Silicon-based waveguide providing passive thermal compensation and method of fabrication thereof
Patent Information
- Application Number
- CN202611382996.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-09-08
- Publication Date
- 2026-10-13
Smart Images
Figure CN122902007A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of semiconductor technology, and in particular to a silicon-based waveguide that provides passive thermal compensation and a method for fabricating the same. Background Technology
[0002] Single-crystal silicon has extremely wide applications in integrated photonics technology; however, its sensitive thermophysical properties severely limit the application of silicon photonic devices based on single-crystal silicon in uncontrolled and wide-temperature environments. Single-crystal silicon exhibits an extremely high positive thermo-optic coefficient (approximately 1.86 × 10⁻⁶) in the near-infrared band (such as the 1550 nm communication wavelength). -4 K -1 Therefore, applying this technology to microring resonators will result in a thermal redshift of the resonant wavelength from 80 pm / K to 90 pm / K, and in large-scale, high-density arrays, there will also be issues with temperature drift and thermal crosstalk. If active temperature controllers such as TECs are used, not only will the device cost be higher, but active feedback tuning will also be required, increasing static power consumption.
[0003] How to counteract the refractive index drift caused by temperature changes through a passive structure has become a technical problem that urgently needs to be solved. Summary of the Invention
[0004] Based on this, a silicon-based waveguide with passive thermal compensation and its fabrication method are provided to solve the technical problem that passive feedback offsetting refractive index drift caused by temperature change increases static power consumption.
[0005] In a first aspect, this application provides a silicon-based waveguide providing passive thermal compensation, comprising: A substrate and a monocrystalline silicon waveguide disposed on the substrate, the monocrystalline silicon waveguide extending along a predetermined crystal orientation; Stress-induced polymer, located on at least one side of the monocrystalline silicon waveguide, and / or on the upper surface of the monocrystalline silicon waveguide; A rigid constraint shell, covering the outer walls and top of the stress-induced polymer, is used to limit the range of thermal expansion of the stress-induced polymer and convert the volume change into a directional thermal stress field after the temperature of the stress-induced polymer rises.
[0006] In some embodiments, the substrate includes a silicon-on-insulator substrate with a 001 main crystal plane, and the axial propagation direction of the single-crystal silicon waveguide is
[110] crystal orientation or Crystal orientation; The stress-induced polymer is located in the optical path-sensitive region of the monocrystalline silicon waveguide.
[0007] In some embodiments, the stress-induced polymer is located on one side of the transverse direction of the monocrystalline silicon waveguide to generate a directional non-uniform mechanical stress field from the directional thermal stress field, resulting in compressive strain in the monocrystalline silicon waveguide along its transverse horizontal width direction. After being modulated by the elasto-optic tensor coupling relationship of the monocrystalline silicon waveguide, the compressive strain in the transverse horizontal width direction negatively changes the effective refractive index of the transverse electric wave polarization fundamental mode.
[0008] In some embodiments, the stress-induced polymer is located above the discontinuous local arc region of the monocrystalline silicon waveguide. The lateral slippage of the stress-induced polymer is restricted by the continuity of the interfacial shear displacement between the bottom surface of the stress-induced polymer and the underlying structure. This allows the stress-induced polymer to apply locally oriented asymmetric compressive stress to the monocrystalline silicon waveguide after the temperature rises, thereby activating the local photoelastic effect of the core of the monocrystalline silicon waveguide.
[0009] In some embodiments, the rigid constraint shell is a hard inorganic dielectric capping layer with a Young's modulus of not less than 50 GPa, and is coated with a stress-induced polymer to construct a fully enclosed three-dimensional physical constraint cavity. The hard inorganic dielectric capping layer includes at least one material selected from silicon nitride, aluminum oxide, and silicon oxide. The linear expansion coefficient of the stress-induced polymer is not less than 30 × 10⁻⁶. -6 K -1 And Young's modulus is not greater than 10 GPa.
[0010] In some embodiments, the silicon-based waveguide is a closed microring resonator, and a stress-induced polymer covers a locally active arc segment of the microring resonator, the perimeter of which is 20% to 95% of the physical circumference of the microring resonator.
[0011] In some embodiments, the coverage area of the stress-induced polymer avoids the preset functional region of the silicon waveguide, the preset functional region including at least one of the following: coupling region, electrode region, P-type intrinsic-N-type PIN junction modulation region, and polarization control region.
[0012] In some embodiments, the silicon-based waveguide is placed in at least one silicon optical device among a microring resonator, a microring filter, a Mach-Zehnder interferometer (MZI) filter, an MZI optical switch, and a microring modulator.
