Wafer-level heterogeneous integrated MEMS circulator and preparation method thereof

Abstract

The invention provides a wafer-level heterogeneous integrated MEMS circulator and a preparation method thereof, and relates to the technical field of MEMS circulators. The method comprises the following steps: etching an opening cavity on the front surface of a first wafer; mounting and fixing the ferrite in the open cavity to obtain a first wafer integrated with the ferrite; the height of the ferrite is greater than the depth of the opening cavity; grinding and polishing the front surface of the first wafer integrated with the ferrite to obtain a ground and polished first wafer; wherein the depth of the opening cavity in the first wafer after grinding and polishing is the same as the height of the ferrite; preparing a circuit layer on the front surface of the second wafer to obtain the second wafer after circuit preparation; and bonding the front surface of the polished first wafer with the front surface of the second wafer after circuit preparation to obtain the MEMS circulator. According to the method, the MEMS circulator can be obtained by adopting wafer-level ferrite integration, wafer grinding and polishing and wafer bonding modes, so that the influence of the size precision of the ferrite on the electrical performance of the MEMS circulator is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of MEMS circulators, and in particular to a wafer-level heterogeneously integrated MEMS circulator and a preparation method thereof. Background Art

[0002] A circulator is a non-reciprocal microwave / RF passive device whose core function is to force electromagnetic wave signals to circulate unidirectionally in a fixed order. The circulator uses ferrite materials (such as YIG yttrium iron garnet) under the action of a strong bias magnetic field to produce a magnetic rotation effect, causing an irreversible phase shift in the direction of electromagnetic wave propagation. For example, in a three-port circulator, the signal is forced to enter port 1 → exit port 2, and then enter port 2 → exit port 3, and the signal is isolated in the reverse direction. A MEMS circulator is a non-reciprocal passive device manufactured based on micro-electromechanical systems (MEMS) technology. It realizes unidirectional circular transmission of microwave signals by integrating a three-dimensional magnetic field control structure with ferrite / magnetic materials.

[0003] The current MEMS circulator fabrication method includes: tape-out of the circuit layer on the upper wafer, tape-out of the cavity and circuit layer on the lower wafer; bonding the upper and lower wafers; dicing the wafers to separate them into individual chips; filling the cavities with ferrite at the chip level; sintering a metal carrier at the chip level to seal the cavities; and bonding a permanent magnet at the chip level to form the final product. Ferrites are typically manufactured using mechanical processing, resulting in poor dimensional consistency. Once the ferrite is placed in the cavity, its surface may be higher or lower than the chip surface due to height inconsistencies. This dimensional variation in the ferrite significantly impacts the electrical performance consistency of the MEMS circulator. Summary of the Invention

[0004] The embodiment of the present invention provides a wafer-level heterogeneously integrated MEMS circulator and a preparation method thereof, so as to solve the problem that the poor dimensional accuracy of ferrite has a significant impact on the electrical performance of the MEMS circulator.

[0005] In a first aspect, an embodiment of the present invention provides a method for preparing a wafer-level heterogeneously integrated MEMS circulator, comprising:

[0006] etching an opening in the front surface of the first wafer;

[0007] Installing and fixing the ferrite in the opening cavity to obtain a first wafer of integrated ferrite; the height of the ferrite is greater than the depth of the opening cavity;

[0008] Grinding and polishing the front surface of the first wafer with integrated ferrite to obtain a ground and polished first wafer; wherein the depth of the opening in the ground and polished first wafer is the same as the height of the ferrite;

[0009] preparing a circuit layer in the second wafer to obtain a second wafer after circuit preparation;

[0010] The front side of the first wafer after grinding and polishing is bonded to the front side of the second wafer after circuit preparation to obtain a MEMS circulator.

[0011] In one possible implementation, the lower longitudinal cross-sections of the opening cavity and the ferrite are both V-shaped with the same angle; the upper width of the opening cavity is greater than the upper width of the ferrite; and the step of installing and fixing the ferrite in the opening cavity to obtain the first wafer with integrated ferrite includes:

[0012] The ferrite in the V-shaped lower portion is mounted and fixed in the V-shaped lower portion of the open cavity toward the open cavity, thereby obtaining a first wafer of integrated ferrite; wherein, after mounting and fixing, a gap is provided between the upper side surface of the ferrite and the upper side wall of the open cavity;

[0013] Accordingly, the step of grinding and polishing the front surface of the first wafer with integrated ferrite to obtain the ground and polished first wafer includes:

[0014] The first wafer with integrated ferrite is loaded between the polishing head and the polishing plate, and the ferrite and the opening cavity are fixed in the vertical direction by the squeezing force between the polishing head and the polishing plate, so that the V-shaped ferrite is positioned in the center of the V-shaped opening cavity;

[0015] The polishing head drives the first wafer and the polishing plate to move relative to each other. The V-shaped side wall of the opening exerts a reaction force on the V-shaped side of the ferrite, fixing the ferrite and the opening in the horizontal direction, and polishing the front side of the first wafer with integrated ferrite.

