JP4572756B2 - Recording method to ferroelectric layer and recording device to ferroelectric layer - Google Patents

Description

Recording method to a ferroelectric layer in a field where a ferroelectric layer is used as a recording medium, and analog recording (stepless recording) or multi-step recording is performed on the recording medium, particularly regarding recording on a rewritable disc-shaped recording medium And a recording device for a ferroelectric layer.

The present invention relates to the improvement of JP-A-2005-149647 by the present inventor. The background art will be described below along JP-A-2005-149647.
A normal ferroelectric has a hysteresis behavior (hysteresis) as shown in FIG. 14 between the applied electric field E and the electric polarization P. Details of this history behavior are described in, for example, “Ferroelectric thin film memory” (published in 1995, Science Forum), and also in JP-A-6-130361 and JP-A-2001-298164. Many are described. The strength of the electric field at which the electric polarization of the ferroelectric material does not increase even when the applied electric field is increased is called a saturation electric field. The polarization at that time is called saturation polarization and is expressed as Pm. The residual polarization Pr is the electrical polarization that remains in the ferroelectric material after the ferroelectric material is exposed to the electric field E and then removed. The residual polarization when an electric field equal to or higher than the saturation electric field is applied to the ferroelectric layer is called saturation residual polarization and is expressed as Pr (m). Here, the saturation electric field theoretically indicates a state in which all parts of the ferroelectric layer are aligned and polarized in one direction, but in an actual ferroelectric layer, there are parts that are not aligned for some reason. May occur. However, if there is no practical problem, ignore it and call it a saturation electric field. When strictly distinguishing, the former is often indicated by Es (saturated) and the latter by Em (maximum). Here, substantial saturation is indicated, and it is expressed as Em. Similarly, Pm described above indicates that the polarization is substantially maximum. An example of the history behavior when the applied electric field is changed from -Em to Em to -Em is the loop of the maximum area in FIG. 14, and is generally called a saturation history curve.

There is a field in which a ferroelectric is used as a recording medium by utilizing the remanent polarization of the ferroelectric. One of the fields is to use a ferroelectric layer as a disk-shaped recording medium. For example, it is a high-density recording method disclosed in Patent Document 1, Patent Document 2, and Patent Document 3.

As shown in FIGS. 15A and 15B, the ferroelectric layer 210 is formed on one surface of the disk 200 and is opposed to the writing electrode 211 supported by the cantilever lever 212. Yes. By applying the electric field E generated by the write signal generation circuit 221 to the write electrode 211, the ferroelectric layer 210 is polarized to generate residual polarization Pr. Recording is performed with the ferroelectric layer 210 and the writing electrode 211 moving relatively. When the recording medium is a disk, writing to the entire surface is performed by a method in which the disk rotates about a rotating shaft 241 driven by a motor 242 and the writing electrode 211 moves to the disk diameter method. . Reading is performed by processing a signal read by the reading electrode (also serving as the writing electrode 211 in this example) by the reading signal generation circuit.

On the other hand, as a writing method when the recording medium does not rotate, the writing electrode moves in one direction and the recording medium moves in a direction perpendicular thereto, and the writing electrode has two directions in a plane. A method of moving is disclosed. In this case, the recording medium is disclosed not in the form of a disc but in the form of a rectangle.

These prior arts are intended for digital recording, that is, binary recording, and remanent polarization is merely described as being in one direction and the opposite direction. That is, binary recording. However, in Japanese Patent Laid-Open No. 11-40759, a ferroelectric layer having characteristics different from usual is used to obtain a state in which the residual polarization is zero in addition to the binary value of the positive and negative saturated residual polarization. Discloses a method of performing three-stage (three-value) recording. However, three-stage recording is the limit.

In principle, a ferroelectric material can be used as a material for analog recording and multistage recording. Here, the analog recording generally means that recording is performed in a stepless manner in response to a stepless change in intensity of a signal (data) to be recorded. It also includes reading the recorded data steplessly. Therefore, it is sometimes called stepless recording. Multi-level recording is also referred to as multi-level recording, where the intensity of a signal to be recorded is applied to a recording medium in a multi-level or multi-level state, and the state recorded on the recording medium is also multi-level (multi-level recording). ) Which is in the state of

In general, analog recording often refers to recording that is temporally continuous on a signal and spatially continuous on a recording medium. However, in the present invention, time (t) and space (T Recording that is discrete) is called analog recording if the recording signal is a stepless signal. The same applies to multi-stage recording. As described above, the divisional recording on the recording medium occurs, for example, when the disc is divided into segments and recorded.

Multi-level recording (multi-level recording) generally refers to recording of three levels (three levels) or more, but the same applies to the present invention. In the present invention, the case of two-stage recording (binary recording) using the fact that there are two directions of saturation remanent polarization is called digital recording.

The case where analog recording is more convenient than digital recording is, for example, the recording of a natural phenomenon or the case where the output is received by a human sense. For example, it is effective for recording a digital camera signal. The intensity of the image signal from the CCD of the digital camera is not completely stepless but consists of a number of steps. It is a human who sees the output signal of the image as an image, and the image is received in an analog manner. The same applies to voice.

