Silicon-phase change material hetero-integrated waveguide structure, non-volatile waveguide phase shifter
By heterogeneously integrating low-loss phase change materials and graphene micro heaters into silicon-based optoelectronic integrated devices, the problems of large size and high power consumption of silicon-based optoelectronic devices are solved, realizing a non-volatile waveguide phase shifter with fast phase modulation and low power consumption.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHANGHAI JIAOTONG UNIV
- Filing Date
- 2023-03-10
- Publication Date
- 2026-07-10
AI Technical Summary
In existing silicon-based optoelectronic integrated devices, the thermo-optical effect has a slow response speed and high power consumption, and the carrier dispersion effect has a small refractive index adjustment range, resulting in large device size and high power consumption, and the device performance is sensitive to environmental changes.
By employing low-loss phase change materials and heterogeneous integration with silicon waveguides, non-volatile phase modulation is achieved by depositing phase change materials on silicon slab layers and combining them with graphene microheaters. The effective refractive index adjustment of the heterogeneous integrated waveguide is optimized by utilizing the reversible transformation of phase change materials between amorphous and crystalline states.
A micron-scale ultra-miniature phase shifter has been realized, which has a fast phase adjustment rate, low power consumption, and non-volatile state, making it suitable for core optical path control devices in integrated optoelectronic chips.
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Figure CN116243423B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to phase shifters, and more particularly to a silicon-phase change material heterogeneous integrated waveguide structure, a non-volatile waveguide phase shifter, and its fabrication method. Background Technology
[0002] Typically, silicon-based optoelectronic integrated devices adjust the refractive index of silicon materials through the thermo-optic effect or the carrier dispersion effect. However, the thermo-optic effect has a relatively slow response time, usually on the order of microseconds; while the carrier dispersion effect has a fast response time, its refractive index adjustment range is limited, typically within 10^64 ohms. -3 The size and power consumption of silicon-based high-speed modulators and optical switches are large, requiring waveguide lengths on the order of millimeters to achieve the π-phase change of transmitted light. While high-Q resonant cavity structures can reduce device size, their operating bandwidth is narrow, and device performance is sensitive to environmental changes. Therefore, integrating phase change materials with significant refractive index changes, fast response speeds, non-volatility, and low loss with silicon heterostructures can further reduce the size and power consumption of silicon phase shifters.
[0003] Low-loss phase change materials (including antimony selenide, antimony sulfide, germanium-antimony-selenium-tellurium, etc.) have attracted widespread attention and research as a new class of materials with excellent optical properties. Phase change materials exhibit reversible amorphous-crystalline phase transitions, meaning that as the temperature increases or decreases, a reversible transition between amorphous and crystalline states occurs near the phase transition temperature, and the transition is non-volatile. Simultaneously, the optical properties of the phase change materials, such as the refractive index, change drastically with the phase transition. Reversible transitions between amorphous and crystalline states can be induced by light, electricity, and heat, such as through off-chip laser writing or on-chip electric heating. The time for a phase change material to transition from a crystalline to an amorphous state is on the order of tens to hundreds of nanoseconds, while the transition time from amorphous to crystalline is on the order of microseconds to tens of microseconds, enabling rapid modulation of the refractive index. Notably, the transition between amorphous and crystalline states in phase change materials exhibits a significant refractive index change in the 1550nm optical communication band. Taking antimony selenide as an example, its refractive index change is as high as ~0.8 at a wavelength of 1550nm. In summary, phase change materials, as novel materials, have attracted increasing attention in the field of optical communication. Summary of the Invention
[0004] This invention addresses the problems of high power consumption for thermo-optical effect regulation and small refractive index regulation range for carrier dispersion effect in existing silicon waveguides, both of which require static power consumption to maintain the regulation state. It proposes a silicon-phase change material heterogeneous integrated waveguide structure, a non-volatile waveguide phase shifter, and their fabrication method.
[0005] To address the above problems, the solution of the present invention is as follows:
[0006] On the one hand, the present invention provides a silicon-phase change material heterogeneous integrated waveguide structure, characterized in that it includes a silicon flat plate layer (1) and a phase change material (5) deposited on the silicon flat plate layer (1).
[0007] The thickness of the silicon plate layer (1) is 40-150 nm, and the thickness of the phase change material (5) is 20-80 nm.
