JPH0660446A - Information recording method - Google Patents

Abstract

PURPOSE:To increase the velocity of the reversion of polarization and to record at high speed by imparting energy other than a voltage on a part of an information recording medium on which the voltage is applied and increasing a number of generated minor carriers. CONSTITUTION:An information recording medium 10 is fixed on a turntable 20 by an air chuck and the table 20 is made to be an electrode on one side for applying the voltage at the time of recording. A movable needlelike electrode 21 is used as the other electrode, one end of an optical fiber is arranged on the upper side of the electrode 21 and a transmitted light 24 irradiates the part of the medium 10 brought into contact with the electrode 21. The light 24 is emitted from a halogen lamp 23 and inputted into the fiber from the other end of the fiber 22. Thus, the light 24 is imparted as energy other than the voltage and increases the generated number of the minor carrier on the part applied with the voltage of the medium 10. Consequently, the velocity of polarization reversion is increased and high speed recording is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording method, and more particularly to a method for recording information on an information recording medium having a semiconductor layer and a ferroelectric layer according to the polarization direction of the ferroelectric substance. It is about.

[0002]

2. Description of the Related Art Japanese Unexamined Patent Publication (Kokai) No. 57-27447 discloses an information recording medium capable of recording various kinds of information such as image signals and audio signals, and further used as a data memory for computers and capable of high-density recording. A semiconductor layer and a ferroelectric layer formed on the semiconductor layer,
It is known that information is recorded depending on the polarization direction of the ferroelectric substance. Recording on this information recording medium is performed by moving a conductive head (electrode) on the ferroelectric layer and applying a voltage to the layer, thereby selectively selecting a predetermined portion of the ferroelectric layer in a predetermined direction. It is performed by polarization. Information reproduction from the information recording medium is performed by detecting a capacitance change of the recording medium due to the depletion layer formed in the semiconductor layer due to the polarization of the ferroelectric substance, by the conductive head.

[0003]

By the way, when information is recorded on the above information recording medium, the recording speed is determined by the polarization inversion speed of the ferroelectric substance. It has been conventionally considered that the speed of this polarization reversal takes a unique value for each ferroelectric material. Although this is true in one aspect, it has been found from the research by the present inventor that the polarization inversion speed may be different even if the ferroelectric materials are the same. When the speed of this polarization reversal decreases, the recording speed naturally decreases, and the time required for information recording increases.

The present invention has been made in view of the above circumstances, and provides an information recording method for increasing the speed of polarization reversal to the limit for each ferroelectric material in any case, thereby enabling high speed recording. It is intended to be provided.

[0005]

According to the information recording method of the present invention, a voltage is applied to an information recording medium having a semiconductor layer and a ferroelectric layer as described above to change the polarization direction of the ferroelectric substance. The information recording method for recording information is characterized in that energy other than voltage for increasing the number of minority carriers generated, that is, light or heat is applied to the portion of the information recording medium to which the voltage is applied. It is a thing.

When light is applied to the voltage application portion, a normal tungsten lamp, halogen lamp, mercury lamp, semiconductor laser, LED or the like can be used as a light source. Then, these light sources may be geometrically arranged to irradiate the entire information recording medium with light, or an optical guide such as an optical system or an optical fiber adopted in an optical disk pickup may be used. Then, the light may be irradiated only to the very periphery of the voltage application electrode.

On the other hand, when heating the voltage application portion, the entire information recording medium may be heated, or the information recording medium surface may be focused as in the case of information recording and reproduction on the optical disc. The heated light beam may be used for local heating.

As the ferroelectric material used in the method of the present invention, an inorganic material is a ferroelectric material having a perovskite structure, barium titanate, a lead titanate-lead zirconate solid solution, bismuth titanate, a tungsten bronze structure. Strontium niobate-barium niobate, glycine sulfate, potassium nitrate, potassium phosphate, C (NH ₂ ) ₃ A
l (SO ₄ ) ₂ 6H ₂ O, sodium nitrite, SbSI
Etc. As the organic ferroelectric material, vinylidene fluoride (VDF) polymer or a copolymer containing the same, odd-order nylon, vinylidene cyanide or a copolymer containing it, vinyl fluoride (V
Examples include F) polymers and copolymers containing them.

