JP2586892B2 - Surface acoustic wave resonator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave (SAW) resonator, and more particularly to a SAW resonator that is reduced in size and has improved manufacturing yield.

(Prior Art) As shown in FIG. 2, a SAW resonator generally has a pair of IDTs 2 placed on the surface of a piezoelectric substrate 1 and reflectors 3 provided on both sides thereof. When such SAW resonators are mass-produced, a large number of identical patterns are arranged in a matrix on a photomask, and these are arranged on a large-area piezoelectric substrate (wafer) 4 by photolithography as shown in FIG. A large number of SAW resonator patterns are formed, and the wafer 4 is divided and cut by dicing in a direction parallel and perpendicular to the normal SAW propagation direction to obtain a large number of SAW resonators. Therefore, both ends of the tip of each SAW resonator are cut perpendicular to the propagation direction, that is, parallel to the electrode at the end of the reflector.

By the way, when the logarithm of the SAW resonator IDT or the number of reflectors is sufficiently large, the vibration energy of the SAW is sufficiently confined between the reflectors, and the amount of entanglement to both ends of the chip is extremely small. The effect due to the reflection is small and does not matter.

On the other hand, as the demand for miniaturization of components has become severer, ultra-miniaturization of SAW resonators is also required, so if the chip length is not sufficient and the number of reflectors becomes limited, Conventionally, in order to compensate for the decrease in the number of reflectors, the reflectivity per reflector is increased by increasing the thickness of the electrode to compensate for the characteristics.

However, there is a limit to the method of increasing the electrode thickness described above, and the effective logarithm of adding the number of reflectors to the IDT logarithm is 200.
If the electrode thickness is less than the pair, even if the electrode thickness is increased to 4% or more of the wavelength
The rate at which the SAW vibration energy is not sufficiently confined between the reflectors and leaks to both ends of the chip increases.

That is, if the phase of the wave reflected at the edges at both ends of the chip coincides with the phase of the resonating wave, Q is improved, and conversely, if the phases of both are reversed, Q is canceled out and Q becomes
Although the SAW wavelength is reduced, the wavelength of the SAW is as small as several μm to several tens of μm.
It is virtually impossible to cut chips from a wafer with an accuracy of less than or equal to the size.

For this reason, in a SAW resonator having a small effective logarithm, when a wafer is cut into chips, the reflected wave of the SAW may or may not match the phase of the resonating wave due to variation in the cutting position, and the Q or CI (crystal) Impedance). Also, in order to eliminate this variation, the chip may be cut at a position where the phase of the reflected wave exactly matches the phase of the resonating wave, or an absorber may be applied to both ends of the chip to absorb the reflected wave. Attempts have been made to prevent the deterioration of characteristics, but in both cases, it is impossible to improve the quality and variation of Q and CI, and the production yield is greatly reduced. there were.

(Object of the Invention) The present invention is a conventional small-sized reflector having a small number of reflectors as described above.
This was done in order to solve the disadvantage of poor production yield of SAW resonators.
It is intended to provide a W resonator.

(Summary of the Invention) In order to achieve the above-mentioned object, in the present invention, the end of the SAW resonator chip is placed in a direction perpendicular to the propagation direction. (N is a positive integer, λ is the wavelength of the SAW, and W is the cross width of the IDT).

Hereinafter, the present invention will be described in detail based on an embodiment shown in the drawings.

FIG. 1 is a view for explaining a SAW resonator pattern and a method for cutting a chip according to an embodiment of the present invention.
Cut quartz, resonance frequency is 61.25MHz, SAW wavelength λ is 50.6
μm, the electrode width of one reflector is 12.65 μm, and the electrode is aluminum. The number of IDTs is 80 and the number of reflectors is 100 on both sides.
The cross width W is 15λ, and the electrode film thickness is 2 μm.

