KR100921434B1 - The method for manufacturing micromirror having sloping electrode using pdms - Google Patents

Abstract

PURPOSE: A method for manufacturing a micromirror having inclined electrode using PDMS is provided to increase a driving angle which is available by forming a bottom electrode to be inclined. CONSTITUTION: A method for manufacturing a micromirror having inclined electrode using PDMS is comprised of the steps: forming a bottom electrode to be inclined as a triangle and patterning a mold so that the top of the tangle is split(S110); injecting PDMS(polydimethylsiloxane stamp) into the patterned mold and hardening it(S120); separating hardened PDMS from the patterned mold in order to form the inclined bottom electrode(S130); and depositing the metal layer on the surface of PDMS in order to supply a voltage to the inclined bottom electrode(S140).

Description

Method for manufacturing micromirror with inclined bottom electrode using PDMS {THE METHOD FOR MANUFACTURING MICROMIRROR HAVING SLOPING ELECTRODE USING PDMS}

The present invention relates to a micromirror manufacturing method, and more particularly, to a micromirror manufacturing method having an inclined bottom electrode using PDMS.

The design of a constant power drive micromirror using a plate electrode takes into account the drive voltage and drive angle from the balance of the electrostatic torque between the electrodes and the mechanical torque of the spring supporting the mirror. In the case of a micromirror using a torsion spring, the torsion spring constant is expressed by Equation 1 below, and when the mirror rotates, the mechanical recovery torque of the spring is proportional to Equation 2 below.

Here, k is a constant depending on the shape of the spring cross section, which depends on the width and thickness of the spring, and the thicker the thickness, the closer to 1/3. In addition, E represents Young's modulus, and V represents Poisson's ratio.

Here, θ is the rotation angle of the mirror, α is the normal rotation angle (the ratio of the actual rotation angle of the mirror to the maximum rotation angle), Z ₀ represents the initial distance between the mirror plate and the bottom electrode. In addition, L means the length from the center of the rotation axis to the end of the mirror.

1 is a schematic diagram for calculating torque by constant power of a bidirectional driving micromirror using constant power. Let the size of the micromirror plate a in FIG. When the distance between the two electrodes is Z ₀ and the displacement of the mirror tip portion is Z _T , the force due to the electrostatic force can be expressed by Equation 3 below.

Here, A is the area of the mirror, permittivity ε ₀ is 8.85 pF / m, V _a is the applied bias voltage, Z (x) means the distance between the electrodes at each x position.

When voltage is applied to the micromirror having the structure as shown in FIG. 1, the torque due to the electrostatic force is summarized as in Equation 4 using constants defined as α, β, as follows.

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The mechanical restoring torque given by the torsion spring is the same as Equation 2 described above. The driving angle of the mirror is determined at the point where the mechanical restoring force by the spring and the electric torque by the electrostatic force represented by Equation 4 are in equilibrium. Therefore, if Equation 2 and Equation 4 are arranged on both sides, the equations can be expressed by the driving voltage and the driving angle. When the micromirror has a size of 210 μm x 210 μm and the spring is axially positioned at the center of the micromirror with a size of 1.2 μm x 8 μm x 42 μm, a graph of the driving angle versus the driving voltage as shown in FIG. 2 can be obtained. As can be seen in FIG. 2, the driving angle of the mirror increases as the applied voltage increases, but when a certain threshold voltage or more is applied, the mirror suddenly sticks to the bottom electrode. This is called pull-in phenomenon, and the applied voltage at which pull-in occurs is called pull-in voltage and the rotation angle at the time of pull-in phenomenon is called pull-in critical angle.

2 is a diagram illustrating a rotation angle of a micromirror according to an applied voltage. 2 (a) shows the increase in driving angle and the pull-in voltage as the applied voltage increases. Gradually decreasing the applied voltage of the pulled-in mirror returns the mirror back to its original state, but at the pull-in voltage, the mirror does not fall from the bottom electrode but at a lower applied voltage. 2 (b) shows the state of the mirror as the applied voltage of the pull-in mirror is decreased. At lower voltages than the pull-in voltage, the mirror separates from the floor. Using this principle, the driving voltage, rotation angle, pull-in voltage, pull-in critical angle, and the like of the micromirror driven with constant power can be designed. In the micromirror driving with constant power according to the voltage difference between the two plates, the plate bottom electrode making the bottom electrode in parallel with the mirror plate has been a common method in the fabrication of the existing constant power driving micromirror and is suitable for various applications. Has been applied.

