DE4333342A1 - Electronic component operating with surface acoustic waves - Google Patents

Abstract

A SAW component having a mode conversion structure (10; 10') on the component substrate (1), in which the mode conversion structure (10; 10') for a substrate material having strong coupling of surface waves to bulk waves is constructed as an electrode finger structure (11; 11') with a geometric period adapted to the coupling and matching metallisation ratio. <IMAGE>

Description

The present invention relates to an electronic surface acoustic wave component according to the Preamble of claim 1.

In electronic components of the generic type, the basically arranged on a piezoelectric substrate Having interdigital converters and reflectors is a part the electrically coupled and in an acoustic surface Chenwelle lost energy in that the Ener not completely decoupled from the interdigital transducers pelt or is reflected by the reflectors, but from runs out of the acoustically active part of the component and so that it becomes disruptive surface waves. These sturgeon surfaces waves can, for example, on the edges of the components are reflected and delayed again in the substrate Interdigital converters or reflectors run in wherever make itself felt as a disturbance. This fact is for example in "IEEE 1986 Ultrasonics Symposium", pages 37 to 42.

From DE-OS 37 31 309 it is with an electronic acoustic surface wave working component of the gat according to the known type, a mode conversion structure for Reduction or elimination of interfering surface waves watch. Such a mode conversion structure is controversial designed like a window and forms an acoustic Surface wave effective disturbances in or on the surface surface of the component substrate. A disadvantage of such Mode conversion structure with parallel and perpendicular to each other right to the main direction of propagation of the sturgeon surface wave aligned electrode strips, however, is still  that the mode conversion structure itself is part of the acu static energy of the surface wave, for example on egg NEN interdigital converter reflected back.

Furthermore, from DE-PS 42 23 001 a component of the in The type in question with a fashion conversion structure knows what is due to main wave propagation partial structures shifted towards each other is. Such a mode conversion structure is also used Elimination of spurious surface waves is not yet optimal.

The present invention is based on the object electronic working with surface acoustic waves Component in the sense of improving the reduction or Eliminate interference surface waves.

This task is done with an electronic with acoustic Surface wave working component of the aforementioned characterize th type according to the invention by the features of solved the part of claim 1.

Developments of the invention are the subject of Unteran sayings.

The invention is illustrated below with the aid of an embodiment game according to the single figure of the drawing tert. The figure shows a schematic representation of a electronic working with surface acoustic waves Component with a mode designed according to the invention conversion structure.

According to the figure of the drawing, a common interdigital transducer 5 of a filter (not shown in more detail) with busbars 6 and 7 and electrode fingers 8 and 9 are provided on a component substrate 1 with side surfaces 2 and 3 and an end face 4 . It should be pointed out that such a structure of an electronic component operating with surface acoustic waves is only an example of embodiments of such components known per se. A special configuration of the component is of no further importance for the present invention.

Furthermore, a mode conversion structure 10 or 10 'with electrode fingers 11 or 11 ' is provided on the component substrate. In this respect, such a component with a mode conversion structure 10 or 10 'provided on the component substrate 1 ' can already be found in the above-mentioned DE-OS 37 31 309 or DE-PS 42 23 001.

According to the invention is now the mode conversion structure 10 or 10 'for a material of the component substrate 1 with strong coupling of surface waves to bulk waves as a periodic cal electrode finger structure from electrode fingers 11 or 11 ' with a period adapted to the coupling in the form of a multiple of the wavelength λ _{SAW of} a surface wave and adapted metallization ratio. The geometric period is the distance from center to center of the electrode fingers, while the metallization ratio is equal to the proportion of the metallized area to the total area in the mode conversion structure.

The geometric period is according to the relationships

as well as their reshaping

is chosen in which
K _SAW the wave vector of the surface acoustic wave,
n an integer,
p the geometric period,
K _BAW the wave vector of the bulk acoustic wave,
f the frequency at which the structure efficiently converts the surface acoustic wave into the bulk acoustic wave,
V _{SAW is} the speed of the surface acoustic wave and
V _BAW mean the speed of the acoustic bulk wave.

