KR100596320B1 - Optical switching device using a micro piezoelectric actuator and method for fabricating same - Google Patents

Abstract

The optical switch element comprises a mirror, first and second actuators for adjusting the tilt angle of the mirror on the x axis, third and fourth actuators for adjusting the tilt angle of the first and second actuators on the y axis, and the first and second actuators. A gimbal for supporting the actuator, and a driving substrate for applying a drive signal to the actuator. The gimbal includes at least one groove or step in its longitudinal direction to prevent the gimbal from bending when the piezoelectric layer is contracted or expanded. In addition, at least one groove or step is formed in the lower portion of the mirror to maintain the flatness of the mirror when the mirror is inclined by the actuator. Since grooves are formed in the lower part of the mirror, the entire surface of the mirror can be used to reflect the optical signal.

Description

Optical switch device using micro piezoelectric actuator and manufacturing method thereof {OPTICAL SWITCHING DEVICE USING A MICRO PIEZOELECTRIC ACTUATOR AND METHOD FOR FABRICATING SAME}

TECHNICAL FIELD OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical switching device using a micro piezoelectric actuator and a method of manufacturing the same. In particular, a deposition process is performed after depositing polysilicon in a groove of a stepped structure, thereby easily performing subsequent deposition and etching processes, and A method of manufacturing an optical switching device having a structure.

Conventional technology

Switching elements used in optical communication systems are an important factor in determining the maximum transmission capacity of a communication system. Recently, optical switches have been widely used for miniaturizing switching elements and increasing switching capacities in optical communication systems. In particular, a switching technology using a micro mirror controlled using a micro electro-mechanical system (MEMS) technology is gaining popularity.

MEMS stands for 3-D microstructure fabrication technology, developed from semiconductor process technology, and is particularly used to fabricate mechanical structures with micron or nano size. Optical switches manufactured using MEMS technology are technically divided into two types according to the optical channel switching method. That is, one of them is in the form using a micro mirror, and the other is in the form using micro fluid having different refractive indices.

Optical switches using micro mirrors are further divided into 2D planar switches having a two-dimensional array and 3D free-spatial switches having a three-dimensional array. The 2D planar switch can easily arrange the optical fiber and has a simple structure by using an on-off mirror, but a large number of ports (for example, 32 × 32 or more) in the switch ( Difficult to embed port) Thus, 3D switches with greater scalability are more suitable for use in backbone networks that require Tbps level capacity.

In general, actuators used in micro devices, such as the optical switches described above, are driven by electrostatic forces. However, the actuator using the electrostatic force has a disadvantage in that it has an increase in driving voltage and has a nonlinear characteristic. In addition, there is a problem that a pull-in phenomenon of the micromirror attached to the substrate occurs, and the optical mirror is precisely controlled by rotating the micromirror about two driving axes, that is, the x and y axes. Difficult to increase the position change.

Therefore, an optical switch element using a proposed micro piezoelectric actuator and a method for manufacturing the same are disclosed in PCT Publication WO03 / 089957. 1 shows an example of an optical switch element using a micro piezo actuator.             

As shown in FIG. 1, for example, when driving the piezoelectric layers 65 of the first and second actuators 60 and 61 to rotate the micromirror 90 about the x axis, When the piezoelectric layer 65 shrinks or expands, the gimbal 160 supporting the first and second actuators 60 and 61 may be bent together. In this case, the shape change of the gimbal 160 is transmitted to the third and fourth actuators 260 and 261 connected to the gimbal 160, which in turn causes a movement on the y axis of the mirror 90. Therefore, it becomes difficult to control the independent movement on the x-axis and the y-axis of the mirror 90, respectively.

Therefore, in order to prevent the coupling between the movement on the x-axis and the movement on the y-axis of the micromirror 90, the longitudinal groove 75 is formed on the gimbal 160 or the gimbal 160 is firstly formed. And another groove 70 in a portion connected to the second actuators 60 and 61. By doing so, the gimbal 160 mirrors the movement on the x-axis of the first and second actuators 60, 61, for example, without affecting the movement on the y-axis of the third and fourth actuators 260, 261. It can be delivered exactly to 90.

As such, in order to form the groove or the step in the gimbal 160 or the like, a step is formed on the drive substrate formed on the semiconductor substrate at the beginning of the manufacturing process of the optical switch element using the micro piezoelectric actuator using a dry or wet etching process. The piezoelectric actuator is formed by depositing and patterning an elastic layer, a bottom electrode layer, a piezoelectric material layer, and a top electrode layer on the stepped driving substrate.

