KR20230128971A - Optical Scanner Design Method and Optical Scanner Spring - Google Patents

Abstract

In a constant power optical scanner using a comb electrode, the discharge problem caused by the narrowing of the gap between the combs is one of the most serious problems. Therefore, the frequencies of resonance modes other than the torsional direction of the mirror, which is the driving direction, must be as high as possible. You should be most careful when
The present invention relates to a spring structure for improving driving stability of a MEMS mirror, and proposes a spring structure for raising a yaw resonance frequency above a certain value, and a phase optimization technique may be introduced as a design method for this purpose.

Description

Optical scanner design method and optical scanner spring {Optical Scanner Design Method and Optical Scanner Spring}

The present invention relates to an optical scanner device, and more particularly, to an optical scanner capable of being driven more stably by designing resonant frequencies other than the driving shaft rotation direction to meet specific requirements or to be sufficiently high. The present invention relates to an optimization design method and an improved structure by exemplifying a spring, which is one of the main components of an optical scanner, in order to implement such an optical scanner.

The optical scanner device 100 as shown in FIG. 1 is a device manufactured using MEMS (MicroElectroMechanical Systems) technology and is in charge of an engine function for scanning a laser beam, and is a small display for lidar sensor or augmented reality. It is a key part used in devices, etc.

The optical scanner device 100 shown in FIG. 1 is composed of a driving body 110, which is a moving part according to the application of a driving voltage, and a stationary body 120 that is fixed without moving. It is connected to the anchor 121 of the fixture 120 through a torsional spring 130. A mirror 111 for reflecting light is formed in the drive body 110, and a drive electrode 142 having a plurality of comb shapes is connected to the wing 115. A plurality of stationary electrodes 141 are formed on the stationary body 120 and are disposed in parallel with the plurality of driving electrodes 142 to form the mirror driving unit 140 . When a driving voltage is applied between the driving electrode 142 and the stationary electrode 141, torque is generated due to static electricity, and the rotational force generated by this torque restores the rotational inertia of the mirror 111 and the spring 130. In the process of achieving dynamic balance with the moment, the mirror 111 formed on the driving body 110 rotates around the driving shaft (x-axis). And looking at the vertical cross-sectional structure of the fixture 120, the upper substrate 125 and the lower substrate 127, and the oxide film insulator 126 for electrical separation between the upper substrate 125 and the lower substrate 127 It may be formed between the upper substrate 125 and the lower substrate 127 . The driving body 110 and the stationary body 120 can be mass-produced by manufacturing each of the silicon-on-insulator (SOI) wafer and the substrate in an integrated structure using microfabrication.

On the other hand, since the resonance-based MEMS optical scanner is driven according to the torsional resonance frequency, it has the advantage of obtaining a large driving angle even with a small input energy. However, when excessive external vibration acts on the electrostatic power optical scanner or when a large voltage is applied between the driving electrode and the fixed electrode formed in a comb structure, the discharge that may occur as the distance between the combs narrows harms the stability of the optical scanner. one of the serious problems. Therefore, it is desirable to design the frequency of other resonance modes as high as possible except for the rotational direction (α) of the mirror, which is the torsional direction. In particular, the vibration mode in the yawing (γ) or spring longitudinal direction (x) Since the movement occurs in a direction in which the gap between the electrodes is narrowed, the possibility of discharge may increase. Since a typical MEMS optical scanner has a resonant frequency in the yaw direction (γ) lower than a resonant frequency in the spring longitudinal direction (x), it is more effective to improve stability by increasing the resonant frequency in the yaw direction (γ).

In order to improve the stability of the optical scanner, the spring structure developed to date as a prior art is as follows. A common structure used for an optical scanner shows the simplest form in an I-shape as shown in FIG.

