Sealed micro-electro-mechanical membrane device
By using a support body and platform of semiconductor material in the microelectromechanical membrane sensor, combined with the design of curved parts and low-modulus sealing strips, the thermal stress drift and waterproof problems caused by welding are solved, achieving a more flexible design and efficient sealing effect.
Patent Information
- Application Number
- CN202411727084.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2024-11-19
- Filing Date
- 2024-11-28
- Publication Date
- 2025-06-06
AI Technical Summary
Existing microelectromechanical membrane sensors are prone to thermal stress problems during welding, resulting in sensing drift, and the use of ceramic substrates limits design freedom, and it is difficult to achieve waterproofing through gel deposition in sensors on suspended platforms.
A microelectromechanical membrane sensor is designed, and the support body and platform are made of semiconductor materials. The platform is suspended on the support body through curved parts, and a sealing strip with low Young's modulus and low thermal expansion coefficient is laid in the gap to form a sealing structure.
Effectively reduces thermal stress drift caused by welding, realizes waterproofing of the sensor, and since the deformation of the substrate does not affect the output, allowing the use of cheaper substrate materials, increasing design flexibility.
Smart Images
Figure CN120097272A_ABST
Abstract
Description
Technical Field
[0001] The present disclosure relates to a sealed micro-electromechanical (MEMS) membrane device and a method for manufacturing a sealed micro-electromechanical membrane device. Background Art
[0002] It is well known that a common problem with MEMS membrane sensors, especially pressure sensors, involves the effects of mounting operations. Typically, MEMS membrane sensors and associated control devices are manufactured as correspondingly different semiconductor chips (sensor chips and control chips or application-specific integrated circuit ASIC chips), which are bonded to a base and included in a package structure. Subsequently, the base is soldered to a printed circuit board or PCB for electrical and mechanical coupling with the user system.
[0003] In the absence of appropriate measures, soldering induces significant thermal stresses which, due to different thermal expansion coefficients, may deform the sensor chip and induce mechanical stresses on the membrane, resulting in a drift of the sensing relative to the calibrated value.
[0004] In order to reduce the negative effects of thermal stress caused by welding, ceramic substrates are sometimes used as a base for assembling sensor chips and control chips. In fact, ceramics have the advantage of high rigidity and therefore little deformation relative to polymer substrates. On the other hand, ceramic substrates are expensive and do not allow the use of some advantageous and very common assembly technologies, such as flip chip or WLCSP (wafer level chip scale packaging) technology. The design freedom of membrane pressure sensors is therefore limited.
[0005] According to different solutions, the film operating as a transducer is formed in a suspension platform obtained from a sensor chip and is connected to the suspension platform by a flexure. The main part of the sensor chip is used as a support for the platform. The flexure can almost completely absorb the deformation of the sensor chip, as well as any impact and vibration, and protect the film from stress. However, if the solution is very effective in reducing the drift caused by thermomechanical stress, it may be difficult to obtain other favorable characteristics in many cases. In fact, in a microelectromechanical pressure sensor, the film is connected to an external fluid to be able to receive a pressure signal to be converted, but at the same time, it is usually useful to protect the same film from the influence of potentially harmful substances (such as dust and moisture). Therefore, the sensitive part of the microelectromechanical membrane device can be embedded in a potting gel, which has the property of transmitting pressure changes from the outside and acts as a barrier for impurities. However, in a sensor with a suspension platform, it may be difficult to obtain waterproofing by gel deposition. Since the gap between the platform, the flexure and the support has a micron size, the gel viscosity may cause problems in filling and cause, for example, bubble formation, which may affect the propagation and conversion of the pressure signal or make waterproofing invalid. Structures with a platform elastically coupled to a support are therefore less compatible with waterproofing. Summary of the invention
[0006] The present disclosure provides a sealed micro-electromechanical device and a method for manufacturing a sealed micro-electromechanical device which enables the described limitations to be overcome or at least mitigated.
