Ferro-electric domain engineering in a ferro-electric thin film for non-linear photonic applications

Abstract

The present disclosure relates to a system for use in a process for poling a ferro-electric material, the system comprising a charged particle beam generator and a control unit configured for controlling the operation of the charged particle beam generator, a grounding electrode structure comprising a grounding frame and a plurality of grounding electrodes attached to the grounding frame, and a support structure configured to support the ferro-electric material during the poling process. The present disclosure further relates to a method of poling a ferro-electric material and a ferro-electric thin film made according to a method of the present disclosure.

Description

[0001] Ferro-electric domain engineering in a ferro-electric thin film for non-linear photonic applications

[0002] The present disclosure relates to a system for use in a process for poling a ferroelectric material, a method of poling a ferro-electric material and a ferro-electric thin film fabricated according to a method of the present disclosure.

[0003] Background

[0004] In the field of nonlinear photonics, ferroelectric materials are widely used for their second-order nonlinear properties, enabling interactions such as second harmonic generation, sum and difference frequency generation, and optical parametric amplification / oscillation. Traditional approaches to achieve these interactions typically involve periodic poling of the ferroelectric material, where an electric field applied across the material reorients the polarisation in a spatially periodic manner. This reorientation creates regions of alternating polarity, referred to as domains, which are critical for phase matching in nonlinear optical processes.

[0005] Conventionally, periodic poling is achieved by placing the ferroelectric material between two electrodes and applying a high electric field across the material. However, this electrode-based technique presents several limitations. First, applying the required high electric fields uniformly over large areas can lead to inconsistencies in domain uniformity, particularly as device sizes increase. Additionally, as the spacing between domains decreases to support shorter interaction wavelengths, the likelihood of domain merging increases. Domain merging is highly detrimental to device efficiency, as even the merging of two domains can severely limit the nonlinear efficiency in devices typically requiring up to 10,000 distinct domains. Achieving uniform periodic poling over a large area, such as an entire wafer, becomes increasingly challenging, especially as the wafer scale expands from individual devices of approximately 1 cm x 1 cm to arrays spanning 10 cm x 10 cm or larger. Despite these challenges, wafer-scale poling is highly desirable due to its compatibility with semiconductor and nanotechnology processes.

[0006] Several efforts have been made to address these challenges, but these solutions often fall short in compatibility with modern nanofabrication techniques. For instance, attempts to create fine poling periods below 1.5 pm using high electric fields have proven challenging due to field instability and difficulty in maintaining periodic precision across the material. Consequently, existing periodic poling techniques are often incompatible with the production of high-density photonic circuits on wafer-scale thin films, limiting the scalability and integration potential of nonlinear photonic devices in advanced applications.

[0007] It is therefore an objective of the present disclosure to provide a method and system for poling ferroelectric materials that overcomes these limitations by using a localized charge injection technique. This approach enables precise, domain-by-domain poling, compatible with nanofabrication tools, and allows for the creation of well-defined periodic poling patterns on wafer-scale ferroelectric thin films without the need for high- dielectric insulating materials.

[0008] Summary

[0009] Considering the prior art described above, it is an objective of the present disclosure to provide a system and method for precise poling of ferroelectric materials. The present invention further aims to address challenges in achieving periodic domain structures, especially on a wafer scale, while maintaining uniformity and scalability for photonic device integration. This solution enables controlled domain inversion in a ferroelectric thin film through a localized charge injection technique that is compatible with standard nanofabrication tools, overcoming the limitations of traditional high-voltage poling methods.

[0010] The present disclosure therefore relates to a system for use in a process for poling a ferro-electric material, the system comprising a charged particle beam generator and a control unit configured for controlling the operation of the charged particle beam generator, a grounding electrode, and a support structure configured to support the ferro-electric material during the poling process.

[0011] The present disclosure further relates to a method of poling a ferroelectric material using a charged particle beam generator, the method comprising the steps of providing a ferro-electric material, a charged particle beam generator and a grounding electrode, identifying a target region of the ferro-electric material to be a charge injection site, placing the grounding electrode at a distance close enough to the charge injection site so as to cause charge redistribution within the ground electrode when charged particles are injected into the charge injection site, irradiating, using the charged particle beam generator, the charge injection site with a beam of charged particles so as to cause polarisation reversal, such as domain inversion, at the target region of the ferro-electric material.

[0012] The present disclosure further relates to a ferro-electric thin film fabricated according to any one of the methods of the present disclosure.

[0013] With the presently disclosed solution, precise periodic poling patterns can be established on wafer-scale ferroelectric thin films. By leveraging localized charge injection and the dynamics of domain growth, this method, referred to as the FLUSH poling method, enables the formation of domains that may extend significantly beyond the distance between the charge injection site and the electrode while minimizing domain broadening, ensuring efficient and scalable production of nonlinear photonic devices integrated on a single chip. It supports advanced optical applications such as frequency conversion, optical parametric oscillation, and quantum light sources.

[0014] Description of the drawings

[0015] The present disclosure will in the following be described in greater detail with reference to the accompanying drawings. Various embodiments are described hereinafter with reference to the drawings. The drawings are examples of embodiments and are intended to illustrate some of the features of the presently disclosed ferro-electric domain engineering solution, and are not limiting to the presently disclosed device and method.

[0016] Fig. 1A a schematic view of prior art electrode-based periodic poling on a photonic integrated circuit (PIC) platform before a high-voltage signal is applied.

[0017] Fig. 1B a schematic view corresponding to Fig. 1A, illustrating the periodically reversed domains after the high-voltage signal is applied.

[0018] Fig. 1C a side view schematic of the prior art electrode-based poling setup on a PIC platform before a high-voltage signal is applied.

[0019] Fig. 1D a side view schematic corresponding to Fig. 1C after the high-voltage signal is applied.

[0020] Fig. 1E a side view schematic similar to Fig. 1 C, with a material stack comprising a ferro-electric thin film, a dielectric or optical insulator layer and another layer. Fig. 2A a schematic view of prior art electrode-based periodic poling on a PIC platform before the application of a high-voltage signal.

[0021] Fig. 2B a schematic view corresponding to Fig. 2A after the high-voltage signal is applied.

[0022] Fig. 2C a side view schematic of the prior art electrode-based poling setup on a PIC platform before applying the high-voltage signal.

[0023] Fig. 2D a side view schematic corresponding to the prior art electrode-based poling setup on a PIC platform shown in Fig. 2C after the high-voltage signal is applied. Fig. 2E a side view schematic of a setup similar to Fig. 2C, with a different material composition below the thin-film ferroelectric crystal.

[0024] Fig. 3A a schematic view of a system of the present disclosure before charge injection

[0025] Fig. 3B a schematic view of the system shown in Fig. 3A, illustrating the periodically reversed domains after charge injection

[0026] Fig. 3C a side view schematic of the system shown in Fig. 3A before charge injection

[0027] Fig. 3D a side view schematic of the system shown in Fig. 3C, illustrating a reversed domain in the ferro-electric thin film after charge injection

[0028] Fig. 4A a lateral piezo force microscopy (PFM) image showing a patterned grounding electrode on a thin-film ferroelectric crystal, demonstrating periodic poling induced by charge irradiation. The poling period is 375 nm.

[0029] Fig. 4B a lateral PFM image of a patterned grounding electrode on a thin-film ferroelectric crystal, illustrating periodic poling induced by charge irradiation with a poling period of 750 nm.

[0030] Fig. 4C a lateral PFM image of a patterned grounding electrode on a thin-film ferroelectric crystal, showing periodic poling induced by charge irradiation, with a poling period of 1500 nm.

[0031] Fig. 4D a lateral PFM image of a patterned grounding electrode on a thin-film ferroelectric crystal, illustrating periodic poling induced by charge irradiation with a poling period of 1110 nm.

[0032] Fig. 5 a lateral PFM image of a photonic integrated circuit waveguide fabricated in a ferroelectric thin film that was periodically poled by charge irradiation prior to waveguide fabrication. The poling period is 3.47 pm, and the waveguide is etched to a depth of 460 nm within a 600 nm thin-film ferroelectric crystal. The PFM image indicates that the periodic poling depth extends beyond 460 nm. Fig. 6 an experimental result demonstrating optical nonlinear conversion from 1424 nm to 712 nm within the periodically poled waveguide shown in Fig. 5.