[0013] In some embodiments, the stress-induced polymer is a fluorinated modified polyimide polymer variant.
[0014] In some embodiments, the silicon-based waveguide further includes; A buffer layer, located between the stress-induced polymer and the monocrystalline silicon waveguide, is used to reduce the overlap of optical mode fields between the input light and the directional thermal stress field generated by the monocrystalline silicon waveguide, and to maintain the stress transmission path of the stress-induced polymer.
[0015] Secondly, this application provides a method for fabricating a silicon-based waveguide that provides passive thermal compensation, comprising: Substrate preparation; A single-crystal silicon waveguide extending along a predetermined crystal orientation is fabricated on a substrate; A stress-induced polymer is prepared on at least one side of the monocrystalline silicon waveguide and / or on the upper surface of the monocrystalline silicon waveguide. A rigid constraint shell is prepared on the outer wall and top of the stress-induced polymer to limit the range of thermal expansion of the stress-induced polymer. After the temperature of the stress-induced polymer rises, the volume change is converted into a directional thermal stress field.
[0016] This application provides a silicon-based waveguide that provides passive thermal compensation. By inducing the polymer to expand in volume after the temperature rises, and using a rigid confinement shell to limit the expansion range, the volume change is converted into a directional thermal stress field, which acts on the single-crystal silicon waveguide to provide passive thermal compensation, thereby offsetting the refractive index drift caused by temperature changes. Attached Figure Description
[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0018] Figure 1 This is a schematic diagram of the process flow for the silicon-based waveguide fabrication method provided in the embodiments of this application; Figure 2 A schematic diagram of the silicon-based waveguide structure provided in Embodiment 1 of this application; Figure 3 A schematic diagram of the silicon-based waveguide structure provided in Embodiment 2 of this application; Figure 4 A schematic diagram of the microring structure provided in Embodiment 3 of this application; Figure 5 This is a schematic diagram of the structure of a locally active arc segment in an embodiment of this application; Figure 6 This is a schematic diagram of the straight waveguide structure in an embodiment of this application. Detailed Implementation
[0019] To facilitate understanding of this application, it will be described in more detail below. However, it should be understood that this application can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to provide a more thorough and complete understanding of the disclosure of this application.
[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular implementations or embodiments only and is not intended to be limiting of the application. The optional scope of the term "and / or" as used herein includes any one of two or more of the related listed items, as well as any and all combinations of the related listed items, including any two related listed items, any more related listed items, or a combination of all related listed items.
[0021] This application provides a silicon-based waveguide, comprising: A substrate and a monocrystalline silicon waveguide disposed on the substrate, the monocrystalline silicon waveguide extending along a predetermined crystal orientation; Stress-induced polymer, located on at least one side of the monocrystalline silicon waveguide, and / or on the upper surface of the monocrystalline silicon waveguide; A rigid constraint shell covers the outer wall and top of the stress-induced polymer to limit the range of thermal expansion of the stress-induced polymer and convert the volume change into a directional thermal stress field after the temperature of the stress-induced polymer rises. A buffer layer, located between the stress-induced polymer and the monocrystalline silicon waveguide, is used to reduce the overlap of optical mode fields between the input light and the directional thermal stress field generated by the monocrystalline silicon waveguide, and to maintain the stress transmission path of the stress-induced polymer.
[0022] In optional embodiments of this application, the substrate may be an insulator such as silicon dioxide. For example, the single-crystal silicon waveguide may be a ridge-shaped or strip-shaped waveguide disposed on a silicon-on-insulator (SOI) substrate with a (001) main crystal plane. The axial propagation direction of the single-crystal silicon waveguide may be, but is not limited to, the
[110] crystal orientation of the single-crystal silicon or Crystal orientation.
[0023] See Figure 1 As shown in the embodiment of this application, a method for fabricating a silicon-based waveguide providing passive thermal compensation is provided, comprising: S101: Substrate fabrication; S102: Fabricate a single-crystal silicon waveguide extending along a predetermined crystal orientation on a substrate; S103: A stress-induced polymer is prepared on at least one side of the monocrystalline silicon waveguide and / or on the upper surface of the monocrystalline silicon waveguide. S104: A rigid constraint shell is prepared on the outer wall and top of the stress-induced polymer to limit the thermal expansion range of the stress-induced polymer and convert the volume change into a directional thermal stress field after the temperature of the stress-induced polymer rises.
[0024] In an optional embodiment of this application, the substrate includes a silicon-on-insulator substrate with a 001 main crystal plane, and the axial propagation direction of the single-crystal silicon waveguide is... Crystal orientation or Crystal orientation.
