KR20040057002A - MEMS Optical Switch using bimorp actuator with lever for displacement amplification And Method thereof - Google Patents

Abstract

PURPOSE: A MEMS type optical switch using a bimorph actuator and a displacement extension lever, and a fabricating method thereof are provided to improve the performance such as stability and extensibility by using the bimorph actuator and the displacement extension lever. CONSTITUTION: A MEMS type optical switch using a bimorph actuator and a displacement extension lever includes an actuator, a displacement extension lever, and a reflector. The actuator includes a pad, a heating bar, and a cooling bar. The heating bar and the cooling bar are connected to the pad. The displacement extension lever is connected to one end of the actuator in order to extend the rotatory power of the actuator to the displacement by using the electric potential difference between the heating bar and the cooling bar. The reflector is connected to the displacement extension lever in order to reflect an optical signal.

Description

MEMS Optical Switch using bimorp actuator with lever for displacement amplification And Method

The present invention relates to a MEMS type optical switch and a method of manufacturing the same. More specifically, a bimorph actuator having a heating bar and a cooling bar having different thicknesses of silicon, a semiconductor material, which is a semiconductor material using a semi-fabric manufacturing process technology. And a low voltage drive MEMs type optical switch manufactured by surface micromachining method using a displacement magnification lever, and a manufacturing method thereof.

In a large-capacity optical communication system to meet consumer's demand for Internet traffic, large-capacity information exchange, and multimedia services in the information society, an optical switch is necessary to change the direction of transmission of optical signals.

The optical switch that changes the direction of the optical transmission is usually defined by the number of inputs (m) and outputs (n) and is an essential part of the optical communication system, and enables high-speed and high-performance information transmission.

Looking at the prior art in the field of optical switches, the patent of US General Electric (US 5,208,880) is a structure in which a mirror is attached to the center of a spring which is bent several times, which is driven by a piezoelectric actuator to form an optical path in the form of an mxn matrix. It can be changed. This structure has the advantage that a long driving distance can be obtained at a low voltage, but a disadvantage is that the precision of position control of the mirror may be reduced.

In the French patent of Alcatel (US 4,759,597), the optical fiber is attached to a seesaw-shaped structure, and two optical fibers are placed at the position where the seesaw stays on either side. do. This structure is excellent in the alignment accuracy of the optical fiber in one state, but is limited to 1x2, there is a scalable problem.

Meanwhile, in the published paper, AT & T (IEEE, Photonics Technology Letters, vol. 10, no. 4, pp. 525-527, April 1988) used a SDA (Scratched Drive Actuator) to mirror the mirror surface made on the silicon surface. It is transforming the optical path by building. However, this method requires a driving voltage of 100 volts and 500 MHz, and also requires feedback control for accurate position control because it is a structure in which the position error of the mirror affects the optical path with serious wear. Do. Presented at the University of Michigan (J. MEMS, vol. 7, no. 2, pp. 207-213, Dec 1998), it implements an optical switch structure with a vertical mirror attached to a planar actuator. A driving voltage of at least 50 volts shall be applied.

Considering the prior art as described above, it can be seen that the prior art has room for improvement in positional accuracy, power consumption, mass productivity, and the like.

Accordingly, the technical problem to be achieved by the present invention is surface micromachining by using a bimorph actuator and a displacement magnification lever, in which the shape of silicon, which is a semiconductor material, is made thin in order to solve the problems of the prior art. To provide a low voltage MEMs type optical switch manufactured by micromachining method.

1 is an overall conceptual diagram of a bimorph actuator according to a preferred embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a cross section taken along the line II ′ of FIG. 1A.

3 is a configuration diagram of a bimorph actuator and a displacement expanding lever according to an exemplary embodiment of the present invention.

4 is a graph showing the relationship of the maximum displacement expansion according to the applied voltage according to the ANSYS analysis results of the drive characteristics of the actuator of the present invention.

FIG. 5 is a diagram showing an actual simulation result showing an analysis result in which displacement may be increased to about 400 μm when 60 V is applied to the bimorph actuator of FIG. 3.

6 is a block diagram of a unit structure for manufacturing an optical switch according to a preferred embodiment of the present invention.

