CAPACITIVE HUMIDITY SENSOR DEVICE

Description

FIELD OF TECHNOLOGY

[0001] The present invention relates to a sensor device for measuring humidity. STATE OF THE ART

[0002] Sensor devices are known for measuring the humidity and temperature of a medium. These consist of a carrier substrate on which sensor components applied using thin- or thick-film technology are arranged. The sensor device disclosed, for example, in US Pat. No. 4,277,742 has a carrier substrate made of an electrically conductive semiconductor material, on which a capacitive humidity sensor is arranged. The capacitive humidity sensor consists of a base electrode, a moisture-permeable cover electrode, and a moisture-sensitive dielectric arranged between the electrodes. Separate from the humidity sensor, in the embodiment shown in Figure 7 of US Pat. No. 4,277,742, a temperature sensor in the form of a planar conductor track is also provided on the semiconductor carrier substrate.A disadvantage of the proposed sensor device, in addition to the large space requirement for the humidity and temperature sensor, is that a relatively complex layer structure with a correspondingly large number of process steps is envisaged during production.

[0003] A sensor device for capacitive humidity measurement is also known from DE 10 2006 018 563 A1. In the exemplary embodiment according to Figure 5A, a capacitive humidity sensor and a reference capacitor or a reference capacitance are arranged adjacent to one another on a semiconductor carrier substrate. The reference capacitor comprises an N-diffusion layer in the semiconductor carrier substrate and a polysilicon layer as electrodes; the silicon oxide layer arranged between the electrodes acts as the dielectric of the reference capacitor. A disadvantage of this sensor device is, on the one hand, the increased space requirement for the humidity sensor and the reference capacitor, which are arranged next to one another. On the other hand, a pre-processed wafer with zones of different doping on the wafer surface is provided as the semiconductor carrier substrate, which increases the costs for such a sensor device.

[0004] Similar devices with adjacently arranged humidity sensors and reference capacitances are also known from the documents US 2013 / 0139587 A1, US 2015 / 0047430 A1 and WO 2010 / 113711 A1. SUMMARY OF THE INVENTION

[0005] The present invention is based on the object of creating a sensor device for measuring humidity which provides sufficient measuring accuracy at low manufacturing costs and is designed to be as compact as possible.

[0006] This object is achieved according to the invention by a sensor device having the features of claim 1.

[0007] Advantageous embodiments of the sensor device according to the invention result from the measures listed in the dependent claims.

[0008] The sensor device according to the invention for measuring humidity consists of an electrically conductive semiconductor carrier substrate, with a capacitive humidity sensor arranged thereon, which comprises a base electrode, a moisture-permeable cover electrode and a moisture-sensitive dielectric arranged between the base and cover electrodes, as well as at least one reference capacitance arranged thereon for evaluating the humidity sensor.

[0009] The base electrode of the capacitive humidity sensor is also a component of the at least one reference capacitance. A passivation layer, to which the base electrode is applied, is arranged on the semiconductor carrier substrate. The reference capacitance comprises the base electrode, the semiconductor carrier substrate, and the passivation layer, with the humidity sensor and the reference capacitance arranged one above the other.

[0010] The passivation layer can be formed from one or more of the following materials: silicon dioxide, silicon oxynitride, silicon nitride

[0011] It is possible that the base electrode is flat and made of electrically conductive material.

[0012] The base electrode can be made of gold and an underlying adhesion and solderability layer.

[0013] Furthermore, it can be provided that the cover electrode is flat and made of electrically conductive material.

[0014] Preferably, the semiconductor carrier substrate is formed from doped semiconductor material.

[0015] According to the invention, a plurality of contacting terminals are formed on the semiconductor carrier substrate, in particular a contacting terminal for the cover electrode, two contacting terminals for the base electrode and a contacting terminal for the semiconductor carrier substrate.

[0016] The contact connections are preferably designed to be planar.

[0017] The contact connections can each have a square or round cross-section.

[0018] It is also possible that the base electrode is made up of several parts.

[0019] In an arrangement with a carrier substrate having a recess, a sensor device according to the invention can be arranged in the region of the recess, wherein the humidity sensor is oriented in the direction of the recess.

