Patent ID: 6959472

Claim:
A method for manufacturing a quartz crystal oscillator, comprising the steps of: forming by at least one of a chemical etching method, a physical etching method, and a mechanical method a quartz crystal tuning fork resonator having a quartz crystal tuning fork base and first and second quartz crystal tuning fork tines each connected to the quartz crystal tuning fork base and having a first main surface and a second main surface opposite the first main surface, the quartz crystal tuning fork resonator having a fundamental mode of vibration and a second overtone mode of vibration each comprised of a flexural mode of an inverse phase, a series resistance R 1 of the fundamental mode of vibration, and a series resistance R 2 of the second overtone mode of vibration; providing an amplification circuit having at least an amplifier, a negative resistance −RL 1 of a fundamental mode of vibration thereof, and a negative resistance −RL 2 of a second overtone mode of vibration thereof; providing a feedback circuit having the quartz crystal tuning fork resonator and a plurality of capacitors; and electrically connecting together the amplifier of the amplification circuit and the quartz crystal tuning fork resonator and capacitors of the feedback circuit; wherein a ratio of an absolute value of the negative resistance −RL 1 of the fundamental mode of vibration of the amplification circuit and the series resistance R 1 of the fundamental mode of vibration of the quartz crystal tuning fork resonator is greater than that of an absolute value of the negative resistance −RL 2 of the second overtone mode of vibration of the amplification circuit and the series resistance R 2 of the second overtone mode of vibration of the quartz crystal tuning fork resonator; and wherein a merit value M 1 of the fundamental mode of vibration of the quartz crystal tuning fork resonator is greater than a merit value M 2 of the second overtone mode of vibration thereof so that the second overtone mode of vibration of the quartz crystal tuning fork resonator is suppressed and a high frequency stability is obtained for the fundamental mode of vibration of the quartz crystal tuning fork resonator, the merit values M 1 and M 2 being defined by the ratios Q 1/r 1 and Q 2 /r 2 , respectively, where Q 1 and Q 2 represent a quality factor of the fundamental mode of vibration and the second overtone mode of vibration, respectively, of the quartz crystal tuning fork resonator and r 1 and r 2 represent a capacitance ratio of the fundamental mode of vibration and the second overtone mode of vibration, respectively, of the quartz crystal tuning fork resonator.