JPS5885617A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To execute an electrode design of a metallic strip reflector, by deciding (alpha) and d/lambda so that the product of an electrode width duty factor (alpha) of said reflector, and d/lambda which has devided electrode width (d) by surface acousitc wave wavelength (lambda) enters within a range of specified numerical value. CONSTITUTION:In a surface acoustic wave device using a piezoelectric substrate 1 whose electromechanical coupling coefficient is comparatively small, among electrode width duty factor alpha (alpha=w/p, (w) and (p) denote electrode finger width and an electrode pitch, respectively) of a metallic strip reflector 4, electrode film thickness (d), reflected surface acoustic wave waveldngth lambda, stopping band width DELTAf, and its center frequency fO, there is relation of DELTAf/f0=C.alpha.d/lambda, and C=0.6- 0.8. Therefore, in order to satisfy request specifications of DELTAf/f0=0.5-1.2% (alpha) and d/lambda are decided so that an expression 1 holds good. That is to say, since the wavelength (lambda) is decided by the center frequency f0 of the reflector, an optimum value can be selected from among a lot of combinations of (alpha) and (d) for satisfying the expression 1, and the number of degrees of freedom of an electrode design becomes large. Accordingly, it is possible to execute a design which has taken reduction of a cost into consideration.

Description

[Detailed description of the invention] The main source is connected to a surface acoustic wave device.

A surface acoustic wave device having a metal strip reflector with a grating structure has a pressure-region substrate 1, as shown in FIG.
Table 1 wave O on the *genus strip reflector 4 and its both 111
Input and output comb shape of Ruru 1 where the Denkanji is the same <*2
tS, and the filter ossification by the input and output comb electrodes 4j7i is given a steep band-stop ossification by the metal strike reflection 1ifi4, as shown in FIG. An a-ki rfj & device using this steep band breakdown voltage characteristic as a frequency standard has been proposed, and the stopband -Δf, which is required as a frequency standard for a comb filter for Jli wave number counting on a TV channel, is 05% of the center frequency am. ~1.2 attacks. Figure 1 (The pitch P of the metal strip reflection a billion shown in ml and the threshold between the surface acoustic wave device V and the center frequency fo = '/2p 12) F!
! 4 karari 1 normal amount - strip reflector (100 million fingers @r
is designed with r = p72. On the other hand, the thickness d of the wax m is the stopband width Δf caused by the reflection of the metal strip.
K has a large influence on the above-mentioned finger width, and usually trial and trial is performed to satisfy the required timeliness for the above-mentioned finger width.
has been decided.

For example, piezoelectric substrate KX cut 112°-turn Y propagation L&
Tlll03 (tantalum lithium, v == 3-
500"/a) using 250 MHz, reflected surface acoustic wave λ = 2P-14,4j-*number of reflection waves N = 250 lt strip anti-reflector injection. , Δ'/A = 1% JQ pressure g I) = 1
To add more than 5dE k 44.

When r = J-56μ corner, set d = α4μ.

Since the degree of suppression is sensitive to the number NK of reflected hot water, by applying s#l to this N, it is possible to satisfy KD, which is almost independent of Δf/jo. Therefore, in practical terms, At thickness d is ”/
Determined by the directness of fe.

In the above-mentioned prior art, the thickness of the gold J11 was determined by the property specification [K], and there was a problem that it was not possible to arbitrarily select the S thickness that was convenient for device manufacturing. jl is also eye 114
? The optimum thickness of the reflective wire to achieve the desired performance and the undesirable comb-shaped thickness (generally d/λ = 5 inches or less) are not necessarily the same, and the wire thickness required for device mounting is not always the same. The film thickness for bonding (IMμ or more) is also different from each other5.
A *14 JailK thickness of type *14 is practically required. For this reason, the manufacturing process for the device becomes complicated, causing an increase in manufacturing costs.

The purpose of the present invention is to eliminate the above-mentioned disadvantages of the prior art, and to
I&Made-in-the-making process The IT of the tube reflector
ilJ [t
, a bullet! The main purpose is to provide direct access to RFI waves.

That is, 1. the present invention is a surface acoustic wave device in which a grete ink-assisted metal strip reflector is formed on a piezoelectric plate, and the stopband width If generated by the reflector is set to the center J.
In a surface acoustic wave device in which a certain specification rate (arrogance) is required for Δ'/fe divided by the wave number 9 and must be satisfied, the above-mentioned 04. o To satisfy the required specification rate, d/λ divided by the weight of the metal strip reflector α and the thickness of the reflector and the surface acoustic wave wavelength λ [however, λ-'4. (V; moderate surface wave, /@; same as above)] and the product [α・d/λ] falls within a certain Oa value @-, and the above α and d/λ are determined. Iron surface acoustic waves! 1efK exists.

The present invention is based on LiTaO5, single crystal, crystal 41) 4fi
In the above-mentioned surface acoustic wave device t using a piezoelectric substrate with a relatively small dal coupling coefficient, the electrode width of the metal strip reflector is calculated by the electrode width d = tair actuator α (= '/p, where sl is the electrode finger width and P is the pole pitch). , Sadatsu d.

The reflected surface acoustic wave wavelength λ, the stopband width Δf in the circumferential aILaW property, and its center frequency afe.

