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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an information recording and/or
reproducing apparatus with high density and large capacity using the
principle of scanning tunnel microscope.
2. Related Background Art
Recently, memory devices and the memory systems have found diverse use in
computers and associated instruments, for example the video disk and the
digital audio disk, and are becoming the core of the electronics industry.
Magnetic memories and semiconductor memories have been the majority of
conventional memory devices, but optical memory devices using an
inexpensive high density record medium are now being developed with recent
progress of laser technology. It is desired to realize a memory device or
recording/reproducing apparatus having a larger memory capacity even in
smaller volume in the prospect of computer use at home and information
industrialization mainly of image.
In the meantime, there has recently been developed a scanning tunnel
microscope (as will be referred to as STM) which permits direct
observation of the electronic structure in the surface atom of a
conductor. Using the STM, measurement can be done at a high resolution in
real space irrespective of whether a sample is a single crystal or an
amorphous material. The STM has an advantage that observation may be
performed in low power and without any damage on a material to be
measured, because it uses the method of detecting a micro current.
Further, the STM can be operated in air or in solution as well as in super
high vacuum, so that it is available for measurement of various materials
and expected to be applied in various fields.
An example of applications is a study on a recording apparatus for writing
information at a high resolution in a sample and a reproducing apparatus
for reading information written in the sample at a high resolution, for
example as described in Japanese Laid-open Patent Application Nos.
63-161552 and 63-161553.
The apparatus uses the same probe as the STM, and performs recording by
applying a pulse voltage between the probe and a record medium to locally
change the conductivity. The record medium employed may be a material that
exhibits switching characteristics with memory function with respect to
volt-ampere characteristic, for example thin film layers of chalcogenides
and K-electron organic compounds. The reproduction may be conducted by
detecting a change of tunnel resistance between a region thus recorded and
the non-recorded region. The record medium for this recording method could
be one which changes its surface shape upon application of voltage on the
probe, similarly effecting recording or reproduction of information.
The apparatus employing such STM technology performs the observation while
the probe electrode and the record medium are brought close to each other
up to about 1 nm. Therefore, the distance must be controlled in the order
of angstrom between the probe and the record medium. Further, in recording
or reproducing information pieces arranged in two-dimensional matrix,
two-dimensional scan of probes must be controlled in the order of several
ten angstroms.
There is a proposal to simultaneously drive numerous probes (in multiple
probe arrangement), enhancing a functional improvement of recording or
reproducing, especially with respect to high speed processing. In such an
arrangement a relative position between each probe and the record medium
must be three-dimensionally controlled at the above-stated accuracies in
an area in which the numerous probes are arranged. This control is
conventionally effected by using a laminated piezo-electric device or a
cylindrical piezo-electric device provided on the probe side or on the
record medium side. These devices can ensure a large displacement amount,
but are not suitable for integrated arrangement. Thus, the devices are not
readily used in the recording/reproducing apparatus of multiple probe
type. A solution to such a problem is disclosed in Japanese Laid-open
Patent Application No. 62-281138, in which each probe is mounted on a
cantilever (one-side-supported beam) with length of several hundred .mu.m
and the cantilever is driven by a piezo-electric force or by an
electrostatic force.
However, the information recording and/or reproducing apparatus of an STM
structure with a plurality of probe electrodes needs to control the
distance between each probe electrode and the record medium precisely in
the order of angstrom, and has a big problem of thermal drift due to
thermal expansion in the arrangement requiring a face aligning mechanism
between the surface of the record medium and the surface including the
tips of the plural probe electrodes.
The thermal drift would be a big hindrance in fabrication or use of a high
density and large capacity recording and/or reproducing apparatus.
Supposing a plurality of probes are disposed on a plane of 1 cm square and
if there is a temperature difference of 1.degree. C. between the probe
side and the record medium, a relative position would change by about 0.1
.mu.m on a two-dimensional plane between the probes and the record medium.
In application as the recording and/or reproducing apparatus, such a
positional change causes a tracking error, a reading error, or the like,
resulting in a fatal defect. It is considered that a precise temperature
control may be carried out using a Peltier element or the like to prevent
the thermal drift. This arrangement, however, makes the thus produced
apparatus complicated and expensive.
