Radio frequency multiplexer

1. A radio frequency multiplexer, comprising:

a send circuit and a receive circuit, each comprising a filter circuit;

a first port to be coupled to an antenna, the send circuit and the receive circuit coupled to the first port;

a second port coupled to the send circuit;

a third port coupled to the receive circuit; and

a portion of the send circuit and a portion of the receive circuit disposed on a single monocrystalline substrate of a same die, wherein:

the send and receive circuits each comprises a multitude of resonators, at least one resonator of the send circuit and at least one resonator of the receive circuit being disposed on the single monocrystalline substrate; and

the send circuit comprises additional resonators disposed on another monocrystalline substrate separated from the single monocrystalline substrate.

2. The radio frequency multiplexer of claim 1 , wherein the send circuit comprises a resonator coupled to the first port and the receive circuit comprises a resonator coupled to the first port, wherein the resonators of the send and receive circuits coupled to the first port are disposed on the same single monocrystalline substrate.

3. The radio frequency multiplexer of claim 1 , wherein the send circuit comprises a series path that includes the at least one resonator of the send circuit and the receive circuit comprises a series path that includes the at least one resonator of the receive circuit.

4. The radio frequency multiplexer of claim 3 , wherein the send circuit comprises at least one parallel path connected to the series path and the at least one parallel path includes a resonator, wherein the resonator of the at least one parallel path of the send circuit is disposed on the single monocrystalline substrate.

5. The radio frequency multiplexer of claim 1 , wherein the additional resonators of the send circuit disposed on the other monocrystalline substrate are included in a series path of the send circuit and are configured to exhibit a temperature coefficient that is lower than the temperature coefficient of the resonators disposed on the single monocrystalline substrate.

6. The radio frequency multiplexer of claim 1 , wherein the filter circuit of the send circuit exhibits a passband and wherein the at least one resonator of the send circuit disposed on the single monocrystalline substrate is configured such that the filter circuit of the send circuit exhibits a high reflexion in a counter band outside the passband.

7. The radio frequency multiplexer of claim 3 , further comprising another send circuit and a fourth port connected to the other send circuit, the other send circuit comprising a series path that includes at least one resonator, wherein the at least one resonator of the send circuit and the at least one resonator of the other send circuit are coupled to different ones of the second and fourth ports.

8. The radio frequency multiplexer of claim 1 , wherein the resonators include a stack of layers disposed on the single monocrystalline substrate, wherein a thicknesses of the layers are the same within different ones of the resonators disposed on the single monocrystalline substrate.

9. The radio frequency multiplexer of claim 1 , wherein the resonators are surface acoustic wave resonators comprising an electrode including layers of different metals disposed on the single monocrystalline substrate and a dielectric layer covering the layers of different metals, wherein thicknesses of the layers of different metals and a thickness of the dielectric layer of the resonators disposed on the single monocrystalline substrate are the same within different resonators.

10. The radio frequency multiplexer of claim 9 , wherein the dielectric layer is a layer of silicon dioxide.

11. The radio frequency multiplexer of claim 1 , wherein the resonators are surface acoustic wave resonators comprising a metal electrode covered by a dielectric layer, wherein a thicknesses of the dielectric layer of the resonators disposed on the single monocrystalline substrate and of the dielectric layer of the resonators disposed on the other monocrystalline substrate are substantially different.

12. The radio frequency multiplexer of claim 1 , wherein the resonators are bulk acoustic wave resonators comprising a piezoelectric layer sandwiched between electrodes disposed on the single monocrystalline substrate, wherein a thicknesses of layers of the bulk acoustic wave resonators disposed on the single monocrystalline substrate are the same within different resonators.

13. The radio frequency multiplexer of claim 9 , wherein the dielectric layer is a layer of silicon dioxide and the single monocrystalline substrate is a monocrystalline piezoelectric substrate or a monocrystalline silicon substrate.