Abstract:
Provided are a biaxial actuator and a method of manufacturing the same. The biaxial actuator includes: a stage unit seesawing in a first direction; a first support unit supporting the stage unit; a stage unit driving unit including first driving comb electrodes outwardly extending from opposite sides of the stage unit in the first direction, and first fixed comb electrodes extending from the first support unit facing the first driving comb electrodes such that the first driving and fixed comb electrodes alternate with each other; a second support unit supporting the first support unit such that the first support unit seesaws in a second direction perpendicular to the first direction; and a first support unit driving unit including second driving comb electrodes installed at the first support unit, and second fixed comb electrodes corresponding to the second driving comb electrodes, wherein the first and second driving comb electrodes and the stage unit are formed at a first level, and the first and second fixed comb electrodes are formed at a second level lower than the first level such that the first and second fixed comb electrodes do not overlap with the first and second driving comb electrodes at a vertical plane.

Description:
BACKGROUND OF THE DISCLOSURE 
   This application claims the priority of Korean Patent Application No. 10-2004-0083537, filed on Oct. 19, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
   1. Field of the Disclosure 
   The disclosure relates to a biaxial micro-electro-mechanical system (MEMS) actuator and a method of manufacturing the same, and more particularly to a biaxial actuator for seesaw driving in two directions and a method of manufacturing the same. 
   2. Description of the Related Art 
   Optical scanners including biaxial actuators can be used for large displays. The driving speed of a biaxial actuator relates to the resolution of a display device, and the driving angle of the biaxial actuator relates to the screen size of the display device. That is, as the driving speed of a micro mirror increases, resolution is improved. Also, as the driving angle of the micro mirror increases, the screen size of the display device increases. Accordingly, in order to realize large display devices with high resolution, optical scanners including biaxial actuators need to operate at high speed and have a high driving angle. 
   However, since the driving speed and the driving angle of the micro mirror are in a trade-off relation, there is a limitation in increasing both the driving speed and the driving angle of the biaxial actuator. 
   Optical scanners used for display devices need to operate at high speed, that is, operate at a resonant frequency during horizontal scanning, but need to operate linearly, that is, operate at a non-resonant frequency during vertical scanning. 
   Conventional actuators designed for resonant driving are hard to operate at a non-resonant frequency. 
   SUMMARY OF THE DISCLOSURE 
   The present invention may provide a biaxial actuator capable of resonant driving during horizontal scanning and non-resonant linear driving during vertical scanning, and a method of manufacturing the biaxial actuator. 
   The present invention may also provide a biaxial actuator having a high driving force and a high driving angle, and a method of manufacturing the biaxial actuator. 
   The present invention may also provide a biaxial actuator, which can be manufactured easily, and a method of manufacturing the biaxial actuator. 
   According to an aspect of the present invention, there may be provided a biaxial actuator comprising: a stage unit seesawing in a first direction; a first support unit supporting the stage unit; a stage unit driving unit including first driving comb electrodes outwardly extending from opposite sides of the stage unit in the first direction, and first fixed comb electrodes extending from the first support unit facing the first driving comb electrodes such that the first driving and fixed comb electrodes alternate with each other; a second support unit supporting the first support unit such that the first support unit seesaws in a second direction perpendicular to the first direction; and a first support unit driving unit including second driving comb electrodes installed at the first support unit, and second fixed comb electrodes corresponding to the second driving comb electrodes, wherein the first and second driving comb electrodes and the stage unit are formed at a first level, and the first and second fixed comb electrodes are formed at a second level lower than the first level such that the first and second fixed comb electrodes do not overlap with the first and second driving comb electrodes at a vertical plane. 
   The stage unit may comprise: a connecting part of which the first driving comb electrodes are formed at an outer surface; and a stage formed at an inner surface of the connecting part. 
   The stage may be a circular plate. 
   The connecting part may be an oval band having the inner surface to which the stage is connected. 
   The first support unit may comprise: a pair of first torsion springs extending from opposite sides of the stage unit in the second direction; and a rectangular moving frame including a pair of first portions parallel to each other and to which the first torsion springs are connected, and a pair of second portions parallel to each other and extending in the second direction, wherein the rectangular moving frame is made up of a first silicon layer to which the first torsion springs are connected, a second silicon layer to which the first fixed comb electrode is connected, and an insulation layer between the first silicon layer and the second silicon layer. 