SUMMARY OF THE INVENTION
The present invention has been accomplished taking into account the
problems as seen in the conventional techniques, and it is, therefore, an
object of the present invention to realize an information recording and/or
reproducing apparatus which can reduce influence of thermal drift while
being low in production cost but high in reliability.
The above object can be achieved by an information recording and/or
reproducing apparatus which performs at least one of record and
reproduction of information in an information record medium with a
plurality of probes, comprising:
a support plate supporting said plurality of probes and segmented into a
plurality of blocks; and
driving means for driving said plurality of blocks independently of one
another.
Also, the object can be achieved by an information recording and/or
reproducing apparatus which performs at least one of record and
reproduction of information in an information record medium with a
plurality of probes, comprising:
an information record medium segmented into a plurality of blocks;
a support plate supporting said plurality of probes; and
driving means for driving said plurality of blocks independently of one
another.
Further, the object can be achieved by an information recording and/or
reproducing apparatus which performs at least one of record and
reproduction of information in an information record medium with a
plurality of probes, comprising:
an information record medium segmented into a plurality of blocks;
a support plate supporting said plurality of probes and segmented into a
plurality of blocks;
first driving means for driving the plurality of blocks of said information
record medium independently of one another; and
second driving means for driving the plurality of blocks of said support
plate independently of one another.
In the arrangement of the present invention the probe support plate or the
record medium is segmented into plural blocks respectively provided with
driving means, so that even if the thermal drift is caused by thermal
expansion so as to change the relative position between the probe support
plate and the record medium a sure reading operation or writing operation
may be executed by moving the blocks independently of one another.
It is important in the present invention to change the relative position
between the record medium and the probes in the plane parallel to the
record medium, but the driving means for each block does not always have
to have a moving mechanism of relative position between the record medium
and the probes in the direction perpendicular to the record medium. In
case that a perpendicular moving mechanism is provided, any force such as
an electrostatic force, a piezo-electric force, and a magnetic force may
be used as a driving force, which may be applied to move either the record
medium or the probes, or both, as described.
The information recording and/or reproducing apparatus of the present
invention performs record or reproduction of information by changing or
detecting a physical quantity concerning the record medium through the
probes. The physical quantity may be any quantity, for example a tunnel
current, a surface electronic state, a shape, etc. In other words, the
apparatus may be one utilizing the scan of probes, as for example in the
scanning tunnel microscope, the interatomic force microscope, the magnetic
force microscope, etc.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a drawing to show the structure of an information recording
and/or reproducing apparatus according to the present invention;
FIG. 2 is a fragmentary plan view of a probe support plate in the apparatus
as shown in FIG. 1;
FIG. 3 is a cross sectional view along the 3--3' line in FIG. 2;
FIG. 4 is a drawing to show recorded bit strings formed on a record medium
as shown in FIG. 1;
FIG. 5 is a fragmentary plan view to show another embodiment of the probe
support plate as shown in FIG. 1;
FIG. 6 is a cross sectional view along the 6--6' line in FIG. 5; and
FIG. 7 is a fragmentary plane view to show another embodiment of the record
medium as shown in FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The preferred embodiments of the present invention will be described in
detail with reference to the accompanying drawings.
FIG. 1 is a drawing to show a basic construction of the information
recording and/or reproducing apparatus according to the present invention.
The information recording and/or reproducing apparatus as shown in FIG. 1
employs the STM structure. In FIG. 1 reference numeral 101 denotes an XY
scan mechanism, 102 a Z-axis control mechanism, 103 a substrate, 104 an
electrode, 105 a record medium, 106 probes, 107 a probe support plate, 108
a multiplexer for switching signals from the plural probes, 109 an XY
driver, 110 a Z-axis driver, 111 a bias power source, and 112 a tunnel
current signal amplifier. The multiplexer 108, the XY driver 109, the
Z-axis driver 110, the bias power source 111, and the signal amplifier 112
are generally controlled by a controller 113.
FIG. 2 is a fragmentary plan view of the probe support plate 107.
