Non-volatile electro-optic modulator of ferroelectric gated colloidal nanocrystals and method of fabrication

Abstract

The application belongs to the technical field of integrated optoelectronics, and discloses a ferroelectric gate-controlled colloidal nanocrystal nonvolatile electro-optic modulator and a preparation method thereof, which comprises a light waveguide cladding layer, a light waveguide layer, a lower electrode layer, a colloidal nanocrystal layer, a ferroelectric dielectric layer and an upper electrode layer, and the light waveguide layer is arranged above the light waveguide cladding layer; the two ends of the light waveguide layer are provided with grating couplers for input and output of optical signals; the colloidal nanocrystal layer is arranged above the light waveguide layer in a covering mode; the lower electrode layer is arranged on one side of the light waveguide layer and connected with the colloidal nanocrystal layer; the ferroelectric dielectric layer is arranged above the colloidal nanocrystal layer in a covering mode, used for changing the polarization state according to an external pulse voltage and controlling the free carrier concentration of the colloidal nanocrystal layer through the polarization state; and the upper electrode layer is arranged above the ferroelectric dielectric layer. The strong plasmonic dispersion effect of the oxide semiconductor colloidal nanocrystal and the residual polarization field of the ferroelectric dielectric layer are utilized to realize the high-efficiency and large-scale expandable nonvolatile electro-optic modulator.

Description

Technical Field

[0001] This invention belongs to the field of integrated optoelectronics technology and relates to a non-volatile electro-optic modulator of ferroelectric grating-controlled colloidal nanocrystals and its preparation method. Background Technology

[0002] The rapid development of artificial intelligence has exacerbated the demand for high-capacity data transmission and efficient matrix operations, making the energy consumption problem of computing systems increasingly prominent. Photonic computing based on photonic integrated circuits, with its advantages of high bandwidth and massive parallel transmission, is expected to break through the high energy consumption bottleneck of traditional electronic computing. Reconfigurable photonic devices, as the core of photonic computing systems, determine the flexibility and efficiency of optical signal modulation and computing functions. However, most existing reconfigurable photonic devices rely on thermo-optic or electro-optic effects, making them volatile devices that require continuous bias to maintain their operating state, thus increasing static power consumption. Therefore, developing on-chip non-volatile electro-optic modulators is crucial.

[0003] Currently, there are significant limitations to the solutions for achieving non-volatile electro-optic modulators: phase change materials utilize the difference in optical constants between crystalline and amorphous states to achieve storage, but high-temperature phase transitions can easily cause thermal crosstalk and material degradation; ferroelectric and ferromagnetic materials achieve non-volatile modulation through domain flipping, but are limited by lattice matching, have complex heterogeneous integration processes, and are constrained by wafer bonding and other processes, making it difficult to balance low power consumption, reliability, and compatibility with large-scale manufacturing. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a non-volatile electro-optic modulator of ferroelectric grating-controlled colloidal nanocrystals and its preparation method.

[0005] To achieve the above objectives, the present invention employs the following technical solution: In a first aspect, the present invention provides a non-volatile electro-optic modulator for ferroelectric grating-controlled colloidal nanocrystals, comprising: an optical waveguide cladding; an optical waveguide layer disposed above the optical waveguide cladding; grating couplers for input and output of optical signals disposed at both ends of the optical waveguide layer; a colloidal nanocrystal layer disposed over the optical waveguide layer; a lower electrode layer disposed on one side of the optical waveguide layer and connected to the colloidal nanocrystal layer; a ferroelectric dielectric layer disposed over the colloidal nanocrystal layer; and an upper electrode layer disposed over the ferroelectric dielectric layer; wherein the ferroelectric dielectric layer is used to change the polarization state according to an applied pulse voltage and to control the free carrier concentration of the colloidal nanocrystal layer through the polarization state.

[0006] Optionally, the colloidal nanocrystalline layer is an indium oxide colloidal nanocrystalline layer, a zinc oxide colloidal nanocrystalline layer, a cadmium oxide colloidal nanocrystalline layer, or a doped oxide semiconductor colloidal nanocrystalline layer; wherein, the doped oxide semiconductor colloidal nanocrystalline layer is obtained by doping indium oxide colloidal nanocrystalline layer, zinc oxide colloidal nanocrystalline layer, or cadmium oxide colloidal nanocrystalline layer with one or more of the following elements: Sn, F, Al, Ga, In, Zr, Hf, Ti, Nb, Ta, Mo, W, and Sb.

[0007] Optionally, the colloidal nanocrystalline layer is prepared using an n-type doped oxide semiconductor colloidal nanocrystalline material; the colloidal nanocrystalline layer undergoes surface ligand exchange treatment.

[0008] Optionally, the material of the optical waveguide layer is Si, SiN, AlN, Ta2O5 or LiNbO3; the structure is a straight waveguide, a Mach-Zehnder interferometer, a directional coupler, a microring resonator or a photonic crystal structure.

[0009] Optionally, the optical waveguide cladding is a SiO2 layer; the upper electrode layer is a metal material layer, a graphene layer, or a transparent conductive oxide layer; and the lower electrode layer is a metal material layer, a graphene layer, or a transparent conductive oxide layer.

[0010] Optionally, the ferroelectric dielectric layer may be a polyvinylidene fluoride-trifluoroethylene layer, an aluminum scandium nitride layer, a hafnium zirconium oxide layer, an aluminum-doped hafnium oxide layer, a lead zirconate titanate layer, a barium titanate layer, a potassium dihydrogen phosphate layer, or a bismuth ferrite layer.