[0007] A micro-electromechanical device and a method for manufacturing the micro-electromechanical device are provided. The micro-electromechanical film sensor includes a support body, the support body contains a semiconductor material and has a recess in a surface; a platform, the platform is accommodated in the recess and is a certain distance from the support body; a flexure, the flexure connects the platform to the support body and is configured to keep the platform suspended in the recess, wherein a gap extends between the support body, the platform and the flexure; a membrane, the membrane is accommodated in the platform and defines a buried cavity contained in the platform; and a sealing strip, the sealing strip extends along the gap on the support body, the platform and the flexure. BRIEF DESCRIPTION OF THE DRAWINGS
[0008] For a better understanding of the present disclosure, reference is made to the accompanying drawings, in which preferred embodiments are provided by way of non-limiting examples, in which:
[0009] Figure 1 is a top view of a micro-electromechanical film sensor according to an embodiment of the present disclosure;
[0010] Figure 2 is along Figure 1 The line II-II intercepts through Figure 1 The cross section of the sensor;
[0011] Figure 3 is a cross section through a micro-electromechanical pressure sensor according to various embodiments of the present disclosure;
[0012] Figures 4 to 13 is a cross section through a semiconductor wafer in a subsequent processing step of a process for manufacturing a micro-electromechanical pressure sensor according to an embodiment of the present disclosure; and
[0013] Fig.14 and Fig.15 is a cross section through a semiconductor wafer during a subsequent processing step in a process for fabricating a micro-electromechanical pressure sensor according to various embodiments of the present disclosure. DETAILED DESCRIPTION
[0014] The following description refers to the arrangements shown in the accompanying drawings; therefore, expressions such as "above", "below", "upper", "lower", "at the top", "at the bottom", "right", "left", etc. relate to the figures and are not to be interpreted in a limiting manner.
[0015] refer to Figure 1 A micro-electromechanical membrane sensor, in particular a pressure sensor, is indicated overall using reference numeral 1 and comprises a support 2 and a platform 3 accommodating a membrane 5 and being connected to the support 2 by means of a bend or bend extension 7 .
[0016] The support 2 is a die of semiconductor material (eg single crystal silicon and / or polycrystalline silicon).
[0017] The platform 3 is housed in a recess 8 obtained in the main face 2a of the support 2 and is kept suspended on the surface 2a of the same support 2 by means of the bend 7. In more detail, the platform 3 has a generally quadrilateral (for example rectangular) shape and is spaced from the surface 2a.
[0018] In one embodiment, the bend 7 is L-shaped and connects the vertex 3a of the platform 3 to the support 2. A first branch or portion 7a of the bend 7 is anchored to the support 2 and extends substantially parallel or coplanar with one side of the platform 3. A second, shorter branch 7b of the bend 7 is continuous and substantially perpendicular or transverse to the first branch 7a and is bonded to the vertex 3a of the platform 3.
[0019] The spiral gap 10 separates the platform 3 and the flexure 7 laterally from the support 2. Specifically, the gap 10 extends between the support 2 and the first branch 7a of the flexure 7, then along the second branch or portion 7b and along three sides of the platform 3, and finally between the platform 3 and the first branch 7a until the second branch 7b of the flexure 7. For example, the gap may have a width between 3 μm and 30 μm, specifically 7 μm in one embodiment.
[0020] The bent piece 7 is spaced apart from the inner surface of the support body 2, which faces the gap 10. The first branch 7a of the bent piece 7 extends from the first inner surface of the support body 2. The second branch 7b is spaced apart from the second inner surface, which is opposite to the first inner surface.
[0021] The flexure 7 has a thickness substantially equal to that of the platform 3 and is shaped so as to allow, within the limits imposed by the size of the gap 10, so-called in-plane movements of the platform 3, i.e. movements substantially parallel to the main face 2a of the support 2 (and to the main face of the platform 3) without deformation of the support 2. Out-of-plane movements substantially perpendicular to the in-plane movements are instead substantially prevented. Possibly, the flexure 7 may allow twisting around the axis of the first branch 7a, which may help to accommodate deformations of the support 2 without transmitting significant strains to the platform 3, for example after thermal stresses.