On the other hand, in the representative diagram of US Patent Publication US 6,795,225 B2 (2004.09.21) (Patent Document 1), the spring is in a V-shape, which is desired by increasing the rotational stiffness in the yaw direction (N3 direction) of the mirror. The goal is to reduce the behavior of the undesirable mirror. 9 of Patent Document 1 exemplifies springs of various structures in which the V-shape is deformed.

In addition, US Patent Publication US 2005/0205514 A1 (2005.09.22) (Patent Document 2) and US Registered Patent Publication US 7,098,571 B2 (2006.08.29) (Patent Document 3), the same as FIG. 9C of Patent Document 1 It can be seen that the V-shaped spring of the structure is used.

In addition, referring to FIG. 2 of Non-Patent Document 1, A rotational comb-driven micromirror with a large deflection angle and low drive voltage, Presented at IEEE 15 ^th MEMS Conference, Las Vegas, NV, USA, 2002, FIG. 9C of Patent Document 1 The same V-shaped spring structure was used in the MEMS optical scanner structure.

As described above, the conventional method for designing the MEMS optical scanner is based on a parametric study based on an analysis model or an intuitive mechanism for the characteristics of the MEMS optical scanner. Therefore, while the existing design result has an intuitive shape that can be predicted, the performance of the device can be maximized by designing an innovative shape that transcends engineering intuition by designing with the topology optimization technique.

Although the spring structure of the conventional optical scanner as described above can achieve the purpose of improving the stability of the optical scanner to a certain extent, it is still not the best performance, so it is necessary to further improve the stability through an optimized design. Referring to the optical scanner structure of FIG. 1 , a mirror and a spring may be manufactured by etching an upper silicon substrate having a constant thickness. Here, the shape of the spring can be determined by distributing the spring materials according to the position on the plane, and this shape determines the structure and characteristics of the spring. In this way, a technique that can maximize specific performance in the process of designing a planar shape is called topological optimization. Topological optimization can improve structural performance by deriving innovative shapes through efficient material distribution. It is a design method that has

Prior art related to such phase optimization is as follows.

In US Patent Publication US 10,824, 780 B2 (2020.11.03) (Patent Document 4), a phase optimization method was applied to a hinge design, which is different from maximizing a resonance frequency.

In Non-Patent Document 2, Optimal design of robust piezoelectric unimorph microgrippers, Applied Mathematical Modeling 55, 2018, a phase optimization technique was applied to reduce unwanted vertical motion while increasing the driving distance of a plane in a MEMS gripper. . Since the MEMS gripper of Non-Patent Document 2 obtains a driving force using the upper and lower piezoelectric layers, it has little to do with the driving direction and application of the electrostatic power optical scanner.

US Patent Publication US 6,795,225 B2 (2004.09.21) US Patent Publication US 2005/0205514 A1 (2005.09.22) US Patent Publication US 7,098,571 B2 (2006.08.29) US Patent Publication US 10,824, 780 B2 (2020.11.03)

A rotational comb-driven micromirror with a large deflection angle and low drive voltage, Presented at IEEE 15th MEMS Conference, Las Vegas, NV, USA, 2002 Optimal design of robust piezoelectric unimorph microgrippers, Applied Mathematical Modeling 55, 2018

An object of the present invention is to propose an optical scanner design method applying a phase optimization method to improve the stability of MEMS optical scanner operation, and to provide a spring structure of an optical scanner designed by the proposed design method. Specifically, an object of the MEMS optical scanner is to increase the stiffness of the yaw direction to increase the corresponding resonant frequency, thereby minimizing the influence of disturbance.

In the present invention, for stable driving of the optical scanner device, a phase design method is proposed in which the objective function is to maximize the resonant frequencies other than the rotational direction of the driving shaft. The design object is a planar structure of a spring connected to a mirror, and the focus is particularly on increasing the resonant frequency of the yaw mode. In addition, the condition that the minimum line width of the designed spring structure should be greater than the size that can be manufactured by the MEMS manufacturing process is reflected in the optimization process.

