide layer, the lower electrode, the piezoelectric layer and the upper electrode form a micro-ring structure or the waveguide layer, the lower electrode, the piezoelectric layer and the upper electrode form a Mach-Zehnder structure; at least one air groove is provided on a side of the silicon substrate away from the buried oxide layer; the material of the piezoelectric layer is at least one of lead zirconate titanate, zinc oxide and aluminum nitride.

[0011] In some specific embodiments, the material of the covering layer is silicon dioxide.

[0012] In some specific embodiments, the air trench is located directly below the waveguide layer and penetrates the silicon substrate and the buried oxide layer.

[0013] In some other specific embodiments, the air grooves are located on both sides of the bottom of the waveguide layer and penetrate the silicon substrate and the buried oxide layer.

[0014] In a preferred embodiment of the present invention, the material of the buried oxide layer is silicon dioxide.

[0015] In a preferred embodiment of the present invention, the material of the protective layer is silicon dioxide.

[0016] In a preferred embodiment of the present invention, the width of the air groove is 0.45-5 μm, and the ratio of its depth to width is (30-150):1.

[0017] In some specific embodiments, the waveguide layer is a strip waveguide, and the strip waveguide has a width of 450 to 500 nm and a thickness of 220 to 300 nm.

[0018] In some other specific embodiments, the waveguide layer is a ridge waveguide, the total height of the ridge waveguide is 220-300 nm, the ridge region height is 50-150 nm, and the ridge region width is 450-660 nm.

[0019] In a preferred embodiment of the present invention, the thickness of the piezoelectric layer is 1 to 3 μm.

[0020] In a preferred embodiment of the present invention, the thickness of the covering layer is 0.5-2.0 μm.

[0021] In a preferred embodiment of the present invention, the thickness of the upper electrode is 150-250 nm.

[0022] In a preferred embodiment of the present invention, the thickness of the lower electrode is 150-250 nm.

[0023] In a preferred embodiment of the present invention, the width of the upper electrode is 1 to 25 μm.

[0024] In a preferred embodiment of the present invention, the width of the lower electrode is 1 to 25 μm.

[0025] In a preferred embodiment of the present invention, the material of the upper electrode is at least one of platinum, titanium and gold.

[0026] In a preferred embodiment of the present invention, the material of the lower electrode is platinum-titanium alloy.

[0027] The present invention also provides a method for preparing the suspension modulator based on stress optical effect, comprising the following steps:

[0028] Cleaning an SOI substrate, wherein the SOI substrate includes a silicon substrate, a buried oxide layer and a top silicon layer; patterning the SOI substrate, and etching a waveguide layer in the top silicon layer to obtain an SOI waveguide;

[0029] Depositing a capping layer on the surface of the SOI waveguide and grinding it flat;

[0030] A lower electrode, a piezoelectric layer, an upper electrode and a protective layer are sequentially stacked on the surface of the covering layer;

[0031] The silicon substrate is thinned, and an air groove is etched on a side thereof away from the buried oxide layer.

[0032] In a preferred embodiment of the present invention, the method for preparing the suspension modulator based on stress-optical effect further comprises the following steps:

[0033] A first through hole is opened in the middle of the protective layer, and a second through hole is opened on one side of the protective layer; a first contact metal electrode in contact with the upper electrode is made in the first through hole, and a second contact metal electrode in contact with the lower electrode is made in the second through hole.

[0034] In a further preferred embodiment of the present invention, the first contact metal electrode includes a first metal wire located in the first through hole and a first metal pad located outside the first through hole, and the second contact metal electrode includes a second metal wire located in the second through hole and a second metal pad located outside the second through hole; the material of the first metal wire, the second metal wire, the first metal pad and the second metal pad is one of gold, copper and aluminum.

