Electroacoustic resonator

Abstract

An electro-acoustic resonator comprises a substrate (3) having a piezoelectric material and an interdigital electrode structure on a top side (33) of the substrate. The electrode structure comprises a first electrode (1) and a second electrode (2), each electrode having a bus bar (20) and a plurality of fingers (10). The fingers of the two electrodes intersect each other. The region of the top side between the two bus bars is subdivided into two barrier regions (113), two trap regions (112) and a track region (111), the trap regions being located between the two barrier regions and the track region being located between the two trap regions. At least some of the fingers each comprise a barrier portion (13), two trap portions (12) and a track portion (11), where the barrier portion is associated with the barrier region closest to the bus bar assigned to the fingers, the trap portions each are associated with one of the trap regions, and the track portion is associated with the track region. The fingers are configured such that the velocity of the main mode of surface acoustic waves in the trap region is less than the velocity in the orbital region. Each electrode includes a plurality of short fingers (30) that are shorter than the fingers. Each short finger is only associated with the barrier region closest to the bus bar assigned to that short finger. The electrodes are configured such that a speed of the primary mode in the barrier region is greater than a speed in the orbital region.

Description

[0001] This application is a divisional application of the Chinese patent application with application date of July 14, 2020, application number 202080054896.5, and invention name “Electroacoustic Resonator”.

[0002] The present invention relates to an electroacoustic resonator.

[0003] One task to be solved is to specify an electroacoustic resonator with fewer spurious modes.

[0004] In accordance with at least one embodiment, an electroacoustic resonator includes a substrate having a piezoelectric material. The substrate may be formed of the piezoelectric material or may include a layer of the piezoelectric material, such as a thin film. For example, the piezoelectric material is lithium tantalate (e.g., LiTaO3), lithium niobate (e.g., LiNbO3), AlN, or quartz.

[0005] According to at least one embodiment, the electroacoustic resonator includes an interdigitated electrode structure on the top side of the substrate. The interdigitated electrode structure is preferably a metal structure. For example, the electrode structure is made of a metal such as Cu or Al or Pt or Ag or Au or Ti or Cr, or a compound or metal alloy thereof. The top side of the substrate is preferably formed of a piezoelectric material. The interdigitated electrode structure may be covered with an additional layer of a dielectric material (e.g., SiO2 or Si3N4) to provide temperature compensation, passivation, or other additional functions.

[0006] According to at least one embodiment, an electrode structure includes a first electrode and a second electrode, each electrode having a bus bar and a plurality of fingers. The fingers of each electrode are electrically connected via the electrode's bus bar. The electrodes can each be composed of a single material or can have a layered structure. The fingers are preferably integrally formed with their assigned bus bar. The electrodes are preferably in direct contact with the piezoelectric material or separated from the piezoelectric material by a thin layer of insulating material. For example, each electrode includes at least 10, at least 50, or at least 100 fingers.

[0007] The busbars of the two electrodes are parallel or substantially parallel to each other. The main extension direction of the busbars is preferably parallel to the longitudinal direction. The direction parallel to the top side and perpendicular to the longitudinal direction is defined as the transverse direction. The fingers of the electrode extend transversely to the busbars, for example, the main extension direction of each finger is parallel to the transverse direction. Preferably, all fingers are parallel or substantially parallel to each other.

[0008] According to at least one embodiment, the fingers of two electrodes interdigitate with each other. However, the fingers of different electrodes are electrically isolated from each other. In other words, the electrodes are interdigitated electrodes. Together, the two electrodes define an interdigital transducer (IDT) of an electroacoustic resonator. For example, the electroacoustic resonator is a SAW resonator.

[0009] According to at least one embodiment, the top side region between the two busbars is subdivided into two barrier regions, two trap regions, and a track region. The trap region is located between the two barrier regions, and the track region is located between the two trap regions. Preferably, each of these regions is a continuous, strip-shaped region having a main extension direction parallel to the longitudinal direction. These regions are arranged one behind the other in the transverse direction.

[0010] According to at least one embodiment, at least some of the fingers (preferably all of the fingers) each include a barrier portion, two trap portions and a track portion. The barrier portion is associated with the barrier area that is closest to the bus bar assigned to the finger. The trap portions are each associated with one of the trap areas. The track portion is associated with the track area. Here, a portion is associated with an area if, in a plan view of the top side of the substrate, it overlaps with the area, preferably completely overlaps with the area. In particular, the association between the portion and the area is one-to-one. If a bus bar and a finger belong to the same electrode, the bus bar is assigned to the finger.