[0033] Fig. 7 a schematic view of the grounding electrode structure, showing the grounding frame, grounding lead electrodes, and grounding electrodes.

[0034] Fig. 8 a schematic view showing various shapes of grounding electrodes, with ends that are rounded, squared, or chamfered or tapered down towards the end of the grounding electrode.

[0035] Detailed description

[0036] A preferred embodiment of the present disclosure relates to a system for use in a process for poling a ferro-electric material, the system comprising a charged particle beam generator and a control unit configured for controlling the operation of the charged particle beam generator, a grounding electrode, and a support structure configured to support the ferro-electric material during the poling process.

[0037] In some embodiments, the grounding electrode has a thickness ranging from 1 nm to 2 pm, or from 1 nm to 10 pm. The thickness may be selected to optimize for effective charge redistribution while minimizing footprint. Structurally, the grounding electrode may, in some examples, comprise of three elements: a grounding frame that provides robust grounding for all charge irradiation locations, a lead section that connects the grounding frame to the electrode stripes, and grounding electrodes (which may be referred to as stripes owing to their geometrical structure), which are arranged in a periodic pattern to achieve the desired poling effect.

[0038] The lead section typically can have a width between 500 nm and 10 pm, or from 500 nm to 100 pm, extending across the entire length of the intended poling pattern to ensure a consistent charge pathway. The electrode stripes can extend from 500 nm to 500 pm in the same direction as the optical axis of the ferroelectric thin film (aligned with the extraordinary refractive index), while being oriented perpendicular to the lead section. Each electrode stripe is spaced at intervals matching the intended poling periodicity relative to adjacent stripes, ensuring precise domain inversion. These stripes may be tapered, squared, or rounded at the termination, and may include various perforations or geometries to control the electric field. The grounding electrode itself can either be grounded or left floating at an arbitrary potential level, allowing flexibility in tuning the field distribution for optimal poling outcomes. In some embodiments, the control unit is configured to receive input, such as user input via a user display, which identifies a target region of the ferro-electric material to be a charge injection site.

[0039] In some embodiments, the control unit is further configured to instruct the charged particle beam generator to irradiate the charge injection site with a beam of charged particles based on the received input.

[0040] In some embodiments, the control unit is configured to receive input, such as user input via a user display, which identifies a plurality of target regions of the ferro-electric material to be a plurality of charge injection sites.

[0041] In some other embodiments, the control unit is further configured to instruct the charged particle beam generator to irradiate the plurality of charge injection sites with a beam of charged particles.

[0042] In some embodiments, the system comprises a plurality of grounding electrodes.

[0043] In some embodiments, the system comprises a grounding electrode structure and the grounding electrode structure comprises the plurality of grounding electrodes.

[0044] In some embodiments, the grounding electrode structure further comprises a grounding frame.

[0045] In some embodiments, the grounding electrode structure further comprises one or more lead electrodes which is / are each attached to the grounding frame.

[0046] In some embodiments, the plurality of grounding electrodes are bar-shaped electrodes.

[0047] In some embodiments, the grounding electrode or at least one of the plurality of grounding electrodes is tapered down to an electrode termination point. In some embodiments, the plurality of grounding electrodes are attached at distributed attachment points along the length of a surface of the grounding frame so as to create an array of electrode elements protruding from the grounding electrode structure.

[0048] In some embodiments, the one or more lead electrodes are attached at distributed attachment points along the length of a surface of the grounding frame and each one of the respective plurality of grounding electrodes is attached to a respective one of the one or more lead electrodes so as to create an array of electrode elements protruding from the grounding electrode structure, wherein each electrode element comprises one of the one or more lead electrodes and one of the plurality of grounding electrodes.

[0049] In some embodiments, the plurality of grounding electrodes are spaced apart from each other.

[0050] In some embodiments, the plurality of grounding electrodes are spaced apart from each other so as to form a comb-like structure on the grounding frame.

[0051] In some embodiments, the plurality of grounding electrodes are equally spaced apart from each other with a separation distance corresponding to an intended poling periodicity.

[0052] In some embodiments, each one of the plurality of grounding electrodes is placed a distance of 0.1 to 100, such as 0.1 to 50, such as 0.2 to 10, such as 0.4 to 3, such as 0.5 to 2, times the poling period from the respective plurality of charge injection sites. Advantageously, such positioning of the grounding electrodes in relation to the charge injection sites allows the process to establish an isolated interaction between the electrode and the charge injection site and to leverage the dynamic growth of domain inversion. This isolation minimizes domain broadening, a common limitation that can significantly reduce the efficiency of poled structures, and enables the formation of domains that extend well beyond the initial charge injection site.

[0053] In some embodiments, the grounding electrode is positioned at a distance from the charge injection site such that the localized electric field induces domain inversion over an area that is at least 2 times, such as at least 5 times, such as at least 10 times, such as at least 100 times, the size of the target region corresponding to the charge injection site.

[0054] In some embodiments, each one of the plurality of grounding electrodes is positioned at a distance from the respective charge injection sites such that the localized electric field induces domain inversion over an area that is at least 1 time, such as 2 times, such as 5 times, such as 10 times, such as at least 100 times, the size of the target region corresponding to the charge injection site. This configuration enables controlled domain growth that extends well beyond the charge injection site, minimizing domain broadening and supporting the creation of precise non-periodic or apodized poling patterns.

[0055] In some embodiments, the ground electrode and / or the plurality of ground electrodes and / or the ground frame is / are electrically conductive or is / are made from conductive material and, optionally, the conductive material comprises chromium and / or gold and / or titanium. The grounding electrode may or may not be in direct contact with the ferro-electric material, such as the ferro-electric thin film. If not in direct contact, the grounding electrode can be spaced from the thin film by a dielectric material, such as SiO2, to control the electric field distribution more precisely.

[0056] In some embodiments, the ground electrodes or at least one of the plurality of ground electrodes comprises an adhesive part configured to adhere the ground electrode to the ferro-electric material.

[0057] In some embodiments, the support structure comprises a top layer and, optionally, the top layer is a dielectric layer.

[0058] In some embodiments, the support structure comprises a top layer which is optically transparent and has a lower refractive index compared with the refractive index of the ferro-electric material. When the ferroelectric material is a ferroelectric thin film arranged on top of the support structure, this configuration enables the confinement of light within an optical waveguide fabricated in the ferroelectric thin film through total internal reflection, thus effectively implementing a dielectric waveguide. In some embodiments, the top layer is made from SiCh. In alternative embodiments, the top layer is made from sapphire.

[0059] In some embodiments, the support structure comprises a substrate and, optionally, the substrate is a Si or LiNbC -based substrate.

[0060] In some embodiments, the top layer is arranged on the substrate so as to create a support stack.

[0061] In some embodiments, the grounding electrode or at least one of the plurality of grounding electrodes each comprises a plurality of features configured to alter the induced electric field created by the grounding electrode or the at least one of the plurality of grounding electrodes.

[0062] In some embodiments, the plurality of features are periodically distributed along its surface.

[0063] In some embodiments, the plurality of features are arranged in a stripe-like pattern.

[0064] In some embodiments, the plurality of features are surface ridges or recesses.

[0065] Another preferred embodiment of the present disclosure relates to a method of poling a ferro-electric material, the method comprising the steps of providing a ferro-electric material, a charged particle beam generator and a grounding electrode, identifying a target region of the ferro-electric material to be a charge injection site, placing the grounding electrode at a distance close enough to the charge injection site so as to cause charge redistribution within the ground electrode when charged particles are injected into the charge injection site, irradiating, using the charged particle beam generator, the charge injection site with a beam of charged particles so as to cause polarisation reversal, such as domain inversion, at the target region of the ferro-electric material.

[0066] In some embodiments, the injection of charged particles into the charge injection site induces charge redistribution within the grounding electrode so as to create an electric field in the region between the charge injection site and the grounding electrode. In some embodiments, the electric field created by the injection of charged particles has an electric field strength greater than the electric coercive field of the ferro-electric material so as to cause polarisation reversal.