FIG. 7 is a layout of a MEMs type optical switch in which the unit structures of FIG. 6 are arrayed.

8A to 8L are flowcharts illustrating a process of manufacturing a MEMs type optical switch according to a preferred embodiment of the present invention.

FIG. 9 is an SEM photograph showing an experimental example in which a PMMA reflection mirror was manufactured by a Liga process for fabricating an optical switch of the present invention.

10A, 10B and 10C are SEM images after the gaseous etching GPE process, the 6: 1 BHF wet etching, and the forced removal of the PMMA reflecting mirror before the etching process, respectively, in the manufacturing process of the PMMA reflecting mirror.

11A and 11B illustrate a situation in which a reflective mirror surface is formed by depositing gold on Cr of a PMMA sheet by E-beam evaporation.

12 is a graph illustrating a result of performing a reflectance experiment to confirm whether the light is completely reflected in the manufactured PMMA reflector.

In order to solve the above-described problems, one aspect of the present invention is a MEM type optical switch including an actuator, a displacement expanding lever, and a reflecting mirror to switch an optical signal, each connected to a pad and a pad, and different from each other. An actuator including a portion having a width and having a heating bar and a cooling bar spaced a predetermined distance from the actuator, and connected to one end of the actuator, and the rotational force generated by the actuator by a potential difference between the heating bar and the cooling bar applied through the pad. According to an aspect of the present invention, there is provided a MEM type optical switch including a displacement expanding lever for expanding with a displacement, and a reflection mirror connected to the displacement expanding lever and configured to reflect an optical signal according to a displacement change of the displacement expanding lever.

The height of the heating bar and the cooling bar is 5um or more, and the spacing between each bar may be 5um, and the portions having the different width thickness of the cooling bar are at least 1/2 the length of the heating bar, and the wide width is 15um It is preferable that it is above. (40V has no special meaning)

In addition, a PMMA reflecting mirror manufactured by LIGA, a micromachining technique using radiant light, is formed. The surface of the PMMA reflector may be coated with aluminum, gold or nickel.

According to another aspect of the present invention, there is provided a method of coating a photoresist on an insulating layer on a substrate to form a metal electrode on a predetermined region, forming a doped polysilicon layer on the metal electrode, and a predetermined mask. Reactive ion etching (RIE) is connected to one end of the actuator and the actuator having a heating bar and a cooling bar spaced apart from each other by a predetermined distance, and the heating bar applied through the pad and cooling Forming a displacement expanding lever for expanding the rotational force generated in the actuator by displacement with a potential difference in a bar, and forming a PMMA reflecting mirror in a Liga process on the entire structure, wherein the PMMA reflecting mirror includes: expanding the displacement Connected to the displacement expansion lever according to the displacement of the lever is configured to reflect the optical signal Provides a method for manufacturing a membrane jeuhyeong optical switch.

In addition, the manufacture of the PMMA reflector, the step of flattening to reduce the step of the solidified by coating with liquid PMMA, the step of depositing a thin metal film for electroplating, and after forming the adhesive to a predetermined thickness, the reflecting mirror Coating a PMMA sheet having a height corresponding to the height, aligning the X-ray mask with the substrate, exposing the radiated light for a desired time, and developing the PMMA to remove PMMA; And forming and developing pads.

Preferably, the mirror surface of the reflective mirror is capable of depositing 2.5 μm thick gold on 50 nm thick chromium (Cr).

Hereinafter, a MEM type optical switching according to a preferred embodiment of the present invention and a manufacturing method thereof will be described in detail. However, embodiments of the present invention illustrated in the following may be modified in many different forms and the scope of the present invention is not limited to the embodiments described in the following. Embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Hereinafter, a bimorph actuator according to a preferred embodiment of the present invention will be described with reference to FIGS. 1 and 2.

1 is an overall conceptual view of a bimorph actuator, and FIG. 2 is a cross-sectional view illustrating a cross section taken along line II ′ of FIG. 1.