[0020] Preferably, on the side of the carrier substrate that is oriented away from the sensor device, the recess is covered with a moisture-permeable membrane made of Teflon mesh.

[0021] Furthermore, the recess in the carrier substrate can be filled with a coating material that enables gas exchange between the humidity sensor and the environment, but keeps liquid away from the humidity sensor. Due to its simple structure, the sensor device according to the invention can be manufactured in only a few process steps, resulting in particularly low manufacturing costs. This is further contributed to by the fact that the sensor device according to the invention is designed as a passive system without integrated signal processing components, allowing the use of a cost-effective semiconductor carrier substrate.

[0022] Due to the intended superimposed arrangement of the capacitive humidity sensor and the reference capacitance, a particularly space-saving design of the sensor device according to the invention is also ensured.

[0023] Furthermore, the sensor device according to the invention can be further processed without the need for packaging or housing, which opens up application possibilities, for example, in which good thermal coupling of the sensor device is required. This can be ensured because, without packaging, the good thermal conductivity of the semiconductor carrier substrate enables efficient thermal coupling of the sensor device in appropriate measurement environments.

[0024] For electrical contacting of the sensor device according to the invention, one possible arrangement variant can simply be soldered onto a carrier substrate in the form of a suitable circuit board. This arrangement eliminates the need for the otherwise required bond connections or ball grid arrays.

[0025] Further details and advantages of the present invention will be explained with reference to the following description of embodiments of the sensor device according to the invention in conjunction with the figures. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] It shows Figure 1a shows a sectional view to explain the basic layer structure in the sensor device according to the invention; Figure 1b shows the layer structure in Figure 1a corresponding, highly simplified electrical equivalent circuit diagram; Figure 2 a perspective view of an embodiment of the sensor device according to the invention; Figure 3 an exploded view of the embodiment of Figure 2 ; Figure 4a a plan view of the embodiment of the sensor device from Figure 2 ; Figures 4b, 4c show different sectional views of the embodiment from Figure 2; Figures 5 and 6 each show views of arrangements with the sensor device according to the invention on different support elements. DESCRIPTION OF THE EMBODIMENTS

[0027] Before using the Figures 2 - 6 A concrete embodiment of the sensor device according to the invention as well as exemplary arrangements with such a sensor arrangement will be explained in detail, with reference to the Figures 1a and 1b the basic structure of the device according to the invention is described.

[0028] The sensor device according to the invention comprises an electrically conductive semiconductor carrier substrate 1, on which certain components for measuring the humidity of a surrounding medium are arranged in the manner described below. A doped semiconductor material, preferably doped silicon, is provided as the conductive semiconductor carrier substrate 1. A corresponding silicon wafer can be used for this purpose, from which a plurality of sensor devices according to the invention can then be manufactured cost-effectively in multiple uses. Since the sensor device according to the invention is designed as a completely passive system, pre-processing of the semiconductor carrier substrate 1 is unnecessary, and a cost-effective 8" wafer, for example, can be used as a suitable silicon wafer. This wafer is not pre-processed using further semiconductor manufacturing processes in order to integrate additional active electronic components into it.In particular, no prior structured doping of the silicon wafer is required. For example, it is possible to use a wafer sold by UniversityWafer, Inc. under the designation "Prime Si + wet SiO2 wafer 8 inch" (orientation (100); 1-side polished; P-type doped (boron), 0.05...0.02 OHM cm; 1000 nm SiO2 (+ / - 5%)).

[0029] As from Figure 1aAs can be seen, an electrically insulating passivation layer 2 is arranged on the semiconductor carrier substrate 1. One or more of the following materials can be provided for the passivation layer: silicon dioxide SiO x , silicon oxynitride SiO x N y , silicon nitride SiN x (where x, y are rational numbers). The further plies or layers, which form the required humidity measurement sensor system, are then arranged one above the other on the passivation layer 2. It is possible that the purchased silicon wafer already has such a passivation layer 2 and that this no longer needs to be applied separately during the production of the sensor device according to the invention.

