High-pressure sensor with a hydrogen barrier layer

Abstract

The invention relates to a high-pressure sensor (10) for measuring the pressure of a hydrogen-containing fluid, comprising a metal substrate (12), a metal membrane (18) which can be deflected into a free area (14) along a normal direction (16) depending on an ambient pressure, measuring means (24) applied in the normal direction (16) above the membrane (18) and each having at least one measuring layer (26) for electrically detecting the membrane deflection, and an insulating layer (30) arranged at least on the membrane (18), wherein at least the membrane (18) is made of a chromium-containing steel and a hydrogen barrier layer (34) spanning at least the membrane (18) is arranged in the normal direction (16) above the membrane (18).

Description

[0001] The invention relates to a high-pressure sensor according to the preamble of claim 1. State of the art

[0002] In DE 10 2005 027 365 A1 a high pressure sensor with a steel substrate, a membrane, an insulating layer and measuring means made of a piezoresistive material, for example a NiCrSi alloy, is described. Disclosure of the invention

[0003] According to the present invention, a high-pressure sensor with the features of claim 1 is proposed. This reduces or prevents hydrogen embrittlement of the metal substrate. Hydrogen diffusion into the substrate can be reduced. The high-pressure sensor can be made more reliable and resistant to environmental influences. The high-pressure sensor can be designed to be space-saving and cost-effective.

[0004] The following refers to the top and bottom sides in relation to the normal direction.

[0005] The high-pressure sensor can be configured to detect ambient pressure starting at 10 bar. For example, it can measure ambient pressures exceeding 100 bar or 1000 bar. The high-pressure sensor can also be used to detect fluid pressure in a fuel cell system, particularly in a vehicle or other installation. The hydrogen-containing fluid can be liquid or gaseous.

[0006] The substrate may have been post-treated to strengthen a chromium oxide layer formed on the surface, in particular by exposure to temperature and / or surface treatment.

[0007] The free space can have a bridge structure in the normal direction below the membrane. The membrane can exhibit a variable thickness in a lateral direction perpendicular to the normal direction due to the bridge structure. The bridge structure can be formed by a cylindrical free space within the substrate, thereby creating a single, integral membrane within the substrate.

[0008] The membrane can be rectangular, oval, or round when viewed in a plane with the normal direction as its normal. The membrane can be made from the substrate in one piece. The membrane and the substrate can be made of the same material.

[0009] The insulating layer can also be applied to the substrate. The insulating layer can be applied directly to the membrane and / or the substrate. The insulating layer can be positioned between the measuring medium layer and the membrane.

[0010] The insulating layer can be composed of silicon oxide, silicon nitride, or metal oxide. The insulating layer can cover the entire top surface of the substrate. The insulating layer can be applied by chemical vapor deposition (CVD). The insulating layer can be applied by plasma-enhanced chemical vapor deposition (PECVD). The insulating layer can be applied directly to the metal substrate.

[0011] The measuring devices can be spaced apart from each other. The measuring devices can be electrically connected to each other in a Wheatstone bridge circuit. The measuring devices can be arranged laterally overlapping the membrane edge where the membrane is attached to the substrate. The measuring devices can be electrically connected, in particular by wire bonding or flip-chip bonding.

[0012] The measuring medium layer can be made of a piezoresistive and / or piezoelectric material. It can also be made of a nickel-chromium-silicon alloy. Depending on the mechanical stresses applied to it, the measuring medium layer can induce a change in electrical resistance or an electrical voltage.

[0013] The hydrogen barrier layer can have a substantially constant thickness, meaning that this is the desired thickness but is subject to manufacturing tolerances. The hydrogen barrier layer can be homogeneous, in particular having a uniform density.

[0014] In the normal direction above the measuring instruments, a protective layer may be applied, in particular for electrical insulation and / or to protect the measuring instruments from environmental influences.

[0015] In a preferred embodiment of the invention, it is advantageous if the hydrogen barrier layer is composed of aluminum oxide. Alternatively or additionally, the hydrogen barrier layer can be composed of silicon nitride, titanium nitride, zirconium oxide, silicon carbide, chromium nitride, or diamond-like carbon (DLC).

