JPS643367B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an excitation electrode and a connection electrode of a tuning fork-shaped piezoelectric vibrator, and to improvements in the vibrator characteristics, particularly series resonant resistance (hereinafter referred to as "CI").

Quartz crystal, which has relatively good frequency-temperature characteristics, is generally used as the piezoelectric material for this type of vibrator, and has been used in particular since tuning fork crystal oscillators have been used as oscillation sources in small devices such as wristwatches. There is a strong demand for smaller resonators. Photolithography, which has been used in semiconductor devices, has emerged as a processing method to meet this demand, and this photolithography technology is used to process crystal diaphragms into tuning fork shapes.

However, since quartz is a piezoelectric single crystal belonging to crystal group 32 and has anisotropy in its crystal coordinate axes (X, Y, Z), when etching it, Etching solutions are selected with due consideration to anisotropy. for example,
When shaping a Z-plate crystal whose main surface is perpendicular to the Z-axis into a tuning fork-shaped diaphragm, an acidic ammonium fluoride (NH ₄ HF ₂ ) solution is used. In addition,
Regarding the relationship with the previous process of this etching process, (1) the process of cleaning the Z plate crystal, (2) the Cr film (lower layer) on both main surfaces of the Z plate crystal to improve the adhesion with the crystal, Step of vapor depositing an Au film (upper layer) to obtain conductivity as an electrode and to serve as a metal resist during etching with an acidic ammonium fluoride solution described later; (3) adhesion of the vapor deposited film to the crystal; (4) Applying photoresist to both main surfaces of the crystal and exposing it to a predetermined tuning fork shape;
(5) Etching the Au film and Cr film with aqua regia and Cr solution to expose the crystal surface around the tuning fork shape; (6) After removing the photoresist, repeat the above process. Apply the same photoresist,
It consists of the steps of exposing and developing a predetermined electrode shape, and (7) etching the crystal with an acidic ammonium fluoride solution in the vertical direction from both principal surfaces to dissolve and remove the crystal around the predetermined tuning fork shape.

However, the crystal obtained by such etching process has two plate-shaped legs 1, as shown in the A-A sectional view in FIG. 1 and the surface view in B.
1' and the plate-shaped base 2 that connects its legs form a tuning fork-shaped crystal diaphragm 3. If you pay attention to the ridges 4 to 13 that border each side, you will notice that they have sharp edges. It can be found that it is formed by
Note that the crystal coordinates (X, Y', Z') in the figure are rotated by 0° to 6° around the X axis due to the relationship with the frequency-temperature characteristics.

In conventional etching-processed tuning fork-shaped crystal diaphragms, the excitation electrodes and connection electrodes were placed directly across the ridges, ignoring the steep portions of each ridge. This tends to occur, and as a means to reduce the CI value, the area of the excitation electrode is increased, and in particular, the excitation electrode on the thickness side (side surface) may be placed as wide as possible up to the ridge, but this is not the case. as desired
It was not possible to reduce the CI value.

The first purpose of the present invention is to eliminate conduction defects in connection electrodes, and the second purpose is to eliminate conduction defects in conventional CI
The purpose is to break through the limits of the CI value and make the CI value even smaller.The third purpose is to maintain good oscillator characteristics even when the tuning fork-shaped diaphragm is downsized.

Figure 2 shows the tuning fork-shaped crystal diaphragm 3 shown in Figure 1.
A cross section of the diaphragm 3 which has been rounded by removing the steep portions of the ridges 4 to 13 is shown.

As a means for removing this steep portion, an etching solution (e.g., acidic ammonium fluoride (NH ₄ HF ₂ ) solution) that etches the tip of the tuning fork-shaped crystal diaphragm 3 in a direction perpendicular to the plane of the diaphragm 3 is used. In contrast, an etching solution (e.g., acetic acid (CH ₃ COOH), sulfuric acid (H ₂ SO ₄ ), hydrochloric acid (HCl), phosphorus Acid (H ₃ PO ₄ ), Nitric acid (HNO ₃ ), Silver chloride (AgCl)
or a hydrofluoric acid (HF) mixture containing either iodine (I) or the like. As a result, the ridge 4
As shown in FIG. 2, 13 to 13 have steep portions removed, resulting in a rounded shape in this example. The removed or rounded shape of this steep part is so small that it cannot be seen with the naked eye, but when observed with a microscope, it was found to be approximately 1/2 the thickness (200μ) of the diaphragm 3 shown in FIG. 2 of this example. /100 (radius approximately 2μ). Note that the upper limit for removing this steep part is until the predetermined shape of the diaphragm 3 can be substantially maintained, and the radius of the rounded shape is the diaphragm 3.
The lower limit is the range in which the effects of the present invention described later can be obtained, and the radius of the rounded shape is up to about 1/500 of the thickness of the diaphragm 3.

