Pressure sensor device and method for manufacturing the same

Abstract

A pressure sensor device (100), - a sensor element (202) having an upper surface (118) and a lower surface (204), the sensor element (202) comprising a membrane (106) configured and arranged to be exposed to a medium, the sensor element (202) comprising at least one sensing element (109) for measuring the pressure of said medium; - a substrate (104) acting as a carrier for said sensor element (202), said substrate (104) comprising glass; Equipped with A pressure sensor device (100) is described in which a connection interface (201) is formed between the sensor element (202) and the substrate (104) by laser welding, and the sensor element (202) and the substrate (104) are connected to each other at the connection interface (201) in a mechanically robust and hermetically sealed manner. Additionally, a method of manufacturing the pressure sensor device (100) is described.

Description

[Technical field]

[0001] The present invention relates to a pressure sensor device.The present invention further relates to a method for manufacturing a pressure sensor device. [Background technology]

[0002] Pressure sensors for differential, relative and absolute pressure are typically hybrid structures made of various functional materials with different thermal expansion coefficients and therefore each exhibits a unique profile of mechanical stress between the bonded materials when exposed to high temperatures (e.g., up to at least 150°C) and low temperatures (e.g., up to at least -40°C).

[0003] Known pressure sensor devices generally consist of a sensor element that is mechanically held and electrically contacted by a combination of various materials so that it can be integrated into a working device for pressure measurement. Mechanical retention of the sensor element cannot be achieved in corrosive media via organic adhesives, because organic adhesives are not always able to withstand corrosive liquids. Therefore, in applications under corrosive conditions, mechanical retention of the sensor element is achieved by inorganic bonding materials, for example hard or soft solder materials, or by bonding glass on a metal or ceramic substrate. In such structures, the difference in the thermal expansion coefficients of the sensor element, the solder material and the substrate is significant, up to 10 ppm / K or more.

[0004] The resulting mechanical stresses can introduce pressure measurement errors due to thermal hysteresis, pressure hysteresis, zero point stability, output stability under pressure, and other uncompensable errors.

[0005] Thus, prior art pressure sensor devices exhibit technical limitations in their accuracy and functionality when exposed to high or low temperatures, which may in some cases limit the functionality of complex technical systems in industrial and automotive applications. Summary of the Invention [Problem to be solved by the invention]

[0006] The object of the present invention is to describe a pressure sensor device and manufacturing method that solves the problems prevailing in the prior art. [Means for solving the problem]

[0007] This problem is solved by a pressure sensor device and a method according to the independent claims.

[0008] According to one aspect, a pressure sensor device is described. The pressure sensor device is designed for determining differential, relative or absolute pressure. The pressure sensor device is designed to reliably and accurately measure the pressure of liquids or gases under corrosive conditions. The pressure sensor device is suitable to withstand corrosive media such as oil, fuel, urea, refrigerants, etc.

[0009] The pressure sensor device is further designed to operate in a wide temperature range, including low temperatures down to at least -40°C and high temperatures up to at least 150°C. The pressure sensor device is further designed to measure liquid or gas pressures in a pressure range extending from 0.05 bar to over 100 bar. The pressure sensor device is suitable for use in motor vehicles, e.g. as a vehicle exhaust gas application and / or in the powertrain. The pressure sensor device is further suitable as a refrigerant pressure sensor or a hydrogen pressure sensor, e.g. for monitoring industrial processes.

[0010] The pressure sensor device comprises at least one sensor element, which may be designed as a MEMS (microelectromechanical system) component. Preferably, the sensor element comprises a silicon chip.

[0011] The sensor element has a membrane, which is designed and arranged to be exposed to a medium, in particular a liquid or a gas. The sensor element has an upper side and a lower side, which are arranged opposite each other. In order to define the orientation of the sensor element, in the following the side of the sensor element on which the membrane is located is called the upper side of the sensor element and the opposite side is called the lower side of the sensor element. At the lower side a medium passage is located in the sensor element, by means of which the pressure-conducting medium can access the membrane from the lower side.

[0012] The sensor element comprises at least one sensing element, preferably a number of sensing elements, which are designed to measure the pressure of the medium, and which are formed on the membrane.

[0013] The pressure sensor device further comprises a substrate. The substrate has a top surface and a bottom surface. The substrate serves as a carrier for the sensor element. The sensor element is arranged on the substrate, in particular on the top surface of the substrate. The substrate is optically transparent. The substrate comprises glass. Preferably, the substrate consists of glass.

