Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
  • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
  • H03H9/02—Details
  • H03H9/125—Driving means, e.g. electrodes, coils
  • H03H9/145—Driving means, e.g. electrodes, coils for networks using surface acoustic waves
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
  • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
  • H03H9/02—Details
  • H03H9/125—Driving means, e.g. electrodes, coils
  • H03H9/145—Driving means, e.g. electrodes, coils for networks using surface acoustic waves
  • H03H9/14502—Surface acoustic wave [SAW] transducers for a particular purpose
  • H03H9/14505—Unidirectional SAW transducers
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
  • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
  • H03H9/02—Details
  • H03H9/125—Driving means, e.g. electrodes, coils
  • H03H9/145—Driving means, e.g. electrodes, coils for networks using surface acoustic waves
  • H03H9/14517—Means for weighting

Definitions

• the field of the invention is that of surface acoustic wave transducers and filters comprising such transducers, used in many fields such as mobile radiocommunication systems for example for filtering of intermediate frequency.
• Transducers also known as SPUDT have replaced bidirectional transducers in many applications due to the reduction in losses that they allow to obtain.
• This type of transducer described in published patent application 2 702 899, is produced by inserting in a transducer cells called transduction cells and so-called reflection cells, and by positioning the cells together so as to have rephased the waves. emitted with the waves reflected in the useful direction and have phase opposition in the other direction.
• These are transducers in which electrodes are distributed designed so that there is a transduction function and a reflection function. It has also been shown in published patent application 2 702 899 that it can be advantageous to produce resonant cavities inside the
• the distance between transduction center and reflection center can be of the form (2n + 1) ⁇ 8 with n integer so that the phases are correct.
• the quality factor Q relating to the ratio of the capacitance to the conductance of the filter and representative of the bandwidth and loss of insertion of the filter is less effective for unidirectional filters with their specific architectures into which asymmetries are introduced than that conventional, symmetrical bidirectional filters.
• the invention proposes a transducer into which is introduced an etching network superimposed on the conventional electrode networks of the acoustic transducers.
• the subject of the invention is a surface wave transducer comprising a substrate on which are deposited two networks of interdigitated electrodes and connected at different polarities so as to create acoustic transduction cells defined by at least two consecutive electrodes of different polarities, characterized in that it further comprises at least one network of etchings separated by mesa, the superposition of the networks of electrodes and of the etching network making it possible to obtain a preferred direction of propagation of the acoustic waves.
• the electrode arrays are symmetrical with respect to an axis located at the center of two consecutive electrodes, of different polarities, the etching network being asymmetrical with respect to said axis.
• the networks of symmetrical electrodes make it possible to keep a powerful coupling factor while the network of asymmetrical etching makes it possible to create the preferred direction of propagation of the acoustic waves.
• the surface wave transducer can comprise a succession of at least two asymmetrical etching networks so as to locally reverse the preferred direction of propagation of the surface waves.
• the electrode networks define sets of 3 electrodes of different width by characteristic wavelength corresponding to the central operating frequency of the transducer in which sets, a first and a second electrode are separated by a distance 3X 16, and are connected to different polarities, the second and a third electrode being separated by a distance ⁇ / 8, so as to define a preferred direction of propagation of the acoustic waves, the electrodes being positioned on the mesa from the engraving network.
• the advantage of such a configuration lies in the increase in the reflection coefficients of the electrodes.
• FIG. 1a illustrates a first example of a transducer according to the invention with 4 electrodes per ⁇ , having a preferred direction of propagation of surface waves
• - Figure 1b illustrates a second example of a transducer according to the invention with 4 electrodes per ⁇ , having a preferred direction of propagation of surface waves opposite to that of the first example of transducer;
• FIG. 2 illustrates a third example of a transducer according to the invention with 4 electrodes per ⁇ locally comprising a first directivity of the surface waves in one direction and locally a second directivity of the surface waves opposite to the first;
• FIG. 3 illustrates a fourth example of a transducer according to the invention with 4 electrodes per ⁇ in which the phase shift between the transduction center and the reflection center is equal to ⁇ / 16;
• - Figure 4 illustrates a fifth example of a transducer according to the invention with 4 electrodes per ⁇ in which the mesa and the engravings do not have the same width
• - Figure 5a illustrates a transducer with two electrodes by ⁇ according to the prior art
• FIG. 5b illustrates a first example of a transducer according to the invention with 2 electrodes per ⁇ , in which the electrodes are positioned astride on etching flanks, of an etching network of period ⁇ 2;
• FIG. 6a and 6b illustrate a second example of a transducer according to the invention with 2 electrodes per ⁇ , in which the electrodes are positioned on mesa or engravings of an etching network of period ⁇ ;
• FIG. 7a illustrates an example of a conventional SPUDT type transducer with 3 electrodes per ⁇ ;
• FIG. 7b illustrates an example of a SPUDT type transducer with 3 electrodes per ⁇ , in which the network of electrodes is superimposed on the etching network;
• Figure 7c illustrates a variant of the example of an undirectional transducer illustrated in Figure 7b.
• the surface wave transducer according to the invention comprises the superposition of networks of electrodes and at least one etching network.
• the substrates used can in particular be quartz, the electrodes can be obtained by metallization, for example of aluminum.
• the substrates used can also advantageously be of the LiNb ⁇ 3, LiTaOs or even Li2B4 ⁇ 7 type.
