Wafer-level heterogeneous integrated MEMS circulator and preparation method thereof

Abstract

The application 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 a ferrite in the opening cavity to obtain a first wafer integrated with the ferrite; the height of the ferrite is greater than the depth of the opening cavity; polishing the front surface of the first wafer integrated with the ferrite to obtain a first wafer after polishing; the depth of the opening cavity in the first wafer after polishing is the same as the height of the ferrite; preparing a circuit layer on the front surface of a second wafer to obtain a second wafer after circuit preparation; and bonding the front surface of the first wafer after polishing with the front surface of the second wafer after circuit preparation to obtain a MEMS circulator.The application can obtain a MEMS circulator by adopting wafer-level integration of ferrite, wafer polishing and wafer bonding, so as to reduce the influence of the size precision of the ferrite on the electrical performance of the MEMS circulator.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of MEMS circulator, and particularly relates to a wafer-level heterogeneous integrated MEMS circulator and a preparation method thereof. BACKGROUND

[0002] A circulator is a non-reciprocal microwave / radio frequency passive device, and its core function is to force electromagnetic wave signals to be transmitted in a fixed sequence in one direction. The circulator uses a ferrite material (such as YIG yttrium iron garnet) to produce a magnetic spin effect under the action of a strong bias magnetic field, so that the direction of electromagnetic wave propagation is irreversibly phase-shifted. For example, in a 3-port circulator, the signals are forced to enter port 1 and exit port 2, and enter port 2 and exit port 3, and the signals are reversely isolated. A MEMS circulator is a non-reciprocal passive device manufactured based on a micro-electro-mechanical system (MEMS) process, and the one-way circulation of microwave signals is achieved by integrating a three-dimensional magnetic field control structure and a ferrite / magnetic material.

[0003] The existing preparation method of the MEMS circulator includes: fabricating a circuit layer on an upper wafer by wafer processing, fabricating a cavity and a circuit layer on a lower wafer by wafer processing; bonding the upper wafer and the lower wafer; wafer dicing to divide into independent chips; filling ferrite into the cavity at the chip level; sintering a metal carrier and plugging the cavity at the chip level; and bonding a permanent magnet at the chip level to form a final product. The ferrite is generally manufactured by mechanical processing, and has poor size consistency. After the ferrite is installed in the cavity, the surface of the ferrite is higher or lower than the surface of the chip due to the inconsistency in height. The size difference of the ferrite has a great influence on the electrical performance consistency of the MEMS circulator. SUMMARY

[0004] The embodiments of the present application provide a wafer-level heterogeneous integrated MEMS circulator and a preparation method thereof, to solve the problem of poor size precision of ferrite and great influence on the electrical performance of the MEMS circulator.

[0005] In a first aspect, the embodiments of the present application provide a preparation method of a wafer-level heterogeneous integrated MEMS circulator, comprising:

[0006] etching an open cavity on the front surface of the first wafer;

[0007] installing 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 open cavity;

[0008] polishing the front surface of the first wafer integrated with the ferrite to obtain a first wafer after polishing; wherein the depth of the open cavity in the first wafer after polishing is the same as the height of the ferrite;

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

[0010] Bond the front surface of the first wafer after polishing and grinding with the front surface of the second wafer after circuit preparation to obtain a MEMS circulator.

[0011] In a possible implementation, the lower longitudinal section shape of the open cavity and the ferrite is a V shape with the same angle; the upper width of the open cavity is larger than the upper width of the ferrite; and the mounting and fixing of the ferrite in the lower V-shaped portion of the open cavity to obtain the first wafer integrated with the ferrite comprises the following steps:

[0012] The V-shaped lower ferrite is mounted and fixed in the V-shaped lower portion of the open cavity towards the open cavity to obtain the first wafer integrated with the ferrite; wherein after the 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] Correspondingly, the polishing and grinding of the front surface of the first wafer integrated with the ferrite comprises the following steps:

[0014] The first wafer integrated with the ferrite is loaded between the polishing head and the polishing disc, the ferrite and the open cavity are fixed in the vertical direction by the extrusion force between the polishing head and the polishing disc, and the V-shaped ferrite is positioned at the center of the V-shaped open cavity;

[0015] The polishing head drives the first wafer to move relative to the polishing disc, the V-shaped side wall of the open cavity exerts a reaction force on the V-shaped side surface of the ferrite in the horizontal direction, the ferrite and the open cavity are fixed in the horizontal direction, and the front surface of the first wafer integrated with the ferrite is polished and ground.

