KR19990039567A - Ferroelectric recording medium and recording method thereof - Google Patents

Abstract

The present invention relates to a ferroelectric recording medium capable of storing information for a long time and a method of recording and reproducing the same. The ferroelectric recording medium according to the present invention has a structure in which lower electrodes / insertion layers / ferroelectric layers / upper electrodes / dielectric layers are sequentially stacked and a tip is disposed thereon to record or reproduce. Once the voltage is applied to the tip to keep the polarized domain stable, the dielectric film is charged when reading and the dielectric is discharged when storing the information, thus maintaining information storage time semi-permanently.

Description

Ferroelectric recording medium and recording method thereof

The present invention relates to a ferroelectric recording medium capable of storing information for a long time and a method of recording and reproducing the same.

1 is a vertical sectional view showing a schematic structure of a conventional ferroelectric recording medium. As shown, the conventional ferroelectric recording medium has a structure in which the ferroelectric layer 20 is laminated on the lower electrode 10. Therefore, the conventional recording and reproducing method is a voltage between the scanning tunneling microscope (STM), the scanning probe microscope (SPM), or the atomic force microscope (AFM) tip 30 and the lower electrode, as shown in Figs. 2A to 2C. After scanning by applying polarization to the ferroelectric layer 20, and forming and recording a domain (domain), the reading at the non-recorded site when applying a voltage that is opposite to the recording when the tip ( 30) The tip is detected by the coulomb force (electrostatic force) in the recorded area without moving. Depending on the applied voltage, a method of pulling the tip may be used. That is, as illustrated in FIG. 2A, when polarization is generated in the ferroelectric layer 20 by applying a voltage (-Vw) between the tip 30 and the lower electrode, information is recorded. 2B shows a state in which information is recorded. Next, as shown in Fig. 2C, in a recording medium in which information is recorded (polarization is formed in the ferroelectric layer), when a read voltage (+ Vr) is applied between the tip 30 and the lower electrode, the polarization of the ferroelectric is applied to the polarization of the ferroelectric. The tip is raised by the electrostatic force (repulsive force) between the dipole and the tip. By sensing this electrostatic force, information can be read.

In this way, information storage using the ferroelectric uses polarization of the ferroelectric. Ferroelectrics are suitable materials for recording media of more than 1 gigabyte because the polarization rate is in nanoseconds. In general, however, it is not easy to maintain information in using a ferroelectric as an information recording medium. That is, there is a problem that the recorded information does not last long. This is because when the ferroelectric is polarized, a domain is formed, and the domain is an electric dipole, and needs a bound charge that can be balanced with the polarity of the dipole. Conventional ferroelectric recording media has no upper electrode and is bound This is because the information cannot be retained for a long time by so-called depolarization, in which domains disappear by themselves due to insufficient charge.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object thereof is to provide a ferroelectric recording medium and a recording / reproducing method thereof capable of maintaining information for a long time without depolarization phenomenon.

1 is a vertical sectional view showing a schematic structure of a conventional ferroelectric recording medium;

2A to 2C are explanatory diagrams for explaining the recording / reproducing method of the ferroelectric recording medium of FIG. 1;

3A to 3C are vertical cross-sectional views each showing a structure of a ferroelectric recording medium according to the present invention;

4A to 4C are explanatory diagrams for explaining the recording / reproducing method of the ferroelectric recording medium of FIG. 3A or 3B;

5A and 5B are explanatory diagrams for explaining the recording / reproducing method of the ferroelectric recording medium of FIG. 3C.

<Description of Symbols for Main Parts of Drawings>

1. Tip 2. Dielectric film or insulator film

3. Upper electrode 4. Ferroelectric

5. Lower electrode 6. Insertion layer

10. Electrode 20. Ferroelectric layer

30. Tips

In order to achieve the above object, the ferroelectric recording medium according to the present invention includes a lower electrode; A ferroelectric layer stacked on the lower electrode; An upper electrode stacked on the ferroelectric; And a dielectric layer stacked on the upper electrode.

