阅读说明：本技术 电容式传感器 (Capacitive sensor ) 是由 M·普拉斯 于 2020-02-19 设计创作，主要内容包括：本发明涉及一种电容式传感器,包括基板(14)和电极结构(10),电极结构(10)包括至少第一电极(11)、第二电极(12)以及布置在第一电极(11)和第二电极(12)之间的感测层(15)。该传感器还包括测量电路(40,500,600),该测量电路被配置为通过在第一测量阶段向第一电极(11)和第二电极(12)施加包括第一电极的第一电位和第二电极的第一电位的第一对电位并且通过在第二测量阶段向第一电极(11)和第二电极(12)施加包括第一电极的第二电位和第二电极的第二电位的第二对电位来测量电极结构的电容。第二电极的第一电位与第二电极的第二电位彼此不同。另一方面涉及一种用于电容感测的方法。(The invention relates to a capacitive sensor comprising a substrate (14) and an electrode structure (10), the electrode structure (10) comprising at least a first electrode (11), a second electrode (12) and a sensing layer (15) arranged between the first electrode (11) and the second electrode (12). The sensor further comprises a measurement circuit (40, 500, 600) configured to measure the capacitance of the electrode structure by applying a first pair of potentials comprising a first potential of the first electrode and a first potential of the second electrode to the first electrode (11) and the second electrode (12) in a first measurement phase and by applying a second pair of potentials comprising a second potential of the first electrode and a second potential of the second electrode to the first electrode (11) and the second electrode (12) in a second measurement phase. The first potential of the second electrode and the second potential of the second electrode are different from each other. Another aspect relates to a method for capacitive sensing.)

1. A capacitive sensor comprising

A substrate (14);

an electrode structure (10) comprising

At least a first electrode (11) and a second electrode (12); and

a sensing layer (15) arranged between the first electrode (11) and the second electrode (12); and

a measurement circuit (40, 500, 600) configured to

Measuring the capacitance of the electrode structure (10) by

Applying a first pair of potentials comprising a first potential of the first electrode and a first potential of the second electrode to the first electrode (11) and the second electrode (12) in a first measurement phase; and

applying a second pair of potentials comprising a second potential of the first electrode and a second potential of the second electrode to the first electrode (11) and the second electrode (12) in a second measurement phase;

it is characterized in that

The first potential of the second electrode (12) and the second potential of the second electrode (12) are different from each other;

wherein

Applying a first pair of potentials and a second pair of potentials such that

0＜＝(V_A1-V_A2)＜＝(V_B2-V_B1)＊C_BE/C_AEOr is or

(V_B2-V_B1)＊C_BE/C_AE＜＝(V_A1-V_A2)＜＝0；

Wherein

V_A1Is the first potential of the first electrode in the first measurement phase;

V_A2is the second potential of the first electrode in the second measurement phase;

V_B1is the first potential of the second electrode in the first measurement phase;

V_B2is the second potential of the second electrode in the second measurement phase;

C_AEis a capacitance between the first electrode and a dummy electrode disposed on a surface of the sensing layer; and

C_BEis the capacitance between the second electrode and a dummy electrode arranged on the surface of the sensing layer.

2. The sensor according to claim 1, wherein the first pair of potentials and the second pair of potentials are selected such that a leakage current between the surface (31) of the sensing layer (15) and an electrical structure (50) surrounding the surface (31) of the sensing layer (15) is minimized, in particular in case the surface (31) of the sensing layer (15) is contaminated or in case condensation occurs on the surface (31) of the sensing layer (15).

3. A sensor according to claim 1 or claim 2, wherein

Applying a first pair of potentials and a second pair of potentials such that

0＜＝(V_A1-V_A2)＜＝(V_B2-V_B1)＊C_BE/C_AE(ii) a Or

(V_B2-V_B1)＊C_BE/C_AE＜＝(V_A1-V_A2)＜0。

4. The sensor of any one of the preceding claims,

wherein a first pair of potentials and a second pair of potentials are applied such that

(V_A1-V_A2)＝(V_B2-V_B1)＊C_BE/C_AE。

5. The sensor of any one of the preceding claims,

wherein the average potential of the first pair of potentials is the same as the average potential of the second pair of potentials.

6. The sensor of any preceding claim, wherein the measurement circuitry (40, 700, 800) is configured to

The resulting charge difference between the first and second measurement phases is sensed at the second electrode (12).

7. A sensor according to any preceding claim, wherein the measurement circuitry comprises switched capacitor circuitry and/or switched current circuitry for generating the first and second pairs of potentials and/or for sensing a resulting charge difference.

8. The sensor of claim 6 or 7, wherein the measurement circuitry (40, 700, 800) is configured to

Transferring the resulting charge difference to a reference capacitor (C)_Int)；

Measuring reference capacitor (C)_Int) The resulting voltage at (c); and

the capacitance of the electrode structure is determined from the resulting voltage.

9. The sensor according to any of the preceding claims 6 to 8, wherein the measurement circuitry (40, 700, 800) is configured such that the resulting charge difference increases in case of contamination of the surface of the sensing layer and/or condensation of liquid, in particular water.

10. The sensor of any one of the preceding claims 6 to 9, wherein

The measurement circuit (40, 700, 800) comprises an offset capacitor (Co);

the measurement circuit (40, 700, 800) is configured to subtract the offset charge from the resulting charge difference.

11. The sensor of any one of the preceding claims 6 to 10, wherein the measurement circuit (40, 700, 800) comprises an integrator (710), in particular a switched capacitor amplifier, the integrator (710) being configured to integrate the resulting charge difference.

12. The sensor of any one of the preceding claims,

wherein

The first potential of the first electrode is the same as the second potential of the second electrode; and

the first potential of the second electrode is the same as the second potential of the first electrode; and in particular wherein

The first potential of the first electrode and the second potential of the second electrode are power supply voltage potentials; and

the first potential of the second electrode and the second potential of the first electrode are ground potentials; or in particular wherein

The first potential of the first electrode and the second potential of the second electrode are ground potentials; and

the first potential of the second electrode and the second potential of the first electrode are power supply voltage potentials.

13. The sensor of any one of the preceding claims, wherein the sensor comprises

A first metal layer (21) comprising a first electrode (11) and a second electrode (12); and

a second metal layer (22) comprising a shielding structure (22).

