Body sound device and method for manufacturing body sound device

Abstract

A body sound device comprising a first electrode (1a; 1b) and a second electrode (2a; 2b); and at least one first electrode (1a; 1b) and the second electrode (2a; 2b), said piezoelectric element (3) being designed in such a way that the piezoelectric element (3) is arranged between the first electrode (1a; 1b) is converted into an acoustic signal in the piezoelectric element (3), said acoustic signal being stored in the second electrode (2a; 2b) of the first electrode signal and the second electrode signal; comprising a further dielectric layer (7) surrounding the first electrode (1a; 1b), said second electrode (2a; 2b) and the piezoelectric element (3) and having a substantially flat surface; wherein at least one separating trench (11a; 11b) is formed in the dielectric layer (7); 11b) which at least partially surrounds the piezoelectric element (3).

Description

Technical Field

[0001] The invention relates to a stereophonic device and a method for producing the stereophonic device. Background Art

[0002] In high-frequency technology, bulk acoustic wave (BAW) components are used as resonators in filters and oscillators. The operating frequency of the component is primarily determined by the layer thickness of the piezoelectric layer and by the speed of sound in the piezoelectric material. In order to achieve higher operating frequencies, the layer thickness must be reduced. Tolerances are therefore becoming increasingly important.

[0003] The capacitance of a BAW component is increased by a lower layer thickness of the piezoelectric material. In order to maintain the wave impedance, the component area must be reduced at the same time. However, the acoustic energy is lost at the edges of the component. When the component is reduced in size, the edge loss increases with the square of the operating frequency. Therefore, conventional BAW component (BAW) technology reaches its limit at about 10 GHz.

[0004] Patent documents US2018 / 085787 A1 and US2013 / 193808 A1 disclose a BAW component in which two different piezoelectric materials with opposite polarities are stacked to maintain low capacitance even at higher operating frequencies, thereby reducing edge losses and achieving higher operating frequencies in the millimeter wave range. Summary of the invention

[0005] The present invention provides a stereophonic device and a method for manufacturing the stereophonic device having the features of independent patent claims.

[0006] Preferred embodiments are the subject matter of the respective dependent claims.

[0007] According to a first aspect, the invention therefore relates to a stereophonic device with a first electrode and a second electrode and a piezoelectric element arranged between the first electrode and the second electrode, wherein the piezoelectric element is designed in such a way that a first electromagnetic signal fed into the first electrode is converted into an acoustic signal in the piezoelectric element, wherein the acoustic signal is converted back into a second electromagnetic signal in the second electrode. The stereophonic device further comprises a dielectric layer, which surrounds the first electrode, the second electrode and the piezoelectric element and has a substantially planar surface. At least one separating groove is formed in the dielectric layer, which at least partially surrounds the piezoelectric element.

[0008] According to a second aspect, the present invention relates to a method for manufacturing a body acoustic device. Therefore, a substrate is provided. In addition, a first electrode, a second electrode and a piezoelectric element arranged between the first electrode and the second electrode are arranged on the substrate, wherein the piezoelectric element is constructed in such a way that a first electromagnetic signal fed into the first electrode is converted into an acoustic signal in the piezoelectric element, wherein the acoustic signal is converted back into a second electrode signal in the second electrode. In addition, a dielectric layer is constructed, which surrounds the first electrode, the second electrode and the piezoelectric element and has a substantially flat surface. In addition, at least one separation groove is constructed in the dielectric layer, which at least partially surrounds the piezoelectric element.

[0009] Advantages of the present invention

[0010] The bulk acoustic device comprises a piezoelectric element as a resonator core element. The resonator core is therefore surrounded by a dielectric. In order to limit interfering parasitic capacitances due to the overlap of leads and electrodes, the device has a substantially flattened surface. Without separation grooves, acoustic energy emission losses occur at the periphery via the dielectric, which can lead to undesired, higher insertion losses. In addition, the chip can bend from the outside due to stress coupling or itself due to temperature bending, thus indirectly coupling stresses into the resonator core via the dielectric. This can lead to deviations in the resonant frequency of the resonator or in the passband edges of the filter component (temperature drift).

