GB2109998A

GB2109998A - Resisters

Info

Publication number: GB2109998A
Application number: GB08232388A
Authority: GB
Inventors: Niels Lervad Anderson; Per Phillipsen
Original assignee: Danfoss AS
Current assignee: Danfoss AS
Priority date: 1981-11-20
Filing date: 1982-11-12
Publication date: 1983-06-08
Also published as: CH659342A5; JPH0145722B2; FR2517056B1; JPS58130502A; FR2517056A1; DE3146020A1; DK503582A; DE3146020C2; GB2109998B

Abstract

A resistor, particularly for resistance thermometers, comprising a carrier of an insulating metal oxide and a thin platinum layer as resistor material, the resistor having been annealed in an oxygen-containing atmosphere after the application of the resistor material, wherein an intermediate layer (2) has been applied to the carrier (1) between the carrier (1) and the platinum layer (3) and comprises a metal joining the carrier (1) and the platinum layer (3) so as to increase the strength of the connection between the platinum layer and carrier. The intermediate layer (2) may be of Ti, Cu or Zr. The carrier (1) is preferably of aluminium oxide but may also be of magnesium oxide. <IMAGE>

Description

SPECIFICATION Resistors This invention relates to a temperature-dependent resistor, particularly for resistance thermometers, comprising a carrier of an insulating metal oxide and a thin platinum layer as resistor material, wherein the resistor is annealed in an oxygen-containing atmosphere after the application of the resistor material.

In a known temperature-dependent resistor of this kind, the thin platinum layer is vapourised directly onto the insulating carrier in vacuum or applied thereto by cathode evaporation (sputtering) to a thickness of about 1 micrometre to 10 micrometres.

To produce meander patterns, a photo-laquer is applied to the platinum flim and partially covered, exposed and developed. The conductor path is then produced by means of ionic etching or other methods. Equalisation of these conductor paths to a particular resistance is effected by means of a laser beam. To produce a particularly high temperature coefficient for the electric resistor, the thin platinum layer is applied in an argon-oxygen mixture by cathode sputtering and is subsequently annealed at temperatures above 800"C, preferably in the range of 10000Cto 1 20G C.

In a resistor which is produced in this manner, there is the danger that the platinum film will tear off easily. For example, it can be torn off the carrier by pulling on a wire that is soldered on. Even peeling off a conventional adhesive tape can result in the platinum layer being torn off.

The invention is based on the problem of providing a temperature-dependent resistor of the aforementioned kind in which there is better adhesion of the platinum layer to the base.

According to the invention, this problem is solved in that an intermediate layer applied to the carrier between the carrier and the platinum layer comprises a metal joining the carrier and the plantinum layer.

The platinum layer will now withstand ae least those forces required for pulling off a wire that is soldered to the platinum layer.

Preferably, the intermediate layer comprises titanium. This ensures particularly high bonding forces.

Preferably, the intermediate layer is vapourised onto the carrier to connect it intimately to the carrier.

The intermediate layer may have a thickness of about 2 nanometres to 5 nanometres, preferably about 2.5 nanometres. Such a small thickness is adequate to ensure a secure hold of the platinum layer on the intermediate layer.

The platinum layer may have a thickness of about 0.4 micrometres to 1.2 micrometres, preferably about 1 micrometres. A layer thickness in this range not only gives the required strength for a soldered connection to the platinum layer but also a comparatively high resistance. This allows as is often required, measurements to be made using relative long connecting conductors - changes in resistance of the conductors having no marked influence.

The platinum layer may be applied to the intermediate layer by vapourising on or by cathode sputtering. This, again, produces a comparatively high strength for the joint between the platinum layer and the intermediate layer, particularly a titanium intermediate layer.

Preferably, the carrier material is aluminium oxide. This material is not only a good insulator but likewise ensures a high strength of the joint between the carrier and the intermediate layer, particularly titanium.

Further, the resistor may be annealed in air. In this way one primarily avoids temperature-dependent departures of the resistance, or those caused by ageing, from the nominal value at the particular temperature.

