Patent Application
20120174658
The invention relates to a measuring cell for the infrared analysis of fluids, a measuring system having such a measuring cell, and a method for producing such a measuring cell.
A measuring cell of this type can be used, for example, for the analysis of oils which are used in technical systems for the transmission of pressures, for lubrication, and/or for cooling. In operation, the oil is subjected to aging and/or fouling, and for the operational reliability of the system, it is critical to be able to check the quality state of the oil in near real time. For this purpose, the wavelength-dependent transmission of the oil can be measured, or the absorption bands can be measured especially in the infrared range, and conclusions can be drawn therefrom regarding the quality of the oil.
Reflection spectrometers with these measuring cells are known, for example, from DE 103 21 472 A1, DE 197 31 241 C2, or EP 0 488 947 A1. Transmission spectrometers are known, for example, from DE 10 2004 008 685 A1 and GB 2 341 925 A.
DE 41 37 060 C2 shows a microcell for infrared spectroscopy.
US 2002/0063330 A1 shows a heat sink and a method for producing this heat sink.
DE 102 44 786 A1 and AT 500 075 B1 show a method for connecting wafers. DE 103 29 866 A1 shows the use of wafer bonding for a piezoelectric substrate with temperature compensation and method for producing a surface wave component.
DE 199 09 692 C1 shows a flow measuring cell for studying a high-speed chemical reaction.
DE 101 04 957 A1 shows a method for producing a three-dimensional micro flow cell.
The object of the invention is to make available a measuring cell which has improved performance characteristics, as well as a pertinent measuring system and a pertinent production method. In one embodiment, the measuring cell and the sensor and emitter are designed to be used even for high operating pressures, and for this purpose they are to exhibit high operational reliability.
This object is achieved by the measuring cell defined in claim 1 as well as the measuring system defined in the independent claim and the production method defined in the independent claim. Particular embodiments of the invention are defined in the dependent claims.
In one embodiment, the object is achieved by a measuring cell for the infrared analysis of fluids, especially by a measuring cell with an allowable operating pressure of more than 20 bar and preferably more than 50 bar, with a flow channel for the fluid which is formed between a first transparent element and a second transparent element, each being transparent at least in sections to infrared radiation, and the infrared radiation can be irradiated into the flow channel via the first element and can exit from the flow channel via the second element, and the two elements are connected fluid-tight to one another with high mechanical strength by a connecting layer of glass-containing material, especially of a sintered glass-ceramic material, which layer is located between the two elements.
Here it is advantageous that even comparatively thick elements, as are necessary for the high pressure use, can be permanently and reliably connected to one another by the connection layer, especially that the connection can be produced without porous spots in spite of the stiffness of the elements which are comparatively thick with respect to high pressure use. In the still unsintered state, by applying a corresponding pressure, the material of the connecting layer can be brought into contact with the surfaces of the two elements such that a topography or ripple of the surfaces of the two elements which may be present is equalized in this way. This is especially advantageous when the measuring cells are fabricated in a panel; i.e., boards or wafers on which a plurality of elements and thus a plurality of measuring cells are implemented at the same time are used, for example, for the components.
For example, the elements in a panel can be formed from a silicon wafer with a thickness of more than 1 mm, especially more than 1.5 mm and preferably more than 2 mm, and the connecting layer in the sintered state has a thickness of more than 50 μm and less than 500 μm, especially more than 100 μm and less than 300 μm, and preferably more than 120 μm and less than 200 μm. The flow channel for the fluid can be a microfluid channel with a length of more than 3 mm, especially more than 6 mm and preferably more than 9 mm, and with a width of less than 10 mm, especially less than 8 mm and preferably less than 6 mm. In the flow channel, there can be one or more spacers by which even under the effect of high pressure the height of the flow channel is kept to a definable value. The spacers can be formed, for example, by webs which run lengthwise to the flow direction. The spacers and/or the geometry of the flow channel can be formed at least in sections by one of the elements and/or by the connecting layer.
In one embodiment, the connecting layer is applied structured to one of the elements or is placed between the two elements. By structuring the connecting layer, for example, the flow channel can be defined, and particularly the two elements bordering the flow channel can also be fundamentally unstructured. Alternatively or in addition, the two elements can also have, at least in sections, a structure which defines the flow channel and which is produced by etching onto the surface. Fundamentally, the connecting layer can also be applied by all methods which are known, for example, from thick film technology.