[0014] The sensor element and the substrate are mechanically firmly and inseparably connected to one another. The sensor element and the substrate are fused or welded to one another. A connection interface is formed between the sensor element and the substrate. The connection interface is the area where the substrate and the sensor element are connected to one another. The connection interface is formed between a lower surface of the sensor element and an upper surface of the substrate.

[0015] The connection interface is produced by laser welding. In other words, the substrate and the sensor element are connected, in particular fused, to one another by laser welding. Laser welding is preferably carried out with ultrashort laser pulses (picosecond range and shorter pulse lengths). The heat supply produced by laser welding is limited locally, i.e. the substrate is not heated completely. Heating occurs only in the bonding area between the substrate and the sensor element, i.e. in the area where the substrate and the sensor element are bonded to one another, and thus fusion of the substrate and the sensor element occurs. In particular, in laser welding with ultrashort laser pulses, light is focused without heat input through the optically transparent substrate to the bonding area, where the heat leads, via multiphoton absorption in the focal area over several tens of micrometers, to a mechanically stable bond of the sensor element and the substrate, and thus to the formation of a connection interface, very locally via fusion.

[0016] The pressure sensor arrangement thereby does not require additional connection means or additional bonding material for the connection of the sensor element and the substrate, the latter being connected to one another in a mechanically robust and gas-tight manner at the connection interface.

[0017] By connecting the sensor element and the substrate by laser welding, additional bonding materials / adhesives that may cause mechanical stress due to different expansion coefficients can be eliminated, thereby providing a particularly long-lived and reliable pressure sensor device. Furthermore, it provides a pressure sensor device that is more accurate and functional when exposed to high temperatures (up to at least 150°C) and low temperatures (e.g., up to at least -40°C) compared to conventional pressure sensor devices.

[0018] According to one embodiment, the substrate has a thermal expansion coefficient that differs from the thermal expansion coefficient of the sensor element by less than 1 ppm / K. As a result, the substrate and the sensor element have approximately the same thermal expansion coefficient. Due to the minimal or complete absence of thermal expansion differences, only minimal or no mechanical stresses occur in the pressure sensor device that can be transferred from the substrate to the sensor chip at high and low temperatures. This provides a particularly reliable pressure sensor device.

[0019] According to an embodiment, the sensor element has a connection base. The connection base is arranged between the sensor element and the substrate. The connection base is arranged on a lower surface of the sensor element. The sensor element and the connection base form a sensor system.

[0020] The connection base mechanically separates the sensor element from the bonding area with the substrate. The connection base is preferably used for very precise pressure sensors. The above-mentioned laser welding with ultrashort laser pulses is possible both for the sensor element and for the connection base between the sensor element and the substrate.

[0021] The connection base comprises glass. Preferably, the connection base consists of glass. Preferably, the connection base comprises a very similar or identical material compared to the substrate material. In particular, the difference between the thermal expansion coefficient of the connection base and the thermal expansion coefficient of the substrate is less than 1 ppm / K. Thereby, the pressure sensor device can be kept almost free from mechanical stress.

[0022] According to one embodiment, the connection base is bonded to the sensor element, for example the connection base is connected to the sensor element by anodic bonding.

[0023] The connection interface is formed between the connection base and the substrate. In other words, the sensor system with the sensor element and the connection base is connected to the substrate by laser welding with ultrashort laser pulses. For this purpose, the laser energy for connecting the substrate and the sensor system is coupled to the side of the substrate opposite the sensor system, i.e., to the bottom side of the substrate.

[0024] According to another aspect, a method for manufacturing a pressure sensor device is described. Preferably, the method produces a pressure sensor device as described above. All features disclosed with respect to the pressure sensor device or the method are correspondingly disclosed with respect to each other aspect and vice versa, even if the respective feature is not explicitly mentioned in the context of the respective aspect. The method comprises the following steps: A) Providing a Substrate, Preferably a Substrate as described above The substrate comprises glass. B) Providing a sensor element, preferably a sensor element as described above. The sensor element preferably comprises a silicon chip. The sensor element has an upper surface and a lower surface. A membrane is formed on the upper surface of the sensor element. Preferably, the substrate has a thermal expansion coefficient that differs from the thermal expansion coefficient of the sensor element by less than 1 ppm / K. C) Step of connecting the substrate and the sensor element in a mechanically robust and hermetically sealed manner by laser welding. The laser welding is carried out with ultrashort laser pulses. The pulse length is in the picosecond and / or femtosecond range. The material of the substrate is completely transparent to the laser wavelength. In this method, light is focused through the optically transparent substrate without heat input therein to the bonding area between the substrate and the sensor element. In the bonding area, the heat leads to a mechanically stable bonding of the sensor element and the substrate very locally via fusion via nonlinear absorption (multiphoton absorption) in the focal area over several tens of micrometers. The laser energy for the connection of the substrate and the sensor element is then transferred to the side of the substrate opposite the sensor element (i.e. to the underside of the substrate). The energy supply is carried out without physical contact with the substrate / sensor element and can be selectively transferred into the desired bonding area.

