Method for detecting corrosion on electrical devices, in particular MEMS loudspeakers

Abstract

The invention relates to a method for detecting corrosion on electrical devices, in particular MEMS loudspeakers (10), which move a displacement element (16) via electrodes (28, 30; 34, 36) connected to first and second contacts (52, 54), comprising the following method steps: First, at least one of the electrodes (28, 30; 34, 36) is selected as the electrode / electrodes (70, 80) to be tested. The at least one electrode (70, 80) to be tested is then connected via at least one additional conductor path (60) via third and fourth contacts (62, 64) and an electrical resistance RElectr. is measured by impressing a current i (66). Either a voltage drop ΔV (68) between the third and fourth contacts (62, 64) is measured by means of a two-conductor measurement (78) or a voltage drop ΔV (68) between the third and fourth contacts (62, 64) is measured by means of a four-conductor measurement (76) when a current i (66) is impressed via fifth and sixth contacts (72, 74) into the electrode / electrodes (70, 80) to be tested or a parallel resistance (82) of a plurality of electrodes (70, 80) to be tested from the number of electrodes (28, 30; 34, 36) is measured.

Description

[0001] R.417169

[0002] - 1 -

[0003] Description

[0004] title

[0005] Method for detecting corrosion on electrical devices, especially MEMS loudspeakers

[0006] Technical field

[0007] The invention relates to a method for detecting corrosion in electrical devices, in particular MEMS loudspeakers, which move a displacement element via electrodes connected to first and second contacts. Furthermore, the invention relates to the use of the corrosion detection method for monitoring electrodes that move components of MEMS devices, in particular MEMS loudspeakers.

[0008] State of the art

[0009] DE 102014106025 A1 relates to a method for manufacturing an electronic circuit. It involves integrating a current measurement into the wiring structure of an electronic circuit. The two-part method comprises forming an electrically conductive wiring structure on a substrate and configuring it to perform a specific function, as well as configuring a second section of the wiring structure to provide information related to the first part of the circuit.

[0010] WO 2014 / 086884 A1 discloses a MEMS sensor for detecting environmental parameters. This solution relates to a device for detecting environmental parameters by means of a plate element oscillating in a plane of a plate. Here, the viscosity of the medium is determined via the resonant frequency of the oscillator in the MEMS sensor. In this application, the plate body oscillates substantially perpendicular to the surface of a wafer. R.417169

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[0012] DE 102017213 765 A1 discloses a sensor element for detecting particles. The sensor element comprises at least two electrodes on a substrate and an oscillating layer between them.

[0013] In MEMS loudspeakers, such as those described in WO 2022 / 117197 A1, a corresponding volume of air within the silicon MEMS chip is displaced to generate sound pressure. This is achieved by deflecting several displacer elements that are movable within the chip plane, for example, bending beams clamped on one or both sides. The force required to move the displacer elements is generated by an electrostatic drive. This drive consists of silicon electrodes, also known as drive electrodes, positioned above and below the displacer element and insulated from each other by an electrical layer, for example, made of silicon nitride or silicon dioxide. The electrical voltage applied between the electrodes and the displacer element across the narrow air gap creates an electrostatic force that deflects the displacer element.Other MEMS, such as gyroscopes and accelerometers, also use polycrystalline silicon electrodes for drive and / or detection. Unlike gyroscopes and accelerometers, where the MEMS is hermetically sealed from the environment by a cover, the electrodes of the MEMS loudspeaker under consideration here are exposed to the ambient air. This leads to anodic oxidation of the silicon electrodes due to small parasitic electrical currents (see Shea et al., Effects of Electrical Leakage Currents on MEMS Reliability and Performance, IEEE Transactions on Device and Materials Reliability, Vol. 4, No. 1).

