U.S. patent application number 11/851579 was filed with the patent office on 2008-11-20 for microfabricated mechanically actuated microtool and methods.
This patent application is currently assigned to GEORGIA TECH RESEARCH CORPORATION. Invention is credited to Mark G. Allen, Yoonsu Choi, Stephen P. DeWeerth, James Ross.
Application Number | 20080284187 11/851579 |
Document ID | / |
Family ID | 36814931 |
Filed Date | 2008-11-20 |
United States Patent
Application |
20080284187 |
Kind Code |
A1 |
Choi; Yoonsu ; et
al. |
November 20, 2008 |
MICROFABRICATED MECHANICALLY ACTUATED MICROTOOL AND METHODS
Abstract
Apparatus and processes are disclosed that provide a
microfabricated microtool having a mechanically actuated
manipulating mechanism. The microtool comprises a tweezer having
flexible arms, and an actuating mechanism. A biological,
electrical, or mechanical component is grasped, cut, sensed, or
measured by the flexible arms. The actuating mechanism requires no
electric power and is achieved by the reciprocating motion of a
smooth, rigid microstructure applied against the flexible arms of
the microtool. In certain implementations, actuator motion is
controlled distally by a tethered cable. A process is also
disclosed for producing a microtool, and in particular, by
micropatterning. Photolithography may be used to form micro-molds
that pattern the microtool or components of the microtool. In
certain implementations, the tweezer and actuating mechanism are
produced fully assembled. In other implementations, the tweezer and
actuating mechanism are produced separately and assembled
together.
Inventors: |
Choi; Yoonsu; (Atlanta,
GA) ; Allen; Mark G.; (Atlanta, GA) ; Ross;
James; (Decatur, GA) ; DeWeerth; Stephen P.;
(Marietta, GA) |
Correspondence
Address: |
THOMAS, KAYDEN, HORSTEMEYER & RISLEY, LLP
600 GALLERIA PARKWAY, S.E., STE 1500
ATLANTA
GA
30339-5994
US
|
Assignee: |
GEORGIA TECH RESEARCH
CORPORATION
Atlanta
GA
|
Family ID: |
36814931 |
Appl. No.: |
11/851579 |
Filed: |
September 7, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11271450 |
Nov 11, 2005 |
|
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11851579 |
|
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60627300 |
Nov 12, 2004 |
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Current U.S.
Class: |
294/115 |
Current CPC
Class: |
B81C 99/002 20130101;
C25D 1/00 20130101; B25J 7/00 20130101; Y10S 294/902 20130101 |
Class at
Publication: |
294/115 |
International
Class: |
B66C 1/00 20060101
B66C001/00 |
Claims
1-16. (canceled)
17. A microfabricated microtool comprising: at least one
mechanically moveable microfabricated single-bodied microarm that
extends from the body and that terminates at a distal end to form a
tip; and a microfabricated mechanically actuating single-bodied
mechanism that contacts at least one mechanically moveable
microfabricated single-bodied microarm and is operative to cause
motion of the least one mechanically moveable microfabricated
single-bodied microarm.
18. The microfabricated microtool recited in claim 17, wherein the
at least one mechanically moveable microfabricated single-bodied
microarm includes at least two mechanically moveable
microfabricated single-bodied flexible microarms, wherein the
microfabricated actuating mechanism comprises a plurality of
contact members that contact lateral surfaces of two flexible
microarms and are mechanically operative to open and close lateral
portions of the tip formed by the two flexible microarms that are
caused by relative motion between the contact members and the
microarms.
19. The microfabricated microtool recited in claim 18, wherein the
microtool comprises a geared rotatable hub from which the at least
one flexible microarm extends and wherein the actuating mechanism
comprises a plurality of gear teeth that engage the geared
rotatable hub to provide movement of the microarm.
20. The microfabricated microtool recited in claim 19, further
comprising a micromanipulator having a shaft and control apparatus
for controlling movement of the shaft of the micromanipulator,
wherein the microfabricated microtool or microfabricated actuating
mechanism is coupled to the micromanipulator, and wherein the
micromanipulator comprises a control member for moving the
actuating mechanism relative to the microtool to open and close the
tip of the microtool.
21. The microfabricated microtool recited in claim 20, wherein the
tip of each the mechanically moveable microfabricated single-bodied
microarms comprises a substantially flat surface, wherein each
surface is opposed to one another.