[0067] In some embodiments, the method comprises providing a plurality of grounding electrodes.

[0068] In some embodiments, the method comprises providing a grounding electrode structure and the grounding electrode structure comprises the plurality of grounding electrodes and, optionally, further comprises a grounding frame and, optionally, wherein the plurality of grounding electrodes are each attached to the grounding frame and spaced apart from each other so as to form a comb-like structure on the grounding frame.

[0069] In some embodiments, a plurality of target regions of the ferro-electric material are identified to be charge injection sites.

[0070] In some embodiments, the plurality of grounding electrodes are equally spaced apart from each other with a separation distance corresponding to an intended poling periodicity.

[0071] In some embodiments, the method comprises irradiating, using the charged particle beam generator, the plurality of charge injection sites with a beam of charged particles so as to cause domain inversion at each one of the plurality of target regions.

[0072] In some embodiments, the plurality of target regions are equally spaced apart on the surface of the ferro-electric material.

[0073] In some embodiments, domain inversion at each one of the plurality of target regions creates a periodically poled ferro-electric material.

[0074] In some embodiments, the method comprises irradiating the plurality of charge injection sites individually one after the other. In some embodiments, each one of the plurality of grounding electrodes is placed at a distance close enough to a respective one of the plurality of charge injection sites so as to cause charge redistribution within each one of the plurality of grounding electrodes when charged particles are injected into the plurality of charge injection sites.

[0075] In some embodiments, the grounding electrode is placed at a distance of less than 30 pm, such as less than 1 pm, such as less than 100 nm, from the charge injection site.

[0076] In some embodiments, each one of the plurality of grounding electrodes is placed at a distance of less than 30 pm, such as less than 1 pm, such as less than 100 nm, from the charge injection site.

[0077] In some embodiments, the charged particle beam generator is oriented such that the direction of propagation of the beam of charged particles is parallel to the optical axis of the ferro-electric material.

[0078] In some embodiments, the beam of charged particles is a continuous beam.

[0079] In some embodiments, the beam of charged particles is a pulsed beam.

[0080] In some embodiments, the method comprises the step of providing a plurality of charged particle beam generators and a respective one of the plurality of charged particle beam generators is used to irradiate a respective one of the plurality of charge injection sites.

[0081] In some embodiments, the injection of charged particles into the ferro-electric material at the charge injection site causes the local electric field strength to be greater than the coercive field of the ferro-electric material.

[0082] In some embodiments, the plurality of target regions of the ferro-electric material is selected such that domain inversion at the corresponding charge injection sites creates a periodic poling pattern.

[0083] In some embodiments, the ferro-electric material is a single crystal thin film. The ferroelectric material being a single crystal thin film ensures that an optical axis of the material that is universally defined, corresponding to the axis of extraordinary refractive index, which preserves non-linear optical effects and poling properties throughout the material. This helps to ensure optimal performance in integrated photonics and nonlinear optical applications.

[0084] In some embodiments, the ferro-electric material is a polycrystal.

[0085] In some embodiments, the ferro-electric material is a ferro-electric thin film comprising lithium niobate. Lithium niobate (LiNbO3) is particularly advantageous due to its high transparency over a broad wavelength range (350 to 5200 nm) and its suitability for applications in nonlinear optics and electro-optics. The material’s unique properties make it ideal for use in optical waveguides and modulators, which are essential in telecommunications and integrated photonics. In some example implementations, the lithium niobate thin film is transferred onto an insulator substrate, such as sapphire or SiO2, using techniques like smart cut or metal-organic chemical vapor deposition (MOCVD). This lithium niobate on insulator (LNOI) platform supports the integration of waveguides and other photonic structures, leveraging lithium niobate’s high second- order nonlinearity, electro-optic response, and broad transparency window to create a versatile, high-performance photonic device platform.

[0086] In some embodiments, the plurality of grounding electrodes are equally spaced apart so as to create a spatially periodic electric field when charged particles are injected into the plurality of charge injection sites.

[0087] In some embodiments, the spatially periodic electric field has a periodicity between 100 nm and 10 pm.

[0088] In some embodiments, the poling process is conducted in a vacuum chamber.

[0089] In some embodiments, the ferro-electric thin film is arranged on a support structure during the poling process.

[0090] In some embodiments, the support structure comprises a substrate and, optionally, the substrate comprises silicon or lithium niobate.

[0091] In some embodiments, the substrate has a thickness in the range of 200 pm to 1000 pm. In some embodiments, the thickness of the ferro-electric thin film is in the range of 10 nm to 500 pm. This thin film can be used as a standalone layer or may be positioned on top of an optical insulator or dielectric, such as SiO2or sapphire, to enhance stability and field distribution. When a secondary material is included beneath the ferroelectric thin film, this layer may have a thickness between 1 nm and 500 pm, supporting flexible configurations for various device requirements. Additionally, the entire assembly can be situated on a carrier material, typically 500 pm thick, made from materials such as silicon, lithium niobate, or sapphire to provide further structural support. The ferroelectric thin film may be oriented with its optical axis (extraordinary refractive index axis) lying in the plane of the film itself, optimizing its electro-optic and nonlinear properties for high-performance photonic applications.

[0092] In some embodiments, the charged particle beam generator is part of an electrode beam lithography system or a scanning electron microscope and the beam of charged particles is a beam of electrons.

[0093] In some embodiments, the charged particle beam generator is a part of an ion implantation system.

[0094] In some embodiments, the support structure comprises a dielectric layer and, optionally, the ferro-electric thin film is arranged on the dielectric layer during the poling process.

[0095] In some embodiments, an optical circuit is fabricated in the ferro-electric thin film prior to irradiating the ferro-electric thin film with the beam of charged particles.

[0096] In some embodiments, the method is performed using any one of the systems described in the present disclosure.

[0097] In some embodiments, during the injection of charged particles the grounding electrode and / or each one of the respective plurality of grounding electrodes is in contact with the surface of the ferro-electric material. In some embodiments, during the injection of charged particles a dielectric material is placed between the ground electrode or the plurality of ground electrodes and the ferro-electric material so as to electrically isolate the ferro-electric material from the ground electrode or the plurality of ground electrodes.

[0098] In some embodiments, the target region(s) is / are discrete points or elongated areas, such as strips, on the surface of the ferro-electric material.

[0099] In some embodiments, the injection of charged particles into the ferro-electric material at the charge injection site creates an indentation in the surface of the ferro-electric material having a depth of less than 10 nm.

[0100] Advantageously, the method is performed by any system described in the present disclosure.

[0101] Another preferred embodiment relates to a ferro-electric thin film fabricated according to any one of the methods described in the present disclosure,

[0102] Examples

[0103] Fig. 1A shows a schematic view of a prior art electrode-based periodic poling setup before a high-voltage signal is applied. In this configuration, grounding frame 101a supports grounding electrodes 102a, which are positioned to enable targeted polarisation inversion within the ferroelectric thin film 104a. A voltage source 106a is connected to the electrode to supply the high-voltage signal, with the ferroelectric thin film 104a aligned along the optical axis 105a of the ferro-electric thin film. This arrangement is prepared for domain inversion to occur upon the application of a high- voltage signal across the system.

[0104] Fig. 1B shows a schematic view corresponding to Fig. 1A, illustrating the setup after a high-voltage signal has been applied. In this configuration, the voltage source 106b has induced an electric field to emanate out of the grounding electrodes 102b. This electric field results in the formation of periodically reversed domains 112b within the thin film, aligned along the optical axis 105b. The applied high-voltage signal thus generates the desired periodic pattern of domain inversion across the ferroelectric material. Fig. 1C shows a side view schematic of the prior art el ectrode- based periodic poling setup before a high-voltage signal is applied. In this configuration, the electrode system include a grounding frame 101c supporting grounding electrodes 102c and another grounding frame 103c, which are all positioned above the ferroelectric thin film 104c. A voltage source 106c is connected to the electrode to apply a high-voltage signal, and the optical axis 105c of the ferroelectric thin film is shown. This arrangement is prepared to enable domain inversion within the ferroelectric material upon application of the high-voltage signal.

