JPH09282725A - Information recording/reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To extract an information signal with good sensitivity by reproducing recording information according to a change in a tunnel current between a probe and a sample. SOLUTION: A specified voltage is applied to a recording medium 102 by a bias applying part 105, and a probe 101 is brought close until a tunnel current is detected. The detected current of the probe 101 is inputted to a bit signal detecting part 106, the bit frequency component of the detected tunnel current is sent to a data extracting processing part 112 as an amplified bit signal, and information recorded beforehand is reproduced from the bit detecting timing of the signal and the positional information of the probe 101 on the medium 102. The reproduced information is sent from the processing part 112 to an image data outputting part, a voice outputting part or an information processing part for using the same as computer numerical data. A relative positional relationship between the medium 102 and the probe 101 is changed by the scanning motion of moving on a movable stage 104 with a control signal outputted from a scanning control part 107 via Y and X scanning signal generating parts 108 and 109.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording / reproducing apparatus utilizing an electric phenomenon generated by applying a voltage between a probe and a sample and bringing them closer to each other, and particularly to a device between the probe and the sample. The present invention relates to an information recording / reproducing apparatus that measures the value of a current flowing through a recording medium and reproduces recorded information from the change in the current signal.

[0002]

2. Description of the Related Art In recent years, a scanning tunneling microscope (hereinafter referred to as an STM) capable of directly observing the electronic structure of a material surface and its vicinity by utilizing a physical phenomenon (tunnel phenomenon or the like) generated by bringing a probe and a sample close to each other. Is abbreviated as [G.
Binning et al. , Helvetica
Physica Acta, 55, 726 (198
2)], real space images can be measured with high resolution regardless of whether they are single crystals or amorphous. In addition, STM has the advantage that it can be observed at low power without damaging the medium due to electric current. Furthermore, it can be used not only in ultra-high vacuum but also in air and solutions and used for various materials. It is expected to have a wide range of applications in academic and research fields.

In the industrial field, in recent years, attention has been paid to the principle of having a spatial resolution of an atomic or molecular size.
JP-A-63-161552 and JP-A-63-1
As disclosed in Japanese Patent Laid-Open No. 61553, application and practical application to an information recording / reproducing apparatus by using a recording layer for a medium have been vigorously pursued. Specifically, in these methods, the SOAZ layer stacked on the Au electrode which is the recording medium is
A Langmeir Blodgett (LB) film is used as a recording medium, and bits are recorded and reproduced on the recording medium. Recording is performed by using a bias applying circuit between the probe and the medium, and applying a voltage as a bias voltage on which continuous pulse waves having peak values of −6 V and +1.5 V are superimposed, between the sample and the probe. Reproduction is performed by scanning the surface of the medium with the probe while applying a constant DC voltage between the probe and the medium. For example, according to this method, the medium shown in FIG.
As schematically shown in FIG. 3, a low resistance portion A is formed in a part of the high resistance LB film. When reproducing, a predetermined D on the Au electrode
When the current flowing through the probe is measured by applying the C voltage, almost no current flows when scanning and moving the high resistance portion (hatched portion B of the LB film in FIG. 6), but the bit recorded once When the probe enters the part, the current value suddenly rises.

Here, looking at the current flowing between the probe and the Au electrode at the time of bit detection, the current flows as shown by the dotted line in FIG. When the scanning speed of the probe is high, the time during which the current is large as shown in (a) is short, and when the scanning speed is low, it seems that a large current is flowing for a long time as shown in (b). become. What is necessary for the above recording / reproducing operation is not necessarily to measure the current value but to detect efficiently that the probe has passed over the bit, but the detected current value contains various noises. Get lost. Particularly in the present invention in which a very small current value must be measured, noise is a big problem.

The cause of the noise is, for example, the local unevenness of the film thickness of the LB film locally lowers the resistance of the non-recorded portion which is originally high resistance in the small film thickness portion, or conversely the film thickness is reduced. In the enlarged portion, the resistance value of the recording portion may not be lowered so much, and the current value may be decreased or increased. In addition, the electric circuit used in the detection and drive system may include noise in the output signal due to power supply noise. There is also noise caused by the influence of the electromagnetic waves from the outside on the detection system electric circuit. Further, although the distance between the medium and the probe is controlled by the piezoelectric element in the present embodiment, it is known that the piezoelectric element causes a drift due to the influence of temperature, etc. It may change, and it may affect the detection current as noise.

In order to suppress the influence of various noises as much as possible, it is effective to remove the noise by utilizing the frequency component of the noise, that is, to use a bandpass filter. Among the above noises, the unevenness of the LB film thickness and the drift of the piezoelectric element are long changes in time, and the frequency components are on the low frequency side. On the other hand, the noise of the circuit system is often on the high frequency side (excluding the 50 Hz noise of the power supply).

