U.S. patent application number 09/413449 was filed with the patent office on 2001-11-29 for magnetic scanning or positioning system with at least two degrees of freedom.
Invention is credited to HAEBERLE, WALTER, LUTWYCHE, MARK I., VETTIGER, PETER.
Application Number | 20010045530 09/413449 |
Document ID | / |
Family ID | 8232883 |
Filed Date | 2001-11-29 |
United States Patent
Application |
20010045530 |
Kind Code |
A1 |
HAEBERLE, WALTER ; et
al. |
November 29, 2001 |
MAGNETIC SCANNING OR POSITIONING SYSTEM WITH AT LEAST TWO DEGREES
OF FREEDOM
Abstract
A scanning or positioning system with at least two degrees of
freedom is provided comprising a supporting base equipped with
magnets, a movable platform equipped with at least two electrical
coils, and suspension elements providing an elastic connection
between the movable platform and the supporting base. The
electrical coils are positioned flat on the movable platform,
thereby forming an essentially flat arrangement with the movable
platform. Combining the flat arrangement with the flat supporting
base yields a scanning or positioning system which is potentially
compact, lightweight and flat and which features fast response, low
power consumption and a relatively large range of motion, e.g. up
to 10 mm. The scanning or positioning system with at least two
degrees of freedom can be used in the field of scanning probe
microscopy or in the field of data storage or imaging.
Inventors: |
HAEBERLE, WALTER;
(WAEDENSWIL, CH) ; LUTWYCHE, MARK I.; (ADLISWIL,
CH) ; VETTIGER, PETER; (LANGNAU, CH) |
Correspondence
Address: |
YOSHIHIRO ICHII
IBM CORPORATION
INTELLECTUAL PROPERTY LAW DEPARTMENT
P O BOX 218
YORKTOWN HEIGHTS
NY
10598
|
Family ID: |
8232883 |
Appl. No.: |
09/413449 |
Filed: |
October 6, 1999 |
Current U.S.
Class: |
250/548 |
Current CPC
Class: |
B82Y 15/00 20130101;
H02K 2201/18 20130101; H02K 99/20 20161101; H02K 41/0354
20130101 |
Class at
Publication: |
250/548 |
International
Class: |
G01N 021/86 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 30, 1998 |
EP |
98120527.1 |
Claims
What is claimed is:
1. A magnetic scanning or positioning system with at least two
degrees of freedom comprising a supporting base equipped with at
least one magnet, a movable platform equipped with at least two
electrical coils, and suspension elements providing an elastic
connection between said movable platform and said supporting base,
wherein said magnet and said electrical coils are arranged in such
a way that translational and/or rotational relative movements of
said movable platform and supporting base are generated when a
current is passed through said electrical coils, and said
electrical coils are positioned flat on or in said movable
platform, thereby forming an essentially flat arrangement with said
movable platform.
2. The system according to claim 1, wherein said supporting base
and the magnet are flat and positioned in such a way that an
essentially flat arrangement is formed.
3. The system according to claim 1, wherein said system is covered
by a sheet comprising a magnetic material to close the magnetic
circuit on top.
4. The system according to claim 1, wherein said electrical coils
are flat coils attached to said movable platform.
5. The system according to claim 1, wherein said electrical coils
are spiral in shape.
6. The system according to claim 1, wherein said electrical coils
constitute an integral part of said movable platform.
7. The system according to claim 1, wherein said electrical coils
constitute the major part of said movable platform concerning
weight or volume.
8. The system according to claim 1, wherein said movable platform
is equipped with additional coils and said supporting base with
additional magnets thereby allowing up to six degrees of
freedom.
9. The system according to claim 1, wherein said suspension
elements or an electrically conducting part of said suspension
elements are used for supplying said current to said electrical
coils.
10. The system according to claim 1, wherein said suspension
elements and said movable platform have been fabricated using the
same substrate, and/or the same process sequence as said movable
platform and/or said electrical coils.
11. The system according to claim 1, wherein said suspension
elements and a supporting frame, to which said suspension elements
are connected, have been fabricated using the same substrate,
and/or the same process sequence.
