WO2016156162A1

WO2016156162A1 - Capacitive pressure sensor

Info

Publication number: WO2016156162A1
Application number: PCT/EP2016/056436
Authority: WO
Inventors: Stefan Kraus; Karl-Peter Hauptvogel; Sascha KOCH; Andreas Rossberg; Thomas Uehlin; Martin BURGARD; Nils Ponath; Ulfert Drewes
Original assignee: Endress+Hauser Gmbh+Co. Kg
Priority date: 2015-04-01
Filing date: 2016-03-23
Publication date: 2016-10-06
Also published as: DE102015105057A1

Abstract

The invention describes a capacitive pressure sensor comprising a measuring diaphragm (1) which is arranged on a main body (3) with the inclusion of the pressure chamber (5), can be subjected to the action of a pressure (p) and can be elastically deformed in a pressure-dependent manner, comprising an active hard solder (7) which connects an outer edge of the measuring diaphragm (1) to an outer edge of an end face of the main body (3) which faces the measuring diaphragm (1), with the inclusion of a pressure chamber (5), and comprising a capacitive electromechanical transducer for detecting by measurement a deflection of the measuring diaphragm (1), which deflection is dependent on the pressure (p) which is to be measured, said capacitive electromechanical transducer comprising at least one capacitor which is formed by a diaphragm electrode (11), which is arranged on a side of the measuring diaphragm (1) which faces the main body (3), and a main body electrode (13), which is formed on an end face of the main body (3) which faces the measuring diaphragm (1), which capacitive pressure sensor can be produced in a cost-effective manner, in particular with little variance in respect of the level of quality, and which is distinguished in that the diaphragm electrode (11) is composed of a semiconducting, doped tantalum oxide, in particular semiconducting, doped tantalum pentoxide (Ta₂O₅).

Description

Capacitive pressure sensor

The invention relates to a capacitive pressure sensor, with a pressure chamber including a pressure chamber arranged on a base body, acted upon by a pressure-elastically deformable measuring membrane, an outer edge of the measuring membrane enclosing the pressure chamber with an outer edge of the measuring membrane facing end side of the body connecting Addition, in particular an active brazing, and a capacitive electromechanical transducer for metrological detection of a dependent of the pressure to be measured deflection of the measuring membrane, the at least one arranged on a side facing the base body side of the measuring membrane membrane electrode and one on one of

Measuring membrane-facing front side of the body arranged arranged base body electrode capacitor comprises. Capacitive pressure sensors can be designed as absolute pressure sensors, as relative pressure sensors or as differential pressure sensors, and are used in industrial applications

Measurement technology used to measure pressures.

In this case, capacitive ceramic pressure sensors, in which at least the

Measuring diaphragm made of ceramic, has the advantage that the ceramic measuring membrane can be exposed directly to the medium whose pressure is to be measured. In this respect, ceramic has particularly advantageous chemical and mechanical properties for use in pressure measurement technology. Esp. are diaphragm seals that transmit the pressure to be measured by means of a pressure-transmitting liquid to the pressure sensor, not required.

In EP 0 445 382 A2 a capacitive ceramic pressure sensor is described, with

- One including a pressure chamber arranged on a base body, can be acted upon with a pressure, pressure-dependent elastically deformable measuring diaphragm, - an outer edge of the measuring membrane enclosing the pressure chamber with an outer edge of the measuring membrane facing end face of the body connecting Aktivhartlötung, and

- A capacitive electromechanical transducer for metrological detection of a dependent of the pressure to be measured deflection of the measuring membrane, the at least one arranged by a arranged on a base body side of the diaphragm membrane electrode and a arranged on one of the measuring membrane facing the end face of the main body electrode body Capacitor includes. These pressure sensors are manufactured by prefabricating the measuring diaphragm and the base body, and the membrane electrode is mounted on the measuring diaphragm and the diaphragm

Base electrode are applied to the body. Subsequently, a solder layer is introduced from an active brazing material between the measuring membrane and the base body, and the assembly is heated under vacuum in total to a lying above the melting temperature of the solder soldering solder.