[0022] The micro-electromechanical pressure sensor 1 may also be provided with a stopper (not shown for simplicity) to further limit the movement of the platform 3 .
[0023] The membrane 5 is formed on the platform 3 and closes the buried cavity 11 on one side, the buried cavity 11 being contained in the platform 3. In one embodiment, the buried cavity 11 is sealed by the membrane 5 and defines a pressure-controlled reference chamber. The membrane 5 is of a semiconductor material, such as single crystal silicon, and can be capacitively coupled to one or more electrodes on the bottom of the buried cavity 11, or provided with a sensitive piezoresistive structure. On a side opposite to the buried cavity 11, the membrane 5 is exposed (directly or indirectly) to the pressure of the external environment. A conductive line (not shown) extends from the membrane 5 along the bend 7 to a pad (not shown) and is used for electrical coupling of the sensor 1 with the outside (e.g., an electronic system in which the sensor 1 is contained).
[0024] In one embodiment, a first dielectric or insulating layer 12, such as silicon oxide, covers the main face 2a of the support 2, the flexure 7 and the platform 3 outside the membrane 5. A second dielectric or insulating layer 13, such as a thin silicon nitride layer, covers the main face 2a of the support 2, the flexure 7 and the platform 3, including the membrane 5.
[0025] The sealing strip 15 extends along the gap 10 on the main surface 2a of the support 2 and partially on the bent piece 7 and the platform 3. The sealing strip 15 is tightly adhered to the support 2, the bent piece 7 and the platform 3 along the edge of the gap 10, and seals the gap 10 and the recess 8 in which the platform 3 is accommodated.
[0026] The sealing strip 15 is made of a material having a low Young's modulus and a low thermal expansion coefficient. Generally, the material forming the sealing strip 15 has a Young's modulus of less than 300 MPa and a thermal expansion coefficient of less than 250 ppm / °C.
[0027] In one embodiment, the sealing strip 15 is a laminate of a polymer material, such as a dry resist.
[0028] according to Figure 3 Referring to the different embodiments, in the micro-electromechanical membrane pressure sensor 100 , the sealing strip indicated here by 115 is an ultraviolet curing ink or UV curing ink, which is deposited on the main face 2 a of the support 2 along the gap 10 .
[0029] The sealing strip allows the sensor to be waterproofed without significantly affecting the thermomechanical stresses transmitted to the membrane. In practice, the presence of material across the gap maintains the decoupling of the platform from the support to transmit the strains that may be generated after deformation of the support. Regardless of the base used, the stresses generated by the assembly operation therefore do not cause significant drifts on the sensor output. For example, in the case of a width of the gap 10 of 7 μm, the combination of the values of the Young's modulus E and the thermal expansion coefficients defined in Table 1 produces very low values of output drift and in any case below 1 mbar.
[0030] Table 1
[0031] E[MPa] CTE[ppm / ℃] Drift [mbar] 10 30 -0.00231 10 180 -0.00563 100 100 -0.59 150 100 -0.98 200 30 -0.404
[0032] Thus, on the one hand, waterproof sensors can also be manufactured using a cheaper base than the ceramic base used to assemble the sensor, since deformations of the base do not affect the output due to the fact that the membrane is formed on a movable platform. On the other hand, the technology used to bond the sensor to the support, in particular the flip chip or WLCSP (wafer level chip scale packaging) technology, can also be used in a more flexible way.
[0033] The selection of the Young's modulus and the lowest thermal expansion coefficient within the above range ensures on the one hand that the gap remains effectively sealed and on the other hand that the sealing strip does not stiffen the structure to such an extent that thermomechanical stresses are transmitted from the support to the platform and thus to the membrane. In addition, the sealing strip may help to limit the displacement of the platform to avoid the action of a stopper that could damage it.
