JPS6038912A - Elastic surface wave device - Google Patents

Abstract

PURPOSE:To prevent characteristic degradation due to electrode reflection and diffraction and also to attain ease of coupling with an external circuit by prolonging the non-crossing part of all interdigital electrodes of a comb-tooth electrode. CONSTITUTION:The electrode pattern is formed on an LiNbO3 substrate. A normal type input electrode 2 having a crossing part 18 with a length W of 200mum and non-crossing parts 19, 19' having a length W', W'' each of 1,200mum and an output electrode 2' with cross width weighting having the same effective aperture and non-crossing part as those of the normal type input electrode are formed with pure Al as the electrode material, a film thickness of 0.1mum and electrode width and space of 1.2mum, the center frequency is 400MHz, the number of pairs of the input normal electrode is 14 pairs, the number of pairs of the output weighted electrode is 60 pairs and the 3dB band width is 30MHz. The radiation conductance at the center frequency is 5.6mm. mohs, the electrode finger conductance Gf of the normal type electrode 2 is 69.1mm. mohs, and the major crossing part of the weighted electrode is dominant to its electrode finger conductance Gf and it is the same as that of the normal type equivalently.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a surface acoustic wave device in which electrode reflection is suppressed.
%, suitable for use at high frequencies such as UIIF! The present invention relates to a surface acoustic wave filter that can expand the degree of freedom in impedance design and simplify matching with external circuits.

[Background of the invention]

In a surface acoustic wave device, one or more interdigital electrodes are provided on a surface acoustic wave substrate. By weighting the pitch of each electrode finger of this interdigital electrode, the amplitude 1
The phase transfer frequency characteristics can be extremely designed. The interdigital electrodes of this surface acoustic wave device reflect surface acoustic waves. Therefore, a delayed signal is generated due to multiple reflections between the electrodes, and the amplitude and
Several countermeasures have been taken to prevent linoggle from occurring in the phase transfer frequency characteristics.

The reflection of surface acoustic waves by the interdigital electrodes described above can be classified into two types: electrical re-radiation and reflection due to acoustic discontinuity. Reflections from the latter acoustic discontinuities are U.S.P.
It is generally believed that the electrode width and blank space are 4 lengths long, and the spherite polar finger, as shown in No. 5,699,564, has two pairs of electrode fingers of the same polarity.

On the other hand, the former electrode reflection due to electrical re-radiation is determined by the relative relationship between the radiation conductance Ga of the transmitted/received wave t= and the contour G of the external circuit.

as a measure of electrode reflection.

is called reflection loss. In order to avoid characteristic deterioration due to % polar reflection, a value of 40 dB or more obtained from subjective evaluation of both TV images, which is the sum of two reflections from the input electrode and the output electrode, is often adopted as the standard for reflection loss.

This means that if the input and output electrodes share equally, -
The reflection loss per electrode is 2 odB, and to achieve this, conventionally, based on Figure 2, Gz/a, >
9, the transmitting and receiving electrode radiation conductance GcL was given as follows. At this time, the filter passing loss is practically used at about 20 dB.

On the other hand, the conductance of the external circuit system is a constant value, often t! 20yrL'U (impedance: 500), so in the conventional method described above, it was necessary to reduce the radiation conductance of the wave transmitting/receiving electrode to 2.2- or less. For this reason, the following two drawbacks occur in the conventional two-electrode configuration in the high frequency region of the VHF high range to the U IfF band or in the case of a narrow fractional bandwidth.

Under certain conditions, the frequency is high or the logarithm is large (narrow band), Ga is measured using the conventional method (2.2 mU).
In order to achieve this, the opening length IF of the electrode must be set small. Therefore, when the weight is set to 1%, characteristic deterioration such as disturbance in the tail of the bandpass characteristic and waviness within the band occurs due to single diffraction due to the small cross width of the electrodes. For example, if the number of bonds is large (0,055n(D), LiNbO3 single crystal-1
In an input normal type, output weighted surface acoustic wave filter with a center frequency of 400 MBz and a 5 dB bandwidth of 50 MIIz using a 28° fY-axis cut and an X-axis direction propagation substrate, the aperture length F is as small as 80μ, or about 8 wavelengths. , 1st
As seen in the characteristics of the above example shown in the figure, the above deterioration is remarkable.