[0025] In an optional embodiment of this application, a buffer layer can also be prepared between the stress-induced polymer and the monocrystalline silicon waveguide in the method for fabricating a silicon-based waveguide that provides passive thermal compensation. This can reduce the overlap of mode fields between the optical mode field and the directional thermal stress field generated by the input light passing through the monocrystalline silicon waveguide, and maintain the stress transmission path of the stress-induced polymer.
[0026] The aforementioned silicon-based waveguide with stress-induced polymer can be placed in at least one silicon optical device among microring resonators, microring filters, Mach-Zehnder interferometer (MZI) filters, MZI optical switches, and microring modulators.
[0027] Assuming the silicon-based waveguide is a closed microring resonator, the stress-induced polymer can cover the local active arc segment of the microring resonator, the perimeter of which is 20% to 95% of the physical circumference of the microring resonator.
[0028] The fabrication of silicon-based waveguides with stress-induced polymers can avoid pre-defined functional regions, which include at least one of the following: coupling region, electrode region, P-type intrinsic-N-type PIN junction modulation region, and polarization control region.
[0029] The rigid constraint shell is a hard inorganic dielectric capping layer with a Young's modulus of not less than 50 GPa, and is coated with stress-induced polymer to construct a fully enclosed three-dimensional physical constraint cavity. The hard inorganic dielectric capping layer includes at least one material selected from silicon nitride, aluminum oxide, and silicon oxide. The linear expansion coefficient of the stress-induced polymer is not less than 30 × 10⁻⁶. -6 K -1 Furthermore, the Young's modulus is not greater than 10 GPa. In the above embodiments, the Young's modulus can be the Young's modulus at room temperature, for example, the Young's modulus at 25°C.
[0030] Assuming that the stress-induced polymer is located above the discontinuous local arc region of the monocrystalline silicon waveguide, the lateral slippage of the stress-induced polymer is restricted by the continuity of the interfacial shear displacement between the bottom surface of the stress-induced polymer and the underlying structure. This allows the stress-induced polymer to apply locally oriented asymmetric compressive stress to the monocrystalline silicon waveguide after the temperature rises, thereby activating the local photoelastic effect at the core of the monocrystalline silicon waveguide.
[0031] Assuming that the stress-induced polymer is located on one side of the transverse direction of the monocrystalline silicon waveguide, so that the directional thermal stress field generates a directional non-uniform mechanical stress field, compressive strain is generated in the monocrystalline silicon waveguide along the transverse horizontal width direction. After the compressive strain in the transverse horizontal width direction is modulated by the elastic-optical tensor coupling relationship of the monocrystalline silicon waveguide, it produces a negative change in the effective refractive index of the transverse electric wave polarization fundamental mode.
[0032] The linear expansion coefficient of a monocrystalline silicon waveguide is smaller than that of a stress-induced polymer. Therefore, when the ambient temperature rises, the stress-induced polymer undergoes mechanical expansion due to heat, and its physical boundaries exhibit resisted expansion deformation. Based on its shape and position, a directional thermal stress field is applied to the monocrystalline silicon waveguide. This directional thermal stress field induces a polarization-dependent negative refractive index change within the monocrystalline silicon waveguide through the anisotropic photoelastic effect, thereby suppressing or offsetting the positive refractive index drift caused by the monocrystalline silicon waveguide's own thermo-optical effect in situ.
[0033] The stress-induced polymer can be located in the optical path-sensitive region of the monocrystalline silicon waveguide. The optical path-sensitive region refers to the area where changes in the optical path will cause a change in the resonant frequency response of a resonant device or a change in the phase difference of an interferometric device. For example, in the straight waveguide regions of the two arms of an interferometer in an MZI optical switch, changes in local temperature can alter the phase difference between the two waveguide arms, causing instability in the switch state. Therefore, the stress-induced polymer described in this application can be placed in the straight waveguide regions of the two arms of the interferometer. The stress-induced polymer can be located on at least one side of the monocrystalline silicon waveguide, and / or on the upper surface of the monocrystalline silicon waveguide.
[0034] In an optional embodiment of this application, it is assumed that the stress-induced polymer is located on one side of the transverse direction of the monocrystalline silicon waveguide, so that the directional thermal stress field generates a directional non-uniform mechanical stress field, causing compressive strain in the monocrystalline silicon waveguide along the transverse horizontal width direction; the compressive strain in the transverse horizontal width direction is converted into a change in refractive index through the elasto-optic effect of the monocrystalline silicon waveguide, causing a negative change in the effective refractive index of the transverse electric wave polarization fundamental mode.