[0016] In a preferred embodiment of the invention, the hydrogen barrier layer is composed of amorphous material. The hydrogen barrier layer can consist exclusively of amorphous material, in particular amorphous aluminum oxide. The amorphous material can have a disordered, irregular material structure. The amorphous material can exhibit isotropic electrical properties.

[0017] In a preferred embodiment of the invention, the hydrogen barrier layer is applied by atomic layer deposition. Atomic layer deposition (ALD) is a thin-film coating process that selectively deposits materials at the atomic level, thereby enabling the production of extremely thin, uniform, and conformal layers.

[0018] In a preferred embodiment of the invention, the chromium-containing steel is a stainless steel. The chromium content of the steel can be at least 10.5% by mass. The carbon content of the steel can be less than 2%, in particular less than 1.5%, by mass.

[0019] In a preferred embodiment of the invention, it is advantageous if the mean thickness of the hydrogen barrier layer is greater than 5 nm, and in particular greater than 20 nm. This allows the hydrogen barrier layer to exhibit sufficient barrier properties against hydrogen diffusion to the metal substrate. The mean thickness can be an average of the thickness over the entire surface of the hydrogen barrier layer.

[0020] In a specific embodiment of the invention, it is advantageous if the mean thickness of the hydrogen barrier layer is less than 100 nm. This prevents mechanical stiffening of the hydrogen barrier layer arranged above the membrane. The mean thickness can be an average of the thickness across the entire surface of the hydrogen barrier layer.

[0021] In a preferred embodiment of the invention, it is advantageous if the hydrogen barrier layer is applied to the insulating layer. However, the hydrogen barrier layer can also be arranged exclusively above the membrane and / or the top surface of the substrate. The hydrogen barrier layer can be applied to the top surface of the insulating layer and to at least one side wall and / or a bottom surface directly on the substrate, differing from the top surface.

[0022] In a preferred embodiment of the invention, it is advantageous if the hydrogen barrier layer covers a surface of the substrate. The hydrogen barrier layer can be arranged completely around the substrate. This allows the metal substrate to be better protected against hydrogen diffusion.

[0023] In a preferred embodiment of the invention, it is advantageous if the hydrogen barrier layer is arranged between the measuring means and the insulating layer. The hydrogen barrier layer can be arranged directly on the insulating layer and / or directly below the measuring means layer. The hydrogen barrier layer can be the only layer arranged between the insulating layer and the measuring means layer. The hydrogen barrier layer can be applied to a top surface of the substrate exclusively on the insulating layer. The hydrogen barrier layer can be applied directly to the substrate on at least one surface of the substrate other than the top surface, for example, a side surface and / or a bottom surface.

[0024] Further advantages and advantageous embodiments of the invention will become apparent from the description of the figures and the illustrations. Character description

[0025] The invention is described in detail below with reference to the illustrations. These show, in detail: Fig. 1: A cross-section of a high-pressure sensor in a special embodiment of the invention. Fig. 2: A time course of a sensor measurement signal of a high-pressure sensor in a further special embodiment of the invention.

[0026] Fig. Figure 1 shows a cross-section of a high-pressure sensor in a specific embodiment of the invention. The high-pressure sensor 10 for measuring the pressure of a hydrogen-containing fluid, in particular pure hydrogen, comprises a metal substrate 12 and a membrane 18 integrally formed in the substrate 12, which is deflectable into a free area 14 of the substrate 12 along a normal direction 16 depending on an ambient pressure. The free area 14 has a bridge structure 20 below the membrane 18 in the normal direction 16, and the membrane 18 has a variable membrane thickness 22 in a lateral direction perpendicular to the normal direction 16 due to the bridge structure 20.

[0027] In the normal direction 16 above the membrane 18, several spaced-apart measuring devices 24 are applied. The measuring devices 24, which are primarily piezoresistive, each comprise a measuring layer 26 for electrically detecting the membrane deflection. The measuring layer 26 is primarily composed of a nickel-chromium-silicon alloy. The measuring devices 24 are primarily arranged to overlap laterally with the membrane edge 28, where the membrane 18 is attached to the substrate 12.

[0028] Furthermore, the high-pressure sensor 10 comprises an insulating layer 30, in particular made of silicon oxide, arranged between the measuring medium layer 26 and the membrane 18. The insulating layer 30 covers the entire top surface of the substrate 12 and is arranged directly on the substrate 12.