Specifically, a method for designing an optical scanner according to an embodiment of the present invention includes setting an optimization reference model; defining an optimization problem; setting an initial optimization model; deriving an optimization virtual model by performing an optimization calculation; and determining a producible optimized final model through post-processing of the virtual model.

In the step of defining the optimization problem, maximization of the yaw resonance frequency of the optical scanner may be set as an objective function of optimization. In addition, a condition for limiting the rotational direction resonance frequency of the optical scanner mirror within a specific error range of a set value may be added.

In addition, in the step of defining the optimization problem, a condition for setting the resonance frequency in the longitudinal direction or in the lateral direction to a reference value or higher may be added, and a condition for limiting the maximum stress to be less than a specific value at a driving angle set as a standard may be added. can be added

In addition, in the step of defining the optimization problem, a condition for limiting the volume ratio of the optimized model to the optimization standard model within a specific value range may be added. The volume ratio may be limited within the range of 0.4 to 0.6.

Further, in the post-processing process for the virtual model, the structure may be maintained if the density variable of phase optimization is greater than or equal to a specific threshold value, and the structure may be changed to non-structure if the density variable is less than or equal to a specific threshold value.

In the post-processing of the virtual model, a rounding structure may be added to a region where maximum stress may occur.

In addition, in the post-processing process for the virtual model, the set value of the density variable of the phase optimization is limited within the range of 0.4 to 0.6, but the line width of the final model optimized can be limited to be larger than the minimum line width that can be made in the MEMS process.

The spring of the optical scanner according to another embodiment of the present invention is a spring 130 of the optical scanner that connects a mirror 111 that reflects light while rotating by a driving voltage and an anchor 121 that is fixed without moving. As a, a V-shaped first end region (S1) connected to the mirror 111 and diverging toward the mirror 111; a V-shaped second end region S2 connected to the anchor 121 and diverging toward the anchor 121; It is located between the first end region S1 and the second end region S2 and is connected to the first end region S1 and the second end region S2, and the mirror 111 and the anchor ( 121), an I-shaped connection portion S3 extending in a direction toward the direction.

In addition, the first end region S1 may include a pair of first branch portions 131 diverging toward the mirror 111 and diverging from each other.

In addition, a first cavity C1 that is an empty space may be formed between the pair of first branch parts 131 and the mirror 111 .

In addition, the second end region S2 may include a pair of second branch portions 132 diverging toward the anchor 121 and diverging from each other.

In addition, a second cavity C2 that is an empty space may be formed between the pair of second branch parts 132 and the anchor 121 .

In addition, a pair of straight parts 134 extending from each of the pair of second branch parts 132 toward the anchor 121 with a small inclination angle may be included.

In addition, an X-shaped internal reinforcement part 130a may be included in a region surrounded by the pair of second branch parts 132 , the pair of straight parts 134 , and the anchor 121 .

Also, the internal reinforcing part 130a may be formed between the second cavity C2 and the anchor 121 .

In addition, a third cavity C3 that is an empty space may be formed between the internal reinforcement part 130a and the anchor 121 .

The phase optimization design method for the spring of the MEMS optical scanner proposed in the present invention enables the stable operation of the scanner, thereby maximizing overall performance. In addition, the optimized spring structure can be derived as a structure that can be manufactured with a semiconductor process, and at the same time, since the frequency of an unwanted resonance mode can be maximized, a very practical spring structure can be obtained. That is, compared to I or V-shaped spring structures of optical scanners, it is possible to keep a small stress state while keeping unnecessary (spurious) vibration modes such as yawing as far away as possible from the torsion mode of the spring, which is the rotation direction of the mirror, A stable optical scanner can be designed effectively.

