A MEMS inertial sensor and a manufacturing method thereof

Abstract

The present invention belongs to the field of micro-electromechanical systems technology, and specifically provides a MEMS inertial sensor, comprising a circuit layer, a first device layer, a second device layer, and a cap layer stacked and bonded in sequence; a plurality of first support beams are provided on the lower surface of the first device layer; 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 cap layer is bonded to the second device layer; and the cap layer and the circuit layer enclose a circuit area. The MEMS inertial sensor provided by the present invention can realize the multifunctionality of the sensor by directly bonding two device layers up and down, and makes the packaging process simpler and the packaging volume smaller. At the same time, it is more cost-effective at the application end compared to a single-layer device structure, which is conducive to improving the process yield and miniaturization of the integrated system.

Description

Technical Field

[0001] The present invention belongs to micro-electromechanical systems, and in particular relates to a MEMS inertial sensor and a manufacturing method thereof. Background Art

[0002] Inertial devices are devices used to measure and sense the motion of objects, primarily gyroscopes and accelerometers. These devices sense an object's angular and linear motion to obtain information such as its attitude, position, and velocity. They are widely used in consumer electronics, in-vehicle navigation, industrial automation, aerospace, and military applications.

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

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

[0005] To this end, the present invention provides a MEMS inertial sensor, comprising a circuit layer, a first device layer, a second device layer and a cap layer stacked and bonded in sequence; 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 cap layer is bonded to the second device layer; and the cap layer and the circuit layer enclose a circuit area.

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

[0007] Specifically, the 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, the first device layer is provided with a plurality of first channels penetrating the first device layer; the second device layer is provided with a plurality of second channels penetrating the second device layer; and the second channels, the first channels, and the circuit area are connected.

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

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

[0011] The present invention also provides a method for manufacturing the above-mentioned MEMS inertial sensor, comprising the following steps:

[0012] S1, manufacturing circuit layer;

[0013] S2, manufacturing a first device layer;

[0014] S3, making a second device layer;

[0015] S4, making a capping layer;

[0016] S5. Bonding: Bonding the circuit layer to the first support beam of the first device layer to enclose a circuit area; bonding the cap layer to the upper surface of the second device layer; bonding the second support beam of the second device layer to the upper surface of the first device layer.

[0017] Specifically, the above step S1 includes:

[0018] S101, providing a first substrate, depositing a first dielectric layer on a surface of the first substrate, and performing patterning on the first dielectric layer to expose a portion of the first substrate;

[0019] S102, depositing a first metal layer, and performing patterning on the first metal layer to expose a portion of the first dielectric layer;

[0020] S103, depositing a second dielectric layer, and patterning the second dielectric layer to expose a portion of the first metal layer;

[0021] S104, depositing a second metal layer to cover the first metal layer and the second dielectric layer, and patterning the second metal layer to form a first electrode;

[0022] S105 , depositing a third dielectric layer to cover the second dielectric layer and the first electrode, and performing patterning on the third dielectric layer to expose the first electrode.

[0023] Specifically, the above step S2 includes:

[0024] S201, providing a second substrate and patterning it; depositing metal on the surface of the second substrate to form a third metal layer, and patterning the third metal layer to expose a portion of the second substrate to form a second electrode;

[0025] S202 , performing patterning on the exposed second substrate, removing a portion of the second substrate, and forming a first support beam.

[0026] Specifically, the above step S5 includes:

[0027] S501, bonding the circuit layer to the first support beam of the first device layer to form a circuit area;

[0028] S502, performing comb-teeth patterning processing on the first device layer to form a first channel penetrating the first device layer;

[0029] S503, bonding a cap layer on the upper surface of the second device layer;

[0030] S504, performing boss patterning processing on the lower surface of the second device layer to form a plurality of second support beams;

[0031] S505, performing comb-teeth patterning processing on the second device layer to form a second channel penetrating the second device layer;

[0032] S506 , bonding the upper surface of the first device layer to the second support beam of the second device layer.

[0033] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0034] 1. The MEMS inertial sensor provided by the present invention can realize the multifunctionality of the sensor by directly bonding two device layers up and down, and makes the packaging process simpler and the packaging volume smaller. At the same time, it is more cost-effective at the application end compared with a single-layer device structure, which is conducive to improving the process yield and miniaturization of the integrated system.