In one embodiment, the connecting layer in the form of a strip, a tape, or a membrane is laminated onto one of the elements or is laminated between the two elements. For example, the connecting layer in membrane form can be placed on a wafer which forms the first elements of a plurality of measuring cells, and a wafer which forms the second elements of the plurality of measuring cells can be placed on the connecting layer, and then the combination can be pressed together and then sintered.
In one embodiment, the connecting layer has exit channels for the exit of organic components from the connecting layer in a process which precedes the sintering. The exit channels can be formed by a lattice-like structure of the connecting layer. Providing these exit channels is especially advantageous in the production of the measuring cells in a panel, because in this case the organic components which are volatile in temperature treatment can emerge laterally.
In one embodiment, the connecting layer is formed from a low-temperature cofired ceramic which preferably has plasticizers. A lamination of the connecting layer by the plasticizers is possible. In the not yet sintered state, the connecting layer is flexible. Components of the connecting layer in this state can be glass, especially borosilicate glass, borofloat glass, and/or quartz glass, ceramic—for example Al2O3—and organic components which volatilize during setting. The mixing of these components ensures the matching of the coefficient of thermal expansion in the temperature range from −50 to +850° C. to the coefficient of thermal expansion of the elements of the measuring cell, especially to the coefficient of thermal expansion of silicon.
In one embodiment, the connecting layer in a temperature range between 0 and 200° C., especially between 0 and 400° C. and preferably between 0 and 600° C., has a coefficient of linear thermal expansion which deviates less than 8 ppm/K, especially less than 5 ppm/K and preferably less than 0.5 ppm/K from the coefficient of linear thermal expansion of at least one of the elements, preferably of the two elements. In this way, good matching of the coefficient of thermal expansion from the connecting layer to the element is ensured so that the thermally induced stresses are low even in the sintered state of the measuring cell, and thus a high operational reliability is guaranteed.
In one embodiment, at least one of the two elements, on one surface forming the boundary for the flow channel, has a surface structure which acts as an antireflection layer and/or filter layer for the infrared radiation and/or as adhesion promoter for the connecting layer. The transmission capacity of the measuring cell for infrared radiation can thus be significantly increased, as a result of which a high signal level arises for the evaluation of the sensor signal. Furthermore, in this way, an optical filter can also be integrated into the measuring cell, by means of which filter the absorption bands of the fluid to be studied can be determined. Moreover, in this way, the adhesive force of the connecting layer can be increased; this is especially advantageous in high pressure operation. The surface structure can be formed by a nanostructure on the surface.
In one embodiment, the surface structure has a plurality of needles with a density of more than 10,000 needles per mm2, especially more than 100,000 needles per mm2, and preferably more than 500,000 needles per mm2. Such needle-shaped elements can be produced, for example, in single-crystalline silicon by self-masked dry etching. The surface structure which has been produced in this way according to its optical appearance is also referred to as “black silicon.”
In one embodiment, the needles have a length of more than 0.3 and less than 30 μm, especially more than 0.5 and less than 15 μm, and preferably more than 0.8 and less than 8 μm. Studies have shown that at this needle length, an especially favorable antireflection behavior for infrared radiation and/or a high adhesion to the connecting layer can be achieved.
In one embodiment, the element has the surface structure also in the region of the connecting layer. Here it is advantageous that the surface structure, alternatively or in addition to its action as antireflection layer, is also used as an adhesion promoter for the connection of the element and the connecting layer. In particular, the needles can penetrate into the structure of the connecting layer, and a large-area connecting layer is thus formed by the high surface: volume ratio of the needles.
In one exemplary embodiment, the two elements are formed from single-crystalline silicon. It has a relatively high coefficient of transmission for infrared radiation and moreover excellent mechanical properties. Moreover, the elements of single-crystalline silicon can be structured in almost any way with high precision in order to define flow channels, using known structuring methods from semiconductor technology, including dry chemical and wet chemical etching methods.
In one embodiment, at least one of the two elements has a thickness of more than 1 mm, especially more than 1.5 mm and preferably more than 2 mm. With such thick elements, especially in conjunction with the material single-crystalline silicon, measuring cells with high mechanical strength, which are thus also suitable for high pressure use, can be produced. The height of the flow channel which is defined by the thickness of the connecting layer can be between 50 and 500 μm, especially more than 80 μm and less than 400 μm, and preferably more than 100 μm and less than 300 μm.