[0034] Figures 4 to 13It is used to manufacture from a semiconductor wafer 20 (eg, single crystal silicon) including a substrate 20' Figure 1 and Figure 2 The process of sensor 1. In the initial step ( Figure 4 ), the substrate 20' is etched to form a grid or matrix of structures 21, such as columns or walls, separated by trenches 22 in the region corresponding to the bottom of the recess 8, which will be defined below.
[0035] Afterwards ( Figure 5 ), an epitaxial layer 20" of controlled thickness is grown and the trench 22 is closed.
[0036] The material forming the structure 21 is redistributed by the annealing step and a cavity 23 is formed, which extends substantially over the entire extent of the recess 8 ( Figure 6 ).
[0037] By repeating the same technique ( Figure 7 The buried cavity 11 and the film 5 are then formed by etching, epitaxial growth and annealing. Specifically, the thickness of the film 5 can be determined by controlling the thickness of the new epitaxial layer, which is not illustrated in detail here. The substrate 20', the epitaxial layer 20" and the new epitaxial layer not shown define the support 2 as it is obtained at the end of the process after cutting the wafer 20. For convenience, Figure 7 Also hereinafter and in the related description, reference will be made to the support 2. The conductive lines of the membrane and, depending on design preferences, the piezoresistive regions (also not shown) are then formed by processing steps not shown.
[0038] After forming the buried cavity 11 and the membrane 5, a first dielectric layer 12 is deposited on the wafer 20 and selectively removed on the membrane 5 and along the path where the gap 10 will be subsequently formed ( Figure 8 ).
[0039] The second dielectric layer 13 is conformally deposited on the wafer 20 ( Fig. 9 ).
[0040] like Fig.10 As shown, an anisotropic etch, such as a trench etch, is then performed along the path of the gap 10 until reaching in depth at least the cavity 23. The trench etch opens the gap 10 and defines the terrace 3, the bend 7 and the recess 8.
[0041] However, it will be appreciated that the structure obtained at this point may also be manufactured using alternative processes, for example using a sacrificial dielectric layer to separate the platform 3 from the substrate 20 and to define the membrane 5 .
[0042] A sheet 25 of polymer material (eg, dry resist) is laminated to wafer 20 ( Fig.11). The first dielectric layer 12 in this step also acts as a spacer and separates the sheet 25 from the membrane 5 and the entrance to the gap 10.
[0043] A resist layer 26 is deposited on the sheet 25 and patterned by a photolithography process, such as Fig.12 As shown, an etching mask 27 is formed, which covers the sheet 25 along the path of the gap 10 and has a shape corresponding to the sealing strip 15.
[0044] The resist layer 26 is exposed and selectively removed using an etching mask 27 to form a sealing strip 15 ( Fig.13 ).
[0045] The etching mask 27 is then removed, and after dicing the wafer 20, Figure 1 and Figure 2 The structure is obtained.
[0046] Alternatively, after the gap 10 is opened and the land 3, the bend 7 and the recess 8 are defined, a strip 115' of UV curable ink is deposited along the gap 10 ( Fig.14 ). In the case where the width of the gap 10 is between 3 μm and 30 μm (as described above), surface tension prevents the UV curing ink from penetrating into the recess 8. Upon exposure to UV radiation ( Fig.15 ) after which the strip 115' partially hardens, remaining within the indicated Young's modulus range, and utilizing the sealing strip 115, Figure 3 The structure is obtained.
[0047] Finally, it is clear that modifications and variations may be made to the devices and methods described herein without thereby departing from the scope of the present disclosure.
[0048] For example, it is particularly advantageous for the platform to be connected to the support at a single point and by means of a single bend, since it minimizes the strains transmitted to the platform and the membrane in the event of a deformation of the support. However, this is not the only possible solution. In practice, depending on design preferences, multiple bends may be included, for example, on opposite sides of the platform. In this case, the gap may be divided into multiple sections and for each section a corresponding sealing strip of the type described may be provided.
