WO2012084460A1

WO2012084460A1 - Electroacoustic resonator

Info

Publication number: WO2012084460A1
Application number: PCT/EP2011/071651
Authority: WO
Inventors: Wolfgang Sauer
Original assignee: Epcos Ag
Priority date: 2010-12-22
Filing date: 2011-12-02
Publication date: 2012-06-28
Also published as: JP5852132B2; DE102010055628A1; DE102010055628B4; JP2014502809A

Abstract

The invention relates to an electroacoustic resonator (10) having two electrodes (11, 12) which each have a collector electrode section (21, 22) and a multiplicity of electrode fingers (1, 2), wherein the electrode fingers (1, 2) are lined up along a first direction, are connected in a conductive manner to the collector electrode sections (21, 22) of the respective electrode (11, 12) and run along a second direction aligned transversely to the first direction, wherein the resonator (10) is an overlap-weighted resonator in which the extent of the overlap region (20) measured along the second direction, in which overlap region the electrode fingers (1, 2) of the two electrodes (11, 12) interlock, varies along the first direction, and wherein the resonator (10) has jumpers (3) between the electrode fingers (1, 2) of each electrode (11, 12), which jumpers each connect a plurality of electrode fingers of the same electrode to each other in a conductive manner at a distance from the collector electrode section (21, 22).

Description

description

Electroacoustic Resonator The invention relates to an electroacoustic resonator. Electroacoustic resonators have a piezoelectric layer and two electrodes, which are arranged, for example, on the surface of the piezoelectric layer. Clearing the two Elect ^¬ each having a plurality of electrode fingers which are connected in common to a collector electrode portion of the electric ^¬ de through which the time-dependent electrical potential is brought to the electrode fingers. The electrode fingers of both electrodes also mesh with each other in a comb shape. At both sides outside the comb-like electrodes each into each other dergreifenden reflectors adjoin, which are similarly formed from many (but both sides ^¬ closed) electrode fingers with a common connector. However, the electrode fingers of the electrodes are electrically connected only at one end; its second end is surrounded by electrode fingers of the other electrode.

Electroacoustic resonators of this construction are also referred to as interdigital transducers (IDTs). As a result of the high-frequency AC voltage (approximately in the range between 100 MHz and a few GHz) high-frequency standing waves are formed in the piezoelectric layer, usually in the form of surface waves as in the case of SAW devices (surface acoustic wave) or in the form of bulk waves as in Case of BAW or GBAW components (bulk acoustic wave or guided bulk acoustic wave).

The present application relates to weighted, in particular overlap-weighted resonators, ie those in which Do not lead the electrode fingers over their entire length (and not over a uniform portion of their length) in the space between adjacent electrode fingers of the respective other electrode, but intermesh with different depths. If one looks at a partial section of the entire resonator surface between the collecting electrode sections of both electrodes, then each electrode locally has shorter and longer electrode fingers in an alternating sequence. The shorter electrode fingers extend only to the edge or to the beginning of the overlap region. Between the short electrode fingers, the long electrode fingers protrude in the overlap area and traverse it. The overlapping area of a weighted resonator, measured along the path of the electrode fingers, is smallest at the edges of the resonator, ie, near the two reflectors, and includes only a small portion near the middle between the collecting electrode portions of both electrodes. In the middle between the two reflectors, however, the overlap area is the largest and covers virtually the entire distance between the two collector electrode sections. Thus, the overlap area widens towards the center of the resonator.

A disadvantage of such an overlap-weighted resonator is that, towards its edges, an increasingly larger one

Trajectory distance along the electrode fingers is to be covered until reaching the overlap region. Via this trace the charge must be transported to the connected electrodes before it even reaches the overlap area, which contributes to the generation of standing waves in the solid state. This applies not only to the locally shorter electrode fingers, but also to the longer electrode fingers, which allow the overlap go through rich. Electrode fingers designed for an excitation frequency of, for example, 2 GHz have a width of, for example, 500 nm and a height of, for example, 100 to 200 nm. As a result of the electrical resistance of the electrode fingers, losses occur in the resonator which lead to other losses (such as elastic losses in the solid state ) and reduce the quality of the resonator. These losses are broadband or cover a wide frequency range. The losses through such supply currents are also greater, the smaller the cross-sectional dimensions of the electrode fingers are dimensioned. It would therefore be desirable to increase the quality of an overlap weighted resonator.