[0011] In a second aspect, the present invention provides a method for fabricating a non-volatile electro-optic modulator of a ferroelectric grating-controlled colloidal nanocrystal, comprising: fabricating an optical waveguide layer on an optical waveguide cladding, fabricating grating couplers at both ends of the optical waveguide layer, and fabricating a lower electrode layer on one side of the optical waveguide layer; fabricating a colloidal nanocrystal layer above the optical waveguide layer using spin coating, inkjet printing, drop coating, blade coating, or solution self-assembly methods, removing excess colloidal nanocrystal layer using laser direct writing and hydrochloric acid wet etching processes, and connecting the colloidal nanocrystal layer to the lower electrode layer; fabricating a covering ferroelectric dielectric layer above the colloidal nanocrystal layer; and fabricating an upper electrode layer above the ferroelectric dielectric layer.

[0012] Optionally, the step of fabricating an optical waveguide layer on the optical waveguide cladding and processing grating couplers at both ends of the optical waveguide layer includes: fabricating an optical waveguide layer on the optical waveguide cladding by means of grooves on both sides using electron beam lithography and plasma etching processes, and processing grating couplers at both ends of the optical waveguide layer; the step of processing a lower electrode layer on one side of the optical waveguide layer includes: defining the shape of the lower electrode layer on one side of the optical waveguide layer using laser direct writing process, and depositing the lower electrode layer using electron beam evaporation technology.

[0013] Optionally, the preparation of the ferroelectric dielectric layer covering the colloidal nanocrystalline layer includes: preparing the ferroelectric dielectric layer covering the colloidal nanocrystalline layer using solution spin coating or atomic layer deposition technology; the preparation of the upper electrode layer covering the ferroelectric dielectric layer includes: using PDMS transfer printing process to peel off the pre-patterned metal electrode layer from the growth substrate and align and transfer it to the upper electrode layer, or using electron beam exposure to define the shape of the upper electrode layer on the ferroelectric dielectric layer and using electron beam evaporation technology to deposit the upper electrode layer.

[0014] Optionally, the fabrication of the optical waveguide layer on the optical waveguide cladding includes: using the SiO2 insulating layer of the SOI chip as the optical waveguide cladding; defining the shape of the optical waveguide layer on the silicon planar layer of the SOI chip using an electron beam exposure process; and fabricating the optical waveguide layer by using a plasma etching process after development, with grooves on both sides.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention relates to a non-volatile electro-optic modulator based on ferroelectric-gated colloidal nanocrystals. Utilizing the strong plasmonic dispersion effect of oxide semiconductor colloidal nanocrystals and the remanent polarization field of the ferroelectric dielectric layer, it heterogeneously integrates these nanocrystals with an optical waveguide, achieving a high-efficiency, scalable non-volatile electro-optic modulator. The colloidal nanocrystal layer, ferroelectric dielectric layer, upper electrode layer, and lower electrode layer together constitute a ferroelectric parallel-plate capacitor structure. Applying pulsed electrical signals to the parallel-plate capacitor through the upper and lower electrode layers alters the remanent polarization state of the ferroelectric dielectric layer, causing a non-volatile change in the free carrier concentration of the colloidal nanocrystal layer. This non-volatile change in the free carrier concentration of the colloidal nanocrystal layer, through the plasmonic dispersion effect, causes non-volatile changes in the real and imaginary parts of the material's refractive index, thereby altering the effective refractive index and absorption loss of light passing through the modulator structure, ultimately changing the phase and intensity of the transmitted light, thus achieving non-volatile electro-optic modulation. By changing the pulse voltage conditions, the polarization direction and degree of ferroelectric domains in the ferroelectric dielectric layer can be controlled, thereby regulating the free carrier distribution of the colloidal nanocrystal layer. Simultaneously, the colloidal nanocrystals exhibit a strong plasmonic dispersion effect, enabling high modulation efficiency and modulation depth. This invention has achieved a compact, high-modulation-efficiency, and non-volatile electro-optic modulator that maintains its state for extended periods in the 1550 nm communication band.

[0016] This invention discloses a method for fabricating a non-volatile electro-optic modulator using ferroelectric grating-controlled colloidal nanocrystals. The colloidal nanocrystal layer can be prepared by spin coating, inkjet printing, drop coating, blade coating, or solution self-assembly, resulting in low fabrication costs. Furthermore, the room-temperature liquid phase processing is simple, not limited by substrate, and fully compatible with existing CMOS processes, facilitating mass production of devices. This effectively solves the problems of cumbersome fabrication and difficult heterogeneous integration currently faced by non-volatile electro-optic modulators, providing a new solution for the large-scale fabrication of on-chip non-volatile electro-optic modulators. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of a non-volatile electro-optic modulator of ferroelectric grating-controlled colloidal nanocrystals according to an embodiment of the present invention.

[0018] Figure 2 This is a top-view optical microscope image of the non-volatile electro-optic modulator of ferroelectric grating-controlled colloidal nanocrystals according to an embodiment of the present invention.

[0019] Figure 3 This is a flowchart illustrating the fabrication method of a non-volatile electro-optic modulator for ferroelectric-controlled colloidal nanocrystals according to an embodiment of the present invention.

[0020] Figure 4 The transmission spectra of the non-volatile electro-optic modulator of ferroelectric grating-controlled colloidal nanocrystals in two opposite polarization states are shown in an embodiment of the present invention.

[0021] Figure 5 The graph shows the output optical power versus voltage of the non-volatile electro-optic modulator of ferroelectric grating-controlled colloidal nanocrystals according to an embodiment of the present invention.