[0016] In a possible implementation, before the ferrite in the V-shaped lower portion is installed and fixed in the V-shaped lower portion of the open cavity toward the open cavity, the method further includes:

[0017] Filling the open cavity with glue, and then opening the cavity after the glue is filled;

[0018] Accordingly, the step of installing and fixing the ferrite in the V-shaped lower portion toward the open cavity in the V-shaped lower portion of the open cavity to obtain the first wafer with integrated ferrite includes:

[0019] Install the ferrite at the bottom of the V-shape toward the open cavity and into the lower part of the V-shape after filling the open cavity with glue;

[0020] The ferrite and the opening cavity are fixed in a vertical direction by external force extrusion, so that the V-shaped ferrite is positioned at the center of the V-shaped opening cavity; wherein, due to the external force extrusion, the glue is filled in the gap between the upper side surface of the ferrite and the upper side wall of the opening cavity;

[0021] The glue is cured by heating under preset conditions to obtain a first wafer with integrated ferrite.

[0022] In a possible implementation, the step of installing and fixing the ferrite in the V-shaped lower portion facing the open cavity into the V-shaped lower portion of the open cavity to obtain the first wafer with integrated ferrite includes:

[0023] Installing the ferrite at the lower portion of the V-shape into the lower portion of the open cavity with the ferrite facing the open cavity, thereby obtaining a first wafer after ferrite installation;

[0024] After the ferrite is installed, a filling layer is grown on the surface of the first wafer to fill the gap between the upper side surface of the ferrite and the upper side wall of the opening cavity to obtain the first wafer with integrated ferrite.

[0025] In a possible implementation, the step of installing and fixing the ferrite in the V-shaped lower portion facing the open cavity into the V-shaped lower portion of the open cavity to obtain the first wafer with integrated ferrite includes:

[0026] A filling layer is grown on the front side of the first wafer after the opening cavity is prepared; the filling layer covers the sidewalls and bottom of the opening cavity; and the thickness of the filling layer is greater than the width of the gap between the upper side surface of the ferrite and the upper sidewall of the opening cavity;

[0027] Removing the filling layer at the bottom of the open cavity by laser etching;

[0028] The ferrite in the V-shaped lower part is mounted and fixed in the V-shaped lower part of the open cavity toward the open cavity to obtain a first wafer of integrated ferrite; wherein the filling layer fills the gap between the upper side of the ferrite and the upper side wall of the open cavity.

[0029] In a possible implementation, the open cavity and the lower portion of the ferrite have a triangular wedge shape, a triangular pyramid shape, or a conical shape.

[0030] In a possible implementation, after polishing the front surface of the first wafer with integrated ferrite, the method further includes:

[0031] The back side of the first wafer after front side grinding and polishing is ground and polished until the opening cavity and the lower V-shaped structure of the ferrite are removed to obtain the ground and polished first wafer.

[0032] In a possible implementation, the upper sidewall of the opening cavity is vertical, and the lower longitudinal section is V-shaped; the first wafer is a silicon wafer with a (100) crystal orientation; and etching the opening cavity on the front side of the first wafer includes:

[0033] An anisotropic etching method is used to etch a C-shaped opening with a vertical sidewall on the front side of a (100) crystal orientation silicon wafer to obtain an etched silicon wafer;

[0034] growing a protective layer on the front side of the silicon wafer after etching;

[0035] Using laser etching to remove the protective layer at the bottom of the C-shaped opening;

[0036] The protective layer is used as a mask, and the silicon wafer is placed in a potassium hydroxide solution for anisotropic etching to prepare a V-shaped structure at the bottom of the U-shaped opening, thereby preparing an opening on the front side of the first wafer.

[0037] In a possible implementation, the anisotropic etching method includes dry etching, picosecond laser etching, or femtosecond laser etching.

[0038] In a second aspect, an embodiment of the present invention provides a wafer-level heterogeneously integrated MEMS circulator, which is manufactured based on the method for manufacturing a wafer-level heterogeneously integrated MEMS circulator as described in any one of the first aspects.

[0039] An embodiment of the present invention provides a wafer-level heterogeneously integrated MEMS circulator and a method for fabricating the same. The MEMS circulator is obtained by integrating ferrite at the wafer level, polishing the wafer, and bonding the wafers. For a single MEMS circulator on a wafer, the wafer is polished after ferrite integration to ensure that the height of the ferrite is consistent with the wafer bonding surface. The ferrite does not protrude from the bonding surface, thus not affecting the reliability of subsequent wafer bonding. The ferrite is not lower than the wafer bonding surface, and the upper and lower wafers clamp the ferrite to prevent positional drift of the ferrite in the MEMS circulator under high-vibration conditions. For multiple MEMS circulators on a wafer, the depth of the opening etched by the semiconductor processing technique is highly accurate, resulting in a high degree of consistency in the depth of the openings of each circulator. After the ferrite is integrated, the wafer is polished, and the depth of the opening determines the height of the ferrite, resulting in a high degree of consistency in the ferrite height of each circulator. This reduces the size differences between the ferrites, facilitating high consistency in the electrical performance of the MEMS circulator. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a flowchart of a method for fabricating a wafer-level heterogeneously integrated MEMS circulator provided by an embodiment of the present invention;

[0041] Figure 2 This is a schematic diagram of the structure after the cavity is etched and opened according to an embodiment of the present invention;

[0042] Figure 3 is a schematic structural diagram of an integrated ferrite according to an embodiment of the present invention;

[0043] Figure 4 1 is a schematic structural diagram of a first wafer after grinding and polishing provided by an embodiment of the present invention;

[0044] Figure 5 is a schematic structural diagram of a second wafer provided by an embodiment of the present invention;

[0045] Figure 6 is a schematic diagram of the structure after bonding provided by an embodiment of the present invention;

[0046] Figure 7 It is a schematic diagram of the grinding and polishing structure provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0047] To help those skilled in the art better understand this solution, the following will clearly describe the technical solutions in the embodiments of this solution in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of this solution, not all of it. Based on the embodiments of this solution, all other embodiments obtained by those skilled in the art without creative work should fall within the scope of protection of this solution.

