Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2002-07-08
2004-07-06
Schwartz, Jordan M. (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S290000, C359S298000
Reexamination Certificate
active
06760146
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a light-modulation element, a GLV device, and a laser display. More particularly, the present invention relates to a light-modulation element including a combined light-reflective film and a membrane-side electrode having a high reflectance, a GLV device including the light-modulation elements, and a laser display including such a GLV device or devices.
Attendant on the progress of miniaturizing technology, attention has been paid to the so-called micromachine (MEMS: Micro Electro-Mechanical System) element and small-type apparatuses incorporating the MEMS element or elements.
The MEMS element is formed as a miniaturized structure on a substrate such as a silicon substrate a glass substrate, and the like, in which a driver for outputting a mechanical driving force and a semiconductor integrated circuit or the like for controlling the driving of the driver are coupled electrically and, further, mechanically. A basic characteristic of the MEMS element lies in that the driver constituted as a mechanical structure is incorporated in a part of the element, and the driving of the driver is performed electrically by application of a coulomb attractive force between electrodes or the like.
The constitution of a light-modulation element will be described by showing as an example the light-modulation element provided in the GLV (Grating Light Valve) device developed as a light-intensity conversion element, namely, a light modulator for laser display, by SLM (Silicon Light Machine) Company.
First, referring to
FIG. 5
, the structure of the GLV device including the light-modulation elements will be described.
FIG. 5
is a perspective view showing the constitution of the GLV device.
As shown in
FIG. 5
, the GLV device
10
is a device in which a plurality of light-modulation elements
12
are disposed densely and in parallel to each other. Each of the light-modulation elements
12
constituting the GLV device
10
is a light-modulation element called MOEMS (Micro Optical Electric Mechanical System) including an electrostatic-driving-type membrane
16
having a light-reflective film
14
on the upper side thereof, and it has the function of modulating the intensity of light reflected by the light-reflective film
14
by diffraction of light through alternate variation of the height of the light-reflective film
14
as a result of mechanical movements of the membrane
16
by an electrostatic attracting force or an electrostatic repelling force.
Next, referring to
FIG. 6
, the constitution of the light-modulation element
12
will be described.
FIG. 6
is a perspective view showing the constitution of the light-modulation element.
As shown in
FIG. 6
, the light-modulation element
12
includes an insulating substrate
18
, such as a glass substrate, a substrate-side electrode
20
composed of a thin Cr film or the like and formed on the insulating substrate
18
, and the electrostatic-driving-type membrane
16
crossing and being astride the substrate-side electrode
20
in a bridge form.
The electrostatic-driving-type membrane
16
and the substrate-side electrode
20
are electrically isolated from each other by a void portion
22
therebetween.
The electrostatic-driving-type membrane
16
includes a bridge member
24
composed of an SiN film provided as an electrode-support member and based on the substrate
18
bridgingly astride the substrate-side electrode
20
, and a combined light-reflective film and membrane-side electrode
14
composed of an Al film of about 100 nm in thickness that is provided on the bridge member
24
oppositely to and in parallel to the substrate-side electrode
20
.
The bridge member
24
is opposed to and spaced by a predetermined gap from the substrate-side electrode
20
so as to secure the void portion
22
therebetween, and it is provided for supporting the combined light-reflective film and membrane-side electrode
14
in parallel to the substrate-side electrode
20
.
In the GLV device
10
, the insulating substrate
18
and the substrate-side electrode
20
thereon are respectively a common substrate and a common electrode for the light-modulation elements
12
, as shown in FIG.
5
.
The electrostatic-driving-type membrane
16
constituted of the bridge member
24
and the combined light-reflective film and membrane-side electrode
14
provided thereon is a portion called a ribbon.
The bridge member
24
may in some cases be of the cantilever type in which only one end of a beam portion extending in parallel to the substrate-side electrode
20
is supported by one column portion, in place of the bridge form shown in
FIG. 6
in which both ends of the beam portion are supported by two column portions, respectively.
The aluminum film (Al film) used as the combined light-reflective film and membrane-side electrode
14
is a metallic film preferable as an optical component material on the ground that (1) it is a metallic film which can be formed comparatively easily, (2) it has a small wavelength dispersion of light reflectance in the visible ray region, (3) a spontaneously oxidized alumina film formed on the surface of the Al film functions as a protective film for protecting the reflective surface, and the like.
On the other hand, the SiN film (silicon nitride film) constituting the bridge member
24
is a film deposited by a low-pressure CVD process. The SiN film is selected on the ground that its physical properties, such as strength and elastic constant, are suitable for mechanical driving of the bridge member
24
.
When a minute voltage is impressed between the substrate-side electrode
20
and the combined light-reflective film and membrane-side electrode
14
opposed to the substrate-side electrode
20
, the electrostatic-driving-type membrane
16
approaches the substrate-side electrode
20
due to an electrostatic phenomenon, and when the impressing of the voltage is stopped, the electrostatic-driving-type membrane
16
is spaced away from the substrate-side electrode
20
into its original state.
Each of the light-modulation elements
12
constituting the GLV device
10
modulates the intensity of the light reflected by the light reflective film
14
by diffraction of light as a result of alternative variation of the height of the light-reflective film
14
through the approaching and spacing actions of the electrostatic-driving-type membrane
16
relative to the substrate-side electrode
20
.
The dynamic characteristics of the membrane
16
driven by utilizing the electrostatic attracting force and electrostatic repelling force are substantially determined by the physical properties of the SiN film formed by a CVD process or the like, and the Al film plays a main role as a mirror or reflector.
In the conventional light-modulation element, however, since the combined light-reflective film and membrane-side electrode is composed of an Al film, there have been the following problems. Namely, although the Al film has the above-mentioned merits, the material is comparatively low in melting point and is soft. Therefore, when a thin Al film of about 100 nm in thickness is formed, differences in thickness of the Al film are generated due to aggregation of aluminum. In addition, when the differences in height are as large as not less than 400 nm, a rough surface reaching to 1 &mgr;m is generated in the Al film, and light reflectance of the Al film is lowered. For example, while the bulk Al film has a light reflectance of about 92% for light with a wavelength of 600 nm, the light reflectance of the conventional light-modulation element
10
is about 86.5% for the wavelength of 600 nm; thus; there is a lowering in reflectance by about 5%.
Besides, when the differences in thickness generated in the Al film are extremely large, the Al film may be broken, resulting in an electrically non-conductive state. In such a case, driving of the membrane cannot be achieved, and the light-modulation element cannot function.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to
Fukui Tatsuo
Ikeda Koichi
Kananen Ronald P.
Rader & Fishman & Grauer, PLLC
Schwartz Jordan M.
Stultz Jessica
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