12. The system according to claim 1, wherein said suspension
elements are elongated beams.
13. The system according to claim 12, wherein said elongated beams
are divided into at least two portions, whereby adjacent portions
form an angle.
14. The system according to claim 13, wherein said angle is a right
angle.
15. The system according to one of claim 1, wherein the movable
platform comprises a substrate made of Si, or SiN.sub.x, or a
ceramic material, or a metal.
16. The system according to one of claim 1, wherein said movable
platform and said at least two electrical coils have been
fabricated by planar and/or thinfilm and/or thickfilm and/or
galvanic processing.
17. The system according to claim 1, wherein the gap between said
magnet and the movable platform and/or said electrical coils is
filled with ferro-fluid.
18. A magnetic scanning or positioning system with at least two
degrees of freedom comprising: a supporting base equipped with at
least two electrical coils, a movable platform equipped with at
least one magnet, and suspension elements providing an elastic
connection between said movable platform and said supporting base,
wherein said magnet and said electrical coils are arranged in such
a way that translational and/or rotational relative movements of
said movable platform and supporting base are generated when a
current is passed through said electrical coils, said electrical
coils are positioned flat on or in said supporting base, thereby
forming an essentially flat arrangement with said supporting base,
and said magnet is positioned flat on or in said movable platform,
thereby forming an essentially flat arrangement with said movable
platform.
19. The system according to claim 1, having at least three degrees
of freedom, wherein said system comprises at least three
controllers and is usable to align two essentially planar devices
and/or to bring two essentially planar devices into contact in such
a way that the surfaces of said devices are kept essentially
parallel.
20. A storage system comprising a storage medium, a writing and/or
sensing device and a magnetic scanning or positioning system for
approaching and scanning said storage medium and said writing
and/or sensing device relative to each other, said magnetic
scanning or positioning system with at least two degrees of freedom
further comprising a supporting base equipped with at least one
magnet, a movable platform equipped with at least two electrical
coils, and suspension elements providing an elastic connection
between said movable platform and said support base, wherein said
magnet and said electrical coils are arranged in such a way that
translational and/or rotational relative movements of said movable
platform and supporting base are generated when a current is passed
through said electrical coils, and said electrical coils are
positioned flat on or in said movable platform, thereby forming an
essentially flat arrangement with said movable platform.
21. A method for fabricating a movable platform with integrated
electrical coils comprising the steps of: producing deep trenches
in a flat substrate, which have the shape of said electrical coils
to be formed, opening the deep trenches from the backside, filling
said deep trenches with an electrically conductive material,
providing a second level metallization.
22. The method according to claim 21, wherein an insulation layer
is grown or deposited on the sidewalls of said deep trenches, if
said substrate is conductive.
23. The method according to claim 21, wherein said deep trenches
are opened from the backside by backside etching.
24. The method according to claim 21, wherein in an additional step
the substrate areas around the movable platform are removed to
release the movable platform from the substrate.
25. The method according to claim 21, wherein the process steps and
said flat substrate are also used to fabricate a supporting frame
and/or suspension elements.
26. The method according to claim 21, wherein said deep trenches
are filled with a conductive material using galvanic plating.
27. The method according to claim 21, wherein narrow bridges in a
sacrificial layer are used to keep said movable platform together
during backside etching and filling of said deep trenches.
28. The method according to claim 27, wherein a conductive seed
layer is used for filling the deep trenches by galvanic
plating.
29. The method according to claim 21, wherein said substrate is a
silicon wafer.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention is related to a magnetic scanning or
positioning system with at least two degrees of freedom.
[0003] 2. Discussion of the Related Art
[0004] Magnetic actuators are ubiquitous. They are economical,
reliable, easy to power and provide good power to weight and power
to volume ratios. They can be found in a large variety of
applications ranging from a large train to the smallest timepiece.
However, most magnetic actuators--even the smallest ones--are still
made using wound coils rather than a batch fabrication process.
