Ferroelectric-based, large-area, high-density nonvolatile optical memory and manufacturing method therefor

Abstract

The present invention relates to a ferroelectric-based, large-area, high-density nonvolatile optical memory which enables optical electric polarization control by focusing light into a nano gap using a metal nano gap structure capable of exceeding a diffraction limit of light, and a manufacturing method therefor. The optical memory comprises: a substrate; first line patterns having a length in a first direction, and formed on the substrate repeatably at regular intervals in a second direction perpendicular to the first direction; a ferroelectric layer formed on the entire surface including the first line patterns; and second line patterns covering the ferroelectric layer in a region where the first line patterns are spaced apart from each other, and filling a space between the first line patterns, wherein a metal nano gap is formed by a side surface of any one of the first line patterns and a side surface of the second line pattern corresponding thereto.

Description

Ferroelectric-based large-area high-density non-volatile optical memory and manufacturing method

[0001] The present invention relates to an optical memory, and specifically to a large-area, high-density non-volatile optical memory based on a ferroelectric material and a method for manufacturing it, which enables optical electric polarization control by using a metal nano-slit structure capable of overcoming the diffraction limit of light to focus light into the nano-slit.

[0002] Technologies that process large amounts of information, such as artificial intelligence (AI), the Internet of Things (IoT), and big data, require memory semiconductors that have a long lifespan and can rapidly process vast amounts of information with low power consumption.

[0003] Much research has been conducted to date for the development of high-density memory devices, an example of which is non-volatile ferroelectric memory (FE-RAM) utilizing ferroelectric materials.

[0004] As semiconductors become smaller and handle larger amounts of information, linewidths at the nanometer level are naturally required; however, such ultra-thin thicknesses have presented electrical limitations in signal control, such as leakage current.

[0005] Unlike such electrical memory, optical memory uses light to read and write signals, resulting in significantly faster data processing speeds compared to memory controlled by conventional electrical signals. Additionally, due to its wide bandwidth, it can be utilized in high-performance computers and data centers handling big data.

[0006] In this way, the storage capacity of optical memory that reads and writes using light interference and scattering phenomena is determined by the wavelength of the incident light, the numerical aperture of the lens used for focus, and the physical size of the grooves and lands.

[0007] However, if the spacing between grooves becomes too narrow, the diffraction limit and interference phenomena of the incident light occur, making it difficult to achieve integration densities higher than current blu-ray disks.

[0008] Therefore, it is necessary to realize high-density optical memory by adopting new ferroelectric materials rather than using existing optical memory structures.

[0009] Conventional perovskite-based ferroelectric materials not only lose their ferroelectricity at thicknesses of a few nanometers (nm) or less, but also face difficulties in application to the current silicon-based semiconductor industry due to low silicon substrate compatibility.

[0010] In addition, there is a limit to integration density because the domain size determining the 0 and 1 states in memory is large. In contrast, hafnium oxide (or hafnium-zirconium oxide) has been theoretically reported to not only ensure ferroelectricity at 1 nm but also enable individual atomic inversion.

[0011] However, the read-write method of light-based devices faces difficulties in achieving complete electric polarization control and inversion due to the mismatch between the polarization direction of the incident light and the out-of-plane electric polarization direction of HZO. In addition, a large coercive field of approximately 1–2 MV / cm² is required to invert the electric polarization of HZO.

[0012] Therefore, there is a need to develop a new optical memory structure that overcomes the problems of selecting new ferroelectric materials and optically controlling out-of-plane electric polarization, rather than the operating principles of conventional optical memory devices.

[0013] The present invention aims to solve the problems of conventional optical memory technology by providing a large-area, high-density non-volatile optical memory based on a ferroelectric material and a method for manufacturing it, which enables optical electric polarization control by using a metal nano-slit structure capable of overcoming the diffraction limit of light to focus light into the nano-slit.

[0014] The present invention aims to provide a ferroelectric-based large-area high-density non-volatile optical memory and a method for manufacturing it, which enables the realization of a ferroelectric-based optical memory with a novel read-write method and ultra-high-speed driving speed by using sub-1 picosecond terahertz light with a vertically aligned HZO structure to overcome the diffraction limit of light without leakage current.

[0015] The present invention aims to provide a large-area, highly integrated non-volatile optical memory based on a ferroelectric material and a manufacturing method that enables not only controlling the thickness of HZO to the angstrom level through atomic layer deposition but also enabling a wafer-level large-area process.