[0035] Compared with the prior art, the present invention has the following beneficial effects: in the present invention, a waveguide is formed by etching the device layer of the SOI waveguide, and the refractive index change of the waveguide and the material of the waveguide surface covering layer is regulated by the inverse piezoelectric effect of the piezoelectric material, and the internal stress distribution of the waveguide is optimized in combination with the structure of the suspended air slot, so as to achieve the effect of efficiently regulating the phase of light. Furthermore, by adjusting parameters such as different waveguide structures, air slot aspect ratios, piezoelectric material thickness, thickness of the waveguide surface covering layer, upper electrode thickness and / or width, lower electrode thickness and / or width, or by combining and adjusting parameters, the device can be applied to different application scenarios, so that the device can be efficiently modulated while maintaining low power consumption, and thus is applicable to optical communication systems with high transmission rates and large communication capacities. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a structural schematic diagram of a modulator in the prior art 1;

[0037] Figure 2 A curve diagram showing the change in the effective refractive index of the optical waveguide in the prior art 1 as a function of the voltage;

[0038] Figure 3 It is a structural schematic diagram of a modulator in the second prior art;

[0039] Figure 4 It is a structural schematic diagram of a modulator in the prior art three;

[0040] Figure 5 is a schematic diagram of the three-dimensional structure of the modulator in Example 1 of the present invention;

[0041] Figure 6 for Figure 5 Cross-sectional view at the middle section A;

[0042] Figure 7 A schematic diagram of the structure of another modulator provided by the present invention;

[0043] Figure 8 Schematic diagram of the process of preparing a modulator in Example 2 of the present invention;

[0044] Fig. 9 Schematic diagram of the structure of the modulator prepared in Example 3 of the present invention;

[0045] Fig.10 is a stress distribution diagram of the modulator on the X-axis when an air slot is provided and the waveguide is a strip waveguide;

[0046] Fig.11 is a stress distribution diagram of the modulator on the Y axis when an air slot is provided and the waveguide is a strip waveguide;

[0047] Fig.12 is a stress distribution diagram of the modulator on the X-axis when no air slot is provided and the waveguide is a strip waveguide;

[0048] Fig.13 is a stress distribution diagram of the modulator on the Y axis when no air slot is provided and the waveguide is a strip waveguide;

[0049] Fig.14 is a stress distribution diagram of the modulator on the X-axis when an air slot is provided and the waveguide is a ridge waveguide;

[0050] Fig.15 is a stress distribution diagram of the modulator on the Y axis when an air slot is provided and the waveguide is a ridge waveguide;

[0051] Fig.16 is a stress distribution diagram of the modulator on the X-axis when no air slot is provided and the waveguide is a ridge waveguide;

[0052] Fig.17 is a stress distribution diagram of the modulator on the Y axis when no air slot is provided and the waveguide is a ridge waveguide;

[0053] Fig.18 A trend diagram of the change in the effective refractive index of the modulator of the present invention as the width of the upper electrode and the width of the air slot change when the waveguide is a ridge waveguide;

[0054] Fig.19 A trend diagram of the change in the effective refractive index of the modulator of the present invention as the thickness of the silicon dioxide covering layer changes when the waveguide is a ridge waveguide;

[0055] Fig. 20 The figure is a trend diagram showing the change in the effective refractive index of the modulator of the present invention as the magnitude of the electric field changes when the waveguide is a ridge waveguide.

[0056] In the figure: 1. SOI waveguide; 11. Silicon substrate; 12. Buried oxide layer; 13. Waveguide layer; 2. Cover layer; 3. Lower electrode; 4. Piezoelectric layer; 5. Upper electrode; 6. Protective layer; 7. Air groove. DETAILED DESCRIPTION

[0057] The following content is combined with the embodiments to clearly and completely describe the technical solution of the present invention so that those skilled in the art can fully understand the present invention. Obviously, the described embodiments are only some preferred embodiments of the present invention, rather than all embodiments. Any equivalent transformation or substitution made by ordinary technicians in this field to the following implementation methods without creative work belongs to the protection scope of the present invention.

