MEMS inertial sensor and manufacturing method thereof

Abstract

The invention belongs to the technical field of micro electro mechanical systems, and particularly provides an MEMS inertial sensor which comprises a circuit layer, a first device layer, a second device layer and a cap layer which are sequentially stacked and bonded. A plurality of first supporting beams are arranged on the lower surface of the first device layer; the plurality of first supporting beams are bonded with the circuit layer; the second device layer is provided with a plurality of second supporting beams; the plurality of second support beams are bonded with the first device layer; the cap layer is bonded with the second device layer; a circuit area is formed between the cap layer and the circuit layer in a surrounding mode. According to the MEMS inertial sensor provided by the invention, by directly bonding the two device layers up and down, the multifunctionality of the sensor can be realized, the packaging process is simpler, the packaging size is smaller, meanwhile, compared with a single-layer device structure, more cost is saved at an application end, and the improvement of the process manufacturing yield and the miniaturization of an integrated system are facilitated.

Description

Technical Field

[0001] The present invention belongs to the field of microelectromechanical systems, and particularly relates to a MEMS inertial sensor and a manufacturing method thereof. Background Art

[0002] Inertial devices refer to devices used to measure and sense the motion state of an object, mainly including gyroscopes and accelerometers. These devices sense the angular motion and linear motion of an object to obtain information such as the attitude, position, and speed of the object, and are widely used in consumer electronics, vehicle navigation, industrial automation, aerospace, military and other fields.

[0003] At present, the manufacturing of inertial sensors mainly focuses on a single device layer. Its sensor structure and function are relatively simple. In most cases at the application end, multiple sensors need to be combined for use. The subsequent packaging process is difficult, the packaging volume is large, and the volume accounts for a relatively large proportion at the application end, resulting in high costs. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problems that the volume of a single-device-layer inertial sensor at the application end accounts for a relatively large proportion and the subsequent packaging process is difficult in the prior art.

[0005] To this end, the present invention provides a MEMS inertial sensor, which includes a circuit layer, a first device layer, a second device layer, and a capping layer that are sequentially stacked and bonded; the first device layer is provided with a plurality of first support beams; the plurality of first support beams are bonded to the circuit layer; the second device layer is provided with a plurality of second support beams; the plurality of second support beams are bonded to the first device layer; the capping layer is bonded to the second device layer; a circuit area is formed by enclosing between the capping layer and the circuit layer.

[0006] Specifically, a plurality of first electrodes corresponding to the first support beams one by one are provided on the above-mentioned circuit layer; the first electrodes are bonded to the first support beams.

[0007] Specifically, the above-mentioned first support beam includes a first support beam body; one end of the first support beam body is connected to the device layer, and the other end is provided with a second electrode; the second electrode is bonded to the first electrode.

[0008] Specifically, a plurality of first channels penetrating the first device layer are opened on the above-mentioned first device layer; a plurality of second channels penetrating the second device layer are opened on the second device layer; the second channels, the first channels, and the circuit area are connected.

[0009] Specifically, a first groove is provided on the surface of the capping layer bonded to the second device layer; the first groove is connected to the circuit area through the second channels and the first channels.

[0010] Specifically, a plurality of third channels penetrating the second device layer are provided on the second device layer; the third channels are located outside the second channels.

[0011] The present invention also provides a manufacturing method of the above MEMS inertial sensor, including the following steps: S1. Manufacture a circuit layer; S2. Fabricate a first device layer; S3. Fabricate a second device layer; S4. Fabricate a capping layer; S5. Bonding: Bond the circuit layer to the first support beam of the first device layer to enclose and form a circuit area; bond the capping layer on the upper surface of the second device layer; bond the second support beam of the second device layer to the upper surface of the first device layer.

[0012] Specifically, the above step S1 includes: S101. Provide a first substrate, deposit a first dielectric layer on the surface of the first substrate, and perform patterning on the first dielectric layer to expose a part of the first substrate; S102. Deposit a first metal layer, and perform patterning on the first metal layer to expose a part of the first dielectric layer; S103. Deposit a second dielectric layer, and perform patterning on the second dielectric layer to expose a part of the first metal layer; S104. Deposit a second metal layer to cover the first metal layer and the second dielectric layer, and perform patterning on the second metal layer to form a first electrode; S105. Deposit a third dielectric layer to cover the second dielectric layer and the first electrode, and perform patterning on the third dielectric layer to expose the first electrode.