14. The sensor of claim 13, wherein the shielding structure (22) is electrically coupled to

A fixed potential, in particular ground potential or supply potential;

a first electrode (11); or

A second electrode (12).

15. The sensor of any one of the preceding claims, wherein the sensor is a capacitive humidity sensor, a capacitive gas sensor, or a capacitive particulate matter sensor.

16. A method for performing capacitance measurements, the method comprising

Providing an electrode structure (10), the electrode structure (10) comprising at least a first electrode (11) and a second electrode (12) and a sensing layer (15) arranged between the first electrode (11) and the second electrode (12);

measuring the capacitance of an electrode structure by

Applying a first pair of potentials comprising a first potential of the first electrode and a first potential of the second electrode to the first electrode (11) and the second electrode (12) in a first measurement phase; and

applying a second pair of potentials comprising a second potential of the first electrode and a second potential of the second electrode to the first electrode (11) and the second electrode (12) in a second measurement phase;

it is characterized in that

The first potential of the second electrode (12) and the second potential of the second electrode (12) are different from each other;

wherein a first pair of potentials and a second pair of potentials are applied such that

0＜＝(V_A1-V_A2)＜＝(V_B2-V_B1)＊C_BE/C_AEOr is or

(V_B2-V_B1)＊C_BE/C_AE＜＝(V_A1-V_A2)＜＝0；

Wherein

V_A1Is the first potential of the first electrode in the first measurement phase;

V_A2is the second potential of the first electrode in the second measurement phase;

V_B1is the first potential of the second electrode in the first measurement phase;

V_B2is the second potential of the second electrode in the second measurement phase;

C_AEis a capacitance between the first electrode and a dummy electrode disposed on a surface of the sensing layer; and

C_BEis the capacitance between the second electrode and a dummy electrode arranged on the surface of the sensing layer.

Technical Field

The present disclosure relates to a capacitive sensor, in particular a capacitive humidity sensor, a capacitive gas sensor and a capacitive particulate matter sensor. Further aspects of the present disclosure relate to a method for capacitive sensing, in particular for capacitive humidity sensing.

Background

Capacitive sensors may be implemented, for example, as humidity sensors, particularly as sensors for sensing the relative humidity of ambient air, widely used in environmental sensing applications.

One type of humidity sensor is a capacitive humidity sensor, which comprises one or more humidity sensitive layers, in particular polymer layers, arranged between two electrodes and interacting with the ambient air. The measured capacity between the two electrodes is related to the humidity of the ambient air, thus establishing a humidity measurement.

One problem with capacitive humidity sensors is that the environment of the sensing layer may not be well defined. In particular, the impedance of the environment may change in an uncontrolled manner. As an example, in case water or another liquid condenses on the humidity sensitive layer or the humidity sensitive layer is contaminated by particles, the measured capacity may drop below 100%. Such saturation events can lead to erroneous measurements. In particular, the corresponding sensor may not be able to distinguish between condensation scenarios and scenarios where the relative humidity is indeed slightly below 100%.

Disclosure of Invention

It is therefore an object of the present invention to provide a capacitive sensor with an improved sensitivity range, in particular a humidity sensor which is capable of detecting condensation scenes.

According to an embodiment of a first aspect of the present invention, there is provided a capacitive humidity sensor comprising a substrate and an electrode structure. The electrode structure comprises at least a first electrode and a second electrode and a sensing layer arranged between the first electrode and the second electrode. The sensing layer may in particular have a humidity sensitive dielectric constant and may therefore be implemented as a humidity sensitive layer. The sensor further comprises a measurement circuit configured to measure the capacitance of the electrode structure by applying a first pair of potentials to the first electrode and the second electrode in a first measurement phase. The first pair of potentials includes a first potential of the first electrode and a first potential of the second electrode. The measurement circuit is further configured to apply a second pair of potentials to the first electrode and the second electrode in a second measurement phase. The second pair of potentials includes a second potential of the first electrode and a second potential of the second electrode. An embodiment of the first aspect is particularly characterized in that the first potential of the second electrode and the second potential of the second electrode are different from each other. According to an embodiment of the first aspect, the first pair of potentials and the second pair of potentials are applied such that they comply with at least one of the following conditions:

0＜＝(V_A1-V_A2)＜＝(V_B2-V_B1)*C_EE/C_AE(ii) a (inequality 1)

Or

(V_B2-V_B1)＊C_BE/C_AE＜＝(V_A1-V_A2) 0. (inequality 2)

In the above formula/condition, V_A1Representing a first potential, V, of the first electrode during a first measuring phase_A2Representing a second potential of the first electrode during a second measurement phase. In addition, V_B1A first potential, V, representing the second electrode in a first measuring phase_B2Representing a second potential of the second electrode during a second measurement phase. C_AEIs the mutual capacitance between the first electrode and a dummy electrode arranged on the surface of the sensing layer, and C_BEIs the capacitance between the second electrode and a dummy electrode arranged on the surface of the sensing layer.

Such implemented capacitive sensors are configured to measure the capacitance of their electrode structure by means of a two-phase measurement. The two-phase measurement includes a first measurement phase and a second measurement phase during which a specific set of potentials is applied to the first electrode and the second electrode. In particular, the first potential of the second electrode and the second potential of the second electrode are different from each other. In other words, the potential of the second electrode is changed between the first measurement phase and the second measurement phase. This is in contrast to prior art sensors in which the potential of the second electrode is kept constant to avoid measuring the parasitic capacitance between the second electrode and ground or other reference potential. Such an implemented sensor offers the advantage that different potentials of the second electrode can be used advantageously to adjust the sensor function for a specific measurement scenario.

In particular, the applicant's studies have shown that by varying the potential of the second electrode between two measurement phases, a sensor according to an embodiment of the invention can be designed in the following way: condensation on the surface of the sensing layer and/or contamination of the sensing layer does not lead to erroneous measurements.

The virtual electrode may be considered as defining and/or measuring a capacitance C_AEAnd C_BEOr more specifically quotient C_AE/C_BEThe electrode of (1). The dummy electrodes are disposed on a surface of the sensing layer. The surface of the sensing layer is the area of the sensing layer adjacent to the ambient air. In other words, the surface of the sensing layer provides an interface with and interacts with ambient air.