However, when the piezoelectric material layer is formed using the spin method while the elastic layer and the lower electrode layer made of, for example, SiNx are deposited and the shape of the step is maintained on the drive substrate on which the step is formed, the step shape There may be a problem that the piezoelectric material layer may not be uniformly formed. In addition, in the case of SiNx, since the stress is large and the film thickness is relatively thin (typically within 1 um), in order to increase the flatness of the final actuator, it is necessary to balance the stresses of the elastic layer of SiNx with the film deposited thereafter. However, there is a problem that the overall manufacturing process is complicated.

Further, in the optical switch element, a step or groove may be formed on the surface of the mirror in order to maintain the flatness of the mirror when the mirror connected to the actuator is moved by the actuator. However, in this case, a problem arises that limits the area where light is reflected on the surface of the mirror.

Summary of the Invention

Accordingly, the present invention is to solve the above problems of the prior art, to stably form the structure of the optical switch in the manufacturing process of the optical switch, to prevent the couple phenomenon of the biaxial movement of the actuator and to the flatness of the mirror It is an object of the present invention to provide an optical switch and a method of manufacturing the same that facilitate the deposition process after the groove or step forming process for maintaining the pressure.

According to the present invention for achieving the object of the present invention, a method for manufacturing an optical switching element using the first, second, third and fourth micro piezoelectric actuator, comprising a driving circuit for generating a drive signal Forming a driving substrate, forming a groove on the driving substrate to maintain flatness of the optical switching element and the mirror, depositing a protective layer on an upper surface of the driving substrate, by the groove Depositing a polysilicon layer so as to fill the stepped shape formed on the protective layer, planarizing a surface of the deposited polysilicon layer, depositing an insulating film on the polysilicon layer, a piezoelectric element layer on the insulating film Forming a piezoelectric layer of each of the actuators by etching the piezoelectric element layer and the insulating film, and patterning the insulating film. A mirror support layer positioned between the first and second actuators, a membrane and a connection portion of each of the actuators, a gimbal supporting the first and second actuators, and connecting the first and second actuators to the mirror support region. Forming first and second transmitters for the first and second transmitters, and third and fourth transmitters for the gimbal to connect the third and fourth actuators, depositing a mirror over the mirror support area, on the optical switching element Forming a passivation layer, removing a portion of the drive substrate corresponding to the bottom surface of the mirror and actuator, and removing the passivation layer and the protective layer.

Brief description of the drawings

The above and other objects and features of the present invention will become apparent from the following detailed description of the invention described with reference to the accompanying drawings.

1A is a perspective view of an optical switching element using a micro piezoelectric actuator according to the prior art.

1B to 1D are enlarged views of main portions 210, 220, and 230 of the micro piezoelectric actuator shown in FIG. 1A.             

2A is a perspective view of an optical switching element using a micro piezo actuator according to a preferred embodiment of the present invention.

2B through 2D are enlarged views of the main portions 310, 320, and 330 of the micro piezo actuator shown in FIG. 2A.

3A is a perspective view of an optical switching element using a micro piezoelectric actuator according to another preferred embodiment of the present invention.

3B-3D are enlarged views of the main portions 410, 420, 430 of the micro piezo actuator shown in FIG. 3A.

4 is a plan view of an optical switching element using the micro piezoelectric actuator shown in FIG. 2A.

5A to 5K show each process of the method of manufacturing the optical switching element using the micro piezoelectric actuator according to the preferred embodiment of the present invention.

Best Mode of Invention

Figure 2A shows a perspective view of an optical switch element using a micro actuator according to a preferred embodiment of the present invention. 2B to 2D are enlarged views of main portions 310, 320 and 330 of the micro piezo actuator shown in FIG. 2A.

2A, the optical switch element includes a mirror 90, first and second actuators 60 and 61, and first and second actuators for adjusting the tilting angle of the mirror 90 on the x-axis. Third and fourth actuators 260 and 261 for adjusting the tilt angle of the mirror 90 on the y-axis by adjusting the tilt angle of 60 and 61. Each of the actuators 60, 61, 260, and 261 of the optical switch element is implemented in the form of a straight line.

Each of the first and second actuators 60 and 61 is a piezoelectric layer formed on at least one of the first membrane 60a, the second membrane 60b, the first membrane 60a and the second membrane 60b. (piezoelectric layer) 65, a connection 22 connected between the first membrane 60a and the second membrane 60b. In addition, the connecting portion 22 includes two elastic bodies 22b and connecting members 22a connected therebetween. Here, a membrane 60a or 60b is connected to one terminal of each elastic body 22b.