[0048] Throughout the specification, claims, and accompanying figures of this solution, the term "including" and any variations thereof mean "including, but not limited to," and are intended to cover non-exclusive inclusions and are not limited to the examples listed herein. Furthermore, the terms "first" and "second," etc., are used to distinguish between different objects, not to describe a specific order.

[0049] The following is a detailed description of the implementation of the present invention with reference to the accompanying drawings:

[0050] Existing MEMS circulator fabrication methods typically involve etching a cavity at the wafer level, dicing it into chip-level wafers, installing ferrite within the cavity, and then sealing the cavity. Variations in ferrite size can significantly impact the MEMS circulator's electrical performance. For example, when the ferrite is too high, it impairs cavity sealing. Alternatively, when the ferrite is too low, the ferrite's position can drift in high-vibration environments. Furthermore, variations in ferrite size between circulators can lead to significant performance variations.

[0051] An embodiment of the present invention provides a wafer-level heterogeneously integrated MEMS circulator and a preparation method thereof. The MEMS circulator is obtained by adopting wafer-level integrated ferrite, wafer polishing and wafer bonding to solve the problem that the ferrite has poor dimensional accuracy and has a significant impact on the electrical performance of the MEMS circulator.

[0052] Figure 1 This is a flowchart of a method for fabricating a wafer-level heterogeneously integrated MEMS circulator according to an embodiment of the present invention. Figure 1 , the preparation method comprises:

[0053] Step 101, etching an opening 11 on the front surface of a first wafer 1;

[0054] It should be noted that step 101 is a wafer-level etching process, that is, etching is performed on the wafer. Using semiconductor processing technology, multiple devices can be processed simultaneously on the wafer. For the sake of convenience, only a certain circulator chip is used as an example for explanation. For example, a plurality of identical openings 11 can be etched on the front of the first wafer 1, and each opening cavities 11 is distributed in a matrix, and each opening cavity 11 corresponds to a circulator. The following steps all have similar correspondences. Furthermore, the semiconductor processing technology in this scheme adopts MEMS processing technology, thereby ultimately obtaining a MEMS circulator.

[0055] For example, the first wafer 1 may be a silicon wafer, for example, a high-resistance silicon wafer or a low-resistance silicon wafer, or for example, a single-sided silicon wafer or a double-sided silicon wafer.

[0056] It should be further noted that the front side of the first wafer 1 is defined relatively. For example, in this embodiment, the bonding surface during wafer bonding is considered the front side. For another example, if it is a single-sided silicon wafer, the smoother polished surface can be considered the front side; if it is a double-sided silicon wafer, either the top or bottom surface can be considered the front side.

[0057] Figure 2 Schematic diagram of the structure after the cavity is etched according to an embodiment of the present invention; Figure 2 The open cavity 11 is a non-enclosed cavity with an opening toward the front surface of the first wafer 1. For example, the open cavity 11 can be prepared using a semiconductor etching process. A typical feature of a semiconductor etching process is that a high-precision etching mask is prepared using a semiconductor photolithography process, and a semiconductor etching process is performed under the shielding of the etching mask. For example, the semiconductor etching process can be dry etching or wet etching. In terms of etching depth control, the processing accuracy of the semiconductor etching process is generally higher than that of mechanical processing.

[0058] In addition, the thickness of the first wafer 1 is generally greater than the thickness of the wafer used in conventional processes. This is because part of the thickness will be removed during the subsequent grinding and polishing steps. The specific thickness of the first wafer 1 is not limited here.

[0059] For example, a circuit layer can be formed on the back of the first wafer, and metalized silicon vias (TSVs) can be formed through the first wafer. The circuit layer on the back of the first wafer can be electrically connected to the circuit layer on the second wafer through the TSVs after a subsequent bonding step.

[0060] Step 102: Mount and fix the ferrite 12 in the opening cavity to obtain a first wafer with the integrated ferrite 12; the height of the ferrite 12 is greater than the depth of the opening cavity;

[0061] Figure 3 is a schematic diagram of the structure of the integrated ferrite provided in an embodiment of the present invention; Figure 3It should be noted that step 102 is wafer-level integration of the ferrites 12 , that is, integrating the ferrites 12 in the respective openings of the first wafer.

[0062] For example, before step 102, a machining process is further included to prepare the ferrite 12 of a target shape. For example, the shape of the ferrite 12 can be a cylinder, a polyhedron or a special-shaped structure.

[0063] Further exemplary, the shape of the ferrite 12 is the same as the shape of the open cavity, so as to facilitate the installation and fixation of the ferrite 12 in the open cavity. Please note that it is not required that the size of the ferrite 12 is the same as the size of the open cavity.