However, when the micromirror is manufactured using the flat electrode as described above, there is a problem that the driving angle of the mirror plate that can be controlled is limited due to the pull-in phenomenon. That is, when the distance between the mirror plate and the bottom electrode is fixed, the rotation angle of the mirror plate can be controlled only within the pull-threshold angle, which is generally used in applications requiring continuous drive angle control. The use of driving micromirrors is an important cause of limitation. In general, to increase the controllable driving angle of the micromirror using the plate electrode, the distance between the mirror plate and the plate bottom electrode should be increased. In this case, however, the driving voltage of the mirror is increased due to the increased spacing between the electrodes. Even in applications that do not require continuous drive angle control, there are two rotations: the initial state where the mirror does not rotate and the pull-in state where the mirror plate is attached to the bottom electrode, as in the case of a digital micromirror developed by TI. Even in the case of the digital method using only the angle, there is a need to reduce the driving voltage for pulling in the mirror according to the circuit conditions.

In addition, after the micromirror adheres to the bottom electrode, adhesion between the mirror plate and the bottom electrode surface may easily occur due to contamination, moisture, and forces acting between the molecules, which causes the mirror to adhere to the bottom electrode. In this case, even after the applied voltage is removed, the mirror is not restored to its original state, and thus the normal operation of the device is impossible. Therefore, in order to reduce the adhesion phenomenon, it is necessary to increase the restoring force of the spring to increase the restoring force of the spring, and at the same time, there is a problem that a new structure is required to prevent the driving voltage from increasing despite the increased strength of the spring. .

The present invention has been proposed to solve the above problems of the conventionally proposed methods, by reducing the driving voltage by forming the bottom electrode in an inclined structure using PDMS, and reducing the distance between the bottom electrode and the driving voltage. It is an object of the present invention to provide a method of manufacturing a micromirror having an inclined bottom electrode using PDMS, which can increase the range of the driving angle which can be controlled by increasing the control angle without increasing the value of. In addition, by increasing the strength of the micromirror spring without increasing the driving voltage, it is possible to increase the resilience, thereby significantly reducing the phenomenon that the micromirror adheres to the floor and realizing the micromirror more resistant to external shock and vibration. Another object is to provide a method of fabricating a micromirror having inclined bottom electrodes using PDMS. In addition, the shape of the inclined bottom electrode can be suitably manufactured not only for the single-axis driving micromirror but also for the two-axis driving micromirror, thereby increasing the controllable driving angle as compared to the constant power driving micromirror using the flat plate electrode. Another object of the present invention is to provide a method of manufacturing a micromirror having an inclined bottom electrode using PDMS, which can reduce an applied voltage required for driving a mirror.

Micromirror manufacturing method having a tilted bottom electrode using a PDMS according to a feature of the present invention for achieving the above object, in the micromirror manufacturing method,

(1) patterning the mold such that the mold is inclined upward and disposed so as to face the center at a predetermined distance from each other;

(2) curing by injecting a poly dimethyl siloxane stamp (PDMS) into the patterned mold;

(3) separating the cured PDMS from the patterned mold to form an inclined bottom electrode;

(4) depositing a metal film on PDMS on which the inclined bottom electrode is formed;

(5) combining and processing the silicon substrate to form a constant power according to the voltage difference with the PDMS at a position spaced above the PDMS;

(6) depositing and patterning aluminum on the processed silicon substrate; And

And (7) etching the silicon substrate using the patterned aluminum as a mask.

Preferably, the step (1) of patterning a mold such that the mold is inclined upward and spaced apart from each other by a predetermined distance may be performed in consideration of the inclination and height of the inclined bottom electrode. (mold) can be patterned.

Preferably, the step (5) of combining and processing the silicon substrate for forming a constant power according to the voltage difference with the PDMS at a position spaced above the PDMS,

Processing the silicon substrate by an anisotropic etching process at a predetermined interval between a micromirror plate and the inclined bottom electrode;

Bonding the processed silicon substrate to the PDMS by a wafer bonding process; And

It may include the step of thinly processing the silicon substrate according to the thickness of a predetermined micromirror.