It should be noted that the virtual electrodes do not actually exist during the sensing operation of the sensor. According to an embodiment, a virtual electrode may be applied on a surface of a sensing layer of a sample sensor to determine a quotient C_AE/C_BEOr it can be used to determine the quotient C by means of simulation_AE/C_BE。

Commercial C_BE/C_AECan be determined in a number of different ways or methods generally known to those skilled in the art.

According to an embodiment, quotient C_BE/C_AECan be determined by simulation according to the Finite Element Method (FEM). For such simulations, commercially available programs may be used, e.g., ComsolAnd (3) software.

According to an embodiment, the FEM simulation derives a quotient C by simulating a geometry of an electrode structure comprising a first electrode, a second electrode and a virtual electrode_BE/C_AE. According to an embodiment, quotient C_BE/C_AEDepending only on the geometry of the electrode structures, it is assumed that the dielectric constant of the dielectric material between the electrode structures is homogenous.

In the case of a symmetrical electrode structure, the quotient C_BE/C_AE＝1。

According to other embodimentsExample, quotient C_BE/C_AECan be determined by measurement, e.g. by using a capacitance formed by C_AEAnd C_BEMeasurement of the resulting capacitive divider. For such measurements, the virtual electrodes may be provided as real electrodes or in other words physically provided on the surface of the sensing layer, e.g. by applying a conductive layer on the surface of the sensing layer.

It should be noted that, in order to ensure that the above-mentioned conditions (inequalities 1 and 2) are satisfied, according to an embodiment, it is not necessary to accurately determine the quotient C_BE/C_AE. Instead, a rough estimation of the quotient can be performed and then the first and second pairs of potentials are selected in the inequality as mentioned above in the following way: the inequality is also satisfied in the worst case of the rough estimation.

According to an embodiment, the geometry of the electrode structure remains constant and does not change during the measurement.

According to an embodiment, the measured capacitance depends on a property or characteristic of the sensing layer, in particular on a property or characteristic of a material of the sensing layer, in particular on a dielectric constant of the sensing layer.

According to an embodiment, the first pair of potentials and the second pair of potentials are selected such that a leakage current between the surface of the sensing layer and the electrical structure surrounding the surface of the sensing layer is reduced, in particular minimized, in particular in case the surface of the sensing layer is contaminated or in case condensation occurs on the surface of the sensing layer.

Such an electrical structure may generally be any electrical structure surrounding the sensing layer. The electrical structure may in particular be an electrical housing and/or a wire or a circuit of the sensor arranged near the sensing layer.

According to an embodiment, the intermediate potential of the first electrode and/or the second electrode between the first measurement phase and the second measurement phase may have any arbitrary shape, in particular a rectangular shape or a sinusoidal shape.

According to an embodiment, the first pair of potentials and the second pair of potentials are applied such that they comply with at least one of the following conditions:

0＜＝(V_A1-V_A2)＜＝(V_B2-V_B1)*C_EE/C_AE(ii) a (inequality 3)

Or

(V_B2-V_B1)*C_BE/V_B1)/C_AE＜＝(V_A1-V_A2) Is less than 0. (inequality 4)

According to such an embodiment, the first potential of the first electrode and the second potential of the first electrode are also different from each other. This increases the charge difference generated between the first and second measurement phases.

According to an embodiment, the first pair of potentials and the second pair of potentials are applied such that they meet the following condition:

(V_A1-V_A2)＜＝(V_B2-V_B1)*C_EE/C_AE

according to an embodiment, the first potential of the first electrode and the second potential of the first electrode are different from each other, and the first potential of the second electrode and the second potential of the second electrode are different from each other.

By changing the potentials of the two electrodes, the sensing signal, in particular the sensed current, of the measuring circuit can be increased.

According to an embodiment, the average potential of the first pair of potentials is the same as the average potential of the second pair of potentials. This embodiment is particularly suitable for sensors having a symmetrical electrode structure, i.e. an electrode structure in which the first and second electrodes are symmetrically arranged with respect to the sensing layer and thus have the same distance to the sensing layer. Thus, the capacitance C between the first electrode and the environment_AEAnd a capacitance C between the second electrode and the environment_BEHave the same value.

Embodiments of the present invention are based on the insight of the inventors of the present invention that in case of condensation the impedance between the surface of the sensing layer and the external electrical structure around the surface of the sensing layer is no longer infinite and this leads to a current loss via this impedance. This current loss therefore reduces the current in the second electrode, and therefore, without countermeasures, the sensor may not be able to distinguish between condensation and humidity scenarios where the humidity is below 100%.

The sensor according to embodiments of the present invention avoids current loss to external electrical structures in case of condensation or other contamination of the sensing layer surface by intelligent selection of potential pairs. This facilitates the measurement circuit to distinguish between the two scenarios.

According to an embodiment, the measurement circuit may particularly be configured to sense a charge difference generated at the second electrode between the first measurement phase and the second measurement phase. Thus, the measurement circuit evaluates the charge difference accumulated between the first and second measurement phases. In other words, the measurement circuit compares the initial state (the state of charge at the end of the first measurement phase) with the final state (the state of charge at the end of the second measurement phase). However, the operation of such a charging cycle need not be considered.

As mentioned above, according to an embodiment, the total capacitance between the first electrode and the second electrode is larger in case of coagulation than in case of no coagulation. Thus, in case of condensation, the resulting charge difference measured by the measurement circuit according to an embodiment of the invention increases.

According to an embodiment, the measurement circuit is configured to transfer the resulting charge difference to the reference capacitor and to measure a resulting voltage at the reference capacitor. According to an embodiment, the measurement circuit is further configured to determine the capacitance of the sensing layer from the resulting voltage.

This is an efficient and reliable way of converting the resulting charge difference into a voltage that can be measured. Since the capacitance of the reference capacitor is known, the capacitance of the sensing layer can be derived from the reference capacitance, the resulting voltage and the potentials applied during the first and second measurement phases.

According to an embodiment, the measurement circuit comprises an offset capacitor and the measurement circuit is configured to subtract the offset charge from the resulting charge difference.

Such an embodiment may be used to transfer charge to a reference capacitor that is symmetric to 0.

According to an embodiment, the measurement circuit comprises an integrator, in particular a switched capacitor amplifier. The switched capacitor amplifier is configured to integrate the resulting charge difference, or in other words, the current flowing through the second electrode, when switching from the first measurement phase to the second measurement phase.