Next, at high frequencies, the susceptance, which includes not only the electrode placement but also the capacitance of the package and external circuit system, becomes a considerably larger armpit '''C1 than the radiation conductance of the transmitting and receiving electrodes, so the susceptance is A coupling circuit including a canceling inductance is required, which not only increases the number of parts, but also causes the disadvantage that the inductance needs to be adjusted.

[Purpose of the invention]

The purpose of the present invention is to eliminate characteristic deterioration due to electrode reflection in the high frequency range of VHF or UHF band, or when the bandwidth is relatively narrow, to eliminate characteristic deterioration due to diffraction, etc., and to eliminate characteristic deterioration due to external circuits. The object of the present invention is to provide a surface acoustic wave device that is easy to match and requires few adjustment steps.

[Summary of the invention]

The present invention comprises a piezoelectric substrate and an input and output transducer formed of mutually intersecting comb-like electrodes provided on the piezoelectric substrate, and each comb-like electrode has an intersecting portion and a non-intersecting portion. In a surface acoustic wave device consisting of an electrode finger and a spar that connects the non-cross-shaped ends of the electrode fingers, the bass groove of one comb-shaped electrode of each transducer and the comb-shaped electrode of the other By lengthening the non-intersecting portions of all the electrode fingers of one comb-like electrode so that the distance between the electrode fingertips and the electrode fingers is sufficiently larger than the distance required to prevent contact with each other, the electrode This prevents characteristic deterioration due to reflection and diffraction, and also facilitates σ coupling with an external circuit.

[Embodiments of the invention]

The present invention will be explained below along with examples.

FIG. 2 is an electrode button diagram showing the electrode shape for explaining the basic principle of the present invention. As is clear from the figure, the length W of the intersecting portion 18 of the electrode fingers 8 is different from the length W of the non-intersecting portion 19, 19.
'Length F', longer than W', non-intersecting part 1
9 and 19' are considered. The related parameters are radiation contourance Gas, electrode finger conductance Gy over the entire electrode, and conductance GL of the external circuit.
It is. Here, the electrode finger conductance G is given by the following formula (11) using the logarithm N and the electrode finger resistance rf per pair (in the case of sugerite electrode fingers, it is given as a value connected in parallel).

Gf-N/rf (1) Also, the resistance of electrode fingers per pair? '7 is given by the following formula.

rt = (Resistance at the non-intersecting part of the ringing opening of the electrode finger of one polarity) + (Resistance at the non-intersecting part of the electrode finger of the other polarity) (2) The above-mentioned reflection loss is linear per pole. It gives me strength.

Here, b-L/GaIc=Gf/a, and the coefficient α was experimentally determined to be 0.0415.

Equation (4), where Equation (3) is set as 2nd and E, calculates the G required to connect the conductance GL to the external circuit and set the return loss per -°a pole to the standard 20 dB. This is the sales method determined by the company.

(4) First, the electrode reflection reduction effect of electrode finger conductance G1 (
(increase in reflection loss) will be explained.

Before gtnottu<, reflection loss is b-L/Ga, C-0f
/G Ga is given as follows.

As an experimental example, the conductance of the external circuit GL = 20m
At tT, L LNbOs single crystal on the substrate, 128° rotation Y
Using axial propagation in the X-axis direction, the transmitting and receiving electrodes are regular type electrodes with a center frequency of 400 Mlz and a logarithm of 14 for both input and output, the electrode material is pure AI't' film thickness 0.1 μm, and the effective aperture length is 200 μ77L. , radiation conductance G (L is 5
．． FIG. 3 shows the relationship between the reflection loss and the length of the non-intersecting portion when the input and output are equal and the change in the conductance G/ of the electrode fingers is made in the extension of the non-intersecting portion. In Figure 3, the vertical axis is the reflection loss per electrode, the horizontal axis is the electrode finger resistance rt, 1Ff, and the polar finger conductor p y s G7 (=
A' / rf), Zenden% Soukuma (W 10F'1Ir'
) at the same time. In FIG. 3, reflection loss increases due to an increase in electrode finger resistance due to the non-intersecting portion of the electrode fingers, and the calculated value of Equation 151 is shown by a solid line.

A showing the experimental value (non-intersecting part not extended, Gy = 622
．． 2m'c)), B (non-interactive 4 head IP"+IT"
-, 500 μm, Gf-177,877In),
C (non-intersecting length IV'0r = 1QQQμm.

