Z-axis micro-electromechanical sensor with improved stress insensitivity

Abstract

Embodiments of the present disclosure generally relate to Z-axis microelectromechanical sensors with improved stress insensitivity. A microelectromechanical sensor device has a detection structure comprising: a base having a top surface; an inertial mass suspended over the top surface of the base and elastically coupled to a rotor anchor so as to perform an inertial motion according to an amount to be detected with respect to the base; and a stator electrode integrally coupled to the base at respective stator anchors and capacitively coupled to the inertial mass so as to generate, in response to the amount to be detected, a differential capacitance variation indicative of the amount to be detected. In particular, as the inertial motion, the inertial mass performs a translational motion along a vertical axis normal to the top surface of the base; and the stator electrode is arranged in a suspended manner over the top surface of the base.

Description

Technical Field

[0001] This disclosure relates to a vertical axis (so-called z-axis) MEMS (microelectromechanical system) sensor device that has improved insensitivity to external stresses or stimuli that constitute interference with the quantity to be detected; the following discussion will explicitly refer to a MEMS sensor device that implements a capacitive type accelerometer, which is configured to detect linear acceleration along the aforementioned z-axis, without implying any loss of versatility. Background Technology

[0002] In general, the detection structure of a MEMS accelerometer includes at least one inertial mass, which is usually defined as a "rotor mass" or simply a "rotor". It can move through inertial effects in the presence of the acceleration to be detected (but this does not mean that the inertial mass must have rotational motion).

[0003] An inertial mass is suspended above a base, which is coupled to a corresponding rotor anchor (fixed to the base) via an elastic element. The elastic element allows the inertial mass to move through inertial effects.

[0004] The detection structure of a MEMS accelerometer also includes a stator electrode, which is fixed and integrally coupled to a substrate and capacitively coupled to a rotor to form one or more detection capacitors (typically in a differential configuration), the capacitance change of which indicates the quantity to be detected.

[0005] Typically, a MEMS accelerometer also includes an electronic readout circuit electrically coupled to the sensing structure, i.e., a so-called ASIC (Application-Specific Integrated Circuit). This electronic readout circuit receives and processes the capacitance change generated by the sensing capacitor at its input to determine the value of acceleration, thereby generating an electrical output signal (which can be provided at the output of the MEMS accelerometer for subsequent processing operations).

[0006] The aforementioned ASIC electronic readout circuits and detection structures are typically fabricated in corresponding dies of semiconductor material, which are housed within a container (so-called a package) that surrounds and protects the die and also provides an electrical connection interface to the outside. In a so-called substrate-level packaging solution, the package is formed by one or more base layers and capping layers that are directly coupled to the die of the MEMS device to form a mechanical and electrical interface to the external device.

[0007] Figure 1A and Figure 1B The detection structure of a known type of vertical axis MEMS accelerometer is shown in the top view and cross-sectional view, respectively, and the detection structure is represented by 1.

[0008] The detection structure 1 includes an inertial mass 2, which has a main extension in the horizontal plane xy (in this example, it has a generally rectangular shape and extends along the first horizontal axis x) and is suspended above a base 3 having a top surface 3a.

[0009] The inertial mass 2 has a window 4 inside that divides the inertial mass into a first part 2a and a second part 2b with an asymmetric mass distribution. In this example, the extension of the first part 2a along the first horizontal x-axis is greater than the corresponding extension of the second part 2b.

[0010] The inertial mass 2 is elastically coupled to the rotor anchor 5, which is centrally located relative to the window 4, via a first torsional elastic element 6a and a second torsional elastic element 6b. The first torsional elastic element 6a and the second torsional elastic element 6b have linear extensions along the second horizontal axis y of the aforementioned horizontal plane xy.

[0011] The first torsional elastic element 6a and the second torsional elastic element 6b define the rotation axis A of the inertial mass 2, which moves by inertial effect in the presence of an external acceleration orthogonal to the horizontal plane xy along the z-axis, and oscillates or "wobbles" about the rotation axis A.

[0012] The detection structure 1 also includes a first stator electrode 8a and a second stator electrode 8b arranged on the substrate 3. The first stator electrode 8a and the second stator electrode 8b are fixedly coupled to the top surface 3a of the substrate 3, below the inertial mass body 2, on the opposite side relative to the window 4.

[0013] Specifically, the first stator electrode 8a is arranged below the first portion 2a of the inertial mass 2, and the second stator electrode 8b is arranged below the second portion 2b of the inertial mass 2, to form a pair of detection capacitors.

[0014] The rotation caused by the inertial effect of the inertial mass 2 around the rotation axis A thus determines the approach / removal of the inertial mass 2 relative to the first stator electrode 8a, and the corresponding relocation / approach of the inertial mass 2 relative to the second stator electrode 8b, thereby causing a change in the differential capacitance of the detection capacitor that indicates the degree of external acceleration.

[0015] In the event of stress and deformation, particularly due to interaction with the package, such as due to changes in temperature or environmental conditions or due to mechanical stress, the previously described detection structure 1 may be affected by measurement errors.