[0025] By connecting using laser welding, it is further possible to eliminate the need for additional bonding agents for connecting the substrate and the sensor element. Due to the minimal or complete absence of thermal expansion differences, only minimal or no mechanical stresses are transferred from the substrate to the sensor chip at high and low temperatures in the pressure sensor device. Thus, a very flexible and efficient method is provided, which produces extremely reliable, highly efficient and long-lasting pressure sensor devices.

[0026] According to an embodiment, before the sensor element is connected to the substrate, in an optional step a connection base is provided. The connection base comprises glass. Preferably, the substrate has a thermal expansion coefficient that differs from the thermal expansion coefficients of the sensor element and the connection base by less than 1 ppm / K. Preferably, the connection base and the substrate comprise the same material.

[0027] The connection base, in particular the upper side of the connection base, is connected to the lower side of the sensor element to form a sensor system comprising the connection base and the sensor element. Preferably, the connection base is connected to the sensor element by anodic bonding.

[0028] The sensor system is then connected, in particular fused, to the substrate by means of the above-mentioned laser welding (laser welding with ultrashort laser pulses). In particular, the lower side of the sensor system is connected to the upper side of the substrate in a mechanically robust and hermetically sealed manner by means of laser welding. The laser energy for connecting the substrate to the sensor system is then transmitted to the side of the substrate opposite the sensor system.

[0029] The drawings described below should not be construed as being to scale, rather, individual dimensions may be shown enlarged, reduced or distorted for better illustration. [Brief description of the drawings]

[0030] [Figure 1] 1 is a cross-sectional view of a pressure sensor device according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] 1 shows a pressure sensor arrangement 100 for measuring absolute, relative or differential pressure. The pressure sensor arrangement 100 is suitable for use in motor vehicles, e.g. as a vehicle exhaust gas application and / or in the powertrain. The pressure sensor arrangement 100 is further suitable, e.g. as a refrigerant pressure sensor or a hydrogen pressure sensor for monitoring industrial processes. The pressure sensor arrangement 100 can be used in a very wide temperature range (e.g. -40°C to 150°C).

[0032] The pressure sensor device 100 comprises a sensor element 202 having an upper surface 118 and a lower surface 204. The sensor element 202 is preferably a silicon chip. The sensor element 202 comprises a membrane 106 on the upper surface 118, which bounds a cavity 107 in an interior region of the pressure sensor device 100 against the outside. The membrane 106 is shaped and arranged to be exposed to a medium (e.g. liquid or gas). On top of the membrane 106, a sensing element 109 is further arranged for measuring the pressure of the medium. Of course, the pressure sensor device 100 may comprise more than one sensing element 109.

[0033] The pressure sensor arrangement 100 further comprises a substrate 104 as a carrier for the sensor element 202. The substrate 104 has an upper surface 115 and a lower surface 114. The sensor element 202 is disposed on or attached to the upper surface 115 of the substrate 202. The sensor element 202 is welded or fused to the upper surface 115 of the substrate 202 as will be described in more detail below.

[0034] The substrate 104 includes glass. The substrate 104 has a coefficient of thermal expansion that differs from the coefficient of thermal expansion of the sensor element 202 by less than 1 ppm / K. Thus, the substrate 104 and the sensor element 202 have approximately the same coefficient of thermal expansion, which results in the reduction or avoidance of mechanical stresses, especially at very high and very low temperatures.

[0035] Between the sensor element 202 and the substrate 104 a connection interface 201 is formed. The connection interface 201 is the area where the sensor element 202 and the substrate 104 are connected, in particular fused, in a mechanically robust and hermetically sealed manner.

