Patent Abstract:
Disclosed is a diffractive micromirror and a method of producing the same. More particularly, the present invention pertains to a diffractive thin-film piezoelectric micromirror, which is operated in a piezoelectric operation manner to assure excellent displacement, operation speed, reliability, linearity, and low voltage operation, and a method of producing the same. The diffractive thin-film piezoelectric micromirror includes a silicon substrate on which a recess is formed to provide an air space to the center thereof, and a piezoelectric mirror layer having a band shape, which is attached to the silicon substrate along both ends of the recess at both ends thereof while being spaced from the bottom of the recess at a center portion thereof and which includes a thin-film piezoelectric material layer to be vertically movable when voltage is applied to the piezoelectric material layer, and thus diffracts an incident light beam.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates, in general, to a diffractive micromirror and a method of producing the same and, more particularly, to a diffractive thin-film piezoelectric micromirror, which is operated in a piezoelectric operation manner to assure excellent displacement, operation speed, reliability, linearity, and low voltage operation, and a method of producing the same. 
     2. Description of the Prior Art 
     Generally, an optical signal processing technology has advantages in that a great amount of data is quickly processed in a parallel manner unlike a conventional digital information processing technology in which it is impossible to process a great amount of data in real time. Studies have been conducted on the design and production of a binary phase only filter, an optical logic gate, a light amplifier, an image processing technique, an optical device, and a light modulator using a spatial light modulation theory. The spatial light modulator is applied to optical memory, optical display device, printer, optical interconnection, and hologram fields, and studies have been conducted to develop a display device employing it. 
     The spatial light modulator is embodied by a reflective deformable grating light modulator  10  as shown in  FIG. 1 . The modulator  10  is disclosed in U.S. Pat. No. 5,311,360 by Bloom et al. The modulator  10  includes a plurality of reflective deformable ribbons  18 , which have reflective surface parts, are suspended above an upper part of a silicon substrate  16 , and are spaced apart from each other at regular intervals. An insulating layer  11  is deposited on the silicon substrate  16 . Subsequently, a sacrificial silicon dioxide film  12  and a low-stress silicon nitride film  14  are deposited. The nitride film  14  is patterned by the ribbons  18 , and a portion of the silicon dioxide film  12  is etched, thereby maintaining the ribbons  18  on the oxide spacer layer  12  by a nitride frame  20 . In order to modulate light having a single wavelength of λ o , the modulator is designed so that thicknesses of the ribbon  18  and oxide spacer  12  are each λ/4. 
     Limited by a vertical distance (d) between a reflective surface  22  of each ribbon  18  and a reflective surface of the substrate  16 , a grating amplitude of the modulator  10  is controlled by applying a voltage between the ribbon  18  (the reflective surface  22  of the ribbon  18  acting as a first electrode) and the substrate  16  (a conductive layer  24  formed on a lower side of the substrate  16  to act as a second electrode). In an undeformed state of the light modulator with no voltage application, the grating amplitude is λ/2 while a total round-trip path difference between light beams reflected from the ribbon and substrate is λ o . Thus, a phase of reflected light is reinforced. Accordingly, in the undeformed state, the modulator  10  acts as a plane mirror when it reflects incident light. In  FIG. 2 , reference numeral  20  denotes the incident light reflected by the modulator  10  in the undeformed state. 
     When a proper voltage is applied between the ribbon  18  and substrate  16 , the electrostatic force enables the ribbon  18  to move downward toward the surface of the substrate  16 . At this time, the grating amplitude is changed to λ/4. The total round-trip path difference is a half of a wavelength, and light reflected from the deformed ribbon  18  and light reflected from the substrate  16  are subjected to destructive interference. The modulator diffracts incident light  26  using the interference. In  FIG. 3 , reference numerals  28  and  30  denote light beams diffracted in +/− diffractive modes (D +1 , D −1 ) in the deformed state, respectively. 
     It has been proven that sticking of the ribbon  18  to the substrate  16  is a common problem of the light modulator  10  during a wet process applied to form a space under the ribbon  18  and during operation of the modulator  10 . There are various methods of reducing the sticking: lyophilization, a dry etching of a photoresist-acetone sacrificial layer, an OTS single layer treatment, use of a hard ribbon and/or a tightened nitride film gained by shortening the ribbon, a method of roughing or wrinkling one or both surfaces of two facing surfaces, a method of forming a reverse rail on the lower part of the ribbon, and a method of changing the chemical properties of the surfaces. In a solid-state sensor and actuator workshop held in June, 1994 at the Hilton Head Island in Scotland, prevention of sticking was reported, which is accomplished by reducing the contact area by forming a reverse rail on the lower part of a bridge and by employing a rough polysilicon layer as disclosed in “a process of finely treating the surface of a deformable grating light valve for high resolution display devices” suggested by Sandeyas, et al., and “a grating light valve for high resolution display devices”, suggested by Apte et al. 
     Moreover, Apte et al. found that mechanical operation of the modulator  10  has a characteristic such that deformation of the ribbon  18  as a function of voltage forms hysteresis. The hysteresis is theoretically based on the fact that an electrostatic attractive force between the ribbon  18  and substrate  16  is a nonlinear function of the deformation, whereas hardness of the ribbon  18  is a substantially linear function of a resilient force by tension.  FIG. 4  is a graph illustrating light output (which indirectly indicates the deformation of the ribbon  18 ) as a function of a voltage between the ribbon  18  and substrate  16 , which shows an induced hysteretic characteristic. Accordingly, when the ribbon  18  is deformed into a down position to come into contact with the substrate  16 , they are latched and require a holding voltage smaller than the original applied voltage. 
