阅读说明：本技术 具有膜电极、对电极、以及至少一个弹簧的传感器
(Sensor with membrane electrode, counter electrode and at least one spring
) 是由 S·巴曾 于 2020-02-25 设计创作，主要内容包括：公开了一种传感器,该传感器具有膜电极、对电极、以及至少一个弹簧。尤其是,根据示例的传感器可以包括：结构(12)；膜电极(14),其作为受到压力的结果是可变形的,并且与结构(12)接触；对电极(16),其被机械地连接到结构(12),并且通过间隙(18)与膜电极(14)分隔开；以及至少一个弹簧(20),其被机械地连接到膜电极(14)和对电极(16),以便在膜电极(14)和对电极(16)之间施加弹性力。(A sensor is disclosed having a membrane electrode, a counter electrode, and at least one spring. In particular, a sensor according to an example may include: a structure (12); a membrane electrode (14) which is deformable as a result of being subjected to pressure and which is in contact with the structure (12); a counter electrode (16) mechanically connected to the structure (12) and separated from the membrane electrode (14) by a gap (18); and at least one spring (20) mechanically connected to the membrane electrode (14) and the counter electrode (16) so as to exert an elastic force between the membrane electrode (14) and the counter electrode (16).)
1. A sensor (10) comprising:
a structure (12);
a membrane electrode (14), said membrane electrode (14) being deformable as a result of being subjected to pressure, and said membrane electrode (14) being in contact with said structure (12);
a counter electrode (16) mechanically connected to the structure (12) and separated from the membrane electrode (14) by a gap (18); and
at least one spring (20) between the membrane electrode (14) and the counter electrode (16) for exerting an elastic force between the membrane electrode (14) and the counter electrode (16).
2. The sensor of claim 1, comprising:
a flexible membrane connection (22) mechanically connecting the membrane electrode (14) to the structure (12).
3. The sensor of claim 2,
the flexible membrane connection (22) is configured to elastically deform at least as a partial result of a bending or movement or deformation of the membrane electrode (16) or a main portion of the membrane electrode (16).
4. The sensor of claim 3,
the flexible membrane connection (22) comprises a cut-out or hole (22d), said cut-out or hole (22d) corresponding to a portion (22b) of the membrane electrode (14) in contact with the structure (12).
5. The sensor of claim 4,
the cut-out or hole (22d) of the membrane connection (22) is arched and/or concentric with the edge (14r) of the membrane electrode (14).
6. The sensor of any one of claims 2 to 5,
the flexible membrane connection (22) comprises springs (22, 23), the springs (22, 23) mechanically connecting the membrane electrode (14) and the structure (12).
7. The sensor of any one of the preceding claims,
the membrane electrode (14) is interposed between a first pair of electrodes (16) and a second pair of electrodes (17) and is spaced apart from the first electrode (16) and the second pair of electrodes (17) by a first gap (18) and a second gap (19), respectively.
8. The sensor of any one of the preceding claims,
the at least one spring (30) is a bimorph spring.
9. The sensor of any one of the preceding claims,
the membrane electrode (14) is cantilevered to the structure (12).
10. The sensor of any one of the preceding claims,
the at least one spring (20) comprises a membrane-side limb (20a, 30a) and a counter-electrode-side limb (20b, 30b), the membrane-side limb (20a, 30a) abutting on the membrane electrode (14) and the counter-electrode-side limb (20b, 30b) abutting on the counter electrode (16).
11. The sensor of any one of the preceding claims,
the at least one spring (20) comprises a plurality of springs.
12. The sensor of claim 11,
the plurality of springs (20) is an array or matrix of springs (20).
13. The sensor of any one of the preceding claims,
the mechanical connection between the membrane electrode (14) and the structure (12) is stress-free.
14. The sensor of any one of the preceding claims,
the membrane electrode (14) presents at least one non-conductive island on which the at least one spring (20) abuts, such that the at least one spring (20) is electrically insulated from the membrane electrode (14).
15. The sensor of any one of the preceding claims,
the at least one spring (20) includes a sloped portion (22c) in the gap (18).
16. The sensor of any preceding claim, implemented as a chip or package.
17. A microphone arrangement comprising a sensor according to any of the preceding claims.
18. A method for manufacturing a semiconductor pressure sensor and/or an acoustic sensor, comprising:
preparing a first element (14, 16) on a substrate (24), wherein the first element (14, 16) is selected between a membrane electrode (14) and a counter electrode (16);
-preparing at least one spring element (20, 30) to abut on said first element (14, 16);
-preparing a second element (14, 16) such that the at least one spring element (20, 30) abuts on the second element (14, 16) and is elastically connected to the first and the second element, wherein the second element (14, 16) is an element selected between the counter electrode (16) and the membrane electrode (14) that is not selected for the first element.