There are nine blocks in total arranged in a matrix of 3.times.3 on a Si
substrate 201 in size of 1 cm.times.1 cm, which are arranged to be capable
of being two-dimensionally driven relative to the Si substrate 201. FIG. 2
shows only one block 202 out of the nine blocks. Each block is sized 500
.mu.m.times.500 .mu.m. The block 202 is supported by hinges 203, 204, 205,
206 surrounding the block 202 and by hinges 207, 208, 209, 210 formed to
connect the block 202 with each central portion of hinge 203, 204, 205,
206.
The hinge 203 constitutes driving means together with an electrode 211
formed on a side of a gap on the block 202 side and with an electrode 212
formed on another side of gap on the Si substrate 201 side, and the block
202 is deformed by an electrostatic force when a voltage is applied
between the electrodes 211 and 212 (separated by the gap of 10 .mu.m).
Deformation of each of the other hinges 204, 205, 206 is essentially the
same as that of the hinge 203. The deformations are independently
controlled by the controller 113 for each block. Each of the hinges 203,
204, 205, 206 is sized in length of 800 .mu.m, in width of 15 .mu.m, and
in thickness of 0.5 mm, and each of the hinges 207, 208, 209, 210 is sized
in length of 200 .mu.m, in width of 15 .mu.m, and in thickness of 1 .mu.m.
Applying a voltage of 0-50 V between the electrodes 211 and 212, the block
202 was moved in .+-.0.5 .mu.m by displacement of the hinges. When the
block 202 is moved by displacing the hinges, two hinges opposing each
other with the block 202 between them should be preferably displaced in
the same direction to prevent the block 202 from having a strain. A value
of voltage applied to the electrodes at each hinge may be suitably
determined taking this into account.
Six cantilevers 213 are formed on the block 202, on each of which a probe
106 is provided for detecting a tunnel current. Each of the cantilevers
213 is sized in length of 220 .mu.m, in width of 80 .mu.m, and in
thickness of 1 .mu.m.
Tunnel currents detected by the six probes 106 formed on the block 202 are
fed to the multiplexer circuit 108, and the multiplexer 108 selects only
tunnel current signals from a block to be read and supplies the signals
through wiring 216 to the controller 113 (as shown in FIG. 1), where read
information is checked.
The entire production process of the above components employs that of Si IC
including the photolithography, the anisotropic etching of Si single
crystal, and so on. Therefore, the components were able to be made at high
precision and in good productivity.
FIG. 3 is a cross sectional view along the 3--3' line in FIG. 2.
A Si wafer 301 has the (100) orientation, and SiN films 304, 305 are formed
on the Si wafer 301 in thickness of 1 .mu.m by the CVD method, forming the
Si substrate 201. Ag is deposited on a tip of each cantilever 213 to form
a probe 106 for detecting a tunnel current. Each probe 106 is connected
through the wiring 216 to the multiplexer circuit 108 made on the Si wafer
301. The electrodes 211, 212 for electrostatic drive are formed facing
each other on side walls substantially perpendicular to the upper surface
of Si substrate 201 in the portion of Si substrate 201 forming each hinge.
The cantilevers 213 as described have no actuating portion and the
cantilevers 213 are brought into a contact with a record medium in
recording and/or reproducing, using the elasticity of the cantilever 213.
Now described is a relative displacement between the cantilevers 213 and
the record medium. As for the vertical displacement in the Z-direction,
that is, in the direction perpendicular to the record medium 105 (see FIG.
1), a coarse movement is performed using the Z-axis control mechanism 102
as shown in FIG. 1. More specifically, the record medium 105 is driven by
a cylindrical piezo-electric device (not shown) arranged above the XY scan
mechanism 101 in FIG. 1. A fine movement is carried out by the passive
drive using the elasticity of cantilevers 213.
The XY scan mechanism 101 as shown in FIG. 1 is used to effect the movement
in the X and Y directions, that is, to effect scanning and tracking in the
direction of plane of record medium. Specifically, a stainless steel frame
on which the record medium 105 is mounted is driven by a laminated
piezo-electric device (not shown).
