WO2020020645A1

WO2020020645A1 - Saw device with a slanted resonator

Info

Publication number: WO2020020645A1
Application number: PCT/EP2019/068586
Authority: WO
Inventors: Gholamreza Dadgar Javid; Christian Huck
Original assignee: RF360 Europe GmbH
Priority date: 2018-07-25
Filing date: 2019-07-10
Publication date: 2020-01-30
Also published as: DE102018118003A1

Abstract

A SAW device comprises on a piezoelectric substrate an acoustic track extending between two acoustic reflectors. Two or more IDT sections (IS1, IS2) are present in the acoustic track and form at least one electroacoustic resonator. Each IDT section has an extension along a respective slanting axis (SA1, SA2) that encloses an angle a with the x-axis (LA). At least two adjacent IDT sections possess different slanting angles (α1, α2).

Description

SAW device with a slanted resonator

The present invention refers to a SAW device that uses a slanted resonator design to suppress spurious transversal modes but has a more compact layout occupying less chip area than present designs. The SAW device may be an

electroacoustic filter or a multiplexer.

Electroacoustic filters, e.g. multiplexers, can be used in wireless communication systems. In such filters

electroacoustic resonators are arranged in a filter topology. Electroacoustic resonators employ the piezoelectric effect to convert between RF signals and acoustic waves. Typical electroacoustic resonators are SAW resonators (SAW = surface acoustic wave) including TCSAW (temperature compensated SAW) , TFSAW (thin film SAW) and GBAW resonators (guided bulk acoustic wave) . In SAW and GBAW resonators comb-shaped electrode structures with interdigitating electrode fingers are arranged on a piezoelectric material. Excited acoustic waves propagate along a surface of the piezoelectric material in a preferred direction parallel to the crystallographic x- axis .

Slanted resonators extend along a slanting axis that encloses a slanting angle with the x-axis. The electrode fingers of the comb-shaped electrode structures extend normal to the x- axis but are continuously shifted to each other in

transversal direction when going from a first finger to an adjacent second finger. However, a slanted resonator design produces specific

disadvantages. As far as an acoustic track with slanted resonators and another acoustic track that is not slanted are arranged on the same chip this requires effectively more chip area than a design where all acoustic tracks are either non- slanted or all slanted.

Hence it is an object to provide a SAW device that avoids the above-mentioned problem.

This and other objects are met by a SAW device according to the independent claim. More detailed features and beneficial embodiments are given by dependent claims.

A SAW device is proposed comprising a piezoelectric material. The piezoelectric material may be a bulk material that is useful for forming a substrate of the SAW device or a thin film layer on an arbitrary carrier substrate. Alternatively, the substrate is cut from a bulk piezoelectric crystal. On top of the piezoelectric material an acoustic track extends between two acoustic reflectors. Two or more IDT sections are arranged in the acoustic track. Each IDT section has an interdigital transducer adapted to excite a SAW propagating along an x-axis. The two or more IDT sections form an

interdigital electrode of an electro acoustic resonator. This interdigital electrode is adapted to excite a SAW propagating parallel to an x-axis defined in the surface of the

substrate, all electrode fingers of the interdigital

electrode being arranged normal to the x-axis.

Each IDT section extends longitudinally along a respective slanting axis that goes through the middle of the IDT section and encloses an angle a with the x-axis of -30° < a £ 30°. A first angle al of a first IDT section is different from a second angle a2 of a second IDT section arranged directly adjacent to the first IDT section in the same acoustic track.

The interdigital electrode comprising the IDT sections has two busbars and electrode fingers extending therefrom.

Electrode fingers and busbar together form the comb-shaped electrode structure. The electrode fingers of two comb-shaped electrode structures are interdigitating and form an overlap region. Opposite to the fingertips of overlapping fingers of the interdigital electrode non-overlapping stub fingers may be present that are connected to the respective opposite busbar. The slanting axis of an IDT section is a slanting axis and extends parallel to the longitudinal extension of the IDT section and thus, the slanting axis is parallel to the extension of the overlap region.

In the following a design comprising such a SAW resonator structure with two IDT sections is called a broken slanted resonator design.