[0008] On the other hand, the present invention also provides a non-volatile waveguide phase shifter, characterized in that it includes a base layer, and a silicon-phase change material heterogeneous integrated waveguide structure and a silicon waveguide mode conversion structure as described in any one of claims 1-3 fixed on the base layer, wherein the two ends of the silicon-phase change material heterogeneous integrated waveguide structure are symmetrically connected to the silicon waveguide mode conversion structure.
[0009] The base layer includes a silicon substrate (3) and a silicon dioxide undercoat (2) attached to the silicon substrate (3);
[0010] The silicon waveguide mode conversion structure includes two silicon waveguide plates (9) arranged symmetrically from narrow to wide, and a ridge waveguide (10) arranged above the two silicon waveguide plates (9) from wide to narrow; an alumina film (4) covers the phase change material (5), and above the alumina film (4) is a single layer of graphene (6), on which is a metal layer, the metal layer including two metal electrodes.
[0011] The widths of the silicon waveguide plate (9) and the ridge waveguide (10) are linear, hyperbolic, or other gradually changing curve shapes, so that the mode field distribution of the transmitted light in the silicon waveguide gradually matches the mode field distribution of the heterogeneous integrated waveguide, thereby achieving efficient coupling between the two structures.
[0012] The thickness of the silicon waveguide plate (9) is 70-150 nm, and the thickness of the ridge waveguide (10) is 70-150 nm.
[0013] The monolayer graphene (6) forms an ohmic contact with the metal electrodes (7, 8). The current flowing through the monolayer graphene (6) generates heat, which is conducted through the alumina film (4) below, providing the heat required for the phase change of the low-loss phase change material (5).
[0014] The thickness of the alumina film (6) is 40-120 nm, and the thickness of the metal layer is 50-300 nm.
[0015] The metal electrode is made of gold, aluminum, copper, or platinum.
[0016] Single-mode silicon waveguides are connected to heterogeneous integrated waveguides via silicon waveguide mode conversion structures (e.g., Figure 1When the incident transverse electric field TE mode passes through a silicon ridge layer whose width gradually narrows, its mode field gradually diffuses downwards into a silicon planar layer whose width gradually widens. The width variations of the planar layer and the ridge waveguide layer can be linear, hyperbolic, or other gradually varying curves, allowing the mode field distribution of the transmitted light in the silicon waveguide to gradually match the mode field distribution of the heterogeneous integrated waveguide, thereby achieving efficient coupling between the two structures. In the heterogeneous integrated waveguide, the optical mode field energy is partially distributed in the low-loss phase change material, thus achieving effective refractive index modulation of the heterogeneous integrated waveguide.
[0017] The phase change materials include, but are not limited to, antimony selenide, antimony sulfide, germanium antimony selenide tellurium, and the materials of the metal electrodes include, but are not limited to, gold, aluminum, copper, and platinum.
[0018] When a low-loss phase change material undergoes a reversible phase transition from amorphous to crystalline state, the real part of its refractive index changes significantly, while the imaginary part remains relatively small. Therefore, optimizing the thickness of the silicon slab layer and the low-loss phase change material in a heterogeneous integrated waveguide can further improve the effective refractive index variation, achieving a π phase shift over a shorter length while maintaining low optical loss and reducing power consumption.
[0019] Compared with the prior art, the present invention has the following advantages:
[0020] This invention employs a low-loss phase change material combined with a silicon waveguide to form a heterogeneous integrated waveguide. Utilizing the reversible transition between amorphous and crystalline states of the phase change material, it achieves efficient adjustment of the effective refractive index of the waveguide, thereby realizing a micrometer-scale ultra-miniature phase shifter. Specifically, (i) directly depositing the low-loss phase change material on a silicon slab to construct the heterogeneous integrated waveguide further enhances the modulation effect of the material's phase change on light waves; (ii) due to the high electron mobility and thermal conductivity of graphene, using graphene as a micro-heater effectively reduces phase change power consumption compared to traditional metal heaters and doped silicon resistance heaters; (iii) furthermore, because the phase change material is non-volatile, it does not require energy to maintain its state after switching, exhibiting the advantage of low power consumption.
[0021] Compared to the thermo-optical effect and carrier dispersion effect phase shifters commonly used in silicon waveguides, the phase shifter of this invention has advantages such as small size, fast phase adjustment rate, low power consumption, and non-volatile state, and can be used as a core optical path control device in integrated optoelectronic chips. Attached Figure Description
[0022] Figure 1 This is a planar top view of the heterogeneous integrated non-volatile waveguide phase shifter based on silicon-low-loss phase change material of the present invention, where 4(6) indicates that there is a single layer of graphene 6 above the alumina film 4.