[0013] Specifically, the above step S2 includes: S201. Provide a second substrate and perform patterning on it; deposit a metal on the surface of the second substrate to form a third metal layer, and perform patterning on the third metal layer to expose a part of the second substrate to form a second electrode; S202. Perform patterning on the exposed second substrate to remove a part of the thickness of the second substrate to form a first support beam.

[0014] Specifically, the above step S5 includes: S501. Bond the circuit layer to the first support beam of the first device layer to enclose and form a circuit area; S502. Perform comb-shaped patterning on the first device layer to form a first channel penetrating the first device layer; S503. Bond the capping layer on the upper surface of the second device layer; S504. Perform boss patterning on the lower surface of the second device layer to form a plurality of second support beams; S505. Perform comb-shaped patterning on the second device layer to form a second channel penetrating the second device layer. S506. Bond the upper surface of the first device layer to the second support beam of the second device layer.

[0015] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. The MEMS inertial sensor provided by the present invention can achieve the versatility of the sensor by directly bonding two device layers up and down, making the packaging process simpler, the packaging volume smaller, and more cost-effective at the application end compared with the single-layer device structure, which is conducive to improving the process production yield and the miniaturization of the integrated system.

[0016] 2. The manufacturing method of the MEMS inertial sensor provided by the present invention can reduce the stress at the bonding interface by directly bonding the silicon wafers of the first device layer and the second device layer, improve the structural stability and precision, and reduce the structural failure rate under vibration environment compared with the traditional packaging. This rigid connection method can also effectively suppress the thermal stress mismatch problem caused by temperature changes and reduce the temperature drift error of the sensor. The two device layers form a three-dimensional mechanical structure through wafer-level bonding, can integrate multifunctional units simultaneously, and realize the synchronous detection of multi-axis inertial parameters to improve the device sensitivity. In addition, the vertical interconnection between the first channel and the second channel between the two device layers and the metal electrodes at the circuit layer interface shortens the signal transmission distance and has a low parasitic capacitance, which can significantly improve the signal-to-noise ratio of weak signals. The second device layer is preferably a silicon wafer with vertical channels, which can be used as the support structure of the inertial mass block to improve the resonance frequency stability.

[0017] 3. The MEMS inertial sensor provided by the present invention uses the first electrode and the second electrode for bonding, directly establishing the electrical interconnection between the circuit layer and the device layer while achieving interface bonding, reducing the difficulty of electrical interconnection. The double-metal bonding interface has high mechanical strength, can effectively resist vibration and impact during the operation of the inertial sensor, and reduce the risk of delamination. At the same time, the thermal expansion coefficient matching of the metal materials is good, which can improve the stability of the device under temperature changes. The heat conduction path formed by the bonding of the metal electrodes helps to quickly conduct the heat generated during the operation of the MEMS device to the packaging substrate, improving the stability and lifespan of the sensor in a high-temperature environment. The first electrode and the second electrode are preferably bonded with heterogeneous metals, and the material characteristics are complementary and optimized, which can achieve low-temperature bonding and avoid damage to the MEMS microstructure caused by high temperature. The metal bonding interface has excellent shear strength, and the failure rate under vibration environment is lower than that of wire bonding, enhancing the reliability.

[0018] The following will further describe the present invention in detail with reference to the accompanying drawings. Description of the Drawings

[0019] Figure 1It is a schematic diagram of the manufacturing of the circuit layer in an embodiment of the present invention; where A-B is the flowchart corresponding to step S101, C is the flowchart corresponding to step S102, D-E is the flowchart corresponding to step S103, F is the flowchart corresponding to step S104, and G-H is the flowchart corresponding to step S105.

[0020] Figure 2 It is a schematic diagram of the manufacturing of the first device layer in an embodiment of the present invention; where A-B is the flowchart corresponding to step S201, and C is the flowchart corresponding to step S202.

[0021] Figure 3 It is a schematic diagram of the manufacturing of the second device layer in an embodiment of the present invention.

[0022] Figure 4 It is a schematic diagram of the manufacturing of the capping layer in an embodiment of the present invention; where A-C is the flowchart corresponding to step S401.