In EP 0 445 382 A2 DE it is described to apply a protective layer of an oxide of the electrode material to the electrodes, which prevents solder which melts during active brazing from flowing over the electrodes. According to EP 0 445 382 A2 DE, electrodes made of tantalum are preferably used for this purpose, on which a protective layer of tantalum pentoxide is arranged.

Tantalum pentoxide is known as an insulator with very high permittivity, and is used e.g. in

Electrolytic capacitors, as well as in the semiconductor industry as - often as high-k

Dielectric called - used high-quality dielectric.

The protective layer of tantalum pentoxide described in EP 0 445 382 A2 DE is produced by thermal or anodic oxidation of the tantalum electrodes. In this case, the application of the electrodes and the generation of the oxide layer on the electrodes represent two separate process steps, which are carried out in two different systems. While the application of the electrodes e.g. takes place in a sputtering system, in which the electrodes are sputtered as a coating on measuring membrane and body, the thermal oxidation takes place in a separate from the sputtering furnace. There is a risk that the surfaces of the electrodes during transport from the sputtering system to the oven by particles, fibers or touch pollute, resulting in rejects.

The thermal oxidation of tantalum electrodes is a time-consuming process that regularly takes several hours, z. B. 4 to 5 hours to complete. In addition to the desired ditantalum pentoxide, it is also possible for lower valent tantalum oxides to form, which leads to a variance of the oxide layers.

In particular, lower-value oxides which form during the thermal oxidation lead to an upper limit on the temperature range in which the tantalum oxide layer can reliably be used as a solder stop. To ensure a reliable solder stop during Aktivhartlötung of measuring diaphragm and body is therefore the

Soldering temperature at which the active brazing is done, according to limit upwards. In addition, the tantalum layer and the oxide layer formed thereon have

different coefficients of thermal expansion, which in a use of the pressure sensor in a wider temperature range to thermomechanical

Can cause voltages that can affect the pressure sensitivity of the measuring membrane.

DE 10 2013 106 045 A1 describes a pressure sensor in which the solder stop and membrane electrode are prepared from the same material system. For this purpose, a membrane electrode is used which has titanium oxide. In contrast to tantalum pentoxide, titanium oxide is conductive and can therefore be used as an electrode material. In this case, non-stoichiometric titanium oxide is preferably used, since the latter has a higher conductivity than stoichiometric titanium oxide. In addition, DE 10 2013 106 045 A1 describes increasing the conductivity of the electrode material by doping with Cr, Nb or W ,. The preparation of the membrane electrode is carried out according to DE 10 2013 106 045 A1, preferably by reactive sputtering.

It is an object of the invention an alternative usable capacitive

Specify a pressure sensor that can be produced inexpensively, and in particular with lower variance in high quality, and to provide a method for its production.

For this purpose, the invention comprises a pressure sensor, with

a pressure diaphragm which can be acted upon by a pressure chamber and which is arranged on a base body and can be acted upon by a pressure, is elastically deformable in a pressure-dependent manner,

- A joining an outer edge of the measuring diaphragm, including the pressure chamber with an outer edge of the measuring membrane facing the front side of the body joining, esp. An active brazing, and

- A capacitive electromechanical transducer for metrological detection of a dependent of the pressure to be measured deflection of the measuring membrane, the at least one arranged on a side facing the base of the measuring membrane membrane electrode and one on one of the measuring membrane facing

Comprises end face of the main body arranged arranged base body electrode capacitor,

characterized by the fact that

the membrane electrode consists of semiconducting, doped tantalum oxide, in particular semiconducting, doped ditantalum pentoxide.

According to a preferred embodiment, the main body electrode consists of semiconducting, doped tantalum oxide, in particular semiconducting, doped ditantalum pentoxide. A development of the invention is characterized in that the doping comprises titanium (Ti), wherein the doped tantalum oxide esp. Doped dopant tallow (Ta ₂ 0 ₅ ), in which a titanium content of the titanium-tantalum metal content of the doped Ditantalpentoxids on the order of 10 mol.%.

