1. Field of the Invention
The present invention relates to a method of adjusting a frequency of an energy-trap type piezoelectric resonance element which utilizes, for example, a thickness extensional vibration mode, a thickness slide vibration mode, or other vibration modes, and more particularly, the present invention relates to a method of adjusting a frequency of an energy-trap type piezoelectric resonance element by controlling the thickness of a vibration electrode.
2. Description of the Related Art
Conventionally, energy-trap type piezoelectric resonance elements have been used for piezoelectric oscillators, piezoelectric filters, and other electronic components. For such a piezoelectric resonance element, it is necessary to minimize variations in resonance frequency and center frequency.
In the manufacture of the above-mentioned piezoelectric resonance element, vibration electrodes are formed in a matrix pattern on the upper surface and lower surface of a piezoelectric mother substrate. The piezoelectric substrate is cut to produce individual piezoelectric resonance elements. However, there has been the tendency for the resonance frequency and the center frequency to change depending on different piezoelectric mother substrates. Moreover, for different individual piezoelectric resonance substrates, even if they are formed from the same piezoelectric resonance mother substrate, the frequencies tend to be different from each other.
For this reason, conventionally, a variety of methods of adjusting the frequency of a piezoelectric resonance element have been proposed.
For example, Japanese Unexamined Patent Application Publication 10-126187 discloses a method of adjusting the frequency of a quartz oscillator. In this method, electrode films having the same thickness depending on a target frequency are formed on both of the main surfaces of a quartz plate. When a frequency is measured and is determined to be higher than the target frequency, an electrode material is added to one of the vibration electrodes to increase the thickness of the electrode to adjust the frequency. If the frequency is lower than the target frequency, a portion of the electrode is removed so as to reduce the thickness of the electrode to adjust the frequency.
However, in the case in which an electrode material is added to one of the vibration electrodes formed on the main surfaces of a piezoelectric plate, or the electrode material is removed so as to reduce the electrode thickness for adjustment of the frequency, the thicknesses of the electrodes formed on the main surfaces become significantly different from each other. Thus, there arises the problem that the electrical characteristics of the component are significantly deteriorated, and an undesirable ripple occurs in a frequency characteristic, due to the difference in thickness of the vibration electrodes formed on both main surfaces of the piezoelectric plate.
In order to overcome the problems described above, preferred embodiments of the present invention provide a method of adjusting a frequency of a piezoelectric resonance element which prevents deterioration of the electrical characteristics and generation of undesirable ripples caused by conventional frequency adjustment methods, such that the frequency of the novel piezoelectric resonance element is highly accurately controlled to achieve a target frequency.
According to a preferred embodiment of the present invention, a method of adjusting a frequency of an energy-trap type piezoelectric resonance element includes the steps of preparing a piezoelectric resonance element including a piezoelectric plate, first and second vibration electrodes formed partially on both of the main surfaces of the piezoelectric plate and opposed to each other with the piezoelectric plate located therebetween, the thickness of the first vibration electrode being larger than that of the second vibration electrode, and processing the first vibration electrode or the second vibration electrode so that the thicknesses of the first and second vibration electrode electrodes are closer to each other, and so that the piezoelectric resonance element has a desired frequency.
Preferably, an electrode film made of metal is formed on the second vibration electrode in the electrode processing step, such that the thickness of the second vibration electrode is increased.
Also preferably, in the electrode processing step, the processing is carried out in such a manner that the thickness of the first vibration electrode is decreased.
Preferably, the method further includes the step of measuring the resonance frequency of the piezoelectric resonator after the step of preparing the piezoelectric resonance element, and the processing is carried out in such a manner that when the resonance frequency is higher than a desired frequency, the thickness of the second vibration electrode is increased, and when the resonance frequency of the piezoelectric resonance element is lower than the desired frequency, the thickness of the first vibration electrode is decreased.
The difference in thickness between the first and second vibration electrodes prior to the electrode processing step is preferably up to about 0.3 xcexcm.
Also preferably, the piezoelectric resonance element further includes first and second lead-out electrodes, and first and second terminal electrodes connected to the first and second lead-out electrodes, formed on both of the main surfaces of the piezoelectric plate, respectively. The first lead-out electrode and the first vibration electrode preferably have a substantially equal thickness, and the second lead-out electrode and the second vibration electrode preferably have a substantially equal thickness, prior to the processing step. During the processing step, the first or second lead-out electrodes are processed together with the first or second vibration electrode in such a manner that the thicknesses of the first and second lead-out electrodes become closer to each other.
Other features, elements, characteristics and advantages of preferred embodiments of the present invention will become apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.