Transistor with workfunction-induced charge layer

• US 6,891,234 B1
• Filed: 04/26/2004
• Issued: 05/10/2005
• Est. Priority Date: 01/07/2004
• Status: Active Grant

• Current Assignee: Acorn Semi, LLC (Acorn Technologies, Inc.)
• Original Assignee: Acorn Technologies, Inc.
• Inventors: Grupp, Daniel E., Connelly, Daniel J., Faulkner, Carl
• Primary Examiner(s): Crane, Sara
• Application Number:
  US10/832,576
• Time in Patent Office: 379 Days
• Field of Search: 257/407, 257/344, 257/408, 257/412
• US Class Current: 257/407
• CPC Class Codes: H01L 29/0847 of field-effect transistors with insulated gate H01L29/0653 takes precedence; with a passive supplementary region between source or drain and substrate related to punch-through, capacity or isolation phenomena H01L29/1079; with LDD or DDD structure H01L29/7833; for thin film transistors H01L29/78618
• CPC Class Codes: H01L 29/41725 Source or drain electrodes for field effect devices with monocrystalline semiconductor on source/drain region H01L29/0843
• CPC Class Codes: H01L 29/4983 with a lateral structure, e.g. a Polysilicon gate with a lateral doping variation or with a lateral composition variation or characterised by the sidewalls being composed of conductive, resistive or dielectric material
• CPC Class Codes: H01L 29/66643 with source or drain regions formed by a Schottky barrier or a conductor-insulator-semiconductor structure
• CPC Class Codes: H01L 29/7831 with multiple gate structure FinFETs or MuGFETs H01L29/7855, thin film transistors H01L29/78645

Abstract

An electrical switching device includes a semiconductor having a channel therein which is proximate to at least on channel tap in an extension region and also to a gate. A conductor (e.g., a metal) is disposed proximate to the extension region but is electrically isolated from both the extension region and the gate (e.g., through the use of one or more insulators). The conductor has a workfunction outside of the bandgap of a semiconductor in the extension region and therefore includes a layer of charge in the extension region. The magnitude and polarity of this layer of charge is controlled through selection of the metal, the semiconductor, and the insulator.

Claims

1. A transistor, comprising a layer of induced charge in a conduction path between a semiconductor channel and a channel tap, the conduction path being proximate to a conductor locally insulated from the layer of induced charge, which conductor is further insulated from a gate of the transistor and possesses a workfunction outside of a bandgap of a semiconductor in a region of the transistor in which the charge is induced.

2. The transistor of claim 1, wherein conductivity between the semiconductor channel and the channel tap is enhanced by at least approximately 10% relative to a reference case where the conductor has a workfunction within or at a boundary of the bandgap of the semiconductor in the region of induced charge.

3. The transistor of claim 1, wherein the channel tap comprises a doped source/drain contact.

4. The transistor of claim 1, wherein the channel tap comprises a metal source/drain contact.

5. The transistor of claim 1, wherein the channel tap comprises a Schottky source/drain contact.

6. The transistor of claim 3, wherein the semiconductor channel is made of a semiconductor selected from a list comprising:

Si, Ge, C, or alloys of Si, Ge and/or C.

7. The transistor of claim 3, wherein the semiconductor channel is made of a semiconductor selected from a list comprising:

a compound of Group IIIA and Group VA elements, an alloy of Group IIIA and Group VA elements, a compound of Groups IIA-B and Group VIA elements, an alloy of Groups IIA-B and Group VIA elements, a compound of Groups IIA-B, Group IIIA, Group IVA, Group VA, and/or Group VIA elements, or an alloy of Groups IIA-B, Group IIIA, Group IVA, Group VA, and/or Group VIA elements.

8. The transistor of claim 3, wherein the semiconductor channel is made of a semiconducting polymer, fulleride, or other molecular carbon-based material.

9. The transistor of claim 5, wherein the semiconductor channel is made of a semiconductor selected from a list comprising:

Si, Ge, C, or alloys of Si, Ge and/or C.

10. The transistor of claim 5, wherein the semiconductor channel is made of a semiconductor selected from a list comprising:

a compound of Group IIIA and Group VA elements, an alloy of Group IIIA and Group VA elements, a compound of Groups IIA-B and Group VIA elements, an alloy of Groups IIA-B and Group VIA elements, a compound of Groups IIA-B, Group IIIA, Group IVA, Group VA, and/or Group VIA elements, or an alloy of Groups IIA-B, Group IIIA, Group IVA, Group VA, and/or Group VIA elements.

