Planar heating element with a PTC resistive structure

Abstract

A planar heating element comprising a PTC resistive structure, which is arranged in a defined surface region of a first surface of a support substrate. The electrical connection contacts for connection to an electrical voltage source are associated with the PTC resistive structure, wherein the PTC resistive structure—starting from the two electrical connection contacts—has at least one internal conductive trace and a parallel connected, external conductive trace. The internal conductive trace has a greater resistance than the external conductive trace and the resistances of the internal conductive trace and external conductive trace are so sized that upon applying a voltage an essentially uniform temperature distribution is present within the defined surface region.

Claims

1. A planar heating element, comprising: a support substrate; a resistive structure disposed on a surface region of the support substrate, the resistive structure including a proximal end portion, a middle portion and a distal end portion, wherein the resistive structure includes an inner conductive trace and an outer conductive trace, which is connected electrically in parallel to the inner conductive trace; and electrical contacts configured to enable connecting a voltage source to the resistive structure, the contacts connected to the resistive structure via corresponding connecting lines, wherein: the inner conductive trace and the outer conductive trace are configured to generate, upon applying a voltage to the contacts, a temperature distribution in the first surface region of the support substrate; each of the inner conductor trace and the external conductor trace has a line width and a film thickness; the inner conductive trace has a greater electrical resistance than the outer conductive trace such that the temperature distribution is substantially uniform due to differences in film thickness, line width and/or length between the inner conductive trace and the outer conductive trace, respectively; and the resistive structure includes at least two overlap structures at the proximal end portion in which each of the inner conductor trace and external conductor trace overlap and connect with the corresponding connecting lines.

2. The planar heating element of claim 1, wherein the resistive structure is further configured to determine temperature measured values such that the resistive structure is both a heating element and a temperature sensor.

3. The planar heating element of claim 1, wherein the resistive structure is of a positive temperature coefficient material.

4. The planar heating element of claim 1, wherein the respective film thicknesses and/or line widths of the inner conductor trace and external conductor trace at or near each respective overlap structure are adapted such that the temperature distribution at the proximal end portion is substantially uniform relative to the middle portion.

5. The planar heating element of claim 1, wherein the inner conductive trace and the outer conductive trace are of the same material.

6. The planar heating element of claim 1, wherein the inner conductive trace and the outer conductive trace are of different materials with different specific resistances.

7. The heating element of claim 1, wherein the inner conductive trace and the outer conductive trace extend essentially parallel to one another in the middle portion.

8. The heating element of claim 1, wherein the inner conductive trace and the outer conductive trace extend toward one another in the proximal end portion adjacent each overlap structure, respectively.

9. The heating element of claim 1, wherein a resistance per unit length of the inner conductive trace and/or the outer conductive trace in the proximal end portion and/or in the distal end portion is greater than the resistance per unit length of the inner conductive trace and/or the outer conductive trace in the middle portion.

10. The heating element of claim 1, wherein, in at least in one subsection of the resistive structure, the line widths and/or the film thicknesses of the inner conductive trace and/or outer conductive trace are varied along a length thereof such that a locally occurring deviation from the uniform temperature distribution is at least approximately negated.

11. The heating element of claim 1, wherein the support substrate is a material having a thermal conductivity such that, upon applying a voltage to the contacts, the resistive structure generates a thermal gradient greater than 50° C./mm between surface region and the contacts.

12. The heating element of claim 1, further comprising an electrically insulating separating layer on or in the support substrate.

13. The heating element of claim 1, further comprising a passivating layer.

14. The heating element of claim 1, wherein the contacts and/or the corresponding connecting lines are manufactured of a noble metal or a noble metal alloy.

15. The heating element of claim 1, wherein each overlap structure between the corresponding connecting lines and the inner conductive trace and outer conductive trace, respectively, is V-shaped, rectangularly shaped or strut-shaped.

16. The heating element of claim 1, wherein the breadth of each overlap structure between the corresponding connecting lines and the inner conductive trace and outer conductive trace, respectively, is greater than a separation between the inner conductive trace and outer conductive trace.

17. The heating element of claim 1, further comprising a second resistive structure configured to determine a temperature and to heat a medium, wherein the second resistive structure is disposed on a surface of the support substrate opposite the surface region.

18. The heating element of claim 1, wherein the internal conductive trace has a greater electrical resistance than the external conductive trace due to differences between the line widths and/or the film thicknesses thereof.

19. The heating element of claim 1, wherein the resistive structure consists essentially of platinum.

20. The heating element of claim 1, wherein the contacts consist essentially of silver or a silver alloy.

21. The heating element of claim 1, wherein the contacts consist essentially of gold with a purity of greater than 95%.

22. A heating apparatus comprising: the heating element according to claim 1; an electrical energy source adapted to supply the resistive structure with power; and a control/evaluation unit configured to control the resistive structure as to generate a predetermined temperature in the surface region.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be explained in greater detail based on the appended drawing, the figures of which show as follows:

(2) FIG. 1 is a plan view of a preferred embodiment of the heating element of the invention;

(3) FIG. 1a is a longitudinal section taken according to the cutting plane A-A of the heating element of the invention shown in FIG. 1;

(4) FIG. 2 is a schematic partial view of the heating element of the invention showing a first embodiment of the overlap between a connecting line and the conductive traces;

(5) FIG. 3 is a schematic partial view of the heating element of the invention showing a second embodiment of the overlap between a connecting line and the conductive traces;

(6) FIG. 4 is a schematic partial view of the heating element of the invention showing a third embodiment of the overlap between a connecting line and the conductive traces;

(7) FIG. 5a is a plan view of a second embodiment of the heating element of the invention, with PTC resistive structure; and

(8) FIG. 5b is a plan view of the rear-side of the heating element shown in FIG. 5a.