According to the method of fabricating a micromirror having an inclined bottom electrode using the PDMS of the present invention, the bottom electrode is formed into an inclined structure using the PDMS, thereby reducing the driving voltage and increasing the distance between the bottom electrode and the driving voltage. By making it possible to increase the size of the micromirror, it is possible to manufacture a micromirror that greatly increases the range of controllable driving angles. In addition, by increasing the strength of the micromirror spring without increasing the driving voltage to increase the resilience, the micromirror can significantly reduce the adhesion of the micromirror to the floor, and at the same time, the micromirror can be more resistant to external shock and vibration. . In addition, the shape of the inclined bottom electrode can be suitably manufactured not only for the single-axis driving micromirror but also for the two-axis driving micromirror, thereby increasing the controllable driving angle as compared to the constant power driving micromirror using the flat plate electrode. The voltage applied for driving the mirror can be reduced.

Hereinafter, with reference to the accompanying drawings, it will be described in detail with respect to the embodiment according to the present invention.

PDMS (Poly DiMethyl Siloxane; PDMS) is a polymer composed of silicon (Si) rather than carbon, so it has a low surface energy (21.6 mJ / m2) because it is chemically stable and can be easily separated without reacting with other materials. Does not cause swelling phenomena with water. In addition, it can easily pass gas, is stable to heat (~ 186 ℃), and can pass light up to 300nm wavelength, and can form polymers cured by ultraviolet rays. It is isotropic in crystal structure and can easily control interface characteristics. It can be said that it is a material suitable as a mold. The biggest advantage of the PDMS as an elastomer is that it can stably adhere to a relatively large area of the circuit substrate, which is equally satisfied with an uneven surface. Therefore, in the present invention, it is possible to more easily form the bottom electrode by using the characteristics of the PDMS, thereby reducing the driving voltage, it is possible to manufacture a micromirror that can greatly increase the range of the controllable driving angle.

3 and 4 are steps illustrating a method of manufacturing a micromirror having an inclined bottom electrode using a PDMS (poly dimethyl siloxane stamp) according to an embodiment of the present invention. As shown in Figure 3 and 4, the method of manufacturing a micromirror having an inclined bottom electrode using a PDMS according to an embodiment of the present invention, first, in consideration of the slope and the final height of the inclined bottom electrode substrate Process as 3 (a). PDMS (100) is put into a mold having a shape of an inclined bottom electrode to be cured. The liquid crystal PDMS is cured as shown in 3 (b) when a certain time elapses at a predetermined temperature or more, and when the cured PDMS is removed from the mold, the inclined shape is shown as 3 (c). Subsequently, when the metal film 110 using the shadow mask 120 is deposited on the surface of the injected PDMS to be used as an electrode for voltage application (3 (d)), the metal film is patterned only on a desired portion, thereby inclining the bottom electrode. Is completed. The micromirror is manufactured using the silicon substrate on the manufactured bottom electrode, which will be described with reference to FIG. 4. First, the silicon substrate 200 is processed using an anisotropic etching process in accordance with the design interval between the micromirror plate and the bottom electrode to be manufactured as shown in 4 (e), through which the driving space of the micromirror is formed. . In this case, the processed silicon substrate 200 is bonded to the PDMS 100 having the bottom electrode through a wafer bonding process, and then CMP (chemical mechanical polishing) as much as the micromirror thickness to fabricate the other surface of the silicon substrate 200. The process is thinly processed. The aluminum 205 is deposited on the thinly processed silicon substrate as shown in 4 (f), the aluminum is patterned according to the shape of the micromirror to be manufactured, and then the patterned aluminum 205 is used as a mask to form a micromirror. As the silicon substrate is etched, the final micromirror is completed. At this time, the finally etched silicon substrate becomes a micromirror plate (mirror plate).

5 is a flowchart of a method for fabricating a micromirror having an inclined bottom electrode using a PDMS according to an embodiment of the present invention. As shown in FIG. 5, the method of manufacturing a micromirror including an inclined bottom electrode using a PDMS according to an embodiment of the present invention includes the steps of patterning a mold (S110), and injecting and curing the PDMS into a mold ( S120), separating the cured PDMS (S130), depositing a metal film on the PDMS (S140), bonding and processing the silicon substrate on the PDMS (S150), and depositing and patterning aluminum on the silicon substrate ( S160), and etching the silicon substrate using a mask (S170).

Step S110 is a process of patterning the mold, in which the mold is inclined upward and is formed to face the center at a predetermined distance. That is, this is to pattern the shape of the inclined bottom electrode in consideration of the inclination and the final height of the inclined bottom electrode to be manufactured.

Step S120 serves to cure PDMS by injecting the mold into the mold, and injects PDMS in a liquid state into the mold patterned in step S110, and hardens when a predetermined time elapses at a predetermined temperature or more.