[0005] Hard disk drives contain magnetic actuators for positioning
the read/write heads. The actuators are usually compact and flat,
but they are only able to generate a one-dimensional rotational
movement. This limits their use to specific applications. Another
design is needed for storage systems where a surface of a storage
medium is to be scanned in x and y direction.
[0006] In the PCT patent application WO 96/07074, as published on
Mar. 7, 1996, and currently owned by the present applicant, a fine
positioning apparatus with atomic resolution is described. The fine
positioning apparatus basically comprises magnetic actuators
and--in the preferred embodiment--mechanical means for damping or
decreasing the motion of said magnetic actuators. The driving
system of said magnetic actuators is similar to a voice coil. The
fine positioning apparatus according to WO 96/07074 is therefore
referred to as `voice coil actuator`. It can be used in the field
of Scanning Probe Microscopy such as Scanning Tunneling Microscopy
(STM) or Atomic Force Microscopy (AFM) and/or in the field of data
storage, where precise positioning of magnetic, optical, electrical
or mechanical writing and sensing devices is crucial.
[0007] In the paper `Microfabrication and parallel operation of
5.times.5 2D AFM cantilever arrays for data storage and imaging` by
M. Lutwyche et al., Proc. IEEE Int'l Workshop on MICRO
ELECTROMECHANICAL SYSTEMS (MEMS' 98), Heidelberg, Germany, Jan.
25-29, 1998, a fine positioning system with 5 degrees of freedom is
presented. A 2D AFM cantilever array is scanned in x and y
direction--i.e. parallel to a surface of the array--using voice
coil actuators with ranges of 30 .mu.m and 15 .mu.m, respectively.
Three additional voice coil actuators, also with a 30 .mu.m-range,
are used in a triangular arrangement to move and level the sample
in z direction--i.e. perpendicular to a surface of the array. The
main disadvantage of said fine positioning system is its volume and
weight.
[0008] For data storage applications as well as in other
applications such as optical beam scanners or optical focusing and
alignment systems, a scanning or positioning system is needed,
which is small, flat, lightweight, and shock resistant and which
features fast response, low power consumption, and a large range of
motion.
SUMMARY OF THE INVENTION
[0009] It is an object of the present invention to overcome the
drawbacks of known scanning or positioning systems.
[0010] It is still another object of the present invention to
provide a scanning or positioning system with at least two degrees
of freedom, which is small, flat and lightweight, and which
features fast response, low power consumption and a potential range
of motion between 1 .mu.m and 10 mm.
[0011] It is still another object of the present invention to
provide a scanning or positioning system which can be fabricated
using common batch fabrication techniques, and to provide a method
for making such scanning or positioning systems.
[0012] This is accomplished by the scanning or positioning system
and fabrication process described in the present application. The
scanning or positioning system comprises a supporting base equipped
with at least one magnet, a movable platform equipped with at least
two electrical coils, and suspension elements providing an elastic
connection between the movable platform and the supporting base.
The magnet and the electrical coils are arranged in such a way that
translational and/or rotational relative movements of the movable
platform and supporting base are generated when a current is passed
through the electrical coils. The electrical coils are positioned
flat on or in the movable platform, thereby forming an essentially
flat arrangement with the movable platform.
[0013] The working principle and the basic arrangement of the coil
windings and permanent magnets are shown in FIGS. 2 and 3. In FIG.
2 the windings are placed in the vertical field of permanent
magnets, whereby one half of the electrical coil is located over a
N-pole and the other half over a S-pole. When a current is passed
through the electrical coil, a force is generated moving the
electrical coil to the left (direction of current flow and magnetic
field as indicated in the drawing).
[0014] In FIG. 3 the windings are placed in the horizontal or
fringe field of permanent magnets, whereby one half of the
electrical coil is located between the poles and the other half
beside one of the poles. When a current is passed through the
electrical coil, a force is generated moving the electrical coil
upwards (in z direction; direction of current flow and magnetic
field as indicated in the drawing). Using two electrical coils
located on opposite sides of the movable platform allows to
generate a tilt about a horizontal axis (x or y tilt). The up and
down movement as well as the x and y tilt have only a limited range
of motion. But nevertheless they are very important for many
applications.