22. The microfabricated microtool recited in claim 20, wherein the
tip of each the mechanically moveable microfabricated single-bodied
microarms comprises a serrated surface, wherein each surface is
opposed to one another.
23. The microfabricated microtool recited in claim 20, wherein the
tip of each the mechanically moveable microfabricated single-bodied
microarms comprises a sharp surface, wherein each surface is
opposed to one another.
24. The microfabricated microtool recited in claim 17, wherein the
tip of at least one mechanically moveable microfabricated
single-bodied microarms comprises insulated conducting surfaces
with isolated conducting microelectrodes.
25. The microfabricated microtool recited in claim 18, wherein the
tip of at least two mechanically moveable microfabricated
single-bodied microarms comprises insulated conducting surfaces
with isolated conducting microelectrodes.
26. The microfabricated microtool recited in claim 20, further
comprising control apparatus for rotating the microtool around an
axis through the microtool.
27. The microfabricated microtool recited in claim 20, wherein the
microtool is connected to a socket formed in the actuating
mechanism.
28. The microfabricated microtool recited in claim 27, wherein the
microtool comprises magnetic material and is magnetically secured
in the socket formed in the actuating mechanism.
Description
BACKGROUND
[0001] The present invention relates in general to microfabricated
devices for grasping, manipulating, and excising microstructures,
such as microcomponents or biological structures, and more
specifically to microtools having grasping and manipulating
mechanisms, such as arms, and mechanical actuator(s) for precisely
manipulating the mechanisms for grasping, releasing, rotating, or
cutting an object or biological component.
[0002] Extraordinary advances are being made in micromechanical
device and microelectronic device technologies. Further, advances
are being made in MicroElectroMechanical Systems ("MEMS") which
comprise integrated micromechanical and microelectronic devices.
The term "microcomponent" is generically used herein to encompass
microelectronic components, micromechanical components, as well as
MEMS components. A need often arises for a suitable mechanism to
grasp microcomponents. For example, a need often arises for some
type of "gripper" device that is capable of grasping a
microcomponent in order to perform pick and place operations with
the microcomponent. Pick and place operations may be performed, for
example, in assembling/arranging individual microcomponents into
larger systems.
[0003] With the advances being made in microcomponents, various
attempts at developing a suitable gripper mechanism for performing
pick-and-place operations have been proposed. This is discussed in
the Handbook of Industrial Robotics, by Shimon Y. N of, chapter 5,
for example. Gripper mechanisms that comprise arms that are
translatable for grasping a microcomponent using an external,
macro-scale translating mechanism have been proposed in the
existing art. For example, U.S. Pat. No. 5,538,305 issued to Conway
et al. discloses a gripper mechanism that comprises a relatively
large mechanism (including a servomotor, drive mechanism, screws,
etc.) for controlling the movement of two arms that are coupled
thereto. In the Conway et al. patent, each of the arms themselves
include a forceps portion that is approximately 7.5 inches (or
about 19.05 centimeters) long, which extends from the mechanism
that controls movement of the arms. Attached to and extending from
the forceps portion of each arm is a replaceable tip that is
approximately 1 inch (or about 2.54 centimeters) long. Accordingly,
in addition to the relatively large size of the mechanism for
controlling movement of the arms, the arms themselves extend from
the mechanism a length of over 20 centimeters. Thus, while such
gripper device may be utilized for grasping microcomponents, the
gripper device is not a micro-scale device, but is instead a
relatively large device.
[0004] Variations in macro-scale translating mechanisms are
presented in U.S. Pat. No. 5,895,084 issued to Mauro. In this
approach, precision engineering is required to fasten or screw
individual arms of the gripper to a support block. The requirement
of the fastener(s), lead screw(s), cam drive(s), and other
macro-sized components places substantial limits on the operation
of the device and makes this device unsuitable for
microfabrication. The structure and size of the Mauro device limits
the minimum size of the objects it can manipulate. Furthermore,
this complication limits the resolution with which the tweezers can
be rotated or three dimensionally positioned. The precision
manufacturing techniques required to produce the microgripper are
expensive, and this expense, coupled with the complex internal
structure, reduces the modularity of the Mauro microgripper.