     U.S. Pat. No. 5,311,360 by Bloom et al. discloses a latching feature which gives a modulator  10  advantages of an active matrix design without the need for active components. Additionally, Bloom et al. describes that this feature is valuable in low power applications where efficient use of available power is very important. However, Bloom et al. discloses the addition of small ridges below ribbons  18  to reduce a contact area, thereby reducing the sticking problem. However, since the substrate of the modulator  10  is used as an optical surface, a process of adding the small ridges to the surface is complicated in that a reflective element of the substrate  16  must be smooth so as to have high reflectance and must be positioned on a planar surface of the ribbon  18 . 
     Typical display devices are formed in 2-D arrays of pixels. Discontinuous images formed by a plurality of pixels are integrated by user&#39;s eyes, thereby forming an aggregate image of pixels constituting a whole image. Unfortunately, prices of such a display device are high because the pixels are overlapped to form a complete array, so the production cost of each pixel is duplicated. The display device comprising pixels is exemplified by televisions or computer systems. Their pixels may be formed by an LCD device or a CRT device. 
     Accordingly, there is required a diffractive grating light valve capable of reducing or removing the sticking between the reflective element and the substrate without a complicated surface treatment adopted to reduce the sticking. 
     As well, a display device is required, which reduces the number of pixels to reduce production costs without reducing image quality while designing a system. 
     To satisfy the above requirements, a conventional improved technology is proposed in Korean Pat. Application No. 10-2000-7014798, entitled “method and device for modulating incident light beam to form 2-D image”, by Silicon Light Machines Inc. 
     In the “method and device for modulating the incident light beam to form the 2-D image”, the diffractive grating light valve includes a plurality of elongate elements each having a reflective surface. The elongate elements are arranged on an upper side of a substrate so that they are parallel to each other, have support ends, and their reflective surfaces lie in array (GLV array). The elongate elements form groups according to display elements. The groups alternately apply a voltage to the substrate, resulting in deformation of the elements. The almost planar center portion of each deformed elongate element is parallel to and spaced from the center portion of the undeformed element by a predetermined distance which is set to ⅓-¼ of the distance between the undeformed reflective surface and the substrate. Thus, the deformed elongate elements are prevented from coming into contact with the surface of the substrate. Sticking between the elongate elements and the substrate is prevented by preventing contact between the elements and substrate. Additionally, the predetermined distance between each deformed elongate element and the substrate is limited so as to prevent hysteresis causing deformation of the elongate elements. 
       FIG. 5  is a side sectional view of an elongate element  100  of a GLV in an undeformed state according to a conventional improved technology. In  FIG. 5 , the elongate element  100  is suspended above a surface of a substrate (including constitution layers) by ends thereof. In  FIG. 5 , reference numeral  102  denotes an air space. 
       FIG. 6  is a plan view of a portion of the GLV including six elongate elements  100 . The elongate elements  100  have the same width and are arranged parallel to each other. The elongate elements  100  are spaced close to each other, so that the elongate elements  100  can be deformed independently from other elements. The six elongate elements  100  as shown in  FIG. 6  preferably form a single display element  200 . Therefore, an array of 1920 elongate elements forms a GLV array having 320 display devices arranged therein. 
       FIG. 7  is a front sectional view of a display element  200  having undeformed elongate elements  100 .  FIG. 7  is a view taken along the line A-A′ of  FIG. 5 . The undeformed state is selected by equalizing a bias on the elongate elements  100  to a conductive layer  106 . Since reflective surfaces of the elongate elements  100  are substantially co-planar, light incident on the elongate elements  100  is reflected. 
       FIG. 8  is a side sectional view of a deformed elongate element  100  of the GLV.  FIG. 8  shows that the deformed elongate element  100  is maintained in the suspended state thereof to be spaced from the surface of the substrate adjacent therebeneath. This is in contrast to the conventional modulator of  FIGS. 1 to 3 . Contact between the elongate element  100  and the surface of the substrate is prevented, thereby avoiding the disadvantages of conventional modulators. However, the elongate element  100  is apt to sag in the deformed state. The reason is that the elongate element  100  is uniformly subjected to an electrostatic attractive force acting toward the substrate in directions perpendicular to a longitudinal direction thereof, whereas tension of the elongate element  100  acts along the length of the elongate element  100 . Therefore, the reflective surface of the elongate element is not planar but curvilinear. 
     However, the center part  102  of the elongate element  100  ( FIG. 8 ) is almost planar, making the contrast ratio of diffracted light, gained by only the center part  102  of the elongate element  100 , desirable. The substantially planar center part  102  has a length that is ⅓ of a distance between post holes  110 . Hence, when the distance between the post holes  110  is 75 μm, the almost planar center part  102  is about 25 μm long. 
