WO2001011348A2

WO2001011348A2 - Measuring device for measuring the dielectric constants of a mass of material

Info

Publication number: WO2001011348A2
Application number: PCT/EP2000/007805
Authority: WO
Inventors: Manfred Greschitz; Klaus Gruber; Franz Helminger; Franz Wolf
Original assignee: Infineon Technologies Ag
Priority date: 1999-08-10
Filing date: 2000-08-10
Publication date: 2001-02-15
Also published as: WO2001011348A3; DE19937745C1

Abstract

A semi-conductor sensor (1) has a capacitively sensitive surface (3) with a first reference area (12) and a test area (14). This is used to determine a reference value Cref,1 for the capacity of a reference mass of material applied to the first reference area (12) and a test value CTest for the capacity of the test mass of material (15) applied to the test area (14). A test dielectric constant εTest can be calculated and output using a reference dielectric constant εref,1, the reference value Cref,1 and the test value CTest.

Description

description

Measuring device for measuring the dielectric constant of a material accumulation

The invention relates to a measuring device for measuring the dielectric constant of a material accumulation.

The dielectric constant denotes a property of a material when it is used as the dielectric of a capacitor. In the case of a capacitor in which two unevenly charged bodies are arranged at a certain distance from one another, the capacitance of the capacitor depends on the size of the surface of the bodies facing one another, on their distance and on the dielectric between the bodies.

In the case of a plate capacitor with two capacitor plates, its capacity is given by the following relationship:

C = ε As

in which :

C capacitance of the two-plate capacitor

A area of the capacitor plate s plate distance ε dielectric constant = ε ₀ • ε _r ε ₀ electrical field constant = 8.85 • 10 ^{~ 12} F Im ε _r dielectric constant (material constant, _e.g. ε _r , _water =

81 / ε _r , air, dry, normal conditions ⁼ 1, 000594, _r , benzene ⁼ 2, 28, As can be seen from the formula given above, there is a relationship between the dielectric constant ε and the dielectric constant ε _r via the electric field constant ε ₀ . The determination of the dielectric constant ε therefore includes the determination of the dielectric constant ε _r . The invention thus relates not only to a measuring device for measuring the dielectric constant of a material accumulation but also to a measuring device for measuring the dielectric constant of a material accumulation. The invention also relates to methods for determining the dielectric constant of a material accumulation if the description describes a method for measuring the dielectric constant of a material accumulation. In the description and in the claims, the term “dielectric constant” is thus used as a synonym for the term “dielectric constant”, even if this is not always emphasized in detail.

It is known in the prior art to measure the dielectric constant of a material accumulation by the ratio of two capacitances of dielectrics, which are accommodated in a three-plate capacitor. The methods known in the prior art are very complex, since high accuracy is required with regard to the boundary conditions when using the dielectrics.

In DE 41 39 356 AI a plate measuring capacitor is described, which consists of three plates, two flat outer electrodes are at the same potential and the counter electrode is in between. The external electrodes serve to shield the alternating fields created for the measurement. DE 93 20 446 Ul describes a capacitive measuring cell for the contactless measurement of volume, density and composition of materials, for example plastics, which is used as a plate capacitor made of electrically conductive material in the form of one made of two side plates, two yokes and a bottom plate existing hollow cuboid is formed with an inner plate symmetrical to the side walls, which is fastened by electrically insulating spacers. The spacers completely fill the area of the electrical boundary field in the inner volume, so that a homogeneous electrical field acts in the two chambers.

FR 2 697 339 AI describes a method for measuring the dielectric constant of a powder, in which the powder and a liquid are introduced between two electrodes, which are arranged opposite one another at a fixed distance, and the dielectric constant of the composite system is determined empirically measures approximate equations into which the mixing ratio of powder and liquid is included.

It is an object of the invention to provide a method and a measuring device for determining the dielectric constant or the dielectric constant of a material accumulation, which allow simple evaluation. This object is achieved according to the invention by the subject matter of the independent claims. Advantageous further developments result from the respective subclaims.