The invention also relates to the structure of a measuring system for the infrared analysis of fluids with a measuring cell as described above, as well as an emitter and a sensor. The measuring system has an emitter for the infrared radiation, for example, a broadband-emitting heat radiator and/or a comparatively narrowband-emitting infrared light emitting diode, and a receiver for the infrared radiation. Emitters and receivers are preferably located on opposite sides of the measuring cell. In one unit, the receiver can have several detector elements by means of which the intensity of the radiation in different wavelength ranges can be measured. For this purpose, the receiver can have several entry windows via which radiation is incident on one of the detector elements. The windows and/or the detector elements can enable filtering.
Likewise, there can also be several emitters with a narrowband emission.
In one embodiment, the measuring system has an installation element with a receiving opening for the measuring cell. The measuring cell can be inserted into the receiving opening, in particular, the receiving opening can be adjusted with respect to its contour at least in sections to the outer contour of the measuring cell which can be, for example, polygonal and/or especially rectangular. The installation element has one entry opening and one exit opening for the fluid. The fluid can enter the flow channel of the measuring cell via the entry opening, and the fluid can emerge from the flow channel of the measuring cell via the exit opening.
The invention also relates to a method for producing a measuring cell, as described above. The connecting layer of glass-containing, especially glass-ceramic material, can be located between the two elements in the not yet sintered state, for example, in the form of a strip or a membrane. The connecting layer here is a green compact. The connecting layer can have calibration markings or openings by means of which the connecting layer can be calibrated to the carrier of the elements. The connecting layer can be present in the form of an unsintered foil and/or can be made from a mixture of borosilicate glass, quartz glass, and aluminum oxide as well as organic solvents.
The connecting layer is laminated as a green compact, for example, with a thickness of 300 μm under a pressure of 250 bar and at a temperature of 70° C., between the two wafers forming the elements.
The connecting layer under this loading flows through the plasticizers which have been introduced in the green compact and equalizes all spacing tolerances between the two elements so that the connecting layer is in contact with the elements over the entire wafer surface.
The elements on their surface facing the connecting layer are nanostructured, for example, with the formation of needles. The needles penetrate into the structure of the connecting layer. Then the sintering process takes place under the action of pressure and temperature. At a temperature starting from approximately 650° C., the glass frits are connected both to all components of the ceramic green compact and also to the needles of the wafers forming the elements. These needles are present in a nanostructure since in particular their lateral dimensions are very small. The application of pressure in the sintering process essentially prevents a lateral shrinkage of the connecting layer. The shrinkage of the connecting layer perpendicular to the surface of the wafers which form the elements can be about 50%.
Other advantages, features, and details of the invention will become apparent from the dependent claims and the following description in which several exemplary embodiments are described in detail with references to the drawings. The features referred to in the claims and in the specification may be critical for the invention individually or in any combination.
The flow channel 10 is formed between a first element 2 and a second element 4; the two elements are transparent to infrared radiation at least in sections and can consist of single-crystalline silicon Infrared radiation can be irradiated into the flow channel 10 via the first element 2, and the infrared radiation can emerge from the flow channel via the second element 4. The two elements 2, 4 are connected to one another fluid-tight with high mechanical strength by a connecting layer 6 located in between, consisting of a glass-containing material, especially of a sintered glass ceramic material.
The measuring system 8, on one side assigned to the first element 2 of the measuring cell 1, has an emitter 36 for infrared radiation. The emitter 36 can be, for example, a comparatively broadband-emitting heating element which in any case has a sufficient radiation intensity in the wavelength range of interest, for example, between 2 and 6 μm. The emitter 36 is preferably detachably fixed on the system housing 28 by means of a fastening element 40 which has a central passage opening 38. The emitter 36 radiates essentially centrally onto the first element 2 of the measuring cell 1.
On the side opposite the measuring cell 1, in the measuring system 8, there is a receiver 42 which is located opposite the outer surface of the second element 4 and preferably centrally with reference to the second element 4 and thus to the measuring cell 1. In the illustrated exemplary embodiment, the receiver 42 has a total of four detector elements 44, 46, of which
The structuring of the tape and/or of the silicon wafers ensures the removal of organics from the tape in the debinding process through added channels. The flatness defects of the elements 2, 4, especially in the production in a panel, are mitigated by the connecting layer 6, especially by its properties prior to the sintering process.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2009 051 853.3 | Oct 2009 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2010/005629 | 9/14/2010 | WO | 00 | 2/29/2012 |