[0016] The present invention aims to provide a large-area, highly integrated non-volatile optical memory based on ferroelectrics and a method for manufacturing it, which allows for the amplification of the terahertz electric field in vertically aligned ferroelectric HZO gaps so that even if the strength of the incident electric field is weak, it can be amplified into a strong electric field for controlling the electric polarization of HZO through the fabricated structure.

[0017] The present invention aims to provide a large-area, highly integrated non-volatile optical memory based on a ferroelectric material and a method for manufacturing it, which has a structure suitable for controlling the optical electric polarization of HZO having an out-of-plane electric polarization direction, such that the polarization direction of a terahertz beam can be incident parallel to the electric polarization direction of HZO deposited on the sidewall.

[0018] Other objectives of the present invention are not limited to those mentioned above, and other unmentioned objectives will be clearly understood by those skilled in the art from the description below.

[0019] A large-area, high-density non-volatile optical memory based on a ferroelectric material according to the present invention for achieving the above-mentioned purpose comprises: a substrate; first line patterns that are repeatedly formed on the substrate with a length in a first direction and spaced apart at a certain interval in a second direction perpendicular to the first direction; a ferroelectric layer formed on the front surface including the first line patterns; and second line patterns that cover the ferroelectric layer in the spaced-apart region of the first line patterns and fill between the first line patterns; wherein a metal nano gap is formed by the side of any one of the first line patterns and the side of the second line pattern corresponding thereto.

[0020] Here, it is characterized by controlling optical electric polarization by focusing light onto a ferroelectric layer filled with metal nano gaps.

[0021] And the ferroelectric layer is characterized by having a shape that is vertically aligned by a first line pattern side and a corresponding second line pattern side.

[0022] And the ferroelectric layer is characterized by being vertically aligned by a first line pattern and a second line pattern to control the mismatch between the polarization direction of light and the electric polarization direction of the ferroelectric layer.

[0023] And the first line pattern is characterized by using titanium nitride (TiN), and the second line pattern is characterized by using gold or silver.

[0024] And the ferroelectric layer is characterized by being a ferroelectric material having out-of-plane electric polarization.

[0025] And the ferroelectric layer is characterized as being hafnium zirconium oxide (HZO) or hafnium dioxide (HfO2).

[0026] And the large-area, high-density non-volatile optical memory based on ferroelectrics is characterized by the unit cell being in the form of a nano-resonator having a resonant frequency in the terahertz region and having an amplification effect of the terahertz electric field in the vertically aligned ferroelectric gap.

[0027] And by having a ferroelectric layer that is vertically aligned by a first line pattern side and a corresponding second line pattern side, it is characterized by performing a read-write operation with a driving speed that overcomes the diffraction limit of light without leakage current using terahertz light at a sub-1 picosecond speed.

[0028] And the ferroelectric layer is characterized by having an S-curve polarization characteristic that exhibits negative capacitance in the ferroelectric single layer when observed through ultrafast polarization switching with maximum femtosecond time resolution.

[0029] A method for manufacturing a large-area, high-density non-volatile optical memory based on a ferroelectric material according to the present invention for achieving other purposes comprises: a step of forming first line patterns that have a length in a first direction and are repeatedly formed at regular intervals in a second direction perpendicular to the first direction on a substrate; a step of forming a ferroelectric layer on the front surface where the first line patterns are formed; and a step of forming second line patterns that cover the ferroelectric layer in the spaced-apart region of the first line patterns and fill between the first line patterns; wherein a metal nano gap is formed by any one of the first line pattern sides and the corresponding second line pattern sides.

[0030] The method is characterized by further including the step of forming a ferroelectric layer, depositing a metal layer identical to the material layer for forming a first line pattern on the front surface, performing heat treatment to provide a surface binding effect on the top and bottom of the ferroelectric layer, and removing the metal layer.

[0031] And the ferroelectric layer is characterized by having a shape that is vertically aligned by a first line pattern side and a corresponding second line pattern side.

[0032] And the first line pattern is characterized by using titanium nitride (TiN), and the second line pattern is characterized by using gold or silver.

[0033] And the ferroelectric layer is characterized as being hafnium zirconium oxide (HZO) or hafnium dioxide (HfO2).

[0034] The step of forming the second line patterns is characterized by forming a metal layer for forming the second line pattern on the front surface so that the space between the first line patterns is filled by an electron beam deposition process, leaving the metal layer for forming the second line pattern filled between the first line patterns by an ion etching process and a tape-based peel-off process, and selectively removing the metal layer for forming the second line pattern located on the upper surface of the first line patterns to form the second line pattern.

[0035] The ferroelectric-based large-area high-density non-volatile optical memory and manufacturing method according to the present invention, as described above, have the following effects.