       FIG. 9  is a front view of the display element  200  in which the deformed elongate elements  100  are alternately arranged.  FIG. 9  is a view taken in the direction of the arrows along the line B-B′ of  FIG. 8 . The elongate ribbons  100  which are not removed are maintained at desired positions by an applied bias voltage. Deformation of the moving elongate ribbons  100  is achieved by alternate applications of operation voltages through the conductive layer  106  to the elongate elements  100 . A vertical distance (d 1 ) is almost constant to the almost planar center part  102  ( FIG. 8 ), thereby limiting the grating amplitude of the GLV. The grating amplitude (d 1 ) may be controlled by adjusting an operation voltage on the operated elongate elements  100 . This results in precision tuning of the GLV in an optimum contrast ratio. 
     As for diffractive incident light having a single wavelength (λ 1 ), it is preferable that the GLV has a grating width (d 1 ) that is ¼ (λ/4) of the wavelength of incident light to assure a maximum contrast ratio in an image to be display deviceed. However, the grating width (d 1 ) requires only a round trip distance that is the same as the sum of a half of the wavelength (λ 1 ) and the whole number of the wavelength (λ 1 ) (i.e. d 1 =λ 1 /4, 3λ 1 /4, 5λ 1 /4, . . . , Nλ 1 /2+λ 1 /4). 
     Referring to  FIG. 9 , the lower side of each elongate element  100  is spaced upward from the substrate by a distance of d 2 . Accordingly, the elongate elements  100  do not come into contact with the substrate during operation of the GLV. This results in avoidance of the sticking problems between the reflective ribbons and the substrate occurring in conventional modulators. 
     With reference to a hysteresis curve shown in  FIG. 4 , since the elongate elements  100  are moved by a distance that is ⅓-¼ of the distance between the elements and substrate to diffract incident light, hysteresis is prevented. 
     However, the light modulator which is manufactured by Silicon Light Machines Inc. and adopts an electrostatic method to control the position of a micromirror is disadvantageous in that an operation voltage is relatively high (usually 30 V or so) and a correlation between the applied voltage and a displacement is nonlinear, and thus, reliability is poor in the course of controlling light. 
     SUMMARY OF THE INVENTION 
     Therefore, the present invention has been made keeping in mind the above disadvantages occurring in the prior arts, and an object of the present invention is to provide a diffractive thin-film piezoelectric micromirror, which is operated by a piezoelectric operation method, unlike a conventional reflective diffractive light modulator operated by an electrostatic operation method, to assure excellent displacement, operation speed, reliability, linearity, and low voltage operation, and a method of producing the same. 
     Another object of the present invention is to provide a diffractive thin-film piezoelectric micromirror, which is operated by a thin-film piezoelectric operation method to make various structure designs on a silicon wafer possible, and a method of producing the same. 
     The above objects can be accomplished by providing a diffractive thin-film piezoelectric micromirror, including a substrate on which a recess is formed to provide an air space to the center thereof; and a piezoelectric mirror layer having a ribbon shape, which is attached to the substrate along both ends of the recess at both ends thereof while being spaced from the bottom of the recess at the center portion thereof and which includes a thin-film piezoelectric material layer to be vertically movable at the center portion thereof when voltage is applied to the piezoelectric material layer, and thus diffracts an incident light beam. 
     Additionally, the present invention provides a diffractive thin-film piezoelectric micromirror, including a substrate on which a recess is formed to provide an air space to the center thereof; a lower supporter which has a ribbon shape, is attached to an upper side of the substrate along both ends of the recess at both ends thereof while being spaced from the bottom of the recess at a center portion thereof, the center portion being vertically movable; and a piezoelectric mirror layer having a ribbon shape, which is laminated on the lower supporter while being spaced from the bottom of the recess of the substrate at both ends thereof and which includes a thin-film piezoelectric material layer to be vertically movable when voltage is applied to both sides of the thin-film piezoelectric material layer, and thus diffracts an incident light beam. 
     Furthermore, the present invention provides a diffractive thin-film piezoelectric micromirror, including a substrate on which a recess is formed to provide an air space to the center thereof; a lower supporter which has a ribbon shape, and is attached to an upper side of the substrate along both ends of the recess at both ends thereof while being spaced from the bottom of the recess at a center portion thereof; a first piezoelectric layer which is positioned on an end of the lower supporter at an end thereof and at a location far from a center of the lower supporter toward the end of the lower supporter by a predetermined distance at the other end thereof, and which includes a first thin-film piezoelectric material layer to shrink and expand so as to provide a first vertical actuating force when voltage is applied to the first thin-film piezoelectric material layer; a second piezoelectric layer which is positioned on the other end of the lower supporter at an end thereof and at a location far from the center of the lower supporter toward the other end of the lower supporter by a predetermined distance at the other end thereof, and which includes a second thin-film piezoelectric material layer to shrink and expand so as to provide a second vertical actuating force when voltage is applied to the second thin-film piezoelectric material layer; and a micromirror layer which is positioned at the center of the lower supporter to diffract an incident light beam. 
     As well, the present invention provides a diffractive thin-film piezoelectric micromirror, including a substrate on which an insulating layer is formed; a lower supporter which has a ribbon shape and is attached to the substrate at both ends thereof while being spaced from the substrate at the center portion thereof by a predetermined distance, the center portion being vertically movable; and a piezoelectric mirror layer which is laminated on the lower supporter while being spaced from the substrate at the center portion thereof, and includes a thin-film piezoelectric material layer to shrink and expand so as to vertically move at the center portion thereof when a voltage is applied to the piezoelectric material layer, and diffracting an incident light beam. 