[0023] Figure 5 It is a schematic diagram of the bonding between the first device layer and the circuit layer in an embodiment of the present invention; where A is the flowchart corresponding to step S501, B is the flowchart corresponding to step S502, and C is the flowchart corresponding to step S503.

[0024] Figure 6 It is a schematic diagram of the bonding between the capping layer and the second device layer in an embodiment of the present invention; where A-B is the flowchart corresponding to step S504, C is the flowchart corresponding to step S505, and D is the flowchart corresponding to step S506.

[0025] Figure 7 It is a schematic diagram of the bonding between the first device layer and the second device layer in an embodiment of the present invention; where A is the flowchart corresponding to step S507, and B is the flowchart corresponding to step S508.

[0026] Figure 8 It is a schematic diagram of the MEMS inertial sensor structure provided by an embodiment of the present invention.

[0027] Reference numerals: 1, circuit layer; 101, first electrode; 2, first device layer; 201, second electrode; 202, first support beam body; 203, first channel; 3, second device layer; 301, second support beam; 302, second channel; 303, third channel; 4, capping layer; 401, first groove. Detailed implementation manners

[0028] The technical solutions in the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Although the representative embodiments of the present invention have been described in detail, those of ordinary skill in the technical field to which the present invention pertains will understand that various modifications and changes can be made to the present invention without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the embodiments, but should be defined by the appended claims and their equivalents.

[0029] The present invention provides a MEMS inertial sensor, which includes a circuit layer, a first device layer, a second device layer, and a capping layer that are sequentially stacked and bonded; the first device layer is provided with a plurality of first support beams; the plurality of first support beams are bonded to the circuit layer; the second device layer is provided with a plurality of second support beams; the plurality of second support beams are bonded to the first device layer; the capping layer is bonded to the second device layer; a circuit area is formed by enclosing between the capping layer and the circuit layer. The shape, size, position, and number of the support beams can be flexibly selected according to actual needs. By directly bonding two device layers up and down, the versatility of the sensor can be achieved, and the packaging process is made simpler, the packaging volume is smaller, and at the application end, it is more cost-effective than a single-layer device structure.

[0030] Specifically, on the surface of the circuit layer bonded to the device layer, generally the upper surface of the circuit layer, there are a plurality of first electrodes; the first electrodes correspond to the first support beams one by one; the first electrodes are bonded to the first support beams.

[0031] Furthermore, the first support beam includes a first support beam body; one end of the first support beam body is connected to the first device layer, and the other end is provided with a second electrode; the second electrode is bonded to the first electrode. The materials of the first electrode and the second electrode can be selected according to needs, and generally Al or Ge is used.

[0032] In one implementation, a plurality of first channels penetrating the first device layer are formed on the first device layer; a plurality of second channels penetrating the second device layer are formed on the second device layer; the second channels, the first channels, and the circuit area are communicated. Thus, the silicon microstructures of the inertial devices are released.

[0033] In another implementation, the surface of the capping layer bonded to the second device layer is provided with a first groove, i.e., a cavity; the first groove is communicated with the circuit area through the second channels and the first channels. A physical isolation space is provided for the mass blocks and the support beams, which helps to reduce the interference caused by the mechanical structure and provides a shock-absorbing effect at the same time, making the measurement more stable and accurate.

[0034] Preferably, a plurality of third channels penetrating the second device layer are provided on the second device layer; the third channels are located outside the second channels.

[0035] The present invention also provides a manufacturing method for a MEMS inertial sensor, comprising the following steps: S1. Fabricate the circuit layer S101. Provide a first substrate and perform alignment marking patterning thereon (refer to part A in Figure 1 ); deposit a first dielectric layer on the surface of the first substrate, and perform patterning on the first dielectric layer to expose a part of the first substrate (refer to part B in Figure 1 ). S102. Refer to part C in Figure 1 , deposit metal on the surface of the first dielectric layer to cover the first dielectric layer and the first substrate, form a first metal layer, and perform patterning on the first metal layer to expose a part of the first dielectric layer; S103. Continuously deposit a second dielectric layer along the stacking direction and perform planarization treatment to cover the first dielectric layer and the first metal layer (refer to part D in Figure 1 ); perform patterning on the second dielectric layer to expose a part of the first metal layer (refer to part E in Figure 1 ). S104. Refer to part F in Figure 1 , continuously deposit metal along the stacking direction to cover the first metal layer and the second dielectric layer, form a second metal layer, perform patterning on the second metal layer to expose a part of the second dielectric layer, and form a first electrode; S105. Continuously deposit a third dielectric layer along the stacking direction and perform planarization treatment to cover the second metal layer and the first electrode (refer to part G in Figure 1 ); perform patterning on the third dielectric layer to expose the first electrode (refer to part H in Figure 1 ).