[0011] In other words, starting from the assigned busbar, at least some of the fingers each comprise a barrier portion, followed by a first trap portion, followed by a track portion, followed by a second trap portion. The second trap portion preferably forms the end of the finger facing away from the busbar. Preferably, each finger consists of only these four portions. Particularly preferably, the width of the finger (measured as the extension of the finger in the longitudinal direction) is constant within each portion. "Constant" means constant within the manufacturing tolerances. However, the width of the finger may be different in different portions. Preferably, the height of the finger (measured as the extension perpendicular to the top side) is also constant within each portion, but may be different in different portions.

[0012] In accordance with at least one embodiment, the fingers are configured such that the velocity of a main mode of a surface acoustic wave in the trap region is less than its velocity in the track region. The surface acoustic wave propagates on the top side of the substrate. The main mode is a surface acoustic wave that propagates in the longitudinal direction and has a certain polarization. For example, the main mode is a Rayleigh surface acoustic wave. Preferably, the velocity of the main mode in the trap region is at most 99%, at most 98%, or at most 97% of the velocity of the main mode in the track region. Additionally or alternatively, the velocity of the main mode in the trap region is at least 93%, at least 94%, or at least 95% of the velocity in the track region.

[0013] During intended operation, the electroacoustic resonator generates a primary mode, ie, the desired surface acoustic wave. The resonator is configured such that during operation, the primary mode is generated and trapped within the track region.

[0014] In accordance with at least one embodiment, each electrode includes a plurality of short fingers. The short fingers are shorter than the long fingers, i.e., the short fingers have a shorter length than the long fingers. The length of the finger / short finger, or the length of a portion of the finger, is the extension in the lateral direction. Each electrode may include at least 10, at least 50, or at least 100 short fingers.

[0015] The short fingers and fingers extend from the same side of their assigned busbars. This means that the short fingers and fingers of an electrode extend from their assigned busbars toward the busbars of other electrodes. Within manufacturing tolerances, the short fingers can all have the same shape. Similarly, within manufacturing tolerances, fingers comprising different portions can all have the same shape.

[0016] According to at least one embodiment, each short finger is associated only with the barrier area closest to the busbar to which it is assigned. In particular, the short fingers do not overlap with the trap area and the track area. Preferably, the width of the barrier area (measured perpendicular to the longitudinal direction) is defined by the length of the assigned short finger.

[0017] In accordance with at least one embodiment, the electrodes are configured such that the speed of the main mode in the barrier region is greater than the speed in the track region. For example, the speed of the main mode in the barrier region is at least 101%, at least 102%, at least 104%, or at least 106% of the speed in the track region. Additionally or alternatively, the speed of the main mode in the barrier region is at most 110%, at most 109%, at most 107%, or at most 105% of the speed in the track region.

[0018] Compared to a resonator with a piston mode design of fingers but without short fingers, the velocity in the barrier region is reduced. The reduction in velocity in the barrier region allows for an increase in the velocity in the trap region, which further allows for suppression of unwanted modes.

[0019] In at least one embodiment, an electroacoustic resonator includes a substrate comprising a piezoelectric material and an interdigitated electrode structure on the top side of the substrate. The electrode structure includes a first electrode and a second electrode, each electrode having a bus bar and a plurality of fingers. The fingers of the two electrodes interdigitate with each other. The region of the top side between the two bus bars is subdivided into two barrier regions, two trap regions, and a track region, wherein the trap region is located between the two barrier regions, and the track region is located between the two trap regions. At least some of the fingers each include a barrier portion, two trap portions, and a track portion, wherein the barrier portion is associated with the barrier region closest to the bus bar assigned to the finger, the trap portion is each associated with one of the trap regions, and the track portion is associated with the track region. The fingers are configured such that the velocity of a main mode of a surface acoustic wave in the trap region is less than that in the track region. Each electrode includes a plurality of short fingers that are shorter than the finger. Each short finger is associated only with the barrier region closest to the bus bar assigned to the short finger. The electrodes are configured such that the velocity of the main mode in the barrier region is greater than that in the track region.