2B and 2C, each elastic body 22b is shown to have a zigzag shape, but the shape of the elastic body 22b may be configured differently. For example, as illustrated in FIGS. 3B and 3C, the elastic body 22b ′ of the connecting portion 22 ′ may be implemented using a spring folded in a vertical direction.

As shown in FIG. 2A, the respective connecting portions 22 of the first and second actuators 60, 61 are preferably located in opposite directions with respect to the mirror 90. In addition, each connecting portion 22 is connected to the mirror 90 through the transmission unit 30, the first and second actuators 60, 61 can adjust the tilt angle of the mirror 90 on the x-axis. .

Each of the third and fourth actuators 260 and 261 may include a piezoelectric layer formed on at least one of the third membrane 260a, the fourth membrane 260b, the third membrane 260a, and the fourth membrane 260b. 265, a connection 42 connected between the third membrane 260a and the fourth membrane 260b. In addition, the connecting portion 42 includes two elastic bodies 42b and a connecting member 42a connected therebetween. Here, a membrane 260a or 260b is connected to one terminal of each elastic body 42b.

2B and 2C, each elastic body 42b is shown to have a zigzag shape, but the shape of the elastic body 42b may be configured differently. For example, as illustrated in FIGS. 3B and 3C, the elastic body 42b ′ of the connection part 42 ′ may be implemented using a spring folded in the vertical direction.

As shown in FIG. 2A, the connecting portions 42 of the third and fourth actuators 260 and 261 are preferably located in opposite directions with respect to the mirror 90. In addition, the connecting portion 42 is, for example, a virtual straight line drawn between the connecting portions 42 located in opposite directions with respect to the mirror 90, likewise located in opposite directions with respect to the mirror 90. It is preferable to be positioned orthogonal to the imaginary line drawn between the connecting portions 22.

Each connecting portion 42 is connected to the gimbal 160 via the transmitting portion 52 so that the third and fourth actuators 260 and 261 can adjust the inclination angles of the first and second actuators 60 and 61. This makes it possible to control the tilt of the mirror 90.

As shown in FIG. 2D, gimbal 160 may be configured to have a groove or step 75 in the longitudinal direction. The groove 75 serves to prevent the gimbal 160 from bending when the piezoelectric layer 65 responds to the driving signal and contracts or expands. If the gimbal 160 is bent when the piezoelectric layer 65 contracts or expands, the inclination of the first and second actuators 60 and 61 may be transmitted to the third and fourth actuators 260 and 261. This makes it difficult to control the movement of the mirror on the x axis independently of the movement on the y axis. Similarly, another groove 70 is formed in the gimbal 160 so that the third and fourth actuators 260 and 261 of the first and second actuators 60 and 61 are not affected. It is possible to accurately transmit the movement on the y axis, that is, the inclination, to the mirror 90.

The grooves 70 and 75 formed in the gimbal 160 are formed inside the gimbal 160 so that they are not visible from the outside. That is, the gimbal 160 has a structure in which several layers are deposited, and the multi-layer gimbal 160 fills the grooves 70 and 75 formed in the lower layer of the multilayer structure with, for example, polysilicon. The surface of the polysilicon may be formed by chemical mechanical polishing (CMP) and depositing at least one layer over the layer of planarized polysilicon.

On the other hand, each of the piezoelectric layers 65 and 265 includes a top electrode, a bottom electrode, and a piezoelectric material layer disposed between the top electrode and the bottom electrode. The piezoelectric material layer includes, for example, PZT, PbTiO ₃ , PLZT, PbZrO ₃ , PLT, PNZT, LiNbO ₃ or LiTaO ₃ . In addition, the upper and lower electrodes are made of a conductive material. That is, the upper electrode is for example Al, Ru, Au, Ag, or RuO ₂ . PT and the like, and the lower electrode includes Ru or Ru, PT, Ta and the like having high conductivity. The upper and lower electrodes are connected to a drive circuit (not shown) through electrode bridges 270 and 271.

As shown in FIG. 2A, the mirror 90 is located between the first and second actuators 60, 61. The mirror 90 may preferably be formed of a metal having a high reflexibility, for example Au or Pt. A mirror support layer including the above-described insulating layer and / or piezoelectric layer may be formed below the mirror 90.

2A and 3A, the mirror 90 is shown as having a circular shape, but the shape of the mirror 90 may be a quadrangular or other polygon.

