JP2001189041A - Storage method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a storage method having durability to external disturbance and executing nanometer-sized minute change which can be erased and storage of information. SOLUTION: Voltage is applied between a semiconductor substrate 106 and a metal thin film 104 provided on the semiconductor substrate 106 by a controlling device 150 through a probe 102. Voltage having high negative polarity, for example about 4 V, is applied to the semiconductor substrate 106 through the probe 102 when the metal thin film has 6.0 nm thickness. Electrons having energy corresponding to the applied voltage are discharged from the probe 102 to the metal thin film 104 and injected into the boundary (joined part) between the metal thin film and the semiconductor substrate. Thus, the region wherein irreversibly transmitted BEEM current is 0 can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a storage method using a change in physical properties of a material and an apparatus therefor.

[0002]

2. Description of the Related Art With the rapid progress of the information society in recent years,
It is an urgent task to increase the density of a recording medium such as a hard disk using magnetic recording. The recording bit density of the magnetic recording system currently used is a maximum of 20 gigabits / square inch at the research level, and a terabit recording technology is targeted for the next generation. If you set this goal, the bit size will be nanometer size, so
It is essential to develop micro-machining technology for the scale.

[0003] Scanning tunneling microscope (STM) and atomic force microscope (AFM)
Some techniques for forming bits by controlling the position of atoms or clusters have been reported. This includes, for example, forming bumps and holes by directly contacting the probe or locally inducing a chemical change under a tunnel current or an electric field which is higher than that of the probe. However, in these cases, (1) the processing is performed on the surface, and therefore, it is easily affected by the atmosphere. (2) It is an irreversible change and the created bit cannot be erased. There were drawbacks such as. An irreversible change is a disadvantage when considering its application as a storage method or device.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of storage which is resistant to disturbances and which is capable of making small changes in erasable nanometer size. Is to provide a storage device using the same.

[0005]

To achieve the above object, the present invention provides a storage medium comprising a metal thin film and a semiconductor substrate, and having a Schottky junction at a junction between the metal thin film and the semiconductor substrate. In contrast, a storage method in which a physical change is caused in the bonding portion to store the data, wherein electrons are injected into the metal thin film from a probe disposed close to the metal thin film, and The information is stored by creating a micro area where the transmission current does not flow through the junction of the semiconductor substrate and the transmission current by applying a positive voltage to the probe to the metal thin film in the micro area. Is stored.

A storage device to which the above-mentioned storage method is applied comprises a storage medium comprising a metal thin film and a semiconductor substrate and having a Schottky junction at a junction between the metal thin film and the semiconductor substrate; A driving unit for driving the probe at a predetermined position on the storage medium by driving the probe relatively to the storage medium and the probe, and applying a predetermined voltage to the probe. Comprising a control unit for applying, by driving electrons from the probe to the metal thin film,
The information is stored by creating a minute area where the transmission current does not flow at the junction between the metal thin film and the semiconductor substrate, and by applying a positive voltage to the metal thin film to the probe in the minute area. A storage device characterized by restoring a transmitted current is also the present invention. The storage device is configured to determine whether a transmission current flows in a minute area at a predetermined position of the storage medium,
Information can be read. The metal thin film constituting the storage medium may be a gold thin film, and the semiconductor substrate may be a silicon substrate. In this way, it is resistant to external disturbances, and it is possible to store information by making a small change in erasable nanometer size.

[0007]

Embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram for explaining a configuration for causing a minute change in a material according to the present invention. In FIG. 1, the control device 150 applies a voltage of the probe 102 to the metal thin film 104 provided on the semiconductor substrate 106. Under the semiconductor substrate 106,
A current due to the passage of electrons from the probe 102 is detected. The semiconductor substrate 106 and the metal thin film 1
04 is kept at the same potential in this configuration. With such a configuration, when electrons are injected from the probe 102 as a tunnel current, some of the incident electrons cross the junction barrier. These electrons form the metal thin film 104 and the semiconductor substrate 10.
6 flows as a BEEM current (transmission current) at the interface (junction) with the control device 6, and this current can be detected by the control device 150.

