Gas sensor and fuel cell vehicle

1. A gas sensor, comprising:

a gas-sensitive body layer disposed above a substrate and including a metal oxide layer;

a first electrode, of which bottom surface is disposed at a same level as a bottom surface of the gas-sensitive body layer, and is disposed above the substrate, and not disposed on an upper surface of the gas-sensitive body layer; and

a second electrode disposed at the same layer level as a layer level of the gas-sensitive body layer above the substrate or disposed on the gas-sensitive body layer, the second electrode being apart from the first electrode by a gap, wherein:

the gas-sensitive body layer has a resistance change characteristic that reversibly transitions to a high-resistance state and a low-resistance state on basis of a voltage applied across the first electrode and the second electrode,

at least a part of the gas-sensitive body layer is exposed to an area corresponding to the gap, and

the gas-sensitive body layer has a resistance that decreases when gas containing a hydrogen atom is in contact with the second electrode.

2. The gas sensor according to claim 1 , wherein the gas-sensitive body layer includes a local region corresponding to the gap, the local region has a degree of oxygen deficiency larger than a degree of oxygen deficiency of the metal oxide layer.

3. The gas sensor according to claim 2 , wherein the gas-sensitive body layer is a laminated structure including (i) a first metal oxide layer comprising a first metal oxide and (ii) a second metal oxide layer comprising a second metal oxide, the second metal oxide having a degree of oxygen deficiency smaller than a degree of oxygen deficiency of the first metal oxide; and

the local region passes through at least the second metal oxide layer, the local region being in contact with at least one of the first electrode and the second electrode, the local region having a degree of oxygen deficiency larger than a degree of oxygen deficiency of the second metal oxide layer.

4. The gas sensor according to claim 3 , wherein at least one of the first metal oxide and the second metal oxide is a transition metal oxide.

5. The gas sensor according to claim 4 , wherein the transition metal oxide is one of tantalum oxide, hafnium oxide, and zirconium oxide.

6. The gas sensor according to claim 2 , wherein:

the second electrode comprises a material that causes catalysis that dissociates a hydrogen atom from a gas molecule containing the hydrogen atom; and

a resistance of the metal oxide layer decreases as the hydrogen atom is dissociated from the gas molecule in a part of the second electrode in contact with the local region, and the dissociated hydrogen atom is bound to an oxygen atom in the local region of the metal oxide layer.

7. The gas sensor according to claim 1 , wherein the second electrode comprises at least one of platinum, iridium, and palladium.

8. The gas sensor according to claim 1 , further comprising:

a measurement circuit that measures a current flowing through the gas-sensitive body layer when a predetermined voltage is applied across the first electrode and the second electrode.

9. The gas sensor according to claim 8 , wherein a concentration of the gas containing a hydrogen atom is determined by measuring time until the current flowing through the gas-sensitive body layer in the gas sensor reaches a predetermined current from start of introduction of the gas containing a hydrogen atom.

10. The gas sensor according to claim 1 , comprising:

a power supply circuit that constantly applies a predetermined voltage across the first electrode and the second electrode.

11. The gas sensor according to claim 2 , wherein an output value of a current flowing through the gas-sensitive body layer differs depending on a size and a resistance state of the local region.

12. A fuel cell vehicle, comprising:

a passenger compartment;

a gas tank compartment in which a tank of hydrogen gas is arranged;

a fuel cell compartment in which a fuel cell is arranged; and

the gas sensor according to claim 1 , wherein

the gas sensor is arranged in at least one of the gas tank compartment and the fuel cell compartment.

13. The gas sensor according to claim 1 , wherein the second electrode is disposed on the gas-sensitive body layer.

14. The gas sensor according to claim 1 , wherein one side surface of the first electrode contacts a side surface of the gas-sensitive body layer and another side surface of the first electrode contacts no side surface of the gas-sensitive body layer.