Strain gauge

1. A strain gauge comprising:

a flexible resin substrate;

a functional layer formed of a metal, an alloy, or a metal compound, directly on one surface of the substrate, the functional layer promoting crystal growth of a resistor;

the resistor formed of a film that includes Cr, CrN, and Cr 2 N and into which an element included in the functional layer is diffused, the resistor being provided on one surface of the functional layer, and the film of the resistor being formed with alpha-chromium as a main component; and

electrodes electrically coupled to the resistor,

wherein a gauge factor of the strain gauge is 10 or more, and

wherein each electrode includes:

a terminal section extending from a corresponding end portion from among end portions of the resistor;

a first metallic layer formed of copper, a copper alloy, nickel, or a nickel alloy, on or above the terminal section; and

a second metallic layer formed of material having better solder wettability than the first metallic layer, on or above the first metallic layer, and

wherein the functional layer including the element that is diffused into the film of the resistor defines a growth face of the alfa-chromium of the resistor.

2. A strain gauge comprising:

a flexible resin substrate;

a functional layer formed of a metal, an alloy, or a metal compound, directly on one surface of the substrate, the functional layer promoting crystal growth of a resistor;

the resistor formed of a film that includes Cr, CrN, and Cr 2 N and into which an element included in the functional layer is diffused, the resistor being provided on one surface of the functional layer, and the film of the resistor being formed with alpha-chromium as a main component; and

electrodes electrically coupled to the resistor,

wherein a temperature coefficient of resistance of the strain gauge is in a range of from −1000 ppm/° C. to +1000 ppm/° C., and

wherein each electrode includes:

a terminal section extending from a corresponding end portion from among end portions of the resistor;

a first metallic layer formed of copper, a copper alloy, nickel, or a nickel alloy, on or above the terminal section; and

a second metallic layer formed of material having better solder wettability than the first metallic layer, on or above the first metallic layer, and

wherein the functional layer including the element that is diffused into the film of the resistor defines a growth face of the alfa-chromium of the resistor.

3. A strain gauge comprising:

a flexible resin substrate;

a functional layer formed of a metal, an alloy, or a metal compound, directly on one surface of the substrate, the functional layer promoting crystal growth of a resistor;

the resistor formed of a film including Cr, CrN, Cr 2 N, on one surface of the functional layer, the film of the resistor being formed with alpha-chromium as a main component; and

electrodes electrically coupled to the resistor,

wherein each electrode includes:

a terminal section extending from a corresponding end portion from among end portions of the resistor;

a first metallic layer formed of copper, a copper alloy, nickel, or a nickel alloy, on or above the terminal section; and

a second metallic layer formed of material having better solder wettability than the first metallic layer, on or above the first metallic layer, and

wherein the functional layer including the element that is diffused into the film of the resistor defines a growth face of the alfa-chromium of the resistor.

4. The strain gauge according to claim 1 , wherein the first metallic layer is an electrolytically plated layer.

5. The strain gauge according to claim 1 , wherein the second metallic layer directly or indirectly covers an upper surface and side surfaces of the first metallic layer.

6. The strain gauge according to claim 1 , wherein the first metallic layer has a thickness of 1 μm or more.

7. The strain gauge according to claim 6 , wherein the first metallic layer has a thickness of 3 μm or more.

8. The strain gauge according to claim 1 , wherein the functional layer includes one or more metals selected from the group consisting of Cr, Ti, V, Nb, Ta, Ni, Y, Zr, Hf, Si, C, Zn, Cu, Bi, Fe, Mo, W, Ru, Rh, Re, Os, Ir, Pt, Pd, Ag, Au, Co, Mn, and Al; an alloy of any metals from among the group; or a compound of any metal from among the group.

9. The strain gauge according to claim 1 , wherein the functional layer includes one or more metals selected from the group consisting of Cr, V, Nb, Ta, Ni, Y, Hf, C, Zn, Bi, Fe, Mo, W, Ru, Rh, Re, Os, Ir, Pt, Pd, Ag, Au, Co, and Mn; an alloy of any metals from among the group; or a compound of any metal from among the group.

10. The strain gauge according to claim 8 , wherein the functional layer further includes one metal compound selected from the group consisting of TiN, TaN, Si 3 N 4 , TiO 2 , Ta 2 O 5 , and SiO 2 .

11. The strain gauge according to claim 8 , wherein the functional layer further includes one metal compound selected from the group consisting of TiN, TaN, Si 3 N 4 , and Ta 2 O 5 .

12. The strain gauge according to claim 8 , wherein the functional layer further includes one alloy selected from the group consisting of FeCr, TiAl, FeNi, NiCr, and CrCu.

13. The strain gauge according to claim 1 , wherein the functional layer protects the resistor from oxidation; suppresses movement of oxygen and moisture present in the substrate into the resistor; and/or improves adhesion between the substrate and the resistor.

14. The strain gauge according to claim 1 , wherein the functional layer is patterned in a same planar shape as the resistor.

15. The strain gauge according to claim 1 , wherein the functional layer has a thickness of from 1 nm to 100 nm.