[0016] In a possible implementation, before the mounting and fixing of the V-shaped lower ferrite in the V-shaped lower portion of the open cavity towards the open cavity, the following step is further included:

[0017] The open cavity is filled with glue to obtain the open cavity filled with glue;

[0018] Correspondingly, the mounting and fixing of the V-shaped lower ferrite in the V-shaped lower portion of the open cavity towards the open cavity to obtain the first wafer integrated with the ferrite comprises the following steps:

[0019] The V-shaped lower ferrite is mounted in the V-shaped lower portion of the open cavity filled with glue towards the open cavity;

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

[0021] The glue is cured under a preset condition to obtain the first wafer integrated with the ferrite.

[0022] In one possible implementation, the step of mounting and fixing the ferrite at the lower part of the V-shape towards the opening, thereby obtaining a first wafer integrating the ferrite, includes:

[0023] The ferrite at the bottom of the V-shape is installed inside the bottom of the V-shape of the opening, facing the opening, to obtain the first wafer after ferrite installation;

[0024] After the ferrite is mounted, a filling layer is grown on the surface of the first wafer to fill the gap between the upper side of the ferrite and the upper sidewall of the opening, thus obtaining the first wafer with integrated ferrite.

[0025] In one possible implementation, the step of mounting and fixing the ferrite at the lower part of the V-shape towards the opening, thereby obtaining a first wafer integrating the ferrite, includes:

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

[0027] The filling layer at the bottom of the opening is removed by laser etching.

[0028] The ferrite at the lower part of the V-shape is mounted and fixed inside the lower part of the opening, facing the opening, to obtain the first wafer of integrated ferrite; wherein, the filling layer fills the gap between the upper side of the ferrite and the upper sidewall of the opening.

[0029] In one possible implementation, the opening and the lower part of the ferrite have shapes including a triangular wedge, a triangular pyramid, or a cone.

[0030] In one possible implementation, after polishing the front side of the first wafer integrating the ferrite, the method further includes:

[0031] The back side of the first wafer after the front side is polished is polished until the opening and the lower V-shaped structure of the ferrite are removed, thus obtaining the polished first wafer.

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

[0033] Anisotropic etching method is used to etch a U-shaped opening perpendicular to the sidewall on the front side of the (100) crystal orientation silicon wafer to obtain the etched silicon wafer;

[0034] A protective layer is grown on the front side of the silicon wafer after etching;

[0035] The protective layer on the bottom of the V-shaped opening cavity is removed by laser etching;

[0036] The silicon wafer is placed in a potassium hydroxide solution for anisotropic etching with the protective layer as a mask to prepare a V-shaped structure at the bottom of the V-shaped opening cavity, thereby obtaining an opening cavity on the front surface 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 application provides a wafer-level heterogeneous integrated MEMS circulator, which is prepared based on the preparation method of the wafer-level heterogeneous integrated MEMS circulator as described in any of the first aspect.

[0039] An embodiment of the present application provides a wafer-level heterogeneous integrated MEMS circulator and a preparation method thereof. The MEMS circulator is obtained by adopting wafer-level integration of a ferrite, wafer grinding and polishing and wafer bonding. On the one hand, for a single MEMS circulator on a wafer, the wafer is ground and polished after the integration of the ferrite, so as 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 higher than the wafer bonding surface, and the upper and lower wafers clamp and fix the ferrite, so as to avoid the position drift of the ferrite in the MEMS circulator in a high-vibration environment. On the other hand, for a plurality of MEMS circulators on a wafer, the depth of the opening cavity etched by a semiconductor processing technology has high precision, and the depth of the opening cavity of each circulator has good consistency. The wafer is ground and polished after the integration of the ferrite, and the depth of the opening cavity determines the height of the ferrite, so that the height of the ferrite of each circulator has good consistency. Thus, the size difference of each ferrite is reduced, which is conducive to achieving high consistency of the electrical performance of the MEMS circulator. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 is an implementation flowchart of the preparation method of the wafer-level heterogeneous integrated MEMS circulator provided by an embodiment of the present application;

[0041] Figure 2 is a structural schematic diagram after etching of the opening cavity provided by an embodiment of the present application;

[0042] Figure 3 is a structural schematic diagram after integration of the ferrite provided by an embodiment of the present application;

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

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

[0045] Figure 6 This is a schematic diagram of the bonded structure provided in an embodiment of the present invention;

[0046] Figure 7 This is a schematic diagram of the grinding and polishing structure provided in an embodiment of the present invention. Detailed Implementation

[0047] To enable those skilled in the art to better understand this solution, the technical solutions in the embodiments of this solution will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this solution, not all of them. Based on the embodiments of this solution, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this solution.

