Electrodisplacive actuator for use in an actuated mirror array

An actuator for tilting the plane of a mounted mirror comprises a substrate having an opening filled with a first metalization; a pair of electrodisplacive members mounted on the substrate, each electrodisplacive member having a side surface in a facing relationship with a second metalization formed therebetween and a grooved surface opposite therefrom with a third metalization formed thereon, the electrodisplacive members further having a polarization selected so that a voltage applied between the second metalization and the third metalization causes one of the electrodisplacive members to vertically expand and the other to vertically contract, thereby tilting the plane of the mounted mirror; a metal layer having predetermined dimensions, provided underneath the second metalization; and an electrically conductive adhesive paste layer disposed between the metal layer and the first metalization for providing an electrical contact therebetween. The metal layer being provided between the second metalization and the paste layer, such that a possible increase of the contact resistance between the first metalization and thesecond metalization is prevented, rendering the tilting operation of the mounted mirror upon application of such voltage to the first metalization controllable or accurate.

FIELD OF THE INVENTION 
The present invention relates to electrodisplacive actuators and, more 
particularly, to electrodisplacive actuators for actuating a mirror array 
mounted thereon in an optical projection video display system. 
BACKGROUND OF THE INVENTION 
In certain of optical projection video display systems, a mirror array is 
illuminated from an optical energy source. In such a system, the 
orientation of each of the mirrors is electronically perturbed to 
determine a propagation path for a beam of light reflecting from each 
mirror. The exact path of the reflected beam which passes through a slit 
determines the intensity of the optical energy which passes therethrough. 
The optical energy exiting from the slit is then focused upon a screen. 
Therefore, the orientation of a mirror directing each of the reflected 
beams through a corresponding slit determines the intensity for each pixel 
in the display. 
Each of the mirrors is controlled by an actuator comprising one or more 
electrodisplacive, e.g., piezoelectric or electrostrictive members upon 
which each mirror is mounted. By applying a DC electrical signal to each 
of the electrodisplacive members, the electrodisplacive members deform, as 
is well known in the art, to thereby, e.g., tilt the plane of the 
reflective surface of the mounted mirror. The amplitude of the DC signal 
controls the degree of the tilting of the mounted mirror. Optical 
projection video display systems and various configurations of such 
actuated mirror arrays are disclosed in, e.g., U.S. Pat. Nos. 5,085,497; 
5,175,465; and 5,185,660. 
In a copending, commonly assigned application, U.S. Ser. No. 08/216,754, 
entitled "ACTUATOR ARRAY AND METHOD FOR THE MANUFACTURE THEREOF", there is 
disclosed yet another actuated mirror array which may be used in such 
optical projection video display systems. FIG. 1 presents a cross 
sectional view of the actuated mirror array which comprises a substrate 1, 
an array 3 of actuators, e.g., 30, 30', 30" and a corresponding array 5 of 
mirrors, e g , 50, 50', 50" . Each of the actuators, e.g., 30, in turn, 
includes a pair of electrodisplacive members 31a, 31b. 
Each electrodisplacive member 31a(31b) has a side surface 32a(32b), a part 
of a grooved surface 33a(33b), a top surface 34a(34b) and a bottom surface 
35a(35b). The side surfaces 32a, 32b of the electrodisplacive members 31a, 
31b are in a facing relationship to each other with a first metalization 
36 formed therebetween. The grooved surface 33a(33b) is formed between the 
top surface 34a(34b) of the electrodisplacive member 31a(31b) of the 
actuator 30 and the top surface 34b'(34a") of the adjacent 
electrodisplacive member 31b'(31a") of an adjacent actuator 30'(30") with 
a second metalization 37a(37b) provided thereon. The second metalization 
37a(37b) is usually coupled to a common ground potential. On the top 
surfaces 34a, 34b of the electrodisplacive members 31a, 31b, a mirror 50 
is mounted. The bottom surfaces 35a, 35b of the electrodisplacive members 
31a, 31b are mounted on the substrate 1. 
Prior to the mounting of the actuator 30 on the substrate 1, an opening 11 
is formed through the substrate 1 at an intermediate location between the 
pair of the electrodisplacive members 31a, 31b. A third metalization 12 
fills the hole. Further, an electrically conductive adhesive paste 13 is 
provided on the third metalization 12. 