[0036] The connection interface 201 is produced by laser welding with ultrashort laser pulses. In other words, the substrate 104 and the sensor element 202 are joined to one another by laser welding, thus without additional joining material. In that way, the introduction of additional components for the connection of the sensor element 202 to the substrate 104 is eliminated. Mechanical stresses caused by the introduction of components with a thermal expansion coefficient significantly different from that of the substrate 104 / sensor element 202 are thus eliminated.

[0037] In the embodiment shown, the pressure sensor arrangement 100 further comprises a connection base 220. The connection base 220 is arranged between the sensor element 202 and the substrate 104 and comprises glass. The thermal expansion coefficient of the connection base 220 differs from the thermal expansion coefficients of the substrate 104 and the sensor element 202 by less than 1 ppm / K. The occurrence of mechanical stresses due to the introduction of elements with significantly different thermal expansion coefficients compared to the thermal expansion coefficients of the substrate 104 / sensor element 202 can thus be avoided.

[0038] The connection base 220 is attached to the sensor element 202. In particular, the connection base 220 and the sensor element 202 are rigidly connected to each other, for example by anodic bonding. The sensor element 202 and the connection base 220 together form the sensor system 102.

[0039] The above-mentioned connection interface 201 is formed between the sensor system 102, in particular the underside of the sensor system 102, and the substrate 104, in particular the upper side 115 of the substrate 104. In that way, the sensor system 102 and the substrate 104 are connected, in particular fused, to one another in a mechanically robust and hermetically sealed manner at the connection interface 201. The laser energy for generating the connection interface 201 is then transmitted to the side of the substrate 104 facing away from the sensor system 102, i.e. the underside 114 of the substrate 104.

[0040] In an alternative embodiment (not explicitly shown), the connection base 220 can also be omitted. This means that the sensor element 202 is in this case connected directly (without intermediate elements) to the substrate 104. In this case, the connection interface 201 is formed between the lower surface 204 of the sensor element 202 and the upper surface 115 of the substrate 104.

[0041] In the following, a method for manufacturing a pressure sensor device, preferably the above-mentioned pressure sensor device 100, is described. All features disclosed with respect to the pressure sensor device 100 or the method are correspondingly disclosed with respect to each other aspect, and vice versa, even if the respective feature is not explicitly mentioned in the context of the respective aspect. The method comprises the following steps:

[0042] In a first step A) a substrate 104 is prepared. The substrate 104 comprises glass, as described above.

[0043] In a second step B), at least one sensor element 202, preferably a plurality of sensor elements 202, is provided. The sensor element 202 preferably comprises a silicon chip. The sensor element 202 has an upper surface 118 and a lower surface 204, with the membrane 106 formed on the upper surface 118. As mentioned above, the substrate 104 has a thermal expansion coefficient that differs from the thermal expansion coefficient of the sensor element 202 by less than 1 ppm / K.

[0044] In a next step C), a mechanically strong and hermetically sealed connection between the substrate 104 and the sensor element 202 is performed by laser welding. The laser energy for the connection between the substrate 104 and the sensor element 202 is transferred to the side of the substrate 104 facing away from the sensor element 202 (i.e. the underside 114 of the substrate 104). The laser welding creates the connection interface 201, i.e. the area where the substrate 104 and the sensor element 202 are firmly connected to each other.

[0045] Laser welding is performed with ultrashort laser pulses. The pulse length is in the picosecond and / or femtosecond range. The material of the substrate 104 is then completely transparent to the laser wavelength. Light is focused through the substrate 104 without heat input therein up to the bonding area between the substrate 104 and the sensor element 202. In this bonding area, the heat leads to the formation of a mechanically stable bond between the sensor element 202 and the substrate 104, i.e. the connection interface 201, very locally via fusion, via nonlinear absorption (multiphoton absorption) in a focal area spanning several tens of micrometers.

[0046] In an optional step, before step C), a connection base 220 is prepared. The connection base 220 comprises glass. The thermal expansion coefficient of the connection base 220 differs from the thermal expansion coefficient of the substrate 104 by less than 1 ppm / K. The connection base 220 is connected to the underside 204 of the sensor element, for example by anodic bonding, to form the sensor system 102.

[0047] In this embodiment, the sensor system 102 is then connected to the substrate 104 by laser welding using the above-mentioned ultrashort laser pulses. That is to say, a connection interface 201 is now formed between the sensor system 102 and the substrate 104. As mentioned above, the welding can only be performed due to the peculiarities of the locally limited heat supply by multiphoton absorption. The laser energy for the connection of the substrate 104 and the sensor system 102 is then transmitted to the side of the substrate 104 opposite the sensor system 102.