[0036] First, a metal nano-slit structure capable of exceeding the diffraction limit of light is used to focus light into the nano-slit, thereby enabling control of optical electric polarization.

[0037] Second, by using terahertz light at sub-1 picosecond speeds with vertically aligned HZO structures, it is possible to realize a ferroelectric-based optical memory with ultra-high driving speed and a new read-write method that overcomes the diffraction limit of light without leakage current.

[0038] Third, through atomic layer deposition, not only can the thickness of HZO be controlled to the angstrom level, but large-area processing at the wafer level is also possible.

[0039] Fourth, the terahertz electric field is amplified in the vertically aligned ferroelectric HZO gap so that even if the strength of the incident electric field is weak, it can be amplified into a strong electric field for controlling the electric polarization of HZO through the fabricated structure.

[0040] Fifth, the polarization direction of the terahertz beam can be incident parallel to the electric polarization direction of the HZO deposited on the sidewall, so that the structure is suitable for controlling the optical electric polarization of HZO having an out-of-plane electric polarization direction.

[0041] FIGS. 1A and 1B are structural diagrams of a large-area, highly integrated non-volatile optical memory based on a ferroelectric material according to the present invention.

[0042] FIGS. 2A and 2B are configuration diagrams illustrating the configuration for controlling electric polarization with an electric field induced by terahertz light having a sub-1 picosecond speed level and the verification of polarization dynamics.

[0043] Figures 3a to 3c show schematic diagrams of nano-resonant structures in the terahertz region, funnel effect characteristics, and graphs of electric field focusing and amplification characteristics according to changes in nano-gap size.

[0044] FIG. 4a is a schematic side view showing the ferroelectric alignment state according to the polarization direction of a terahertz pulse incident on a nano-gap.

[0045] Fig. 4b shows a dark field optical microscope image of a loop nanogaps filled with HZO and a cross-sectional transmission electron microscope (TEM) image of a 7 nm wide HZO layer in the vertical direction between the Ag and TiN films.

[0046] Figure 4c shows the simulated horizontal electric field distribution around the 7 nm nano-gap between the Ag and TiN films.

[0047] FIG. 4d shows the magnitude of the electric field across the nano-gap amplified by a terahertz pump (E gap ) characteristic graph

[0048] Figure 5 shows the free energy diagrams for the electric polarization of a dielectric (left) and a ferroelectric (right), and a schematic diagram of an MFM nano-gap denoted by TR-TPTP.

[0049] Figure 6 shows the ultrafast switching dynamics characteristics of the electric polarization of HZO and the graph of ferroelectric electric polarization with respect to an electric field.

[0050] FIGS. 7a to 7h are cross-sectional views of the manufacturing process of a large-area, highly integrated non-volatile optical memory based on a ferroelectric material according to the present invention.

[0051] Hereinafter, preferred embodiments of the ferroelectric-based large-area high-density non-volatile optical memory and manufacturing method according to the present invention will be described in detail as follows.

[0052] The features and advantages of the ferroelectric-based large-area high-density non-volatile optical memory and manufacturing method according to the present invention will become apparent from the detailed description of each embodiment below.

[0053] FIGS. 1a and 1b are structural diagrams of a large-area, high-density non-volatile optical memory based on a ferroelectric material according to the present invention.

[0054] The terms used in this disclosure have been selected to be as widely used and general as possible, taking into account their functions within this disclosure; however, these terms may vary depending on the intent of those skilled in the art, case law, the emergence of new technologies, etc. Additionally, in specific cases, terms have been selected at the applicant's discretion, and in such cases, their meanings will be described in detail in the relevant description of the invention. Therefore, terms used in this disclosure should be defined not merely by their names, but based on their meanings and the overall content of this disclosure.

[0055] When a part of a specification is described as "including" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0056] The large-area, high-density non-volatile optical memory based on a ferroelectric material and the manufacturing method according to the present invention enable optical electric polarization control by using a metal nano-gap structure capable of overcoming the diffraction limit of light to focus light into the nano-gap.

[0057] To this end, the present invention may include a configuration that enables the realization of a ferroelectric-based optical memory with a novel read-write method and ultra-high driving speed that overcomes the diffraction limit of light without leakage current by using sub-1 picosecond terahertz light by a vertically aligned HZO structure.

[0058] The present invention may include a configuration that enables not only controlling the thickness of HZO to the angstrom level through atomic layer deposition but also enabling a wafer-level large-area process.

[0059] The present invention may include a configuration that allows the terahertz electric field to be amplified in vertically aligned ferroelectric HZO gaps so that even if the strength of the incident electric field is weak, it can be amplified into a strong electric field for controlling the electric polarization of HZO through the fabricated structure.