Step S130 is a process of separating the cured PDMS from the patterned mold to form a sloped bottom electrode to be used in the micromirror as a step of separating the cured PDMS.

Step S140 is a step of depositing a metal film on the PDMS, which is a process of depositing a metal film to be used as an addressing line, that is, an electrode for applying a voltage to an inclined bottom electrode formed of the PDMS when driven by a micromirror. To this end, depositing a metal film using a shadow mask on the surface of the injected PDMS may pattern the metal film only on a desired portion. For example, a nickel film or aluminum may be used as the metal film.

Step S150 serves to bond the silicon substrate on the PDMS. This is a step of combining and processing the silicon substrate 200 for forming the electrostatic power according to the voltage difference with the PDMS at a position spaced above the PDMS 100, through which the drive space of the micromirror is formed. This step S150 may be divided into the following detailed processes. First, a silicon substrate is processed by an anisotropic etching process according to a predetermined interval between the mirror plate of the micromirror and the inclined bottom electrode of the micromirror to be manufactured, and the PDMS and wafer bonding process in which the bottom electrode inclined the processed silicon substrate is formed. By the process of bonding by, the silicon substrate can be divided into the process of thinly processed according to the thickness of the predetermined micromirror, the process of thinning the silicon substrate can be made by the CMP process.

Step S160 serves to deposit and pattern aluminum on the silicon substrate, and pattern the aluminum to match the shape of the micromirror to be manufactured.

Step S170 serves to etch the silicon substrate using a mask. This is a process of etching a silicon substrate in the shape of a micromirror to be manufactured using aluminum patterned in step S160 as a mask. After the etching process is completed, a micromirror having a final inclined bottom electrode is completed.

6 is a schematic diagram of a micromirror fabricated by a micromirror fabrication method having an inclined bottom electrode using a PDMS according to an embodiment of the present invention. As shown in FIG. 6, a micromirror having an inclined bottom electrode according to an embodiment of the present invention may be formed in a form in which the mirror plate and the support structure of the micromirror are formed, and the mirror plate and the inclined form. The formed bottom electrode and the addressing line are formed including the PDMS 100, and the PDMS 100 and the silicon substrate 200 are combined by a wafer bonding process to form a micromirror.

The mirror plate formed on the silicon substrate 200 has a shape surrounding the outside of the inner mirror plate 210 and the inner mirror plate driven based on one drive shaft, and has a drive shaft perpendicular to the drive shaft of the inner mirror plate. It includes an outer frame 220 having. This mirror plate is composed of an inner mirror plate 210 and an outer frame 220 having a drive shaft in a direction perpendicular to the mirror plate, and each is driven by an inclined bottom electrode corresponding to the drive shaft. It becomes possible.

The bottom electrode formed by the PDMS 100 may be divided into a first electrode for driving the inner mirror plate 210 and a second electrode for driving the outer frame 220, each bottom electrode being an inner mirror plate. And to form an inclined bottom electrode independently of the position of the outer frame. By replacing the shape of the bottom electrode with the inclined structure instead of the conventional flat plate, the driving voltage is reduced, and the distance from the bottom electrode can be increased without increasing the driving voltage, thereby greatly increasing the range of controllable driving angles. It can have the effect.

The first electrode of the bottom electrode is for forming the inclined bottom electrode with the inner mirror plate 210, and may be configured in a conical shape to form the inclined bottom electrode with the inner mirror plate 210. The electrode may be configured in a wedge type to form the outer frame 220 and the inclined bottom electrode. The second electrode, which is the bottom electrode for driving the outer frame, and the first electrode, which is the bottom electrode for driving the inner mirror plate, are independently separated to enable two-axis driving. At this time, the slope and final height of the inclined bottom electrode is determined by the width of the patterned mold and the distance between the electrodes in the process of first patterning the mold to cure the PDMS. I can make it.