[0058] Directional terms mentioned in this article, such as words such as "upper surface", "upper", "lower", "top" and the like, refer to directions in the accompanying drawings. Therefore, directional terms are only used for illustration and are not used to limit the present invention. Ordinal numbers used in this article, such as "first", "second", etc., are only used for descriptive purposes to distinguish similar objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. The methods not described in detail in the following embodiments are all conventional methods well known to those skilled in the art. All etching processes in the embodiments can be dry-etched to improve work efficiency.

[0059] Example 1

[0060] Reference Figure 5 and Figure 6 , this embodiment provides a suspended air modulator based on stress optical effect, including an SOI waveguide 1, a covering layer 2 covering the SOI waveguide 1, a lower electrode 3 deposited on the upper surface of the covering layer 2, a piezoelectric layer 4 arranged on the upper surface of the lower electrode 3, an upper electrode 5 deposited in the middle of the upper surface of the piezoelectric layer 4, and a protective layer 6 covering the upper surface of the upper electrode 5. The SOI waveguide 1 includes, from bottom to top, a silicon substrate 11, a buried oxide layer 12 and a waveguide layer 13. The waveguide layer 13, the lower electrode 3, the piezoelectric layer 4 and the upper electrode 5 form a micro-ring structure. An air groove 7 is provided on one side of the silicon substrate 11 away from the buried oxide layer 12. The air groove 7 is located directly below the waveguide layer 13. The depth of the air groove 7 ( Figure 6 The upper Y-axis direction (i.e., the direction from the silicon substrate 11 to the lower electrode) penetrates the silicon substrate 11 and the buried oxide layer 12. By controlling the depth and width of the air groove 7 ( Figure 6 The upper X-axis direction, that is Figure 6 The stress distribution inside the SOI waveguide 1 is adjusted by adjusting the direction of the cross section A perpendicular to the Y axis. In this embodiment, the cover layer 2 is a silicon dioxide layer.

[0061] The above-mentioned suspended air modulator based on stress optical effect regulates the refractive index change of the waveguide and the silicon dioxide covering layer through the inverse piezoelectric effect of the piezoelectric layer, and optimizes the stress distribution inside the waveguide in combination with the structure of the air groove, thereby achieving the effect of efficiently regulating the phase of light.

[0062] In this embodiment, the thickness of the piezoelectric layer 4 ( Figure 6 The thickness of the cover layer 2 ( Figure 6 The width of the upper electrode 5 ( Figure 6 The width of the air slot 7 ( Figure 6 The material of the piezoelectric layer 4 is lead zirconate titanate, the material of the buried oxide layer 12 is silicon dioxide, the material of the protective layer 6 is silicon dioxide, the material of the lower electrode 3 is platinum-titanium alloy, and the material of the upper electrode 5 is platinum. In addition, the material of the piezoelectric layer 4 can also be zinc oxide or aluminum nitride; the material of the upper electrode 5 can also be titanium or gold or any combination of platinum, titanium and gold.

[0063] The modulator in this embodiment is a ring resonant cavity type micro-ring modulator, and the waveguide layer 13 is a strip waveguide. The width of the strip waveguide ( Figure 6 The X-axis direction) is 450nm, and the height (or thickness, Figure 6 In other embodiments, the waveguide layer 13 may also be a ridge waveguide (see Figure 8 ). The total height of the ridge waveguide ( Figure 6 The ridge area is 220nm in the Y-axis direction, the height of the ridge area is 130nm, and the width of the ridge area ( Figure 6 The upper X-axis direction) is 470nm.

[0064] In other embodiments, the modulator may also be Figure 7 ( Figure 7 From left to right is the Z axis direction, Z axis and Figure 6 The waveguide layer 13, the lower electrode 3, the piezoelectric layer 4 and the upper electrode 5 constitute a Mach-Zehnder structure.

[0065] The above-mentioned air suspension modulator based on stress optical effect can be obtained by controlling the number, depth and width of the air slots 7, the thickness of the cover layer 2, the structure of the waveguide layer 13, the thickness of the piezoelectric layer 4, the width of the upper electrode 5, the thickness of the upper electrode 5 ( Figure 6 Y-axis direction), the width of the lower electrode 3, the thickness of the lower electrode 3 ( Figure 6 The stress distribution inside the waveguide can be regulated by one or a combination of multiple methods such as the Y-axis direction, so as to achieve the purpose of regulating the change of the effective refractive index of light.