[0014] 2, June 2004). The chemical reaction that takes place converts the silicon into silicon oxide. This alters the electrical resistance and capacitance of the electrodes, which can lead to impaired electrical function. Furthermore, oxide growth can progress to the point where the oxide grows into the air gap, leading to particle formation and potentially even mechanical blockage of the displacer movement. In the aforementioned publication by Shea et al., a test structure for detecting the oxidation of polysilicon structures is presented generally and completely independent of the MEMS loudspeaker application. This test structure consists of a meandering polysilicon conductor surrounded by a counter electrode. Between the conductor and the counter electrode R.417169

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[0016] An electrical voltage can be applied to stimulate targeted oxide growth. Furthermore, the electrical resistance of the conductor track can be measured using appropriate circuitry. The conversion of polysilicon to oxide during oxidation increases the electrical resistance, which can then be measured electrically and used as an indicator of oxide growth.

[0017] Disclosure of the invention

[0018] According to the invention, a method is proposed for detecting corrosion on electrical devices, in particular MEMS loudspeakers, which move a displacement element via electrodes connected to first and second contacts, comprising the following method steps:

[0019] a) Selection of at least one electrode to be tested from a number of electrodes,

[0020] b) Connecting the at least one electrode to be tested to the third and fourth contacts via at least one additional conductor track and measuring the electrical resistance REiektr. by applying a current i, Ci) Measuring a voltage drop AV between the third and fourth contacts in a two-wire measurement, or

[0021] C2) Measurement of a voltage drop AV between the third and fourth contacts in a four-wire measurement and application of the current i via the fifth and sixth contacts to at least one electrode to be tested or

[0022] C3) Measurement of a parallel resistance of several electrodes to be tested from the number of electrodes.

[0023] The method proposed according to the invention eliminates the need for additional electrodes or test structures for corrosion detection, so that in the case of MEMS loudspeakers the chip area usable for sound generation is not reduced.

[0024] In an advantageous further development of the method proposed according to the invention, the at least one selected electrode to be tested continues to move the displacer element unimpeded during method steps a), b), c1) or a), b), c2) or a), b), c3). R.417169

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[0026] In an advantageous further development of the method proposed according to the invention, it is provided that the at least one electrode to be tested can be selected arbitrarily from the number of electrodes.

[0027] Furthermore, the method proposed according to the invention advantageously provides that all electrodes can be selected as being to be tested from the number of electrodes.

[0028] In an advantageous further development of the method proposed according to the invention, it is further provided that, according to process step Ci), in the two-wire measurement, a further electrode to be tested is contacted via the fifth and sixth contacts, the resistance REiektr. of which is measured independently of the electrode to be tested.

[0029] In one embodiment of the method proposed according to the invention for detecting corrosion on electrical devices, in particular MEMS loudspeakers, which move a displacement element via electrodes connected to first and second contacts, the following process steps are carried out:

[0030] a) Selection of at least one electrode to be tested from a number of electrodes,

[0031] b) Contacting the at least one electrode to be tested by means of additional contact points using a conductor that also serves as an electrical supply line,

[0032] Ci) Performing a resistance measurement using a two-wire measurement with third and fourth contacts, or

[0033] C2) Performing a resistance measurement using a four-wire measurement with contacts three to six.

[0034] In a further development of this design variant, all electrodes can also be contacted at additional contact points via conductors. R.417169

[0035] - 5 -

[0036] Furthermore, the invention relates to a method for performing a self-test for corrosion detection of a MEMS loudspeaker using an ASIC and a measurement of the electrical resistance REiektr. at at least one electrode to be tested.

[0037] - a comparison of the measured electrical resistance REiektr. with a reference value RRSE, which corresponds to a non-corroded condition,

[0038] - Performing a threshold comparison between a determined difference AR from REiektr. and RRSE with a threshold S,

[0039] - if the threshold value S is exceeded, a negative self-test is detected,

[0040] - If the threshold value S is not reached, a positive self-test is detected.

[0041] Furthermore, the invention relates to the use of the methods for detecting corrosion for monitoring electrodes that serve to actuate components of a MEMS device, in particular a MEMS loudspeaker.

[0042] Advantages of the invention

[0043] The solution proposed according to the invention provides a method that allows for the in-situ oxidation of electrodes of a MEMS device, particularly a microspeaker, to be performed on and with the electrodes themselves, instead of using dedicated and abstract test structures, and for this purpose to be used for self-testing. The electrodes of the MEMS device in question, particularly a microspeaker, are electrically contacted in such a way that, in addition to their function as drive electrode(s), their electrical resistance can be measured, which can then be used as an indicator of possible corrosion. The advantage of the solution proposed according to the invention lies primarily in the fact that no additional electrodes or test structures for corrosion detection are required, and the already limited chip area can be used for the actual speaker function.Furthermore, for the significance of the resistance measurement, it is particularly advantageous to detect the oxidation state at the actual electrode itself instead of an abstract test structure whose corrosion state depends on the actual electrode. R.417169.

