SAW resonator and RF filter including SAW resonator

Abstract

An improved SAW resonator (SAWR) is provided, which has improved power endurance and heat resistance and prevents device failure. The SAW resonator has a carrier substrate (S) and an electrode structure (ES, EF) on a piezoelectric material (PM, PL). Further, the resonator has a shunt path (PCPP) parallel to the electrode structure and arranged such that an RF signal bypasses the electrode structure. The shunt path has a temperature-dependent electrical conductance, which has a negative temperature coefficient of resistance.

Description

Technical Field

[0001] This invention relates to SAW resonators (SAW = Surface Acoustic Wave), which offer improved power endurance and heat resistance and protect corresponding equipment from failure. Furthermore, this invention relates to RF filters including at least one such resonator. Background Technology

[0002] In mobile communication systems, RF filters are needed to distinguish between desired and unwanted RF signals. RF filters can be utilized in the front-end systems of mobile communication devices. For example, a transmission filter between a power amplifier and the antenna port is used to ensure that only the transmitted signal propagates to the antenna port. In the received signal path, the received signal is used to transmit the received signal, particularly at the receive port to isolate the transmitted signal.

[0003] RF filters, such as RF filters that work with sound waves, include electroacoustic resonators. Specifically, SAW resonators that work with surface acoustic waves (SAWs) include electrode structures arranged on a piezoelectric material. The electrode structures include interdigitated electrodes whose fingers connect to a busbar. The resonator of the RF filter is exposed to RF power. Ohmic losses or other energy dissipation effects in the electrodes cause energy to be converted from RF energy into heat. Accordingly, the heated resonator suffers a shift in characteristic frequencies, such as the resonant frequency or anti-resonant frequency, due to the expansion of the piezoelectric layer and changes in material properties (e.g., elastic stiffness at elevated temperatures). Furthermore, if the resonator is, for example, part of a bandpass filter configuration, the passband will shift in frequency, and the corresponding self-heating of the resonator will cause additional losses. If the temperature rises above a certain critical value, permanent damage may occur, leading to permanent failure of the corresponding filter component.

[0004] Temperature changes are a problem for electroacoustic filters because temperature shifts cause a shift in characteristic frequencies, such as the center frequency of a bandpass filter. Furthermore, increased temperature typically leads to increased insertion loss, resulting in reduced power efficiency.

[0005] Electroacoustic resonator structures are sensitive to temperature increases because their stacked construction can be compromised, for example, through the acoustic migration of atoms.

[0006] In particular, the trend toward miniaturization has led to an increase in the number of functions while reducing size, resulting in an increase in power density. Increased power density usually leads to increased power dissipation density, which further compromises the miniaturization of electroacoustic structures. Summary of the Invention

[0007] Therefore, there is a need for a SAW resonator that has improved power endurance and heat resistance, prevents failures, and complies with specifications regarding temperature-induced frequency drift.

[0008] Therefore, a SAW resonator and an RF filter including the SAW resonator are provided according to embodiments of the present disclosure. Other embodiments provide preferred embodiments.

[0009] The SAW resonator includes a carrier substrate, an electrode structure, and a piezoelectric material disposed between the carrier substrate and the electrode structure. Further, the resonator includes a shunt path parallel to the electrode structure, configured to allow RF signals to bypass the electrode structure. The shunt path has temperature-dependent (electrical) conductivity. In this resonator, the electrode structure can be configured with interdigitated electrodes, each comprising electrode fingers disposed on the piezoelectric material and connected to a bus. Specifically, electrode fingers of opposite polarity are connected to opposite buses.

[0010] The carrier substrate serves as a carrier to support the corresponding functional structure disposed above the substrate. The piezoelectric material provides a piezoelectric axis, which, due to the piezoelectric effect, combines with the orientation of the electrode structure to switch between the RF signal and the acoustic wave when an RF signal is applied to the electrode structure.

[0011] The temperature dependence of the shunt path conductance provides the resonator with adequate functionality under normal operating parameters. Preferably, the shunt path conductance increases with increasing temperature. Therefore, at high temperatures, for example, above the critical temperature, the shunt path conductance is high enough to bypass RF power to protect the sensitive functional structure of the resonator.

[0012] Because the shunt path has temperature-dependent conductivity, this SAW resonator offers improved power endurance and heat resistance, and inherent fault protection. Therefore, this resonator can protect the corresponding RF filter or RF filter components from temperature-induced failures.