[0066] It should be noted that when the width of the air slot 7 is 0.45-5 μm and the ratio of its depth to width is (30-150):1, the purpose of regulating the effective refractive index of light can be achieved. The smaller the width of the air slot, the better the regulation effect and the stronger the mechanical effect. For example, when the width of the air slot 7 is gradually reduced to 0.45-4 μm, 0.45-3 μm, 0.45-2 μm, and 0.45-1 μm, the change in the effective refractive index increases successively, and the mechanical effect increases successively. By controlling the number of air slots 7, the purpose of regulating the effective refractive index of light can also be achieved.

[0067] When the waveguide layer 13 is a strip waveguide with a width of 450 to 500 nm (for example, a width of 450 nm, 455 nm, 460 nm, 470 nm, ... 500 nm) and a thickness of 220 to 300 nm (for example, a thickness of 220 nm, 221 nm, 222 nm, 225 nm, 230 nm, ... 300 nm), the purpose of regulating the effective refractive index of light can be achieved. When the waveguide layer 13 is a ridge waveguide, the total height of the ridge waveguide is 220-300nm (for example, the total height is 220nm, 225nm, 230nm, 235nm...300nm), the ridge area height is 50-150nm (for example, the ridge area height is 50nm, 52nm, 54nm, 55nm, 60nm, 70nm, 90nm...150nm), and the ridge area width is 450-660nm (for example, the ridge area width is 450nm, 455nm, 470nm, 480nm, 500nm, 600nm...660nm), the purpose of regulating the effective refractive index of light can be achieved.

[0068] When the thickness of the piezoelectric layer 4 is 1-3 μm, the purpose of regulating the effective refractive index of light can be achieved.

[0069] When the thickness of the cover layer 2 is 0.5-2.0 μm, the purpose of regulating the effective refractive index of light can be achieved.

[0070] When the thickness of the upper electrode 5 is 150-250 nm, the purpose of regulating the effective refractive index of light can be achieved.

[0071] When the width of the upper electrode 5 is 1-25 μm, the purpose of regulating the effective refractive index of light can be achieved.

[0072] When the thickness of the lower electrode 3 is 150-250 nm, the purpose of regulating the effective refractive index of light can be achieved.

[0073] When the width of the lower electrode 3 is 1-25 μm, the purpose of regulating the effective refractive index of light can be achieved.

[0074] Example 2

[0075] like Figure 8 As shown, taking a ridge waveguide as an example, this embodiment provides a method for preparing a suspended air modulator based on stress optical effect, comprising the following steps:

[0076] S1. Clean the SOI substrate. The SOI substrate includes a silicon substrate, a buried oxide layer (BOX) and a top silicon layer. The SOI substrate is patterned, and a ridge waveguide with a total height of 220 nm, a ridge height of 130 nm and a ridge width of 470 nm is etched in the top silicon layer by an inductively coupled plasma-reactive ion etching (ICP-RIE) method to obtain a waveguide layer. The material of the buried oxide layer is silicon dioxide.

[0077] S2. Deposit a cover layer on the surface of the ridge waveguide by thermal oxidation deposition, and smoothen the cover layer by chemical mechanical polishing (CMP) process. The cover layer is made of silicon dioxide and has a thickness of 1 μm.

[0078] S3, sputtering a lower electrode with a thickness of 200 nm and a width of 15 μm on the surface of the cover layer by an evaporation deposition method. The material of the lower electrode is a platinum-titanium alloy (Pt / Ti).

[0079] S4. A piezoelectric layer with a thickness of 2 μm is prepared on the surface of the lower electrode by magnetron sputtering. The material of the piezoelectric layer is lead zirconate titanate.

[0080] S5. On the surface of the piezoelectric layer, an upper electrode with a thickness of 200 nm and a width of 7 μm is formed by evaporation deposition. The material of the upper electrode is platinum (Pt).