[0035] Assuming a stress-induced polymer (SIP) is located above a discontinuous local arc region of a monocrystalline silicon waveguide, the lateral slippage of the SIP is restricted by the continuity of interfacial shear displacement between its bottom surface and the underlying structure. This allows the SIP to apply locally oriented asymmetric compressive stress to the monocrystalline silicon waveguide upon temperature rise, thereby activating the localized photoelastic effect at the core of the waveguide. This locally oriented asymmetric compressive stress is predominantly composed of compressive stress perpendicular to the interface.
[0036] The rigid constraint shell is a hard inorganic medium layer with a Young's modulus of not less than 50 GPa, and is covered with a stress-induced polymer to construct a fully enclosed three-dimensional physical constraint cavity. The hard inorganic medium capping layer includes at least one material selected from silicon nitride, alumina, and silicon oxide. The linear expansion coefficient of the stress-induced polymer is not less than 30 × 10⁻⁶. -6 K -1 Furthermore, the Young's modulus is not greater than 10 GPa. When the temperature rises, the free expansion of the surface of the polymer stress-generating medium is restricted by the rigid constraint shell. Isotropic hydrostatic pressure accumulates in the three-dimensional physical constraint cavity of the rigid constraint shell, and is transformed into lateral horizontal compressive stress acting on the single-crystal silicon waveguide core through the contact boundary, thereby exciting the stress photoelastic tuning effect of the single-crystal silicon core. Assuming the thickness of the buffer layer is 20nm to 100nm (such as silicon oxide with a Young's modulus of approximately 70GPa), its thickness is much smaller than the characteristic dimensions of the stress-induced polymer and the rigid constraint shell (0.5μm to 5μm), and the Young's modulus of the buffer layer is significantly higher than that of the stress-induced polymer. Mechanically, the buffer layer can be regarded as a rigid gasket in the stress transmission path of the stress-induced polymer, and has a limited impact on the transmission efficiency of hydrostatic pressure and lateral stress. Optically, the buffer layer can moderately isolate the near-field peak of the optical mode in the single-crystal silicon waveguide from the stress-induced polymer with strong absorption and / or large refractive index difference, reduce the overlap ratio of the mode field between the optical field and the stress-induced polymer, thereby reducing material absorption loss and propagation loss caused by local refractive index abrupt changes.
[0037] This application provides a silicon-based resonator, the shape of which can be ring, rounded rectangle, etc.
[0038] Stress-induced polymers are placed in locally active arc segments (such as the non-functional segments of microring resonators, the rounded non-functional segments of rounded rectangular resonators, etc.) to reduce refractive index drift caused by temperature changes.
[0039] In optional embodiments of this application, since the silicon-based waveguide provides passive thermal compensation, it is suitable for a variety of silicon optical devices. The passive thermal compensation of this silicon-based waveguide can be used in wavelength-stable resonant devices, such as microring resonators and microring filters. Alternatively, the passive thermal compensation of this silicon-based waveguide can be used in switch-state-stable interferometric devices, such as Mach-Zehnder interferometer (MZI) optical switches and cascaded MZI filters. Alternatively, the passive thermal compensation of this silicon-based waveguide can be used in modulators with stable modulation operating points, such as microring modulators. The passive thermal compensation of this silicon-based waveguide effectively suppresses temperature drift without additional power consumption, significantly improving the reliability of the device in variable temperature environments.
[0040] Assuming the ambient temperature rises from 25°C to 65°C, the temperature rise is ΔT = 40K. The thermo-optical coefficient of single-crystal silicon material at 1550nm wavelength is approximately 1.86 × 10⁻⁶. -4K -1 The refractive index change of a single-crystal silicon waveguide due to the thermo-optical effect is as follows:
[0041] The refractive index change in a single-crystal silicon waveguide due to the thermo-optic effect is represented by dn / dT, which is the thermo-optic coefficient of single-crystal silicon material. It describes the temperature-dependent refractive index change of optical materials and represents the amount of refractive index change caused by a unit temperature change. At ΔT = 40K, .
[0042] According to the elastic-optical tensor relationship of single-crystal silicon, mechanical strain can cause anisotropic changes in refractive index, and the corresponding change in refractive index can be calculated using the following formula:
[0043] Where n represents the refractive index of the single-crystal silicon waveguide when it is not subjected to strain, and the subscript i represents the i-th component of the elasto-optic tensor of the single-crystal silicon material. This represents the change in refractive index of a single-crystal silicon waveguide after strain. The elasto-optic tensor component represents the intrinsic parameter of a single-crystal silicon material, used to describe the coupling relationship between mechanical strain and changes in optical properties. This represents the j-th component of the strain tensor that describes the mechanical strain of a single-crystal silicon material. This indicates the summation over all strain components, meaning that strain in all directions works together to affect the change in refractive index.
