MEMS transducer

Abstract

A MEMS transducer includes a deflectable membrane, the deflectable membrane including two first layers and a second layer disposed between the two first layers. The two first layers include low stress silicon nitride and the second layer includes doped silicon.

Description

Technical Field

[0001] Examples of this disclosure relate to microelectromechanical systems (MEMS) transducers. Specifically, examples relate to MEMS transducers having stacked low-stress nitride films (e.g., stacked low-stress nitride films with or without wrinkles). Examples relate to MEMS acoustic transducers, such as microphones, such as single-backplane (SBP) microphones. Other examples relate to vibration sensors, such as bone conduction microphones, or sound pickup units (VPUs), such as accelerometers. Background Technology

[0002] MEMS transducers, such as those that convert vibrations (like pressure waves or mechanical vibrations) into electrical signals, use deflectable films. One aspect of the performance of such deflectable films is their vibrational characteristics. In particular, low damping over the frequency range of the application can be beneficial. However, achieving good vibrational characteristics is often for the purpose of high robustness of the film. For example, MEMS transducers use thick, fully clamped or free-floating films to provide sufficient robustness. The trade-off between good vibrational performance and high robustness often results in high complexity in production or the introduction of special techniques involving higher costs or time delays.

[0003] Therefore, it is desirable to provide a MEMS transducer that offers an improved compromise between good vibration performance, high robustness, and low complexity in production. Summary of the Invention

[0004] Examples of this disclosure provide a MEMS transducer including a deflectable film comprising two first layers and a second layer disposed between the two first layers. The two first layers comprise low-stress silicon nitride, while the second layer comprises doped silicon.

[0005] Advanced implementation methods are defined by the subject matter of the dependent claims. Attached Figure Description

[0006] Examples of this disclosure are described in more detail below with reference to the accompanying drawings, in which:

[0007] Figure 1 The illustration shows an example of a MEMS transducer according to the present disclosure, and in particular a membrane of a MEMS transducer;

[0008] Figure 2 The illustration shows a MEMS transducer with wrinkles, specifically the membrane of the MEMS transducer.

[0009] Figure 3 The illustration shows a capacitive MEMS transducer according to an example.

[0010] Figure 4The illustration shows a capacitive MEMS transducer with a wrinkled membrane and planar electrodes according to an example.

[0011] Figure 5 The illustration shows a capacitive MEMS transducer with a wrinkled membrane and planar electrodes according to another example.

[0012] Figure 6 The illustration shows a capacitive MEMS transducer with a suspended mass block according to an example.

[0013] Figure 7 The illustration shows a capacitive MEMS transducer with planar electrodes and a suspended mass block, according to an example.

[0014] Figure 8 The illustration shows a capacitive MEMS transducer with planar electrodes and a suspended mass block according to another example;

[0015] Figure 9 The illustration shows a conventional MEMS transducer. Detailed Implementation

[0016] Examples of the present disclosure will now be described in more detail with reference to the accompanying drawings, in which identical or similar elements, or elements having the same or similar functions, are assigned the same reference numerals or identified by the same names. In the following description, numerous details are set forth to provide a comprehensive illustration of the examples of the present disclosure. However, it will be apparent to those skilled in the art that other examples can be implemented without these specific details. Furthermore, features of the different examples described herein can be combined with each other unless otherwise specifically indicated.

[0017] Figure 1 The illustration shows an example of a MEMS transducer 10 according to the present disclosure. The MEMS transducer 10 includes a deflectable film 12 comprising two first layers 20 and a second layer 30. The second layer 30 is disposed between the two first layers 20. The two first layers 20 comprise low-stress silicon nitride. The second layer 30 comprises doped silicon, such as doped polycrystalline silicon.

[0018] The examples of this disclosure rely on the finding that composite film structures comprising a layer (between two layers comprising low-stress silicon nitride, including doped silicon) provide particularly low stress within the film, resulting in high robustness, and in particular a trade-off between robustness and improved vibrational or acoustic performance. Specifically, the examples rely on the idea that the combination of silicon nitride (which provides high robustness) and doped silicon facilitates the use of silicon nitride, which, when used alone, could result in high stress.

[0019] Furthermore, the examples of the disclosed structures can be manufactured with relatively low complexity and cost. In the examples, the disclosed MEMS transducers can be manufactured using widely available methods. In other words, the examples of this disclosure relate to improving the problem region by modifying the membrane stack and thus reveal designs for acoustic transducers (e.g., microphones) with very high mechanical compliance or acoustic performance and high robustness, to improve robustness without (substantially) sacrificing performance.