[0081] S6. Etching the piezoelectric layer and patterning the upper electrode and the lower electrode.

[0082] S7, depositing a protective layer on the device structure obtained in step S6 by plasma enhanced chemical vapor deposition (PECVD). The material of the protective layer is SiO2.

[0083] S8, a first through hole is formed in the middle of the protective layer, the first through hole penetrates the protective layer, and the bottom thereof is the upper surface of the upper electrode. A second through hole is formed on one side of the protective layer, the second through hole penetrates the protective layer and the piezoelectric layer, and the bottom thereof is the upper surface of the lower electrode.

[0084] S9, filling the first through hole and the second through hole with metal and preparing a first contact metal electrode and a second contact metal electrode, wherein the first contact metal electrode contacts the upper electrode and the second contact metal electrode contacts the lower electrode.

[0085] S10, thinning the silicon substrate and etching the silicon substrate by deep reactive ion etching (DRIE); then etching the buried oxide layer by reactive ion etching (RIE) method, the etching width is the same as the etching width of the silicon substrate, and an air groove is obtained. The air groove runs through the silicon substrate and the buried oxide layer, and its depth extends to the surface of the ridge waveguide layer away from the lower electrode. The width of the air groove is 0.45μm and the depth is 60μm.

[0086] Example 3

[0087] The preparation method of the suspension modulator based on stress optical effect in this embodiment is basically the same as that in embodiment 2, except that:

[0088] In step S1, the total height of the ridge waveguide is 220 nm, the ridge height is 50 nm, and the ridge width is 660 nm.

[0089] The thickness of the covering layer in step S2 is 0.5 μm.

[0090] In step S3 , the thickness of the lower electrode is 150 nm and the width is 25 μm.

[0091] The material of the piezoelectric layer in step S4 is zinc oxide with a thickness of 1 μm. The number of air slots 7 in step S10 is two (eg Fig. 9 As shown), the two air grooves 7 are respectively located at two sides of the bottom of the waveguide layer 13, and each penetrates the silicon substrate 11 and the buried oxide layer 12, and each extends to the surface of the cover layer 2 away from the lower electrode 3.

[0092] In step S5 , the material of the upper electrode is titanium (Ti), the thickness is 150 nm, and the width is 25 μm.

[0093] In step S10 , the width of the air groove is 3 μm and the depth is 90 μm.

[0094] Example 4

[0095] The preparation method of the suspension modulator based on stress optical effect in this embodiment is basically the same as that in embodiment 2, except that:

[0096] In step S1, a strip waveguide with a height of 300 nm and a width of 500 nm is etched in the top silicon layer by inductively coupled plasma-reactive ion etching (ICP-RIE).

[0097] The thickness of the covering layer in step S2 is 2.0 μm.

[0098] In step S3 , the thickness of the lower electrode is 250 nm and the width is 1 μm.

[0099] In step S4, the material of the piezoelectric layer is aluminum nitride, and the thickness is 3 μm.

[0100] In step S5 , the material of the upper electrode is gold (Au), the thickness is 250 nm, and the width is 1 μm.

[0101] The width of the air groove is 4 μm and the depth is 600 μm.

[0102] It should be noted that when the waveguide layer is a strip waveguide, the preparation method is the same as that in Example 2, except that the shape and size of the waveguide layer etched in step S1 are different, which will not be described here. When the thickness of the strip waveguide is 220nm and the width is 450-500nm, the requirements of the modulator of the present invention can be met.

[0103] Example 5

[0104] This embodiment studies the stress distribution of modulators with different structures.

[0105] 5.1. Reference Figure 6 The structural parameters and test conditions of the modulator are as follows: the width of the upper electrode 5 is 7 μm; the width of the air slot 7 is 0.45 μm. The electric field is 1 V / μm.