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[0045] The information about the corrosion state can then be used, for example, for a self-test of the MEMS component, in particular a MEMS loudspeaker.

[0046] Brief description of the drawings

[0047] Embodiments of the invention are explained in more detail with reference to the drawings and the following description.

[0048] They show:

[0049] Figures 1a and 1b show a schematic diagram of a displacement element including drive electrodes.

[0050] Figure 2 shows a wiring variant for resistance measurement at an electrode,

[0051] Figure 3 shows another wiring electrode with additional contacts,

[0052] Figure 4 shows the contacting of another electrode to be tested via additional contacts K5 and K6,

[0053] Figure 5 shows a wiring variant for detecting the parallel resistance of three electrodes.

[0054] Figures 6-6.3 show a further embodiment of the electrode proposed according to the invention, in which the electrode to be tested is contacted at additional contact points via a conductor, as well as details in top view with and without electrodes.

[0055] Figure 7 shows a flowchart of a self-test for the detection of corrosion.

[0056] Embodiments of the invention R.417169

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[0058] In the following description of embodiments of the invention, identical or similar elements are designated by the same reference numerals, and repeated descriptions of these elements are omitted in individual cases. The figures represent the subject matter of the invention only schematically.

[0059] Figures 1a and 1b show schematic diagrams of a displacement element with drive electrodes, such as those used in MEMS components, especially micro loudspeakers 10.

[0060] Figures 1a and 1b show that a MEMS micro loudspeaker 10, depicted here only schematically, has a first cover 12 and a second cover 14 opposite it. At least one displacement element 16 is located between the first cover 12 and the second cover 14. This element can be moved from a rest position 18 to a deflected position 20 and vice versa. Above and below the displacement element 16, which has a double-T-shaped cross-section, upper electrodes 26 and lower electrodes 32 are located. The upper electrodes 26 are each formed by a first upper electrode 28 and a second upper electrode 30, while the lower electrodes 32 are formed by a first lower electrode 34 and a second lower electrode 36 arranged parallel to it.An insulator 22 runs between the first cover 12 and the upper electrodes 26; the same applies to the second cover 14 and the lower electrodes 32, between which an insulator 22 is also arranged.

[0061] A first air gap 24 runs below the upper electrodes 26 and the displacement element 16, while a second air gap 38 extends between the lower electrodes 32 and the underside of the double-T-shaped displacement element 16.

[0062] The dashed position of the displacement element 16 indicates its deflected position 20.

[0063] Figure 1b shows in a dashed line representation the displacer element 16 moved into its deflected position 20, with the first cover 12R.417169 in this representation.

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[0065] The first upper electrode 28 and the second upper electrode 30 are essentially parallel to each other. A first driving potential 56 is applied to the first upper electrode 28, while a second driving potential 58 (V2) is applied to the second upper electrode 30.

[0066] Figure 2 shows a wiring diagram 50, according to which a single drive electrode 70 is selected as the electrode 70 to be tested from the first and second upper electrodes 28, 30, which are only shown schematically here. This electrode is contacted by at least one additional conductor 60 such that its electrical resistance REiektr. can be determined by a two-wire measurement 78. While the first and second upper electrodes 28, 30 are each contacted by first and second contacts 52, 54, the electrode 70 to be tested, selected in Figure 2, is electrically contacted by further contacts, namely a third contact 62 and a fourth contact 64. A current i 66 is impressed into the electrode 70 to be tested via the additional third and fourth contacts 62, 64. A voltage drop AV 68 between the third and fourth contacts 62, 64 is then measured.