[0016] Due to the varying coefficients of thermal expansion and the different Young's moduli of the constituent materials, the packages of microelectromechanical sensors actually deform with temperature changes; this can cause corresponding deformation in the substrate housing the sensing structure within the package. Similar deformation can occur due to material aging or specific external stresses, such as from soldering onto the printed circuit board or from the absorption of moisture by the materials constituting the package.

[0017] like Figure 2 As illustrated, in cases where the substrate 3 deforms, for example due to thermal stress (such as cooling), the top surface 3a of the substrate 3 may bend or dent (for clarity, Figure 2 (This deformation is shown in an emphasized manner), which causes the stator electrodes 8a and 8b to approach the inertial mass 2 in the initial static state without external acceleration.

[0018] In particular, in the above Figure 1B In the equation, the theoretical distance at rest without deformation is denoted by g0, and... Figure 2 In the middle, x 1,ΔT and x 2,ΔT These are displacements relative to the state at rest due to the deformation of the substrate 3 (these displacements are variables that are functions of temperature, or generally functions of all external effects that can cause the deformation of the substrate 3).

[0019] The aforementioned displacement causes the following changes in the values ​​of the detection capacitors, represented by C1 and C2 (these changes are undesirable as long as they are independent of the acceleration being detected):

[0020] as well as

[0021]

[0022] Similarly, in a manner not shown, due to the expansion of the top surface 3a of the substrate 3, heating (ΔT>0) causes the following undesirable changes in the values ​​of the sensing capacitors C1 and C2, this time due to the movement of the stator electrodes 8a and 8b away from the inertial mass 2 in their initial rest state:

[0023] as well as

[0024]

[0025] These capacitive changes cause an undesirable modification (so-called drift or offset) to the output signal provided by the MEMS accelerometer when at rest, referred to as "zero g level," and result in errors in acceleration detection.

[0026] To overcome this shortcoming, people have proposed a variety of solutions, but none of them are entirely satisfactory.

[0027] In particular, some solutions envision the optimization of the acceleration detection structure.

[0028] For example, US 2011 / 0023604 discloses a detection structure for a MEMS accelerometer, in which the positioning of the rotor anchor relative to the stator electrodes (which are arranged on the top surface of the substrate) is optimized to reduce changes in electrical parameters due to substrate deformation. In particular, the rotor and stator anchor are arranged to be strictly close to each other, i.e., as close as possible to each other in a way that is compatible with the manufacturing process.

[0029] In this solution, there are physical limitations (related to the size of the anchor) and technical limitations (related to manufacturing technology) that cannot effectively eliminate the drift error of the output signal provided by the MEMS accelerometer (in fact, there is always a certain distance between anchor positions, despite compatibility with manufacturing processes).

[0030] Other solutions envision optimization at the packaging level; for example, the use of ceramic substrates with reduced sensitivity to deformation has been proposed.

[0031] However, these solutions present greater challenges in the manufacturing process and are typically more expensive; furthermore, ceramic packages are generally larger than traditional plastic packages. Summary of the Invention

[0032] This disclosure aims to address the aforementioned problems, and in particular aims to provide a microelectromechanical sensor device that has improved stability and reduces the drift of its electrical characteristics relative to external stimuli such as thermal changes, mechanical or environmental stresses, or other external stimuli of various natures.

[0033] This disclosure relates to an apparatus comprising a substrate having a first surface. An anchor is coupled to the substrate. An inertial mass is suspended above the first surface of the substrate and elastically coupled to the anchor. A first stator electrode is coupled to the substrate and has a second surface spaced apart from the first surface of the substrate by a first distance, the second surface facing away from the substrate. A second stator electrode is coupled to the substrate and spaced apart from the first stator electrode by the anchor, the second stator electrode having a third surface spaced apart from the first surface of the substrate by a second distance, the second distance being smaller than the first distance, the third surface facing away from the substrate. Attached Figure Description

[0034] To better understand this disclosure, preferred embodiments thereof are now described purely by way of non-limiting example and with reference to the accompanying drawings, in which:

[0035] Figure 1Aand Figure 1B These are, respectively, a top view and a schematic cross-sectional view of the detection structure of a known type of vertical axis MEMS accelerometer;

[0036] Figure 2 yes Figure 1B A schematic diagram of the detection structure under deformation of the corresponding substrate;

[0037] Figure 3A Figures 3A and 3B are respectively a top view and a schematic cross-sectional view along line II-II of the detection structure of the vertical axis MEMS accelerometer according to the first embodiment of the present solution;

[0038] Figure 4 is a schematic diagram of the detection structure in Figure 3B under the deformation of the corresponding substrate;

[0039] Figure 5A and Figure 5B These are, respectively, a top view and a schematic cross-sectional view along line VV of the detection structure of a vertical axis MEMS accelerometer according to another embodiment of this solution;

[0040] Figure 6A and Figure 6B These are, respectively, a top view of another variant of the detection structure along line VI-VI and a schematic cross-sectional view along line VI-II; and

[0041] Figure 7 This is an overall block diagram of an electronic device including a MEMS sensor device, according to another aspect of this solution. Detailed Implementation

[0042] As will be discussed in detail below, one aspect of this solution envisions a detection structure for a MEMS sensor device (particularly a vertical z-axis accelerometer), wherein stator electrodes are arranged in a fully suspended manner relative to the underlying substrate and differentially relative to an inertial mass to which they are capacitively coupled (i.e., a first stator electrode is arranged below the inertial mass, and a second stator electrode is arranged above the inertial mass). In this case, the inertial mass is elastically coupled to the substrate so that, in the presence of an external acceleration acting along the same vertical axis, it can perform translational motion along the vertical axis by inertial effects.