[0035] 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, thereby improving the structural stability and precision, and reducing the structural failure rate in a vibration environment compared to 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, and multifunctional units can be integrated at the same time to achieve synchronous detection of multi-axis inertial parameters and improve device sensitivity. In addition, the two device layers are vertically interconnected with the metal electrodes at the interface of the circuit layer through the first channel and the second channel, which shortens the signal transmission distance, reduces the parasitic capacitance, and can significantly improve the signal-to-noise ratio of weak signals. The second device layer is preferably a silicon wafer with a vertical channel, which can be used as a support structure for the inertial mass block to improve the stability of the resonant frequency.

[0036] 3. The MEMS inertial sensor provided by the present invention uses a first electrode and a second electrode for bonding, and directly establishes electrical interconnection between the circuit layer and the device layer at the same time as the interface is combined, which reduces the difficulty of electrical interconnection. The bimetallic 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 of metal materials is well matched, which can improve the stability of the device under temperature changes. The heat conduction path formed by the metal electrode bonding helps to quickly conduct the heat generated when the MEMS device is working to the packaging substrate, thereby improving the stability and life of the sensor in a high temperature environment. The first electrode and the second electrode are preferably bonded with heterogeneous metals, and the material properties 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, and the reliability is enhanced.

[0037] The present invention will be described in further detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 AB is a flowchart corresponding to step S101, C is a flowchart corresponding to step S102, DE is a flowchart corresponding to step S103, F is a flowchart corresponding to step S104, and GH is a flowchart corresponding to step S105.

[0039] Figure 2 1 is a schematic diagram of manufacturing the first device layer in an embodiment of the present invention; AB is a flow chart corresponding to step S201, and C is a flow chart corresponding to step S202.

[0040] Figure 3 This is a schematic diagram of manufacturing the second device layer in an embodiment of the present invention.

[0041] Figure 4 1 is a schematic diagram of manufacturing a capping layer in an embodiment of the present invention; wherein AC is a flow chart corresponding to step S401.

[0042] Figure 5 Schematic diagram of bonding between the first device layer and the circuit layer in an embodiment of the present invention; wherein A is a flowchart corresponding to step S501, B is a flowchart corresponding to step S502, and C is a flowchart corresponding to step S503.

[0043] Figure 6 AB is a flowchart corresponding to step S504, C is a flowchart corresponding to step S505, and D is a flowchart corresponding to step S506.

[0044] Figure 7Schematic diagram of bonding between the first device layer and the second device layer in an embodiment of the present invention; wherein A is a flowchart corresponding to step S507, and B is a flowchart corresponding to step S508.

[0045] Figure 8 Schematic diagram of the structure of a MEMS inertial sensor provided by an embodiment of the present invention.

[0046] Figure 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, cap layer; 401, first groove. DETAILED DESCRIPTION

[0047] The technical solutions of 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 the embodiments. Although the representative embodiments of the present invention have been described in detail, it will be understood by those skilled in the art 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.

[0048] The present invention provides a MEMS inertial sensor, comprising a circuit layer, a first device layer, a second device layer, and a cap layer stacked and bonded in sequence; 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 cap layer is bonded to the second device layer; the cap layer and the circuit layer enclose a circuit area. 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 multifunctionality of the sensor can be achieved, and the packaging process can be simplified, the packaging volume can be smaller, and at the same time, it is more cost-effective than a single-layer device structure at the application end.

[0049] Specifically, the surface where the circuit layer is bonded to the device layer is generally the upper surface of the circuit layer, and is provided with a plurality of first electrodes; the first electrodes correspond one-to-one to the first support beams; and the first electrodes are bonded to the first support beams.

[0050] 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 and second electrodes can be selected as needed, and are generally Al or Ge.

[0051] In one embodiment, the first device layer is provided with a plurality of first channels penetrating the first device layer; the second device layer is provided with a plurality of second channels penetrating the second device layer; the second channels, the first channels, and the circuit area are connected, thereby releasing the silicon microstructure of the inertial device.

