JP3118654B2 - Information processing device and scanning tunneling electron microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information processing apparatus or a scanning tunneling electron microscope (STM) for two-dimensionally scanning a medium with a probe and performing recording and reproduction by physical interaction between the medium and the probe. Specifically, it relates to probe access control and information recording / reproducing methods.
The present invention relates to an STM and a small and high-density information processing apparatus to which the principle of the STM is applied.

[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 on and near the surface of a material has been developed [G. Binnig et. al. ,
Helvetica Physica Acta. 5
5.726 (1982)], which makes it possible to observe a real space image with high resolution irrespective of single crystal or non-crystal, and that this STM can be measured at low power with little damage to the sample material due to current. It has advantages, and operates not only in an ultra-high vacuum but also in the air and in a solution, and can be applied to various materials.

In STM, when a voltage is applied between a metal probe and a conductive sample to approach a distance of about 1 nm,
The phenomenon that a tunnel current occurs is used. Recently, for example, Japanese Patent Application Laid-Open Nos. 63-161552 and
As disclosed in JP-A-3-161553, this ST
Many proposals have been made to apply an M principle to configure an information processing apparatus mainly for ultra-high density recording / reproduction. That is,
The probe electrode corresponding to the STM probe gives physical deformation on the recording medium corresponding to the sample, or changes the electronic state of the medium surface to record information. It is said that by using a method for reproducing information, large-scale information can be recorded and reproduced at a high density of the order of molecules and atoms.

Among the above recording methods, in order to impart physical deformation, a sharp recording probe is pressed against a recording medium to be depressed, and a hole is formed by applying a pulse voltage on a recording medium such as graphite. What can be done recently has been reported. That is, by bringing the probe electrode close to the surface of the recording medium and applying a voltage between the two with a pulse width of 3 to 8 V and 1 to 100 μs, a hole having a diameter of about 40 Å can be formed. Can be used as well. On the other hand, in order to perform recording by changing the electronic state, there is known a method in which a voltage is applied between a recording medium, a base electrode, and a probe electrode to change the electrical resistance characteristics of a minute portion. Attention has been paid to its ease.

[0005] As the recording medium, a material exhibiting a memory switching characteristic in voltage-current characteristics, for example, a thin film layer of chalcogenides or a π-electron organic compound is used. For example, a Langmuir-Blodgett method ( A film obtained by forming an appropriate organic substance accumulation film by the LB method is used.

As a probe electrode, for example, one in which a tip of a needle such as tungsten, Pt-Ir, Pt or the like is mechanically polished and then electropolished is attached to a piezoelectric element, and displacement is controlled by an applied voltage. . As a method of manufacturing a flexible portion for moving a probe electrode, for example, a semiconductor processing technology is used to form a fine structure on one substrate (KE Peterson. “Silicon”).
as Mechanical Material ".
Proceedings of the IEEE. 7
0 vol. 420p, 1982). Thereby, for example, it is possible to provide a hole portion 30 in the single-crystal silicon substrate 21 shown in FIG. 9, provide the tongue-shaped fine movement mechanism 2 in the silicon substrate 21 with cantilever support, and attach the probe electrode 1 to the tip thereof. became.

The tongue-shaped portion 2 is composed of a layered piezoelectric element and electrodes. By applying a voltage between the electrodes, the probe electrode moves in a direction perpendicular to the plane of the single-crystal silicon substrate 21 (Z-axis direction). Change. With respect to the displacement in the XY directions, the silicon substrate or the opposing medium is placed on a scannable stage to perform relative movement. Of course, at this time, it is possible to realize a storage device having a converter array in which a plurality of tongue-shaped portions 2 are arranged. In addition to the cantilever portion 2 having such a cantilever structure, a bridge-like double-supported beam structure is also known.

[0008]

The formation of a probe having a fine movement mechanism by micromachining is very significant in reducing the size, capacity, and speed of an information processing apparatus. However, on the other hand, the signal system for driving and the signal system for recording / reproducing are so close to each other that crosstalk and deterioration of the S / N ratio are caused.

SUMMARY OF THE INVENTION It is an object of the present invention to reduce or eliminate coupling between a drive system signal and a recording / reproducing signal, thereby enabling precise displacement control and improvement of reproducibility and stability of recording / reproducing. And a scanning tunneling electron microscope.

[0010]

To achieve the above object, the present invention provides a means for bringing a probe and a medium close to each other, a means for applying or detecting a signal via a probe, and controlling the position of the probe. a fine adjustment mechanism for at least chromatic performed, and the signal during the application or period for detecting, that is with the <br/> information processing apparatus provided with a switch mechanism temporarily disconnecting the drive signal applied to the fine movement mechanism It is in.

