Micromechanical device and method for manufacturing a micromechanical device

Abstract

Micromechanical device (1a; 1b; 1c), comprising a carrier substrate (2); a sensor device (3) which is spaced apart from a surface section (4) of the carrier substrate (2) by means of spring elements (9) on the carrier substrate (2), so that the sensor device (3) is oscillatable relative to the surface section (4);and at least one stopper element (51, 52) arranged on the sensor device (3) and / or on the surface section (4) of the support substrate (2), which limits a deflection of the sensor device (3) in the direction of the surface section (4), wherein a first stopper element (51) is arranged on the sensor device (3) and a second stopper element (52) is arranged on the surface section (4), so that the sensor device (3) can only be deflected until the first stopper element (51) touches the second stopper element (52), and wherein the first stopper element (51, 52) has a first electrical conductor (61, 62) and the second stopper element (51, 52) has a second electrical conductor (61, 62), and wherein the device (1a; 1b;1c) further comprises an evaluation device which is designed to measure a capacitance between the first electrical conductor (61, 62) and the second electrical conductor (61, 62) and to determine, taking into account the measured capacitance, a moisture content in the area between the sensor device (3) and the surface section (4).

Description

The present invention relates to a micromechanical device which can be used to measure a physical quantity, such as ambient pressure. The invention further relates to a method for manufacturing a micromechanical device. State of the art Micromechanical pressure sensors are used to determine pressure and mechanical loads in portable devices and in industrial and domestic equipment. An example of such a pressure sensor is known from German patent application DE 10 2010 031197 A1. However, these sensors not only register external pressure fluctuations but are also sensitive to vibrations of the housing. Often, it is desirable to eliminate or at least reduce the influence of these vibrations. Further prior art is known from the patent applications DE 10 2009 000 407 A1 , US 2017 / 0 144 881 A1 , DE 10 2014 212 340 A1 and DE 10 2009 000 053 A1. Disclosure of the invention The invention discloses a micromechanical device with the features of claim 1 and a method for manufacturing a micromechanical device with the features of claim 8. According to a first aspect, the invention relates to a micromechanical device comprising a support substrate and a sensor assembly, which is arranged at a distance from a surface section of the support substrate and is attached to the support substrate by means of spring elements. The sensor assembly is thus designed to be oscillatable relative to the surface section. At least one stop element is arranged on the sensor assembly and / or on the surface section of the support substrate, which limits the deflection of the sensor assembly in the direction of the surface section. According to a second aspect, the invention relates to a method for manufacturing a micromechanical device. An integrated circuit and a MEMS structure are provided, wherein the MEMS structure has a sensor device which is oscillatibly arranged by means of spring elements. At least one stop element is arranged on the sensor device and / or on a surface section of the integrated circuit. The MEMS structure is connected to the integrated circuit such that the sensor device is oscillatable relative to the surface section of the integrated circuit, and wherein a deflection of the sensor device in the direction of the surface section is limited by the at least one stop element. Preferred embodiments are the subject of the respective dependent claims. Advantages of the invention The micromechanical device according to the invention, due to its suspension via spring elements, enables a certain degree of decoupling of the sensor assembly from the substrate. To ensure sufficiently good decoupling, the spring elements must also be sufficiently flexible to deflect the sensor assembly in response to external vibrations and thereby compensate for unwanted lateral influences. At the same time, the invention prevents damage to the sensor assembly or to other components arranged on the substrate. For this purpose, stop elements are provided that limit the vibration or deflection of the sensor assembly. The stop elements thus serve as intended contact points to prevent direct contact between the sensor assembly and the surface of the substrate or even breakage of the spring elements due to overloading.This can prevent potential abrasion and chipping of particles in the event of a collision between the sensor device and the surface section. According to the invention, a first stop element is arranged on the sensor device and a second stop element is arranged on the surface section. The sensor device can thus only be deflected until the first stop element touches the second stop element. The distance between the first stop element and the second stop element is always less than the distance between a region of the sensor device and an opposite region of the surface section of the support substrate. This ensures that only the stop elements can touch each other. According to the invention, the first stopper element has a first electrode and the second stopper element has a second electrode. The device also includes an evaluation unit that measures the capacitance between the first and second electrodes. Based on the measured capacitance, the evaluation unit determines the humidity in the area between the sensor and the surface section. This is based on the physical principle that a change in the humidity of the air acting as a dielectric between the first and second electrodes results in a change in its relative permittivity. For example, the relative permittivity of air without water is 1.0059, while in a saturated state, the relative permittivity