[0060] The present invention may include a configuration that allows the polarization direction of a terahertz beam to be incident parallel to the electric polarization direction of HZO deposited on the sidewall, thereby having a structure suitable for controlling the optical electric polarization of HZO having an electric polarization direction out of plane.

[0061] As shown in FIG. 1a and FIG. 1b, the ferroelectric-based large-area high-density non-volatile optical memory according to the present invention comprises a first line pattern (20) that has a length in a first direction and is repeatedly formed at regular intervals in a second direction perpendicular to the first direction on a substrate (10), a ferroelectric layer (30) formed on the front surface including the first line pattern (20), and a second line pattern (40) that covers the ferroelectric layer (30) in the spaced-out area of ​​the first line patterns (20) and fills between the first line patterns (20).

[0062] Here, a metal nano gap is formed by one side of the first line pattern (20) and the side of the corresponding second line pattern (40).

[0063] In one embodiment of the present invention, the width of the metal nano-slit can be set to a size between 1 nm and 10 nm such that light is focused into the metal nano-slit beyond the diffraction limit of light, but is not limited thereto.

[0064] And the ferroelectric layer (30) has a shape that is vertically aligned by the first line pattern (20) side and the corresponding second line pattern (40) side.

[0065] And the ferroelectric layer (30) is vertically aligned by the first line pattern (20) and the second line pattern (40) to control the mismatch between the polarization direction of light and the electric polarization direction of the ferroelectric layer (30).

[0066] And light is focused onto a vertically aligned ferroelectric layer (30) filled with metal nano gaps to enable optical electric polarization control.

[0067] Here, the first line pattern (20) can be formed using titanium nitride (TiN), and the second line pattern (40) can be formed using gold or silver, but is not limited thereto.

[0068] And the ferroelectric layer (30) uses a ferroelectric material having an out-of-plane electric polarization to control the electric polarization of the ferroelectric gap material using a metal nano gap structure.

[0069] Materials with planar electric polarization cannot be used as ferroelectric materials to fill metal nanogaps due to the problem of directional mismatch between the polarization of incident light and the electric polarization of the material.

[0070] And the ferroelectric layer (30) may be hafnium zirconium oxide (HZO) or hafnium dioxide (HfO2), but is not limited thereto.

[0071] The reason for using such a material as a ferroelectric layer (30) in the present invention is as follows.

[0072] Zirconium-doped hafnium zirconium oxide (Hf 0.5 Zr 0.5 O2, HZO) has strong ferroelectricity (large electric polarization value) and high retention and durability, and is capable of CMOS compatible processes that allow for atomic layer deposition (ALD).

[0073] When hafnium oxide undergoes polarization alignment and switching by an external electric field, oxygen atoms (O) move, and at this time, local switching of oxygen atoms is possible through the flat phonon band of hafnium oxide (HfO2).

[0074] Due to these characteristics, unlike conventional perovskite materials such as PbTiO3 or BaTiO3 in which a domain consists of clusters of atoms, individual atomic switching within a unit cell is made possible.

[0075] Therefore, the domain size can be at the level of an atomic length (0.51 nm), allowing 1 bit of information to be stored in 4 oxygen atoms, and when applied to memory semiconductors, the integration density can be improved.

[0076] The large-area, high-density non-volatile optical memory based on the ferroelectric material according to the present invention has a unit cell in the form of a nano-resonator having a resonant frequency in the terahertz region, and has an amplification effect of the terahertz electric field in the vertically aligned ferroelectric gap.

[0077] And by having a shape in which the ferroelectric layer (30) is vertically aligned with the side of the first line pattern (20) and the side of the corresponding second line pattern (40), it performs a read-write operation with a driving speed that overcomes the diffraction limit of light without leakage current using terahertz light at a sub 1 picosecond speed.

[0078] As described above, the present invention uses a metal nano-gap structure capable of exceeding the diffraction limit of light, rather than a conventional optical memory structure and a read-write method utilizing light scattering and interference phenomena.

[0079] A new device and fabrication method are provided that overcome the mismatch between the polarization direction of light and the electric polarization direction of HZO by vertically aligning HZO with a thickness of several nanometers between two metals, and simultaneously enable optical electric polarization control by focusing light into a nano-slit.

[0080] This suggests the possibility of developing technology capable of observing ultra-fast electric polarization control of ferroelectrics and dynamic changes in non-equilibrium states in novel ferroelectric-based optical memory structures.

[0081] The characteristics of the large-area, high-density non-volatile optical memory based on a ferroelectric structure according to the present invention having such a structure are described in detail as follows.

