Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2002-08-14
2004-10-19
Sugarman, Scott J. (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
Reexamination Certificate
active
06806991
ABSTRACT:
TECHNICAL FIELD
The present invention is in general related to manipulation of a stage and, more particularly, to manipulation of a fully released stage in a decoupled manner according to closed-loop feedback with sub-micron accuracy.
BACKGROUND OF THE INVENTION
Scanning probe microscopes (SPMs) are devices which manipulate a scanning probe with sub-atomic accuracy to scan the surface of a sample object or material. For example, the scanning tunneling microscope (STM) is a solid-state microscope based on the principle of quantum mechanical tunneling of electrons between a sharp tip and a conducting sample. The tip of an STM is an extremely sharp metal tip. The tip is mounted on a system of piezoelectric drives which are controllable with sub-atomic precision. The scanning process begins by bringing the tip within a few Angstroms of the conducting sample surface. At such separations, the outer electron orbitals of the tip and the sample overlap. Accordingly, on the application of a bias voltage between the tip and the surface, electrons tunnel through the vacuum barrier via the quantum mechanical tunneling effect, even though the tip and the surface are not in physical contact. By scanning the tip across the sample surface, it is possible to image directly the three-dimensional real space structure of a surface at atomic resolutions.
To provide the necessary scanning resolution, scanning operations of an SPM are typically implemented utilizing a piezo element.
FIG. 1A
depicts a block diagram of a typical SPM
100
according to the prior art. The sample
103
to be scanned is placed on stage
102
. Control means
105
causes a suitable voltage to be applied to piezo element
104
. In response to the applied voltage, piezo element
104
controllably expands. Utilizing suitably designed piezo element
104
, the expansion may occur in any of the X-direction, Y-direction, and Z-direction. In typical operations, control means
105
controls the vertical distance (in the Z-direction) between scanning tip
101
and sample
103
. Also, control means
105
causes piezo element
104
to move scanning tip
101
over sample
103
according to, for example, a raster pattern in the X and Y-directions. The control of piezo element
104
may utilize various feedback techniques such as examining the tunneling current associated with scanning tip
101
. Also, other feedback techniques may be utilized such as optical feedback, capacitive feedback, and piezo-resistive feedback (not shown). The imaging signal associated with scanning tip
101
may be provided to imaging system
106
for suitable processing. When piezo element
104
is utilized, the dimensions of SPM
100
are typically on the order of ten centimeters. Accordingly, the scanable area of an object placed on stage
102
is quite small relative to the size of SPM
100
.
Moreover, XY stages that are controllable on precise resolutions are used for a variety of applications. For example, XY stages may be utilized to control a micro-lens for optical applications.
FIG. 1B
depicts XY stage
150
according to the prior art which is operable to control lens
155
. XY stage
150
comprises a plurality of cascaded thermal actuators (
151
-
154
). The thermal actuators (
151
-
154
) are mechanically coupled to lens
155
via respective general purpose flexures which are generally known for use to facilitate actuation in Micro-Electrical-Mechanical (MEMs) devices. Actuators
152
and
154
enable displacement of lens
155
in the Y-direction and actuators
151
and
153
enable displacement of lens
155
in the X-direction. However, the design of XY stage
150
does not fully decouple the manipulation of lens
155
in the X and Y directions. Specifically, displacement of lens
155
in the X-direction by actuators
151
and
153
will also cause some amount of displacement in the Y-direction. Likewise, displacement of lens
155
in the Y-direction by actuators
152
and
154
will also cause some amount of displacement in the X-direction.
Thus, known structures that manipulate high resolution XYZ stages either (1) are associated with coupled movement where actuation in one direction causes a lesser degree of actuation in another direction; (2) require bulky piezo elements to achieve the desired non-coupled movement; or (3) are permanently anchored to the substrate on which they were fabricated.
Additionally, it is appropriate to note that various techniques exist for post-fabrication assembly of MEMs devices. For example, “flip-chip” bonding is well-known in the art for bonding two discrete structures after fabrication of the structures. However, flip-chip bonding is problematic, because it imposes a relatively simple mechanical design via the bonding of a first flat surface to a second flat surface. Thus, flip-chip bonding prevents assembly of structures with surface features and, hence, reduces the potential complexity of devices assembled utilizing this technique.
BRIEF SUMMARY OF THE INVENTION
The present invention is directed to a system and method which are operable to manipulate a fully released stage to provide decoupled movement that is controlled by suitable closed-loop feedback. In embodiments of the present invention, the XY positioning of the stage may be advantageously manipulated using a first plurality of actuators (e.g., comb drives, parallel plate actuators, shaped memory alloy (SMA) actuators, electrothermal actuators, piezo stack actuators, and/or the like) and a second plurality of actuators. In embodiments of the present invention, the actuators are implemented as flexure amplified banks of bent beams that each occupy approximately 400 microns in length. By utilizing actuators of this scale, the total size of the device may be significantly reduced. In embodiments of the present invention, the entire device may be approximately one millimeter in length.
Moreover, the actuators may be advantageously coupled to flexures which are, in turn, coupled to the stage. The actuators and the flexures are positioned and operate in a mirrored manner. Specifically, when it is desired to actuate the stage in the X-direction, two corresponding mirrored actuators are supplied current. The actuators move the stage in the desired direction via the coupled flexures. It shall be appreciated that the same actuators that cause the actuation in the X-direction may also produce undesired forces in the Y-direction. If the undesired forces are not addressed by embodiments of the present invention, the forces will produce coupled movement. However, embodiments of the present invention utilize the mirrored positioning and flexures to balance the undesired forces in the Y-direction. Thus, the total torque on the stage is approximately zero. Actuation in the Y-direction may also utilize a mirror positioning and operation of movements to decouple movement in the Y-direction. Thus, actuation in the X-direction and the Y-direction are fully decoupled. A third actuator may also be utilized to actuate the stage in the Z-direction. Also, suitable feedback structures (capacitive, optical, piezo-resistive, and/or the like) may be utilized to control the manipulation of the stage.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation,
Ellis Matthew D.
Geisberger Aaron
Sarkar Neil
Hanig Richard
Haynes and Boone LLP
Sugarman Scott J.
Zyvex Corporation
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