[0020] In electroacoustic resonators, in addition to the desired main mode, there are also several unwanted (stray) modes. These unwanted modes are modes that do not propagate along the propagation direction of the main mode (= longitudinal direction) and may have all possible polarizations, as well as modes with the same propagation direction as the main mode but with a polarization different from the main mode. Generally, it is impossible to find an electrode structure design that allows suppressing all unwanted modes. This is especially the case in material systems with high electroacoustic coupling and / or small distances between the main mode and unwanted modes of different polarizations. In SAW filters composed of such resonators, the remaining unwanted modes may cause notches in the passband and at the filter edges, group delay ripples, trimming problems and / or reduced power durability.

[0021] In order to suppress unwanted transverse modes (i.e. modes with non-zero propagation in a transverse direction perpendicular to the longitudinal direction), the fingers of the electrode can be formed using a so-called piston mode design, in which the fingers are subdivided into a barrier section, two trap sections and a track section. The trap sections can be designed so that the velocity of the main mode in the associated trap region is less than the velocity in the track region. This can be achieved, for example, by using metal dots in the trap section in order to increase the mass of the trap section compared to the track section. However, this can be problematic for high-frequency resonators, in which the spacing between adjacent fingers must be small. Production methods are often not sufficient to accurately place the metal dots on very small structures.

[0022] The inventors of the present invention conceived the concept of additionally using short fingers in the electrodes. These short fingers reduce the velocity of surface acoustic waves propagating in the longitudinal direction in the barrier regions flanking the trap region. As a result, the velocity in the trap region does not need to be as low as it would be without the short fingers, eliminating the need for metal dots in the trap region. This approach saves costs and avoids manufacturing constraints due to dot alignment accuracy and minimum dot size.

[0023] A further advantage of short fingers is that they offer an additional degree of freedom when optimizing the resonator for suppression of unwanted modes. Indeed, by adjusting the width and / or length and / or height of the short fingers, the velocity of the surface acoustic waves in the barrier region can be adjusted, and in this way, the suppression of modes with a transverse propagation direction can be optimized. Furthermore, by optimizing the design of the short fingers, modes with unwanted polarizations can also be further suppressed.

[0024] According to at least one embodiment, the width and / or height of the fingers in the trap region are greater than the width and / or height in the track region. By increasing the width and / or height, the mass loading of the fingers in the trap region is increased compared to the track region, thereby reducing the velocity of the main mode in the trap region compared to the track region. For example, for each finger, the width and / or height in the trap region is at least 105%, at least 110%, at least 130%, or at least 150% of the width and / or height in the track region. Additionally or alternatively, for each finger, the width and / or height in the trap region is at most 250%, at most 200%, or at most 150% of the width and / or height in the track region.

[0025] According to at least one embodiment, the short fingers and / or the barrier portion of the fingers are thinner and / or narrower than the track portion of the fingers. For example, the height and / or width of the short fingers and / or the barrier portion is at most 90%, at most 80%, or at most 70% of the height and / or width of the track portion. Additionally or alternatively, the height and / or width of the short fingers and / or the barrier portion is at least 20%, at least 40%, or at least 50% of the height and / or width of the track portion.

[0026] By reducing the width and / or height of the short fingers and / or the barrier portion of the fingers, the mass loading in the barrier area can be reduced compared to the track area, with the result that the velocity of the main mode is increased compared to the track area.

[0027] According to at least one embodiment, the short fingers are shorter than the barrier portion. For example, the length of the short fingers is at most 80%, or at most 90%, or at most 95% of the length of the barrier portion of the fingers. Additionally or alternatively, the length of the short fingers is at least 70%, or at least 80% of the length of the barrier portion.

[0028] According to at least one embodiment, the width and / or height of the short fingers are the same as the width and / or height of the barrier portion of the fingers. Here and hereinafter, two elements having the same height and / or width and / or length means elements having the same height and / or width and / or length within the limits of manufacturing tolerances. For example, a deviation of at most 10% or at most 5% may occur.

[0029] According to at least one embodiment, the height of the fingers in the trap portion is the same as their height in the track portion. In this case, the width of the fingers in the trap portion is preferably greater than their width in the track portion. Preferably, the height of the short fingers and fingers in the barrier portion is also the same as their height in the track portion. In this case, the width of the short fingers and / or the barrier portion is preferably less than their width in the track portion.