[0030] For humidity measurement, a capacitive humidity sensor is provided in the sensor device according to the invention, which comprises a base electrode 3, a moisture-permeable cover electrode 5 and a moisture-sensitive dielectric 4 arranged between the base and cover electrodes 3, 5. As can be seen from Figure 1aAs can be seen, the base electrode 3, which is flat and made of an electrically conductive material, is applied to the passivation layer 2. The base electrode 3 can consist of gold, for example, and an underlying adhesion and solderability layer made of nickel Ni or nickel-chromium NiCr. The dielectric 4 arranged above the base electrode 3 is preferably a polymer such as polyimide, the capacitance of which changes in a defined manner depending on the humidity. In this regard, reference will be made below to a humidity-dependent measuring capacitance C_RH. The moisture-permeable cover electrode 5 in the present exemplary embodiment is also flat and consists of an electrically conductive material, for example chromium. The moisture permeability of the cover electrode 5 can be ensured by a suitable porous or cracked structure thereof.Through this structure, the surrounding medium, whose moisture content is to be measured, comes into contact with the moisture-sensitive dielectric 4. As an alternative to a flat, cracked cover electrode, the cover electrode can also be structured in the form of meandering paths; furthermore, perforated structures can also function as cover electrodes.

[0031] According to the invention, the base electrode 3 in the sensor device is used not only as part of the capacitive humidity sensor, but also as a component of at least one reference capacitance C_REF. Such a reference capacitance C_REF is used together with the measuring capacitance C_RH in a known manner for determining the humidity in the surrounding medium. Regarding a suitable method for determining the humidity using a reference capacitance C_REF, reference is made, for example, to EP 1 574 847 B1 of the applicant, the content of which is hereby expressly incorporated by reference. The reference capacitance C_REF is determined as shown in Figure 1aAs can be seen in the sensor device according to the invention, it is formed from the aforementioned base electrode 3, the semiconductor carrier substrate 1, and the passivation layer 2 arranged therebetween, which here functions as a dielectric. The base electrode 3 of the humidity sensor thus also forms one of the two electrodes of the reference capacitance C_REF; the second electrode of the reference capacitance C_REF is formed by the semiconductor carrier substrate 1. It is therefore no longer necessary to form a separate reference capacitance C_REF for humidity determination in the sensor device; rather, the inherently present, usually undesirable capacitance between the base electrode 3 and the semiconductor carrier substrate 1 is used as the reference capacitance C_REF.

[0032] The associated contact terminals, via which the sensor device according to the invention is connected to a humidity measuring circuit arrangement (not shown in the figures), are shown in Figure 1b designated DE1, GE1, and CR1. Here, the contact terminal DE1 is used to contact the cover electrode 5, the contact terminal GE1 is used to contact the base electrode 3, and the contact terminal CR1 is used to contact the semiconductor carrier substrate 1.

[0033] In connection with the simplified electrical equivalent circuit diagram of the sensor device according to the invention in Figure 1bIt should be noted that to accurately represent the real conditions, other effects must be taken into account, such as parasitic capacitances that develop between different components. Given such effects, it is advantageous if the electrical resistance of the semiconductor substrate 1, which in the case of silicon is subject to a wide range of fluctuation (1 ... 10 Ω • cm), is in the order of magnitude of the series resistance of the measuring capacitance C_RH, and thus this parameter for the reference capacitance C_REF is similar to that for the measuring capacitance C_RH.

[0034] The dual use of the base electrode 3 for the measuring capacitance C_RH and for the at least one reference capacitance C_REF provided by the invention considerably simplifies the manufacture of the sensor device according to the invention. Overall, significantly fewer process steps are required for applying functionally relevant layers. The manufacturing costs of the sensor device according to the invention can thus be reduced.

[0035] A concrete embodiment of the sensor device 10 according to the invention is described below with reference to Figures 2, 3 and 4a - 4c. Figure 2 shows a perspective view of the sensor device 10, Figure 3 an exploded view of the sensor device 10, Figure 4a a plan view of the sensor device 10 and the Figures 4b and 4c Sectional views along the Figure 4a marked directions B and C.

[0036] A passivation layer 12 in the form of silicon dioxide is applied to the semiconductor carrier substrate 11, which is square in shape in this case and is made of doped silicon. The remaining layers of the sensor device 10 according to the invention are then arranged one above the other on the passivation layer 12. Typical dimensions of the semiconductor carrier substrate 11 are in the range of 2.3 mm (length) x 2.3 mm (width) x 0.725 mm (thickness). Using an 8" wafer, up to 5,000 sensor devices according to the invention can be manufactured from such a wafer.

