Micromechanical sensor comprising an electrically decoupled top electrode

Abstract

The invention relates to a micromechanical sensor (10) for capacitively measuring at least one environmental variable, the micromechanical sensor comprising: an edge region (30) which defines a cavity (32); a membrane (28) which spans at least sections of a cavity (32) and can be deflected into the cavity (32) in a vertical direction depending on the environmental variable; at least one measurement capacitance (12) which can be varied depending on the environmental variable and has a first upper electrode (Mt), which is coupled to the membrane (28), and an opposite first lower electrode (Mb); at least one reference capacitance (K1, K2, K3, K4) having a second upper electrode (Nt), fixed in each case with respect to the edge region (30), and an opposite second lower electrode (Nb), wherein the second upper electrode (Nt) is electrically decoupled from the membrane (28).

Description

[0001] Micromechanical sensor with electrically decoupled upper electrode

[0002] The invention relates to a micromechanical sensor according to the preamble of claim 1.

[0003] State of the art

[0004] DE 102020214 757 A1 describes a capacitive pressure sensor comprising a diaphragm adjacent to a gas-tight internal volume within a housing component of the pressure sensor. The diaphragm can deform when there is a pressure difference between the internal and external pressures. A measuring electrode is attached to the diaphragm, the position of which can change due to the diaphragm's warping. This position change leads to a change in the measuring capacitance, which consists of the measuring electrode and an associated measuring counter electrode. In addition, the sensor comprises at least one fixed reference capacitance with two reference electrodes that are firmly attached to the housing component and whose position does not change due to the diaphragm's warping. As a result, the reference capacitance remains unaffected by the diaphragm's movement.

[0005] Disclosure of the invention

[0006] According to the present invention, a micromechanical sensor with the features of claim 1 is proposed. This allows stray capacitances at the output potential to be reduced or prevented. The ambient variable can be detected more accurately and reliably. The measurement can be performed with less sensitivity to external electromagnetic influences.

[0007] The sensor can be a pressure sensor. The pressure sensor can be an absolute pressure sensor, in particular a barometric pressure sensor, or a differential pressure sensor. The sensor can be a capacitive pressure sensor. The sensor can be a microelectromechanical (MEMS) sensor. The ambient variable can be a fluid pressure, in particular a water pressure and / or air pressure.

[0008] The membrane can be deflectable depending on the fluid pressure. The membrane can be held directly or indirectly at the edge region. The cavity can be delimited by the edge region at least in a direction perpendicular to the vertical direction. The cavity can be filled with a fluid. A reference fluid pressure can exist in the cavity. The cavity can have a vacuum.

[0009] The cavity can be formed as a recess in a layer or layer structure. The edge region can be an edge of the layer or layer structure that borders the cavity. The membrane can be formed integrally with the layer or layer structure.

[0010] The references to upper and lower electrodes refer to the vertical direction. The first lower electrode can be fixed relative to the edge region. The first lower electrode can be positioned vertically opposite the first upper electrode. The distance between the first upper and lower electrodes in the vertical direction can vary depending on the membrane deflection.

[0011] The first lower electrode and / or the second lower electrode can be arranged on a carrier element. The carrier element can form a substrate or be arranged on a substrate. The edge region can be accommodated on the carrier element. The edge region can be firmly connected to the carrier element. The carrier element can be constructed of silicon, polysilicon, glass, silicon nitride, or silicon dioxide.

[0012] The first and / or second lower electrode may comprise a conductive layer, in particular a polysilicon layer and / or a metal layer. The first and / or second electrode may be arranged on the carrier element. An insulating layer may be arranged between the carrier element and the first and / or second lower electrode. The insulating layer may be composed of silicon nitride or silicon dioxide.

[0013] The first upper electrode, the first lower electrode, the second upper electrode and / or the second lower electrode can be arranged at least partially, preferably completely, with respect to a direction perpendicular to the vertical direction or with respect to two directions each perpendicular to the vertical direction and to each other, overlapping the membrane.

[0014] In a preferred embodiment of the invention, it is advantageous if the second upper electrode is electrically decoupled from the first upper electrode. The first upper electrode and the membrane can have the same electrical potential.