According to such a configuration, during the period of applying or detecting a signal through the probe, the voltage applied to the fine movement mechanism is in a floating state by turning off the switch, and has an electric potential to the probe signal system. Can be eliminated. As a result, coupling from the drive system signal to the probe system, which is a small signal, is significantly reduced or eliminated.

In the above arrangement, it is preferable to use a cantilever type actuator utilizing an inverse piezoelectric effect of a piezoelectric body as a means for bringing the probe and the medium close to each other. Constitution is also a preferred means.

Further, in the above-described configuration, if an observation sample is used instead of a medium, a scanning tunneling electron microscope capable of observing the sample surface with a tunnel current can be provided.

[0014]

Embodiments of the present invention will be described below.

FIG. 1 is a block diagram showing an information processing apparatus according to a first embodiment of the present invention. In FIG. 1, reference numeral 3 denotes a recording medium, and a probe electrode 1 provided on a cantilever type fine movement mechanism 2 is opposed to the recording medium. The fine movement mechanism 2 is formed by a laminated piezoelectric element (cantilever type actuator), and is capable of minute displacement in the Z direction.

The coarse movement in the Z direction is provided on a support of the fine movement mechanism 2 (not shown), so that the distance between the probe 1 and the medium 3 can be largely changed. The displacement and scanning in the XY directions parallel to the medium surface are performed by a scanning mechanism (not shown) provided on the medium support. In such an apparatus, while performing XY scanning, a tunnel current signal detected by a probe is amplified by a current amplifier 4 and compared with a reference value by an error amplifier 6, and the fine movement mechanism 2 is driven by a driver 8 so that the tunnel current becomes constant. Servo control driven by Reference numeral 12 denotes a display device for displaying reproduction information and the like. The low-pass filter 7 is employed for the purpose of removing noise and improving the stability of the control system. 1
0 is a switch provided on the output side of the driver for the drive system of the fine movement mechanism, 11 is a switch for turning on / off the probe signal, 5 is a sample and hold for holding such a signal, and these are timing generation circuits. 9 is controlled.

The procedure for forming the fine movement mechanism using the above-described piezoelectric element will be described below with reference to FIG. First, a 500-nm-thick silicon nitride film 22 was formed as an insulating film on the surface of a silicon semiconductor substrate 21 by high-frequency sputtering (FIG. 2).
(A)). Next, after an opening 23 (1 μm width) was provided in the nitride film through a photolithography process, a piezoelectric bimorph having a laminated structure of a metal electrode and a piezoelectric material was formed on the nitride film (FIGS. 2B to 2B). e)). As the electrode material, Au was used for the base electrode 24 and Cr was used for the lower electrode, and Al was used for the intermediate electrode 26 and the upper electrode 27. Also, the piezoelectric layer 2
For ZnO, ZnO (film thickness 1.2 μm) deposited by high frequency sputtering was used. Further, after covering the entire bimorph element fabricated as described above with a protective layer 29 made of a silicon nitride film deposited by a sputtering method, a probe 1 having a conical projection made of vapor-deposited Au is formed. Was. Further, anisotropic etching using a KOH aqueous solution as an etchant was performed from the lower portion of the substrate, and a void portion was provided in the opening 30 to obtain a probe unit having a schematic cross section shown in FIG.

In such a cantilever, a bimorph-structure piezoelectric element is bent by a voltage difference applied between the electrodes 26 and 27 and between the electrodes 26 and 24, and the probe is displaced in the Z direction. The probe wiring electrode 31 is shown in FIG.
As shown in the figure, it is formed on the same plane as the upper electrode 27.

Here, since the wiring electrode 31 is arranged at a distance of about several μm to 10 μm from the upper electrode 27, the coupling capacitance between the electrodes and the leakage resistance become problems. In addition, there is a coupling capacitance and a leakage resistance between the wiring electrode 31 and the intermediate electrode 26, and actually using the above-mentioned known cantilever,
When the displacement control in the direction is performed, the driving signal is superimposed by the tunnel current detected through the probe, and it is difficult to stably perform the precise control with the feedback gain increased.

However, during the period when the signal is detected by the probe,
By separating the drive signal to the cantilever, the electrode 2
The voltages applied to 7, 26 and 24 are in a floating state and have no potential. As a result, the electrodes 31 and
7, the flow of current between the electrodes 31 and 26 is suppressed,
Crosstalk is improved. On the other hand, the voltage applied to the cantilever is between the electrodes 27 and 26 and between the electrodes 26 and 24.
It is held for a certain period of time by a capacitor formed between them. That is, if the period during which the drive signal is disconnected is shorter than the discharge time of the capacitor, the displacement of the cantilever is maintained.