[0007]

On the other hand, the bit signal to be reproduced often has a width in its frequency band. One reason is that the scanning speed of the probe is not always constant because the memory system requires reproduction at various transfer rates as typified by video special reproduction. For example, 10
It is also conceivable to reduce the scanning speed to 1/10 in 1/10 slow reproduction or the like. In this case, the main frequency component of the bit reproduction signal drops to 1/10.

Another problem is the variation in bit size. For example, if the tip shape of the probe varies, the bit diameter may be as small as 5 nm at one time and as large as 20 nm at another time. In this case, the frequency will change about four times. As described above, when the bandpass filter is used when the frequency component of the current signal at the time of bit detection has a width, the reproduction sensitivity is extremely lowered under a certain condition. For example, the solid line waveforms in FIGS. 5A and 5B are obtained by passing the current signal indicated by the dotted line through a bandpass filter having a certain frequency characteristic, but the peak values of the flowing current (dotted line) are the same. However, the peak value of the waveform (solid line) after passing through the bandpass is different, and the value was swiftly scanned (a).
Then you can see that the sensitivity has dropped. This is because the band of the filter does not match the frequency component of the bit signal. In the bit detection in the latter stage, it is generally considered that a certain threshold voltage (J _Th in the figure) is determined, and a voltage exceeding it is recognized as a bit. Is caused, which leads to an increase in error rate of information reproduction, which is a problem.

Therefore, the present invention solves the above-mentioned problems in the prior art, information signals can be extracted from the detection signals with high sensitivity, and information can be obtained with good reproducibility under the same scanning conditions. An object is to provide a recording / reproducing device.

[0010]

In order to solve the above problems, the present invention provides a scanning mechanism for scanning a probe and a recording medium in parallel, and a voltage application for applying a voltage between the probe and the recording medium. Means, and at least a fine signal detecting means for detecting a fine signal obtained from a tunnel current value flowing between the probe and the recording medium during parallel scanning by the scanning mechanism,
In an information recording / reproducing apparatus for recording / reproducing information, the fine signal detecting means has a signal amplifying means for amplifying only the vicinity of a specific frequency band. In the present invention, the frequency band of the signal amplifying means can be set based on the frequency band of the information signal calculated from the scanning information from the scanning mechanism. Further, in the present invention, the information recording / reproducing apparatus is configured to have a storage unit that stores the scanning information from the scanning mechanism and the frequency band amplified by the signal amplification unit of the fine signal detection unit in association with each other. Can be taken. Further, in the present invention, the fine signal detection means calls the amplification frequency band corresponding to the scanning information of the scanning mechanism from the information stored in the storage means, and based on that calls the frequency band of the signal amplification means. It can be set, and the frequency band to be amplified can be set arbitrarily.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention achieves the above-described object of the present invention with the above-described structure. More specifically, a recording and reproducing bias is provided between the medium substrate and the probe. In a recording / reproducing apparatus having a bias applying circuit for applying and a current detecting means for detecting a current signal flowing between a probe and a medium substrate, a band pass filter is applied to a signal detected at the time of reproduction to record. The probe is configured to adjust the band of the filter according to the linear velocity at which the probe scans the medium when the information signal is taken out, and the circuit constants for realizing the band according to the scanning condition are stored. It is possible to extract the information signal from the detection signal with high sensitivity and also to obtain the information with good reproducibility under the same scanning condition, by configuring it so as to also have a memory means for That.

[0012]

The present invention will be described below in detail with reference to examples. [Embodiment 1] FIG. 1 shows the basic configuration of the present invention. A predetermined voltage is applied to the recording medium 102 by the bias applying unit 105, and the probe 101 installed on the cantilever 103 is installed.
It shows a state in which the tunnel current J _T has been approached until the observation. The process of bringing the probe 101 close to the recording medium 102 until the tunnel current _JT is observed was performed with high accuracy by the coarse and fine movement mechanisms, although not shown in this configuration diagram. The tunnel current J _T is detected by the probe 101 and then input to the bit signal detection unit 106, which is a characteristic part of the present invention, and the bit signal is detected from the current signal. Thereafter, the detected bit signal is sent to the data extraction processing unit 112 for information reproduction, and reproduction as information is performed.