is 1.77. Accordingly, a change in capacitance between the two electrodes occurs.By measuring the capacitance, the humidity can be determined. A relationship between capacitance and humidity can be empirically established and recorded in a table. According to a further development of the device, a reference electrode is arranged on the surface section, and a second reference electrode is arranged on a region of the support substrate that is spaced apart from the surface section and adjacent to the sensor device. The distance between this region and the surface section is fixed. For example, the reference electrodes are arranged on spatially fixed areas of the surface section and the region, respectively. The evaluation device is further configured to measure a reference capacitance between the first and second reference electrodes and to determine the moisture content taking this reference capacitance into account. Since the reference capacitance is measured between two spatially fixed reference electrodes, it is not affected by vibrations of the support substrate.By comparing the time course of the measured capacity with the time course of the measured reference capacity, it can be determined whether a change in capacity is due to a change in humidity or to vibration of the substrate. Thus, the influence of external vibrations or movements of the substrate can be considered and eliminated when calculating humidity. According to another embodiment, the reference capacity can also be measured directly and used to calculate humidity. According to a preferred embodiment of the device, the evaluation unit is configured to measure a resonant frequency of an oscillation of the sensor device relative to the surface section and to determine the humidity taking this resonant frequency into account. Humidity influences the quality factor of the oscillation system and thus the resonant frequency. By empirically determining the relationship between resonant frequency and humidity, which can, for example, be stored in a table, the humidity can be directly determined from the resonant frequency. According to a further development of the device, the hardness of the impact surface of the first stop element differs from the hardness of the impact surface of the second stop element. The impact surfaces are defined as the areas where the stop elements touch. This choice of material reduces the impact of an impact, as the softer stop element with the lower hardness can absorb the energy more effectively. Preferably, the hardness of the impact surface of the second stop element is lower than the hardness of the impact surface of the first stop element. Even if cracks and damage occur during the collision of the stop elements, this will usually only affect the second stop element with the lower hardness. The first stop element, which is connected to the sensor device, is protected, thus preventing damage to the more sensitive sensor device. For example, the impact surface of the first stop element can consist of a softer metallic layer, such as an aluminum-copper layer (AlCu layer), while the impact surface of the second stop element consists of a harder passivation layer, such as a nitride layer. According to a preferred embodiment, a surface of the sensor device facing the surface section of the support substrate has a passivation layer. For example, a nitride layer may be formed on this surface. The first stopper element is formed on this surface, with the passivation layer being interrupted in a region around the first stopper element. Thus, the passivation layer is either removed in this region or no passivation layer is formed at all. Upon collision of the stopper elements, cracks can form, which may, for example, originate in a passivation layer formed on a surface of the first stopper element. However, since the passivation layer is interrupted around the first stopper element, these cracks cannot propagate further, and the sensor device is thus better protected against damage.In particular, changes to the measurement conditions of the sensor element due to liquid penetrating cracks are prevented, as these do not even form in the area of ​​the signal transducer. According to a preferred embodiment of the device, the evaluation unit is further configured to measure ambient pressure based on a measurement signal from the sensor device and taking into account the determined humidity. Since the electrodes are formed in or on the stopper elements, the humidity in the immediate vicinity of the sensor device is determined. According to a preferred embodiment of the device, the evaluation unit is further configured to calculate an acceleration of the sensor element towards the surface section of the support substrate, taking into account the determined capacitance and preferably also the determined reference capacitance. In particular, the evaluation unit can compare a change in capacitance with a change in the reference capacitance. Since the reference electrodes are spatially fixed relative to each other, the change in the reference capacitance is essentially independent of the acceleration of the sensor element, but depends only on changes in other external parameters, such as the humidity of the air. The evaluation unit can correct the measured change in capacitance based on the measured change in the reference capacitance.The corrected change in capacitance then depends only on the acceleration of the sensor element towards the surface section of the substrate. This allows the evaluation unit to determine the acceleration of the sensor element. According to a preferred embodiment of the device, the carrier substrate has an integrated circuit comprising a surface section. Furthermore, the carrier substrate has a MEMS structure arranged on or attached to the integrated circuit. The sensor device is arranged in a recess of the MEMS structure and connected to the MEMS structure via spring elements. According to a preferred embodiment of the device, the sensor assembly comprises a