Particularly small departures of the resistance from the nominal value are obtained if the resistor is annealed at a temperature of about 1200"C to 1425 C, preferably at about 1300 C.

For this purpose, a heat treatment duration of only about one hour will be sufficient.

The present invention also provides a resistor comprising an electrically insulating support having a thin coating of electrical resistance material, wherein a metal coating is provided between the resistance coating and the support affixing the resistance coating to the support.

The present invention further provides a resistance thermometer including a resistor according to the invention.

A resistor constructed in accordance with the presenet invention will now be described, by way of example only, with reference to the accompanying drawing, wherein Fig. lisa side elevation of the resistor; Fig. 2 is a plan view of the Fig. 1 resistor, and Fig. 3 is an error diagram for different resistors constructed according to the invention.

Referring to the accompanying drawings and first of all to Figs. 1 and 2, the temperature-dependent resistor constists of an electrically insulating carrier (substrate) 1, ain intermediate layer 2 and a platinum layer 3.

The carrier 1 consits of an insulating metal oxide layer, which is preferably aluminium oxide but could be other metal oxides such as magnesium oxide.

The intermediate layer 2 consists of a metal, preferably titanium, but may instead comprise copper. It has a thickness of about 2 nanometres to 5 nanometres, preferably about 2.5 nanometres, and is preferably vapourised onto the carrier 1 after heating the carrier 1 to about 250"C, but it can instead be applied by cathode sputtering.

The platinum layer forms the temperature-dependent resistor material and has a thickness of about 0.4 micrometres to 1.2 micrometres, preferably 0.5 micrometre to 1 micrometre. In the same way as the intermediate layer 2, it is constructed in meander (serpentine) form by the photoresist method and vapourised onto the intermediate layer 2 or applied by cathode sputtering. The meander form can, however, also be produced by burning away with the aid of a laser beam.

The finished resistor is, prior to producing the meander form, annealed (heat treated) in an ox ygen-containing atmosphere, preferably air, namely at a temperature of about 11 0'C to 1425 C, preferably at a tesupe-ture of about 1200 C to 13000, the most favourable temperature being about 1300 C, to achieve very small departures of its resistance from tile nominal value at the particular operating temperature. After annealing, the meander form is produced and thereafter there is fine equalisatisn of its resistance, ikewise by burning away with the aid of a laser beam. Finally, there is another annealing step.

Table I hereunder contains different embodiments of resistors having the basic construction of Figs. 1 and 2 and differing in the temperature during annealing, the thickness of platinum layer and the intermediate metal layer and having 3 nominal resistance of 100 ohm at 0 C. The intermediate layer thickness is 2.5 nanometre. Annealing took place in atmospheric air for about one hour. The carrier 1 consisted of aluminium oxide.

Example Annealing Platinum intermediate Temperature Layer Layer lOG) Thickness a 500 0.38-0.5 Cu, sputtered on b 850 c 1200 d 1400 " Titanium, vaporised on e 1375 0.5 f 1425 1 g 1375 1 h 1300 1 Fig. 3 illustrates the departure of the resistance of the various examples of Table I in dependence on the operating temperature. The diagram includes two tolerance ranges i A and + B according to the German Industrial Standard shown in broken and chain-dotted lines respectively, the tolerance range + A being narrower than that of + B.

As shown in Fig. 3, the departures from the nominal value in Examples a, band cvery rapidly exceed the tolerance ranges A and B wheras in the cases of Examples dand ethey lie in the narrower tolerance range + A at least between -50 C and + 1402C and are still narrower in Examples f, g and h at least above 0 C and remain within the tolerance range I A over a still largertemeprature range, the departures in Example h being the smallest at least up to about 145 C. In the temperature range of about -30 C to about + 180 C, which is very often of interest; Example h therefore proves to be the most favourable.

The strength with which the platinum layer 2 and the carrier 1 are connected is in all cases so high that on pulling on a conductor soldered to the platinum layer 2, the solder is torn and pulling off a conventional adhesive tape sticking to the platinum layer 2 will not cause the platinum layer 2 to be torn off.