[0013] If this resonator is part of the RF filter in a mobile communication system, excessively high temperatures may cause temporary drops in phone calls or data transmission, and consequently, faster battery depletion. However, once the normal operating temperature is reached, permanent malfunctions are prevented, and normal functionality is restored without permanently damaging the device.

[0014] Therefore, a conductive path is introduced to temporarily act as a shunt path. This reduces self-heating and damage due to energy dissipation within sensitive structures (e.g., due to ohmic and acoustic losses) and prevents irreversible damage, thus providing inherent self-protection. The conductivity of the shunt path can be customized in a manner that provides the specified protection performance within a specified power and temperature range.

[0015] SAW resonators can also include reflective structures. The electrode structures of the resonator can be arranged between the reflective structures.

[0016] Reflective structures help confine acoustic energy within the resonator. They prevent acoustic energy from deviating from the resonator's acoustic path along the longitudinal direction. Furthermore, the reflective structure can be positioned near the electrode structure and connected to ground potential. Therefore, a grounded reflective structure can at least partially establish a shunt path.

[0017] The piezoelectric material may be contained within the piezoelectric layer, and the SAW resonator may be a TF-SAW resonator (TF-SAW = thin film surface acoustic wave).

[0018] The characteristic of TF-SAW resonators is that the piezoelectric material is not provided as a bulk material, as is the case with conventional SAW resonators, but rather as a thin film. The thin film material is characterized by being provided using wafer bonding techniques or thin film deposition techniques (e.g., sputtering, physical vapor deposition, chemical vapor deposition, molecular beam epitaxy, etc.).

[0019] TF-SAW resonators have the following characteristics: corresponding shunt paths can be introduced through simple construction devices, as explained further below.

[0020] SAW resonators may include protective elements. These protective elements have temperature-dependent conductivity and are components that establish shunt paths.

[0021] The protective element can be a separate circuit element specifically designed to provide a specific temperature dependence of conductivity.

[0022] However, protection elements can also be implemented using different structures of SAW resonators, which are designed to provide temperature dependence of conductivity.

[0023] Correspondingly, SAW resonators may have a stacked layer configuration. The electrode structures, contact structures, and other conductive structures that form the various parts of the signal line are arranged on a piezoelectric material. The conventional path of the resonator's RF power is to enter the resonator at the input electrode, pass through the resonator's functional structure, and exit the resonator at the output electrode. The main functional structure consists of electrode fingers arranged on the piezoelectric material.

[0024] In traditional SAW resonators, the material beneath the electrode structure is designed to have high resistivity in order to improve the resonator's insertion loss, particularly in the passband. Conversely, shunt paths can at least partially result in structures or layers beneath the electrode structure that are less intuitive in terms of the usual way SAW resonators are designed.

[0025] The carrier substrate may include silicon.

[0026] Silicon is a well-known material in the semiconductor device field and offers high purity and good crystallization facet quality.

[0027] SAW resonators can include a shunt layer between the carrier substrate and the piezoelectric material.

[0028] In particular, the shunt layer can have a temperature dependence on its conductivity, such that the shunt path of the SAW resonator passes at least partially through the shunt layer beneath the electrode structure.

[0029] The shunt layer may include polycrystalline silicon.

[0030] The conductivity of the shunt layer may be less than 10 at temperatures below 100°C. -3 The conductivity is 1 / Ωcm, while at temperatures above 200°C, it may be higher than 10. -3 1 / Ωcm.

[0031] Temperature dependence of shunt path conductance can be obtained through doping.

[0032] Two-dimensional electron gas may form a layer with parasitic surface conductance (PSC) within or at the interface of the shunt layer, providing optimal temperature dependence of conductivity. The properties of the charge carrier can be selected by means of doping or by choosing appropriate materials with suitable crystal structures.

[0033] SAW resonators can include a compensation layer between the carrier substrate and the piezoelectric material.

[0034] The compensation layer can be a temperature compensation layer, which is used to compensate for temperature-induced drift in characteristic frequencies.

[0035] If the temperature of a conventional SAW resonator changes, it modifies the material properties (such as the material's stiffness parameters and density), negatively impacting its size and wave velocity. This can cause frequency drift in characteristic frequencies, such as the passband center frequency or the frequency position on the passband sides.

[0036] To counteract these negative temperature-induced changes, a compensation layer is provided that has an inherent temperature dependence on the characteristic properties, enabling temperature compensation and reducing or even eliminating the total drift of the characteristic frequency.

[0037] The compensation layer may include a material selected from silicon oxide, doped silicon oxide, silicon dioxide, doped silicon dioxide, and fluorine-doped silicon dioxide.