cavity and a membrane spanning the cavity. The sensor assembly is thus designed as a pressure sensor assembly. Brief description of the drawings Figure 1 shows a schematic cross-sectional view of a micromechanical device according to one embodiment of the invention; Figure 2 shows a schematic cross-sectional view of a micromechanical device according to a further embodiment of the invention; Figure 3 shows a schematic cross-sectional view of a detail of a micromechanical device according to a further embodiment of the invention; and Figure 4 shows a flowchart to explain a method for manufacturing a micromechanical device according to one embodiment of the invention. In all figures, identical or functionally equivalent elements and devices are designated with the same reference numerals. The numbering of process steps serves for clarity and generally does not imply a specific chronological order. In particular, several process steps can be performed simultaneously. Description of the exemplary implementations Fig. 1 shows a schematic cross-sectional view of a micromechanical device 1a according to an embodiment of the invention. The micromechanical device 1a has a support substrate 2, which is composed of a MEMS structure 21 and an integrated circuit or ASIC 22, which are connected to each other via bond connections 100 with eutectic alloys. A measuring channel 84 runs between the MEMS structure 21 and the integrated circuit 22. The MEMS structure 21 includes a sensor device 3, which can be used to measure pressure in the measuring channel 84. The sensor device 3 has a diaphragm 91 that hermetically seals a cavity 92 formed in a substrate of the sensor device 3. A reference gas at a reference pressure is located in the cavity 92. Mechanical stresses or changes in pressure in the measuring channel 84 relative to the reference pressure generate deflections or vibrations of the diaphragm 91, which can be detected by known measuring elements, for example, piezoelectric elements. A corresponding electrical signal is transmitted to an evaluation unit (not shown) and used by it to measure the ambient pressure or the mechanical stress. The sensor assembly 3 is attached to the surrounding substrate by means of spring elements 9. The sides of the sensor assembly 3 facing away from the integrated circuit 22 are separated from the surrounding substrate by corresponding air channels 81, 83. For this purpose, a hole pattern is created on the back side by photolithography, and trenches 82 are formed by anisotropic etching, terminating in the bulk silicon. By switching off the passivation and sputtering components in the DRIE etching process, a cavity or air channel 81 is formed at the end of the trenches 82 by subsequent isotropic etching, separating the back side of the sensor assembly 3 from the surrounding substrate. The lateral air channels 83 are formed by creating trenches on the front side, with ribs being left out.The bridges are transformed into spring elements 9 by cutting them open on the back side, so that the sensor element 3 is connected to the surrounding support substrate only by the spring elements 9. The sensor assembly 3 is thus suspended so that possible vibrations of the support substrate and external stress, such as from the package, can be compensated for by the spring elements 9. Through the air channels 81, 83, the measuring channel 84 is in fluidic communication with the surrounding air, so that the ambient pressure can be determined by measuring the pressure in the measuring channel 84. The sensor device 3 can oscillate, in particular in the normal direction, i.e., in the direction of a surface section 4 of the integrated circuit 22. First stop elements 51 and second stop elements 52 are formed on opposite sides of the surface section 4 and an opposing surface 40 of the sensor device 3 along the normal direction. During a large deflection of the sensor device 3, a first stop element 51 arranged on the surface 40 of the sensor element 3 contacts the opposite second stop element 52 formed on the surface section 4 of the integrated circuit 22. In the embodiment shown in Fig. 1, two pairs of first and second stop elements 51, 52 are formed in opposite edge regions of the surface 40 of the sensor device 3 to ensure uniform contact and to suppress any potential generation of torques. According to further embodiments, however, only a single pair of stop elements 51, 52 or a plurality of pairs of stop elements 51, 52 may be provided. The stopper elements 51, 52 have electrical conductors or leads or electrodes 61, 62, which are preferably arranged on a surface of the stopper elements 51, 52. The electrical conductors 61, 62 are connected to each other via the spring elements 9 and the bond connections 100 and are routed accordingly to bond pads, which can be located on the MEMS structure 21 or on the integrated circuit 22. An electrical signal, dependent on a capacitance between the electrical conductors 61, 62 or stopper elements 51, 52, is output to the evaluation unit. Reference electrodes 71 and 72 are provided, wherein a first reference electrode 71 is formed on, within, or on the surface section 4 of the integrated circuit 22, and a second reference electrode 72 extends in a section of the MEMS structure 21 opposite the normal direction. An electrical signal is measured between reference electrodes 71 and 72 as a function of a reference capacitance and transmitted to the evaluation unit. The evaluation device is designed to determine the humidity of the air between the sensor device 3 and the integrated circuit 22 based on the measured capacitance and the measured reference capacitance. This can be achieved either by evaluating the capacitance and the reference capacitance themselves, or by analyzing changes in the capacitance or the reference capacitance. The magnitude or behavior of the capacitance and the reference capacitance depends on the humidity. A relationship between the corresponding values ​​of the capacitance or reference capacitance and a