1 shows a typical structure of a MEMS optical scanner in plane and cross section.
2 shows a simplified optimization reference model for finite element analysis of an optical scanner.
3 shows the resonant frequency and mode shape of the optical scanner optimization reference model.
4 shows a form in which electrodes are narrowed in a resonance mode of an optical scanner optimization reference model.
5 shows an initial model for optimizing the phase of a spring for an optical scanner.
FIG. 6 shows five stages of designing phase optimization of an optical scanner, including a reference model, definition of an optimization problem, an initial model, a virtual model after optimization, and a final optimized model with post-processing.
7 shows the structure of a final model that can be produced by performing an optimization design for a spring of an optical scanner.
8 is a comparison of resonant frequencies and mode shapes in an initial model of an optical scanner and an optimized final model.
FIG. 9 compares the maximum stress generated in the initial model and the final optimized model of the spring for the optical scanner.
10 shows a spring structure extracted by reflecting the optimization result of the optical scanner.

Referring to the drawings, a design method of an optical scanner according to the present invention and a derived spring structure will be described in detail. Specific structural or functional descriptions presented in the embodiments of the present invention are merely exemplified for the purpose of explaining embodiments according to the concept of the present invention, and embodiments according to the concept of the present invention may be implemented in various forms. In addition, it should not be construed as being limited to the embodiments described in this specification, and should be understood to include all modifications, equivalents, or substitutes included in the spirit and scope of the present invention.

In general, when a MEMS optical scanning lidar is loaded onto a vehicle such as a car or a drone, it is subjected to continuous disturbance, and in the case of an electrostatic power scanner, the gap between the comb electrodes narrows, resulting in damage due to discharge or shock. It can be. There are yaw (γ) and deformation in the x-axis direction as the types of behavior in which the gap between the combs narrows, but more attention should be paid because the resonant frequency of yaw is generally lower than the vibration of the spring in the axial direction (x). In the present invention, the influence of disturbance is minimized by increasing the stiffness of the MEMS optical scanner in the yaw direction to increase the resonance frequency.

That is, the present invention relates to a spring structure for improving the driving stability of a MEMS mirror, and introduces a topology optimization technique as a design method for raising the resonant frequency for the yaw mode to a certain value or more, and as a result We propose a spring structure of the optical scanner. To explain this in more detail, among the deformations in the in-plane direction of the electrostatic power optical scanner using the comb electrode, the resonance frequency in the yaw and spring longitudinal directions is raised to the maximum, thereby securing stiffness against disturbances that induce deformation in the corresponding direction can do. Naturally, the optical scanner must be designed to coincide with a target driving frequency within a certain error range with respect to the rotational direction around the driving axis of the mirror (x-axis in FIG. 1).

A detailed description of this is as follows. When a phase-optimized design is applied to a spring for an optical scanner, the resonance frequency of the yaw mode can be increased to maximize stiffness in that direction, and bending in the vertical direction (z) showing relatively low frequency characteristics. ) mode, it is desirable to design so that the resonant frequency is not lower than that of the reference model. Here, the resonant frequency (f ) in the direction of rotation around the drive shaft (x-axis) is proportional to ( k _t /J) ^1/2 when the rotational moment of inertia of the mirror is J and the torsional stiffness of the spring is k _t is determined by Therefore, considering that J and driving frequency (f) are generally determined in advance according to the user's requirements, the optimal design can be limited to the spring structure to have a predetermined k _t value.

In addition, the minimum line width of the spring structure determined as the final optimized model must be designed to be larger than the line width that can be manufactured in the MEMS manufacturing process, and when twisting occurs in the spring as much as the driving angle set in the required standard, the resulting maximum stress is crystalline silicon ( crystalline silicon) can additionally reflect the condition that the tolerance should not be exceeded. In this way, using the phase optimization design for the spring structure, it is possible to design a stable optical scanner against disturbance and high voltage.

A method for optimizing a phase of an optical scanner according to an embodiment of the present invention includes the steps of 1) setting an optimization reference model; 2) defining an optimization problem; 3) setting an initial optimization model; 4) deriving a virtual model by performing optimization; 5) determining a producible final optimized model through post-processing;

First, as a first step, a step of setting an optimization reference model will be described.