A preferred development is characterized in that

the semiconductive membrane electrode has an impedance dependent on the temperature of the measuring membrane, and

- A measuring circuit is provided, which is the temperature-dependent impedance, in particular its ohmic component, or dependent on the temperature-dependent impedance

Measuring variable, esp. A time constant of a charging and / or discharging the capacitor formed by the membrane electrode and the main body electrode or one of a caused by the capacitor in an AC circuit

Phase shift between AC and AC voltage dependent variable, esp. A dielectric power loss of the capacitor or tangent of a loss angle, or a quality or attenuation of a condenser containing, esp. In resonance operated, resonant circuit determined.

A development of the preferred embodiment provides that

the measuring circuit based on the impedance or the impedance-dependent

Measured variable determines a temperature of the measuring membrane, and in particular for the compensation of a temperature-dependent measurement error of the pressure sensor provides or used. A further development of the preferred embodiment provides that

- The measuring circuit based on the impedance or the impedance-dependent

Measured a temperature of the measuring membrane determines, and

- The measuring circuit in the determination of the temperature compensation of a

Dependence of the impedance on the pressure-dependent deformation of the measuring membrane makes.

Furthermore, the invention comprises a method for producing a pressure sensor according to the invention, which is characterized in that

- Basic body and measuring membrane are provided,

the membrane electrode is applied to the side of the measuring membrane facing the base body, in particular by gas-phase deposition, in particular by physical vapor deposition, in particular by sputtering, in particular by DC or magnetron sputtering, is applied,

- The main body electrode on the diaphragm facing the end face of the

Main body is applied, esp. By vapor deposition, esp. By physical vapor deposition, in particular by sputtering, esp. By DC or magnetron sputtering applied, and

- Body and diaphragm are connected by active brazing. According to one embodiment of the method, sputtering takes place by means of a sputtering target consisting of a semiconducting, doped ditantalpine oxide, in particular titanium-doped ditantalum pentoxide.

The invention has the advantage that the membrane electrode consisting of semiconducting, doped tantalum oxide, esp. Doped Ditantalpentoxid, at the same time forms a Lotstopp, which counteracts an inflow of molten active brazing material into the pressure chamber of the pressure sensor during the Aktivhartlötens. In addition, the membrane electrodes can be produced in a single process step comparatively quickly and inexpensively with low variance. Since the doped tantalum pentoxide is semiconducting, the membrane electrode can be deposited by DC or magnetron sputtering. Thus, no high-frequency sputtering system is required, as required for sputtering insulators. By means of DC and magnetron sputtering, thin, essentially non-porous layers can be produced in reproducibly high quality. DC and magnetron sputtering moreover has the advantage that the composition of the sputtered layers is easier to control than reactive sputtering.

There is no need for a separate operation to create a solder stop layer on the membrane electrode. Accordingly, the required transport between two plants, and the associated risk of contamination, is also eliminated.

The invention and its advantages will now be explained in more detail with reference to the figure of the drawing, in which an embodiment is shown. Fig. 1 shows: a capacitive pressure sensor.

Fig. 1 shows a section through an embodiment of a pressure sensor. This comprises a pressure membrane p acted upon and pressure-dependent elastically deformable measuring membrane 1, which is arranged on a base body 3. The measuring diaphragm 1 and preferably also the base body 3 are made of ceramic, e.g. made of aluminum oxide

(AI2O ₃ ), and are pressure-tightly connected to each other with the inclusion of a pressure chamber 5. For this purpose, an outer edge of the main body 3 facing side of

Measuring membrane 1, including the pressure chamber 5 by means of a joint 7,

preferably an active brazing, connected to an outer edge of the measuring membrane 1 facing end side of the base body 3. The illustrated pressure sensor can be designed as an absolute pressure sensor. In that case, the pressure chamber 5 enclosed under the measuring diaphragm 1 is evacuated. Alternatively, it can be configured as a relative pressure sensor, in that the pressure chamber 5 is supplied with a reference pressure p _ref , for example an atmospheric pressure, via a bore 9 leading through the main body 3, shown in dashed lines in FIG. 1, relative to that acting on the measuring diaphragm 1 Pressure p is to be detected.