[0030] A sufficiently deep trap region (i.e., a trap region with a low main mode velocity) can usually be achieved by using a trap portion with an increased height, for example, by using metal dots. However, in high-frequency resonators, small structure sizes are required. Therefore, the application of metal dots can be difficult. However, for the present invention, the trap portion can be selected to have the same height as the track portion, because due to the reduced velocity of the main mode in the barrier region, the trap depth does not have to be selected as deep.

[0031] According to at least one embodiment, in each electrode, the fingers and the short fingers are arranged in an alternating manner. In particular, in each electrode, there are short fingers between each pair of fingers, and there are fingers between each pair of short fingers.

[0032] According to at least one embodiment, with respect to the propagation direction of the main mode (i.e. the longitudinal direction), each short finger is located at the same height as the fingers of the corresponding other electrodes. This means that the center line passing through the short finger (the center line extending in the transverse direction) also passes through the fingers of the other electrodes. Preferably, the center line of the short finger is also the center line of the fingers of the other electrodes at the same height. Preferably, the distance from each short finger to the fingers of the other electrodes located at the same height is at most 10% or at most 5% of the distance between the two bus bars. Additionally or alternatively, the distance from each short finger to the fingers of the other electrodes at the same height is at most 0.5·λ or at most 0.4·λ or at most 0.3·λ, where λ is the wavelength of the main mode in the track area. The distance between two objects is defined here as the length of the shortest connection between the two objects.

[0033] According to at least one embodiment, the electroacoustic resonator is part of an RF filter. The RF filter can be used in a communication device, such as a mobile phone. The RF filter can be a bandpass filter. The resonant frequency of the electroacoustic resonator is, for example, at least 0.4 GHz, at least 2.5 GHz, at least 6 GHz, or at least 8 GHz.

[0034] Further preferred embodiments and developments of the electroacoustic resonator are described below with reference to the accompanying drawings. Identical or similar elements and elements with the same function are denoted by the same reference numerals in the drawings. The drawings and the proportions of the elements shown in the drawings are not to be considered to be true to scale. On the contrary, individual elements (particularly layers) may be shown exaggerated in size for better presentation and / or a better understanding.

[0035] In the attached figure:

[0036] Figures 1 to 4 An exemplary embodiment of an electroacoustic resonator is shown in different views, and

[0037] Figure 5 and Figure 6 The properties of the electroacoustic resonator are shown based on the diagram.

[0038] Figure 1 A first exemplary embodiment of an electroacoustic resonator is shown in plan view. Figure 2 The cross-sectional view (when cutting through the cutting plane AA') shows Figure 1 The electroacoustic resonator includes a substrate 3 comprising a piezoelectric material (e.g., LiNbO3). The substrate 3 includes a top side 33 made of the piezoelectric material. For example, the substrate 3 includes a thin film of the piezoelectric material. The cut angles of the piezoelectric material are, for example, (0°, 38°, 0°). The cut angles (λ', μ, θ) are Euler angles that define the orientation of the top surface of the piezoelectric material relative to the crystal axes of the piezoelectric material. This definition is based on the international standard IEC 62276:2016.

[0039] An electrode structure is applied to the top side 33 of the substrate. The electrode structure is made of a metal, such as Cu. The electrode structure includes a first electrode 1 and a second electrode 2. Both electrodes 1 and 2 include a busbar 20 and a plurality of fingers 10. The busbars 20 extend in a longitudinal direction L. The fingers 10 extend in a transverse direction T, perpendicular to the longitudinal direction L, and perpendicular to the busbars 20.

[0040] Between the busbars 20 , the top side 33 of the substrate 3 is subdivided into two barrier regions 113 , two trap regions 112 , and one track region 111 . Regions 111 , 112 , and 113 are each formed as strips, with their main extension direction along the longitudinal direction L. Regions 111 , 112 , and 113 are arranged one behind the other along the transverse direction T. The track region 111 is located between two trap regions 112 . The two trap regions 112 and the track region 111 are located between two barrier regions 113 . Each barrier region 113 is adjacent to a busbar 20 .

[0041] Each finger 10 includes a barrier portion 13 adjacent to the busbar 20 of the assigned electrode. A first trap portion 12, a track portion 11, and a second trap portion 12 are arranged downstream of the barrier portion 13 in this order, in the direction away from the busbar 20. The barrier portion 13 is associated with / overlaps a barrier region 113 adjacent to the assigned busbar 20. The trap portion 12 is associated with / overlaps a trap region 112, and the track portion 11 is associated with / overlaps a track region 111.