[0064] It should be noted that the ferrite 12 should be installed at the bottom of the opening, that is, the ferrite 12 should be stuffed into the bottom of the opening as much as possible to improve the accuracy of the subsequent grinding and polishing process. It should also be noted that the ferrite 12 should be fixed in the opening to prevent it from falling out of the opening and to fix the relative position of the ferrite and the opening during subsequent processing steps to improve the accuracy of the grinding and polishing process.

[0065] In addition, it should be noted that the height of the ferrite after installation and fixation is greater than the depth of the opening, that is, the ferrite is higher than the front surface of the first wafer, which is also to facilitate the next grinding and polishing process.

[0066] Step 103: grinding and polishing the front surface of the first wafer with the integrated ferrite to obtain a ground and polished first wafer; wherein the depth of the opening in the ground and polished first wafer is the same as the height of the ferrite;

[0067] It should be noted that step 103 is wafer-level grinding and polishing, which may be performed by, for example, a chemical mechanical polishing process.

[0068] Figure 4 is a schematic structural diagram of the first wafer after grinding and polishing provided by an embodiment of the present invention; Figure 4 In the first wafer with integrated ferrite, the ferrite protrudes from the front surface of the wafer. During wafer-level polishing, the protruding ferrite is first polished away, and then the ferrite and wafer front surfaces are polished simultaneously. After polishing the ferrite and wafer front surfaces simultaneously to a certain extent, the depth of the opening and the height of the ferrite are aligned, resulting in the polished first wafer.

[0069] For example, the stopping condition of the polishing may be that the thickness of the first wafer reaches a target thickness.

[0070] It should be noted that polishing at least removes the portion of the ferrite that protrudes from the front surface of the first wafer. For example, the front surface of the first wafer with integrated ferrite is polished to remove the portion of the ferrite that protrudes from the front surface of the first wafer, thereby obtaining a polished first wafer. The depth of the opening in the first wafer after polishing is the same as the height of the ferrite. It should be noted that in order to ensure that the depth of the opening in the first wafer after polishing is the same as the height of the ferrite, the ferrite must be fixed to the opening in step 102.

[0071] Steps 101 to 103 above describe the preparation steps for the first wafer. Step 104 below describes the preparation steps for the second wafer. It should be noted that the first and second wafers are prepared independently of each other, and there is no specific order in which they are prepared. It suffices to complete the preparation of the first and second wafers before bonding in step 105.

[0072] Step 104 , preparing a circuit layer 21 in the second wafer 2 to obtain a second wafer 2 after circuit preparation;

[0073] Figure 5 is a schematic structural diagram of the second wafer provided in an embodiment of the present invention; Figure 5 It should be noted that the circuit layer 21 can be prepared in the second wafer 2 by using semiconductor processing technology. For example, the circuit layer 21 can be prepared by using processes such as metal evaporation, photolithography masking, and circuit etching.

[0074] It should be noted that the circuit layer 21 in the MEMS circulator is used to transmit radio frequency signals. For example, the radio frequency signal at one port of the circuit layer 21 is transmitted to the ferrite, and then transmitted from the ferrite to another port of the circuit layer 21.

[0075] Exemplarily, preparing a circuit layer in the second wafer includes: preparing a circuit layer on the front and back of the second wafer, respectively, and preparing a metallized silicon through-hole via (TSV) penetrating the second wafer to electrically connect the circuit layers on the front and back. Further exemplarily, preparing a circuit layer 21 in the second wafer 2 includes: preparing an interface circuit on the back of the second wafer 2; preparing a coupling circuit on the front of the second wafer 2; preparing a silicon through-hole via (TSV) penetrating the wafer in the second wafer 2, the silicon through-hole via connecting the interface circuit on the back and the coupling circuit on the front. The coupling circuit is used for radio frequency signal transmission between the circuit layer 21 and the ferrite.

[0076] Step 105 , bonding the front surface of the first wafer after grinding and polishing to the front surface of the second wafer 2 after circuit fabrication to obtain a MEMS circulator.

[0077] Figure 6 is a schematic diagram of the structure after bonding provided by an embodiment of the present invention; Figure 6It should be noted that step 105 is wafer-level bonding, that is, bonding between the first wafer and the second wafer. After bonding, the circuit layer of the second wafer inputs and outputs RF signals, and the ferrite of the second wafer realizes unidirectional transmission of RF signals.

[0078] Exemplarily, after wafer-level bonding, the process further includes: dicing the bonded wafer to obtain independent MEMS circulator chips. Further exemplary, the MEMS circulator chips are welded onto a metal carrier.

[0079] It should be noted that, depending on the ferrite material, it may be necessary to set a permanent magnet on the back side of the second wafer after bonding.

[0080] The present invention provides a method for fabricating a wafer-level heterogeneously integrated MEMS circulator, which utilizes wafer-level ferrite integration, wafer polishing, and wafer bonding to obtain a MEMS circulator chip. The chip can then be packaged into a MEMS circulator device.

[0081] On the one hand, for a single MEMS circulator on a wafer, the wafer is polished after the ferrite is integrated to ensure that the height of the ferrite is consistent with the wafer bonding surface; the ferrite does not protrude from the bonding surface and does not affect the reliability of subsequent wafer bonding; the ferrite is not lower than the wafer bonding surface, and the upper and lower wafers clamp the ferrite to prevent the position of the ferrite in the MEMS circulator from drifting in a high-vibration environment.

