BAW resonator with improved power durability and heat resistance and RF filter comprising a BAW resonator

Abstract

A BAW resonator (BAWR) with improved power durability and improved heat resistance is provided. The resonator comprises a layer stack with a piezoelectric material (PM) between a bottom electrode (ELI) and a top electrode (EL2) and a shunt path parallel (PCPP) to the layer stack provided to enable an RF signal to bypass the layer stack, e.g. to ground (GND). The shunt path (PCPP) has a temperature dependent conductance with a negative temperature coefficient, NTC, of resistance. When the temperature of the device rises due to high power operation, currents that would otherwise permanently damage the device are shunted to ground or another dedicated terminal by the temperature dependent shunt path. Upon cooling down normal operation is resumed.

Claims

1. A bulk acoustic wave (BAW) resonator, comprising: a layer stack with a bottom electrode, a top electrode and a piezoelectric material between the bottom electrode and the top electrode; and a shunt path, parallel to the layer stack, connecting a ground potential to at least one of the top electrode or the bottom electrode, wherein the shunt path has a temperature dependent conductance configured to enable a radio frequency (RF) signal to bypass the layer stack or permit the RF signal to be input into the layer stack depending on a temperature of the shunt path.

2. The BAW resonator of claim 1, further comprising an acoustic mirror below the bottom electrode, wherein the acoustic mirror establishes an element of the shunt path.

3. The BAW resonator of claim 1, wherein: the BAW resonator is arranged on a carrier substrate, and the carrier substrate establishes an element of the shunt path.

4. The BAW resonator of claim 1, further comprising a protection element, wherein the protection element establishes an element of the shunt path.

5. The BAW resonator of claim 1, wherein the BAW resonator is arranged on a carrier substrate comprising Silicon.

6. The BAW resonator of claim 5, wherein the Silicon is doped Silicon.

7. The BAW resonator of claim 6, wherein the doped Silicon has a conductivity below 10-3 1/Ω cm at temperatures below 100° C. and a conductivity above 10-3 1/Ω cm at temperatures above 200° C.

8. The BAW resonator of claim 1, wherein a Silicon Oxide layer is arranged between the bottom electrode and a carrier substrate.

9. The BAW resonator of claim 8, wherein the Silicon Oxide layer has a thickness between 100 nm and 600 nm.

10. The BAW resonator of claim 1, wherein the temperature dependent conductance of the shunt path is configured to: enable the RF signal to bypass the layer stack when the temperature of shunt path exceeds a temperature threshold; and permit the RF signal to be input into the layer stack when the temperature of the shunt path is less than or equal to the temperature threshold.

11. The BAW resonator of claim 1, wherein the shunt path comprises a section with a doping level different from a surrounding of the section.

12. A radio frequency (RF) filter, comprising: a bulk acoustic wave (BAW) resonator, the BAW resonator comprising: a layer stack with a bottom electrode, a top electrode and a piezoelectric material between the bottom electrode and the top electrode; and a shunt path, parallel to the layer stack, connecting a ground potential to at least one of the top electrode or the bottom electrode, wherein the shunt path has a temperature dependent conductance configured to enable an RF signal to bypass the layer stack or permit the RF signal to be input into the layer stack depending on a temperature of the shunt path.

13. The RF filter of claim 12, comprising an acoustic mirror below the bottom electrode, wherein the acoustic mirror establishes an element of the shunt path.

14. The RF filter of claim 12, wherein: the BAW resonator is arranged on a carrier substrate, and the carrier substrate establishes an element of the shunt path.

15. The RF filter of claim 12, further comprising a protection element, wherein the protection element establishes an element of the shunt path.

16. The RF filter of claim 12, wherein the BAW resonator is arranged on a carrier substrate comprising Silicon.

17. The RF filter of claim 16, wherein the Silicon is doped Silicon, and the doped Silicon has a conductivity below 10-3 1/Ω cm at temperatures below 100° C. and a conductivity above 10-3 1/Ω cm at temperatures above 200° C.

18. The RF filter of claim 12, wherein the shunt path comprises a section with a doping level different from a surrounding of the section.

19. The RF filter of claim 12, wherein a Silicon Oxide layer is arranged between the bottom electrode and a carrier substrate.

20. The RF filter of claim 19, wherein the Silicon Oxide layer has a thickness between 100 nm and 600 nm.

Description

(1) In the figures:

(2) FIG. 1 shows a basic embodiment of a BAW resonator;

(3) FIG. 2 shows the possibility of utilizing an acoustic mirror;

(4) FIG. 3 illustrates the application within a ladder-type like topology;

(5) FIG. 4 illustrates the connection of series resonators in the signal path;

(6) FIG. 5 illustrates the use of a dielectric material;

(7) FIG. 6 illustrates the use of a protection element;

(8) FIG. 7 illustrates an equivalent circuit diagram of a ladder-type like topology used to illustrate different effects;

(9) FIG. 8 shows the forward transmission of a corresponding RF filter at a usual temperature;

(10) FIGS. 9 and 10 show the influence of a parallel RC element as a thermal loss component on a single series resonator; and

(11) FIGS. 11 to 17 show insertion losses for different resistance and capacitance values.

(12) FIG. 1 shows a basic embodiment of a BAW resonator BAWR on a carrier substrate S. The BAW resonator comprises a bottom electrode EL1, a top electrode EL2 and a piezoelectric layer with a piezoelectric material PM sandwiched between the bottom electrode and the top electrode. The sandwich construction is arranged on the carrier substrate S. The environment of the resonator BAWR and in particular the environment's temperature dependence of conductance is chosen such that a parallel conductance protection path PCPP is obtained that can shunt unwanted RF power bypassing the layer stack.