The busbars may be arranged parallel to each other and parallel to the slanting axis. In a IDT section that is slanted relative to the x-axis the electrode fingers are still normal to the x-axis but no more normal to the slanting axis of the IDT section.

Alternatively the busbars are not parallel to the slanting axis and - together with the x-axis - include an angle smaller than the angle between the slanting axis and the x- axis . In a preferred embodiment the busbars are parallel to the x- axis. Such an arrangement needs stub fingers of different lengths filling out a respective triangle of the non-overlap regions between the overlap region and a respective busbar.

Preferably, non-overlapping stub fingers are also present in those SAW devices too where the busbars are extending

parallel to the slanting axis.

At least one overlap region of an IDT section of the SAW device is slanted. Due to the slanted orientation the overlap between a first and an adjacent second electrode finger is shifted towards a transversal direction normal to the x-axis by a small amount relative to the overlap between the second and an adjacent third electrode finger. The at least one further IDT section may be slanted too or may have a slanting angle a equal to zero.

Such a SAW device provides additional degrees of freedom when designing the SAW device that may be a filter. The angled arrangement of different IDT sections allows to optimally exploit the surface area without losing too much space and hence without wasting precious surface area while spurious transversal modes are still suppressed.

Preferably a first slanting angle ai of a first IDT section can be chosen to be between 5° and 20°, while a second slanting angle 0,2 of a second IDT section can be chosen to be between -5° and -20°. In this context and by definition an angle of a positive value has to be understood to denote an angle that is measured counterclockwise while a negative angle denotes an angle measured clockwise. In a preferred embodiment a first slanting angle ai of a first IDT section has the same absolute value like the slanting angle 0,2 of an adjacent second IDT section but has an inverse sign.

By this angle combination the first IDT section is slanted towards the x-axis while the second IDT section is slanted to extend away from the x-axis or vice versa. In both cases the two adjacent IDT sections form a V-shaped arrangement that encloses an angle between 140°and 170°.

According to a first general embodiment the first and second IDT section belong to the same interdigital electrode and thus have at least one common busbar. Hence, a bent or broken resonator is achieved. Such a resonator can be used as a one- port resonator in a filter topology.

Already known slanted resonators have only one linear

extension and in known slanted designs all slanted resonators of a respective SAW device have the same slanting angle.

When two adjacent IDT sections share one common busbar and on the opposite side of the interdigital transducer two busbar sections are electrically separated from each other, an electrical and acoustical series connection of the two IDT sections is achieved.

If two adjacent IDT sections together form a resonator they may also share all their busbars. Then, both IDT sections are circuited in parallel. Three or more IDT sections can form a zigzag topology that allows saving even more surface area on the substrate that can be used for other structures or for reducing the size of the SAW device.

In a zigzag topology the angles of subsequent IDT sections are alternatingly higher and lower than the respective angle of the foregoing IDT section. This means a series of at least three subsequent slanting angles ai to 0₃ with the condition (Xi > a.2 < a.3 or

Ol < 02 > 03.

In a specific embodiment the following may be true:

Ol = 03 = ^— 02.

In a zigzag topology or in an arrangement of just two

adjacent IDT sections the absolute values of a first angle Oi and a second angle 0₂ may be equal but not equal to zero that | Oi | = 10₂ I and 0₂ = - ai . For more than two IDT sections this can be true for each pair of neighbored IDT sections. Then a symmetrical arrangement is achieved.

In a zigzag topology two IDT sections may be electrically circuited in series and form a single elongated resonator.

In a beneficial embodiment two subsequent IDT sections form a V-shaped arrangement with two legs. The area between the two legs can then be used to place there a passive element that can be formed by a metallized structure on the surface of the substrate. The passive element may be electrically connected to at least one of the IDT sections. Such passive elements can be used as matching elements of the SAW device e.g. of a SAW filter device. These elements may be connected to one or more IDT sections in series or in parallel. The passive element may be a capacitance or an inductance. By arranging such a passive element between the two legs of a V-shaped arrangement of two subsequent IDT sections an efficient space management can easily be achieved.