[0082] FIGS. 2a and 2b are configuration diagrams showing the configuration for controlling electric polarization with an electric field induced by terahertz light having a sub-1 picosecond speed level and the verification of polarization dynamics.

[0083] The ferroelectric-based large-area high-density non-volatile optical memory structure according to the present invention implements the electrical polarization alignment and switching of HZO using light rather than an electrical method.

[0084] In particular, if electric polarization is controlled by an electric field induced by terahertz light having a sub-1 picosecond speed, a fast AC voltage can be applied to the material.

[0085] At this time, since HZO has an out-of-plane electric polarization, using vertically aligned HZO combined with the nano-gap structure according to the present invention enables not only overcoming the diffraction limit of light but also rapid polarization switching in which light oxygen atoms can switch individually.

[0086] According to one embodiment of the present invention having such characteristics, an operation is implemented by applying terahertz pump-terahertz probe spectroscopy (THz pump-THz probe spectroscopy) in which a terahertz pump pulse electric field strong enough to rotate the electric polarization of 7 nm thick HZO is applied using a nano-gap structure (amplified into an electric field strong enough to rotate the electric polarization within the nano-gap), and a terahertz probe pulse beam of much smaller intensity is used to time-resolvedly detect the electric polarization alignment effect by the pump (intensity such that the electric polarization cannot be rotated).

[0087] Figures 3a to 3c are schematic diagrams of nano-resonant structures in the terahertz region, funnel effect characteristics, and graphs of electric field focusing and amplification characteristics according to changes in nano-gap size.

[0088] Unlike light in the visible / near-infrared wavelength range, terahertz waves have very long wavelengths on the order of a few millimeters. However, when a nano-gap structure of a Metal-Insulator-Metal structure, in which a dielectric material is filled between two metals, is utilized, the terahertz magnetic field creates a surface current according to Maxwell's Ampere's law, causing surface current to flow on the surfaces of the two metals and charge to accumulate at both ends of the two metals like a capacitor.

[0089] At this time, when the two ends of the two metals come close to the nanometer level, a larger electric field is induced at both ends (funneling effect), which allows for electric field focusing even through a 1 nm gap beyond the diffraction limit of light.

[0090] This means that it is possible to fabricate optical memory with an integration density of several nanometers.

[0091] Therefore, unlike conventional optical memory read / write technology which has a physical scaling limitation and a light diffraction limit because grooves are directly engraved in the substrate, the present invention manufactures a non-volatile ferroelectric-based optical memory with a new read / write method by utilizing terahertz waves and nano-gap structures to implement a structure in which a ferroelectric material is placed inside the gap.

[0092] The present invention has the advantage of being able to control the thickness of HZO to the angstrom level through atomic layer deposition, as well as enabling large-area processing at the wafer level.

[0093] Accordingly, there is an amplification effect of the terahertz electric field in the vertically aligned ferroelectric HZO gap. Therefore, even if the strength of the incident electric field is weak, it has the advantage of being amplified into a strong electric field for controlling the electric polarization of HZO through the fabricated structure, and the polarization direction of the terahertz beam can be incident parallel to the electric polarization direction of HZO deposited on the sidewall, making it a structure suitable for controlling the optical electric polarization of HZO having an out-of-plane electric polarization direction.

[0094] Figure 4a is a side schematic diagram showing the ferroelectric alignment state according to the polarization direction of a terahertz pulse incident on a nano-gap.

[0095] Figure 4a shows THz loop nanogaps that can be filled with various oxide materials such as HfO2 or HZO prepared by atomic layer lithography.

[0096] When linearly polarized THz light is incident on an opaque metal film, a surface current is induced, and charges accumulate near the edges of the nano-gap.

[0097] When surface current flows around the nano-gap and charges accumulate near the metal edge, the THz electric field can be amplified by more than a few thousand times depending on the oxide material in nano-gap smaller than 10 nm, and the enhanced THz electric field near the nano-gap can reach an amplitude of up to tens of MV / cm.

[0098] Figure 4b is a dark field optical microscope image of a loop nano-gap filled with HZO and a cross-sectional transmission electron microscope (TEM) image of a 7 nm wide HZO layer in the vertical direction between Ag and TiN films.

[0099] In one embodiment of the present invention, to induce ferroelectricity in an HZO thin film, titanium nitride (TiN) is used as an initial metal layer to promote the formation of an orthorhombic crystal phase.

[0100] The metallic properties of TiN were verified through THz-time domain spectroscopy (THz-TDS), and it exhibits Drude-like behavior at THz frequencies.

