A crystal unit includes a crystal element, excitation electrodes, and a container. The crystal element vibrates in a thickness-shear mode. The excitation electrodes are disposed on front and back surfaces of the crystal element. The crystal element is mounted to the container. The excitation electrodes are disposed on the crystal element. When a thickness of the crystal element is expressed as T, and a total thickness of the excitation electrodes disposed on the front and back surfaces of the crystal element is expressed as t, a ratio t/T is from 0.026 to 0.030.

A crystal unit includes a crystal element, excitation electrodes, and a container. The crystal element vibrates in a thickness-shear mode. The excitation electrodes are disposed on front and back surfaces of the crystal element. The crystal element is mounted to the container. The excitation electrodes are disposed on the crystal element. When a thickness of the crystal element is expressed as T, and a total thickness of the excitation electrodes disposed on the front and back surfaces of the crystal element is expressed as t, a ratio t/T is from 0.026 to 0.030.

A third through hole is formed in a crystal resonator plate of a crystal resonator to penetrate between a first main surface and a second main surface. A through electrode of the third through hole is conducted to a first excitation electrode. A seventh through hole is formed in a first sealing member of the crystal resonator to penetrate between a first main surface and a second main surface. The through electrode of the third through hole is conducted to the through electrode of the seventh through hole. The third through hole is not superimposed to the seventh through hole in plan view.

A third through hole is formed in a crystal resonator plate of a crystal resonator to penetrate between a first main surface and a second main surface. A through electrode of the third through hole is conducted to a first excitation electrode. A seventh through hole is formed in a first sealing member of the crystal resonator to penetrate between a first main surface and a second main surface. The through electrode of the third through hole is conducted to the through electrode of the seventh through hole. The third through hole is not superimposed to the seventh through hole in plan view.

In at least one embodiment, the electric component comprises a first BAW-resonator (1), a second BAW-resonator (2) electrically connected to the first BAW-resonator and a carrier substrate (3) with a top side (30) on which the BAW-resonators are arranged. The first and the second BAW-resonator each comprise a bottom electrode (11,21) and a top electrode (12,22). The bottom electrodes are in each case located between the carrier substrate and the respective top electrode. A first piezoelectric layer (13) is arranged between the top electrode and the bottom electrode of the first BAW-resonator and laterally protrudes from the first BAW-resonator. The second BAW-resonator is mounted on the first piezoelectric layer in a region laterally next to the first BAW-resonator and comprises a second piezoelectric layer (23) between its top electrode and its bottom electrode. The two piezoelectric layers may have different thickness to realize resonators with different resonance frequencies on the same die.

A method of manufacturing a bulk acoustic wave filter is provided, including: forming an acoustic reflection air cavity, a sacrificial layer, a seed layer, a lower electrode layer and a piezoelectric layer of n resonators on a substrate in sequence, wherein n is greater than or equal to 2; taking N from 1 to n for respectively repeating following steps: forming an N-th metal hard mask layer, defining an effective area of a first resonator to an N-th resonator by using a photolithography process, removing the N-th metal hard mask layer outside the effective area of the first resonator to the N-th resonator, oxidizing the piezoelectric layer outside the effective area of the first resonator to the N-th resonator to form an N-th oxidized part of the piezoelectric layer, and etching the N-th oxidized part of the piezoelectric layer; removing the metal hard mask layer of the effective area of the first resonator to the N-th resonator, so as to form the piezoelectric layer having different thicknesses of the first resonator to the N-th resonator; and forming an upper electrode layer on the piezoelectric layer having different thicknesses of the first resonator to the N-th resonator.

An elastic wave device includes a supporting substrate, a high-acoustic-velocity film stacked on the supporting substrate and in which an acoustic velocity of a bulk wave propagating therein is higher than an acoustic velocity of an elastic wave propagating in a piezoelectric film, a low-acoustic-velocity film stacked on the high-acoustic-velocity film and in which an acoustic velocity of a bulk wave propagating therein is lower than an acoustic velocity of a bulk wave propagating in the piezoelectric film, the piezoelectric film is stacked on the low-acoustic-velocity film, and an IDT electrode stacked on a surface of the piezoelectric film.

An elastic wave device includes a supporting substrate, a high-acoustic-velocity film stacked on the supporting substrate and in which an acoustic velocity of a bulk wave propagating therein is higher than an acoustic velocity of an elastic wave propagating in a piezoelectric film, a low-acoustic-velocity film stacked on the high-acoustic-velocity film and in which an acoustic velocity of a bulk wave propagating therein is lower than an acoustic velocity of a bulk wave propagating in the piezoelectric film, the piezoelectric film is stacked on the low-acoustic-velocity film, and an IDT electrode stacked on a surface of the piezoelectric film.

A vibration element includes a base and a vibrating arm extending from the base. The vibrating arm includes an arm positioned between the base and a weight. A weight film is disposed on the weight. The weight has a first principal surface and a second principal surface in a front and back relationship with respect to a center plane of the arm. A center of gravity of the weight is located between the first principal surface and the center plane of the arm. A center of gravity of the weight film is located between the second principal surface and the center plane of the arm.

A vibration element includes a base and a vibrating arm extending from the base. The vibrating arm includes an arm positioned between the base and a weight. A weight film is disposed on the weight. The weight has a first principal surface and a second principal surface in a front and back relationship with respect to a center plane of the arm. A center of gravity of the weight is located between the first principal surface and the center plane of the arm. A center of gravity of the weight film is located between the second principal surface and the center plane of the arm.