KR100561858B1 - Recording material comprising ferroelectric layer, nonvolatile memory device comprising the same, and methods of writing and reading data for the memory device - Google Patents

Abstract

Disclosed are a recording medium including a ferroelectric film, a nonvolatile memory device including the same, and a method of recording and reproducing data of the memory device. The present invention provides a recording medium including a lower electrode sequentially stacked, a ferroelectric film formed on the lower electrode and recording data, a barrier layer formed on the ferroelectric film, and a semiconductor layer formed on the barrier layer. to provide. In addition, the present invention provides a recording medium of a nonvolatile memory device including a probe used for recording and reproducing data. In addition, the present invention provides a data recording method for applying a recording voltage to the probe and the lower electrode in contact with the semiconductor layer, and a data reproducing method for determining a residual polarization state of the ferroelectric film by applying a read voltage to the probe and the semiconductor layer. to provide.

Description

Recording medium comprising a ferroelectric film, nonvolatile memory device comprising the same, and recording and reproducing data of such a memory device {recording material comprising ferroelectric layer, nonvolatile memory device comprising the same, and methods of writing and reading data for the memory device}

1 is a cross-sectional view showing the configuration of a recording medium according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a process of recording data on the recording medium shown in FIG. 1.

3 and 4 show changes in energy band of a semiconductor layer provided between a barrier layer and a probe when data is recorded on a recording medium of the present invention including a ferroelectric film having a small polarization amount.

5 and 6 illustrate changes in energy bands of the semiconductor layer provided between the barrier layer and the probe when the ferroelectric film of the recording medium shown in FIG. 1 is a material having a large polarization amount.

FIG. 7 is a graph showing current-voltage characteristics between the semiconductor layer and the probe along the polarization direction of the ferroelectric film when the ferroelectric film of the recording medium shown in FIG. 1 is a material having a large polarization amount.

8 is a cross-sectional view illustrating a recording medium equivalent to the recording medium on which the data of FIG. 2 is recorded and a process of reading data therefrom.

FIG. 9 is a graph showing current-voltage characteristics between the semiconductor layer and the probe along the polarization direction of the ferroelectric film when the ferroelectric film of the recording medium shown in FIG. 1 is a material having a small polarization amount.

FIG. 10 shows the result of measuring current-voltage characteristics between the second semiconductor layer and the platinum probe according to the gate voltage Vg when the equivalent recording medium shown in FIG. 8 is equivalent to the recording medium including the ferroelectric film having a small polarization amount. The graph shown.

FIG. 11 is a graph illustrating a change in resistance of a conductive oxide layer according to the polarization direction of the ferroelectric layer domain. FIG.

12 is a graph showing the current-voltage characteristics of the equivalent recording medium when the equivalent recording medium shown in FIG. 8 is equivalent to the recording medium including the ferroelectric film having a large polarization amount.

FIG. 13 shows the result of measuring the current-voltage characteristic between the second semiconductor layer and the platinum probe according to the gate voltage Vg when the equivalent recording medium shown in FIG. 8 is equivalent to the recording medium including a ferroelectric film having a large polarization amount. FIG. The graph shown.

14 is a cross-sectional view showing a process of reading data from a recording medium on which data is recorded by the method shown in FIG.

* Description of the symbols for the main parts of the drawings *

10: lower electrode 12: ferroelectric film

12a, 12b: first and second ferroelectric films 14: barrier layer

15, 15a, 17a: depletion layer 16, 34: first and second semiconductor layers

17: dense layer 20: probe

30: semiconductor substrate 32: insulating film

Da, Db, Dc: first to third domain

D: Domain E: Electric Field

P: polarization directions S1, S2, S3: first to third shifts

A, B, C: residual polarization of the first to third domains

G1 to G13: first to thirteenth graphs

1. Field of Invention

The present invention relates to a recording medium and a memory device including the same, a method of writing and reading data of the memory device, and more particularly, to a recording medium including a ferroelectric film, a nonvolatile memory device including the same, and a nonvolatile memory device. A data recording and reproducing method.

2. Description of related technology

As the demand for small electronic products such as portable communication devices and electronic notebooks increases, the necessity of ultra-small, highly integrated nonvolatile memory devices is increasing. However, the conventional hard disk, which is a data storage medium, has a limitation in reducing its size, making it difficult to miniaturize. Flash memory may be an alternative to hard disks, but the density of flash memory is difficult to achieve. As a result, there is a growing need for new ultra-high density non-volatile memory devices. Among these, interest in memory devices using scanning probes (hereinafter, referred to as probes) is increasing as the new ultra-high density nonvolatile memory devices.

In the case of an ultra-small high-density memory device using a probe for reading data, ferroelectric films, ferromagnetic films, thermoplastic resins, thermosetting resins, and the like have been considered as data recording media.

The method of reading data from the recording media listed above includes a method of detecting a force acting on a probe such as electrostatic force, magnetostatic force, piezoelectric force, and the like, a method of detecting a change in electrical characteristics of a recording medium such as a difference in electrical conductivity or a difference in thermal conductivity, and the like. There is this.