[0048] The term "comprising" and any other variations thereof in the specification, claims, and accompanying drawings of this invention mean "including but not limited to," and are intended to cover a non-exclusive inclusion, not limited to the examples listed herein. Furthermore, the terms "first" and "second," etc., are used to distinguish different objects, not to describe a specific order.

[0049] The implementation of the present invention will be described in detail below with reference to the accompanying drawings:

[0050] Current methods for fabricating MEMS circulators typically involve etching cavities at the wafer level, dicing them into chip-level wafers, installing ferrites within the cavities, and then sealing the cavities. Variations in ferrite size can significantly impact the electrical performance of MEMS circulators. For example, excessively high ferrite size can affect the sealing effect of the cavities. Conversely, excessively low ferrite size can cause ferrite displacement under high vibration conditions. Furthermore, differences in ferrite size between different circulators also lead to significant performance variations.

[0051] This invention provides a wafer-level heterogeneous integrated MEMS circulator and its fabrication method. By employing wafer-level integrated ferrite, wafer polishing, and wafer bonding, a MEMS circulator is obtained, thus solving the problem that the poor dimensional accuracy of ferrite has a significant impact on the electrical performance of the MEMS circulator.

[0052] Figure 1 This is a flowchart illustrating the fabrication method of a wafer-level heterogeneous integrated MEMS circulator provided in an embodiment of the present invention. (Refer to...) Figure 1 The preparation method includes:

[0053] Step 101: Etch an opening 11 on the front side of the first wafer 1;

[0054] It should be noted that step 101 is a wafer-level etching process, i.e., etching is performed on the wafer. Using semiconductor processing technology, multiple devices can be fabricated simultaneously on a wafer. For ease of explanation, only one circulator chip will be used as an example. For instance, multiple identical openings 11 can be etched on the front side of the first wafer 1, with each opening 11 arranged in a matrix, and each opening 11 corresponding to one circulator. The following steps follow a similar correspondence. Furthermore, the semiconductor processing technology in this solution employs MEMS processing technology, thereby ultimately obtaining a MEMS circulator.

[0055] For example, the first wafer 1 can be a silicon wafer. For example, a high-resistivity silicon wafer or a low-resistivity silicon wafer. As another example, a single-sided silicon wafer or a double-sided silicon wafer.

[0056] It should be further clarified that the front side of the first wafer 1 is defined relatively. For example, in this scheme, the bonding surface during wafer bonding is considered the front side. As 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 This is a schematic diagram of the structure after etching the opening provided in an embodiment of the present invention; see reference. Figure 2 The opening 11 is a non-closed cavity with its opening facing the front side of the first wafer 1. Exemplarily, the opening 11 can be fabricated using a semiconductor etching process. A typical feature of semiconductor etching is the use of semiconductor photolithography to prepare a high-precision etching mask, under which the semiconductor etching process is performed. For example, the semiconductor etching process can be dry etching or wet etching. In terms of etching depth control, the processing precision of semiconductor etching processes is generally higher than that of mechanical processing methods.

[0058] In addition, the thickness of the first wafer 1 is usually greater than that used in conventional processes. This is because a portion of the thickness is removed during subsequent grinding and polishing steps. The specific thickness of the first wafer 1 is not specified here.

[0059] For example, a circuit layer may also be fabricated on the back side of the first wafer, and through-silicon vias (TSVs) may be fabricated throughout the first wafer. The circuit layer on the back side of the first wafer can be electrically connected to the circuit layer of the second wafer after a subsequent bonding step via the TSVs.

[0060] Step 102: The ferrite 12 is installed and fixed inside the opening to obtain the first wafer of integrated ferrite 12; the height of the ferrite 12 is greater than the depth of the opening.

[0061] Figure 3 This is a schematic diagram of the integrated ferrite structure provided in an embodiment of the present invention; see reference. Figure 3It should be noted that step 102 is wafer-level integration of the ferrite 12, i.e. integrating the ferrite 12 in each opening cavity of the first wafer.