The bit signal is a signal obtained by amplifying the frequency component of the detected bit of the tunnel current, and the data extraction processing unit 112 records it in advance based on the bit detection timing of the signal and the probe position information on the medium. Play some information. This part will be described later in detail. Although not shown, the reproduced information from the data extraction processing unit 112 is followed by an image data output unit, an audio output unit, or an information processing unit such as used as numerical data of a computer. Further, the relative positional relationship between the recording medium 102 and the probe 101 can be changed by the scanning movement of the movable stage 104. Specifically, the stage 104 has an actuator provided therein, and in response to a drive signal sent from the Y scanning signal generating unit 108 and the X scanning signal generating unit 109 through the amplifier 110, the recording medium surface in-plane direction (XY direction).
Move the recording medium to. Each scanning signal generation unit (108,
109) generates a scanning signal based on control information such as an offset position, a scanning frequency, a main scanning (X scanning) width, and a sub scanning (Y scanning) width according to a control signal output from the scanning control unit 107 of all stages.

Next, details of the operation of the bit signal detector 106, which is a characteristic part of the present invention, will be described with reference to the drawings. The bit signal detector 106 has an internal configuration as shown in FIG. The obtained current signal is first input to the preamplifier 201 and amplified with a predetermined amplification degree. For this preamplifier part, a transistor circuit as shown in FIG. 3 was used. The transistors T1 and T2 have a current amplification factor of about 1000 times, and when connected to Darlington, the preamplifier as a whole has an amplification factor of 10 ⁶ . Rs has a resistance of 10 MΩ and R1 has a resistance of 10 kΩ. The power supply voltage is + 15V for + V and -1 for -V
5V is used. Output was made with an emitter follower to lower the output impedance. Next, the current signal output from this preamplifier is amplified as it is as a current and input to the bandpass filter 202 in the subsequent stage.

An outline of the circuit of the bandpass filter 202 is shown in FIG. The input signal is passed through SW1 and the low frequency components are first cut by the coupling capacitors Cc1-3. Next, this AC signal is cut into high-frequency components by an LPF using an OP amplifier U and capacitors Cf1 to Cf1 for its feedback. Rf is 1 MΩ, Rc is 1
The maximum amplification factor of 10 ⁴ is obtained in this circuit using 00Ω. It should be noted that this OP amplifier uses a small signal and a wide band. Here, by appropriately adjusting the values of Cc1 to 3 and Cf1 to 3, it is possible to obtain a desired bandpass filter. The switch control circuit 401 operates according to the frequency component of the bit signal to be detected. For example, in this embodiment, a bit is formed by applying a pulse voltage to the recording medium of the LB film / Au electrode by a probe according to the method described above, and the size of the bit that can be formed in this case was about 10 nm. The linear velocity of the probe depends on the frequency of reciprocal scanning and the scanning width. For example, when the scanning region is 5 μm and the scanning frequency is 10 Hz, the linear velocity of the probe is 100 μm.
Since it is m / sec, the time required for the probe to pass over the bit is 0.1 msec. By taking the reciprocal, the frequency of the bit signal becomes 10 kHz. By performing the same calculation, 100 kHz for a frequency of 100 Hz and 1 for a frequency of 1 Hz
kHz. Here, the aforementioned Cc1 to 3 and Cf1 to 3
Cc1 and Cf1 and Cc2 and Cf by adjusting
2. By combining Cc3 and Cf3, the characteristics shown in FIG. 7 can be obtained.

The switch control circuit 401 in FIG. 4 switches the switch in response to the scanning frequency information sent from the scanning control unit 107 in FIG. 1, and matches the pass band of the BPF with the frequency band of the bit signal. As a result, when the scanning frequency is 1 Hz, 10 Hz, or 100 Hz, the switch is automatically switched, and bit detection can be performed with high sensitivity. Further, when the scanning width is also changed, the sensitivity can be adjusted by obtaining a pair of Cc and Cf by the same method as above and switching them with a switch. Further, the user can manually control the switch by the input device 111, and the pass band of the BPF can be manually set in order to adjust the signal level.

[Second Embodiment] A second embodiment of the present invention will be described with reference to FIGS. As described above, the frequency component of the bit signal measured by the frequency of the reciprocating scanning of the probe and the scanning width will be changed, but the frequency of the reproduced bit signal will also depend on the size of the recorded bit. Changes. The cause is the tip shape of the probe. When the probe shape is sharp, a small bit is formed,
When it is dull, large bits tend to be formed. In such a case, the bandpass filter 20 shown in FIG.
It becomes necessary to finely adjust the pass band of 2. Further, the adjustment is changed depending on the shape of the probe used, so that the sensitivity is lowered in one probe in a certain band and in another probe in the same band.