When the above-mentioned light irradiation is carried out, the ferroelectric layer is formed of a material that absorbs light as little as possible, or is formed in a film thickness that allows light to sufficiently pass therethrough, in order to reach the semiconductor layer. It is necessary. In addition, windows for allowing light to pass through may be provided in the ferroelectric layer at a certain interval.

On the other hand, as the semiconductor layer, a substrate made of a semiconductor may be used as it is. Alternatively, a semiconductor layer may be formed on the substrate by using plastic, glass, or metal in which guide grooves or pits or pits indicating sector information are provided in advance as the substrate. As well-known semiconductors in this case, Si, G
e, III-V group compound semiconductors represented by GaAs, and further II-VI group compound semiconductors can be used. Moreover, polypyrrole, polythiophene, etc. can be used as an organic semiconductor. These may be single crystal, polycrystal or amorphous. The semiconductor resistivity is 0.
It is good to set about 01Ωcm to 1000Ωcm, preferably 1Ω
cm to 100 Ωcm.

Among these semiconductors, n-type or p-type silicon doped with impurities is preferable, and the impurity concentration in silicon is about 10 ¹⁹ to 10 ²³ m ⁻³ , preferably
It is 10 ²⁰ to 10 ²² m ^-3 .

[0012]

First, as described above, the point that the polarization inversion speed is different even if the ferroelectric materials are the same will be described in detail. According to the research conducted by the present inventor, when recording is performed by applying + and-alternate voltages to the information recording medium, the polarization reversal speed becomes small on a specific side. For example, when a p-type semiconductor is used for the semiconductor layer, it is the side to which + voltage is applied,
When a type semiconductor is used, it is the side to which a voltage is applied. In these cases, focusing on the fact that the direction of the applied voltage coincides with the direction in which the depletion layer is formed in the semiconductor layer, the cause of the decrease in the polarization inversion speed is that the ferroelectric layer side of the semiconductor layer is It is presumed that the polarization inversion is rate-determined by the number of inversion carriers that should be accumulated on the surface.

Therefore, when voltage is applied to the information recording medium and light is irradiated in parallel with it in order to increase the number of minority carriers generated, conventionally, in the case where the polarization inversion becomes slow as described above, the polarization inversion occurs. It was confirmed that the speed obviously increased. It is considered that this action is mainly due to the result that electron-hole pairs are generated by the photons incident on the semiconductor layer, and these electron-hole pairs additively contribute as inversion carriers.

The preferable wavelength of the light with which the information recording medium is irradiated depends on the material constituting the semiconductor layer, and it is desirable to use the light in the wavelength range where the absorption coefficient and the quantum conversion efficiency of the semiconductor material are high. For example, when a semiconductor made of Si is used, it is desirable to use light having a wavelength of about 400 to 1000 nm, and especially about 700 nm.

On the other hand, the preferable intensity of the irradiation light depends on the polarization of the material forming the ferroelectric layer, the recording voltage, and the nature of the minority carriers in the semiconductor layer, and the required recording. It may be appropriately set in consideration of the speed, that is, the polarization inversion speed. For example, when the above-mentioned materials are used as the ferroelectric material and a semiconductor layer made of Si is used and the polarization inversion speed is desired to be set to about 0.1 μsec, the light intensity is set to 100 W / m ² or more. desirable. This is a light intensity such that a portion having a diameter of 1 mm is irradiated with 0.1 mW of light.

The polarization reversal speed is similarly improved by irradiating the information recording medium with light as described above or by heating the voltage application portion of the information recording medium. In that case, it is considered that electron-hole pairs are generated by the thermal excitation, and they contribute additively as inversion carriers. When this heating is performed, the information recording medium is usually heated to 100 ° C. or higher.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on the embodiments shown in the drawings. <Embodiment 1> FIG. 1 shows an example of an apparatus for carrying out the information recording method of the present invention, and FIG. 2 conceptually shows a side sectional shape of an information recording medium 10 on which information is recorded by this method. It is shown in. First, the information recording medium 10 will be described.