[0062] Exemplarily, before step 102, a mechanical processing process is further included to prepare the ferrite 12 into a target shape. Exemplarily, the shape of the ferrite 12 can be a cylinder, a multi-faceted cylinder or a special-shaped structure.

[0063] Further exemplarily, the shape of the ferrite 12 is the same as that of the opening cavity, so as to facilitate mounting and fixing the ferrite 12 in the opening cavity. It should be noted that the size of the ferrite 12 is not required to be the same as that of the opening cavity.

[0064] It should be noted that the ferrite 12 is mounted to the bottom of the opening cavity, i.e. the ferrite 12 is inserted into the bottom of the opening cavity as much as possible, so as to improve the accuracy of subsequent polishing processing. It should be further noted that the ferrite 12 is fixed in the opening cavity, one purpose is to avoid the ferrite from falling off from the opening cavity, and another purpose is to fix the relative position of the ferrite and the opening cavity in subsequent processing steps, so as to improve the accuracy of polishing processing.

[0065] In addition, it should be noted that the height of the ferrite after mounting and fixing is greater than the depth of the opening cavity, i.e. the ferrite is higher than the front surface of the first wafer, which is also for facilitating the next polishing process.

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

[0067] It should be noted that step 103 is wafer-level polishing, for example, a chemical mechanical polishing process can be used for wafer-level polishing.

[0068] Figure 4 is a structural schematic diagram of the polished first wafer provided by the embodiment of the present application; refer to Figure 4 In the first wafer with the integrated ferrite, the ferrite protrudes from the front surface of the wafer. During wafer-level polishing, the protruding ferrite is first polished and removed, and then the ferrite and the front surface of the wafer are polished synchronously. After synchronous polishing of the ferrite and the front surface of the wafer to a certain extent, the depth of the opening cavity can be the same as the height of the ferrite, and the polished first wafer is obtained.

[0069] Exemplarily, the stop condition of polishing can be that the thickness of the first wafer reaches a target thickness.

[0070] It should be noted that the polishing and grinding at least removes the part of the ferrite protruding from the front surface of the first wafer. For example, the front surface of the first wafer with the integrated ferrite is polished and ground to remove the part of the ferrite protruding from the front surface of the first wafer, to obtain a first wafer after polishing and grinding; wherein the depth of the open cavity in the first wafer after polishing and grinding is the same as the height of the ferrite. It should be noted that in order to make the depth of the open cavity in the first wafer after polishing and grinding the same as the height of the ferrite, the ferrite must be fixed with the open cavity in step 102.

[0071] The above steps 101 to 103 illustrate the preparation steps of the first wafer. The following step 104 illustrates the preparation steps of the second wafer. It should be noted that the first wafer and the second wafer are prepared independently of each other, and there is no sequence between the two. As long as the preparation of the first wafer and the second wafer is completed before step 105 bonding, it is acceptable.

[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 structural schematic diagram of the second wafer provided by the embodiment of the present application; refer to Figure 5 It should be noted that the circuit layer 21 in the second wafer 2 can be prepared by using a semiconductor processing technology. For example, the circuit layer 21 can be prepared by using metal evaporation, photolithography mask, circuit etching and the like.

[0074] It should be noted that the circuit layer 21 in the MEMS circulator is used for transmitting radio frequency signals. For example, the radio frequency signal of a certain port of the circuit layer 21 is transmitted to the ferrite, and then transmitted to another port of the circuit layer 21 by the ferrite.

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

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

[0077] Figure 6 is a structural schematic diagram of the bonded wafer provided by the embodiment of the present application; refer to Figure 6It should be noted that the wafer-level bonding in step 105 is the bonding of the first wafer and the second wafer. After the bonding, the circuit layer of the second wafer inputs and outputs the radio frequency signal, and the ferrite of the second wafer realizes one-way transmission of the radio frequency signal.

[0078] For example, after wafer-level bonding, it further includes: slicing and cutting the bonded wafer to obtain independent MEMS circulator chips. Further, the MEMS circulator chip is welded on a metal carrier.

[0079] It should be noted that, according to different ferrite materials, a permanent magnet may be arranged on the back of the second wafer after bonding.

[0080] The embodiment of the application provides a preparation method of a wafer-level heterogeneous integrated MEMS circulator, which obtains a MEMS circulator chip by adopting wafer-level integrated ferrite, wafer grinding and polishing and wafer bonding.

[0081] On the one hand, for a single MEMS circulator on a wafer, the wafer is ground and polished after the ferrite is integrated, so as 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 and fix the ferrite, so as to avoid the position drift of the ferrite in the MEMS circulator in a high-vibration environment.