     Furthermore, the present invention provides a diffractive thin-film piezoelectric micromirror, including a substrate on which an insulating layer is formed; a lower supporter which has a ribbon shape and is attached to both ends of the substrate at both ends thereof while being spaced from the substrate at the center portion thereof by a predetermined distance, the center portion being vertically movable; a first piezoelectric layer which is positioned on an end of the lower supporter at an end thereof and at a location far from the center of the lower supporter toward the end of the lower supporter by a predetermined distance at the other end thereof, and which includes a thin-film piezoelectric material layer to shrink and expand so as to be vertically moved when voltage is applied to the piezoelectric material layer; a second piezoelectric layer which is positioned on the other end of the lower supporter at an end thereof and at a location far from the center of the lower supporter toward the other end of the lower supporter by a predetermined distance at the other end thereof, and shrinks and expands so as to be vertically moved when a voltage is applied thereto; and a micromirror layer which is positioned at the center of the lower supporter to diffract an incident light beam. 
     Furthermore, the present invention provides a method of producing a diffractive thin-film piezoelectric micromirror, including a first step of forming a mask layer on a silicon wafer and patterning the mask layer to form a recess; a second step of forming a sacrificial layer so as to fill the recess formed in the first step; a third step of forming a piezoelectric mirror layer on the silicon wafer in which the recess is filled; a fourth step of etching the piezoelectric mirror layer formed in the third step to form a plurality of ribbons and removing the sacrificial layer to form the diffractive thin-film piezoelectric micromirror. 
     Furthermore, the present invention provides a method of producing a diffractive thin-film piezoelectric micromirror, including a first step of forming a mask layer on a silicon wafer and patterning the mask layer to form a recess; a second step of forming a sacrificial layer so as to fill the recess formed in the first step; a third step of forming a lower supporter on a silicon substrate in which the recess is filled; a fourth step of forming a pair of piezoelectric mirror layers on the lower supporter formed in the third step in such a way that each of the piezoelectric mirror layers is positioned on the remaining portion of the substrate other than the recess at an end thereof and at a location far from the center of the recess outward by a predetermined distance at the other end thereof, and the piezoelectric mirror layers are opposite to each other; a fifth step of forming a micromirror layer on the center portion of the lower supporter; and a sixth step of etching a pair of piezoelectric mirror layers and the lower supporter to form a plurality of ribbons and removing the sacrificial layer to form the diffractive thin-film piezoelectric micromirror. 
     Furthermore, the present invention provides a method of producing a diffractive thin-film piezoelectric micromirror, including a first step of laminating a sacrificial layer on a silicon substrate, forming a mask layer, and etching the resulting substrate to form a raised part; a second step of laminating a lower supporter on the silicon substrate on which the raised part is formed in the first step; a third step of forming a piezoelectric mirror layer on the lower supporter formed in the second step; and a fourth step of etching the piezoelectric mirror layer formed in the third step to form a plurality of ribbons and removing the sacrificial layer to form the diffractive thin-film piezoelectric micromirror. 
     Furthermore, the present invention provides a method of producing a diffractive thin-film piezoelectric micromirror, including a first step of laminating a sacrificial layer on a silicon substrate, forming a mask layer, and etching the resulting substrate to form a raised part; a second step of laminating a lower supporter on the silicon substrate on which the raised part is formed in the first step; a third step of forming a pair of piezoelectric mirror layers on the lower supporter formed in the second step in such a way that each of the piezoelectric mirror layers is positioned on the remaining portion of the substrate other than the raised part at an end thereof and at a location far from the center of the raised part outward by a predetermined distance at the other end thereof, and the piezoelectric mirror layers are opposite to each other; a fourth step of forming a micromirror layer on the center of the lower supporter; and a fifth step of etching a plurality of piezoelectric mirror layers and the lower supporter to form a plurality of ribbons and removing the sacrificial layer to form the diffractive thin-film piezoelectric micromirror. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates a grating light modulator adopting an electrostatic method according to a conventional technology; 
         FIG. 2  illustrates reflection of incident light by the grating light modulator adopting the electrostatic method according to the conventional technology in an undeformed state; 
         FIG. 3  illustrates diffraction of incident light by the grating light modulator in a deformed state due to an electrostatic force according to the conventional technology; 
         FIG. 4  illustrates a hysteresis curve for the grating light modulator adopting the electrostatic method according to the conventional technology; 
         FIG. 5  is a side sectional view of a column-type diffractive grating light valve adopting an electrostatic method according to a conventional improved technology; 
         FIG. 6  is a plan view of a portion of the grating light valve (GLV) including six elongate elements corresponding to a single display element according to the conventional improved technology; 
         FIG. 7  is a front sectional view of the display element of the GLV including the six elongate elements according to the conventional improved technology, which reflects incident light in an undeformed state; 
         FIG. 8  is a side sectional view of an elongate element of the GLV according to the conventional improved technology, which is deformed by an electrostatic force; 
         FIG. 9  is a front sectional view of the display element of the GLV including the six alternately arranged elongate elements, which diffracts incident light in a deformed state caused by an electrostatic force according to the conventional improved technology; 
         FIGS. 10   a  to  10   j  illustrate production of a diffractive thin-film piezoelectric micromirror having a recess according to an embodiment of the present invention; 
         FIGS. 11   a  to  11   c  illustrate various diffractive thin-film piezoelectric micromirrors having recesses, in which piezoelectric materials are not deformed; 
         FIGS. 12   a  to  12   c  illustrate various diffractive thin-film piezoelectric micromirrors having recesses, in which piezoelectric materials are deformed; 
         FIGS. 13   a  to  13   b  illustrate operation of a display element in which diffractive thin-film piezoelectric micromirrors having recesses and the same or different dimensions are alternately arranged, and  FIG. 13   c  illustrate operation of a display element in which diffractive thin-film piezoelectric micromirrors having recesses are arranged at regular intervals; 
         FIGS. 14   a  to  14   h  illustrate production of a thin-film piezoelectric light modulator having a raised part according to another embodiment of the present invention; 
         FIGS. 15   a  to  15   c  illustrate various diffractive thin-film piezoelectric micromirrors having raised parts, in which piezoelectric materials are not deformed; 
         FIGS. 16   a  to  16   c  illustrate various diffractive thin-film piezoelectric micromirrors having raised parts, in which piezoelectric materials are deformed; and 
         FIGS. 17   a  to  17   b  illustrate operation of a display element in which diffractive thin-film piezoelectric micromirrors having raised parts and the same or different widths are alternately arranged, and  FIG. 17   c  illustrate operation of a display element in which diffractive thin-film piezoelectric micromirrors having raised parts are arranged at regular intervals. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, a detailed description will be given of a preferred embodiment according to the present invention, referring to  FIGS. 10   a  to  10   j.    