Therefore, it is expensive and difficult to swap out or replace
microtools of various shapes and sizes.
[0005] Additionally, microgripper devices (e.g., those fabricated
using a microfabrication process) have been proposed in the
existing art. As described more fully below, microgripper devices
have been proposed that comprise grasping mechanisms (e.g., arms)
and a microactuator mechanism (e.g., electrothermal actuator or
electrostatic actuator) for moving the grasping mechanisms for
grasping a microcomponent. Such microactuator mechanisms may be
included within the grasping mechanism. For instance, the arms of a
microgripper device may comprise electrothermal or electrostatic
actuators for generating movement of the arms for grasping a
microcomponent. Thus, rather than having the actuation mechanism in
an external, macro-scale device as in the gripper disclosed in the
Conway et al. patent, microgripper devices have been proposed in
the existing art that include, in a micro-scale device, arms and an
actuation mechanism for moving the arms (although, the power supply
and/or control circuitry for powering the actuation mechanism to
generate movement of the arms may be arranged external to the
microgripper).
[0006] An example of one type of microgripper in the existing art
is a microtweezer taught by Keller, et al., in "Microfabricated
High Aspect Ratio Silicon Flexures," MEMS Precision Instruments,
1998; and "Hexsil Tweezers for Teleoperated Microassembly," by C.
G. Keller and R. T. Howe, IEEE Micro Electro Mechanical Systems
Workshop, 1997, pp. 72-77. The microtweezers proposed in Hexsil
Tweezers for Teleoperated Microassembly has two parallel arms that
are operable, through electrothermal actuation, to move toward or
away from each other, which may enable the arms to grasp a
microcomponent between them. More specifically, each arm is
positionally fixed at one end and is movable at the opposing end
(which may be referred to as the arm's "released end"). Each arm
effectively comprises an electrothermal actuator (or thermal
expansion actuator beam) that is operable, responsive to electric
power being applied thereto, to cause the released end of the arm
to move in a direction away from the opposing arm. Therefore,
electric power may be applied to the microtweezer device to cause
the released ends of the tweezer arms to spread apart.
[0007] In the above-described microtweezer device, applying greater
power to the electrothermal actuators causes the arms to spread
further apart, while reducing the amount of applied power causes
the arms to return toward each other. Accordingly, to maintain a
given position of the arms (other than their powered-off position)
or to maintain a particular gripping force against an object being
grasped (other than the force applied when the device is
powered-off), power must be maintained to the arms.
[0008] U.S. Pat. No. 5,072,288 issued to MacDonald et al. provides
another example of a microgripper proposed in the existing art. The
microgripper disclosed in the MacDonald et al. patent has two
parallel arms that are operable, through electrostatic actuation,
to move toward or away from each other, which may enable the arms
to grasp a microcomponent between them. Each arm is positionally
fixed at one end and is movable at an opposing end (referred to as
the arm's "released end"). Each arm comprises an
electrically-conductive beam (e.g., having metal lines) that is
operable, responsive to electric power being applied thereto, to
cause the released end of the arm to move in a direction away from
the opposing arm or in a direction toward the opposing arm.
Therefore, electric power may be applied to the microgripper device
to cause the released ends of its arms to spread apart or to
compress together to achieve a tweezing action.
[0009] The microgripper device disclosed in the MacDonald et al.
patent uses electrostatic forces between the arms to generate the
tweezing action. Application of a step function potential
difference between the arms (by applying potentials to the
electrically-conductive beam forming each arm) may generate either
an attracting or repelling electrostatic force between the charged
arms, depending on the polarity of the potential. Accordingly, to
maintain a given position of the arms (other than their powered-off
position) or to maintain a particular gripping force against an
object being grasped (other than the force applied when the device
is powered-off), power must be maintained to the arms.
[0010] With microgrippers of the existing art, such as those
proposed in Hexsil Tweezers for Teleoperated Microassembly and in
the MacDonald et al. patent, the range of motion of the
microgripper arms is relative to their length. That is, the longer
the arms, the greater the range of motion that may be achieved
through the above-described electrothermal or electrostatic
actuation of the arms. For instance, the microtweezers proposed in
Hexsil Tweezers for Teleoperated Microassembly have arms that are 8
millimeters (mm) in length by 1.5 mm wide by 45 micrometers (.mu.m)
thick. The released ends of the arms are able to be displaced
through electrothermal actuation to allow for a separation distance
of 35 .mu.m. To achieve greater separation, the arms may be
implemented having a greater length. In general, the range of
motion associated with an electrothermal actuator is limited to
approximately 0.5 to approximately 10 percent of the overall length
of the actuator's arms. However, in general, increasing the length
of the arms decreases their rigidity (particularly if their
thickness is not also increased), which may in turn decrease their
gripping force.
