Field-effect transistor devices having proximity contact features

1. A radio-frequency (RF) device comprising:

an insulator layer;

a field-effect transistor (FET) having terminals for a gate, a source, and a drain, the FET implemented on an active silicon layer formed over the insulator layer;

a substrate layer implemented under the insulator layer; and

a proximity electrode implemented to extend at least partially through the insulator layer, and positioned to be laterally offset from a nearest edge of the FET by an offset distance that is less than 5 μm, the proximity electrode configured to receive a voltage and generate an electric field between the proximity electrode and a region generally underneath the FET.

2. The RF device of claim 1 further comprising an electrical connection implemented to provide a signal to the proximity electrode to adjust an operating condition of the FET.

3. The RF device of claim 1 further comprising a substrate contact feature implemented to provide an electrical connection to the substrate layer.

4. The RF device of claim 3 wherein the substrate contact feature is positioned to be laterally spaced from the FET by a distance greater than or equal to 5 μm.

5. The RF device of claim 1 wherein the offset distance is less than or equal to 4 μm.

6. The RF device of claim 5 wherein the offset distance is less than or equal to 2 μm.

7. The RF device of claim 1 wherein the proximity electrode is configured to extend through the insulator layer and contact at least a portion of the substrate layer.

8. The RF device of claim 1 further comprising an interface layer implemented between the substrate layer and the insulator layer.

9. The RF device of claim 8 wherein the interface layer includes a trap-rich layer.

10. The RF device of claim 9 wherein the proximity electrode is configured to extend through the insulator layer but not the trap-rich layer.

11. The RF device of claim 9 wherein the proximity electrode is configured to extend through the insulator layer and the trap-rich layer.

12. The RF device of claim 1 wherein the substrate layer includes a plurality of doped regions having amorphous and high resistivity properties.

13. The RF device of claim 12 wherein the proximity electrode is configured to extend through the insulator layer but not the doped regions.

14. The RF device of claim 12 wherein the proximity electrode is configured to extend through the insulator layer and the doped regions.

15. The RF device of claim 1 wherein the substrate layer is a silicon handle layer.

16. The RF device of claim 1 wherein the insulator layer includes a buried oxide (BOX) layer.

17. A radio-frequency (RF) module comprising:

a packaging substrate configured to receive a plurality of devices; and

a switching device mounted on the packaging substrate, the switching device including a field-effect transistor (FET) having terminals for a gate, a source, and a drain, the FET implemented on an active silicon layer formed over an insulator layer and a substrate layer implemented under the insulator layer, the switching device further including a proximity electrode implemented to extend at least partially through the insulator layer, and positioned to be laterally offset from a nearest edge of the FET by an offset distance that is less than 5 μm, the proximity electrode configured to receive a voltage and generate an electric field between the proximity electrode and a region generally underneath the FET.

18. The RF module of claim 17 wherein the RF module is a switch module.

19. The RF module of claim 17 wherein the substrate layer is part of a silicon-on-insulator (SOI) substrate.

20. A wireless device comprising:

a transceiver configured to process radio-frequency (RF) signals;

an RF module in communication with the transceiver, the RF module including a switching device having a field-effect transistor (FET) having terminals for a gate, a source, and a drain, the FET implemented on an active silicon layer formed over an insulator layer and a substrate layer implemented under the insulator layer, the switching device further including a proximity electrode implemented to extend at least partially through the insulator layer, and positioned to be laterally offset from a nearest edge of the FET by an offset distance that is less than 5 μm, the proximity electrode configured to receive a voltage and generate an electric field between the proximity electrode and a region generally underneath the FET; and

an antenna in communication with the RF module, the antenna configured to facilitate transmitting or receiving of the RF signals.