[0029] The membrane 18 and the substrate 12 are made of a chromium-containing steel. This allows a chromium oxide layer to form on the surface 32 of the substrate 12 as a corrosion protection layer, which protects the substrate 12 from corrosion. The steel is specifically a stainless steel.

[0030] Furthermore, a hydrogen barrier layer 34 is arranged in the normal direction 16 above the membrane 18 and spans at least the entire surface of the membrane 18. This reduces or prevents the diffusion of hydrogen from the surrounding fluid to the substrate 12, thereby preventing embrittlement of the substrate 12 and the membrane 18.

[0031] The hydrogen barrier layer 34 is applied completely to the entire surface 32 of the substrate 12 and to the top surface of the substrate 12 on the insulating layer 30. The hydrogen barrier layer 34 is located on the top surface between the measuring elements 24 and the insulating layer 30. Specifically, the hydrogen barrier layer 34 is positioned directly on the insulating layer 30 and directly below the measuring element layer 26.

[0032] The hydrogen barrier layer 34 is composed primarily of amorphous aluminum oxide and is deposited, for example, by atomic layer deposition. The mean thickness 40 of the hydrogen barrier layer 34 can be greater than 20 nm to provide sufficient barrier properties against hydrogen diffusion. In particular, the mean thickness 40 is less than 100 nm to limit stiffening of the deflectable membrane 18.

[0033] Fig. Figure 2 shows a time course of a sensor measurement signal from a high-pressure sensor in a further specific embodiment of the invention. The time course in days d of the measured sensor measurement signal 42 of the high-pressure sensor, expressed as an electrical voltage in volts, is shown in comparison to a measured sensor measurement signal 44 of a high-pressure sensor according to the prior art. It can be seen that the sensor measurement signal 42 reliably enables the measurement of the fluid pressure 46 in bar of the hydrogen-containing fluid, whereas the sensor measurement signal 44, due to the diffusion of hydrogen into the metal substrate and thus due to impairment of the material structure of the substrate, including the membrane, reaches a saturation value of the sensor voltage, here at 4.6 V, which means that pressure measurement is no longer possible after four days. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2005 027 365 A1

[0002]

Claims

[1] High-pressure sensor (10) for measuring the pressure of a hydrogen-containing fluid, comprising a metal substrate (12), a membrane (18) made of metal which can be deflected into a free area (14) along a normal direction (16) depending on an ambient pressure, measuring means (24) applied in the normal direction (16) above the membrane (18) and each having at least one measuring layer (26) for electrical detection of the membrane deflection, an insulating layer (30) arranged at least on the membrane (18), characterized by , that at least the membrane (18) is made of a chromium-containing steel and a hydrogen barrier layer (34) spanning at least the membrane (18) is arranged in the normal direction (16) above the membrane (18). [2] High pressure sensor (10) according to claim 1, characterized by, that the hydrogen barrier layer (34) is composed of aluminium oxide. [3] High pressure sensor (10) according to claim 1 or 2, characterized by , that the hydrogen barrier layer (34) is composed of amorphous material. [4] High pressure sensor (10) according to any one of the preceding claims, characterized by , that the hydrogen barrier layer (34) is applied by atomic layer deposition. [5] High-pressure sensor (10) according to any one of the preceding claims, characterized by , that the chromium-containing steel is a stainless steel. [6] High-pressure sensor (10) according to any one of the preceding claims, characterized by , that the mean layer thickness (40) of the hydrogen barrier layer (34) is greater than 5 nm. [7] High pressure sensor (10) according to any one of the preceding claims, characterized by , that the mean layer thickness (40) of the hydrogen barrier layer (34) is less than 100 nm. [8] High-pressure sensor (10) according to any one of the preceding claims, characterized by , that the hydrogen barrier layer (34) is applied to the insulating layer (30). [9] High-pressure sensor (10) according to any one of the preceding claims, characterized by , that the hydrogen barrier layer (34) covers a surface (32) of the substrate (12). [10] High pressure sensor (10) according to any one of the preceding claims, characterized by , that the hydrogen barrier layer (34) is arranged between the measuring means (24) and the insulating layer (30).

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