[0105] Fig. 1D shows a side view schematic corresponding to Fig. 1C after a high-voltage signal has been applied. In this configuration, the voltage source 106d has activated the grounding frames 101e, 103e and the grounding electrodes 102d, creating an electric field that extends through the ferroelectric thin film 104d. This electric field induces the formation of periodically reversed domains 112d within the thin film, visible along the optical axis 105d. The applied high-voltage signal results in a controlled pattern of domain inversion, achieving the desired periodic structure within the ferroelectric material.

[0106] Fig. 1 E shows a side view schematic similar to Fig. 1 C, with a material stack comprising a ferroelectric thin film 104e, a dielectric or optical insulator layer 114e, and a substrate 115e. In this configuration, the electrode system includes a grounding frame 101e supporting grounding electrodes 102e and another grounding frame 103e, positioned above the material stack. A voltage source 106e is connected to the electrodes to apply a high-voltage signal, and the optical axis 105e of the ferroelectric thin film is shown. This material stack may influence the electric field distribution and impact the efficiency of domain inversion within the ferroelectric material.

[0107] Fig. 2A shows a schematic view of another prior art electrode-based periodic poling setup before a high-voltage signal is applied. In this configuration, grounding frames 201a and 203a both support grounding electrodes 202a, which are positioned to facilitate targeted polarization inversion within the ferroelectric thin film 204a. The thin film 204a is part of a material stack that includes a dielectric or optical insulator layer 114e and a substrate 115e. A voltage source 206a is connected to the electrodes to supply the high-voltage signal, and the optical axis 205a of the ferroelectric thin film is shown. This arrangement is prepared to achieve domain inversion across the ferroelectric material upon application of the high-voltage signal.

[0108] Fig. 2B shows a schematic view corresponding to Fig. 2A, illustrating the setup after a high-voltage signal has been applied. In this configuration, the voltage source 206b has induced an electric field to emanate from the grounding electrodes 202b, supported by grounding frames 201b and 203b. This electric field results in the formation of periodically reversed domains 212b within the ferroelectric thin film 204b, aligned along the optical axis 205b. The applied high-voltage signal generates the desired periodic pattern of domain inversion across the ferroelectric material.

[0109] Fig. 2C shows a side view schematic of another prior art electrode-based periodic poling setup on a photonic integrated circuit (PIC) platform before a high-voltage signal is applied. In this configuration, grounding frames 201c and 203c both support grounding electrodes 202c, which are positioned above the ferroelectric thin film 204c to enable targeted polarization inversion. A voltage source 206c is connected to the electrodes to supply the high-voltage signal, and the optical axis 205c of the ferroelectric thin film is shown. This setup is configured to achieve domain inversion in the ferroelectric material upon application of the high-voltage signal.

[0110] Fig. 2D shows a side view schematic corresponding to Fig. 2C after a high-voltage signal has been applied. In this configuration, the voltage source 206d has activated grounding frames 201 d and 203d, along with grounding electrodes 202d, creating an electric field that extends through the ferroelectric thin film 204d. This electric field induces the formation of periodically reversed domains 212d within the thin film, visible along the optical axis 205d. The applied high-voltage signal produces a controlled pattern of domain inversion, resulting in the desired periodic structure within the ferroelectric material.

[0111] Fig. 3A shows a schematic view of the present disclosure's system for periodic poling on a ferro-electric platform before charge injection. In this configuration, lead electrode 301a supports grounding electrodes 302a and 303a, which are positioned to facilitate targeted polarization inversion within the ferroelectric thin film 304a. The spacing between the grounding electrodes 302a may vary depending on the specifications of the intended poling period, and the distances between adjacent grounding electrodes may be equal, corresponding to the poling period, or may vary along the length 311a to achieve, for example, apodization or chirping.

[0112] Apodization refers to varying the poling period in such a way that the nonlinear optical signal generated by the poled area exhibits a bell-shaped spectral profile rather than a sine-shaped spectral profile. Chirping, on the other hand, involves varying the poling period along the direction of the lead electrode 301a. For example, the spacing between adjacent grounding electrodes 302a may start at 1 pm on one side of the lead electrode 301a and gradually increase to 5 pm on the opposite side of the lead electrode 301a. This configuration allows the poled area to support broadband operation, where one wavelength is optimized on one end of the structure and another wavelength is optimized on the other.

[0113] The length of the grounding electrodes may be between 1 to 200 microns. A non- uniform electric field across the ferroelectric material may be created by a combination of the geometry and the applied voltage. Charge injection sites 317a are positioned to enable precise control over the domain inversion process along the optical axis 305a of the ferroelectric thin film. This arrangement is designed to produce domain inversion across the ferroelectric material upon charge injection.

[0114] Fig. 3B shows a schematic view corresponding to Fig. 3A, illustrating the system after charge injection has been applied. In this configuration, the grounding electrode structure comprises the lead electrode 301b, which is connected to the electrical ground 307b, and grounding electrodes 302b. The injection of charge into the charge injection sites 317b induces a redistribution of charge within the grounding electrodes 302b, creating a non-uniform electric field across the ferroelectric thin film 304b. This electric field induces the formation of periodically reversed domains 312b within the thin film. The distances between adjacent grounding electrodes 302b may be equal, as is the case in the system shown in Fig. 3B, and correspond to the poling period, or the grounding electrodes may be attached to the lead electrode 301b at unequal distances along its length 311b to create an apodized periodic poling. The resulting domain pattern is visible along the optical axis 305b, achieving the desired periodic structure within the ferroelectric material. Fig. 3C shows a side view schematic of the system according to the present disclosure before charge injection. In this configuration, the grounding electrode structure comprises the lead electrode 301c, which is connected to the electrical ground 307c and grounding electrodes 302c, positioned above the ferroelectric thin film 304c. The optical axis of the ferro-electric thin film is also shown.

[0115] Fig. 3D shows a side view schematic corresponding to Fig. 3C after charge injection has been applied. In this configuration, the grounding electrode structure comprises the grounding frame 301 d, which is connected to the electrical ground 307d, and grounding electrodes 302d, positioned above the ferroelectric thin film 304d. The charge is injected close to the grounding electrodes 302d, such as within a distance of 30 microns or within 0.1 to 10 times the intended poling period. The poling periodicity is related to the separation distance between adjacent grounding electrodes 302d. This charge injection induces a redistribution of charge within the grounding electrodes 302d, creating a non-uniform electric field across the ferroelectric thin film 304d. This electric field results in the formation of periodically reversed domains 312d within the thin film, with the inverted ferroelectric domain flushing through and beyond the charge injection location.

[0116] An optional buffer layer 319d, which may be composed of silica, a polymer, or conductive material, may be applied to influence the charge injection process. The buffer layer 319d serves as an intermediary between the charge injection point and the ferroelectric thin film 304d. By introducing this layer, the deposition of injected charges can occur at least partly above the ferroelectric film rather than directly within it. This design enables precise control over the depth reached by the injected charges, offering a greater degree of repeatability and reliability compared to direct adjustments of the charge injection beam parameters. Moreover, the buffer layer may help to slow down the charge injection process, providing additional control over the interaction between the charges and the ferroelectric layer.

[0117] The inclusion of the buffer layer 319d provides several advantages. First, it may reduce process non-uniformities that could arise from imperfections in the shape or positioning of the grounding electrodes 302d. Second, the buffer layer may decrease the likelihood of physical damage to the ferroelectric thin film 304d, such as breakage or mechanical stress induced by the charge injection process. Third, it may improve the overall precision and stability of the charge injection mechanism, particularly in applications requiring consistent and reproducible domain formation.

[0118] Additionally, a dielectric layer 322d, such as SiO2, may be applied on the grounding electrodes 302d to further regulate the electric field distribution. By finely controlling the thickness of the dielectric layer, this layer can reduce the impact of imperfections in the electrodes and enable precise engineering of the electric field distribution. This allows for improved poling control without requiring adjustments to the settings of the beam generator. This provides an alternative or supplementary solution to modifying the shape of the electrode tips as a means for engineering a particular electric field distribution, thereby offering greater flexibility in design optimization.