[0052] In another embodiment, a first groove, or cavity, is provided on the surface where the cap layer and the second device layer are bonded. The first groove connects to the circuit area via the second channel and the first channel. This provides physical isolation for the mass block and support beam, helping to reduce interference caused by the mechanical structure and providing shock absorption, resulting in more stable and accurate measurements.

[0053] 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.

[0054] The present invention also provides a method for manufacturing a MEMS inertial sensor, comprising the following steps:

[0055] S1. Manufacturing circuit layer

[0056] S101, providing a first substrate, and performing a patterning process on the substrate (refer to Figure 1 A portion of the first substrate is deposited on the first dielectric layer, the first dielectric layer is patterned to expose a portion of the first substrate (refer to Figure 1 Part B);

[0057] S102. Reference Figure 1 In part C, metal is deposited on the surface of the first dielectric layer to cover the first dielectric layer and the first substrate to form a first metal layer, and the first metal layer is patterned to expose a portion of the first dielectric layer;

[0058] S103, continue to deposit the second dielectric layer along the stacking direction and planarize it so that it covers the first dielectric layer and the first metal layer (refer to Figure 1 The second dielectric layer is patterned to expose part of the first metal layer (refer to Figure 1 (Part E);

[0059] S104. Reference Figure 1 In the middle F portion, metal is continuously deposited along the stacking direction to cover the first metal layer and the second dielectric layer to form a second metal layer. The second metal layer is patterned to expose a portion of the second dielectric layer to form a first electrode.

[0060] S105, continue to deposit the third dielectric layer along the stacking direction and planarize it, covering the second metal layer and the first electrode (refer to Figure 1The third dielectric layer is patterned to reveal the first electrode (refer to Figure 1 (see Section H in the figure).

[0061] S2. Making the first device layer

[0062] S201, providing a second substrate, and performing a patterning process on the second substrate (refer to Figure 2 A portion in the middle); depositing metal on the surface of the second substrate to form a third metal layer, and patterning the third metal layer to expose a portion of the second substrate to form a second electrode (refer to Figure 2 Part B);

[0063] S202, reference Figure 2 In the middle C part, the exposed second substrate is patterned to remove part of the thickness of the second substrate to form a first support beam so that a certain space can be formed between the circuit layer during bonding; the first support beam preferably 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.

[0064] S3, making the second device layer

[0065] S301, reference Figure 3 , providing a third substrate as the second device layer, and performing an alignment mark graphical processing on the third substrate.

[0066] S4. Make the cap layer

[0067] S401, providing a fourth substrate, and performing an alignment mark patterning process on it (refer to Figure 4 A portion in the middle); depositing a fourth dielectric layer on the surface of the fourth substrate and planarizing it (refer to Figure 4 Part B in the figure), the fourth dielectric layer and the fourth substrate are patterned to remove part of the fourth dielectric layer and part of the thickness of the fourth substrate below it, forming a plurality of first grooves (cavities) (refer to Figure 4 The volume of the cavity can be controlled by adjusting the cavity depth without increasing the cavity area.

[0068] S5. Bonding

[0069] S501, reference Figure 5 In part A, the first electrode of the circuit layer is bonded to the second electrode of the first device layer. Since the second substrate has been patterned, part of the thickness of the second substrate is removed to form the first support beam. During bonding, the second substrate and the third dielectric layer will not interfere with each other, thus protecting the electrodes. Figure 5 In part B, the second substrate of the first device layer is thinned;

[0070] S502, reference Figure 5In the middle C part, the second substrate of the first device layer is subjected to comb-tooth patterning to form a plurality of first channels penetrating the second substrate, that is, the second substrate is structurally released to form a first mass block as a suspended structure;

[0071] S503, reference Figure 6 In the middle AB part, the lower surface of the cap layer is bonded to the upper surface of the third substrate of the second device layer, and the third substrate is thinned;

[0072] S504, reference Figure 6 In the middle C portion, the alignment mark of the third substrate is opened to form a third channel penetrating the third substrate; the lower surface of the third substrate is patterned with bosses to form a plurality of second support beams;

[0073] S505, reference Figure 6 In the middle D portion, the third substrate is patterned with comb teeth to form a plurality of second channels penetrating the third substrate. That is, the third substrate is structurally released to form a second mass block as a suspended structure. The first groove is connected to the second channel. The third channel is located outside the plurality of second channels.