The pressure sensor comprises an electromechanical transducer which serves to metrologically detect a pressure-dependent deformation of the measuring diaphragm 1. This includes e.g. at least one capacitor with a depending on the pressure-induced deflection of the measuring membrane 1 changing capacity of a on a base body 3 facing side of the measuring membrane 1 applied membrane electrode 1 1 and one of the measuring membrane 1 facing end of

Base body 3 applied base body electrode 13 has. The membrane electrode 1 1 extends over the base body 3 facing side of the measuring membrane 1 to the joint 7, and is preferably on the preferably as Aktivhartlötung

trained joining 7 electrically contacted. The electrical connection of the

Counterelectrode 13 is preferably carried out via a contact pin 15 inserted in a bore leading through the base body 3, e.g. a tantalum pin, which produces an electrically conductive connection to the main body electrode 13.

The pressure-dependent capacity of this capacitor or its changes are detected by a connected to the membrane electrode 1 1 and the main body electrode 13, not shown here measurement circuit and converted into a pressure-dependent measurement signal, which then to display, for further processing and / or Evaluation is available.

According to the invention, the membrane electrode 1 1 consists of semiconducting, doped

Tantalum oxide, preferably of semiconducting, doped ditantalum pentoxide (Ta20 ₅ ).

For doping, this is particularly suitable for doping with titanium (Ti). For this purpose, in particular a doping is suitable in which the titanium content of the titanium-tantalum metal content of the doped

Ditantalpentoxids on the order of about 10 mol.% Is. Such a doping is described in US Pat. No. 3,402,078, where it is used to produce a porous cathode of a fuel cell. To produce the cathodes there is described a process in which titanium oxide and tantalum pentoxide are mixed in a mixing ratio corresponding to the desired titanium content, and ground, dried, roasted and sieved in ethanol, and from this by means of a

water-based solution a spreadable mass is generated, which is then on site applied, dried and then fired. However, porous electrodes are unsuitable for use in pressure sensors, since porous electrodes in the pressure chamber 5 absorb moisture penetrating, which then to impairments of the

Measuring characteristics of the pressure sensor leads.

Preferably, not only the membrane electrode 1 1, but also the main body electrode 13 of the doped, semiconducting tantalum oxide, preferably the doped semiconducting Ditantalpentoxid (Ta20 ₅ ). Doped tantalum pentoxide has the advantage that it is due to the doping in

is sufficiently conductive to be suitable as an electrode material, and at the same time during the active brazing of measuring diaphragm 1 and body 3 forms a Lotstopp used for Aktivhartlötung active brazing, which prevents an inflow of Aktivhartlots in the pressure chamber 5 during the soldering process.

In addition, the semiconductive membrane electrode 1 1 has the advantage of having a temperature-dependent impedance as a semiconductor. These

Temperature dependence may be on the in the unpublished German

Patent application DE 10 2013 1 14 734.8 the Applicant 20.12.2013 described manner be used to determine the temperature of the measuring diaphragm 1 by means of a corresponding measuring circuit, this measuring circuit then

Preferably, to compensate for a temperature-dependent measurement error of the

Pressure sensor provides or uses. For this purpose, by means of a measuring circuit, not shown here, the impedance of the membrane electrode 1 1, in particular its ohmic component, or dependent on the temperature-dependent impedance

Measured variable determined. As described in DE 10 2013 1 14 734.8, for this purpose, a measured variable dependent on the temperature-dependent impedance of the membrane electrode 1 1 of the capacitor formed by the membrane electrode 1 1 and the main body electrode 13 can be detected by measurement using the measuring circuit. In particular, a time constant of a charging and / or discharging process of the

Capacitor, or one of a caused by the capacitor in an AC circuit phase shift φ between AC and AC voltage dependent variable, such as a dielectric loss of the

Capacitor or a tangent of the loss angle δ, or a quality or attenuation of a condenser-containing, e.g. operated in resonance, resonant circuit.

In this case, in the determination of the temperature of the measuring membrane 1 based on the impedance-dependent measurement preferably a compensation of a dependence of the impedance of the pressure-dependent deformation of the measuring membrane 1 made, the deformation of the measuring membrane 1 can be determined by the capacitance of the capacitor. Although the invention is described herein using the example of only a single membrane electrode 1 1 and a single body electrode 13 having pressure sensor, it is of course completely analogous also in connection with capacitive

Pressure sensors can be used, which have further electrodes. An example of this are pressure sensors described in DE 10 201 1078 557 A1, the electromechanical transducers of which have two capacitors, one of which is formed by the membrane electrode and a first main body electrode arranged centrally on the end face of the main body facing the measuring diaphragm, and a second main body electrode which is surrounded on the outside by the membrane electrode and the first main body electrode is formed.