humidity value can be empirically determined. Using a corresponding data table, the evaluation device can determine the humidity if the capacitance or reference capacitance is known. The reference capacitance can be used, in particular, to eliminate the influence of external vibrations on changes in capacitance.If, for example, only the capacitance changes while the reference capacitance remains essentially constant, the evaluation unit can recognize that the change in capacitance is merely a result of a movement of the sensor device towards the surface section 4 of the integrated circuit 22. More generally, to compensate for such relative movements, the influence of these movements on the capacitance or on the change in capacitance can be factored out, for example, using the appropriately weighted reference capacitance, in order to obtain a value that can be used for calculating the humidity. The evaluation device can be further configured to determine the mass of water in the air. For this purpose, the evaluation device estimates the mass of the water based on the measured humidity. The determined mass of the water is then used as a parameter in a correction function for calculating the pressure. The correction function describes the influence of the mass of the water on the measured pressure. The pressure correction using the correction function is preferably performed using a closed-loop method. According to further embodiments, a comb electrode is formed in the region of the first stopper element 51 and / or the second stopper element 52. The change in capacitance of the comb electrode is influenced by the humidity of the air, so that the humidity of the air can be measured by measuring the capacitance or the change in capacitance. Figure 2 illustrates a cross-sectional view of a micromechanical device 1b according to a further embodiment of the invention. The view shown is rotated 180 degrees compared to Figure 1. Device 1b essentially corresponds to device 1a described above, so only the differences will be discussed in more detail. The following section will focus in particular on the layer structure of device 1b illustrated in Figure 2. Accordingly, the integrated circuit has 22 oxide layers 208, 209, 211 and an intermediate silicon substrate 210. The surface section 4 opposite the MEMS substrate 21 has a nitride layer as a passivation layer 207. The second stopper element 52 has a layer 212 made of an aluminum-copper material, which is at least partially coated with the passivation layer 207. However, a central area of ​​the surface of the second stopper element 52, which is intended as a contact surface with the first stopper element 51, is free of the passivation layer 207. The MEMS substrate 21 is coated on a side facing the surface section 4 of the integrated circuit 22 with oxide layers 201, 202 and an outer nitride layer as passivation layer 203. In the area of ​​the first stopper element 51, the passivation layer 203 is interrupted. The first stopper element 51 has a barrier layer 204 made of titanium nitride and a metallization layer 205 made of an aluminum-copper material, which are coated with the passivation layer 203. Further contact elements 301, 302, 303 can be provided on the surface 40 of the sensor element 3, which are designed for electrical contacting, for example, the membrane 91. A minimum distance d1 between the surface section 4 and the sensor device 3 in the rest position is preferably about 1 to 2 micrometers, more preferably 1.4 micrometers, and is greater than a minimum distance d2 between the first stop element 51 and the second stop element 52, which is, for example, between 0.5 and 1 micrometer, and preferably 0.8 micrometers. Figure 3 illustrates a cross-sectional view of a detail of a device 1c according to a further embodiment of the invention. The device 1c can otherwise correspond to one of the devices 1a, 1b described above. In the embodiment illustrated in Figure 3, the passivation layer 203, which covers the surface 40 of the sensor element 3 and the barrier layer 204 as well as the metallization layer 205 of the first stopper element 51, is exposed in an annular region 400 around the first stopper element 51. Fig. 4 illustrates a flowchart to explain a method for manufacturing a micromechanical device 1a, 1b, 1c. In a first process step S1, an integrated circuit 22 and a MEMS structure 21 are provided. The MEMS structure has a sensor device which is designed to be oscillatable by means of spring elements. Thus, the sensor device 3 can be exposed by the back and front etching described above, whereby the spring elements 9 are recessed. The sensor device 3 is therefore arranged to be oscillatable and can oscillate, in particular, in a normal direction, i.e., perpendicular to the surface of the sensor device 3. The sensor device 3 is preferably designed as a pressure sensor and can have a cavity 92 and a membrane 91 spanning the cavity 92. In a process step S2, at least one first stopper element 51 is formed on a surface 40 of the sensor device 3 by depositing or exposing metallic layers and passivation layers. At least one second stopper element 52 is formed on a surface section 4 of the integrated circuit 22 by depositing or exposing metallic layers and passivation layers. In process step S3, the MEMS structure 21 is bonded to the integrated circuit 22. The MEMS structure 21 and the integrated circuit 22 are positioned relative to each other such that the sensor device 3 can oscillate relative to the surface section 4 of the integrated circuit 22. After bonding the MEMS structure 21 to the integrated circuit 22, a first stop element 51 and a second stop element 52 are positioned opposite each other along the normal direction. The deflection of the sensor device 3 in the direction of the surface section 4 is thus limited by the stop elements 51 and 52. The provision of the various layer structures can be achieved through known deposition methods and etching processes, so a detailed description is unnecessary here.

