Film resistor and thin-film sensor with a piezoresistive layer

Abstract

A film resistor and a thin-film sensor are disclosed. In an embodiment a film resistor includes a piezoresistive layer including a first transition metal carbide.

Claims

1. A film resistor comprising: a piezoresistive layer comprising a first transition metal carbide as a main constituent and at least one additive material selected from the group consisting of transition metal nitrides, second transition metal carbides and mixtures thereof, wherein the first transition metal carbide contains a transition metal selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W and combinations thereof.

2. The film resistor according to claim 1, wherein the first transition metal carbide is Cr3C2.

3. The film resistor according to claim 1, wherein the first transition metal carbide is based on the formula MC.sub.x, and wherein M=Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W and combinations thereof and x is 1.

4. A thin-film sensor comprising: a first film resistor according to claim 1; a membrane on which the first film resistor is arranged; and a support body to which the membrane is fastened, the membrane being configured to be movable relative to the support body.

5. The thin-film sensor according to claim 4, wherein the membrane and the support body comprise a material selected from the group consisting of ceramic and metal.

6. The thin-film sensor according to claim 5, wherein the membrane and the support body comprise a material selected from the group consisting of stainless steel and yttrium-stabilized zirconium oxide.

7. The thin-film sensor according to claim 4, further comprising a second film resistor, wherein the second film resistor includes a piezoresistive layer comprising the first transition metal carbide.

8. The thin-film sensor according to claim 7, wherein one of the first or second film resistor is configured to measure temperature.

9. The film resistor according to claim 7, wherein the piezoresistive layer of the second film resistor comprises the at least one additive material selected from the group consisting of transition metal nitrides, second transition metal carbides and mixtures thereof.

10. The film resistor according to claim 1, wherein the additive material is tungsten carbide.

11. The film resistor according to claim 1, wherein the first transition metal carbide and the additive material form a mixed crystal.

12. The film resistor according to claim 1, wherein the first transition metal carbide is polycrystalline.

13. The film resistor according to claim 12, wherein crystals of the first transition metal carbide have an oxide layer on their surface.

14. The film resistor according to claim 1, wherein the piezoresistive layer has a coefficient of thermal expansion in a range from 9 ppm/K to 15 ppm/K inclusive.

15. The film resistor according to claim 1, further comprising electric contacts comprising the first transition metal carbide.

16. A film resistor comprising: a piezoresistive layer comprising a first transition metal carbide as a main constituent and at least one additive material selected from the group consisting of transition metal nitrides, second transition metal carbides and mixtures thereof, wherein the first transition metal carbide contains a transition metal selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W and combinations thereof; and electric contacts comprising the first transition metal carbide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Particular embodiments of the invention will be illustrated in detail with the aid of the FIGURE and exemplary embodiments.

(2) The sole FIGURE shows a schematic sectional view of a thin-film sensor as per one exemplary embodiment.

(3) In the exemplary embodiments and FIGURES, identical, similar or similarly acting elements can in each case be denoted by the same reference numerals. The elements depicted and their relative sizes should not be considered to be true-to-scale; rather, individual elements can be depicted excessively large for better visibility and/or in the interests of better understanding.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(4) The FIGURE shows a schematic sectional view of a thin-film sensor as per an exemplary embodiment. The support body 30 has an opening 31. Other shapes of the support body 30, which are not shown here, are likewise conceivable. For example, the support body 30 can be shaped so that the membrane 20 is fastened thereto only at one of its lateral margins.

(5) A membrane 20 is applied to the support body 30 in such a way that it is freely movable relative to the support body 30 between the support body 30, within the opening 31.

(6) In particular, the membrane 20 can be bent or can oscillate relative to the support body 30.

(7) The film resistor 10 which contains the piezoresistive layer 11 is located on the membrane 20, especially in the region in which the membrane 20 is freely movable relative to the support body 30. At two opposite ends of the piezoresistive layer 11 there are electric contacts 40 which are electrically contacted via bond wires 50.

(8) When the membrane 20 experiences a deformation, the piezoresistive layer 11 is also deformed, which due to the piezoresistive effect leads to a change in resistance, which can be detected by the contacts 40.

(9) The thin-film sensor can also have a plurality of film resistors 10 (not shown here). For example, the thin-film sensor can have four film resistors. The film resistors 10 can be connected to form a measurement bridge by means of which, for example, a pressure can be measured. Forces on and strain of the membrane 20 can likewise be measured.

(10) In this exemplary embodiment, the piezoresistive layer 11 contains Cr.sub.3C.sub.2 as main constituent. This can form mixed crystals with additive materials, for example other nitrides or carbides of the transition metals, in particular with WC. The contacts 40 likewise contain Cr.sub.3C.sub.2 as main constituent. The support body 30 and the membrane 20 consist of stainless steel or YSZ.

(11) The piezoresistive layer and also the membrane 20 and the support body 30 have coefficients of expansion matched to one another, for example a coefficient of expansion of in each case 10 ppm/K. As a result, no stress arises between the membrane 20 and the film resistor 10 during the measurement, which stress could lead to drifts or destruction of the thin-film sensor.