Mesa-type AT-cut quartz-crystal vibrating piece and quartz-crystal device

A quartz-crystal device comprising:

• a mesa-type AT-cut quartz-crystal vibrating piece comprising:
• a rectangular excitation unit and a peripheral region formed on the periphery of the excitation unit and having a thickness less than a thickness of the excitation unit;
• wherein the thickness of the excitation unit is denoted as Tm, and a length of the excitation unit along the crystallographic x-axis of the excitation unit is denoted as Mx, a minimum value of the crystal impedance is acquired within the range of Mx/Tm being 15.7 or larger and 18.0 or smaller;
• and
• wherein a size of the excitation unit at the minimum value is implemented in the Mx/Tm ratio.

A quartz-crystal device comprising:

• a mesa-type AT-cut quartz-crystal vibrating piece for vibrating at 38.400 MHz, comprising:
• a rectangular excitation unit and a peripheral region formed on the periphery of the excitation unit and having a thickness less than a thickness of the excitation unit, is represented by the following ratio:
• (Tm−Ts)/Tm;
• wherein the thickness of the excitation unit is defined as Tm (μm) and the thickness of the peripheral region is defined as Ts (μm);
• and
• wherein the ratio (Tm−Ts)/Tm comprises a value 0.048 or larger and 0.2 or smaller.