[0082] On the other hand, for multiple MEMS circulators on a wafer, the opening cavity etched by a semiconductor processing process has high depth precision, and the depth of the opening cavity of each circulator has good consistency. After the ferrite is integrated, the wafer is ground and polished, the depth of the opening cavity determines the height of the ferrite, and the height of the ferrite of each circulator has good consistency. Therefore, the size difference of each ferrite is reduced, and the influence on the electrical performance of the MEMS circulator is reduced.

[0083] The inventors of the present application found in the actual research and development process that the MEMS circulator is prone to fragmentation in a high-frequency and high-power application scenario. Further, it is found that high frequency and high power cause large self-heating of the MEMS circulator, and large working temperature difference. In order to fix the ferrite in the opening cavity, the ferrite and the cross-sectional size of the opening cavity are usually set to be the same, for example, both are cylindrical with the same diameter. Even, in order to strengthen the fixing strength, interference fit is adopted, that is, the outer diameter of the ferrite is slightly larger than the inner diameter of the opening cavity. However, the thermal expansion coefficients of the wafer material and the ferrite are quite different, and when the ferrite expands more than the wafer opening cavity in the working temperature difference, the wafer material is prone to fragmentation, and finally the performance of the circulator fails.

[0084] The V-shaped structure and the preset gap mode are adopted in the embodiment of the application to solve the problem of easy fragmentation of the MEMS circulator in a high-frequency and high-power application scenario.

[0085] Figure 7 is a schematic diagram of a grinding and polishing structure provided by the embodiment of the application; refer to Figure 7 In a possible implementation, the lower longitudinal section of the open cavity and the ferrite are both V-shaped with the same angle; the upper width of the open cavity is greater than the upper width of the ferrite.

[0086] For example, the direction of the open cavity is upward, and the reverse direction is downward.

[0087] Further, the open cavity and the ferrite are divided into upper and lower parts. The longitudinal sections of the upper and lower parts are set to different shapes. For example, the longitudinal section of the lower part of the open cavity is V-shaped, and the longitudinal section of the lower part of the ferrite is also V-shaped, and the angles of the two V shapes are the same. For another example, the upper longitudinal sections of the open cavity and the ferrite are rectangular. For another example, the longitudinal sections of the open cavity and the ferrite are similar to the shape of a sharpened pencil.

[0088] For example, the lower part of the open cavity and the ferrite includes a triangular wedge shape, a triangular pyramid shape or a conical shape.

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

[0090] It should be further noted that the upper width of the open cavity is greater than the upper width of the ferrite, and the purpose is to form a gap between the ferrite and the open cavity to avoid the deformation of the ferrite being greater than the open cavity and avoiding the open cavity being cracked in a high-frequency and high-power application scenario. Therefore, the lower part of the open cavity and the ferrite is set to be V-shaped, one of the purposes is to position the ferrite at the center of the open cavity, and the other purpose is to fix the position of the ferrite during the grinding and polishing process to improve the grinding and polishing processing precision. The following are specific ferrite integration steps and grinding and polishing steps. If the position of the ferrite is horizontally offset during the subsequent assembly process, the original electrical performance design indicators will be deviated; the position of the ferrite on different devices is not uniform, which will also cause poor performance consistency.

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

[0092] For example, the opening cavity faces upward, and the V-shaped lower part of the ferrite faces downward and is placed in the opening cavity. Due to the larger opening cavity and the smaller ferrite, the ferrite can fall into and be fixed in the opening cavity by using the gravity of the ferrite itself. Moreover, since the ferrite and the lower part of the opening cavity are both V-shaped, the ferrite can be automatically positioned at the center of the opening cavity. The above describes the integration of the ferrite, and the following describes the polishing of the ferrite.

[0093] In some embodiments, corresponding to the step 103, the polishing of the front surface of the first wafer integrated with ferrite to obtain the first wafer after polishing includes:

[0094] In the step 1031, the first wafer integrated with ferrite is loaded between the polishing head 3 and the polishing disc 4, the ferrite and the opening cavity are fixed in the vertical direction by the extrusion force between the polishing head 3 and the polishing disc 4, and 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 disc 4 generally faces upward. If the ferrite is fixed in the opening cavity by relying on the self-weight, a temporary pressing plate can be arranged above the first wafer to press the ferrite. After the first wafer and the temporary pressing plate are turned over by 180° and buckled on the polishing disc 4, the temporary pressing plate is removed. At this time, the first wafer presses the ferrite and is buckled on the polishing disc 4, so that the direction of the first wafer and the fixed relationship of the ferrite are not changed after the turning over.