The record medium 105 used in the present embodiment was made such that Au
was evaporated on a glass substrate and four layers of polyimide LB film
were then built up in thickness of about 15 .ANG. over the Au layer. In
this arrangement, when a pulse voltage was applied between a probe 216 on
a cantilever 213 and the Au layer of undercoat in record medium 105, the
electrical resistivity of record medium changed approximately two figures,
and the change state of electric resistivity was maintained so as to
enable information recording. The change area of electrical resistivity
had a very small size of 100 .ANG..times.100 .ANG., enabling super high
density recording.
After that, reproduction was carried out using the same probe 106 as in
recording. A bias voltage of lower voltage value than the pulse voltage in
recording was applied between the probe 106 and the Au layer in the above
record medium 105, and a change in tunnel current was read between the
probe and the Au layer to detect a portion different in electrical
resistivity on the record medium 105, whereby it was confirmed that
information record and reproduction could be effected by the same probe.
The following experiment was carried out to check whether the influence of
drift due to a temperature change could be removed. Fifty four probes on
the Si substrate 201 were operated in parallel at an ambient temperature
of 20.degree. C. to write information as record bit trains by the
above-described method.
FIG. 4 is a drawing to schematically show the state of record bit trains
formed on the record medium 105 in the writing as described above.
In FIG. 4, numeral 402 denotes a record bit, and numerals 403, 404, 405,
406, and so on record areas recorded by the respective blocks. Then,
information reading was carried out using the record bits at ambient
temperature of 25.degree. C. in the above method. Out of the fifty four
probes, a probe in the left upper block was set as a reference, and
two-dimensional positioning was carried out between the record medium 105
and the probes 106 by totally driving the probe support plate 107 by the
XY scan mechanism 101. A deviation amount caused by temperature drift in
the record area 403 was within a space between record bit trains (which is
about 20 nm), so that the recorded information could correctly be read. In
the other blocks positions of tips of probes were deviated from the record
bit positions written because of the temperature drift, so that reading
was impossible. Then, reading positions of recorded bits were adjusted by
independently displacing the nine blocks by the electrostatic force as to
compensate the deviation amount caused by the temperature drift, which
enabled correct reproduction of recorded information.
Another embodiment of the present invention will be next described.
The present embodiment has a similar arrangement to the preceding
embodiment, in which the probe support plate is divided into blocks of
3.times.3 and each block is displaced by a piezo-electric force.
FIG. 5 is a fragmentary plan view of a probe support plate used in the
present embodiment.
Nine blocks in total arranged in a matrix of 3.times.3 are produced on a Si
substrate 501 having a size of 1 cm.times.1 cm, which are arranged to be
capable of being two-dimensionally driven relative to the Si substrate
501. Among the blocks only one block 502 is shown in FIG. 5.
Each block is sized in 500 .mu.m.times.500 .mu.m. The block 502 is
supported by hinges 503, 504, 505, 506 surrounding the block 502 and by
hinges 507, 508, 509, 510 formed to connect the block 502 with each
central portion of hinge 503, 504, 505, 506. A segmental piezo-electric
layer 511 is provided on each of the hinges 503, 504, 505, 506.
Cantilevers 512, probes for tunnel current detection 513, a multiplexer 514
and wiring 515 are substantially the same as the cantilevers 213, the
probes for tunnel current detection 106, the multiplexer 108, and the
wiring 216, respectively, in FIG. 1 or in FIG. 2 showing the prior
embodiment.
FIG. 6 is a cross sectional view along the line 6--6' in FIG. 5.
In FIG. 6 a SiN film 602 is formed on a Si wafer 601, forming the Si
substrate 501. The Si wafer 601 is removed by etching in a portion of each
hinge to leave only SiN film 603, and an electrode 604 is formed of Au
film on the SiN film 603. Separate piezo-electric layers 511.sub.,
511.sub.2 are formed of a ZnO film in thickness of 1 .mu.m on the
electrode 604 as the piezo-electric layer 511 as shown in FIG. 5.
Electrodes 607, 608 are formed of Au film on the piezo-electric layers
511.sub.1, 511.sub.2, respectively. Applying electric fields different in
sign between the electrodes 604 and 607 and between the electrodes 604 and
608, each of the hinges 503, 504, 505, 506 (see FIG. 5) is deformed. When
a voltage of 0--10 V is applied, the block 502 is displaced in .+-.0.2
.mu.m.