[0011] Therefore, according to the invention, at least one separation groove is introduced into a resonator core surrounded by a dielectric, which serves as both an acoustic insulation groove and a stress coupling groove. On the one hand, stress coupling is reduced on the resonator core in this way. On the other hand, the acoustic energy around the resonator core is stored and it cannot be lost, because the sound cannot pass through the separation groove due to the high acoustic impedance difference between the dielectric-air or dielectric-vacuum on the surface. On the third hand, similar to the side molding of the resonator core, the shape and position of at least one insulating groove better suppress unexpected side wave modes (Lateralmoden) (English: spurious modes). Therefore, the bulk acoustic device according to the present invention minimizes the acoustic energy loss and thermal drift effects while maintaining robustness with respect to environmental influences. In addition, smaller insertion losses and smaller acoustic crosstalk (cross talk) are generated between adjacent bulk acoustic devices on the (filter) chip.

[0012] According to one embodiment of the bulk acoustic device, the separating trench is embodied in the dielectric as a wall-shaped and / or column-shaped recess, wherein at least the plane of the piezoelectric resonator core is included.

[0013] According to one embodiment of the stereo acoustic device, the at least one separating trench completely surrounds the piezoelectric element.

[0014] According to one embodiment, the stereophonic device comprises at least one lead leading to the first electrode and / or the second electrode, wherein the at least one lead passes over or under the at least one separating trench.

[0015] According to one embodiment of the bulk acoustic device, the membrane spans over at least one separating trench, wherein feeds to the first electrode and / or the second electrode are formed in the membrane. The separating trench can thus also completely surround the resonator core.

[0016] According to one embodiment of the stereophonic device, a cavity is formed below the second electrode, wherein the cavity is fluidically connected to the separating trench. The separating trench thus enables a pressure comparison between the cavity and the surroundings.

[0017] According to one embodiment of the stereophonic device, at least one separating trench is at least partially provided with a passivation layer. The passivation layer protects against moisture absorption and can prevent premature chemical aging. Advantageously, the passivation layer has a layer thickness that corresponds to a quarter of the acoustic wavelength of the central passage frequency of the resonator core in the passivation material.

[0018] According to one embodiment of the body acoustic device, a plurality of body acoustic devices as resonators can be suitably connected to one another in a circuit in a so-called conductor- and / or grating arrangement. Thus, a filter assembly can be realized which is permeable for a specific frequency range and which can be designed for each frequency band, for example, in mobile communication. With the aid of such a filter, signal interference between the transmission channel and the reception channel can be avoided not only in the communication module of the mobile terminal device but also in the base station.

[0019] Higher frequencies require smaller layer thicknesses, which leads, for example, to higher requirements regarding the layer thickness accuracy. Conventionally, the lateral dimensions of the resonator must be scaled down simultaneously with the reduction in layer thickness in order to compensate for the increase in capacitance caused by the reduction in layer thickness and to be able to maintain a target impedance value of, for example, 50Ω. However, scaling down can lead to higher acoustic energy losses, since the ratio of the periphery to the resonator area is thereby increased.

[0020] According to one embodiment of the body acoustic device, the piezoelectric element therefore comprises at least two piezoelectric layers with rectified polarity and at least one intermediate layer between the at least two piezoelectric layers. The acoustic layer thicknesses of the piezoelectric layers and the intermediate layers correspond respectively to odd multiples (1x, 3x, ...) of the half acoustic wavelength of the acoustic signal to be transmitted. The capacitance is thus reduced by the insertion of at least one additional intermediate layer and one further piezoelectric layer. The insertion of the additional piezoelectric layer and at least one intermediate layer corresponds to the series connection of an additional series capacitor, which allows the acceptance of a single correspondingly larger value, because in the case of a series connection the inverse of the single capacitance is added to the inverse of the total capacitance. In this way, the lateral dimensions of the resonator can be larger than in the case without an intermediate layer. As a result, smaller edge losses occur and the resonator can be designed and used for higher frequencies.

[0021] In order not to destroy the resonance, the acoustic total layer thickness of the intermediate layer is adapted to the acoustic target wavelength of the intermediate layer. The acoustic total layer thickness of the piezoelectric element thus corresponds to an odd multiple (1x, 3x, . . . ) of half the acoustic wavelength.

[0022] At least one further piezoelectric layer on the second electrode serves for efficient conversion of the electromagnetic waves back into acoustic waves at the second electrode.

