Film resistor and thin-film sensor

Abstract

A film resistor and a film sensor are disclosed. In an embodiment a film resistor includes a piezoresistive layer comprising a M.sub.1+nAX.sub.n phase, wherein M comprises at least one transition metal, A comprises a main-group element, and X comprises carbon and/or nitrogen, and wherein n=1, 2 or 3.

Claims

1. A film resistor comprising: a piezoresistive layer comprising a M.sub.1+nAX.sub.n phase, wherein M comprises at least one transition metal, A comprises a main-group element, and X comprises carbon and/or nitrogen, and wherein n=1, 2 or 3.

2. The film resistor according to claim 1, wherein M comprises a single transition metal or two transition metals M1, M2.

3. The film resistor according to claim 1, wherein M comprises at least one of Sc, Ti, V, Cr, Mn, Zr, Nb, Mo, Hf or Ta, and wherein A is one of Al, Si, P, S, Ga, Ge, As, Cd, In, Sn, Tl, Pb or Bi.

4. The film resistor according to claim 1, wherein the piezoresistive layer consists essentially of the M.sub.1+nAX.sub.n phase.

5. The film resistor according to claim 1, wherein the piezoresistive layer comprises an oxide, a nitride or a carbide.

6. The film resistor according to claim 5, wherein the oxide is present at least in part as a surface oxide of the piezoresistive layer.

7. The film resistor according to claim 1, wherein the piezoresistive layer has a coefficient of thermal expansion of between 8 ppm/K and 14 ppm/K inclusive.

8. The film resistor according to claim 1, wherein the piezoresistive layer has a specific resistance of greater than 1 μΩ/m at a temperature of 20° C.

9. The film resistor according to claim 1, wherein the piezoresistive layer has a k factor, which indicates a ratio of a relative change in resistance (ΔR/R) to a relative change in length (ΔL/L) of the piezoresistive layer, of greater than 2.

10. A thin-film sensor comprising: the film resistor according to claim 1.

11. The thin-film sensor according to claim 10, further comprising: a membrane, on which the film resistor is arranged; and a carrier body, to which the membrane is fastened such that the membrane is movable relative to the carrier body.

12. The thin-film sensor according to claim 11, wherein one of the film resistors is arranged in a region of the carrier body or the membrane which undergoes less deformation than other regions of the carrier body or the membrane, and wherein this film resistor is configured to measure temperature.

13. The thin-film sensor according to claim 11, wherein the membrane and the carrier body comprise stainless steel or yttrium-stabilized zirconium.

14. The thin-film sensor according to claim 11, wherein the membrane and the carrier body consist essentially of an M.sub.1+nAX.sub.n phase, wherein M comprises at least one transition metal, A comprises a main-group element, X comprises carbon and/or nitrogen, wherein n=1, 2 or 3, and wherein the thin-film sensor comprises an insulator which insulates the piezoresistive layer from the carrier body and the membrane.

15. The thin-film sensor according to claim 10, wherein the thin-film sensor comprises a plurality of film resistors, which are connected to form a bridge circuit in the form of a full bridge or a half bridge.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention is explained below on the basis of the appended figures.

(2) FIG. 1 shows a thin-film sensor according to a first exemplary embodiment.

(3) FIG. 2 shows a thin-film sensor according to a second exemplary embodiment.

(4) FIG. 3 shows a thin-film sensor according to a third exemplary embodiment.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(5) FIG. 1 shows a thin-film sensor 1 comprising a film resistor 2 with a piezoresistive layer 3. The film resistor 2 further comprises two electrodes 4. The electrodes 4 are arranged at opposite ends of the piezoresistive layer 3.

(6) The thin-film sensor 1 comprises a membrane 5 and a carrier body 6. The membrane 5 is fastened to the carrier body 6 in such a way that the membrane 5 may move relative to the carrier body 6. In particular, the membrane 5 may vibrate relative to the body 6. In this case, a central area of the membrane 5 may be bent. The film resistor 2 is arranged on the membrane 5. The piezoresistive layer 3 may to this end be deposited directly on the membrane 5. In particular, the film resistor 2 is arranged in the region of the membrane 5 which is mobile relative to the carrier body 6.

(7) If the membrane 5 then deforms as a consequence of pressure exerted thereon, this leads to deformation of the piezoresistive layer 3. In this case, the piezoelectric effect results in an electrical signal which may be detected by the electrodes 4.

(8) The thin-film sensor 1 preferably comprises four film resistors 2, which are interconnected to yield an electrical resistance bridge. The resistance bridge is preferably a Wheatstone bridge. On the basis of electrical signals detected by these film resistors 2, a pressure exerted on the thin-film sensor 1 may be calculated.

(9) The thin-film sensor 1 described here is suitable not only for measuring a pressure but also for measuring forces and for measuring elongation of the membrane 5.

(10) The piezoresistive layer 3 may comprise an M.sub.1+nAX.sub.n phase. In this case, the piezoresistive layer 3 may comprise a pure M.sub.1+nAX.sub.n phase or mixed phases (M1,M2).sub.1+nAX.sub.n, M.sub.1+nA(C.sub.yN.sub.1−y).sub.n or (M1,M2).sub.1+nA(C.sub.yN.sub.1−y).sub.n. The piezoresistive layer 3 may either consist of the M.sub.1+nAX.sub.n phase or comprise a mixture of the M.sub.1+nAX.sub.n phase with an oxide, a nitride or a carbide.

(11) The membrane 5 and the carrier body 6 may comprise stainless steel or yttrium-stabilized zirconium. The piezoresistive layer 3 comprises a coefficient of thermal expansion which differs only slightly from the coefficients of thermal expansion of the membrane 5 and of the carrier body 6. Alternatively, the membrane 5 and the carrier body 6 may also comprise a ceramic material or a metal or consist of the ceramic material or the metal.

(12) The piezoresistive layer 3 shown in FIG. 1 is cuboidal. Alternatively, the piezoresistive layer 3 may be meander-shaped. A meander shape has the advantage over a cuboidal shape of greater length between the two electrodes 4 while occupying the same volume.

(13) FIG. 2 shows a second exemplary embodiment of the thin-film sensor 1. Here, the membrane 5 and the carrier body 6 consist of the same material as the piezoresistive layer 3. To prevent electrical short circuits between the membrane 5 and the piezoresistive layer 3, an insulator 7 is additionally arranged between the piezoresistive layer 3 and the membrane 5. The insulator 7 is a layer consisting of a non-conductive material.

(14) FIG. 3 shows a third exemplary embodiment, in which the membrane 5 is fastened to the carrier body 6 only on one side. The membrane 5 may accordingly be bent relative to the carrier body 6.