19. The method of claim 18, further comprising:
depositing a sacrificial material (26) over the first elements (14, 16) after the first elements (14) have been prepared;
preparing the at least one spring element (20) and the second element (16) by at least one of the following steps:
removing the sacrificial material (26) in selected locations (26 a);
depositing spring element material over the selected locations (26 a);
depositing a second element material over the spring element material; and
the remaining sacrificial material (26) is removed.
20. The method of claim 18 or 19,
the spring element material is the same material as the first element material or the second element material.
Technical Field
This document relates to a sensor (e.g., a pressure sensor and/or an acoustic sensor, e.g., for a microphone) having a membrane electrode, a counter electrode, and at least one spring interposed between the membrane electrode and the counter electrode.
The present document also relates to methods for manufacturing sensors, such as the sensors described above.
Background
A pressure sensor, such as an acoustic sensor, may include at least two electrodes (e.g., at least one membrane electrode and at least one counter electrode). For example, the membrane electrode may be deformable as a result of being subjected to pressure (e.g., pressure caused by sound). The counter electrode may be non-deformable, and the counter electrode may be fixed to a fixed structure. The membrane electrode may be attached to a fixed structure of the sensor corresponding to the membrane edge.
The membrane electrode may be fabricated so that there is a tensile stress, for example: for counteracting attractive electrostatic forces between the membrane electrode and the counter electrode.
By virtue of the deformation due to the pressure, a high concentration of stress can be defined to correspond to the membrane edge. Thus, the robustness of the sensor as a whole is reduced.
Due to the assembly process, thermal expansion of the different package materials and aging of the material package causes additional stress between the membrane electrode and the counter electrode. This additional stress changes the compliance of the membrane, thereby reducing sensitivity, for example. This causes significant yield loss.
Because the edges of the membrane electrode are fixed to the structure, large area movement of the membrane is limited. Thus, the overall signal amplitude is reduced. As a result, the chip delivers a limited signal and/or the signal-to-noise ratio (SNR) is reduced. In general, the sensor needs to be designed larger than necessary, thus increasing the cost of achieving satisfactory signal and SNR values.
Furthermore, tolerances during manufacture result in imperfect positioning of the membrane electrode. Therefore, it is often necessary to perform a calibration to adapt a specific position of the membrane with respect to the structure. Therefore, without calibration, it is difficult to achieve the result that different sensors (nominally identical) operate with exactly the same sensitivity. However, calibration implies a complication of software and hardware.
Furthermore, the stress on the membrane also depends on the external temperature. Thus, it is difficult to implement a sensor that will function in all climatic conditions.
Limited mechanical robustness can cause field failures and require additional measurements, limitations and costs. Thicker films need to be used.
This document is therefore directed to techniques for at least partially reducing the above-mentioned deficiencies.
Disclosure of Invention
According to an example, there is provided a sensor comprising: structure; a membrane electrode that is deformable as a result of being subjected to pressure, and that is in contact with the structure; a counter electrode mechanically connected to the structure and separated from the membrane electrode by a gap; and at least one spring between the membrane electrode and the counter electrode to apply an elastic force between the membrane electrode and the counter electrode.
According to an aspect, the sensor may include: a flexible membrane connector connecting the membrane electrode to the structure.
According to an example, there is provided a method for manufacturing a semiconductor pressure sensor and/or an acoustic sensor, the method comprising:
preparing a first element on a substrate, wherein the first element is selected between a membrane electrode and a counter electrode;
preparing at least one spring element, the at least one spring element abutting on the first element;
preparing a second element such that the at least one spring element abuts on the second element and such that the at least one spring element is elastically connected to the first element and the second element, wherein the second element is a counter electrode or a membrane electrode, wherein the second element is an element selected between the counter electrode and the membrane electrode that is not selected for the first element.
Drawings
Fig. 1, 2 show a sensor according to an example.
Fig. 3 shows an element according to an example.
Fig. 4 and 5 illustrate a sensor according to an example.
Fig. 6-9 illustrate elements according to examples.
Fig. 10 to 17 show intermediate steps according to the method.
Fig. 18 shows a sensor according to an example.