For this purpose, the measuring device according to the invention for measuring the test dielectric constant of a test material collection has the following features: a semiconductor sensor with a capacitively sensitive surface, the capacitively sensitive surface having at least a first reference area and a test area, a detection circuit which is designed such that a first reference value for the capacity of a first reference material accumulation applied to the first reference area and a test value for the capacity of the test material accumulation applied to the test area can be determined, an evaluation circuit which is designed such that a first reference dielectric constant corresponding to the first reference value can be stored and that a test dielectric constant can be calculated and output from the first reference dielectric constant, from the first reference value and from the test value.

With the device according to the invention, a particularly advantageous use of a semiconductor sensor with a capacitively sensitive surface is possible. The use of the semiconductor sensor permits a particularly simple embodiment of the measuring device according to the invention, since a semiconductor sensor with a capacitively sensitive surface allows the dielectric to be evaluated in a precise manner Properties of a substance applied to the surface allowed.

The method according to the invention, which is carried out with the measuring device according to the invention, provides for the following steps:

Applying a first reference material accumulation to the first reference area and storing a first reference dielectric constant of the first reference material accumulation in the evaluation circuit, applying a test material accumulation to the test area, the detection circuit being caused to make the capacitance of the first reference material accumulation as the first reference value and the capacitance of the test material accumulation to be determined as a test value, and the evaluation circuit is further prompted to determine a test dielectric constant from the first reference dielectric constant, from the first reference value and from the test value, in particular by means of a three-sentence calculation. The test dielectric constant is obtained by multiplying the reference dielectric constant by the quotient of the test value and reference value.

Non-linear methods can also be used to determine the test dielectric constant.

With the method according to the invention, the test dielectric constant of a test material accumulation can be determined particularly easily, since only a certain amount of a test material accumulation has to be applied to an area of the capacitively sensitive surface of the semiconductor sensor. By pressing the evaluation circuit the test dielectric constant is output immediately and without further manual actuation.

Furthermore, the use of a semiconductor sensor with a capacitively sensitive surface is particularly advantageous in the measuring device and method in accordance with the invention because semiconductor sensors are generally designed in such a way that the capacitively sensitive surface has a large number of individually scannable capacitively sensitive surface areas. In this way, a certain number of surface areas can be combined in such a way that the reference area is formed, while another plurality of capacitively sensitive surface areas form the test area. The object on which the invention is based can thus be achieved with a single sensor module.

In a further development of the invention, the capacitively sensitive surface of the semiconductor sensor has a second reference area, the detection circuit being designed such that a second reference value for the

Capacity of a second reference material accumulation applied to the second reference area can be determined. The evaluation circuit is designed such that a second reference dielectric constant assigned to the second reference value can be stored and that a test dielectric constant can be calculated and calculated from the first dielectric constant, from the second dielectric constant, from the first reference value, from the second reference value and from the test value can be spent. In the method according to the invention, such

Measuring device causes the evaluation circuit to determine the test dielectric constant by means of an interpolation method from the first reference Dielectric constants, from the second reference dielectric constant, from the first reference value, from the second reference value and from the test value. With the configuration of the measuring device according to the invention described above, the method according to the invention allows a particularly precise determination of the dielectric constant of a material accumulation on which the measurement is based. Process tolerances can be eliminated particularly easily by using two reference values in connection with an interpolation method. Nonlinear calculation methods can also be used.

Especially when using a semiconductor sensor with a capacitively sensitive surface, it is particularly advantageous if the capacitances of the material accumulations applied to the semiconductor sensor can be determined selectively at those locations that are covered by the material accumulations. This can be achieved in a simple manner in the case of semiconductor sensors whose capacitively sensitive surface is constructed as a matrix of numerous capacitively sensitive individual sensors, each individual sensor being able to be addressed individually via row and column lines. This means that all individual sensors can be scanned individually during a measurement, only those

Measurement results from individual sensors are used for evaluation, on which a state that has changed in relation to the environment appears.