At present, digital signal processing technology has advanced, and even analog signals such as voice are digitized and recorded by A-D conversion, and the readout of the recorded signal and the subsequent signal processing are digital. A D-A conversion is performed at a stage close to the final stage so that it can be received by a human. However, if data can be recorded / reproduced in analog form, the data amount and data processing amount can be reduced. If multi-stage recording is possible, the amount of data is reduced by DD conversion even for binary digital data, leading to an improvement in processing speed.

In analog recording, it is always a problem how much linearity (direct proportional relationship) is obtained between input and output. In analog recording, as the relationship between the intensity of a signal to be recorded and the intensity of a signal reproduced from the recorded state is linearly proportional without any correction, it is easier to use and has a wider range of applications. The same applies to multistage recording. Further, it is more preferable that the frequency response is flat from a low frequency to a high frequency. In general, a ferroelectric has a polarization reversal speed of several microseconds. Therefore, basically, there is a possibility that the frequency response can be broadened.

Japanese Patent Laid-Open No. 9-63294 discloses a method of using a ferroelectric substance for analog recording, although it is an invention of a memory cell. The method will be described below with reference to FIG.

First, a configuration in which the ferroelectric layer Fm is sandwiched between a pair of electrodes X and Y is created (FIG. 16B). This is called a memory cell. A series of electrical signals shown in FIG. 16A is applied between the electrode X and the electrode Y. That is, first, a first pulse Ve having an electric field larger than the coercive electric field of a ferroelectric substance (which is considered to be better understood as a saturation electric field) is applied to a memory cell from a pair of electrodes to a ferroelectric layer. This is applied to polarize the ferroelectric to the polarization state P in the first direction (the downward direction in FIG. 16B) of the two states of polarization. Next, a second pulse Vw having an electric field in a direction opposite to that of the first pulse is applied to the electrode to have a domain having a polarization in the first direction and a polarization in the opposite direction (upward polarization P). A partially polarized state in which domains are mixed is set (FIG. 16C). Since the partial polarization state can be controlled steplessly by this second pulse, analog recording can be performed.

The state shown in FIG. 16B is a process for erasing remanent polarization (hereinafter referred to as previous history) already recorded in the ferroelectric layer, in order to perform multi-step recording and analog recording. Is a necessary process. If an electric field for writing new data is applied without going through this process, the resulting remanent polarization varies depending on the previous history. The reason is that the ferroelectric has a hysteresis characteristic. In the state of FIG. 16B, that is, the state of saturation polarization, the previous history is erased, and when new data is written thereafter, reproducible remanent polarization is obtained.

Japanese Patent Laid-Open No. 9-91776 discloses that the method of Japanese Patent Laid-Open No. 9-63294 is applied to a state in which the write electrode and the ferroelectric layer move relatively. In other words, the ferroelectric layer is brought into a saturation polarization state with the first pulse, and then an electric field in the opposite direction is applied with the second pulse to bring it into a partial polarization state.

The problem of this method is that the range in which the writing electric field and the remanent polarization are in a linear relationship is narrow and the width of the recordable electric field is narrow, as will be described in detail later in the section of action and effect. However, the sensitivity is high.

On the other hand, known documents such as Patent Document 1, Patent Document 2, and Patent Document 3 do not describe the process of erasing the previous history of the ferroelectric layer. Since this is always in the saturation polarization state (the state of FIG. 16B and the polarization direction is reversed) at the time of writing, the previous history of the ferroelectric layer is erased. Therefore, the process of erasing the previous history is unnecessary. Further, even if the process of erasing the previous history is performed, the process cannot be performed because the ferroelectric layer and the electrode are relatively moved.

Another method is described in JP-A-11-305257. This is an invention of reducing the power consumption by using a ferroelectric in the gate insulating layer of a TFT in an active liquid crystal display device.

In the invention, a method is disclosed in which the polarization state of the ferroelectric gate insulating film is set to a required value in a multistep or stepless manner. In this method, as a method of erasing the previous history of the ferroelectric layer, an alternating pulse electric field whose electric field decreases with time, or a method of erasing the previous history of the ferroelectric layer by alternating current is used. Thereafter, a voltage to be recorded is applied to obtain residual polarization. However, in the method targeted by the present invention, since the previous history erasing electrode and the ferroelectric layer are relatively moved, this method cannot be applied.

The inventor of the present application provides the following method in Japanese Patent Application Laid-Open No. 2005-149647 to solve the above-mentioned problems to be solved in the background art, and to perform multi-stage recording and analog using a ferroelectric layer as a recording medium. As a recording method for a ferroelectric layer for recording and a recording device for a ferroelectric layer, a method and an apparatus having better linearity of input / output characteristics than the conventional method could be realized.

That is, in performing analog recording or multi-step recording on the ferroelectric layer while the ferroelectric layer and the writing means are relatively moved, the writing means applies an electric field to the ferroelectric layer. Prior to recording, a method of erasing the previous history by applying an electric field equal to or higher than the saturation electric field of the ferroelectric layer by the previous history erasing means, which is applied to the dielectric layer. The electric field generated by the previous history eraser is an electric field that alternates between positive and negative. There is provided a method for recording on a ferroelectric layer, wherein the positive and negative values become substantially zero during alternating three or more cycles.

Further, as an actual device, recording on a ferroelectric layer characterized in that it is a device for analog recording or multi-step recording on a ferroelectric layer formed on a substrate of a disk by a disk drive method. Equipment was provided.

