WO2003065027A1

WO2003065027A1 - Sensor field for measuring humidity and a method for producing the same

Info

Publication number: WO2003065027A1
Application number: PCT/DE2003/000039
Authority: WO
Inventors: Max Zellner; Jörg NAUNDORF
Original assignee: Siemens Aktiengesellschaft
Priority date: 2002-01-31
Filing date: 2003-01-08
Publication date: 2003-08-07
Also published as: DE10203816C1

Abstract

First conductor strips (5), a first insulation layer (6), fine structures comprising first electrodes (51), second conductor strips (7), second electrodes (71) and subsequently a layer (8) sensitive to humidity are successively applied to a base layer (3), which is preferably flexible. The first electrodes (51) are connected to corresponding first conductor strips (5) by means of through-platings. The invention also relates to a method for producing said sensor field.

Description

Sensor field for moisture measurement and method for its production Description

Thin-film sensors with moisture-sensitive layers are used to measure the moisture. The challenge here is the development of reproducible and sensitive measuring principles for the detection of moisture as well as the manufacturability of the sensors with reliable and inexpensive planar technologies.

In a typical structure of a thin-film sensor, the moisture is detected by means of a capacitance measurement with the aid of film electrodes on a rigid substrate and a water-vapor-permeable cover electrode above the moisture-sensitive layer. The common counter electrode on the surface must allow unimpeded access of the water molecules to the active layer. Such sensors are, for example, in H.-R. Tränkler, E. Obermeier: "Sensor technology, manual for practice and

Wissenschaft ", Springer Verlag, 1998, pages 1247 and 1248.

A sensor field for a capacitively measuring fingerprint sensor is known from WO 00/13130, which is located in another field.

Sensor known.

The invention has for its object to provide a sensor field for moisture measurement, which in addition to being highly sensitive to a change in moisture on the

Sensor surface simultaneously allows a spatially resolved detection of moisture and can be implemented using cost-effective thin-film technology.

The object is achieved by the inventions specified in the independent claims. Advantageous further developments can be found in the subclaims. The sensor field makes it possible to carry out moisture measurements according to a simple and very sensitive measuring principle, in which the change in the stray capacitance as a result of a change in the dielectric constant in one of the

Moisture-sensitive layer exposed to ambient moisture is measured locally locally.

The moisture sensitive layer is moisture sensitive in that it has the ability to

To adsorb and / or desorb water molecules. The dielectric constant of water exceeds that of most dielectrics and therefore leads to the desired change in capacitance.

With regard to responsiveness and reproducibility, a moisture-sensitive layer is suitable e.g. appropriately prepared polyimide, polyamide or cellulose acetate.

In principle, the multiplicity of electrodes present in a sensor field according to claim 1 can be used in two ways. On the one hand, electrodes can be interconnected, which significantly increases the sensitivity of the sensor field.

However, it is particularly preferred to read out the electrodes in a spatially resolved manner via the associated conductor tracks. This means that moisture can be measured with the sensor field in a spatially resolved manner.

Depending on the desired spatial resolution, the sensor field can have a corresponding number of electrodes per square millimeter.

The sensor field can be constructed using thin film technology on a rigid substrate or as a flexible fine structure. The development according to claim 3 enables the construction of the sensor field on a base layer made of inexpensive organic material. If a flexible organic material is used according to claim 4, the sensor field can be broken in chip cards or the like without risk of breakage. be used.

The development according to claim 5 brings further advantages through the use of inexpensive commercially available films.

According to claim 6, a film made of a thermostable polyimide is preferred, especially since this enables the finished sensor field to be used without problems, even at elevated ambient temperatures. The film can then be obtained by applying a planarization of a very high surface quality, which enables the formation of the finest metallic structures.

A method for producing a sensor field with a moisture-sensitive layer contains the steps specified in claim 11. Advantageous refinements of the method result analogously to the previously described advantageous refinements of the sensor field and analogously to the method for producing a sensor field shown in WO 00/13130.

An exemplary embodiment of the invention is explained in more detail below with reference to the drawings.

Show it

FIG. 1 shows a plan view of the sensor field of a capacitively measuring moisture sensor in a highly simplified schematic illustration, Figure 2 shows the equivalent circuit of that shown in Figure 1

3, the measuring principle of the sensor field shown in FIG. 1, FIG. 4 a section along the line IV-IV of FIG. 1, and FIG. 5 a plan view of a finished moisture sensor.