FIG. 8 corresponds to FIG. 4 of the first embodiment and shows a portion of the bandpass filter 202 in FIG. A capacitor array C803 is used instead of the coupling capacitor, and a capacitor array F804 is used instead of the feedback capacitor. The contents of each capacitor array are shown in FIG. The switch control circuit 801 supplies 19 switch control signals to the capacitor array in the form of a bus. The types of capacitors are 1pF, 2pF, 3pF, 5pF 20pF, 30pF, 50pF 200pF, 300pF, 500pF 2nF, 3nF, 5nF 20nF, 30nF, 50nF 200nF, 300nF and 500nF. This allows the array to set 1 pF to 1.111111 μF with a resolution of 1 pF. At this time, each capacity is c1 =
1 pF to c19 = 500 nF, and the control signals of the switch control circuit 801 for controlling it are set to s1 to s19.
And When the set capacity is Cs, if Cs-cx ≧ 0, the operation of turning on sx is x = 19, 18, 17 ...
And go. By doing so, the set capacitance value can be expressed by turning on and off the signals of s1 to s19.

Next, the overall operation of the BPF of FIG. 8 will be described. When the reproduction scanning is started, first, the bit signal is detected by the preset capacity of the capacitor array. If the bands do not match here, the operator manually scans the switch and
Adjust the passband of F. When the setting is completed, the switch control circuit 801 stores the set capacity for the scan information in the buffer memory 802. Next, when the scanning conditions are changed, the same scanning is performed and the buffer memory 8
In 02, the coupling and feedback capacitor capacities are stored as 19-bit data s1 to s19 in association with the scan information. By doing this,
When the reproduction condition is returned to the original condition, the switch control circuit 801 extracts the condition of each capacitor capacity from the buffer memory 802 and automatically sets it. Once
By setting a pair of optimum capacitor capacitances for a certain probe and a certain scanning condition, it becomes possible to automatically operate the BPF with the optimum sensitivity when reproducing again with the probe and the scanning condition.

[0020]

According to the present invention, it is possible to detect the presence or absence of a bit with high sensitivity by the above configuration.
It is possible to reduce reading errors in recording / reproducing information, eliminate the need to provide redundant bits for extra error correction, and improve the recording density. Also,
According to the present invention, with the above configuration, it is possible to efficiently cut out the frequency components other than the frequency component of the bit signal, reduce various noise countermeasures, and simplify the system.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a configuration diagram of a bit signal detection unit.

FIG. 3 is a circuit diagram of a preamplifier.

FIG. 4 is a circuit diagram of a bandpass filter according to the first embodiment.

FIG. 5 is a diagram illustrating pulse characteristics of a bandpass filter.

FIG. 6 is a conceptual diagram showing a relationship between a bit on a recording medium and a scanning probe.

FIG. 7 is an example of frequency characteristics of a bandpass filter.

FIG. 8 is a circuit diagram of a bandpass filter according to a second embodiment.

FIG. 9 is a schematic circuit diagram of a capacitor array.

[Explanation of symbols]

 101: probe 102: recording medium 103: cantilever 104: movable stage 105: bias application unit 106: bit signal detection unit 107: scanning control unit 108: Y scanning signal generation unit 109: X scanning signal generation unit 110: amplifier 111: Input device 112: Data extraction processing unit 201: Preamplifier 202: Bandpass filter 401: Switch control circuit 801: Switch control circuit 802: Buffer memory 803: Capacitor array C 804: Capacitor array F

Claims (5)

[Claims] 1. A scanning mechanism for scanning a probe and a recording medium in parallel, a voltage applying means for applying a voltage between the probe and the recording medium, and a probe and a recording medium during parallel scanning by the scanning mechanism. And at least a fine signal detecting means for detecting a fine signal obtained from a tunnel current value flowing between
An information recording / reproducing apparatus for recording / reproducing information, wherein the fine signal detecting means has a signal amplifying means for amplifying only the vicinity of a specific frequency band. 2. The frequency band of the signal amplifying means is set based on the frequency band of the information signal calculated from the scanning information from the scanning mechanism.
An information recording / reproducing apparatus according to claim 1. 3. The information recording / reproducing apparatus has storage means for storing scanning information from the scanning mechanism and frequency bands amplified by the signal amplification means of the fine signal detection means in association with each other. The information recording / reproducing apparatus according to claim 1 or 2, characterized in that: 4. The fine signal detection means calls an amplification frequency band corresponding to the scanning information of the scanning mechanism from the information stored in the storage means, and sets the frequency band of the signal amplification means based on the calling. The information recording / reproducing apparatus according to claim 3, wherein 5. The fine signal detecting means is capable of arbitrarily setting a frequency band to be amplified.
Alternatively, the information recording / reproducing apparatus according to claim 4.