Patent ID: 8604565

Claim:
A physical quantity detection device comprising: an insulating layer; a semiconductor layer disposed on a surface of the insulating layer; and a first electrode and a second electrode for detecting a physical quantity disposed in the semiconductor layer, wherein the first electrode has a first wall part disposed in the semiconductor layer and protruding along with a direction crossing the surface of the insulating layer, wherein the second electrode has a second wall part disposed in the semiconductor layer and protruding along with a direction crossing the surface of the insulating layer, wherein at least one of the first wall part and the second wall part includes a pair of diaphragms and a cover part, wherein the pair of diaphragms faces each other so that a hollow cylinder having an opening opposite to the insulating layer is provided, wherein the cover part covers the opening of the hollow cylinder, wherein one of the pair of diaphragms faces the other one of the first wall part and the second wall part or one of a pair of diaphragms in the other one of the first wall part and the second wall part, wherein the hollow cylinder provides a hollow portion having a predetermined reference pressure, wherein a distance between the one of the pair of diaphragms and the other one of the first wall part and the second wall part or a distance between the one of the pair of diaphragms and the one of the pair of diaphragms in the other one of the first wall part and the second wall part is changed in accordance with pressure difference between the predetermined reference pressure and a pressure of an outside of the hollow portion when a physical quantity is applied to the pair of diaphragms, and wherein the physical quantity is detected based on a capacitance between the first electrode and the second electrode, the capacitance being varied with the distance.