[0038] The thickness of the compensation layer can be between 0.01λ and 1λ, where λ is the wavelength of the acoustic master mode of the resonator.

[0039] The thickness of the shunt layer can be between 0.01λ and 1λ.

[0040] While the piezoelectric material is located within the piezoelectric layer, the SAW resonator may include a shunt layer between the carrier substrate and the piezoelectric material. Therefore, this resonator is a TF-SAW resonator. Further, the resonator has a compensation layer between the shunt layer and the piezoelectric layer. The carrier substrate comprises silicon or is composed of silicon. The shunt layer comprises polycrystalline silicon and has a thickness between 0.01λ and 1.0λ. The compensation layer comprises silicon oxide and has a thickness between 0.01λ and 1.0λ. The piezoelectric layer comprises lithium tantalate and has a thickness between 0.01λ and 1.0λ. The electrode structure comprises aluminum as its main component and has a thickness between 0.02λ and 0.2λ. In this text, λ is the acoustic wavelength of the resonator's dominant mode.

[0041] Other materials besides lithium tantalate are also possible. Therefore, piezoelectric materials may include or be composed of lithium niobate, quartz, or similar materials.

[0042] The orientation of the carrier substrate (e.g., including silicon) is such that the Euler angles relative to the acoustic propagation direction of the resonator master mode are (0°±10°, 0°±10°, 45°±10°) or (45°±10°, 54°±10°, 0°±10°).

[0043] In this case, Euler angles (λ, μ, θ) are defined as follows: firstly, based on a set of axes x, y, z as the crystal axes of the substrate.

[0044] The first angle λ specifies the amount by which the x-axis and y-axis rotate about the z-axis, with the x-axis rotating in the direction of the y-axis. Therefore, a new set of axes x', y', and z' emerges, where z = z'.

[0045] In further rotation, the z' and y' axes rotate about the x' axis by an angle μ. In this case, the y' axis rotates along the z' axis. Therefore, a new set of axes x”, y”, z” appears, where x' = x”.

[0046] During the third rotation, the x” axis and y” axis rotate about the z” axis by an angle θ. In this case, the x” axis rotates along the y” axis. This results in a third set of axes x”’, y”’, z”’, where z” = z”’.

[0047] In this configuration, the x”' and y”' axes are parallel to the substrate surface. The z”' axis is the normal to the substrate surface. The x”' axis specifies the direction of sound wave propagation.

[0048] This definition conforms to the international standard IEC 62276, 2005 05, Annex A1.

[0049] As described above, an RF filter may include one or more SAW resonators.

[0050] RF filters can be configured in a trapezoidal shape, in which one or more series resonators are electrically connected in series in the signal path and one or more parallel resonators in the corresponding number of shunt paths electrically connect the signal path to ground.

[0051] Within an RF filter, a single SAW resonator can be protected from temperature-induced failure. However, two or more, or all, resonators are shunt via a shunt path. Attached Figure Description

[0052] The accompanying schematic diagram illustrates the main aspects of the SAW resonator or RF filter and details of a preferred embodiment.

[0053] In the attached diagram:

[0054] Figure 1 This illustrates the basic principle of the traffic splitting path;

[0055] Figure 2 The diagram illustrates the implementation of an RF filter;

[0056] Figure 3 The illustration shows the possibility of dedicated protective components;

[0057] Figure 4 The possible and preferred paths for traffic splitting are shown;

[0058] Figure 5 The diagram illustrates the equivalent circuit of the basic components arranged in a trapezoidal shape.

[0059] Figures 6 to 8 The diagram shows... Figure 5 The electrical properties of the basic structure shown are illustrated at different temperatures, thus demonstrating the conductivity configuration;

[0060] Figures 9 to 11 The diagram illustrates the reversible effect of temperature increase. Detailed Implementation

[0061] Figure 1This demonstrates the fundamental possibility of protecting electrode structures from permanent damage by utilizing the customized conductivity of the material beneath the electrode structure. The SAW resonator SAWR includes electrode structures ES, such as electrode fingers EF shown in the sagittal plane of the corresponding components. The electrode structure ES is disposed on a piezoelectric material PM contained within a piezoelectric layer PL. The piezoelectric material PM is disposed on a carrier substrate S. A shunt path follows a parallel conductive protection path PCPP from the electrode element before the electrode structure ES to a location after the electrode structure ES. Therefore, excess RF power can be shunt to protect the sensitive structure of the resonator.

