JPH0427806A - Scanning-type tunnel microscope - Google Patents

Abstract

PURPOSE:To control the interval between a probe and a body to be measured at a constant value by providing a low-pass filter circuit which is set at a frequency region lower than the frequency corresponding to a minute shape that appears in a tunnel current in a feedback loop. CONSTITUTION:A tunnel current (i) is made to flow across a disk 2 and a probe 3. The tunnel current (i) undergoes logarithm conversion and integration, and the obtained gap control signal is sent into an actuator 4. At this time, a frequency region fA contained in the tunnel current (i) is fed back to the actuator 4 from an LPF circuit 17. Therefore, the interval between the probe 3 and the disk 2 can be controlled at a constant value of 1nm without the effects of the waviness of the disk 2, the mounting state on a turntable (inclination and dispersion in flatness), vibration of surrounding parts and the like. Thus, a large amount of data can be accurately read out.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to a scanning tunneling microscope.

(Conventional technology) A scanning tunneling microscope (STM) has a lateral resolution of approximately 0.
．． O3 nm allows a large amount of information to be obtained from a small area. The principle of this scanning tunneling microscope is explained as follows. A probe is placed at an interval of about 1 nm with respect to a constant object, such as a disk, and a bias voltage is applied between the disk and the probe to cause a tunnel current to flow between the disk and the probe. . Then, this tunnel current is detected and feed-hacked by performing I/VC current/voltage conversion and logarithmic conversion processing, and the distance between the disk and the probe is controlled to be constant at the above-mentioned interval, and the tunnel current at the time of parenthesis is The shape of the disk is detected from the change in . However, a large amount of information can be read by recording information in a concave and convex shape on the disk.

By the way, in the above-described scanning tunneling microscope, it is necessary to control the distance between the disk and the probe to be close to about 1011 and constant. However, the disc had undulations, and the disc was not properly installed in the reader! 3 (variations in inclination and flatness); due to surrounding vibrations, etc., the distance between the disk and the probe cannot be controlled at a constant level, and even worse, the probe may collide with the disk. For example, when reading information recorded on a disc created to the same standard as an optical disc, the waviness of the optical disc is set by the International Organization for Standardization 1 (ISO) to be 600 μm or less; The distance from the probe is larger than 1r+s+l, and the probe collides with the disk reliably. Further, the above-mentioned waviness of the disk is caused by the disk surface being vibrated due to the mounting state of the disk in a reading device, surrounding vibrations, and the like. This vibration of the disk surface is included in the read signal.

(Problem to be Solved by the Invention) As described above, if the disk has undulations, the distance between the disk and the probe cannot be controlled at a constant level, and the probe may collide with the disk, making it difficult to read information accurately. It was difficult.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a scanning tunneling microscope that can control the distance between the object to be measured and the probe to a constant value and read information accurately.

[Structure of the Invention] (Means for Solving the Problems) The present invention allows a tunnel current to flow between an object to be measured and a probe provided on a displacement element, and performs logarithmic transformation, integral processing, etc. on this tunnel current. In a scanning tunneling microscope, the probe is fed back to the displacement element as a gap control signal to make the probe follow the shape of the object to be measured and read the minute shape recorded on the object. This is a scanning tunneling microscope that attempts to achieve the above object by providing a low-pass filter circuit set in a frequency range lower than the corresponding frequency.

(Function) By providing such a means, a tunnel current is caused to flow between the object to be measured on which a minute shape is formed and the probe provided on the displacement element, and this tunnel current can be subjected to logarithmic conversion, integral processing, etc. Then, in the feedback loop that sends the gap control signal to the displacement element, a frequency lower than the frequency corresponding to the microscopic shape appearing in the tunnel current is foot-hacked by the displacement element by a low-pass filter circuit, and the probe can be probed without being affected by waviness. The distance between the object and the object to be measured is controlled to be constant.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a scanning tunneling microscope.

The table 1 is provided with a turntable, and a disc-shaped disk 2, which is an object to be measured, is placed on the turntable. Information is recorded on this disk 2 by uneven shapes, and 2a indicates one recording track. A probe 3 is arranged above this disk 2, and this probe 3 is provided on an actuator 4. As shown in FIG. 2, this actuator 4 includes a bimorph piezoelectric element 5 and a conductive wire 6 made of aluminum, and a probe 3 is provided on the conductive wire 6. The actuator 4 formed in this manner can obtain a displacement of approximately 1111 in the direction of arrow (A). Note that a bias voltage setting device 7 is connected between the disk 2 and the probe 3, and a bias voltage is applied between the disk 2 and the probe 3. Therefore, a tunnel current flows between the disk 2 and the probe 3, and this tunnel current flows through the conductor 6 and is sent to the probe controller 10.