The information recording medium 10 comprises a semiconductor layer 11 and an organic ferroelectric layer 13 formed thereon with an insulating layer 12 interposed therebetween. In this embodiment, the semiconductor substrate is used as it is for the semiconductor layer 11
As this substrate, a p-type silicon wafer having a resistivity of 5 Ωcm and an impurity concentration of 5 × 10 ²¹ m ^-3 is used. The insulating layer 12 is formed by layering silicon oxide (SiO ₂ ) in a thickness of 50 nm on the silicon wafer by a thermal oxidation method. On top of this, an organic ferroelectric VDF / TrFE copolymer (VDF of 65 mol
%) Thin film to form the organic ferroelectric layer 13.

This thin film formation is performed as follows, for example. First, the VDF / TrFE copolymer was dissolved in methyl ethyl ketone (MEK) at 10 wt%,
The rotation speed of this solution is 5000 rp using a commercially available spin coater.
It is applied on a silicon wafer under the condition of shaking off for 10 seconds at m. Then, this coating film is annealed in an air atmosphere in an oven at 145 ° C. for 2 hours to give a film thickness of 1 μm.
A thin film of VDF / TrFE copolymer is formed.

It is not always necessary to provide the insulating layer 12 between the semiconductor layer 11 and the organic ferroelectric layer 13, but
Providing this insulating layer 12 is more preferable because problems such as carrier injection into the ferroelectric substance can be avoided. When silicon is used as the semiconductor as in this embodiment, the insulating layer 12 is made of S.
It is desirable to form it from iO ₂ , and its film thickness is 100 nm.
The following is preferable.

The information recording medium 10 having the above structure is shown in FIG.
Information is recorded by the device. In this case, the information recording medium 10 is fixed to the turntable 20 by an air chuck or the like as shown in the figure, and the turntable 20 is used as one electrode for voltage application during recording. A movable needle electrode 21 is used as the other electrode for applying the voltage. In this example, as the needle electrode 21, a tungsten needle having a bottom surface diameter of 50 μm and plated with gold is used. This needle electrode 21
One end of the optical fiber 22 is disposed above the optical fiber 22, and the light 24 emitted from the optical fiber 22 is applied to the portion of the information recording medium 10 in contact with the needle electrode 21. This light 24 is emitted from the halogen lamp 23 and is incident on the optical fiber 22 from the other end thereof, and the light intensity on the information recording medium 10 is about 100 W / m ² .

With the above turntable 20 fixed,
By applying a voltage from the pulse power supply 25 to the organic ferroelectric layer 13 via the needle electrode 21 and the turntable 20 while the needle electrode 21 is brought into contact with the organic ferroelectric layer 13 side of the information recording medium 10. The portion of the organic ferroelectric material facing the needle electrode 21 is polarized in a predetermined direction. Thereby, information can be recorded with this polarization direction.

When electrical polarization is generated in the ferroelectric layer 13 in this way, as shown in FIG. 1, the polarization direction of the ferroelectric layer 13 is downward (direction facing the semiconductor layer 11 side). Since a depletion layer 14 is generated in the semiconductor layer 11, this depletion layer 14
The recorded information can be read by detecting a change in the electrostatic capacitance due to a known pickup circuit.

In the present embodiment, in order to evaluate the polarization reversal, the needle electrode 21 has an amplitude of ± 100 V as a signal voltage and a pulse width.
A voltage of 10 msec was applied and the polarization reversal time, that is, the recording time was measured. The recording time is the time until the electric charge accumulated in Ca in FIG. 1 is measured and it is saturated. Note that FIG. 3 shows the waveform of this pulse voltage and the change state of the charge accumulated in Ca. In the figure, the first recording voltage with a pulse width of 100 msec is for initialization to make the polarization directions of the ferroelectric layer 12 uniform.

The results of examining the recording time as described above are shown in Table 1 together with the result of Comparative Example 1. This comparative example 1
Is the same recording device and information recording medium as those of the first embodiment.
Information recording was performed in the same manner as in Example 1 except that 10 was used and the halogen lamp 23 was turned off.