Gy = 103.7 m'U), D (non-intersecting length W
'10F' = 1600, IF7L, Gy = 69
．． 177LU), E (non-intersecting length IV'10F"=
It is shown that the values at each point of 2400 μm % Gy = 47.9 mT) agree.

Next, a first embodiment of the present invention will be described.

FIG. 4 is a t-pole diagram showing the first embodiment of the present invention. The electrode tab shown in FIG. 4 is formed on the same L 1NbO substrate as in the experimental example of FIG. 3. Intersection part 1B with length F = 2ooμm similar to Figure 2, length F'2F' =
A normal type input electrode 2 with a non-intersecting part 19.19' of a 1200μ door, and an output electrode 2' having the same effective opening and non-intersecting part as the regular input electrode and cross width weighting, are t&
The film thickness is 0.1μ77L using pure AI as the coating material, and the polar line width is
The blank space is 1.2μm, and the center frequency is 4001
dllz, the number of pairs of input normal electrodes is 14, the number of pairs of output weighted electrodes is 60, and the 5 dB bandwidth is 50 MHz. The radiation conductance at the center frequency is 5.6 mry in both cases, and the electrode finger conductance Gf is 69.1 mtJ for the regular electrode 2.

In terms of weighting, the electrode finger conductance Gy is dominated by its main intersection (main lobe), and is equivalently similar to the normal type.

The length of the above-mentioned non-intersecting portion 18 in the first embodiment is determined by setting the return loss calculated value given by equation (51) to 20 dB when considering an external circuit with contourance GL = 20 yatJ. (The combined input and output reflection loss is 40 dB.) On the other hand, if the length of the non-intersecting part of the electrode fingers is 1, for example, in the above example, II"+F"==
Since the length is 2400 μm, as an auxiliary means, an external circuit It5 having a conductance GL as shown in FIG.
17 and the surface acoustic wave device 14 coupling circuit 15, i3
Using the parallel resistance (conductance G,) as ', -
It is practical to set the reflection loss per electrode to 20 dB (also L〈is the total input and output “C40cl!B”) because it can shorten the non-crossing portion of the pole fingers.In this case, GL is set to Gt +
Replace with Gp.

By applying equation (4), G and G are determined.

An example based on the above idea will be shown as a second example. The planar configuration and other aspects of this embodiment are the same as those of the first embodiment described above, except that the non-intersecting portion length W'=lV'=500 μm for both input and output, and the parallel conductance Gp i 21.3 mυ. The experimental results of this example are shown in FIG. 6 (symbol q). In Figure 6.

to an external circuit with conductance GL = 20 mT).

The horizontal axis K is the equivalent external conductance (GL + Gy) connected to the parallel conductance GP, and the passing loss.

The vertical axis shows the reflection loss (for both input and output electrodes). In Figure 6, GL== 2Qm PitoG, = 21.3m
The sum of U is 413 mU, and the reflection loss of the input and output 2 electrodes is 40
I reached my goal with dlJ. On the other hand, the passing loss remains at 25 dB and does not become extremely large.

As a third example, a case will be shown in which the length of the non-intersecting portion of the second example is changed to H7'=W'=ysoμm.

The experimental results of this example are shown in FIG. 6 (symbol D1) similarly to the second example, and conductance GL = 20yyz
In the external circuit of tT, the parallel conductance is 107? By connecting L■, the reflection loss of the two input and output electrodes reached the target of 40 dB, and the one-pass loss was 22 dB.

As a fourth embodiment of the present invention, output weighting is performed in the third embodiment! This shows the case where the non-intersecting portions are not extended at the poles. The electrode terminal of this embodiment is shown in FIG. In this example, the reflection loss of the output weighting t without non-intersection extension is small, and the external circuit j1 at GL=20
14 dB for 8, parallel conductance Gp =
When connecting 2t3 mTJ, it is 18tLE, but with the regular electrode with non-crossing part extension, GZ = 20771
For the external circuit of υ, the return loss is 18.2 dB and the parallel conductance Gp.

2t5mU was connected, and the reflection loss was 22dB, so the combined input and output reflection loss reached the target value of 40dB.Next, as an example of ratio 5 of the present invention, improvements were made to the electrode structure of the non-straightened part. In the electrode structure shown in FIG. 8, the case is shown in FIG.
In the effective opening 18, splint electrode fingers are used, but in the non-intersecting parts 19 and 19', two adjacent electrode fingers of the same polarity are combined into one, and the 'RL pole distance is one electrode finger of the effective opening. It is the same as the width, and the resistance value of the non-crossover part is double, so
Compared to the case shown in Fig. 2, the length of the non-intersecting part is only 4, which has the advantage of making the device smaller. On the contrary, in the fifth embodiment, the film thickness may be increased.