The bottom surfaces 35a, 35b of the electrodisplacive members 31a, 31b are 
then mounted on the substrate 1 with the first metalization 36 centered 
around the electrically conductive adhesive paste 13. An addressable 
driver (not shown) mounted to the lower surface of the substrate 1 may 
then apply a voltage to the third metalization 12 for a desired tilting of 
the mirror 50. The voltage may be developed in accordance with the 
corresponding pixel intensity in an optical projection video display 
system of the type disclosed in the above-referenced U.S. Pat. No. 
5,185,660. 
In such actuators, however, the contact resistance between the first 
metalization 36 and the third metalization 12 can be undesirably increased 
due to a possible uneven distribution of the conductive particles in the 
paste 13, which may render inadequate or improper the tilting operation of 
the mirror 50 upon application of such voltage to the third metalization. 
SUMMARY OF THE INVENTION 
Therefore, it is a primary object of the present invention to provide an 
actuator free from such increased contact resistance problem. 
In accordance with one aspect of the present invention, there is provided 
an actuator comprising: 
a substrate having an opening therethrough, said opening being filled with 
a first metalization; 
a pair of electrodisplacive members, each of said members having a bottom 
surface, a side surface, a part of a grooved surface and a top surface, 
the bottom surfaces of said members being bonded on the substrate, the 
side surfaces of said members being in a facing relationship to each other 
with a second metalization formed therebetween, said grooved surface being 
formed between the top surface of each of said members of said actuator 
and the top surface of an adjacent electrodisplacive member from an 
adjacent actuator in an array of such actuators and provided with a third 
metalization thereon, the top surfaces of said members being attached with 
a mirror mounted thereon, said members further having a polarization 
selected so that a voltage applied between their respective second 
metalization and third metalization causes one of said members to 
vertically expand and the other to vertically contract, thereby tilting 
the mounted mirror; 
a metal layer having predetermined dimensions, provided underneath said 
second metalization; and 
an electrically conductive adhesive paste layer disposed between said first 
metalization and said metal layer for providing an electrical contact 
therebetween. 
In accordance with another aspect of the invention, there is provided an 
actuator comprising: 
a substrate having an opening therethrough, said opening being filled with 
a first metalization; 
a pair of electrodisplacive members, each of said members having a bottom 
surface, a side surface, a part of a grooved surface, a part of a recessed 
surface and a top surface, the bottom surfaces of said members being 
bonded on the substrate, the side surfaces of said members being in a 
facing relationship to each other with a second metalization formed 
therebetween, said grooved surface being formed between the top surface of 
each of said members of said actuator and the top surface of an adjacent 
electrodisplacive member from an adjacent actuator in an array of such 
actuators and provided with a third metalization thereon, said recessed 
surface being formed between the bottom surface of each of said members of 
said actuator and the bottom surface of the adjacent electrodisplacive 
member from the adjacent actuator in the array, the top surfaces of said 
members being attached with a mirror mounted thereon, said members further 
having a polarization selected so that a voltage applied between their 
respective second metalization and third metalization causes one of said 
members to vertically expand and the other to vertically contract, thereby 
tilting the mounted mirror; 
a metal layer provided over said bottom surfaces of said members; and 
an electrically conductive adhesive paste layer disposed between said metal 
layer and said first metalization for providing an electrical contact 
therebetween.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 2, there is shown a cross sectional view of an 
actuated mirror array employing actuators of a preferred embodiment of the 
present invention. 
As shown in FIG. 2, the actuated mirror array comprises a substrate 1, an 
array 3 of actuators, e.g., 30, 30', 30" and a corresponding array 5 of 
mirrors, e.g., 50, 50', 50". 
As the previously described actuator of the copending, commonly assigned 
application, U.S. Ser. No. 08/216.754, entitled "ACTUATOR ARRAY AND METHOD 
FOR THE MANUFACTURE THEREOF", each of the actuators, e.g., 30 includes a 
pair of electrodisplacive members 31a, 31b. (As all of the actuators, 
e.g., 30, 30', 30", are identical, the following description will be given 
with respect to the actuator 30 only.) 
Further, each electrodisplacive member 31a(31b) has a side surface 
32a(32b), a part of a grooved surface 33a(33b), a top surface 34a(34b) and 
a bottom surface 35a(35b). The side surfaces 32a, 32b of the 
electrodisplacive members 31a, 31b are in a facing relationship to each 
other with a first metalization 36 formed therebetween. The grooved 
surface 33a(33b) is formed between the top surface 34a(34b) of the 
electrodisplacive member 31a(31b) of the actuator 30 and the top surface 
34b'(34a") of the adjacent electrodisplacive member 31b'(31a") of an 
adjacent actuator 30'(30") with a second metalization 37a(37b) provided 
thereon. The second metalization 37a(37b) is usually coupled to a common 
ground potential. On the top surfaces 34a, 34b of the electrodisplacive 
members 31a, 31b, a mirror 50 is mounted by using. e.g., a method 
disclosed in another copending, commonly owned application, U.S. Ser. No. 