In an advantageous development, at least one vessel wall is provided on the capacitively sensitive surface of the semiconductor sensor in each case in the area around a reference area and / or around the test area a closable vessel can be formed. In particular, it is also provided that an open vessel is formed in the area around the test area. With such a measuring device, the method according to the invention, in which the reference material accumulation is chosen as the liquid, can be carried out particularly simply and reliably. Then the liquid is poured into the vessel formed by the vessel walls and held there. According to the invention, the reference material collection can be chosen as air or as a solid. The material to be tested is advantageously applied to the open vessel on the test area before a measurement is started.

The method according to the invention with the device according to the invention also includes that the evaluation circuit outputs a test dielectric constant calculated from the test dielectric constant, which results from the evaluation of the sensor measurements.

In the invention, a capacitively sensitive surface sensor is loaded with reference materials such as air (ε _r = 1) or water (ε _r = 81) and with the material to be examined. The size of the available capacities is measured and output as a digital value. Existing

Process tolerances can be eliminated using the reference materials. This has the advantage that an inexpensive sensor can be used to determine a capacitance value. Furthermore, the measured value is output directly, whereby a simple and compact modular design is made possible. The invention is illustrated in more detail in the drawing using an exemplary embodiment.

FIG. 1 shows a cross section through a semiconductor sensor according to the invention of a measuring device according to the invention,

FIG. 2 shows a top view of the semiconductor sensor from FIG. 1,

FIG. 3 shows a schematic block diagram of a measuring device according to the invention with the semiconductor sensor from FIGS. 1 and 2 and

FIG. 4 shows a diagram which illustrates the evaluation of a measurement with the measuring device from FIG. 3.

Figure 1 and Figure 2 show a semiconductor sensor 1. Figure 2 shows a plan view of the semiconductor sensor 1, while Figure 1 illustrates a cross section along a line A-A shown in Figure 2 through the semiconductor sensor 1.

The semiconductor sensor 1 has a semiconductor substrate 2, which has a rectangular outline in the plan view according to FIG. 2. The surface of the semiconductor substrate 2 is provided with a capacitively sensitive surface 3, which is divided into a large number of capacitively sensitive surface areas, which are not shown in detail in this view. Each of the capacitively sensitive surface areas can be scanned via two electrical lines, which are combined to form a connection line bundle 4, which leads away from an end face of the semiconductor substrate 2. Above the capacitively sensitive surface 3 and along its outer contour, a circumferential vertical border wall 5 is provided, which is closed on all sides. A first delimitation wall 6 and a second delimitation wall 7 are arranged within the enclosure wall 5 and connect the two longitudinal walls of the enclosure wall 5 with one another, so that a first reference space 8, a second reference space 9 and a test space 10 on the surface 3 are tightly delimited from one another as best seen in Figure 1.

The first reference space 8 and the second reference space 9 are each closed by a ceiling wall 11. The first reference space 8 is filled with nitrogen, while the second reference space 9 is filled with distilled water. A first reference area 12 of the capacitively sensitive surface 3, which is delimited by the bordering wall 5 and by the first delimitation wall 6, is thus completely exposed to nitrogen. A second reference area 13 of the capacitively sensitive surface 3, which is delimited by the border wall 5, by the first delimitation wall 6 and by the second delimitation wall 7, is completely wetted with distilled water.

A test area 14 of the capacitively sensitive surface 3 is delimited by the border wall 5 and by the second delimitation wall 7. Its surface is in contact with a test material collection 15 which has been introduced into the test space 10. As can be seen particularly clearly in FIG. 2, the test material collection 15 does not cover the entire surface of the test area 14, but only that part which is located within the outline 16 of the test material collection 15. FIG. 3 shows a schematic block diagram of a measuring device 20 according to the invention, which contains the semiconductor sensor 1 from FIG. 1 and FIG. 2.

