JPH0515528U - AT-cut overtone crystal unit - Google Patents

Abstract

(57) [Summary] [Purpose] An AT-cut overtone crystal resonator that has a simple structure and can oscillate at an overtone frequency with an unadjusted oscillator circuit without using a coil. [Structure] A large-area main electrode is provided facing the central portion of the front and back plate surfaces of the crystal piece that is excited by the thickness shear vibration cut out from the XZ 'plane of the crystal of the crystal, and the X of this main electrode is provided.
Sub electrodes with a small area are formed on the front and back plate surfaces on both sides in the axial direction, one pair of sub electrodes is connected to one main electrode, and the other pair of sub electrodes is connected to the other main electrode. In addition, the mass per unit area of the auxiliary electrode is set to 3 to 20 times the mass per unit area of the main electrode.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an AT-cut overtone crystal resonator that can easily oscillate overtone using an unadjusted oscillator circuit.

[0002]

[Prior Art]

 Recently, many electronic devices use piezoelectric vibrators, such as crystal oscillators, as a reference for frequency and time. In particular, crystal oscillators are manufactured and used in large quantities because they are inexpensive and highly efficient due to advances in manufacturing technology. Vibration modes of such a crystal unit include various vibration modes such as bending vibration, flexural vibration, and thickness vibration. In a crystal unit with a resonance frequency of MHz order, the thickness shear vibration mode is mainly used. The resonance frequency of the crystal unit excited by such a thickness shear vibration mode is inversely proportional to the thickness of the crystal piece. Therefore, for example, the thickness of a vibrator having a resonance frequency of 10 MHz is about 0.167 mm, and the thickness of a vibrator having a resonance frequency of 30 MHz is about 0.056 mm. In other words, the thickness of the crystal piece becomes thinner and the frequency becomes higher in inverse proportion to the resonance frequency, and it becomes extremely difficult to manufacture due to problems such as the strength and processing of the crystal piece. For this reason, when a crystal unit with a high resonance frequency is required, an overtone mode is used. In the overtone mode, resonance occurs at a frequency that is an odd multiple of the resonance frequency of the fundamental wave, and modes such as the 3rd, 5th, and 7th modes are generally used. The order is the constant of the oscillator circuit, for example, tuning on the output side. Determined by the circuit constants. However, such an overtone oscillator circuit requires a coil, that is, an inductance because a tuning circuit is provided to suppress the resonance of the fundamental wave in a circuit manner. However, it is difficult to reduce the inductance of the tuning circuit in particular, and there is a problem that adjustment is required.

By the way, in recent years, in order to miniaturize the oscillation circuit, make it unadjusted, and maintain high frequency accuracy for a long period of time, for example, a crystal oscillator and an integrated circuit are integrated to form an unadjusted crystal oscillation circuit. A large number of small oscillators are manufactured and used. However, the oscillator circuit having such a configuration cannot use the overtone mode because it does not have a tuning circuit. For this reason, the maximum oscillating frequency is generally limited to about 30 MHz due to the processing limit of the crystal piece. Therefore, some crystal oscillators have been proposed that can oscillate at an overtone frequency by using an unadjusted oscillator circuit by suppressing the fundamental vibration mode. For example, there is one that suppresses the fundamental vibration mode by transmitting and attenuating the vibration energy of the fundamental wave to the support part of the crystal element. However, in such a case, there is a problem that the frequency adjustment is extremely difficult due to variations in the distance between the support of the quartz piece and the electrodes. It is also considered to suppress the fundamental wave vibration mode by making the electrodes unevenly distributed on the periphery of the crystal piece, or by making the size of the electrode approximately the same as the size of the crystal piece. However, there is a problem that even such a thing cannot sufficiently suppress the fundamental vibration.

[0004]

[Problems to be solved by the device]

 The present invention has been made in view of the above circumstances, and it is possible to oscillate at an overtone frequency with an unadjusted oscillation circuit without using a coil, and an AT tone overtone crystal vibration with a simple structure is also possible. The purpose is to provide children.

[0005]

[Means for Solving the Problems]

 According to the present invention, a main electrode having a large area is provided facing the central portion of the front and back plate surfaces of a crystal piece that excites thickness shear vibration cut out from the XZ 'plane of the crystal of the crystal, and the main electrode X Sub electrodes with a small area are formed on the front and back plate surfaces on both sides in the axial direction, one sub electrode pair is connected to one main electrode, and the other sub electrode pair is connected to the other main electrode. In addition, the mass per unit area of the sub-electrode is 3 to 20 times the mass per unit area of the main electrode.