[0043] As will be discussed in detail, in this way, any possible deformation caused by the encapsulation in the substrate does not require any modification to the relative distance between the stator electrodes and the inertial mass in the stationary state, making the detection virtually insensitive to deformation, thereby preventing any possible modification to the output signal provided by the MEMS accelerometer at rest (eliminating the aforementioned zero-g level drift).

[0044] In particular, according to one aspect of this solution, the detection structure comprises two semiconductor material (particularly epitaxial silicon) overlay structural layers that are independent and appropriately processed (e.g., by trench etching and removal of the sacrificial layer) to define the structural elements of the detection structure (particularly the aforementioned stator electrode and the aforementioned inertial mass).

[0045] As will be described in detail below, a first stator electrode is defined in a first structural layer and a second stator electrode is defined in a second structural layer. An inertial mass body obtained by utilizing the two structural layers, which faces the two stator electrodes at a certain interval, is located above or below the stator electrodes in the vertical direction (with different configurations).

[0046] For example, the detection structure formed by the aforementioned stacked structural layers can be performed using the manufacturing process described in detail in Italian patent application 102020000011755 filed on May 20, 2020, in the name of the applicant.

[0047] In short, the process envisions growing a first thick epitaxial layer on a substrate, for example, made of monocrystalline silicon, which covers a first sacrificial layer of dielectric material, which is then partially removed by etching (e.g., using hydrofluoric acid vapor). The first sacrificial layer has an opening that defines an anchoring region for the first epitaxial layer to the substrate.

[0048] The first epitaxial layer constitutes a first structural layer, in which a first trench is formed, for example, by dry silicon etching; the first trench is empty or subsequently filled with dielectric material and defines a structural element of the detection structure or the bottom of the structural element (i.e., closer to the substrate); conductive regions (defining pads and electrical interconnects) are formed below the first sacrificial layer at an anchoring region to the substrate of the first epitaxial layer and separated from the top surface of the substrate by the dielectric layer so as to enable electrical biasing of the structural element.

[0049] Next, the manufacturing process envisions forming a second sacrificial layer of dielectric material on the first epitaxial layer, and defining the second sacrificial layer to form sacrificial regions that are separated from each other by openings.

[0050] Then, a second epitaxial layer with a thickness less than (e.g., equal to half) of the first epitaxial layer is formed on the first epitaxial layer and the sacrificial region; the second epitaxial layer is in direct contact with the first epitaxial layer at the opening and constitutes a second structural layer, in which a structural element of the detection structure or the top of the structural element (i.e., away from the substrate) is defined by forming a second trench.

[0051] The process then envisions partially or completely removing the sacrificial region again by etching (e.g., using hydrofluoric acid vapor) to release the structural elements of the detection structure at both higher and lower levels.

[0052] It should be noted that after etching, the structure of the second epitaxial layer can be in direct (mechanical and electrical) contact with the underlying structure of the first epitaxial layer, or it can be separated from the underlying first epitaxial layer by an empty region (gap) to be suspended above the first epitaxial layer. Furthermore, both structures obtained from the first epitaxial layer or the second epitaxial layer can be suspended above the substrate.

[0053] The method typically also includes a final step involving coupling a cap by inspecting the bonding layer (e.g., of the glass frit) on top of the stack of the first and second structural layers of the structure. This cap serves a sealing function (potentially an hermetically sealed seal) and aims to protect the inspected structure from external environmental factors (humidity, dust, etc.) and impacts.

[0054] refer to Figure 3A The top view and cross-sectional view of Figure 3B now describe a first embodiment of this solution regarding the detection structure of a vertical axis MEMS accelerometer.

[0055] The detection structure represented by 10 includes an inertial mass 12, which has a main extension in the horizontal plane xy and, in this example, has a generally rectangular shape in the plan view, with its long side along the first horizontal x-axis.

[0056] An inertial mass 12 is suspended above a semiconductor material (particularly silicon) substrate 13 and elastically coupled to a rotor anchor 15, which is disposed in the center of a window 14 located inside the inertial mass 12 and is formed by a cylindrical or columnar structure integral with respect to the substrate 13. The main extending plane of the inertial mass 12 is substantially parallel to the top surface 13a of the substrate 13.

[0057] Specifically, the inertial mass 12 is coupled to the rotor anchor 15 via a first elastic element 16a and a second elastic element 16b. In the presence of an external acceleration acting along the vertical axis z, the first elastic element 16a and the second elastic element 16b, through their torsional and bending deformations, can cause the inertial mass 12 to translate along the vertical axis z via inertial effects (these elastic elements 16a, 16b are therefore compliant with torsion and bending along the vertical z-axis and are rigid relative to other translational or rotational movements in the horizontal plane xy).

