Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2002-06-18
2004-07-06
Dang, Hung Xuan (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S295000
Reexamination Certificate
active
06760143
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a micromirror actuator and, more particularly, to a micromirror actuator, which can be driven by attractive electrostatic forces and can have a wide range of driving angles with the use of a low driving voltage.
This application is based on Korean Patent Application No. 2001-36092 filed on Jun. 23, 2001, the disclosure of which is incorporated herein by reference in its entirety.
2. Description of the Related Art
Micromirrors are generally used in various fields including an optical communication field. For example, micro-optical cross connects (MOXCs) are devices for selecting an optical path and thus allowing an optical signal to be transmitted from an input terminal to a predetermined output terminal, and micromirrors are the most important components of MOXC.
Micromirror actuators, which can maintain a micromirror at a predetermined angle, have been manufactured by using many different methods and having various structures.
FIGS. 1A and 1B
are views illustrating a conventional micromirror actuator using attractive electrostatic forces and including an elastic element, such as a torsion spring. Referring to
FIGS. 1A and 1B
, a micromirror
14
is formed horizontally, over a substrate
11
with a spring unit
13
supported by a protrusion
12
formed on the substrate
11
. The micromirror
14
is formed to be capable of rotating, and a lower electrode
15
is formed under the micromirror
14
. If external voltage is applied to the micromirror
14
and the lower electrode
15
, attractive electrostatic forces are generated between the micromirror
14
and the lower electrode
15
, as shown in FIG.
1
B. Due to the electrostatic forces, the micromirror
14
supported by the spring unit
13
inclines over the substrate
11
at a predetermined angle.
The range, in which the driving angle of the micromirror actuator driven by attractive electrostatic forces can be controlled by external voltage, is strictly restricted due to the special characteristics of the method of driving the micromirror actuator. In other words, if a voltage not less than a predetermined level, i.e., threshold voltage, is applied between the spring unit
13
and the micromirror
14
, attractive electrostatic force generated by the applied voltage is always stronger than the elastic restoring force of the spring unit
13
. Thus, the distance between the micromirror
14
and the lower electrode
15
becomes shorter. This can be described more thoroughly with reference to Equation (1).
F
=
ϵ
AV
2
d
2
(
1
)
In Equation (1), F represents an attractive electrostatic force, &egr; represents a dielectric constant, A represents the area of an electrode, V represents a potential difference, and d represents the distance between the electrodes. In general, the intensity of the attractive electrostatic force acting between the electrodes is inversely proportional to the square of the distance between the electrodes but is proportional to the square of a voltage applied to the electrodes. Accordingly, as the distance d between the electrodes decreases, the influence of the voltage applied to the electrodes on the attractive electrostatic force between the electrodes increases. In addition, the range, in which the driving angle of a micromirror can be controlled by the voltage applied to the electrodes, becomes very sensitive to a potential difference between the electrodes.
On the other hand, as the distance d between the electrodes increases, the influence of the voltage applied to the electrodes on the attractive electrostatic force between the electrodes, decreases, and the range, in which the driving angle of a micromirror can be controlled by the voltage applied to the electrodes, expands. However, the voltage applied to the electrodes must be increased to obtain a desired angle of the micromirror, and the height of a sacrificial layer formed in manufacturing of a micromirror actuator must be increased.
SUMMARY OF THE INVENTION
To solve the above-described problems, it is an aspect of the present invention to provide a micromirror actuator, which is capable of obtaining a larger driving angle with the use of a lower driving voltage by forming a stepped electrode in a trench (thus lower than in
FIGS. 1A and B
) so as to make the difference between the lower electrode and a micromirror vary.
According to the present invention, a micromirror actuator comprises a substrate, spring units elastically supported by protrusions formed on the substrate, a micromirror connected to the spring units and capable of rotating, trenches formed in the substrate at either side of the protrusions to correspond to the surface of the micromirror and lower electrodes formed in each of the trenches. Lower electrodes may include an electrode formed at the bottom and sidewall of each of the trenches or between the trenches. Trenches may have vertical, slanted or stepped sidewalls. Further, in order to enlarge the range of the driving angle of the micromirror, the distance between the lower electrodes and the micromirror is varied as well as the distance between the lower electrodes and their size.
REFERENCES:
patent: 6431714 (2002-08-01), Sawada et al.
patent: 6459523 (2002-10-01), Ueda
patent: 6487011 (2002-11-01), Donath et al.
patent: 2002/0141038 (2002-10-01), Mori
patent: 2003/0076576 (2003-04-01), Neukermans et al.
patent: 8-21966 (1996-01-01), None
Dang Hung Xuan
Samsung Electronics Co,. Ltd.
Tra Tuyen
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