[0015] A preferred embodiment of the invention is advantageous in which the first upper electrode has a first electrical input potential and the second upper electrode has a second electrical input potential. The electrical input voltage can be applied between the first and second input potentials. The input voltage can be a predetermined supply voltage, in particular an alternating voltage, a pulsed voltage, for example, a square-wave voltage, or a direct voltage.

[0016] A preferred embodiment of the invention is advantageous in which the first lower electrode and the second lower electrode are electrically connected to each other and have the same electrical potential. This prevents stray capacitances between the lower electrodes of the measuring capacitance and the reference capacitance.

[0017] In a specific embodiment of the invention, it is advantageous if the electrical potential of the first and second lower electrodes is an electrical output potential. The first and second input potentials can shield the output potential from external electromagnetic influences. The output potential can form an output voltage with a reference potential, in particular a ground. The output voltage can be dependent on the ambient variable via the deflection of the membrane and the change in the distance of the measuring capacitance.

[0018] The output potential can form an output voltage relative to a reference potential, in particular an earth.

[0019] In a specific embodiment of the invention, it is advantageous if the measuring capacitance and the reference capacitance are electrically connected in series. The output potential can be applied between the measuring capacitance and the reference capacitance. The input voltage can be applied across the measuring capacitance and the reference capacitance. Thus, with such a further configuration, a bridge circuit, for example, with two measuring capacitances and two reference capacitances, can be implemented.

[0020] A preferred embodiment of the invention is advantageous in which the second upper electrode of the reference capacitance is accommodated on one side and has a self-supporting region extending away from the receptacle. The second upper electrode of the reference capacitance can be accommodated by at least one support. The support can face toward or away from the first upper electrode with respect to the self-supporting region.

[0021] In an advantageous embodiment of the invention, the first upper electrode, the first lower electrode, the second upper electrode, and the second lower electrode are arranged entirely within the cavity. The electrical connection of the first lower electrode, the second upper electrode, and / or the second lower electrode can be routed away from the cavity, at least in sections, below the edge region. The electrical connection can be designed, at least in sections, as a buried conductor layer.

[0022] A preferred embodiment of the invention is advantageous in which the first lower electrode is completely surrounded by the electrical potential of a second lower electrode of a further reference capacitance. The further reference capacitance can have a second upper electrode that has the same electrical potential as the second lower electrode of the reference capacitance.

[0023] In a specific embodiment of the invention, it is advantageous if the first lower electrode is electrically connected via a second upper electrode of the further reference capacitance. The electrical potential at the first lower electrode can be applied via the second upper electrode of the further reference capacitance. The electrical potential for the first lower electrode can be applied spatially with the second upper electrode of the further reference capacitance across the second lower electrode of the further reference capacitance. The first lower electrode, the second upper electrode of the further reference capacitance, and the second lower electrode of the reference capacitance can be electrically connected to one another and have the same electrical potential.

[0024] Further advantages and advantageous embodiments of the invention emerge from the description of the figures and the illustrations.

[0025] Character description

[0026] The invention is described in detail below with reference to the figures. They show in detail:

[0027] Figure 1 : A top view of a micromechanical sensor in a special

[0028] Embodiment of the invention.

[0029] Figure 2: A cross section along AA from Figure 1.

[0030] Figure 3: A cross section along BB from Figure 1.

[0031] Figures 4 to 7: A top view of the upper and lower electrodes of a micromechanical sensor in a further specific embodiment of the invention. Figure 8: A top view of the upper electrodes of a micromechanical sensor in a further specific embodiment of the invention.

[0032] Figure 9: A plan view of a micromechanical sensor in another specific embodiment of the invention.

[0033] Figure 10: A cross-section along AA from Figure 9.

[0034] Figure 11: A plan view of a micromechanical sensor in another specific embodiment of the invention.

[0035] Figure 1 shows a top view of a micromechanical sensor in a specific embodiment of the invention. The micromechanical sensor 10 is preferably a capacitive pressure sensor for capacitively measuring at least one ambient variable, preferably a fluid pressure as ambient pressure, on a membrane that can be deflected in a vertical direction depending on the ambient variable. The membrane and an edge region of the sensor that accommodates it are hidden here.