[0119] The optical axis of the ferroelectric thin film is also shown, indicating the alignment of the domain pattern.

[0120] Fig. 4A shows a lateral piezo force microscopy (PFM) image of the ferroelectric thin film 404a, illustrating the results of periodic poling induced by charge injection. In this configuration, grounding electrodes (not shown in this figure) have been positioned to create a non-uniform electric field across the thin film, resulting in a series of periodically reversed domains 412a within the material. The poling period in this example is 375 nm, demonstrating a high-resolution pattern that aligns with the intended poling periodicity. The periodic domain structure is visible along the optical axis of the thin film, confirming the successful inversion of domains achieved through the system and method of the present disclosure.

[0121] Figs. 4B-D show lateral piezo force microscopy (PFM) images similar to Fig. 4A, but with poling periods of 750 nm, 1500 nm and 1110 nm.

[0122] Fig. 5 shows a lateral piezo force microscopy (PFM) image of a photonic integrated circuit waveguide fabricated in a ferroelectric thin film 504 that was periodically poled by charge injection prior to waveguide fabrication. The poling period is 3.47 pm, and the waveguide is etched to a depth of 460 nm within a 600 nm thin-film ferroelectric crystal. The PFM image indicates that the periodic poling extends the full etching depth of the waveguide, confirming the successful alignment and depth control of domain inversion within the ferroelectric material. Fig. 6 shows optical nonlinear evidence stemming from the periodically poled photonic integrated waveguide, converting light at approximately 1424 nm to light at a 712 nm wavelength through a second harmonic generation (SHG) nonlinear process. Fig. 6a illustrates the experimental setup used to achieve energy conversion in the periodically poled photonic integrated waveguide, which includes a laser source, fiber polarization controller (FPC), device under test (DUT), and an optical spectrum analyser (OSA).

[0123] Fig. 6B displays the output spectrum through the periodically poled photonic integrated waveguide, confirming successful energy conversion to the 712 nm wavelength.

[0124] Fig. 7 shows a schematic view of the grounding electrode structure, comprising grounding frame 721, lead electrodes 701, and ground electrodes 702. The grounding frame 721 has a hole in the center, with the lead electrodes 701 attached to opposite ends of the grounding frame across this hole. The ground electrodes 702 are then attached along the lengths of the lead electrodes 701. The ground electrodes 702 may be equally spaced along the lead electrodes, with the separation distance (defined as the distance separating adjacent ground electrodes) corresponding to the intended poling periodicity. This configuration is designed to provide controlled charge distribution across the ferroelectric thin film during the poling process, enabling precise domain inversion by generating a localized electric field in the targeted poling regions.

[0125] Fig. 8 shows a schematic view illustrating various shapes of ground electrodes 802. The ends of the ground electrodes may be rounded, squared, chamfered, or tapered, allowing for flexibility in design to optimize the electric field distribution and control the poling pattern. These different geometries provide options to tailor the localized electric field effect across the ferroelectric thin film for improved domain inversion precision.

[0126] The charge injection process is controlled by the diameter of the charge beam and / or the spatial resolution of the charge injection tool (as well as, in some embodiments, the inclusion of an optional layer, such as optional layer 319d shown in Fig. 3D), enabling precise configuration of the poling pattern. Charge injection can be spatially designed to create either a continuous line or discrete points, offering flexibility for various poling designs. The charge injection may be offset from the termination of the electrode stripe by a distance of 0.1 to 10 times the intended poling period length. Injecting charge at this distance initiates a flush-type poling process, where the inverted domain begins nucleation at the electrode stripe termination and propagates toward the charge injection site. Remarkably, this domain propagation does not stop at the injection site but continues to flush through and beyond it, resulting in poled domains significantly longer than the distance between the electrode stripe termination and charge injection site.

[0127] By positioning the charge injection site close to the electrode stripe termination, this method effectively prevents domain broadening, allowing for periodic poling with precision limited only by the electrode resolution. In contrast to traditional poling methods — where a high voltage pulse applied to patterned electrodes poles all domains simultaneously — this flush poling method enables one-domain-at-a-time poling. This incremental approach ensures that each domain's poling process is entirely independent of its neighboring domains, thereby enhancing the repeatability and precision of the process.

[0128] This method removes limitations on the size of the sample to be poled, making it applicable to both individual chips (approximately 1 cm2) and wafer-scale ferroelectric thin films. Additionally, compared to traditional techniques, this domain engineering method is inherently more resilient to imperfections in the poled pattern. The flushing dynamics depend primarily on electrode geometry and the precise location of charge injection sites, rendering the process less sensitive to thin-film inhomogeneities. After charge injection, the site is minimally marked by a circular indentation less than 10 nm deep, allowing for high-quality, repeatable poling with negligible disruption to the thin film's surface.

[0129] Further details of drawings

[0130] 101 a-e, 201 a-e, 301 a-e - lead electrode

[0131] 102a-e, 202a-e, 302a-e, 402a-d, 702 - grounding electrodes

[0132] 103a-e, 203a-e - another grounding frame

[0133] 104a-e, 204a-e, 304a-e, 404a-e, 504 - ferro-electric thin film

[0134] 105a-e, 205a-e, 305a-e - optical axis of the ferro-electric crystal

[0135] 106a-e, 206a-e - voltage source

[0136] 107a-e, 207a-e, 307a-e - electrical ground

[0137] 108a-e, 208a-e, 308a-e, 808 - length of the individual element in a comb-like electrode 109a-e, 209a-e, 309a-e - period in the comb-like electrode 110a-e, 210a-e - distance between signal and ground electrode in prior art methods 111a-e, 211a-e, 311a-e - total length of the periodiaclly poled area.

[0138] 112b, 112d, 212b, 212d, 312b, 312d, 412a-d, 512 - inverted domains

[0139] 113c-e, 213c-e, 313c, 313d - electrode thickness

[0140] 114e, 214e - dielectric layer or optical insulator layer

[0141] 115e, 215e - substrate

[0142] 316b, 316d - distance between the charge injection sites and the grounding electrode 317a, 317b, 317d - charge injection sites

[0143] 318b - length of the inverted domain

[0144] 319d - optional buffer layer

[0145] 322d - dielectric layer

[0146] 520 - photonic integrated waveguide

[0147] 721 - grounding frame

[0148] 522 - periodicity of the inverted domains

[0149] 701 - lead electrodes

[0150] 702 - ground electrodes

[0151] Items

[0152] 1. Charged beam flush poling for (use in) fabricating optical nonlinear integrated devices, comprising

[0153] • a thin-film ferro-electric material on which o a plurality of grounding electrode is patterned, o a plurality of charge injection sites is defined, wherein the distance between the grounding electrode and charge injection site is such to create flush poling wherein:

[0154] • Flush poling takes place when the charge is injected close to the grounding electrode, wherein close is defined as 0 - 100 times, or 0 - 10 times, the poling periodicity, allowing the inverted ferro-electric domain to flush through and beyond the charge injection location.

[0155] • The charge is injected translationally along the optical axis (axis of extraordinary refractive index) with respect to the terminated electrode stripes.

[0156] • The negative / positive charge is injected such to create an electric field opposite to the direction of the spontaneous polarization of the ferroelectric thin-film. The created electric field, as a consequence of the injected charge, is higher than the coercive field of the ferro-electric thin- film, resulting in the spontaneous polarization of the ferro-electric thin- film to switch orientation.

[0157] • The properties of the inverted domain are due to the geometrical properties of the electrodes and injection sites and only marginally affected by small variations in the properties of the ferro-electric thin film.

[0158] • The numerous inverted domains are implemented individually one after the other, any numerical sequence thereof, or continuously.

[0159] 2. The charge injected flush poling in 1, wherein the ferro-electric thin-film is defined on a dielectric / optical insulator, such as SiCh.

[0160] 3. The charge injected flush poling in 1, wherein the ferro-electric thin-film defined on a dielectric / optical insulator, such as SiCh, which again is defined on a substrate, such as Si or LiNbCh.

[0161] 4. The charge injected flush poling as in the preceding items, wherein the substrate is mechanically stable.

