JPH0150979B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention records information signals by accumulating charges using an information recording medium formed by forming an insulating film on a semiconductor substrate, and The present invention relates to an information recording medium used in a signal recording and reproducing apparatus that detects changes and reproduces recorded information signals.

[Technical background of the invention and its problems]

Conventional disk-type information recording media include magnetic disks, optical disks, and capacitive disks. Magnetic disks have the advantage of being able to perform recording, playback, and erasing electromagnetically, and can be played back immediately after recording, but unless the track width is wide, sufficient playback is not possible. However, it has the disadvantage of short recording time. On the other hand, optical discs use laser beams for recording and reproducing, so the track width can be narrowed and extremely high-density recording can be performed.
For example, 60 minutes of video and audio signals can be recorded on one side of a disk with a diameter of about 30 cm, but after recording, several chemical and physical processes are essentially required to obtain a playable disk. This is a drawback. Also, since this method is irreversible recording,
It is very difficult to erase and re-record.

On the other hand, an information recording medium having a structure in which an oxide film is formed on a semiconductor substrate and a nitride film, for example, is formed as an insulating film having a charge storage function is used, and a recording electrode that moves relatively on this recording medium is used. A recording signal voltage is applied through the nitride film, and the signal is recorded by accumulating charges in the nitride film.On the other hand, the recorded signal is reproduced by static electricity generated by a depletion layer in the semiconductor substrate that occurs in response to the accumulated charges in the nitride film. A new signal recording and reproducing device has been proposed that detects changes in capacitance through a reproducing electrode that moves relatively over a recording medium. This method allows for extremely high-density recording, similar to optical discs, and also allows for erasing and
It has the excellent feature of being relatively easy to re-record.

However, since a high voltage pulse of 40 to 50 V is required as the recording signal voltage, a considerable amount of current flows through the recording electrode. Therefore, there was a problem in that it was difficult to make the life of the recording electrode sufficiently long.

[Purpose of the invention]

An object of the present invention is to form an insulating film on a semiconductor substrate to enable high-density signal recording, reproduction, and erasing.
It is an object of the present invention to provide an information recording medium that allows re-recording, lowers the voltage required for recording, and significantly increases the lifespan of recording electrodes.

[Summary of the invention]

In the information recording medium according to the present invention, a second insulating film having a charge storage function is formed on a semiconductor substrate via a first insulating film, and the second insulating film has a larger band gap than the second insulating film. A third insulating film is formed, and a fourth insulating film of alumina film, tantalum oxide film or A structure in which a titanium oxide film is formed, or a second insulator film having a charge storage function is formed on a semiconductor substrate via a first insulator film, and further formed on an electrode support and its side surface. The recording electrode has a structure in which an alumina film, a tantalum oxide film, or a titanium oxide film is formed as a third insulating film having a larger band gap than the second insulating film on the uppermost layer in contact with the tip of the recording electrode. Then, during recording, the recording electrode is brought into contact with the recording medium and moved relatively, and at the same time, a recording signal voltage is applied via the recording electrode, thereby accumulating charges in the second insulating film by the tunnel effect. On the other hand, during reproduction, the recorded signal is reproduced by detecting the change in capacitance due to the depletion layer in the semiconductor substrate, which occurs depending on the state of charge accumulation in the second insulator film, via the reproduction electrode. do.

〔Effect of the invention〕

According to this invention, not only is the recording density high and recording/reproducing/erasing possible, but also the charge storage capacity is improved by the presence of the third insulating film newly provided in the recording medium with a large band gap. By reducing the voltage necessary for recording without reducing the voltage, the life of the recording electrode can be extended.

In addition, in this invention, the uppermost layer in contact with the electrode support and the tip of the recording electrode is an alumina film, a tantalum oxide film, or a titanium oxide film, all of which have extremely high hardness and a dielectric constant of 1. ,
Since it is larger than the oxide film or nitride film used as the second insulating film, it reduces the possibility of scratches on the recording medium due to contact between the electrode support and the recording electrode, and reduces the voltage required for recording. It doesn't have to be expensive.