[0037] The base electrode 13 used according to the invention both for the measuring capacitance C_RH and for the reference capacitance C_REF in the sensor device 10 is in the present embodiment - as can be seen in particular from Figure 3As can be seen, it is formed in the form of a circular area with a diameter of approximately 1.4 mm. The material for the base electrode 13 in this example is gold with an underlying adhesion and solderability layer of Ni or NiCr.

[0038] The moisture-permeable cover electrode 15 is also flat and circular in this case and has a suitable porous or cracked structure. In this embodiment, the material used for the cover electrode 15 is chromium.

[0039] The contact terminal of the base electrode 13 is designated 10.4 in the figures. As also Figure 3As can be seen, this contact connection 10.4, like the other contact connections 10.1, 10.2 for the semiconductor carrier substrate 11 and the contact connection 10.3 for the cover electrode 15, is each planar. Not shown in the figures is an additional layer at the contact connections 10.1, 10.2 for the semiconductor carrier substrate 11, for example, an aluminum layer, which is provided beneath the contact connections 10.1, 10.2 and prevents the metal-silicon junction from acting as a Schottky diode. The various contact connections 10.1 - 10.4 can have a square cross-section, as shown in the figures; alternatively, a round cross-section for the contact connections 10.1 - 10.4 is also possible.

[0040] According to Figure 4bThe gold contact terminal 10.4 of the base electrode 13 is arranged immediately laterally adjacent to the base electrode 13 in the same layer plane on the passivation layer 12. Also on the passivation layer 12 is Figure 4c the contact terminal 10.3 of the cover electrode 15 is placed, but spatially separated from the base electrode 13. As can be seen from Figure 3 As can be seen, this contact connection 10.3 is also placed in the base electrode plane, but is electrically insulated from the base electrode 13 and electrically connected to the cover electrode 15 located above it.

[0041] Such a design of the sensor device 10 according to the invention allows for further processing without additional housing or packaging. For example, it is possible to further process the sensor device 10 using a flip-chip process, in which it is automatically placed directly over a recess on a circuit board or printed circuit board and electrically contacted via the contact terminals 10.1 - 10.4 using solder paste. Using an underfiller between the circuit board and the sensor device, the contact terminals 10.1 - 10.4 of the sensor device 10 can be fixed to the circuit board and protected from mechanical damage.

[0042] Of course, further mounting variants can also be realized in connection with the sensor device 10 according to the invention, in which the contacting could be carried out via conductive adhesives, bond connections, solder bumps, etc., depending on the arrangement.

[0043] If a temperature measurement is required for signal evaluation in addition to the measured value of the capacitive humidity sensor, a cost-effective NTC temperature sensor can be used as the temperature sensor. This can be installed in a suitable manner next to the sensor device according to the invention on a circuit board or printed circuit board.

[0044] Based on the Figures 5 and 6 Finally, two possibilities are illustrated by way of example of how an arrangement can be formed on a carrier substrate using the sensor device according to the invention.

[0045] A first arrangement with a sensor device 110 according to the invention is shown in Figure 5shown in a sectional view. As can be seen from this figure, the sensor device 110 is arranged in the region of a circular recess 130 of a carrier substrate 125; the recess 130 has a diameter of approximately 2 mm in the present example. The humidity sensor arranged on the semiconductor carrier substrate 111 as explained above, with base electrode 113, moisture-sensitive dielectric 114 and cover electrode 115, is oriented in the direction of the recess 130 and arranged above the recess 130. Of the total of four contact connections, Figure 5Only two contacting terminals 110.2, 110.4 are visible. These are connected to the corresponding contacting areas 123, 124 on the carrier substrate 125 via electrically conductive connecting material 121, 122 in the form of solder; in this exemplary embodiment, copper is provided as the material for the contacting areas 123, 124. The carrier substrate 125 is embodied as a printed circuit board made of FR4 material and has a thickness of approximately 1 mm. Not shown in the figure are electrical conductor tracks in the carrier substrate 125, via which the sensor device 110 is connected to further components (also not shown).