In the MEMS optical scanner, when a voltage is applied between the fixed electrode and the driving electrode, a torsion occurs in the spring due to electrostatic force and the mirror rotates. In order to analyze this behavior, an optimization reference model, which is a simplified finite element model for the MEMS optical scanner shown in FIG. 1, is shown in FIG. 2. Mirrors and comb electrodes in which displacement does not occur in the optimization standard model can be excluded from the analysis domain. In addition, the electrostatic force generated in the comb electrode can be replaced with forced displacement based on the rotation axis (x-axis in FIG. 1). Therefore, the optimization reference model of FIG. 2 is a silicon shell structure with a certain thickness (70 μm in the example of the present invention) connected by two springs on both sides of the mirror, and the reflective metal on the mirror surface is very thin, about 0.3 μm. may not be taken into account.

Next, the step of defining the optimization problem as the second step will be described.

FIG. 3 shows an analysis result for the resonance mode of the optical scanner optimization reference model shown in FIG. 2 . 3(a) is a resonant mode corresponding to torsional deformation (torsional, n=1), which is an operating mode of the MEMS optical scanner, and FIGS. 3(b) and 3(c) show symmetrical (n=2) and asymmetrical ( It is the bending mode of n = 3). Figures 3 (d), 3 (e) and 3 (f) are deformations in the plane direction, respectively, in the lateral direction (n = 4, lateral transverse, y direction in Fig. 1), yawing (n = 8, yawing, Fig. 1 γ direction) and the resonance mode in the longitudinal direction (n = 19, longitudinal, x direction).

Since deformation in the plane direction as shown in FIGS. 3(d), 3(e), and 3(f) causes a change in the distance between the driving electrode and the fixed electrode, it may cause a failure of the optical scanner, and FIG. 4 is an optimization standard. In the model, specific examples of the change in spacing between electrodes are shown. Among them, in the lateral deformation mode of FIG. 4 (a), there is a concern about the problem because the frequency is not high at n = 4, but the problem can be alleviated by providing sufficient clearance in the longitudinal direction between the electrodes. On the other hand, the deformation in the longitudinal direction of FIG. 4(c) can be ignored because it appears in a very high-order vibration mode (n=19) in a typical optical scanner. However, since the deformation in the yaw direction in FIG. 4(b) causes rotation in the γ direction (see FIG. 1), the problem of reducing the gap between electrodes is serious, and the vibration mode is n = 8, so the resonant frequency is not very high. It is necessary to maximize the resonant frequency by reinforcing the stiffness in the corresponding direction.

In this way, in order to increase the resonant frequency of the yaw mode, the phase optimization of the spring structure can be performed, and the optimization problem can be defined as follows.

Objective function: maximization of f _yaw

Constraint 1: [ K (r) - w _n ² M (r)] Ψ _n = 0

Constraint 2: 0 < r _min ≤ r _i ≤ r _max ≤ 1

Constraint 3: (1-ε _t1 ) f _t1 ≤ f _t2 ≤ (1+ε _t1 ) f _t1

Constraint 4: f _sb2 ≥ f _sb1

Constraint 5: f _ab2 ≥ f _ab1

Constraint 6: V _f > V _f0

Here, f _yaw of the objective function is the resonance frequency for the yaw mode of the optical scanner, K , M , w _n , Ψ _n represents the stiffness matrix, the mass matrix, the nth resonant frequency, and the nth order mode shape, respectively. In constraints 1 and 2, r represents the normalized density between 0 and 1. In constraints 3, 4, and 5, f _t1 , f _sb1 , f _ab1 are the resonant frequencies of the torsional, symmetric bending, and asymmetric bending modes for the reference model, respectively, and f _t2 , f _sb2 , f _ab2 is a comparison value corresponding to f _t1 , f _sb1 , and f _ab1 in the final optimized model. In Constraint 6, V _f means the volume ratio of the reference model and the optimized model of the spring, and V _f0 represents a predetermined value.

