Radio frequency isolation using substrate opening

1. A method for fabricating a radio-frequency device, the method comprising:

providing a field-effect transistor formed over an oxide layer formed on a substrate layer;

removing at least a portion of the substrate layer to form an opening exposing at least a portion of a backside of the oxide layer, the opening being positioned to enhance radio-frequency performance for one or more components of the radio-frequency device; and

applying a cap layer over the opening to form an air-filled cavity between the backside of the oxide layer and the cap layer.

2. The method of claim 1 further comprising thinning the substrate layer prior to said removing the at least a portion of the substrate layer.

3. The method of claim 1 wherein the cap layer has visual markings thereon to assist with laser marking.

4. The method of claim 1 wherein the cap layer includes an adhesive tape layer.

5. The method of claim 1 wherein the cap layer includes a plastic lid structure.

6. The method of claim 1 wherein the cap layer includes an additional replacement substrate layer.

7. The method of claim 1 further comprising at least partially filling the opening with a dielectric filler.

8. The method of claim 7 wherein the cap layer is applied to the dielectric filler.

9. The method of claim 1 further comprising applying a handle wafer to the radio-frequency device to provide mechanical stability for the radio-frequency device.

10. A radio-frequency device comprising:

a field-effect transistor implemented over an oxide layer;

a patterned semiconductor substrate layer on which the oxide layer is formed, the substrate layer including a backside trench defined at least in part by side wall portions of the substrate layer;

a cap layer disposed over the backside trench and forming an air-filled cavity between the oxide layer and the cap layer; and

one or more electrical connections connected to the field-effect transistor.

11. The radio-frequency device of claim 10 wherein the substrate layer is a thinned substrate layer.

12. The radio-frequency device of claim 10 wherein the cap layer has visual markings thereon to assist with laser marking.

13. The radio-frequency device of claim 10 further comprising dielectric filler material disposed within the trench.

14. The radio-frequency device of claim 13 further comprising a dielectric layer disposed on a backside of the substrate layer.

15. A wireless device comprising:

a transceiver configured to process radio-frequency signals;

a radio-frequency module in communication with the transceiver, the radio-frequency module including a switching device having a field-effect transistor implemented over an oxide layer and a patterned semiconductor substrate layer including an opening defined at least in part by a side wall of the substrate layer and a portion of a backside of the oxide layer, the switching device further including a cap layer disposed over the opening to form an air-filled cavity between the oxide layer and the cap layer, the switching device further including one or more electrical connections connected to the field-effect transistor; and

an antenna in communication with the radio-frequency module, the antenna configured to facilitate transmitting and/or receiving of the radio-frequency signals.

16. The wireless device of claim 15 wherein the substrate layer is a thinned substrate layer.

17. The wireless device of claim 15 wherein the cap layer has visual markings thereon to assist with laser marking.

18. The wireless device of claim 15 further comprising dielectric filler contained within the opening.

19. The wireless device of claim 18 further comprising a dielectric layer disposed on a backside of the substrate layer.