[0046] In this arrangement variant, the conductive connecting material 121, 122 between the contact terminals 110.2, 110.4 of the sensor device 110 and the contact areas 123, 124 of the carrier substrate 125 is designed in the form of so-called "wettable pads." This means that an automatic visual inspection of the solder connections is possible at this point. Defective solder connections can thus be easily identified during the production process, and the corresponding units can be sorted out.

[0047] On the side of the carrier substrate 125 facing away from the sensor device, a moisture-permeable membrane 140 is arranged in the region of the recess 130. This membrane can be made of Teflon mesh, for example, and serves to protect the sensor device 110 from dirt and liquids.

[0048] Particularly advantageous is the Figure 5The arrangement shown further ensures good heat transfer between the top side of the semiconductor carrier substrate 111 and the humidity sensor arranged on the opposite side. The arrangement can be arranged, for example, glued onto the top side of a motor vehicle to detect condensation on a windshield. Thanks to the good thermal coupling, the humidity sensor can then assume the temperature of the windshield, allowing the condensation temperature of the windshield to be measured directly without the need for a separate temperature sensor.

[0049] A second arrangement with a sensor device 210 according to the invention is finally shown in the sectional view in Figure 6 explained.

[0050] As in the previous example, the sensor device 210 is arranged in the region of a circular recess 230 of a carrier substrate 225, wherein the recess 230 again has a diameter of approximately 2 mm. In contrast to the previous arrangement, the carrier substrate 225 is now designed as a so-called flexible circuit board made of polyimide material, which has a thickness of only approximately 50 µm. The humidity sensor arranged on the semiconductor carrier substrate 211 with base electrode 213, moisture-sensitive dielectric 214 and cover electrode 215 is, as before, oriented in the direction of the recess 230 and arranged above the recess 230. Of the total of four contact connections, the Figure 6 Only two contact terminals 210.2, 210.4 are visible. These are also connected to the corresponding contact areas 223, 224 on the carrier substrate 225 via electrically conductive connecting material 221, 222 in the form of solder.

[0051] In contrast to the previously explained variant, the area around the connecting material between the sensor device 210 and the carrier substrate 225 is now filled with an underfiller material 250. A suitable epoxy resin can be used for this purpose, for example. The sensor device 210 is bonded to the carrier substrate 225 via the underfiller material 250, which, on the one hand, results in mechanical relief of the solder joints or in the area of ​​the connecting material 221, 222. On the other hand, the recess 230 in the carrier substrate 225 can be sealed to the side with the components arranged thereon.

[0052] As a further difference to the previous embodiment, it should be mentioned that the recess 230 of the carrier substrate 225 as shown in Figure 6visibly filled with a coating material 260. The coating material 260 enables gas exchange between the humidity sensor of the sensor device 210 and the environment, while also keeping liquid away from the humidity sensor. This prevents dirt and water in liquid form from being kept away from the humidity sensor. Furthermore, the metallic components of the humidity sensor are protected from possible deposits and corrosion.

[0053] If this arrangement is used to detect condensation on a windshield in a motor vehicle, the flexible circuit board together with the sensor device can be pressed directly onto the windshield by appropriate bending; this in turn results in good heat exchange between the windshield and the sensor device.

[0054] In addition to the exemplary embodiments described above, there are of course further possible embodiments within the scope of the present invention.

[0055] For example, to construct arrangements as shown in the examples of Figures 5 and 6 Of course, other carrier substrates can also be used which differ in material and / or thickness from the variants explained above.

[0056] Furthermore, it is possible for the base electrode to be constructed in multiple parts. In the case of a two-part base electrode, this can comprise two concentrically arranged base electrode parts, namely a central, circular, first base electrode part and a circular-ring-shaped second base electrode part that encloses the first base electrode part. Furthermore, a two-part construction would be possible in which a first and a second base electrode part are each shaped like a circular segment, with both circular segments forming a circular shape of the base electrode.