According to an embodiment, the integrator, in particular the switched capacitor amplifier, is implemented as an operational amplifier. Such a switched capacitor amplifier circuit can be realized and manufactured in an efficient manner.

According to an embodiment, the first potential of the first electrode is the same as the second potential of the second electrode, and the second potential of the first electrode is the same as the first potential of the second electrode.

Such a simplified set of potentials with only two different voltages facilitates efficient design and manufacturing of the measurement circuit.

In particular, the first potential of the first electrode and the second potential of the second electrode are power supply voltage potentials, the first potential of the second electrode and the second potential of the first electrode are ground potentials or the first potential of the first electrode and the second potential of the second electrode are ground potentials, and the first potential of the second electrode and the second potential of the first electrode are power supply voltage potentials.

Such a simplified set of potentials facilitates efficient design and manufacturing of the measurement circuit, in particular because the ground and supply voltage potentials of the corresponding integrated circuit can be used and no further voltage generation or voltage conversion is required.

According to an embodiment, the sensor comprises a first metal layer comprising the first electrode and the second electrode and a second metal layer comprising the shielding structure. The shielding structure may comprise a plurality of shielding electrodes.

The shielding structure performs shielding of an electromagnetic field. Furthermore, such a shielding structure may provide an etch stop and thus facilitate efficient manufacturing of the sensor.

According to an embodiment, the shielding structure is electrically coupled to a ground potential.

According to such an embodiment, the parasitic capacitance between the second electrode and ground is measured.

According to an embodiment, the shielding structure is electrically coupled to the first electrode.

According to such an embodiment, the parasitic capacitance between the second electrode and ground is measured as a factor of two.

According to an embodiment, the shielding structure is electrically coupled to the second electrode.

According to such an embodiment, the parasitic capacitance between the second electrode and ground is not measured.

According to an embodiment of another aspect of the invention, a method for performing capacitance measurements is provided. The method comprises the step of providing an electrode structure comprising at least a first electrode, a second electrode and a sensing layer arranged between the first electrode and the second electrode. The method comprises the further step of measuring the capacitance of the electrode structure by applying a first pair of potentials to the first and second electrodes in a first measurement phase and by applying a second pair of potentials to the first and second electrodes in a second measurement phase.

The first pair of potentials includes a first potential of the first electrode and a first potential of the second electrode. The second pair of potentials includes a second potential of the first electrode and a second potential of the second electrode. The first potential of the second electrode and the second potential of the second electrode are different from each other.

According to an embodiment, the method further comprises sensing a resulting charge difference between the first measurement phase and the second measurement phase at the second electrode and transferring the resulting charge difference to the reference capacitor. Furthermore, the method may comprise the step of measuring a resulting voltage at the reference capacitor and determining the capacitance of the electrode structure from the resulting voltage.

Further advantageous embodiments are listed in the dependent claims and in the following description.

Drawings

The present invention will be better understood and objects other than those set forth above will become apparent from the following detailed description thereof. This description makes reference to the accompanying drawings, in which:

FIG. 1 illustrates a cross-sectional view of a capacitive humidity sensor in accordance with an embodiment of the present invention;

FIG. 2 illustrates a partial cross-sectional view of the humidity sensor of FIG. 1 including a schematic of capacitances involved in a measurement method according to an embodiment of the present invention;

FIG. 3 is a corresponding electrical equivalent circuit schematic of the partial cross-sectional view of FIG. 2;

FIG. 4 shows an electrical equivalent circuit representing a "normal" measurement scenario, without significant contamination or condensation of the surface of the sensing layer;

FIG. 5 shows an electrical equivalent circuit representing a "local" contamination or condensation scenario of the surface of the sensing layer;

FIG. 6 shows an electrical equivalent circuit representing a "global" contamination or condensation scenario involving large scale contamination or condensation of the surface of the sensing layer;

FIG. 7a shows a measurement circuit for measuring the capacitance of an electrode structure of a sensor according to an embodiment of the invention in a first measurement phase;

FIG. 7b shows the measurement circuit of FIG. 5a in a second measurement phase;

FIG. 8a shows a measurement circuit for measuring the capacitance of an electrode structure of a sensor in a first measurement phase according to another embodiment of the invention;

FIG. 8b shows the measurement circuit of FIG. 6a in a second measurement phase;

FIG. 9 illustrates a flow chart of method steps for a method of performing a humidity measurement;

FIG. 10 shows a cross-sectional view of a capacitive sensor of a measurement arrangement according to an embodiment of the invention;

FIG. 11 shows a corresponding electrical equivalent circuit of the exemplary measurement arrangement of FIG. 10;

FIG. 12 shows a top view of the sensor of FIG. 10 formed for measuring quotient C_AE/C_BEAn exemplary measurement arrangement of, and

FIG. 13 shows quotient C for measuring another electrode structure_AE/C_BEIs shown in the figure.

Detailed Description

FIG. 1 shows a cross-sectional view of a capacitive sensor 100 according to an embodiment of the invention. The capacitive sensor 100 may in particular be embodied as a humidity sensor and comprises an electrode structure 10, which electrode structure 10 comprises a first electrode 11 and a second electrode 12. In this example, the sensor 100 comprises three first electrodes 11 and two second electrodes 12. A sensing layer 15 is arranged between the first electrode 11 and the second electrode 12. The first electrode 11 is also denoted as electrode a and the second electrode 12 is also denoted as electrode B. The electrode structure 10 forms a first or top metal layer 21. The sensing layer 15 has a moisture sensitive dielectric constant and thus the electrode structure 10 has a moisture sensitive capacitance and may comprise or consist of a polymer. The sensing layer 15 extends between the first electrode 11 and the second electrode 12 and is shown in a diagonal pattern. The sensor 100 further comprises a dielectric layer 18, which provides electrical insulation between the first metal layer 21 and the second metal layer 22. The second metal layer 22 may also be denoted as a penultimate metal layer. The second metal layer 22 comprises a plurality of electrodes 23, which may in particular be electrically coupled to ground potential and are accordingly denoted as ground electrodes. The second metal layer 22 forms a shielding structure 22. According to other embodiments, the second metal layer 22, in particular the electrode 23, may be coupled to the first electrode 11 or the second electrode 22.