Likewise, the invention is of course completely analogous even in capacitive ceramic

Differential pressure sensors can be used, the at least one including an

Pressure chamber arranged on a base body can be acted upon with a pressure, pressure-dependent elastically deformable measuring membrane, the outer edge is connected to the inclusion of a pressure chamber with an outer edge of the measuring diaphragm facing end of the body via a joint, esp. An active brazing, and at least one capacitive electromechanical transducer comprising at least one arranged by a arranged on a side facing the base of the measuring membrane membrane electrode and a capacitor arranged on one of the measuring membrane facing end side of the base body arranged base electrode.

Pressure sensors according to the invention are produced by prefabricating the measuring membrane 1 and base body 3, the membrane electrode 1 1 on

the side of the measuring diaphragm 1 facing the main body 3 is applied, and the main body electrode 13 is applied to the end face of the main body 3 facing the measuring diaphragm 1. The application of the membrane electrode 1 1 and the main body electrode 13 is preferably carried out by vapor deposition, preferably by physical

Gas phase deposition, in particular by sputtering. For this purpose, a sputtering target consisting of semiconducting, doped ditantalum pentoxide (Ta ₂ O ₅ ), which is doped with, for example, titanium, is preferably used. The application of the membrane electrode 1 1 and the main body electrode 13 is preferably carried out by means of DC or magnetron sputtering. By DC, as well as by magnetron sputtering can thin, in

Substantially non-porous layers can be produced in reproducibly high quality. DC and magnetron sputtering moreover has the advantage that the composition of the sputtered layers is easier to control than is the case with reactive sputtering. When applying the membrane electrode 1 1 at the same time an electrical connection of the counter electrode 13 can be provided by the contact pin 15, for example a tantalum pin, is inserted into the leading through the body 3 bore, and produces an electrically conductive connection to the main body electrode 13 ,

In contrast to the tantalum electrodes provided at the outset known from the prior art with a protective layer of ditantalum pentoxide produced by thermal oxidation, no further operation is required for producing the electrodes according to the invention. The entire manufacturing process of the electrodes thus takes place in a single system. Accordingly, no transport of the components from one system to another is required, in which the surfaces of the components could be contaminated by particles, fibers or touch. This avoids rejects. In addition, the sputtering process is a relatively fast executable process, which usually takes about 30 minutes. In comparison, for thermal oxidation of tantalum electrodes, several hours, e.g. 4 to 5 hours, needed.

Subsequently, measuring diaphragm 1 and base 3 including the

Pressure chamber 5 pressure-tightly connected by active brazing. For this purpose, a solder layer is arranged between the outer facing edges of the base body 3 and the measuring membrane 1 to be joined by the joining 7. The

Lotschicht can e.g. in the manner described in EP 490 807 A1 as solder paste or in the form of a preformed solder preform, e.g. a solder ring, are introduced. As a result, joints 7 having a height of greater than or equal to 30 μm can be produced. A lower minimum height of the measuring membrane 1 and base 3 connecting joint 7 and, consequently, to achieve a higher

Measuring accuracy of a more advantageous smaller electrode spacing can be achieved in accordance with a method described in DE 10 2010 043 1 19 A1, in which the solder layer is deposited by means of vapor deposition on one of the joining surfaces or proportionally on both

Joining surfaces is applied. As a result, joints 7 can be produced with a height of the order of magnitude of 10 μm.