   The second support unit may comprise: a pair of second torsion springs extending from the second portions of the first support unit in the first direction; and a rectangular fixed frame including a pair of second portions parallel to each other to which the second torsion springs are connected, and a pair of first portions parallel to each other extending in the first direction, wherein each of the fixed frame and the second torsion springs is made up of the first silicon layer, the second silicon layer, and the insulation layer. 
   The first support unit driving unit may comprise first extending members extending from the first level of the moving frame parallel to the second torsion springs, wherein the second driving comb electrodes extend from the first extending members towards the first portions of the second support unit that face the first extending members, wherein the second fixed comb electrodes extend from second extending members that extend from the second silicon layer of the second support unit to correspond to the first extending members. 
   The first and second driving comb electrodes may be electrically connected to each other via the first silicon layer of the second torsion springs, the second silicon layer of the fixed frame may have four electrically isolated portions such that voltage is separately applied to drive the stage unit in the first direction and in the second direction, and the second silicon layer of the moving frame may have two electrically isolated portions such that voltage is separately applied from the second silicon layer of the second torsion springs. 
   The biaxial actuator may further comprise: third driving comb electrodes formed at an inner surface of the connecting part; a base formed under the first support unit; and third fixed comb electrodes formed on the base to correspond to the third driving comb electrodes. 
   The biaxial actuator may further comprise a conductive layer formed on the base to electrically connect the corresponding first fixed comb electrodes and third fixed comb electrodes. 
   The stage unit, the stage unit driving unit, the first support unit, the second support unit, and the first support unit driving unit may be manufactured as one silicon-on-insulator (SOI) substrate. 
   The first torsion springs may be meander springs. 
   According to another aspect of the present invention, there may be provided a biaxial actuator comprising: a stage unit seesawing in a first direction; a first support unit supporting the stage unit; a stage unit driving unit including first driving comb electrodes outwardly extending from opposite sides of the stage unit in the first direction, and first fixed comb electrodes extending from the first support unit facing the first driving comb electrodes such that the first driving and fixed comb electrodes alternate with each other; a second support unit supporting the first support unit such that the first support unit seesaws in a second direction perpendicular to the first direction; and a first support unit driving unit including second driving comb electrodes installed at the first support unit, and second fixed comb electrodes corresponding to the second driving comb electrodes, wherein the first and second driving comb electrodes and the stage unit are formed at a first level, the first and second fixed comb electrodes are formed at a second level lower than the first level and at a third level higher than the first level such that the first and second fixed comb electrodes do not overlap with the first and second driving comb electrodes at a vertical plane. 
   According to still another aspect of the present invention, there may be provided a method of manufacturing a biaxial actuator comprising: (a) preparing a first substrate in which a first silicon layer, an insulation layer, and a second silicon layer are sequentially stacked, and etching the second silicon layer to form a rectangular moving frame portion, first fixed comb electrodes inwardly extending from opposite sides of the moving frame in a first direction, a rectangular fixed frame portion surrounding the moving frame portion, a second torsion spring portion connecting between the moving frame portion and the fixed frame portion in the first direction, and second fixed comb electrodes extending from a first portion of the second silicon layer of the fixed frame portion, parallel to the second torsion spring portion, towards the second torsion spring portion; (b) respectively forming electrode pads on central portions of one opposite sides and the other opposite sides of a glass substrate; (c) etching inner areas of the fixed frame portion on the glass substrate; (d) bonding the second silicon layer of the first substrate on the glass substrate; (e) forming an electrode pad in an area corresponding to the fixed frame portion on the first silicon layer; (f) etching the first silicon layer to form a stage unit, first driving comb electrodes formed at an outer surface of the stage unit to alternate with the first fixed comb electrodes, the moving frame portion, first torsion springs connecting the moving frame portion and the stage unit in a second direction perpendicular to the first direction, the fixed frame portion, the second torsion spring portion, and second driving comb electrodes extending from an extending member extending from the first silicon layer of the moving frame parallel to the second torsion spring portion to alternate with the second fixed comb electrodes; and (g) etching an exposed insulation layer. 