[0101] As shown in Fig. 4b, optical and scanning transmission electron microscope images indicate that nano gaps of 7 nanometers can be easily formed along the loop and a vertical configuration can be formed between the TiN and silver film.

[0102] Figure 4c is a simulated horizontal electric field distribution around a 7 nm nano gap between Ag and TiN films.

[0103] To explain the THz field enhancement across the entire HZO nano-slit, numerical simulations show that the THz field near the nano-slit is enhanced by 180 times, appearing as a funnel-shaped distribution of the horizontal electric field due to the resonance of the loop nano-slit.

[0104] This result indicates that THz electromagnetic waves exclusively pass through nano-gaps due to the opaque metal film, enabling background-free transmittance measurements.

[0105] We measured the transmittance through a nano-gap array with various crystal phases using a THz-TDS system and experimentally verified the electric field (Egap) across the nano-gap by applying vector diffraction theory to these measurements.

[0106] FIG. 4d shows the magnitude of the electric field across the nano-gap amplified by a terahertz pump (E gap It is a characteristic graph.

[0107] Fig. 4d shows E for the amorphous and monoclinic phases of HfO2 nano-gaps and the orthorhombic phase of HZO nano-gaps. gap This represents the measured time tracking of.

[0108] Peak intensity (E) of the incident THz field transmitted through the substrate inc Even though ) is approximately 70 kV / cm, the maximum E for the orthorhombic phase of HZO nanogaps gap It was improved to a maximum of about 8 MV / cm.

[0109] In the present invention, the dielectric constant of such oxide materials inside nano-gaps can be estimated at THz frequencies by comparing experiments and simulations based on the resonant THz field amplitude spectrum.

[0110] Amorphous and monoclinic HfO2 both exhibit similar dielectric constants of about 6.3, whereas orthorhombic HZO exhibits a significantly higher constant of 16 operating at THz frequencies.

[0111] Figure 5 is a free energy diagram for the electric polarization of a dielectric (left) and a ferroelectric (right), and a schematic diagram of an MFM nano-gap denoted as TR-TPTP.

[0112] Figure 6 shows the ultrafast switching dynamics characteristics of the electric polarization of HZO and the graph of the ferroelectric electric polarization with respect to the electric field.

[0113] The terahertz probe pulse was fixed at the point in time (Egap, probe) that generates the maximum electric field in the time domain, and the change in transmission of HZO was monitored in real time by irradiating the terahertz pump pulse according to the time delay (Delay-time).

[0114] When a time-dependent terahertz pump pulse is incident, a strong electric field is induced in the ferroelectric material by the terahertz pump.

[0115] Next, the electric polarization state of HZO is changed by the terahertz pump pulse, and at this time, oxygen atoms move and generate a displacement current.

[0116] The transmittance of the probe pulse detecting this changes, and this is equivalent to the relative change in displacement current.

[0117] By integrating the rate of change of relative displacement current measured through a terahertz probe, the change in the charge of HZO can be obtained, and by dividing this by the capacitor area (A), it is expressed as the rate of change of electric polarization of HZO (delta P).

[0118] If we plot the change in electric polarization value (delta P-Egap, pump) with respect to the value of the electric field across the gap, we can observe an S-shaped curve showing negative capacitance that reflects the intrinsic properties of the ferroelectric material according to the Landau-Ginsberg-Devonshire theoretical model, unlike the ferroelectric hysteresis curve obtained from general electrical observations.

[0119] The characteristics of the large-area, high-density non-volatile optical memory based on the ferroelectric material according to the present invention are observed using a terahertz spectrometer as follows.

[0120] By using a terahertz spectrometer for ultrafast polarization switching with maximum femtosecond time resolution, the negative capacitance of a nanometer-thick ferroelectric monolayer can be observed in real time, allowing for the direct verification of non-equilibrium intrinsic properties.

[0121] Ferroelectrics exhibiting negative capacitance characteristics can lower the strength of the electric field (anti-electric field) at which polarization switches, so utilizing them as devices can significantly improve power efficiency.

[0122] Therefore, low voltage and low power operation become possible, and through a new read-write method using ultra-high-speed polarization switching technology utilizing light, it can be utilized as a next-generation non-volatile optical memory device capable of simultaneous high integration and low power operation without leakage current even at a thickness of several nanometers.

[0123] The manufacturing process of a large-area, high-density non-volatile optical memory based on a ferroelectric material according to the present invention is described in detail as follows.

[0124] FIGS. 7a to 7h are cross-sectional views of the manufacturing process of a large-area, high-density non-volatile optical memory based on a ferroelectric material according to the present invention.