[Embodiments of the invention]

FIG. 1 is a diagram showing the basic configuration of a signal recording/reproducing apparatus according to an embodiment of the present invention. In the figure,
The information recording medium 10 is formed by forming a silicon oxide film (SiO ₂ ) with a thickness of about 20 Å as a first insulating film 12 on a semiconductor substrate 11 , such as an n-type or p-type silicon single crystal or polycrystalline substrate, by thermal oxidation. Then, a silicon nitride film (Si ₃ N ₄ ) having a thickness of, for example, several Å to several tens of Å is formed by CVD or the like as a second insulating film 13 having a charge storage function. A silicon oxide film of 30 to 40 Å is deposited again on the insulator film 13 as the third insulator film 14.
and finally a fourth layer as a wear-resistant protective film.
As the insulating film 15, an alumina (Al ₂ O ₃ ) film is formed to a thickness of about several tens of angstroms to a hundred and more tens of angstroms.

The silicon oxide film as the third insulator film 14 may be oxidized by thermal oxidation or chemical treatment. Further, the second insulating film 13 and the fourth insulating film 15 do not need to be alumina films as long as they have a large band gap, a dielectric constant as large as possible, and high hardness. may be a tantalum oxide (Ta ₂ O ₅ ) film or a titanium oxide (TiO ₂ ) film.

When recording a signal, a recording electrode 17 thinly attached to the side surface of a needle-shaped electrode support 16 such as a sapphire needle is brought into contact with the surface of the recording medium 10.
By rotating the
8 is applied to the recording electrode 17. At this time, the first insulator film 1 is removed from the semiconductor substrate 11 due to the tunnel effect.
Charges pass through 2 and are trapped in the second insulator film 13. As a result, a signal is recorded in the form of accumulated charges in the second insulating film 13. This accumulated charge 19 then creates a depletion layer 20 in the semiconductor substrate 11 .

Next, the recording mechanism in this embodiment will be explained in more detail. Figure 2a shows the band structure of a conventional recording medium in which only a first insulating film (SiO ₂ ) and a second insulating film (Si ₃ N ₄ ) are formed on a semiconductor substrate (silicon substrate). The energy difference between the valence band and conduction band of each layer,
In other words, it represents the band gap (forbidden band width). Signal recording using a recording medium with this structure involves applying a positive voltage to the electrodes, causing current to flow through the oxide film (SiO ₂ ) and nitride film (Si ₃ N ₄ ), respectively.
The mechanism is such that the difference between the current in the oxide film and the current in the nitride film becomes an accumulated charge and is accumulated in the nitride film.

In such conventional three-layer recording media, it is difficult to make the nitride film too thin due to the decrease in the charge trapping cross section of the nitride film and the increased probability of pinhole occurrence, and as a result, recording As the voltage required for this increases, the current flowing through the nitride film flows into the recording electrode, which shortens the life of the recording electrode.

On the other hand, according to the embodiment of the present invention shown in FIG. 1, as is clear from the band structure shown in FIG. Since the third insulating film 14 (oxide film) with a large bandgap is present, the current flowing through the second insulating film 13 is considerably suppressed, making it possible to limit the current flowing into the recording electrode 17.

In addition, in the recording medium having this structure, by forming the third insulating film 14, the second insulating film 13, which could not be made thinner due to the charge trapping cross section and pinholes, can be reduced to about 50 Å. It became possible to make it as thin as possible. That is, the second insulator film 1
Even if a pinhole occurs in the third insulator 3, the pinhole is filled by forming the third insulator 14 thereon. Furthermore, when the second insulating film 13 is made thinner, the number of trap levels in this insulating film 13 decreases, but this insulating film 13 and the third insulating film 1
A new trap level is generated at the interface with the second insulating film 13 to compensate for the decreased number of trap levels in the second insulating film 13. Not much different from the media. In this way, in the recording medium shown in Figure 1,
The current flowing through the recording electrode 17 can be reduced, and at the same time, the second insulating film 13 for charge storage can be
It is possible to reduce the voltage required for recording by reducing the thickness of the electrode, which has the advantage of extending the life of the electrode and simplifying the recording circuit.