Such a passive element may be a capacitance that can be coupled to an inner busbar of the first leg of the V-shaped arrangement of IDT sections. However it may also advantageous to place the passive element between the two legs without contacting the element to any of the busbars of the V-shaped arrangement .

The passive element, e. g. an inductance or a capacitance, can be used as a matching element.

It is possible that two or more passive elements that may be of the same or of different kind are arranged on the surface of the substrate between the legs of a V-shaped arrangement of two adjacent IDT sections.

But any other conducting element of the SAW device may also be alternatively coupled to the passive element and at least one IDT section.

- Finally, a SAW device may comprise different forms of resonators and IDT sections arranged in a multitude of acoustic tracks. One track comprises two or more slanted IDT sections with different slanting angles a. Further, each of the other tracks independently comprises an arrangement of

- just one slanted IDT section, or

- two or more resonators with one or more IDT sections each comprising one slanted IDT section, or - one resonator with one or more IDT sections having a slanting angle a of zero degrees.

In such a SAW device at least two of the tracks have

different arrangements. All possible embodiments as explained above can be realized in a single SAW device on one and the same substrate. Hence such a device adds a variety of

additional degrees of freedom for the designer of the SAW device e.g. the filter device.

The SAW device may have a substrate that is cut from a crystal ingot. Moreover the SAW device may be embodied as TCSAW device (= temperature compensated SAW) that comprises an additional layer of a material with a positive temperature coefficient of frequency. Alternatively the invention can be embodied in a TFSAW (= thin film SAW device) formed from a wafer as mentioned above with subsequent thinning of wafer thickness. The piezoelectric wafer may be wafer-bonded to an arbitrary carrier substrate before thinning. A TFSAW may also be formed by epitaxial deposition of a piezoelectric material on a carrier substrate thereby including one or more

additional layer to provide a desired functionality to the TFSAW wafer.

The SAW device may have electrode fingers and opposing stub fingers with a transversal gap between the electrode finger and the facing tip of a respective stub finger that is minimized to be for example between lOOnm and 500nm. It is advantageous to minimize the transversal gap thereby

respecting photolithography restrictions as well as power durability and ESD obligations during fabrication. According to another embodiment the SAW device may have a IDT section whose busbars are oriented parallel to the slanting axis and the length of the stub fingers is chosen from 0.5l to 5 l wherein l is the wavelength of the acoustic wave propagating in the acoustic track.

According to yet another embodiment the SAW device may have two adjacent IDT sections belonging to the same resonator but having different lengths and different slanting angles.

In a more specified embodiment the device is arranged on a substrate comprising a thin film or a bulk material of lithium tantalite LT with a crystal orientation y-cut rot 42XY or y-cut rot 50XY.

The device has a slanted IDT section with a preferred

slanting angle a of |a| = 10° ± 2° and stub fingers of a preferred length from 2l ± 0.5 l.

In the following section the invention will be explained in more detail with reference to specific embodiments and the related figures. The figures are only schematic and may depict some details in enlarged form or may fail to show possible details that are described or shown at another location or figure.

Figure 1A shows a schematic depiction of a first embodiment of the electroacoustic resonator with two IDT sections enclosing different angles with the x-axis,

Figure IB shows more details of the IDT section that is depicted only schematically in Figure 1A; Figure 2 shows another embodiment of two IDT sections

enclosing different angles with the x-axis;

Figure 3 shows four subsequent IDT sections that form a zigzag arrangement;

Figure 4 shows simulated admittance curves of a structure according to Figure 1A compared with a structure as shown in Figure IB;

Figure 5 shows schematically different ways of circuiting two subsequent IDT sections that are slanted relative to each other;

Figures 6A and 6B show two subsequent IDT sections that are connected via different passive elements;

Figure 7 shows a slanted IDT section with busbars oriented in parallel to the x-axis and resulting in stub fingers of different length;

Figure 8 shows an arrangement of two IDT sections slanted to the x-axis with different angles but with two common busbars that are oriented in parallel to the x-axis with stub fingers of varying length;