However, a new problem has occurred. First, an electrode for erasing the previous history is required. That is, as the basic configuration, three types of electrodes for erasing the previous history, writing, and reading are required, resulting in an increase in cost. In order to reduce the number of electrodes, the previous history erasure, writing, and reading can be performed with one electrode. However, after erasing the previous history, writing is performed after the disk has been rotated once. The speed was not increased. Further, in order to read the written place, it was necessary to wait for the disk to make one more rotation. In addition, when writing and reading are performed with different electrodes, and when the previous history erasure and writing are performed with one electrode, after the previous history erasing, it is necessary to write the disc after one rotation, and writing takes time. It took.
JP-A-8-31027 Japanese Patent Laid-Open No. 9-91776 JP-A-10-289495

The present invention has been made in view of the above problems, and is to find a recording method and a recording apparatus that have a simple electrode configuration and a short writing time when analog recording is performed on a ferroelectric layer.

The invention described in claim 1
When analog recording is performed by applying an electric field by the writing means to the ferroelectric layer while the ferroelectric layer is moving relative to the writing means, the writing means applies the electric field to the ferroelectric layer. A method of recording by applying to
The electric field applied to the ferroelectric layer is an electric field applied by the writing means with an electric signal superimposed with an AC electric signal so that the analog electric signal to be recorded is recorded as a comprehensive line ,
The previous history of the ferroelectric layer is erased by alternating the positive and negative electric fields from the electric field having a strength equal to or higher than the saturation electric field of the ferroelectric layer due to a change in the relative position of the ferroelectric layer and the writing means. The method of analog recording on a ferroelectric layer is characterized in that writing is performed while writing.

The invention described in claim 2
When the ferroelectric layer is moved relative to the writing means, an electric field by the writing means is applied to the ferroelectric layer to perform multi-step recording. A method of recording by applying to a layer,
The electric field applied to the ferroelectric layer is a multistage amplitude electrical signal that approximates the pulsed multistage electrical signal to be recorded at the maximum frequency fm, and the alternating current is recorded so that the electrical signal is recorded as a comprehensive line. the electrical signal superposed signals is a field applied by the writing means,
Due to the change in the relative position of the ferroelectric layer and the writing means, the previous history of the ferroelectric layer is erased by attenuating the electric field at least greater than the saturation electric field of the ferroelectric layer while alternating between positive and negative. The method is a multi-step recording method on a ferroelectric layer, wherein writing is performed while writing.

The invention according to claim 3
3. A ferroelectric recording apparatus according to claim 1, wherein said ferroelectric layer has a writing electrode as a writing means and a reading electrode as a reading means. It is a recording device for a body layer.

The invention according to claim 4
4. The recording device for a ferroelectric layer according to claim 3, wherein the writing electrode also serves as the reading electrode.

The invention described in claim 5
5. The ferroelectric material according to claim 3, wherein the recording device is a recording device for performing analog recording or multistage recording on a ferroelectric layer formed on a substrate of a disk by a disk drive system. Recording device to the layer.

According to the present invention, as a recording method for a ferroelectric layer for performing analog recording using a ferroelectric layer as a recording medium, and a recording device for a ferroelectric layer, previous history erasure and writing are simultaneously performed with one electrode. Thus, an electrode configuration is simpler than that of the conventional method, a writing time is short, and a low-cost recording method and apparatus can be realized.

FIG. 1 shows an example of the structure of a recording apparatus used in the method for recording on a ferroelectric layer according to claim 1. In FIG. 1, a ferroelectric layer 12 is formed on a disk-like substrate 10 via a back electrode 11 and rotates about its axis. The back electrode 11 is formed on the entire back surface where the ferroelectric layer 12 is at least on the surface.

The write signal is formed in the write signal generator 13 by superimposing the AC voltage and the analog signal to be recorded. An example of the voltage waveform is shown in FIG. This voltage is applied to the ferroelectric layer 12 as an electric field formed between the writing electrode 15 at the tip thereof and the back electrode 11 of the ferroelectric layer 12 through the writing head 14 as writing means. The By the mechanism described later, the previous history (previously recorded) of the ferroelectric layer is erased, and at the same time, the desired analog signal to be recorded or the multi-stage signal is a ferroelectric that provides input / output characteristics with good linearity. Recorded as body layer remnant polarization.

On the other hand, the signal of the electric polarization state recorded on the ferroelectric layer 12 is detected as a local electric field strength by the reading electrode 17 at the tip of the reading head 16, and the reading signal 18 is acted by the action of the reading head 16. Is taken out to the outside. Writing and reading can be performed independently. Note that the writing electrode 15 and the reading electrode 17 are held in a state where they are not in contact with the ferroelectric layer 12.

The waveform of the electrical signal generated by the write signal generator illustrated in FIG. 2 will be described below. This waveform is obtained by superimposing an analog signal to be recorded and a constant voltage alternating current. Here, the AC frequency is several times higher than the highest frequency of the signal to be recorded. For example, as shown in FIG. 2, an alternating voltage having a high frequency has a waveform in which the intermediate value of the potential varies depending on a signal to be recorded having a low frequency. From another perspective, the envelope is the signal to be recorded. Here, the height of the AC voltage is set so that the electric field directly below the writing electrode 15 generated by the AC voltage is larger than the saturation electric field of the ferroelectric layer. As a result of the setting, as described later, the previous history of the ferroelectric layer is erased. Note that the structure of the writing electrode is preferably a needle-like structure in which the electric field is concentrated in a narrow region as much as possible in order to increase the resolution (recording density).