For example, a metal thin film and a semiconductor substrate are formed of gold (A
u) and silicon (Si), and a silicon substrate doped with phosphorus (P) at 2 × 15 cm ⁻³ will be described as an example. In the thin film forming method, first, a silicon substrate is treated with a hydrofluoric acid aqueous solution (5% HF aqueous solution) so that Si atoms on the outermost surface of the wafer are bonded to hydrogen to be stabilized and become a hydrophobic surface. A hydrogen termination process is performed. Thereafter, the silicon substrate is placed in a high-vacuum vacuum deposition chamber, and gold is deposited. During deposition, the silicon substrate is kept at room temperature. The deposition rate was measured by Rutherford backscattering spectroscopy (RBS), and the amount of gold deposition was controlled by time. The IV (current-voltage) characteristics between the gold thin film and the silicon substrate are also measured to examine the electrical characteristics of the interface. The ideal coefficient which is a coefficient indicating a deviation from the ideal theoretical IV characteristic (defined as e / kT × V / (lnI)) is, in the case of the above example,
1.11.

In FIG. 1, the Au / Si (111) formed in this way is used for the probe 102 and the silicon substrate 106 when the thickness of the gold thin film is 6.0 nm. A voltage having a high negative polarity of about 4 V is applied. As a result, electrons are emitted from the probe 102 with corresponding energy, sent to the gold thin film 104, and injected into the interface (junction) between the gold thin film and silicon. The reference potential in this case is a gold thin film, and the silicon substrate and the gold thin film have the same potential.

FIG. 2A shows a state before injecting electrons in the configuration as shown in FIG. 1, and FIG. 2B shows the result. 2 (a) and 2 (b) are images observed with a scanning tunneling microscope (STM).
The right side of FIG. 2B shows an image observed with a ballistic electron emission microscope (BEEM). FIG.
As shown in the STM image of (a), the granular structure of the gold thin film has an average horizontal size of about 15 nm. The measured BEEM (Balistic electron) spectrum is 0.8 V, which indicates that the interface (junction) between the gold thin film and the semiconductor substrate is in Schottky junction and the height of the Schottky barrier is 0. .8 eV. The BEEM current image shown on the right side of FIG. 2 (a) is generally uniform, but a shape depending on the particles of the gold thin film layer can be seen.

The STM shown on the left side of FIG.
A high negative voltage (for example, about 4
When V) is applied, electrons having the corresponding energy are emitted to the interface (junction) through the thin film layer of gold. The electrons emitted at a higher energy than this normal state (3 eV) change the interface. ST taken after applying voltage (-3.6V in this example, about 5 seconds)
The M image and the BEEM image are shown in FIG. The changed area is shown as a black shading in the BEEM image (FIG. 2B, right side: bias voltage -1.6 V). This size is about 40 nm. BEEM measured
In the current spectrum (not shown) of the current (transmission current),
BEEM up to -1.62V for the changed area
No current is observed. That is, it means that the transmission probability in this region is 0. Figure 2 showing the form of the surface
(B) As shown in the figure on the left, a layered or faceted surface can be seen together with the particles of the original round gold thin film.

When a bias voltage having the opposite polarity is applied to the probe in the changed area, the changed area becomes smaller and finally disappears. A series of erasing steps S
The TM / BEEM image is shown in FIG. In FIG. 3, the left side is the STM image, the middle is the BEEM image, and the right side is a diagram that illustrates the change in an easy-to-understand manner. FIG.
(A) shows a region where a BEEM current does not flow after a large negative voltage is applied. A positive voltage (1.34 V) was applied to the probe to scan over a region (47 nm × 47 nm) including the changed portion. As a result, FIG.
As shown in (b), the changed area is the BE of the initial value.
Restore the EM current value. Three dark areas remain at the interface, but these were also reduced to 1 by continuous scanning at a positive voltage.
Erase one by one. Measured BE for recovered area
The EMI-V spectrum shows the Schottky
The barrier shows 0.8 eV, which is the same as the other parts. It should be noted that the changed area remains as it is for one hour or more before being erased.

From the STM image obtained at the same time as the BEEM image, it is considered that the change of the interface is caused by the particles of the gold thin film as the minimum unit with respect to writing and erasing (see FIG. 3). The change in the particle structure of the gold thin film can be better understood in the figure (right side in FIG. 3), which is shown together with the BEEM image (middle in FIG. 3) and clearly illustrates the change. By applying a high negative voltage, certain particles along with the sectioned plane are formed in the corresponding parts (see FIG. 3 (a)). When a positive bias voltage is applied to the probe to scan over the changed area, the crystal grains break down into five parts and one large grain returns to the original BEEM current and the other four Two small parts do not conduct BEEM current (see FIG. 3 (b)). After another scan, of the remaining four
The two parts come together with nearby particles. One on the left will be with the particles having the original BEEM current and the other on the right will be with the parts without the BEEM current (FIG. 3).
(C)). The BEEM by the third and fourth scans
Portions where there is no current are swallowed one by one (see FIGS. 3 (d) and 3 (e)). The dark area in the BEEM image
Finally, all disappear (see FIG. 3E).