[0020] For example, doping of silicon in the second layer 30 can help reduce stress in the film 12, or can allow for the tuning of the stress in the second layer, thereby tuning the stress of the entire film 12. Stress tuning can help, for example, configure the vibrational / acoustic characteristics of the film 12 according to the desired application of the MEMS transducer.

[0021] In the example, the concentration of the dopant in the silicon is 10. 19 cm -3 With 10 21 cm -3 Within the range between.

[0022] For example, the deflectable membrane 12 can oscillate when excited by pressure oscillations (such as acoustic waves or mechanical vibrations) caused by, for example, the acceleration of a MEMS transducer.

[0023] For example, the deflectable membrane 12 can be supported by a support structure 60, such as... Figure 1 For illustrative purposes only. For example, support structure 60 may support or fix the deflectable membrane 12 along its circumference. The circumference may refer to the boundary of the deflectable membrane 12 extending in the plane in which the layers of the membrane 12 extend.

[0024] For example, the deflectable film can be circular.

[0025] In the example, the deflectable film 12 may have a radius in the range of 200 μm to 750 μm or in the range of 250 μm to 500 μm.

[0026] In the example, the two first layers 20 are made of low-stress silicon nitride. Alternatively or additionally, the second layer 30 is made of doped silicon (e.g., doped polysilicon).

[0027] In the example, the second layer 30 is arranged to be adjacent to each of the two first layers 20. In other words, in the example, the second layer 30 is adjacent to each of the two first layers 20.

[0028] In one example, the deflectable film 12 consists of two first layers 20 and a second layer 30.

[0029] For example, low-stress silicon nitride can refer to silicon nitride with stress below a predetermined value. For example, the stress in silicon nitride may be related to the ratio of silicon to nitrogen in the silicon nitride.

[0030] In the example, the low-stress silicon nitride of the first layer 20 has internal stress in the range of 10 MPa to 500 MPa, or in the range of 10 MPa to 200 MPa, or in the range of 20 MPa to 100 MPa.

[0031] For example, tensile stresses above 20 MPa or above 10 MPa may be advantageous for the fabrication of membrane 12, while stresses below 500 MPa, 200 MPa, or 100 MPa may be advantageous for vibration or acoustic properties.

[0032] In the example, the stoichiometric fraction of silicon in low-stress silicon nitride exceeds that in Si3N4. In other words, the silicon fraction in low-stress silicon nitride can be higher than 3 / 7.

[0033] For example, the silicon content in low-stress silicon nitride can be less than 70%. In other words, in this example, the silicon content in low-stress silicon nitride is in the range of 3 / 7 to 7 / 10. In another example, the silicon content in low-stress silicon nitride is in the range of 45% to 60%.

[0034] A silicon ratio of over 3 / 7 provides low internal stress in silicon nitride.

[0035] In the example, one or both of the two first layers 20 have a thickness in the range of 10 nm to 150 nm or in the range of 20 nm to 100 nm.

[0036] For example, thickness refers to the dimension in a direction perpendicular to the plane (in which the first and second layers extend).

[0037] In the example, the two first layers have the same thickness. Therefore, for example, the deflectable membrane can be constructed to be symmetrical, which is beneficial for vibrational or acoustic properties.

[0038] In the example, the second layer 30 has a thickness in the range of 100 nm to 500 nm or in the range of 150 nm to 350 nm.

[0039] In other words, as mentioned above... Figure 1 The MEMS transducer may include a stacked film composed of polycrystalline silicon and low-stress silicon nitride, which has a low total stress compared to, for example, a film composed of only polycrystalline silicon, due to the highly doped polycrystalline silicon and silicon-rich silicon nitride (which provides high acoustic compliance and higher robustness).

[0040] Figure 2 Another example of a MEMS transducer 10 is illustrated. About Figure 1 All the details described can optionally be in Figure 2 The MEMS transducer 10 is implemented individually or in any combination. According to Figure 2 For example, the deflectable membrane includes at least one pleat (ring structure) 40.

[0041] For example, pleats 40 can further reduce the total membrane stress, thereby improving acoustic compliance.

[0042] For example, the wrinkles 40 of the deflectable film include two first layers 20 and a second layer 30. In other words, the two first layers 20 and the second layer 30 can be affected by the wrinkles or can extend through the wrinkles. The silicon nitride coating on the wrinkles can provide better robustness of the film 12.