[0106] When the waveguide layer 13 is a strip waveguide with a width of 450 nm and a height of 220 nm, the stress distribution diagrams of the modulator with air slots 7 on the X-axis and Y-axis are as follows: Fig.10 and Fig.11 The stress distribution diagrams of the modulator without air slot 7 on the X-axis and Y-axis are shown as follows: Fig.12 and Fig.13 shown.

[0107] When the waveguide layer 13 is a ridge waveguide with a width of 470 nm, a total height of 220 nm, and a ridge region height of 130 nm, the stress distribution diagrams of the modulator with air slots 7 on the X-axis and Y-axis are respectively as follows: Fig.14 and Fig.15 The stress distribution diagrams of the modulator without air slot 7 on the X-axis and Y-axis are shown as follows: Fig.16 and Fig.17 shown.

[0108] from Figures 10 to 17 It can be seen that regardless of whether the modulator structure is provided with an air slot or not, the stress δ along the X-axis direction can be seen in the stress distribution diagram. x and the stress δ along the Y-axis Y The maximum stress is concentrated in the waveguide core, and the main stress is caused by δ x When the electric field is 1V / μm, the upper electrode width is 7μm, and the air slot width is 0.45μm, the strip waveguide and ridge waveguide δ xThe maximum stress magnitudes are 24.7MPa and 32.8MPa respectively. In addition, by comparing the stress distribution of the structure without air slots with that of the structure with air slots, it can be seen that the stress is greatly increased. x The maximum value increased from 6.52MPa to 24.7MPa, δ Y The maximum value increased from 1.65MPa to 8.82MPa; the δ of the ridge waveguide x The maximum value increased from 10.1MPa to 32.8MPa, δ Y The maximum value increases from 1.95MPa to 12.5MPa, resulting in a huge improvement in the effective refractive index change.

[0109] 5.2. Since the stress-optical effect causes the change in the refractive index of the material to be related to the stress magnitude, the ridge waveguide is used as an example to study the change in the effective refractive index of the modulator (△n eff ) changes with the width of the upper electrode and the width of the air slot. The electric field is 1V / μm. The piezoelectric layer material is PZT, and the thickness is 2μm. The trend of the measured effective refractive index change is as follows Fig.18 As shown in the figure, when the air slot width is in the range of 0.45 to 4 μm, as the width of the upper electrode changes, the effective refractive index changes to the maximum at an upper electrode width of 7 μm. When the upper electrode width is greater than 0 and does not exceed 45 μm, the smaller the air slot width, the greater the change in effective refractive index, which means that a smaller air slot width has a stronger mechanical effect.

[0110] 5.3. Taking the ridge waveguide as an example, the effect of the thickness change of the silicon dioxide cover layer in the modulator structure on the change of the effective refractive index is studied. The electric field is 1V / μm. The width of the upper electrode is 7μm. The piezoelectric layer material is PZT, and the thickness is 2μm. The measured trend of the effective refractive index change is as follows: Fig.19 As shown. It can be seen from the figure that when the thickness of the silica covering layer is 0.5-2.0μm, as the thickness of the silica covering layer increases, the stress transmission to the waveguide is limited, resulting in a decrease in the magnitude of the change in the effective refractive index. Taking into account the absorption loss of the lower electrode to the waveguide, it is necessary to consider the optimal thickness of the silica covering layer. When the silica covering layer is 1μm thick, the loss to the ridge waveguide is relatively small. At the same time, it can be seen from the figure that when the air slot width is in the range of 0.45-4μm, as the air slot width decreases, the change in the effective refractive index becomes greater.

[0111] 5.4. Taking the ridge waveguide as an example, the change of the effective refractive index of the modulator with the change of the electric field is studied. The width of the upper electrode is 7μm. The piezoelectric layer material is PZT, and the thickness is 2μm. The thickness of the silicon dioxide cover layer is 1μm. The measured results are as follows Fig. 20As shown in the figure, when the width of the air slot is in the range of 0.45 to 4 μm, as the electric field increases, the stress transmitted to the waveguide by the inverse piezoelectric effect of the driving piezoelectric layer increases, resulting in a change in the effective refractive index. When the electric field is 10 V / μm and the width of the air slot is 0.45 μm, the effective refractive index changes by 1.3×10 -3 , has reached the order of magnitude of electro-optic modulators based on carrier dispersion effects.