FIG. 1 shows a highly simplified schematic illustration of a partial top view of the sensor field of a sensor arrangement for measuring moisture, the multilayer structure of the sensor field being apparent from the section shown in FIG. 4 along the line IV-IV.

In the production of the sensor field shown in FIGS. 1 and 4, a rigid auxiliary carrier 1 made of borosilicate glass is assumed. In order to guarantee the adhesion of the subsequent structure on the auxiliary carrier 1 with certainty, an adhesive layer 2 made of titanium is applied by sputtering. A base layer 3 is then applied to this adhesive layer 2. In the illustrated

Exemplary embodiment, this base layer 3 is a film made of a thermostable polyimide, e.g. BCB, which has a thickness of 50 microns and is applied by lamination. The base layer 3 is then planarized by spinning on an insulation material, this process being shown in FIG. 4 by a planarization 4 shown separately.

The subsequent generation of metallic fine structures in the form of a family of first conductor tracks 5 can in principle be carried out using subtractive technology, additive technology or semi-additive technology. In the exemplary embodiment described, the first conductor tracks 5 are produced semi-additively. A planarization 4 is sputtered onto the planarization 4, which is sputtered over the entire area with a layer sequence of titanium and palladium Drawing not shown photoresist applied and structured so that, for example, galvanically gold or galvanically or chemically copper can be deposited on the freely developed conductor pattern. After stripping the photoresist, the areas of the layer sequence of titanium and palladium which do not correspond to the desired first conductor tracks 5 are then removed by selective etching up to the surface of the planarization 4.

A photostructurable first insulation layer 6 is then applied to the first conductor tracks 5, into which holes 61 which have a diameter of 25 μm, for example, are made by exposure and development. During the subsequent production of a second layer of metallic fine structures in the form of first electrodes 51, second conductor tracks 7 and second electrodes 71, plated-through holes are then produced in the area of the holes 61, which connect the first electrodes 51 to associated underlying conductor tracks 5 in an electrically conductive manner. The above-mentioned second layer of fine metallic structures is again produced semi-additively in the described embodiment.

It can be seen from the schematic illustration according to FIG. 1 that the family of first conductor tracks 5 and the family of second conductor tracks 7 cross orthogonally. It can also be seen that the second electrodes 71 are formed by widened areas of the second conductor tracks 7 and that the first electrodes 51 and the second electrodes 71 form a kind of pixel field, the pixel grid of which is 70 μm in the exemplary embodiment shown. The first conductor tracks 5 end at the ends in connections for transmission lines AS, while the second conductor tracks 7 end at the ends in connections for reception lines AE. The sensor field is then connected to evaluation electronics via the connections AS and AE. It can also be seen from FIG. 4 that a moisture-sensitive layer 8 is finally applied to the second layer of metallic fine structures and consists, for example, of polyimide, polyamide or cellulose acetate.

FIG. 3 shows an equivalent circuit diagram of the sensor field shown schematically in FIG. 1. Capacities C are formed in each case between the first conductor tracks 5 and the orthogonally crossing second conductor tracks 6. These capacitances C are stray capacitances between adjacent first electrodes 51 and second electrodes 71 (cf. FIG. 1). In the exemplary embodiment described, C <10FF.

In the case of the sensor field described, which could also be referred to as a passive sensor array, the stray field between adjacent first electrodes 51 and second electrodes 71 now serves as a measurement variable for the detection of moisture which penetrates into the layer 8 which is sensitive to moisture from the environment. This principle, also referred to as the fringing field measuring principle, can be seen from FIG. Here, the stray field between a first electrode 51 and an adjacent second electrode 71 is designated SF. The moisture that has penetrated into the moisture-sensitive layer 8 changes the dielectric constant, the stray field SF and thus the measured capacitance.

FIG. 5 shows a plan view of a finished moisture sensor, in which the sensor field is denoted by S. In the area of a magnifying glass L it can be seen that the structure of the sensor field F corresponds to the structure of the sensor field shown schematically in FIG. On the base layer 3, the two sides of the sensor field S lead transmission lines SL to a chip CH arranged below the sensor field S. This chip CH is the evaluation electronics of the moisture sensor. From the bottom starting from the sensor field S, receive lines EL lead to the chip CH.

Rectangular pulses, for example, are supplied to the first electrodes 51 (see FIG. 1) of the passive sensor field S via the transmission lines SL, while the reception lines EL detect the change in the stray field SF caused by the moisture between the first and second electrodes 51 and 71 (see FIG. 3). detect and thereby enable the chip CH to measure the moisture in the environment. A spatially resolved moisture measurement is also possible due to the grid-shaped arrangement of the electrodes. Depending on the desired spatial resolution, the size and spacing of the electrodes can be dimensioned accordingly during manufacture.