[0096] For example, the back surface of the first wafer is fixed on the polishing head 3. When the ferrite and the opening cavity are extruded in the vertical direction by the extrusion force between the polishing head 3 and the polishing disc 4, the V-shaped ferrite is automatically positioned at the center of the V-shaped opening cavity. At the same time, there is a gap between the upper part of the ferrite and the upper part of the opening cavity.

[0097] In the step 1032, the polishing head 3 drives the first wafer to move relative to the polishing disc 4, the V-shaped side wall of the opening cavity exerts a reaction force on the V-shaped side surface of the ferrite in the horizontal direction to fix the ferrite and the opening cavity, and the front surface of the first wafer integrated with ferrite is polished.

[0098] For example, the relative movement between the polishing head 3 and the polishing disc 4 is horizontal relative movement. For reference, the relative movement between the polishing head 3 and the polishing disc 4 is horizontal relative movement. Figure 7In order to ensure that the polishing rate of each position on the wafer is the same, the coaxial relative rotation movement is generally not used. Instead, the polishing head 3 rotates around the polishing disc 4, and the relative movement between the polishing head 3 and the polishing disc 4 can be simplified as horizontal relative movement within a certain range.

[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 the present solution, the lower part of the ferrite is designed in a V shape to provide a lateral support force to offset the horizontal force, so as to avoid the tilting of the ferrite during the polishing process. The size of the lateral support force of the V-shaped lower part of the ferrite is also affected by the pressing 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 and avoid the positional deviation.

[0100] In the embodiments of the present application, the gap between the ferrite and the open cavity is provided to avoid the deformation of the ferrite being greater than the open cavity and avoid the open cavity being cracked in the high-frequency and high-power application scenarios. Further, by providing the open cavity and the ferrite in a V shape, the ferrite is positioned at the center of the open cavity during the polishing process, and a lateral support force is provided during the polishing process to fix the position of the ferrite, so as to improve the machining precision of the ferrite after polishing.

[0101] In addition, it should be noted that if the lower part of the open cavity and the ferrite is in a triangular wedge shape, the relative movement direction of the polishing head 3 and the polishing disc 4 is perpendicular to the triangular wedge shape.

[0102] In the above embodiments, the V-shaped structure of the open cavity and the ferrite is used to fix the ferrite during polishing. The following embodiments provide other auxiliary methods to assist in fixing the ferrite.

[0103] In some embodiments, in step 102, molten paraffin can be poured into the open cavity, and then the ferrite is pressed and fixed in the open cavity. After the paraffin is cooled and solidified, the polishing process in step 103 is performed. After the polishing process, the paraffin can be cleaned and removed.

[0104] In the embodiments of the present application, the paraffin is used to temporarily fix the ferrite, which can facilitate the fixation of the position of the ferrite during the integration and polishing steps, so as to improve the machining precision of the ferrite after polishing.

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

[0106] The open cavity is filled with glue to obtain a glue-filled open cavity.

[0107] Correspondingly, the V-shaped lower part of the ferrite is mounted and fixed in the V-shaped lower part of the opening cavity to obtain a first wafer integrated with the ferrite, including:

[0108] The V-shaped lower part of the ferrite is mounted in the V-shaped lower part of the opening cavity after filling the glue in the opening cavity;

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

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

[0111] For example, 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] In the embodiment of the application, the position of the ferrite can be fixed in the integration and polishing steps by filling the glue in the opening cavity, so as to improve the processing precision of the ferrite after polishing. In addition, without removing the glue, the anti-vibration capability can be enhanced when the MEMS circulator is actually applied subsequently.

[0113] In a possible implementation, the V-shaped lower part of the ferrite is mounted and fixed in the V-shaped lower part of the opening cavity to obtain a first wafer integrated with the ferrite, including:

[0114] The V-shaped lower part of the ferrite is mounted in the V-shaped lower part of the opening cavity to obtain a first wafer after mounting the ferrite;

[0115] A filling layer is grown on the surface of the first wafer after mounting the ferrite to fill the gap between the upper side of the ferrite and the upper side wall of the opening cavity, so as to obtain the first wafer integrated with the ferrite.