[0023] The bulk acoustic device enables the development of higher frequency ranges with an improved performance with respect to thermal drift. A high-frequency signal can be fed in (input) at a first electrode of the bulk acoustic device. The high-frequency signal is a first electromagnetic wave which is converted back into an acoustic wave by the piezoelectric element at the first electrode and back into a second electromagnetic wave at the opposite second electrode. At a given electromagnetic or acoustic frequency, the acoustic wavelength λ is obtained according to the following formula a The speed of sound c of the corresponding layer material s :

[0024] λ a =c s / f

[0025] As long as the thickness of the piezoelectric layer and the acoustic layer of the intermediate layer stack is d p Therefore, the corresponding converted electromagnetic wave (ie, sound signal) is an odd multiple (1x, 3x, ...) of half the sound wavelength, that is:

[0026] d p =(n+1 / 2)*λ a

[0027] For n={0, 1, ...}, the input signal is transmitted and furthermore reflected. The bulk acoustic device can thus be used as a bulk acoustic resonator.

[0028] According to a further embodiment, the stereo acoustic device comprises a plurality of piezoelectric layers, wherein an intermediate layer is respectively located between two consecutive piezoelectric layers.

[0029] According to another embodiment of the body acoustic device, the intermediate layer is formed by a single layer, the acoustic layer thickness of the single layer corresponding to an odd multiple (1x, 3x, . . . ) of half the acoustic wavelength of the acoustic signal to be transmitted, ie the target wavelength.

[0030] According to another embodiment of the body acoustic device, at least one intermediate layer consists of a plurality of sublayers, wherein the sum of the acoustic layer thicknesses of the sublayers corresponds to an odd multiple (1x, 3x, ...) of half the acoustic wavelength of the acoustic signal to be transmitted. For example, the intermediate layer comprises two sublayers, whose wavelengths are:

[0031] λ a / 4+λ a / 4=λ a / 2

[0032] or:

[0033] λ a / 4+5λ a / 4=3λ a / 2

[0034] or:

[0035] 3λ a / 4+3λ a / 4=3λ a / 2

[0036] Here, the first summed number specifies the acoustic layer thickness of the respective first sublayer and the second summed number specifies the acoustic layer thickness of the second sublayer. However, the principle can be transferred in an analogous manner to more than two sublayers.

[0037] According to another embodiment of the bulk acoustic device, the acoustic layer thickness of the piezoelectric layer and the intermediate layer corresponds to a corresponding half acoustic wavelength of the acoustic signal to be transmitted. In other words, according to the invention, the total acoustic layer thickness of the piezoelectric element is 3λ a / 2. The fundamental resonance (ie n=0, lowest order) thus occurs in the intermediate layer and the piezoelectric layer. This is advantageous because in this case the highest quality factor occurs, the filter edge can be particularly steep and the insertion losses can be particularly low.

[0038] According to another embodiment of the stereophonic device, the material of the intermediate layer includes a dielectric, such as silicon oxide, silicon nitride, silicon carbide, aluminum oxide or diamond-like carbon (DLC). Preferred materials have intrinsically low dielectric and / or acoustic damping and an adapted thermal expansion coefficient.

[0039] According to another embodiment of the stereophonic device, at least one intermediate layer is assembled in multiple layers, for example from layers with odd multiples of λ (1x, 3x, ...). a / 4 layer thickness of the acoustic Bragg reflector. Suitable material pairs for the reflector are characterized by the difference in the sound speed of the materials and minimal material damping. Possible materials are, for low sound speeds: titanium (Ti), tantalum (Ta) or copper (Cu), for example, or for high sound speeds: aluminum (Al), nickel (Ni), tungsten (W) or molybdenum (Mo).

[0040] According to a further embodiment of the body acoustic device, a combination of dielectric and semiconductor and / or metal layers is provided as intermediate layer(s).

[0041] According to another embodiment of the stereophonic device, the different intermediate layers described above can be present in any combination with one another. For example, the piezoelectric element can have more than two piezoelectric layers and more than one intermediate layer. In this case, at least one intermediate layer is composed of an odd multiple of λ. a A single layer of λ / 2 layer thickness is formed, and another intermediate layer is formed by λ with an odd multiple (1x, 3x, ...) a A multilayer acoustic Bragg reflection layer with a thickness of / 4 layers is formed.

