Piezoelectric resonator, filter, and electronic communication device

A piezoelectric resonator comprising:

• a substrate;
• a vibration unit disposed on the substrate and having a structure in which at least one pair of an upper electrode and a lower electrode are opposed to each other, the upper and lower electrodes sandwiching the upper and lower surfaces of an internal thin-film portion including at least one layer of a piezoelectric thin-film;
• and
• an external thin-film portion provided under the lower electrode and including at least one layer of one of a piezoelectric thin-film and a dielectric thin-film;
• wherein
• the vibration unit is vibrated in an n-th harmonic, where n is an integer of 2 or greater, the upper electrode and the lower electrode are located substantially in the positions of the loops of the n-th harmonic;
• wherein
• the external thin-film portion includes an SiQ2 thin-film as a major component;
• the internal thin-film portion includes AIN as a major component;
• and
• nodes of the n-th harmonic exist in the internal and external thin-film portions.