Here, in the writing signal generator 13, the frequency of the AC signal superimposed on the analog signal to be recorded is at least four times higher than the highest frequency of the analog signal to be recorded. Necessary to obtain the minimum linearity input / output characteristics required for In order to obtain input / output characteristics having better linearity, the frequency is preferably 6 times or more, and the linearity of the input / output characteristics improves as the magnification increases. However, even if the magnification is about 10 times or more, the linearity of the input / output characteristics is not improved so much. However, there is a limit in terms of the impedance of the write signal system from the write signal generator to the write electrode. Therefore, a structure and configuration of a write signal system that makes the impedance as low as possible is preferable. The writing electrode is preferably a needle-like electrode because the recording density can be increased and the impedance can be lowered.

Since the writing electrode and the ferroelectric layer move relative to each other, the electric field generated by the writing needle electrode during writing applied to the ferroelectric layer increases as the two approach each other. It becomes maximum just below the electrode and decreases with increasing distance. FIG. 7 schematically shows changes in the strength of the electric field applied to the ferroelectric layer that decreases after reaching the maximum.

When the relative speed is low, the analog signal to be recorded is too tightly packed in a narrow portion, and if the recording density exceeds the maximum recording density determined by the characteristics of the ferroelectric layer and the writing electrode, faithful recording cannot be performed.

On the other hand, until the electric field applied to the ferroelectric layer changes from the maximum to substantially zero, the electric polarization of the ferroelectric layer periodically changes due to the AC component, but if the number of cycles is 3 or less, The residual electric polarization faithful to the analog signal to be recorded is not formed on the ferroelectric layer. Four or more cycles are required. Therefore, the frequency of the AC signal is preferably as high as possible, but there is a limitation due to the impedance of the write signal system as described above. Although the polarization reversal speed of the ferroelectric is less than microseconds, the frequency range in which this speed is not a problem is the subject of the present application.

In the following, by the writing method of the present invention, the previous history of the ferroelectric layer (data already written and stored as remanent polarization) is erased, and desired data is written as remanent polarization in the ferroelectric layer. Describe the process.

First, the influence of the magnitude and distribution of the electric field generated by the writing electrode is almost the same as in the case of JP-A-2005-149647, and will be described below with reference to FIG. Since these ultimately affect the resolution (recording density), the resolution according to the writing method of the present invention is almost the same as the resolution in JP-A-2005-149647.

Based on FIG. 4, the state of remanent polarization caused by a method of supplying a multi-stage signal or analog signal continuous in time to the writing electrode and recording it on the ferroelectric layer will be described below. In this case, it is assumed that the previous history erasure of the ferroelectric layer is performed by continuously applying a saturation electric field over the entire target portion.

As an ideal writing electrode, it is assumed that the electric field distribution directly generated by the electrode is uniform and the electric field at other locations is zero. First, a case where the electric field is changed while the ferroelectric layer is moving immediately below the writing electrode will be examined below.

When the writing electric field changes from weak to strong and when it changes from strong to weak, the state of remanent polarization is slightly different due to the hysteresis characteristics of the ferroelectric. In the case of changing from weak to strong, the portion that is weakly polarized (weakly polarized portion) immediately below the writing electrode is in a strongly polarized state (strongly polarized state). On the other hand, when the writing electric field changes from strong to weak, the remnant polarization of the portion that was strongly polarized immediately below the writing electrode remains strongly polarized. Therefore, for example, as shown in FIG. 4A, the strong (++) signal electric field is terminated at t = 1 in (b) after the strong (++) signal electric field is applied at t = 0. The upward polarization is large until a weak (+) signal electric field is applied. T = 2 in (c) is a state in which the ferroelectric layer has moved to the middle of the electrode after applying a weak signal, and the front half of the ferroelectric layer is proportional to the electric field weakness. The degree of polarization is small. (D) shows a state in which the ferroelectric layer passes halfway under the write electrode in a state where the intensity of the write signal is weak. Further, (d) shows a state in which the ferroelectric layer has moved to the exit of the write electrode while the write signal is weak. Next, when a strong signal is applied just before the tip of the portion recorded with the write signal being weak passes through the exit of the write electrode, the polarization due to the weak signal previously recorded as shown in (e) Is erased to a polarization state corresponding to a strong signal. Accordingly, the resolution (recording density) is twice the size (width) of the writing electric field in the moving direction.

In practice, the electric field generated by the writing electrode is not uniform, and does not discontinuously become zero at the end of the electrode, but continuously decreases. Therefore, although the resolution slightly changes from the above analysis result, it can be said that the resolution is approximately twice the width of the writing electrode.