[0042] According to another embodiment of the bulk acoustic device, the material of the piezoelectric layer comprises aluminum nitride (AlN) or scandium-doped aluminum nitride (ScAlN). This is advantageous since the high acoustic velocity allows relatively large layer thicknesses. Other possible materials are zinc dioxide (ZnO2), lithium niobate (LiNbO3) or lithium tantalate (LiTaO3).

[0043] According to another embodiment of the bulk acoustic device, the first electrode and / or the second electrode is designed as an acoustic Bragg reflector - similar to the intermediate layer already described above. The Bragg reflector layer can thus be inserted between the substrate and the piezoelectric element, for which reason the loss of acoustic energy in the substrate can be avoided in order to keep the insertion losses small. This is an SMR (solidly mounted resonator) structure. Due to the better thermal coupling to the substrate, the SMR structure can be advantageously used in applications in which high powers must be handled, for example in base stations and in the transmission path of mobile radio terminals.

[0044] According to another embodiment of the stereophonic device, the undercut The first and / or second electrode (and thus the piezoelectric element) is thus a FBAR (film bulk acoustic resonator) structure. In this case, the electrode-air surface reflects the sound, and since the FBAR structure has a smaller insertion loss, this is advantageous for a larger bandwidth and for the transmission path of a mobile wireless terminal.

[0045] According to another embodiment, the body acoustic device is usable as a high-precision clock crystal, in a filter element for frequencies in the GHz range (especially also greater than 10 GHz) or as a gravity harmonic sensor. The body acoustic device can be used in particular for high-frequency systems, for example in the mobile radio field (20 GHz-100 GHz) or in the radar field.

[0046] Further advantages, features and details of the invention emerge from the following description, in which various exemplary embodiments are described in detail with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Here it is shown:

[0048] Figure 1 : A schematic cross-sectional view of a stereophonic device according to an embodiment of the present invention;

[0049] Figure 2 : With Figure 1 A schematic top view of a chip of a bulk acoustic device shown in FIG.

[0050] Figure 3 : a schematic cross-sectional view of a stereophonic device according to another embodiment of the present invention;

[0051] Figure 4 : With Figure 3 A schematic top view of a chip of a bulk acoustic device shown in FIG.

[0052] Figure 5 : a schematic cross-sectional view of a stereophonic device according to another embodiment of the present invention;

[0053] Figure 6 : With Figure 5 A schematic top view of a chip of a bulk acoustic device shown in FIG.

[0054] Figure 7 : Flowchart of a method for manufacturing a stereo acoustic device according to an embodiment of the present invention.

[0055] In all figures, identical or functionally identical elements and devices are provided with the same reference symbols. The numbering of the method steps is unambiguous and does not generally imply a specific chronological sequence. In particular, multiple method steps can also be performed simultaneously. DETAILED DESCRIPTION

[0056] Figure 1A cross-sectional view of a stereophonic device 100 is shown. The stereophonic device 100 comprises a substrate 4 on which a second acoustic Bragg reflector 2a is arranged. The second Bragg reflector 2a comprises a plurality of sublayers 21 to 26 with alternating higher and lower sound velocities or acoustic damping. In addition, a first acoustic Bragg reflector 1a is provided, which can be assembled similarly.

[0057] The first Bragg reflector 1 a consists of an electrically conductive material and serves as a first electrode, and the second Bragg reflector 2 a also consists of an electrically conductive material and serves as a second electrode.

[0058] A piezoelectric element 3 is arranged between the second Bragg reflector 2a and the first Bragg reflector 1a. The first electromagnetic signal fed into the second Bragg reflector 1a via the first lead 6 is converted into an acoustic signal in the piezoelectric element 3 during operation. As long as the acoustic resonance condition is met, the acoustic signal is converted back into a second electromagnetic signal in the first Bragg reflector 2a, and the second electromagnetic signal is output via the through hole 9 and the second lead 5.

[0059] The piezoelectric element 3 comprises two essentially identical piezoelectric layers 31, 33 with rectified polarity and an intermediate layer 32 between the two piezoelectric layers 31, 33. The acoustic layer thicknesses of the piezoelectric layers 31, 33 and the intermediate layer 32 each correspond to an odd multiple (1x, 3x, ...) of half the acoustic wavelength of the acoustic signal to be transmitted, i.e. a predetermined acoustic wavelength (a corresponding predetermined pass-through frequency of the body acoustic device). Preferably, the corresponding half acoustic wavelength of the desired pass-through frequency is matched to the piezoelectric layers 31, 33 and to the intermediate layer 32 as a first resonance based on the piezoelectric element 3 (see the indicated wave).