[0042] In addition to the fingers 10, each electrode 1, 2 also includes short fingers 30 extending from the busbar 20. In each electrode 1, 2, one short finger 30 is arranged between each pair of fingers 10. The short fingers 30 are associated with and overlap only the barrier region 113 adjacent to the assigned busbar 20. With respect to the longitudinal direction L, each short finger 30 is located at the same height as the fingers 10 of the corresponding other electrode.

[0043] exist Figure 1 and Figure 2 During operation of the electroacoustic resonator shown in , a main mode of a surface acoustic wave is generated, which propagates in the longitudinal direction with a specific polarization. The main mode is essentially trapped in the track region 111. The trapping portion 12 of the finger 10 is selected so that the speed of the main mode is reduced in the trapping region 112 compared to the track region 111. This is achieved by forming the trapping portion 12 wider than the track portion 11, which results in an increased mass loading in the trapping region 112 compared to the track region 111. However, the height of the finger 10 in the track portion 12 is the same as in the track portion 11 (see Figure 2 ), which is advantageous with regard to the production of the finger 10.

[0044] The short fingers 30 are designed to have a reduced width compared to the track portion 11. The barrier portion 13 of the finger 10 has the same width as the track portion 11. The heights of the short fingers 30 and the barrier portion 13 are the same as in the track portion 11. Due to the reduced width of the short fingers 30, the speed of the main mode in the barrier region 113 is greater than that in the track region 111, but is smaller than when the short fingers 30 are not used.

[0045] The resulting velocity profile is Figure 5 The x-axis represents the transverse direction T. The y-axis represents the velocity of the main mode. During the operation of the resonator, the velocity profile is generated. Figure 6 The profile of the amplitude of the main mode is shown in the graph of . Here, the x-axis also represents the transverse direction T. The y-axis represents the amplitude of the main mode. As can be seen, due to the design of the electrode structure, the main mode amplitude has an almost rectangular shape with an almost flat shape in the track region 111 and steep sides in the trap region 112. In the case where the main mode has such a profile, the unwanted mode propagating in the transverse direction is almost completely suppressed. Figure 5 and Figure 6 , the small gap region between the track region 112 and the barrier region 113 that was visible in the previous figures is not indicated.

[0046] Figure 3 A second exemplary embodiment of an electroacoustic resonator is shown. The resonator is shown only in cross-section. For example, a plan view would be different from Figure 1 Same as in . Figure 2 Compared with the electroacoustic resonator, Figure 3 The electroacoustic resonator has fingers 10 that are taller in trap portion 12 than in track portion 11. This helps further reduce the velocity of the main mode in track region 112. Increased height 12 can be used instead of increased width. Furthermore, the height of fingers 10 in barrier portion 13 can be smaller than in track portion 11. Similarly, the height of short fingers 30 can be smaller than the height of fingers 10 in track portion 11.

[0047] Figure 4 A third exemplary embodiment of an electroacoustic resonator is shown, now again in a plan view on the top side 33 of the substrate 3 . Figure 4 The electroacoustic resonator and Figure 1 The electroacoustic resonator of also differs in that the width of the fingers 10 in the barrier portion 13 is now reduced compared to the width in the track portion 11. In this way, Figure 1 Compared with the case of φ , the speed of the main mode in the barrier region 113 increases.

[0048] Figure 3 and Figure 4 The electroacoustic resonators have similar characteristic velocity profiles and similar main mode amplitude profiles, such as Figure 5 and Figure 6 As shown in .

[0049] The invention described herein is not restricted to the description in conjunction with the exemplary embodiments. Rather, the invention comprises any novel feature and any combination of features, in particular any combination of features in the patent claims, even if the feature or combination itself is not explicitly stated in the patent claims or the exemplary embodiments.