[0044] In an optional embodiment of this application, before fabricating the silicon-based waveguide, the refractive index change of the single-crystal silicon waveguide caused by the thermo-optic effect can be obtained by combining the complete crystal axis rotation relationship and the elastic-optic coefficient through finite element simulation, thereby simulating the position, shape and size of the stress-induced polymer.
[0045] In an optional embodiment of this application, assuming the single-crystal silicon waveguide has a width of 450nm, the lateral confinement is weaker than the vertical confinement, the refractive index of its stress-induced polymer is 1.5 to 1.7, and the refractive index of the rigid confinement shell material is 2.0, then the refractive index of the stress-induced polymer is higher than that of the standard silicon oxide cladding, which will increase the proportion of evanescent field entering the polymer, resulting in a significant difference in the local mode field distribution compared with conventional waveguides using standard silicon oxide cladding.
[0046] The material of the stress-induced polymer can be a fluorinated modified polyimide polymer variant.
[0047] For example, stress-induced polymers employ low-CH content polymer variants such as fluorinated polyimide, which can be prepared by copolymerization-curing reaction of polyamic acid, surface-modified silica nanocages, and modifiers in a solvent.
[0048] For example, stress-induced polymers are prepared by reacting fluorinated polyimide variants containing trifluoromethyl side chains with 6FDA (hexafluorodianhydride) type polyamic acid, aminated surface-modified silica nanocages, and perfluorooctyl modifiers in a solvent. The proportion of CH bonds in the trifluoromethyl side chain type fluorinated polyimide variants is much lower than that in conventional polyimides.
[0049] For example, stress-induced polymers are prepared by reacting 5FBODA-type fluorinated polyamic acid, fluorosilane-modified silica nanocages, and fluorinated diamine modifiers in DMAc solvent using perfluorinated aromatic ring fluorinated polyimide variants. This process achieves extremely low hydrogen content by substituting a large number of CH bonds with fluorine atoms.
[0050] See Figure 2 The first embodiment shown assumes that the silicon-based waveguide in the first embodiment adopts a fully open local asymmetric strip stress structure.
[0051] The silicon-based waveguide includes a silicon substrate 201, a buried oxide layer 202, a monocrystalline silicon waveguide 203, a stress-induced polymer 204, and a rigid constraint shell 205. The buried oxide layer 202 covers the entire silicon substrate 201. The stress-induced polymer 204 and the rigid constraint shell 205 are bonded to one side of the monocrystalline silicon waveguide 203, respectively. The rigid constraint shell 205 covers the top of the monocrystalline silicon waveguide 203. The area directly above the stress-induced polymer 204 is empty. The rigid constraint shell 205 is bonded to the left side, and the monocrystalline silicon waveguide 203 and the rigid constraint shell 205 are bonded to the right side from bottom to top.
[0052] The fabrication process of this structure may include, but is not limited to: On a standard (001) main crystal plane silicon-on-insulator (SOI) substrate, the SOI may include a buried oxide layer 202. The thickness of the silicon layer above the buried oxide layer 202 may be 220 nm. A single-crystal silicon waveguide 203 (the single-crystal silicon waveguide is a strip-shaped single-crystal silicon optical waveguide) with a cross-sectional dimension of 450 nm × 220 nm is fabricated in the silicon layer. Its axial extension direction is y =
[110] , and the horizontal width direction of the waveguide is x = Direction. A silicon dioxide cladding layer with a thickness of approximately 1 to 2 μm is deposited above the monocrystalline silicon waveguide 203 (which can cover the entire waveguide and the buried oxide layer above it) to serve as a rigid constraint shell 205. Through photolithography and etching processes, silicon dioxide is locally removed in the left bias region of the monocrystalline silicon waveguide to form a deep trench. PMMA (Polymethyl Methacrylate, with a linear thermal expansion coefficient of 1000000%) is then spin-coated and cured within this deep trench. As a stress-induced polymer 204, the top surface of the stress-induced polymer 204 is open to the air.
[0053] In optional embodiments of this application, spin-coated curable polymethyl methacrylate can also be replaced with modified polyimide, and no limitation is made herein.
