Electricity: magnetically operated switches – magnets – and electr – Electromagnetically actuated switches – Polarity-responsive
Reexamination Certificate
2002-07-26
2004-03-02
Donovan, Lincoln (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Electromagnetically actuated switches
Polarity-responsive
C200S181000, C361S233000
Reexamination Certificate
active
06700465
ABSTRACT:
Priority is claimed to Patent Application No. 2001-73574 filed in Republic of Korea on Nov. 24, 2001, herein incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a micro-switching device actuated by low voltage, using an electrostatic attraction.
2. Description of the Related Art
In general, an RF switch is a kind of switch for turning a device on or off by using electrostatic attraction to bring a structure into contact with a signal line. In this case, a predetermined voltage is applied to the signal line so as to generate an electrostatic attraction required. Here, the voltage required is determined by the rigidity of a spring supporting a microstructure. Preferably, the spring has low rigidity so as to allow actuation by a low voltage.
When a microstructure constituting a micro device is in contact with a signal line or an electrode, they may, however, be adhered to each other. This problem may also occur when a voltage is applied to and then removed from an electrode. As a result, the microstructure is kept in contact with the signal line, thereby preventing the proper switching control of the micro device.
To solve this problem, the restoring capability of an actuated structure must be strengthened, to make the actuated structure return back to its original position. Thus, the structure has to be supported by a spring of high rigidity. However, as described above, the voltage applied to an electrode must be increased in order to use a spring of high rigidity. Nevertheless, a spring of high rigidity is often adopted in a micro switching device at the present time, so as to prevent the adhesion of a micro device to a signal line or an electrode. As a result, the necessary voltage is increased, and thus it is very difficult to make a micro switching device that can be actuated by a low voltage.
FIG. 1A
is a perspective view of a conventional micro-switching device. The micro-switching device is supported by anchors
13
, which are fixed onto a substrate, and springs
14
which are formed on the anchors
13
, and includes a membrane
15
above the substrate, a lower electrode
11
corresponding to the membrane
15
, and insulating layers
12
. If a voltage is applied to the lower electrode
11
, an electrostatic attraction is generated to actuate the springs
14
. Then, the membrane
15
approaches the lower electrode
11
due to the electrostatic attraction, comes into contact with a signal line
16
, and is then switched on.
FIGS. 1B and 1C
are views for explaining defects of a conventional micro-switching device. Here, for convenience's sake, the defects are diagrammatically viewed with regard to a general representation of a conventional micro-switching device.
FIG. 1B
is a view of a micro-switching device in which a membrane
15
is actuated by applying power to a lower electrode
11
, and
FIG. 1C
is a view of the micro-switching device in which the membrane
15
is actuated and approaches closely to the lower electrode
11
. More specifically, while the membrane
15
is not in contact with the lower structure of the lower electrode
11
and insulating layers
12
, with its body held by the springs
14
, an electrostatic attraction is generated between the membrane
15
and the lower electrode
11
when a voltage is applied to the lower electrode
11
, thereby attracting the membrane
15
to the lower electrode
11
. At this time, the more closely the membrane
15
approaches the lower electrode
11
, the more the electrostatic attraction between the membrane
15
and the lower electrode
11
is increased. As a result, the displacement of the membrane
15
increases. Then, the displacement of the springs
14
increases to increase their restoring capability.
Here, the electrostatic attraction between the membrane
15
and the lower electrode
11
is calculated by the following equation:
F
E
=
1
2
ϵ
AV
2
(
g
0
-
U
z
)
2
(
1
)
wherein F
E
denotes an electrostatic attraction, A denotes a corresponding area, V denotes voltage applied to the lower electrode
11
, U
z
denotes the driving distance of the membrane
15
, and g
0
denotes a distance between the membrane
15
and the lower electrode
11
. As shown in the equation (1), an increase in the driving distance U
z
of the membrane
15
results in an increase in the electrostatic attraction F
E
.
The restorability capability of the springs
14
can be expressed by the following equation:
F
s
=kU
z
(2)
wherein Fs denotes the restoring capability of the springs
14
, k denotes a spring constant, and Uz denotes the displacement of the membrane
15
. From the equation 2, it is noted that the restoring capability Fs of the springs
14
increases linearly according to the displacement of the membrane
15
.
FIG. 2
is a graph illustrating the relationship between the restoring capability of the springs
14
and the electrostatic attraction due to the displacement of the membrane
15
. This graph reveals that the electrostatic attraction changes greatly, and the restoring capability of the springs
14
changes linearly, according to the driving distance of the membrane
15
. The electrostatic attraction may be greater than or less than the restoring capability of the springs
14
according to the displacement of the membrane
15
. This is caused by the use of a spring having a relatively large spring constant, or a low voltage applied to the lower electrode
11
. Then, the driving distance of the membrane
15
is limited, i.e., it is actuated to a predetermined point and does not operate, and thus cannot function as a switch. However, referring to
FIG. 2
, the electrostatic attraction is always greater than the restoring capability of the springs
14
, at which time the membrane
15
becomes in contact with the lower structure of the lower electrode
11
, the insulating layer
12
, and the signal line
16
, due to the electrostatic attraction. At this time, the membrane can function as a switch.
Once a voltage is applied to the lower electrode
11
, the membrane
15
comes into contact with the signal line
16
, i.e. it is switched on, and thus the electrostatic attraction is far greater than the restoring capability of the springs
14
. Then, the voltage is removed to make the membrane
15
switch off. However, adhesion, which is an inherent property of a micro device, may occur between the membrane
15
and the lower structure of the lower electrode
11
, the insulating layer
12
and the signal line
16
, thereby reducing the restoring capability of the springs
14
. To prevent a reduction in the restoring capability of the springs
14
, a spring having a large spring constant K may be used, but this is disadvantageous because a high voltage must be applied to the lower electrode
11
.
The above problem can be solved by applying a predetermined force to the micro-switching device so that the membrane can return back to its original position without using a spring of high rigidity. That is, a spring of low rigidity is used, and means for applying a predetermined force onto the micro-switching device is additionally installed to separate the membrane from a lower structure.
For instance, electrodes for applying a driving force may be installed at the top as well as the bottom of the membrane. To actuate a microstructure and make it return back to its original position, a voltage is applied to the upper and lower electrodes of a microstructure. Then, the membrane may be driven in both directions, i.e. upward and downward, and thus can be easily separated from the electrodes to return to its original state. However, this method is disadvantageous in that the manufacturing process is complicated, thereby reducing the yield. Also, in fact, it is difficult to obtain sufficient restoring force to actuate the microstructure and return it to its original state with a low voltage.
SUMMARY OF THE INVENTION
To solve the above problems, it is an object of the present invention to provide a micro-switching d
Burns Doane , Swecker, Mathis LLP
Rojas Bernard
LandOfFree
Micro-switching device actuated by low voltage does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Micro-switching device actuated by low voltage, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Micro-switching device actuated by low voltage will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3220028