Unlike Japanese Patent Laid-Open No. 2005-149647, in the writing method of the present invention, the previous history of the ferroelectric layer is not erased by applying a saturated electric field in advance as shown in FIG. Elimination is performed by setting the alternating electric field strength due to the above to a saturation electric field or more. Accordingly, if the speed at which the ferroelectric layer passes through the electrode portion is too high, a portion where a saturation electric field is not applied is generated, and the previous history is not completely erased. In order to avoid this phenomenon, the size of the region that reaches or exceeds the saturation electric field by the writing electrode is W, the time required for one turn of the ferroelectric layer to pass is t, and the frequency of the alternating electric field for writing is f In this case, it is necessary that at least W / t> f. Therefore, to increase the recording density, it is effective to increase f as much as possible.

In the method disclosed in Japanese Patent Laid-Open No. 2005-149647, an electric field that alternates between positive and negative is used as the previous history erasing electric field, but there is one place (one segment, one track) to be erased, and a plurality of alternating The process of erasing the previous history using the pulse of FIG. 6 (FIGS. 6A and 6B) or alternating current (FIG. 6C) will be described below with reference to FIGS. The same applies when erasing and rewriting the entire recording.

When erasing, the maximum intensity of the previous history erasing electric field is equal to or higher than the saturation electric field of the ferroelectric layer. The number of alternations should be about several times. If the number of times of alternating is small, the previous history erasing effect becomes incomplete, and the correlation (reproducibility) between the writing electric field and the residual electric field decreases. For this reason, the accuracy of analog recording and multi-value recording decreases. Depending on the reproducibility required, it is desirable to alternate for at least three cycles. Usually, it is sufficient to alternate 5 to 6 times. However, when high reproducibility is required, an alternating electric field for previous history erasing is applied many more times.

FIG. 7 illustrates how the applied electric field changes as the ferroelectric layer approaches the erasing electrode, passes below, and moves away. The previous history erasing electrode generates an alternating electric field having a constant strength. The increase or decrease in the strength of the electric field applied to the ferroelectric layer is drawn to be linear, but actually it depends on the shape of the electrode. FIG. 8 shows the history of polarization in the ferroelectric layer at that time. The polarization eventually converges near the origin.

A method of erasing the history by gradually decreasing the electric field is described in JP-A-11-305257. In this case, the positions of the erasing electrode and the ferroelectric layer are fixed, and the erasing electric field is set to the time. Has been reduced. FIG. 9 shows the relationship between the writing electric field E and the remanent polarization Pr at the time of writing when the previous history is erased and initialized by the method using this alternating electric field that attenuates.

The reason will be described below with reference to FIG. However, this is a case where the degree of attenuation of the applied history erasing electric field is assumed to be substantially smooth, that is, an ideal case. In FIG. 7, the applied electric field alternates about 3.5 cycles from the maximum (saturation electric field) to zero, but this level is not substantially smooth, and the initialization polarization curve is slightly deviated from the origin. Not smooth. FIG. 9 is an initialization curve in an ideal case where the number of alternating times is large enough to be regarded as infinite. If the number of times of alternating is substantially about 10 cycles, a smooth initialization curve almost passing through the origin as shown in FIG. 9 is obtained.

The initialization polarization curve of FIG. 5 is an envelope of the turning point of the decrease in polarization P when the previous history is erased by the dotted line of FIG. 8, that is, the initialization method using the method using an alternating electric field. When the write electric field E is applied, the polarization P is generated along this line. The residual polarization Pr becomes a value according to a hysteresis curve (minor loop) corresponding to the generated polarization P. That is, in FIG. 5, the ferroelectric layer polarized to P1 by the electric field of E1 has a residual polarization of Pr1 when the electric field is zero, but the curves P1 to Pr1 are minor loops in which the polarization of P1 is the maximum polarization. Is part of. When an electric field of −E2 is applied in the negative direction, it is polarized to −P2, and the residual polarization becomes −Pr2. Using FIG. 5 and the minor loop, the relationship between the write electric field and the remanent polarization can be obtained on the diagram. The results are shown in FIGS. 3A and 3B show the results of studying the writing process to the ferroelectric layer in the present invention using this method.

As an initialization method, in a method using an alternating electric field that gradually decreases and the maximum electric field is equal to or higher than the saturation electric field Em, a range of about −7 to +7 in FIG. 5 may be used as the range of the write electric field. it can. Further, the range in which the writing electric field E and the remanent polarization Pr have a substantially linear relationship is wide from -3 to +3, and the linearity is high, which is suitable for analog recording. Further, since the gradient of the relationship between the writing electric field and the recorded residual polarization is gentle, there is little need to control the electric field with high accuracy. The preceding history erasing process and writing process in JP-A-2005-149647 have been described above.

Note that, when performing multi-stage recording by the method disclosed in Japanese Patent Laid-Open No. 2005-149647, the case of using a temporally continuous recording signal is described, but a temporally discontinuous pulsed recording signal is similarly described. It can be used and also in the method and apparatus of the present invention.

It is presumed that the previous history erasing process and the writing process in the present invention are based on the following mechanism. This will be described with reference to FIG.
FIG. 3A shows the case where the electric field (signal electric field) due to the signal to be recorded is zero, that is, in a portion where the short-time average voltage is zero as shown by point A in FIG. In FIG. 3A, the recording electric field changes with time when the ferroelectric layer moves relatively from directly below the writing electrode to a place where the electric field by the writing electrode does not reach. It is a state of. In addition, the state of the change in electrical polarization of the ferroelectric layer with time is shown.