The sensor 100 includes a base substrate 14, and a second metal layer 22, a dielectric layer 18, a first metal layer 21, and a sensing layer 15 are formed on the base substrate 14. The base substrate 14 may in particular be a semiconductor substrate, for example a Si substrate.

The sensing layer 15 has a surface 31 facing the sensing environment 30. The sensing environment 30 may be a gas, in particular ambient air, surrounding the sensor. The sensing environment 30 is shown by a dotted pattern. The sensing environment 30 comprises a local sensing environment 30a and a further sensing environment 30b near the surface 31 of the sensing layer 15. The further sensing environment 30b comprises a wider or in other words larger sensor area and may also be denoted as a wider, remote or distant sensing environment. In fig. 2, the further sensing region 30b is illustrated as having a lower density of dots than the density of the local sensing environment 30 a. The surface 31 of the sensing layer 15 establishes an interface between the sensing layer 15 and the sensing environment 30. Thus, the surface 31 may also be denoted as an environmental interface 31.

The ambient air interacts with the sensing layer 15, in particular via the surface 31 of the sensing layer 15. More particularly, moisture from the ambient air diffuses into the sensing layer 15, thereby changing the dielectric constant of the sensing layer 15 between adjacent electrodes 11 and 12, and thereby changing the capacitance of the electrode structure 10. This change in capacitance can be measured to sense the humidity of the ambient air 30. In other words, the humidity sensor 100 derives the humidity of the ambient air or more generally of the gaseous environment surrounding the humidity sensor 100 from the capacitance of the electrode structure 10.

For such measurements, a measurement circuit may be connected to the first electrode 11 and the second electrode 12.

FIG. 2 shows a partial cross-sectional view 200 of a humidity sensor, more particularly a cut-away portion 101 of the sensor 100 as shown in FIG. 1, including a schematic of the capacitance to be considered for a measurement method according to an embodiment of the present invention.

Fig. 3 shows a corresponding schematic electrical equivalent circuit 300 of the partial cross-sectional view 200 of fig. 2.

The partial cross-sectional view 200 and the electrical equivalent circuit 300 include a main capacitor C between a first electrode a and a second electrode B_MAIN. The first electrode A is coupled to a potential V_AAnd the second electrode B is coupled to a potential V_B。

The partial cross-sectional view 200 and the electrical equivalent circuit 300 include the first electrode 11 and a first reference node N on the surface 31 of the sensing layer 15_E1Capacitance C between_AEAnd a second reference node N on the surface 31 of the second electrode 12 and the sensing layer 15_E2Capacitance C between_BE. In other words, the capacitance C_AECan also be defined as the mutual capacitance between the first electrode 11 and a dummy electrode arranged on the surface 31 of the sensing layer 15, and C_BEOr may be defined as the capacitance between the second electrode 12 and the dummy electrode.

Capacitor C_AECan be expressed as an interface capacitance C_AEAnd a capacitor C_BECan be expressed as an interface capacitance C_BE. The electrical equivalent circuit 300 comprises the electrode A and the fixed potential V of the electrode 23_GParasitic capacitance C between (in particular, ground potential)_APAnd electrode B and electrode 23 of electrode 23 fixed potential V_GParasitic capacitance C between (in particular, ground potential)_BP。

Furthermore, the electrical equivalent circuit 300 comprises an ambient capacitance C_E. Environmental capacitance C_ECan be considered as a capacitance between two imaginary "points" of the sensing environment 30, in particular between two imaginary points on or on top of the surface 31 of the sensing layer 15, in particular at the reference node N_E1And N_E2The capacitance between them. The ambient capacitance can also be expressed as a surface capacitance.

Furthermore, the electrical equivalent circuit 300 comprises a first reference node N_E1And a third reference node N_E3Impedance Z between_0AAnd a second reference node N_E2And a third reference node N_E3Impedance Z between_0B. Third reference node N_E3Is also coupled to a floating potential V_EThe imaginary node of (a). Impedance Z_0AAnd impedance Z_0BMay be resistive, capacitive and/or inductive and may be considered as a local impedance of the local sensing environment 30a near the surface 31 of the sensing layer 15. Impedance Z_0AAnd Z_0BCan be independent of C_MAIN、C_AEAnd C_BEBut is changed.

Furthermore, the electrical equivalent circuit 300 comprises a third reference node N_E3And a fourth reference node N_E4Impedance Z between₀. Fourth reference node N_E4Is also coupled to the potential V₀The imaginary node of (a). Impedance Z₀Can be considered as the impedance between a local sensing environment 30a near the surface 31 of the sensing layer 30 and another sensing environment 30b of the sensor 100. Impedance Z₀Can be independent of C_MAIN、C_AE、C_BE、Z_0AAnd Z_0BBut is changed. Potential V₀Can be considered to be a given remote potential of the sensor. In particular, it may be defined as the average potential of the electrical structure 50 around the surface 31 of the sensing layer 15. The electrical structures 50 surrounding the surface 31 of the sensing layer 15 are shown collectively as a single line. The electrical structure 50 may comprise any other electrical structure, such as a wire, an electronic circuit or a sensor, towards which a leakage current I may occur via the sensing environment 30 in case of condensation or contamination of the surface of the sensing layer_L。

According to an embodiment, a virtual electrode may be considered to be a virtual electrode that may be used by passing C through_EShort-circuiting to measure C_AEAnd C_BEThe electrode of (1). Thus, for such measurements, Z may be assumed_0A＝Z_0B＝Z₀0 and N_E1＝N_E2＝N_E3. For example, the short circuit may be performed by applying a conductive layer on the surface of the sensing layer.

According to an embodiment of the invention, a measurement circuit 40 is provided, said measurement circuit 40 measuring the dielectric constant of the sensing layer 15 by applying a first pair of potentials to the first electrode a and the second electrode B in a first measurement phase. Then, in a second measurement phase, the measurement circuit 40 applies a second pair of potentials to the first electrode a and the second electrode B.

Referring now to fig. 4, 5 and 6, three different measurement scenarios are considered.

More particularly, fig. 4 shows an electrical equivalent circuit representing a "normal" or otherwise conventional measurement scenario, without significant contamination or condensation of the surface 31 of the sensing layer 15. For this case, it is generally assumed that Z_0A，Z_0B，Z₀Absolute value of (2)>>max(l/(w*C_E)，1/(W*C_AE)，1/(W*C_BE) W is the excitation frequency of the first and second electrodes. This assumption can be further reduced to an assumption

Z_0A＝Z_0B＝Z₀＝∞。

The latter assumption leads to a simplified electrical equivalent circuit 400. Thus, the first electrode 11 and the second electrode 12 pass through the main capacitor C_MAINAnd C_AE、C_BEAnd C_EAre electrically connected in a parallel arrangement of the series arrangement of (a).