Fig. 19 shows an intermediate step according to the method.
Detailed Description
Fig. 1 shows a sensor 10 according to an example. The sensor 10 may be a pressure sensor. The pressure sensor 10 may be an acoustic sensor (e.g., for a microphone) or a pressure sensor (e.g., for measuring an external pressure, such as atmospheric pressure). The sensor 10 may be a semiconductor device. The sensor 10 may be a micro-electromechanical system (MEMS). The sensor 10 may be an embedded device. The sensor 10 may be an on-chip device. The sensor 10 may be a package, or the sensor 10 may be enclosed in a package. Sensor 10 may include structure 12. The structure 12 may be fixed. Structure 12 may comprise (or be contained in) a chip and/or a package.
The sensor 10 may operate as a capacitor having two electrodes at a variable distance (gap) and thus a variable capacitance. The capacitance may vary depending on the distance between the electrodes. In general, the larger the distance, the smaller the capacitance, and vice versa. In general, it means the inverse ratio between the distance between the electrodes and the capacitance.
The sensor 10 may include a membrane electrode 14 (e.g., of an electrically conductive material). The membrane electrode 14 may be flexible (e.g., of a flexible and/or elastomeric material). The membrane electrode 14 may be deformed as a result of being subjected to pressure (e.g., pressure vibration such as sound). Membrane electrode 14 may be in contact with structure 12. For example, membrane electrode 14 may be cantilevered to structure 12. The membrane electrode 14 may be non-rigidly secured to the structure 12 (e.g., a non-stressed membrane). The membrane electrode 14 may be suspended (e.g., by a spring or other resilient element, such as a flexible membrane connection). The membrane electrode 14 may present a first surface 14a (which may be an exposed surface) and a second surface 14d (which may be a non-exposed surface).
The sensor 10 may include a counter electrode 16 (e.g., of a conductive material). The counter electrode 16 may be a rigid material. The counter electrode 16 may be a back plate. The counter electrode 16 may be mechanically connected to the structure 12 (e.g., fixed to the structure 12 and/or suspended by the structure 12). The counter electrode 16 may present a first surface 16b (which may be a non-exposed surface) and a second surface 16d (which may be an exposed surface).
The counter electrode 16 may be understood to operate with the membrane electrode 14 to form a capacitor. The counter electrode 16 may be separated from the membrane electrode 14 by a gap 18.
The counter electrode 16 may include an e-hole 16 c. The aperture 16c may, among other things, allow fluid communication between the outside of the membrane electrode 14 and at least one surface 14a through the counter electrode 16.
The counter electrode 16 together with the membrane electrode 14 can operate as a capacitor with a variable capacitance. The gap 18 may be an air gap (other fluids may be used in different environments; for example, in a submerged environment, the gap 18 may be filled with water). The gap 18 may operate as a dielectric in a capacitor, which in this case is variable. The resulting capacitor has a variable capacitance based on the variable gap 18, which in turn can vary based on pressure, for example. Capacitors with variable capacitance may also be used as audio/acoustic/sound sensors (e.g., operating as microphones): for example, the acoustic vibration may be measured based on the modification of the gap 18.
The sensor 10 may extend according to a thickness direction (vertical in fig. 1) and a horizontal plane orthogonal to the thickness direction (in fig. 1, the horizontal plane extends in the horizontal direction and a direction into and out of the sheet). The sensor 10 may extend more in the horizontal plane than in the thickness direction. The membrane electrode 14 and the counter electrode 16 may extend predominantly planar (e.g. in a horizontal plane). The gap 18 may have a volume extending mainly horizontally, but the height of the gap 18 may vary at least in the thickness direction. The deformation of the membrane electrode 14 may be regarded as deformation in the thickness direction, for example: the height of the gap 18 is reduced and/or increased in the thickness direction in accordance with the pressure (and the capacitance of the capacitor is changed accordingly). The membrane electrode 14 and the counter electrode 16 may at least partially overlap each other as seen in the thickness direction.
The membrane electrode 14 may have a surface 14a, and the surface 14a may face a surface 16b of the counter electrode 16, the surface 14a and the surface 16b being separated by a gap 18. Surface 16b may be an interior (non-exposed) surface. Although in fig. 1 the membrane electrode 14 is more internal than the counter electrode 16, in other examples the relative positions of the surfaces of the membrane electrode 14 and the counter electrode 16 may be reversed.