[0011] Microgrippers requiring power may experience dynamic
fluctuations in the conductivity of the device. Additionally, these
devices may produce stray electrostatic fields that can influence
the object one is trying to manipulate.
[0012] It would be desirable to have gripping devices, methods of
manufacture, and gripping processes that improve upon the
above-described devices and processing techniques and that does not
require the use of electrical power for operation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The various features and advantages of the present invention
may be more readily understood with reference to the following
detailed description taken in conjunction with the accompanying
drawings, wherein like reference numerals designate like structural
elements, and in which:
[0014] FIGS. 1a and 1c illustrate top views of exemplary
embodiments of a microfabricated tool for grasping, manipulating,
and excising microstructures; FIG. 1b illustrates an end view of
the microfabricated microtool.
[0015] FIG. 2 illustrates the principle of operation of the
tool;
[0016] FIG. 3 illustrates an exemplary driving mechanism for the
tool;
[0017] FIGS. 4a-4c illustrates different tip profiles for the
tool;
[0018] FIG. 5 illustrates an exemplary multi-tool
microstructure;
[0019] FIG. 6a-6g illustrate exemplary processing steps performed
to fabricate an exemplary tool;
[0020] FIGS. 7a and 7b illustrate fabrication of multiple
tweezer-boxes using a single step micro-molding process, and FIG.
7c is an bottom end view of a fabricated tweezer box produced using
the single step micro-molding process taken along the lines 7c-7c
in FIG. 7b;
[0021] FIG. 8 is an enlarged exploded view that illustrates
fabrication of a tweezer body using a single step micro-molding
process; and
[0022] FIGS. 9a-9c illustrate an alternative implementation of the
tool that allows microlesioning or microcutting.
DETAILED DESCRIPTION
[0023] Referring to the drawing figures, FIGS. 1a and 1c
illustrates an exemplary embodiments of a microfabricated tool 10,
or microtool 10, for grasping, manipulating, and excising
microstructures. FIGS. 1a and 1c illustrate top views of
reduced-to-practice embodiments of the microtools 10, which include
an actuating mechanism 11 comprising a tweezer box 11, and a
tweezer 12. FIG. 1b illustrates an end view of the microtool
10.
[0024] As used herein, the term "microfabricated" refers to a
component or portion of a component that is fabricated in part
using lithographic techniques or processes. This involves using
photolithography to pattern a desired structure. In general, the
size of the structure is only limited by the optical resolution
that can be achieved by the photolithographic process. As used
herein, the term "microtool" refers to a device or structure that
is "unified" or "single-bodied" (i.e., not assembled from multiple
components), and in general relates to any movable microfabricated
component.
[0025] The actuating mechanism 11 or tweezer box 11 comprises two
separated stepped rectangular structures that are separated by a
gap in which the tweezer 12 is disposed. The tweezer box 11 steps
laterally away from the tweezer 12 and has a contact member 13,
such as a dimple 13, formed on each lateral inner surface. The
tweezer 12 comprises a rectangular body 12a, or tweezer grip 12a,
that is disposed between the separated stepped rectangular
structures of the tweezer box 11. A working end of the tweezer 12
comprises two outwardly bowed flexible microarms 15 that extend
from the tweezer grip 12a that terminate at distal ends to form a
tip 14. Alternatively, the tweezer 12 may comprise at least one
flexible microarm 15 and at least one fixed microarm 15. There is a
gap between the microarms 15 at the tip 14. The dimples 13 of the
tweezer box 11 contact lateral surfaces of the outwardly bowed
flexible microarms 15.
[0026] The fully-mechanical microtools 10 thus comprise two parts:
the tweezer 12 and tweezer box 11. The tweezer box 11 encloses the
proximal half of the tweezer 12 and moves laterally along the
tweezer 12 to regulate the opening and closing of the tip 14. In
operation, the tweezer box 11 is movable along the tweezer grip 12a
of the tweezer 12, and the dimples 13 slide along the adjacent
surfaces of the outwardly bowed flexible microarms 15 to open and
close the tip 14 in response.