   According to yet another aspect of the present invention, there may be provided a method of manufacturing a biaxial actuator comprising: (a) preparing a first substrate in which a first silicon layer, an insulation layer, and a second silicon layer are sequentially stacked, and etching the second silicon layer to form a rectangular moving frame portion, first fixed comb electrodes inwardly extending from opposite sides of the moving frame in a first direction, a rectangular fixed frame portion surrounding the moving frame portion, a second torsion spring portion connecting between the moving frame portion and the fixed frame portion in the first direction, second fixed comb electrodes extending from a first portion of the second silicon layer of the fixed frame portion, parallel to the second torsion spring portion, towards the second torsion spring portion, and third fixed comb electrodes formed inside the moving frame and extending in the first direction; (b) respectively forming electrode pads on central portions of one opposite sides and the other opposite sides of a glass substrate, and forming a conductive layer connecting the first fixed comb electrodes and the third fixed comb electrodes; (c) etching an upper portion between the fixed frame portion and the moving frame portion in the glass substrate such that a lower portion of the fixed frame portion and the moving frame portion are connected; (d) bonding the second silicon layer of the first substrate on the glass substrate; (e) grinding a lower portion of the glass substrate by CMP to separate a portion attached to the fixed frame portion from a portion attached to the moving frame portion; (f) forming an electrode pad in an area corresponding to the fixed frame portion on the first silicon layer; (g) etching the first silicon layer to form a stage unit including a stage and a connecting part of which the stage is formed at an inner surface, first driving comb electrodes formed at an outer surface of the connecting part to alternate with the first fixed comb electrodes, third driving comb electrodes formed at an area inside the connecting part to alternate with the third fixed comb electrodes, the moving frame portion, first torsion springs connecting the moving frame portion and the connecting part in a second direction perpendicular to the first direction, the fixed frame portion, the second torsion spring portion, and second driving comb electrodes extending from an extending member extending from the first silicon layer of the moving frame parallel to the second torsion spring portion to alternate with the second fixed comb electrodes; and (h) etching an exposed insulation layer. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
       FIG. 1  is a schematic perspective view of a biaxial actuator according to a first embodiment of the present invention; 
       FIG. 2  is a plan view of the biaxial actuator of  FIG. 1 ; 
       FIG. 3  is a sectional view of the biaxial actuator taken along line III-III of  FIG. 2 ; 
       FIG. 4  is a sectional view of the biaxial actuator taken along line IV-IV of  FIG. 2 ; 
       FIG. 5  is a sectional view of the biaxial actuator taken along line V-V of  FIG. 2 ; 
       FIG. 6  is a plan view for explaining an electrical path of the biaxial actuator of  FIG. 2 ; 
       FIG. 7  is a timing diagram obtained when a voltage is applied to the biaxial actuator according to the first embodiment of the present invention; 
       FIG. 8  is a sectional view of a biaxial actuator according to a second embodiment of the present invention; 
       FIGS. 9 and 10  are schematic sectional views of a biaxial actuator according to a third embodiment of the present invention; 
       FIGS. 11A through 11E  are sectional views illustrating steps of manufacturing a base substrate; 
       FIGS. 12A through 12C  are sectional views illustrating steps of manufacturing a lower part of a main body structure; and 
       FIGS. 13A through 13F  are sectional views illustrating steps of manufacturing an upper part of the main body structure when the lower structure and the main body structure are combined. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention will now be described more fully with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. The sizes of elements shown in the drawings may be exaggerated, if needed, or sometime the elements may be omitted for a bettering understanding of the present invention. However, such ways of description do not limit the scope of the technical concept of the present invention. 
     FIG. 1  is a schematic perspective view of a biaxial actuator according to a first embodiment of the present invention.  FIG. 2  is a plan view of the biaxial actuator of  FIG. 1 .  FIGS. 3 through 5  are sectional views respectively taken along lines III-III, IVIV, and V-V of  FIG. 2 . 
   Referring to  FIGS. 1 and 2 , a stage unit may include a stage  100  that has a mirror (not shown) formed on a surface thereof, and a connecting part  110 . The stage  100  may be a circular plate with a minimum area for light reflection. The connecting part  110  may be an oval band, and the stage  100  may be connected to an inner circumferential surface in a direction of the shorter diameter of the connecting part  110 . The reason why such a circular stage  100  may be used is to reduce the load of the stage  100  and increase a driving force. 