[0125] The present invention provides a method for fabricating a device with a metal-ferroelectric-metal structure of titanium nitride (TiN)-HZO-gold or silver (Au or Ag) based on an atomic layer lithography method.

[0126] First, as shown in FIG. 7a, a material layer (72) for forming a first line pattern is deposited on a silicon substrate (71) by sputtering.

[0127] The material layer (72) for forming the first line pattern uses TiN, rather than a precious metal such as gold, to effectively express the ferroelectricity of HZO through the surface binding effect.

[0128] Here, the thickness of the material layer (72) for forming the first line pattern is several hundred nanometers.

[0129] Next, as shown in FIG. 7b, a photoresist is applied to the front surface and selectively patterned to form a photoresist pattern layer (73) for the first line pattern patterning.

[0130] And as shown in FIG. 7c, the material layer (72) for forming the first line pattern is selectively removed by a reactive ion etching process using a photoresist pattern layer (73) to form the first line pattern (72a).

[0131] Next, as shown in FIG. 7d, a ferroelectric layer, i.e., an HZO layer (74), with a thickness of 7 nm, is deposited on the front surface where the first line pattern (72a) is formed by atomic layer deposition (ALD) with hafnium and zirconium in equal proportions.

[0132] And as shown in FIG. 7e, an upper metal layer (75) is deposited once again on the HZO layer (74) deposited on the front surface along the shape of the first line pattern (72a) by sputtering, and heat treatment is performed to provide a surface binding effect on the top and bottom of the HZO layer (74).

[0133] HZO grown via atomic vapor deposition does not exhibit ferroelectricity due to a lack of distinct crystallinity, which is because a specific crystalline phase exists where ferroelectricity is expressed.

[0134] Therefore, the present invention aims to effectively induce a specific crystal phase (orthorhombic phase) in which ferroelectricity is expressed by providing a surface binding effect, while simultaneously suppressing other crystal phases (monoclinic phase, etc.) to increase ferroelectricity.

[0135] In other words, the surface binding effect is intended to create a specific crystal phase (orthorhombic phase) rather than the most stable monoclinic phase that HZO can have in terms of energy.

[0136] Next, as shown in Fig. 7f, the upper metal layer (75) is removed by a wet etching process.

[0137] And as shown in Fig. 7g, a metal layer (76) for forming a second line pattern is formed on the front surface by an electron beam deposition process so that the spaces between the first line patterns (72a) are filled.

[0138] Next, as shown in FIG. 7h, a metal layer (76) for forming a second line pattern filled between the first line patterns (72a) is left by an ion etching process and a tape-based peel-off process, and a metal layer (76) for forming a second line pattern located on the upper surface of the first line patterns (72a) is selectively removed to form a second line pattern (76a).

[0139] A ferroelectric-based large-area high-density non-volatile optical memory is fabricated by such a process, comprising: first line patterns (72a) that are repeatedly formed on a substrate with a length in a first direction and spaced apart at regular intervals in a second direction perpendicular to the first direction; a ferroelectric layer (74) formed on the front surface including the first line patterns (72a); and second line patterns (76a) that cover the ferroelectric layer (74) in the spaced-out area of ​​the first line patterns (72a) and fill between the first line patterns (72a).

[0140] In the ferroelectric-based large-area high-density non-volatile optical memory according to the present invention, a metal nano gap is formed by one of the first line pattern sides and the corresponding second line pattern sides.

[0141] The large-area, high-density non-volatile optical memory based on a ferroelectric material and the manufacturing method according to the present invention described above enable optical electric polarization control by focusing light into the nano-slit using a metal nano-slit structure capable of overcoming the diffraction limit of light. By utilizing terahertz light at a sub-1 picosecond speed through a vertically aligned HZO structure, it enables the realization of a ferroelectric-based optical memory with an ultra-high operating speed and a new read-write method that overcomes the diffraction limit of light without leakage current.

[0142] As explained above, it will be understood that the present invention is implemented in a modified form without departing from the essential characteristics of the invention.

[0143] Therefore, the described embodiments should be considered in an illustrative rather than a limiting sense, and the scope of the invention is defined by the claims rather than the foregoing description, and all variations within the equivalent scope should be interpreted as being included in the invention.

[0144] The present invention relates to an optical memory, and specifically to a large-area, high-density non-volatile optical memory based on a ferroelectric material and a method for manufacturing it, which enables optical electric polarization control by using a metal nano-slit structure capable of overcoming the diffraction limit of light to focus light into the nano-slit.

