A MEMS micromirror array with a heterogeneous structure

Abstract

The application discloses a MEMS micromirror array with a heterogeneous structure, and aims to solve the problem of electrostatic crosstalk caused by high voltage of edge micromirrors. The micromirror array is divided into a central region and an edge region in a planar layout, the central region adopts micromirrors of a first structure, and the edge region adopts micromirrors of a second structure; the number of comb tooth layers of the micromirrors of the second structure in the vertical direction is more than that of the micromirrors of the first structure. In this way, the driving voltage of the micromirrors in the edge region is reduced, and the problem of electrostatic crosstalk caused by capacitive coupling is improved; meanwhile, the thermal stress caused by dynamic power consumption is reduced, the silicon wafer is prevented from deforming due to thermal stress, and the service life of the micromirror array is prolonged.

Description

Technical Field

[0001] This invention relates to the field of microelectromechanical systems (MEMS) technology, and more specifically to a MEMS micromirror array with a heterogeneous structure. Background Technology

[0002] In large-scale optical cross-connect (OCS) systems based on three-dimensional microelectromechanical systems (3D MEMS), there are typically two opposing micromirror arrays (IMMA and OMMA). To achieve unobstructed optical path switching from any port of the IMMA to any port of the OMMA, each micromirror unit in the array needs to possess a large-angle two-dimensional deflection capability. Due to differences in optical path geometry, micromirrors located in the central region of the IMMA array have smaller optical path differences to reach the micromirrors in the OMMA array, requiring smaller mechanical deflection angles. However, micromirrors located at the edges or corners of the IMMA array require extremely large physical deflection angles to project beams onto the diagonal edges of the OMMA array.

[0003] In existing technologies, the entire micromirror array typically uses a uniform layer of stationary comb teeth and a layer of moving comb teeth to form staggered vertical comb teeth. This "isomorphic design" has shortcomings. In order to make the micromirrors at the edge of the array reach the limit deflection angle, an ultra-high driving voltage, such as 100V-150V or higher, must be applied. The high voltage induces strong capacitive coupling and edge electric field, causing serious electrical crosstalk.

[0004] Therefore, the design of micromirror arrays needs to address the electrostatic crosstalk problem caused by the high voltage of the edge micromirrors. Summary of the Invention

[0005] This invention provides a MEMS micromirror array with a heterogeneous structure to solve the electrostatic crosstalk problem caused by high voltage in edge micromirrors.

[0006] This invention provides a MEMS micromirror array with a heterogeneous structure. The micromirror array is divided into a central region and an edge region in a planar layout. The central region uses micromirrors with a first structure, and the edge region uses micromirrors with a second structure. The micromirrors with the second structure have more comb layers in the vertical direction than the micromirrors with the first structure.

[0007] In a preferred embodiment, the first structure of the micromirror includes two layers of comb teeth, namely a stationary comb tooth layer and a moving comb tooth layer, with the moving comb tooth layer located above the stationary comb tooth layer in the vertical direction; the second structure of the micromirror includes three layers of comb teeth, namely a first stationary comb tooth layer, a moving comb tooth layer and a second stationary comb tooth layer, with the moving comb tooth layer located between the first stationary comb tooth layer and the second stationary comb tooth layer in the vertical direction.

[0008] In a preferred embodiment, the boundary between the edge region and the center region is defined by different operating voltages preset by the system.

[0009] In a preferred embodiment, the driving circuit of the micromirror with the second structure is configured such that when the micromirror is deflected in a specific direction, a voltage is applied to one side of the first stationary comb layer and a voltage is applied to one side of the second stationary comb layer. The sides of the first stationary comb layer and the sides of the second stationary comb layer to which the voltages are applied are diagonally corresponding. The torsional torque of the micromirror is increased by the synergistic electrostatic attraction between the upper and lower diagonals.

[0010] In a preferred embodiment, each micromirror of the second structure applies the same driving voltage to the first stationary comb layer, and applies a corresponding driving voltage to the second stationary comb layer according to the deflection angle that the micromirror of the second structure needs to achieve.

[0011] In a preferred embodiment, the comb tooth distribution density and / or comb tooth size of the second static comb tooth layer of the micromirror with the second structure is greater than the comb tooth distribution density and / or comb tooth size of the first static comb tooth layer.