[0058] In this configuration, the first elastic element 16a and the second elastic element 16b have linear extensions along the first horizontal axis x and are arranged on opposite sides of the rotor anchor 15 relative to the second horizontal axis y. Specifically, the first elastic element 16a and the second elastic element 16b are coupled to the rotor anchor 15 via first connecting element 17a and second connecting element 17b, respectively, and the first connecting element 17a and the second connecting element 17b have linear extensions along the second horizontal axis y.

[0059] The first elastic element 16a and the second elastic element 16b are also connected to the inertial mass 12 by an additional connecting element 27 having a general extension along the second horizontal axis y and a decoupling elastic portion 27′ for elastic decoupling relative to the inertial mass 12.

[0060] In this embodiment, the inertial mass body 12 is divided into a first half 12a and a second half 12b by the window 14, and the mass is basically symmetrically distributed relative to the central anchor 15.

[0061] The detection structure 12 also includes a first stator electrode 18a and a second stator electrode 18b. In this case, the first stator electrode 18a and the second stator electrode 18b are arranged to be suspended above the substrate 13. They are integrally coupled to the substrate 13 through a first stator anchor 19a and a second stator anchor 19b, respectively. The first stator anchor 19a and the second stator anchor 19b are formed by a cylindrical or columnar structure integral with the substrate. In particular, the stator electrodes 18a and 18b are suspended from the corresponding stator anchors 19a and 19b in a cantilever manner.

[0062] In this embodiment, the first stator electrode 18a and the second stator electrode 18b have a basic rectangular shape that extends along the second horizontal axis y in a plan view.

[0063] Furthermore, the first stator anchor 19a and the second stator anchor 19b are substantially aligned with the rotor anchor 15 along the first horizontal axis x, and are arranged very close to each other along the first horizontal axis x at a relatively short distance (e.g., at the minimum distance allowed by the manufacturing process).

[0064] Specifically, the first stator electrode 18a and the second stator electrode 18b are arranged facing the first half 12a and the second half 12b of the inertial mass body 12 on opposite sides relative to the vertical axis z, respectively. In the illustrated embodiment, the first stator electrode 18a is arranged above the thickness reduction portion 12a′ of the first half 12a of the inertial mass body 12, while the second stator electrode 18b is arranged below the corresponding thickness reduction portion 12b′ of the second half 12b of the inertial mass body 12.

[0065] More specifically, in this embodiment, the first stator electrode 18a is disposed in the second structural layer 10″ of the detection structure 10, which is arranged at a higher level and at a greater distance from the top surface 13a of the substrate 13. The reduced thickness portion 12a′ of the inertial mass 12 is disposed in the first structural layer 10′ of the detection structure 10, which is arranged at a lower level, i.e., at a shorter distance from the top surface 13a of the substrate 13 along the vertical axis z (it should be noted that during the manufacturing process, the second structural layer 10″ is formed after the first structural layer 10″, as described previously with reference to patent application 102020000011755).

[0066] Therefore, the second stator electrode 18b is disposed in the first structural layer 10′ of the detection structure 10, and the corresponding thickness reduction portion 12b′ of the inertial mass body 12 is formed in the second structural layer 10″.

[0067] Specifically, the first structural layer 10′ and the second structural layer 10″ are epitaxial silicon layers grown on the top surface 13a of the substrate 13, and are at least partially electrically and / or mechanically decoupled from each other, as described above with reference to the teachings of the aforementioned Italian patent application 102020000011755.

[0068] In this embodiment, the thickness of the second stator electrode 18b, for example, along the vertical axis z, is greater than the thickness of the first stator electrode 18a, and the thickness of the thickness reduction portion 12a′ is greater than the thickness of the thickness reduction portion 12′ of the inertial mass body 12 (the thickness of the first structural layer 10′ is less than the thickness of the second structural layer 10″). However, a solution is conceivable in which the thicknesses of the first structural layer 10′ and the second structural layer 10″ are substantially the same.

[0069] When at rest, the facing distance or gap between the first stator electrode 18a and the second stator electrode 18b, represented by g, and the corresponding thickness reduction portions 12a′ and 12b′ of the inertial mass body 12 substantially correspond.

[0070] Therefore, in this embodiment, the detection structure 10 is substantially symmetrical with respect to the first horizontal axis x and the second horizontal axis y; similarly, the rotor anchor 15 defines the center of symmetry of the construction of the detection structure 10.

[0071] In this embodiment, the first elastic element 16a and the second elastic element 16b are also formed in the second structural layer 10″ of the detection structure 10 in a manner not shown here, so that, for example, their thickness is less than the thickness of the inertial mass 12 and their width is less than the width of their longitudinal extension.

[0072] In the presence of an external acceleration acting along the vertical axis z, the inertial mass 12 translates upward or downward, resulting in a differential type of relative displacement with respect to the first stator electrode 18a and the second stator electrode 18b, and a corresponding change in differential capacitance indicating the value of the external acceleration.

[0073] Advantageously, the described detection structure 10 is substantially insensitive to deformation of the package and substrate 13 caused by external stress.

[0074] As schematically shown in Figure 4, in fact, considering the proximity of the anchor and the corresponding fully suspended configuration relative to the base 13, the deformation of the base 13 (e.g., bending due to thermal stress (ΔT<0) caused by cooling) affects both the inertial mass 12 and the stator electrodes 18a, 18b in a similar manner in this case.