In the step of defining the above optimization problem, the objective function is exemplified by maximizing f _yaw to improve stability. Constraint 1 is an expression for obtaining the frequency of each resonance mode, and r in Constraint 2 represents the range of density normalized to a value between 0 and 1. For example, r _min = 0.001 and r _max = 1 can be used. there is. Constraint 3 is a condition to match the optimized resonant frequency to the resonant frequency of the twist mode, which is a set operating condition, within a given error (ε _t1 ) range, and typically 1 to 2% can be applied. Constraints 4 and 5 mean that the performance is prevented from deteriorating by setting the optimized result not to be lower than the resonant frequency for bending of the reference model. Constraint 6 is for the volume ratio (V _f ) of the reference model and the optimization model. As a result of simulation while varying the corresponding variable, if it is less than 0.4, the optimization calculation does not converge well, so V _f0 = 0.4 cannot be used. there is.

Next, the step of setting the initial optimization model as the third step will be described.

FIG. 5 shows an initial model of a spring constructed from the optimization reference model of FIG. 2 in order to apply phase optimization to an optical scanner design. Here, the driving electrode and the mirror only perform functions of electrostatic power driving and laser reflection, and are excluded from the design area because deformation does not occur. On the other hand, since the spring, as a part connecting the mirror and the anchor, has the greatest influence on the vibration characteristics of the optical scanner, it can be included in the design area. On the other hand, in order to secure design flexibility and obtain good optimization results, it is desirable to widen the spring area of the basic model. The distance between the phase optimization design area and the driving electrode may be set to 5um considering that the minimum line width of the MEMS process is 5um.

Next, as the fourth step, a step of deriving a virtual model after performing an optimization calculation will be described.

6 shows the entire phase optimization process step by step, including steps 1, 2, and 3 so far. The optimization problem of Fig. 6(b) is defined based on the reference model of Fig. 6(a), and when phase optimization is performed on the initial optimization model set in Fig. 6(c), the optimization virtual model as shown in Fig. 6(d) is obtained. You can get it. Such a virtual model is difficult to actually manufacture because the density variable r is composed of a continuous distribution between 0 (r _min ) and 1 (r _max ).

As the last step 5, the step of determining the final optimized model that can be produced through post-processing of the virtual model will be described.

In order to be able to manufacture an optimized spring structure with the MEMS process, post-processing is required to change the density variable r to 1 if it is greater than or equal to a specific critical value and to change it to 0 if it is less than or equal to 0 so that there is no structure. For example, when post-processing is performed with a threshold value of 0.5, an optimized final model as shown in FIG. 6(e) can be obtained.

7 shows the spring structure of the optimized final model. In the example in which phase optimization was performed, all line widths came out to be 35 μm or more, and because of this, it can be seen that springs can be manufactured because it is larger than the minimum line width of 5 μm in the MEMS process.

Meanwhile, FIG. 10 shows a spring structure extracted by reflecting the optimization result of the optical scanner. Hereinafter, a structure of a spring of an optical scanner according to an embodiment of the present invention will be described with reference to FIG. 10 .

The spring 130 of the optical scanner according to an embodiment of the present invention connects a mirror 111 that reflects light while rotating by a driving voltage and an anchor 121 that is fixed without moving. The spring 130 of the optical scanner is connected to the mirror 111 and includes a V-shaped first end region S1 diverging toward the mirror 111 . The second end region S2 is connected to the anchor 121 and is formed in a V shape diverging toward the anchor 121 . Between the first end region S1 and the second end region S2, the mirror 111 and the anchor 121 are connected to the first end region S1 and the second end region S2. ) An I-shaped connection portion S3 extending in a direction toward is formed.

The first end region S1 includes a pair of first branch portions 131 diverging toward the mirror 111 and diverging from each other, and the pair of first branch portions 131 and the mirror 111 A first cavity C1, which is an empty space, is formed between ).