[0048] The final step is separation to provide the individual pressure sensor devices 100.

[0049] The description of the subject matter presented herein is not limited to individual specific embodiments, but rather the features of the individual embodiments can be combined with each other in any combination, insofar as this is technically meaningful. [Explanation of symbols]

[0050] 100 Pressure sensor device 102 Sensor System 104 Substrate 106 Membrane 107 Cavity 109 Detector element 114 Bottom of the board 115 Top of the board 118 Top surface of sensor element 201 Connection Interface 202 Sensor element 204 Underside of sensor element 220 Connection Base

Claims

1. A pressure sensor device (100), - a sensor element (202) having an upper surface (118) and a lower surface (204), the sensor element (202) comprising a membrane (106) configured and arranged to be exposed to a medium, the sensor element (202) comprising at least one sensing element (109) for measuring the pressure of said medium; - a substrate (104) acting as a carrier for said sensor element (202), said substrate (104) comprising glass; Equipped with a connection interface (201) produced by laser welding is formed between the sensor element (202) and the substrate (104), the sensor element (202) and the substrate (104) being connected to each other at the connection interface (201) in a mechanically robust and hermetically sealed manner, A pressure sensor device (100).

2. The pressure sensor arrangement (100) of claim 1, comprising no connection means for connecting the sensor element (202) to the substrate (104).

3. The pressure sensor arrangement (100) of claim 1 or 2, wherein the substrate (104) has a thermal expansion coefficient that differs from the thermal expansion coefficient of the sensor element (202) by less than 1 ppm / K.

4. The pressure sensor arrangement (100) of claim 1 or 2, wherein the sensor element (202) comprises a silicon chip.

5. The pressure sensor arrangement (100) of claim 1 or 2, wherein the at least one sensing element (109) is disposed on the membrane (106).

6. The pressure sensor arrangement (100) of claim 1 or 2, wherein the medium is a liquid or a gas.

7. The pressure sensor device (100) of claim 1 or 2, wherein laser energy is transmitted to the underside (114) of the substrate (104) to create the connection interface (201) and / or the laser welding is performed by ultrashort laser pulses.

8. The pressure sensor apparatus (100) of claim 1 or 2, further comprising a connection base (220) disposed between the sensor element (202) and the substrate (104), the connection base (220) comprising glass.

9. 9. The pressure sensor device (100) of claim 8, wherein the connection base (220) is bonded to the sensor element (202), and the connection interface (201) is formed between the connection base (220) and the substrate (104).

10. The pressure sensor arrangement (100) of claim 8, wherein the connection base (220) is connected to the sensor element (202) by anodic bonding.

11. The pressure sensor arrangement (100) of claim 8, wherein the substrate (104) has a coefficient of thermal expansion that differs from the coefficient of thermal expansion of the connection base (220) by less than 1 ppm / K.

12. A method for manufacturing a pressure sensor device (100), comprising the steps of: A) providing a substrate (104) comprising glass; B) providing at least one sensor element (202), said sensor element (202) having an upper surface (118) and a lower surface (204), said membrane (106) being formed on said upper surface (118); C) connecting said substrate (104) and said sensor element (202) in a mechanically robust and hermetically sealed manner by laser welding, during which a connection interface (201) is formed between said substrate (104) and said sensor element (202).

13. The method of claim 12, wherein the laser energy for connecting the substrate (104) and the sensor element (202) is delivered to a surface of the substrate (104) opposite the sensor element (202).

14. 14. The method of claim 12 or 13, wherein the laser welding is performed by ultrashort laser pulses.

15. 14. The method according to claim 12 or 13, wherein before step C), a connection base (220) is prepared, the connection base (220) comprising glass, and the connection base (220) is connected to the lower surface (204) of the sensor element (202) to form the sensor system (102).

16. The method of claim 15, wherein the connection base (220) is connected to the sensor element (202) by anodic bonding.

17. The method of claim 15, wherein the sensor system (102) is connected to the substrate (104) by laser welding using ultrashort laser pulses.

18. 20. The method of claim 17, wherein laser energy for connecting the substrate (104) and the sensor system (102) is transmitted to a side of the substrate (104) opposite the sensor element (102).

19. The method of claim 12, wherein the substrate (104) has a thermal expansion coefficient that differs from the thermal expansion coefficient of the sensor element (202) and / or the connection base (220) by less than 1 ppm / K.

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