Figure 9 shows two slanted IDT sections of a one-port

resonator arranged between two reflectors; and

Figure 10 shows a SAW device comprising a number of different acoustic tracks with different arrangements of resonators and IDT sections. Figure 1A shows a simple embodiment of the invention

comprising two adjacent IDT sections RSI and RS2 in a

simplified depiction. A first IDT section IS1 extends along a first slanting axis LAI that includes an angle cxl to the x- axis where the x-axis is the propagation direction of the acoustic wave. The directly adjacent second IDT section IS2 includes a slanting angle cx2 to the x-axis where cxl is not equal to cx2. The second IDT section IS2 extends parallel to the second slanting axis LA2. For clarity reason each

slanting axis LAi is depicted adjacent to the respective resonator section ISi. The slanting angles oq may have absolute values between 0 and 30 degrees. An optimized slanting angle is chosen in dependence on the piezoelectric material and the desired properties of the SAW device that the depicted arrangement is a part of. For simplicity reasons Figure 1A does not show the acoustic reflectors or the further elements that are necessary for forming a resonator.

Figure IB shows an exemplary IDT section IS depicting most important parts thereof. The IDT section IS comprises two busbars BB, BB' from which electrode fingers EF are extending to interdigitate alternatingly . The electrode fingers EF are oriented normal to the x-axis and form an overlap region that extends parallel to a slanting axis LA. A slanting angle a is measured between the x-axis and the slanting axis LA. The busbars BB may be oriented in parallel to the slanting axis or alternatively deviate from such a parallel orientation.

Not shown are stub fingers that are present in a preferred IDT section design in the non-overlap region that is arranged between the overlap region and a respective busbar. If the orientation of the busbar BB deviates from the orientation of a slanting axis LA a non-overlap region yields having a triangular shape (shown in Figure 7 or 8 for example) . Preferably the overlap between two adjacent electrode fingers EF is the same along the whole length of the IDT section IS and more preferably is the same in all IDT sections RS .

Figure 2 shows another embodiment of how two adjacent IDT sections RSI, RS2 can be arranged relative to one another. In this example the first IDT section IS1 includes a slanting angle cxl to the x-axis while the second IDT section IS2 extends parallel to the x-axis such that the slanting angle of the second IDT section IS2 is 0. Further, the length of the depicted two IDT sections is different but may also be the same.

Figure 3 shows a zigzag arrangement of subsequent IDT

sections RS . Depicted are four IDT sections RSI to RS4, but a zigzag arrangement can generally be achieved with three or more IDT sections. Each IDT section IS comprises a slanting angle that is enclosed between the slanting axis LA of the respective IDT section and the x-axis. Each IDT section may have a different slanting angle. Each IDT section may have a length that may be equal for all IDT sections. Moreover, the length may be different for two adjacent IDT sections or may be different for all of the IDT sections.

Each of the IDT sections includes a slanting angle to the x-axis where the slanting angles of two subsequent IDT sections RSn, RS(n+l) are different. As shown in Figure 3 a zigzag arrangement of IDT sections may extend as a whole in parallel to the x-axis but it is also possible that the zigzag topology extends with an angle relative to the x-axis. This means that not only IDT sections are slanted but also the total zigzag arrangement can be slanted against the x- axis . Moreover, despite a symmetric arrangement of IDT sections is preferred the arrangement may also have no symmetry element.

As already explained, different IDT sections RS may be electrically connected or not. However, in all cases

different IDT sections within one track belong to the same resonator .

Figure 5 shows exemplarily in respective block diagrams four different possibilities for electrically connecting two adjacent IDT sections RS that are arranged within an acoustic track between two reflectors RF. The figure is drawn

schematically only and does not show any geometrical detail such as a slanting angle of at least one of the IDT sections RSI, RS2.

Figure 5A shows two adjacent IDT sections RSI, RS2 within one acoustic track. One busbar is common to both IDT sections.

The other busbar is divided so that each IDT section has its own busbar section separated from the busbar section of the other IDT section. The resulting structure is an electrical series connection of first and second IDT section IS1, RS2 between a first and a second terminal Tl, T2.