08/216,755, entitled "MIRROR ARRAY AND METHOD FOR THE MANUFACTURE 
THEREOF". (To perform the mounting, and each mounting described 
hereinbelow, an epoxy may be used.) The bottom surfaces 35a, 35b of the 
electrodisplacive members 31a, 31b are mounted on the substrate 1. 
The polarization of the electrodisplacive members 31a, 31b is selected so 
that when a voltage is applied between their respective first metalization 
36 and the second metalization 37a or 37b, each member will deform in a 
vertical direction determined by the polarity of the applied voltage. By 
placing the side surfaces 32a, 32b of the electrodisplacive members 31a, 
31b in a facing relationship, the application of an identical voltage will 
cause one of the electrodisplacive members 31a, 31b to expand and the 
other of the electrodisplacive members 31a, 31b to contract vertically, 
thereby titling the mirror 50 as desired. 
To apply such voltage, a third metalization 12 is formed on the substrate 1 
by way of, e.g., first forming an opening 11 through the substrate 1 at an 
intermediate location between the pair of the electrodisplacive members 
31a, 31b, and then filling the hole with the third metalization. The third 
metalization 12 is made to be in electrical contact with the first 
metalization 36 via an electrically conductive, adhesive, silk-screen 
printed paste 13 disposed therebetween when the mounting of the actuator 
30 on the substrate 1 is completed. 
However, unlike the actuator of the copending, commonly assigned 
application, U.S. Ser. No. 08/216,754, entitled "ACTUATOR ARRAY AND METHOD 
FOR THE MANUFACTURE THEREOF", in accordance with the preferred embodiment 
of the present invention, before the mounting of the actuator 30, a thin 
metal layer 38 having predetermined dimensions is further provided 
underneath the first metalization 36 by, e.g., sputtering or vapor 
deposition and photolithography, to be in contact with the paste 13 when 
the mounting of the actuator 30 on the substrate 1 is completed. The 
predetermined dimensions are chosen so as to widen the contact area 
between the first metalization 36 and the paste 13 but not to include such 
metal layers 38', 38"of the adjacent actuator 30', 30". As a result, a 
possible increase of the contact resistance between the first metalization 
36 and the third metalization 12 can be prevented, rendering the tilting 
operation of the mirror 50 upon application of a voltage to the first 
metalization 36 controllable or accurate. 
Alternatively, as shown in FIG. 3, in accordance with another preferred 
embodiment of the present invention, also before the mounting of the 
actuator 30, the bottom surfaces 35a, 35b of the electrodisplacive members 
31a, 31b are first metalized by using, e.g., sputtering or vapor 
deposition, and then both physically and electrically separated from the 
bottom surfaces 35b', 35a" of the adjacent electrodisplacive members 31b', 
31a" of the adjacent actuators 30', 30" by forming two respective recesses 
39a, 39b thereamong. Subsequently, electrically conductive adhesive paste 
13 is provided over the bottom surfaces 35a, 35b of the electrodisplacive 
members 31a, 31b by using a known dipping technique. This will eliminate 
otherwise necessary silk-screen printing of the paste 13 on the third 
metalization 12. Thereafter, the bottom surfaces 35a, 35b of the 
electrodisplacive members 31a, 31b are mounted on the substrate 1 
proximate the opening 11 while providing a widened electrical contact 
between the first metalization 36 and the third metalization 12 via the 
metal layer 38 and the paste 13. 
In either of the embodiments, an addressable driver (not shown) mounted to 
the lower surface of the substrate 1 may then be employed to apply a 
voltage to the third metalization 12 for a desired tilting of the mirror 
50. The voltage may be developed in accordance with the corresponding 
pixel intensity in an optical projection video display system of the type 
disclosed in the above-referenced U.S. Pat. No. 5,185,660. 
While the present invention has been shown and described with reference to 
the particular embodiments, it will be apparent to those skilled in the 
art that many changes and modifications may be made without departing from 
the spirit and scope of the invention as defined in the appended claims.