[0036] The micromechanical sensor 10 comprises a measuring capacitance 12 that can be varied depending on the ambient variable. It has a first upper electrode Mt, which is constructed from a plurality of electrode elements 14 and is coupled to the membrane, and an opposite first lower electrode Mb, shown in dashed lines, which is fixed relative to the edge region. Thus, the first upper electrode Mt can be moved relative to the first lower electrode Mb depending on the ambient variable, and the measuring capacitance 12 can be varied depending on the ambient variable.

[0037] Furthermore, a total of four reference capacitors are arranged, each with a second upper electrode Nt positioned opposite the edge region and an opposite second lower electrode Nb. The second upper electrodes Nt of the reference capacitors also consist of several individual electrode elements 14, which are spaced apart from the second lower electrodes Nb in a vertical direction via supports 16. The first upper electrode Mt is mechanically decoupled from the second upper electrodes Nt, and the second upper electrodes Nt are mechanically decoupled from the membrane.

[0038] The first lower electrode Mb and the second lower electrodes Nb are each flat.

[0039] The second upper electrode Nt of a first reference capacitance K1 and the second upper electrode Nt of a second reference capacitance K2 opposite the first reference capacitance K1 in a first direction R1 are fixed on one side by the supports 16 and have a self-supporting region 18 extending away from the supports 16. The supports 16 face the first upper electrode Mt with respect to the self-supporting region 18. The second upper electrode Nt of a third reference capacitance K3 and the second upper electrode Nt of a fourth reference capacitance K4 opposite the third reference capacitance K3 in a second direction R2 perpendicular to the first direction R1 are fixed on both sides by the supports 16.

[0040] A first electrical input potential P1 is applied to the first upper electrode Mt and, in particular, also to the membrane. A second electrical input potential P2 is applied to the second upper electrodes Nt of the first and second reference capacitors K1, K2, which, together with the first input potential P1, forms an input voltage. The second input potential P2 is electrically applied by electrode elements 14 of the second reference capacitor K2, which are extended outwardly along the first direction R1 for this purpose and form a contact region 20.The supports 16 are electrically conductive and transmit the second input potential P2 to a first conductor track L1, shown here in dashed lines, arranged vertically below the second upper electrodes Nt, which runs along the second direction R2. The conductor track L1 transmits the input potential P2 to the second lower electrodes Nb of the third and fourth reference capacitances K3, K4, to which the second input potential P2 is thus also applied. A second conductor track L2, shown here in dashed lines, is arranged opposite the first conductor track L1 with respect to the first direction R1. The supports 16 of the second reference capacitance K2 are electrically connected to the second conductor track L2.

[0041] An electrical output potential PA is present at the second upper electrodes Nt of the third and fourth reference capacitances K3, K4, at the second lower electrodes Nb of the first and second reference capacitances K1, K2 and at the first lower electrode Mb of the measuring capacitance 12. The output potential PA is applied via a contact region 22, shown here in dashed lines, to which a third conductor track L3 is electrically connected. The third conductor track L3 connects the second lower electrodes Nb of the first and second reference capacitances K1, K2. A first part 24 of the supports 16 of the second upper electrode Nt of the third reference capacitance K3 are electrically connected to the third conductor track L3. The third conductor track L3 transmits the output potential PA to the second lower electrode Nb of the first and second reference capacitances K1, K2.A fourth conductor track L4 is arranged opposite the third conductor track L3 with respect to the second direction R2 and also connects the second lower electrode Nb of the first and second reference capacitors K1, K2. A first part 24 of the supports 16 of the second upper electrode Nt of the fourth reference capacitor K4 are electrically connected to the fourth conductor track L4.

[0042] The first, second, third and fourth conductor tracks L1, L2, L3, L4 are in particular arranged completely within the cavity 32.