In the moisture sensor shown in Figure 5, the connections AS and AE shown in Figure 1 are omitted. The transmission lines SL are designed as continuations of the first conductor tracks 5 on the base layer 3. In a corresponding manner, the receiving lines EL are designed as continuations of the second conductor tracks 7 on the first insulation layer 6.

In general, a structure of the moisture sensor in film technology enables reliable and cost-effective production in thin-film technology. At the same time, there are advantages in terms of weight, the ability to withstand alternating bending and assembly in complicated installation positions. An additional water vapor-permeable electrode on the moisture-sensitive layer 8 is not necessary in the selected measuring principle.

The design of the sensor field enables a high local resolution (typical electrode grid <200 μm) and a quick response (<100 ms). The sensor field for moisture measurement can be used, for example, in the automotive sector for climate and indoor air management. Another preferred area of application is in the pharmacy in the storage of medicines and the spatially resolved measurement of the water content of pharmaceutical products.

Further application examples are in device technology for sensors for ventilation control, rain detection, for moisture deposits on walls, cooling ceilings, surfaces, where the flexible sensor field for moisture measurement can be used particularly advantageously due to individual adaptability to the surface.

Finally, due to the high sensitivity, fire detection by determining the air humidity as a fire parameter is possible.

Claims

claims

1. Sensor field for moisture measurement, with a base layer (3) made of an electrically insulating material; several first arranged on the base layer (3)

Conductor tracks (5); a first insulation layer (6) made of an electrically insulating material applied to the base layer (3) and the first conductor tracks (5); a plurality of first electrodes (51) arranged on the first insulation layer (6), which are connected in an electrically conductive manner via vias to associated first conductor tracks (5) underneath; - A plurality of second ones arranged on the first insulation layer (6) and crossing the first conductor tracks (5)

Conductor tracks (7); a plurality of second electrodes (71) which are arranged on the first insulation layer (6) and are electrically conductively connected to assigned second conductor tracks (7); and with one on the first insulation layer (6), the first

Electrodes (51), the second conductor tracks (7) and the second electrodes (71) applied moisture-sensitive layer (8).

2. Sensor field according to claim 1, characterized in that moisture can be measured in a spatially resolved manner by the sensor field.

3. Sensor field according to claim 1 or 2, characterized in that the base layer (3) consists of an organic material.

4. Sensor field according to one of the preceding claims, characterized in that the base layer (3) consists of a flexible organic material.

5. Sensor field according to claim 4, characterized by a base layer (3) in the form of a film.

6. Sensor field according to claim 5, characterized by a film made of a thermostable polyimide.

7. Sensor field according to claim 5 or 6, characterized by a on the base layer (3) applied planarization (4) made of an electrically insulating material.

8. Sensor field according to one of the preceding claims, characterized in that in the first insulation layer (6) holes (61) are made which are metallized to form the plated-through holes between the first conductor tracks (5) and the associated first electrodes (51).

9. Sensor field according to one of the preceding claims, characterized in that the first conductor tracks (5) and the second conductor tracks (7) cross orthogonally.

10. Sensor field according to one of the preceding claims, characterized in that the second electrodes (71) are formed by widened areas of the second conductor tracks (7).

11. Method for producing a sensor field for

Moisture measurement with the following steps:

Applying a thin base layer (3) made of a flexible organic material on a rigid auxiliary carrier (1); - Generation of a plurality of first conductor tracks (5) arranged on the base layer (3); Applying a first insulation layer (6) to the base layer (3) and the first conductor tracks (5); Making holes (61) in the insulation layer (6); Formation of a plurality of first electrodes (51), a plurality of second electrodes crossing the first conductor tracks (5)

Conductor tracks (7) and a plurality of second electrodes (71) on the first insulation layer (6), the first electrodes (51) being metallized with holes (61) in the insulation layer (6) with associated first conductor tracks (5) underneath are connected in an electrically conductive manner and the second electrodes (71) are connected in an electrically conductive manner to assigned second conductor tracks (7); Applying a moisture-sensitive layer (8) to the first insulation layer (6), the first electrodes (51), the second conductor tracks (7) and the second electrodes (71);

Detachment of the base layer (3) from the auxiliary carrier by the action of laser radiation (LS), which is directed through the auxiliary carrier (1) onto the base layer (3), the auxiliary carrier (1) consisting of a for detaching the base layer (3) used laser radiation (LS) is at least largely transparent material.