1 and 2, the bimorph actuator includes two pads 10 and 11, a heating bar 16, and a cooling bar 14 on the silicon oxide film 12 as an insulating film. The cooling bar 14 which thickened the shape of the same material and the heating bar 16 which was thinned are connected. Naturally, it can be composed of different materials instead of bimorph actuators of the same material. The cooling bar 14 is divided into B and C portions, and the B portion is similar to the thickness of the A region of the heating bar 16, and the C portion is larger than the thickness of the A region of the heating bar 16. It is. Therefore, when a current is applied by applying a potential difference to the pads 10 and 12, heat is generated because the resistance of the heating bar 16 having a small cross-sectional area is large, and thus thermal expansion is relatively large. The rotating force of bending the bar toward the bar 14 is generated. If the rotational force is enlarged with the displacement expanding lever 18, not only large displacement can be obtained but also large force can be obtained even at a low driving voltage.

The tip displacement of the bimorph actuator due to the thermal effect can be expressed by the following equation (1).

Dx = a DT _BC l ² / [g (0.7707 + 0.38129 t ² / g ² )] (1)

Here, a is the thermal coefficient of expansion, the temperature difference between the heating bars (B, C) is DT _BC , the length is l, the distance between the center axis of the heating bar and the cooling bar is g, the thickness of the cooling bar is t (Fig. 2).

Next, with reference to FIG. 3, the structure of the bimorph actuator and the displacement expansion lever 18 is demonstrated. Anchors on the opposite sides of the two pads 10 and 11 are increased in proportion to the temperature difference between the heating bar 16 and the cooling bar 14 generated by giving a constant potential difference and in proportion to the square of the length. The basic driving principle is to push the displacement expansion lever 18 attached to 20 with a rotational force and to enlarge the displacement by the displacement expansion lever 18.

On the other hand, by using a thermal drive force, electrostatic force, electromagnetic force, piezoelectric force instead of the bi-morph type actuator may be configured to obtain a large displacement and a large force in combination with the displacement expansion lever.

When coupled-field analysis is performed with ANSYS, a crossover occurs between the heating bar 16 and the cooling bar 14 depending on the geometric shape. In order to avoid this phenomenon, the height of each bar 14, 16 should be at least 5um, and the distance between each bar 14,16 should be at least 5um, and the wide width of the cooling bar 14 should be at least 15um. It should be seen that the length should be at least 1/2 of the length of the heating bar (16).

Next, the relationship of the maximum displacement expansion according to the applied voltage according to the ANSYS analysis of the driving characteristics is shown in FIG. As shown in FIG. 4, when the height is 12um, a displacement of 100um or more may be obtained when 30V is applied, and when the height is 12um, the displacement may vary within about 5um in the left and right directions when 30V is applied, respectively. It is preferable to space it apart.

FIG. 5 is an actual simulation result diagram showing an analysis result capable of expanding displacement of about 60 μm when 60 V is applied.

Next, the unit structure and the layout of the MEMs type optical switch will be described.

FIG. 6 is a diagram illustrating a configuration of a unit structure for manufacturing a large displacement optical switch, and FIG. 7 is a layout of a MEMs type optical switch configured by arraying unit structures.

The optical switch of Figure 6 can open and close the light between the optical fiber for input and output, in consideration of the degree of the light spread according to the distance having a large stroke of more than 200um (stroke) is a drive chain that can produce a large driving force at low voltage A combination of the frame actuator and the displacement expanding lever was constructed.

The rotational force is generated by two bimorph actuators on both sides of the curved spring. This rotational force is transmitted to the lever to increase displacement, and when concentrated force is applied to the center of the spring, the central structure with the reflecting mirror moves forward in the horizontal direction. At this time, the light from the input optical fiber changes the path of the light to the output optical fiber. Therefore, once moved, no more power supply is required and has stable driving characteristics.

In this case, the wiring height is generally 1 ~ 1.5um, so it should be deposited considering the maximum 2mA / um per wiring, and it should be moved forward rather than back moving due to the restoring force of the spring. It is desirable to apply more voltage at the time.

Hereinafter, a method for manufacturing a MEMs type optical switch of the present invention will be described with reference to the manufacturing process with reference to FIGS. 8A to 8L.