[0162] 5. The charge injected flush poling according to any of the preceding items, wherein the substrate is electrically conductive.

[0163] 6. The charge injected flush poling according to any of the preceding items, wherein the substrate comprises a separating layer separating the ferro-electric thin-film and the substrate.

[0164] 7. The charge injected flush poling according to any of the preceding items, wherein the separating layer comprises an electro-optical material or optical insulator layer.

[0165] 8. The charge injected flush poling according to any of the preceding items, wherein the electrodes are comprised of a material allowing adhesion to the ferro-electric thin film and conductivity, such as Cr, Au or Ti.

[0166] 9. The charge injected flush poling according to any of the preceding items, wherein the electrodes are spaced from the ferro-electric thin film with any dielectric material, such as SiCh.

[0167] 10. The charge injected flush poling according to any of the preceding items, wherein the electrodes are located in contact with the ferro-electric thin-film.

[0168] 11. The charge injected flush poling according to any of the preceding items, wherein the plurality of electrode stripes termination are located at a distance of 100x, preferably 10x, preferably 5x or more preferably 1x or less from the charge injection area.

[0169] 12. The charge injected flush poling according to any of the preceding items, wherein the grounding electrode comprise a plurality of features periodically distributed along its length.

[0170] 13. The charge injected flush poling according to any of the proceeding items, wherein the plurality of features is a plurality of stripe-like pattern, wherein the plurality of turns are angle shaped, round shaped or a combination thereof.

[0171] 14. The charge injected flush poling according to any of the preceding items, wherein the plurality of features is a plurality of perforations or absence of grounding electrode material.

[0172] 15. The charge injected flush poling according to any of the preceding items, wherein the features periodically distributed along the length of the grounding electrode are plurality of electrode stripe located on both sides of the lead electrode.

[0173] 16. The charge injected flush poling according to any of the proceeding items, wherein the electrode stripes comprise a width and a height comparable to the intended poling period.

[0174] 17. The charge injected flush poling according to any of the proceeding items, wherein the protuberances and the electrode stripes are comprised of the same material.

[0175] 18. The charge injected flush poling according to any of the preceding items, wherein the plurality of features periodically distributed along the length of the electrode length is configured to induce a periodic electric field. The charge injected flush poling according to any of the preceding items, wherein the cross-sectional shape of the grounding electrode and ferro-electric thin-film is constant along the length of the poling area. The charge injected flush poling according to any of the preceding items, wherein the cross-sectional shape of the grounding electrode and ferro-electric thin-film varies along the length of the poling area. The charge injected flush poling according to any of the preceding items, wherein the poling creates a poling period between 1 nm to 100 urn. The charge injected flush poling according to any of the preceding items, wherein the charge injection is performed with an electrode beam lithography system. The charge injected flush poling according to any of the preceding items, wherein charge injection is performed with a scanning electron microscope / focused ion beam system. The charge injected flush poling according to any of the preceding items, wherein charge injection is performed with an ion implantation system. The charge injected flush poling according to any of the preceding items, wherein the optical circuitry has been fabricated in the ferro-electric thin-film prior to performing flush poling. The charge injected flush poling according to any of the preceding items, wherein the ferro-electric thin-film is between 10 nm and 1000 pm, and optionally 10 nm and 500 urn thick. The charge injected flush poling according to any of the preceding items, wherein the charge injection may or may not create a circular indentation of more or less than 10 nm depth in the ferro-electric thin-film, or any other layer sitting on top of the ferro-electric thin-film layer. A method for systematically injecting the charge to create the flush poling for realizing nonlinear integrated devices, comprising the steps of

[0176] • Patterning a grounding electrode directly on a ferro-electric thin-film, or on a material stack consisting of a ferro-electric thin-film. A grounding electrode consisting of as many (or more) electrode stripes than intended poling periods.

[0177] • A charged beam with beam position control (higher resolution than the intended poling period) o Charged beam with acceleration voltage between 1 and 1000 kV o Spatial resolution equal or higher than the intended poling period.

[0178] • at least one electrode inducing an electrical field for switching the ferro-electric domains, resulting in periodic poling.

[0179] • at least charge injection area for inducing an electrical field for switching the ferro-electric domains, resulting in periodic poling. Charged beam flush poling for (use in) fabricating optical nonlinear integrated devices, comprising

[0180] • a thin-film ferro-electric material on which o a plurality of grounding electrode is patterned, o a plurality of charge injection sites is defined, wherein the distance between the grounding electrode and charge injection site is such to create flush poling wherein:

[0181] • The flush poling takes place when the charge is injected close to the grounding electrode, wherein close is defined as 0 - 100 times, such as 0 - 10 times, the poling periodicity, which may allow the inverted ferroelectric domain to flush through and beyond the charge injection location.

[0182] • The charge is injected translationally along the optical axis (axis of extraordinary refractive index) with respect to the terminated electrode stripes.

[0183] • The negative / positive charge is injected such to create an electric field opposite to the direction of the spontaneous polarization of the ferroelectric thin-film. The created electric field, as a consequence of the injected charge, is higher than the coercive field of the ferro-electric thin- film, resulting in the spontaneous polarization of the ferro-electric thin- film to switch orientation.

[0184] • The charge is injected repeatedly into the same charge injection site, or any combination of charge injection sequential pattern among the charge injection sites.

[0185] • The properties of the inverted domain are due to the geometrical and / or electrical properties of the electrodes and injection sites and only marginally affected by small variations in the properties of the ferroelectric thin film.

[0186] • The numerous inverted domains are implemented individually one after the other or any numerical sequence thereof.

[0187] • Optionally, the method can include a beam source capable of operating with multiple foci simultaneously (similar to multi-foci laser writing techniques), enabling parallel domain implementation for enhanced efficiency. A method for systematically injecting the charge to create the flush poling as in 1 for realizing nonlinear integrated devices, comprising the steps of:

[0188] • Patterning a grounding electrode directly on a ferro-electric thin-film, or on a material stack consisting of a ferro-electric thin-film. A grounding electrode consisting of as many (or more) electrode stripes than intended poling periods.

[0189] • A charged beam with beam position control (higher resolution than the intended poling period)

[0190] • Charged beam with acceleration voltage between 1 and 1000 kV

[0191] • Spatial resolution equal or higher than the intended poling period.

[0192] • At least one electrode causing an electrical field for switching the ferroelectric domains, resulting in periodic poling.

[0193] • At least one charge injection area for causing an electrical field for switching the ferro-electric domains, resulting in periodic poling. The charge injected flush poling in 1, wherein the ferro-electric thin-film is defined on a dielectric / optical insulator, such as SiCh. 32. The charge injected flush poling in 1, wherein the ferro-electric thin-film defined on a dielectric / optical insulator, such as SiO2, which again is defined on a mechanically stable substrate, such as Si, SiO2 or LiNbOs.

[0194] 33. The charge injected flush poling as in the preceding claims, wherein an optical circuit, or any circuit thereof, has been fabricated in the ferro-electric thin-film prior to performing the charge injected flush poling.

[0195] 34. The charge injected flush poling according to any of the preceding claims, wherein the substrate is electrically conductive.

[0196] 35. The charge injected flush poling according to any of the preceding claims, wherein the substrate comprises a separating layer separating the ferro-electric thin-film and the substrate. And wherein the separating layer may comprise an electro-optic material.

[0197] 36. The charge injected flush poling according to any of the preceding items, wherein the domains are poled individually (one after the other) and the electrode (or a part of it) is engineered in such a way to act like a charges emitting / receiving element causing flush poling in the ferroelectric material upon charge implantation in one of the injection sites.

[0198] 37. The charge injected flush poling according to any of the preceding claims, wherein the electrodes are comprised of a material allowing adhesion to the ferro-electric thin film and conductivity, such as Cu, Cr, Au, Ti or ITO.

[0199] 38. The charge injected flush poling according to any of the preceding claims, wherein the electrodes are spaced from the ferro-electric thin film with any dielectric material, such as SiO2.

[0200] Statements

[0201] 1. A system for use in a process for poling a ferro-electric material, the system comprising: a charged particle beam generator and a control unit configured for controlling the operation of the charged particle beam generator, a grounding electrode, and a support structure configured to support the ferro-electric material during the poling process.