[0075] Therefore, in a stationary state, without external acceleration, there is essentially no relative motion between the inertial mass 12 and the stator electrodes 18a and 18b (in other words, the separation distance or gap g0 at rest does not change).

[0076] Advantageously, the output signal provided by the MEMS accelerometer at rest will not be subject to undesirable modifications, and there will be virtually no drift or change in the "zero g level".

[0077] In addition, the described solution has other advantages.

[0078] First, unlike the traditional solution for the wobbling seesaw motion of an inertial mass (where only a portion of the unbalanced mass contributes to the motion through inertial effects), in this case, the entire footprint of the inertial mass 12 translating along the vertical axis z actively contributes to the motion due to inertia.

[0079] Furthermore, in this case, the full-scale range does not depend on the size of the electrodes; in particular, when the sizes of the stator electrodes 18a and 18b change, the full-scale value and stability remain essentially unchanged. Conversely, in the aforementioned conventional solution for the rotational motion of an inertial mass, an increase in the size of the stator electrodes leads to a decrease in the full-scale value and stability.

[0080] Furthermore, due to the translational configuration of the inertial mass 12, the described solution again demonstrates a full-scale range that is completely symmetrical with respect to the external acceleration acting upward or downward along the vertical axis z, which is also different from the conventional solution described above.

[0081] Furthermore, the detection structure 10 is less affected by parasitic capacitance, and therefore, due to the suspended configuration of the stator and rotor electrodes, the detection structure 10 is less sensitive to noise, the stator and rotor electrodes are far from the substrate 13 and separated from adjacent elements by an air gap (or a gap typically filled by residual gas generated by the packaging operation).

[0082] refer to Figure 5A and Figure 5B Another embodiment of the solution is now described, which can effectively suppress the second-order parasitic effect caused by the deformation of the substrate 13 and the parasitic vibration mode of the structure.

[0083] In this embodiment, the detection structure, again indicated by 10, includes two pairs of stator electrodes that are capacitively coupled to the inertial mass 12 in a differential manner. On the opposite side of the rotor anchor 15, the electrodes are coupled to the first half 12a and the second half 12b of the inertial mass 12, respectively.

[0084] In each pair, one stator electrode is arranged above the corresponding thickness reduction portion of the inertial mass 12, and the other is arranged below the corresponding thickness reduction portion of the inertial mass 12, as discussed in detail above.

[0085] In this configuration, the first stator electrode 18a and the second stator electrode 18b form a first pair of electrodes, which are differentially capacitively coupled to the first half 12a of the inertial mass 12 at the corresponding thickness reduction portion 12a′. In this example, the first stator electrode 18a is positioned above the corresponding thickness reduction portion 12a′ of the first half 12a of the inertial mass 12, and the second stator electrode 18b is positioned below the corresponding thickness reduction portion 12a′ of the first half 12a of the inertial mass 12.

[0086] The detection structure 10 also includes a third stator electrode 18c and a fourth stator electrode 18d, which form a second pair of stator electrodes and are capacitively coupled to the second half 12b of the inertial mass body 12 in a differential manner.

[0087] In a similar manner to that described above, the third stator electrode 18c and the fourth stator electrode 18d are also arranged to be suspended above the substrate 13. The third stator electrode 18c and the fourth stator electrode 18d are integrally coupled to the substrate 13 through corresponding third stator anchors 19c and fourth stator anchors 19d, which are composed of cylindrical or columnar structures integral with the substrate.

[0088] In this example, the third stator electrode 18c is arranged above the corresponding thickness reduction portion 12b′ of the second half 12b of the inertial mass 12, and the fourth stator electrode 18d is arranged below the corresponding thickness reduction portion 12b′ of the second half 12b of the inertial mass 12.

[0089] In this embodiment, the stator electrodes 18a-18d have a generally rectangular shape in the plan view and extend along the first horizontal axis x. Furthermore, in this case, the rotor anchor 15 and the stator anchors 19a-19d are aligned along the second horizontal axis y and arranged close to each other again.

[0090] In this case, the detection structure 10 also has a substantially symmetrical configuration with respect to the first horizontal axis x and the second horizontal axis y (i.e., the rotor anchor 15 defines the center of symmetry of the detection structure 10).

[0091] The operating principle of the detection structure 10 remains essentially unchanged from that discussed earlier. Advantageously, the presence of two pairs of stator electrodes arranged on opposite sides of the rotor anchor 15 enables the suppression of undesirable second-order effects, also caused by deformation of the substrate 13, through a double differential configuration.

[0092] Figure 6A and Figure 6B Another embodiment of the solution is shown, in which the other embodiment is also able to effectively suppress second-order parasitic effects.

[0093] This embodiment and about Figure 5A and Figure 5B The difference in the described embodiment is that the stator electrodes 18a-18d (in this case having a basic rectangular shape extending along the second horizontal axis y) are arranged side by side along the first horizontal axis x. Therefore, the first stator anchor 19a and the second stator anchor 19b, and thus the third stator anchor 19c and the fourth stator anchor 19d, are here aligned in pairs along the first horizontal axis x.