In order to explain the present invention in more detail, FIG. 4 shows an example of specific timing of each signal. In the figure, S
D and SR represent the ON / OFF states of the switch 10 and the probe signal system switch 11 inserted in the cantilever drive system, respectively (Hi corresponds to ON and Lo corresponds to OFF). This signal is a clock signal CL in the timing generation circuit 9.
Synchronized with K.

Now, when SD is on, the drive system is connected to the cantilever, and the voltage Vdrv applied to the piezoelectric body reaches a desired drive voltage. At this time, SR may be on, but is preferably off considering coupling from the probe signal system to the drive system or malfunction such as saturation of the current amplifier 4 due to the drive system signal.

Next, when SD is turned off, Vdrv is gradually discharged, but is charged again after n clocks (period T) to reach a desired voltage. After m clocks after SD is turned off, sample and hold 5 while SR is on
To apply a sample signal ST to detect a probe signal. At this time, a good signal without crosstalk is obtained because SD is off. ST is also repeated in a cycle T.
Therefore, although the servo control system shown in FIG. 1 is a discrete value system, there is no problem if the sampling interval T is sufficiently shorter than the signal band, and it is not possible to use such a control system as digital control using a computer or the like. Easy.

(Embodiment 2) FIG. 5 is a top view of a fine mechanism using a cantilever type piezoelectric element on which a probe according to a second embodiment of the present invention is installed. In this embodiment, the common electrode 32 in which the probe wiring electrode 31 and the cantilever upper electrode 27 are integrated is used. The system configuration and control timing are the same as in the first embodiment. As long as SD and SR are not turned on at the same time, a good probe signal can be detected as in the first embodiment, and a stable and precise control and a reproduced signal with high reproducibility can be obtained.

Embodiment 3 FIG. 6 shows an information processing apparatus according to a third embodiment of the present invention in which a plurality of cantilevers and probes are arranged. 61 is an XY direction scanning drive circuit, 70 is a recording medium, 75 is a tracking pattern (a concave groove or a pattern having a different surface electronic state) on the recording medium, 71
Is a stage and medium base, 72 is a multi-probe head, 73 is a cantilever, 74 is a probe electrode, 62,
64 is a driver and piezo actuator for driving the stage in the X direction, and 63 and 65 are Y stages.
A driver and a piezo actuator that drive in the direction. Reference numeral 67 denotes a piezo actuator for driving the multi-probe head in the X direction. Reference numeral 68 denotes a plurality of built-in control circuits provided for each probe so as to perform data input / output for each probe and drive control in the Z-axis direction in parallel. Control circuit section.

Reference numeral 66 denotes a tracking control circuit which detects the position signal of the tracking pattern from the comparison between the tunnel current signal from 68 and the tracking edge detection level, measures the tracking deviation, and drives the actuator 67 to correct the deviation. is there.

The control of each cantilever in this embodiment is performed in the same manner as in the first embodiment. Tracking of the tracking pattern is performed by an actuator 67 attached to the multi-probe head.

As the recording medium 70, a recording medium formed of a material having a memory effect on the switching characteristics of voltage and current was formed on a substrate 71. In this embodiment, a substrate 71 prepared by epitaxially growing gold on a flat substrate such as glass or mica is prepared, and squarium-based material having a memory effect on the switching characteristics of voltage and current is prepared on this substrate.
Using bis-6-octylazulene, a two-layer monomolecular film was formed on the substrate electrode by the Langmuir-Blodgett method (LB method).

As in the first embodiment, a switch element is inserted in a signal line connected to each probe and the cantilever. One specific circuit example is shown in FIG.

SD and SR are switch elements of a cantilever driving system and a probe signal reading system, respectively, as in the first embodiment. The detected probe signal is supplied to the sample and hold element ST provided in the Z-axis control circuit 68 as in the first embodiment.
(Not shown) and connected to an error amplifier circuit. SW,
SE is a switch element connected to the recording pulse applying circuit and the erasing pulse applying circuit, respectively. ON / OFF of each switch is controlled at the timing shown in FIG.
Each switch element is a MOS type switch manufactured on a silicon wafer by a conventionally known semiconductor technology, and the cantilever is formed on the silicon substrate by using the same process as in the first embodiment.