[0043] A second part 26 of the supports 16 of the second upper electrode Nt of the third reference capacitance K3 are electrically connected to the first lower electrode Mb. A second part 26 of the supports 16 of the second upper electrode Nt of the fourth reference capacitance K4 are also electrically connected to the first lower electrode Mb. Thus, the output potential PA is transferred from the contact region 22 via the first part 24 of the supports 16 of the second upper electrode Nt of the third reference capacitance K3 to the second upper electrode Nt of the third reference capacitance K3 and via the second part 26 of the supports 16 of the second upper electrode Nt of the third reference capacitance K3 to the first lower electrode Mb, thus bridging the second lower electrode Nb of the third reference capacitance K3.

[0044] Furthermore, the output potential PA is transmitted via the third conductor track L3 to the second lower electrode Nb of the first reference capacitance K1 and the second lower electrode Nb of the second reference capacitance K2, and from there to the fourth conductor track L4. The output potential PA is transmitted from the fourth conductor track L4 via the first part 24 of the supports 16 of the second upper electrode Nt of the fourth reference capacitance K4 to the second upper electrode Nt of the fourth reference capacitance K4 and via the second part 26 of the supports 16 of the second upper electrode Nt of the fourth reference capacitance K4 to the first lower electrode Mb, thus bridging the second lower electrode Nb of the fourth reference capacitance K4.

[0045] The second upper electrode Nt of each of the first, second, third and fourth reference capacitances K1, K2, K3, K4 is electrically decoupled from the first upper electrode Mt and the membrane 28.

[0046] The measuring capacitance 12 and the reference capacitance with the individual reference capacitances K1, K2, K3, K4 can be electrically connected in series using the configuration shown and described, with the output potential PA as a tap between the measuring capacitance 12 and the reference capacitance. The first input potential P1 is applied to one side of the measuring capacitance 12, and the second input potential P2 is applied to the other side of the reference capacitance, thus providing the input voltage across the measuring capacitance 12 and the reference capacitance. Figure 2 shows a cross-section along AA from Figure 1. The first upper electrode Mt consists of several electrode elements 14 connected to the membrane 28. The membrane 28 is supported at the edge region 30 and spans a cavity 32 defined by the edge region 30.The membrane 28 is deflectable into the cavity 32 depending on the ambient size outside and thus moves the first upper electrode Mt of the measuring capacitance 12 with respect to the fixed first lower electrode Mb, which is arranged on a carrier element 34, in particular a silicon substrate with an insulating layer.

[0047] The first upper electrode Mt, the first lower electrode Mb, the second upper electrode Nt of the third and fourth reference capacitances K3, K4, and the second lower electrode Nb of the third and fourth reference capacitances K3, K4 are arranged entirely within the cavity 32. The first lower electrode Mb and the second lower electrode Nb of the third and fourth reference capacitances K3, K4 are arranged on the carrier element 34. The first upper electrode Mt is spaced apart from the first lower electrode Mb in the vertical direction Rv, and the second upper electrode Nt of the third reference capacitance K3 is spaced apart from the second lower electrode Nb of the third reference capacitance K3; the same applies to the fourth reference capacitance K4.

[0048] The first lower electrode Mb is designed to cover the entire surface and is electrically connected to the second upper electrode Nt of the third and fourth reference capacitances K3, K4 via the supports 16. The first lower electrode Mb is electrically separated from the second lower electrode Nb of the third and fourth reference capacitances K3, K4. The contact region 22 applies the output potential PA to the second upper electrode Nt of the third reference capacitance K3 via the first part 24 of the supports 16. The output potential PA is applied to the first lower electrode Mb via the second part 26 of the supports 16.

[0049] Figure 3 shows a cross section along BB of Figure 1. The first upper electrode Mt and the first lower electrode Mb of the measuring capacitance 12, the second upper electrode Nt of the first reference capacitance K1 and the second upper electrode Nt of the second reference capacitance K2 and the second lower electrode Nb of the first reference capacitance K1 and the second lower electrode Nb of the second reference capacitance K2 are arranged completely within the cavity 32.

[0050] The second lower electrode Nb of the first reference capacitance K1 is arranged on the carrier element 34. The second upper electrode Nt of the first reference capacitance K1 is electrically connected via buried layers 35. Apart from the electrical connection of the contact region 20, the second upper electrode Nt of the first reference capacitance K1 and the second upper electrode Nt of the second reference capacitance K2 are each supported on one side of the carrier element 34 via the supports 16 and spaced apart from the carrier element in the vertical direction Rv.