[0067] In contrast, the representation according to Figure 3 shows two further contacts, namely a fifth contact 72 and a sixth contact 74. Using the fifth and sixth contacts 72, 74, a four-wire measurement 76 can be implemented, which enables a more precise measurement of the electrical resistance REiektr. at the at least one electrode 70 to be tested. A current i 66 is impressed into the electrode 70 or electrodes 70, 80 to be tested via the fifth and sixth contacts 72, 74, and the voltage drop AV 68 between the third and fourth contacts 62, 64 is measured.The electrode 70 to be tested, selected as above according to the wiring diagrams 50 in Figures 2 and 3, can be chosen arbitrarily and can also drive the associated displacement element 16 as shown in Figures 1a and 1b, so that there is no disadvantage for the loudspeaker operation, for example of the MEMS micro loudspeaker 10.

[0068] The electrodes 70, 80 to be tested can be selected arbitrarily. Furthermore, several or all electrodes 28, 30; 34, 36 can be contacted according to the procedure outlined above, so that a local, dhR417169

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[0070] Electrode corrosion affecting not all electrodes 28, 30; 34, 36 can be detected. Further embodiments for a two-wire measurement 78 are shown in Figures 4 and 5.

[0071] Figure 4 shows a wiring diagram 50 in which one electrode 70 and another electrode 80 to be tested are connected via the fifth and sixth contacts 72 and 74. This allows the resistance of the second electrode 80 to be measured independently of the resistance REiektr. of the first electrode 70 to be tested.

[0072] Figure 5 shows a schematic wiring scheme 50 in which a measurement of a parallel resistance 82 can be made from three electrodes selected from electrodes 28, 30; 34, 36.

[0073] Figures 6 to 6.3 illustrate a further embodiment of the corrosion detection method proposed according to the invention, in which the electrode to be tested, in this case the additional electrode 80, is connected via contact points 86 to a conductor 84, which, in the embodiment shown in Figure 6, extends, for example, vertically. This conductor 84 also serves as the electrical supply line. A four-wire measurement 76 is performed via the contacts 3 to 6 shown in Figure 6, i.e., the third contact 62, the fourth contact 64, the fifth contact 72, and the sixth contact 74, or a two-wire measurement 78 is performed via the third and fourth contacts 62 and 64. An advantage of this is that the space requirement for additional conductor tracks in the wiring variants shown in Figures 2, 3, 4, and 5 above is eliminated.In the embodiment shown in Figure 6, it is also possible to contact several electrodes 28, 30; 34, 36.

[0074] Figures 6.1 to 6.3 provide further details of the representation according to Figure 6. Figure 6.1 shows a top view of the first upper electrode 28 and the second upper electrode 30 extending parallel to it above the displacer element 16, whereas Figure 6.2 shows a top view without depicting the electrodes, i.e., directly showing the displacer element 16, a lead 84, and a contact point 86.

[0075] - 10 -

[0076] Figure 6.3 shows a section through the representation according to Figure 6.1 (BB), in which the first cover 12 extends above the insulator 22. Below this, the first upper electrode 28 and the second upper electrode 30 run essentially parallel to each other, with the first upper electrode 28 being connected to the electrical supply line 84 via contact point 86 in the section view of Figure 6.3. The displacement element 16 is shown in its rest position 18.

[0077] Figure 7 shows a flowchart of a self-test for corrosion detection. This test can be performed, for example, using a control module required for the operation of the MEMS micro loudspeaker 10, which is, for example, an ASIC. This ASIC also has a device for measuring the electrical resistance REiektr. and is electrically connected to the measuring contacts, i.e., the third contact 62, the fourth contact 64, the fifth contact 72, or the sixth contact 74. The electrical resistance of at least one electrode 70 to be tested is measured by the methods of the invention described above and compared with a global reference value RRet, i.e., the same for all components, which corresponds to a non-corroded state of a component. The reference value can also be determined component-specifically during final calibration and stored in an ASIC.In the method proposed according to the invention as shown in Figure 7, after a resistance measurement 90 of the electrical resistance REiektr., the difference AR 92 to the reference value is calculated such that a difference AR 92 is determined from the difference between the measured electrical resistance of an electrode 70 REiektr. and RRet. to be tested. In a threshold comparison 94, it is determined whether the determined difference AR is above or below a threshold S. If the determined difference AR is above the threshold S, a self-test is negative 98; if the determined difference is below the threshold S, the self-test is positive 96, i.e., the self-test is considered passed.