The memory device that detects the domain polarization state of the ferroelectric film using piezoelectric power uses a lock-in amplifier. Therefore, miniaturization is difficult.

The method of writing data to the above-described recording media includes a method of inverting the domain of the ferroelectric film or the domain of the ferromagnetic film by using a probe, and applying heat to an area in which data of the recording medium is to be recorded to phase change or damage the area. It is a method to make it.

The latter method is slow in writing and difficult to read and write repeatedly.

On the other hand, miniature highly integrated memory devices combining the above-listed methods are also introduced. These memory elements can be divided into a case in which the probe is not in contact with the recording medium and a case in which the probe is not in contact.

When reading data without contact between the probe and the recording medium, a separate feedback back circuit is required to keep the distance between the probe and the recording medium constant. Therefore, it is practically difficult to miniaturize the memory element so that it is easy to carry.

On the other hand, when the probe is in contact with the recording medium, the wear of the probe and the recording medium is a problem, especially the wear of the recording medium is a big problem. In addition, when the probe is in contact with the recording medium, the reading speed of the data is limited by the resonance frequency (usually 1 MHz or less) of the cantilever supporting the probe.

SUMMARY OF THE INVENTION The present invention has been made in an effort to improve the above-described problems of the prior art, and is suitable for miniaturizing a memory device, and is used for a nonvolatile memory device capable of speeding up reading while preventing wear of a recording medium. In providing a medium.

Another object of the present invention is to provide a nonvolatile memory device having the recording medium.

Another object of the present invention is to provide a method of writing data to the recording medium in the nonvolatile memory device.

Another object of the present invention is to provide a method of reading data from the recording medium in the nonvolatile memory device.

In order to achieve the above technical problem, the present invention includes a lower electrode, a ferroelectric film formed on the lower electrode and the data is recorded, a barrier layer formed on the ferroelectric film and a semiconductor layer formed on the barrier layer A recording medium of a nonvolatile memory device is provided.

According to an embodiment of the present invention, the ferroelectric film may be a PZT film, an STO film, a BTO film, or a PTO film. The barrier layer may be a yttrium oxide film Y ₂ 0 ₃ or an aluminum oxide film Al ₂ 0 ₃ of a given thickness. In addition, the semiconductor layer may be a semiconductor layer forming a Schottkey junction with the metal of the probe portion.

In order to achieve the above technical problem, the present invention provides a non-volatile memory device having a recording medium on which data is recorded, and a probe used to write data to and read data from the recording medium. ,

A recording layer is formed on the lower electrode, the ferroelectric film on which the data is recorded, and the barrier layer formed on the ferroelectric film; And it provides a non-volatile memory device comprising a semiconductor layer formed on the barrier layer.

In this case, the ferroelectric film, the barrier layer and the semiconductor layer are as described above.

The probe may be made of a metal forming a Schottky junction with the semiconductor layer.

In order to achieve the above another technical problem, the present invention is used to record data on the recording medium, and to read data from and to the recording medium in which a lower electrode, a ferroelectric film, a barrier layer and a semiconductor layer are sequentially stacked. In the data writing method of a nonvolatile memory device having a probe,

A write voltage is applied to the lower electrode and the probe while the probe is in contact with the surface of the semiconductor layer.

In this case, the ferroelectric film, the barrier layer, the semiconductor layer and the probe are as described above.

The present invention also provides a recording medium in which a lower electrode, a ferroelectric film, a barrier layer, and a semiconductor layer are sequentially stacked, for recording data on and reading data from the recording medium. A data reading method of a nonvolatile memory device having a probe, the method comprising: a first step of applying a read voltage between the probe and the semiconductor layer while contacting the probe with a surface of the semiconductor layer; and the probe and the semiconductor And a second step of determining a residual polarization state of the ferroelectric film by measuring a current (resistance) between the layers.

In this case, the ferroelectric film, the barrier layer and the semiconductor layer are as described above.

The first step may include sequentially applying different first and second read voltages between the probe and the semiconductor layer.

The second step includes measuring a first current (first resistance) between the probe and the semiconductor layer due to the first read voltage, and the probe and the semiconductor layer due to the second read voltage. The method may include measuring a second current (second resistance) therebetween and determining a difference between the first and second currents (first and second resistances) to determine a residual polarization state of the ferroelectric film. The probe may be made of a metal forming a Schottky junction with the semiconductor layer.

By using the recording medium of the present invention, since the probe and the ferroelectric film do not directly contact each other, wear of the ferroelectric film can be prevented. In addition, using the reading method of the present invention, since the reading process is simple, the reading speed can be increased while maintaining the high density storage capacity of the data. In addition, since no additional equipment is required to read and write data, the memory device can be miniaturized.

Hereinafter, a recording medium including a ferroelectric film according to an exemplary embodiment of the present invention, a nonvolatile memory device including the same, and a data recording and reproducing method of the memory device will be described in detail with reference to the accompanying drawings. In this process, the thicknesses of layers or regions illustrated in the drawings are exaggerated for clarity.