It has been noted that the presence of at least one spring 20 interposed between the membrane electrode 14 and the counter electrode 16 (e.g., in the gap 18) is beneficial for the sensor 10. At least one spring 20 may be mechanically connected to both the membrane electrode 14 and the counter electrode 16. The at least one spring 20 may at least partially support the membrane electrode 14. The at least one spring 20 and the membrane electrode 14 may be fixed and/or adhered to each other. The at least one spring 20 may at least partially support the membrane electrode 14. The at least one spring 20 and the membrane electrode 14 may be fixed and/or adhered to each other. In some cases, the counter electrode 16 may at least partially support the membrane electrode 14 by at least one spring 20. The at least one spring 20 may be an elastic member that applies an elastic force between the membrane electrode 14 and the counter electrode 16. Particularly by virtue of the use of at least one spring 20, tensile stresses at the edge of the membrane electrode 14 can be reduced or avoided.
For example, structure 12 may include a substrate 24, and substrate 24 may include a backside etch layer 25. The structure 12 may include a capping portion 26 (e.g., to cap an oxide such as TEOS, tetraethyl orthosilicate). Between the cover portion 26 and the substrate 24, a stop layer 28 (e.g., a stop layer of a stop oxide material) may be disposed in some regions of the substrate 24.
As can be seen from fig. 1, the structure 12 may include a membrane electrode terminal 32, the membrane electrode terminal 32 being electrically connected to the membrane electrode 14 (e.g., by conductive connections obtained in conductive holes). The structure 12 may comprise a counter electrode terminal 31, the counter electrode terminal 31 being electrically connected to the counter electrode 16 (for example, by another conductive connection obtained in a conductive hole). The terminals 31 and 32 may be electrically connected to internal or external circuitry, and/or external devices and other components (e.g., through terminal paths and/or through external pads). Passivation layer 33 may be provided to make contact between the metal layers forming terminals 31 and/or 32 and/or cover portion 26.
The at least one spring 20 may include a membrane side leg 20a and/or a counter electrode side leg 20b, the membrane side leg 20a abutting on the membrane electrode 14 (e.g., abutting surface 14a), the counter electrode side leg 20b abutting the counter electrode 16 (e.g., abutting surface 16 b). At least one of the legs 20a and 20b may be affixed and/or adhered to the respective membrane electrode 14 or counter electrode 16. The main portion 20c of the spring 20 may be mechanically connected between the membrane side leg 20a and the counter electrode side leg 20 b.
In an example, a plurality of springs 20 may be placed between the membrane electrode 14 and the counter electrode 16. In an example, the plurality of springs 20 are arranged in an array and/or matrix (e.g., at regular distances from each other). In the example, the plurality of springs 20 are arranged so as to have the same spring constant, or have spring constants varying by 1% or 5% at maximum between different springs 20. The main portion 20c may provide elasticity. The main portion 20c of the spring 20 may extend generally in the oblique direction. The different springs 20 may have the same or similar tilt angles within a tolerance of 1% or 5%. The inclination may provide flexibility. The inclination may influence the spring constant. The length of the main portion 20c of the spring 20 is generally no more important than the inclination.
A flexible membrane connection 22 may be provided to mechanically connect (e.g., support and/or hold and/or secure) the membrane electrode 14 to the structure 12. The flexible membrane connectors 22 may be elastically deformed (e.g., in the thickness direction) at least in part as a result of deflection (e.g., by pressure) of the membrane electrode 14. The flexible film connection 22 may comprise a transverse spring. The flexible film connectors 22 may allow electrical conduction. The flexible membrane connection 22 may be obtained from the same material as the membrane electrode 14. The flexible membrane connection 22 may be obtained by modifying (e.g., by cutting or perforating) a portion of the membrane electrode 14.
As illustrated by fig. 2, in operation, the membrane electrode 14 may be deformed between a first position (the gap 18 at a first height in the thickness direction as a result of being subjected to a first pressure) and a second position (the gap 18 at a second height in the thickness direction as a result of being subjected to a second pressure) so as to vary between the first capacitance and the second capacitance. For example, as a result of being subjected to a corresponding plurality of pressures, a plurality of other locations (e.g., intermediate locations) may be obtained and result in a plurality of corresponding capacitances. As can be seen from fig. 2, also by virtue of the use of at least one spring 20 and/or by its combined effect with the elastic deformation of the flexible film connection 22, a more uniform deflection (uniform film deflection) is obtained, wherein the gap 18 tends to be uniform along the horizontal plane.