[0043] For example, the folds 40 may extend along (e.g., parallel to) the circumference of the deflectable membrane 12, such as... Figure 2 The cross-section shown.

[0044] In one example, the fold 40 has an extension in a direction perpendicular to the deflectable film (e.g., in a direction perpendicular to the plane in which the deflectable film extends), ranging from 0.5 to 2 times the thickness of the deflectable film. In other words, the fold can extend 0.5 to 2 times the thickness of the deflectable film from the plane defined by the main surface region 14 of the film 12.

[0045] In one example, the deflectable film 12 comprises a piezoelectric material.

[0046] Piezoelectric materials can be used to provide electrical signals that depend on the deflection of the deflectable membrane 12.

[0047] For example, the deflectable film may include another layer comprising a piezoelectric material. This other layer may be positioned adjacent to one of the two first layers 20, or positioned between the two first layers 20, to contact the doped silicon of the second layer 30. In this example, the other layer comprising the piezoelectric material does not necessarily extend over the entire film 12, but may be disposed within a region of the deflectable film.

[0048] In other words, the MEMS transducer 10 can be implemented as a piezoelectric MEMS transducer. Alternatively, the MEMS transducer 10 can be implemented as a capacitive MEMS transducer, as will be described below.

[0049] Figure 3Another example of a MEMS transducer 10 is illustrated. In this example, the MEMS transducer 10 also includes a rigid electrode 50, which is arranged opposite to the deflectable membrane 12. The rigid electrode can also be referred to as a backplate. The rigid electrode 50 can be insensitive to acoustic pressure (e.g., acoustic pressure). For example, the rigid electrode 50 can be a high-hardness membrane, such as a perforated high-hardness membrane. Note that... Figure 3 Only one part of the MEMS transducer 10 is shown, namely the left part of the full view of the MEMS transducer 10, which is close to the left part of the optional support structure 60.

[0050] The rigid electrode 50 can be used as a reference for capacitive measurements of the deflection of the deflectable film perpendicular to the plane in which the deflectable film extends. For example, capacitive measurements can be performed between the rigid electrode 50 and the second layer 30, and the second layer 30 can be conductive due to silicon doping.

[0051] Therefore, the rigid electrode 50 can be conductive. For example, the rigid electrode may include a conductive layer.

[0052] In other words, the MEMS transducer 10 can realize a capacitive transducer, such as a single-backplane transducer (e.g., a single-backplane acoustic transducer).

[0053] For example, MEMS transducer 10 can be a MEMS microphone or a MEMS speaker.

[0054] Despite Figure 3 The rigid electrode is illustrated as having multiple layers, but the rigid electrode 50 can alternatively be implemented as a single uniform layer or having two or more layers (e.g., Figure 3 The three shown represent a multi-layered structure.

[0055] Note, as an example, Figure 3 A combination of a rigid electrode 50 and a deflectable film 12 is shown, both structures being implemented with wrinkles. However, the features of the wrinkled deflectable film 12 can be implemented independently of the features of the MEMS transducer 10 including the rigid electrode 50. Thus, in another example, Figure 1 The deflectable film 12 of the MEMS transducer 10 may include wrinkles, for example, not combined with rigid electrodes. In other words, although Figure 3 A rigid electrode is shown in combination with a deflectable film 12 having pleats, but the implementation of the pleats is independent of the MEMS transducer 10 having a rigid electrode. Figure 3 Other examples of transducers can be implemented without folds.

[0056] In one example, the rigid electrode 50 has wrinkles 45, which can be positioned, for example, to correspond with the wrinkles 40 of the deflectable film. This structure is easy to manufacture.

[0057] Figure 4 The diagram illustrates the relationship between... Figure 3 Another example of a MEMS transducer 10 similar to the one described above, except that the rigid electrode 50 is implemented as planar or non-creased (e.g., without creases). Similar to... Figure 3 , Figure 4 Only one part of the MEMS transducer 10 is shown, namely the left part of the full view of the MEMS transducer 10, which is close to the left part of the optional support structure 60.

[0058] The combination of a corrugated membrane with a flat (planar, non-corrugated) backplate can improve the device's sensitivity, signal-to-noise ratio (SNR), and robustness.

[0059] For example, chemical mechanical polishing (CMP) can be considered an intermediate step in removing wrinkles from rigid electrodes to provide a flat, rigid electrode.