The second end region S2 includes a pair of second branch parts 132 diverging toward the anchor 121 and widening from each other, and the pair of second branch parts 132 and the anchor 121 ), a second cavity C2, which is an empty space, is formed between them.

FIG. 7 shows a more specific example of the structure of the optical scanner spring of FIG. 10 . Hereinafter, with reference to FIG. 7, a more detailed structure of the spring structure of the optical scanner according to the second embodiment of the present invention will be described.

A pair of straight parts 134 extending from each of the pair of second branch parts 132 toward the anchor 121 with a small inclination angle are formed.

An X-shaped internal reinforcement part 130a is formed in a region surrounded by the pair of second branch parts 132, the pair of straight parts 134, and the anchor 121, and the internal reinforcement part 130a is formed between the second cavity C2 and the anchor 121 .

An empty third cavity C3 is formed between the internal reinforcing part 130a and the anchor 121 .

Looking closely at the characteristics of the optimally designed spring structure, the X-shaped internal reinforcement part 130a is additionally included. As another example of the optimized spring structure, a fractal structure is reflected, and the X-shaped internal reinforcement A smaller X-shaped structure may be positioned inside the left portion of portion 130a.

FIG. 8 compares vibration modes calculated from the reference model of FIG. 2 and the optimized final model of FIG. 6 (d). (a), (c), (e), and (g) of FIG. 8 show torsion, symmetric bending, asymmetric bending, and yawing modes of the reference model, respectively, and FIG. 8 (b), (d), and (f) , (h) represents the resonant mode of the optimized final model. The torsional resonant frequency error of the two models is within 2%, indicating that the operating mode is well maintained. In addition, since the resonant frequencies of the symmetric and asymmetric bending modes are similar to those of the reference model according to constraints 4 and 5, it can be confirmed that the performance has not changed. In contrast, since the yaw resonance frequency is increased by more than two times compared to the reference model according to the function of the objective function, the stability of the optical scanner is improved without deterioration of other performance.

On the other hand, the maximum stress generated in the optical scanner influences the lifespan. 9 compares the maximum stress calculated for the reference model and the optimized model of the optical scanner. To this end, when forcible displacement is applied to the driving electrode of each MEMS optical scanner at a mechanical scanning angle corresponding to the required standard (the example in the present invention is 7.5 degrees, corresponding to an optical driving angle of 30 degrees), FIG. 9 ( As shown in a) and (b), the stress distribution for the reference model and the final model can be extracted. As shown in Fig. 9(d), the maximum stress of the final model is 1.78 GPa, which is higher than that of the reference model, but is still lower than the yield stress (7 GPa) of crystalline silicon, which is a constituent material of the MEMS optical scanner, and thus has a significant effect on the lifespan. may not give However, in order to lower the maximum stress of the final model than that of the reference model, either add the condition as a limiting condition in the second stage of setting the initial model for optimization, or round the area where the maximum stress occurs in the post-processing of the virtual model. structure can be added.

As above, for the stable operation of the MEMS optical scanner, the spring phase optimization design method and the resulting structural characteristics of the spring were explained. All embodiments of the present invention described so far are based on increasing the resonant frequency of the yaw mode, but when an optical scanner is applied or the disturbance received by a moving object is different, phase optimization can be performed targeting a resonant mode other than yaw. there is. In addition, the embodiment of the present invention has been described limited to the spring structure of the optical scanner, but can be extended to the entire structure including mirrors and electrodes. In addition, in all embodiments, the contents of the invention have been described using a 1-axis optical scanner as an example, but in practice, the invention is not limited thereto and, for example, a 2-axis optical scanner can be used.

The above description is merely illustrative of the technical idea of the present invention, and those skilled in the art will be able to make various modifications, changes, and substitutions without departing from the essential characteristics of the present invention. . Therefore, this embodiment is not intended to limit the technical idea of the present invention, but to explain, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be construed according to the claims below, and all technical ideas within the equivalent range should be construed as being included in the scope of the present invention.