In general, silicon structures are etched by reactive ion etching (RIE) to etch vertical mirrors of tens to hundreds of micrometers or more. Due to the high damage, the insertion loss and the crosstalk become very large when applied to the optical switch, and thus it cannot be applied to the optical switch for large capacity transfer of more than several hundred um. Therefore, in order to avoid such a fundamental problem and to implement a large-capacity optical switching device, micromachining technology using radiated light has been applied to the optical switch device manufacturing. At this time, the reflecting mirror was manufactured in a Liga process with a size of 80um x 80um x 200um in height.

First, the process of forming the above-described bimorph actuator and the displacement expansion lever will be described. A silicon oxide film 102, which is an insulating film, is formed on an SOI structure having a thickness of several tens of um (for example, 12 um) or the silicon substrate 100 (FIG. 8A). The photoresist 104 is coated to remain in a predetermined region (FIG. 8B), and for example, a metal 106 such as molybdenum (Mo) is deposited to perform a developing process (FIG. 8C). Thereafter, an n + polysilicon layer 108 is deposited on top of all, and heat treatment is performed (FIG. 8D). Next, after the photoresist layer 110 is coated to form a device portion, patterning and reactive ion etching (RIE) are performed to form a bimorph actuator and a displacement expanding lever, which are structures of an optical switch device. And develop (FIG. 8F).

Next, in order to perform a liga process by radiation, it was baked with acetone: photoresist (acetone: PR = 10: 1), baked at 90 ^° C. for 100 sec, and then liquid PMMA (polymethylmethacrylate) (112) on the front side. ) And harden in a natural state (Fig. 8g). If the step is severe, a planarization process may be performed until the entire silicon surface is exposed (FIG. 8H).

An adhesive (adhesion promoter, such as MMA, etc.) 114 is formed to a thickness of 500 kPa or less and coated with a PMMA sheet 116 of a reflecting mirror height (eg, 200um height, etc.) (FIG. 8H).

Thereafter, a thin metal film (eg, 150-200 nm, such as Cr, Ti, Ni, etc.) may be deposited for electroplating as needed.

The height of the PMMA according to the radiation (X-ray) exposure time is about 3um / min. At this time, it is preferable to be careful not to damage the fine pattern because it is pressed with a force of about 3kg. In addition, the damage of the PMMA during the exposure to radiation does not rise to 350 ^o C or more, so it is assumed that the damage by the radiation does not occur. After the actual radiation exposure, the PMMA is discolored, but the manufactured X-ray mask 150 is aligned with the substrate, and then the radiation is exposed and developed for a desired time to completely remove the PMMA (FIG. 8I). In addition, if necessary, a micromirror and a pad may be formed of a metal through an electroplating process and developed to form a reflective mirror (FIG. 8J).

Next, in order to remove the sacrificial layer oxide film 102 under the structure, a gas-phase etching HF GPE (gas-phase etching) process is performed, and the sacrificial layer oxide film 102 is etched by a desired depth and width (FIG. 8K). Metal electrodes already formed during electroplating must be cut to allow light to pass through before or after vapor phase etching, and if the cross section is not smooth, care must be taken because alignment with the optical fiber is problematic.

Finally, 2.5 μm thick gold is deposited on 50 nm thick chromium (Cr) with an E-beam evaporation to form a mirror surface that is a PMMA reflector (FIG. 8L).

Hereinafter, FIG. 9 is a SEM photograph showing an experimental example in which a PMMA reflective mirror having a size of W80umxD80umxH200um was manufactured by a Liga process using a sample including an oxide film and a silicon structure and an X-ray mask. As shown in the photo, it can be seen that the PMMA reflection mirror is well formed on the oxide film and the silicon structure.

On the other hand, the PMMA for the 30 minutes gas phase etching GPE process and 20 minutes 6: 1 BHF wet etching process used in the present invention to form a PMMA reflecting mirror and remove the sacrificial layer oxide film under the silicon structure by the Riga process The stability of PMMA reflector was analyzed through acid resistance test. 10A, 10B and 10C show SEM images after the forced removal of the PMMA reflector after the gaseous etching GPE process, after the 6: 1 BHF wet etching, and before the etching process, respectively.

FIG. 10A is an SEM image after the vapor etching GPE process (process shown in FIG. 8K), and FIG. 10B is an SEM image of the PMMA reflecting mirror on the silicon structure after 6: 1 BHF wet etching. After the various etching processes, the PMMA reflecting mirror on the silicon structure is basically collapsed and the bonding area with the silicon is almost unaffected and is completely bonded.