First, a recording medium including a ferroelectric film of a nonvolatile memory device according to an embodiment of the present invention (hereinafter referred to as the recording medium of the present invention) will be described.

Referring to FIG. 1, when recording data, the recording medium of the present invention records data recorded in the lower electrode 10 to which a predetermined voltage is applied, the ferroelectric film 12 to which data is written, and the ferroelectric film 12. In reading, a first semiconductor layer 16 to which a predetermined voltage is applied is provided, and a barrier layer 14 is provided between the ferroelectric film 12 and the first semiconductor layer 16. The barrier layer 14 serves as a gate oxide film while preventing the reaction between the first semiconductor layer 16 and the ferroelectric film 12 in the manufacturing process of the recording medium of the present invention. The ferroelectric film 12 may be a ferroelectric material having excellent polarization characteristics in a direction perpendicular to the film. In addition, the ferroelectric film 12 may be a first ferroelectric film having a first polarization amount or a second ferroelectric film having a second polarization amount greater than the first polarization amount when a voltage is applied. When the polarization amount of the ferroelectric film 12 is large and small, the effect of the ferroelectric film 12 on the current-voltage characteristics of the first semiconductor layer 16 provided on the ferroelectric film 12 is different, which will be described later. do.

The first and second ferroelectric films may be the same material or different materials. When the first and second ferroelectric films are the same material, the polarization amounts may be different by different thicknesses, but the polarization amounts may be different by varying the conditions of the manufacturing process even when the thicknesses are the same.

For example, when the first and second ferroelectric films are PZT films having the same thickness, the first ferroelectric film may be formed under a composition condition having a large ratio of Zr to Ti. The second ferroelectric film may be formed under a compositional condition in which the ratio of Zr to Ti is small. By forming in this way, the polarization amounts of the first and second ferroelectric films can be varied. In addition, when the first ferroelectric film is a PZT film, its polarization amount is enough to form a depletion layer 15 as shown in FIG. 3, and when the second ferroelectric film is a PZT film, its polarization amount is shown in FIG. 5. As described above, the dense layer 17 is formed.

The ferroelectric film 12 is preferably a PZT (Pb (Zr, Ti) O ₃ ) film, but other ferroelectric films, such as an STO (SrTiO ₃ ) film, a BTO (BaTiO ₃ ) film, or a PTO (PbTiO ₃ ) film. Can be. The ferroelectric film 12 may be provided in a thin film, thick film, or bulk state. The barrier layer 14 may be a yttrium oxide film Y ₂ O ₃ or an aluminum oxide film Al ₂ O ₃ having a thickness less than 100 nm. However, while preventing the reaction between the first semiconductor layer 16 and the ferroelectric film 12, the polarization characteristics of the ferroelectric film 12 and the resistance characteristics or current characteristics of the first semiconductor layer 16 according to the polarization characteristics are not affected. Any material layer that is not used may be the barrier layer 14. The first semiconductor layer 16 used as the upper electrode is preferably an n-type silicon layer, but may be any type of semiconductor layer forming a Schottkey junction with the probe. The surface of the first semiconductor layer 16 is in contact with the probe 20 when recording and reproducing data, as shown in FIGS. 2 and 14.

Next, a method of recording data on the recording medium shown in FIG. 1 will be described with reference to FIG.

As shown in Fig. 2, a probe 20 in contact with the first semiconductor layer 16 is used to record data on the recording medium of the present invention. The probe 20 includes a first portion 20a in contact with the surface of the first semiconductor layer 16 and a second portion 20b for supporting the first portion 20a. The first portion 20a is preferably formed of platinum (Pt), but may be any metal capable of forming a Schottky junction with the first semiconductor layer 16. For example, the first portion 20a may be formed of gold (Au). The second portion 20b is formed of silicon (Si) or nitride film (Si 3 N 4).

The specific process of recording data on the recording medium of the present invention using the probe 20 is as follows.

First, a voltage is applied between the probe 20 and the lower electrode 10 while bringing the probe 20 into contact with the surface of the first semiconductor layer 16. By applying the voltage, an electric field E toward the lower electrode 10 exists between the probe 20 and the lower electrode 10. Since the probe 20 is sharp, the electric field E is concentrated below the probe 20. The electric field E forms a domain D in the predetermined region of the ferroelectric film 12. Reference numeral P denotes the direction of residual polarization of the domain (D). The direction P of the residual polarization may be reversed depending on the voltage applied to the probe 20 and the lower electrode 10. The kind of data recorded on the ferroelectric film 12 varies depending on the direction P of the residual polarization. For example, when the direction P of the residual polarization is directed toward the probe 20 as shown in the drawing, data 1 may be regarded as being recorded, and the direction P of the residual polarization is directed toward the lower electrode 10. The case can be considered that data 0 is recorded. Of course, the opposite is also possible.

On the other hand, in the data recording process as shown in Fig. 2, is the ferroelectric film 12 the first ferroelectric film having the first polarization amount, or the polarization amount having the second polarization amount greater than the first polarization amount? Even when the energy band of the first semiconductor layer 16 in contact with the probe 20 changes depending on whether the second ferroelectric film is formed, and the ferroelectric film 12 is any one of the first and second ferroelectric films, The energy band of the first semiconductor layer 16 varies according to the polarization direction of the ferroelectric film.

