Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2003-05-27
2004-11-02
Schwartz, Jordan M. (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S295000, C359S254000, C359S242000
Reexamination Certificate
active
06813061
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrostatic machine element, a light diffraction modulation element and an image display device using the same, and for example a light diffraction modulation element like a diffraction grating type light valve reflecting and diffracting light, and a two-dimensional image display device using the same.
2. Description of the Related Art
It is known a method in which luminous flux from a one-dimensional image display element is scanned by a light scanning means and the scanned flux is projected to an image forming means to form a two-dimensional image, for the purpose of improving a resolution of an image in an image forming device like a projector or a printer (U.S. Pat. No. 5,982,553). As the one-dimensional image display element, a grating light valve (GLV) developed by Silicon Light Machine Corporation in U.S.A. is known (Japanese Patent No. 3164824, U.S. Pat. No. 5,841,579).
The GLV is composed of a micro machine phase reflection type diffraction grating utilizing a diffraction phenomenon of light. The GLV has a light switching function, and electrically controls an ON/OFF control of a light to enable a digital image display.
The GLV formed as a one-dimensional array is scanned by a scanning mirror to obtain a two-dimensional image. Therefore, compared with normal two-dimensional display devices, in case of using the GLV, although the number of pixels at a vertical direction are same as that of them, since the number of pixels at a lateral direction may be at least one, the number of pixels needed for displaying a two-dimensional image is small. Further, a size of an electrode portion of the GLV called as a ribbon element is extremely small, so the GLV can display the image at a high resolution, at a high-speed switching and with a broad band width. In addition, the GLV can be operated at a low application voltage, so the GLV has been expected to realize a display device of extremely miniaturization.
The two-dimensional image display device using such the one-dimensional image display element GLV enable an extremely smooth and a natural image expression compared with the normal two-dimensional image display devices, for example a projection type display device using a liquid crystal panel, because boundaries between pixels does not exist in the GLV. Moreover, lasers of red, green and blue as the three primary colors are used as light sources and these lights are mixed to achieve a superior display performance enabling an image expression of extremely broad and natural color reproduction range, which is not achieved by a prior art.
A ribbon element of the GLV is a micro machine driven by electrostatic force and displaced or deformed, and one of fine electrostatic machine elements.
FIGS.
10
(
a
) and (
b
) are views explaining a structure and an operation of an electrostatic machine element in GLV.
FIG.
10
(
a
) is a schematic cross-section view showing a structure of an electrostatic machine element as the related art. As shown in FIG.
10
(
a
), an electrostatic machine element
100
is formed by a lower electrode
102
as a lower structure composed of a polysilicon on a substrate
101
of silicon or a glass, and a dielectric film
103
for protecting the lower electrode
102
and composed of silicon oxide (SiO
2
) on the lower electrode
102
. Further, the electrostatic machine element
100
is also formed by an upper electrode
105
as an upper structure composed of for example aluminum on a dielectric film
104
composed of silicon nitride (SiN). The dielectric film
104
and the upper electrode
105
compose a single ribbon element. In the state shown in FIG.
10
(
a
), a voltage is not applied between the upper electrode
105
and the lower electrode
102
and the electrostatic machine element
100
is in an OFF state.
FIG.
10
(
b
) is a schematic cross-section view showing a structure of an electrostatic machine element. As shown in FIG.
10
(
b
), when a certain drive voltage is applied between the upper electrode
105
and the lower electrode
102
, an electrostatic force (Coulomb force) is caused between the upper electrode
105
and the lower electrode
102
(It is called as an ON state). As a result, for example, the upper electrode
105
is mechanically displaced or deformed (warp) to the lower electrode
102
side. The amount of displacement or deformation (warp) (the movement amount) a
1
is nm (nano meter) order and corresponds to a value of a drive voltage. When a plurality of electrostatic machine elements
100
are arranged in parallel, a reflection type diffraction grating is formed by the warp or the movement amount a
1
to generate a diffraction light.
FIG.
11
(
a
) is a cross-section view showing an electrostatic machine element at time to and FIG.
11
(
b
) is a cross-section view showing an electrostatic machine element at time t
1
.
In a micro machine device for forming an opposed electrodes through a dielectric film and performing drive by an electrostatic force like the electrostatic machine element
100
, as shown in FIG.
11
(
a
) and (
b
), a drive voltage is applied to make the upper electrode
105
a high electric potential and the lower electrode
102
a low electric potential to be the ON state. The upper electrode
105
is displaced in a direction of the lower electrode
102
with the distance a
1
. However, a phenomenon has been observed that the position of the upper electrode
105
is gradually displaced in the direction of a position of the OFF state with the elapse of time.
Specifically, in FIG.
11
(
a
), the drive voltage shown in FIG.
10
(
b
) is applied to displace the upper electrode
105
to the lower electrode
102
side by the distance a
1
at the time t
1
. At time t
1
after the elapse of time, the upper electrode
105
is returned in a direction opposed to the lower electrode
102
side to be at a distance a
2
smaller than the distance a
1
compared with the distance before the drive voltage is applied.
This phenomenon is considered by which the electrostatic force between the upper electrode
105
and the lower electrode
102
is weak.
As shown in FIG.
10
(
a
), in an atmosphere at a high vacuum, molecules existing in low density for example moisture are deposited to the dielectric films
103
and
104
. As shown in FIG.
10
(
b
) and FIG.
11
(
a
), when the drive voltage is applied at around 20V for example between the upper electrode
105
and the lower electrode
102
, since the distance between the dielectric film
103
and
104
is around 1 &mgr;m, a high electric field at around 20 V/10
−4
cm=2×10
5
V/cm is formed between the upper electrode
105
and the lower electrode
102
.
When the molecules for ionizing regularly in a normal temperature like H
2
O molecules adheres to the dielectric films
103
and
104
or floats between the electrodes, the molecules for ionizing regularly described above (charged particles) repeat ionization and bonding in the state of adhering to the surface or floating between the dielectric films
103
and
104
to keep equilibrium of the particles. Even if adding the high voltage described above in this state, these ionized charged particle are restrained by an adhesion force of the dielectric films
103
and
104
, so that they cannot immediately apart from the dielectric films
103
and
104
. Then, aparting from the dielectric films
103
and
104
with the elapse of time, as shown in FIG.
11
(
b
), the charged particles move between the dielectric films
103
and
104
along with the direction of the electric field.
Specifically, the voltage is applied to the upper electrode
105
at a high electric potential and a low electric potential is applied to the lower electrode
102
as described above, so that a positive charge adhered to the dielectric film
104
of the upper electrode
105
moves to the dielectric film
103
of the lower electrode
102
and a negative charge adhered to the dielectric film
103
of the lower electrode
102
moves to the dielectric film
Taguchi Ayumu
Tamada Hitoshi
Frommer William S.
Frommer & Lawrence & Haug LLP
Megerditchian Samuel H.
Schwartz Jordan M.
Sony Corporation
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