FIG. 7 is a view illustrating a rotation angle d of a micromirror according to a voltage applied to a micromirror having an inclined bottom electrode and a micromirror having a conventional flat bottom electrode according to an embodiment of the present invention. As shown in FIG. 7, the micromirrors having the inclined bottom electrode and the micromirror having the flat bottom electrode are applied to each micromirror according to Equations 1 to 4 described above. The rotation angle according to the voltage can be calculated. 7 (a) represents a conventional flat electrode in which the bottom electrode is made parallel to the mirror plate, 7 (b) is a micromirror having an inclined bottom electrode, and 7 (c) is an area of the inclined bottom electrode is micro The case where it is formed small compared with a mirror plate is shown, respectively. As shown in 7 (b) and 7 (c), the inclined bottom electrode has the effect of reducing the effective distance between the micromirror plate and the bottom electrode, thereby increasing the electrostatic power for the same applied voltage. Therefore, by inclining the bottom electrode, the applied voltage is changed to the electrostatic power more efficiently than the flat electrode. As can be seen from the calculation result shown in FIG. 7, the driving voltage of the micromirror is greatly reduced in the case of 7 (b) compared to the case of 7 (a). That is, the voltage and pull-in voltage for moving the same angle are reduced. As a result, when the inclined bottom electrode is used, the driving voltage is higher than that of the micromirror using the flat electrode even though the distance between the micromirror plate and the PDMS is increased. You can design smaller or equal, which means that you can increase the range of controllable angle of rotation. In addition, the above equations (1) through (4) maintain the same driving voltage while increasing the strength of the spring, thereby reducing the adhesion phenomenon and producing a more robust micromirror in an external environment such as shock or vibration. You can check it. In addition, it can be seen from FIG. 7 that if the area of the bottom electrode is designed to be smaller than that of the micromirror plate as in the structure of 7 (c), it has a larger driving angle control range when the distance between the micromirror plate and the PDMS is the same. have. That is, there is an advantage that the pull-in critical angle can be largely increased for the same initial interval, so that it can be used for applications requiring a larger control driving angle range. In addition, by forming the bottom electrode in a conical shape, it serves as an inclined bottom electrode and at the same time has an effect that the adhesion phenomenon can be prevented from occurring when the micromirror plate touches the floor at any rotation angle.

The present invention described above may be variously modified or applied by those skilled in the art, and the scope of the technical idea according to the present invention should be defined by the following claims.

1 is a schematic diagram for calculating torque by constant power of a bidirectional drive micromirror using constant power;

2 is a view illustrating a rotation angle of a micromirror according to an applied voltage.

3 and 4 are steps showing a micromirror manufacturing method having a slanted bottom electrode using a PDMS according to an embodiment of the present invention.

5 is a flow chart of a method for fabricating a micromirror having an inclined bottom electrode using a PDMS according to an embodiment of the present invention.

6 is a schematic view of a micromirror fabricated by a micromirror fabrication method having an inclined bottom electrode using PDMS according to an embodiment of the present invention.

7 is a view illustrating a rotation angle of a micromirror according to a voltage applied to a micromirror having an inclined bottom electrode and a micromirror having a conventional flat bottom electrode according to an embodiment of the present invention.

<Explanation of symbols for main parts of the drawings>

10: mold

100: PDMS

110: metal film

120: mask

200: silicon substrate

205: aluminum

210: internal mirror plate

220: outer frame

Claims (3)

In the micromirror manufacturing method, (1) patterning a mold such that the inclined bottom electrode is inclined upward in a triangular shape, and the center of the inclined upward electrode is disposed to face each other at a predetermined distance; (2) curing by injecting a poly dimethyl siloxane stamp (PDMS) into the patterned mold; (3) separating the cured PDMS from the patterned mold to form an inclined bottom electrode; (4) depositing a metal film on the surface of the PDMS to apply a voltage to the inclined bottom electrode formed by the PDMS; (5) bonding and processing a silicon substrate at a position spaced above the PDMS to form a constant power according to a voltage difference with an inclined bottom electrode formed by the PDMS; (6) depositing and patterning aluminum on the processed silicon substrate; And (7) etching the silicon substrate using the patterned aluminum as a mask, the method of manufacturing a micromirror having an inclined bottom electrode using PDMS. The method (1) according to claim 1, wherein the step (1) of inclining the upper side and patterning the mold so that the central part is disposed to face each other at a predetermined distance, A method of fabricating a micromirror having inclined bottom electrodes using PDMS, characterized in that the mold is patterned so as to match the inclination and height of the inclined bottom electrode to be manufactured. The method of claim 1, wherein the step (5) of combining and processing the silicon substrate for forming a constant power according to the voltage difference with the PDMS at positions spaced above the PDMS, Processing the silicon substrate by an anisotropic etching process at a predetermined interval between a micromirror plate and the inclined bottom electrode; Bonding the processed silicon substrate to the PDMS by a wafer bonding process; And And fabricating the silicon substrate to a predetermined thickness of the micromirror.

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