[0023] Figure 2 This is a schematic diagram of the AA' cross-sectional structure of the phase modulation region of the heterogeneous integrated non-volatile waveguide phase shifter based on silicon-low-loss phase change material according to the present invention.
[0024] Figure 3 This is a schematic diagram of the BB' (CC') cross-sectional structure of the silicon waveguide mode conversion structure region on both sides of the heterogeneous integrated non-volatile waveguide phase shifter based on silicon-low-loss phase change material according to the present invention.
[0025] Figure 4 The diagram shows the normalized electric field distribution of the silicon and antimony selenide heterostructured waveguide in the embodiment at a working wavelength of 1550 nm. (a) shows the electric field distribution of the waveguide cross section when antimony selenide is in an amorphous state, (b) shows the electric field distribution of the waveguide cross section when antimony selenide is in a crystalline state, (c) shows the electric field distribution along the longitudinal centerline of the waveguide when antimony selenide is in an amorphous state, and (d) shows the electric field distribution along the longitudinal centerline of the waveguide when antimony selenide is in a crystalline state.
[0026] Figure 5 The normalized distribution of electric field intensity along the light transmission direction plane at a working wavelength of 1550 nm is shown in the example, where (a) antimony selenide is in the amorphous state and (b) antimony selenide is in the crystalline state.
[0027] Figure 6 The transmission spectrum scan results of the embodiment are in the wavelength range of 1500nm-1600nm, where (a) antimony selenide is in the amorphous state and (b) antimony selenide is in the crystalline state.
[0028] Figure 7 The embodiments show the heating electric pulses used in the amorphization and crystallization processes and the corresponding temperature changes and distributions, wherein (a) is the change of the minimum temperature in antimony selenide and the electric pulse used in amorphization over time, (b) is the change of the minimum temperature in antimony selenide and the electric pulse used in crystallization over time, (c) is the temperature distribution of the waveguide cross section at the end of the amorphization heating pulse, and (d) is the temperature distribution of the waveguide cross section at the end of the crystallization heating pulse. Detailed Implementation
[0029] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. These embodiments are based on the technical solutions of the present invention and provide detailed implementation methods and operating procedures; however, the scope of protection of the present invention is not limited to the following embodiments.
[0030] Figure 1 and Figure 2 These are schematic diagrams of the planar top view and cross-sectional structure of the heterogeneous integrated non-volatile waveguide phase shifter based on silicon-low-loss phase change material according to the present invention. Figure 3This is a schematic cross-sectional view of the mode converter of the silicon waveguide on both sides. As shown in the figure, the embodiment of the heterogeneous integrated non-volatile waveguide phase shifter based on silicon-low-loss phase change material of the present invention consists of, from bottom to top, a silicon substrate 3, a silicon dioxide lower cladding layer 2, a silicon planar layer 1, a low-loss phase change material antimony selenide 5, an alumina thin film 4, a single-layer graphene 6, and a metal layer. The metal layer includes two metal electrodes 7 and 8. The silicon planar layer 1 and the low-loss phase change material antimony selenide 5 constitute a heterogeneous integrated waveguide.
[0031] In this embodiment, the silicon dioxide cladding layer has a thickness of 2 μm, the silicon flat plate layer has a thickness of 70 nm, the low-loss phase change material is antimony selenide with a thickness of 40 nm, the aluminum oxide film has a thickness of 80 nm, a single layer of graphene is used to obtain lower optical loss, the metal electrode material is gold with a thickness of 100 nm, and for the silicon waveguide mode conversion structure connected to the heterogeneous waveguide, the silicon flat plate layer has a thickness of 70 nm and the silicon ridge layer has a thickness of 150 nm.
[0032] Under the action of an applied voltage, antimony selenide undergoes a reversible phase transition from amorphous to crystalline state. Since the refractive index difference between the amorphous and crystalline states is large, a heterogeneous integrated waveguide with a length of ~5.2μm can be used to realize the π phase shift of the transmitted light and obtain efficient phase modulation.