[0012] In a preferred embodiment, the torsion beam width of the micromirror with the second structure is greater than the torsion beam width of the micromirror with the first structure.

[0013] In a preferred embodiment, the ratio of the number of stationary comb teeth of the micromirror with the second structure to the number of stationary comb teeth of the micromirror with the first structure is not less than 2, thereby reducing the driving voltage of the micromirror with the second structure by more than 30% and lowering the voltage output requirements of the driving circuit.

[0014] In a preferred embodiment, the mirror surface of the micromirror with the second structure is elliptical or polygonal, while the mirror surface of the micromirror with the first structure is circular or rectangular.

[0015] In a preferred embodiment, the micromirrors are any one or a combination of one-dimensional moving micromirrors and two-dimensional moving micromirrors, thereby satisfying different optical cross-interconnections of the micromirror array.

[0016] In a preferred embodiment, a transition region is also included between the central region and the edge region. Along the radial direction from the central region through the transition region to the edge region, the number of comb teeth in the second static comb layer of the micromirror of the second structure gradually increases.

[0017] In a preferred embodiment, the boundaries of the edge region, transition region, and center region are defined by different operating voltages preset by the system.

[0018] This invention proposes a "center-edge heterogeneous" MEMS micromirror array architecture. By deploying different types of micromirror structures in the center and edge regions, the micromirrors in the edge regions with larger corner requirements are optimized from one layer of static comb teeth to two layers of static comb teeth. This allows the same angle that can be achieved with high voltage in isomorphic structures to be achieved with a lower driving voltage, reducing electrical crosstalk within the micromirror array and avoiding the design challenge of the driving chip needing to be compatible with ultra-large voltage output spans from 0 to 200V. This also reduces the electrical control cost of the system. Attached Figure Description

[0019] Figure 1 This is a side view of a MEMS micromirror array based on existing technology;

[0020] Figure 2 This is a front view of a single-layer static comb micromirror in a current MEMS micromirror array.

[0021] Figure 3 This is a side view of a single-layer static comb micromirror in a current MEMS micromirror array.

[0022] Figure 4 This is a side view schematic diagram of a MEMS micromirror array with a heterogeneous structure according to an embodiment of the present invention;

[0023] Figure 5 This is a front view schematic diagram of a single two-layer static comb micromirror in a MEMS micromirror array with a heterogeneous structure according to an embodiment of the present invention.

[0024] Figure 6 This is a side view schematic diagram of a single two-layer static comb micromirror in a MEMS micromirror array with a heterogeneous structure according to an embodiment of the present invention.

[0025] Figure 7 These are the electrostatic torque simulation results of the two-layer static comb micromirror according to an embodiment of the present invention;

[0026] Figure 8 This is a side view schematic diagram of a MEMS micromirror array with a transition region according to an embodiment of the present invention. Detailed Implementation

[0027] The following is in conjunction with the appendix Figure 1 Appendix Figure 2 and attached Figure 3 This paper provides a detailed explanation of existing MEMS micromirror array technologies.

[0028] like Figure 1 The existing MEMS micromirror arrays shown are all composed of Figure 2, Figure 3 The matrix shown consists of a single layer of stationary comb-tooth micromirrors. The micromirror array includes a substrate layer 101, an electrical insulating layer 102, a stationary comb-tooth layer 103, and a moving comb-tooth layer 104. Each micromirror structure includes: the stationary comb-tooth layer 103 includes a stationary comb-tooth frame 1031 and stationary comb teeth 1032, which are connected; the moving comb-tooth layer 104 includes a moving comb-tooth frame 1041, moving comb teeth 1042, a torsion beam 1043, and a reflecting mirror 1044, which connects the reflecting mirror 1044 and the moving comb-tooth frame 1041; and the moving comb teeth 1042 are fixed on both sides of the reflecting mirror 1044. When a positive voltage V0 is applied to the stationary comb tooth 1032 on one side and zero voltage is applied to the moving comb tooth 1042, the moving comb tooth 1042 moves downward under the action of electrostatic force, causing the middle reflecting mirror surface 1044 to rotate, thereby controlling the reflection angle of the incident beam and realizing the switching of the optical transmission path.