   The connecting part  110  may be supported by a first support unit including first torsion springs  210  and a rectangular moving frame  200  such that the connecting part  110  can seesaw in a first direction (X-direction). The first torsion springs  210  may be meander springs. 
   The first support unit may be supported by a second support unit including second torsion springs  310  and a rectangular fixed frame  300  such that the first support unit can seesaw in a second direction (Y-direction) perpendicular to the first direction. Accordingly, the stage  100  supported by the first support unit and the second support unit may move in two directions. 
   In detail, the stage  100  may be connected to the rectangular moving frame  200  via the two first torsion springs  210  that may be formed in the second direction. Accordingly, the stage  100  may be supported to seesaw around the first torsion springs  210 . Further, since the first torsion springs  210  are meander springs, the length of second portions  200   y  of the moving frame  200 , which will be explained later, may be reduced and a driving angle at a non-resonant frequency may increase. 
   The first torsion springs  210  may be respectively connected to centers of first portions  200   x  of the rectangular moving frame  200 . The second torsion springs  310  may be respectively connected to centers of the second portions  200   y  of the rectangular moving frame  200 . The rectangular moving frame  200  may include the two first portions  200   x  that are parallel to each other and extend in the first direction, and the two second portions  200   y  that may be parallel to each other and extend in the second direction. The rectangular fixed frame  300  may surround the rectangular moving frame  200 . The rectangular fixed frame  300  may include first portions  300   x  that may extend in the first direction, and second portions  300   y  that may extend in the second direction. The second torsion springs  310  connected to the centers of the second portions  200   y  may also be connected to centers of the second portions  300   y  of the rectangular fixed frame  300 . The second torsion springs  310  may extend in the first direction. Accordingly, the moving frame  200  may be supported to seesaw around the second torsion springs  310 . 
   As shown in  FIGS. 1 and 3 , the moving frame  200 , the fixed frame  300 , and the second torsion springs  310  may be a multi-tiered structure having multiple layers  201 ,  202 , and  203 ,  301 ,  302 , and  303 , and  311 ,  312 , and  313 . The multi-tiered structure may be a silicon-on-insulator (SOI) substrate including highly doped first silicon layers  201 ,  301 , and  311 , second silicon layers  203 ,  303 , and  313 , and SiO 2  insulation layers  202 ,  302 , and  312  between the first silicon layers and the second silicon layers. Reference numerals  204  and  304  denote a first base and a second base, respectively, which may be insulation substrates, such as glass substrates. The multi-tiered structure will be understood through an explanation about a method of manufacturing an actuator according to the present invention. 
   A stage unit driving unit causing the stage  100  to seesaw, as shown in  FIGS. 3 through 5 , may include first driving comb electrodes  120  formed outside the connecting part  110  and the first fixed comb electrodes  220  extending from the second silicon layer  202  of the moving frame  200  to alternate with the first driving comb electrodes  120 , and third driving comb electrodes  130  formed inside the connecting part  110  and third fixed comb electrodes  250  being formed on the first base  204  to correspond to the third driving comb electrodes  130 . Since the fixed comb electrodes may be vertically formed and the corresponding comb electrodes may extend from different level of silicon layers from each other, the comb electrodes may be easily manufactured as it will be described later, and electrical paths may be easily formed. 
   In the meantime, a first support unit driving unit that causes the first support unit to seesaw may be interposed between the moving frame  200  and the fixed frame  300 . As shown in  FIGS. 1 and 2 , first extending members  230  may extend from the first silicon layer  201  of the second portions  200   y  of the moving frame  200  toward the second portions  300   y  of the fixed frame  300  that is connected to the second portions  200   y  by the second torsion springs  310 . Second driving comb electrodes  240  may be formed at a side surface of the first extending members  230 . Second extending members  340  may extend from the second silicon layer  303  of the fixed frame  300  to correspond to the first extending members  230 . Second fixed comb electrodes  350  may be formed on a side surface of the second extending members  340  facing the first extending members  230  to correspond to the second driving comb electrodes  240 . The comb electrodes  240  and  350  alternate with each other as shown in  FIG. 4 , and extend from silicon layers of different levels. 