[0051] Figures 4 to 7 show a plan view of the upper and lower electrodes of a micromechanical sensor in a further specific embodiment of the invention. Figure 4 a) shows the upper electrodes with the supports and Figure 4 b) shows the lower electrodes of the micromechanical sensor 10 from Figure 1. As shown in Figure 4 b), the first lower electrode Mb is completely enclosed by the second input potential P2, with respect to the first direction R1 by the first and second conductor tracks L1, L2 and with respect to the second direction R2 by the second lower electrode Nb of the third and fourth reference capacitances K3, K4. The second lower electrode Nb of the first reference capacitance K1 and the second lower electrode Nb of the second reference capacitance K2 are electrically connected to one another by the third and fourth conductor tracks L3, L4 and have the same potential as the first lower electrode Mb, here the output potential PA.The second lower electrode Nb of the third reference capacitance K3, the second lower electrode Nb of the fourth reference capacitance K4 and the third and fourth conductor tracks L3, L4 have the second input potential P2.

[0052] As shown in Figure 4 a), the first lower electrode Mb is electrically connected to the contact region 22, as shown in Figure 4 b), via the second upper electrode Nt of the third reference capacitance K3.

[0053] The structure in Figure 5 is similar to that in Figure 4 except for the following differences. As shown in Figure 5 b), the first lower electrode Mb and the second lower electrode Nb of the first and second reference capacitances K1, K2 are directly connected to one another. The first and second conductor tracks L1, L2 thus run along the edge. The second input potential P2 is applied via the contact area 20 to the first conductor track L1 and, via this, to the second lower electrode Nb of the third reference capacitance K3 and the second lower electrode Nb of the fourth reference capacitance K4.

[0054] As shown in Figure 5 a), the second upper electrode Nt of the third and fourth reference capacitances K3, K4 is enlarged at the expense of the area of ​​the second upper electrode Nt of the first and second reference capacitances K1, K2. The supports 16 of the second upper electrode Nt of the first reference capacitance K1 are electrically connected to the edge-side first conductor track L1 shown in Figure 5 b), and the supports 16 of the second upper electrode Nt of the second reference capacitance K2 are electrically connected to the edge-side second conductor track L2 shown in Figure 5 b). The structure in Figure 6 is similar to that in Figure 4 except for the following differences. As shown in Figure 6 a), the second upper electrodes Nt of the first, second, third and fourth reference capacitances K1, K2, K3, K4 have the same potential, here the output potential PA. The second input potential P2 is applied via the contact region 20 at the level of the second upper electrodes Nt of the first reference capacitance K1 and via supports 16.For this purpose, the second upper electrode Nt of the first reference capacitance K1 is left out.

[0055] As shown in Figure 6 b), the output potential PA is applied via the contact area 22 via the third conductor track L3 to the first conductor track L1 and the second conductor track L2, which thus have the output potential PA. The first and second conductor tracks L1, L2 are also electrically connected to the fourth conductor track L4, which also has the output potential PA. The first, second, third, and fourth conductor tracks L1, L2, L3, L4 enclose the second lower electrodes Nb of the first, second, third, and fourth reference capacitances K1, K2, K3, K4 at the edges.

[0056] As shown in Figure 6 a), the supports 16 of the second upper electrodes Nt of the first and second reference capacitances K1, K2 are arranged at the edges and are electrically connected to the first and second conductor tracks L1, L2, as shown in Figure 6 b).

[0057] The structure in Figure 7 is similar to that of Figure 6 except for the following differences. As shown in Figure 7 a), the supports 16 of the second upper electrodes Nt of the first and second reference capacitors K1, K2 are arranged on the inside and are electrically connected to the first lower electrode Mb shown in Figure 7 b).

[0058] As shown in Figure 7 b), the first and second conductor tracks are dispensable, and the second lower electrodes Nb of the first and second reference capacitances K1, K2 are arranged at the edges. The second input potential P2 is applied directly to the second lower electrode Nb of the first reference capacitance K1 via the contact region 20.