Actually, since the electric field changes with time, it is only a short time to be symmetric as shown in FIG. 3A, but when the relative velocity between the writing electrode and the ferroelectric layer is high. Corresponding to the fact that the signal electric field is zero, the electric field applied to the ferroelectric layer is almost symmetrical in the positive and negative directions up to a place where the electric field by the writing electrode does not reach. If the initial applied electric field is greater than or equal to the saturation electric field of the ferroelectric layer, whatever the previous history, that is, the magnitude of the remanent polarization, all depends on the saturation electric field. Erased. The electric polarization induced in the ferroelectric layer moves on a symmetrical hysteresis curve that decreases with time, and the residual polarization finally becomes zero. That is, in FIG. 3A, the signal is recorded with zero polarization. In this case, even if it is not completely zero, the electric field applied to the ferroelectric layer can be regarded as substantially zero as long as the residual polarization is acceptable as noise.

On the other hand, FIG. 3B shows the case where the write signal voltage is Vt and the corresponding write signal electric field is Et, that is, the case at point B in FIG. In this case, the electric field applied to the ferroelectric layer is biased by Et. If the electric field initially applied is equal to or higher than the saturation electric field of the ferroelectric layer, the previous history is completely erased. Then, the electrical polarization induced in the ferroelectric layer decreases with time until the relative position of the writing electrode and the ferroelectric layer moves away and the electric field of the writing electrode does not reach. However, since there is a bias, it moves on an asymmetric hysteresis curve as shown in the figure, and finally a residual polarization Pr is generated, resulting in a recorded signal.

That is, when an alternating current having a frequency several times higher than the highest frequency of the electrical signal to be recorded is superimposed on the signal to be recorded and applied to the ferroelectric layer by the writing electrode, the electric field applied immediately below the electrode Until the minimum strength of the ferroelectric layer is greater than the saturation electric field of the ferroelectric layer and the electrode and the recorded portion of the ferroelectric layer are moved away to a place where the strength of the applied electric field can be regarded as substantially zero. When the number of applied alternating electric fields is several times or more, the magnitude of remanent polarization recorded in the ferroelectric layer is recorded in the ferroelectric layer when recorded by the method of Japanese Patent Application No. 2003-38751. The remanent polarization is almost the same.

In order to improve the input / output characteristics, the frequency of the alternating current superimposed here needs to be at least four times the highest frequency of the electrical signal to be recorded, and preferably 6 to 7 times or more. The input / output characteristics improve as the AC frequency increases, but the effect reaches its peak and is hardly worth 10 times or more. Further, the number of times of alternating until the electric field by the electrode becomes substantially zero is required at least 4 times, preferably 6 to 7 times or more. On the other hand, there is almost no value for 10 times or more.

However, as described above, the higher the AC frequency, the better from the viewpoint of resolution (recording density). For example, when used for recording audio, the maximum frequency is usually about 20 kHz. Therefore, the frequency of the alternating current to be superimposed is 200 kHz even if it is 10 times, and it can be sufficiently handled by a normal signal circuit. However, a recording density higher than the recording density based on the minimum polarization size of the ferroelectric layer is impossible in principle.

In claim 2, as a method for the multi-stage amplitude electrical signals that approximates the multi-stage signal pulsed at a maximum frequency f _m is to be recorded using the highest passing frequency f _m, for example, as a band-pass filter There is a method for limiting the frequency range of a signal. As another method, a pulsed signal to be recorded can be used as a trigger to generate a signal in proportion to the amplitude of the pulsed signal whose frequency is f and whose amplitude is to be recorded. And that more than four times the least f _m the frequency of the alternating current to be superposed, it is necessary to perform faithful multistage recording the amplitude is the same as described above with respect to claim 1.

The actual structure will be described with reference to the structural schematic diagram described in the first embodiment shown in FIG. In FIG. 11, the distance between the tip of the write electrode 112 and the recording surface of the ferroelectric recording (use) disk affects the electric field strength, and is therefore controlled to be as constant as possible during writing. The control mechanism for the position in the height direction is not shown in order to make the drawing easy to see, but the same mechanism as the control mechanism shown in the reading head unit is used. In addition, the recording position is adjusted by a mechanism that moves the column portion to which the cantilever lever 113 is attached in the horizontal direction. As a mechanism for that purpose, for example, a method of moving the table with the cantilever lever shown in the figure in the horizontal direction, a mechanism of moving the cantilever lever in the radial direction of the disk, and a table with the cantilever lever attached are shown. There is a method of combining rotating mechanisms. In addition, a position control mechanism and a tracking mechanism used in a CD or DVD recording disk device can be used.

On the other hand, the reading electrode 116 is attached to a portion near the tip of the cantilever lever of the reading head portion in FIG. As a method of reading the remanent polarization of the ferroelectric layer, when the reading electrode exerts an electric attractive force or repulsive force with the remanent polarization of the ferroelectric layer immediately below, a method of detecting the height of the reading electrode Is used. Actually, for example, the height direction is measured by a reading electrode position detection mechanism that detects the reflection angle of light, and the reading position control mechanism (reading electrode position control device and reading electrode height control device 118) For example, a position control device using an electrostatic force or a magnetic force provided in the position control device unit is adjusted using a feedback mechanism so that the gap between the disk and the disk becomes constant. As the reading method, for example, as shown in the drawing, the recording signal on the reading electrode and the disk, that is, the strength of the control signal for applying an electrostatic force acting between the electric polarization to the position control device and the height direction of the reading electrode. There is a method of obtaining from the position value.