After the introduction or application of the solder layer, the arrangement formed by the main body 3, the solder layer and the measuring membrane 1 is heated in total to a soldering temperature above the melting temperature of the active hard solder and heated there over a longer period of time, in particular a period of 5 min to 15 min, held. Alternatively, a described in DE 10 201 1 005 665 A1

Aktivhartlötverfahren be used in which the solder layer is completely melted under vacuum by laser radiation. During the active brazing, the membrane electrode 1 1, which adjoins the active hard solder, acts as a solder stop, which counteracts an inflow of molten active brazing solder into the pressure chamber 5. The achieved by DC or magnetron sputtering precise adjustment of the composition of the membrane electrode 1 1 has the advantage that on the targeted adjustment of the composition of the temperature range by the membrane electrode 1 1 forms an effective Lotstopp, can be increased.

measuring membrane

body

pressure chamber

coincidence

drilling

Membrane electrode

G ro d body electrodes e

Claims

claims

1. Pressure sensor, with

- one including a pressure chamber (5) on a base body (3)

arranged, with a pressure (p) acted upon, pressure-dependent elastically deformable measuring diaphragm (1),

- One of an outer edge of the measuring membrane (1) including the pressure chamber (5) with an outer edge of one of the measuring membrane (1) facing end side of the base body (3) connecting joint (7), esp. An active brazing, and

- A capacitive electromechanical transducer for metrological detection of the pressure to be measured (p) dependent deflection of the measuring diaphragm (1), the at least one arranged on one of the base body (3) facing side of the measuring diaphragm (1) membrane electrode (1 1 ) and a capacitor formed on one of the measuring diaphragm (1) facing the end face of the base body (3) arranged base electrode (13) capacitor,

characterized in that

the membrane electrode (1 1) of semiconducting, doped tantalum oxide, esp.

semiconducting, doped Ditantalpentoxid (Ta ₂ 0 ₅ ) consists.

Pressure sensor according to claim 1, characterized in that

the main body electrode (13) of semiconducting, doped tantalum oxide, esp.

semiconducting, doped Ditantalpentoxid (Ta ₂ 0 ₅ ) consists.

Pressure sensor according to claim 1 or 2, characterized in that

the doping comprises titanium (Ti), wherein the doped tantalum oxide esp. Doped

Ditantalum pentoxide (Ta ₂ 0 ₅ ) is in which a titanium content of the titanium-tantalum metal content of the doped Ditantalpentoxids is of the order of 10 mol.%.

4. Pressure sensor according to claim 1, characterized in that

- The semiconducting membrane electrode (1 1) one of the temperature of the measuring membrane

(1) has dependent impedance, and

a measuring circuit is provided which monitors the temperature-dependent impedance, in particular its ohmic component, or a measured variable dependent on the temperature-dependent impedance, in particular a time constant of a charging and / or charging time

Discharge of the through the membrane electrode (1 1) and the basic body

Electrode (13) formed capacitor or one of a caused by the capacitor in an AC circuit phase shift (φ) between

AC and AC dependent measure, in particular a dielectric power dissipation of the capacitor or tangent of a loss angle (δ), or a quality or attenuation of a condenser containing, esp. In resonant, resonant circuit determined.

Pressure sensor according to claim 4, characterized in that

the measuring circuit determines a temperature of the measuring diaphragm (1) on the basis of the impedance or the quantity dependent on the impedance,

and esp. To compensate for a temperature-dependent measurement error of

Pressure sensor provides or uses. 6. Pressure sensor according to claim 4, characterized in that

the measuring circuit determines a temperature of the measuring diaphragm (1) on the basis of the impedance or the quantity dependent on the impedance, and

- The measuring circuit in the determination of the temperature compensation of a dependence of the impedance of the pressure-dependent deformation of the

Measuring diaphragm (1) performs.

A method of manufacturing a pressure sensor according to claim 1, characterized

marked that

- Basic body (3) and measuring diaphragm (1) are provided,

- The membrane electrode (1 1) on the base body (3) facing side of the measuring membrane (1) is applied, esp. By vapor deposition, esp. By physical vapor deposition, esp. By sputtering, esp. By

DC or magnetron sputtering is applied,

- The main body electrode (13) on the measuring membrane (1) facing

End face of the base body (3) is applied, esp. By

Gas phase deposition, in particular by physical vapor deposition, in particular by sputtering, in particular by DC or magnetron sputtering applied, and

- Body (3) and measuring diaphragm (1) are connected by active brazing.

Method according to claim 7, characterized in that

the sputtering takes place by means of a sputtering target consisting of a semiconducting, doped ditantalpine oxide (Ta ₂ O ₅ ), in particular with titanium (Ti) doped ditantalum pentoxide (Ta ₂ O ₅ ).