RF filter device

Abstract

Embodiments of the present disclosure relate to an RF filter device comprising: a resonator structure comprising a bulk acoustic wave (BAW) resonator, the resonator structure comprising an active structure and an acoustic mirror, where the active structure comprises a bottom electrode, a top electrode, and a piezoelectric material between the bottom electrode and the top electrode; and another circuit comprising at least one of an LC circuit, an LCR circuit, an active circuit element, a switch, an RF switch, a logic circuit, another electroacoustic resonator or an RF filter wherein the acoustic mirror is arranged on one or more layers between a layer comprising the active structure and a layer comprising the another circuit.

Description

[0001] Divisional Application Instructions

[0002] This application is a divisional application of a patent application with an application date of July 1, 2019, application number 201980048000.X, and name “RF filter device”. Technical Field

[0003] The present invention relates to an RF filter arrangement having a compact construction and good electrical properties. Background Art

[0004] Mobile communication devices require RF filter devices to separate desired signals from undesired signals. Typically, RF filter devices include resonators such as electroacoustic resonators. Electroacoustic resonators use the piezoelectric effect to convert between RF signals and sound waves.

[0005] However, the current trend towards miniaturization and towards a greater number of electrical functions requires smaller components with an increased number of circuit elements. Correspondingly, it is difficult to maintain a certain isolation between different sections of the circuit of the corresponding RF filter device.

[0006] Conventional RF filter arrangements use BAW resonators (BAW=bulk acoustic wave) as electroacoustic resonators in the filter topology.

[0007] However, in the case of conventional resonators, it is difficult to meet modern specifications while arranging more circuit elements in a smaller volume.

[0008] Therefore, there is a need for RF filter devices that can be manufactured in smaller spatial dimensions and provide better electrical performance. Summary of the invention

[0009] To this end, an RF filter device is provided. The following provides preferred embodiments.

[0010] The RF filter device includes a resonator structure and another circuit. The resonator structure includes an active structure and an acoustic mirror. The active structure includes a bottom electrode, a top electrode, and a piezoelectric material between the bottom electrode and the top electrode. The acoustic mirror is arranged between the active structure and the other circuit.

[0011] The RF filter arrangement may be an RF filter assembly including a filter structure that may be used in modern communication equipment.

[0012] The resonator structure of the RF filter device includes the elements necessary to build an electroacoustic resonator, for example for use in an RF filter. One part of the resonator structure is an active structure. Another part of the resonator structure is an acoustic mirror. The active structure has a piezoelectric material between a bottom electrode and a top electrode, and this sandwich construction can be used to convert between an RF signal applied to the electrodes and an acoustic wave, for example a longitudinal acoustic wave propagating between the electrodes.

[0013] In order to confine the acoustic energy to the resonator structure, the acoustic mirror acts as a reflective structure for the acoustic waves and reflects the acoustic waves back to the active structure.

[0014] If a high quality factor Q of the resonator is to be achieved, a high reflection coefficient of the acoustic mirror is required.

[0015] An acoustic mirror typically comprises a stack of layers of different acoustic impedance. Each interface between a low acoustic impedance layer and a high acoustic impedance layer (or vice versa) reflects sound waves to some extent. Multiple alternating layers of low and high acoustic impedance and corresponding multiple such interfaces can provide a high reflection coefficient overall to achieve a high-Q resonator.

[0016] The bottom electrode may be implemented in a bottom electrode layer. The top electrode may be implemented in a top electrode layer, and the piezoelectric material may be provided in the piezoelectric material layer.

[0017] BAW resonators can be FBAR type resonators and SMR type resonators. In FBAR type resonators (FBAR = film bulk acoustic resonator), a cavity is arranged below the bottom electrode to confine the acoustic energy. In SMR type resonators, an acoustic mirror is arranged between the bottom electrodes of the resonator. Therefore, the present RF filter device has an SMR type resonator.

[0018] The piezoelectric material may be provided as a single crystal piezoelectric material or a polycrystalline piezoelectric material.The electrodes comprise a conductive material such as a metal.

[0019] The distance between the electrodes, ie the thickness of the piezoelectric layer, primarily determines the operating frequency of the resonator. Specifically, the distance primarily determines λ / 2, ie half the wavelength of the employed acoustic longitudinal wave.