[0027] FIG. 2 illustrates operation of the microtools 10 shown in
FIGS. 1a and 1b. A microprobe station 20 comprises a
micromanipulator 21 that houses x, y, and z axis control knobs 22,
23, 24 that control the x, y, and z positions of the tweezer tip
14. The micromanipulator 21 has a shaft 27 extending therefrom to
which the microtool 10 is attached. A tethered cable release 26
having a slidable inner cable 26a is secured to the
micromanipulator 21 and shaft 27. The slidable inner cable 26a is
coupled to the tweezer box 11, for example, to control its
movement.
[0028] A tip control knob 25 precisely regulates opening and
closing of flexible microarms 15 by way of the tethered cable
release 26 and slidable inner cable 26a. A fifth knob may be added
to allow for axial rotation of the tweezer tip 14, if desired. The
fifth knob comprises control apparatus for rotating the microtool
10 around an axis through the microtool. For example, simple axial
rotation may be achieved by creating a mechanism to rotate the
micromanipulator shaft 27, thus rotating the microtool 10. More
complicated systems may be put in place to rotate that tweezer box
11 independently of the shaft 27 that it is tethered to.
[0029] The microtool 10 is fastened into place on the
micromanipulator shaft 27 where one would normally secure a probe
needle and sharp electrodes. The axis knobs 22, 23, 24 control the
x, y, and z location of the microtool 10. The tethered cable
release 26 connects the tip control knob 25 to the tweezer box 11.
The opening and closing of the tweezer tip 14 is then precisely
controlled by the movement of the tweezer box 11 by way of the
tethered cable release 26 and the tip control knob 25. The tip
control knob 25 may be custom fit to the body of the microprobe
station 20, or an optic field or other rotary knob may be used,
which is commercially available on some systems.
[0030] Coaxial Line Feed and "Socketing"
[0031] For an end-user or consumer, it is important that the
microtool 10 be easily connected to and disconnected from the shaft
27 of the micromanipulator 21. Furthermore, it is important that
the driving mechanism for the tweezer box 11 does not induce any
unwanted motion or stress in the microtool 10. The driving
mechanism should be able to be easily and securely fastened (as
opposed to permanently anchored) to the tweezer box 11. An
exemplary way to insure these desired characteristics is disclosed
below.
[0032] In an exemplary embodiment of the microtool 10, such as is
shown in FIG. 1 or 2, opening and closing of the tweezer tip 14 is
regulated by moving the tweezer box 11 with respect to a fixed
tweezer 12. It is also possible to achieve controlled, precise
motion of the tweezer tip 14 by performing the opposite task,
namely, moving the tweezer 12 with respect to a fixed tweezer box
11. In either case, the tweezer box 11 or the tweezer 12 must be
fastened to either the micromanipulator shaft 27 (to be fixed in
place) or the driving mechanism (to allow movement). There are, in
fact, dozens of ways to create secure and temporary connections.
Among them are sockets, hooks and hoops, and screw pin fasteners,
for example. One novel way to achieve a secure and reliable
connection is to take advantage of the material properties of the
tweezer box 11. The microtool 10 may be constructed from
electroplated Ni--Fe, so that magnetic attraction may provide a
means of attachment.
[0033] In currently reduced-to-practice embodiments of the
microtool 10, the motion of the tweezer box 11 is achieved by
rotating the tip control knob 25, which translates this action into
lateral motion of the tethered cable release 26. As an alternative
to this approach, one could run the cable 26a or driving mechanism
through the center of a hollow shaft that it is fixed to the
micromanipulator 27. This approach, referred to a coaxial line
feed, is illustrated in FIG. 3.
[0034] As is shown in FIG. 3, the driving mechanism (i.e., cable
26a) is run through the center of the shaft 27 of the
micromanipulator 21. In this case, the tweezer box 11 is securely
fastened to the shaft 27, and the fastened tweezer box 11 is
allowed to move laterally to regulate the opening and closing of
the tip 14. The opposite action may also be performed, where the
tweezer box 11 is fixed and the tweezer 12 is allowed to move.