100: optical scanner element
110: driving body
111: mirror
115: wing
120: fixture
121: Anchor
125: upper substrate
126 insulator
127: lower substrate
130: spring
140: mirror driving unit
141: fixed electrode
142: drive electrode
S1: first end region
S2: second end area
S3: Connection
131: first branch
132: second branch
134: straight part
C1: first cavity
C2: second cavity
C3: third cavity
130a: internal reinforcement

Claims (19)

As a design method of an optical scanner,
setting an optimization criterion model;
defining an optimization problem;
setting an initial optimization model;
deriving an optimization virtual model by performing an optimization calculation; and
A method for designing an optical scanner comprising: determining an optimized final model that can be manufactured through post-processing of the virtual model. According to claim 1,
In the step of defining the optimization problem,
An optical scanner design method that sets the maximization of the optical scanner's yaw resonance frequency as the objective function of optimization. According to claim 2,
In the step of defining the optimization problem,
An optical scanner design method that adds a condition limiting the rotational direction resonance frequency of an optical scanner mirror within a specific error range of a set value. According to claim 1,
In the step of defining the optimization problem,
An optical scanner design method that adds a condition to set the longitudinal or lateral resonant frequency above the reference value. According to claim 1
In the step of defining the optimization problem,
An optical scanner design method that adds a condition limiting the maximum stress to be less than a specific value at a drive angle set as a standard. According to claim 1
In the step of defining the optimization problem,
An optical scanner design method of adding a condition limiting the volume ratio of the optimized model to the optimization standard model within a specific value range. According to claim 6,
An optical scanner design method characterized in that the volume ratio is limited to within the range of 0.4 to 0.6. According to claim 1,
In the post-processing process for the virtual model, the optical scanner design method maintains the structure if the density variable of phase optimization is greater than or equal to a specific threshold, and changes it to no structure if less than that. According to claim 8,
An optical scanner design method of adding a rounding structure to a region where maximum stress may occur in a post-processing process for the virtual model. According to claim 1 or 8,
In the post-processing process for the virtual model, the setting value of the density variable of the phase optimization is limited to within the range of 0.4 to 0.6, but the line width of the final optimized model is limited to be greater than the minimum line width that can be made in the MEMS process. How to design a scanner. As a spring 130 of an optical scanner that connects a mirror 111 that reflects light while rotating by a driving voltage and an anchor 121 that is fixed without moving,
a V-shaped first end region S1 connected to the mirror 111 and diverging toward the mirror 111;
a V-shaped second end region S2 connected to the anchor 121 and diverging toward the anchor 121;
It is located between the first end region S1 and the second end region S2 and is connected to the first end region S1 and the second end region S2, and the mirror 111 and the anchor ( 121) and an I-shaped connecting portion S3 extending in a direction toward the optical scanner. According to claim 11,
The first end region (S1) includes a pair of first branch portions (131) diverging from each other while diverging toward the mirror (111). According to claim 12
A spring of an optical scanner in which a first cavity C1, which is an empty space, is formed between the pair of first branch parts 131 and the mirror 111. According to claim 11,
The second end region (S2) includes a pair of second branch portions (132) diverging toward the anchor (121) and diverging from each other. According to claim 14
A spring of an optical scanner in which a second cavity C2, which is an empty space, is formed between the pair of second branch parts 132 and the anchor 121. According to claim 15
A spring of an optical scanner comprising a pair of straight parts 134 extending from each of the pair of second branch parts 132 toward the anchor 121 with a small inclination angle. According to claim 16
A spring of an optical scanner comprising an X-shaped internal reinforcing portion 130a in an area surrounded by the pair of second branch portions 132, the pair of straight portions 134, and the anchor 121. . According to claim 17
The internal reinforcing part (130a) is formed between the second cavity (C2) and the anchor (121), the spring of the optical scanner. According to claim 18
A spring of an optical scanner in which a third cavity C3, which is an empty space, is formed between the internal reinforcing part 130a and the anchor 121.