On the other hand, at least one groove or step 91 may be formed to maintain the flatness and reflexibility of the mirror 90 itself when the mirror 90 is inclined by the actuator. In this case, the groove 91 formed in the mirror 90 is formed in the lower portion of the mirror 90 so that it is not visible from the outside. That is, the mirror 90 has a structure in which several layers are deposited, and the multilayer mirror 90 fills the surface of the polysilicon after filling the groove 91 formed in the lower layer of the multilayer structure with polysilicon. Chemical mechanical polish (CMP) treatment and depositing at least one layer over the layer of planarized polysilicon. By doing so, not only the flatness of the mirror 90 can be maintained, but also the problem of limiting the reflectivity or the reflection area of the mirror 90 can be solved by forming a groove on the surface of the mirror 90.

Hereinafter, a method of manufacturing an optical switch device including a micro piezoelectric actuator according to a preferred embodiment of the present invention described with reference to FIGS. 2A to 3D and 3A to 3D will be described.

5A to 5K illustrate each step of the method of manufacturing the optical switch element using the micro piezoelectric actuator according to the preferred embodiment of the present invention. 5A to 5K are views of the cross section along the line A-A 'of the optical switch device according to the preferred embodiment of the present invention as shown in FIG. For convenience of explanation, in Figs. 5A to 5K, some components of the optical switch element are shown not to scale.

First, as shown in FIG. 5A, a driving substrate 2 including a driving circuit for generating a driving signal is formed on a semiconductor substrate (not shown). Then, grooves are formed on the driving substrate 2 through dry or wet etching. The grooves formed in the drive substrate 2 become grooves or steps formed in or under the gimbal and mirror in the optical switch element finally formed. By the groove formed on the driving substrate 2, the optical switch element of the present invention can maintain flatness without being affected by the contraction and expansion of the actuator.

As shown in FIG. 5B, a protection layer 4 is deposited on the drive substrate 2. The protective layer 4 serves to prevent the driving substrate 2 from being damaged in a subsequent process and to prevent the layers deposited on the protective layer 4 from being etched together when the driving substrate 2 is etched. The protective layer 4 may include, for example, SiO ₂ or SiNx.

Next, as shown in FIG. 5C, a polysilicon layer 199 is formed over the protective layer 4. At this time, the polysilicon layer 199 is formed by the following process. That is, first, polysilicon is deposited on the protective layer 4, and heat treatment is performed at about 1000 degrees or more for about 2 to 3 hours to remove residual stress. Since the polysilicon thus treated has no residual stress, it is less affected by other layers or films subsequently deposited on it. The heat treated polysilicon layer 199 is planarized by a chemical mechanical polishing (CMP) process. The planarization of the surface of the polysilicon layer 199 may maintain flatness of the piezoelectric layer and the mirror deposited in a subsequent process.

The insulating layer 200 (eg, SiO ₂ or SiNx), the lower electrode layer 202 (eg, platinum layer), and the piezoelectric material layer 204 are deposited on the polysilicon layer 199 in order. do. The piezoelectric material layer 204 may include, for example, PZT, PbTiO ₃ , PLZT, PbZrO ₃ , PLT, PNZT, LiNbO _3, or LiTaO ₃ . An upper electrode layer 2 (16, for example, a platinum layer) is deposited on the piezoelectric material layer 204. The upper and lower electrode layers 206 and 202 and the piezoelectric material layer 204 are piezoelectric layers. device layer).

Next, as shown in Figs. 5E to 5G, the piezoelectric element layer is etched to form a required portion of the piezoelectric element layer (parts corresponding to piezoelectric actuators, gimbals, mirrors, and the like). That is, as shown in FIG. 5G, piezoelectric layers 65 of the first and second actuators 60, 61 are formed over the insulating layer 200. In addition, a ring pattern 92 surrounding the circumference of the mirror is formed on the insulating layer 200. Although not shown in FIG. 5G, piezoelectric layers 265 of the third and fourth actuators are formed on the insulating layer 200.

5E to 5G, the upper electrode layer 206, the piezoelectric material layer 204, and the lower electrode layer 202 are shown to be sequentially formed by etching, but the upper electrode layer and the piezoelectric element layer may be processed once using a mask. It may be formed as.             

Next, as shown in FIG. 5H, the insulating layer 200 is etched, and a portion thereof is removed. That is, the insulating layer 200 is patterned to form the membranes 60a and 60b of the first and second actuators 60 and 61. In addition, membranes 260a and 260b of the third and fourth actuators 260 and 261 are formed. At this time, an elastic body 22b (not shown) is also formed connected between the membranes 60a and 60b and the connecting portion 22a. In addition, an elastic body 42b (not shown) is also formed connected between the membranes 260a and 260b and the connecting portion 42a.

In addition, a gimbal 160 supporting the first and second actuators 60 and 61 is formed and connected to the third and fourth actuators 260 and 261 through the transmission unit. In addition, another transmission is formed to connect the first and second actuators 60, 61 to the mirror. As shown in FIG. 5H, the mirror support region 200a is formed when the insulating layer 200 is etched. Next, a mirror 90 is formed on the mirror support area 200a.