For this purpose, this application proposes an electroacoustic resonator with two electrodes, each of which has a collecting electrode section and a multiplicity of electrode fingers,

wherein the electrode fingers are aligned along a first direction, are connected to the collecting electrode portions of the respective electrode, and run along a second direction that is transverse to the first direction,

wherein the resonator is an overlap-weighted resonator in which the extent of the overlap area measured along the second direction, in which the electrode fingers of both electrodes intermesh, varies along the first direction,

- Wherein the resonator between the electrode fingers of the respective electrode has line bridges, each of which meh ^¬ rere electrode fingers of the same electrode spaced from the collecting electrode portion conductively connect with each other.

According to this resonator, additional conductive connecting ^pieces are thus present between the electrode fingers of each electrode provided, which short-circuit the electrode fingers with each other. These wire bridges are spaced from the collecting electrode portions of the respective electrode, preferably at the edge of the overlapping area. The positions of the jumpers then follow the contours of the overlap region of the resonator and are accordingly spre ^¬ accordingly at the edges of the resonator (near the reflectors et ^¬ wa arranged in the middle between two electrodes, whereas portions in the Resonatormitte relatively close to the Sammelelektroden- both electrodes The conductor ^bridges proposed here, which represent additional conductor track sections in the direction across or at least obliquely to the electrode fingers, allow the direct flow of equalizing currents along the respective edge of the overlap area, but only between electrode fingers thereof

Electrode. These equalizing currents reduce the losses of supply currents which otherwise increase greatly in the vicinity of the reflectors and thus improve the quality of the resonator. The wire bridges proposed herein may preferably be in the same plane as the electrodes including theirs

Electrode fingers themselves be arranged and thus already be considered as part of the pattern in the structuring of the metal layer of both electrodes. Nevertheless, despite the wire bridges proposed here, the finger-shaped structure is retained inside the resonator surface, since the cable bridges short-circuit the electrode fingers only locally, ie in a very small longitudinal section of the electrode fingers. Some exemplary embodiments will be described below with reference to the figures. Show it: Figure 1 is a schematic plan view of a herkömmli ^¬ chen piezoelectric resonator, Figures 2A to 2F enlarged detail views of various ner From guide forms of resonators having line bridges, Figures 3A to 3D are overall views of resonators, according to some embodiments of the Figures 2A to 2F, 4A a schematic cross-sectional view of a piezo ^¬ electric resonator,

FIG. 4B shows a schematic cross-sectional view of a ^{piezoelectric} resonator with additional layers,

FIG. 5 the dependence of the admittance Y of the resonator on the frequency f of the waves generated in the resonator,

6 shows the course of the reflection factor S and

FIG. 7 shows a tabular list of measured parameters for characterizing the resonator quality for resonators without or with line bridges. 1 shows a schematic plan view of the conductor ^¬ web plane 25 of a conventional piezoelectric resonator 10, wherein because of the symmetrical construction, only the one (left) half is illustrated. Between two reflectors 23 and 24 (see Figures 4A and 4B), an array of two electrodes 11, 12 each having a collecting electrode portion 21 and 22 and a plurality of electrode fingers 1, 2 connected thereto extends. The resonator is overlap weighted, ie, the overlap area 20 in which the Electrode fingers 1, 2 of both electrodes intermesh comb-shaped, ie overlap, extends only between two edges R, which continue to move towards the reflectors 23, 24 back further. In the middle of the resonator (right in the illustrated detail of Figure 1) is the

Width of the overlap area 20 largest. Only within the overlap region, the electrode fingers 1, 2 of the first electrode 11 and the second electrode 12 of ent ^¬ against opposite sides intermesh forth. On the other hand, on each side outside the overlapping area, electrode fingers are only one of the two electrodes 11; 12 arranged.