       FIGS. 10   a  to  10   j  illustrate production of a diffractive thin-film piezoelectric micromirror having a recess according to an embodiment of the present invention. 
     Referring to  FIG. 10   a , a mask layer  1002  is formed in a thickness of 0.1-1.0 μm through a thermal oxidation process on a silicon wafer  1001 , and then patterned for silicon etching. 
     With reference to  FIG. 10   b , the silicon is etched in a predetermined thickness, using a solution capable of etching the silicon, such as TMAH or KOH, and the mask layer  1002  is then removed. In this regard, it is possible to conduct a dry etching as well as a wet etching. 
     Referring to  FIG. 10   c , an insulating and etching prevention layer  1003  is formed on the etched silicon according to the thermal oxidation process. That is to say, the insulating and etching prevention layer  1003 , such as SiO 2 , is formed on a surface of the silicon wafer. 
     Referring to  FIG. 10   d , a polysilicon (Poly-Si) or an amorphous-Si is deposited on an etched portion of the silicon wafer  1001  according to low pressure chemical vapor deposition (LPCVD) or plasma chemical vapor deposition (PECVD) processes to form a sacrificial layer  1004  for an air space, and the resulting silicon wafer is polished to be flattened at a surface thereof. In this respect, in the case of using a silicon on insulator (SOI), the deposition of the polysilicon and polishing may be omitted. 
     Subsequently, silicon nitrides, such as Si 3 N 4 , are deposited in a preferable thickness of 0.1-5.0 μm according to the LPCVD or PECVD processes, and SiO 2  is deposited in a thickness of 0.1-5 μm according to thermal oxidation or PECVD processes, but this procedure may be omitted according to necessity. 
     Referring to  FIG. 10   e , a lower supporter  1005  for supporting the piezoelectric material is deposited on the silicon wafer  1001 . A material constituting the lower supporter  1005  may be exemplified by Si oxides (e.g. SiO 2 , etc.), Si nitrides (e.g. Si 3 N 4 , etc.), ceramic substrates (Si, ZrO 2 , Al 2 O 3  and the like), and Si carbides. The lower supporter  1005  may be omitted, if necessary. 
     Referring to  FIG. 10   f , a lower electrode  1006  is formed on the lower supporter  1005 , in which examples of material for the lower electrode  1006  may include Pt, Ta/Pt, Ni, Au, Al, RuO 2  and the like. In this case, the material is deposited in a thickness of 0.01-3 μm using sputtering or evaporation processes. 
     Referring to  FIG. 10   g , a piezoelectric material  1007  is formed in a thickness of 0.01-20.0 μm on the lower electrode  1006  according to a wet process (screen printing, sol-gel coating and the like) or a dry process (sputtering, evaporation, vapor deposition and the like). Both longitudinal type and transverse type piezoelectric materials may be used as the piezoelectric material  1007 . Examples of the piezoelectric material may include PzT, PNN-PT, ZnO and the like, and the piezoelectric electrolytic material contains at least one selected from the group consisting of Pb, Zr, Zn, or titanium. 
     Referring to  FIG. 10   h , an upper electrode  1008  is formed on the piezoelectric material  1007 , in which a material of the upper electrode may be exemplified by Pt, Ta/Pt, Ni, Au, Al, and RuO 2 . In this case, the upper electrode is formed in a thickness of 0.01-3 μm using the sputtering or evaporation processes. 
     Referring to  FIG. 10   i , a micromirror  1009  is attached to the upper electrode  1008 , in which examples of a material of the micromirror include a light-reflective material, such as Ti, Cr, Cu, Ni, Al, Au, Ag, Pt, and Au/Cr. 
     At this time, the upper electrode  1008  may be used as the micromirror, or a separate micromirror may be deposited on the upper electrode  1008 . 