[0202] 2. The system according to statement 1, wherein the control unit is configured to receive input, such as user input via a user display, which identifies a target region of the ferro-electric material to be a charge injection site.

[0203] 3. The system according to any preceding statement, wherein the control unit is further configured to instruct the charged particle beam generator to irradiate the charge injection site with a beam of charged particles based on the received input.

[0204] 4. The system according to any preceding statement, wherein the control unit is configured to receive input, such as user input via a user display, which identifies a plurality of target regions of the ferro-electric material to be a plurality of charge injection sites.

[0205] 5. The system according to any preceding statement, wherein the control unit is further configured to instruct the charged particle beam generator to irradiate the plurality of charge injection sites with a beam of charged particles.

[0206] 6. The system according to any preceding statement, wherein the system comprises a plurality of grounding electrodes.

[0207] 7. The system according to any preceding statement, wherein the system comprises a grounding electrode structure and the grounding electrode structure comprises the plurality of grounding electrodes.

[0208] 8. The system according to any preceding statement, wherein the grounding electrode structure further comprises a grounding frame.

[0209] 9. The system according to any preceding statement, wherein the grounding electrode structure further comprises one or more lead electrodes which is / are each attached to the grounding frame. 10. The system according to any preceding statement, wherein the plurality of grounding electrodes are bar-shaped electrodes.

[0210] 11. The system according to any preceding statement, wherein the grounding electrode or at least one of the plurality of grounding electrodes is tapered down to an electrode termination point.

[0211] 12. The system according to any preceding statement, wherein the plurality of grounding electrodes are attached at distributed attachment points along the length of a surface of the grounding frame so as to create an array of electrode elements protruding from the grounding electrode structure.

[0212] 13. The system according to any preceding statement, wherein the one or more lead electrodes are attached at distributed attachment points along the length of a surface of the grounding frame and each one of the respective plurality of grounding electrodes is attached to a respective one of the one or more lead electrodes so as to create an array of electrode elements protruding from the grounding electrode structure, wherein each electrode element comprises one of the one or more lead electrodes and one of the plurality of grounding electrodes.

[0213] 14. The system according to any preceding statement, wherein the plurality of grounding electrodes are spaced apart from each other.

[0214] 15. The system according to any preceding statement, wherein the plurality of grounding electrodes are spaced apart from each other so as to form a comblike structure on the grounding frame.

[0215] 16. The system according to any preceding statement, wherein the plurality of grounding electrodes are equally spaced apart from each other with a separation distance corresponding to an intended poling periodicity.

[0216] 17. The system according to any preceding statement, wherein the ground electrode and / or the plurality of ground electrodes and / or the ground frame is / are electrically conductive or is / are made from conductive material and, optionally, the conductive material comprises chromium and / or gold and / or titanium.

[0217] 18. The system according to any preceding statement, wherein the ground electrodes or at least one of the plurality of ground electrodes comprises an adhesive part configured to adhere the ground electrode to the ferro-electric material.

[0218] 19. The system according to any preceding statement, wherein the support structure comprises a top layer and, optionally, the top layer is a dielectric layer.

[0219] 20. The system according to any preceding statement, wherein the support structure comprises a top layer which is optically transparent and has a lower refractive index compared with the refractive index of the ferro-electric material.

[0220] 21. The system according to any preceding statement, wherein the top layer is made from SiCh.

[0221] 22. The system according to any preceding statement, wherein the support structure comprises a substrate and, optionally, the substrate is a Si or LiNbCh- based substrate.

[0222] 23. The system according to any preceding statement, wherein the top layer is arranged on the substrate so as to create a support stack.

[0223] 24. The system according to any preceding statement, wherein the grounding electrode or at least one of the plurality of grounding electrodes each comprises a plurality of features configured to alter the induced electric field created by the grounding electrode or the at least one of the plurality of grounding electrodes.

[0224] 25. The system according to any preceding statement, wherein the plurality of features are periodically distributed along its surface.

[0225] 26. The system according to any preceding statement, wherein the plurality of features are arranged in a stripe-like pattern. 27. The system according to any preceding statement, wherein the plurality of features are surface ridges or recesses.

[0226] 28. A method of poling a ferro-electric material, the method comprising the steps of: providing a ferro-electric material, a charged particle beam generator and a grounding electrode, identifying a target region of the ferro-electric material to be a charge injection site, placing the grounding electrode at a distance close enough to the charge injection site so as to cause charge redistribution within the ground electrode when charged particles are injected into the charge injection site, irradiating, using the charged particle beam generator, the charge injection site with a beam of charged particles so as to cause polarisation reversal, such as domain inversion, at the target region of the ferro-electric material.

[0227] 29. The method according to statement 28, wherein the injection of charged particles into the charge injection site induces charge redistribution within the grounding electrode so as to create an electric field in the region between the charge injection site and the grounding electrode.

[0228] 30. The method according to statement 28 or statement 29, wherein the electric field created by the injection of charged particles has an electric field strength greater than the electric coercive field of the ferro-electric material so as to cause polarisation reversal.

[0229] 31. The method according to any one of statements 28 to 30, wherein the method comprises providing a plurality of grounding electrodes.

[0230] 32. The method according to any one of statements 28 to 31, wherein the method comprises providing a grounding electrode structure and the grounding electrode structure comprises the plurality of grounding electrodes and, optionally, further comprises a grounding frame and, optionally, wherein the plurality of grounding electrodes are each attached to the grounding frame and spaced apart from each other so as to form a comb-like structure on the grounding frame. The method according to any one of statements 28 to 32, wherein a plurality of target regions of the ferro-electric material are identified to be charge injection sites. The method according to any one of statements 28 to 33, wherein the plurality of grounding electrodes are equally spaced apart from each other with a separation distance corresponding to an intended poling periodicity. The method according to any one of statements 28 to 34, wherein each one of the plurality of grounding electrodes is placed a distance of 0.1 to 50, such as 0.2 to 10, such as 0.4 to 3, such as 0.5 to 2, times the poling period from the respective plurality of charge injection sites. The method according to any one of statements 28 to 35, wherein the grounding electrode is positioned at a distance from the charge injection site such that the localized electric field induces domain inversion over an area that is at least 2 times, such as at least 5 times, such as at least 10 times, such as at least 100 times, the size of the target region corresponding to the charge injection site. The method according to any one of statements 28 to 36, where each one of the plurality of grounding electrodes is positioned at a distance from the respective charge injection sites such that the localized electric field induces domain inversion over an area that is at least 2 times, such as at least 5 times, such as at least 10 times, such as at least 100 times, the size of the target region corresponding to the charge injection site. The method according to any one of statements 28 to 37, wherein the method comprises irradiating, using the charged particle beam generator, the plurality of charge injection sites with a beam of charged particles so as to cause domain inversion at each one of the plurality of target regions. 39. The method according to any one of statements 28 to 38, wherein the plurality of target regions are equally spaced apart on the surface of the ferro-electric material.

[0231] 40. The method according to any one of statements 28 to 39, wherein domain inversion at each one of the plurality of target regions creates a periodically poled ferro-electric material.

[0232] 41. The method according to any one of statements 28 to 40, wherein the method comprises irradiating the plurality of charge injection sites individually one after the other.

[0233] 42. The method according to any one of statements 28 to 41 , wherein each one of the plurality of grounding electrodes is placed at a distance close enough to a respective one of the plurality of charge injection sites so as to cause charge redistribution within each one of the plurality of grounding electrodes when charged particles are injected into the plurality of charge injection sites.

[0234] 43. The method according to any one of statements 28 to 42, wherein the grounding electrode is placed at a distance of less than 30 pm, such as less than 1 pm, such as less than 100 nm, from the charge injection site.

[0235] 44. The method according to any one of statements 28 to 43, wherein each one of the plurality of grounding electrodes is placed at a distance of less than 30 pm, such as less than 1 pm, such as less than 100 nm, from the charge injection site.

