Micromechanical pressure sensor

Abstract

Micromechanical pressure sensor (100), comprising: - a pressure sensor frame (20); - a pressure sensor core (10) connected to the pressure sensor frame (20) by means of a spring element (15), wherein the pressure sensor core (10) represents a pressure-sensitive part of the pressure sensor (100) and comprises at least one sensor membrane (14) and a cavity (11); - a rear grid (21) formed in the pressure sensor frame (20); and - at least one connecting element (19) formed between the rear grid (21) and the pressure sensor core (10) for connecting the pressure sensor core (10) to the pressure sensor frame (20).

Description

[0001] The invention relates to a micromechanical pressure sensor. The invention further relates to a method for manufacturing a micromechanical pressure sensor. State of the art

[0002] Modern packaging techniques necessitate the mechanical decoupling of the pressure-sensitive part of a pressure sensor, in the form of a pressure sensor membrane, from the rest of the sensor using special spring designs. This makes it independent of AVT (assembly and connection technology) influences. A new trend in pressure sensors is to mechanically decouple the pressure-sensitive part, the pressure sensor membrane, from the rest of the sensor using special spring designs, thereby increasing accuracy.

[0003] External influences that put the pressure sensor under mechanical stress (e.g. bending) include, for example, mechanical stresses due to a molding process, a construction with several materials with different coefficients of thermal expansion, stress from soldered connections of the assembled sensor on an external circuit board, etc.

[0004] In the following, such a setup will be referred to as a so-called "stress-decoupled pressure sensor".

[0005] A micromechanical pressure sensor in which a pressure difference is measured as a function of a deformation of a sensor membrane is known, for example, from DE 10 2004 006 197 A1.

[0006] Further prior art is disclosed in the patent applications US 2017 / 0 013 363 A1, US 2016 / 0 187 370 A1, US 2015 / 0 110 302 A1, DE 10 2010 061 340 A1 and US 2015 / 0 078 592 A1. Disclosure of the invention

[0007] It is an object of the present invention to provide an improved, in particular a stress-robust, micromechanical pressure sensor.

[0008] The task is solved according to a first aspect using a micromechanical pressure sensor, comprising: - a pressure sensor frame; - a pressure sensor core connected to the pressure sensor frame by means of a spring element, wherein the pressure sensor core represents a pressure-sensitive part of the pressure sensor and comprises at least one sensor membrane and a cavity; - a back grid formed in the pressure sensor frame; and - at least one connecting element formed between the back grid and the pressure sensor core for connecting the pressure sensor core to the pressure sensor frame.

[0009] In this way, the pressure sensor core is prevented from deflecting and striking the backside grid or the topside wafer under high external mechanical stress by the connecting element. This advantageously provides a high degree of robustness for the micromechanical pressure sensor.

[0010] This provides an optimized connection between the pressure sensor core and the pressure sensor frame, achieving pressure resistance and robustness against mechanical stress decoupling. This supports optimized operating behavior of the micromechanical pressure sensor. In this way, a micromechanical pressure sensor with a pressure sensor diaphragm that is fully isolated on all sides and features an optimized connection to the pressure sensor core, thus realizing an efficient stress decoupling structure.

[0011] According to a second aspect, the task is solved by a method for manufacturing a micromechanical pressure sensor, comprising the steps: - Providing a pressure sensor frame; - Providing a pressure sensor core connected to the pressure sensor frame by means of a spring element, wherein the pressure sensor core represents a pressure-sensitive part of the pressure sensor and comprises at least one sensor membrane and a cavity; - Forming a backside grid in the pressure sensor frame, wherein at least one connection element formed between the backside grid and the pressure sensor core is provided for connecting the pressure sensor core to the pressure sensor frame.

[0012] Preferred embodiments of the micromechanical pressure sensor are the subject of dependent claims.

[0013] An advantageous further development of the micromechanical pressure sensor provides that at least one connecting element is centrally attached to the backplate and centrally to the pressure sensor core. This ensures a symmetrical force application to the pressure sensor core, which improves mechanical robustness.

[0014] A further advantageous embodiment of the micromechanical pressure sensor is characterized by the fact that at least one connecting element is designed as a round column. This provides a specific design of the connecting element with good mechanical properties.

[0015] A further advantageous development of the micromechanical pressure sensor involves designing at least one of the connecting elements as a square column. This provides an alternative, mechanically robust design for the connecting element.

[0016] A further advantageous development of the micromechanical pressure sensor is characterized by the fact that the connecting element has a defined number of round and / or square columns. In this way, the mechanical connection of the pressure sensor core to the pressure sensor frame can be further improved.

