Electrical generator or motor structure – Non-dynamoelectric – Charge accumulating
Reexamination Certificate
2001-05-15
2004-08-31
Tamai, Karl (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Charge accumulating
Reexamination Certificate
active
06784592
ABSTRACT:
BACKGROUND OF THE INVENTION:
1. Field of the Invention
The present invention relates generally to micro-machined actuators. The present invention also generally relates to methods for manufacturing and operating micro-machined actuators.
2. Description of the Related Art
FIG. 1
illustrates a micro-machined actuator
10
according to the related art. The actuator
10
illustrated includes a stator wafer
20
at the bottom thereof and a rotor wafer
40
above the stator wafer
20
. The rotor wafer
40
includes a section, called a micro-mover
50
, that is separated from the rest of the rotor wafer
40
. The micro-mover
50
is connected to the rest of the rotor wafer
40
via suspensions
60
. The wafers
20
,
40
are bonded together by a bond material
70
that both holds the wafers
20
,
40
together and separates them a specified distance.
On the surface of the stator wafer
20
closest to the rotor wafer
40
is a series of stator electrodes
80
. On the surface of the micro-mover
50
closest to the stator wafer
20
are formed a series of actuator electrodes
90
. Although, for the purposes of clarity, only five stator electrodes
80
and four actuator electrodes
90
are illustrated in
FIG. 1
, typical micro-machined actuators
10
according to the related art include many more electrodes
80
,
90
than those illustrated.
The stator wafer
20
typical contains the electronics of the actuator
10
and makes up half of the motor that moves the micro-mover
50
, as will be discussed below. The stator wafer
20
is typically made from materials that can be micro-machined (e.g., silicon).
The rotor wafer
40
is typically on the order of 100 microns thick. The rotor wafer
40
must also be micro-machinable, hence it too is often made from silicon. As stated above, the micro-mover
50
generally consists of a portion of the rotor wafer
40
that has been separated from the remainder of the rotor wafer
40
but that remains attached by suspensions
60
. Hence, the micro-mover
50
is also typically on the order of 100 microns thick and made from a micro-machinable material.
The suspensions
60
are designed to allow the micro-mover
50
to have in-plane motion while restricting the micro-mover
50
out-of-plane motion. In other words, the suspensions
60
are designed to allow the micro-mover
50
to move horizontally relative to the stator wafer
20
and to restrict the micro-mover
50
from moving vertically. A variety of suspensions
60
are known in the art and are designed with different amounts of in-plane compliance and out-of-plane stiffness. However, none of these suspensions
60
can prevent out-of-plane motion completely.
The bond material
70
typically is a metallic, thin-film material. The type of bond material
70
used depends upon several factors. Commonly, the bond material
70
is chosen so as to provide electrical conductivity between the various wafers
20
,
40
. The bond material
70
is also chosen on its ability to hermetically seal the chamber in which the micro-mover
50
resides.
The stator electrodes
80
consist of inter-digitated metal lines formed on the surface of the stator wafer
20
closest to the micro-mover
50
. The actuator electrodes
90
are another set of inter-digitated metal lines formed on the micro-mover
50
. Each metal line that makes up an electrode
80
,
90
is approximately one to two microns wide and can have a length of up to one or two millimeters. A one to two micron gap typically exists between any two electrodes
80
,
90
.
The actuator electrodes
90
typically cover a substantial portion of the micro-mover
50
, which itself can have a total area of between one and two square millimeters. The electrodes
80
,
90
can be made up of various metals that are generally compatible with semiconductors. Such metals include, but are not limited to, molybdenum, aluminum and titanium.
FIG. 2
illustrates a cross-sectional view of a micro-machined actuator
10
taken across the plane A—A defined in FIG.
1
. In operation, the actuator
10
operates by moving the micro-mover
50
relative to the stator wafer
20
. In order to move the micro-mover
50
relative to the stator wafer
20
, the voltages of selected stator electrodes
80
and actuator electrodes
90
are raised and lowered in a specific pattern in order to alter the electric fields emanating from the electrodes
80
,
90
.
For example, the actuators electrodes
90
can have their voltages set in a pattern where a first electrode
90
would be placed at an operating voltage such as 40 volts, the electrode
90
adjacent to it would be grounded, the next electrode
90
would be at 40 volts, and the remaining electrodes would have their voltages set in a similar manner. The stator
80
, on the other hand, could have their voltages set in a pattern that is not quite alternating. For example, a first stator electrode
80
could be set to a high voltage, a second stator electrode
80
immediately adjacent to the first could be set to a low voltage, a third stator electrode
80
adjacent to the second could be set to a high voltage, a fourth stator electrode
80
adjacent to the third could be set to a low voltage, adjacent fifth and sixth stator electrodes
80
could be set to high voltages and a seventh adjacent stator electrode
80
could be set to a low voltage. This seven-electrode
80
voltage pattern could then be repeated for all of the stator electrodes
80
in the actuator
10
.
In order to move the micro-mover
50
, the pattern of the voltages in the stator electrodes
80
is changed by increasing or decreasing the voltage on one or more of the stator electrodes
80
. Such voltages changes alter the distribution of the electric fields present between the stator electrodes
80
and actuator electrodes
90
. Therefore, the attractive and repulsive forces between the stator electrodes
80
and actuator electrodes
90
are also altered and the position of the micro-mover
50
is changed until these forces are balanced.
In other words, as the stator electrode
80
voltages are changed, new, low-energy potential regions are created where the forces generated by the electric fields balance the mechanical forces exerted on the micro-mover
50
by the suspensions
60
. Hence, once the voltages of the stator electrodes
80
have been changed to a new pattern, the micro-mover
50
repositions itself.
An unwanted side effect of the electric fields is the out-of-plane component of the attractive forces between the stator electrodes
80
and the actuator electrodes
90
. These attractive forces pull the micro-mover
50
towards the stator wafer
20
and, if too great, allow the actuator electrodes
90
and stator electrodes
80
to come into close enough contact that they electrically “short out” and fuse together. Such an event causes catastrophic failure of the actuator
10
.
Although the suspension
60
is designed to be sufficiently stiff to restrict the out-of-plane movement of the micro-mover
50
, it is difficult to design a suspension
60
that simultaneously provides the required in-plane mobility of the micro-mover
50
and restricts out-of-plane motion. Hence, to date, micro-machined actuators
10
have been susceptible to catastrophic failure.
Fusing of the stator electrodes
80
and the actuators electrodes
90
can also occur if an external jolt is applied to the system. For example, if the micro-chip that contains the micro-machined actuator
10
is tapped or jolted, enough additional physical force in the out-of-plane direction could be transferred to the micro-mover
50
and stator wafer
20
configuration to sufficiently overcome the suspension
60
stiffness and to fuse together the stator electrodes
80
and actuator electrodes
90
.
Hence, what is needed is a micro-actuator that prevents out-of-plane motion of the micro-mover relative to the stator wafer.
What is also needed is a micro-actuator capable of being tapped or jolted, for example, without having the outside force cause catastrophic failure of the device.
BRIEF SUMMARY OF THE INVENTION
According to o
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