With the miniaturization of various communication devices or electronic devices, piezoelectric vibrating devices such as crystal oscillators or crystal controlled oscillators need to be downsized. A crystal vibrating piece using piezoelectric vibrating devices is attached to a ceramic package by thermosetting resin. On this occasion, the thermosetting resin is heated up either 150° C. or 250° C. to attach the crystal vibrating piece. Therefore, the crystal vibrating piece is heated up either 150° C. or 250° C. as well. Also, when a packaged piezoelectric vibrating device is mounted to an epoxy laminate, the piezoelectric vibrating device is treated with heat by a solder reflow furnace and the crystal vibrating piece in the package is also heated up to 200° C.
After the temperature of piezoelectric vibrating device became 200° C. through the heat treatment, the piezoelectric vibrating device is back to a room temperature. However, sometimes piezoelectric vibrating devices are not back to a designated primary frequency form a varied frequency. In such a case, those products are considered as defective products at the shipment. Supposedly, when such defective products of piezoelectric vibration devices are mounted to the epoxy laminate, they go through a heat treatment such as solder reflow furnace. Inside of the solder reflow furnace is set to 180° C. or 250° C. and after ten seconds, the piezoelectric vibrating device is treated with heat. As described above, after the piezoelectric vibrating device is treated with heat, its frequency is varied as well, even if it is back to a room temperature, and the whole epoxy laminate is considered as defective products. Japanese Unexamined Patent Application Publication No. 2003-17977 disclosed that although such piezoelectric vibrating device considered as a defective product, it is acknowledged that it vibrated proper frequency after few months because remaining stress of crystal vibrating piece was released.
However, if it does not work properly for few months, the product cannot be shipped. Especially, when it is more than 100 MHz, it tends to have a greater frequency change.
Therefore, the purpose of this invention is to provide a piezoelectric vibrating piece and piezoelectric vibrating device having less frequency change for a heat change a heat treatment.