[0017] A further advantageous development of the micromechanical pressure sensor is characterized by the fact that the connecting element is designed as a connecting element injected through the backplate between the pressure sensor core and the backplate. This enables the simple provision of a connecting element with good mechanical properties.

[0018] A further advantageous embodiment of the micromechanical pressure sensor is characterized by the fact that the injected connecting element is a polymer or silicone rubber. In this way, further embodiments of the connecting element with favorable mechanical properties are provided, with silicone rubber being a soft adhesive that is easy to apply.

[0019] A further advantageous development of the micromechanical pressure sensor is characterized by the fact that the connecting element is shaped identically to the through-holes of the back grating. In this way, a periodicity of the back grating is advantageously utilized, thereby simplifying the lithographic steps in the fabrication of the connecting element. For example, a hexagonal or square periodicity of the back grating can be exploited in this way.

[0020] A further advantageous embodiment of the micromechanical pressure sensor is characterized by the fact that the connecting element has a diameter of approximately 5 µm to approximately 50 µm, preferably approximately 20 µm to approximately 30 µm. This provides favorable geometric dimensions for the connecting element.

[0021] Further advantageous developments of the micromechanical pressure sensor are characterized by a spring element designed to provide optimized mechanical stress decoupling between the pressure sensor core and the pressure sensor frame. This allows for advantageous optimization of the spring element without requiring it to provide mechanical robustness for connecting the pressure sensor core. As a result, greater design freedom for the spring element is advantageously provided.

[0022] The invention is described in detail below with reference to several figures, including further features and advantages. Identical or functionally equivalent elements have the same reference numerals. The figures are intended in particular to illustrate the essential principles of the invention and are not necessarily drawn to scale. For the sake of clarity, not all reference numerals may be shown in all figures.

[0023] Disclosed device features result analogously from corresponding process features and vice versa. This means, in particular, that features, technical advantages, and embodiments relating to the micromechanical pressure sensor result analogously from corresponding embodiments, features, and technical advantages of the method for manufacturing a micromechanical pressure sensor, and vice versa.

[0024] The figures show: Fig. 1 a cross-sectional view of a micromechanical pressure sensor; Fig. 2 a cross-sectional view of an embodiment of the proposed micromechanical pressure sensor; Fig. 3 a top view of an embodiment of the proposed micromechanical pressure sensor; Fig. 4 a basic representation of a backside grid with a connecting element; Fig. 5 a basic representation of a variant of the backside grid with a connecting element; and Fig. 6 a basic sequence of an embodiment of a method for manufacturing a micromechanical pressure sensor. Description of embodiments

[0025] A key concept of the present invention is in particular the provision of an improved, especially a robust and stress-decoupled micromechanical pressure sensor.

[0026] A basic structure of a known micromechanical pressure sensor 100 is shown in a cross-sectional view in Fig. Figure 1 shows the pressure-sensitive part of the pressure sensor 100, hereinafter referred to as the pressure sensor island or pressure sensor core 10, comprising a sensor membrane 14 measuring approximately 500 µm x 500 µm, a cavity 11 (vacuum reference cavity), and a surrounding mechanical stabilization structure (not shown). The pressure sensor core 10 has a sensor membrane 14 in which piezoresistive elements are formed for detecting deformation of the sensor membrane 14.

[0027] The pressure sensor core 10 is electrically and mechanically coupled to the pressure sensor frame 20. All of these elements are located in a further cavity 13, which is bounded on one side (below the pressure sensor core 10) by an ASIC 30 and on the other side (above the pressure sensor core 10) by a back-side grid 21. The pressure sensor frame 20 is coupled to an electronic component in the form of an ASIC 30, which is connected via bonding elements 40 (not shown in the figure). Fig. 1) is electrically connected to the outside.

[0028] The backside grid 21 is produced by photolithography by creating a hole pattern in the silicon substrate and subsequently etching the silicon substrate. The etching process is preferably a perpendicular or anisotropic etching process, preferably a deep reactive ion etching (DRIE) process. The backside grid 21 provides access openings for etching the aforementioned cavity 13.

[0029] External mechanical excitations (for example, if the pressure sensor 100 falls and hits the ground) can cause the pressure sensor core 10 to be accelerated very strongly, thereby deflecting the stabilizing springs (not shown) very far and possibly damaging or destroying them.

[0030] For this reason, in the known variant of the micromechanical pressure sensor 100 from Fig. 1. It is necessary to provide a relatively thick pressure sensor core 10 with a large distance to the rear grid 21. In the case of a large deflection, the maximum mechanical loads on the springs are comparatively high.

