Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Including integrally formed optical element
Reexamination Certificate
1998-03-31
2001-03-20
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Including integrally formed optical element
C356S224000, C356S241400, C356S004050
Reexamination Certificate
active
06204080
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a method for manufacturing a thin film actuated mirror array in an optical projection system, and more particularly to a method for manufacturing a thin film actuated mirror array in an optical projection system for enhancing a light efficiency and for preventing damages of an active matrix, an actuator and a reflecting member.
In general, light modulators are divided into two groups according to their optics. One group is a direct light modulator such as a cathode ray tube (CRT), and the other group is a transmissive light modulator such as a liquid crystal display (LCD), a digital mirror device (DMD), and an actuated mirror array (AMA). The CRT projects a superior qualitative picture on a screen, but a weight, a volume, and a manufacturing cost of the CRT increase according to the magnification of the screen. The LCD has a simple optical structure, so a weight and a volume of the LCD are less than those of the CRT. However, the LCD has a poor light efficiency of under 1 to 2% due to light polarization. And, there are another problems in a liquid crystal material of the LCD such as sluggish response and overheating. Thus, the DMD and the AMA have been developed to solve these problems. Now, the DMD has a light efficiency of about 5% while the AMA has a light efficiency of above 10%. The AMA enhances a contrast of a picture projected on a screen, so the picture is more apparent and brighter. The AMA is not affected by the polarization of rays of incident light. Also, the AMA is not affected by the polarization of a reflected light. Therefore, the AMA is more efficient than the LCD or the DMD.
FIG. 1
shows a schematic diagram for showing an engine system of a conventional AMA disclosed in U.S. Pat. No. 5,126,836 (issued to Gregory Um).
Referring to
FIG. 1
, a incident light from a light source
1
passes through a first slit
3
and a first lens
5
and is divided into red, green and blue lights according to the Red.Green.Blue (R.G.B) system of color representation. After the divided red, green, and blue lights are respectively reflected by a first mirror
7
, and second mirror
9
, and a third mirror
11
, the reflected lights are respectively incident on AMA devices
13
,
15
, and
17
corresponding to the mirror
7
,
9
, and
11
. The AMA devices
13
,
15
, and
17
respectively tilt the mirrors installed therein, so the rays of incident light are reflected by the mirrors. In this case, the mirrors installed in the AMA devices
13
,
15
, and
17
are tilted according to the deformation of active layers formed under the mirrors. The rays of reflected light by the AMA devices
13
,
15
, and
17
pass a second lens
19
and a second slit
21
and form a picture on a screen (not shown) by means of a projection lens
23
.
In most case, zinc oxide (ZnO) is used as a material forming the active layer. However, lead zirconate titanate (PZT: Pb(Zr, Ti)
0
3
) has been found to have a better piezoelectric property than ZnO. PZT is a complete solid solution made of lead zirconate (PbZrO
3
) and lead titanate (PbTiO
3
). At a high temperature, PZT exists in a paraelectric phase whose crystal structure is a cubic. While at a room temperature, PZT exists in an antiferroelectric phase whose crystal structure is an orthorhombic, in a ferroelectric phase whose crystal structure is a rhombohedral, or in a ferroelectric phase whose crystal structure is a tetragonal according to the composition ratio of Zr to Ti.
The PZT has a morphotropic phase boundary (MPB) of the tetragonal phase and the rhombohedral phase where the composition ratio of Zr to Ti is 1:1. PZT has a maximum dielectric property and piezoelectric property at the MPB. The MPB does not lie in a specific composition ratio but lies over a relatively wide region where the tetragonal phase and the rhobohedral phase coexist. The phase coexistent region of PZT is reported differently depending on researchers. Various theories such as thermodynamic stability, compositional fluctuation, and internal stress have been suggested as the reason for the phase coexistent region. Nowadays, a PZT thin film can be manufactured by various processes such as a spin coating method, a chemical vapor deposition (CVD) method, or a sputtering method.
The AMA is generally divided into a bulk type AMA and a thin film type AMA. The bulk type AMA is disclosed in U.S. Pat. No. 5,469,302 (issued to Dae-Young Lim). The bulk type AMA is formed as follows. A ceramic wafer having a multilayer ceramic where metal electrodes are inserted is mounted on an active matrix having transistors. After sawing the ceramic wafer, a mirror is mounted on the ceramic wafer. However, the bulk type AMA has some disadvantages that very accurate process and design are required, and the response of an active layer is slow. Therefore, the thin film AMA that can be manufactured by using semiconductor manufacturing technology has been developed.
The thin film AMA is disclosed at U.S. Ser. No. 08/814,019 entitled “THIN FILM ACTUATED MIRROR ARRAY IN AN OPTICAL PROJECTION SYSTEM AND METHOD FOR MANUFACTURING THE SAME, which is now pending in USPTO and is subject to an obligation to the assignee of this application.
FIG. 2
is a plan view for showing a thin film actuated mirror array in an optical projection system disclosed in a prior application of the assignee of this application,
FIG. 3
is a perspective view for showing the thin film actuated mirror array in an optical projection system in
FIG. 2
, and
FIG. 4
is a cross-sectional view taken along the line A
1
-A
2
of FIG.
3
.
Referring to
FIGS. 2
to
4
, the thin film AMA has a substrate
50
, an actuator
65
formed on the substrate
50
and a reflecting member
71
formed on the actuator
65
.
The substrate
50
has an electrical wiring (not shown) for receiving a first signal from outside and transmitting the first signal, a connecting terminal
51
formed on the electrical wiring and connected to the electrical wiring, a passivation layer
52
formed on the electrical wiring and the connecting terminal
51
, and an etching stop layer
53
formed on the passivation layer
51
. The etching stop layer
53
protects the substrate
50
and the passivation layer
52
during successive etching process. Preferably, the electrical wiring has a metal oxide semiconductor (MOS) transistor (not shown) for switching operation.
The actuator
65
has a supporting layer
57
, a bottom electrode
59
formed on the central portion of the supporting layer
57
, an active layer
61
formed on the bottom electrode
59
, a top electrode
63
formed on the active layer
61
, a common line
67
formed on a portion of the supporting layer
57
and connected to the top electrode
63
, and a post
70
formed on a portion of the top electrode
63
. The supporting layer
57
has a first portion attached to the etching stop layer
53
having the connecting terminal
51
formed thereunder and a second portion formed parallel to the etching stop layer
53
. An air gap
55
is interposed between the supporting layer
57
and the etching stop layer
53
.
Referring to
FIG. 4
, the actuator
65
has a via contact
73
formed in the inside of a via hole
72
which is formed perpendicularly to the connecting terminal
51
from a portion of the supporting layer
57
having the connecting terminal
51
formed thereunder and a bottom electrode connecting member
75
formed from the via contact
73
to the bottom electrode
59
. A first signal, a picture signal, is applied from outside to the bottom electrode
59
through the electrical wiring, the connecting terminal
51
, the via contact
73
, and the bottom electrode connecting member
75
. At the same time, a second signal, a bias signal, is applied to the top electrode
63
from outside through the common line
67
so that the active layer
61
formed between the top electrode
63
and the bottom electrode
59
is deformed. Preferably, the supporting layer
57
has a T shape and the bottom electrode
59
having a rectangula
Daewoo Electronics Co. Ltd.
Pillsbury & Winthrop LLP
Rocchegiani Renzo
Smith Matthew
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