[0054] See Figure 3 The second embodiment shown assumes that the silicon-based waveguide in the second embodiment adopts a three-dimensional fully enclosed confined cavity structure.
[0055] The silicon-based waveguide includes: a silicon substrate 201, a buried oxide layer 202, a monocrystalline silicon waveguide 203, a stress-induced polymer 204, a rigid constraint shell 205, and a buffer layer 206. The buried oxide layer 202 is located above the silicon substrate 201 and covers the entire silicon substrate 201. The outer side of the monocrystalline silicon waveguide 203 is covered by the buffer layer 206. The left and right sides of the buffer layer are covered by the stress-induced polymer 204. The outer side (left and right sides and top side) of the stress-induced polymer is covered by the rigid constraint shell 205.
[0056] The standard (001) silicon-on-insulator (SOI) on the main crystal plane may include a silicon substrate 201, a buried oxide layer 202, and a silicon layer. The thickness of the buried oxide layer can be 2 μm. Assuming that the silicon-based waveguide is located in a micro-ring structure and the buried oxide layer is a BOX layer, since the single-crystal silicon waveguide is continuously formed on the silicon layer of the SOI substrate and is firmly bonded to the underlying BOX layer, the micro-ring structure formed thereby has stable mechanical constraints. The thermal stress generated by the stress-induced polymer 204 mainly acts on the corresponding waveguide region in the form of local strain, without causing overall displacement of the entire micro-ring structure.
[0057] A single-crystal silicon waveguide 203 with a cross-sectional dimension of 450nm × 220nm (this single-crystal silicon waveguide is a strip-shaped single-crystal silicon optical waveguide) is fabricated in a silicon layer of silicon-on-insulator (SOI) on a standard (001) main crystal plane. Its axial extension direction is y =
[110] , and the horizontal width direction of the waveguide is x = Direction. A buffer layer with a thickness of 20 nm to 100 nm is deposited on the surface of the monocrystalline silicon waveguide 203, so that the buffer layer 206 covers the top and sidewalls of the monocrystalline silicon waveguide 203. Trenches for accommodating stress-induced polymer 204 are formed on both sides of the monocrystalline silicon waveguide 203, and the stress-induced polymer 204 is filled in the trenches. A rigid inorganic dielectric capping layer is deposited on top of the buffer layer and the stress-induced polymer 204 to form a rigid constraint shell.
[0058] The modified polyimide used in the stress-induced polymer 204 has a significantly higher transition temperature (above 300°C) to ensure compatibility with the subsequent rigid capping layer deposition process. In an optional embodiment, the modified polyimide can be a fluorinated modified polyimide to suppress the vibrational absorption of CH bonds in the 1550nm band. Buffer layers 206 are provided between the sidewalls of the monocrystalline silicon waveguide 203 and the stress-induced polymer 204, and between the top of the monocrystalline silicon waveguide 203 and the rigid constraint shell, to reduce the overlap of the optical mode field of the monocrystalline silicon waveguide 203, the mode field of the stress-induced polymer 204, and the rigid constraint shell, thus constructing a fully closed three-dimensional micro-stress cavity.
[0059] The rigid confinement shell is deposited using a low-temperature process, such as low-temperature PECVD (Plasma Enhanced Chemical Vapor Deposition), with a process temperature of approximately 200–250°C, which is lower than the glass transition temperature of the polyimide used, in order to avoid affecting the stability of the stress-induced polymer 204.
[0060] The rigid constraint shell can be made of silicon nitride (Si3N4, Young's modulus of about 100 to 300 GPa).
[0061] If modified polyimide is used (typical parameter: Young's modulus) Poisson's ratio linear thermal expansion coefficient As a stress-generating medium, the bulk modulus of silicon nitride can be estimated in the following ways:
[0062] K represents the bulk modulus of the stress-induced polymer. This represents the Young's modulus of stress-induced polymers. This represents the Poisson's ratio of the stress-induced polymer.
[0063] Assuming the ambient temperature rise remains at ΔT = 40K, the strong displacement constraint provided by the outer Si3N4 rigid shell restricts the release path of the stress-induced surface deformation of the polymer 204. Its constrained thermal expansion behavior is largely dominated by the bulk modulus K, resulting in the accumulation of isotropic hydrostatic pressure within the closed cavity. Estimated using the standard formula, this pressure is approximately:
[0064] Let K be the isotropic hydrostatic pressure of the polymer within the cavity, and K be the bulk modulus of the polymer. The linear thermal expansion coefficient of the polymer is . This represents the change in temperature.