[0062] Figure 2 The trapezoidal configuration of the RF filter is illustrated in a top perspective view. Three series resonators SR are electrically connected in series between the input port IN and the output port OUT. Further, three shunt paths, each including a parallel resonator PR, electrically connect the signal path to ground. The parallel conductance protection path PCPP establishes the possibility of conducting excess RF power directly from the input port IN to ground potential at higher temperatures, preventing permanent damage to the resonators.

[0063] Figure 3 The illustration illustrates the possibility of providing a dedicated protection element (PE) integrated into a parallel conductivity protection path (PCPP). The protection element has specific temperature-dependent conductivity characteristics. The protection element can be disposed on, above, or embedded beneath the surface of the piezoelectric material.

[0064] Figure 4 The illustration shows a preferred embodiment in which a shunt layer SL is provided between the carrier substrate S and the piezoelectric layer PL. The shunt layer has a thickness- and temperature-dependent conductivity to achieve the desired conductivity.

[0065] Optionally, the resonator has a compensation layer CL. The compensation layer can be disposed between the carrier substrate S and the piezoelectric layer PL. In particular, the compensation layer CL can be disposed between the shunt layer SL and the piezoelectric layer PL. However, the compensation layer CL can also be disposed between the carrier substrate S and the shunt layer SL.

[0066] Because the resistivity of the piezoelectric material, the compensation layer material, and the carrier substrate material is limited, other corresponding parallel shunt paths may exist. However, special dedicated shunt paths can be provided that carry most of the excess RF power, for example, 90% or more of the excess RF power that should be diverted around the sensitive structure.

[0067] Figure 5The equivalent circuit diagram of the basic element in a trapezoidal configuration is shown. A series resonator SR is connected in the signal path between the input port IN and the output port OUT of the basic element. Further, a parallel resonator PR is connected in the shunt path that electrically connects the signal path SP to ground. The environment of the corresponding resonators is modeled through a series configuration including a capacitor element CE, a resistor element RE, and another capacitor element CE. The series configuration is electrically paralleled to both the series and parallel resonators.

[0068] Figure 5 The equivalent circuit diagram shown is about Figures 6 to 11 The basis for consideration.

[0069] exist Figure 6 The matrix element S is shown in the figure. ij (Transmission: S) 21 and reflection: S 11 The figures also include the corresponding values ​​for power, current, and voltage. Specifically, curve 1 illustrates the insertion loss (S0). 21 Curve 2 illustrates the reflectance (S). 11 Curves 3 and 4 represent power loss P, where curve 3 represents the power loss in a series resonator and curve 4 represents the power loss in a parallel resonator.

[0070] exist Figure 6 The lower part of the diagram provides the corresponding values ​​for current (solid line) and voltage (dashed line). Curve 3 represents a series resonator, while curve 4 represents a parallel resonator. Figure 6 The features shown represent Figure 5 The low conductivity configuration of the shunt paths represented by the resistive and capacitive elements in the circuit. Therefore, Figure 6 The diagram illustrates the normal operating mode and normal operating temperature.

[0071] In comparison, Figure 7 The diagram illustrates the curves showing how increased temperature leads to an increase in the conductivity of the shunt paths around each resonator. It is clearly evident that power consumption is significantly reduced.

[0072] Furthermore, Figure 8 The diagram illustrates the characteristics under high-temperature conditions with high electrical conductivity. Power consumption is primarily zero, while the reflection coefficient is primarily equal to 100%.

[0073] Figure 9 The diagram illustrates the no-load circuit configuration at normal operating temperature (S). 21 ) and on-load circuit configuration (S' 21 Insertion loss in ).

[0074] In comparison, Figure 10 The diagram illustrates the configuration of the load circuit S' 21The insertion loss increases significantly, which is the same situation shown by the self-heating of the resonator leading to a temperature rise.

[0075] Furthermore, Figure 11 The diagram shows the insertion loss of the resonator after it has cooled down. It has largely recovered. Figure 9 The initial filter characteristics shown prevent permanent damage.

[0076] SAW resonators and RF filters are not limited to the details described above and shown in the figures. Resonators may include other components. In particular, the electrode structure may include a multi-layered construction that helps shape the dominant acoustic mode and helps suppress unwanted acoustic modes. RF filters may include other circuit elements, such as additional filter stages; in particular, resonator cascading is possible to further reduce stress on the resonators.

