Quartz crystal resonator

A quartz crystal resonator, comprising:

• a quartz crystal resonator element having a main surface including an X axis (electrical axis) and a Z′ axis of an inclination rotated at an angle (y) equal to or greater than 36.4 degrees and equal to or smaller than 40.5 degrees from a Z axis (optical axis) around the X axis, a main vibrating portion vibrating at a predetermined resonance frequency (f) and a supporting portion integrally formed with the main vibrating portion in such a manner as to be formed peripherally to surround the main vibrating portion;
• two covers having a thermal expansion coefficient equal to or greater than 6 ×10−6 per degrees centigrade and equal to or smaller than 10 ×10−6 per degrees centigrade and bonded to the supporting portion so as to sandwich the quartz crystal resonator element therebetween:
• a circuit section, which is disposed under a lower cover and is electrically connected with the quartz crystal resonator element;
• and
• a circuit substrate, which is located under the circuit section,
• the quartz crystal resonator element having a first recessed groove and a second recessed groove formed on at least one main surface, and
• each of the first recessed groove and the second recessed groove having three sides, each of the three sides of the first recessed groove and the three sides of the second recessed groove extending around the main vibrating portion.