This has the advantage that wire bonding is easy.

In addition, instead of extending the non-intersecting part, it is possible to increase the electrode finger resistance by reducing the thickness of the polar phase film. , variations, reliability, fluctuations in weighting due to resistance, etc. become problems.

The non-intersecting portion extension of the present invention is effective in avoiding the above-mentioned problems.

, [Effects of the Invention] According to the present invention, the VHF high frequency range or higher (approximately 2001 MIz)
In surface acoustic wave devices used at higher frequencies than above, or in relatively narrow bands @ (fractional bandwidth 10% or less), disturbances in amplitude and phase (group delay time) can be prevented by suppressing the maximum length of radiation to 40 dB or less. Since a larger radiation conductance and effective aperture can be obtained than in the focused, secondary, and undetermined ranges, as shown in FIG. A good frequency a characteristic without any disturbance can be obtained, and a fixed parallel resistor can be simply used as shown in FIG. 5 without using an inductance coupling circuit that requires adjustment.

We were able to reduce the number of parts and proceed with unspoken reduction.

[Brief explanation of the drawing]

Fig. 1 shows the frequency characteristics of a conventional surface acoustic wave device, Fig. 2 is a plan view of the electrode structure according to the present invention in which the non-intersecting parts of the electrode fingers are extended, and Fig. 3 shows reflection loss and non-intersecting parts. A characteristic diagram showing the relationship between lengths, FIG. 4 is an electrode batten diagram showing one embodiment of the present invention, FIG. 5 is a circuit diagram explaining a coupling circuit in which conductances are connected in parallel, and FIG. 6 is a diagram showing one embodiment of the present invention. the second of
．． A characteristic diagram showing the relationship between reflection loss 1 passage loss and parallel conductance in the third embodiment, FIG. 7 is an electrode batten diagram schematically showing the fourth embodiment of the present invention, and FIG. 8 is a diagram of the present invention. FIG. 9 is a characteristic diagram showing frequency characteristics improved by the present invention. [Explanation of symbols] 2.2'; surface acoustic wave transmitting/receiving electrode 3; bonding pad 4; bus electrode 5; power supply 6; internal conductance of power supply 6'; load conductance 8; electrode N5I0. S!
,...,SN;1. Z, ..., Nth electrode pair 15.13'; parallel resistance (conductance G,) 14;
Surface acoustic wave device 15.15'; Coupling circuit section 16; Signal source 17; Load 18; Effective aperture 19; Non-intersecting electrode finger 19'; Non-intersecting electrode finger A having a different polarity from 19; Gf=622
．． 27110 (no extension at non-intersection) B; G
j = 177.8m'C) (') Case C; Gy =
105.7rnT) 0) m combination D; Gj ” 69
．． 1n(IJ (1) tJJ combination E; Gy =
47.9rnT) case C1; foot measuring point Dl showing the second embodiment; side foot point showing the third embodiment Attorney Patent Attorney Akira Takahashi 4 Figure 3' Den et al.

Claims (1)

[Claims] 1) Consisting of a piezoelectric substrate and input and output transducers each consisting of intersecting comb-like electrodes provided on the piezoelectric substrate, each comb-like electrode having an intersecting portion. From the non-intersecting part 1. Consisting of curved electrode fingers and a connecting bus bar at the side end of the non-intersecting part of the electrode fingers, the bus bar of one comb-shaped electrode of each converter and the center and pole phase tip of the comb-shaped lightning five poles of each converter are connected. 5. The surface acoustic wave is characterized in that the non-intersecting portions of all electrode fingers of one comb-shaped electrode are lengthened so that the spacing between the two electrodes is sufficiently larger than the spacing required to prevent contact with each other. Device. 2) The magnitude of the radiation conductance G of the pole for transmitting and receiving waves should be 4 or more than the connected external simultaneous conductance GL, and the number of pairs of wave transmitting and receiving electrodes N and the pair of ta finger resistances rt to N
When the electrode finger conductance Gf, defined as /rl, is extended at the non-intersecting part, b = GZ / Ga
, c = Gy/Ga, and the surface acoustic wave device according to claim 1, characterized in that it satisfies the following relationship by c. ≧2DdE