[0112] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. For any person skilled in the art, the present invention may have various changes and modifications. Any simple equivalent changes and modifications made according to the scope of protection of the present invention and the contents of the specification should be included in the scope of protection of the present invention.

Claims

1. A suspension modulator based on stress optical effect, characterized in that: The invention comprises an SOI waveguide, a covering layer covering the SOI waveguide, a lower electrode deposited on the upper surface of the covering layer, a piezoelectric layer arranged on the upper surface of the lower electrode, an upper electrode deposited in the middle of the upper surface of the piezoelectric layer, and a protective layer covering the upper surface of the upper electrode; the SOI waveguide comprises a silicon substrate, a buried oxide layer and a waveguide layer from bottom to top; the waveguide layer, the lower electrode, the piezoelectric layer and the upper electrode form a micro-ring structure or the waveguide layer, the lower electrode, the piezoelectric layer and the upper electrode form a Mach-ZnO2 structure. The piezoelectric layer has a piezoelectric structure; at least one air groove is provided on a side of the silicon substrate away from the buried oxide layer; the depth of the air groove penetrates the silicon substrate and the buried oxide layer in the direction from the silicon substrate to the lower electrode; the width of the air groove is 0.45~4μm, and the ratio of its depth to width is (30~150):1; the material of the piezoelectric layer is at least one of lead zirconate titanate, zinc oxide and aluminum nitride; the thickness of the covering layer is 0.5~1.0μm; the width of the upper electrode is 1~20μm.

2. The suspension modulator based on stress optical effect according to claim 1, characterized in that: The waveguide layer is a strip waveguide, the width of the strip waveguide is 450-500nm, and the thickness is 220-300nm; or the waveguide layer is a ridge waveguide, the total height of the ridge waveguide is 220-300nm, the ridge area height is 50-150nm, and the ridge area width is 450-660nm.

3. The suspension modulator based on stress optical effect according to claim 1, characterized in that: The thickness of the piezoelectric layer is 1-3 μm.

4. The suspension modulator based on stress optical effect according to claim 1, characterized in that: The thickness of the upper electrode is 150-250 nm; or / and the thickness of the lower electrode is 150-250 nm.

5. The suspension modulator based on stress optical effect according to claim 1, characterized in that: The width of the lower electrode is 1-25 μm.

6. The suspension modulator based on stress optical effect according to claim 1, characterized in that: The material of the upper electrode is at least one of platinum, titanium and gold; or / and the material of the lower electrode is platinum-titanium alloy.

7. The method for preparing the suspension modulator based on stress optical effect according to any one of claims 1 to 6, characterized in that: The following steps are involved: Cleaning an SOI substrate, wherein the SOI substrate includes a silicon substrate, a buried oxide layer and a top silicon layer; patterning the SOI substrate, and etching a waveguide layer in the top silicon layer to obtain an SOI waveguide; Depositing a capping layer on the surface of the SOI waveguide and grinding it flat; A lower electrode, a piezoelectric layer, an upper electrode, and a protective layer are sequentially stacked on the surface of the covering layer; The silicon substrate is thinned, and an air groove is etched on a side thereof away from the buried oxide layer.

8. The preparation method according to claim 7, characterized in that: The following steps are involved: A first through hole is opened in the middle of the protective layer, and a second through hole is opened on one side of the protective layer; a first contact metal electrode in contact with the upper electrode is made in the first through hole, and a second contact metal electrode in contact with the lower electrode is made in the second through hole.

9. The preparation method according to claim 8, characterized in that: The first contact metal electrode includes a first metal wire located in the first through hole and a first metal pad located outside the first through hole, and the second contact metal electrode includes a second metal wire located in the second through hole and a second metal pad located outside the second through hole; the materials of the first metal wire, the second metal wire, the first metal pad and the second metal pad are all one of gold, copper and aluminum.

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