[0077] List of reference numerals

[0078] CE: Capacitor Components

[0079] CL: (Temperature) Compensation Layer

[0080] EF: Electrode finger

[0081] ES: Electrode Structure

[0082] GND: Grounding potential

[0083] IN: Input port

[0084] OUT: Output port

[0085] PCPP: Shunt path, parallel conductance protection path

[0086] PE: Protective component

[0087] PL: Piezoelectric layer

[0088] PM: Piezoelectric materials

[0089] PP: Parallel Path

[0090] PR: Parallel resonator

[0091] RE: Resistive element

[0092] S: Support substrate

[0093] SAWR: SAW resonator

[0094] SL: Streaming Layer

[0095] SP: Signal Path

[0096] SR: Series resonator

Claims

1. A surface acoustic wave (SAW) resonator, comprising: A carrier substrate, an electrode structure, and a piezoelectric material disposed between the carrier substrate and the electrode structure; as well as A shunt path is arranged and configured to have temperature-dependent conductivity, such that the RF signal at the input of the electrode structure can bypass the electrode structure according to the temperature of the shunt path.

2. The SAW resonator according to claim 1 further includes a reflective structure, wherein the electrode structure is arranged between the reflective structures.

3. The SAW resonator according to claim 1, wherein the piezoelectric material is contained in a piezoelectric layer, and the SAW resonator is a thin-film surface acoustic wave (TF-SAW) resonator.

4. The SAW resonator of claim 1 further includes a protection element, wherein the protection element is an element that establishes the shunt path.

5. The SAW resonator according to claim 1, wherein the carrier substrate comprises silicon.

6. The SAW resonator of claim 1 further includes a shunt layer between the carrier substrate and the piezoelectric material, the shunt layer forming at least a portion of the shunt path.

7. The SAW resonator of claim 6, wherein the shunt layer comprises polysilicon.

8. The SAW resonator of claim 6, wherein the piezoelectric material is located in the piezoelectric layer, and wherein the SAW resonator further comprises a compensation layer between the shunt layer and the piezoelectric layer.

9. The SAW resonator of claim 1, wherein the temperature-dependent conductivity of the shunt path is based on doping.

10. The SAW resonator according to claim 1, further comprising a compensation layer between the carrier substrate and the piezoelectric material.

11. The SAW resonator of claim 10, wherein the compensation layer comprises silicon oxide, doped silicon oxide, silicon dioxide, or doped silicon dioxide.

12. The SAW resonator according to claim 1, further comprising: A shunt layer is located between the carrier substrate and the piezoelectric material, wherein the piezoelectric material is located in the piezoelectric layer; as well as A compensation layer is located between the current shunt layer and the piezoelectric layer, wherein: The carrier substrate includes silicon. The shunt layer comprises polycrystalline silicon and has a thickness between 0.01λ and 1.0λ. The compensation layer comprises silicon oxide and has a thickness between 0.01λ and 1.0λ. The piezoelectric layer comprises lithium tantalate and has a thickness between 0.01λ and 1.0λ. The electrode structure comprises Al as its main component, and its thickness is between 0.02λ and 0.2λ. λ is the acoustic wavelength of the dominant mode of the SAW resonator.

13. The SAW resonator of claim 12, wherein the carrier substrate is oriented such that the Euler angles relative to the acoustic propagation direction of the main mode of the SAW resonator are (0°±10°, 0°±10°, 45°±10°) or (45°±10°, 54°±10°, 0°±10°).

14. An RF filter comprising a SAW resonator according to any one of claims 1 to 13.

15. A surface acoustic wave (SAW) resonator, comprising: A carrier substrate, an electrode structure, and a piezoelectric material disposed between the carrier substrate and the electrode structure; A shunt path, parallel to the electrode structure and provided to allow RF signals to bypass the electrode structure, wherein the shunt path has temperature-dependent conductivity; as well as The current shunt layer is located between the carrier substrate and the piezoelectric material.

16. The SAW resonator of claim 15, wherein the shunt layer comprises polysilicon.

17. The SAW resonator of claim 16, wherein the shunt layer: The conductivity is less than 10 at temperatures below 100°C. -3 1 / Ωcm; and The conductivity is greater than 10 at temperatures above 200°C. -3 1 / Ωcm.

18. The SAW resonator of claim 15, wherein the piezoelectric material is located in the piezoelectric layer, and wherein the SAW resonator further comprises a compensation layer between the shunt layer and the piezoelectric layer.

19. The SAW resonator of claim 15, wherein the shunt layer forms at least a portion of the shunt path.

20. The SAW resonator of claim 15, wherein the temperature-dependent conductance of the shunt path is at least partially based on the doping in the shunt layer.

Images