Further, as the reading electrode 116, there is a method of reading a signal recorded as a change in resistance value by using, for example, a material whose resistance value changes depending on the intensity of an electric field. Also in this case, when polarization due to electrostatic induction occurs in the electrode and the height direction of the electrode changes, the read recording signal is corrected based on the information from the height position detection device.

In the case of reading, it is necessary to move the reading electrode to the recorded position, but the mechanism is the same as that used for the writing electrode.

FIG. 12 shows the configuration of an apparatus for writing and reading with a single head. As in the case of FIG. 11, the data to be recorded is mixed with a signal having a frequency of at least four times by the signal generator for writing to become a superimposed signal, which is connected to the write electrode and the ground side of the disk. Recording is performed on the ferroelectric layer by an electric field formed by the tip and the disk surface. For reading, there are a method of using an electrostatic force as in FIG. 11 and a method of using a material whose electric resistance varies depending on the strength of an electric field for an electrode. The apparatus configuration is simpler than the apparatus shown in FIG. 11, but it is necessary to select a material suitable for writing and suitable for reading as the electrode material. Further, when reading a recorded signal, even if it is desired to read it immediately after recording, it will be at least after one revolution.

FIG. 11 shows an embodiment of the recording apparatus of the present invention, which is used for recording and reproducing audio. A disk drive recording apparatus comprising a ferroelectric layer formed on a disk substrate having a function capable of performing analog recording of sound by the method according to claim 1. The one described in FIG. 11 of Japanese Patent Application No. 2000-387571 is basically used, and has a writing head portion and a reading head portion, and can be read while writing. The structure of the reading head unit including the reading electrode is the same as that described in Japanese Patent Application No. 2000-387571.

This will be described below with reference to FIG. The audio signal to be recorded has a frequency band of 20 Hz to 20 kHz. The audio signal is written by a writing signal generator and superimposed with 200 kHz alternating current. One of the output signals is connected to the back surface of the ferroelectric recording disk, one being the ground side, and the other is connected to the writing electrode attached to the tip of the cantilever 112 of the writing head. When there is no signal to be recorded, that is, when the output signal intensity is zero, the maximum value of the electric field formed by the tip of the writing electrode and the ground plane of the disk immediately below it is the value of the ferroelectric layer. It is adjusted to be 1.2 times the saturation electric field.

The ferroelectric disk 110 is formed by depositing ITO (film thickness 0.2 μm) as a back electrode on a disk-shaped (diameter 120 mm, thickness 1.0 mm) glass substrate by a sputtering method, and a ferroelectric substance thereon. As a layer, lead zirconate titanate (film thickness: 100 nm) is formed by sputtering. A rotation driving hole is formed at the center of the glass substrate, and the ITO electrode and the conductive rotation driving shaft can be electrically connected.
The ferroelectric disk 110 is rotated at 1800 rpm by a rotating mechanism 114.

Each of the writing electrode 112 and the reading electrode 116 was a platinum wire, and the tip was polished to a radius of curvature of 200 nm by an electrolytic polishing method. The writing electrode 112 and the reading electrode 116 are both attached near the tip of the cantilever lever 113. The support portion of the cantilever lever 113 is attached to the XY moving mechanism, and the electrode portion can be moved to a necessary place. Although not shown, the cantilever lever is kept at a certain distance from the ferroelectric layer by the air levitation method used in the magnetic disk device.

A constant potential is applied to the reading electrode 116 from the reading electrode position controller, and an electric attractive force or repulsive force acts between the reading electrode 116 and the remanent polarization recorded in the ferroelectric layer. Therefore, the sensor unit including the reading electrode 116 moves in the vertical direction. The back reflecting surface is irradiated with the laser beam 115, the reflected light is detected by the optical sensor 117, a signal enters the position detection sensor, and the vertical position of the reading electrode 116 is detected. The detected signal is input as a feedback signal to the position control power supply unit, and is controlled by the position control device 118 so that the reading sensor unit maintains a fixed position and does not move up and down. Further, the magnitude of the control signal is taken out as the magnitude of the remanent polarization, that is, the magnitude of the recorded signal.

Note that, when the magnitude of the remanent polarization recorded by the electric field of the reading electrode 116 changes, the writing electrode is rewritten after reading. This is not necessary if the potential of the reading electrode is kept at 0.

When a pulse signal is recorded by the apparatus of the present invention, it is possible to achieve a ferroelectric layer polarization region of 0.2 mm, a bit period of 0.4 mm, and a recording density of 400 Mb / cm ² . In the case of a pulse signal, the signal to be recorded is recorded as a signal having a frequency of 20 kHz that is the upper limit of processing of the signal generator for writing. Further, when an audio signal is recorded and reproduced, it is not necessary to digitize the signal to be thinned out or interpolated, so that a highly faithful reproduced sound can be obtained.