This probe control device 10 has a function of receiving a tunnel current and displacing the actuator 4 according to the tunnel current value to cause the probe 3 to follow the shape of the disk 2. Specifically, the configuration is as follows. l/V
A conversion circuit 11 is provided, and a tunnel current is input manually to this I/V conversion circuit 11, and its conversion output is sent to a display device 12 and a logarithmic conversion circuit 13. The conversion output of the pair/number conversion circuit] 3 is sent to the addition circuit 14, and this addition circuit 14 has a gap bias setting circuit 15.
The gap bias voltage is input from The gap bias voltage sets the distance between the disk 2 and the probe 3 to 1nIII.
This is the reference voltage value for constant control. The added output of this adder circuit 14 is sent to a low-pass filter circuit 17 through an integrating circuit]6. This low-pass filter circuit 17 has a power of 20kHz as shown in FIG.
It is set in the frequency region fA below z. by the way,
The frequency range fB included in the tunnel current when the information is read is 130 MHz to 370 MHz centered around a frequency of 250 MHz, as shown in FIG. For example, taking an optical disc as an example, information is recorded in bits with a depth of 0.1 μm, a width of 0.6 μm, and an interval of 1.6 μm. If the disk rotates at a speed of about 600 rpm, it will generate 250 Mbit/sec.
Information is read at a transfer speed of approximately Note that with a scanning tunneling microscope, information can be read even when the density is increased to 0.1 μm or less in width and 0.2 μm in interval. Therefore, things included in the frequency domain fA (20 kHz or less) include the waviness of the disc 2 and the state of installation on the turntable (
variations in inclination and flatness), vibrations in the surroundings, etc. Among these, ambient vibration has the highest frequency, and its value is about 20 kHz. The filter output of this low-pass filter circuit 17 is amplified by a high-voltage amplifier circuit 18 and supplied to the actuator 4.

Next, the operation of the scanning tunneling microscope configured as described above will be explained.

As the turntable rotates, the disk 2 and probe 3
When a bias voltage is applied between the two, the tunnel current i changes depending on the surface shape of the disk 2, as shown in FIG. This tunnel current i flows through the conductor 6 and is sent to the I/V conversion circuit 11 of the probe control device 10. Then, the tunnel current 1 is converted into a voltage signal according to the current value by the I/V conversion circuit 11 and sent to the logarithmic conversion circuit 13, where it is logarithmically converted and added to the adder circuit 14.
sent to. This adder circuit 14 calculates a deviation voltage between the logarithmically converted output and the gear bias voltage and sends it to an integrating circuit 16, which integrates the deviation voltage and sends it to a low-pass filter circuit 17. In this low-pass filter circuit 17, 20k is applied according to the frequency domain fA shown in FIG.
Passes frequency components below Hz. Therefore, the frequency components that pass through this filter circuit 17 are affected by the undulation of the disc 2 and its attachment to the turntable! ! (variations in inclination and flatness) and surrounding vibrations. The filter output containing this frequency component is amplified by the high voltage amplifier circuit 18 and fed back to the actuator 4.

Here, when the disk 2 has waviness as shown in FIG. 4, the tunnel current l includes information such as the frequency component Da of the waviness of the disk 2, as shown in Sa shown in FIG. However, the frequency component Da included in the tunnel current is fed back to the actuator 4 through the low-pass filter circuit 17, so that the distance e between the probe 3 and the disk 2 is controlled to be constant as shown in FIG. to follow the shape of the disc 2. As a result, the voltage signal sent to the display device 12 has the frequency component Da removed and becomes only the information component as shown in sb shown in FIG.

In this way, in the above embodiment, a tunnel current 1 is caused to flow between the disk 2 and the probe 3, and this tunnel current 1
is subjected to logarithmic conversion and integration processing and sent as a gap control signal to the actuator 4, and at this time, the frequency range fA included in the tunnel current 1 is fed back to the actuator 4 by the low-pass filter circuit 17.
The distance between the probe 3 and the disk 2 can be controlled to a constant value of 1r+III without being affected by the waviness of the disk 2, the mounting condition on the turntable (inclination, variations in flatness), surrounding vibrations, etc., and a large amount of information can be obtained. can be read accurately.

Note that the present invention is not limited to the above-mentioned embodiment, and may be modified without departing from the spirit thereof. For example, as the actuator 4, a laminated piezoelectric element 20 as shown in FIG. 6 may be used.

[Effects of the Invention] As described above in detail, the present invention provides a scanning tunneling microscope that can control the distance between the object to be measured and the probe to a constant value and read information accurately.

[Brief explanation of the drawing]

1 to 5 are diagrams for explaining an embodiment of a scanning tunneling microscope according to the present invention, in which FIG. 1 is a configuration diagram, FIG. 2 is a specific configuration diagram of an actuator, and FIG. 3
4 is a diagram showing the tracking of the probe, FIG. 5 is a waveform diagram of tunnel current, and FIG. 6 is a diagram showing a modification of the actuator. 1... table, 2... disk, 3... probe,
4...actuator, 7...bias voltage setting device,
10... Probe control device, 11... I/V conversion circuit, 12
... Display device, 13... Logarithmic conversion circuit, 14...
Addition circuit, 15... Gap bias setting circuit, 16
...Integrator circuit, 17...Low pass filter circuit, 1
8...High voltage amplifier circuit. Applicant's Representative Patent Attorney Takehiko Suzue

Claims (1)

[Claims] A tunnel current is passed between the object to be measured and a probe provided on the displacement element, and this tunnel current is subjected to logarithmic conversion, integration processing, etc., and fed back to the displacement element as a gap control signal to cause the probe to move to the displacement element. In a scanning tunneling microscope that reads a minute shape recorded on the object to be measured by following the shape of the object to be measured, the feedback loop is set to a frequency region lower than a frequency corresponding to the minute shape appearing in the tunnel current. A scanning tunneling microscope characterized by being equipped with a low-pass filter circuit.