KR-102962390-B1 - Fabrication Methods and Design of Large-Area, High density, Non-Volatile optical storage based on ferroelectric materials

KR102962390B1KR 102962390 B1KR102962390 B1KR 102962390B1KR-102962390-B1

Abstract

The present invention relates to a large-area, high-density non-volatile optical memory based on a ferroelectric material and a method for manufacturing such that optical electric polarization control is possible by focusing light into a nano-gap using a metal nano-gap structure capable of exceeding the diffraction limit of light. The invention 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. A metal nano-gap is formed by the side of any one of the first line patterns and the side of the corresponding second line pattern.

Inventors

박형렬
이형택
김계현
이준희
채승철
엄선혜
지강선
손창희
김대식
박노정
송명섭

Assignees

울산과학기술원
서울대학교산학협력단

Dates

Publication Date: 20260511
Application Date: 20241212

Claims (16)

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 metal nano gap is formed by a first line pattern side of any one of the above first line patterns and a corresponding second line pattern side, and A large-area, high-density, non-volatile optical memory based on a ferroelectric material, characterized by focusing light onto a ferroelectric layer filled with metal nano-gaps to control optical electric polarization, and the ferroelectric layer being a ferroelectric material having out-of-plane electric polarization.
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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.
In claim 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.
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.
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In claim 1, the ferroelectric layer is, Ferroelectric-based large-area high-density non-volatile optical memory characterized by being hafnium zirconium oxide (HZO) or hafnium oxide ( HfO2 ).
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.
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.
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.
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 metal nano gap is formed by a first line pattern side of any one of the above first line patterns and a corresponding second line pattern side, and A method for manufacturing a large-area, high-density, non-volatile optical memory based on a ferroelectric material, characterized by focusing light onto a ferroelectric layer filled with metal nano-gaps to control optical electric polarization, and wherein the ferroelectric layer is a ferroelectric material having electric polarization in an out-of-plane direction.
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.
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.
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.
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 ( HfO₂ ).
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.

Description

Fabrication Methods and Design of Large-Area, High-Density, Non-Volatile Optical Storage Based on Ferroelectric Materials 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. 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. 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. 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. 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. 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. 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. Therefore, it is necessary to realize high-density optical memory by adopting new ferroelectric materials rather than using existing optical memory structures. 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. 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. 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. 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. 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. 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. 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. 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. 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. Figure 4c shows the simulated horizontal electric field distribution around the 7 nm nano-gap between the Ag and TiN films. Figure 4d is a graph showing the magnitude of the electric field (E gap ) across the nano gap amplified by a terahertz pump. 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. Figure 6 shows the ultrafast switching dynamic