[0036] S2. Fabricate the first device layer S201. Provide a second substrate and perform alignment marking patterning thereon (refer to part A in Figure 2 ); deposit metal on the surface of the second substrate to form a third metal layer, and perform patterning on the third metal layer to expose a part of the second substrate to form a second electrode (refer to part B in Figure 2 ). S202. Refer to part C in Figure 2 , perform patterning on the exposed second substrate to remove a part of the thickness of the second substrate to form a first support beam so as to form a certain space between the first support beam and the circuit layer during bonding; the first support beam preferably includes a first support beam body formed by a part of the second substrate and a second electrode formed at one end of the first support beam body.

[0037] S3. Fabricate the second device layer S301. Refer to Figure 3 , provide a third substrate as the second device layer, and perform alignment mark patterning on the third substrate.

[0038] S4. Fabricate a capping layer S401. Provide a fourth substrate, and perform alignment mark patterning on it (refer to Figure 4 part A therein); deposit a fourth dielectric layer on the surface of the fourth substrate and planarize it (refer to Figure 4 part B therein), perform patterning on the fourth dielectric layer and the fourth substrate, remove a part of the fourth dielectric layer and a part of the thickness of the fourth substrate below it to form a plurality of first grooves (cavities) (refer to Figure 4 part C therein). The volume of the cavity can be adjusted by the cavity depth, and there is no need to increase the cavity area.

[0039] S5. Bonding S501. Refer to Figure 5 part A therein, bond the first electrode of the circuit layer to the second electrode of the first device layer. Since the second substrate has been patterned and a part of the thickness of the second substrate has been removed to form a first support beam, the second substrate and the third dielectric layer will not interfere during bonding, protecting the electrodes; refer to Figure 5 part B therein, thin the second substrate of the first device layer; S502. Refer to Figure 5 part C therein, perform comb-shaped patterning on the second substrate of the first device layer to form a plurality of first channels penetrating the second substrate, that is, perform structural release on the second substrate to form a first mass block as a suspension structure; S503. Refer to Figure 6 parts A - B therein, bond the lower surface of the capping layer to the upper surface of the third substrate of the second device layer, and thin the third substrate; S504. Refer to Figure 6 part C therein, open the alignment mark of the third substrate to form a third channel penetrating the third substrate; perform boss patterning on the lower surface of the third substrate to form a plurality of second support beams; S505. Refer to Figure 6 part D therein, perform comb-shaped patterning on the third substrate to form a plurality of second channels penetrating the third substrate, that is, perform structural release on the third substrate to form a second mass block as a suspension structure; the first groove communicates with the second channel; the third channel is located outside the plurality of second channels; S506. Refer to Figure 7 part A therein, bond the second substrate (first mass block) of the first device layer to the second support beam of the second device layer, so that the first groove and the second channel communicate with the circuit region through the corresponding first channels; the third channel communicates with the circuit region through the corresponding first channels; S507. Refer to Figure 7 In part B of the figure, the fourth substrate of the capping layer and the first substrate of the circuit layer are thinned

[0040] Next, the effects of the MEMS inertial sensor and its manufacturing method of the present invention are studied through specific embodiments

[0041] Embodiment 1: Refer to Figure 8 This embodiment provides a MEMS inertial sensor, including a circuit layer, a first device layer, a second device layer, and a capping layer

[0042] Among them, a plurality of first electrodes are provided on the upper surface of the circuit layer

[0043] A plurality of first support beams corresponding to the first electrodes one by one are provided on the lower surface of the first device layer; the first support beam includes a first support beam body; one end of the first support beam body is connected to the first device layer, and a second electrode is provided at the other end; a plurality of first channels penetrating the first device layer are provided on the first device layer