[0094] Therefore, the stator anchors 19a-19d are arranged in a lateral position around the rotor anchor 15 (or have central symmetry with respect to the rotor anchor 15), so that the anchors can be arranged at the center of the footprint of the detection structure 10 and are even less apart from each other.

[0095] Therefore, the above embodiments can allow for greater insensitivity to stress and the final deformation of the substrate 13.

[0096] also, Figure 7 An electronic device 30 is shown, in which a vertical axis microelectromechanical acceleration sensor device, denoted here as 31, can be used.

[0097] In addition to the detection structure 10 described above, the microelectromechanical sensor device 31 also includes an ASIC circuit 33, which provides a relative readout interface (and may be located in the same die as the die used to manufacture the detection structure 10, or may be located in a different die, which in any case can be housed in the package).

[0098] Electronic device 30 is, for example, a portable mobile communication device, such as a mobile phone, a PDA (personal digital assistant), a portable computer, but may also be a digital audio player with voice recording capability, a camera or video camera, a controller for video games, etc.; electronic device 30 is generally capable of processing, storing and / or transmitting and receiving signals and information.

[0099] Electronic device 30 includes a microprocessor (CPU) 34 and an input / output (I / O) interface 35 connected to the microprocessor 34. The CPU 34 receives acceleration signals detected by a microelectromechanical sensor device 31. The I / O interface 35 includes, for example, a keypad and a display. Additionally, electronic device 30 may include a speaker 37 for generating sound at an audio output (not shown) and internal memory 38.

[0100] The advantages of the microelectromechanical sensor device based on this solution are clearly evident from the above description.

[0101] In any case, it is emphasized again that this solution allows for the substantial elimination of any drift in the electrical performance of the detection structure 10 caused by deformation of the substrate 13, external stress, and stimuli (e.g., temperature changes or changes in mechanical stress), for example, due to soldering to a printed circuit board or certain other properties (such as aging or moisture absorption).

[0102] Therefore, the detection structure 10 is very stable and is independent of the usage and assembly conditions in the corresponding package.

[0103] Finally, it is obvious that modifications and changes may be made to the content described and illustrated herein without departing from the scope of this disclosure.

[0104] In particular, the described solution can be applied to single-axis sensors, as well as to biaxial or triaxial sensors capable of detecting acceleration (or different amounts) also along a first horizontal axis x and / or along a second horizontal axis y (these sensors are provided with additional moving and stationary structures and electrodes arranged in a suitable manner for this purpose).

[0105] In addition, this solution can generally be applied to different types of MEMS sensor devices that require the detection of capacitance changes.

[0106] A microelectromechanical sensor device with a detection structure (10) can be summarized as including: a substrate (13) having a top surface (13a); an inertial mass (12) suspended above the top surface (13a) of the substrate (13) and elastically coupled to a rotor anchor (15) to perform inertial motion relative to the substrate (13) according to the quantity to be detected; and stator electrodes (18a, 18b) at corresponding stator anchors (19a, 19b). The inertial mass (12) is coupled to the substrate (13) and capacitively coupled to the inertial mass (12) in response to the quantity to be detected, thereby generating a differential capacitance change indicating the quantity to be detected. The inertial mass (12) is configured to perform translational motion along a vertical axis (z) orthogonal to the top surface (13a) of the substrate (13) as the inertial motion. The stator electrodes (18a, 18b) are suspended above the top surface (13a) of the substrate (13).

[0107] The stator electrode may include at least one first stator electrode (18a) and a second stator electrode (18b), wherein at least one first stator electrode (18a) and a second stator electrode (18b) are arranged on opposite sides of the inertial mass (12) with a certain distance (g) between them.

[0108] The first stator electrode and the second stator electrode (18a, 18b) can be suspended in a cantilever manner above the top surface (13a) of the substrate (13) from the corresponding first stator anchor and the second stator anchor (19a, 19b). The first stator anchor and the second stator anchor (19a, 19b) are composed of a cylindrical or columnar structure integral with the substrate (13).

[0109] The first stator electrode 18a and the second stator electrode 18b can be arranged above and below the corresponding thickness reduction portions (12a′, 12b′) of the inertial mass body (12), respectively.

[0110] The first stator electrode (18a) can be disposed in the second structural layer (10″) of the detection structure (10) arranged at a higher level, and the thickness reduction portions (12a′, 12b′) of the inertial mass (12) facing each other are disposed in the first structural layer (10′) of the detection structure (10), which is arranged at a lower level relative to the substrate (13); and the second stator electrode (18b) can be disposed in the first structural layer (10′), and the corresponding thickness reduction portions (12a′, 12b′) of the inertial mass (12) facing each other are disposed in the second structural layer (10″) of the detection structure (10).

[0111] The first and second structural layers (10′, 10″) mentioned above may be epitaxial silicon layers grown on the top surface (13a) of the substrate (13), and the epitaxial silicon layers are at least partially electrically and / or mechanically decoupled from each other.

[0112] The aforementioned inertial mass (12) may be internally defined by a window (14), which divides the inertial mass into a first half and a second half (12a, 12b) having a substantially symmetrical mass distribution relative to the rotor anchor (15); wherein the aforementioned first stator electrode (18a) may be capacitively coupled to the first half (12a) of the aforementioned inertial mass (12), and the aforementioned second stator electrode (18b) may be capacitively coupled to the second half (12b) of the aforementioned inertial mass (12).