[0015] The flat arrangement of the movable platform and the
electrical coils opens new possibilities for the construction and
fabrication of the movable parts. Lightweight construction is
enhanced in particular. A feature which is desired for fast
response and low power consumption. The sensitivity to shocks and
vibrations is reduced too. The resonant frequency is in the order
of 100 Hz to 1 kHz for a range of motion between 100 .mu.m and 1
mm.
[0016] Another advantageous feature of the scanning or positioning
system with at least two degrees of freedom is its relatively large
range of motion in horizontal direction.
[0017] NOTE: A piezoelectric actuator has a range of motion of
about 10 .mu.m or less.
[0018] Combining the flat arrangement of the movable platform and
the electrical coils with a flat supporting base and flat
(permanent) magnets yields a scanning or positioning system, which
is potentially compact, lightweight, and flat and which has a good
power to volume and power to weight ratio. The scanning or
positioning system can be used in a large variety of applications
including present and future data storage and imaging systems. The
outer dimensions of such a storage system could be about 20
mm.times.20 mm.times.4 mm for the complete system.
[0019] NOTE: The smallest version of the known voice coil scanner
has outer dimensions of about 30 mm.times.30 mm.times.30 mm.
[0020] Various modifications and improvements of the scanning or
positioning system are as follows:
[0021] Power performance of the scanning or positioning system can
be improved by placing a component part comprising a ferro-magnetic
material on the side opposite to the permanent magnets e.g. by
covering the system with a magnetic steel sheet which closes the
magnetic circuit on top. This decreases the reluctance and makes
the magnetic field more uniform. The cover sheet may have an
opening, where the movable platform can be accessed.
[0022] The movable platform may be equipped with discrete flat
coils which are attached e.g. by gluing or soldering.
[0023] Good flatness is achieved when the coils are spiral in
shape, i.e. when the coil windings lay all in one single plane.
[0024] The fabrication is simplified considerably when the movable
platform and the suspension elements are fabricated as one part. In
this case it is possible to use the same substrate and/or process
sequence for the fabrication. In the same way the movable platform
and suspension elements can be combined with a supporting frame, to
which said suspension elements are connected. Using the same
substrate allows to apply batch or other mass production
techniques.
[0025] Batch processing can also be applied when the electrical
coils are an integral part of the movable platform. If the coils
are located on the movable platform, the processes used are similar
as in printed circuit board fabrication, whereby additive or
subtractive processing may be used. Thick film processing may also
be applied. If the coils are located in the movable platform,
similar process steps as in the fabrication of integrated circuits
are used. In both cases, the movable platform, the electrical coils
and the electrical conductors needed to connect the coils can be
fabricated in the same process sequence.
[0026] Of course it is also possible to combine the fabrication of
the movable platform and electrical coils with the fabrication of
the suspension elements and the supporting frame. Beside economical
benefits batch processing has also the advantage that the resulting
components exhibit maximum flatness.
[0027] Suitable substrates are e.g. oxidized silicon wafers or flat
sheets consisting of SiN.sub.x or a ceramic material or a
metal.
[0028] Optimum power to weight and power to volume ratios can be
achieved when the electrical coils constitute the major part of the
movable platform. Such a movable platform can be fabricated using
the process described in the claims and the Detailed Description
section.
[0029] Up to six degrees of freedom are possible, when the movable
platform is equipped with additional coils and the supporting base
with additional permanent magnets.
[0030] The suspension elements may have the form of long narrow
beams. This has several advantages especially when the beams are
fabricated together with the movable platform using the same
substrate and/or the same process sequence. Long narrow beams will
help to decrease stiffness of the platform suspension and to
increase fatigue-life of the beams.
[0031] In a modification said long narrow beams are divided into at
least two portions, whereby adjacent portions form a right angle.
This allows an extended length by carrying the beams around the
movable platform and free deformation in more than one
direction.
[0032] System performance might be improved by using a ferro-fluid
to close part of the air gap between the permanent magnets and the
electrical coils. This allows better cooling of the electrical
coils.