[0050] List of reference numerals:

[0051] 1. First electrode

[0052] 2 Second electrode

[0053] 3 Substrate

[0054] 10 fingers

[0055] 11 Track section

[0056] 12 Trap Section

[0057] 13 Barrier section

[0058] 20 busbars

[0059] 30 short fingers

[0060] 33 Top side

[0061] 111 track area

[0062] 112 Trap Area

[0063] 113 Barrier Area

[0064] T Horizontal direction

[0065] L Longitudinal direction

Claims

1. An electroacoustic resonator, comprising: Piezoelectric substrate; a first electrode including a first bus bar, wherein the first electrode is part of an electrode structure formed on the piezoelectric substrate; as well as a first plurality of fingers comprising at least one short finger coupled to the first electrode in a first barrier region of the electrode structure and at least one finger coupled to the first electrode and extending to a first trap region of the electrode structure, the at least one short finger in the first barrier region having a reduced width compared to the at least one finger extending to the first trap region.

2. The electroacoustic resonator according to claim 1, further comprising: a second electrode comprising a second bus bar, wherein the second electrode is part of the electrode structure; as well as A second plurality of fingers includes at least one short finger coupled to the second electrode in a second barrier region of the electrode structure, the at least one short finger in the second barrier region having a reduced width compared to the at least one finger. 3 . The electroacoustic resonator according to claim 2 , wherein the first trap region is located between the first barrier region and the second barrier region. 4 . The electroacoustic resonator of claim 3 , wherein the electrode structure comprises the first trap region and the second trap region, and wherein the track region of the electrode structure is located between the first trap region and the second trap region. 5 . The electroacoustic resonator of claim 4 , wherein the first plurality of fingers have a width greater in the first trap region than in the track region. 6 . The electroacoustic resonator of claim 4 , wherein the at least one finger extends through the first barrier region and the track region to the first trap region.

7. The electroacoustic resonator of claim 6, wherein a finger of the at least one finger comprises a barrier portion in the first barrier region of the electrode structure, a first trap portion in the first trap region of the electrode structure, and a track portion in the track region of the electrode structure.

8. The electroacoustic resonator according to claim 7, wherein a width of the barrier portion of the finger is the same as a width of the track portion of the finger.

9. The electroacoustic resonator of claim 7, wherein the finger further comprises a second trap portion in a second trap region of the electrode structure.

10. The electroacoustic resonator of claim 2, wherein the first plurality of fingers of the first electrode are electrically isolated from the second plurality of fingers of the second electrode.

11. The electroacoustic resonator of claim 1, wherein the at least one short finger in the first barrier region has a reduced length compared to the at least one finger.

12. The electroacoustic resonator of claim 1, wherein the electrode structure is formed on a top side of the piezoelectric substrate.

13. The electroacoustic resonator of claim 1, wherein the at least one short finger is associated only with the first barrier region that is closest to a bus bar assigned to the at least one short finger.

14. The electroacoustic resonator of claim 1, wherein the at least one short finger comprises a plurality of short fingers, and wherein the at least one finger comprises a plurality of fingers. 15 . The electroacoustic resonator of claim 14 , wherein the plurality of short fingers and the plurality of fingers are arranged in an alternating manner along the first electrode.

16. An electroacoustic resonator, comprising: Piezoelectric substrate; as well as an interdigitated electrode disposed on or over the piezoelectric substrate and comprising: First bus bar; Second bus bar; a first plurality of fingers extending from the first bus bar toward the second bus bar; a second plurality of fingers extending from the second bus bar toward the first bus bar and interdigitated with the first plurality of fingers; A first plurality of short fingers extends from the first bus bar, each of the first plurality of short fingers extending toward a corresponding finger in at least a portion of the second plurality of fingers, a gap existing between an end of each short finger in the first plurality of short fingers and the corresponding finger in the at least a portion of the second plurality of fingers, wherein a width of each short finger in the first plurality of short fingers is smaller than a width of an adjacent finger in the first plurality of fingers.

17. The electroacoustic resonator according to claim 16, further comprising a second plurality of short fingers extending toward corresponding fingers in at least a portion of the first plurality of fingers, a gap existing between an end of each short finger in the second plurality of short fingers and the corresponding finger in the at least a portion of the first plurality of fingers, wherein a width of each short finger in the second plurality of short fingers is smaller than a width of an adjacent finger in the second plurality of fingers.

18. The electroacoustic resonator of claim 16 , wherein along the first plurality of fingers extending in a direction toward the second bus bar, a first barrier region is defined in a gap between the first bus bar and ends of the second plurality of fingers, followed by a first trap region, a track region, and a second trap region, wherein the first plurality of fingers overlap the second plurality of fingers, and wherein the first trap region and the second trap region have increased widths and heights relative to the track region.

Images