[0035] Microtool Styles
[0036] The microtool tip 14 may have any desired two dimensional
form, so that the microtool 10 can be easily modified to
accommodate various objects or tasks. Some examples of these
modifications are shown in FIGS. 4a-4c.
[0037] FIG. 4a shows a microtool 10 with a serrated tips 14a. FIG.
4b shows a microtool 10 formed from symmetrically opposing sharp
microtips 14b. FIG. 4c shows an insulated microtool 10 with
insulated conductive microtips 14c or traces and isolated recording
microelectrodes 14d that may be used for electrophysiological
measurements.
[0038] FIG. 5 illustrates an exemplary multi-microtool 10. As is
shown in FIG. 5, parallel microactuation is achieved by
interconnecting multiple individual microtools 11 so that multiple
tweezer 12 are arranged parallel to each other. In this particular
embodiment, forward motion of the tweezer box 11 with respect to
the tweezer tip 14 causes a component 16 to press the tweezer tips
14 together. Backward motion of the tweezer box 11 causes pins 17
to open the tweezer tip 14. There exists some slack, or space,
between the mechanisms 16, 17 that cause opening and closing.
[0039] Fabrication Processes
[0040] The microtools 10 may be fabricated using at least two
different processes. In a first process or method, the tweezer 12
and tweezer box 11 are patterned together. This process has the
advantage that the actuator mechanism is virtually unlimited in its
geometry. For example, the dimples 15 may be on the inside of the
microtool 10, and no assembly is required to complete the microtool
10. However, this process requires more layers and more substrate
surface area. In a second process or method, the tweezer 12 and
tweezer box 11 are each built up separately in a single layer and
then assembled.
[0041] In the first method, fabrication of the microtool 10 employs
four masks, and uses conventional surface micromachining
technology. FIGS. 6b-6g illustrates an exemplary fabrication
sequence and will be discussed in detail below. FIG. 6a illustrates
a top view of the fabricated microtool 10 that is produced by the
fabrication sequence shown in FIGS. 6b-6g. Various components of
the microtool 10 are fabricated by repeatedly defining and filling
micromolds. These molds can be filled by an number of techniques
known in the art, including doctor-blading, injection, or casting.
Preferably, the mold is filled using electrodeposition. While the
electroplating molds easily separate components horizontally,
sacrificial layers are used to separate components vertically.
Together, the horizontal and vertical separation of components
creates a freedom of movement that allows individual mechanisms to
interact to perform the desired function. In total, three
electroplating operations are performed. In the first operation,
the base of the tweezer grip 12a and tweezer box 11 are formed. The
second operation continues to build up the tweezer grip 12a while
forming the side walls of the tweezer box 11 and tweezer tip 12.
The final electroplating operation completes the tweezer grip 12a
and forms the top of the tweezer box 11. Two sacrificial layers 56,
61 separate the tweezer tip 12 from the top and bottom of the
tweezer box 11, and an additional sacrificial layer 52 separates
the tweezer 10 from the substrate.
[0042] Referring to FIGS. 6b-6g, first, an SiO2 sacrificial layer
52 is deposited by PECVD onto a substrate 51. Exemplary substrates
51 include silicon or glass. A copper plating base 53 is then
deposited onto the sacrificial layer 52 using a DC sputterer. Next,
AZ4620 photoresist 54 is deposited and patterned to form an
electroplating mold. As is shown in FIG. 6c, nickel-iron (Ni--Fe)
55 is then electroplated, forming the bottom portion of the tweezer
grip 12a and tweezer box 11. Next, as is shown in FIG. 6d, Shipley
1827 photoresist 56 is prepared as a sacrificial layer that
facilitates separation of the tweezer tips 14 from the tweezer box
11 after fabrication. A copper seed layer 57 is applied, and as is
shown in FIG. 6e, nickel-iron 59 is electroplated in AZ 4620
photoresist molds 58 formed on the seed layer 57 to form the
tweezer tip 14, side walls of the tweezer box 11, and tweezer grip
12a. Shipley 1827 photoresist 61 is patterned, once again, to form
the sacrificial layer that vertically separates the tweezer tip 12
from the top of the tweezer box 11. A copper seed layer 62 is
deposited, and a final layer of AZ4620 photoresist 63 is patterned
to define the electroplating mold for the tweezer grip 12a and the
top of the tweezer box 11. Next, the mold is filled with
electroplated nickel-iron 64. Finally to release the tweezer 10,
the different sacrificial layers comprising photoresist 54, 56
copper 53, 57, 62 and SiO2 52, are removed with acetone, copper
etchant and buffered oxide etchant (BOE), respectively, thus
producing the tweezer 12.