Claims

1. Substrate; First line patterns having a length in a first direction and repeatedly formed at regular intervals in a second direction perpendicular to the first direction on a substrate; A ferroelectric layer formed on the front surface including a first line pattern; It includes second line patterns that cover the ferroelectric layer in the spaced region of the first line patterns and fill between the first line patterns; A ferroelectric-based large-area high-density non-volatile optical memory characterized by the formation of a metal nano gap by any one of the above-mentioned first line pattern sides and a corresponding second line pattern side.

2. A large-area, high-density, non-volatile optical memory based on a ferroelectric material, characterized by controlling optical electric polarization by focusing light onto a ferroelectric layer filled with metal nano-gaps in claim 1.

3. In claim 1, the ferroelectric layer is, Ferroelectric-based large-area high-density non-volatile optical memory characterized by having a shape vertically aligned by a first line pattern side and a corresponding second line pattern side.

4. In Clause 3, the ferroelectric layer is, Ferroelectric-based large-area high-density non-volatile optical memory characterized by being vertically aligned by a first line pattern and a second line pattern to control the mismatch between the polarization direction of light and the electric polarization direction of the ferroelectric layer.

5. A ferroelectric-based large-area high-density non-volatile optical memory according to claim 1, characterized in that the first line pattern is formed using titanium nitride (TiN) and the second line pattern is formed using gold or silver.

6. In claim 1, the ferroelectric layer is, Ferroelectric-based large-area high-density non-volatile optical memory characterized by being a ferroelectric material having out-of-plane electric polarization.

7. In Clause 6, the ferroelectric layer, Ferroelectric-based large-area high-density non-volatile optical memory characterized by being hafnium zirconium oxide (HZO) or hafnium oxide (Hfnium dioxide, HfO2).

8. In claim 1, the ferroelectric-based large-area high-density non-volatile optical memory is, Ferroelectric-based large-area high-density non-volatile optical memory characterized by unit cells forming a nano-resonator shape having a resonant frequency in the terahertz region and having an amplification effect of the terahertz electric field in vertically aligned ferroelectric gaps.

9. In claim 1, by having a shape in which the ferroelectric layer is vertically aligned by a first line pattern side and a corresponding second line pattern side, A ferroelectric-based large-area high-density non-volatile optical memory characterized by performing read-write operations with a driving speed that overcomes the diffraction limit of light without leakage current using sub-1 picosecond terahertz light.

10. In claim 1, the ferroelectric layer is, Ferroelectric-based large-area high-density non-volatile optical memory characterized by having S-curve polarization characteristics exhibiting negative capacitance in a ferroelectric single layer during observation via ultrafast polarization switching with maximum femtosecond time resolution.

11. A step of forming first line patterns on a substrate having a length in a first direction and being repeatedly formed at regular intervals in a second direction perpendicular to the first direction; A step of forming a ferroelectric layer on the front surface where the first line pattern is formed; The method includes the step of forming second line patterns that cover the ferroelectric layer in the spaced region of the first line patterns and fill between the first line patterns; A method for manufacturing a large-area, high-density, non-volatile optical memory based on a ferroelectric material, characterized in that a metal nano gap is formed by any one of the above first line pattern sides and a corresponding second line pattern side.

12. In claim 11, the step of forming a ferroelectric layer is carried out, and A metal layer identical to the material layer for forming the first line pattern is deposited on the front surface, and heat treatment is performed to provide a surface confinement effect from the top and bottom of the ferroelectric layer, and A method for manufacturing a large-area, high-density, non-volatile optical memory based on a ferroelectric material, characterized by further including a step of removing a metal layer.

13. In claim 11, the ferroelectric layer is, A method for manufacturing a large-area, high-density, non-volatile optical memory based on a ferroelectric material, characterized by having a shape that is vertically aligned by a first line pattern side and a corresponding second line pattern side.

14. A method for manufacturing a large-area, high-density, non-volatile optical memory based on a ferroelectric material, characterized in that, in claim 11, the first line pattern is formed using titanium nitride (TiN) and the second line pattern is formed using gold or silver.

15. In claim 11, the ferroelectric layer is, A method for manufacturing a large-area, high-density, non-volatile optical memory based on a ferroelectric material, characterized by being hafnium zirconium oxide (HZO) or hafnium oxide (Hfnium dioxide, HfO2).

16. In claim 11, the step of forming the second line patterns is, A metal layer for forming a second line pattern is formed on the front surface by an electron beam deposition process so that the spaces between the first line patterns are filled, and A method for manufacturing a large-area, high-density, non-volatile optical memory based on a ferroelectric material, characterized by forming a second line pattern by leaving a metal layer for forming a second line pattern filled between first line patterns using an ion etching process and a tape-based peel-off process, and selectively removing the metal layer for forming a second line pattern located on the upper surface of the first line patterns.

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