[0113] The aforementioned inertial mass (12) may internally define a window (14), which divides the inertial mass into a first half and a second half (12a, 12b) with a substantially symmetrical mass distribution relative to the rotor anchor (15); wherein the aforementioned first stator electrode and second stator electrode (18a, 18b) may be capacitively coupled to the first half (12a) of the aforementioned inertial mass (12) and form a first pair of differential electrodes; and the aforementioned stator electrode may further include a third stator electrode (18c) and a fourth stator electrode (18d), the third stator electrode (18c) and the fourth stator electrode (18d) being arranged facing the second half (12b) of the inertial mass (12) on opposite sides relative to the vertical axis (z) and forming a second pair of differential electrodes.

[0114] The stator electrodes (18a-18d) may have corresponding stator anchors (19a-19d); and the stator anchors and the rotor anchors (15) may be arranged close to each other in a central manner relative to the detection structure (10), wherein the rotor anchors (15) define the center of symmetry of the detection structure (10).

[0115] The stator anchors (19a-19d) can be arranged symmetrically around the rotor anchor (15) with respect to the center of symmetry.

[0116] The stator anchors (19a, 19b) can be aligned with the rotor anchors (15) along the horizontal axes (x, y) of the horizontal plane (xy), and the top surface (13a) of the base is parallel to the horizontal plane (xy).

[0117] The aforementioned inertial mass (12) can be elastically coupled to the rotor anchor (15) via elastic elements (16a, 16b) to conform to the bending along the vertical axis (z).

[0118] The aforementioned elastic elements (16a, 16b) may have a longitudinal extension along a horizontal axis of a horizontal plane (xy), the aforementioned top surface (13a) of the aforementioned base is parallel to the aforementioned horizontal plane (xy), and the aforementioned elastic elements (16a, 16b) may be coupled to the aforementioned rotor anchor (15) via connecting elements (17a, 17b), the aforementioned connecting elements (17a, 17b) having an extension along another horizontal axis of a horizontal plane (xy), which is transverse to the aforementioned horizontal axis.

[0119] The above-described detection structure (10) can realize a single-axis accelerometer, which is configured to detect acceleration acting along the above-described vertical axis (z).

[0120] This disclosure also relates to an apparatus comprising: a substrate having a first surface; an anchor; an inertial mass suspended above the first surface of the substrate and elastically coupled to the anchor; and a first stator electrode coupled to the substrate, the first stator electrode having a second surface spaced apart from the first surface of the substrate by a first distance, the second surface facing away from the substrate. The apparatus further includes a second stator electrode coupled to the substrate and spaced apart from the first stator electrode by the anchor, the second stator electrode having a third surface spaced apart from the first surface of the substrate by a second distance, the second distance being smaller than the first distance, the third surface facing away from the substrate.

[0121] The inertial mass includes a window having a first extension, a second extension, and a third extension. The first extension is anchored within the first extension along a first direction. The second extension is along a second direction transverse to the first direction. The third extension is along the second direction and spaced apart from the second extension by the first extension. A first stator electrode and a second stator electrode are cantilevered above the aforementioned first surface of the substrate from a strut structure coupled to the substrate. The inertial mass includes a first step and a second step, the first step being aligned with the first stator electrode and the second step being aligned with the second stator electrode.

[0122] The present invention also relates to a suspended mass comprising: a first surface opposite to a second surface; a third surface located between the first and second surfaces; and an opening. A central anchor is coupled to a substrate and is located within the opening. A first electrode is coupled to the substrate and configured to interact with the third surface of the suspended mass. A second electrode is coupled to the substrate and configured to interact with the third surface of the suspended mass. The first electrode includes a first surface facing away from the substrate, and the second electrode includes a second surface facing away from the substrate, the second surface of the second electrode being closer to the substrate than the first surface of the first electrode. The first electrode includes a first dimension from the substrate to the first surface of the first electrode, and the second electrode includes a second dimension from the substrate to the second surface of the second electrode, the second dimension being smaller than the first dimension.

[0123] The various embodiments described above can be combined to provide other embodiments. All U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications, and non-patent publications mentioned in this specification and / or listed in the application data sheets are incorporated herein by reference. If desired, aspects of the embodiments may be modified to employ concepts from various patents, applications, and publications to provide other embodiments.

[0124] Based on the detailed description above, these and other changes can be made to the embodiments. Generally, the terminology used in the appended claims should not be construed as limiting the claims to the specific embodiments disclosed in the specification and claims, but should be construed as including all possible embodiments and the full scope of equivalents that are entitled to by those claims. Therefore, the claims are not limited to this disclosure.

Claims

1. An apparatus comprising: The substrate has a first surface; anchor; An inertial mass body is suspended above the first surface of the substrate and elastically coupled to the anchor; as well as A first stator electrode is coupled to the substrate, the first stator electrode having a second surface, the second surface being spaced apart from the first surface of the substrate by a first distance, and the second surface facing away from the substrate; A second stator electrode, coupled to the substrate and spaced apart from the first stator electrode by the anchor, has a third surface spaced from the first surface of the substrate by a second distance, the second distance being smaller than the first distance, and the third surface facing away from the substrate. The inertial mass is elastically coupled to the anchor via an elastic element to perform translational motion along the vertical axis, conforming to curvature along the vertical axis; and The first stator electrode and the second stator electrode are arranged on opposite sides of the inertial mass body at a certain interval, facing each other relative to the vertical axis.