Figure 5B shows two IDT sections having the same arrangement of busbars like shown in Figure 5A but with a different circuiting. Each busbar or busbar section of the IDT sections has its own electrical terminal T which allows to circuit both IDT sections RSI RS2 in parallel or in series.

Figure 5C shows an arrangement wherein each of the two depicted IDT sections RSI, RS2 has its own busbars on both sides of the interdigital transducer such that no galvanic contact exists between the two IDT sections. Notwithstanding that, the four terminals of the two IDT sections allow an arbitrary mutual circuiting of the two IDT sections.

Figure 5D shows the simplest arrangement of two adjacent IDT sections that share both busbars. A first and a second busbar are common to both IDT sections RSI, RS2. Each busbar is coupled to a respective terminal T on a respective side of the arrangement .

The arrangements shown in Figures 5A to 5D can represent one- port resonators while Figure 5C can also be circuited as a two-port resonator.

Each two subsequent IDT sections RSI, RS2 with different slanting angles form a V-shaped arrangement. There is some space between the inner legs of the V-shaped arrangement for arranging therein an element like a passive element PE.

Figure 6A shows a very general depiction of such an

arrangement that uses the free space between the two legs of the V-shaped arrangement. A passive element PE may be

interconnected to one or both IDT sections or to any other element of the SAW device or of the circuit the SAW device is arranged in. The passive element may be capacitance or an inductance for example.

Figure 6B shows an arrangement with two IDT sections

circuited in series between a first and a second terminal Tl, T2. Here, the passive element interconnects a first busbar connected to terminal Tl and the opposite busbar. But as explained above any other interconnection to any element of the SAW device is possible too. The passive element PE may be used as a matching element of the SAW device.

An arrangement where the free space between the two legs of the V-shaped arrangement is used by placing any element of the SAW device or a circuit there results in a better

exploitation of the available space. Then it is possible to reduce the area of the SAW device because the space for the additional element like the passive element PE is saved at another location on the surface of the substrate.

Figure 7 shows an IDT section IS comprising one interdigital transducer. The transducer comprises a first and a second busbar BB1, BB2. Electrode fingers EF are extending from each busbar to interdigitate in an overlap region OR. Between the tip of an electrode finger EF and the busbar that is not connected to this electrode finger EF, a stub finger SF is arranged. Thereby the non-overlap region between the overlap region and a respective busbar BB is filled with stub fingers and the non-overlapping section of the electrode fingers EF.

A further feature of the depicted interdigital transducer is the orientation of the overlap region OR that is parallel to the slanting axis of this IDT section. Contrary to the formerly described arrangements, the busbars are not parallel to the slanting axis. Hence, the overlap region OR is

orientated along the slanting axis LA and LA is slanted against the linearly extending busbars. This means that each non-overlap region of the IDT section is a triangle. Then the stub fingers SF have necessarily various lengths to

completely fill the non-overlap region NOR. However, one of the middle axes LA may be oriented in parallel to the x-axis such that besides the unavoidable transversal gap and optionally short stub fingers SF no non-overlap region NOR is formed adjacent to this IDT section IS.

Figure 8 shows the arrangement of two such IDT sections RSI, RS2, each having a different slanting angle a relative to the x-axis. Both adjacent IDT sections share their busbars BB1, BB2 so that each common busbar has a linear and straight extension that may be arranged parallel to the x-axis but not parallel to the slanting axis of any of the two IDT sections. Here too, the schematically depicted non-overlap region NOR between the overlap region OR and the opposing busbar BB is filled with stub fingers SF.

According to a variant the non-overlap region NOR may be covered with a continuous metal layer that can be formed by structuring one or more busbars accordingly. Then, a

respective busbar section has triangular shape.

Resonators formed by at least one IDT section are arranged within an acoustic track between two reflectors RF. As only one slanted resonator is present in the acoustic track the SAW device forms a one-port SAW resonator.