   In the present embodiment, at least three electrical paths may be needed for the motion of the stage  100 , and three electrical paths may be needed for the motion of the moving frame  200 . Here, when the ground is maintained at the same electric potential, five electrical paths may be needed.  FIG. 6  is a plan view of the actuator of  FIG. 2  for explaining an electrical path of the actuator. In  FIG. 6 , black portions  601  and  602  are electrically isolated portions, and reference numerals P 1 , P 2 , P 3 , P 4 , and P 5  denote electrode pads for wiring with an external circuit. The electrode pads P 2  through P 5  are disposed between two electrically isolated portions  601 . 
   Referring to  FIG. 6 , the first electrode pad P 1  may be disposed on the second portions  300   y  (at the left side on the drawing), and electrically connected to the first through third driving comb electrodes  120 ,  130 , and  240  via the first silicon layer  311  of the second torsion springs  310  and the first torsion spring  210 . Here, the first pad P 1  may act as a virtual ground. The second and third pads P 2  and P 3  may be electrically connected to the second silicon layer  303  of the first portions  300   x  of the fixed frame  300  that may be electrically isolated by the electrically isolated portions  601 . Accordingly, an electrical circuit for producing an electrostatic force may be formed between the second fixed comb electrodes  350  and the second driving comb electrodes  240 . Meanwhile, the fourth pad P 4  and the fifth pad P 5  are electrically connected between the second silicon layer  303  of the second portions  300   y  of the fixed frame  300  and the second silicon layer  313  of the second torsion springs  310 . The fourth pad P 4  and the fifth pad P 5  may be electrically connected to the moving frame  200  via the second silicon layer  313  of the second torsion springs  310 . The second silicon layers  203  of the two second portions  200   y  of the moving frame  200  to which the fourth and fifth pads P 4  and P 5  are connected may be electrically separated by the electrically isolated portions  602 . The fourth and fifth pads P 4  and P 5  may be connected to the fixed comb electrodes  220  via the second silicon layer  313  of the second torsion springs  310 , and the third fixed comb electrodes  250 , as shown in  FIG. 4 , may be electrically connected to the first fixed comb electrodes  220  by a conductive layer  206  formed on the first base  204 . 
   The operation of the biaxial actuator according to the present embodiment will now be explained in detail. 
   First, if a predetermined voltage is applied to the electrode pad P 5  when the electrode pad P 1  is at a ground voltage, the stage  100  may seesaw in a positive x-direction due to an electrostatic force between the first and third fixed comb electrodes  220  and  250  and the first and third driving comb electrodes  120  and  130 . In contrast, if the predetermined voltage is applied to the electrode pad P 4 , the stage may seesaw  100  in a negative x-direction. 
   Further, if a predetermined voltage is applied to the electrode pad P 2 , the stage  100  is driven in a negative y-direction due to an electrostatic force between the second driving comb electrodes  240  and the second fixed comb electrodes  350 . If the predetermined voltage is applied to the electrode P 3 , the stage  100  is driven in a positive y-direction. Accordingly, the stage  100  can be driven in two directions. 
     FIG. 7  is a timing diagram when a voltage is applied to the biaxial actuator of the present invention. 
   Referring to  FIG. 7 , a sine wave pulse voltage with a 180-degree phase shift was applied to the electrode pads P 2  and P 3  for a horizontal scanning (see  FIG. 7A ). A triangular wave voltage with a 180-degree phase shift was applied to the electrode pads P 4  and P 5  for a vertical scanning in two directions (see  FIG. 7B ). A step pulse was applied to the electrode pads P 4  and P 5  in case of vertical scanning in one direction (see  FIG. 7C ). Here, a frequency of 22.5 kHz was used for the horizontal scanning, and a frequency of 60 Hz was used for the vertical scanning to perform a non-resonant linear driving. The second torsion springs  310  are designed such that a resonant frequency is approximately 1 kHz or more for the linear driving of the vertical scanning. According to results obtained using the ANSYS program, a driving angle was 8° or more when a driving frequency was 22.5 kHz in the horizontal scanning, and a resonant frequency was 1200 Hz in the vertical scanning. A driving angle was 4.5 to 5.0° when the driving frequency was 60 Hz in the vertical scanning. 
     FIG. 8  is a sectional view of a biaxial actuator according to a second embodiment of the present invention. The actuator may be structured such that the third driving comb electrodes  130 , the third fixed comb electrodes  250 , the first base  204 , and the conductive layer  206  that electrically connects between the first fixed comb electrodes  220  and the third fixed comb electrodes  250  are removed from the actuator shown in  FIG. 4 . 