Claims

Micromechanical device (1a; 1b; 1c), comprising a carrier substrate (2); a sensor device (3) which is spaced apart from a surface section (4) of the carrier substrate (2) by means of spring elements (9) on the carrier substrate (2), so that the sensor device (3) is oscillatable relative to the surface section (4);and at least one stopper element (51, 52) arranged on the sensor device (3) and / or on the surface section (4) of the support substrate (2), which limits a deflection of the sensor device (3) in the direction of the surface section (4), wherein a first stopper element (51) is arranged on the sensor device (3) and a second stopper element (52) is arranged on the surface section (4), so that the sensor device (3) can only be deflected until the first stopper element (51) touches the second stopper element (52), and wherein the first stopper element (51, 52) has a first electrical conductor (61, 62) and the second stopper element (51, 52) has a second electrical conductor (61, 62), and wherein the device (1a; 1b;1c) further comprises an evaluation device which is designed to measure a capacitance between the first electrical conductor (61, 62) and the second electrical conductor (61, 62) and to determine, taking into account the measured capacitance, a moisture content in the area between the sensor device (3) and the surface section (4). Device (1a; 1b; 1c) according to claim 1, wherein a first reference electrode (71, 72) is arranged on the surface section (4) and a second reference electrode (71, 72) is arranged on a region of the support substrate spaced apart from the surface section (4) and adjacent to the sensor device (3), wherein a distance between the region and the surface section (4) is fixed, and wherein the evaluation device is further configured to measure a reference capacitance between the first and the second reference electrode (71, 72) and to further determine the moisture taking into account the reference capacitance. Device (1a; 1b; 1c) according to one of claims 1 or 2, wherein the evaluation device is configured to measure a resonance frequency of an oscillation of the sensor device (3) relative to the surface section (4) and to determine the moisture taking into account the resonance frequency. Device (1a; 1b; 1c) according to one of claims 1 to 3, wherein the hardness of an impact surface of the first stopper element (51) differs from the hardness of an impact surface of the second stopper element (52). Device (1a; 1b; 1c) according to one of claims 1 to 4, wherein the evaluation device is further configured to measure an ambient pressure and / or an acceleration of the sensor device (3) on the basis of a measurement signal from the sensor device (3) and taking into account the determined humidity. Device (1a; 1b; 1c) according to one of the preceding claims, wherein the carrier substrate (2) comprises: an integrated circuit (22) which has the surface section (4), and a MEMS structure (21) which is arranged on or at the integrated circuit, wherein the sensor device (3) is arranged in a recess of the MEMS structure (21) and is connected to the MEMS structure via the spring elements (9). Device (1a; 1b; 1c) according to one of the preceding claims, wherein the sensor device (3) has a cavity (92) and a membrane (91) spanning the cavity (92) and is designed as a pressure sensor. Method for manufacturing a micromechanical device (1a; 1b; 1c), comprising the steps: providing (S1) an integrated circuit (22) and a MEMS structure (21), wherein the MEMS structure has a sensor device (3) which is designed to be oscillatable by means of spring elements (9); forming (S2) at least one stopper element (51, 52) arranged on the sensor device (3) and / or on a surface section (4) of the integrated circuit (22), wherein a first stopper element (51) is formed on the sensor device (3) and a second stopper element (52) is formed on the surface section (4), such that the sensor device (3) can only be deflected until the first stopper element (51) touches the second stopper element (52);and connecting (S3) the MEMS structure (21) with the integrated circuit (22) such that the sensor device (3) is oscillatable relative to the surface section (4) of the integrated circuit (22), wherein a deflection of the sensor device (3) in the direction of the surface section (4) is limited by the at least one stopper element (51, 52), and wherein a first electrical line (61, 62) is formed on the first stopper element (51, 52) and a second electrical line (61, 62) is formed on the second stopper element (51, 52), and wherein further an evaluation device is formed which is configured to measure a capacitance between the first electrical line (61, 62) and the second electrical line (61, 62) and to determine a humidity in the area between the sensor device (3) and the surface section (4) taking into account the measured capacitance.

Images