Seki K'f/j, -E C・α@'/2, C-(
We found that there is a relationship between 16 and αaco@, and arbitrarily set α, d to satisfy the above formula for 45R specification Δf/f.
Is it possible to select combinations? # value. ∆f for dwarf
/4 is the metal strip (polarity factor α, l
Although it varies greatly depending on the IE thickness d and the number N of electrodes, there is no doubt that these varying factors are related to the reflection property. Therefore, we have Li
TtxO, α, d, and N dependence of the At strip reflection t1 time using a single-crystal piezoelectric substrate #p fine 11C
14. Since that time, it has become clear that the fluctuation of 7bL character with respect to the change in N can be a practically sufficient black value for α and d, and the relationship between α and d and] Shino is 1g5m.
As shown in , Δbα;C・α・T(C−0,6~t1
8) We found that the relationship in (1) holds true. From this n.

lf7 included; To satisfy the required specifications of α5 to t2.

α and λ may be determined so that α006≦α114≦α02 (2) holds.

4"Ep, the central IR wave number of the AI strike reflector is the wave length λ (= n, ν is determined by the plane wave velocity and tIt plane wave velocity.

The optimum value can be selected from among countless combinations of α and d that satisfy the above formula (21), and the degree of freedom in electrode design is dramatically increased compared to the conventional method.

It is now possible to design electrodes that take manufacturing costs into consideration, and fr
A desired surface acoustic wave device can be provided.

Hereinafter, Honkaku will be explained in detail using a specific example. As a practical example of the present invention,
Input and output comb-shaped electrodes (center frequency 250 MHz, bandwidth ■Ez.

At@thickness α1~IIL2μm), center frequency k = 230 JtHz', (surface wave wavelength 1447111) tli stop band width Δf -2,5J for both wax values.
Inx (Δ” ”” '), e Orthogonal D - This article describes a surface acoustic wave filter with a skin*a standard in which A!* strip reflectors with an A of 15 dB or more are placed.The wire bonding reliability during filter mounting is Taking this into consideration, the Atg thickness of the bonding pad needs to be at least α6, and in order to share the thickness of the Al stripsig reflection 1sO and this bonding pad, the thickness of the reflector was set to 17μ in this example. Therefore, from Equation (2), by designing the reflection 11!
- realized. At this time, the number N of electrodes is 250, ensuring a degree of suppression of 15 tB or more.

As described above, according to the present invention, it is easy to realize an elastic surface having a desired reflective coating using an arbitrary At metal thickness, and it is possible to achieve an optimal metal strip reflective surface in terms of manufacturing process. Elastic table rjji wave-Jj that allows for device electrode design
It is obvious that & direct can be obtained.

In Kamikii JIIf1, LiTgO,
Although a single crystal is used, the same effect as in the above embodiment can be obtained using a material (such as crystal) in which 3 is less than or equal to 1 in the tg and fk number.

According to the present invention, as shown above, the strip reflection-oi
It is possible to freely set the electrode, and the electrode design is ideal for the art process. A surface acoustic wave device with a metal strip reflector has been obtained, and the manufacturing cost has been significantly reduced. I was able to provide some protection.

A perspective view showing an elastic type device having an elastic tItIlir wave arrangement, jl! Figure 1C chrysanthemum is the A-A cross-sectional view of 嬬1id (嬬), recommendation 2- is the note diagram of the shoulder wave ridge of the surface acoustic wave position of Jai1 figure, 4
Figure 5 shows wL Kyokusuri Day 7 Actor α; One and Roto, which has been styled with a one-plane wave wavelength, has a thickness of d7/λ (α・l), and the center of Senzu Teijo, l4ajL number 1. It is a diagram showing the relationship between 娨 (b upper band - Δf) normalized by .

1... Piezoelectric substrate 2... Manual comb-shaped electrode 5.
...Meriki comb-shaped electrode 4...Metal strip reflection - 5...wL 櫨 finger (width) Daidannintobetsushi thin 88 Rishin 1st breast milk 2 difficult +. Zhou Jinu

Claims (1)

[Claims] t A surface acoustic wave t&pupil in which a metal strip reflector with a grete ink structure is formed on four ridged plates, and the stop band I and 7f generated by the single reflector is defined as its center J4 wave. Regarding 'β de divided by jo, [elastic formula l111TIJ which requires a constant discharge rate (s) and needs to satisfy this t
jL apparatus odor ℃, front 1Δjyl, ol! To satisfy the required specification rate, the metal strip reflection coefficient αL ffl L, α-'/p (
d/2 [however, λ
-V/j, (V; table rTJtIIL speed, 9; same as Ken 1)] and the horizontal [α・1] is a constant pardon soul - I enters
An elastic surface aIL device whose 411 mold is formed by determining IK upper limit α and d/λ. 2, ``j/f, (D'1JllI rate (excellent) -fi
(An elastic table rTJ wave device of the range d fringe 1 term of ffdI when it is within the range of 15 to t2-O. &α・'/J is within the range of 16 to 2, Kikyo's surface acoustic wave device. 4 α ・ d / λ ) 4 km; C ・ α ・
The surface acoustic wave device according to claim 1, which is derived from the 1111 coefficient equation of d/λ [C-α6~(L8, constant)].