[0020] The further circuit of the RF filter device may include a single circuit element or a plurality of circuit elements, which provide another function of the RF filter device to comply with the trend of providing more electrical functions by a single device.

[0021] The acoustic mirror may be arranged below the bottom electrode of the active structure or above the top electrode of the active structure. Correspondingly, another circuit and its constituent circuit elements are arranged below the acoustic mirror or above the acoustic mirror, respectively.

[0022] By arranging the acoustic mirror between the active structure and the further circuit, electromagnetic decoupling between the active structure and the further circuit is obtained and the isolation between the active structure and the further circuit is improved.

[0023] Hence, due to the improved isolation, the integration density of circuit elements in the RF filter device is increased and smaller spatial dimensions and / or an improved electrical response of the device may be obtained.

[0024] Correspondingly, the acoustic mirror can establish an electromagnetic shield. In particular, the electromagnetic shielding achieved by the acoustic mirror can electrically decouple the active structure of the resonator structure from another circuit.

[0025] In order to further improve the decoupling, the lateral dimensions of the acoustic mirror may exceed the lateral dimensions of the active structure arranged at one side of the acoustic mirror and the lateral dimensions of the further circuit arranged at the respective other side of the mirror. Thus, the acoustic mirror extends in a lateral direction beyond the active structure and / or the further circuit.

[0026] In order to provide electromagnetic shielding, preferably at least one layer of the acoustic mirror has a high electrical conductivity. To this end, preferably the acoustic mirror comprises at least one layer of a specific low resistivity material.

[0027] Conventional mirrors comprise a layer structure, the material of which is selected solely on the basis of its acoustic properties. In order to provide good electromagnetic shielding, it is now proposed to select the material of the mirror both on the basis of its acoustic properties and on the basis of its electrical properties. It has been found that a good shielding effect can be obtained substantially without sacrificing sufficiently good acoustic properties.

[0028] Thus, the resonator and other circuit components implemented in another circuit can be highly decoupled without sacrificing the acoustic properties of the resonator.

[0029] The acoustic mirror may be conductive and connected to ground potential.

[0030] Conventional BAW resonators have mirror materials chosen according to their acoustic properties. Typical materials for high acoustic impedance layers are W (tungsten) or similar heavy metals. Typical materials for low acoustic impedance layers are silicon oxides, such as silicon dioxide and similar materials.

[0031] Neither tungsten nor silicon dioxide is an excellent electrical conductor, but offers good acoustic (impedance) properties.

[0032] Thus, an acoustic mirror having at least one high conductivity layer or an acoustic mirror that is electrically conductive as a whole substantially improves shielding compared to conventional mirrors.

[0033] In particular, an acoustic mirror that is electrically conductive, since each layer of the mirror is electrically conductive, substantially improves the decoupling of circuit components arranged at opposite sides of the mirror.

[0034] The acoustic mirror may include one or more first acoustic impedance layers and one or more second acoustic impedance layers. The second acoustic impedance is greater than the first acoustic impedance. The first acoustic impedance layer and the second acoustic impedance layer include metal.

[0035] The mirror layers can also consist of metal.

[0036] In such a layer system, the charges moving within the layer system have a relatively short path in the material with a relatively high resistivity. In particular, since the corresponding current direction is not directed in the horizontal direction within the layer with low conductivity, the path length of the charge particles is substantially reduced to the thickness of the layer with the lower conductivity material. The higher conductivity layer establishes a shunt path and provides a preferred layer for charge transport.

[0037] The material of the layer having the acoustic impedance selected from the first acoustic impedance and the second acoustic impedance may have an electrical conductivity of Al (aluminum) or higher.

[0038] Aluminum or a material with higher conductivity can be used as a material for one of the two acoustic impedances. Specifically, aluminum can be used for a material that establishes a lower acoustic impedance, or aluminum can be used as a main component of a low acoustic impedance layer.

[0039] Correspondingly, an acoustic mirror comprising layers of tungsten and aluminum is generally electrically conductive and provides good shielding due to the electrical conductivity of aluminum or its corresponding substitutes.

[0040] The material of the layer having an acoustic impedance selected from the first acoustic impedance and the second acoustic impedance may include Al (aluminum), Al alloys such as AlCu (aluminum-copper), Cu (copper) or Cu alloys such as CuNb (copper-niobium), SiO2 or SiOC or consist thereof. In addition, the material of the layer of the corresponding other acoustic impedances includes W (tungsten), Au (gold), Pt (platinum), AlN (aluminum nitride), Ta2O5 or consist thereof.