[0057] In the case of such two-part base electrode structures, the areas of the various base electrode parts, as well as the thickness of the passivation layer and the moisture-sensitive dielectric, can be selected such that a specific relationship results between the measuring capacitance C_RH and the, in this case, multiple reference capacitances C_REF1, C_REF2. Thus, a first reference capacitance C_REF1 forms, for example, between the first base electrode part and the semiconductor carrier substrate, and a second reference capacitance C_REF2 between the second base electrode part and the semiconductor carrier substrate. Preferably, in the case where the first base electrode part has a smaller area than the second base electrode part, the above-mentioned parameters are selected such that the following relationship applies: C _ REF 1 < C _ RH < C _ REF 2

[0058] Here, C_RH denotes the measuring capacitance, which covers the entire humidity range between 0...100%RH plus any varying thicknesses of the dielectric due to process variations.

Claims

1. Sensor apparatus (10) for measuring moisture, consisting of an electrically conductive semiconductor carrier substrate (1; 11; 111; 211), having - a capacitive moisture sensor arranged thereon that comprises a base electrode (3; 13; 113; 213), a moisture-permeable top electrode (5; 15; 115; 215) and a moisture-sensitive dielectric (4; 14; 114; 214) arranged between the base and top electrodes (3, 13, 113, 213; 5, 15, 115, 215), and - at least one reference capacitance (C_REF; C_REF1; C_REF2) arranged thereon for evaluating the moisture sensor, - wherein the base electrode (3; 13; 113; 213) of the capacitive moisture sensor is furthermore part of the at least one reference capacitance (C_REF; C_REF1; C_REF2), - wherein on the semiconductor carrier substrate (1; 11; 111; 211) a passivation layer (2; 12; 112; 212) is arranged, to which the base electrode (3; 13; 113; 213) is applied, and multiple contact-connection terminals (GE1; DE1; CR1; 10.1 - 10.4) are formed for connection to a moisture measurement circuit arrangement, in particular at least one contact-connection terminal (DE1; 10.3) for the top electrode (5; 15; 115; 215), at least one contact-connection terminal (GE1; 10.4) for the base electrode (3; 13; 113; 213) and at least one contact-connection terminal (CR1; 10.1; 10.2) for the semiconductor carrier substrate (1; 11; 111; 211), and - wherein the reference capacitance (C_REF; C_REF1; C_REF2) comprises the base electrode (3; 13; 113; 213), the semiconductor carrier substrate (1; 11; 111; 211) and the passivation layer (2; 12; 112; 212), and - wherein the moisture sensor and the reference capacitance (C_REF; C_REF1; C_REF2) are arranged above one another.

2. Sensor apparatus according to Claim 1, wherein the passivation layer (2; 12; 112; 212) is produced from one or more of the following materials: silicon dioxide, silicon oxynitride, silicon nitride.

3. Sensor apparatus according to at least one of the preceding claims, wherein the base electrode (3; 13; 113; 213) is two-dimensional and produced from electrically conductive material.

4. Sensor apparatus according to Claim 3, wherein the base electrode (3; 13; 113; 213) is produced from gold and an underlying adhesive and solderable layer.

5. Sensor apparatus according to at least one of the preceding claims, wherein the top electrode (5; 15; 115; 215) is two-dimensional and produced from electrically conductive material.

6. Sensor apparatus according to at least one of the preceding claims, wherein the semiconductor carrier substrate (1; 11; 111; 211) is produced from doped semiconductor material.

7. Sensor apparatus according to Claim 1, wherein each of the contact-connection terminals (GE1, DE1, CR1; 10.1 - 10.4) is in planar form.

8. Sensor apparatus according to Claim 1, wherein each of the contact-connection terminals (GE1, DE1, CR1; 10.1 - 10.4) has a square or round cross section.

9. Sensor apparatus according to at least one of the preceding claims, wherein the base electrode (3; 13; 113; 213) is in multipartite form.

10. Arrangement having a carrier substrate (125; 225) that has a recess (130; 230), comprising a sensor apparatus (110; 210) according to one of the preceding claims arranged in the region of the recess (130; 230), the moisture sensor being oriented in the direction of the recess (130; 230).

11. Arrangement according to Claim 10, wherein the recess (130) is covered by a moisture-permeable diaphragm (140) made of Teflon mesh on that side of the carrier substrate (125) that is oriented to face away from the sensor apparatus (110).

12. Arrangement according to Claim 10, wherein the recess (230) in the carrier substrate (225) is filled with a coating material (260) that permits an exchange of gas between the moisture sensor and the surroundings but keeps liquid away from the moisture sensor.