Varactor device with backside contact

1. An apparatus comprising:

a substrate;

a first insulator layer;

a first contact, wherein the first insulator layer is disposed between the first contact and the substrate;

a second insulator layer in contact with the substrate; and

a second contact that extends at least partially through the second insulator layer, wherein the substrate is disposed between the second insulator layer and the first insulator layer, and wherein the substrate includes a first doped region, a second doped region, and a signal path region between the first doped region and the second doped region.

2. The apparatus of claim 1 , further comprising:

a third contact, the first doped region disposed between the third contact and the second insulator layer, wherein a capacitance associated with the signal path region is adjustable based on a bias voltage applied to the third contact; and

a fourth contact, the second doped region disposed between the fourth contact and the second insulator layer.

3. The apparatus of claim 2 , wherein the bias voltage is configured to cause a change in a width of a depletion region of the substrate.

4. The apparatus of claim 2 , wherein the fourth contact is configured to receive the bias voltage to adjust a width of a second depletion region of the substrate.

5. The apparatus of claim 1 , wherein the substrate, the first insulator layer, the first contact, the second insulator layer, and the second contact are included in a varactor device.

6. The apparatus of claim 1 , wherein the first doped region comprises a p-type region, and wherein the second doped region comprises an n-type region.

7. The apparatus of claim 1 , wherein the first doped region and the second doped region each comprise an n-type region.

8. The apparatus of claim 1 , wherein the first contact is configured to receive a radio-frequency (RF) signal.

9. The apparatus of claim 1 , wherein the first insulator layer is comprised of a dielectric material.

10. The apparatus of claim 1 , wherein the second contact comprises a backside contact that is disposed on a backside of the substrate.

11. The apparatus of claim 1 , wherein the substrate comprises silicon, wherein the substrate comprises a silicon on insulator (SOI) structure, and wherein the second contact is a backside contact extending through an insulator of the SOI structure.

12. The apparatus of claim 1 , further comprising a die, wherein the die comprises the first contact and the second contact.

13. The apparatus of claim 12 , further comprising a device that includes a mobile device, a computer, a set top box, a music player, a video player, an entertainment unit, a navigation device, a communications device, a personal digital assistant (PDA), or a fixed location data unit, wherein the die is integrated within the device.

14. The apparatus of claim 1 , wherein the first contact is configured to receive a signal, and wherein the second contact is configured to receive the signal from the first contact via a signal path.

15. The apparatus of claim 14 , wherein the signal comprises a radio frequency (RF) signal, and wherein the second contact is configured to generate a filtered version of the RF signal.

16. The apparatus of claim 15 , wherein a capacitance of a capacitive region is based on a width of a first depletion region of the substrate, and further comprising a third contact, the third contact configured to receive a bias voltage to adjust the width of the first depletion region.

17. The apparatus of claim 16 , further comprising a fourth contact, the fourth contact configured to receive the bias voltage to adjust a width of a second depletion region of the substrate.

18. The apparatus of claim 17 , wherein the capacitance is based further on the width of the second depletion region.

19. An apparatus comprising:

means for forming a capacitive region;

first means for inhibiting a flow of charge carriers;

means for providing a first signal, wherein the first means for inhibiting the flow of charge carriers is positioned between the means for providing the first signal and the means for forming a capacitive region;

second means for inhibiting a flow of charge carriers, the second means for inhibiting the flow of charge carriers in contact with the means for forming the capacitive region; and

means for receiving a second signal, the means for receiving the second signal extending at least partially through the second means for inhibiting the flow of charge carriers, wherein the means for forming the capacitive region is disposed between the first means for inhibiting the flow of charge carriers and the second means for inhibiting the flow of charge carriers, and wherein the means for forming the capacitive region includes a first doped region, a second doped region, and a signal path region between the first doped region and the second doped region.

20. The apparatus of claim 19 , wherein the means for providing the first signal comprises a front-side contact, and wherein the means for receiving the second signal comprises a backside contact.

21. The apparatus of claim 19 , further comprising means for biasing using a bias voltage, wherein a capacitance of the capacitive region is based on the bias voltage.

22. The apparatus of claim 21 , wherein the means for biasing includes a third contact.

23. The apparatus of claim 22 , wherein the means for biasing further includes a fourth contact.

24. The apparatus of claim 19 , wherein the means for providing and the means for receiving are integrated within a mobile device.

25. An apparatus comprising:

a substrate having a first side and an opposite second side;

a first contact of a varactor device spaced from the first side of the substrate;

an insulator layer disposed on the second side of the substrate; and

a second contact of the varactor device, the second contact extending at least partially through the insulator layer and in physical contact with the substrate, wherein the substrate includes a first doped region, a second doped region, and a signal path region between the first doped region and the second doped region.

26. The apparatus of claim 25 , further comprising:

a third contact, the first doped region disposed between the third contact and the insulator layer; and

a fourth contact, the second doped region disposed between the fourth contact and the insulator layer.

27. The apparatus of claim 25 , further comprising a die, wherein the die comprises the first contact and the second contact.

28. The apparatus of claim 27 , further comprising a device that includes a mobile device, a computer, a set top box, a music player, a video player, an entertainment unit, a navigation device, a communications device, a personal digital assistant (PDA), or a fixed location data unit, wherein the die is integrated within the device.

29. An apparatus comprising:

a substrate;

a first contact of a varactor device;

a second contact of the varactor device, wherein the first contact and the second contacts are disposed on opposite sides of the substrate, and wherein the second contact extends through an insulator layer and is in physical contact with the substrate;

a third contact of the varactor device coupled to the substrate, the third contact configured to receive a bias voltage; and

a fourth contact of the varactor device, the fourth contact coupled to the third contact, the fourth contact configured to receive the bias voltage.

30. The apparatus of claim 29 , further comprising:

a signal path between the first contact and the second contact; and

a silicon on insulator (SOI) structure that includes an insulator layer and the substrate, wherein the substrate comprises silicon, and wherein the second contact extends through the insulator layer.