Fig. 3 shows an example of the membrane electrode 14 shown from both the direction perpendicular to the thickness direction (part (a) in fig. 3) and the direction perpendicular to the horizontal plane (part (b) in fig. 3). Note that part (a) in fig. 3 is equivalent to fig. 10, and refers to an intermediate step for manufacturing the sensor of fig. 1. In contrast, part (b) in fig. 3 refers to the final configuration of the membrane electrode 14.
The membrane electrode 14 may include a main portion 14 ', the main portion 14 ' providing the surface 14a, and/or the main portion 14 ' being used as an electrode of a capacitor. The flexible membrane connection 22 may be achieved by a cut-out or aperture 22d in the membrane electrode 14 (e.g., an arcuate portion, e.g., concentric with the edge 14r of the membrane electrode 14), the cut-out or aperture 22d corresponding, e.g., to a portion 22b of the membrane electrode 14, the portion 22b of the membrane electrode 14 being in contact with the structure 12 (e.g., the portion 22b may be sandwiched in the structure 12, e.g., between the cover portion 26 and the substrate 24 or a stop layer 28 of the substrate 24; the portion 22b may be cantilevered to the structure 12). The cut-outs or apertures 22d may be closer to the edge 14r of the membrane electrode 14 than to the center of the membrane electrode 14. The cut-out or hole 22d may be closer to the portion 22b of the membrane electrode 14 than to the center of the membrane electrode 14. In this example, the cut or hole 22d forming the flexible film connector 22 is arcuate (e.g., arcuate), and/or the cut or hole 22d forming the flexible film connector 22 is cut concentrically to the perimeter of the main portion of the film electrode 14. The slit or hole 22d may be a through-slit or through-hole, and the slit or hole 22d may pass through the entire thickness of the membrane electrode in the thickness direction.
When the membrane electrode 14 is deformed (e.g. by means of pressure), the flexible membrane connection 22 may be correspondingly deformed: for example, a cutout or aperture 22d in membrane electrode 14 may allow main portion 14' to move more uniformly relative to portion 22b, thereby maintaining a generally uniform height in gap 18 (see fig. 2) along a horizontal plane.
A stop layer 28 may be disposed between the membrane electrode 14 (and/or the membrane connector 22) and the substrate 24.
In the example of fig. 1, the membrane electrode 14 is cantilevered to the structure 12. At least one spring 20 (e.g., in combination with a flexible film connection 22) may allow the height of the gap 18 to be maintained uniform in a horizontal plane. As can be seen by comparing fig. 1 and 3, the portion 22b of the membrane electrode 14 may be directly connected to the structure 12 and/or in contact with the structure 12, whereas most or all of the edge 14r of the membrane electrode 14 is not mechanically connected to the structure 22. The at least one spring 20 may still be in contact with both the membrane electrode 14 and the counter electrode 16.
The example of fig. 3 may allow movement in a horizontal direction (e.g., right to left in fig. 2) and in a thickness direction (e.g., vertical in fig. 2). An effective electrical connection is achieved. As can be seen from fig. 3, the cut-out or hole 22d may be a partial cut-out or hole, and thus the membrane electrode 14 may find an electrical path towards the membrane electrode terminal 32 (e.g. by being connected to the portion 22b of the structure 12).
Additionally or alternatively, the flexible membrane connection 22 may include a spring 23, the spring 23 exerting a resilient force between the membrane electrode 14 and the structure 12 (fig. 4). For example, the structure 12 may include a segmented portion 27, at least one spring 20 (which may or may not be part of the counter electrode 16). The membrane electrode 14 may be elastically suspended to the spring 23 (or supported or fixed by the spring 23). The spring 23 may have at least one, some, or all of the features of the at least one spring 20 described above (and thus these features are not repeated here). The spring 23 may be elastically deformed at least as part of the movement of the membrane electrode 14. When providing the spring 23, the cut-outs or holes shown in fig. 3 may be avoided. The spring 23 may allow the connection of the membrane electrode 14 with the membrane electrode terminal 32 through the segmented portion 27. The spring 23 may be a conductive material. Instead of one single spring 23, a plurality of springs may be used.
Hybrid solutions can also be obtained: the membrane electrode 14 may be partially suspended and partially supported by the structure 12 having low tensile stress.