[0029] Each micromirror in the entire micromirror array is driven by a uniform driving voltage. In order for the micromirrors at the edge of the array to reach the extreme deflection angle, an ultra-high driving voltage, such as 100V-150V or higher, must be applied, while the micromirrors in the central region can use a lower voltage. Therefore, the driving voltage of the entire micromirror array must be high voltage. As a result, the micromirrors at the edge of the array induce strong capacitive coupling and edge electric field, causing serious electrical crosstalk. In addition, the use of high voltage to drive all the micromirrors in the array leads to a certain waste of high voltage design.

[0030] The following is in conjunction with the appendix Figure 4 Appendix Figure 5 and attached Figure 6 The specific implementation of the MEMS micromirror array with heterogeneous structure provided in the embodiments of the present invention will be described in detail.

[0031] The MEMS micromirror array with heterogeneous structure provided in this embodiment of the invention is divided into a central region and an edge region in a planar layout. The central region adopts a micromirror with a first structure, and the edge region adopts a micromirror with a second structure. The micromirror with the second structure has more comb layers in the vertical direction than the micromirror with the first structure.

[0032] The first type of micromirror includes two layers of comb teeth, namely a stationary comb tooth layer and a moving comb tooth layer, with the moving comb tooth layer located above the stationary comb tooth layer in the vertical direction; the second type of micromirror includes three layers of comb teeth, namely a first stationary comb tooth layer, a moving comb tooth layer and a second stationary comb tooth layer, with the moving comb tooth layer located between the first and second stationary comb tooth layers in the vertical direction.

[0033] The boundaries between the edge region and the center region are defined by different operating voltages preset by the system. The driving circuit of the second type of micromirror is set as follows: when the micromirror is deflected in a specific direction, a voltage is applied to one side of the first stationary comb layer and a voltage is applied to one side of the second stationary comb layer. The sides of the first stationary comb layer and the sides of the second stationary comb layer that are respectively voltaged are diagonally corresponding. Through the synergistic electrostatic attraction between the upper and lower diagonals, the torsional torque of the micromirror is increased.

[0034] In practical implementation, the central region of the micromirror array can employ a micromirror structure consisting of one layer of stationary comb teeth and one layer of moving comb teeth, that is, as shown in the figure. Figure 1 The existing micromirror array technology shown employs a micromirror structure consisting of two layers of stationary comb teeth and one layer of moving comb teeth in the edge region of the micromirror array. The boundary between the central region and the edge region is defined by the maximum safe operating voltage threshold preset by the micromirror array system. Defined, for example, 100V. The driving voltage of a single-layer static comb micromirror corresponding to the required deflection angle of the micromirror is less than... The microscope is drawn into the central region; larger than The microscope is drawn into the edge region.

[0035] like Figure 4 The MEMS micromirror array shown has a heterogeneous structure. The micromirrors in the central region adopt a single-layer stationary comb micromirror structure, while the micromirrors in the edge regions adopt a two-layer stationary comb micromirror structure, including a base layer 101, an electrically insulating layer 102, a first stationary comb layer 103, a moving comb layer 104, and a second stationary comb layer 105. Figure 5 and Figure 6 The specific structure of the MEMS micromirror array shown includes a stationary comb layer 103 comprising a stationary comb frame 1031 and stationary comb teeth 1032, which are connected together; a movable comb layer 104 comprising a movable comb frame 1041, movable comb teeth 1042, a torsion beam 1043, and a reflecting mirror 1044, which connects the reflecting mirror 1044 and the movable comb frame 1041, and the movable comb teeth 1042 are fixed on both sides of the reflecting mirror 1044; and a second stationary comb layer 105 comprising a second stationary comb frame 1051 and a second stationary comb tooth 1052. When a positive voltage V0 is applied to the stationary comb tooth 1032 on one side and the second stationary comb tooth 1052 on the opposite side at the same time, and zero voltage is applied to the moving comb tooth 1042, under the action of electrostatic force, the stationary comb tooth 1032 on one side will attract the moving comb tooth on that side to move downward, and the second stationary comb tooth 1052 on the opposite side will attract the moving comb tooth on that side to move upward, driving the middle reflecting mirror 1044 to rotate, thereby controlling the reflection angle of the incident beam and realizing the switching of the optical transmission path.

[0036] Each micromirror of the second structure applies the same driving voltage to the first stationary comb layer. Depending on the required deflection angle of the micromirror of the second structure, a corresponding driving voltage is applied to the second stationary comb layer. In this way, the driving voltage of the second stationary comb layer can be higher or lower than that of the first stationary comb layer, thereby allowing for flexible distribution of the driving voltage applied to the first and second stationary comb layers according to the total deflection angle required by the micromirror.