The measuring device 20 also includes a detection circuit 21 which is connected to the semiconductor sensor 1 via the bundle of connecting lines 4. Furthermore, an input keyboard 22 is provided on the detection circuit 21, via which a first reference dielectric constant ε _ref , ι and a second reference dielectric constant ε _ref can be entered in the detection circuit 21.

The measuring device 20 is also provided with an evaluation circuit 23 which is connected to a display unit 24.

To carry out the method according to the invention, the procedure for determining the dielectric constant of the test material collection 15 is as follows.

First, the test material collection 15 is introduced into the test space 10, so that the test area 14 of the capacitively sensitive surface 3 of the semiconductor substrate 2 is covered with the test material collection 15.

The first reference dielectric constant ε _ref , ι of the nitrogen located in the first reference space 8 and the second reference dielectric constant ε _ref , of the distilled water located in the second reference space 9 are then entered into the measuring device 20, specifically via the input keyboard 22. The detection circuit 21 passes these values ε _ref; ι and ε _ref , ₂ on to the evaluation circuit 23, where they are stored.

Thereafter, the detection circuit 21 is caused to measure the capacitance of the nitrogen located in the first reference space 8 and of the distilled water located in the second reference space 9 and to pass them on to the evaluation circuit 23 as values C _ret , ι and C _rer , ₂ . Finally, the capacitance C _{test is determined} at those points in the test area 14 which are covered with the test material accumulation 15. Only those capacitively sensitive surface areas of the test area 14 that are located within the outline 16 according to FIG. 2 are used. The other capacitively sensitive surface areas of the test area 14 are detected by the detection circuit 21, but are not used to calculate the value C _Test , since their capacity differs significantly from the capacity of the test material collection 15.

Finally, the test dielectric constant ε _{test is determined} by the evaluation circuit 23 and output as a digital value via the display unit 24. To determine the test dielectric constant ε _test , the procedure according to FIG. 4 is followed, according to which a straight line is laid through the points determined by C _ref , ι and ε _ref , ι or by C _re f, 2 and ε _re f, 2 and the to C _Tes t associated value ε _Tes t with the help of the beam set is calculated. This procedure is also known as the so-called linear interpolation method.

The test dielectric constant of the test material accumulation 15 can be determined directly from the test dielectric constant ε _test , which can be used to draw a conclusion about the underlying material and its properties.

With the exemplary embodiments shown in FIGS. 1 to 3, measurements can also be carried out if either only the first reference space 8 or only the second reference space 9 is used to calculate the test

Dielectric constant ε _Tes t of the test material accumulation be used 15th In this case, a simple rule of three is then sufficient to determine the test dielectric constant ε _{Te based} on the reference dielectric constant ε _ref , ι, the measured capacitance Cref i and the measured capacitance C _Tes t.

Claims

claims

1. Measuring device (20) for measuring the test dielectric constant of a test material collection (15), which has the following features: a semiconductor sensor (1) with a capacitively sensitive surface (3), the capacitively sensitive surface (3) having at least a first reference range (12) and a test area (14), a detection circuit (21) which is designed such that a first reference value C _ref , ι for the capacity of a first reference material collection applied to the first reference area (12) and a test value C _Tes t for the capacity of the on the

Test area (14) applied test material accumulation (15) can be determined, an evaluation circuit which is formed such that a first reference value C _ref, ι corresponding first reference dielectric constant ε _ref, ι can be stored and that from the first reference dielectric constant ε _re f, ι, from the first reference value C _re f, ι and from the test value C _test the test dielectric constant £ τ _{est can be} calculated and output.

2. Measuring device according to one of the preceding claims, characterized in that the capacitively sensitive surface (14) has a second reference area (13), the detection circuit being designed such that a second reference value C _re f, 2 for the capacitance one to the second reference area (13) coated second reference material collection is determined, and wherein the evaluation circuit (23) is formed so that a second reference value C _ref, ₂ assigned second reference dielectric constant ε _ref, ₂ can be stored and that from the first reference dielectric constant ε _r ef, ι # from the second reference dielectric constant ε _re f, 2 from the first reference value C _re f, ir from the second reference value C _re f, 2 and from the test value C _Test the test - dielectric constant ε _Tes t is predictable and can be output.