[0033] In a modification of the scanning or positioning system, the
(permanent) magnets are located on or in the movable platform and
the electrical coils on or in the supporting base. In this case the
movable platform and the suspension elements can be made of a thin
magnetic steel sheet. The supporting base is preferably also made
of magnetic steel. This allows to achieve a thin air gap and a high
magnetic induction giving the system a high power performance.
[0034] The scanning or positioning system can be used to advantage
in data storage systems. Such a system may comprise a storage
medium with nm-sized magnetic storage elements, one or several
magnetic read/write heads located e.g. on an Atomic Force
Microscope (AFM) cantilever, and said scanning or positioning
system, which is used to approach, to align and to scan the storage
medium with the magnetic read/write heads.
[0035] The invention can also be used to advantage in approach
systems. Such a system comprises a planar device, e.g. a flat
substrate which needs to be patterned, and a second device as e.g.
an AFM cantilever or an array of AFM cantilevers each with one or
several apertures. During patterning the cantilevers act as shadow
masks as addressed in copending patent application 98118283.5 filed
on Sep. 28, 1998, currently assigned to the present applicant. The
approach system further comprises said scanning or positioning
system, at least three controllers for the z movement and x and y
rotation, and at least three sensors for detecting the bending of
the cantilevers at three different locations. The output signal of
the sensors is fed to the controllers. The approach system can be
used to approach the substrate with the cantilever array so that
the surfaces of the substrate and the cantilever array are
essentially parallel, and to maintain the cantilever array at
constant height with respect to the substrate.
[0036] The scanning or positioning system can also be used to
advantage in scanning probe systems such as AFM or STM systems and
applications. Due to the large range of motion it allows coarse as
well as fine positioning.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] The invention is described in detail below with reference to
the following schematic drawings. All the figures are for the sake
of clarity not shown in real dimensions, nor are the relations
between the dimensions shown in a realistic scale.
[0038] FIGS. 1a & 1b show a top view and cross section of a
first embodiment of the invention with two degrees of freedom
(movement in x and y direction).
[0039] FIGS. 2 and 3 illustrate the working principle and the basic
arrangement of coil windings and permanent magnets for motion in x
and y direction (FIG. 2) and in z direction (FIG. 3).
[0040] FIG. 4 shows an embodiment wherein the scanning or
positioning system is covered with a magnetic steel sheet.
[0041] FIG. 5 shows an embodiment of the invention with 5 degrees
of freedom.
[0042] FIGS. 6a to 6i illustrate a fabrication process, in
accordance with the present invention, for manufacturing a movable
platform with integrated electrical coils.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE
INVENTION
[0043] In a first embodiment of the invention a scanning or
positioning system with two degrees of freedom is described
(movement in x and y direction). The top view and cross section are
shown in FIGS. 1a and 1b. The scanning or positioning system
comprises a supporting base 6 equipped with six permanent magnets
7.1 and 7.2 preferably of equal size, which produce a static
magnetic field. Note that any other kind of magnet, such as
electromagnets, can be used instead. The four outer magnets 7.1
have all the same polarization (N-poles), whereas the two inner
magnets 7.2 have opposite polarization (S-poles), as indicated in
FIG. 1b. The supporting base 6 is preferably made of magnetic
steel, thereby closing the magnetic circuit between N- and S-poles
on the lower side. The magnetic field on the upper side is
schematically represented in FIG. 1b by the magnetic lines of force
8. In the present embodiment, the outer dimensions of the
supporting base 6 are about 20 mm.times.20 mm, and the thickness
about 3 mm. The permanent magnets 7.1 and 7.2 do not protrude above
the supporting base 6, so that the arrangement consisting of the
supporting base 6 and the permanent magnets 7.1 and 7.2 is
essentially flat. Essentially flat means that the aspect ratio R of
the overall length to the overall thickness is greater than 4:1
(i.e. R>4), and typically about 10:1 (R=10) or even greater.