The current i flowing to the second electrode 12 in this normal case_bnIt can be calculated as follows:

the term d/dt is generally representative of the applied voltage V_AAnd V_BThe derivative of (c). In the case of a two-phase measurement with a fixed voltage applied during the two phases, this is indicated in the two phasesThe difference between the voltages applied in each phase.

As can be seen from the above equation, by changing the potentials of the first and second electrodes, the current i can be increased_bnAnd thus the sensor signal, or in other words the sensing signal of the measuring circuit, can be increased.

For further consideration below, the following initial assumptions should be made.

And

this will facilitate consideration of relational operators ≧ and ≦.

It should be noted, however, that equivalent considerations may be made for the opposite assumption, i.e.

And

in the latter case, the corresponding sign and relationship operators must also be reversed.

Fig. 5 shows an electrical equivalent circuit representing a contamination or condensation situation assuming local or small scale contamination or condensation of the surface 31 of the sensing layer 15. For such local contamination or condensation scenarios, Z is generally assumed_0AAnd Z_0BAbsolute value of (2)<<1/(W*C_E) Wherein w is the excitation frequency of the first and second electrodes, and Z₀Absolute value of (2)>>Z_0A，Z_0B. This can be further simplified to

Z_0A＝Z_0B0; and

Z₀＝∞。

the latter assumption leads to a simplified electrical equivalent circuit 500. Thus, the first electrode 11 and the second electrode 12 pass through the main capacitor C_MAINAnd C_AEAnd C_BEAre electrically connected in a parallel arrangement of the series arrangement of (a).

In such a local contamination scenario, the current i flows to the second electrode 12_BlThen can be calculated as follows:

thus i in this scenario_Bl＞i_Bn。

More particularly, it is preferred that the first and second,

thus, there is one less capacitance in the series arrangement, i.e., C_EThis results in a larger total capacitance.

In the example of a humidity sensor with local condensation on the surface of the sensing layer, an increase in the current at the second electrode will be interpreted as a larger capacitance and thus a larger humidity. This still does not cause any problems, since such local condensation can be interpreted as maximum humidity. Therefore, this case can be ignored for the following considerations.

Fig. 6 shows an electrical equivalent circuit representing a contamination or condensation scenario assuming large area or scale contamination or condensation of the surface 31 of the sensing layer 15. Such large areas of contamination or condensation include, inter alia, contamination or condensation scenarios that extend beyond the sensing layer 15 and may therefore result in leakage currents to the electrical structure 50 surrounding the sensing layer 15. For this case, it is generally assumed that Z_0A、Z_0B、Z₀Absolute value of (2)<<1/(W*C_E) Where w is the excitation frequency of the first and second electrodes. This assumption can be further reduced to an assumption

Z_0A＝Z_0B＝Z₀＝0。

The latter assumption leads to a simplified electrical equivalent circuit 500, where C_EIs short-circuited.

Then to the second electrode 12_BgIt can be calculated as follows:

thus i_BgBecomes independent of C_AEAnd through C_BEIs only dependent onAnd no longer depends on

According to an embodiment of the invention, the electrode current i for the second electrode_BThe following conditions are expected:

i_Bg≥i_Bn。

in other words, in case of large area contamination or large area condensation ("global contamination"), the current at the second electrode 12 should be higher than in normal measurement scenarios. Thus, in the case of a large amount of contamination/condensation, the sensor will deliver a larger sensor signal. For the following considerations, assume

In other words, suppose V₀And remain constant over time. This may be achieved, for example, by appropriate placement of the circuits, lines and wires of the electrical structure 50 in the periphery of the electrode structure as known to electronic circuit design engineers. In particular, this can be achieved by avoiding the placement of clock lines near the electrode structure, in particular near the surface of the sensor chip. The above conditions may then also be specified as follows:

i_Bn≤i_B9

in general C_BE/C_EIs unknown, varies with the dielectric constant of the sensing layer and also depends on the dielectric constant of the sensing environment. For unknown C_BE/C_EIs used forThe most difficult condition of (A) is C_BE/C_E0 or C_EInfinity, and the conditions are further simplified to

Together with initial assumptions

And

commercial C_BE/C_AEDetermined by the geometry of the electrode structure. It does not change over time and does not change depending on the measurand.

For the two-stage measurement provided according to an embodiment of the present invention, including the first measurement stage and the second measurement stage, the above condition may be expressed as follows.

0＜＝(V_A1-V_A2)＜＝(V_B2-V_B1)*C_BE/C_AE(ii) a (inequality 1)

Or

(V_B2-V_B1)*C_EE/V_AE＜＝(V_A1-V_A2) Is less than 0. (inequality 2)

In the above formula V_A1A first potential, V, representing the first electrode 11 in a first measuring phase_A2A second potential, V, representing the first electrode 11 in a second measuring phase_B1Is the first potential of the second electrode 12 in the first measurement phase, and V_B2Is the second potential of the second electrode 12 in the second measurement phase. V_A1、V_A2、V_B1And V_B2Reached at the end of the respective measurement phase. The transition from the first measurement phase to the second measurement phase can have any course.

According to an embodiment, the set of conditions comprises the following conditions:

(V_A1-V_A2)＝(V_B2-V_B1)*C_BE/C_AE

in the special case of a symmetrical arrangement of the first electrode 11 and the second electrode 12, in particular in the case of a first electrode 11 and a second electrode 12 having the same distance to the surface 31 of the sensing layer 15, the quotient C_BE/C_AE1. Thus, the above-mentioned condition for such a symmetrical arrangement of the electrodes may be expressed as

(V_A1-V_A2)＝(V_B2-V_B1)。

In other words, the average potential of the first pair of potentials is the same as the average potential of the second pair of potentials.

In other words, the average potential of the electrodes a and B is kept constant during the first and second measurement phases.

When the potential on electrode B varies between the first and second measurement phases, parasitic capacitance C is also measured, assuming electrode 23 is at ground potential_BP。

Commercial C_BE/C_AECan be determined in a number of different ways. As mentioned above, this determination is only required in the case of an asymmetric electrode arrangement, whereas in a symmetric electrode arrangement the quotient is 1.