[0059] Figure 8 shows a top view of the upper electrodes of a micromechanical sensor in another specific embodiment of the invention. The structure is similar to that of Figure 5 except for the following differences. The first upper electrode Mt is extended along the first direction R1 toward the edge and takes up space there at the expense of the length of the second upper electrode Nt of the first and second reference capacitors K1, K2. This allows the area of ​​the first upper electrode Mt of the measuring capacitor 12 to be increased.

[0060] Figure 9 shows a top view of a micromechanical sensor in another specific embodiment of the invention. The structure in Figure 9 is similar to that of Figure 5 except for the following differences. The second upper electrode Nt of the first reference capacitance K1 and the second upper electrode Nt of the second reference capacitance K2 are partially recessed for support means 36, which form stop elements for limiting the maximum deflection of the membrane, which is masked here by the edge region.

[0061] Figure 10 shows a cross-section along AA from Figure 9. The support means 36 comprise support elements 38 on the membrane 28, which can abut against support surfaces 40 on the carrier element 34 that are opposite in the vertical direction Vr. The support surfaces 40 are preferably grounded or have the same electrical potential as the membrane 28. The support elements 38 can stiffen the membrane 28.

[0062] Figure 11 shows a top view of a micromechanical sensor in another specific embodiment of the invention. The structure in Figure 11 is similar to that of Figure 6 except for the following differences. The second upper electrode Nt of the first reference capacitance K1 and the second upper electrode Nt of the second reference capacitance K2 are partially recessed for support means 36, which form stop elements for limiting the maximum deflection of the membrane, which is masked here by the edge region.

Claims

Patent claims 1. Micromechanical sensor (10) for the capacitive measurement of at least one environmental variable, comprising an edge region (30) delimiting a cavity (32), a membrane (28) spanning the cavity (32) at least in sections and deflectable in a vertical direction into the cavity (32) depending on the environmental variable, at least one measuring capacitance (12) which can be varied depending on the environmental variable and has a first upper electrode (Mt) which is coupled to the membrane (28) and an opposite first lower electrode (Mb), at least one reference capacitance (K1, K2, K3, K4) with a second upper electrode (Nt) which is fixed in each case relative to the edge region (30) and a second lower electrode (Nb) which is opposite, characterized in that the second upper electrode (Nt) is electrically decoupled from the membrane (28).

2. Micromechanical sensor according to claim 1, characterized in that the second upper electrode (Nt) is electrically decoupled from the first upper electrode (Mt).

3. Micromechanical sensor (10) according to claim 1 or 2, characterized in that the first upper electrode (Mt) has a first electrical input potential (P1) and the second upper electrode (Nt) has a second electrical input potential (P2).

4. Micromechanical sensor (10) according to one of the preceding claims, characterized in that the first lower electrode (Mb) and the second lower electrode (Nb) are electrically connected to one another and have the same electrical potential.

5. Micromechanical sensor (10) according to claim 4, characterized in that the electrical potential of the first and second lower electrodes (Mb, Nb) is an electrical output potential (Pa).

6. Micromechanical sensor (10) according to one of the preceding claims, characterized in that the measuring capacitance (12) and the reference capacitance (K1, K2, K3, K4) are electrically connected in series.

7. Micromechanical sensor (10) according to one of the preceding claims, characterized in that the second upper electrode (Nt) of the reference capacitance (K1, K2, K3, K4) is accommodated on one side and has a self-supporting region (18) extending away from the receptacle.

8. Micromechanical sensor (10) according to one of the preceding claims, characterized in that the first upper electrode (Mt), the first lower electrode (Mb), the second upper electrode (Nt) and the second lower electrode (Nb) are arranged entirely within the cavity (32).

9. Micromechanical sensor (10) according to one of the preceding claims, characterized in that the first lower electrode (Mb) is completely enclosed by the electrical potential of a second lower electrode (Nb) of a further reference capacitance (K1, K2, K3, K4).

10. Micromechanical sensor (10) according to claim 9, characterized in that the first lower electrode (Mb) is electrically connected via a second upper electrode (Nt) of the further reference capacitance (K1, K2, K3, K4).

Images