Accordingly, in the process of reading data from the recording medium, the current-voltage characteristic of the first semiconductor layer 16 depends on the polarization amount and the polarization direction of the ferroelectric film 12.

Specifically, as shown in FIGS. 3 and 4, when the first ferroelectric film 12a having the first polarization amount is provided between the lower electrode 10 and the barrier layer 14, the first ferroelectric film The width of the depletion layer 15 appearing in the first semiconductor layer 16 varies depending on the polarization direction of 12a.

3 and 4, when the polarization direction of the first ferroelectric film 12a faces the barrier layer 14 (FIG. 3), the polarization direction is lower than the width of the depletion layer 15 in FIG. 3. It can be seen that the width of the depletion layer 15a in the facing (FIG. 4) is wider. This means that the resistance of the first semiconductor layer 16 is increased when the polarization direction of the first ferroelectric film 12a is directed toward the lower electrode 10. The change in conduction band energy level Ec of the first semiconductor layer 16 also reflects this result. In other words, when the conduction band energy level Ec of the first semiconductor layer 16 shown in FIGS. 3 and 4 is compared, when the polarization direction of the first ferroelectric film 12a faces the barrier layer 14 (FIG. 3). It can be seen that the energy level Ec of the conduction band becomes higher when facing the lower electrode 10 than ().

3 and 4, reference numerals E _F and Ev denote changes in Fermi levels and valence bands of the first semiconductor layer 16, respectively.

5 and 6, when the second ferroelectric film 12b having the second polarization amount is provided between the lower electrode 10 and the barrier layer 14, the second ferroelectric film 12b. The characteristics of the first semiconductor layer 16 vary depending on the polarization direction of.

As shown in FIG. 5, when the polarization direction of the second ferroelectric film 12b is directed toward the barrier layer 14, an accumulation layer (accumulation layer) is applied to the first semiconductor layer 16 due to a large polarization amount ( 17) is formed. Referring to the change of the conduction band energy level Ec of the first semiconductor layer 16, the resistance of the first semiconductor layer 16 is lowered by the overdense layer 17, but the first semiconductor layer 16 and the probe ( It can be seen that the potential barrier between 20) is increased.

Accordingly, when the second ferroelectric film 12b is provided and the data is read from the recording medium whose polarization direction is directed to the barrier layer 14, the current-voltage characteristic of the recording medium, that is, the first semiconductor layer 16 The current-voltage characteristic between and the platinum probe 20 is shifted from the first graph G1 to the second graph G2 as shown in FIG.

On the contrary, as shown in FIG. 6, when the polarization direction of the second ferroelectric film 12b is directed toward the lower electrode 10, the depletion layer 17a is wider than the first semiconductor layer 16 due to the large polarization amount. Is formed. Referring to the conduction band energy level Ec ′ of the first semiconductor layer 16, the depletion direction of the second ferroelectric film 12b is directed toward the barrier layer 14 by the depletion layer 17a. It can be seen that the resistance of layer 16 is high, but the potential barrier between first semiconductor layer 16 and platinum probe 20 is low.

Accordingly, when the second ferroelectric film 12b is provided and the data is read from the recording medium whose polarization direction is directed to the lower electrode 10, the current-voltage characteristic of the recording medium is shown in FIG. 2 is moved from the graph G2 to the third graph G3.

When the second graph G2 and the third graph G3 of FIG. 7 are compared, when the polarization direction of the second ferroelectric film 12b is directed toward the lower electrode 10, the first semiconductor layer 16 and the platinum probe (20) (or the current flowing between the first semiconductor layer 16 and the metal layer capable of forming a Schottky junction) increases in proportion to the increase in voltage, and the polarization direction of the second ferroelectric film 12b is changed to the barrier layer ( It can be seen that the current flowing toward 14) increases rapidly with voltage. This means a change in resistance and potential barriers.

As described above, the first semiconductor layer 16 in contact with the platinum tower needle 20 of the recording medium in accordance with the magnitude and polarization direction of the polarization amount of the ferroelectric film 12 of the recording medium as shown in FIG. Since the current-voltage characteristic, that is, the resistance characteristic varies, data can be read from the recording medium shown in FIG.

The process of reading data from the recording medium shown in FIG. 1 is a process of measuring current-voltage characteristics (resistance characteristics) between the first semiconductor layer 16 and the platinum probe 20 of the recording medium.

In order to implement the process of measuring the current-voltage characteristic (resistance characteristic) between the first semiconductor layer 16 and the platinum probe 20 of the recording medium, the inventors write data to the recording medium shown in FIG. An equivalent recording medium (hereinafter referred to as an equivalent recording medium) was made, and the current-voltage characteristics of the equivalent recording medium were measured. The equivalent recording medium is shown in FIG.