3. Measuring device according to claim 1 or claim 2, characterized in that the semiconductor sensor (1) is designed such that the capacitively sensitive surface (3) has a plurality of individually scannable capacitively sensitive surface areas.

4. Measuring device according to claim 3, characterized in that the capacitances of the first reference material accumulation applied to the first reference region (12), the second reference material accumulation applied to the second reference region (13) and / or the test material accumulation (15) applied to the test region (14) ) can be determined selectively at those points of the capacitively sensitive surface (3) which are covered by the first reference material collection, by the second reference material collection and / or by the test material collection (15).

5. Measuring device according to one of the preceding claims, characterized in that the semiconductor sensor (1) on the capacitively sensitive

Surface (3) in each case in the area around the first reference area (12), around the second reference area (13) and / or around the test area (14) vessel walls (5,

6, 7).

Measuring device according to claim 5, characterized in that In the area around the first reference area (12) and / or around the second reference area (13), a closable vessel (8, 9) is formed.

7. Measuring device according to claim 5 or claim 6, characterized in that an open vessel (10) is formed in the area around the test area (14).

8. Measuring device according to one of the preceding claims, characterized in that the evaluation circuit (23) is designed so that from the test-dielectric constant ε _Tes t a test Dielek- trizitätszahl ε _r, τest predictable and can be output.

9. A method for determining the test dielectric constant ε _{test of} a test material accumulation (15), in particular a liquid, which has the following steps:

Providing a measuring device (20) according to one of claims 2 to 8,

Applying a first reference material collection to the first reference area (12) and storing a first reference dielectric constant ε _ref , ι the first reference material collection in the evaluation circuit (23),

Applying the test material accumulation (15) to the test area (14), whereby the detection circuit (21) is caused to determine the capacity of the first reference material accumulation as the first reference value C _re f, ι and the capacity of the test material accumulation (15) as the test value C _Test determine z, and wherein the evaluation circuit (23) is caused to determine the test dielectric constant ε _test from the first reference dielectric constant ε _ref , i _/ from the first reference value C _re f, ι and from the test value C _Test z, and in particular using a linear three-rate calculation.

10. A method for determining the dielectric constant ε _Tes t-test of a test material accumulation (15), in particular a liquid, comprising the following steps: - provision of the measuring device according to one of claims 2 to 8,

Applying a first reference material accumulation to the first reference area (12) and storing a first reference dielectric constant ε _ref , ι the first reference material accumulation in the evaluation circuit (23),

Applying a second reference material collection to the second reference region (13) and storing a second reference dielectric constant ε _ref , _{2 of} the second reference material collection in the evaluation circuit (23),

Applying a test material accumulation (15) to the test area (14), wherein said detection circuit (23) is caused, the capacitance of the first reference accumulation of material as the first reference value C _re f, i / _ref, the capacity of the second reference material accumulation as a second reference value C, ι and to determine the capacity of the test material accumulation (15) as test value C _Tes t, and whereby the evaluation circuit (23) is caused to carry out the following steps:

Determine the test dielectric constant ε _test from the first reference dielectric constant ε _ref , i _/ from the second reference dielectric constant _re , 2 / from the first reference value C _re f, ι, from the second reference value C _re f, 2 and from Test value C _test / and in particular by means of a linear interpolation method.

11. A method for determining the test dielectric constant ε _{test of} a test material accumulation according to claim 9 or claim 10, characterized in that the first collection of reference material and / or the second

Reference material collection is selected as the liquid.

12. A method for determining the test dielectric constant ε of a test material collection according to one of claims 9 to 11, characterized in that the first reference material collection and / or the second reference material collection is selected as the gas.

13. A method for determining the test dielectric constant ε of a test material collection according to one of claims 9 to 12, characterized in that the evaluation circuit (23) is caused to test the test dielectric constant ε _test a test dielectric number ε _r , τest to calculate and spend.