DETAILED DISCUSSION IN CONJUNCTION WITH THE DRAWINGS

(9) FIG. 1 shows a plan view of a preferred embodiment of the heating element 1 of the invention. The external dimensions of the PTC resistive structure 2 limit the defined surface region 3, respectively the heated zone. The PTC resistive structure is virtually divided into three different portions: A first end portion 10, which adjoins the connection contacts 6, respectively the electrical connecting lines 15, a middle portion 11, which adjoins the first end portion 10, and a second end portion 12, which adjoins the middle portion 11. Between the connection contacts 6 and the electrical connecting lines 15, there is an overlap 16b of defined length. Likewise, there is between each connecting line 15 and the conductive traces 8, 9 an overlap 16a.

(10) The internal conductive trace 8 and the external conductive trace 9 of the PTC resistive structure 2 extend approximately parallel and are connected electrically in parallel. The internal conductive trace 8 has a greater resistance than the external conductive trace 9. The resistances of the internal conductive trace 8 and external conductive trace 9 are so sized that upon applying a voltage an essentially uniform temperature distribution is present within the defined surface region 3. This defined surface region is also referred to as the heated zone and is indicated in FIG. 1 by the dashed line on the outer edge of the PTC resistive structure 2.

(11) The cold zone, thus the region, where essentially room temperature reigns, lies in the region of the connection contacts 6. In the transitional region lying between the heated zone and the cold zone, same as in the outer region of the defined surface region 3, the temperature gradient is very high. As a result of the high temperature gradient, the heated zone is largely limited to the defined surface region 3. The high temperature gradient is achieved by the choice of a support substrate 5 with low thermal conductivity. Other information in this regard is provided above.

(12) In the case of the illustrated form of embodiment, the internal conductive trace 8 and the external conductive trace 9 are manufactured of the same material. As mentioned above, platinum is preferably used as material of the conductive traces 8, 9. The different resistances of the conductive traces 8, 9 are implemented via different cross sectional areas and/or lengths of the internal conductive trace 8 and external conductive trace 9.

(13) A preferred dimensioning of the heating element of the invention, respectively of the chip of the invention, is given above.

(14) Evident from FIG. 1 is that the connecting lines 15, which—as indicated above—are preferably of gold, likewise vary in width: following the first portion 10, the width is smaller and therewith the resistance greater than in the region, which adjoins the connection contacts 6. In this way, it is achieved that the thermal conductivity does not increase. In connection with the smaller thermal conductivity of gold compared with platinum, the desired large temperature gradient is achieved in the transitional region from the heated zone to the cold zone.

(15) FIG. 1a shows a longitudinal section taken on the cutting plane A-A of the heating element 1 of the invention shown in FIG. 1. Arranged on both surfaces 4, 19 of a support substrate 5 is a separating layer 14. The substrate 5 is preferably zirconium oxide with a thickness of 300 μm, while the separating layers 14 have, in each case, a thickness of 15 μm. Applied on the separating layer 14 on the surface 4 of the support substrate 5 is the PTC resistive structure 2. The PTC resistive structure is composed of platinum with a thickness of 8 μm.

(16) The above described dimensioning of the PTC resistive structure 2 is not limited to the mentioned values. Each of the explicitly mentioned values can be varied as much as desired upwardly or downwardly. How the dimensioning of the variants is embodied in detail lies within the skill of the art.

(17) In the case of a preferred embodiment of the invention, the connection contacts 6 are manufactured of silver and have a thickness of 10 μm. The electrical connecting line 15 between the connection contacts 6 and the PTC resistive structure 2 are of gold and are 4 μm thick. In the region of the overlap 16b, the connection contacts 6 and the electrical connecting lines 15 overlap, while in the region of an overlap 16a, the electrical connecting lines 15 and the conductive traces 8, 9 of the PTC resistive structure overlap. The surfaces 4, 19 of the planar heating element 1 are sealed with a passivating layer 13. The passivating layer 13 has a thickness of 15 μm. The functions of the individual layers were explained above. The sensitivity of the planar heating element amounts at room temperature without applying the heating voltage to 3700 ppm/K (+−100 ppm/K). The thicknesses of the individual layers are given by way of example. Each of the explicitly mentioned values of the preferred embodiment can be varied upwardly or downwardly as much as desired. How the dimensioning is embodied in detail lies within the skill of the art.

(18) FIGS. 2, 3, and 4 show schematically partial views of the heating element of the inventions 1 with different embodiments of the overlap 16a between one of the connecting lines 15 and the connected conductive traces 8, 9. The overlap 16a in FIG. 2 has a strut shaped embodiment, the overlap 16a in FIG. 3 is rectangularly shaped and the overlap 16a in FIG. 4 has a V shape. The overlap 16a between the connecting lines 15 and the conductive traces 8, 9 in the first end portion 10 of the PTC resistive structure 2 is so embodied relative to its geometric parameters that the physical heating properties of the PTC resistive structure 2 are at least approximately unchanged, respectively are almost identical with the properties in the defined surface region 3 containing the heated zone. The materials and the special features, which occur in the regions of the overlap 16a, 16b, have been described above, so that a repetition here is omitted.

(19) FIG. 5a shows a plan view of a second embodiment of the heating element 1 of the invention with PTC resistive structure 2, while FIG. 5b shows a plan view of the rear side 19 of the heating element 1 shown in FIG. 5a. A meander shaped temperature sensor 18 is arranged on the rear side 19. Furthermore, FIG. 5a also shows schematically the heating apparatus of the invention with heating element 1, electrical voltage source 7 and control/evaluation unit 17.