Referring to FIG. 8, the equivalent recording medium includes a semiconductor substrate 30 to which a gate voltage Vg is applied. The insulating film 32 is provided on the semiconductor substrate 30, and the second semiconductor layer 34 is provided on the insulating film 32.

The inventor used a silicon substrate doped with conductive impurities as the semiconductor substrate 30, and used a silicon oxide film (SiO 2) as the insulating film 32. An n-type silicon layer was used as the second semiconductor layer 34.

On the other hand, as shown in FIG. 2, when data is recorded on the recording medium, residual polarization exists in the domain D of the ferroelectric film 12. Therefore, a charge distribution due to residual polarization is formed on the surface (hereinafter referred to as a contact surface) in contact with the barrier layer 14 of the first semiconductor layer 16. For example, when the direction P of the residual polarization is directed toward the platinum probe 20, a negative charge is formed on the contact surface of the first semiconductor layer 16, and the direction P of the residual polarization is the lower electrode. When facing (10), a positive charge is formed on the contact surface of the first semiconductor layer 16.

The inventors have described a recording medium having a ferroelectric film 12 having a first ferroelectric film having a first polarization amount (hereinafter referred to as a first recording medium) or a recording medium having a ferroelectric film 12 having a second ferroelectric film having a second polarization amount. The gate voltage Vg was applied to the semiconductor substrate 30 to make the equivalent recording medium in a state equivalent to that of the second recording medium.

First, the case where the equivalent recording medium is made to be equal to the first recording medium will be described.

When a positive gate voltage Vg, for example, + 2V is applied to the semiconductor substrate 30 (hereinafter, referred to as a first case), the surface is in contact with the insulating film 32 of the second semiconductor layer 34. A negative charge is induced at. Therefore, the state of the second semiconductor layer 34 in the first case is that the residual polarization P toward the probe 20 exists in the domain D of the ferroelectric film 12 in the recording medium shown in FIG. It is equivalent to the state of the first semiconductor layer 16. Therefore, in the first case, the change of the energy band of the second semiconductor layer 34 may have the same tendency as the change of the energy band Ec or Ev of the first semiconductor layer 16 shown in FIG. 3.

In addition, when a negative gate voltage Vg, for example, -2V is applied to the semiconductor substrate 30 (hereinafter, referred to as a second case), the insulating film 32 of the second semiconductor layer 34 and Positive charges are induced at the contacting surfaces. Therefore, the second semiconductor layer 34 in the second case has a residual polarization P toward the lower electrode 10 in the domain D of the ferroelectric film 12 in the recording medium shown in FIG. 2. It is equivalent to the state of the first semiconductor layer 16 at the time. Therefore, in the second case, the change of the energy band of the second semiconductor layer 34 may have the same tendency as the change of the energy band Ec or Ev of the first semiconductor layer 16 illustrated in FIG. 4.

In order to measure the current flowing in the second semiconductor layer 34 between the platinum probe 20 and the insulating film 32 in the first and second cases, the inventors have used the platinum probe 20 as the second semiconductor layer 34. In contact with the surface of the semiconductor substrate 30 and applying the gate voltage Vg according to the first or second case to the semiconductor substrate 30. V) was applied.

FIG. 9 shows voltage-current characteristics measured for the equivalent recording medium, that is, voltage-current characteristics of the second semiconductor layer 34 when the equivalent recording medium is equivalent to the recording medium provided with the first ferroelectric film. .

In FIG. 9, reference numeral G5 denotes a fifth graph showing the result measured in the first case, and G6 denotes the sixth graph showing the result measured in the second case. In addition, reference numeral G4 is a reference graph showing when the gate voltage Vg is not applied to the semiconductor substrate 30, and is a fourth graph.

Referring to the fifth and sixth graphs G5 and G6 of FIG. 9, as the voltage V applied to the second semiconductor layer 34 increases, the probe 20 may be applied in the first and second cases. It can be seen that the current flowing between the second semiconductor layer 34 also increases.

However, the amount by which the current flowing in the second semiconductor layer 34 increases is different in the first case and the second case. In other words, while the voltage V applied to the probe 20 and the second semiconductor layer 34 is the sensing voltage Vs, the second current I2 flows in the second semiconductor layer 34 in the first case. In the second case, a first current I1 much less than the second current I2 flows through the second semiconductor layer 34.

Second semiconductor in the second case through comparison of the depletion layers 15 and 15a formed in the first semiconductor layer 16 of the recording medium shown in FIGS. 3 and 4, which are equivalent to the first and second cases. Since the area of the depletion layer formed in the layer 34 will be much wider than the depletion layer formed in the second semiconductor layer 34 in the first case, the second current I2 is much larger than the first current I1. This is a natural result.

As described above, since the difference between the values of the first and second currents I1 and I2 in the first and second cases is large, when the current is measured from the second semiconductor layer 34, the current is measured by the first. And in which of the second cases it is readily apparent.

In other words, when the ferroelectric film is provided under the second semiconductor layer 34 instead of applying the gator voltage Vg to the semiconductor substrate 30, the current flowing through the second semiconductor layer 34 is measured so that the ferroelectric film remains. The polarization direction (data value recorded in the ferroelectric film) P can be known.