[0026]

[Table 1]

V used in Example 1 and Comparative Example 1
The intrinsic polarization reversal rate of DF / TrEE copolymer is about 10μ
sec. Therefore, in this embodiment, it is considered that the recording speed is limited by the property of the ferroelectric material itself. Since there are ferroelectric materials having an inherent polarization reversal speed faster than 10 μsec, the use of them also makes it possible to further increase the recording speed.

On the other hand, in Comparative Example 1 in which light irradiation is not performed, the recording time when a + voltage is applied is significantly longer than that in Example 1. The semiconductor layer used in Comparative Example 1 is p-type, and the depletion layer is formed on the + potential side. Therefore, as described above, it is considered that when the + voltage is applied, the number of inversion carriers generated is small and the polarization inversion is delayed. On the other hand, by performing light irradiation as in Example 1, it is considered that the number of minority carriers generated increases and the recording time is shortened to a value determined by the property of the ferroelectric material itself as described above. To be

<Embodiment 2> Next, using the same information recording medium 10 and recording apparatus as in Embodiment 1, it was investigated whether or not polarization reversal can be normally performed even if recording is performed with a short recording pulse width. The evaluation of polarization reversal was performed by measuring the electrostatic capacity of the information recording medium 10 as in the actual signal reproduction. The capacitance measurement was performed using a commercially available LCR meter.

First, initialization is performed to make polarization uniform by a minus pulse (-200 V), and then an initial value of capacitance is measured, and then a pulse voltage of +100 V (pulse width is 20 μse).
Recording was performed for two times (c, 20 msec), and the electrostatic capacity after recording was similarly measured. The results are shown in Table 2. In Comparative Example 2, recording is performed in the same manner as in Example 2 except that light irradiation is not performed.

[0031]

[Table 2]

As shown in Table 2, in Comparative Example 2 in which no light irradiation was performed, the recording time, that is, the pulse width was 20 m.
Assuming sec, the capacitance Ca is 0.12pF from the initial value of 0.15pF
The recording time is 20μse, although the recording is done after falling to F.
It can be seen that when the value is set to be short, the capacitance does not change from the initial value and recording cannot be performed.

On the other hand, Example 2 in which light irradiation was performed
In, even if the recording time is set as short as 20 μsec,
It can be seen that the recording time is reduced as in the case of 20 msec, and normal recording can be performed.

[0034]

As described in detail above, in the information recording method of the present invention, polarization is achieved by applying energy other than the voltage for increasing the number of minority carriers to the portion of the information recording medium to which the voltage is applied. The reversal speed is sufficiently increased, which enables extremely high speed recording.

[Brief description of drawings]

FIG. 1 is a schematic side view showing an example of an apparatus for carrying out the method of the present invention.

2 is a schematic view showing a side cross-sectional shape of an information recording medium on which information is recorded by the apparatus of FIG.

FIG. 3 is a graph showing a waveform of a recording voltage and a state of change of inversion charge in the device of FIG.

[Explanation of symbols]

 10 Information recording medium 11 Semiconductor layer 12 Insulating layer 13 Ferroelectric layer 14 Depletion layer 20 Turntable 21 Needle-shaped electrode 22 Optical fiber 23 Halogen lamp 24 Light emitted to information recording medium 25 Pulsed power supply

Claims (3)

[Claims] 1. Information for recording information by applying a voltage to an information recording medium having a semiconductor layer and a ferroelectric layer formed on the semiconductor layer to record information according to the polarization direction of the ferroelectric. In the recording method, an energy other than a voltage for increasing the number of minority carriers generated is applied to the portion of the information recording medium to which the voltage is applied. 2. Information for recording information according to a polarization direction of the ferroelectric substance by applying a voltage to an information recording medium having a semiconductor layer and a ferroelectric layer formed on the semiconductor layer. In the recording method, a portion of the information recording medium to which the voltage is applied is irradiated with light, which is an information recording method. 3. Information for recording information by applying a voltage to an information recording medium having a semiconductor layer and a ferroelectric layer formed on the semiconductor layer to record information according to the polarization direction of the ferroelectric. In the recording method, the portion of the information recording medium to which the voltage is applied is heated.