[0049] Furthermore, the material forming the sealing strip is not limited to the described materials.
[0050] A micro-electromechanical film sensor comprises: a support (2), the support (2) comprising a semiconductor material and having a recess (8) in a surface (2a); a platform (3), the platform (3) being accommodated in the recess (8) at a distance from the support (2); a bending piece (7), the bending piece (7) connecting the platform (3) to the support (2) and being configured to keep the platform (3) suspended in the recess (8), wherein a gap (10) extends between the support (2), the platform (3) and the bending piece (7); a membrane (5), the membrane (5) being accommodated in the platform (3) and defining a buried cavity (11) contained in the platform (3); and a sealing strip (15; 115), the sealing strip (15; 115) extending along the gap (10) on the support (2), the platform (3) and the bending piece (7).
[0051] The material of the sealing strip (15; 115) has a Young's modulus of less than 300 MPa.
[0052] The material of the sealing strip (15; 115) has a thermal expansion coefficient of less than 250 ppm / °C.
[0053] The sealing strip (15) is part of a sheet of polymer material.
[0054] The material of the sealing strip (15; 115) is selected between dry resist and UV curing ink.
[0055] The platform (3) has a polygonal shape, and wherein the bent piece (7) has a first branch (7a) and a second branch (7b), the first branch (7a) being anchored to the support (2) and extending parallel to one side of the platform (3), and the second branch (7b) being continuous with the first branch 7a and joined to the platform (3).
[0056] The gap (10) has a spiral shape and separates the platform (3) and the bend (7) laterally from the support (2).
[0057] The gap (10) extends between the support (2) and the first branch (7a) of the bend (7), around the platform (3) and between the platform (3) and the first branch (7a).
[0058] The gap (10) has a width between 3 μm and 30 μm.
[0059] A method for manufacturing a micro-electromechanical film sensor comprises: forming a recess (8), a platform (3) and a flexure (7) in a wafer (20) comprising a semiconductor material, wherein the recess (8) is in a surface (2a), the platform (3) is accommodated in the recess (8) at a certain distance from a support (2), the flexure (7) connects the platform (3) to the support (2) and is configured to keep the platform (3) suspended in the recess (8), wherein a gap (10) extends between the support (2), the platform (3) and the flexure (7); forming a membrane (5), the membrane (5) being accommodated in the platform (3) and defining a buried cavity (11) contained in the platform (3); and forming a sealing strip (15; 115), the sealing strip (15; 115) extending along the gap (10) on the support (2), the platform (3) and the flexure (7).
[0060] The material of the sealing strip (15; 115) has a Young's modulus of less than 300 MPa.
[0061] The material of the sealing strip (15; 115) has a thermal expansion coefficient of less than 250 ppm / °C.
[0062] Forming the sealing strip (15) includes laminating a sheet (25) of a polymer material on a wafer (20); forming a mask (27) covering the sheet (25) along the gap (10) and having a shape corresponding to the sealing strip (15); and using the mask (27) to selectively expose and remove the resist layer (26).
[0063] The sheet (25) is dry resist.
[0064] Forming the sealing strip (115) includes: depositing a UV curing ink strip (115') along the gap (10); and exposing the UV curing ink strip (115') to ultraviolet radiation to cure it.
[0065] The various embodiments described above can be combined to provide further embodiments. Aspects of the embodiments can be modified as necessary to employ the concepts of the various patents, applications and publications to provide further embodiments.
[0066] These and other changes can be made to the embodiments in light of the above detailed description. In general, in the appended claims, the terms used should not be interpreted as limiting the claims to the specific embodiments disclosed in the specification and claims, but should be interpreted to include all possible embodiments and the full range of equivalents to which such claims are entitled. Therefore, the claims are not limited by this disclosure.