[0033] The fabrication process described in the above embodiments can be, but is not limited to, the following steps: First, the silicon substrate on the insulator is cleaned; then, electron beam lithography is performed, including spin coating of photoresist, electron beam exposure, and development and fixing processes; after electron beam lithography, inductively coupled plasma etching is required to obtain the desired silicon waveguide structure; for phase change materials, electron beam lithography is also required first, followed by sputtering deposition of the phase change material using a multi-target magnetron sputtering deposition system, and then a lift-off process is performed to complete the patterning; subsequently, electron beam lithography is performed on the alumina thin film layer, and the alumina thin film is deposited using plasma-enhanced atomic layer deposition equipment, and after deposition, a lift-off process is performed to complete the patterning; graphene needs to be transferred to the substrate with the alumina thin film deposited by wet transfer, and then patterned using electron beam lithography and oxygen plasma etching processes; finally, electron beam lithography is performed on the metal layer, the metal material is deposited by electron beam evaporation, and the patterning is completed using a lift-off process.
[0034] Figure 4 This is a normalized electric field intensity distribution at 1550 nm wavelength for the TEO mode in a heterogeneous integrated waveguide when antimony selenide is in both amorphous and crystalline states. Figure 5The diagram shows the normalized electric field intensity distribution along the light transmission plane in both amorphous and crystalline states of antimony selenide. During the phase transition from amorphous to crystalline, the refractive index of antimony selenide changes from 3.29+0i to 4.05+0i, a change 2-3 orders of magnitude higher than that of silicon's carrier dispersion effect. Correspondingly, the change in the effective refractive index of the heterogeneous integrated waveguide can be obtained; simulation calculations show a change of 0.155 in the real part of the effective refractive index. The loss of the heterogeneous integrated waveguide changes from 0.062 dB / μm to 0.056 dB / μm before and after the antimony selenide phase transition. Therefore, for a 5.2 μm long phase shifter, the insertion loss is only 0.3 dB.
[0035] Figure 6 The transmission spectra of the device in the 1500nm-1600nm wavelength range are shown for antimony selenide in both amorphous and crystalline states. The transmission spectra reveal that the transmittance of the device is higher than 0.88 regardless of whether antimony selenide is in an amorphous or crystalline state.
[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.
Claims
1. A non-volatile waveguide phase shifter, characterized in that, include: The base layer includes a silicon substrate (3) and a silicon dioxide undercoat (2) attached to the silicon substrate (3). A silicon-phase change material heterogeneous integrated waveguide structure fixed on the substrate; the silicon-phase change material heterogeneous integrated waveguide structure includes: A silicon flat panel layer (1) has a thickness of 40~150 nm; and, The phase change material (5) deposited on the silicon flat plate layer (1) has a thickness of 20~80nm; The silicon planar layer (1) and the phase change material (5) constitute a heterogeneous integrated waveguide for achieving efficient non-volatile modulation of the phase of the transmitted light; and A silicon waveguide mode conversion structure is symmetrically arranged at both ends of a silicon-phase change material heterogeneous integrated waveguide structure. The silicon waveguide mode conversion structure includes two silicon waveguide plates (9) arranged symmetrically from narrow to wide, and a ridge waveguide (10) arranged above the two silicon waveguide plates (9) from wide to narrow; an alumina film (4) covers the phase change material (5), and above the alumina film (4) is a single layer of graphene (6), on which is a metal layer, the metal layer including two metal electrodes (7, 8).
2. The non-volatile waveguide phase shifter according to claim 1, characterized in that, The phase change material (5) is antimony selenide, antimony sulfide, or germanium-antimony-selenium-tellurium.
3. The non-volatile waveguide phase shifter according to claim 1, characterized in that, The widths of the silicon waveguide plate (9) and the ridge waveguide (10) are linear, hyperbolic, or other gradually changing curve shapes, so that the mode field distribution of the transmitted light in the silicon waveguide gradually matches the mode field distribution of the heterogeneous integrated waveguide, thereby achieving efficient coupling between the two structures.
4. The non-volatile waveguide phase shifter according to claim 1, characterized in that, The thickness of the silicon waveguide plate (9) is 70~150nm, and the thickness of the ridge waveguide (10) is 70~150nm.
5. The non-volatile waveguide phase shifter according to claim 1, characterized in that, The monolayer graphene (6) forms an ohmic contact with the metal electrodes (7, 8). The current flowing through the monolayer graphene (6) generates heat, which is conducted through the alumina film (4) below, providing the heat required for the phase change of the low-loss phase change material (5).
6. The non-volatile waveguide phase shifter according to claim 1, characterized in that, The thickness of the alumina film (4) is 40~120nm, and the thickness of the metal layer is 50~300nm.
7. The non-volatile waveguide phase shifter according to claim 1, characterized in that, The metal electrode is made of gold, aluminum, copper, or platinum.