[0082] Furthermore, for multiple MEMS circulators on a wafer, the depth of the cavity etched using semiconductor processing techniques is highly precise, resulting in consistent depth across all circulators. After integrating the ferrites, the wafer is polished, and the cavity depth determines the ferrite height, ensuring consistent ferrite height across all circulators. This minimizes dimensional variation among the ferrites, minimizing their impact on the MEMS circulator's electrical performance.

[0083] During the actual research and development process, the inventors of the present application discovered that MEMS circulators are prone to fragmentation in high-frequency, high-power application scenarios. It was further discovered that high frequency and high power lead to large self-heating of the MEMS circulator and a large operating temperature difference. In order to fix the ferrite in the open cavity, the cross-sectional dimensions of the ferrite and the open cavity are usually set to the same, for example, both are cylinders with the same diameter. In order to strengthen the fixing strength, an interference fit is even adopted, that is, the outer diameter of the ferrite is slightly larger than the inner diameter of the open cavity. However, the thermal expansion coefficients of the wafer material and the ferrite are quite different. Under conditions with a large operating temperature difference, when the degree of expansion of the ferrite is greater than the degree of expansion of the wafer open cavity, it is easy to cause the wafer material to fragment, and eventually the circulator performance fails.

[0084] The embodiment of the present invention adopts a V-shaped structure and a preset gap method to solve the problem that the MEMS circulator is prone to fragmentation in high-frequency and high-power application scenarios.

[0085] Figure 7 This is a schematic diagram of the grinding and polishing structure provided by an embodiment of the present invention; Figure 7 In a possible implementation, the lower longitudinal sections of the opening cavity and the ferrite are both V-shaped with the same angle; the upper width of the opening cavity is greater than the upper width of the ferrite;

[0086] For example, the direction of the opening of the cavity is used as a reference to define up and down. For example, the direction in which the opening of the cavity faces is up, and the opposite direction is down.

[0087] As a further example, the open cavity and the ferrite are divided into an upper portion and a lower portion. The longitudinal cross-sections of the upper and lower portions are configured to have different shapes. For example, the longitudinal cross-section of the lower portion of the open cavity is V-shaped, and the longitudinal cross-section of the lower portion of the ferrite is also V-shaped, with the two V-shapes having the same angle. For another example, the longitudinal cross-sections of the upper portions of the open cavity and the ferrite are rectangular. For another example, the longitudinal cross-sections of the open cavity and the ferrite are configured to resemble the shape of a sharpened pencil.

[0088] Exemplarily, the shapes of the open cavity and the lower portion of the ferrite include a triangular wedge shape, a triangular pyramid shape, or a cone shape.

[0089] It should be noted that in step 101, when etching the opening cavity on the front side of the first wafer, the shape of the opening cavity defined in the above embodiment can be etched. Before the ferrite is installed and fixed in the opening cavity, the shape of the ferrite defined in the above embodiment can be processed.

[0090] It should be further explained that the upper width of the opening cavity is greater than the upper width of the ferrite. The purpose is to form a gap between the ferrite and the opening cavity, so as to avoid the deformation of the ferrite being greater than the opening cavity and the cracking of the opening cavity in high-frequency and high-power application scenarios. Therefore, the lower part of the opening cavity and the ferrite is set to be V-shaped. One purpose is to position the ferrite in the center of the opening cavity, and the second purpose is to fix the position of the ferrite during the grinding and polishing process to improve the grinding and polishing accuracy. The following are the specific ferrite integration steps and grinding and polishing steps. If the ferrite position is horizontally offset during the subsequent assembly process, it will deviate from the original electrical performance design indicators; if the position of the ferrite on different devices is not uniform, it will also cause poor performance consistency.

[0091] In some embodiments, correspondingly, the step 102 of installing and fixing the ferrite in the open cavity to obtain the first wafer of integrated ferrite includes: installing and fixing the ferrite in the V-shaped lower part facing the open cavity in the V-shaped lower part of the open cavity to obtain the first wafer of integrated ferrite; wherein, after installation and fixing, a gap is provided between the upper side surface of the ferrite and the upper side wall of the open cavity.

[0092] For example, place the ferrite with the open cavity facing upward and the V-shaped lower portion facing downward. Because the open cavity is relatively large and the ferrite is relatively small, the ferrite's own gravity allows it to fall into the cavity and become fixed. Furthermore, because both the ferrite and the lower portion of the open cavity are V-shaped, the ferrite automatically positions itself in the center of the cavity. This describes the integration of the ferrite. The following describes the polishing of the ferrite.

[0093] In some embodiments, correspondingly, step 103 of grinding and polishing the front surface of the first wafer with integrated ferrite to obtain the ground and polished first wafer includes:

[0094] Step 1031: Load the first wafer with integrated ferrite between the polishing head 3 and the polishing plate 4. Use the squeezing force between the polishing head 3 and the polishing plate 4 to fix the ferrite and the opening cavity in the vertical direction, so that the V-shaped ferrite is positioned at the center of the V-shaped opening cavity.

[0095] It should be noted that the polishing head 3 generally faces downward, and the polishing plate 4 generally faces upward. If the ferrite is held in place within the opening by its own weight, a temporary pressure plate can be placed above the first wafer to hold the ferrite in place. The first wafer and the temporary pressure plate are flipped 180° and then attached to the polishing plate 4. The temporary pressure plate is then removed. At this point, the first wafer, holding the ferrite in place, sits upside down on the polishing plate 4, ensuring that the first wafer and ferrite remain fixed in the same orientation.