[0043] The second method separately produces the tweezer-box 11 and
tweezer 12 in a single step. In this process the tweezers 12 and
tweezer box 11 are each produced separately using a single step
micro-molding process, allowing for massive increases in scale with
corresponding decreases in manufacturing time and materials. FIGS.
7a and 7b illustrate fabrication of the tweezer box 11. As is shown
in FIG. 7a, a vertical micro-mold 70 is formed on a substrate 51.
As is shown in FIG. 7b, copper 72 is deposited in voids 71 of the
micro-mold 70 to form the tweezer box 11. In this approach, the
tweezer boxes 11 are formed in a vertical direction. One advantage
to this approach is that the tweezers 12 may be built using
significantly fewer processing steps. Additionally, this process
increases volume while decreasing production costs. FIG. 7c is an
bottom end view of a fabricated tweezer box 11 produced using the
single step micro-molding process shown in FIGS. 7a and 7b, taken
along the lines 7c-7c in FIG. 7b. The outer and next-adjacent lines
of the tweezer box 11 shown in FIG. 7c correspond to side walls of
the tweezer box 11, while the inner line defines the inner edge of
the dimples 13.
[0044] FIG. 8 is an enlarged exploded view that illustrates
fabrication of the tweezers 12. A horizontal micro-mold 75 is
fabricated on a substrate 51 having voids corresponding to the
tweezers 12 illustrated in FIG. 8. Copper is deposited in voids 76
of the micro-mold 77 to form the tweezers 12. The tweezers 12 may
be made from plastics or electroplated metals. PDMS
(poly(dimethylsiloxane)) or other materials may be used to define a
micro-mold 75 for plastics. For photolithography, SU-8 or other
photoresist materials may be used to define an electroplating
micro-mold 52 for metals such as Ni--Fe.
[0045] The microtool 10 may be employed in many different fields,
including biology and MEMS/electronics. The manufacturing process
and general principles of operation lends itself to producing
microtools 10 with various geometries, functions, and materials.
Therefore, it is possible to customize a microtool 10 to fit a
particular task or application. For example, it is possible to
produce biological micrograbber and microlesioning tools that are
sterile and disposable. Furthermore, it is possible to pattern and
insulate conductive traces on the tweezers 13 that open up at
microelectrodes for the purpose of electrophysiological recording.
The microtool 10 may also be customized for electronic
applications, the electrical and mechanical properties of the
microtool 10 may be readily controlled.
[0046] Dimensions
[0047] Reduced-to-practice embodiments of the microtools have been
fabricated with the following dimensions. In one embodiment shown
in FIG. 1a, the tweezer box 11 has a length of 2.35 mm, and a width
of 0.437 mm. The length of the arms on which the dimples 15 are
formed is 1.343 mm. The dimples 15 are located about 0.4 mm from
the end of the tweezer box 11 adjacent to the tip 13. The dimples
15 have a diameter of 0.057 mm. The tweezer 12 has a thickness of
0.15 mm at its back portion distal from the tip 13. The gap at the
end of the tip 13 is 0.04 mm, the thickness of the microarms 15 at
the end of tip 14 is 0.01 mm and the tip 14 has a width of 0.02 mm.
The tip 14 is angled at 4 degrees.
[0048] In another embodiment, the tweezer box 11 has a length of
1.1 mm, and a width of 0.2 mm where it surrounds the tweezer 13.
The dimples are located about 0.2 mm from the end of the tweezer
box 11 adjacent to the tip 14. The dimples 15 have a diameter of
0.029 mm. The tweezer box 11 is stepped outward to 0.8 mm and has
an extended length of 1.7 mm. The tweezer 12 has a thickness of
1.075 mm at its back portion distal from the tip 13. The gap at the
end of the tip 14 is 0.02 mm, the thickness of the microarms 15 at
the end of tip 14 is 0.01 mm, and the tip 14 has a width of 0.01
mm. The tip 14 is angled at 4 degrees.