[0065] The hydrostatic pressure acts on the sidewall of the monocrystalline silicon waveguide, resulting in compressive normal stress in the lateral horizontal direction. Apply in the form of (the negative sign indicates compression).
[0066] Substituting the above hydrostatic pressure into the elastic-optical relation formula, the corresponding change in refractive index is:
[0067]
[0068] Among them, Young's modulus Poisson's ratio refractive index Elastic tensor components , . This indicates the change in refractive index corresponding to the relationship between the elasto-optical effect and the photoluminescence. This represents the refractive index change that primarily modulates the TE polarization fundamental mode. The stress in the embodiments of this application... The overlying layer can be observed to contain approximately A change in refractive index (birefringence) on the order of magnitude can achieve a local thermo-optical coefficient compensation of approximately 17%. This can reduce the thermally induced wavelength drift of silicon-based microring resonators from 85 pm / K to the order of 71 pm / K.
[0069] The aforementioned buffer layer is made of silicon dioxide and can have a thickness of 20nm to 100nm.
[0070] See Figure 4 As shown, assuming that Figure 3 The three-dimensional closed-loop confined cavity stress element from Example 2 is applied to a closed microring resonator. This closed microring resonator has a radius of approximately 10 μm. Silicon-based waveguides can be fabricated using the process described in Example 2; however, the stress-induced polymer does not cover the entire microring structure of the closed microring resonator, but rather only in the locally active arc segments of the microring structure (see Example 2). Figure 5The active arc segment is covered by the uncovered stress-induced polymer waveguide, while the remaining arc segments retain the ordinary silicon waveguide structure. The local active arc segments are connected to the ordinary waveguide of the uncovered stress-induced polymer through a continuous monocrystalline silicon waveguide. The stress-induced polymer has a gradual start and / or gradual termination along the waveguide propagation direction to reduce mode perturbation and propagation loss.
[0071] Stress-induced polymers (SIPs) comprise 20% to 95% of the total circumference of the microring. When the coverage of SIPs is relatively small, the passive compensation effect is relatively weak, but the original structure of the device is preserved to a greater extent. When the coverage of SIPs increases, a greater overall compensation effect can be obtained, but factors such as device layout, process implementation, and optical performance should be considered in combination.
[0072] As an optional example, the coverage of the stress-induced polymer is set to η=80%, and the local refractive index change estimated in Example 2 is obtained. Further calculations were performed. When the ambient temperature rise ΔT = 40K, the refractive index change caused by the thermo-optical effect of the single-crystal silicon waveguide is approximately... In this case, the overall effective refractive index of the microring structure of the closed microring resonator can be approximately expressed by the following formula:
[0073] Substituting the coverage η of the stress-induced polymer into 80%, we obtain:
[0074] The silicon-based waveguide that provides passive thermal compensation reduces the overall thermal-optical drift by approximately 13% compared to the uncompensated case.
[0075] For the same device, under the condition that the local stress effect remains basically consistent, with different coverage rates of stress-induced polymers, the overall compensation effect increases with the increase of coverage rate. This compensation effect can be further optimized by combining factors such as polymer material parameters, constrained cavity structure, waveguide size, and stress distribution through finite element simulation, which is not limited here.
[0076] See Figure 6 As shown in the optional embodiment of this application, the straight waveguide of the rounded rectangular resonator is part of the resonant cavity. Its effective refractive index change will change the optical path length of the resonant cavity and affect the resonant wavelength. Therefore, stress-induced polymer can be set in the straight waveguide area according to the thermal compensation requirements.
[0077] In other silicon photonic devices requiring local thermal compensation, such as Mach-Zehnder interferometers (MZIs) and spiral delay lines, stress-induced polymers can be placed in the optical path-sensitive region. The stress-induced polymer can be located on one side of the optical path-sensitive region to generate a directional non-uniform mechanical stress field from the directional thermal stress field. This causes compressive strain along the horizontal width of the single-crystal silicon waveguide. This compressive strain, modulated by the elastic-optical tensor coupling relationship of the single-crystal silicon waveguide, negatively alters the effective refractive index of the transverse electric wave polarization fundamental mode.
[0078] This application provides a local stress compensation scheme suitable for silicon-based waveguides, applied to passive thermal compensation. It achieves a comprehensive balance between temperature drift compensation capability, device performance, and process integration without changing the fabrication equipment. This provides a feasible implementation method for the engineering application of silicon-based waveguides in high-density WDM (Wavelength Division Multiplexing) and CPO (Co-packaged optics) systems.
[0079] In optional embodiments of this application, spin-coated curable polymethyl methacrylate can also be replaced with modified polyimide, and no limitation is made herein.