The following Table II summat sews two advantageous basic examples for the production of a resistor according to the invention. These examples differ substantially only in the nature of forming the pattern (for example of meander form) by means of a laser on the one hand and photoresist technology on the other hand.

Tablell Laser Technology 1. Cleaning of carrier 2. Vapourising titanium on. Layer thickness about 2.5 namometre 3. Vapourising platinum on. Layer thickness about 0.5 to 1 micro metre 4. Annealing at about 1100 to 14250C, prefer ably 13000C. Duration: about 1 hour 5. Forming the pattern by partially burning the titanium and platinum layers away 6. Final annealing 7. Fine equilisation by laser 8. Separating the compo site structure into smaller resistor elements 9. Applying terminals 10. Encapsulation Photoresist Technology 1. Cleaning of carrier 2. Applying photo-laquer 3. Exposure through mask 4. Removing photo-laquer at exposed places 5. Vaporising titanium on.

Layer thickness about 2.5 nanometre 6. Vapourising platinum on.

Layer thickness about 0.5 to 1 micrometre 7. Annealing at about 1100 to 1425on, preferably about 13000C. Duration: about 1 hour 3. Removal of unexposed photo-laquer to produce the pattern 9. Digital andior ansiog equilisation of the resistor by means of laser 10. Separation of composite structure into smaller resistor elements 11. Application of terminals 12. Encapsulation Departures of the illustrated examples fall within the scope of this invention. Thus, zirconium can be used for the intermediate layer 2 instead of copper or titanium.

Claims

1. A resistor comprising an electrically insulating support having a thin coating of electrical resistance material, wherein a metal coating is provided between the resistance coating and the support affixing the resistance coating to the support.

2. A resistor as claimed in Claim 1, in which the metal coating comprises titanium.

3. A resistor as claimed in Claim 1 or Claim 2, in which the metal coating has been vapourised onto the support.

4. A resistor as claimed in any one of Claims 1 to 3, in which the metal coating has a thickness of about 2 nanometres to 5 nanometres.

5. A resistor as claimed in Claim 4, in which the thickness is about 2.5 nanometres.

6. A resistor as claimed in any one of Claims 1 to 5, in which the resistance coating has a thickness of about 0.4 micrometresto 1.2 micrometres.

7. A resistor as claimed in Claim 6, in which the resistance coating has a thickness of about 1.0 micrometres.

8. A resistor as claimed in any one a Claims 1 to 7, in which the resistance coating has been applied to the metal coating by vapourisation or by cathode evaporation.

9. A resistor according to one o Claims 1 to 8, in which the support material is a metal oxide.

10. A resistor as claimed in Claim 9, in which the resistor material is aluminium oxide.

11. A resistor as claimed in any one of Claims 1 to 10, in which the resistor has been annealed.

12. A resistor as claimed in Claim 11 in which the resistor has been annealed in an ox;gen-containing atmosphere.

13. A resistor as claimed in Claim 12, in which the resistor has been annealed in air.

14. A resistor as claimed in any one of Claims 11 to 13, in which the resistor is annealed at a temperature of about 12000C to 1425C.

15. A resistor as claimed in Claim 14, in which the temperature is 1300do.

16. A resistor as claimed in any one of Claim 11 to 15, in which the resistor is annealed for about one hour.

17. A resistor as c5ai.-S1ed in any c?ne OT C'airns to 16, in which the resistance coating is platinum.

18. A temperature-dependent resistor, particularly for resistance thermometers, comprising a carrier of an insulating metal oxide and a thin platinum layer as resistor material, wherein the resistor is annealed in an oxygen-containing atmosphere after the application of the resistor material, characterised in that an intermediate layer applied to the carrier between the carrier and the platinum layer comprises a meal joining the carrier and the platinum layer.

19. A resistor substantially as hereinbefore described with reference to, and as illustrated by Figs 1 and 2 of the accompanying drawings.

20. A resistor constructed in accordance with Table I or Table II.

21. A resistance thermometer including a resistor as claimed in any one of Claims 1 to 20.