[0096] For example, the backside of the first wafer is fixed to the polishing head 3. When the compressive force between the polishing head 3 and the polishing plate 4 vertically compresses the ferrite and the open cavity, the V-shaped ferrite is automatically positioned in the center of the V-shaped open cavity. At the same time, a gap exists between the upper portion of the ferrite and the upper portion of the open cavity.

[0097] In step 1032, the polishing head 3 drives the first wafer and the polishing plate 4 to move relative to each other. The V-shaped side wall of the opening exerts a reaction force on the V-shaped side of the ferrite, fixing the ferrite and the opening in the horizontal direction, and polishing the front side of the first wafer with integrated ferrite.

[0098] Exemplarily, the relative movement between the polishing head 3 and the polishing plate 4 is horizontal relative movement. Figure 7To ensure the same polishing rate at every location on the wafer, the polishing head 3 typically does not rotate relative to the polishing plate 4. Instead, the polishing head 3 rotates while simultaneously revolving around the axis of the polishing plate 4. Therefore, within a certain range, the relative motion between the polishing head 3 and the polishing plate 4 can be simplified as horizontal relative movement.

[0099] It should be noted that there is a gap between the upper part of the ferrite and the upper part of the open cavity. When the upper part of the ferrite is subjected to the horizontal force of the polishing disc 4, the upper part will tilt in the direction of the horizontal force. In this solution, the lower part of the ferrite is set to a V shape to provide a lateral support force to offset the above-mentioned horizontal force, which can avoid the ferrite from tilting during the grinding and polishing process. The lateral support force of the lower part of the V-shaped ferrite is also affected by the squeezing force of the polishing head 3. Generally, the downward pressure of the polishing head 3 is large, and the force applied to the V-shaped side wall is large, and the static friction force on the V-shaped side wall is large. Therefore, the lateral support force of the V-shaped open cavity on the ferrite is also large, which can fix the ferrite and the open cavity in the horizontal direction to avoid position displacement.

[0100] The present invention provides a gap between the ferrite and the opening cavity to prevent the ferrite from deforming more than the opening cavity and cracking the opening cavity in high-frequency, high-power applications. Furthermore, by arranging the opening cavity and ferrite in a V-shaped lower portion, the ferrite is positioned in the center of the opening cavity during polishing, providing lateral support and securing the ferrite during polishing, thereby improving the machining accuracy of the ferrite after polishing.

[0101] It should also be noted that if the shape of the opening cavity and the lower portion of the ferrite is a triangular wedge, illustratively, the relative movement direction of the polishing head 3 and the polishing plate 4 is perpendicular to the triangular wedge.

[0102] In the above embodiment, the ferrite is fixed during grinding and polishing by means of the open cavity and the V-shaped structure of the ferrite. The following embodiment provides other auxiliary methods to assist in fixing the ferrite.

[0103] In some embodiments, in step 102, melted paraffin wax may be poured into the opening cavity, and the ferrite may be squeezed and fixed in the opening cavity. After the paraffin wax cools and solidifies, the polishing process of step 103 may be performed. After the polishing process, the paraffin wax may be cleaned and removed.

[0104] In the embodiment of the present invention, paraffin wax is used to temporarily fix the ferrite, which can facilitate fixing the position of the ferrite during the integration and grinding and polishing steps, thereby improving the processing accuracy of the ferrite after grinding and polishing.

[0105] In a possible implementation, before the ferrite in the V-shaped lower portion is installed and fixed in the V-shaped lower portion of the open cavity toward the open cavity, the method further includes:

[0106] Filling the open cavity with glue, and then opening the cavity after the glue is filled;

[0107] Accordingly, the step of installing and fixing the ferrite in the V-shaped lower portion toward the open cavity in the V-shaped lower portion of the open cavity to obtain the first wafer with integrated ferrite includes:

[0108] Install the ferrite at the bottom of the V-shape toward the open cavity and into the lower part of the V-shape after filling the open cavity with glue;

[0109] The ferrite and the opening cavity are fixed in a vertical direction by external force extrusion, so that the V-shaped ferrite is positioned at the center of the V-shaped opening cavity; wherein, due to the external force extrusion, the glue is filled in the gap between the upper side surface of the ferrite and the upper side wall of the opening cavity;

[0110] The glue is cured by heating under preset conditions to obtain a first wafer with integrated ferrite.

[0111] Exemplarily, the hardness of the glue after curing is lower than that of the ferrite and the first wafer. The thermal expansion coefficient of the glue after curing is lower than that of the ferrite and the first wafer. For example, the glue can be epoxy resin.

[0112] By filling the cavity with glue, the present invention facilitates securing the ferrite during assembly and polishing, improving the machining accuracy of the ferrite after polishing. Furthermore, by not removing the glue, the MEMS circulator's vibration resistance is enhanced during subsequent practical applications.

[0113] In a possible implementation, the step of installing and fixing the ferrite in the V-shaped lower portion facing the open cavity into the V-shaped lower portion of the open cavity to obtain the first wafer with integrated ferrite includes:

[0114] Installing the ferrite at the lower portion of the V-shape into the lower portion of the open cavity with the ferrite facing the open cavity, thereby obtaining a first wafer after ferrite installation;

[0115] After the ferrite is installed, a filling layer is grown on the surface of the first wafer to fill the gap between the upper side surface of the ferrite and the upper side wall of the opening cavity to obtain the first wafer with integrated ferrite.

