Microminiature movable device

Details Microminiature movable device Microminiature movable device

2002-03-19

2003-08-05

Lester, Evelyn (Department: 2873)

Optical: systems and elements

Optical modulator

Light wave temporal modulation

C359S291000, C359S223100

Reexamination Certificate

active

06603591

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a microminiature movable device and, more particularly, to a microminiature movable device in which an auxiliary electrode is formed on a stationary substrate together with a stationary electrode to prevent a movable electrode plate from sticking or adhering to the stationary substrate.
To facilitate a better understanding of the present invention, a description will be given first, with reference to
FIGS. 1A and 1B
, of a prior art example of a microminiature movable device.
The illustrated microminiature movable device is manufactured using a silicon (Si) single crystal wafer as the starting substrate through application of micromachining technology including thin-film growth, photolithography and etching techniques. The silicon single crystal wafer is ultimately machined into such a square support frame
10
as depicted in
FIGS. 1A and 1B
. The support frame
10
has formed integrally therewith anchor parts
11
located centrally on a pair of opposed sides of the frame, flexures
19
extended inwardly from the anchor parts
11
and a rectangular movable electrode plate
12
connected centrally at its both sides to inner ends of the flexures
19
.
On the top of the movable electrode plate
12
there are formed four micro-nirrors
13
having their reflecting surfaces held perpendicular to the movable electrode plate
12
. Reference numeral
10
a
denotes a countersink bored through the support frame
10
. Fixedly mounted on the underside of the support frame
10
in a manner to cover the countersink
10
a
is a stationary electrode substrate or plate
80
with a film-formed stationary electrode
84
on the top thereof, the stationary electrode plate
80
being in spaced parallel relation to the movable electrode plate
12
. Reference numerals
14
and
14
′ denote output optical fibers or optical waveguides, and
15
and
15
′ denote input optical fibers or optical waveguides. Incidentally,
FIGS. 1A and 1B
show the case where the miniature movable device is an optical switch.
Now, the operation of the optical switch will be described below with reference to
FIGS. 2A
to
2
D.
Referring first to
FIGS. 2A and 2B
, light transmitted over the input optical fibers
14
and
14
′ is emitted from their end faces, and propagate through the space to the micro-mirrors
13
, by which it is reflected for incidence on the output optical fibers
15
and
15
′. This state will hereinafter referred to as a steady state.
Turning next to
FIGS. 2C and 2D
, when a voltage is applied across the stationary electrode
84
and the movable electrode plate
12
to generate therebetween static electricity in a direction in which they attract each other, the movable electrode plate
12
is driven downwardly, by which the flexures
19
are elastically deformed, and consequently, the movable electrode plate
12
is displaced downward. The micro-mirrors
13
formed on the top of the movable electrode plate
12
are also displaced downward, and hence they go down below the optical paths of the light emitted from the end faces of the input optical fibers
14
and
14
′. In this case, the light emitted from the end face of the input optical fiber
14
is no longer intercepted by the micro-mirrors
13
, and it travels in a straight line and impinges on the output optical fiber
15
′. Similarly, the light emitted from the light emitted from the end face of the input optical fiber
14
′ strikes on the output optical fiber
15
. In this way, the optical paths to the output optical fibers
15
and
15
′ can be switched spatially without using solid optical waveguides as of transparent synthetic resin.
In the above-described microminiature movable device, the movable electrode plate
12
and the flexures
19
are both so thin, in general, that they are small in their elastic restoring force. And, the underside of the movable electrode plate
12
is smooth, whereas the top of the stationary electrode
84
is also smooth and is stained and moist as well, allowing polarization in the electrode surface and generating van der Waals forces, too. Under these conditions, when the movable electrode plate
12
is displaced downward to bring its underside into contact with the top of the stationary electrode
84
, they adhere to each other and do not separate immediately, sometimes disturbing smooth switching operation. Incidentally, such adhesion can be avoided, for example, by roughening either one or both of the underside surface of the movable electrode plate
12
and the top surface of the stationary electrode
84
. However, roughening either one or both of the two contacting surfaces involves some additional process steps, and hence it introduces complexity in the manufacture of the microminiature movable device.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a microminiature movable device adapted so that the movable electrode plate, when brought into contact with the stationary electrode, can be separated therefrom relatively easily.
The microminiature movable device according to the present invention comprises:
A microminiature movable device comprising:
a stationary electrode substrate having a centrally-disposed protrusion with a stationary electrode formed on its top;
auxiliary electrode means formed on said stationary electrode substrate at a position adjacent said protrusion and at a level lower than said stationary electrode;
a movable electrode part having an area opposite said stationary electrode and said auxiliary electrode means;
at least two flexures resiliently supporting at one end said movable electrode part at at least two places of its marginal edge; and
a support frame secured to said stationary electrode substrate, for fixedly supporting the other ends of said flexures to hold said movable electrode plate so that it can be engaged with or disengaged from said stationary electrode.


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patent: 5793519 (1998-08-01), Furlani et al.
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patent: 5999303 (1999-12-01), Drake
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patent: 6431714 (2002-08-01), Sawada et al.
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patent: 0725408 (1996-08-01), None
patent: 8339939 (1996-12-01), None
patent: 10162713 (1998-06-01), None
Kato, et al., “Development of 4×4 MEMS optical switch,” IEEE/LEOS International Conference on Optical MEMS, Kauai, HI, Aug. 21-24, 2000, pp. 95-96. (2000).

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