Claims
1. A micro-electromechanical film sensor, comprising: A support body, the support body is made of a semiconductor material and has a recessed portion, the recessed portion being in the surface; a platform, wherein the platform is in the recess and is at a certain distance from the support body; a flexure connecting the platform to the support and configured to hold the platform suspended in the recess, wherein a gap extends between the support, the platform, and the flexure; a membrane in the platform and defining a buried cavity contained in the platform; as well as A sealing strip extends along the gap on the support body, the platform and the bending member. 2 . The sensor according to claim 1 , wherein the material of the sealing strip has a Young's modulus of less than 300 MPa. The sensor according to claim 1 , wherein the material of the sealing strip has a thermal expansion coefficient of less than 250 ppm / ° C. 4 . The sensor of claim 1 , wherein the sealing strip is part of a sheet of polymer material.
5. The sensor according to claim 1, wherein the material of the sealing strip is selected between dry resist and UV curing ink.
6. A sensor according to claim 1, wherein the platform has a polygonal shape, and wherein the bent piece has a first branch and a second branch, the first branch is anchored to the support body and extends coplanarly with one side of the platform, and the second branch is continuous with the first branch 7a and is joined to the platform.
7. The sensor of claim 6, wherein the gap has a spiral shape and separates the platform and the flexure laterally from the support.
8. The sensor of claim 6, wherein the gap extends between the support and the first branch of the flexure, around the platform and between the platform and the first branch.
9. The sensor of claim 1, wherein the gap has a width between 3 μm and 30 μm.
10. A method for manufacturing a micro-electromechanical film sensor, comprising: In a wafer comprising semiconductor material, a recess is formed in a surface, the platform is received in the recess at a distance from a support, the flexure connects the platform to the support and is configured to hold the platform suspended in the recess, wherein a gap extends between the support, the platform and the flexure; forming a membrane, the membrane being received in the platform and defining a buried cavity, the buried cavity being contained in the platform; as well as A sealing strip is formed, which extends along the gap on the support body, the platform and the bending member. The method according to claim 10 , wherein the material of the sealing strip has a Young's modulus of less than 300 MPa.
12. The method of claim 10, wherein the material of the sealing strip has a thermal expansion coefficient of less than 250 ppm / °C.
13. The method of claim 10, wherein forming the sealing strip comprises: laminating a sheet of polymer material onto the wafer; forming a mask, the mask covering the sheet along the gap and having a shape corresponding to the sealing strip; as well as The mask is used to selectively expose and remove the resist layer.
14. The method of claim 13, wherein the sheet material is dry resist.
15. The method of claim 10, wherein forming the sealing strip comprises: Depositing a UV curable ink strip along the gap; as well as The UV curable ink strips are exposed to ultraviolet radiation to allow curing.
16. A device comprising: a substrate having a recessed portion in the first surface, the recessed portion having a second surface, the second surface being opposite to the first surface; a gap defining an inner surface of the substrate, the gap extending from the first surface of the substrate to the second surface of the recess; a suspension platform above the second surface of the recess; an extension coupling the suspended platform to the substrate, the extension extending from a first inner surface of the substrate, the first inner surface being transverse to the first surface of the substrate; a buried cavity in the suspension platform and above the second surface of the recess; as well as A sealing strip is provided on the gap.
17. The device of claim 16, wherein the extension comprises a first portion and a second portion, the first portion extending through the gap transversely to the second portion, the first portion extending along a first direction to the second portion, the second portion extending in a second direction transverse to the first direction. 18 . The device of claim 17 , wherein the first portion of the extension extends from the first inner surface of the substrate, and the second portion is spaced apart from a second inner surface of the substrate, the second inner surface being opposite to the first inner surface.
19. The device of claim 18, wherein the extension has a first dimension, the first dimension is greater than a second dimension, the first portion extends along the first direction by the first dimension, and the second portion extends along the second direction by the second dimension.
20. The device of claim 16, further comprising an insulating layer on the first surface of the substrate and the suspended platform, the sealing bar being on a portion of the insulating layer.