[0022] Wherein: 1-upper electrode layer; 2-ferroelectric dielectric layer; 3-colloidal nanocrystalline layer; 4-lower electrode layer; 5-optical waveguide layer; 6-optical waveguide cladding; 7-grating coupler. Detailed Implementation

[0023] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0024] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0025] The present invention will now be described in further detail with reference to the accompanying drawings: Addressing the challenges of heterogeneous material integration, high processing temperatures, complex processes, limited substrate compatibility, and difficulties in large-scale fabrication of on-chip non-volatile electro-optic modulators in the prior art, colloidal nanocrystals offer a new material basis for achieving low-damage, low-cost, and scalable on-chip electro-optic modulation. Specifically, colloidal nanocrystals can be prepared using liquid-phase chemical methods and stably dispersed in solvents. They can then be used to form semiconductor functional thin films through spin coating, inkjet printing, drop coating, blade coating, or transfer printing, offering advantages such as low equipment requirements, high material utilization, low processing costs, and strong batch production capabilities. Compared to traditional heterogeneous integration materials that rely on high-vacuum deposition, epitaxial growth, high-temperature crystallization, or wafer bonding, the film formation process of colloidal nanocrystals can typically be carried out at room temperature, causing less damage to the already fabricated optical waveguides, electrodes, and substrate structures, making them more suitable for integration in the back-end processes of on-chip photonic chips. Meanwhile, the composition, size, doping elements, surface ligands, and free carrier concentration of colloidal nanocrystals can all be adjusted during synthesis or post-processing, giving them a high degree of control over their conductivity, optical constants, and plasma response, which is beneficial for achieving efficient electro-optic modulation coupled with optical waveguide modes. However, relying solely on colloidal nanocrystal materials is still insufficient to achieve stable non-volatile state maintenance. Therefore, this invention combines the advantages of solution processing and strong plasma dispersion modulation of colloidal nanocrystals with the residual polarization modulation mechanism of ferroelectric dielectric layers, achieving on-chip non-volatile electro-optic modulation while reducing the complexity of heterogeneous integration processes and minimizing chip structure damage.

[0026] See Figure 1 In one embodiment of the present invention, a non-volatile electro-optic modulator based on ferroelectric-gated colloidal nanocrystals is provided, which offers a more flexible approach to on-chip non-volatile optical modulation based on the ferroelectric-doped charge storage structure. Specifically, the non-volatile electro-optic modulator based on ferroelectric-gated colloidal nanocrystals of the present invention includes an optical waveguide cladding layer 6, an optical waveguide layer 5, a lower electrode layer 4, a colloidal nanocrystal layer 3, a ferroelectric dielectric layer 2, and an upper electrode layer 1.

[0027] The optical waveguide layer 5 is disposed above the optical waveguide cladding layer 6; grating couplers 7 for input and output of optical signals are disposed at both ends of the optical waveguide layer 5; a colloidal nanocrystalline layer 3 is disposed above the optical waveguide layer 5; a lower electrode layer 4 is disposed on one side of the optical waveguide layer 5 and connected to the colloidal nanocrystalline layer 3; a ferroelectric dielectric layer 2 is disposed above the colloidal nanocrystalline layer 3; and an upper electrode layer 1 is disposed above the ferroelectric dielectric layer 2. The ferroelectric dielectric layer 2 is used to change the polarization state according to the applied pulse voltage and to control the free carrier concentration of the colloidal nanocrystalline layer 3 through the polarization state.

[0028] For example, the colloidal nanocrystal layer 3 can be achieved by coating solution-prepared oxide semiconductor colloidal nanocrystals onto the upper surface of the optical waveguide layer 5. Simultaneously, based on the structural design where the ferroelectric dielectric layer 2 is disposed above the colloidal nanocrystal layer 3, the upper electrode layer 1 is disposed above the ferroelectric dielectric layer 2, and the lower electrode layer 4 on one side of the optical waveguide layer 5 is connected to the colloidal nanocrystal layer 3, a ferroelectric parallel-plate capacitor with an upper electrode layer-ferroelectric dielectric layer-colloidal nanocrystal layer-lower electrode layer structure is obtained. Electrical signals can be input through the upper electrode layer 1 and the lower electrode layer 4. Furthermore, grating couplers 7 are introduced at both ends of the optical waveguide layer 5 to realize the input and output of optical signals.

[0029] The purpose of this invention is to overcome the shortcomings of existing on-chip non-volatile electro-optic modulators in terms of heterogeneous material integration, process complexity, substrate compatibility, and large-scale fabrication. Solution-processable oxide semiconductor colloidal nanocrystals can be used as the electro-optic modulation functional layer material coupled with optical waveguides. Taking advantage of their low-cost liquid-phase synthesis, room-temperature film formation, easy large-area processing, minimal damage to the substrate and the fabricated photonic structure, and high degree of freedom in composition and carrier concentration control, this invention reduces the dependence of traditional non-volatile electro-optic modulators on complex processes such as high-temperature phase transitions, epitaxial growth, lattice matching, or wafer bonding.

[0030] Meanwhile, this invention combines a colloidal nanocrystal layer with a ferroelectric dielectric layer, utilizes the non-volatile nature of the residual polarization field of the ferroelectric dielectric layer to control the free carrier concentration in the colloidal nanocrystal layer, and changes the effective refractive index and absorption loss in the optical waveguide through the plasmonic dispersion effect of the colloidal nanocrystal, thereby realizing an on-chip electro-optic modulator that combines low-damage heterogeneous integration, high modulation efficiency, and non-volatile state retention capability.

[0031] In summary, the non-volatile electro-optic modulator of ferroelectric gate-controlled colloidal nanocrystals of this invention utilizes the strong plasmonic dispersion effect of oxide semiconductor colloidal nanocrystals and the residual polarization field of the ferroelectric dielectric layer, heterogeneously integrating them with an optical waveguide to achieve a high-efficiency, scalable non-volatile electro-optic modulator. Specifically, the colloidal nanocrystal layer 3, the ferroelectric dielectric layer 2, the upper electrode layer 1, and the lower electrode layer 4 together constitute a ferroelectric parallel-plate capacitor structure. Applying pulsed electrical signals to the parallel-plate capacitor through the upper electrode layer 1 and the lower electrode layer 4 can change the residual polarization state of the ferroelectric dielectric layer 2, causing a non-volatile change in the free carrier concentration of the colloidal nanocrystal layer 3. This non-volatile change in the free carrier concentration of the colloidal nanocrystal layer 3 can cause non-volatile changes in the real and imaginary parts of the material's refractive index through the plasmonic dispersion effect, thereby altering the effective refractive index and absorption loss of the light passing through the modulator structure, and ultimately changing the phase and intensity of the transmitted light, thus achieving non-volatile electro-optic modulation. By changing the pulse voltage conditions, the polarization direction and degree of the ferroelectric domains in the ferroelectric dielectric layer 2 can be controlled, thereby regulating the free carrier distribution of the colloidal nanocrystal layer 3. At the same time, the colloidal nanocrystals have a strong plasma dispersion effect, which can achieve high modulation efficiency and modulation depth.