In addition, a large difference in the current flowing through the second semiconductor layer 34 according to the first and second cases also greatly varies the resistance of the second semiconductor layer 34 in the first and second cases. Means that. Therefore, even in the case of measuring the resistance at the sensing voltage Vs from the second semiconductor layer 34, it is easy to know in which of the first and second cases the resistance is measured.

Since the recording medium shown in FIG. 2 and the recording medium shown in FIG. 8 are equivalent, the measurement results of the second semiconductor layer 34 are also applied to the first semiconductor layer 16 of the recording medium shown in FIG. Can be.

FIG. 10 is an experimental example of the results shown in FIG. 9, wherein the second semiconductor layer (with the gate voltage Vg applied to the semiconductor substrate 30 of the equivalent recording medium fixed at + 2V, 0V, and -2V) is shown. When the voltage V applied to 34 is increased, a change in current flowing through the second semiconductor layer 34 is shown.

In FIG. 10, reference numeral G7 denotes a seventh graph showing a change in current flowing through the second semiconductor layer 34 when the gate voltage Vg is fixed to −2V, and G8 denotes a gate voltage Vg of 0V. An eighth graph showing a change in current when is performed. G9 represents a ninth graph showing a change in current when the gate voltage Vg is fixed to + 2V.

Comparing the seventh to ninth graphs G7, G8, and G9 of FIG. 10, the seventh to ninth graphs G7, G8, and G9 while the voltage V applied to the second semiconductor layer 34 increases. ) You can see that they are both increasing. However, as the voltage V applied to the second semiconductor layer 34 exceeds 2V, it can be seen that a large gap occurs between the seventh graph G7 and the ninth graph G9. This result is in exact agreement with the result predicted in FIG. 9.

FIG. 11 shows a change in the resistance of the conductive oxide layer under the ferroelectric layer according to the direction of residual polarization of the domain of the ferroelectric layer.

In FIG. 11, reference numerals Da, Db, and Dc denote first to third domains Da, Db, and Dc of the ferroelectric film, respectively. The first to third domains Da, Db, and Dc are adjacent to each other. Reference numerals A, B, and C denote residual polarizations of the first to third domains Da, Db, and Dc, respectively. Further, reference figures "+" and "-" respectively indicate directions of residual polarizations A, B, and C. FIG. + Indicates that the residual polarizations A, B, and C are arranged in the direction entering from the ground, and − indicates that the residual polarizations A, B, and C are arranged in the direction coming out to the ground. For example, when the first to third domains Da, Db, and Dc are all +, as shown in the lower part of the figure, the residual polarization direction of the first to third domains Da, Db, and Dc is All of them indicate the direction from the ground.

In the meantime, reference numerals S1 to S3 denote first to third shifts, respectively.

The first shift S1 remains in the first domain Da while the directions of the residual polarizations A, B, and C of the first to third domains Da, Db, and Dc are all “+”. Only the direction of polarization A is shifted to "-".

The second shift S2 is in a state where the directions of the residual polarizations A, B, and C of the first to third domains Da, Db, and Dc are “−”, “−”, and “+”, respectively. Only the direction of the residual polarization B of the second domain Db is shifted to "+".

The third shift S3 is obtained when the directions of the residual polarizations A and C of the first and third domains Da and Dc are fixed among the first to third domains Da, Db and Dc. Only the direction of the residual polarization B of the second domain Db is shifted from "+" to "-" or vice versa.

Referring to FIG. 11, when the directions of the residual polarizations A, B, and C of the first to third domains Da, Db, and Dc are all positive (hereinafter, referred to as a third case), the ferroelectric When the resistance of the conductive oxide film corresponding to the first to third domains Da, Db, and Dc, which are located under the film, is the lowest, and the directions of the residual polarizations A, B, and C are all − , The fourth case), the resistance of the conductive oxide film is the highest. In the third case, when the residual polarization direction of any one of the first to third domains Da, Db, and Dc is shifted in the opposite direction, the resistance of the semiconductor layer is increased. On the other hand, when the residual polarization direction of any one of the first to third domains Da, Db, and Dc is shifted in the opposite direction in the fourth case, the resistance of the conductive oxide film is reduced.

As a whole, the more domains with a positive polarization direction, the lower the resistance of the conductive oxide film, and the more domains with a negative -polarization direction, the higher the resistance of the conductive oxide film.

Next, the case where the equivalent recording medium is made in the same state as the second recording medium including the second ferroelectric film having a large polarization amount will be described.

In this case, the gate voltages Vg of + 25V and -25V are applied to the semiconductor substrate 30, and the respective cases are hereinafter referred to as fifth and sixth cases. In the fifth and sixth cases, the charges induced on the surface of the second semiconductor layer 34 in contact with the insulating layer 32 are the same as those of the first and second cases except that the amount of induced charges increases. .

In the fifth case, since the polarization direction of the second ferroelectric film provided in the second recording medium faces the semiconductor layer in contact with the probe, the energy of the second semiconductor layer 34 of the equivalent recording medium in the fifth case. The band change can be seen to be the same as the change of the energy band Ec or Ev of the first semiconductor layer 16 shown in FIG. 5.