[0044] The scanning or positioning system further comprises a
movable platform 1 equipped with four electrical coils 2 which are
spiral in shape, a supporting frame 5, and four suspension elements
4 providing an elastic connection between the movable platform 1
and the supporting frame 5. The arrangement consisting of the
movable platform 1 and the electrical coils 2 is also essentially
flat, i.e. the aspect ratio R is greater than 4:1 (R>4) and
typically about 15:1 (R=15). All unused areas on the movable
platform 1 are cut off in order to keep the mass as low as
possible. The connections of the electrical coils 2 to external
power supplies are for the sake of clarity not shown in FIGS. 1a
and 1b. The connections could be made using e.g. discrete wiring,
or a second level of metallization for connecting the inner end of
the electrical coils 2, and for connecting the electrical coils 2
to external terminals using electrical conductors running via the
suspension elements 4.
[0045] The electrical coils 2 come to lie in the vertical field of
the permanent magnets 7.1 and 7.2, whereby the S-poles 7.2 are
shared by all electrical coils 2. The permanent magnets 7.1 and 7.2
and the movable platform 1 are separated by a gap, so that they do
not make contact. In operation, a current passing through one of
the electrical coils 2 generates a force in x or y direction, i.e.
parallel to a surface of the movable platform 1. A translational
movement is generated when the vector of current flow in opposite
electrical coils is equal, an additional angular moment and
rotational movement around the z axis is generated when the vector
of current flow in opposite electrical coils is not equal (i.e.
different in direction or magnitude). In order to achieve proper
translational movements, the force generated by a single current
carrying coil or a group of coils must be in line with the reaction
force of the platform suspension. This is best achieved by a
symmetrical arrangement of the electrical coils 2 and the
suspension elements 4. In the present embodiment, a pair of coils
is used each for the x and y movement, and the arrangement of the
electrical coils 2 is axially symmetrical, exhibiting four fold
symmetry. The arrangement of the suspension elements 4 is axially
symmetrical too, and also exhibiting four fold symmetry. All four
suspension beams have the same shape and the same spring constant.
The attachment to the movable platform 1 and the supporting frame 5
is usually also symmetrical, and preferably located in the centers
or corners of the platform and frame outline.
[0046] The movable platform 1 with the electrical coils 2, the
supporting frame 5, and the suspension elements 4 are fabricated in
the same process sequence using batch fabrication techniques.
Following fabrication process may be used: Starting with a larger
substrate such as a oxidized silicon wafer, the electrical coils 2
are made by e.g. deposition of a seed layer followed by a
lithography and etching step. The conductors are then built up
using galvanic plating. The movable platform 1, the supporting
frame 5 and the suspension elements 4 are defined in a second
lithography and etching step. The movable platform 1 with the
electrical coils 2, the supporting frame 5, and the suspension
elements 4 thus produced have an overall thickness of about 0.8 mm
and form an essentially flat arrangement having an aspect ratio R
of about 27. The outer dimensions of the complete scanning or
positioning system are typically about 20 mm.times.20 mm.times.4
mm.
[0047] In the most basic embodiment (not illustrated in any
Figure), the scanning or positioning system with two degrees of
freedom (e.g. movement in x and y direction) comprises the
supporting base 6 equipped with just one (permanent) magnet 7.1 or
7.2 with either N- or S- pole up. The supporting base 6 is
preferably made of magnetic steel, thereby closing the magnetic
circuit on the lower side. The system further comprises the movable
platform 1 equipped with only two electrical coils, the supporting
frame 5, and four suspension elements 4 providing an elastic
connection between said movable platform 1 and said supporting
frame 5. The electrical coils 2 are placed partially, e.g. with one
half in the vertical field of the (permanent) magnet 7.1 or 7.2,
whereby one coil is placed along the length and one along the width
of the permanent magnet 7.1 or 7.2. The permanent magnet 7.1 or 7.2
and the movable platform 1 are separated by a gap, so that they do
not make contact. In operation, a current passing through one of
the electrical coils 2 generates a force in x or y direction, i.e.
parallel to a surface of the movable platform 1.