[0060] Figure 3 and Figure 4 An opening for pressure equalization in the rigid electrode 50 is also shown, which can be optionally implemented.

[0061] Figure 5 Another example of a MEMS transducer 10 is illustrated, which can be based on Figure 4 MEMS transducers. For example... Figure 5 As shown, when implementing a capacitive transducer, the MEMS transducer 10 may include a contact structure 72 for electrically contacting the rigid electrode 50, and another contact structure 73 for electrically contacting the deflectable film 12, particularly the second layer 30 of the deflectable film 12. The MEMS transducer may optionally further include a contact structure 71 for electrically contacting the substrate 62, on which a support structure 60 may be disposed.

[0062] Figure 6 Another example of a MEMS transducer 10 is illustrated, which may be similar to or correspond to the one described above. Figure 3 The MEMS transducer described is, Figure 6 The MEMS transducer 10 can be a capacitive transducer. Figure 6 The MEMS transducer 10 also includes a suspended mass 80, which can optionally be connected via, for example... Figure 6 The attachment structure 82 is attached to the deflectable film 12. Similar to... Figure 3 , Figure 6 Only one part of the MEMS transducer 10 is shown, namely the left part of the full view of the MEMS transducer 10, which is close to the left part of the optional support structure 60.

[0063] The suspended mass 80 can be used as an inertial mass. For example, the MEMS transducer 10 can be used to implement an acceleration sensor or a vibration sensor.

[0064] Figure 7 Another example of a MEMS transducer 10 is illustrated, which may be similar to or correspond to the one described above. Figure 6 The described MEMS transducer 10, except that the deflectable film 12 and the rigid electrode 50 are implemented as planar or non-creased (e.g., without creases). Similar to... Figure 3 , Figure 7 Only one part of the MEMS transducer 10 is shown, namely the left part of the full view of the MEMS transducer 10, which is close to the left part of the optional support structure 60.

[0065] Figure 8 Another example of a MEMS transducer 10 is illustrated, which can correspond to the following: Figure 5 The MEMS transducer 10 is described, but additionally includes information about Figure 6 and Figure 7 The suspended mass block 80 is described.

[0066] like Figure 8 As illustrated, the deflectable diaphragm 12 may include an vent 19 for pressure equalization. This feature is related to... Figure 8 Other details (such as the suspended mass 80, the implementation as a capacitor transducer, and the folds 40) are irrelevant.

[0067] Figure 9 The illustration shows a conventional single-backplane MEMS transducer 99, which includes a landing pad 16 disposed on a deflectable membrane 92. The landing pad can be used to protect the membrane 92 from damage by spacers 56 disposed on a backplane 93, which prevent the membrane 92 from sticking to the backplane 93.

[0068] Due to the increased robustness of the deflectable membrane 12 caused by the use of a first layer 20 including low-stress nitrides, examples of this disclosure can be implemented without a landing pad, thereby reducing production costs.

[0069] Furthermore, conventional MEMS transducers may require a cone 17 on the suspension of the membrane 92 at the support structure 60. In contrast, the examples of this disclosure may have a cone or not at the suspension of the deflectable membrane 12, for example, with a rigid suspension.

[0070] In addition, such as Figure 9 As shown, but also as Figure 5 and Figure 8As shown, compared to portion 66 of the support structure 60 disposed above the deflectable membrane, portion 68 of the support structure 60 disposed below the deflectable membrane can extend further to the center of the deflectable membrane (in a direction about the plane of the deflectable membrane), thereby increasing the robustness of the deflectable membrane. This excess can be referred to as a full-stack support FSS. Due to the enhanced robustness of the deflectable membrane 12 according to this disclosure, an FSS may not be necessary, as... Figure 3 , 4 As shown in 6 and 7.

[0071] although Figure 9 The illustration shows a MEMS transducer without a suspended mass, but regarding... Figure 9 The advantages of the examples of this disclosure explained herein are equally applicable to MEMS transducers with suspended mass blocks.

[0072] While some aspects have been described as features within the context of a device, it is clear that such descriptions can also be considered descriptions of corresponding features of a method.