[0116] It should be noted that the filling layer is grown using a semiconductor coating growth method, such as evaporation and sputtering. The characteristic of semiconductor coating growth methods is that they can grow thin films uniformly on all exposed surfaces.

[0117] Exemplarily, the filling layer has a lower hardness than the ferrite and the first wafer. The filling layer has a lower thermal expansion coefficient than the ferrite and the first wafer. For example, the filling layer can be a polyimide film.

[0118] By filling the gap between the ferrite and the cavity with a semiconductor coating after the ferrite is installed, the present invention facilitates securing the ferrite in place during the polishing process, thereby improving the machining accuracy of the polished ferrite. Furthermore, by not removing the filling layer, the vibration resistance of the MEMS circulator can be enhanced in subsequent practical applications.

[0119] In a possible implementation, the step of installing and fixing the ferrite in the V-shaped lower portion facing the open cavity into the V-shaped lower portion of the open cavity to obtain the first wafer with integrated ferrite includes:

[0120] A filling layer is grown on the front side of the first wafer after the opening cavity is prepared; the filling layer covers the sidewalls and bottom of the opening cavity; and the thickness of the filling layer is greater than the width of the gap between the upper side surface of the ferrite and the upper sidewall of the opening cavity;

[0121] Removing the filling layer at the bottom of the open cavity by laser etching;

[0122] The ferrite in the V-shaped lower part is fixed in the V-shaped lower part of the open cavity toward the open cavity to obtain a first wafer of integrated ferrite; wherein the filling layer fills the gap between the upper side of the ferrite and the upper side wall of the open cavity.

[0123] It should be noted that the thickness of the filling layer is greater than the width of the gap between the upper side of the ferrite and the upper sidewall of the opening. Therefore, after the ferrite is inserted into the opening, the filling layer can be squeezed to secure the ferrite. Furthermore, the filling layer has a lower hardness and thermal expansion coefficient than the ferrite and the first wafer, which can also prevent wafer material breakage in subsequent high-frequency, high-power applications.

[0124] By first growing a filler layer, then laser-modifying and removing the filler layer at the bottom of the opening cavity, and then installing the ferrite, this embodiment of the present invention facilitates the positioning of the ferrite during the polishing process, thereby improving the processing accuracy of the ferrite after polishing. Furthermore, by not removing the filler layer, the vibration resistance of the MEMS circulator can be enhanced in subsequent practical applications.

[0125] In a possible implementation, after polishing the front side of the first wafer with integrated ferrite, the method further includes: polishing the back side of the front-polished first wafer until the opening cavity and the lower V-shaped structure of the ferrite are removed to obtain the polished first wafer.

[0126] In the embodiment of the present invention, the V-shaped structure is removed by grinding and polishing the back side of the first wafer, thereby avoiding the influence of the V-shaped structure on the performance of the circulator.

[0127] The following examples illustrate the processing method of the V-shaped opening cavity.

[0128] In a possible implementation, the upper sidewall of the opening cavity is vertical, and the lower longitudinal section is V-shaped; the first wafer is a silicon wafer with a (100) crystal orientation; and etching the opening cavity on the front side of the first wafer includes:

[0129] An anisotropic etching method is used to etch a C-shaped opening with a vertical sidewall on the front side of a (100) crystal orientation silicon wafer to obtain an etched silicon wafer;

[0130] growing a protective layer on the front side of the silicon wafer after etching;

[0131] Using laser etching to remove the protective layer at the bottom of the C-shaped opening;

[0132] The protective layer is used as a mask, and the silicon wafer is placed in a potassium hydroxide solution for anisotropic etching to prepare a V-shaped structure at the bottom of the U-shaped opening, thereby preparing an opening on the front side of the first wafer.

[0133] In some embodiments, the anisotropic etching method includes dry etching, picosecond laser etching, or femtosecond laser etching.

[0134] The embodiment of the present invention utilizes a combination of dry etching and wet etching and prepares a V-shaped structure based on the anisotropic etching characteristics of a silicon wafer, thereby processing an opening cavity with relatively high dimensional accuracy.

[0135] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing a wafer-level heterogeneously integrated MEMS circulator, characterized in that: include: etching an opening in the front surface of the first wafer; Installing and fixing the ferrite in the open cavity to obtain a first wafer with integrated ferrite; The height of the ferrite is greater than the depth of the opening; Grinding and polishing the front surface of the first wafer with integrated ferrite to obtain a ground and polished first wafer; wherein the depth of the opening in the ground and polished first wafer is the same as the height of the ferrite; preparing a circuit layer in the second wafer to obtain a second wafer after circuit preparation; The front side of the first wafer after grinding and polishing is bonded to the front side of the second wafer after circuit preparation to obtain a MEMS circulator.