[0041] The other circuit may include a passive circuit element, an impedance element, a capacitive element, a resistive element, an LC circuit, an LCR circuit, an active circuit element, a switch, an RF switch, a logic circuit, another resonator, another electro-acoustic resonator, and / or an RF filter.

[0042] Thus, SMR type resonators and other circuit elements (e.g., integrated passive devices, such as L, C or R elements or switches) can be integrated within the device, such as monolithically integrated within the device. Such integration can be used to create software reconfigurable filters.

[0043] In particular, in the case where the mirror establishes good isolation between the circuit components (despite their spatial proximity), a stacked arrangement of more than one electroacoustic resonator and more than one further circuit can be used. Correspondingly, multiple filter functions and corresponding circuit systems for control logic and switches can be integrated in a small volume. Thus, in the case where switches are used to select a signal path that selectively employs one or several of the multiple RF filters to provide a duplex mode of the corresponding device, software reconfigurable filters can be used.

[0044] Correspondingly, the device may further include an additional acoustic mirror. The active structure is arranged between the acoustic mirror and the additional acoustic mirror. Thus, an additional space shielded from the active structure is provided to accommodate an additional circuit system.

[0045] Correspondingly, the device may further include an additional circuit. The additional acoustic mirror is arranged between the active structure and the additional circuit element.

[0046] The stacking principle can be extended to n active structures and n+1 acoustic mirrors of the resonator, so that each active structure is arranged between two adjacent acoustic mirrors. Space for arranging circuit systems decoupled from the corresponding active structures is provided below the reflector arranged below the active structure and above the reflector arranged above the active structure. n can be 1, 2, 3, 4, 5 or a larger integer.

[0047] The resonator structure and another circuit may be monolithically integrated.

[0048] Monolithic integration in the context of this device refers to circuit elements that are implemented using substantially identical processing steps. The corresponding processing steps are well known in the semiconductor industry, for example. The processing steps for creating a bottom electrode, a top electrode, a piezoelectric layer, or a mirror layer can also be used to deposit materials for circuit elements of other circuits. Capacitive elements can be implemented by depositing the material of the bottom electrode, depositing a dielectric material on the bottom electrode, and depositing a top electrode on the dielectric material. Inductive elements can be implemented by providing a dielectric layer, depositing a conductive material on the dielectric layer, and constructing a conductor segment (e.g., in a coiled or similar shape) in the conductive layer.

[0049] Furthermore, semiconductor materials, conductive materials, and dielectric materials may be used to create switching and control logic circuitry in a layer configuration of two or more layers.

[0050] Accordingly, a monolithically integrated device including multiple functions may be provided in a smaller volume compared to a heterogeneous integrated assembly having a resonant structure attached to one chip and semiconductor-based circuitry on another chip with both chips arranged on a common carrier substrate.

[0051] The resonator structure and another circuit can create a bandpass filter or a bandstop filter.

[0052] Of course, multiple filter functions may be implemented to, for example, create a duplexer or a higher order multiplexer.

[0053] The resonator structure and the further circuit may be arranged on a carrier.

[0054] The carrier may be a carrier including silicon, for example, a silicon chip. The filter structure and the circuit system structure may be monolithically integrated inside or at an interface of the carrier.

[0055] The RF filter means may be a software configurable RF filter.

[0056] In software configurable RF filter logic circuitry, it is embedded together with the filter circuitry to create a monolithic block. The logic circuitry controls the signal path of the signal routed through the selected RF filter, for example, via switches. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Main aspects and details of preferred embodiments of the present RF filter arrangement are shown in the attached schematic diagrams.

[0058] In the attached picture:

[0059] Figure 1 An RF filter device having an acoustic mirror arranged between an active structure and another circuit is shown;

[0060] Figure 2 The possibility of placing an active structure between two acoustic mirrors to create a dual conductive Bragg mirror configuration is illustrated;

[0061] Figure 3 illustrates the use of a decoupling volume above an additional acoustic mirror by arranging additional circuitry; and

[0062] Figure 4 A duplexer topology with a filter having a ladder-shaped circuit topology is illustrated as a possible application of an RF filter device. DETAILED DESCRIPTION

[0063] Figure 1 An RF filter device FD is shown comprising an acoustic mirror AM, an active structure AS and a further circuit FEC. The active structure AS together with the acoustic mirror AM creates a resonator structure, i.e. an electroacoustic resonator of the SMR type. The further circuit FEC comprises or consists of circuit elements which should be electromagnetically decoupled from the active structure AS. The acoustic mirror AM is arranged between the active structure AS and the further circuit FEC.

