Patent ID: 7950282

Claim:
An acceleration sensor comprising: a piezoelectric vibration device; an oscillation circuit; and a detection circuit, wherein the piezoelectric vibration device includes a substrate, an insulation layer formed above the substrate, a vibration section forming layer formed above the insulation layer, a vibration section formed in a cantilever shape in a first opening section that penetrates the vibration section forming layer and having a base section affixed to the vibration section forming layer and two beam sections extending from the base section, a second opening section that penetrates the insulation layer and formed below the first opening section and the vibration section, and a piezoelectric element section formed on each of the beam sections, the piezoelectric element section including a lower electrode, a piezoelectric layer formed on the lower electrode, and an upper electrode formed on the piezoelectric layer, the lower electrode having a larger area than an area of the piezoelectric layer, extending in a first direction toward the first opening section to a greater extent than the piezoelectric layer and the upper electrode, and extending in a second direction, opposite the first direction, to a greater extent than the piezoelectric layer and the upper electrode, the oscillation circuit vibrates the piezoelectric vibration device at a resonance frequency, and the detection circuit detects a change in the frequency of vibrations of the piezoelectric vibration device which is caused by an acceleration applied in a direction in which the beam sections extend, and outputs a signal corresponding to the acceleration based on the change in the frequency.