JPH0954992A - Memory reading out method and device by electrostatic capacitance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the surface density of data by actively controlling the contact pressure of a disk surface and a contact stylus. SOLUTION: The contact stylus 1 having a sharp tip is brought into contact with the surface of the disk 3 on which the data is previously recorded in a manner as to locally change an electrostatic capacitance and the displacement of this contact stylus 1 is measure. The contact pressure between the contact stylus 1 and the disk 3 surface is controlled from the displacement. The voltage is impressed between the contact stylus 1 and the disk 3, the position between the contact stylus 1 and the disk 3 is relatively changed and the electrostatic capacitance between the contact stylus 1 and the disk 3 is measured, by which the data recorded on the disk 3 is read.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording / reading apparatus and method for a video disc or the like.

[0002]

2. Description of the Related Art Reading of a memory using capacitance is adopted in a video disc. In the RCA CED system and the JVC VHD system using this method, the unevenness recorded on the disk surface is detected as a capacitance change using a contact needle. The contact needle is called a stylus and has a metal electrode on the front surface of the probe of diamond or sapphire. The electrode thickness is 100 to 200
In nm, the width is 1000 to 2500 nm.

[0003]

However, in the above-mentioned prior art, since the contact pressure between the disk surface and the contact needle is not actively controlled, there is a limit to reducing the contact pressure. There are problems such as damage. Further, the surface density of data is limited by the size of the electrode during recording and reproduction, but there is a problem that the surface density of data is poor because the electrode is large.

The present invention has been made in view of the above problems, and a memory reading method and a reading method capable of actively controlling the contact pressure between the contact needle and the disk surface to improve the surface density of data. The purpose is to provide a device.

[0005]

Therefore, in the memory reading method of the present invention, a contact needle having a sharp tip is brought into contact with a disk on which data is recorded so that the capacitance locally changes beforehand, and the contact needle is contacted. The displacement amount of the contact needle and the disk surface is controlled from the displacement amount, a voltage is applied between the contact needle and the disk, and the positions of the contact needle and the disk are relatively changed. Then, the data recorded on the disc is read by measuring the electrostatic capacitance between the contact needle and the disc (claim 1).

In this case (Claim 1), the disc is locally provided with materials having different electrical characteristics,
It is preferable that the data is recorded depending on the presence or absence of the material (claim 2). Further, the memory reading device of the present invention, a cantilever having a contact needle, a detecting means for detecting the amount of bending of the cantilever, a control means for controlling the contact pressure between the contact needle and the disk from the amount of bending of the cantilever, A voltage applying unit that applies a voltage between the contact needle and the disk, a capacitance sensor that measures the electrostatic capacitance between the contact needle and the disk, and the positions of the contact needle and the disk are relatively moved. And a drive system (claim 3).

[0007]

A cantilever 2 having a length of 1 mm or less having a probe 1 having an R at the tip of about 100 nm or less as shown in FIG. 1 is used. As a result, a contact pressure of 10 ⁻⁶ Newton or less can be easily achieved. The probe 1 of this cantilever 2 with a probe is brought into contact with the surface of the disk 3, the cantilever 2 is irradiated with laser light, and the reflected light is detected by the two-split photodetector 4. Thereby, the displacement of the cantilever 2 is detected. The contact pressure can be obtained from this displacement and the spring constant of the cantilever 2. The cantilever 2 is moved toward or away from the disk 3 in order to maintain a predetermined contact pressure. This cantilever displacement measurement using laser light is used in an atomic force microscope and is known as an optical lever method.

The capacitance between the disk 3 and the contact needle 1 varies depending on the location on the surface of the disk, as shown in FIG.
Adopt a disc like. In this disk, an insulator 6 is formed on a metal or semiconductor substrate 5. The insulating film 6 defines the capacitance between the substrate 5 and the contact needle 1 by changing the distance between the substrate 5 and the contact needle 1. The insulating film 6 also serves to protect the data recorded on the disc. Further, if the surface of the insulating film 6 is finished to be flat, the relative movement between the contact needle 1 and the disk 3 is also smoothed.

In the disk of FIG. 2, the electrostatic capacitance between the contact needle and the disk is different between position A and position B as shown in FIG. By measuring this electrostatic capacitance, it becomes possible to read data from the disk. Various other methods can be used for recording on the disc. FIG. 4 shows some possible recording methods.

In FIG. 4A, the materials of the insulating films 8 and 9 formed on the semiconductor substrate are different. Therefore, although the insulating films 8 and 9 have the same film thickness, the capacitance between the contact needle 1 and the silicon substrate 7 can be changed by the different dielectric constants. Specifically, for example, the insulating film 8
Is made of Si ₃ N ₄ , and the insulating film 9 is made of BaTiO ₃ .

FIG. 4B shows that Si is formed on the silicon substrate 10.
An insulating film 11 made of O ₂ is formed, and a metal film 12 is formed in the insulating film 11. Data is recorded depending on the presence or absence of the metal film 12. In FIG. 4C, an impurity-doped region 15 is formed in the silicon substrate 13, and the insulating film 1 is formed on the silicon substrate 13 and the region 15.
4 are formed. That is, data is recorded depending on the presence or absence of the area 15.