Fig. 5 shows a modification in which the membrane electrode 14 is interposed between the first and second counter electrodes 16, 17 and is spaced apart from the first and second counter electrodes 16, 17 by first and second gaps 18, 19, respectively. At least one spring 20 may be located between the membrane electrode 14 and the first counter electrode 16 (e.g. the most exposed or outermost one), however no spring is provided between the membrane electrode 14 and the second counter electrode 17 (e.g. the more inner or non-exposed one). In some examples, a spring 20 may be provided to connect the membrane electrode 14 with both the first and second pairs of electrodes 16, 17. In the latter case (the spring 20 connecting the membrane electrode 14 with both the first and second pair of electrodes 16, 17), the membrane electrode 14 and the first and second pair of electrodes 16, 17 may operate as two different capacitors (e.g., two series capacitors) with variable capacitance based on pressure.
Fig. 6 to 8 show examples of elements of the spring 20 and the counter electrode 16 in a horizontal plane.
In fig. 6, the membrane-side foot 20a of the spring 20 (the membrane-side foot 20a may abut the surface 14a of the membrane electrode 14) abuts on the membrane electrode 14 (not shown). The counter electrode-side foot 20b of the spring 20 abuts on the surface 16b of the counter electrode 16. As can be appreciated by comparing fig. 6 with fig. 1, 2, 4 and 5, while the feet 20a and 20b may generally extend in a horizontal direction, the main portion 20c of the spring 20 may generally extend in an oblique direction. It has been noted that the length of the main portion 20c of the at least one spring 20 is (in general) not important.
The at least one spring 20 may be a conductive material (e.g., a doped semiconductor material or a metallic material), which may be the same as the material of the counter electrode 16. In an example, the at least one spring 20 and the counter electrode 16 may be integral with each other.
In order to avoid a short circuit between the membrane electrode 14 and the counter electrode 16 via the at least one spring 20, the membrane electrode 14 may present (e.g. in some parts of the surface, at least in the surface 14a) non-conductive islands. Thus, even though the at least one spring 20 may be a metal or a conductive material, it does not cause a short circuit between the counter electrode 16 and the membrane electrode 14. A typical material for the at least one spring 20 may be polysilicon or SiNi. Additionally or alternatively to using the island(s), the at least one spring 20 may have an electrically insulating layer on the outside. In other variations, at least one spring 20 may be an electrically insulating material.
Fig. 7 shows an example in which the counter electrode 16 is shown from above with respect to fig. 1 (i.e. differently from fig. 6). In this example, the at least one spring 20 is integral and of the same material as the counter electrode 16. The membrane side legs 20a may abut the membrane electrode 14 (i.e., the exposed surface 14a of the membrane electrode 14).
Fig. 8 shows another example, in which the counter electrode 16 is shown from below with respect to fig. 1, the elements 24, 25 and 14 not being shown. As can be seen, in this case, the main portion 20c of the at least one spring 20 has a spiral shape, thus increasing the elastic properties of the at least one spring 20. Other shapes may be selected.
Fig. 9 shows an example in which the at least one spring is at least one bimorph spring 30. The at least one bimorph spring 30 may be a spring that, when manufactured, moves the membrane electrode 14 (in the thickness direction, as indicated by arrow 30') towards a position further away from the counter electrode 16, i.e. naturally increases the height of the gap 18. The at least one bimorph spring 30 may be such that the main portion 30c between the membrane-side foot 30b (abutting the counter electrode 16) and the membrane-side foot 30a (abutting the membrane electrode 14) is formed of a pair of intermediate portions (e.g., different materials) arranged adjacent to each other.
The use of bimorph springs 30 bent from the counter electrode 16 after removal of the sacrificial layer can significantly increase the range of motion. Thus, the limitations (typical for the prior art) when high sound pressure levels are reached are overcome.
In fig. 9, the relative position between the membrane electrode 14 and the counter electrode 16 is reversed in this example relative to the example of fig. 1. This inversion may be performed for any of the examples above or below.
Fig. 18 shows another example of the sensor 10, in which at least one (e.g., a plurality of) vertical springs 60 constitutes a vertical spring, and the vertical spring 60 is elongated through the gap 18 in the thickness direction. The at least one vertical spring 60 may be made of a flexible material. Here, the at least one vertical spring 60 may be obtained by a vertical connection between the membrane electrode 14 and the counter electrode 16.