2. The device of claim 1, wherein the inertial mass includes a window having a first extension, a second extension and a third extension, the first extension being along a first direction, the anchor being within the first extension, the second extension being along a second direction transverse to the first direction, and the third extension being along the second direction and spaced apart from the second extension by the first extension.

3. The device of claim 2, wherein the first stator electrode and the second stator electrode are cantilevered above the first surface of the substrate from a strut structure coupled to the substrate.

4. The device of claim 2, wherein the inertial mass includes a first step and a second step, the first step being aligned with the first stator electrode and the second step being aligned with the second stator electrode.

5. The device of claim 4, wherein the inertial mass is part of a first structural layer and the first stator electrode is part of a second structural layer, the second structural layer being further spaced from the substrate than the first structural layer, the second stator electrode being part of the first structural layer.

6. The device of claim 5, wherein the first structural layer and the second structural layer are epitaxial silicon layers grown on the first surface of the substrate, the epitaxial silicon layers being at least partially electrically and mechanically decoupled from each other.

7. The device of claim 2, wherein the inertial mass body internally defines a window, the window forming a first half and a second half having a substantially symmetrical mass distribution relative to the anchor, the first stator electrode being capacitively coupled to the first half of the inertial mass body and the second stator electrode being capacitively coupled to the second half of the inertial mass body.

8. The device of claim 2, wherein the inertial mass body internally defines a window that divides the inertial mass body into a first half and a second half with a substantially symmetrical mass distribution relative to the anchor, the first stator electrode and the second stator electrode being capacitively coupled to the first half of the inertial mass body and forming a first pair of differential electrodes; and The third and fourth stator electrodes are arranged facing the second half of the inertial mass, on opposite sides, and form a second pair of differential electrodes.

9. The device of claim 8, wherein the first stator electrode and the second stator electrode have corresponding first stator anchors and second stator anchors, the first stator anchors and the second stator anchors and the anchors are arranged centrally close to each other relative to the inertial mass, the anchors defining the center of symmetry of the inertial mass.

10. The device of claim 9, wherein the elastic element has a longitudinal extension along a first horizontal axis of a horizontal plane, the first surface of the substrate is parallel to the horizontal plane, and the elastic element is coupled to the anchor by a connecting element having an extension along a second horizontal axis of the horizontal plane, the second horizontal axis being transverse to the first horizontal axis.

11. An apparatus comprising: Base; Central anchor; A suspended mass includes a first surface and a second surface, wherein the first surface is further away from the substrate than the second surface. The opening has a central extension, a first side extension, and a second side extension, wherein the first side extension is separated from the second side extension through the central extension; first recess; as well as second recess; A first electrode is located between the central anchor and the suspended mass. The first electrode has a third surface that is coplanar with the first surface of the suspended mass. The first electrode is coupled to the substrate and spaced apart from the substrate by a first distance. The first electrode overlaps with the first recess. The second electrode is located between the central anchor and the suspended mass, and is separated from the first electrode by the central anchor. The second electrode is coupled to the substrate and separated from the substrate by a second distance. The second electrode overlaps with the second recess. The suspended mass is elastically coupled to the central anchor via an elastic element to perform translational motion along the vertical axis, conforming to curvature along the vertical axis; and The first electrode and the second electrode are arranged on opposite sides of the suspended mass body at a certain interval, facing each other relative to the vertical axis.

12. The device of claim 11, comprising a first anchor located between the central anchor and the first electrode and a second anchor located between the central anchor and the second electrode, the suspended mass overlapping the first anchor and the second anchor.

13. The device of claim 12, comprising a first gap located between the base and a portion of the first anchor.

14. The device of claim 12, wherein the first anchor includes a fourth surface facing the suspended mass and closer to the substrate than the third surface of the first electrode.

15. An apparatus comprising: Base; The suspended mass includes: The first surface is opposite to the second surface; A third surface, located between the first surface and the second surface; and Opening; A central anchor, coupled to the base and located in the opening; A first electrode, coupled to and spaced apart from the substrate by a first distance, is configured to interact with the third surface of the suspended mass; and The second electrode, coupled to the substrate and spaced apart from the substrate by a second distance, is configured to interact with the third surface of the suspended mass. The suspended mass is elastically coupled to the central anchor via an elastic element to perform translational motion along the vertical axis, conforming to curvature along the vertical axis; and The first electrode and the second electrode are arranged on opposite sides of the suspended mass body at a certain interval, facing each other relative to the vertical axis.

16. The device of claim 15, wherein the first electrode includes a first surface facing away from the substrate and the second electrode includes a second surface facing away from the substrate, the second surface of the second electrode being closer to the substrate than the first surface of the first electrode.

17. The device of claim 16, wherein the first electrode includes a first dimension from the substrate to the first surface of the first electrode and the second electrode includes a second dimension from the substrate to the second surface of the second electrode, the second dimension being smaller than the first dimension.

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