Figures 2A to 2F show enlarged detail views of some embodiments of resonators, in which transverse to the electrode fingers extending cable bridges are provided. Shown are enlarged sections approximately in the region of the lower edge R, above which the Überlap ^¬ pungsbereich 20 begins. Furthermore, a partial section of the collecting electrode section 21 of the lower, first electrode 11 is shown by way of example in FIGS. 2A and 2C. De ^¬ ren lead electrode fingers la to ld (shown interrupted) to the edge R of the overlap region 20, wherein each ^¬ the second electrode finger la, lc of the first electrode 11 leads into the overlap region 20. The other, shorter electrode finger lb, ld of the first electrode 11 extending outside of the overlap region 20 will come in the overlapping ^¬ pungsbereich 20, the electrode fingers 2b, 2d of the second

Electrode 12 counter. In FIGS. 2A to 2F, the electrode fingers of the second electrode 12 are shown hatched. According to Figure 2A, line 20 bridges 3 (or short bridging ^¬ cables) are provided along the edge of the overlap area R ^¬ pungsbereichs connecting adjacent electrode fingers of the first electrode conducting with each other and preferential wise transversely, ie perpendicular to them. Such Lei ^¬ tung bridges are provided along both edges of the overlap region R 20th In particular, (not shown) corresponding lead bridges connecting the electrode fingers of the second electrode 12 are provided along the other, upper edge R of the overlapping area. Ge ^¬ Mäss the disclosed embodiment of Figure 2A connects each cable bridge 3 two mutually next adjacent electrode fingers (the same electrode).

FIG. 2B shows an embodiment, which is also shown in FIG. 3A as an overall view. Here connects each Lei ^¬ tung bridge 3 two übernächstbenachbarte (longer) ^¬ line linking the respective electrodes; In FIG. 2B, the electrode fingers 1a and 1c or 1c and le are concrete. The Leitungsbrü ^¬ bridges 3 thus separate the intervening, shorter

Electrode fingers lb and ld from the oncoming longer electrode fingers 2b, 2d of the second electrode 12, which traverse the overlap region 20. The transverse conductor bridges 3 are provided only at the level of the two electrodes 11, 12, but not in the region of the reflectors 23 and 24 (compare FIGS. 3A and 4).

In the embodiment according to FIG. 2C, each line bridge 3 additionally connects the middle, shorter electrode finger 1b or ld with the adjacent longer electrode fingers. Otherwise, the structure and the course of the conductive structures is similar within the interconnect layer 25 demje ^¬ Nigen the figure 2B. FIG. 2D shows an embodiment which is shown as an overall view in FIG. 3B. Here are ^¬ addition to those three jumpers still trace sections 5 which are included neither in the first nor in the second Elect ^¬ rode. As a result, electric charge reduced peaks or stress maxima at the ends of the electrode fingers. In contrast, the lead bridges 3 connect (as in FIG. 2B) two longer ^adjacent electrode fingers of the respective electrode to one another. As shown in Figure 3B, the conductor track sections 5 are disposed the edges R of the overlapping region 20 along with ^¬.

FIG. 2E shows an embodiment which is shown as an overall view in FIG. 3C. Here, in contrast to FIG. 2D, the structures corresponding to the conductor track sections 5 are conductively connected to the line bridges 3; They thus form electrode finger extensions 7 (ie additional small intermediate fingers), which are arranged at the same height as the shorter electrode fingers 1b, 1d, over which the respective conductor bridge 3 passes. Figure 2F shows an execution ^¬ for example, which is shown as an overall view in Figure 3D. Here, the lead bridges 3 connect not only the longer-adjacent, longer electrode fingers 1a and 1c and the respective electrode finger extensions 7 with each other, but additionally (in contrast to FIG. 2E) the shorter electrode finger 1b.

According to all of these embodiments, which are merely exemplary, the line bridges enable a loss-poorer potential equalization along the edges R of the overlapping area 20, since the losses caused as a result of feed resistors are reduced and the quality of the Re ^¬ sonators is improved. In particular, in the vicinity of both Re ^¬ reflectors where the distance of the edges R of the Überlappungsbe- Reich 20 of de collecting electrode portions 21, 22 of both electrodes 11, 12 is greatest, the conduit bridges 3 enable effective acceleration potential supply to the overlap region 20 zoom. The overall views in FIGS. 3A to 3D have already been explained with reference to FIGS. 2A to 2F. In contrast, Figure 3D shows some additional features and elements, which will be discussed below.