10C is a SEM photograph after the forced removal of the PMMA reflection mirror before the etching process. The A and B parts of the silicon structure surface were torn off before etching, and part of the lower part of the PMMA reflector and the surface of the structure was broken and removed during the removal of the PMMA reflection mirror. see.

Meanwhile, as shown in FIGS. 11A and 11B, 2.5 μm thick gold was deposited on Cr 50 nm of the PMMA sheet by E-beam evaporation to form a reflective mirror surface. Next, reflectance experiments were conducted to see if the light was fully reflected at the 1330 nm and 1550 nm wavelengths for optical communications. 12 is a graph showing the results. The measured reflectance was 91.3% at 1330 nm and 92.1% at 1550 nm with a UV Spectrometer (Model U-3501 from Hitachi).

It can be seen from the above various embodiments that the MEM type optical switch manufactured by the surface micromachining method using the bimorph actuator and the displacement expansion lever can be manufactured.

Although the technical idea of the present invention has been described in detail according to the above preferred embodiment, it should be noted that the above-described embodiment is for the purpose of description and not of limitation. In addition, it will be understood by those skilled in the art that various modifications are possible within the scope of the technical idea of the present invention.

As described above, according to the present invention, the MEMS type optical switch of the present invention for changing the direction of transmission of an optical signal in a large-capacity optical communication system uses a bimorph actuator and a displacement magnification lever for low voltage driving, large displacement expansion, and driving. It is to provide a low voltage MEMs type optical switch manufactured by a micromachining method having improved performance in terms of stability and expandability.

Claims (8)

In the MEMs type optical switch configured to include an actuator, a displacement expanding lever and a reflection mirror to switch an optical signal, An actuator having a heating bar and a cooling bar, each pad being connected to the pad and having portions having different thicknesses and spaced apart from each other by a predetermined distance; A displacement magnification lever connected to one end of the actuator and configured to enlarge, by displacement, the rotational force generated in the actuator by a potential difference between the heating bar and the cooling bar applied through the pad; And And a reflection mirror connected to the displacement expansion lever and configured to reflect an optical signal according to the displacement change of the displacement expansion lever. The method of claim 1, The height of the heating bar and the cooling bar is more than 5um, the spacing between each bar is characterized in that the MEMs type optical switch. The method of claim 1, The portion having the thickness of the different width of the cooling bar is at least 1/2 of the length of the heating bar, the wide width of the MEMS type optical switch, characterized in that more than 15um. The method of claim 1, MEMS type optical switch characterized in that to form a PMMA reflective mirror made of LIGA, a micromachining technology using radiated light The MEM type optical switch according to claim 4, wherein the PMMA reflective mirror surface is coated or electroplated with aluminum, gold or nickel. Coating a photoresist on an insulating layer on the substrate and remaining in a predetermined region to form a metal electrode; Forming a doped polysilicon layer on the metal electrode; Reactive ion etching (RIE) with a predetermined mask is connected to one end of the actuator and the actuator having a heating bar and a cooling bar spaced apart from each other by a predetermined distance, and applied through the pad Forming a displacement expansion lever on the heating bar and the cooling bar to expand the rotational force generated in the actuator by displacement due to a potential difference; And Forming a PMMA reflection mirror on the entire structure by a Liga process; The PMMA reflective mirror is a manufacturing method of the MEMS type optical switch, characterized in that configured to reflect the optical signal connected to the displacement expansion lever in accordance with the displacement change of the displacement expansion lever. The method of claim 6, Production of the PMMA reflecting mirror, Coating with liquid PMMA and flattening to reduce stepped hardening; Depositing a thin metal film for electroplating; After forming the adhesive to a predetermined thickness, coating a PMMA sheet having a height corresponding to the reflection mirror height; Aligning the X-ray mask with the substrate and then exposing and developing radiation for a desired time to remove the PMMA; And Forming and developing a micro-mirror and pad with a metal through an electroplating process. The method of claim 7, wherein The mirror surface of the reflective mirror is a method of manufacturing a MEMS type optical switch, characterized in that formed by depositing 2.5um thick gold on 50nm chromium (Cr).