   An actuator according to a third another embodiment of the present invention shown in  FIGS. 9 and 10  further includes a driving unit that is disposed on a stage unit and drives the stage in two directions. 
     FIGS. 9 and 10  are schematic sectional views of the actuator according to a third embodiment of the present invention. The same elements as those in the first embodiment may be given the same reference numerals, and a detailed explanation thereof will not be given. 
   Referring to  FIGS. 2 ,  9 , and  10 , on the basis of a first level on which a stage unit and driving comb electrodes are formed, the same structure of the second level of the first embodiment may be formed on the first level. That is, a moving frame  200 ′, a fixed frame  300 ′, and second torsion springs  310 ′ are made of a multi-tiered structure having multiple layers  201 ,  202 ,  203 ,  202 ′, and  203 ′,  301 ,  302 ,  303 ,  302 ′, and  303 ′, and  311 ,  312 ,  313 ,  312 ′, and  313 ′. The multi-tiered structure may be an SOI substrate having highly doped first silicon layers  201 ,  301 , and  311 , second silicon layers  203 ,  303 , and  313 , third silicon layers  203 ′,  303 ′, and  313 ′, and first insulation layers  202 ,  302 , and  312  and second insulation layers  202 ′,  302 ′, and  312 ′ between the silicon layers. Reference numerals  204 ,  304 , and  204 ′ respectively denote first through third bases, which may be insulation substrates, such as glass substrates. 
   First through third fixed comb electrodes  220 ′,  350 ′, and  250 ′, second extending members  340 ′ are formed at a third level over the first level to respectively correspond to first through third fixed comb electrodes  220 ,  350 , and  250 , second extending members  340  formed at the second level under the first level. A conductive layer  206 ′ is formed on the third level to correspond to a conductive layer  206 . 
   The actuator of the present embodiment, as shown in  FIG. 10 , is driven in two directions by applying a ground voltage Vg to the driving comb electrodes and voltages V 1  through V 4  to electrodes that are formed on the second and third levels to be point-symmetric about the stage  100 . Since voltage is simultaneously applied to the fixed electrodes that are diagonally formed, the actuator of the third embodiment has a higher driving force than the actuator of the first embodiment, and can be driven more stably. 
   A method of manufacturing an actuator according to a fourth embodiment of the present invention will now be explained in steps. In the present embodiment, a method of manufacturing the actuator of the first embodiment will be exemplarily explained below. Through the description of the manufacturing method, the detailed structure of the actuator of the first embodiment will be more clearly understood. The constituent elements shown in  FIGS. 1 through 6  are cited with reference numerals, if necessary. 
   1. Manufacture of Base Substrate 
   Referring to  FIG. 11A , after a Pyrex glass  400  with a thickness of 400 μm is prepared, a photoresist  402  may be patterned on the glass  400  to expose portions corresponding to electrode pads P 4  and P 5  and a conductive layer  206 . 
   Although not shown, predetermined portions corresponding to electrode pads P 2  and P 3  may also be exposed. 
   Referring to  FIG. 11B , the portions exposed by the photoresist  402  may be etched to a depth of approximately 2000 Å, and then, the photoresist  402  may be removed. 
   Referring to  FIG. 11C , an Au/Cr film may be deposited on the glass  400  to a thickness of 4000/200 Å and then may be patterned to form the electrode pads P 2  through P 5  and the conductive layer  206  (for the electrode pads P 2  and P 3 , see  FIG. 6 ). 
   Referring to  FIG. 11D , a dry film resist (DFR) film may be coated on the glass  400  to cover electrodes, and then, may be patterned. An opening portion  404   a  corresponds to an area between a fixed frame  300  and a moving frame  200  of an actuator. 
   Referring to  FIG. 11E , exposed portions of the Pyrex glass  400  may be etched by sand blasting, and the DFR film  400  may be removed to complete a glass base substrate  400 . Here, the portions subjected to sand blasting may be partially etched such that the glass base substrate  400  may be integrally formed. 