With the dimensioning of the mode conversion structure 10 or 10 'given above, surface interference waves are efficiently converted into bulk waves as they pass through the structure due to the interaction with the electrode fingers 11 and 11 '. In contrast to the surface wave, these waves are not guided on the crystal surface, but rather plunge quickly into the component substrate 1 . The spurious surface wave, which energy is extracted by this bulk wave radiation, is damped and thus reduced or eliminated.

The invention underlying investigations for a practical embodiment with LiNbO₃-YZ as the material for the component substrate 1 have given excellent results if a periodic electrode finger structure with a geometric period of 1.8 to 2.0 × λ _{SAW is} provided, where λ is the Wavelength of the surface acoustic wave means. For LiTaO₃ -36 ° red as a material for the Bauelemen tesubstrat 1 , the corresponding period is about 3.8 to 4.5 × λ _SAW .

The electrode fingers structure may be in a development of OF INVENTION dung an open electrode fingers structure 10 with non-stationary interconnected electrode fingers 11, a short-circuited structure having interconnected Elek trodenfingern 11 'or a combination of open and shorted electrode fingers 11 and 11'. The metallization ratio can be, for example, equal to 0.5. In order to indicate these two embodiments of the mode conversion structure in FIG. 1 side by side, the mode conversion structure 10 is extended with open electrode fingers 11 and the mode conversion structure 11 'with short-closed electrode fingers 11 ' is shown in dashed lines, a combination for reasons of clarity not being specifically illustrated. Finally, the periodic electrode finger structure 10 does not necessarily have to be perpendicular to the direction of wave expansion. It can also be inclined without restricting the function, which in turn is not specifically shown. In the case of inclination, the geometric period must be selected such that its projection and the direction of wave propagation also obey the relationships given above.

Claims (9)

1. Electronic work with acoustic surface waves of the component with at least one on a component substrate ( 1 ) provided an interference surface wave converting a volume wave mode conversion structure ( 10 ; 10 ') in a surface area of the component substrate ( 1 ) in which the occurrence of surface waves undesirable is characterized in that the mode conversion structure ( 10 ; 10 ′) for a substrate material with strong coupling of surface waves to bulk waves as a periodic electrode finger structure ( 11 ; 11 ′) with a geometric period adapted to the coupling in the form of a multiple of the wavelength λ _{SAW of} the surface wave and adapted metallization ratio, where λ _{SAW means} the wavelength of the surface wave. 2. Component according to claim 1, characterized in that the geometric period according to the relationships as well as their reshaping is chosen in which
K _SAW the wave vector of the surface acoustic wave,
n an integer,
p the geometric period,
K _BAW the wave vector of the bulk acoustic wave,
f the frequency at which the structure efficiently converts the surface acoustic wave into the bulk acoustic wave,
V _SAW the speed of the acoustic surface wave and
V _BAW mean the speed of the acoustic bulk wave. 3. Component according to claim 1 and 2, characterized in that a periodic elec trode finger structure with a geometric period of about 1.8 to 2.0 × λ _{SAW is} provided as substrate material for LiNbO₃-YZ. 4. The component according to claim 1 and 2, characterized in that for LiTaO₃ -36 ° red a periodic electrode denfinger structure with a geometric period of about 3.8 to 4.5 × λ _{SAW is} provided as the substrate material. 5. Component according to one of claims 1 to 4, characterized in that a me tallization ratio of 0.5 is provided. 6. Component according to one of claims 1 to 5, characterized in that open electrode fingers ( 11 ) are provided as a periodic electrode finger structure ( 10 ). 7. Component according to one of claims 1 to 5, characterized in that as a periodic electrode finger structure ( 10 ') short-circuit electrode fingers ( 11 ') are provided. 8. Component according to one of claims 1 to 5, characterized in that as pe riodic electrode finger structure ( 10 ) both open and short-circuited electrode fingers ( 11 or 11 ') are vorgese hen. 9. Component according to one of claims 1 to 8, characterized in that the pe riodische electrode finger structure ( 10 ) is inclined.