[0044] A plurality of second support beams are provided on the lower surface of the second device layer; a plurality of second channels penetrating the second device layer and a plurality of third channels are provided on the second device layer; the third channels are located outside the second channels

[0045] A plurality of first grooves are provided on the lower surface of the capping layer

[0046] The first electrodes of the circuit layer are bonded to the second electrodes of the first device layer. The upper surface of the first device layer is bonded to the second support beams of the second device layer, and the second channels and the third channels are respectively communicated with the corresponding first channels. The lower surface of the capping layer is bonded to the upper surface of the device layer, and a circuit area is formed by enclosing between the capping layer and the circuit layer. The first grooves are communicated with the first channels through the second channels, and the third channels are not communicated with the first grooves

[0047] The MEMS inertial sensor provided in this embodiment can achieve the versatility of the sensor by directly bonding two device layers up and down, and at the same time makes the packaging process simpler, the packaging volume smaller, and more cost-saving at the application end compared with the single-layer device structure

[0048] Embodiment 2: This embodiment provides a manufacturing method of a MEMS inertial sensor, including the following steps S1. Manufacture the circuit layer S101. Provide a wafer as a substrate and perform alignment marking patterning on it; deposit SiO2 on the substrate surface to form a dielectric layer and perform patterning to expose part of the substrate S102. Deposit metal Al on the surface of the dielectric layer to cover the dielectric layer and the substrate, forming a metal layer, and perform patterning on the metal layer to expose part of the dielectric layer; S103. Continue to deposit SiO2 along the stacking direction to form a dielectric layer and perform planarization, so that after covering the previous dielectric layer and the metal layer, perform patterning to expose part of the metal layer; S104. Continue to deposit metal Al along the stacking direction to cover the metal layer and the SiO2 dielectric layer, and perform patterning to expose part of the SiO2 dielectric layer, forming the first electrode; S105. Continue to deposit SiO2 along the stacking direction to cover the metal layer and the dielectric layer, and perform planarization and patterning to form the first electrode.

[0049] S2. Fabricate the first device layer S201. Provide a silicon wafer as the substrate and perform patterning on the alignment marks; deposit metal Ge on the surface of the substrate to form a metal layer, perform patterning on the metal layer, and expose part of the substrate to form the second electrode; S202. Perform patterning on the exposed substrate to remove part of the thickness of the substrate, forming the first support beam, so as to form a certain space between the support beam and the circuit layer during bonding; the support beam includes a first support beam body formed by part of the second substrate and a second electrode formed at one end of the first support beam body.

[0050] S3. Fabricate the second device layer [[ID=ID=17]] S301. Provide a silicon wafer as the second device layer and perform patterning on the alignment marks of the silicon wafer. <ID=

[0051] S4. Fabricate the capping layer S401. Provide a silicon wafer as the substrate and perform patterning on the alignment marks; deposit SiO2 on the surface of the substrate to form a dielectric layer and perform planarization, perform patterning on the dielectric layer and the substrate, remove part of the dielectric layer and part of the thickness of the substrate below it, forming a plurality of first grooves (cavities). The volume of the cavity can be adjusted by the cavity depth, and there is no need to increase the cavity area.

[0052] S5. Bonding S501. Bond the first electrode (Al) of the circuit layer to the second electrode (Ge) of the first device layer. Since the substrate of the first device layer has been patterned to remove part of the thickness of the substrate to form a support beam, no interference will be formed during bonding to protect the electrodes; thin the substrate of the first device layer; S502. Perform comb-shaped patterning on the substrate of the first device layer to form a plurality of first channels penetrating the substrate, that is, perform structural release on the substrate to form the first mass block as a suspension structure; S503. Bond the side of the dielectric layer (SiO2) of the capping layer to the upper surface of the silicon wafer (Si) of the second device layer, and thin the silicon wafer of the second device layer; S504. Open the alignment marks of the second device layer to form a third channel penetrating the second device layer; perform boss patterning on the lower surface of the second device layer to form a plurality of second support beams; S505. Perform comb patterning on the second device layer to form a plurality of second channels penetrating the second device layer, that is, release the structure of the second device layer to form a second mass block as a suspension structure; the first groove communicates with the second channel; a plurality of second channels can be correspondingly opened for each third groove; the third channel is located on the periphery of the plurality of second channels; S507. Bond the substrate (the first mass block) of the first device layer to the second support beams of the second device layer, so that the first groove and the second channel communicate with the circuit area through the corresponding first channel, and the third channel communicates with the circuit area through the corresponding first channel; S508. Thin the substrates of the capping layer and the circuit layer.