   2. Manufacture of Lower Part of Main Body Structure 
   Referring to  FIG. 12A , as an upper structure material, a silicon-on-insulator (SOI) substrate  500  in which an SiO 2  insulation layer  502  with a thickness 1 to 2 μm may be formed as an etch stop layer between a first silicon layer  501  and a second silicon layer  503  may be prepared. A photoresist mask  504  having a predetermined shape may be formed on the second silicon layer  503 . Here, portions covered by the mask  504  may be a third fixed comb electrode portion W 1 , a first fixed comb electrode portion W 2 , a moving frame portion W 3 , a second extending member portion W 4 , a fixed frame portion W 5 , and a second fixed comb electrode portion (not shown) extending from the fixed frame portion W 5 . 
   Referring to  FIG. 12B , portions on the second silicon layer  503 , which are not covered by the mask  504 , may be etched in an Inductively Coupled Plasma Reactive Ion Etching (ICPRIE) method to expose the insulation layer  502  through exposed areas of the mask  504 . After etching is completed, the mask  504  may be removed by stripping. 
   Referring to  FIG. 12C , third fixed comb electrodes  250 , first fixed comb electrodes  220 , the moving frame  200 , second extending members  340 , and a fixed frame  300  may be formed on the insulation layer  502 , and second fixed comb electrodes  350  extends from the fixed frame  340 . 
   3. Bonding Between Base Substrate and Lower Part of Main Body Structure and Manufacture of Upper Part of Main Body Structure 
   Referring to  FIG. 13A , the substrate  500  from which the second silicon layer  503  is etched may be bonded to the glass base substrate  400  obtained through the above-described process. An anodic bonding may be used herein and the second silicon layer  503  contacts the glass base substrate  400 . Here, a portion of the electrode pads P 2  through P 5  may be exposed from the fixed frame  300 . Next, a top surface of the first silicon layer  501  may be grinded by a chemical mechanical polishing (CMP) method to a thickness of approximately 70 μm. 
   Referring to  FIG. 13B , the glass substrate  400  may be grinded by CMP to separately form an inner glass substrate (i.e., a first base  204 ) and an outer glass substrate (i.e., a second base  304 ). 
   Referring to  FIG. 13C , an Au/Cr film may be deposited on the first silicon layer  501  to a thickness of 4000/200 □, and then patterned to form an electrode pad P 1 . 
   Referring to  FIG. 13D , a photoresist mask  506  having a predetermined shape may be formed on the first silicon layer  501 . Here, portions covered by the mask  506  may be a stage portion W 6 , a connecting part portion W 7 , a first driving comb electrode portion W 8 , a moving frame portion W 9 , a first extending member portion W 10 , a fixed frame portion W 11 , and second and third driving comb electrode portions (not shown). 
   Referring to  FIG. 13E , portions on the first silicon layer  501 , which are not covered by the mask  506 , may be etched by ICPRIE to expose the insulation layer  502  through exposed areas of the mask  506 . 
   Referring to  FIGS. 13F , the insulation layer  502  exposed by the mask  506  may be removed. Then, the mask  506  may be removed. A stage  100 , a connecting part  110 , first driving comb electrodes  120 , the moving frame  200 , first extending members  230 , a fixed frame  300 , second and third driving comb electrodes  240  and  130  may be formed. 
   Next, if the actuator is used as an optical scanner, a reflective layer (not shown) having a reflexibility of 99% or more may be formed on a top surface of the stage  100  to minimize a damage due to laser beams. 
   Although the method of manufacturing the actuator of the first embodiment has been explained, since methods of manufacturing the actuators of the second and the third embodiments can be performed according to the fourth embodiment, a detailed explanation thereof will not be given. 
   As described above, the actuator according to the present invention may seesaw in two directions, and may include the stage unit driving unit that drives the stage in a resonant manner in the first direction and the first support unit driving unit that drives the first support unit in a non-resonant linear manner in the second direction. Therefore, the biaxial actuator may be used as an optical scanner for a display that requires a high speed horizontal scanning and a linear vertical scanning. 
   In the meantime, the method of manufacturing the actuator according to the present invention electrically separate the torsion springs used in the vertical scanning as double lines, such that an upper line can be used as an electrical path for the driving comb electrodes and a lower line can be used as an electrical path for the fixed comb electrodes. Furthermore, since the driving comb electrodes and the fixed comb electrodes may be formed at different levels, the biaxial actuator may be easily manufactured, thereby reducing manufacturing costs. 
   While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.