[0116] It should be noted that the growth of the filling layer is in a semiconductor film growth mode. For example, it can be evaporation and sputtering. The semiconductor film growth mode is characterized by uniform growth of a thin film on all exposed surfaces.

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

[0118] The embodiment of the present application fills the gap between the ferrite and the opening cavity by adopting the semiconductor coating method after the ferrite is installed, so that the position of the ferrite can be fixed in the polishing and grinding step, and the processing precision of the ferrite after polishing and grinding is improved. In addition, without removing the filling layer, the anti-vibration capability can be enhanced when the MEMS circulator is actually applied subsequently.

[0119] In a possible implementation, the installing and fixing the ferrite of the V-shaped lower part in the V-shaped lower part of the opening cavity to obtain the first wafer integrated with the ferrite comprises:

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

[0121] The filling layer on the bottom of the opening cavity is removed by adopting the laser etching method;

[0122] The installing and fixing the ferrite of the V-shaped lower part in the V-shaped lower part of the opening cavity to obtain the first wafer integrated with the ferrite; wherein the filling layer fills the gap between the upper side of the ferrite and the upper side wall of the opening cavity.

[0123] It should be noted that the thickness of the filling layer is greater than the gap width between the upper side of the ferrite and the upper side wall of the opening cavity, so that the ferrite is inserted into the opening cavity, and the filling layer can fix the ferrite by extrusion. Further, the hardness of the filling layer is lower than that of the ferrite and the first wafer, and the thermal expansion coefficient of the filling layer is lower than that of the ferrite and the first wafer, so that the wafer material can also be prevented from being broken in subsequent high-frequency and high-power applications.

[0124] The embodiment of the present application fills the gap between the ferrite and the opening cavity by adopting the semiconductor coating method after the ferrite is installed, so that the position of the ferrite can be fixed in the polishing and grinding step, and the processing precision of the ferrite after polishing and grinding is improved. In addition, without removing the filling layer, the anti-vibration capability can be enhanced when the MEMS circulator is actually applied subsequently.

[0125] In a possible implementation, after the front surface of the first wafer integrated with the ferrite is polished and ground, the back surface of the first wafer is also polished and ground until the lower V-shaped structure of the opening cavity and the ferrite is removed, and the first wafer after polishing and grinding is obtained.

[0126] The embodiment of the present application removes the V-shaped structure by polishing and grinding the back surface of the first wafer, so that the influence of the V-shaped structure on the performance of the circulator can be avoided.

[0127] The following embodiment illustrates 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 shape is V-shaped; the first wafer is a (100) crystal direction silicon wafer; the opening cavity etched on the front surface of the first wafer comprises:

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

[0130] A protective layer is grown on the front surface of the etched silicon wafer;

[0131] A laser etching method is used to remove the protective layer at the bottom of the U-shaped opening cavity;

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

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

[0134] The embodiments of the present application use a combination of dry etching and wet etching, and prepare a V-shaped structure based on the anisotropic etching characteristics of the silicon wafer, so that an opening cavity with high dimensional accuracy can be processed.

[0135] The above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the same; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for fabricating a wafer-level heterogeneous integrated MEMS circulator, characterized in that, include: An opening is etched on the front side of the first wafer; The ferrite is mounted and fixed inside the opening to obtain the first wafer of integrated ferrite. The height of the ferrite is greater than the depth of the oral cavity; The front side of the first wafer integrating ferrite is polished to obtain the polished first wafer; wherein the depth of the opening in the polished first wafer is the same as the height of the ferrite. A circuit layer is fabricated in a second wafer to obtain a second wafer after circuit fabrication. The front side of the polished first wafer is bonded to the front side of the second wafer after circuit fabrication to obtain a MEMS circulator.

2. The fabrication method of the wafer-level heterogeneous integrated MEMS circulator as described in claim 1, characterized in that, The lower longitudinal cross-sectional shape of both the opening and the ferrite is a V-shape with the same angle; the upper width of the opening is greater than the upper width of the ferrite; the process of mounting and fixing the ferrite inside the opening to obtain the first wafer of integrated ferrite includes: The ferrite at the lower part of the V-shape is mounted and fixed inside the lower part of the V-shape of the opening, thus obtaining the first wafer of integrated ferrite; wherein, after mounting and fixing, there is a gap between the upper side of the ferrite and the upper sidewall of the opening. Accordingly, the polishing of the front side of the first wafer integrating ferrite to obtain the polished first wafer includes: The first wafer integrating ferrite is loaded between the polishing head and the polishing disk. The ferrite and the opening are fixed in the vertical direction by the extrusion force between the polishing head and the polishing disk, so that the V-shaped ferrite is positioned at the center of the V-shaped opening. The polishing head drives the first wafer to move relative to the polishing disk. The V-shaped sidewall of the opening applies a reaction force to 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 integrating the ferrite.