[0053] The above examples are only illustrative of the present invention and do not constitute a limitation on the protection scope of the present invention. Any design identical or similar to the present invention falls within the protection scope of the present invention.

Claims

1. A MEMS inertial sensor, characterized in that: It includes a circuit layer, a first device layer, a second device layer, and a capping layer that are sequentially stacked and bonded; the first device layer is provided with a plurality of first support beams; the plurality of first support beams are bonded to the circuit layer; the second device layer is provided with a plurality of second support beams; the plurality of second support beams are bonded to the first device layer; the capping layer is bonded to the second device layer; a circuit region is formed by enclosing between the capping layer and the circuit layer.

2. The MEMS inertial sensor according to claim 1, wherein: A plurality of first electrodes corresponding to the first support beams one by one are provided on the circuit layer; the first electrodes are bonded to the first support beams.

3. The MEMS inertial sensor according to claim 2, characterized in that: The first support beam includes a first support beam body; one end of the first support beam body is connected to the first device layer, and the other end is provided with a second electrode; the second electrode is bonded to the first electrode.

4. The MEMS inertial sensor according to claim 1, wherein: A plurality of first channels penetrating the first device layer are formed on the first device layer; a plurality of second channels penetrating the second device layer are formed on the second device layer; the second channels, the first channels, and the circuit region are connected.

5. The MEMS inertial sensor according to claim 4, characterized in that: A first groove is provided on the surface of the capping layer bonded to the second device layer; the first groove is connected to the circuit region through the second channels and the first channels.

6. The MEMS inertial sensor according to claim 4, wherein: A plurality of third channels penetrating the second device layer are provided on the second device layer; the third channels are located outside the second channels.

7. The manufacturing method of the MEMS inertial sensor according to any one of claims 1-6, characterized in that, It includes the following steps: S1. Manufacture the circuit layer; S2. Fabricate the first device layer; S3. Fabricate the second device layer; S4. Fabricate the capping layer; S5. Bonding: Bond the circuit layer to the first support beams of the first device layer; bond the capping layer to the upper surface of the second device layer; bond the second support beams of the second device layer to the upper surface of the first device layer.

8. The manufacturing method of the MEMS inertial sensor according to claim 7, wherein The step S1 includes: S101. Provide a first substrate, deposit a first dielectric layer on the surface of the first substrate, and perform patterning on the first dielectric layer to expose a part of the first substrate; S102. Deposit a first metal layer, perform patterning on the first metal layer to expose a part of the first dielectric layer; S103. Deposit a second dielectric layer, perform patterning on the second dielectric layer to expose a part of the first metal layer; S104. Deposit a second metal layer to cover the first metal layer and the second dielectric layer, and perform patterning on the second metal layer to form the first electrodes; S105. Deposit a third dielectric layer to cover the second dielectric layer and the first electrodes, and perform patterning on the third dielectric layer to expose the first electrodes.

9. The manufacturing method of the MEMS inertial sensor according to claim 7, characterized in that, The step S2 includes: S201. Provide a second substrate and perform patterning on it; deposit a metal on the surface of the second substrate to form a third metal layer, and perform patterning on the third metal layer to expose a part of the second substrate to form the second electrodes; S202. Perform patterning on the exposed second substrate to remove a part of the thickness of the second substrate to form the first support beams.

10. The manufacturing method of the MEMS inertial sensor according to claim 7, characterized in that, The step S5 includes: S501. Bond the circuit layer to the first support beams of the first device layer; S502. Perform comb-shaped patterning on the first device layer to form the first channels penetrating the first device layer; S503. Bond the capping layer to the upper surface of the second device layer; S504. Perform boss patterning on the lower surface of the second device layer to form a plurality of second support beams; S505. Perform comb-shaped patterning on the second device layer to form a second channel that penetrates the second device layer; S506. Bond the upper surface of the first device layer to the second support beam of the second device layer.

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