[0074] S506, reference Figure 7 In the middle A section, the second substrate (first mass) of the first device layer is bonded to the second support beam of the second device layer, so that the first groove and the second channel are connected to the circuit area through the corresponding first channel; and the third channel is connected to the circuit area through the corresponding first channel;

[0075] S507, reference Figure 7 In part B, the fourth substrate of the capping layer and the first substrate of the circuit layer are thinned.

[0076] The effects of the MEMS inertial sensor and the manufacturing method thereof of the present invention are studied below through specific embodiments.

[0077] Example 1: Reference Figure 8 This embodiment provides a MEMS inertial sensor, including a circuit layer, a first device layer, a second device layer and a cap layer.

[0078] Wherein, a plurality of first electrodes are provided on the upper surface of the circuit layer.

[0079] A plurality of first support beams corresponding one-to-one to the first electrodes 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 the other end is provided with a second electrode; a plurality of first channels passing through the first device layer are opened on the first device layer.

[0080] 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.

[0081] A plurality of first grooves are formed on the lower surface of the cap layer.

[0082] The first electrode of the circuit layer is bonded to the second electrode of the first device layer. The upper surface of the first device layer is bonded to the second support beam of the second device layer. The second channel and the third channel are connected to the corresponding first channel. The lower surface of the cap layer is bonded to the upper surface of the device layer. The cap layer and the circuit layer enclose a circuit area. The first groove is connected to the first channel through the second channel, and the third channel is not connected to the first groove.

[0083] The MEMS inertial sensor provided in this embodiment can realize the multifunctionality of the sensor by directly bonding two device layers up and down, and makes the packaging process simpler and the packaging volume smaller. At the same time, it is more cost-effective at the application end than a single-layer device structure.

[0084] Embodiment 2: This embodiment provides a method for manufacturing a MEMS inertial sensor, comprising the following steps:

[0085] S1. Manufacturing circuit layer

[0086] S101, providing a wafer as a substrate and performing alignment mark patterning on the wafer; depositing SiO2 on the surface of the substrate to form a dielectric layer, and performing patterning to expose a portion of the substrate;

[0087] S102, depositing metal Al on the surface of the dielectric layer to cover the dielectric layer and the substrate to form a metal layer, and patterning the metal layer to expose a portion of the dielectric layer;

[0088] S103, continuing to deposit SiO2 along the stacking direction to form a dielectric layer and planarizing it so that it covers the previous dielectric layer and the metal layer, and then performing patterning to expose part of the metal layer;

[0089] S104, continuing to deposit metal Al along the stacking direction to cover the metal layer and the SiO2 dielectric layer, and performing patterning to expose a portion of the SiO2 dielectric layer to form a first electrode;

[0090] S105 , continue depositing SiO 2 along the stacking direction to cover the metal layer and the dielectric layer, and perform planarization and patterning processing to form a first electrode.

[0091] S2. Making the first device layer

[0092] S201, providing a silicon wafer as a substrate, and performing an alignment mark patterning process on the wafer; depositing metal Ge on the surface of the substrate to form a metal layer, patterning the metal layer, and exposing a portion of the substrate to form a second electrode;

[0093] S202. Performing graphic processing on the exposed substrate, removing part of the thickness of the substrate, and forming a first support beam so that a certain space can be formed between 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.

[0094] S3, making the second device layer

[0095] S301 , providing a silicon wafer as a second device layer, and performing an alignment mark patterning process on the silicon wafer.

[0096] S4. Make the cap layer

[0097] S401: Provide a silicon wafer as a substrate and perform patterning of alignment marks on it. Deposit SiO2 on the substrate surface to form a dielectric layer and planarize it. Pattern the dielectric layer and substrate, removing portions of the dielectric layer and the underlying thickness of the substrate to form a plurality of first recesses (cavities). The volume of the cavities can be controlled by adjusting the cavity depth, without increasing the cavity area.

[0098] S5. Bonding

[0099] 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, a portion of the substrate thickness is removed to form a support beam, which will not cause interference during bonding and protect the electrodes. The substrate of the first device layer is thinned.