Thus, in FIG. 3D, for example, the shape of the two collecting electrode sections 21, 22 of the electrodes at the transition to the electrode fingers 1, 2 of both electrodes 11, 12 is shown in more detail. In particular, it can be seen here that the jeweili ^¬ gen electrode fingers clear sections directly from the relevant Sammelelekt- 21, 22 and emanate collecting electrode strips and are directly connected to it. Collecting electrode and the connected electrode fingers thus form a uninter- rupted, continuous comb-shaped structure (beispielswei ^¬ se in the form of a structured metal layer, Metalllegie ^¬ approximate layer or metal layer sequence in the interconnect layer 25, whose plan view is shown in Figure 3D). Also in FIGS. 1, 2A to 2F and 3A to 3E, the transition (schematically illustrated) between the collecting electrodes and the electrode fingers is formed in the same way as in FIG. 3D. For the sake of completeness, contact connections 8, 9 of both electrodes are indicated in FIG. 3D; they can be introduced at any other place and shaped differently; Figure 3D shows only the presence of the two contact terminals 8, 9. Furthermore, the coordina ^¬ tenkreuz are in Figure 3D in that the electrode fingers 1, 2

(As in the other, previously explained figures) are lined up along a first direction x and along a second direction y, which has transverse to the first direction x, extend.

The cable bridges do not necessarily have to run within the track plane 25, but can also about it or below it. Thus, vias or other contacts can lead from the electrode fingers to a higher or lower level in which the cable bridges are arranged. FIG. 3D furthermore shows that the overlapping region 20 extending between the two edges R is narrower along the second direction y than the resonator surface F, ie, the distance between the collecting electrode sections 21, 22 of both electrodes. The extent or width of the overlapping area 20 measured along the direction y decreases, in particular in the vicinity of the reflectors 23, 24. The conductor bridge bridges or intermediate connections between the electrode fingers proposed here improve the resonator properties. Incidentally, in the embodiments of this application, a plurality of line bridges, in particular a pair of two closely spaced line bridges may also be provided instead of a single illustrated line bridge.

FIG. 4A shows, purely schematically, a cross-sectional view of a piezoelectric resonator 10 whose conductor track plane 25 has been shown in plan view in FIGS. 1, 2A to 2F and 3A to 3D. Below the conductor track plane 25, a piezoelectric layer is arranged, on the Oberflä ^¬ che, the two electrodes 11, 12 and the two reflectors 23, 24 are structured.

FIG. 4B schematically shows a cross-sectional view of a piezoelectric resonator whose conductor track plane 25 is shown in plan view in FIGS. 1, 2A to 2F and 3A to 3D. The resonator is constructed as outlined in Figure 4A, but one or more dielectric layers 26 and / or 27 are here on the conductor track plane zusätz ^¬ Lich still applied. The layers 26 and / or 27 can be used for the purpose of temperature compensation and / or to compensate for manufacturing-related fluctuations in the frequency position by subsequent removal / trimming. Again, the dimensions are not necessarily to scale.

A suitable material for the conductor track plane Bede ^¬ ADORABLE dielectric layer 26 for temperature compensation, for example, Si02 due to its thermal properties. As a material for an overlying trim layer 27 is due to its high bending stiffness, for example, Si3N4 in question.

Figure 5 shows, depending on the frequency of the waves generated in the resonator (preferably surface waves, alternatively bulk waves) the admittance Y, i. the complex

Conductance of the resonator. The real part and imaginary part as well as the amount of admittance are plotted against each other in FIG. At a frequency of about 1970 MHz, the resonance occurs, whereas at about 2110 MHz the antiresonance occurs. Further secondary maxima identifiable above in FIG. 5 are caused by other unwanted effects which, however, lie outside the usable wavelength range between resonance and antiresonance. In FIG. 5, the admittance is plotted in each case for a conventional resonator without line bridges (curve I) and for the resonator proposed here with additional interconnect bridges 3 (curve II). The vertical axes are scaled logarithmically; the real and imaginary parts as well as the admittance Y (f) are each plotted on a logarithmic scale [dB] above the frequency [MHz].