[0064] The active structure has a bottom electrode BE, a top electrode TE and a piezoelectric material PM arranged between the bottom electrode BE and the top electrode TE. The acoustic mirror comprises a mirror layer of a first material M1 and a second material M2. The layers of different materials M1, M2 are arranged alternately in the vertical direction to establish an acoustic Bragg mirror. The first material M1 and the second material M2 have different acoustic impedances. The acoustic impedance of the material is determined by the specific gravity of the material and the stiffness parameter of the material (e.g., Young's modulus). The interface between materials of different acoustic impedances reflects sound waves. Therefore, the acoustic energy is confined to the active area of ​​the resonator, i.e., the upper layer of the active structure and the mirror AM.

[0065] The acoustic mirror AM preferably comprises a layer with sufficiently high conductivity so that an electromagnetic shielding is provided to protect the further circuit FEC from harmful influences generated at the location of the active structure AS.

[0066] The acoustic mirror AM or at least one or more mirror layers of the mirror may be electrically connected to a constant potential, for example a ground potential.

[0067] Figure 2 The possibility of providing an additional acoustic mirror AAM arranged above the active structure AS is illustrated, such that the active structure AS is arranged between the acoustic mirror AM (arranged below the active structure AS) and the additional acoustic mirror AAM (arranged above the active structure AS). Thus, the active structure AS is clamped between the two acoustic mirrors. Both mirrors preferably comprise an electrically conductive layer, such that the environment of the active structure AS, in particular the area below and above the active structure AS, is shielded from harmful influences emanating from the active structure AS.

[0068] Figure 3 The possibility of using the volume above the additional acoustic mirror AAM to arrange additional circuits AEC is illustrated, which are also shielded from the active structure AS.

[0069] In principle, it is possible to have a layer structure with multiple acoustic mirrors and circuit elements stacked on top of each other, for example another circuit with sensitive circuit elements or active structures. Thus, the principle of using acoustic mirrors to provide shielded areas can be extended to multiples of two, three, four, five, six or more acoustic mirrors corresponding to three, five, six, seven and more areas to be shielded from harmful influences.

[0070] Figure 4 Possible applications of RF filter devices are illustrated. The resonator structure and / or another circuit as well as further resonator structures and additional circuits can be used to build RF filters, such as bandpass filters or bandstop filters. The filter can have a ladder filter topology. Several filters can be combined to build a multiplexer.

[0071] The ladder filter topology has a series resonator electrically connected in series in the signal path between the first port and the second port. In addition, the parallel resonator PR is arranged in a shunt path that electrically connects the signal path to the ground potential. One or more RF filters may be connected or coupled to a common port, for example, an antenna port. The antenna port may be connected to an antenna AN. The filter provided to guide the transmitted signal is a transmit filter TXF. The transmit filter TXF blocks the received signal. The filter provided to guide the received signal is a receive filter RXF. The receive filter RXF blocks the transmitted signal. Between the transmit filter TXF and the receive filter RXF of a duplexer or a higher degree of multiplexer, a matching circuit provided to establish impedance matching between the common port and the filter may be arranged. For example, the element of the matching circuit may be implemented as an element of another circuit or additional circuit in the RF filter device together with the resonator structure of the series resonator or parallel resonator of the corresponding filter.

[0072] The RF filter device is not limited to the technical details and the embodiments shown above. It is also possible to include additional circuit elements, additional active circuits (such as low noise amplifiers or power amplifiers). Therefore, the RF filter device can also be a combined power amplifier and filter module.

[0073] Reference numerals list

[0074] AAM: Attached Acoustic Mirror

[0075] AEC: Additional Circuitry

[0076] AM: Sound Mirror

[0077] AN:Antenna

[0078] AS: Active Structure

[0079] BE: Bottom Electrode

[0080] FD: RF filter device

[0081] FEC: Another Circuit

[0082] M1: The first material layer of the acoustic mirror

[0083] M2: The second material layer of the acoustic mirror

[0084] PM: Piezoelectric Materials

[0085] PR: Parallel Resonator

[0086] RXF: Receive filter

[0087] SR: Series Resonator

[0088] TE: Top Electrode

[0089] TXF: Transmit filter.