Overall, the above examples present several important advantages. The compliance of the membrane electrode 14 is generally not defined by tensile stress, and the compliance of the membrane electrode 14 is generally unaffected by external forces. Rather, the compliance of the membrane electrode 14 is generally determined by the bending stiffness of the material designed and used to fabricate the at least one spring 20, 30, 60. Importantly, the bending stiffness of the material is a particularly stable parameter: the characteristics of the sensors will not change easily over time and nominally identical sensors will have the same or similar behavior.
Higher stability and yield can be achieved for sensor production. A calibration function can usually be avoided because it can be ensured that the actual parameters of different sensors with the same nominal parameters do not vary too much.
The system cost can also be reduced. The counter electrode(s) 18 and/or 19 can be designed with thinner layers and greater acoustic permeability, thus reducing noise contribution and resulting in a higher signal-to-noise ratio SNR.
In addition, reliability is improved. In the event of particle intrusion, the local compliance of the membrane electrode 14 can be modified, but overall sensitivity variations are limited, at least by means of the elastic action exerted by the at least one spring 20, 30 or 60.
In several examples, at least one surface of the membrane electrode 14 (e.g., the surface 14a facing the counter electrode 16 but spaced apart from the counter electrode 16 by at least one spring) and/or at least one surface of the counter electrode 16 (e.g., the surface 16b facing the membrane electrode 14 but spaced apart from the membrane electrode 14 by at least one spring) can be a non-convex surface: a bump or other protrusion may not be entirely necessary. This is because at least one spring 20, 30 or 60 can maintain a safe distance between the membrane electrode 14 and the counter electrode 16. Therefore, the following aspects would not be possible: in operation, the membrane electrode 14 and the counter electrode 16 will be in contact with each other, thereby remaining attached to each other by virtue of unintended electrostatic attraction. Nevertheless, a small number of protrusions may be provided to increase safety and maintain at least a small gap between the membrane electrode 14 and the counter electrode 16 when the membrane electrode 14 is in contact with the counter electrode 16.
In the example of fig. 5, while the surface 14a, which is spaced from the first pair of electrodes 16 by the at least one spring 20, is non-convex, the surface 14b presents a protrusion 14b ', which protrusion 14 b' protrudes in the second gap 19 towards the second pair of electrodes 17. Therefore, in the event that the membrane electrode 14 is accidentally brought into contact with the counter electrode 16, the protrusions 14 b' can avoid the membrane electrode 14 from being completely attached to the counter electrode 16 by electrostatic attraction. By avoiding a complete attachment between the membrane electrode 14 and the counter electrode 16, the projections 14 b' can thus be used in gaps (such as gap 19) that are free of springs.
Fig. 10-14 illustrate fabrication steps of a method for fabricating an example of a sensor (e.g., sensor 10 of fig. 1) as described above.
First (fig. 10), a substrate 24 (which may include a stop layer 28) may be fabricated.
The membrane electrode 14 may be placed or otherwise prepared over the substrate 24 and/or the stop layer 28 (where the flexible membrane connection 22 includes a cut-out or aperture 22d as shown in fig. 3, the cut-out or aperture 22d may be made or placed before the membrane electrode 14 is applied to the substrate 24 or stop layer 28, or after the membrane electrode 14 is applied to the substrate 24 or stop layer 28).
Subsequently, a covering material 26 (which may be a sacrificial material that is subsequently at least partially removed) may be deposited on the substrate 24 (fig. 11), for example at least in the areas that will constitute the gaps 18 and/or in the peripheral portions of the structure 12. The capping material 26 may be a capping oxide.
At least one hole 26a (e.g., a through hole) may be implemented, for example, in a selected location of the covering material 26 (e.g., which will accommodate at least one spring 20). The at least one aperture 26a may be conical or slanted (other shapes are also possible). The plurality of holes 26a preferably have side wall angles that are identical to each other or vary maximally by 1% or 5%, in order to obtain springs 20 having identical or very similar spring constants. The at least one hole 26a may be obtained by etching (e.g., by using a dry or wet TEOS etch) or other removal technique. The at least one hole 26a may at least partially expose the surface 14a, and the at least one spring 20 will abut the surface 14 a. The exposed portions of surface 14a may correspond to, for example, non-conductive islands of surface 14 a: in the case where the spring would be a conductive and/or highly doped material, the island would allow the membrane electrode 14 to be insulated from the counter electrode 16. For example, the non-conductive islands may be deposited after the creation of the holes 26 a.