In FIG. 4D, the metal layer 18 is formed in the silicon substrate 16, and the insulating film 17 is formed on the silicon substrate 16 and the metal layer 18. Therefore, data is recorded depending on the presence or absence of the metal layer 18.

[0013]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. FIG.
FIG. 3 is a block diagram showing an apparatus used for performing disk reading by capacitance.

In this example, dC / dV was used as the signal. A triangular wave having an amplitude of 1 V was generated at 100 kHz by the AC voltage source 29 and the DC voltage source 30, and this triangular wave was applied to the disk 24 via the sample table 25. The capacitance between the contact needle 23 and the disk 24 is detected by the capacitance sensor 28, and after passing through a bandpass filter (not shown) for reducing noise, refer to the triangular wave generated by the AC voltage source 29. The signal strength was measured by a lock-in amplifier arranged in the control device 31 as a signal, and the output from the lock-in amplifier was converted into a digital signal by the A / D converter and captured by the personal computer 32 as data.

The displacement of the cantilever is detected by using the optical lever method. The light emitted from the laser light source 17 is reflected by the cantilever 22 and enters the two-divided photodetector 20. The output from each photodetector is converted into a voltage by an I / V amplifier arranged in the processing device 21, and then each output of the two-divided photodetector is converted by a differential amplifier also arranged in the processing device 21. Get the difference. This signal is input to the control device 31, and based on this signal, the control device 31 inputs a signal for controlling the driving of the three-dimensional actuator 26 in the Z direction to the drive source 27. This constitutes a feedback system that keeps the displacement of the cantilever 22 constant. Keeping the displacement of the cantilever 22 constant is realized by moving the disk 24 in a direction toward or away from the cantilever by the actuator 26. At this time, the surface shape of the disk can be measured at the same time by capturing the signal input from the processing device 21 to the control device 31 into the computer 32.

In this embodiment, the disk 24 is moved in two independent directions in which the cantilevers 22 are orthogonal to the surface of the disk 24. 2 independent signals for moving the controller 3
1 is input to the driving voltage source 27. FIG. 6 is a schematic cross-sectional view of the disc used in the example. Using a lithographic technique, 1 micron repeated dots are formed on a silicon substrate 33 with a thickness of 2 nm of NiC.
After forming with r34, silicon oxide was applied to a thickness of 50 nm by sputtering vapor deposition. The silicon substrate 33
Although not shown on the back surface of the
Was vapor-deposited, and then gold was vapor-deposited. The thickness of this film is arbitrary.

When dC / dV was measured using this disk, no bias voltage dependency was observed when the contact needle was on NiCr34. In contrast, the contact needle is NiC
Bias dependence was observed in the absence of r. The signal difference is large when the bias voltage is around 4 V and around -1 V, and is schematically shown in FIGS. 6B and 6C.
The difference in bias between 4V and -1V is considered to be due to the silicon of the substrate. The size of the dots recorded on the disk surface can be reduced to 0.1 micron or smaller, and the recording surface density is dramatically improved. Further, the amount of information is further increased by combining it with the unevenness information on the disc surface. Furthermore, since the surface of the disk used in this example is covered with an insulating film, it is stable against external disturbance such as scratches.

[0018]

As described above, according to the present invention, the contact pressure between the contact needle and the disk surface can be actively controlled, and by using the contact needle having a sharp tip, the surface density of data can be improved. It is possible to improve.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a cantilever with a contact needle and a disc.

FIG. 2 is a schematic configuration diagram of a disc.

FIG. 3 is a schematic diagram showing the principle of reading information from a disc.

FIG. 4 is a schematic diagram showing some information recording methods.

FIG. 5 is a schematic block diagram of a reading device.

FIG. 6 is a schematic view of the disc used in the example and the obtained signal.

[Explanation of symbols]

 1, 23 ... Contact needle 2, 22 ... Cantilever 3, 24 ... Disk 4, 20, ... Two-divided photodetector 5, 7, 10, 13, 16 ... Substrate 6, 8, 9, 11, 14, 17 ... Insulating film 19 ... Laser 21 ... Processing device 25 ... Sample stage 26 ... Three-dimensional actuator 27 ... Driving voltage source 28 ... Capacitance sensor 29・ ・ ・ AC voltage source 30 ・ ・ ・ DC voltage source 31 ・ ・ ・ Control device 32 ・ ・ ・ Computer

Claims (3)

[Claims] 1. A contact needle having a sharp tip is brought into contact with a disk on which data is recorded so that the electrostatic capacitance locally changes, and the displacement of the contact needle is measured. The contact pressure between the needle and the disk surface is controlled, a voltage is applied between the contact needle and the disk, the positions of the contact needle and the disk are relatively changed, and the contact needle and the disk are A memory read method for reading the data recorded on the disk by measuring the capacitance between the two. 2. The method according to claim 1, wherein the discs are locally provided with materials having different electrical characteristics, and the data is recorded depending on the presence or absence of the material. 3. A cantilever having a contact needle, detection means for detecting the amount of bending of the cantilever, control means for controlling the contact pressure between the contact needle and the disk based on the amount of bending of the cantilever, and the contact. Voltage applying means for applying a voltage between the needle and the disc, a capacitance sensor for measuring the capacitance between the contact needle and the disc, and a drive for relatively moving the positions of the contact needle and the disc A memory reading device having a system.