[0032] In practical applications, this invention has realized a compact, high-modulation-efficiency, and non-volatile electro-optic modulator that maintains its non-volatile state for a long time in the 1550 nm communication band.

[0033] In one possible embodiment, the colloidal nanocrystalline layer 3 is an indium oxide colloidal nanocrystalline layer, a zinc oxide colloidal nanocrystalline layer, a cadmium oxide colloidal nanocrystalline layer, or a doped oxide semiconductor colloidal nanocrystalline layer; wherein the doped oxide semiconductor colloidal nanocrystalline layer is obtained by doping indium oxide colloidal nanocrystalline layer, zinc oxide colloidal nanocrystalline layer, or cadmium oxide colloidal nanocrystalline layer with one or more of the following elements: Sn, F, Al, Ga, In, Zr, Hf, Ti, Nb, Ta, Mo, W, and Sb.

[0034] Explaining this, the colloidal nanocrystalline layer 3 can be designed as an oxide semiconductor colloidal nanocrystalline layer, such as an indium oxide (In₂O₃) colloidal nanocrystalline layer, a zinc oxide (ZnO) colloidal nanocrystalline layer, a cadmium oxide (CdO) colloidal nanocrystalline layer, or a doped oxide semiconductor colloidal nanocrystalline layer prepared by doping with one or more elements. The colloidal nanocrystalline layer 3 is located below the ferroelectric dielectric layer 2. Under the influence of the residual polarization field of the ferroelectric dielectric layer 2, it accumulates / depletes free charges at the interface, causing a change in the free charge concentration distribution in the material, thereby altering the real and imaginary parts of the material's refractive index.

[0035] In one possible implementation, the colloidal nanocrystalline layer 3 is prepared using an n-type doped oxide semiconductor colloidal nanocrystalline material; the colloidal nanocrystalline layer 3 undergoes surface ligand exchange treatment.

[0036] Explanatoryly, the use of n-type doping ensures the presence of a large number of free carriers in the material that can be effectively modulated by the ferroelectric dielectric layer, thereby achieving significant electro-optic modulation efficiency through the plasma dispersion effect.

[0037] Meanwhile, the surface ligand exchange treatment replaces the original insulating long-chain organic ligands on the surface of the colloidal nanocrystals with short-chain ligands or inorganic ions, which greatly reduces the contact resistance between nanocrystals and transforms the colloidal nanocrystal layer 3 from a high-resistivity state to a good conductive semiconductor film. This ensures that the residual polarization electric field of the ferroelectric dielectric layer 2 can efficiently regulate the concentration of free carriers inside the nanocrystal layer.

[0038] For example, one possible processing method is as follows: Nitrosonium tetrafluoroborate (NOBF4) is dissolved in N,N-dimethylformamide (DMF) to obtain a NOBF4 solution with a concentration of 20 mg / ml; simultaneously, In2O3 colloidal nanocrystals are stably dispersed in n-hexane solvent at a concentration of 50 mg / ml; subsequently, 5 ml of NOBF4 solution is mixed with 0.5 ml of In2O3 nanocrystal solution and shaken thoroughly, during which the long-chain ligands on the surface of the nanocrystals are replaced by short-chain ligands, causing them to transfer from the n-hexane solvent to the DMF solvent and remain stably suspended; finally, excess n-hexane is removed, and toluene is added to the colloidal nanocrystal solution suspended in DMF to precipitate it. After centrifugation, the toluene is removed, and the nanocrystals are redissolved in DMF to obtain a colloidal nanocrystal solution with a concentration of 25 mg / ml. Subsequently, the colloidal nanocrystal solution is layered to obtain colloidal nanocrystal layer 3 after surface ligand exchange treatment.

[0039] In one possible implementation, the material of the optical waveguide layer 5 is Si, SiN, AlN, Ta2O5 or LiNbO3; the structure is a straight waveguide, a Mach-Zehnder interferometer, a directional coupler, a microring resonator or a photonic crystal structure.

[0040] Specifically, the phase and loss of light transmission in the optical waveguide layer 5 are modulated by the changes in the real and imaginary parts of the refractive index of the colloidal nanocrystalline layer 3.

[0041] Explaining this, by matching different materials and structures, modulation efficiency, device size, process compatibility, and application scenarios can be flexibly balanced. Specifically, materials such as Si, SiN, AlN, Ta2O5, or LiNbO3 are mature platforms in integrated photonics, featuring low loss, high refractive index contrast, and CMOS compatibility (e.g., Si, SiN). LiNbO3 also possesses its own electro-optic effect that can be synergistically modulated. Straight waveguides provide the simplest phase accumulation region, Mach-Zehnder interferometers can convert refractive index changes into intensity modulation with high extinction ratios, microring resonators significantly reduce device size and improve modulation sensitivity through resonance enhancement, and directional couplers and photonic crystals are suitable for special needs such as power distribution and slow light enhancement, respectively. Therefore, this setup allows modulators to be designed with material-structure synergy according to specific indicators (such as power consumption, bandwidth, footprint, and extinction ratio), thereby covering diverse application scenarios from high-speed communication to reconfigurable photonic computing.

[0042] In one possible implementation, the optical waveguide cladding 6 is a SiO2 layer; the upper electrode layer 1 is a metal material layer, a graphene layer, or a transparent conductive oxide layer; and the lower electrode layer 4 is a metal material layer, a graphene layer, or a transparent conductive oxide layer.