In the present invention, an insertion layer is further provided between the lower electrode and the ferroelectric layer to reduce fatigue in the manufacturing process, and an insertion layer for reducing fatigue in the manufacturing process is further provided between the upper electrode and the ferroelectric layer. The upper electrode may be formed of a semiconductor material, and an insulating layer may be provided instead of the dielectric layer.

In addition, the recording and reproducing method of the ferroelectric recording medium according to the present invention in order to achieve the above object, in the recording and reproducing method of the ferroelectric recording medium laminated in the order of the lower electrode / ferroelectric / upper electrode / dielectric layer (A) Using the potential difference between the tip and the lower electrode to form a bond charge in the dielectric layer to record " 1 "; (B) grounding the upper electrode to induce a bond charge of the dielectric layer to be discharged to the upper electrode to store a record; And (c) reading " 1 " by applying a potential difference of the same polarity less than the potential difference to the tip to induce a bond charge of the upper electrode to the dielectric layer to recharge the dielectric layer; And (d) inducing the confinement charge of the recharged dielectric layer to be discharged to the upper electrode by grounding the upper electrode again and storing the record as it is.

In the present invention, the step (a) may be a step of recording "0".

In addition, the recording and reproducing method of the ferroelectric recording medium according to the present invention in order to achieve the above object, in the recording and reproducing method of the ferroelectric recording medium stacked in the order of the lower electrode / ferroelectric / upper electrode, (A) the tip Applying a potential difference between the lower electrode and the lower electrode to record "1"; And (b) reading a "1" by applying a potential difference of opposite polarity smaller than the potential difference to the tip.

In the present invention, the step (a) may be a step of recording "0".

A ferroelectric recording medium and a recording / reproducing method thereof according to the present invention will be described in detail with reference to the drawings.

3A to 3C are vertical cross-sectional views each showing the structure of a ferroelectric recording medium according to the present invention. As shown, the ferroelectric recording medium according to the present invention has a basic structure in which the ferroelectric layer 4, the upper electrode 3, and the dielectric material 2 are sequentially stacked on the lower electrode 5. In order to prevent fatigue in the manufacturing process, as shown in FIGS. 3A and 3B, an insertion layer 6 is further formed between the lower electrode 5 and the ferroelectric layer 4. Furthermore, as shown in FIG. 3A, an insertion layer 6 ′ may also be formed between the ferroelectric layer 4 and the upper electrode 3. In addition, as shown in FIG. 3C, the dielectric layer 2 may be used as a recording medium without being laminated on the upper electrode 3. The principle of operation will be described later with reference to FIGS. 5A and 5B.

The method of recording and reproducing a ferroelectric recording medium having such a structure uses the upper electrode 3, and when the insulator film 2 or the dielectric film (including the ferroelectric) is formed and recorded thereon, the conventional method is used. In order to store, the electric charges temporarily induced in the dielectric film 2 are bound to the upper electrode 3 so as to be bound to the upper electrode 3. When reading the recorded information, it is read in a conventional manner, but within the voltage range in which the unrecorded part is not polarized, the bound charge of the already recorded part is directed toward the dielectric film 2 to select a voltage range capable of detecting it. . This will be described in detail as follows.

First, as shown in FIG. 4A, a domain is formed while scanning by applying a voltage (-Vw) between the lower electrode 5 and the tip 1 in a conventional manner. In order to retain the recorded information, as shown in FIG. 4B, when the upper electrode 3 is grounded, the bond charges formed on the dielectric film 2 disappear, and instead, the bond charges are formed on the upper electrode 3. . When a bond charge is formed on the upper electrode 3 made of a metal or conductive ceramic, the domain remains semi-permanently because it forms a stable electrical balance. Then, when reading the recorded information, use the same polarity voltage as the applied voltage at the time of recording, but scan with a voltage (Vr <Vw) smaller than the voltage used at the time of recording. At the site, the charges of the upper electrode 3 disappear as the dielectric film 2 is charged again. At this time, since the electric charge is supplied through the tip while the dielectric film 2 is charged, an electrical signal is detected. Once read, the confinement charges are formed again on the dielectric film 2 as in the beginning of writing by the formed domain, so that the upper electrode 3 is grounded again for retaining information for the next reproduction.