[0078] If the determined difference AR between the field-measured value REiktr. and the difference value RRet. exceeds a threshold value S, the self-test indicates electrode corrosion and thus a possible functional impairment of the MEMS micro loudspeaker 10. R.417169

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[0080] The method proposed according to the invention can advantageously be used in its various forms or embodiments for MEMS components with electrodes for driving or detection.

[0081] The invention is not limited to the embodiments described here and the aspects highlighted therein. Rather, within the scope specified by the claims, a multitude of modifications are possible that fall within the bounds of what is considered skilled in the art.

Claims

R.417169 - 12 - Claims 1. Method for detecting corrosion on electrical devices, in particular MEMS loudspeakers, which move a displacement element (16) via electrodes (28, 30; 34, 36) connected to first and second contacts (52, 54), comprising the following method steps: c) Selection of at least one electrode to be tested (70, 80) from a number of electrodes (28, 30; 34, 36), d) Connecting the at least one electrode to be tested (70, 80) to the third and fourth contacts (62, 64) via at least one additional conductor track (60) and measuring the electrical resistance REiektr. (90) by applying a current i (66), Ci) Measurement of a voltage drop AV (68) between the third and fourth contacts (62, 64) in a two-wire measurement (78), or C2) Measurement of a voltage drop AV (68) between the third and fourth contacts (62, 64) in a four-wire measurement (76) and imprinting the current i (66) via the fifth and sixth contacts (72, 74) into the at least one electrode to be tested (70, 80) or C3) Measurement of a parallel resistance (82) of several electrodes to be tested (70, 80) of the number of electrodes (28, 30; 34, 36).

2. Method according to claim 1, characterized in that the at least one selected electrode (70, 80) to be tested moves the displacer element (16) during method steps a), b), c1) or a), b), c2) or a), b), c3).

3. Method according to claims 1 and 2, characterized in that the at least one electrode (70, 80) to be tested is arbitrarily selected from the number of electrodes (28, 30; 34, 36). R.417169 - 13 - 4. Method according to claims 1 and 2, characterized in that all electrodes (70, 80) to be tested are selected from the number of electrodes (28, 30; 34, 36).

5. Method according to claims 1 to 4, characterized in that according to method step Ci) in the two-wire measurement (78) a further electrode (80) to be tested is contacted via fifth and sixth contacts (72, 74), the resistance REiektr. of which is measured independently of the electrode (70) to be tested.

6. Method for detecting corrosion on electrical devices, in particular MEMS loudspeakers (10), which move a displacement element (16) via electrodes (28, 30; 34, 36) connected to first and second contacts (52, 54), comprising the following method steps: c) Selection of at least one electrode to be tested (70, 80) from a number of electrodes (28, 30; 34, 36), d) Contacting the at least one electrode to be tested (70, 80) via contact points (86) by means of a conductor (84) which also serves as an electrical supply line, Ci) Performing a resistance measurement (90) with a two-wire measurement (78) with third and fourth contacts (62, 64), or C2) Performing a resistance measurement (90) with a four-wire measurement (76) with third to sixth contacts (62, 64; 72, 74).

7. Method according to claim 6, characterized in that all electrodes (28, 30; 34, 36) are contacted at contact points (86) via conductors (84).

8. Method for self-testing for corrosion detection of a MEMS loudspeaker (10) using an ASIC and a measurement of the electrical resistance REiektr. (90) at at least one electrode (70, 80) to be tested according to claims 1 to 5 or 6 to 7, with - a comparison of the measured electrical resistance REiektr. with a reference value RRe t., which corresponds to a non-corroded condition, R.417169 - 14 - - Performing a threshold comparison (94) between a determined difference AR from Electr. and RRet with a threshold S, - if the threshold S is exceeded, a negative self-test (98) is detected, - if the threshold S is not reached, a positive self-test (96) is detected.

9. Use of the methods for detecting corrosion according to claims 1 to 5 or 6 to 7 for monitoring electrodes (28, 30; 34, 36) for activating components of MEMS devices, in particular MEMS loudspeakers (10).

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