(13) FIG. 2 illustrates the possibility of utilizing an acoustic mirror between the sandwich construction and the carrier substrate S. In particular, the acoustic mirror AM comprises a plurality of layers with a low acoustic impedance LIL and layers of a high acoustic impedance HIL stacked iteratively one above the other. Generally, the materials with the high acoustic impedance HIL comprise a metal that has a high conductance. The material of the layer of the low acoustic impedance LIL is chosen—at least along the parallel conductance protection path PCPP indicated by the arrow—such that the corresponding protection function is obtained.

(14) FIG. 3 illustrates a top view onto a plurality of resonators, SR, PR arranged on the carrier substrate S. Series resonators SR are electrically connected in series in the signal path between an input port IN and an output port OUT. Parallel resonators PR in corresponding parallel paths electrically connect the signal path to ground GND. At least one resonator, e.g. a series resonator SR or a parallel resonator PR or a plurality of resonators are shunted at corresponding temperatures via the parallel conductance protection path PCPP. It is possible that the parallel conductance protection path directly conducts an excess of RF power from the input port IN to ground GND. This is possible, e.g., by arranging the signal lines in contact with the carrier substrate S such that the corresponding temperature dependent conductance is obtained.

(15) FIG. 4 shows the possibility of arranging a plurality of BAW resonators BAWR, e.g. series resonators as shown in FIG. 3, on the carrier substrate S such that the carrier substrate S is at least in direct contact with one segment of the signal path, e.g. an external contact EC at one section and at another section. Thus, via the parallel conductance protection path PCPP an excess of RF power can be directly conducted between the external connections EC.

(16) FIG. 5 illustrates the possibility of the use of a dielectric material DM. A dielectric material DM that has a temperature independent and low conductance can be used to electrically isolate one or a plurality of resonators from a direct contact to the parallel conductance protection path PCPP.

(17) FIG. 6 shows the possibility of using a dedicated protection element PE arranged at a specific position on a carrier substrate S together with signal lines electrically connecting the protection element PE to the signal path and to a ground potential, e.g. via a conducting structure CS.

(18) The protection element PE has a material chosen such that the wanted temperature dependent conductance is obtained. To that end, the protection element can have a piece of doped silicon, for example. Other materials such as gallium arsenide (GaAs) are also possible.

(19) The arrows in FIG. 6 indicate the direction of wanted RF signals parallel to the signal path and the direction of unwanted RF signals parallel to the shunt path where the filter functionality ensures that unwanted signals are not provided at the output of the filter.

(20) FIG. 7 shows an equivalent circuit diagram of a ladder-type like topology comprising three series resonators and three shunt resonators in corresponding shunt paths. Parallel to each resonator is a parallel connection of a resistance element and a capacitance element. The equivalent circuit diagram shown in FIG. 7 is utilized to determine preferred material values to determine the temperature dependent conductance of the parallel conductance protection path.

(21) FIG. 8 illustrates the insertion loss of the topology of FIG. 7 of normal operating parameters. It can be seen that in a passband having 1.96 GHz as a center frequency, the insertion loss is very low.

(22) FIG. 9 illustrates the response of a single resonator to varying temperatures of the parallel conductance protection path. For example FIG. 9 illustrates a decrease of insertion loss at the anti-resonance frequency for decreasing temperatures. With decreasing temperatures the temperature dependent resistance R decreases, this degrades the quality factor at the anti-resonance frequency.

(23) Similarly to FIG. 9 FIG. 10 illustrates a degradation of the coupling factor when the capacitance parallel to the resonator as shown in the equivalent circuit diagram of FIG. 8 increases with temperature and causes a frequency shift.

(24) FIG. 11 shows an increase in insertion loss with increased temperatures. The different curves in FIG. 11 correspond to simulated resistance values of the parallel conductance protection path (5000 ohms, 2000 ohms, 1000 ohms, 500 ohms, 200 ohms, 100 ohms).

(25) Similarly, FIGS. 12 to 17 show an increase in insertion loss with a decrease in resistance (5000 ohms, 2000 ohms, 1000 ohms, 500 ohms, 200 ohms, 100 ohms) while the capacity of the parallel capacitance element of the protected resonator is increased from 0 picofarad (FIG. 11) to 0.1 pF (FIG. 12), 0.2 pF (FIG. 13), 0.5 pF (FIG. 14), 1 pF (FIG. 15), 2 pF (FIG. 16) and finally 5 pF (FIG. 17).

(26) Thus, a self-protection system for BAW resonators and filters employing BAW resonators that does not need additional control circuitry is provided.

(27) The BAW resonator and the RF filter are not limited to the details and embodiments described above and shown in the figures. Resonators can comprise further layers and structures, e.g. for establishing preferred acoustic modes.

(28) RF filters can comprise further resonating or non-resonating circuit elements.

(29) In particular, conventional means to improve power durability and heat resistance, such as cascading resonators, are also possible.

LIST OF REFERENCE SIGNS

(30) AM: acoustic mirror BAWR: BAW resonator CS: conducting structure EC: external contact EL1: bottom electrode EL2: top electrode f: frequency GND: ground HIL: layer of a high acoustic impedance IL: insertion loss IN: input port LIL: layer of a low acoustic impedance OUT: output port PCPP: parallel conductance protection path PE: protection element PM: piezoelectric material PR: parallel resonator S: carrier substrate SL: signal line SR: series resonator