[0049] Alternative Microtools Using Similar Means of
Microactuation
[0050] It is possible to use the `tweezer box` style of actuation
to perform entirely different actions other than those produced by
flexing microarms 15. FIGS. 9a-9c illustrate a microlesioning tool
10a that can be produced using the processes discussed above and
that is actuated using the same external means (microprobe station
20 or micromanipulator 21) as the microtools 10 described above.
This microtool 10 may be used in tandem with the more traditional
microtools 10 described above.
[0051] More particularly, FIGS. 9a-9c illustrate an alternative
implementation of the microtool 10a that allows rotation of a
cutting device 37. The tweezer box 11 is generally rectangular and
slides within inner sidewalls of an outer housing 30. The housing
30 comprises a shaft 34. A lateral portion 31 of the tweezer box 11
extends along one of an inner wall of the housing 30 and has gear
teeth 32 formed along its inner edge.
[0052] The cutting device 37 comprises a circular hub 33 having
gear teeth 35 formed around a portion of its periphery. The hub 33
is rotatable around the shaft 34. The cutting device 37 is
positioned so that the gear teeth 32, 35 of the tweezer box 11 and
cutting device 37 mesh. The cutting device 37 has an arm 36
extending from the hub 33. The arm 36 tapers at the distal end to
form a tip 14 configured as a cutting edge.
[0053] Lateral movement of the tweezer box 11 within the housing 30
causes corresponding rotation of the hub 33 via the meshed gear
teeth 32, 35 resulting in rotational movement of the cutting device
37. FIGS. 9a-9c illustrate three exemplary rotational positions of
the cutting device 37 resulting from movement of the tweezer box 11
within the housing 30.
[0054] Thus, processes for manipulating components, microtools 10
for implementing the process, and processes for manufacturing the
microtools 10 or at least parts of them have been disclosed. The
disclosed embodiments have advantages over the prior art in that
they make possible the simple, precise, fully mechanical and
cost-effective micromechanical manufacture of microtools 10 for
precise manipulation, positioning, measuring, and sensing of
biological, electrical, and mechanical components having typical
dimensions from the sub-micrometer range to the lower millimeter
range.
[0055] The microtools 10 or individual microtool parts may be
produced using conventional micromachining technologies, and in
particular, the microtools 10 may be constructed using
electroplating and micro-molding techniques. Different exemplary
processes may be used to manufacture the microtools 10. In a first
exemplary process, the microtool 10 is built up in three separate
layers that produce a fully assembled microtool 10 and mechanical
actuating structure. In a second exemplary process, the microtool
10 and actuating structures are built up independently in a single
layer and assembled together. Using either process, the microtool
10 can be easily modified to accommodate various objects or
tasks.
[0056] Variations in the function, size, and style of the microtool
10 may be achieved using the disclosed processes. For example, the
microtool 10 may be modified to perform electrophysiological
recording measurements. In a particular embodiment, microelectrodes
12b are patterned and electrically isolated on the tip 14 of the
microtool 10. Further, the microtool 10 may be modified to produce
microcutting or microlesioning tools. In a particular embodiment,
the tip 14 of the microtool 10 is sculpted to have sharp
symmetrically opposing edges.
[0057] The microfabricated mechanically actuated mechanism of the
microtool 10 requires no power and provides delicate and precise
control over the position of its flexible arms 15. The fully
mechanical actuating mechanism for tip closure is achieved by the
reciprocating motion of a smooth, rigid microstructure (tweezer box
11) applied against the flexible arms 15 of the microtool 10. The
tip 14 of the microtool 10 may be angled, so that the translation
of lateral motion of the actuator to the motion of the microtool
arms 15 is significantly reduced. In a reduced-to-practice
embodiment, 100 .mu.m of lateral motion translates into 10 .mu.m of
tip closure. This allows for submicron resolution of the motion of
the microtool arms 15 for a large range of microtool sizes.
[0058] Thus, microfabricated mechanically actuated microtools and
methods have been disclosed. It is to be understood that the
above-described embodiments are merely illustrative of some of the
many specific embodiments that represent applications of the
principles discussed above. Clearly, numerous and other
arrangements can be readily devised by those skilled in the art
without departing from the scope of the invention.
* * * * *