As can be seen above in FIG. 5, the real part of the admittance decreases in the range from approximately 2030 to 2110 MHz. over a conventional resonator (ie, versus curve I), which improves the quality of the resonator. In addition, as un ^¬ th the minimum at 2110 MHz is seen in Figure 5 on the basis of the magnitude of the admittance Y, more pronounced; Here, the drop is steeper on both sides of the antiresonant and also reaches a smaller minimum value than in the curve I. Also the improved quality of the equipped with the line bridges resonator (curve II) can be seen. Admittedly, according to the imaginary part of the admittance Y, the antiresonance frequency is somewhat reduced, albeit only slightly.

FIG. 6 shows in a Smith chart the scattering parameter (S parameter) calculated from the resonator admittance Y (f) and the reference admittance of the measuring station Z0 = 50 ohms.

S (f) = (1-Z0 * Y (f)) / (1 + Z0 * Y (f))

As a function of the frequency. According to the admittance function Y (f) shown in FIG. 5 from 1900 MHz to 2300 MHz, the S-parameters I and II plotted in FIG. 6 pass through the Smith chart in the clockwise direction. The left intersection with the real axis corresponds to the resonance frequency and the right intersection to the real axis of the anti-resonance frequency. In the region of interest between resonance and antiresonance (upper imaginary half-plane in FIG. 6), in the improved resonator (curve II), the approximately semicircular path in FIG. 6 has a larger radius (or a larger average distance from the center of the drawn radius with radius 1) as the curve I. The scattering parameter S (f) is located in the resonator according to the invention over a wide range further outward, ie closer to the unit circle, and is thus lossy. In particular ver ^¬ wrestlers the jumpers between the electrode fingers the existing losses in the frequency range starting at the resonance frequency beyond the antiresonance addition. The additional conductor track sections 5 without contact connection or the electrode finger extensions 7 (FIGS. 2D to 2F) can also counteract the reduction in the frequency at which antiresonance occurs. In the lower imaginary half plane (ie outside the technically used Frequency Ranges ^¬ Kingdom) detectable abnormalities stem from the insertion of the volume radiation (ie formation of bulk waves) the remainder of parasitic effects such as the upper band edge of the acoustic stop band of the finger grid and the increase ^¬.

The present application thus provides an electroacoustic, weighted interdigital transducer (IDT) of improved quality. In FIG. 7, parameters for characterizing the resonator qualities for measurements of in each case four resonators (1 to 4) without line bridges and four resonators (5 to 8) with line bridges are summarized in a table. Plotted are numerical values for the resonance quality Qs in the case of resonance

(quality short) and in the anti-resonant case (quality open) and the average Qt = 0.5 (Qo + Qs). Further, the Fre ^¬ frequencies for resonance (fs) and the anti-resonant frequency (fo) are given in MHz. The comparison of the numerical values of the resonators 5 to 8 (corresponding to curve II correspond in Figures 5 and 6) with those of the resonators 1 to 4 (corresponding to the curve I in Figure 5 and 6) it is evident that by the Leitungsbrü ^¬ can be made between Electrode fingers the quality of the anti-resonance Qo is increased by about 20 percent. In the penultimate column of FIG. 7, the pole-zero distance PZD (pole zero distance) is also shown in FIG

PZD = (fo - fs) / (0.5 x (fo + fs)) applied, which reduces only slightly by the lead bridges from about 7 percent to about 6.8 percent. As a white ^¬ direct measure of the resonator in the last column of Figure 7, the "Figure of Merit" according to (FoM = PZD Qt x) is given as a further quality parameters; This shows an increase and thus an improvement of about 10 percent in the case of the resonators 5 to 8.

Incidentally, the width and / or length of the conductor bridges 3, the conductor track sections 5 and / or the electrode finger extensions 7 can be varied and, in particular, smaller or larger than the width and / or length of the electrode fingers. The line bridges 3 thus reduce the existing losses in a frequency range starting from the series resonance to beyond the anti-resonance. In this way, ver ^¬ improved resonators can be det verwen- for example, in Interconnections to piezoelectric filter or duplexer components.