• the etching techniques are well mastered on such quartz type substrates and in particular the technique known as ICP (Inductive Coupled Plasma) using a high energy plasma and allowing mass production at low cost of etched devices.
• ICP Inductive Coupled Plasma
• the width of the etchings can be different from the width of the mesa and in particular smaller, according to certain variants, the etching width being equal to the electrode width.
• a preferred direction of propagation of surface waves is created by virtue of the presence of the etching network.
• the electrodes are distributed symmetrically on the substrate with a period ⁇ / 4.
• Such a structure has a good coupling coefficient but remains bidirectional.
• the reflections created by the electrodes cancel each other out and no preferred direction of propagation of the acoustic waves is generated with such a configuration.
• the invention proposes to superimpose an etching network to reveal additional reflections and this asymmetrically with respect to a central axis C defined between two electrodes connected to different polarities and symbolized in the diagram by a + sign and a - sign , in Figure 1a.
• FIG. 1 b illustrates a configuration in which the preferred direction of propagation of the acoustic waves is opposite to that of FIG. 1a.
• the distance between consecutive electrodes can advantageously be equal to the distance between a mesa and a consecutive etching.
• the transducer according to the invention can comprise a succession of implantation according to FIG. 1a and of implantation according to FIG. 1b, as illustrated in FIG. 2.
• the transducer according to the invention can comprise a succession of implantation according to FIG. 1a and of implantation according to FIG. 1b, as illustrated in FIG. 2.
• this type of installation at the level of the axis AA ′ there is a break in the periodicity of the etching network so as to pass continuously from an etching network of first type Rj as shown in Figure 1a, to a second type of etching network Rj + i, as shown in Figure 1b.
• Such a configuration has the advantage of a much easier technology than that conventionally used in this type of transducer for which it is difficult to locally move the position between a transduction center and a reflection center in order to obtain the directional reversal. wish.
• FIG. 3 illustrates a configuration in which a transduction center is distant from an engraving flank by a distance of ⁇ 16, ie a phase shift of 22.5 °. In this configuration, the electrodes are aligned with the flanks of etchings which can represent technological ease.
• the mesa and the engravings have the same widths, however the latter may also advantageously be of different width.
• the engravings can have a width equal to ⁇ / 8 while the mesa have a width equal to 3 ⁇ / 8.
• this lattitude it becomes very simple to change the width or the position of the etchings locally in the transducer, so as to modify the phase and the amplitude of the reflection coefficient.
• the examples described above all relate to transducers of 4 electrodes per ⁇ , in which the preferred directivity of the surface waves is easily obtained.
• the transducers with two electrodes by ⁇ illustrated in FIG. 5a, have very high and stronger coupling coefficients than in the transducers with 4 electrodes by ⁇ but are nevertheless bidirectional, the reflections between electrodes being in phase and this symmetrically.
• the superposition of an etching network in this type of transducer advantageously overcomes this drawback.
• this type of transducer has a technological advantage since it makes it possible to fabricate electrode networks with a pitch twice as large as the pitch required in transducers with 4 electrodes per ⁇ .
• transducers with 2 electrodes per ⁇ include electrodes of width ⁇ / 4 separated by a pitch ⁇ / 2, as illustrated in Figure 5a.
• the waves emitted at an electrode Ej are in phase with the waves reflected by the consecutive electrode Ej + 1 and vice versa for the waves emitted at Ej + 1 and those reflected by the electrode Ej.
• the invention proposes to position the electrodes on the etching flanks as illustrated in FIG. 5b.
• the reflection coefficient is referenced rg.
• the reflection coefficient is referenced -rg * .
• the reflection coefficient is referenced -re *.
• the reflection coefficient r located at the center of the electrode is given by the following formula
• Equations (1) and (2) impose the condition
• the first example of a transducer with 2 electrodes per ⁇ which has just been described still requires a technology in which the electrodes must be deposited at the intersection of mesa and of etching, which is not very easy.
• the invention also proposes another configuration of transducer with 2 electrodes per ⁇ , but of more direct technology.
• This type of transducer works at the second harmonic. It has the advantage of offering a wider geometry than the geometries described above and is particularly advantageous for applications at very high frequencies.
• FIG. 7a illustrates a transducer with 3 electrodes per ⁇ , two electrodes are spaced by ⁇ / 4, to cancel the sharp reflections of said electrodes; indeed, a wave emitted by an electrode is in phase opposition with respect to the wave reflected by the consecutive electrode separated from the distance ⁇ / 4.
• the third electrode separated by a distance of 3 ⁇ / 8 from the consecutive electrode acts as a reflector.
• the invention proposes a variant of transducer, in which the reflection coefficients of the electrodes are improved by increasing the thickness of electrodes without increasing the thickness of metallization as illustrated in FIG. 7b.
• Such technology also makes it possible to use a single mask to produce the etching network and the electrode metallization network.

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• Physics & Mathematics (AREA)
• Acoustics & Sound (AREA)
• Surface Acoustic Wave Elements And Circuit Networks Thereof (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=9526884

Family Applications (1)

Country Status (8)

Families Citing this family (15)

Family Cites Families (5)

• 1998
  • 1998-05-29 FR FR9806834A patent/FR2779289B1/fr not_active Expired - Fee Related
• 1999
  • 1999-05-28 US US09/463,578 patent/US6414414B1/en not_active Expired - Fee Related
  • 1999-05-28 JP JP2000552770A patent/JP2002517933A/ja not_active Withdrawn
  • 1999-05-28 CA CA002297799A patent/CA2297799A1/fr not_active Abandoned
  • 1999-05-28 WO PCT/FR1999/001265 patent/WO1999063662A1/fr not_active Ceased
  • 1999-05-28 CN CNB998007587A patent/CN1155153C/zh not_active Expired - Fee Related
  • 1999-05-28 EP EP99920942A patent/EP1000465A1/de not_active Withdrawn
  • 1999-05-28 KR KR1020007000798A patent/KR20010022225A/ko not_active Abandoned

Non-Patent Citations (1)

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