In the apparatus of Example 1, the writing electrode and the reading electrode are shared. FIG. 12 shows a schematic diagram of the structure. The read / write head portion of Example 1 was used as the writing / reading head portion. Writing can be performed while erasing the previous history of the ferroelectric layer. However, the connection to the electrode is switched between writing and reading. Therefore, it cannot be read while writing.

The position control device 118 can suppress a change in the distance between the ferroelectric layer and the writing / reading electrode 121 due to a writing electric field during writing.

FIG. 13 shows an outline of an apparatus in which one electrode disclosed in JP-A-2005-149647 is used. First, the signal of the erasing signal generator is connected to the electrode to erase the previous history of the ferroelectric layer at the place where writing is desired. Thereafter, since the connection to the electrode is switched to the signal generator for writing and writing is performed, it takes time to write as compared with the apparatus of FIG.

It is a schematic block diagram of the apparatus used for the recording method to the ferroelectric layer based on this invention. It is an example of a voltage waveform of a write signal generated by a write signal generator. It is explanatory drawing of the write-in process to the ferroelectric layer concerning this invention. It is explanatory drawing of the mode of polarization of the electric field for writing, and a ferroelectric layer for description of resolution | decomposability. It is a graph which shows the relationship between the write electric field when a previous history is erase | eliminated by the initialization method by the method of applying a decaying alternating electric field, and remanent polarization. It is explanatory drawing which shows the example of the alternating electric field for previous history erasure | elimination, (a) is a several pulse to alternate, (b) The pulse to which it alternates continuously, (c) Alternating current. FIG. 5 is a graph showing a change over time after the electric field strength applied to one point of a moving ferroelectric layer reaches a maximum value when an alternating electric field or an alternating electric field having a constant intensity is applied by a previous history erasing electrode; . 8 is a history of polarization in the ferroelectric layer when the electric field of FIG. 7 is applied. It is a graph which shows the relationship between the ideal write electric field to the ferroelectric layer which erased the previous history by the initialization method by the method of applying a decaying alternating electric field, and remanent polarization. It is a graph which shows the analog signal discrete in time (t) and space (T), and its recording example. 1 is a schematic configuration diagram of a recording device for a ferroelectric layer according to Example 1. FIG. 6 is a schematic configuration diagram of a recording device for a ferroelectric layer according to Embodiment 2. FIG. It is the structure schematic of the recording apparatus to the ferroelectric layer of the structure of one electrode in a prior art. It is a graph which shows the example of the hysteresis of a ferroelectric substance. 2A is a conceptual diagram illustrating an example of a conventional recording apparatus using a ferroelectric film, and FIG. It is explanatory drawing which shows the state of the electric signal and the polarization of a ferroelectric layer which show the example of the conventional method which performs analog recording to a ferroelectric film.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Substrate 11 ... Surface electrode 12 ... Ferroelectric layer 13 ... Write signal generator 14 ... Writing head 15 ... Writing needle electrode 16 ... Reading head 17 ... reading needle electrode 18 ... reading signal 110 ... ferroelectric recording disk 112 ... writing electrode 113 ... cantilever lever 114 ... rotating mechanism 115 ..Laser beam 116... Reading electrode 117... Optical sensor 118... Electrode height control device 119... Read signal 131 .. writing and reading (and erasing) electrode 200 ... disk 210 ... ferroelectric layer 211 ... writing electrode 212 ... cantilever 221 ... write signal generation circuit 241 ... rotating shaft 242 ... motor

Claims (5)

When analog recording is performed by applying an electric field by the writing means to the ferroelectric layer while the ferroelectric layer is moving relative to the writing means, the writing means applies the electric field to the ferroelectric layer. A method of recording by applying to
The electric field applied to the ferroelectric layer is an electric field applied by the writing means with an electric signal superimposed with an AC electric signal so that the analog electric signal to be recorded is recorded as a comprehensive line ,
The previous history of the ferroelectric layer is erased by alternating the positive and negative electric fields from the electric field having a strength equal to or higher than the saturation electric field of the ferroelectric layer due to a change in the relative position of the ferroelectric layer and the writing means. An analog recording method for a ferroelectric layer, wherein writing is performed while writing. When the ferroelectric layer is moved relative to the writing means, an electric field by the writing means is applied to the ferroelectric layer to perform multi-step recording. A method of recording by applying to a layer,
The electric field applied to the ferroelectric layer is a multistage amplitude electrical signal that approximates the pulsed multistage electrical signal to be recorded at the maximum frequency fm, and the alternating current is recorded so that the electrical signal is recorded as a comprehensive line. the electrical signal superposed signals is a field applied by the writing means,
Due to the change in the relative position of the ferroelectric layer and the writing means, the previous history of the ferroelectric layer is erased by attenuating the electric field at least greater than the saturation electric field of the ferroelectric layer while alternating between positive and negative. A multi-step recording method for a ferroelectric layer, wherein writing is performed while writing. 3. A ferroelectric recording apparatus according to claim 1, wherein said ferroelectric layer has a writing electrode as a writing means and a reading electrode as a reading means. Recording device for body layer 4. The recording device for a ferroelectric layer according to claim 3, wherein the writing electrode also serves as the reading electrode. 5. The ferroelectric material according to claim 3, wherein the recording device is a recording device for performing analog recording or multistage recording on a ferroelectric layer formed on a substrate of a disk by a disk drive system. Recording device to layer.