An experiment of recording / reproducing / erasing using such an apparatus was performed as follows. Each probe uses a probe signal detection and Z-axis control circuit 68 to apply a bias voltage of 1
Stop at the position where the probe current becomes 1 nA under the condition of 00 mV. At this time, SD, SR, and ST perform control at the same timing as in the first embodiment. Next, the recording medium 70 is caused to scan the probe 74 in the XY directions by the XY scanning circuit 61. At this time, the probe is held by the 305 at a fixed distance from the surface of the recording medium. In this state, SR
SW is turned on instead of turning on (recording). SW is specifically connected to a bias power supply of +6 V.
While W is on, a pulse having a peak value of +6 V is applied between the probe and the recording medium. When the probe returned to the place where the pulse was applied again after waiting for the XY scan, the detected probe current instantaneously increased to about 0.1 μA. It is read that the detected current at the recording position is increased by about two digits (reproduction). Further, when the probe is again XY-scanned and reaches the recording bit position, S is replaced with S instead of SR.
When a pulse having a peak value of -4 V is applied (erased) to the recording medium by turning E on, the probe current detected at that position thereafter returns to 1 nA. The above recording / playback /
Erasing can be repeated stably. Further, as shown in FIG. 8, similar experiments can be independently performed on a plurality of probes, and it is understood that the present invention is also useful in an information processing apparatus using multiple probes.

[0032]

According to the present invention described above, it is possible to suppress or eliminate the crosstalk between the fine movement mechanism control signal and the probe detection or application signal, thereby achieving stable position control and S / N.
It is possible to obtain a detection signal with an improved ratio and a recording / reproducing with high reproducibility.

[Brief description of the drawings]

FIG. 1 is a block diagram of an information processing apparatus according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a procedure for forming a bimorph-driven cantilever type piezoelectric element.

FIG. 3 is a schematic view (plane and cross section) of the outer shape of a cantilever.

FIG. 4 is a timing chart of voltages applied to a switch element and a piezoelectric body.

FIG. 5 is a schematic external view of a cantilever according to a second embodiment of the present invention.

FIG. 6 is a block diagram of an information processing apparatus according to a third embodiment of the present invention.

FIG. 7 is a circuit diagram showing a j-th cantilever, a connected signal, and a switch element.

FIG. 8 is a drive timing chart of the switch element.

FIG. 9 is a schematic view showing a cantilever-type fine movement mechanism and a probe electrode provided on the fine movement mechanism.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Probe 2 Fine movement mechanism 3 Medium 4 Current amplifier 5 Sample hold 6 Error amplifier 7 Low-pass filter 8 Driver 9 Timing generation circuit 10 Drive system signal separation switch 11 Probe system signal separation switch 12 Display device 21 Silicon semiconductor substrate 22 Silicon nitride film 23 Opening Part 24 Base electrode 25 Piezoelectric layer 26 Intermediate electrode 27 Upper electrode 29 Protective layer 30 Opening 31 Probe wiring electrode 32 Shared electrode 61 XY scanning drive circuit 62 Driver 63 Driver 64 X piezo actuator 65 Y piezo actuator 66 Tracking Control circuit section 67 Actuator 68 Z-axis control circuit section 70 Recording medium 71 Base 72 Multi-probe head 73 Cantilever 74 Probe electrode 75 Tracking pattern

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shunichi Shido 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Katsunori Hatana 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon (56) References JP-A-2-116044 (JP, A) JP-A-3-503463 (JP, A) Kiyoshi Takimoto and four others, “Switching memory function of LB film under STM” , IEICE Technical Report, IEICE, March 18, 1994, Vol. 524, pp. 7-12 (58) Fields surveyed (Int. Cl. ⁷ , DB name) G01N 13/10-13/24 G11B 9/00-9/14 G11B 7/34 H01J 37/28 JICST file (JOIS)

Claims (5)

(57) [Claims] At least a means for bringing a probe and a medium close to each other, a means for applying or detecting a signal via the probe, and a fine movement mechanism for controlling the position of the probe, and during the period for applying or detecting the signal the information processing apparatus characterized by comprising a switch mechanism for disconnecting the drive signal applied to the fine movement mechanism temporarily. 2. The information processing apparatus according to claim 1, wherein a cantilever-type piezoelectric body is used as a mechanism constituting a part or all of a means for bringing the probe and the medium close to each other. 3. The information processing apparatus according to claim 1, further comprising a plurality of probes facing the medium. 4. The information processing apparatus according to claim 1, further comprising: a plurality of probes facing the medium; and means for independently driving an approach mechanism of the probes. 5. At least means for bringing a probe close to a sample surface, means for detecting a tunnel current via the probe, and a fine movement mechanism for controlling the position of the probe,
And a switch mechanism for temporarily disconnecting a drive signal applied to the fine movement mechanism during a period of detecting the tunnel current .