Further, in the sixth case, since the polarization direction of the second ferroelectric film provided in the second recording medium faces the lower electrode, in the sixth case, the energy band of the second semiconductor layer 34 of the equivalent recording medium changes. The same can be seen as the change of the energy band Ec 'or Ev' of the first semiconductor layer 16 shown in FIG.

In order to measure the current-voltage characteristic between the platinum probe 20 and the second semiconductor layer 34 of the equivalent recording medium in the fifth and sixth cases, the inventors use the platinum probe 20 as the second semiconductor layer. The second semiconductor layer 34 and the platinum probe 20 are in contact with the surface of the semiconductor substrate 34 while the gate voltage Vg according to the fifth or sixth case is applied to the semiconductor substrate 30. Voltage V was applied.

The voltage-current characteristic of the equivalent recording medium measured in this manner, that is, the voltage-current characteristic (resistance characteristic) between the second semiconductor layer 34 and the platinum probe 20 is shown in FIG.

In FIG. 12, reference numeral G10 denotes the second semiconductor layer 34 and the platinum probe 20 while a positive gate voltage Vg is applied to the semiconductor substrate 30 of the equivalent recording medium shown in FIG. 8. ) Is a tenth graph showing current-voltage characteristics between the second semiconductor layer 34 and the platinum probe 20 when a predetermined voltage V is applied. In addition, reference numeral G11 indicates that a predetermined voltage V is applied between the second semiconductor layer 34 and the platinum probe 20 while a negative gate voltage Vg is applied to the semiconductor substrate 30. An eleventh graph showing current-voltage characteristics between the second semiconductor layer 34 and the platinum probe 20 at the time is shown. Vg (+) indicates that the gate voltage Vg applied to the semiconductor substrate 30 is a positive voltage, and Vg (−) indicates that the gate voltage Vg is a negative voltage.

Referring to the tenth and eleventh graphs G10 and G11 of FIG. 12, in the fifth case (the tenth graph) equivalent to the case where the polarization direction of the second ferroelectric film faces the barrier layer, While the current rapidly increases as the sensing voltage applied between the semiconductor layer 34 and the platinum probe 20 increases, the sixth case is equivalent to the case in which the polarization direction of the second ferroelectric film is directed toward the lower electrode. The current in the graph increases in proportion to the increase in the sensing voltage.

Therefore, as shown in FIG. 12, if the resistance is measured at the first and second sensing voltages Vs1 and Vs2, and the resistances measured at the sensing voltages are referred to as the first resistor RVs1 and the second resistor RVs2. In the fifth case, the first resistor RVs1 and the second resistor RVs2 have different values, but in the sixth case, they are substantially the same.

As described above, since the resistance values measured at different sensing voltages are different from each other, the polarization direction of the second ferroelectric layer may be read by measuring whether the resistance changes at different sensing voltages. Since the polarization direction of the second ferroelectric film indicates data recorded on the recording medium, it is possible to determine whether the data recorded on the recording medium is "1" or "0" by measuring the resistance change at different sensing voltages. have.

FIG. 13 shows measurement results of current-voltage characteristics between the second semiconductor layer 34 and the platinum probe 20 of the equivalent recording medium shown in FIG.

In order to measure the current-voltage characteristics between the second semiconductor layer 34 and the platinum probe 20, the inventors have a gate voltage (Vg) of + 25V and -25V on the semiconductor substrate 30 of the equivalent recording medium. The current flowing between the second semiconductor layer 34 and the platinum probe 20 was measured while increasing the voltage V applied between the second semiconductor layer 34 and the platinum probe 20.

In FIG. 13, a twelfth graph G12 is applied between the second semiconductor layer 34 and the platinum probe 20 while a gate voltage Vg of -25V is applied to the semiconductor substrate 30 of the equivalent recording medium. The result of measuring the current flowing between the second semiconductor layer 34 and the platinum probe 20 while increasing the voltage V to be obtained is shown (corresponding to the sixth case). The thirteenth graph G13 is a voltage applied between the second semiconductor layer 34 and the platinum probe 20 while a gate voltage Vg of + 25V is applied to the semiconductor substrate 30 of the equivalent recording medium. The result of measuring the current flowing between the second semiconductor layer 34 and the platinum probe 20 while increasing (V) is shown (corresponding to the fifth case).

Comparing the twelfth and thirteenth graphs G12 and G13 of FIG. 13, the twelfth and thirteenth graphs G12 and G13 are applied until the voltage V applied to the second semiconductor layer 34 becomes 4V. It can be seen that the slopes do not all change. However, it can be seen that the slope of the thirteenth graph G13 increases rapidly as the voltage V applied to the second semiconductor layer 34 exceeds 4V. This result is in exact agreement with the result predicted in FIG. 12.