According to an embodiment, quotient C_BE/C_AECan be determined by simulation according to the Finite Element Method (FEM), for example by ComsolAnd (3) software. For such simulation, virtual electrodes on the surface 31 of the sensing layer 15 are provided.

According to other embodiments, quotient C_BE/C_AECan be determined by measurement, e.g. based on the capacitance C_AEAnd C_BEThe measurement of the formed capacitive divider.

The latter embodiment will be described in more detail below with reference to fig. 10 and 11. Fig. 10 shows a cross-sectional view of a capacitive sensor 1000, which substantially corresponds to the sensor 100 of fig. 1. However, sensor 1000 includes a conductive layer 1010 on surface 31 of sensing layer 15. Sensor 1000 is set up to measure quotient C_AE/C_BEExemplary measurement arrangements of (1). The conductive layer 1010 establishes a dummy electrode 13. The virtual electrode 13 can be considered as a measuring electrode, in particular for measuring the quotient C_AE/C_BEThe auxiliary measuring electrode of (1). Conductive layer 1010 can be a metal layer that has been applied, for example, by spraying or sputtering. According to an embodiment, such a layer may be, for example, a sputtered gold layer (AU layer) having a thickness of, for example, 100 nm. The gold layer may be connected to existing pads, which may be wire bonded or in contact with probes.

The conductive layer 1010 may be applied only once or for only one sample sensor in order to determine the quotient C for the corresponding series of sensors_BE/C_AE. The measurements may be performed in a laboratory environment. As mentioned, this approach is particularly useful for asymmetric electrode arrangements, whereas for symmetric arrangements, the quotient C_BE/C_AEIt can be assumed to be 1.

Fig. 11 shows a corresponding electrical equivalent circuit of an exemplary measurement arrangement. In contrast to the electrical equivalent circuit of fig. 6, the electrical equivalent circuit of fig. 11 does not include the capacitor C_MAIN、C_APAnd C_BP. The latter capacitance can be omitted or omitted, since the first electrode 11 and the second electrode 12 operate for measurement at a given voltage potential.

In a first measurement step, a predefined set V of voltages_A1And V_B1Are applied to the first electrode 11 and the second electrode 12, respectively. According to an embodiment, V is selected as follows_A1And V_B1：

V_A1＝V_B1＝0V。

The potential V of the conductive layer 1010 is then measured_E1。

In a further step (second step), another (different) set V of voltages_A2And V_B2Applied to the first electrode 11 and the second electrode 12, respectively, wherein the set of voltages is specifically chosen such that V_A2＝-V_B2E.g. V_A21V and V_B2-1V. The change in voltage potential of the conductive layer 1010, i.e., V, is then measured_E2Which is composed of C_AEAnd C_BEIs determined.

Due to the capacitance C_AEAnd C_BEArranged in series, thus a capacitance C_AEAnd C_BEUpper corresponding charge Q_CAEAnd Q_CBEIn particular the charge difference DeltaQ_AEAnd Δ Q_BEAre equal to each other.

Thus, the number of the first and second electrodes,

ΔQ_AE＝C_AE*(ΔV_A-ΔV_E)＝ΔQ_BE＝V_BE*(ΔV_E-ΔV_B)，

wherein

ΔV_A＝(V_A2-V_A1)，ΔV_B＝(V_B2-V_B1)，ΔV_E＝(V_B2-V_E1)。

Thus, quotient C_BE/C_AECan be determined as

C_EB/C_AE＝(ΔV_A-ΔV_E)/(ΔV_E-ΔV_B)。

According to yet another embodiment, one may not measure quotient C directly_BE/C_AEBut is an indirect measurement.

More particularly, two measurements may be performed, the first measurement, in which the sensing environment provides 100% or approximately 100% relative humidity. Such relative humidity may be provided by, for example, suitable laboratory equipment, such as by slowly cooling a sealed environment (e.g., a sealed box containing the sensor) until condensation occurs. By continuously measuring the sensor capacitance, the difference in sensor signal before and after setting can be determined. Should be directed to V_A1、V_A2、V_B1And V_B2Repeats this process at different levels.

Furthermore, a second measurement is performed, wherein a condensation layer is applied to the sensing layer 30, corresponding to the global contamination/condensation scenario shown in fig. 6. Such a coagulation layer may be applied, for example, by applying a thin layer of water on the sensing layer 30.

According to an embodiment, the voltage potential V_A1、V_A2、V_B1And V_B2Then selected by experiment/experiment in the following way: the resulting charge difference at the second electrode is the same for measurements at 100% relative humidity as for measurements in the global contamination/condensation scenario.

Thus, in inequality 1, for example, the inequality numbers may be replaced with equal numbers and the quotient C_BE/C_AECan be derived as follows:

(V_A1-V_A2)＝(V_B2-V_B1)*C_BE/C_AE。

this can be rewritten as:

C_BE/C_AE＝(V_A1-V_A2)/(V_B2-V_B1)。

it should be noted thatTo ensure that inequalities 1 or 2 are satisfied, it is not necessary, according to an embodiment, to determine quotient C in an accurate or precise manner_BE/C_AE. Instead, quotient C can be implemented_BE/C_AEAnd then select the voltage value, for example in inequality 1 or 2 as mentioned above, such that the inequality is satisfied even in the estimated worst scenario.

As an example, suppose V is in inequality 1_A1＝2V，V_A21V and quotient C_BE/C_AE0.75. The difference V can then be selected, for example_B2-V_B1Large enough, e.g. 3V, to multiply the product (V) in any case_B2-V_B1)*C_BE/C_AENot less than 1V. At a difference (V)_B2-V_B1) In the example of 3V, even for quotient C_BE/C_AEThe inequality 1 may also be satisfied when the estimated value is 0.34 instead of 0.75.

Fig. 7a and 7b show a measurement circuit 700 for measuring the capacitance of a sensing layer of a sensor (e.g. the sensor of fig. 1) according to an embodiment of the invention. More particularly, fig. 7a shows the measurement circuit 700 in a first measurement phase and fig. 7b shows the measurement circuit 700 in a second measurement phase.

The measurement circuit 700 comprises a first circuit part 701 and a second circuit part 702.