[0031] Fig. Figure 2 shows a cross-sectional view of an embodiment of the proposed micromechanical pressure sensor 100. It can be seen that the pressure sensor core 10 is connected to the rear grid 21 by means of a single connecting element 19. This connection advantageously prevents the pressure sensor core 10 from deflecting and, in combination with suitably designed spring elements 15, minimizes the mechanical stress that can be coupled from the pressure sensor frame 20 into the pressure sensor core 10. Advantageously, the design of the connecting element 19 allows the spring element 15 (not shown) to be relatively soft, thus providing high robustness and high stress decoupling for the micromechanical pressure sensor 100.

[0032] Preferably, the connecting element 19 is designed as a central suspension of the pressure sensor core 10 to the backside grid 21, wherein the connecting element 19 is arranged centrally on the backside grid 21 and centrally on the pressure sensor core 10. In combination with a suitably designed spring element 15, which enables good mechanical decoupling and provides a stable base for electrical conductors (not shown), a mechanically robust and stress-decoupled micromechanical pressure sensor 100 can be realized in this way. The aforementioned electrical conductors can, for example, be diffused into the spring element 15 or designed as metal conductors.

[0033] The mechanical stress decoupling is maintained despite the rigid connection of the pressure sensor core 10 to the back grid 21, because if the micromechanical pressure sensor 100 bends, which can be caused, for example, by different coefficients of thermal expansion of different materials, the bending is not transmitted to the pressure sensor core 10 due to the point suspension of the pressure sensor core 10 to the back grid 21, preferably centrally. Advantageously, this method provides an increase in drop resistance by decoupling the pressure sensor core 10 from the rest of the micromechanical pressure sensor 100 by means of springs and the central connection 19 on the back grid 21.

[0034] In this way, the pressure sensor 100 can be highly robust against accelerations that can occur, for example, when a pressure sensor 100 installed in a mobile device (e.g., a smartphone) hits the ground after a free fall. The connecting element 19 prevents the pressure sensor core 10 from deflecting relative to the rest of the micromechanical pressure sensor 100, thereby avoiding large mechanical stresses in the spring element 15 or spring elements 15.

[0035] Another advantage of the connecting element 19 lies in the greater design freedom it allows for the spring elements 15, as these can be optimized for mechanical stress decoupling and are not subject to any restrictions regarding high mechanical stress due to accelerations.

[0036] This makes it advantageous that the connecting element 19 can be combined with any spring design (e.g., regarding shape and size). For this reason, the spring elements 15 are designed and dimensioned to provide maximum stress decoupling of the pressure sensor core 10 from the pressure sensor frame 20.

[0037] It has been found that optimized stress decoupling can be achieved by dimensioning the connecting element with a diameter of approximately 5µm to approximately 50µm, preferably from approximately 20µm to approximately 30µm.

[0038] Fig. Figure 3 shows a top view of an embodiment of the proposed micromechanical pressure sensor 100 from below, i.e., in a direction from the ASIC 30 (not shown) to the backplate 21 (not shown). The pressure sensor frame 20 is visible, which is connected to the pressure sensor core 10 by means of a spring element 15. A connection element 16 is provided for connecting the spring element 15 to the pressure sensor core 10. A further connection element 17 is provided for connecting the spring element 15 to the pressure sensor frame 20. The pressure sensor frame 20 is indicated externally as a black outline around the remaining part of the micromechanical pressure sensor 100, with the pressure sensor frame 20 representing the mechanical base.Advantageously, the mechanical stress decoupling effect of the spring element 15 can be optimized with the aid of the preferably central connecting element 19, which connects the pressure sensor core 10 to the rear grid 21 (not shown). For this purpose, the spring element 15 can be designed to be so soft that it couples as little moment as possible onto the pressure sensor core 10.

[0039] Fig. Figure 3 shows an exemplary spring design including the central connection element 19. The pressure sensor core 10, consisting of the sensor membrane 14, four piezoresistive elements 12 that detect deformation of the sensor membrane 14, and the surrounding pressure sensor frame 20 are visible. Electrical conductors 18 extending from the piezoresistive elements 12 are visible, transmitting electrical signals from the piezoresistive elements 12 to the ASIC 30. For clarity, the path of the conductors 18 on the spring element 15 is not shown. Also visible is the centrally formed connection element 19 for the mechanically rigid coupling of the pressure sensor core 10 to the rear grid 21.

[0040] The Fig. 4 and Fig. Figure 5 shows two possible variants of the backside grid 21 and resulting possible embodiments of a centrally formed connecting element 19. For the sake of clarity, the through-holes of the backside grid 21 are shown in dark, so that the substrate material (e.g. silicon) in which the through-holes of the backside grid 21 are formed is shown in light in the figures.