[0073] As can be seen from the foregoing detailed description, various features are combined in the examples for the purpose of simplification. The approach of this disclosure should not be construed as reflecting an intention to require more features than are expressly recited in each claim. Rather, as reflected in the following claims, the subject matter may exist in fewer than all the features of a single disclosed example. Therefore, the appended claims are thus incorporated into the detailed description, wherein each claim may stand alone as a separate example. While each claim may stand alone as a separate example, it should be noted that although dependent claims may refer in the claims to a specific combination with one or more other claims, other examples may also include combinations of the subject matter of a dependent claim with each other dependent claim or combinations of each feature with other dependent or independent claims. Such combinations are presented herein unless it is stated that a particular combination is not intended. Furthermore, even if a claim is not directly dependent on an independent claim, it is intended to include the features of that claim in any other independent claim.

[0074] The examples above are merely illustrative of the principles of this disclosure. It should be understood that modifications and variations of the arrangements and details described herein will be readily apparent to others skilled in the art. Therefore, it is intended to be limited only by the scope of the claims of the patent pending examination, and not by the specific details presented through the description and interpretation of the examples herein.

Claims

1. A MEMS transducer (10) comprising a deflectable membrane (12). The deflectable film (12) comprises two first layers (20) and a second layer (30) disposed between the two first layers (20). The two first layers (20) comprise low-stress silicon nitride, and the second layer (30) comprises doped silicon.

2. The MEMS transducer (10) according to claim 1, wherein the deflectable film (12) comprises at least one fold (40).

3. The MEMS transducer (10) according to claim 2, wherein the wrinkles (40) extend along the circumference of the deflectable film (12).

4. The MEMS transducer (10) according to claim 2 or 3, wherein the wrinkles (40) extend in a direction perpendicular to the deflectable film (12) in a range between 0.5 times and 2 times the thickness of the deflectable film (12).

5. The MEMS transducer (10) according to any one of the preceding claims, wherein the two first layers (20) are made of low-stress silicon nitride, and / or wherein the second layer (30) is made of doped silicon, for example, doped polycrystalline silicon.

6. The MEMS transducer (10) according to any one of the preceding claims, wherein the low-stress silicon nitride has internal stress in the range of 10 MPa to 500 MPa, or in the range of 10 MPa to 200 MPa, or in the range of 20 MPa to 100 MPa.

7. The MEMS transducer (10) according to any one of the preceding claims, wherein the stoichiometric portion of silicon in the low-stress silicon nitride exceeds the stoichiometric portion of silicon in Si3N4.

8. The MEMS transducer (10) according to any one of the preceding claims, wherein one or both of the two first layers (20) have a thickness in the range of 10 nm to 150 nm or in the range of 20 nm to 100 nm.

9. The MEMS transducer (10) according to any one of the preceding claims, wherein the two first layers (20) have the same thickness.

10. The MEMS transducer (10) according to any one of the preceding claims, wherein the second layer (30) has a thickness in the range of 100 nm to 500 nm or in the range of 150 nm to 350 nm.

11. The MEMS transducer (10) according to any one of the preceding claims, wherein the second layer (30) is arranged adjacent to each of the two first layers (20).

12. The MEMS transducer (10) according to any one of the preceding claims, wherein the deflectable film (12) is circular, and wherein the radius of the deflectable film (12) is in the range of 200 μm to 750 μm or in the range of 250 μm to 500 μm.

13. The MEMS transducer (10) according to any one of the preceding claims, wherein the concentration of the dopant in the doped silicon is 10. 19 cm -3 With 10 21 cm -3 Within the range between.

14. The MEMS transducer (10) according to any one of the preceding claims further includes a rigid electrode (50) arranged opposite to the deflectable film (12).

15. The MEMS transducer (10) according to claim 14 is a single-backplane sound transducer.

16. The MEMS transducer (10) according to claim 14 or 15, wherein the rigid electrode (50) is planar.

17. The MEMS transducer (10) according to any one of claims 14 to 16, wherein the rigid electrode (50) is free of wrinkles.

18. The MEMS transducer (10) according to any one of claims 1 to 13, wherein the deflectable film (12) comprises a piezoelectric material.

19. The MEMS transducer (10) according to any one of the preceding claims is a MEMS microphone or a MEMS speaker.

20. The MEMS transducer (10) according to any one of claims 1 to 18 further includes a suspended mass (80) attached to the deflectable membrane (12).

21. The MEMS transducer (10) according to any one of claims 1 to 18 or 20 is a MEMS acceleration sensor or a MEMS vibration sensor.

22. The MEMS transducer (10) according to any one of the preceding claims, wherein the doped silicon is doped polycrystalline silicon.

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