Figure 4 shows the simulation results of a one-port resonator with two slanted IDT sections with different slanting angles forming a V-shaped arrangement as depicted in Figure 8, for example. As a reference a SAW resonator comprising one slanted IDT section only is used, as shown in Figure 7 for example. Both resonators are comparable in their static capacitance due to the same active aperture given by the area of the overlap region OR. Figure 4 shows the real part, the imaginary part and the absolute value of the admittance. From the figure it can be taken that the admittance curves of a slanted geometry as known from the art, and a broken slanted geometry according to the invention (with two IDT sections slanted differently to the x-axis) have a comparable course. Within the stop band of the resonator nearly no difference can be recognized. It seems that a broken slanted design according to the invention makes the curve more even with smaller ripple in the upper stop band half. Beyond the two stop bands the admittance of the broken slanted design shows more ripple which seems to be due to the occurrence of longitudinal Fabry-Perot resonance that occurs more strongly at the interface of two adjacent IDT sections including an angle greater than 0 there between.

Figure 9 is another depiction of a one-port resonator with two slanted IDT sections to form a V-shaped arrangement. Here too, each busbar BB1, BB2 is common to both IDT sections RSI, RS2, is extending linearly and may be arranged in parallel to the x-axis or not. This means that triangular non-overlapping regions are formed between the overlap regions OR1, OR2 and the neighboured busbar BB . In Figure 9, the overlap region OR is depicted to be the area between the two dotted lines. At the same time the dotted line is the location of the finger gap between the tip of an overlapping electrode finger and the opposing stub finger. It is preferred that the

transversal gap is as small as possible. With the present available technology, a small gap of 100 nm to 500 nm can be achieved .

On both sides of the shown resonator a respective acoustic reflector RF1, RF2 is placed to enclose the acoustic energy there between. The dotted lines extend into part of the respective reflector which means that the reflector fingers of each acoustic reflector RF are partly interdigitating despite being electrically shorted. Alternatively, the gaps need not extend into the reflector such that each reflector finger is connected to both reflector busbars.

From Figure 9 it can further be seen that the aperture that is defined by the transversal length of a finger overlap is shifted along the x-axis from finger to finger in y- direction. But the shift is small enough that the apertures that have the greatest shift relative to the outermost aperture at the beginning or the end of the resonator still have a mutual overlap when looking parallel to the x-axis. This means that the coupling between different ends of a IDT section is still high enough to allow suitable operation of the resonator.

Figure 10 exemplarily shows a SAW device comprising a number of resonators that may be divided into slanted IDT sections as well as resonators that are not divided into IDT sections and resonators that are not slanted relative to the x-axis.

In the left part two V-shaped arrangements of two IDT

sections each arranged adjacent to each other so that the IDT sections of the two arrangements are cascaded in parallel to each other. In the right part of the depicted circuit a zigzag arrangement of IDT sections is shown. The top

resonator shown in the circuit and the bottom resonator comprise one IDT section only that forms no slanting angle to the x-axis. By such an arrangement of differently oriented resonators and IDT sections an optimal exploitation of the available space can be achieved without strong performance degradation . The invention has been explained with reference to a limited number of embodiments and figures but is not restricted to the shown embodiments. The broadest scope of the invention is defined by the combination of features given in claim 1.

List of used reference symbols

IDT interdigital transducer with

EF electrode fingers and

SF stub fingers

BB busbar

IS IDT section ,

RF acoustic reflector

X x-axis (propagation direction of SAW)

LA slanting axis

a angle between x-axis and slanting axis

PE passive element embodied as

OR overlap region

NOR non-overlap region

T terminal of IDT section

Claims

1. A SAW device comprising

- a substrate having at least a layer of a piezoelectric material

- an acoustic track on the piezoelectric material

extending between two acoustic reflectors

- two or more IDT sections (IS (IS) of an interdigital

electrode arranged in the acoustic track

wherein

- the interdigital electrode is adapted to excite a SAW propagating parallel to an x-axis defined in the surface of the substrate, all electrode fingers of the

interdigital electrode being arranged normal to the x- axis

- each IDT section (ISn) has a slanting axis that encloses a slanting angle a_n with the x-axis of -30° £ a_n £ 30°

- a first angle ai of a first IDT section (IS1) is set

different from a second angle 0,2 of a second IDT section (IS2) arranged directly adjacent to the first IDT section ( IS1 ) .