[0041] In both cases, a periodicity ( Fig. 4: hexagonal periodicity, Fig. 5: rectangular or square periodicity) of the through holes of the backside grid 21 in the area of ​​the central connection element 19 are recessed so that the pressure sensor core 10 remains connected to the backside grid 21 there. The shape and size of the central connection element 19 can be arbitrarily implemented within the grid periodicity of the backside grid 21.

[0042] Instead of leaving a single column as a connection element 19 in the substrate material, it can also be provided that a polymer is injected locally through the backside grid 21, which then acts as the central connection element 19. For such a realization of the connection element 19, for example, a soft silicone rubber or a polymer is conceivable, for which known screen printing processes can be used.

[0043] Furthermore, the following additional variants, not shown in the figures, are conceivable for the connecting element 19: - several round / rectangular columns of the type found in Fig. 4 or Fig. 5 are shown - round / rectangular column with a recess in the middle of the column - several round / rectangular columns with / without a recess in the middle of the column - Round / rectangular column(s) with / without a recess in the column center, which are arranged at least partially outside the center of the rear grid 21 and thus at least partially realize a decentralized connection of the pressure sensor core 10 to the rear grid 21. This variant can offer advantages, in particular, for spring elements 15 suspended on one side (not shown).

[0044] Fig. Figure 6 shows a basic procedure for manufacturing a micromechanical pressure sensor 100.

[0045] In step 200, a pressure sensor frame 20 is provided.

[0046] In step 210, a pressure sensor core 10 is provided, which is connected to the pressure sensor frame 20 by means of a spring element 15.

[0047] In step 220, a backside grid 21 is formed in the pressure sensor frame 20, wherein at least one connection element 19 formed between the backside grid 21 and the pressure sensor core 10 is provided for connecting the pressure sensor core 10 to the pressure sensor frame 20.

[0048] Although the invention has been described above using a piezoresistive micromechanical pressure sensor, it is also conceivable that the micromechanical pressure sensor is capacitive.

[0049] The person skilled in the art can therefore also realize embodiments of the invention that are not disclosed or only partially disclosed beforehand, without deviating from the core of the invention.

Claims

[1] Micromechanical pressure sensor (100), comprising: - a pressure sensor frame (20); - a pressure sensor core (10) connected to the pressure sensor frame (20) by means of a spring element (15), wherein the pressure sensor core (10) represents a pressure-sensitive part of the pressure sensor (100) and comprises at least one sensor membrane (14) and a cavity (11); - a rear grid (21) formed in the pressure sensor frame (20); and - at least one connecting element (19) formed between the rear grid (21) and the pressure sensor core (10) for connecting the pressure sensor core (10) to the pressure sensor frame (20). [2] Micromechanical pressure sensor (100) according to claim 1, characterized by , that at least one connecting element (21) is centrally connected to the rear grid (21) and centrally to the pressure sensor core (10). [3] Micromechanical pressure sensor (100) according to claim 1 or 2, characterized by, that at least one connecting element (19) is designed as a round column. [4] Micromechanical pressure sensor (100) according to claim 1 or 2, characterized by , that at least one connecting element (19) is designed as a square column. [5] Micromechanical pressure sensor (100) according to any one of the preceding claims, characterized by , that the connecting element (19) has a defined number of round and / or square columns. [6] Micromechanical pressure sensor (100) according to any one of the preceding claims, characterized by , that the connecting element (19) is designed as a connecting element injected through the backside grid (21) between the pressure sensor core (10) and the backside grid (21). [7] Micromechanical pressure sensor (100) according to claim 6, characterized by that the injected connecting element is a polymer or a silicone rubber. [8] Micromechanical pressure sensor (100) according to any one of the preceding claims, characterized by , that the connecting element (19) is shaped identically to the through holes of the rear grid (21). [9] Micromechanical pressure sensor (100) according to any of the preceding claims, characterized by , that the connecting element (19) has a diameter of approximately 5µm to approximately 50µm, preferably of approximately 20µm to approximately 30µm. [10] Micromechanical pressure sensor (100) according to any one of the preceding claims, characterized by , that the spring element (15) is designed in such a way as to provide optimized mechanical stress decoupling between the pressure sensor core (10) and the pressure sensor frame (20). [11] Method for manufacturing a micromechanical pressure sensor (100) comprising the steps: - Providing a pressure sensor frame (20); - Providing a pressure sensor core (10) connected to the pressure sensor frame (20) by means of a spring element (15), wherein the pressure sensor core (10) represents a pressure-sensitive part of the pressure sensor (100) and comprises at least one sensor membrane (14) and a cavity (11); - Forming a backside grid in the pressure sensor frame (20), wherein at least one connection element (19) formed between the backside grid (21) and the pressure sensor core (10) is provided for connecting the pressure sensor core (10) to the pressure sensor frame (20).

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