[0236] 45. The method according to any one of statements 27 to 44, wherein each one of the plurality of grounding electrodes is placed

[0237] 46. The method according to any one of statements 28 to 45, wherein the charged particle beam generator is oriented such that the direction of propagation of the beam of charged particles is parallel to the optical axis of the ferro-electric material. 47. The method according to any one of statements 28 to 46, wherein the beam of charged particles is a continuous beam.

[0238] 48. The method according to any one of statements 28 to 47, wherein the beam of charged particles is a pulsed beam.

[0239] 49. The method according to any one of statements 28 to 48, wherein the method comprises the step of providing a plurality of charged particle beam generators and a respective one of the plurality of charged particle beam generators is used to irradiate a respective one of the plurality of charge injection sites.

[0240] 50. The method according to any one of statements 28 to 49, wherein the injection of charged particles into the ferro-electric material at the charge injection site causes the local electric field strength to be greater than the coercive field of the ferro-electric material.

[0241] 51. The method according to any one of statements 28 to 50, wherein the plurality of target regions of the ferro-electric material is selected such that domain inversion at the corresponding charge injection sites creates a periodic poling pattern.

[0242] 52. The method according to any one of statements 28 to 51 , wherein the ferroelectric material is a single crystal thin film.

[0243] 53. The method according to any one of statements 28 to 52, wherein the ferroelectric material is a polycrystal.

[0244] 54. The method according to any one of statements 28 to 53, wherein the ferroelectric material is a ferro-electric thin film comprising lithium niobate.

[0245] 55. The method according to any one of statements 28 to 54, wherein the plurality of grounding electrodes are equally spaced apart so as to create a spatially periodic electric field when charged particles are injected into the plurality of charge injection sites. 56. The method according to any one of statements 28 to 55, wherein the spatially periodic electric field has a periodicity between 100 nm and 10 pm.

[0246] 57. The method according to any one of statements 28 to 56, wherein the poling process is conducted in a vacuum chamber.

[0247] 58. The method according to any one of statements 28 to 57, wherein the ferroelectric thin film is arranged on a support structure during the poling process.

[0248] 59. The method according to any one of statements 28 to 58, wherein the support structure comprises a substrate and, optionally, the substrate comprises silicon or lithium niobate.

[0249] 60. The method according to any one of statements 28 to 59, wherein the substrate has a thickness in the range of 200 pm to 1000 pm.

[0250] 61. The method according to any one of statements 28 to 60, wherein the thickness of the ferro-electric thin film is in the range of 10 nm to 500 nm.

[0251] 62. The method according to any one of statements 28 to 61, wherein the charged particle beam generator is part of an electrode beam lithography system or a scanning electron microscope and the beam of charged particles is a beam of electrons.

[0252] 63. The method according to any one of statements 28 to 62, wherein the charged particle beam generator is a part of an ion implantation system.

[0253] 64. The method according to any one of statements 28 to 63, wherein the support structure comprises a dielectric layer and, optionally, the ferro-electric thin film is arranged on the dielectric layer during the poling process.

[0254] 65. The method according to any one of statements 28 to 64, wherein an optical circuit is fabricated in the ferro-electric thin film prior to irradiating the ferroelectric thin film with the beam of charged particles. 66. The method according to any one of statements 28 to 65, wherein the method is performed using the system according to any one of statements 1 to 27.

[0255] 67. The method according to any one of statements 28 to 66, wherein during the injection of charged particles the grounding electrode and / or each one of the respective plurality of grounding electrodes is in contact with the surface of the ferro-electric material.

[0256] 68. The method according to any one of statements 28 to 67, wherein during the injection of charged particles a dielectric material is placed between the ground electrode or the plurality of ground electrodes and the ferro-electric material so as to introduce a buffer layer between the ferro-electric material and the ground electrode or the plurality of ground electrodes.

[0257] 69. The method according to any one of statements 28 to 68, wherein the target region(s) is / are discrete points or elongated areas, such as strips, on the surface of the ferro-electric material.

[0258] 70. The method according to any one of statements 28 to 69, wherein the injection of charged particles into the ferro-electric material at the charge injection site creates an indentation in the surface of the ferro-electric material having a depth of less than 10 nm.

[0259] 71. The method according to any one of statements 28 to 70, wherein the method is performed by a system defined according to any one of statements 1 to 27.

[0260] 72. A ferro-electric thin film fabricated according to any one of the methods according to statements 28 to 71 .

Claims

38CLAIMS1 . A method of poling a ferro-electric material, the method comprising the steps of: providing a ferro-electric material, a charged particle beam generator and a grounding electrode, identifying a target region of the ferro-electric material to be a charge injection site, placing the grounding electrode at a distance close enough to the charge injection site so as to cause charge redistribution within the ground electrode when charged particles are injected into the charge injection site, irradiating, using the charged particle beam generator, the charge injection site with a beam of charged particles so as to cause polarisation reversal, such as domain inversion, at the target region of the ferroelectric material.

2. The method according to claim 1 , wherein the injection of charged particles into the charge injection site induces charge redistribution within the grounding electrode so as to create an electric field in the region between the charge injection site and the grounding electrode.

3. The method according to any one of claims 1 - 2, wherein the method comprises providing a grounding electrode structure and the grounding electrode structure comprises a plurality of grounding electrodes and, optionally, further comprises a grounding frame and, optionally, wherein the plurality of grounding electrodes are each attached to the grounding frame and spaced apart from each other so as to form a comb-like structure on the grounding frame.

4. The method according to any one of claim 3, wherein: a plurality of target regions of the ferro-electric material are identified to be charge injection sites, the plurality of grounding electrodes are spaced apart from each other with a separation distance corresponding to an intended poling periodicity, and each one of the plurality of grounding electrodes is placed a distance of 0.1 to 100, such as 0.2 to 10, such as 0.4 to 3, such as 0.5 to 2, times the poling period from the respective plurality of charge injection sites.

395. The method according to any one of claims 1 - 4, wherein the grounding electrode is placed at a distance of less than 300 pm, such as less than 1 pm, such as less than 100 nm, from the charge injection site.

6. The method according to any one of claims 1 - 5, wherein a plurality of target regions of the ferro-electric material are identified to be charge injection sites; and the method comprises the step of providing a plurality of charged particle beam generators and a respective one of the plurality of charged particle beam generators is used to irradiate a respective one of the plurality of charge injection sites.

7. The method according to any one of claim 6, wherein the plurality of target regions of the ferro-electric material is selected such that domain inversion at the corresponding charge injection sites creates a periodic poling pattern.

8. The method according to any one of claims 1 - 7, wherein the ferroelectric material is a single crystal thin film, wherein, optionally, the thickness of the ferro-electric thin film is in the range of 10 nm to 1000 pm and, optionally, wherein an optical circuit is fabricated into the ferro-electric thin film prior to irradiating the ferroelectric thin film with the beam of charged particles.

9. The method according to any one of claims 1 to 8, wherein the plurality of grounding electrodes are spaced apart so as to create a spatially periodic electric field when charged particles are injected into the plurality of charge injection sites and, optionally, wherein the spatially periodic electric field has a periodicity between 100 nm and 100 pm.

10. The method according to any of claims 1 - 9, wherein during the injection of charged particles the grounding electrode and / or each one of the respective plurality of grounding electrodes is in contact with the surface of the ferro-electric material.

11. The method according to any one of claims 1 - 10, wherein the injection of charged particles into the ferro-electric material at the charge injection site creates an indentation in the surface of the ferro-electric material having a depth of less than 10 nm.4012. A system for use in a process for poling a ferro-electric material, the system comprising: a charged particle beam generator and a control unit configured for controlling the operation of the charged particle beam generator, a grounding electrode, and a support structure configured to support the ferro-electric material during the poling process.

13. The system according to claim 12, wherein the support structure comprises one or both of: a top layer wherein, optionally, the top layer is a dielectric layer; and a substrate wherein, optionally, the substrate is a Si or LiNbCh-based substrate.

14. The system according to claim 12 or claim 13 wherein the control unit is configured to cause the system to perform the steps of any of claims 1 - 11.

15. A computer program product comprising computer program code configured to cause a processor, when the computer program code is run on the processor, to control a system of any of claims 12 - 14 to carry out the method of any of claims 1 - 11.

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