[0043] Explain why: the SiO2 layer has a much lower refractive index (approximately 1.45) than waveguide core layers (such as Si and SiN), effectively confining the light field within the waveguide for transmission. Simultaneously, as a standard CMOS dielectric material, it enables high-quality, low-defect thin-film deposition. Metallic materials (such as Cr / Au and Al) provide the lowest resistivity and stable electrical contacts, while graphene, with its atomic-level thickness, high carrier mobility, and visible-infrared transparency, is suitable for applications requiring optical transmission or ultra-thin electrodes. Transparent conductive oxides (such as ITO and IZO) are both conductive and do not obstruct the light path, making them particularly suitable for integration with vertical optical coupling structures or applications requiring top-side light entry / exit functionality. Therefore, this configuration allows modulators to flexibly balance low-resistance drive, optical transparency requirements, and CMOS process compatibility, adapting to various application architectures ranging from high-speed electro-optic switches to transparent reconfigurable photonic devices.

[0044] In one possible implementation, the ferroelectric dielectric layer 2 is a polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE)) layer, an aluminum scandium nitride (AlScN) layer, a hafnium zirconium oxide (HZO) layer, an aluminum-doped hafnium oxide (HAO) layer, a lead zirconate titanate (PZT) layer, a barium titanate (BaTiO3) layer, a potassium dihydrogen phosphate (KH2PO4) layer, or a bismuth ferrite (BiFeO3) layer.

[0045] Explain that the range of selectable materials for the ferroelectric dielectric layer 2 covers a variety of ferroelectric materials, including organic, nitride, oxide, and perovskite materials, providing high design flexibility for devices in terms of process temperature, coercive field, remanent polarization, and integration path. Specifically, organic ferroelectrics such as P(VDF-TrFE) can be spin-coated at low temperatures, perfectly matching the liquid-phase processing technology of colloidal nanocrystals, and eliminating the need for high-temperature crystallization steps, thus avoiding thermal damage; nitride or hafnium-doped oxide ferroelectrics such as AlScN, HZO, and HAO have thin-film deposition temperatures compatible with CMOS front-end processes (typically ≤400℃), and moderate coercive fields, with thicknesses that can be miniaturized to the nanometer scale, which is beneficial for reducing driving voltage; traditional perovskite ferroelectrics such as PZT, BTO, and BFO, although requiring higher crystallization temperatures, have remanent polarizations of tens of µC / cm², enabling stronger charge control capabilities for colloidal nanocrystal layers. Therefore, this configuration allows the modulator to select the most suitable ferroelectric dielectric material based on specific application requirements (such as low thermal budget, high polarization field, or ultra-low voltage drive), thereby achieving an optimal trade-off between modulation speed, retention characteristics, cycle durability, and process compatibility.

[0046] In one possible implementation, see Figure 2 The structure of the non-volatile electro-optic modulator of the ferroelectric grating-controlled colloidal nanocrystal is shown when the structure of the optical waveguide layer 5 adopts a silicon microring resonator.

[0047] The working principle of the non-volatile electro-optic modulator of ferroelectric-controlled colloidal nanocrystals of this invention is as follows: The colloidal nanocrystalline layer 3, the ferroelectric dielectric layer 2, the upper electrode layer 1, and the lower electrode layer 4 together constitute a ferroelectric parallel plate capacitor structure. By applying pulsed electrical signals to the parallel plate capacitor through the upper electrode layer 1 and the lower electrode layer 4, the residual polarization state of the ferroelectric dielectric layer 2 can be changed, and the non-volatile aggregation or depletion of the free carrier concentration in the colloidal nanocrystalline layer 3 can be caused. Thus, the refractive index and absorption of light can be changed according to the plasma dispersion effect. The colloidal nanocrystalline layer 3 covers the optical waveguide layer 5, and the changes in its refractive index and light absorption act on the optical signal of the optical waveguide, causing modulation of the optical signal transmission phase and loss.

[0048] The non-volatile change in the free carrier concentration in the colloidal nanocrystalline layer 3 can induce non-volatile changes in the real and imaginary parts of the material's refractive index through the plasmonic dispersion effect. This alters the effective refractive index and absorption loss of light passing through the modulator structure, ultimately changing the phase and intensity of the transmitted light, thus achieving non-volatile electro-optic modulation. The direction of the remanent polarization field in the ferroelectric dielectric layer 2 is controlled by the sign of the applied pulse voltage signal, while the intensity of the remanent polarization field is controlled by the pulse amplitude, width, and number of pulses of the applied pulse electrical signal. The electron concentration in the colloidal nanocrystalline layer 3 is determined by the direction and intensity of the remanent polarization field in the ferroelectric dielectric layer 2, thereby enabling non-volatile electrical modulation of its light refraction and absorption.

[0049] See Figure 3 In another embodiment of the present invention, a method for fabricating a non-volatile electro-optic modulator of ferroelectric-gated colloidal nanocrystals is provided, comprising the following steps: S1: An optical waveguide layer 5 is fabricated on the optical waveguide cladding 6, and grating couplers 7 are fabricated at both ends of the optical waveguide layer 5, and a lower electrode layer 4 is fabricated on one side of the optical waveguide layer 5.

[0050] S2: A colloidal nanocrystal layer 3 is prepared on the optical waveguide layer 5 using spin coating, inkjet printing, drop coating, scraping coating or solution self-assembly method, and excess colloidal nanocrystal layer 3 is removed by laser direct writing and hydrochloric acid wet etching process, and the colloidal nanocrystal layer 3 is connected to the lower electrode layer 4.

[0051] S3: A ferroelectric dielectric layer 2 is prepared on top of the colloidal nanocrystalline layer 3.

[0052] S4: Prepare an upper electrode layer 1 above the ferroelectric dielectric layer 2.