     Referring to  FIG. 10   j , after such a mother body of a diffractive thin-film piezoelectric micromirror array is patterned using a mask layer, such as a photoresist, the micromirror  1009 , upper electrode  1008 , piezoelectric material  1007 , lower electrode  1006 , and lower supporter  1005  are etched to form the diffractive thin-film piezoelectric micromirror array. Subsequently, the sacrificial layer  1004  is etched using XeF 2  gas. 
     Heretofore, there has been described removal of the sacrificial layer  1004  after the diffractive thin-film piezoelectric micromirror array is formed from the mother body of the diffractive thin-film piezoelectric micromirror array, but the micromirror array may be formed after the sacrificial layer  1004  is removed. 
     In other words, a hole is formed in a portion of the mother body of the diffractive thin-film piezoelectric micromirror array, on which the lower supporter  1005  is not formed, and the sacrificial layer  1004  is etched using XeF 2  gas. Subsequently, the mother body of the diffractive thin-film piezoelectric micromirror array is patterned using the mask layer, such as the photoresist, and the micromirror  1009 , upper electrode  1008 , piezoelectric material  1007 , lower electrode  1006 , and lower supporter  1005  are etched to form the micromirror array. 
       FIGS. 11   a  to  11   c  illustrate various diffractive thin-film piezoelectric micromirrors having recesses, in which piezoelectric materials are not deformed. 
       FIG. 11   a  illustrates that a sacrificial layer of a silicon wafer is replaced with an air space, and thus, a piezoelectric material is partially spaced from a surface of a substrate and supported by ends thereof. Additionally, a lower electrode  1006   a , a piezoelectric material layer  1007   a , an upper electrode  1008   a , and a micromirror  1009   a  are positioned on a lower supporter  1005   a.    
       FIG. 11   b  illustrates that a sacrificial layer of a silicon wafer is replaced with an air space, and thus, a piezoelectric material is partially spaced from a surface of a substrate and supported by ends thereof. In this respect, a micromirror  1009   b  is positioned on the center part of a lower supporter  1005   b . Furthermore, a lower electrode  1006   b , a piezoelectric material layer  1007   b , and an upper electrode  1008   b  are positioned on both ends of a lower supporter  1005   b.  To produce such a diffractive thin-film piezoelectric micromirror, after the upper electrode  1008   b  is formed, the center portions of the lower electrode  1006   b , piezoelectric material layer  1007   b , and upper electrode  1008   b  are etched, and the micromirror  1009   b  is then formed on the center part. 
       FIG. 11   c  illustrates that a sacrificial layer of a silicon wafer is replaced with an air space, and thus, a piezoelectric material is partially spaced from a surface of a substrate and supported by ends thereof. In this regard, a lower electrode  1006   c , a piezoelectric material layer  1007   c , an upper electrode  1008   c , and a micromirror  1009   c  are positioned on the center part of a lower supporter  1005   c.    
       FIGS. 12   a  to  12   c  illustrate various diffractive thin-film piezoelectric micromirrors having recesses, in which piezoelectric materials are deformed. 
       FIG. 12   a  shows that when voltage is applied to upper and lower parts of a piezoelectric material  1007   a , a lower supporter  1005   a , a lower electrode  1006   a , a piezoelectric material layer  1007   a , an upper electrode  1008   a , and a micromirror  1009   a  are warped downward by contractile and expansive forces of the piezoelectric material. At this time, the contractile force acts on the piezoelectric material  1007   a  in a horizontal direction, causing the piezoelectric material  1007   a  to shrink in a horizontal direction. However, since a lower side of the piezoelectric material  1007   a  is firmly attached to the lower supporter  1005   a , the contractile force causes the piezoelectric material  1007   a  to be warped downward. 
       FIG. 12   b  shows that when voltage is applied to upper and lower sides of a piezoelectric material layer  1007   b  positioned on both ends of a lower supporter  1005   b , a contractile force is generated in a horizontal direction. At this time, the contractile force acts on the piezoelectric material  1007   b  in the horizontal direction, causing the piezoelectric material  1007   b  to shrink in the horizontal direction. However, since a lower side of the piezoelectric material  1007   b  is firmly attached to the lower supporter  1005   b , the contractile force causes the piezoelectric material  1007   b  to be warped upward. As a result, the lower supporter  1005   b  and a micromirror  1009   b  positioned on the center of the lower supporter  1005   b  are warped upward. 
       FIG. 12   c  shows that when voltage is applied to upper and lower sides of a piezoelectric material  1007   c  positioned on the center of a lower supporter  1005   c , a lower electrode  1006   c , a piezoelectric material layer  1007   c , an upper electrode  1008   c , and a micromirror  1009   c  are warped upward. 
       FIG. 13   a  illustrates operation of a display element in which diffractive thin-film piezoelectric micromirrors having recesses and the same dimensions are arranged. The diffractive thin-film piezoelectric micromirrors are vertically moved by the application of voltage. 
       FIG. 13   b  illustrates operation of a display element in which diffractive thin-film piezoelectric micromirrors having recesses and different dimensions are alternately arranged. The diffractive thin-film piezoelectric micromirrors are vertically moved by the application of voltage. 
       FIG. 13   c  illustrates operation of a display element in which diffractive thin-film piezoelectric micromirrors having recesses and the same dimension are arranged. At this time, the micromirrors are formed on a whole upper side of an insulating layer to diffract incident light. 
       FIGS. 14   a  to  14   h  illustrate production of a thin-film piezoelectric light modulator having a raised part according to another embodiment of the present invention. 