A and B in FIG. 3 are perspective views showing the electrode arrangement on the front and back sides, respectively. Here, 2
An example of the arrangement of terminal electrodes is shown.

The excitation electrodes that are to vibrate the tuning fork in response to an input signal of a predetermined resonance frequency (32.768 KHz) are excitation electrodes 14 and 15 on both main surfaces of the leg part 1, and excitation electrodes 16 and 17 with full width on both side surfaces. Furthermore, excitation electrodes 18 and 19 are provided on both main surfaces of the leg portion 1', and excitation electrodes 20 and 21 are provided on both side surfaces of the leg portion 1' to the full width thereof, respectively.
Cr film (film thickness 300A) and upper layer Au film (film thickness 700A)
It is attached by vapor deposition technology. Similarly, the connection electrodes of the leg portion 1 include a connection electrode 22 that connects the excitation electrodes 14 and 15, a connection electrode 23 that connects the excitation electrodes 15 and 21, a connection electrode 24 that connects the excitation electrodes 16 and 17, and the connection electrode 24 that connects the excitation electrodes 14 and 15. Similarly, the connection electrodes in section 1' are connection electrode 25, which connects excitation electrodes 18 and 19, and connection electrode 2, which connects excitation electrodes 19 and 17.
6 and a connecting electrode 2 that connects the excitation electrodes 20 and 21.
7 are attached to each. These connecting electrodes 2
2 to 27 are the legs 1, 1' or the base 2 of the diaphragm 3.
As shown in the figure, it is placed astride the ridge (the steep part has been removed). In addition, base 2
A relatively large area metal film 28, 2 is formed on both main surfaces of the
9 is attached in the same manner as the excitation electrode and connection electrode described above, applies an input vibration here, and connects the diaphragm 3
This is the end electrode that holds the .

The tuning fork-shaped crystal resonator of the present example constructed in this manner can completely eliminate conduction defects in the connection electrodes, and furthermore, the excitation electrodes, especially the excitation electrodes on both sides, can be Because it is placed in the ridge and acts effectively on the ridge as an excitation,
In addition to making the CI value smaller (conventional CI value: 10 kΩ reduced to 7 kΩ with the present invention), and reducing its dispersion (conventional CI value dispersion: 4 kΩ reduced to 2 kΩ with the present invention), Quality can be improved.

The above advantages extend to the advantage that it is possible to further reduce the dimensions of the tuning fork shape, and that the vibrator characteristics, for example, frequency-temperature characteristics, can appear faithfully.

The present invention has been described above based on examples, but
In addition to quartz, the piezoelectric material may be lithium tantalate single crystal, and the electrode arrangement is not limited to that shown in FIG. 3, but various patterns can be considered.

[Brief explanation of drawings]

FIG. 1 shows a tuning fork-shaped crystal diaphragm after etching, with A being a sectional view taken along line A-A and B being a surface view. FIG. 2 is a cross-sectional view of a tuning fork-shaped crystal diaphragm with the steep edge portion removed. FIG. 3 shows an embodiment in which electrodes are arranged on the tuning fork-shaped crystal diaphragm shown in FIG. 2, and FIG. 3 is a perspective view in which the front and back sides are connected. 1, 1'... Leg, 2... Base, 3... Tuning fork-shaped crystal diaphragm, 4, 5, 6, 7, 8, 9, 10, 1
1, 12, 13...ridge, 14, 15, 16, 1
7, 18, 19, 20, 21...excitation electrode, 2
2, 23, 24, 25, 26, 27... connection electrodes.

Claims (1)

[Claims] 1 Etching the outer shape of a tuning fork-shaped piezoelectric diaphragm, which has a tuning fork shape with two plate-shaped legs and a plate-shaped base that connects the legs, using an etching liquid that etches in a direction perpendicular to the plane of the diaphragm. After processing, the ridges are etched using an etching solution that etches almost equally on two sides of the diaphragm bordering the ridges to remove the steep portions of the ridges, and a tuning fork is placed on each side of the legs. A tuning fork-shaped piezoelectric vibrator, characterized in that an excitation electrode to be vibrated is arranged, and a connecting electrode is arranged to connect the excitation electrodes to each other, straddling the ridge of the leg or the base. Production method.