[0060] The through hole 9 and the resonator core composed of the first Bragg reflector 1a, the second Bragg reflector 2a and the piezoelectric element 3 are surrounded by a dielectric layer 7, which has a substantially flat surface. A passivation layer 8 is located above the leads 5, 6 and the dielectric layer 7. A separation trench 11a is formed in the dielectric layer 7, and the passivation layer also covers the surface of the separation trench 11a.

[0061] Figure 2 Shown with two Figure 1 FIG. 1 is a schematic top view of a chip of a stereo acoustic device 100 . Figure 1 Corresponds to a cross-sectional view along plane AA. Figure 2 It can be seen that the separation trench 11 a partially surrounds the piezoelectric element 3 laterally, namely in this case from three sides.

[0062] The separation groove 11 a prevents crosstalk to the adjacent bulk acoustic device 100. The piezoelectric resonator core and the dielectric layer 7 directly surrounding it together form a peninsula or half-mesa delimited by the separation groove 11 .

[0063] Figure 3 A cross-sectional view of another stereophonic device 200 is shown and Figure 4 The corresponding top view is shown. Figure 1 and Figure 2 Unlike the stereophonic device 100 shown in FIG. 1 , the separating trench 11 b in this embodiment completely surrounds the piezoelectric element 3 laterally, ie from all four sides. The piezoelectric resonator core and the dielectric layer 7 directly surrounding it thus form an island or a mesa delimited by the separating trench 11 b.

[0064] Figure 5 A cross-sectional view of another stereophonic device 300 is shown and Figure 6 The corresponding top view is shown. Figure 3 and Figure 4 Unlike the stereophonic device 200 shown in FIG. 1 , the electrodes 1 b, 2 b provided here are not designed as acoustic Bragg reflectors. Therefore, the second electrode 2 b is undercut, so that a cavity 10 is formed to which the separation groove 11 b can be connected. The thickness of the electrodes 1 b, 2 b is matched to the wavelength of the pass frequency. The membrane 12 bridges the separation groove 11 b. A lead can also be formed to pass over from above, which leads pass over the separation groove 11 b from above by means of the membrane 12 at least in the upper lead area.

[0065] Figure 7 A flow chart showing a method for manufacturing a stereophonic device is shown. Figures 1 to 6 The stereo acoustic apparatuses 100 to 300 are shown in FIG.

[0066] In a first method step S1 , a substrate 4 , for example composed of silicon, is provided.

[0067] In a second method step S2, first electrodes 1a, 1b, second electrodes 2a, 2b, and a piezoelectric element 3 arranged between the first electrodes 1a, 1b and the second electrodes 2a, 2b are formed on a substrate 4. To this end, the second electrode 2a can be first formed on the substrate 4. The piezoelectric element 3 is then formed on the second electrode 2a. Finally, the first electrode 1a is formed on the piezoelectric element 3. The first and / or second electrodes 1a, 1b, 2a, 2b can be formed as Bragg reflector layers.

[0068] In a further method step S3, a dielectric layer 7 is formed which surrounds the first electrodes 1a, 1b, the second electrodes 2a, 2b and the piezoelectric element 3. The dielectric layer 7 is planarized so that the dielectric layer 7 has a substantially planar surface.

[0069] In a further method step S4 , the contact holes are opened as far as the second electrodes 2 a , 2 b .

[0070] In method step S5 , the contact holes are filled and the surface is planarized. Optionally, a wiring layer is applied.

[0071] In method step S6 , at least one acoustic separation trench 11 a , 11 b is etched.

[0072] In method step S7 , the passivation layer 6 is formed.

[0073] The piezoelectric element 3 is configured such that a first electromagnetic signal fed into the first electrode 1a is converted into an acoustic signal in the piezoelectric element 3, wherein the acoustic signal is converted back into a second electromagnetic signal in the second electrode 2a. The piezoelectric element 3 comprises at least two piezoelectric layers 31, 33, preferably with rectified polarity, and at least one intermediate layer 32 between the at least two piezoelectric layers 31, 33. The acoustic layer thicknesses of the piezoelectric layers 31, 33 and the intermediate layer 32 each correspond to an odd multiple (1x, 3x, ...) of a half acoustic wavelength of the acoustic signal to be transmitted.