[0048] In another embodiment shown in FIG. 4 the scanning or
positioning system is covered with a magnetic steel sheet 42. The
opening 41 in the center of the magnetic steel sheet 42 is optional
and depends on the application. The movable platform 1 is equipped
with four electrical coils 2, two of which are shown in the cross
section in FIG. 4. The scanning or positioning system further
comprises a supporting base 6 equipped with 4 pairs of permanent
magnets 7.1 and 7.2, of which two pairs are shown in the cross
section of FIG. 4. The permanent magnets 7.1 and 7.2 and the
electrical coils 2 are located outside the opening 41 to take full
advantage of said magnetic steel sheet 42. In operation, a current
passing through one of the electrical coils 2 generates a force in
x or y direction, i.e. parallel to a surface of the movable
platform 1. Due to the magnetic steel sheet 42 at the top, the
reluctance of the magnetic circuit is decreased, while the magnetic
induction and power efficiency is increased. In addition, the
magnetic field between the permanent magnets 7.1 and 7.2 and the
magnetic steel sheet 42 is more uniform than the open field of the
first embodiment. A typical application are storage systems. Such a
system may comprises a storage medium 44 located on the movable
platform 1 and a read/write head 45 located on the supporting base
6. In another application not shown in FIG. 4 an AFM cantilever
could be attached to the movable platform 1. The cantilever may be
used to scan a surface of an external device. In this case said
opening 41 in the magnetic steel sheet 42 will be needed.
[0049] Another embodiment of the invention is shown in FIG. 5. It
is a planar scanning or positioning system with 5 degrees of
freedom. The scanning or positioning system comprises a movable
platform 1 equipped with 9 electrical coils 2, a supporting frame
5, and four suspension elements 4 providing an elastic connection
between said movable platform 1 and said supporting frame 5. The
outer dimensions of the supporting frame 5 are about 20 mm.times.20
mm. The nine electrical coils 2 have following functions: 2 are for
the x, 2 are for the y and 1 for the z motion, and 2 each for the x
and y rotation. With an extra coil, a z rotation would also be
possible. The arrangement of said electrical coils 2 is shown in
the upper part of FIG. 5. Said suspension elements 4 have the shape
of long narrow beams, i.e. the ratio of their length to their width
is more than 10 and typically about 40, and each beam is divided
into two portions which form a right angle. Alternatively, the
suspension elements 4 could e.g. comprise relatively large elements
made of an elastomeric material. In the present embodiment, said
long narrow beams mainly consist of two copper-conductors running
parallel at narrow distance. Said copper-conductors are used for
supplying current to said electrical coils 2. Three of the
conductors are used as ground, leaving one each for the x, y and z
motion and the two rotations. The length of the suspension elements
is determined so that a current of 0.5 A provides a motion of about
1 mm in x and y direction and of about 100 .mu.m in z direction.
This gives a resonant frequency in the order of 100 Hz. A current
of 0.5 A will cause a temperature rise in the order of 2 degrees C.
The scanning or positioning system further comprises six permanent
magnets 7.1 and 7.2 placed in a plane under the movable platform 1,
whereby the poles are shared by several coils. The permanent
magnets 7.1 and 7.2 are separated from the movable platform 1 by a
gap so that they do not make contact. The arrangement of the
permanent magnets 7.1 and 7.2 is shown in the lower part of FIG. 5.
The permanent magnets 7.1 and 7.2 are located on a supporting base
which is for the sake of clarity not shown in FIG. 5. In operation,
a current passing through the electrical coils 2 generates a force
which moves the movable platform 1 in x, y or z direction or
rotates it a little about the x or y axis. The electrical coils 2
are integrated in the movable platform 1 and are fabricated in the
same process sequence as the suspension elements 4 and the
supporting frame 5 using the batch process described in the next
paragraph.
[0050] A batch process for fabricating a movable platform 1 with
integrated electrical coils 2 is described. Suspension elements 4
and a supporting frame 5 may also be fabricated in the same
sequence. The process is illustrated in FIGS. 6a to 6i. Said
process starts with a larger substrate 61, such as a oxidized
silicon wafer about 500 .mu.m thick with about 1 .mu.m of thermal
oxide on both sides.