3. The fabrication method of the wafer-level heterogeneous integrated MEMS circulator as described in claim 2, characterized in that, Before installing and fixing the ferrite at the lower part of the V-shape towards the opening, the method further includes: The opening is filled with glue, and the opening is opened after the glue is filled. Accordingly, the step of mounting and fixing the ferrite at the lower part of the V-shape towards the opening to obtain the first wafer of integrated ferrite includes: Install the ferrite at the bottom of the V-shape into the bottom of the opening after filling with glue, with the opening facing the opening. The ferrite and the opening are fixed vertically by external extrusion, so that the V-shaped ferrite is positioned at the center of the V-shaped opening; wherein, under external extrusion, the adhesive fills the gap between the upper side of the ferrite and the upper sidewall of the opening. The adhesive is heated and cured under preset conditions to obtain the first wafer of integrated ferrite.

4. The method for fabricating a wafer-level heterogeneous integrated MEMS circulator as described in claim 2, characterized in that, The step of mounting and fixing the ferrite at the lower part of the V-shape towards the opening to obtain the first wafer of integrated ferrite includes: The ferrite at the bottom of the V-shape is installed inside the bottom of the V-shape of the opening, facing the opening, to obtain the first wafer after ferrite installation; After the ferrite is mounted, a filling layer is grown on the surface of the first wafer to fill the gap between the upper side of the ferrite and the upper sidewall of the opening, thus obtaining the first wafer with integrated ferrite.

5. The method for fabricating a wafer-level heterogeneous integrated MEMS circulator as described in claim 2, characterized in that, The step of mounting and fixing the ferrite at the lower part of the V-shape towards the opening to obtain the first wafer of integrated ferrite includes: A filling layer is grown on the front side of the first wafer after the opening is prepared; the filling layer covers the sidewalls and bottom of the opening; the thickness of the filling layer is greater than the gap width between the upper side of the ferrite and the upper sidewall of the opening; The filling layer at the bottom of the opening is removed by laser etching. The ferrite at the lower part of the V-shape is mounted and fixed inside the lower part of the opening, facing the opening, to obtain the first wafer of integrated ferrite; wherein, the filling layer fills the gap between the upper side of the ferrite and the upper sidewall of the opening.

6. The method for fabricating a wafer-level heterogeneous integrated MEMS circulator as described in claim 2, characterized in that, The opening and the lower part of the ferrite are shaped like a triangular wedge, a triangular pyramid, or a cone.

7. The method for fabricating a wafer-level heterogeneous integrated MEMS circulator as described in claim 2, characterized in that, After polishing the front side of the first wafer of the integrated ferrite, the process further includes: The back side of the first wafer after the front side is polished is polished until the opening and the lower V-shaped structure of the ferrite are removed, thus obtaining the polished first wafer.

8. The method for fabricating a wafer-level heterogeneous integrated MEMS circulator as described in claim 1, characterized in that, The upper sidewall of the opening is vertical, and the lower longitudinal cross-section is V-shaped; the first wafer is a (100) oriented silicon wafer; the etching of the opening on the front side of the first wafer includes: Anisotropic etching method is used to etch a U-shaped opening perpendicular to the sidewall on the front side of the (100) crystal orientation silicon wafer to obtain the etched silicon wafer; A protective layer is grown on the front side of the silicon wafer after etching; The protective layer at the bottom of the U-shaped opening is removed by laser etching. Using the protective layer as a mask, the silicon wafer is placed in a potassium hydroxide solution for anisotropic etching, and a V-shaped structure is prepared at the bottom of the U-shaped opening to obtain the opening on the front side of the first wafer.

9. The method for fabricating a wafer-level heterogeneous integrated MEMS circulator as described in claim 8, characterized in that, The anisotropic etching methods include dry etching, picosecond laser etching, or femtosecond laser etching.

10. A wafer-level heterogeneously integrated MEMS circulator, characterized in that, It was prepared based on the method for fabricating a wafer-level heterogeneous integrated MEMS circulator as described in any one of claims 1 to 9.

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