2. The SAW device of the foregoing claim,

wherein the first angle ai is set to 5° < ai < 15°

wherein the second angle 0,2 is set to -5° > op > -15°.

3. The SAW device of one the foregoing claims

wherein the first and the second IDT section (IS1, IS2) belong to the same interdigital electrode and thus have at least one common busbar.

4. The SAW device of one the foregoing claims,

comprising three or more IDT sections (IS1,IS2, ISn) that are arranged in a zigzag topology such that the slanting angles of a subsequent IDT section (IS_n) are alternatingly higher and lower than the slanting angle of the respective foregoing IDT section (IS_n-i).

5. The SAW device of the foregoing claim,

wherein the absolute values of a first slanting angle ai and a second slanting angle 0,2 are equal 0,2 = - ai .

6. The SAW device of one the foregoing claims,

wherein the IDT sections form just one interdigital electrode arranged in the acoustic track between the two reflectors such hat the device constitutes a one-port SAW resonator.

7. The SAW device of one the foregoing claims,

- wherein two subsequent IDT sections (IS1,IS2) form a V- shaped arrangement with two legs

- wherein the area between the two legs is occupied by a passive element (PE) formed by a metallization on the surface of the substrate

- wherein the passive element is electrically connected to at least one of the resonator IDT sections (IS) .

8. The SAW device of the foregoing claim,

wherein the passive element (PE) is a capacitance or an inductance coupled to an inner busbar of a leg.

9. The SAW device of one the foregoing claims,

wherein the passive element (PE) is a capacitance coupling the inner busbars of two IDT sections belonging to different resonators .

10. The SAW device of one the foregoing claims, wherein each IDT section (IS) has electrode fingers (EF) alternatingly connected to a first and a second busbar (BB) wherein electrode fingers are connected to first and second busbar and mutually overlap in an overlap region (OR) wherein a non-overlapping region is arranged between a respective busbar and the overlap region (OR)

wherein stub fingers are arranged in the non-overlapping region (NOR)

wherein the angle a between the busbars (BB) and the x-axis is different from the angle a between the slanting axis (LA) and the x-axis.

11. The SAW device of one the foregoing claims,

wherein the angle between the busbars and the x-axis is zero and the angle a between the slanting axis (LA) and the x- axis is greater than zero.

12. The SAW device of one the foregoing claims,

comprising a multitude of acoustic tracks

wherein each track independently comprises an arrangement chosen from the group of

- just one slanted IDT section (IS), or

- two or more slanted IDT sections (IS) with different slanting angles a, or

- two or more cascaded resonators with one or more IDT sections (IS) , or

- one resonator with one or more IDT sections (IS) having a slanting angle a of zero degrees

wherein at least two of the tracks have different

arrangements chosen from the above group.

13. The SAW device of one the foregoing claims,

embodied as a thin film SAW device with or without

temperature compensation means, a temperature compensated bulk SAW, a non-compensated bulk SAW device or a GBAW.

14. The SAW device of one the foregoing claims,

wherein a transversal gap between an electrode finger and the facing tip of a respective stub finger is minimized to be between 100 nm and 500 nm.

15. The SAW device of one the foregoing claims,

wherein the busbars (BB) of a IDT section (IS) are oriented parallel to the slanting axis (LS) and the length of the stub fingers is from 1.5 l to 2.5 l wherein l is the wavelength of the acoustic main mode propagating in the acoustic track.

16. The SAW device of one the foregoing claims,

wherein two adjacent IDT sections (IS) of the same

interdigital electrode have different lengths and different slanting angles.

17. The SAW device of one the foregoing claims,

arranged on a substrate comprising a thin film or a bulk material of LT with a crystal orientation y-cut rot 42XY or y-cut rot 50XY

having a slanted IDT section (IS) with a slanting angle a of |a| = 10° ± 2°

stub fingers of a length from 1.5 l to 2.5 l

a transversal gap between the tips of an overlapping finger and a respective stub finger is set to about 350 nm or less.