During scanning with a positive voltage, the initial BEE
It is important that the particles of the gold thin film having the M current do not change their morphology, and the particles having no BEEM current become unstable with respect to scanning by the positive voltage, and change to the original morphology. . In the series of erasing processes, the boundary between the region without the BEEM current and the initial region exactly coincides with the boundary between the particles of the gold thin film. It is clear that there are no particles or mixed parts. These particles and B
The relationship with the EEM current is that the structural change of the gold particles is BEE
This suggests that it is associated with a change in M current. Basically, it can be seen that the writing and erasing processes use individual particles of the gold thin film as their change units. For this reason, by changing the particle diameter of the gold thin film, the changing region can be reduced.

By using a change in the BEEM current in such a region, a high-density storage medium (recording medium)
Can be configured, and a storage device using this storage medium can be configured. FIG. 4 is an example of such a storage medium and storage device. FIG. 4A shows a configuration example of the storage medium 210. FIG. 4A shows an example in which a gold thin film 212 is used as a metal thin film and silicon 214 is used as a semiconductor substrate. The disk-shaped storage medium 210 configured in this manner is
It is installed in a storage device as shown in (b) to write, read and erase information. Therefore, this storage medium 2
A probe 2 that can move relatively to any position of 10
22. In the example shown in FIG. 4B, as shown by the arrow, the storage medium 210 is constantly rotated by the driving device 252, and the probe 222 can be moved in the radial direction by the driving device 250. The position of the probe 222 may be controlled, for example, by providing a position control track on the medium and reading the track.

Information is written by applying the above-mentioned voltage and the like to the probe 222 by the voltage control unit 220 to change the property of the storage medium 210 with respect to the BEEM current at an arbitrary position. Reading of information is performed by applying a voltage to the probe 222 and determining whether a BEEM current at a specific position of the storage medium 210 flows. The information is erased by moving the probe 222 to the position of the information to be erased and applying a positive voltage.

As described above, it is possible to cause a reversible change in the BEEM current (transmission current) with respect to the interface (bonding portion) between the semiconductor and the metal thin film on the nanoscale. This phenomenon is suitable for high-density storage and recording in the following two items. (1) The written area is erasable and protected by a metal thin film. (2) Since the change occurs in units of metal particles, the unit of change can be reduced by, for example, depositing the metal particles at a low temperature to reduce the size.

[0018]

As described above, high-density erasable storage can be performed by using the present invention.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a configuration that causes a change in a minute area.

FIG. 2 is a diagram showing a change with respect to an interface.

FIG. 3 is a diagram showing that a change in an interface is eliminated.

FIG. 4 is a diagram illustrating a configuration of a storage device.

[Explanation of symbols]

 102 Probe 104 Metal thin film 106 Semiconductor substrate 150 Controller 210 Storage medium 212 Gold thin film 214 Silicon substrate 220 Voltage controller 222 Probe 250 Driver 252 Driver

Claims (5)

[Claims] 1. A storage medium comprising a metal thin film and a semiconductor substrate and having a Schottky junction at a junction between the metal thin film and the semiconductor substrate, storing the storage medium by causing a physical change in the junction. A memory method, in which electrons are injected into the metal thin film from a probe disposed close to the metal thin film, so that a small area where a transmission current does not flow to the junction between the metal thin film and the semiconductor substrate is reduced. A storage method wherein information is stored by creating the information, and a transmission current is recovered by applying a positive voltage to the metal thin film to the probe in the minute area. 2. The storage method according to claim 1, wherein the metal thin film forming the storage medium is a gold thin film, and the semiconductor substrate is a silicon substrate. 3. A storage device for storing, comprising: a metal thin film and a semiconductor substrate; a storage medium having a Schottky junction at a junction between the metal thin film and the semiconductor substrate; A driving unit that relatively drives the storage medium and the probe to drive the probe to a predetermined position on the storage medium; and applies a predetermined voltage to the probe. And a control unit for performing the above operation. By driving electrons from the probe into the metal thin film, a small area where a transmission current does not flow in the junction between the metal thin film and the semiconductor substrate is created. And storing a transmitted current in the minute area by applying a positive voltage to the probe to the metal thin film. 4. The storage device according to claim 3, wherein the storage device reads information depending on whether or not a transmission current flows to a minute area at a predetermined position of the storage medium. 5. The storage device according to claim 3, wherein the metal thin film forming the storage medium is a gold thin film, and the semiconductor substrate is a silicon substrate.