As described with reference to Fig. 5A, since the steps for maintaining the flatness of the mirror are already formed in the lower portion of the mirror support area 200a, that is, the driving substrate 2, the mirror of the optical switch element is formed. Even when the tilting operation is performed, the flatness of the mirror itself can be maintained. In addition, since the step is formed below the mirror itself, there is an advantage that the entire surface of the mirror can be used as a reflection area.

In FIG. 5H, the mirror support area 200a consists of one layer, that is, a portion of the insulating layer 200, but in the etching process shown in FIGS. 5A-5C, without etching the portion where the mirror is to be deposited, The mirror support area 200a may be configured to include the multilayers 200, 202, 204, and 206. In this case, the mirror 90 may be formed using a method different from that described with reference to FIG. 5H. That is, the mirror 90 is formed by patterning a mirror layer deposited on the entire surface of the mirror support region 200a, or a mask is formed on a portion other than a portion where the mirror 90 is formed on the mirror support region 200a. It may be formed later by depositing the mirror 90.

Next, a PR (photo resist) layer (not shown) is formed over the structure shown in FIG. 5H. In addition, development and metal deposition processes for forming an electrode bridge for connecting the actuator to the pad of the driving circuit are performed.

Then, as shown in FIG. 5I, a passivation layer 6 is deposited over the structure shown in FIG. 5H. A portion of the drive substrate 2 is then selectively removed so that the lower portion of the protective layer 4 is exposed through the palate 8 (see FIG. 5J). Finally, as shown in Fig. 5K, the passivation layer 6 and the protective layer 4 are etched. The optical switch element thus formed has an advantage that the operation of the mirror and the actuator is not limited because the lower part of the mirror and the actuator is exposed.

In the present embodiment, the optical switching element using the piezoelectric actuator has been described, but the technique applied to the present embodiment can also be applied to MEMS elements such as an optical scanner, an optical attenuator, an optical array, an optical motor, and the like. In addition, the optical switching element according to the present invention can also be used as one component of the optical switching element of the M x N array.

Although the present invention has been described with reference to the preferred embodiments, various modifications are possible without departing from the scope of the invention as set forth in the claims below.

Claims (8)

In the method of manufacturing the optical switching element using the first, second, third and fourth micro piezo actuators, Forming a driving substrate comprising a driving circuit for generating a driving signal, Forming grooves on the driving substrate to maintain flatness of the optical switching element and the mirror; Depositing a protective layer on an upper surface of the driving substrate; Depositing a polysilicon layer to fill the stepped shape formed on the protective layer by the groove; Planarizing the surface of the deposited polysilicon layer, Depositing an insulating film on the polysilicon layer, Forming a piezoelectric element layer on the insulating film, Etching the piezoelectric element layer and the insulating film to form piezoelectric layers of each of the actuators, Patterning the insulating film to provide a mirror support layer positioned between the first and second actuators, a membrane and a connection portion of each of the actuators, a gimbal to support the first and second actuators, and the first and second actuators to support the mirrors. Forming first and second transmitters for connecting to an area, third and fourth transmitters for connecting the third and fourth actuators to the gimbal, Depositing a mirror over the mirror support area, Forming a passivation layer on the optical switching element, Removing a portion of the drive substrate corresponding to the bottom surface of the mirror and actuator, Removing the passivation layer and the protective layer. The method of claim 1, After depositing the polysilicon layer, heat treating the deposited polysilicon at about 1000 degrees for about 2 to 3 hours. The method of claim 1, Planarizing the surface of the polysilicon layer is performed by chemical mechanical polishing (CMP). The method of claim 1, And the piezoelectric element layer has an upper electrode, a lower electrode, and a piezoelectric material layer disposed between the upper and lower electrodes. The method of claim 1, And a piezoelectric layer of each of the actuators having a top electrode, a bottom electrode, and a layer of piezoelectric material positioned between the top and bottom electrodes. The method of claim 1, Removing the portion of the drive substrate is performed by any one of dry and wet etching or a combination of these methods. The method of claim 1, Forming a groove in the drive substrate, wherein the groove is formed in a portion of the drive substrate corresponding to a portion in which the gimbal and the mirror are formed. The method of claim 1, After patterning the insulating film, Depositing a photo resist (PR) layer on the optical switch device; Developing a portion on the PR layer corresponding to a portion where an electrode bridge connecting each of the actuators to the driving circuit is formed; Depositing a metal on the PR layer, Patterning the metal to form the electrode bridge, Removing the PR layer.

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