[0053] In the fabrication method of the non-volatile electro-optic modulator with ferroelectric gate-controlled colloidal nanocrystals of this invention, the colloidal nanocrystal layer can be prepared by solution processing methods such as spin coating, inkjet printing, drop coating, blade coating, or solution self-assembly. This method offers advantages such as low equipment requirements, high material utilization, low processing costs, and ease of large-area film formation. Compared with traditional non-volatile electro-optic modulator fabrication methods that rely on high-vacuum deposition, epitaxial growth, high-temperature crystallization, or wafer bonding, the film formation process of the colloidal nanocrystal layer can typically be carried out at room temperature. This reduces thermal and process damage to the fabricated optical waveguides, electrodes, and substrate structures, facilitating integration in the back-end processes of on-chip photonic chips. Furthermore, the composition, size, doping elements, surface ligands, and free carrier concentration of the colloidal nanocrystals can be adjusted through synthesis and post-processing, giving the colloidal nanocrystal layer high degree of controllability in conductivity, optical constants, and plasma response, which is beneficial for improving the flexibility of device structure design and performance optimization. Therefore, the fabrication method of the present invention can effectively reduce the difficulty and process complexity of heterogeneous integration of on-chip non-volatile electro-optic modulators, improve substrate compatibility and mass production capability, and provide a new solution for low-cost, low-damage, and scalable on-chip non-volatile electro-optic modulator fabrication.

[0054] In one possible implementation, the fabrication of the optical waveguide layer 5 on the optical waveguide cladding 6 and the processing of grating couplers 7 at both ends of the optical waveguide layer 5 includes: fabricating the optical waveguide layer 5 on the optical waveguide cladding 6 by means of grooving on both sides using electron beam lithography and plasma etching processes, and processing grating couplers 7 at both ends of the optical waveguide layer 5.

[0055] Explaining this, by leveraging the high resolution of electron beam lithography and the anisotropy of plasma etching, combined with a layout design strategy involving two-sided grooving, a single-step integrated fabrication of the optical waveguide and grating coupler was achieved, ensuring low optical loss and high process yield. Specifically, electron beam lithography can overcome the diffraction limit of ultraviolet optics, precisely defining waveguide widths and grating periods at sub-micron or even nanoscale, meeting the stringent requirements of single-mode transmission and efficient coupling; plasma etching, through a synergistic physical / chemical process, obtains nearly vertical waveguide sidewalls, significantly reducing sidewall scattering loss; and the two-sided grooving method refers to symmetrically etching deep grooves on both sides of the waveguide, which on the one hand suspends or isolates the waveguide core layer to enhance optical field confinement, and on the other hand simultaneously defines the concave and convex tooth structure of the grating coupler, thus eliminating additional alignment and overlay steps.

[0056] In one possible implementation, the processing of the lower electrode layer 4 on one side of the optical waveguide layer 5 includes: defining the shape of the lower electrode layer 4 on one side of the optical waveguide layer 5 using a laser direct writing process, and depositing the lower electrode layer 4 using an electron beam evaporation technique.

[0057] Explaining this, the high flexibility of laser direct writing and the high-quality film formation of electron beam evaporation technology enable high-precision, low-damage fabrication of the lower electrode layer, ensuring excellent electrical contact with the subsequent colloidal nanocrystalline layer. Specifically, laser direct writing eliminates the need for masks required by traditional photolithography, allowing for rapid definition of the lower electrode shape based on the design pattern. This is particularly suitable for the multi-variable, small-batch development needs during device parameter optimization. Electron beam evaporation, on the other hand, deposits metal under high vacuum. Its high-energy, highly directional evaporation particles result in dense, low-roughness metal films with strong adhesion to the substrate, avoiding plasma damage that may be introduced by sputtering processes. Furthermore, this combined process allows for direct electrode fabrication next to the pre-fabricated optical waveguide structure, without requiring high-temperature or chemically active environments, thus completely preserving the optical performance of the waveguide layer and grating coupler.

[0058] In one possible implementation, the preparation of the ferroelectric dielectric layer 2 covering the colloidal nanocrystalline layer 3 includes: preparing the ferroelectric dielectric layer 2 covering the colloidal nanocrystalline layer 3 using solution spin coating or atomic layer deposition techniques.

[0059] In one possible implementation, the preparation of the upper electrode layer 1 above the ferroelectric dielectric layer 2 includes: using a PDMS transfer process to peel off a pre-patterned metal electrode layer from the growth substrate and align and transfer it above the ferroelectric dielectric layer 2, or using electron beam exposure to define the shape of the upper electrode layer 1 above the ferroelectric dielectric layer 2 and using electron beam evaporation technology to deposit the upper electrode layer 1.

[0060] Explained, a combination of solution spin coating / atomic layer deposition and PDMS transfer / electron beam exposure was used to achieve non-destructive processing of the heat-sensitive and surface-sensitive colloidal nanocrystalline layer 3, while ensuring uniform polarization of the ferroelectric film and precise patterning of the upper electrode. Specifically, when preparing the ferroelectric dielectric layer 2, solution spin coating (suitable for organic ferroelectrics such as P(VDF-TrFE)) can form a film at room temperature without high-temperature annealing, completely avoiding damage to the ligand structure and photoelectric properties of the colloidal nanocrystals; atomic layer deposition (suitable for oxide ferroelectrics such as HZO and AlScN) utilizes self-limiting surface reactions to grow ferroelectric films with precise thickness (sub-nanometer), excellent conformability, and no pinholes at low temperatures, which is particularly suitable for covering the colloidal nanocrystalline layer 3 with nanoscale roughness. During the fabrication of the top electrode, the PDMS transfer process uses a flexible stamp to physically peel the pre-fabricated ultrathin metal electrode from the growth substrate, and then attaches it to the surface of the ferroelectric dielectric layer 2 through an alignment system. This process involves no chemical solvents, high temperatures, or high-energy particle bombardment, making it the electrode fabrication method with the least interference to the ferroelectric polarization state. Meanwhile, electron beam lithography combined with electron beam evaporation provides an in-situ, high-precision electrode definition scheme, enabling sub-micron-level electrode linewidths and edge steepness, suitable for high-speed modulator designs requiring dense electrode arrays or extremely small capacitive loads. Therefore, this process combination ensures that the ferroelectric dielectric layer 2 maintains its intrinsic remanent polarization intensity and fatigue resistance, while also guaranteeing the adhesion and conductivity of the top electrode, ultimately achieving a ferroelectric gate structure with low leakage current, high breakdown voltage, and excellent polarization reversal durability.