[0051] First deep trenches 64 are defined, which have the shape of
the electrical coils 2 to be formed. FIG. 6a shows the silicon
wafer 61 with the deep trenches 64. The deep trenches 64 could be
produced as follows: The wafer 61 is coated with a resist, which is
patterned using a mask defining the lateral shape of the electrical
coils 2 and connections. Along the windings and connections narrow
bridges 63, about 10 .mu.m wide are left every 1 mm. First the
oxide 62 is etched either by a wet or dry process. A deep trench
anisotropic etch is then carried out, about 380 .mu.m deep into the
wafer 61. This is followed by a 5 .mu.m isotropic etch which
undercuts the oxide 62 and releases the bridges 63.
[0052] The wafer is then re-oxidized so that the deep trenches 64
have an isolating oxide coat 65.
[0053] Then a seed layer 68 is deposited as shown in FIGS. 6b and
6c: A layer of titanium--for adhesion--and a layer of copper, about
1 .mu.m thick are deposited on the front side. The undercut of the
oxide 62 effects, that the metal 66 at the bottom of said deep
trenches 64 is not contacted to the top. Thus, when 20 .mu.m of
copper are electroplated on the top, the bottom of the deep
trenches 64 is not plated. The copper at the bottom of the deep
trenches 64 can be etched away using wet etching.
[0054] FIG. 6d shows the wafer 61 after opening of the deep
trenches 64 from the backside. This can be done as follows: The
oxide 62 is removed from the back of the wafer 61 and the silicon
from the backside is wet etched in tetramethyl ammonium hydroxide
(TMAH) until the bottom of the deep trenches 64 is reached. On the
backside, the oxide 70 at the bottom of the deep trenches 64 is
left. During backside etching the wafer 61 is held intact by the
bridges 69 which are relatively rigid owing to their 20 .mu.m
copper coat.
[0055] In FIG. 6e the deep trenches 64 have been filled with a
conductive material. This could be done as follows: The oxide 70 at
the bottom of the deep trenches 64 can be removed either by e.g.
dry etch, wet etch or simply by mechanical means, for example by
brushing with a small paint brush. The wafer 61 is now mounted
backside up in an electroplater, and copper is plated to fill the
deep trenches 64 using the front side copper (68, 69) as a
seed.
[0056] Next a second level metallization 77 is applied as shown in
FIGS. 6f to 6h. The second level metallization 77 could be produced
as follows: The copper 71 on the front side is etched back until
there are no shorts between the windings of the coil(s). Then a
fresh copper contact layer 73 is evaporated onto the backside. A
photo resist 75 with good insulation properties e.g. an epoxy, PMA
or PMMA based photo resist is then spun onto the front side and
patterned. This photo resist 75 has two functions. First it defines
the final release structure of the movable platform 1 and of
additional parts like the suspension elements 4 or the supporting
frame 5. The second function is to act as dielectric insulation
between the windings and connections in the deep trenches 64 and
the second metallization layer 77 which connects the various
electrical coils 2 together. Via holes are made in the photo resist
75 for contacting the electrical coils 2. A seed layer of titanium
and copper is then deposited and patterned by wet etch to define
the second metallization wiring. The seed layer is then
electroplated with copper, about 15 .mu.m thick, to form the second
level metallization 77. The 1 .mu.m contact layer 73 on the
backside is then etched away by wet etching.
[0057] The final step is shown in FIG. 6i: The movable platform 1
is released from the substrate 61 by removing the substrate areas
around the movable platform 1. This can be done by e.g. Deep
Reactive Ion Etching using the insulating photo resist 75 and the
copper as an etch mask. The suspension element 4 and the supporting
frame 5 can be released from the substrate 61 in the same step.
[0058] It is to be noted that the above mentioned process steps
need not to be executed in the given order.
[0059] Typical applications of the described scanning or
positioning system include
[0060] scanning probe systems such as Atomic Force Microscopy (AFM)
or Scanning Tunneling Microscopy (SMT) systems and their
applications,
[0061] data storage systems,
[0062] optical beam scanners,
[0063] integrated optical alignment systems,
[0064] focusing systems,
[0065] fine positioning in robotics,
[0066] consumer products like video cameras.
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