In order to keep the domain homogeneous and directional, it is preferable that the ferroelectric is made of single crystal or epitaxy, and it is preferable that fatigue does not occur. In order to satisfy all of these, it is desirable to form a multilayer together with a conductive ceramic in addition to a single electrode to grow ferroelectric in epitaxy or single crystal form and to avoid fatigue under the influence of the conductive ceramic. . Thus, the interlayer 6 is fabricated between the electrode and the ferroelectric, and the interlayer material may use a conductive ceramic or a metal. Therefore, the electrode also uses a conductive ceramic, a semiconductor, or a metal. In addition, the multilayer may be three or more layers. Examples of the conductive ceramics include metal oxides such as RuO _x , IrO _x , and the like.

5A and 5B are explanatory diagrams for explaining the recording / reproducing method of the ferroelectric recording medium of FIG. 3C. As shown, this recording medium has a structure without a dielectric layer on the upper electrode 3. However, since air exists between the upper electrode 3 and the tip 1, this air is used as a dielectric. That is, as shown in FIG. 5A, when the tip 1 is applied with a voltage (-Vw) between the tip 1 and the lower electrode 5 at regular intervals from the upper electrode 3, the ferroelectric layer 4 is applied. Polarization occurs (domains are formed). In this way, a bond charge is formed in the upper electrode 3 from air. This is the "write" process. Next, as illustrated in FIG. 5B, a voltage (+ Vr) having a polarity opposite to that at the time of “write” is applied to sense and read an electrostatic force by the domain.

As described above, the ferroelectric recording medium according to the present invention has a structure in which the lower electrode / insertion layer / ferroelectric layer / upper electrode / dielectric layer are sequentially stacked and a tip is disposed thereon to record or reproduce. Once the voltage is applied to the tip to keep the polarized domain stable and the dielectric film is charged when reading and the dielectric is discharged when the information is stored, the information storage time can be semi-permanently maintained.

Claims (10)

Lower electrode; A ferroelectric layer stacked on the lower electrode; An upper electrode stacked on the ferroelectric; And A dielectric layer stacked on the upper electrode; A ferroelectric recording medium, comprising: The method of claim 1, And an insertion layer between the lower electrode and the ferroelectric layer to reduce fatigue in the manufacturing process. The method of claim 2, And an insertion layer between the upper electrode and the ferroelectric layer to reduce fatigue in the manufacturing process. The method according to claim 2 or 3, And the lower electrode, the upper electrode, and the insertion layer are each formed of at least one of a metal, a conductive ceramic, and a semiconductor. The method of claim 4, wherein And the upper electrode is formed of a semiconductor material. The method of claim 1, An insulating layer is provided in place of the dielectric layer. A recording / reproducing method of a ferroelectric recording medium stacked in the order of a lower electrode / ferroelectric / upper electrode / dielectric layer, (A) forming a bond charge in the dielectric layer using the potential difference between the tip and the lower electrode to record " 1 "; (B) grounding the upper electrode to induce a bond charge of the dielectric layer to be discharged to the upper electrode to store a record; And (C) reading " 1 " by applying a potential difference of the same polarity less than the potential difference to the tip to induce a bond charge of the upper electrode to the dielectric layer to recharge the dielectric layer; And (D) grounding the upper electrode again to induce the constrained charge of the recharged dielectric layer to be discharged to the upper electrode and storing the record as it is; And a recording and reproducing method of a ferroelectric recording medium. The method of claim 7, wherein And the step (a) is a step of recording " 0 ". A recording and reproducing method of a ferroelectric recording medium stacked in the order of a lower electrode / ferroelectric / upper electrode, (A) recording a "1" by applying a potential difference between the tip and the lower electrode; And (B) reading a "1" by applying a potential difference of opposite polarity smaller than the potential difference to the tip; And a recording and reproducing method of a ferroelectric recording medium. The method of claim 9, And the step (a) is a step of recording " 0 ".