     Referring to  FIG. 14   a , an insulating and etching prevention layer  2002  is formed on a silicon wafer according to the thermal oxidation process. That is to say, the insulating and etching prevention layer  2002  made of SiO 2  is formed on a surface of the silicon wafer. 
     Additionally, a polysilicon (Poly-Si) or an amorphous-Si is deposited on the insulating and etching prevention layer  2002  of the silicon wafer  2001  according to LPCVD or PECVD processes to form an air space, and the resulting silicon wafer is polished to be flattened at a surface thereof to form a sacrificial layer  2003 . 
     Subsequently, a mask layer  2004  is formed in a thickness of 0.1-3.0 μm through a thermal oxidation process on the sacrificial layer  2003 , and then patterned for silicon etching. 
     With reference to  FIG. 14   b , silicon is etched using a solution capable of etching silicon, such as TMAH or KOH, in a predetermined thickness, and the mask layer  2004  is then removed. 
     Next, after silicon nitrides, such as Si 3 N 4 , are deposited in a preferable thickness of 0.1-5.0 μm according to the LPCVD or PECVD processes, SiO 2  is deposited in a thickness of 0.1-3 μm according to thermal oxidation or PECVD processes, but this procedure may be omitted according to necessity. 
     Successively, referring to  FIG. 14   c , a lower supporter  2005  for supporting a piezoelectric material is deposited on the insulating and etching prevention layer  2002  and sacrificial layer  2003 . In this case, a material constituting the lower supporter  2005  may be exemplified by Si oxides (e.g. SiO 2 , etc.), Si nitrides (e.g. Si 3 N 4 , etc.), ceramic substrates (e.g. Si, ZrO 2 , Al 2 O 3  and the like), and Si carbides. The lower supporter  2005  may be omitted, if necessary. 
     Referring to  FIG. 14   d , a lower electrode  2006  is formed on the lower supporter  2005 , in which examples of material for the lower electrode  2006  may include Pt, Ta/Pt, Ni, Au, Al, RuO 2  and the like, and the material is deposited in a thickness of 0.01-3 μm using sputtering or evaporation processes. 
     Referring to  FIG. 14   e , a piezoelectric material  2007  is formed in a thickness of 0.01-20.0 μm on the lower electrode  2006  according to a wet process (screen printing, sol-gel coating and the like) or a dry process (sputtering, evaporation, vapor deposition and the like). Both longitudinal type and transverse type piezoelectric materials may be used as the piezoelectric material  2007 . Examples of the piezoelectric material may include PZT, PMN-PT, PLZT, AIN, ZnO and the like, and the piezoelectric electrolytic material contains at least one selected from the group consisting of Pb, Zr, Zn, or titanium. 
     Referring to  FIG. 14   f , an upper electrode  2008  is formed on the piezoelectric material  2007 , in which a material of the upper electrode may be exemplified by Pt, Ta/Pt, Ni, Au, Al, Ti/Pt, IrO 2  and RuO 2 , and the upper electrode is formed in a thickness of 0.01-3 μm using the sputtering or evaporation processes. 
     Referring to  FIG. 14   g , a micromirror  2009  is attached to the upper electrode  2008 . Examples of a material of the micromirror include a light-reflective material, such as Ti, Cr, Cu, Ni, Al, Au, Ag, Pt, and Au/Cr. 
     At this time, the upper electrode  2008  may be used as the micromirror, or a separate micromirror may be deposited on the upper electrode  2008 . 
     Referring to  FIG. 14   h , after such a mother body of a diffractive thin-film piezoelectric micromirror array is patterned using a mask layer, such as a photoresist, the micromirror  2009 , upper electrode  2008 , piezoelectric material  2007 , lower electrode  2006 , and lower supporter  2005  are etched to form the diffractive thin-film piezoelectric micromirror array. Subsequently, the sacrificial layer  2003  is etched using XeF 2  gas. 
     Heretofore, there has been described removal of the sacrificial layer  2003  after the diffractive thin-film piezoelectric micromirror array is formed from the mother body of the diffractive thin-film piezoelectric micromirror array, but the micromirror array may be formed after the sacrificial layer  2003  is removed. 
     In other words, a hole is formed in a portion of the mother body of the diffractive thin-film piezoelectric micromirror array, in which the lower supporter  2005  is not formed, the sacrificial layer  2003  is etched using XeF 2  gas. The mother body of the diffractive thin-film piezoelectric micromirror array is patterned using the mask layer, such as the photoresist, and the micromirror  2009 , upper electrode  2008 , piezoelectric material  2007 , lower electrode  2006 , and lower supporter  2005  are etched to form the micromirror array. 
       FIGS. 15   a  to  15   c  illustrate various diffractive thin-film piezoelectric micromirrors having raised parts, in which piezoelectric materials are not deformed. 
       FIG. 15   a  illustrates that a sacrificial layer of a silicon wafer is replaced with an air space, and thus, a piezoelectric material is partially spaced from a surface of a substrate and supported by ends thereof. Additionally, a lower electrode  2006   a , a piezoelectric material layer  2007   a , an upper electrode  2008   a , and a micromirror  2009   a  are positioned on a lower supporter  2005   a .  FIG. 15   a  is different from  FIG. 11   a  in that a portion of the piezoelectric material is raised upward and spaced from an insulating and etching prevention layer. 