In FIG. 1, the end of the chip is inclined by α = tan ⁻¹ (nλ / 2W) (n is a positive integer) in a direction perpendicular to the SAW propagation direction, that is, in parallel with the electrode 4 at the end of the reflector. For example, if n = 1, the inclination is α = tan ^-1 {(λ / 2) / 15λ} = 1.9 °.

Thus, in the range of the crossover width W, the wave reflected by the edge of the chip is
There are places where the phase of the wave matches and where it does not. That is, in the width of the crossover width W, there is a place where the phase is matched and Q is improved, and a place where the phase is not matched and Q is deteriorated. On average, neither is good nor bad, and the absorber is applied to the edge of the chip. Approximately the same effect can be obtained.

As shown in FIG. 4, the relationship between the gap d between the electrode at the end of the reflector and the edge of the chip and Q becomes better or worse at a cycle of λ / 2. Therefore, the edge width of the chip must be
In contrast, if the angle is tilted by λ / 2, the degree of coincidence of the phase of the reflected wave is averaged, and as described above, it does not get better or worse, and eventually the variation of Q and CI decreases, and extremely The manufacturing yield is improved as much as there is no worsening.

FIG. 5 is a diagram showing the distribution of CI variation when the end of the chip is cut in parallel with the electrode at the end of the reflector as shown in FIG. 2, and FIG. 6 is a diagram showing the distribution of the chip according to the present invention. FIG. 7 is a diagram showing the variation of CI when the end is inclined by 1.9 ° with respect to the electrode at the end of the reflector, and the number of both is 200. As is apparent from these results, the average value is almost equal between the case where the chip is tilted and the case where the chip is not tilted, but the variation when the chip is tilted is greatly improved. In other words, the effect of the reflected wave at the edge of the chip is averaged within the range of the crossover width, as if the absorber were applied to the edge, and the reflected wave did not show the effect of deteriorating the CI, resulting in a production yield. Is improved. The same result was obtained for Q in this distribution.

If the inclination angle α is determined, the effect is the same even if the cutting position on the chip is slightly shifted left and right if it is parallel to this.

Although only the case of one one-port SAW resonator has been described above, the present invention is also applicable to a two-channel SAW resonator having two one-port resonators. For example, when a pattern of two resonance frequencies of 61.25 MHz and 67.25 MHz is formed on one chip, the end inclined cutting angle α of the chip is adjusted to an angle with a smaller number of reflectors on the lower frequency side (61.25 MHz). Alternatively, it may be adjusted to the average value of the optimum values at both ends. However, if the cross width normalized by the wavelength is the same, the angle α has the same value in both cases.

Further, the present invention relates to a two-port SAW resonator, a slip wave resonator, a leaky SAW resonator, a Love wave type resonator, a multi-pair IDT type SAW resonator.
It can be applied to any IDT-excited resonator such as a resonator.

(Effect of the Invention) Since the present invention is configured as described above, it is remarkable in improving the production yield of a SAW resonator in which the length of a chip is limited by miniaturization and the number of reflectors is extremely reduced. effective.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view for explaining cutting of a SAW resonator chip according to the present invention by tilting its end, and FIG. 2 is a view showing a cut shape of a normal SAW resonator chip. FIG. 3 is a view showing a number of SAW resonator patterns formed on a piezoelectric substrate wafer,
FIG. 4 is a diagram showing the relationship between the gap between the electrode at the end of the reflector and the end of the chip and Q, FIG. 5 is a diagram showing the variation in CI by the conventional cutting method, and FIG. By way
It is a figure which shows the dispersion | variation of CI.

Claims (1)

(57) [Claims] In a surface acoustic wave (SAW) resonator in which an interdigital transducer (IDT) electrode is placed on a piezoelectric substrate and reflectors are provided on both sides thereof, the cross width of the IDT is W and the wavelength of the SAW is λ. Wherein the edge of the piezoelectric substrate is cut at an angle of α = tan ⁻¹ (nλ / 2W) (where n is a positive integer) with respect to a direction perpendicular to the SAW propagation direction. Child.