[0037] In the second structure of the micromirror, the tooth distribution density and / or tooth size of the second stationary comb layer are greater than those of the first stationary comb layer. This further reduces the total driving voltage. The advantage of this design is that the tooth parameters of the first and second stationary comb layers can be flexibly allocated according to the driving voltage requirements.

[0038] By introducing a double-layered static comb into the micromirror with the second structure, the equivalent driving torque of the system is doubled while maintaining the maximum deflection angle, thus allowing the stiffness coefficient K of the torsion beam to double as well. This is based on the dynamic equation of torsional vibration of the micromirror. The micromirror rotation response time can be derived. The micromirror rotation response time can be observed. With torsional stiffness It is inversely proportional to the square root. Doubled The reduction is approximately 30%. To better support the reduced rotational response time of the micromirror in the second structure, the width of the torsion beam in the second structure is greater than that in the first structure. Specifically, in the above formula... This represents the deflection angle of the microscope. Let be the moment of inertia of the micromirror. The damping coefficient is... The stiffness coefficient of the torsional beam is... This is the electrostatic driving torque of the micromirror.

[0039] One specific implementation of this invention is as follows: the ratio of the number of stationary comb teeth of the micromirror with the second structure to the number of stationary comb teeth of the micromirror with the first structure is not less than 2, thereby reducing the driving voltage of the micromirror with the second structure by more than 30% and lowering the voltage output requirements of the driving circuit.

[0040] The mirrors of the second type of micromirror are elliptical or polygonal, while those of the first type are circular or rectangular. The shape of the incident light spot varies depending on its position within the micromirror array. Typically, the incident light spot will be nearly circular on the mirror surface at the center of the array, and nearly elliptical on the mirror surfaces at the edges. Designing the mirror surfaces of the center and edge regions with different shapes helps to reduce the overall size of the micromirror array.

[0041] The micromirrors in the micromirror array are either one-dimensional or two-dimensional moving micromirrors, thus satisfying different optical cross-interconnections of the micromirror array.

[0042] Figure 7 The diagram shows the electrostatic torque simulation results of a two-layer static comb micromirror and a one-layer static comb micromirror used in an embodiment of the present invention. The upper line represents the electrostatic torque simulation data for the two-layer static comb micromirror, and the lower line represents the electrostatic torque simulation data for the one-layer static comb micromirror. Under the same conditions of thickness, width, and number of comb teeth for the first and second static comb teeth, the electrostatic torque of the two-layer static comb micromirror is twice that of the one-layer static comb micromirror. Based on the electrostatic torque... Corner and driving voltage Calculation formula The driving voltage of the micromirror array is reduced by about 30% when two layers of static comb-tooth micromirrors are used in the edge region. Taking the existing MEMS micromirror array as an example, the central and edge regions all use one layer of static comb-tooth micromirrors. To achieve a rotation angle of ±4° for the micromirrors in the central region, a driving voltage of 100V is required. To achieve a rotation angle of ±6° for the micromirrors in the edge region, a driving voltage of 150V is required. Assuming an electrostatic crosstalk coupling coefficient of 1%, when a voltage of 150V is applied to the edge micromirror A, the crosstalk voltage of the adjacent micromirror B is 1.5V. The torque increase caused by crosstalk is 450°, and the angle increase caused by crosstalk is 0.121°. After adopting a two-layer static comb micromirror structure for the edge region micromirrors, the driving voltage decreased from 150V to 105V. Based on an estimated electrostatic crosstalk coupling coefficient of 1%, applying a 105V voltage to edge micromirror A results in a crosstalk voltage of 1.05V for the adjacent micromirror B. The torque caused by crosstalk increases by 220.5, and the angle caused by crosstalk increases by 0.059°. Thus, adopting a two-layer static comb micromirror structure for the edge region micromirrors can improve the crosstalk voltage and angle changes caused by crosstalk to adjacent micromirrors. Detailed data comparison is shown in Table 1, revealing the evaluation of crosstalk parameters for heterogeneous MEMS micromirror arrays.

[0043]

[0044] The two-layer static comb micromirror structure at the edge of the micromirror array can also be a biaxial micromirror, which better enables the reflective mirror to deflect freely in both the X and Y axes, and is more in line with the current needs of 3D MEMS optical cross-connection.