Here, the fourth insulating film 15 (alumina film, tantalum oxide film, or titanium oxide film) as the uppermost layer is
Recording medium 10, electrode support 16, and electrode support 1
It acts as a protective film to prevent the surface of the recording medium 10 from being scratched due to contact with the recording medium 7. That is, the material of the electrode support 16 is generally sapphire or the like, and the alumina film, tantalum oxide film, or titanium oxide film that is the fourth insulating film 15 are all harder than the electrode support 16, so that the recording medium 10 is not scratched. It is possible to enable stable recording and playback without adding a .

On the other hand, when reproducing a recorded signal, as shown in FIG. As a result, a change in capacitance occurs between the portion where charge is accumulated and the portion where no charge is accumulated, so this capacitance change may be detected via the reproducing electrode. For example, by applying a high frequency signal through a reproducing electrode, changes in capacitance can be detected.
By extracting the signal in the form of an AM modulated wave, the signal can be easily reproduced in exactly the same way as a conventional capacitive video disk player.

FIG. 3 shows another embodiment of this invention,
This is an example in which an alumina film (Al ₂ O ₃ ) having a thickness of about 100 Å is formed as the third insulating film 21, and the fourth insulating film is removed.

FIG. 4 shows the band structure of a recording medium having this structure. This recording medium has a four-layer structure including the semiconductor substrate 11, but since the bandgap of alumina as the third insulating film 21 in the fourth layer is larger than that of the nitride film, the recording mechanism is similar to that of the previous embodiment. This is almost the same as in the case of a recording medium with a five-layer structure, and the current flowing through the second insulating film 13 is
Due to the presence of the insulating film 21, the current flowing to the recording electrode 17 can be reduced. Furthermore, the thickness of the second insulating film 14 can be reduced,
Moreover, since the dielectric constant of alumina, which is the third insulating film 21, is larger than that of the oxide film and nitride film, which are the first and second insulating films 12 and 13, the voltage required for recording can be further lowered. As a result, the life of the recording electrode 17 can be extended. Furthermore, by using a material for the electrode support 16 that has a lower hardness than the alumina film on the uppermost layer of the recording medium 10, stable recording and reproduction can be performed without damaging the recording medium 10.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a signal recording and reproducing device according to an embodiment of the present invention, and FIG.
A diagram showing the band structure of a layer structure recording medium and a five-layer structure recording medium in FIG. 1, FIG. 3 a diagram showing the configuration of another embodiment of the present invention, and FIG. FIG. 3 is a diagram showing a band structure of a medium. 10... Information recording medium, 11... Semiconductor substrate,
12...First insulator film (oxide film), 13...Second insulator film (oxide film), 14...Third insulator film (oxide film), 15...Fourth insulator Membrane (oxide film), 16...electrode support, 17...recording electrode,
18... Recording signal voltage, 19... Accumulated charge, 20
... Depletion layer, 21 ... Third insulator film (alumina film).

Claims (1)

[Claims] 1. A second insulating film having a charge storage function is formed on a semiconductor substrate via a first insulating film, and a third insulating film having a larger band gap than the second insulating film is formed on the second insulating film. A fourth insulating film such as alumina film, tantalum oxide film or titanium oxide film is formed on the uppermost layer in contact with the electrode support and the tip of the recording electrode formed on the side surface thereof. An information recording medium characterized by forming a film. 2. The information recording medium according to claim 1, wherein the first insulating film is an oxide film, the second insulating film is a nitride film, and the third insulating film is an oxide film. 3. A second insulator film having a charge storage function is formed on the semiconductor substrate via the first insulator film, and the electrode support thereon and the tip of the recording electrode formed on the side surface of the second insulator film are brought into contact with each other. An information recording medium characterized in that an alumina film, a tantalum oxide film, or a titanium oxide film is formed as a third insulating film having a larger bandgap than the second insulating film on the uppermost layer. 4. The information recording medium according to claim 3, wherein the first insulating film is an oxide film and the second insulating film is a nitride film.