Claims

1. An RF filter device, comprising: A resonator structure comprising a bulk acoustic wave (BAW) resonator, the resonator structure comprising an active structure and an acoustic mirror, wherein the active structure comprises a bottom electrode, a top electrode, and a piezoelectric material between the bottom electrode and the top electrode; as well as Another circuit, the other circuit comprising at least one of an LC circuit, an LCR circuit, an active circuit element, a switch, an RF switch, a logic circuit, another electroacoustic resonator or an RF filter, wherein the acoustic mirror is arranged on one or more layers between the layer comprising the active structure and the layer comprising the other circuit. 2 . The RF filter device of claim 1 , wherein the acoustic mirror is configured to create an electromagnetic shield.

3. The RF filter device of claim 1, wherein the acoustic mirror is conductive and connected to ground potential.

4. The RF filter device according to claim 1, wherein: The acoustic mirror includes: one or more layers having a first acoustic impedance, and one or more layers having a second acoustic impedance, the second acoustic impedance being greater than the first acoustic impedance; and The one or more layers of the first acoustic impedance and the one or more layers of the second acoustic impedance include metal. 5 . The RF filter device of claim 4 , wherein the one or more layers having the first acoustic impedance and the one or more layers having the second acoustic impedance have an electrical conductivity equal to or greater than an electrical conductivity of aluminum.

6. The RF filter device according to claim 4, wherein: The one or more layers having the first acoustic impedance include Al, Al alloy, Cu or Cu alloy, SiO2 or SiOC, and The layers other than the one or more layers having the first acoustic impedance and the one or more layers having the second acoustic impedance include W, Au, Pt, AlN, or Ta2Os5.

7. The RF filter device according to claim 4, wherein: The one or more layers having the first acoustic impedance include aluminum; and The one or more layers having the second acoustic impedance include tungsten W. 8 . The RF filter device according to claim 1 , further comprising an additional acoustic mirror, wherein the active structure is arranged between the acoustic mirror and the additional acoustic mirror.

9. The RF filter device according to claim 8, further comprising an additional circuit, wherein the additional acoustic mirror is arranged between the active structure and the further circuit.

10. The RF filter device of claim 1, wherein the resonator structure and the further circuit are monolithically integrated.

11. The RF filter device of claim 1, wherein the resonator structure and the further circuit establish a bandpass filter or a bandstop filter.

12. The RF filter device according to claim 1, wherein the resonator structure and the further circuit are arranged on a carrier.

13. The RF filter device of claim 1, wherein the RF filter device is a software configurable RF filter.

14. The RF filter device of claim 1, wherein a lateral dimension on each side of the acoustic mirror exceeds a lateral dimension of the another circuit.

15. An RF filter device comprising: A resonator structure comprising a bulk acoustic wave (BAW) resonator, the resonator structure comprising an active structure and an acoustic mirror, wherein the active structure comprises a bottom electrode, a top electrode, and a piezoelectric material between the bottom electrode and the top electrode; as well as Another circuit, wherein the acoustic mirror is arranged on one or more layers between a layer including the active structure and a layer including the another circuit, and wherein a lateral dimension on each side of the acoustic mirror exceeds a lateral dimension of the another circuit.

16. The RF filter device of claim 15, wherein the acoustic mirror is configured to create an electromagnetic shield.

17. The RF filter device of claim 15, wherein the acoustic mirror is conductive and connected to ground potential.

18. The RF filter device of claim 15, wherein: The acoustic mirror includes: one or more layers having a first acoustic impedance, and one or more layers having a second acoustic impedance, the second acoustic impedance being greater than the first acoustic impedance; and The one or more layers of the first acoustic impedance and the one or more layers of the second acoustic impedance include metal.

19. The RF filter device of claim 18, wherein the one or more layers having the first acoustic impedance and the one or more layers having the second acoustic impedance have an electrical conductivity equal to or greater than an electrical conductivity of aluminum.

20. The RF filter device of claim 18, wherein: The one or more layers having the first acoustic impedance include aluminum; and The one or more layers having the second acoustic impedance include tungsten (W).

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