[0045] Figure 8 The image shows a MEMS micromirror array with a heterogeneous structure and a transition region, according to an embodiment of the present invention. Figure 4In contrast, the micromirror array is divided into a central region, a transition region, and an edge region from the center to the edge. Along the radial direction from the central region through the transition region to the edge region, the number of teeth in the second static comb layer of the second structure of the micromirror gradually increases. Of course, the boundaries of the edge region, the transition region, and the central region are defined by different preset operating voltages of the micromirror array system.

[0046] The MEMS micromirror array with a heterogeneous structure provided in this invention uses a single-layer static comb micromirror in the central region and a two-layer static comb micromirror structure in the edge region. This reduces the driving voltage of the edge region micromirrors and improves the electrostatic crosstalk problem caused by capacitive coupling. Furthermore, reducing the driving voltage of the edge region micromirrors can reduce the thermal stress caused by the dynamic power consumption of the micromirrors. Under ultra-high voltage of 150V, the insulating oxide layer is not a perfect insulator and will generate microampere-level leakage current, which will cause the chip to heat up. With hundreds or thousands of micromirrors working simultaneously in the micromirror array, heat accumulation can cause thermal stress deformation of the silicon wafer, changing the surface shape of the micromirrors. Reducing the thermal stress can effectively reduce the above-mentioned adverse effects and extend the service life of the micromirror array.

[0047] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A MEMS micromirror array, characterized in that: The micromirror array is divided into a central region and an edge region in a planar layout. The central region uses micromirrors with a first structure, and the edge region uses micromirrors with a second structure. The micromirrors with the second structure have more comb layers in the vertical direction than the micromirrors with the first structure.

2. The micromirror array according to claim 1, characterized in that, The first type of micromirror includes two layers of comb teeth, namely a stationary comb tooth layer and a moving comb tooth layer, wherein the moving comb tooth layer is located above the stationary comb tooth layer in the vertical direction; the second type of micromirror includes three layers of comb teeth, namely a first stationary comb tooth layer, a moving comb tooth layer and a second stationary comb tooth layer, wherein the moving comb tooth layer is located between the first stationary comb tooth layer and the second stationary comb tooth layer in the vertical direction.

3. The micromirror array according to claim 1, characterized in that, The boundaries between the edge and center regions are defined by different operating voltages preset by the system.

4. The micromirror array according to claim 2, characterized in that, The driving circuit of the micromirror with the second structure is configured such that when the micromirror is deflected in a specific direction, a voltage is applied to one side of the first stationary comb layer and a voltage is applied to one side of the second stationary comb layer. The sides of the first stationary comb layer and the sides of the second stationary comb layer that are respectively voltaged are diagonally corresponding. The torsional torque of the micromirror is increased by the synergistic electrostatic attraction between the upper and lower diagonals.

5. The micromirror array according to claim 2 or 4, characterized in that, Each micromirror of the second type applies the same driving voltage to the first stationary comb layer, and applies a corresponding driving voltage to the second stationary comb layer according to the deflection angle that the micromirror of the second type needs to achieve.

6. The micromirror array according to claim 2, characterized in that, The comb tooth distribution density and / or comb tooth size of the second static comb tooth layer of the micromirror with the second structure are greater than the comb tooth distribution density and / or comb tooth size of the first static comb tooth layer.

7. The micromirror array according to claim 2, characterized in that, The width of the torsion beam of the micromirror with the second structure is greater than the width of the torsion beam of the micromirror with the first structure.

8. The micromirror array according to claim 2, characterized in that, The ratio of the number of stationary comb teeth of the micromirror with the second structure to the number of stationary comb teeth of the micromirror with the first structure is not less than 2, thereby reducing the driving voltage of the micromirror with the second structure by more than 30% and lowering the voltage output requirements of the driving circuit.

9. The micromirror array according to claim 1 or 2, characterized in that, The mirror surface of the micromirror with the second structure is elliptical or polygonal, while the mirror surface of the micromirror with the first structure is circular or rectangular.

10. The micromirror array according to claim 1, characterized in that, The micromirrors can be any one or a combination of one-dimensional and two-dimensional moving micromirrors, thereby satisfying different optical cross-interconnections of the micromirror array.

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