[0080] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0081] The above embodiments are merely illustrative of several implementation methods of this application, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application.
Claims
1. A silicon-based waveguide providing passive thermal compensation, characterized in that, include: A substrate and a single-crystal silicon waveguide disposed on the substrate, the single-crystal silicon waveguide extending along a predetermined crystal orientation; Stress-induced polymer is located on at least one side of the monocrystalline silicon waveguide, and / or on the upper surface of the monocrystalline silicon waveguide; A rigid constraint shell, covering the outer wall and top of the stress-induced polymer, is used to limit the range of thermal expansion of the stress-induced polymer and to convert the volume change into a directional thermal stress field after the temperature of the stress-induced polymer rises.
2. The silicon-based waveguide according to claim 1, characterized in that, The substrate includes a (001) silicon-on-insulator substrate with a main crystal plane, and the axial propagation direction of the single-crystal silicon waveguide is [110] crystal orientation or Crystal orientation; The stress-induced polymer is located in the optical path-sensitive region of the monocrystalline silicon waveguide.
3. The silicon-based waveguide according to claim 1, characterized in that, The stress-induced polymer is located on one side of the transverse direction of the monocrystalline silicon waveguide, so that the directional thermal stress field generates a directional non-uniform mechanical stress field, which compresses strain in the transverse horizontal width direction of the monocrystalline silicon waveguide; the compressive strain in the transverse horizontal width direction is modulated by the elastic-optical tensor coupling relationship of the monocrystalline silicon waveguide, and then negatively changes the effective refractive index of the transverse electric wave polarization fundamental mode.
4. The silicon-based waveguide according to claim 1, characterized in that, The stress-induced polymer is located above the discontinuous local arc region of the monocrystalline silicon waveguide. The lateral slippage of the stress-induced polymer is restricted by the continuity of the interfacial shear displacement between the bottom surface of the stress-induced polymer and the underlying structure. This allows the stress-induced polymer to apply locally oriented asymmetric compressive stress to the monocrystalline silicon waveguide after the temperature rises, thereby activating the local photoelastic effect of the core of the monocrystalline silicon waveguide.
5. The silicon-based waveguide according to claim 1, characterized in that, The rigid constraint shell is a hard inorganic dielectric capping layer with a Young's modulus of not less than 50 GPa, and it covers the stress-induced polymer to construct a fully enclosed three-dimensional physical constraint cavity. The hard inorganic dielectric capping layer includes at least one material selected from silicon nitride, aluminum oxide, and silicon oxide. The linear expansion coefficient of the stress-induced polymer is not less than 30 × 10⁻⁶. -6 K -1 And Young's modulus is not greater than 10 GPa.
6. The silicon-based waveguide according to claim 1, characterized in that, The silicon-based waveguide is a closed microring resonator, and the stress-induced polymer covers a local active arc segment of the microring resonator. The perimeter of the local active arc segment is 20% to 95% of the physical circumference of the microring resonator.
7. The silicon-based waveguide according to claim 1, characterized in that, The stress-induced polymer covering area avoids the preset functional area of the silicon waveguide, which includes at least one of the following: coupling area, electrode area, P-type intrinsic-N-type PIN junction modulation area, and polarization control area.
8. The silicon-based waveguide according to claim 1, characterized in that, The silicon-based waveguide is placed in at least one silicon optical device among a microring resonator, a microring filter, a Mach-Zehnder interferometer (MZI) filter, an MZI optical switch, and a microring modulator.
9. The silicon-based waveguide according to claim 1, characterized in that, The stress-induced polymer is a fluorinated polyimide polymer variant.
10. The silicon-based waveguide according to claim 1, characterized in that, The silicon-based waveguide also includes; A buffer layer, located between the stress-induced polymer and the monocrystalline silicon waveguide, is used to reduce the overlap of the optical mode field generated by the input light passing through the monocrystalline silicon waveguide and the directional thermal stress field, and to maintain the stress transmission path of the stress-induced polymer.
11. A method for fabricating a silicon-based waveguide providing passive thermal compensation, characterized in that, include: Substrate preparation; A single-crystal silicon waveguide extending along a predetermined crystal orientation is fabricated on the substrate; A stress-induced polymer is prepared on at least one side of the monocrystalline silicon waveguide and / or on the upper surface of the monocrystalline silicon waveguide. A rigid constraint shell is prepared on the outer wall and top of the stress-induced polymer to limit the range of thermal expansion of the stress-induced polymer, thereby converting the volume change into a directional thermal stress field after the temperature of the stress-induced polymer rises.