[0061] In one possible implementation, the fabrication of the optical waveguide layer 5 on the optical waveguide cladding 6 includes: using the SiO2 insulating layer of the SOI chip as the optical waveguide cladding 6; defining the shape of the optical waveguide layer 5 on the silicon planar layer of the SOI chip using an electron beam lithography process; and then fabricating the optical waveguide layer 5 by using a plasma etching process after development, with grooves on both sides.

[0062] Explanatoryly, the method for fabricating the non-volatile electro-optic modulator of the ferroelectric grating colloidal nanocrystal of the present invention can be based on on-chip fabrication of SOI (silicon-on-insulator) chip. SOI chip is a three-layer structure material, with a silicon planar layer on top, a SiO2 insulating layer in the middle, and a bulk silicon substrate on the bottom.

[0063] For example, based on an SOI chip, the thickness of the silicon plate layer is 220 nm, the thickness of the SiO2 insulating layer is 2 µm, and the structure of the optical waveguide layer 5 adopts a micro-ring resonator. The fabrication method of the non-volatile electro-optic modulator of the ferroelectric grating-controlled colloidal nanocrystal of the present invention includes the following steps: Step 1: On a clean SOI chip, the shape of the optical waveguide layer 5 is defined by electron beam lithography. After development, the optical waveguide layer 5 and the grating couplers 7 at both ends of the optical waveguide layer 5 are fabricated by plasma etching in the form of grooves on both sides.

[0064] Step 2: Define the shape of the lower electrode layer 4 using laser direct writing process. After development, deposit Cr / Au electrodes with a thickness of 5 nm / 40 nm using electron beam evaporation technology. After stripping, obtain the lower electrode layer 4 with a specific pattern shape.

[0065] Step 3: Using spin coating, inkjet printing, drop coating, scraping coating or solution self-assembly method, a colloidal nanocrystal layer 3 is prepared above the optical waveguide layer 5 using oxide semiconductor colloidal nanocrystals. The excess colloidal nanocrystal layer 3 is removed using laser direct writing and hydrochloric acid wet etching process, so that the colloidal nanocrystal layer 3 is connected to the lower electrode layer 4.

[0066] Step 4: Using spin coating, a 200 nm P (VDF-TrFE) layer, i.e. ferroelectric dielectric layer 2, is prepared on the SOI chip.

[0067] Step 5: Using PDMS transfer technology, the pre-patterned metal electrode layer is peeled off from the growth substrate and precisely aligned and transferred to the ferroelectric dielectric layer 2, or the shape of the upper electrode layer 1 is defined by electron beam exposure technology and the upper electrode layer 1 is deposited by electron beam evaporation technology.

[0068] This invention introduces solution-processed colloidal nanocrystals and a ferroelectric dielectric layer into an optoelectronic chip, realizing a reliable, non-volatile electro-optic modulator that is CMOS-compatible and can be integrated on a large scale. It can be used in fields such as in-memory computing and optical neural networks.

[0069] In one possible implementation, a non-volatile electro-optic modulator of a 310-micrometer-long ferroelectric grating-controlled colloidal nanocrystal is integrated into a silicon microring resonator. The transmitted light power is measured via a grating coupler 7, yielding a significant change in the resonant wavelength with pulse voltage at the same resonant level, and a scanning curve of the transmitted light power versus external voltage at a fixed wavelength. See [link to relevant documentation]. Figure 4 When the lower electrode layer 4 is grounded and a ±20V pulse voltage with a width of 2s is applied to the upper electrode layer 1, compared to -20V, the application of a 20V pulse voltage causes a 98pm blue shift in the microring resonant wavelength, and the quality factor decreases from 11000 to 9400. This proves that the modulator can modulate the real and imaginary parts of the optical refractive index through pulse voltage. See also Figure 5By fixing the laser wavelength at the initial resonant wavelength, corresponding to the lowest output optical power, the curve of output optical power changing with applied voltage was tested. When the applied voltage scanned from -20V to 20V, a voltage exceeding 10V caused the output optical power to rise rapidly and maintain a high output optical power during subsequent scans, thus proving that the non-volatile electro-optic modulator of the present invention has a non-volatile function.

[0070] In summary, this invention addresses the current limitations of on-chip non-volatile electro-optic modulators, which struggle to balance low power consumption, reliability, and compatibility with large-scale manufacturing. It proposes a CMOS-compatible ferroelectric gate-controlled colloidal nanocrystal non-volatile electro-optic modulator that combines the substrate compatibility of colloidal nanocrystals (solution preparation), large-scale integration capabilities, and high modulation efficiency with the stable maintenance and cycling stability of the residual polarization field in the ferroelectric dielectric layer 2. This invention is expected to drive the development of optoelectronic chips towards high integration and low power consumption.