The first circuit portion 701 comprises an electrode arrangement with a first electrode a/11, a second electrode B/12 and a sensing layer in between. The left circuit part 701 also comprises a voltage generator, which is not shown as such, but only the supplied voltage. The voltage generator of the measuring circuit 700 supplies a potential V to the second electrode B of the electrode arrangement in a first measuring phase_DDAnd a ground potential is supplied to the first electrode a. The capacitance to be sensed is denoted by Cs. A parasitic capacitance C is arranged between the second electrode B and ground_P1。

The second circuit portion 702 forms an integrator 710, in particular a switched capacitor amplifier. The integrator 710 is configured to integrate the resulting charge difference, as will be explained below. The integrator 710 is implemented as a switched capacitor amplifier and includes an operational amplifier 711. Operational amplifierThe positive input of the amplifier 711 is connected to ground. The feedback path being via an integrating capacitor C_INTThe output of the operational amplifier 711 is coupled to the negative (inverting) input of the operational amplifier 711. Integrating capacitor C_INTMay also be denoted as reference capacitors. The negative input terminal is connected to the output terminal via a parasitic capacitor C_P2Coupled to ground. In a first measuring phase, the integrating capacitor C_INTAnd (4) short-circuiting. Furthermore, during the first measurement phase, the second circuit portion 702 is not connected to the first circuit portion 701.

In a second measurement phase, as shown in fig. 7b, the voltage generator of the measurement circuit supplies a potential V to the first electrode a of the electrode structure_DDAnd a ground potential is supplied to the second electrode B. The second circuit portion 702 is coupled to the first circuit portion 701 during a second measurement phase. More specifically, the negative input of the operational amplifier 711 is coupled to the second electrode B. Therefore, the ground potential of the second electrode B is provided by the virtual ground of the operational amplifier 711. Furthermore, an integrating capacitor C_INTNo longer short-circuited.

The measurement circuit 700 may be switched between the first measurement phase and the second measurement phase by a suitable switch as will be apparent to a person skilled in the art. For ease of illustration, the corresponding switches are not shown in fig. 7a and 7 b.

In a second measurement phase, as shown in fig. 7B, the measurement circuit 700 is configured to transfer the resulting charge difference generated at the second electrode B to the integrating capacitor C_INT. In other words, the integrator 710 integrates the current flowing through the first electrode and the second electrode during the second measurement phase.

Integrating capacitor C_INTA reference capacitor is formed.

Measurement circuit 700 is at reference capacitor C_INTThe resulting voltage V is provided at the output of the sum operational amplifier 711_out. Resulting voltage V_outWhich can then be used by the sensor to determine the dielectric constant and corresponding relative humidity of the sensing layer.

Fig. 8a and 8b show a measurement circuit 800 for measuring the dielectric constant of a sensing layer of a sensor (e.g. the sensor of fig. 1) according to an embodiment of the invention. More particularly, fig. 8a shows the measurement circuit 800 in a first measurement phase and fig. 8b shows the measurement circuit 800 in a second measurement phase.

Measurement circuit 800 includes a first circuit portion 701, a second circuit portion 702, and a third circuit portion 803. The circuit parts 701 and 702 correspond to the circuit parts 701 and 702 shown and described with reference to fig. 7a and 7 b.

The third circuit portion 803 includes an offset capacitance Co. In a first measurement phase, the offset capacitance Co uses a voltage V_DDCharge to an offset charge Qo.

In the second measurement phase, an offset capacitor Co is coupled between ground and the negative input of the operational amplifier 711. Thus, the measurement circuit 800 is configured to subtract the offset charge Qo from the resulting charge difference. This provides the advantage that the resulting charge difference can be measured in a symmetrical manner. More particularly, the integrating capacitance C_INTCan use a charge signal Q symmetrical to 0_sense-Qo charging. More particularly, (Q)_{sense_max}-Qo)＝-(Q_{sense_min}-Qo)。

FIG. 9 illustrates a flow chart of method steps for a method of performing relative humidity measurements. The method may for example be performed with a sensor according to an embodiment of the invention as described above.

At step 910, an electrode structure including at least a first electrode and a second electrode is provided.

At step 920, a sensing layer is provided. The sensing layer is disposed between the first electrode and the second electrode and has a moisture sensitive dielectric constant. The first electrode, the sensing layer and the second electrode form a capacitor.

At step 930, a first measurement phase is performed and a first pair of potentials is applied to the first and second electrodes.

At step 940, a second measurement phase is performed and a second pair of potentials is applied to the first and second electrodes.

The first pair of potentials includes a first potential of the first electrode and a first potential of the second electrode. The second pair of potentials includes a second potential of the first electrode and a second potential of the second electrode. The first potential of the second electrode and the second potential of the second electrode are different from each other.

At step 950, the charge difference generated at the second electrode between the first measurement phase and the second measurement phase is sensed by a measurement circuit, in particular a readout circuit. More particularly, a change in the charge of the capacitor between the first and second measurement phases results in a current passing through the first and second electrodes. The current in the second electrode is integrated resulting in a charge difference seen across the capacitor.

At step 960, the resulting charge difference is transferred to a reference capacitor, particularly to a capacitor having a known capacitance.

At step 970, the resulting voltage is measured at the reference capacitor. From this measured voltage, the capacitance of the electrode structure can be determined. The measured capacitance of the electrode structure is a measure of the sensed ambient humidity.

FIG. 12 illustrates a top view 1200 of the sensor 1000 of FIG. 10, forming a sensor for measuring C according to an embodiment of the present invention_AE/C_BEExemplary measurement arrangement of quotient. The virtual electrode 13 applied for measurement purposes covers the entire surface 31 of the sensing layer 15. The first electrodes 11 and the second electrodes 13 are arranged below the virtual electrodes 13 and are implemented as interdigitated electrodes.

FIG. 13 shows a method for measuring quotient C in accordance with another embodiment of the present invention_AE/C_BETop view 1300 of an exemplary measurement arrangement.

According to an embodiment of the invention, the measurement arrangement 1300 further comprises a virtual electrode 13 covering the sensing layer of the sensor. However, in the embodiment of fig. 13, the first electrodes 11 and the second electrodes 12 are not interdigital electrodes, but have only a simple rectangular shape.

It should be noted that many other electrode configurations may be used for the first and second electrodes, depending on the embodiment.