Thermopile sensor and sensor array

A thermopile sensor comprising:

• a p-type portion that includes a p-type material and has a first phononic crystal in which first holes are arranged in a plan view;
• and
• an n-type portion that includes an n-type material and has a second phononic crystal in which second holes are arranged in a plan view,
• wherein the p-type portion and the n-type portion constitute a thermocouple,
• wherein a thermal conductivity of the n-type material is higher than a thermal conductivity of the p-type material,
• wherein the thermopile sensor satisfies at least one condition selected from the group consisting of the following (I) and (II):
• (I) a boundary scattering frequency of phonons in the first phononic crystal is different from a boundary scattering frequency of phonons in the second phononic crystal;
• and
• (II) a ratio of a sum of areas of the first holes to an area of the first phononic crystal in the plan view of the first phononic crystal is different from a ratio of a sum of areas of the second holes to an area of the second phononic crystal in the plan view of the second phononic crystal, and
• wherein the thermopile sensor satisfies at least one condition selected from the group consisting of the following (Ib) and (IIb):
• (Ib) the boundary scattering frequency of phonons in the second phononic crystal is higher than the boundary scattering frequency of phonons in the first phononic crystal;
• and
• (IIb) a ratio of the sum of the areas of the second holes to an area of the n-type portion in the plan view of the n-type portion is greater than a ratio of the sum of the areas of the first holes to an area of the p-type portion in the plan view of the p-type portion.