       FIG. 15   b  illustrates that a sacrificial layer of a silicon wafer is replaced with an air space, and thus, a piezoelectric material is partially spaced from a surface of a substrate and supported by ends thereof. In this respect, a micromirror  2009   b  is positioned on the center part of a lower supporter  2005   b . Furthermore, a lower electrode  2006   b , a piezoelectric material layer  2007   b , and an upper electrode  2008   b  are positioned on both ends of the lower supporter  2005   b . To produce such a diffractive thin-film piezoelectric micromirror, after the upper electrode  2008   b  is formed, the center portions of the lower electrode  2006   b , piezoelectric material layer  2007   b , and upper electrode  2008   b  are etched, and the micromirror  2009   b  is then formed on the center part.  FIG. 15   b  is different from  FIG. 11   b  in that a portion of the piezoelectric material is raised upward and spaced from an insulating and etching prevention layer. 
       FIG. 15   c  illustrates that a sacrificial layer of a silicon wafer is replaced with an air space, and thus, a piezoelectric material is partially spaced from a surface of a substrate by ends thereof. In this regard, a lower electrode  2006   c , a piezoelectric material layer  2007   c , an upper electrode  2008   c , and a micromirror  2009   c  are positioned on the center part of a lower supporter  2005   c.    FIG. 15   c  is different from  FIG. 11   c  in that a portion of the piezoelectric material is raised upward and spaced from an insulating and etching prevention layer. 
       FIGS. 16   a  to  16   c  illustrate various diffractive thin-film piezoelectric micromirrors having raised parts, in which piezoelectric materials are deformed. 
       FIG. 16   a  shows that when voltage is applied to upper and lower sides of a piezoelectric material  2007   a , a lower supporter  2005   a , a lower electrode  2006   a , a piezoelectric material layer  2007   a , an upper electrode  2008   a , and a micromirror  2009   a  are warped downward by contractile and expansive forces of the piezoelectric material. At this time, the contractile force acts on the piezoelectric material  2007   a  in a horizontal direction, endeavoring the piezoelectric material  2007   a  to shrink in a horizontal direction. However, since a lower side of the piezoelectric material  2007   a  is firmly attached to the lower supporter  2005   a , the contractile force causes the piezoelectric material  2007   a  to be warped downward. 
       FIG. 16   b  shows that when voltage is applied to upper and lower sides of a piezoelectric material layer  2007   b  positioned on both ends of a lower supporter  2005   b , a contractile force is generated in a horizontal direction. At this time, the contractile force acts on the piezoelectric material  2007   b  in the horizontal direction, causing the piezoelectric material  2007   b  to shrink in the horizontal direction. However, since a lower side of the piezoelectric material  2007   b  is firmly attached to the lower supporter  2005   b , the contractile force enables the piezoelectric material  2007   b  to be warped upward. As a result, the lower supporter  2005   b  and a micromirror  2009   b  positioned on the center of the lower supporter  2005   b  are warped upward. 
       FIG. 16   c  shows that when voltage is applied to upper and lower parts of a piezoelectric material  2007   c  positioned on the center of a lower supporter  2005   c , a lower electrode  2006   c , a piezoelectric material layer  2007   c , an upper electrode  2008   c , and a micromirror  2009   c  are warped upward. 
       FIG. 17   a  illustrates operation of a display element in which diffractive thin-film piezoelectric micromirrors having raised parts and the same width are arranged. The diffractive thin-film piezoelectric micromirrors are vertically moved by the application of voltage. 
       FIG. 17   b  illustrates operation of a display element in which diffractive thin-film piezoelectric micromirrors having raised parts and different widths are alternately arranged. The diffractive thin-film piezoelectric micromirrors are vertically moved by the application of voltage. 
       FIG. 17   c  illustrates operation of a display element in which diffractive thin-film piezoelectric micromirrors having raised parts are arranged at regular intervals. The micromirrors are formed on an upper side of an insulating layer to diffract incident light. 
     Meanwhile, the specification of the present invention describes only a piezoelectric material layer consisting of a single layer, but the piezoelectric material layer may comprise multiple layers so as to realize low voltage operation. At this time, the lower and upper electrodes consist of multiple layers. 
     In other words, it is possible to construct in such a manner that a first lower electrode, a first piezoelectric material layer, a first upper electrode, a second lower electrode, a second piezoelectric material layer, a second upper electrode, a third lower electrode . . . are sequentially laminated upward. 
     As described above, use of a piezoelectric sensor makes a correlation between voltage and displacement linear, whereas the correlation is nonlinear in the case of an electrostatic method according to a conventional technology. 
     Compared to the electrostatic method, the present invention is advantageous in that it is possible to gain the desired displacement at a relatively low voltage and to gain a high operation speed. 
     Another advantage of the present invention is that since it is possible to reliably control displacement of a ribbon, it is possible to achieve a gray scale control unlike the electrostatic method. 
     Furthermore, in the present invention, in the course of producing a piezoelectric micromirror array, it is possible to design various lengths and widths of ribbons, and thus, it is easy to tune light efficiency so as to satisfy requirements of relevant applications. 
     The diffractive thin-film piezoelectric micromirror and the production of the same according to the present invention have been described in an illustrative manner, and it is to be understood that the terminology used is intended to be in the nature of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, it is to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

Technology Classification (CPC): 6