[0006]

【Example】

 An embodiment of the present invention will be described in detail below with reference to a plan view showing an electrode structure of a crystal unit shown in FIG. 1 and a sectional view taken along the line AA of FIG. 1 shown in FIG. In the figure, reference numeral 1 is an AT-cut thickness-slipped quartz crystal piece formed into a round plate from an X-Z 'plane obtained by cutting a quartz crystal at a predetermined angle with respect to its crystal axis. In addition, in order to suppress the vibration of the fundamental wave and to easily excite the vibration of the overtone, the crystal piece 1 is not chamfered at the peripheral portion. Then, the main electrode 2 having a large area is formed in the center of the front and back plate surfaces of the crystal piece 1 in an inverted symmetrical manner. The main electrode 2 is square or circular. Then, band-shaped sub-electrodes 3 each having a small area are arranged on both sides of the main electrode 2 in the X-axis direction with a predetermined gap. The sub-electrodes 3 are formed so as to face the front and back plates, respectively, and one sub-electrode set facing each other is connected to one main electrode, and the other sub-electrode set is connected to the other main electrode. There is. The main electrode 2 and the sub electrode 3 are metal thin films formed by, for example, vacuum deposition. Therefore, the mass per unit area of the auxiliary electrode is set to 3 to 20 times the mass per unit area of the main electrode. For this reason, the sub-electrode is made of a metal having a large specific gravity, such as gold, so as to suppress the resonance of the fundamental wave, and the main electrode is made of an aluminum having a small specific gravity so that the overtone resonance can be efficiently excited. It is formed by using a metal such as, and the thickness of each is adjusted so as to satisfy the mass per unit area described above.

By the way, in the AT-cut thickness-slip crystal oscillator, overtone vibrational displacement is ubiquitous in the central portion of the crystal piece, whereas fundamental wave vibrational displacement is present over the entire plate surface of the crystal piece. .. Further, when these vibration displacements are viewed in the axial direction of the crystal, a large displacement 4 is generated in the X-axis direction as shown in the plan view of the equal displacement surface shown in FIG. 3, whereas the displacement in the Z'-axis direction is small. Therefore, if a sub-electrode with a large mass is placed in the X-axis direction, which causes a large displacement of the plate surface of the crystal element, the vibration of the overtone is hardly affected, while the vibration of the fundamental wave is significantly suppressed. It However, if the mass per unit area of the sub-electrode is less than 3 times that of the main electrode, the vibration of the fundamental wave cannot be suppressed sufficiently, so the lower limit is set to 3 times, and if it exceeds 20 times, the mass of the sub-electrode is The upper limit is set to 20 times in order to prevent the vibration of overtone because it becomes too large. With this structure, we measured the characteristics of a crystal unit with a resonance frequency of 44 MHz at the third overtone using a 5.5 mm diameter round crystal plate, and the crystal impedance of the fundamental wave vibration was 400 Ω on average. Its average for the third overtone was 25Ω. Therefore, it is possible to oscillate at an overtone frequency by using an unadjusted oscillator circuit that does not use a coil. Can be obtained. Since the electrode structure of the oscillator is simple, it is easy to design and suitable for mass production, and it is possible to obtain a crystal oscillator that is extremely useful industrially.

[0008]

[Effect of the device]

 As described above in detail, if the crystal oscillator of the present invention is used, overtone oscillation can be performed using an unadjusted oscillator circuit, and a compact oscillator with a compact shape can be configured by combining with an oscillator circuit integrated. It is possible to provide an AT-cut overtone crystal resonator that can be used.

[0009]

[Brief description of drawings]

FIG. 1 is a plan view showing an electrode structure of a crystal resonator according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view taken along the line AA of FIG.

FIG. 3 is a diagram illustrating vibration displacement of a plate surface of the crystal unit shown in FIG.

[Explanation of symbols]

 1 Crystal piece 2 Main electrode 3 Sub electrode

Claims (1)

[Scope of utility model registration request] 1. A main electrode having a large area is provided so as to face a central portion of front and back plate surfaces of a crystal piece that is excited by a thickness shear vibration cut out from an XZ 'plane of a crystal of quartz. Sub electrodes with small areas are formed on the front and back plate surfaces on both sides in the X-axis direction, one pair of sub electrodes is connected to one main electrode, and the other pair of sub electrodes is connected to the other main electrode. An AT-cut overtone crystal resonator, wherein the mass per unit area of the auxiliary electrode is 3 to 20 times that of the main electrode.