Claims

1. A stereophonic device (100; 200; 300) comprising a first electrode (1a; 1b) and a second electrode (2a; 2b); A piezoelectric element (3) is arranged between the first electrode (1a; 1b) and the second electrode (2a; 2b), wherein: The piezoelectric element (3) is designed in such a way that a first electromagnetic signal fed into the first electrode (1a; 1b) is converted into an acoustic signal in the piezoelectric element (3), wherein the acoustic signal is converted back into a second electromagnetic signal in the second electrode (2a; 2b); A dielectric layer (7) is provided, the dielectric layer (7) surrounds the first electrode (1a; 1b), the second electrode (2a; 2b) and the piezoelectric element (3) and has a substantially flat surface; Therein, at least one separating trench (11a; 11b) is formed in the dielectric layer (7), the separating trench (11a; 11b) at least partially surrounding the piezoelectric element (3).

2. The stereophonic device (100; 200) according to claim 1, comprising at least one lead to the first electrode (1a; 1b) and / or the second electrode (2a; 2b), wherein: The at least one lead passes over at least one separation trench (11a; 11b) from below.

3. The stereo acoustic device (300) according to claim 1 or 2, wherein: A membrane (12) spans the at least one separation trench (11a; 11b), wherein leads to the first electrode (1a; 1b) and / or the second electrode (2a; 2b) are formed in the membrane (12).

4. The stereophonic device (300) according to any one of the preceding claims, comprising a cavity (10) formed below the second electrode (2a; 2b), wherein: The cavity (10) and the separation groove (11a; 11b) are fluidically connected.

5. The stereophonic device (100; 200; 300) according to any one of the preceding claims, wherein: The at least one separation trench (11a; 11b) is at least partially provided with a passivation layer.

6. The stereo acoustic device (100; 200; 300) according to any one of the preceding claims, wherein: The piezoelectric element (3) comprises at least two piezoelectric layers (31, 33); and The acoustic layer thicknesses of the piezoelectric layers (31, 33) respectively correspond to odd-numbered multiples of half the acoustic wavelength of the acoustic signal to be transmitted.

7. The stereophonic device (100; 200; 300) according to any one of the preceding claims, wherein: The first electrode (1a; 1b) and / or the second electrode (2a; 2b) are designed as acoustic Bragg reflectors.

8. The stereophonic device (100; 200; 300) according to any one of the preceding claims, wherein The piezoelectric element (3) comprises at least two piezoelectric layers (31, 33) and at least one intermediate layer (32) between the at least two piezoelectric layers (31, 33), wherein the material of the intermediate layer (32) comprises, in particular, a dielectric.

9. A method for manufacturing a stereophonic device (100; 200; 300), comprising the steps of: Providing (S1) a substrate (4); A first electrode (1a; 1b), a second electrode (2a; 2b), and a piezoelectric element (3) arranged between the first electrode (1a; 1b) and the second electrode (2a; 2b) are formed (S2) on the substrate (4), wherein: The piezoelectric element (3) is designed such that a first electromagnetic signal fed into the first electrode (1a; 1b) is converted into an acoustic signal in the piezoelectric element (3), wherein the acoustic signal is converted back into a second electromagnetic signal in the second electrode (2a; 2b). forming (S3) a dielectric layer (7), the dielectric layer (7) surrounding the first electrode (1a; 1b), the second electrode (2a; 2b) and the piezoelectric element (3) and having a substantially flat surface; and At least one separation groove (11a; 11b) is formed (S6) in the dielectric layer (7), the separation groove (11a; 11b) at least partially surrounding the piezoelectric element (3).

10. The method according to claim 9, wherein: A membrane (12) spans the at least one separation trench (11a; 11b), wherein leads to the first electrode (1a; 1b) and / or the second electrode (2a; 2b) are formed in the membrane (12).

11. The method according to claim 9 or 10, wherein: A cavity (10) is formed below the second electrode (2a; 2b), wherein the cavity (10) and the separating trench (11a; 11b) are fluidically connected.

Images