As shown in fig. 12, the at least one spring 20 may be prepared, for example, by depositing material over the at least one aperture 26a, and in particular over the surface(s) of the at least one aperture 26 a. As shown by fig. 12, the portion of the spring 20 adjacent to the membrane electrode 14 will constitute a membrane side leg 20a of the spring 20. The portion of the spring 20 on the other side (and which may project in a flush direction) relative to the leg 20a will constitute the counter electrode side leg 20b of at least one spring 20. The intermediate portion of the spring 20, which is obliquely extended along the boundary of the hole 26a, will constitute the main portion 20c of at least one spring 20.
The counter electrode side foot 20b (for example, the upper side of the counter electrode side foot 20b in the thickness direction) may be exposed. Therefore, the upper side of the counter electrode side foot 20b and the layer of the covering material 26 may be caused to be flush with each other in the upper surface 26e thereof in the thickness direction. As shown in fig. 13, the flush upper surface 26e will be used for the subsequent step of preparing the mechanical contact of the counter electrode 16 with the at least one spring 20. To make the upper surface 26e more flush, chemical mechanical polishing may be performed.
In a subsequent step, the counter electrode 16 may be prepared and/or configured so as to abut on the at least one spring 20 (e.g., on the counter electrode side foot 20 b). Thereafter, the remaining region(s) of the cover material 26 (e.g., at least those regions occupying the volume to be occupied by the gaps 18) may be etched or otherwise removed to obtain the structure of fig. 1.
The counter electrode 16 and the at least one spring 20 may be made of the same material (see fig. 19).
In the above and below methods, the membrane electrode 14 may be the first element, and the counter electrode 16 may be the second element. However, the operation may be reversed such that the first element to be placed over the substrate 24 is the counter electrode 16 and the membrane electrode 14 is the second element to be placed over the substrate 24.
Fig. 14-17 illustrate a method for manufacturing a dual pair electrode sensor similar to the sensor of fig. 5.
Fig. 14 shows a step in which a second (more inner) counter electrode 17 is placed on top of the substrate 24 and/or the cover layer 26.
As can be seen in fig. 15, a second layer 26b of a capping material (e.g., a capping oxide) may be deposited over the second pair of electrodes 17. Thereafter, the membrane electrode 14 may be deposited over the second layer of cover material 26 b.
As shown in fig. 16, a third layer 26c of cover material (cover oxide) may be placed over the membrane electrode 14. Thereafter, at least one spring 20 is placed, for example, after a hole 26a (e.g., a tapered or angled hole) has been made in the third layer 26c of cover material.
Thereafter, as illustrated by fig. 17, a first (more outer) counter electrode 16 may be placed on the at least one spring 20 and the third layer 26c of cover material. Thereafter, the layers 26, 26b, and 26c of the cover material may be at least partially etched or otherwise removed. A similar procedure to the variant of fig. 13 may be performed, in case it is contemplated to make the at least one spring 20 and the first pair of electrodes 16 from the same material. Basically, when step f (fig. 16) is reached, any of the steps discussed with reference to fig. 12 and 13 may be performed.
When the bimorph spring(s) 30 are used, an advantage is obtained: after the cover material 26 has been removed, the bimorph spring 30 will bend, thus naturally increasing the height of the gap 18.
Fig. 18 shows another example of a vertical spring 60 (e.g., extending in the thickness direction) having a flexible material. Here, the spring may be obtained by a vertical connection between the membrane electrode 14 and the counter electrode 16.
To make the example of fig. 18, at least one of the following steps may be performed:
1) etching at least one vertical hole into the cover material 26;
2) the at least one vertical hole is filled with a material that is more etch resistant than the cover material, creating at least one column extending from the membrane electrode 14 in the thickness direction.
3) The remaining capping material is etched (while the at least one pillar, which is more resistant to etching, is resistant to the etchant).
4) The counter electrode 16 (with the spring 60 attached thereto) is applied to the etched portion, the counter electrode 16 abutting against at least one of the pillars (which thus acts as a spacer).
5) At least one pillar is etched (in some cases, the pillar may remain part of the counter electrode 16).
The shape of the spring 60 may vary and may be a long, straight cantilever, a loop, a spiral, or any other shape.
The example of removing material as described above may be performed by etching (e.g., dry or wet etching) for at least one of the above steps. For at least one of the above steps, the etching may be anisotropic etching or isotropic etching. For at least one of the above steps, a TEOS etch may be used.
For example, to remove material, at least one of the above steps may include a chemical mechanical polishing step.
When a material (e.g., a cover material) is inserted, at least one of the above steps may include a lithography step (e.g., a photolithography step).