2. The method for preparing a wafer-level heterogeneously integrated MEMS circulator according to claim 1, wherein: The lower longitudinal cross-sections of the opening cavity and the ferrite are both V-shaped with the same angle; the upper width of the opening cavity is greater than the upper width of the ferrite; and the step of fixing the ferrite in the opening cavity to obtain a first wafer with integrated ferrite includes: The ferrite in the V-shaped lower portion is mounted and fixed in the V-shaped lower portion of the open cavity toward the open cavity, thereby obtaining a first wafer of integrated ferrite; wherein, after mounting and fixing, a gap is provided between the upper side surface of the ferrite and the upper side wall of the open cavity; Accordingly, the step of grinding and polishing the front surface of the first wafer with integrated ferrite to obtain the ground and polished first wafer includes: The first wafer with integrated ferrite is loaded between the polishing head and the polishing plate, and the ferrite and the opening cavity are fixed in the vertical direction by the squeezing force between the polishing head and the polishing plate, so that the V-shaped ferrite is positioned in the center of the V-shaped opening cavity; The polishing head drives the first wafer and the polishing plate to move relative to each other. The V-shaped side wall of the opening exerts a reaction force on the V-shaped side of the ferrite, fixing the ferrite and the opening in the horizontal direction, and polishing the front side of the first wafer with integrated ferrite.

3. The method for preparing a wafer-level heterogeneously integrated MEMS circulator according to claim 2, wherein: Before the ferrite of the V-shaped lower portion is installed and fixed in the V-shaped lower portion of the open cavity toward the open cavity, the method further includes: Filling the open cavity with glue, and then opening the cavity after the glue is filled; Accordingly, the step of installing and fixing the ferrite in the V-shaped lower portion toward the open cavity in the V-shaped lower portion of the open cavity to obtain the first wafer with integrated ferrite includes: Install the ferrite at the bottom of the V-shape toward the open cavity and into the lower part of the V-shape after filling the open cavity with glue; The ferrite and the opening cavity are fixed in a vertical direction by external force extrusion, so that the V-shaped ferrite is positioned at the center of the V-shaped opening cavity; wherein, due to the external force extrusion, the glue is filled in the gap between the upper side surface of the ferrite and the upper side wall of the opening cavity; The glue is cured by heating under preset conditions to obtain a first wafer with integrated ferrite.

4. The method for preparing a wafer-level heterogeneously integrated MEMS circulator according to claim 2, wherein: The step of mounting and fixing the ferrite in the V-shaped lower portion facing the open cavity into the V-shaped lower portion of the open cavity to obtain a first wafer with integrated ferrite includes: Installing the ferrite at the lower portion of the V-shape into the lower portion of the open cavity with the ferrite facing the open cavity, thereby obtaining a first wafer after ferrite installation; After the ferrite is installed, a filling layer is grown on the surface of the first wafer to fill the gap between the upper side surface of the ferrite and the upper side wall of the opening cavity to obtain the first wafer with integrated ferrite.

5. The method for preparing a wafer-level heterogeneously integrated MEMS circulator according to claim 2, wherein: The step of mounting and fixing the ferrite in the V-shaped lower portion facing the open cavity into the V-shaped lower portion of the open cavity to obtain a first wafer with integrated ferrite includes: A filling layer is grown on the front side of the first wafer after the opening cavity is prepared; the filling layer covers the sidewalls and bottom of the opening cavity; and the thickness of the filling layer is greater than the width of the gap between the upper side surface of the ferrite and the upper sidewall of the opening cavity; Removing the filling layer at the bottom of the open cavity by laser etching; The ferrite in the V-shaped lower part is fixed in the V-shaped lower part of the open cavity toward the open cavity to obtain a first wafer of integrated ferrite; wherein the filling layer fills the gap between the upper side of the ferrite and the upper side wall of the open cavity.

6. The method for preparing a wafer-level heterogeneously integrated MEMS circulator according to claim 2, wherein: The open cavity and the lower portion of the ferrite have shapes including a triangular wedge shape, a triangular pyramid shape or a cone shape.

7. The method for preparing a wafer-level heterogeneously integrated MEMS circulator according to claim 2, wherein: After polishing the front surface of the first wafer of the integrated ferrite, the method further comprises: The back side of the first wafer after front side grinding and polishing is ground and polished until the opening cavity and the lower V-shaped structure of the ferrite are removed to obtain the ground and polished first wafer.

8. The method for preparing a wafer-level heterogeneously integrated MEMS circulator according to claim 1, wherein: The upper sidewall of the opening cavity is vertical, and the lower longitudinal section is V-shaped; the first wafer is a silicon wafer with a (100) crystal orientation; the etching opening cavity on the front side of the first wafer includes: An anisotropic etching method is used to etch a C-shaped opening with a vertical sidewall on the front side of a (100) crystal orientation silicon wafer to obtain an etched silicon wafer; growing a protective layer on the front side of the silicon wafer after etching; Using laser etching to remove the protective layer at the bottom of the C-shaped opening; The protective layer is used as a mask, and the silicon wafer is placed in a potassium hydroxide solution for anisotropic etching to prepare a V-shaped structure at the bottom of the U-shaped opening, thereby preparing an opening on the front side of the first wafer.

9. The method for preparing a wafer-level heterogeneously integrated MEMS circulator according to claim 8, wherein: The anisotropic etching method includes dry etching, picosecond laser etching or femtosecond laser etching.

10. A wafer-level heterogeneously integrated MEMS circulator, characterized in that: The device is manufactured based on the method for manufacturing a wafer-level heterogeneously integrated MEMS circulator as claimed in any one of claims 1 to 9.

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