[0071] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A non-volatile electro-optic modulator for ferroelectric-controlled colloidal nanocrystals, characterized in that, include: Optical waveguide cladding (6); An optical waveguide layer (5) is disposed above the optical waveguide cladding (6); grating couplers (7) for input and output of optical signals are disposed at both ends of the optical waveguide layer (5). A colloidal nanocrystalline layer (3) is disposed over the optical waveguide layer (5); The lower electrode layer (4) is disposed on one side of the optical waveguide layer (5) and connected to the colloidal nanocrystal layer (3); A ferroelectric dielectric layer (2) is disposed over the colloidal nanocrystalline layer (3); The upper electrode layer (1) is disposed above the ferroelectric dielectric layer (2); Among them, the ferroelectric dielectric layer (2) is used to change the polarization state according to the applied pulse voltage, and to control the free carrier concentration of the colloidal nanocrystal layer (3) through the polarization state.

2. The non-volatile electro-optic modulator of ferroelectric grating-controlled colloidal nanocrystals according to claim 1, characterized in that, The colloidal nanocrystal layer (3) is an indium oxide colloidal nanocrystal layer, a zinc oxide colloidal nanocrystal layer, a cadmium oxide colloidal nanocrystal layer, or a doped oxide semiconductor colloidal nanocrystal layer. The doped oxide semiconductor colloidal nanocrystals are obtained by doping indium oxide colloidal nanocrystals, zinc oxide colloidal nanocrystals, or cadmium oxide colloidal nanocrystals with one or more of the following elements: Sn, F, Al, Ga, In, Zr, Hf, Ti, Nb, Ta, Mo, W, and Sb.

3. The non-volatile electro-optic modulator of ferroelectric grating-controlled colloidal nanocrystals according to claim 1, characterized in that, The colloidal nanocrystal layer (3) is prepared using an n-type doped oxide semiconductor colloidal nanocrystal material; the colloidal nanocrystal layer (3) undergoes surface ligand exchange treatment.

4. The non-volatile electro-optic modulator of ferroelectric grating-controlled colloidal nanocrystals according to claim 1, characterized in that, The material of the optical waveguide layer (5) is Si, SiN, AlN, Ta2O5 or LiNbO3; the structure is a straight waveguide, a Mach-Zehnder interferometer, a directional coupler, a micro-ring resonator or a photonic crystal structure.

5. The non-volatile electro-optic modulator of ferroelectric grating-controlled colloidal nanocrystals according to claim 1, characterized in that, The optical waveguide cladding (6) is a SiO2 layer; The upper electrode layer (1) is a metal material layer, a graphene layer, or a transparent conductive oxide layer; The lower electrode layer (4) is a metal material layer, a graphene layer, or a transparent conductive oxide layer.

6. The non-volatile electro-optic modulator of ferroelectric grating-controlled colloidal nanocrystals according to claim 1, characterized in that, The ferroelectric dielectric layer (2) is a polyvinylidene fluoride-trifluoroethylene layer, an aluminum scandium nitride layer, a hafnium zirconium oxide layer, an aluminum-doped hafnium oxide layer, a lead zirconate titanate layer, a barium titanate layer, a potassium dihydrogen phosphate layer, or a bismuth ferrite layer.

7. A method for fabricating a non-volatile electro-optic modulator of ferroelectric grating-controlled colloidal nanocrystals according to any one of claims 1 to 6, characterized in that, include: An optical waveguide layer (5) is fabricated on the optical waveguide cladding (6), and grating couplers (7) are fabricated at both ends of the optical waveguide layer (5), and a lower electrode layer (4) is fabricated on one side of the optical waveguide layer (5). A colloidal nanocrystal layer (3) is prepared on the optical waveguide layer (5) by spin coating, inkjet printing, drop coating, scraping or solution self-assembly. Excess colloidal nanocrystal layer (3) is removed by laser direct writing and hydrochloric acid wet etching process, and the colloidal nanocrystal layer (3) is connected to the lower electrode layer (4). A ferroelectric dielectric layer (2) is prepared on top of the colloidal nanocrystalline layer (3); An upper electrode layer (1) is prepared above the ferroelectric dielectric layer (2).

8. The method for preparing the non-volatile electro-optic modulator of ferroelectric grating-controlled colloidal nanocrystals according to claim 7, characterized in that, The process of fabricating an optical waveguide layer (5) on the optical waveguide cladding (6) and processing grating couplers (7) at both ends of the optical waveguide layer (5) includes: Using electron beam lithography and plasma etching, an optical waveguide layer (5) is fabricated on the optical waveguide cladding (6) by grooving on both sides, and grating couplers (7) are fabricated at both ends of the optical waveguide layer (5). The process of fabricating the lower electrode layer (4) on one side of the optical waveguide layer (5) includes: The shape of the lower electrode layer (4) is defined by laser direct writing process on one side of the optical waveguide layer (5), and the lower electrode layer (4) is deposited by electron beam evaporation technology.

9. The method for preparing the non-volatile electro-optic modulator of ferroelectric grating-controlled colloidal nanocrystals according to claim 7, characterized in that, The preparation of the ferroelectric dielectric layer (2) covering the colloidal nanocrystalline layer (3) includes: A ferroelectric dielectric layer (2) was prepared on top of the colloidal nanocrystalline layer (3) using solution spin coating or atomic layer deposition techniques. The fabrication of the upper electrode layer (1) above the ferroelectric dielectric layer (2) includes: Using PDMS transfer process, the pre-patterned metal electrode layer is peeled off from the growth substrate and transferred to the ferroelectric dielectric layer (2), or the shape of the upper electrode layer (1) is defined on the ferroelectric dielectric layer (2) by electron beam exposure, and the upper electrode layer (1) is deposited by electron beam evaporation technology.

10. The method for preparing the non-volatile electro-optic modulator of ferroelectric grating-controlled colloidal nanocrystals according to claim 7, characterized in that, The fabrication of the optical waveguide layer (5) on the optical waveguide cladding (6) includes: The SiO2 insulating layer of the SOI chip is used as the optical waveguide cladding (6). The shape of the optical waveguide layer (5) is defined on the silicon plate layer of the SOI chip by electron beam exposure process. After development, the optical waveguide layer (5) is fabricated by plasma etching process with grooves on both sides.

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