Using the same record medium as in the preceding embodiment, the writing of
record bits was carried out at ambient temperature of 20.degree. C. and
the reading of recorded bits at ambient temperature of 22.degree. C.
Accurate recording and/or reproducing of information was conducted by
independently controlling the blocks in the same manner as in the
preceding embodiment.
Still another embodiment of the present invention will be next explained.
A probe plate employed in this embodiment is similar to those in the prior
embodiments, and a record medium is such that Au is evaporated onto a Si
wafer and four layers of polyimide LB film are formed in about 15 .ANG. on
the Au layer. The information recording and/or reproducing method is the
same as in the prior embodiments.
FIG. 7 is a fragmentary plan view of the record medium used in the present
embodiment.
Each construction and size of a Si substrate 701, a block 702 in which
information is recorded, and hinges 703, 704, 705, 706, 707, 708, 709, 710
supporting the block 702 are the same as those of the Si substrate 201,
the block 202 in which the probes for recording information are formed,
and the hinges 203, 204, 205, 206, 207, 208, 209, 210 supporting the block
202, respectively, as shown in the prior embodiment.
A comb-shaped electrode 712 is formed on the hinge 703 by impurity doping
and photolithography, and a similar comb-shaped electrode 711 is formed to
oppose the comb-shaped electrode 712 on the Si substrate 201 side. Numeral
713 denotes a wiring portion. The same comb-shaped electrodes are formed
on each of the hinges 704, 705, 706, which are omitted to denote for
brevity of illustration.
A gap is approximately 1 .mu.m between the above comb-shaped electrodes
711, 712, a size of comb is so defined as to form teeth each of 10
.mu.m.times.50 .mu.m along a distance of 0.5 mm, and the number of comb
pairs is 10-20. When a voltage of 0-50 V was applied between the
comb-shaped electrodes 711 and 712, the hinges 703, 704, . . . were
deformed, whereby the block 702 was displaced in .+-.0.3 .mu.m.
Using the probe plate and the record medium as described, writing of record
bits was carried out at ambient temperature of 20.degree. C. and reading
of recorded bits at ambient temperature of 30.degree. C. Accurate
information record and/or reproducing was effected in the same manner as
in the prior embodiments by independently controlling the respective
blocks on the probe side and on the record medium side.
Even though the temperature upon reading was higher in the present
embodiment than that in the prior embodiments, accurate information
reading was made in the same manner as in the prior embodiments. This
result shows that the amount of thermal drift itself becomes decreased and
an adjustable range is widened, because the substrates of probe and record
medium both are of Si and because the probe plate and the record medium
both are segmented in blocks. Thus, the apparatus may be used in a wider
range of temperature.
Although the driving means is driven by the electrostatic force or by the
piezo-electric force in the embodiments as described, the driving force is
not limited to these, but may be selectively used depending upon a shape
or an arrangement of recording and/or reproducing apparatus.
Although the above description concerns the case in which the control of
the respective blocks are carried out in reading in the embodiments, the
blocks may be controlled in either of writing and reading with a record
medium in which record positions are predetermined, which would allow more
accurate information record and/or reproduction.
As so arranged as described, the present invention may show the following
advantages. (1) Moving the record medium or the probes in accordance with
the thermal drift caused by thermal expansion, the influence of thermal
drift may be reduced and a bit size of information record may be made
smaller, achieving a record and/or reproduction apparatus with a high
density and a large capacity. (2) Since the control is conducted for each
block, a load on electric control system may be lighter, providing an
inexpensive, reliable recording/reproducing apparatus. Also, sufficient
dimensions may be secured for the portion which is displaced in the record
medium plane, so that a recording and/or reproducing apparatus may be
provided with a large operation margin and with high reliability and
durability. (3) The probes, the record medium, and the substrates may be
selected without taking the difference of thermal expansion into
consideration, and therefore a material excellent in recording and
reproducing properties may be used as the record medium, whereby a
recording and/or reproducing apparatus may be provided with high
reliability.
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