While many details are set forth in the foregoing description, they should be construed as illustrative of preferred embodiments, rather than to limit the scope of the invention. For example, those skilled in the art may form the recording medium shown in FIG. 1 in duplicate. For example, the lower electrode 10 may be provided with a semiconductor layer to be used as a ferroelectric film, a barrier layer and a semiconductor layer. And it may be further provided with a probe for recording data on the ferroelectric film provided under the lower electrode, and reproducing the recorded data. Therefore, the scope of the present invention should not be defined by the described embodiments, but should be determined by the technical spirit described in the claims.

As described above, the recording medium according to the present invention includes a semiconductor layer and a lower electrode respectively above and below the ferroelectric film on which data is stored, and a barrier layer between the semiconductor layer and the ferroelectric film. As a result, the probe and the ferroelectric film do not directly contact each other when writing data to the ferroelectric film and reading data recorded on the ferroelectric film. Therefore, wear of the ferroelectric film can be prevented.

In addition, the present invention simply reads the data recorded in the ferroelectric film by applying a read voltage between the semiconductor layer and the probe, which is much simpler than in the prior art. Therefore, by using the data recording medium and the data reading method of the present invention, the data reading speed can be made faster while maintaining the high density storage capacity of the data.

In addition, memory devices can be miniaturized because no additional equipment is required for reading and writing data.

Claims (21)

Lower electrode; A ferroelectric film formed on the lower electrode and recording data; A barrier layer formed on the ferroelectric film; And And a semiconductor layer formed on the barrier layer. The recording medium of claim 1, wherein the ferroelectric film is a PZT film, an STO film, a BTO film, or a PTO film. The recording medium of claim 1, wherein the barrier layer is a yttrium oxide film (Y ₂ 0 ₃ ) or an aluminum oxide film (Al ₂ 0 ₃ ). The recording medium of claim 1, wherein the semiconductor layer is a semiconductor layer that forms a Schottkey junction with an external metal. A non-volatile memory device having a recording medium on which data is recorded and a probe used to record data on and to read data from the recording medium. The recording medium, Lower electrode; A ferroelectric film formed on the lower electrode and recording data; A barrier layer formed on the ferroelectric film; And And a semiconductor layer formed on the barrier layer. The nonvolatile memory device of claim 5, wherein the ferroelectric film is a PZT film, an STO film, a BTO film, or a PTO film. 6. The nonvolatile memory device of claim 5, wherein the barrier layer is a yttrium oxide film (Y ₂ 0 ₃ ) or an aluminum oxide film (Al ₂ 0 ₃ ). 6. The nonvolatile memory device of claim 5, wherein the semiconductor layer is a semiconductor layer that forms a Schottky junction with a metal of the probe portion. 6. The nonvolatile memory device of claim 5, wherein the probe is made of a metal forming a Schottky junction with the semiconductor layer. A recording medium including a lower electrode, a ferroelectric film formed on the lower electrode, on which data is recorded, a barrier layer formed on the ferroelectric film, and a semiconductor layer formed on the barrier layer, and recording data on the recording medium. And a method of writing data in a nonvolatile memory device having a probe used to read data from the recording medium. And a write voltage is applied to the lower electrode and the probe while the probe is in contact with the surface of the semiconductor layer. The method of claim 10, wherein the ferroelectric film is a PZT film, an STO film, a BTO film, or a PTO film. The method of claim 10, wherein the barrier layer is a yttrium oxide film (Y ₂ 0 ₃ ) or an aluminum oxide film (Al ₂ 0 ₃ ). 12. The method of claim 10, wherein the semiconductor layer is a semiconductor layer that forms a Schottky junction with a metal of the probe portion. 12. The method of claim 10, wherein the probe is made of metal forming a Schottky junction with the semiconductor layer. A recording medium including a lower electrode, a ferroelectric film formed on the lower electrode, on which data is recorded, a barrier layer formed on the ferroelectric film, and a semiconductor layer formed on the barrier layer, and recording data on the recording medium. And a data reading method of a non-volatile memory device having a probe used to read data from the recording medium. A first step of applying a read voltage between the probe and the semiconductor layer while contacting the probe with a surface of the semiconductor layer; And And measuring a current (resistance) between the probe and the semiconductor layer to determine a residual polarization state of the ferroelectric film. 16. The method of claim 15, wherein the ferroelectric film is a PZT film, an STO film, a BTO film, or a PTO film. 16. The method of claim 15, wherein the barrier layer is a yttrium oxide film (Y ₂ 0 ₃ ) or an aluminum oxide film (Al ₂ 0 ₃ ). 16. The method of claim 15, wherein the semiconductor layer is a semiconductor layer forming a Schottky junction with a metal of the probe portion. 16. The method of claim 15, wherein the first step includes sequentially applying different first and second read voltages between the probe and the semiconductor layer. The method of claim 19, wherein the second step, Measuring a first current (first resistance) between the probe and the semiconductor layer due to the first read voltage; Measuring a second current (second resistance) between the probe and the semiconductor layer due to the second read voltage; And And determining a residual polarization state of the ferroelectric film by obtaining a difference between the first and second currents (first and second resistors). 21. The method of claim 15 or 20, wherein the probe is made of a metal forming a Schottky junction with the semiconductor layer.

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