Reference sign list

1; la, lb, ... electrode fingers of the first electrode

2; 2a, 2b,... Electrode finger of the second electrode 3 conduction bridge

5 trace section

7 electrode finger extension

8, 9 contact connection

10 resonator

11 first electrode

12 second electrode

20 overlap area

21, 22 collecting electrode section

23, 24 reflector

25 trace level

F resonator surface

fo anti-resonant frequency

fs resonance frequency

PZD Resonance Antiresonance Distance

R edge

Qo anti-resonance quality

Qs resonance quality

Qt medium grade

x first direction

y second direction

Claims

claims

An electroacoustic resonator (10) having two electrodes (11, 12) each having a collecting electrode portion (21, 22) and a plurality of electrode fingers (1, 2),

- Wherein the electrode fingers (1, 2) along a first direction (x) are lined, with the Sammelelektrodenab- sections (21, 22) of the respective electrode (11, 12) are conductively connected and along a second direction (y), the transverse to the first direction (x) points, run,

wherein the resonator (10) is an overlap-weighted resonator in which the extent of the overlap region (20) measured along the second direction (y), in which the electrode fingers (1, 2) of both electrodes (11, 12) intermesh, varies along the first direction (x),

- Wherein the resonator (10) between the electrode fingers (1, 2) of the respective electrode (11, 12) has line bridges (3), each of a plurality of electrode fingers of the same electrode spaced from the collecting electrode portion (21, 22) conductively connect together.

2. Resonator according to claim 1,

characterized in that

the lead bridges (3) of each electrode (1; 2) along the collecting electrode section (21; 22) of the respective ones

Electrode (1, 2) facing edge (R) of the Überlappungsbe ^¬ rich (20) are arranged.

3. Resonator according to claim 1 or 2,

characterized in that

the conductor bridges (3) of each electrode (1, 2) are arranged at a distance from the collecting electrode section (21, 22), this distance between the respective line bridge (3) and the collecting electrode portion (21, 22) along the first direction (x) varies.

4. Resonator according to one of claims 1 to 3,

characterized in that

(3) any two next adjacent jumper electric ^¬ denfinger (la, lb, lc, ld, le;. 2a, 2b, 2c) of the same Elect ^¬ rode (1, 2) to each short-circuits.

5. Resonator according to one of claims 1 to 4,

characterized in that

each line bridge (3) has two adjacent neighbors

Electrode fingers (la, lc, le, 2b, 2d) of the same electrode (1, 2) short-circuit each other.

6. Resonator according to one of claims 1 to 5,

characterized in that

the line bridges (3) with ^¬ connect two übernächstbenachbarte electrode fingers (la, lc) of the same electrode (1) to one another and an interposed middle electrode fingers (lb) of the same electrode (1) pass.

7. Resonator according to one of claims 1 to 6,

characterized in that

respectively between the pipe bridge (3) and zoom reaching the level with the middle electrode finger (lb) Electric ^¬ denfinger (2b) of the other electrode (12) is arranged a Leiterbahnab ^¬ cut (5), which neither the first (11) nor to the second electrode (12) is connected.

8. Resonator according to one of claims 1 to 7,

characterized in that in each case an electrode finger extension (7) is connected to the respective line bridge (3) and extends in the direction of the other electrode (2) from the line bridge (3) at the level of the middle electrode finger (1b).

9. Resonator according to claim 7 or 8,

characterized in that

along the conductor track sections (5) and / or the Elektrodenfin ^¬ gerfortsätze (7) have a length which is chosen either uniform lent or within the resonator surface (F) with the position of the conductor track sections (5) and / or the electrode finger extensions (7) the first direction (x) varies.

10. Resonator according to one of claims 1 to 9,

characterized in that

in that one or more line bridges (3) are respectively provided between the electrode fingers (1, 2), the line bridges (3) along the second direction (y) having a dimension and / or a distance from one another which are equal to or greater than is the width of the electrode fingers (1, 2) along the first direction (x).