[0100] S502 , performing comb-tooth patterning processing on the substrate of the first device layer to form a plurality of first channels penetrating the substrate, that is, performing structural release on the substrate to form a first mass block as a suspended structure;

[0101] S503, bonding one side of the dielectric layer (SiO2) of the cap layer to the upper surface of the silicon wafer (Si) of the second device layer, and thinning the silicon wafer of the second device layer;

[0102] S504, opening the alignment mark of the second device layer to form a third channel penetrating the second device layer; performing boss patterning on the lower surface of the second device layer to form a plurality of second support beams;

[0103] S505, performing comb-tooth patterning on the second device layer to form a plurality of second channels penetrating the second device layer, that is, performing structural release on the second device layer to form a second mass block as a suspended structure; the first groove is connected to the second channel; each third groove may correspond to a plurality of second channels; the third channel is located outside the plurality of second channels;

[0104] S507, bonding the substrate (first mass) of the first device layer to the second support beam of the second device layer, so that the first groove and the second channel are connected to the circuit area through the corresponding first channel, and the third channel is connected to the circuit area through the corresponding first channel;

[0105] S508 , performing thinning processing on the substrate of the cap layer and the substrate of the circuit layer.

[0106] The above examples are merely illustrative of the present invention and do not limit the scope of protection of the present invention. Any design that is identical or similar to the present invention falls within the scope of protection 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 cap layer that are stacked and bonded in sequence; 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 cap layer is bonded to the second device layer; the cap layer and the circuit layer are enclosed to form a circuit area; the first device layer is provided with a plurality of first channels that pass through the first device layer; the second device layer is provided with a plurality of second channels that pass through the second device layer; the second channels, the first channels and the circuit area are connected.

2. The MEMS inertial sensor according to claim 1, wherein: A plurality of first electrodes corresponding one to one with the first support beams 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, wherein: 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 first groove is provided on the surface where the cap layer and the second device layer are bonded; the first groove is connected to the circuit area through the second channel and the first channel.

5. The MEMS inertial sensor according to claim 1, wherein: The second device layer is provided with a plurality of third channels penetrating the second device layer; the third channels are located outside the second channels.

6. The method for manufacturing a MEMS inertial sensor according to any one of claims 1 to 5, wherein: The following steps are involved: S1, manufacturing circuit layer; S2, manufacturing a first device layer; S3, making a second device layer; S4, making a capping layer; S5. Bonding: bonding the circuit layer to the first support beam of the first device layer; bonding the cap layer to the upper surface of the second device layer; bonding the second support beam of the second device layer to the upper surface of the first device layer.

7. The method for manufacturing a MEMS inertial sensor according to claim 6, wherein: The step S1 comprises: S101, providing a first substrate, depositing a first dielectric layer on a surface of the first substrate, and performing patterning on the first dielectric layer to expose a portion of the first substrate; S102, depositing a first metal layer, and performing patterning on the first metal layer to expose a portion of the first dielectric layer; S103, depositing a second dielectric layer, and patterning the second dielectric layer to expose a portion of the first metal layer; S104, depositing a second metal layer to cover the first metal layer and the second dielectric layer, and patterning the second metal layer to form a first electrode; S105 , depositing a third dielectric layer to cover the second dielectric layer and the first electrode, and performing patterning on the third dielectric layer to expose the first electrode.

8. The method for manufacturing a MEMS inertial sensor according to claim 6, wherein: The step S2 comprises: S201, providing a second substrate and patterning it; depositing metal on the surface of the second substrate to form a third metal layer, and patterning the third metal layer to expose a portion of the second substrate to form a second electrode; S202 , performing patterning on the exposed second substrate, removing a portion of the second substrate, and forming a first support beam.

9. The method for manufacturing a MEMS inertial sensor according to claim 6, wherein: The step S5 comprises: S501, bonding the circuit layer to the first support beam of the first device layer; S502, performing comb-teeth patterning processing on the first device layer to form a first channel penetrating the first device layer; S503, bonding a cap layer on the upper surface of the second device layer; S504, performing boss patterning processing on the lower surface of the second device layer to form a plurality of second support beams; S505, performing comb-teeth patterning processing on the second device layer to form a second channel penetrating the second device layer; S506 , bonding the upper surface of the first device layer to the second support beam of the second device layer.

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