11. The transistor of claim 5, wherein the semiconductor channel is made of a semiconducting polymer, fulleride, or other molecular carbon-based material.

12. The transistor of claim 1, wherein the conductor is electrically connected to the channel tap.

13. The transistor of claim 3, wherein the conductor is electrically connected to the channel tap.

14. The transistor of claim 5, wherein the conductor is electrically connected to the channel tap.

15. The transistor of claim 6, wherein the conductor is electrically connected to the channel tap.

16. The transistor of claim 7, wherein the conductor is electrically connected to the channel tap.

17. The transistor of claim 8, wherein the conductor is electrically connected to the channel tap.

18. The transistor of claim 9, wherein the conductor is electrically connected to the channel tap.

19. The transistor of claim 10, wherein the conductor is electrically connected to the channel tap.

20. The transistor of claim 10, wherein the conductor is electrically connected to the channel tap.

21. The transistor of any of claims 1, or 3-20 inclusive, wherein the conductor has a workfunction no greater than 0.2 volts below an electron affinity of the semiconductor in the region of the transistor in which the charge is induced.

22. The transistor of any of claims 1, or 3-20 inclusive, wherein the conductor has a workfunction no greater than 0.4 volts below an electron affinity of the semiconductor in the region of the transistor in which the charge is induced.

23. The transistor of any of claims 1, or 3-20 inclusive, wherein the conductor has a workfunction no greater than 0.8 volts below an electron affinity of the semiconductor in the region of the transistor in which the charge is induced.

24. The transistor of any of claims 1, or 3-20 inclusive, wherein the conductor has a workfunction no greater than 1.6 volts below an electron affinity of the semiconductor in the region of the transistor in which the charge is induced.

25. The transistor of any of claims 1, or 3-20 inclusive, wherein the conductor has a workfunction no less than 0.2 volts more than a bandgap greater than an electron affinity of the semiconductor in the region of the transistor in which the charge is induced.

26. The transistor of any of claims 1, or 3-20 inclusive, wherein the conductor has a workfunction no less than 0.4 volts more than a bandgap greater than an electron affinity of the semiconductor in the region of the transistor in which the charge is induced.

27. The transistor of any of claims 1, or 3-20 inclusive, wherein the conductor has a workfunction no;

less than 0.8 volts more than a bandgap greater than an electron affinity of the semiconductor in the region of the transistor in which the charge is induced.

28. The transistor of any of claims 1, or 3-20 inclusive, wherein the conductor has a workfunction no less than 1.6 volts more than a bandgap greater than an electron affinity of the semiconductor in the region of the transistor in which the charge is induced.

29. The transistor of any of claims 1, or 3-20 inclusive, wherein a first insulator which separates the conductor from the layer of induced charge has a first thickness less than or approximately equal to twice a second thickness of a second insulator which separates the gate from the semiconductor channel.

30. The transistor of any of claims 1, or 3-20 inclusive, wherein a first insulator which separates the conductor from the layer of induced charge has a first per-area capacitance greater than or approximately equal to half a second per-area capacitance of a second insulator which separates the gate from the semiconductor channel.

31. The transistor of any of claims 1, or 3-20 inclusive, wherein the conductor is a metal consisting primarily of one or more rare earth elements, as determined by atomic fraction.

32. The transistor of any of claims 1, or 3-20 inclusive, wherein the conductor is Er, or an alloy of primarily Er, as determined by atomic fraction.

33. The transistor of any of claims 1, or 3-20 inclusive, wherein the conductor is Yb, or an alloy of primarily Yb, as determined by atomic fraction.

34. The transistor of any of claims 1, or 3-20 inclusive, wherein the conductor is Mg, or an alloy of primarily Mg, as determined by atomic fraction.

35. The transistor of any of claims 1, or 3-20 inclusive, wherein the conductor is Pt, or an alloy of primarily Pt, as determined by atomic fraction.

36. The transistor of any of claims 1, or 3-20 inclusive, wherein the conductor is Ir or an alloy of primarily Ir, as determined by atomic fraction.

37. The transistor of any of claims 1, or 3-20 inclusive, wherein the conductor is a degenerately-doped n-type semiconductor.

38. The transistor of any claims 1, or 3-20 inclusive, wherein the conductor is a degenerately-doped p-type semiconductor.

39. The transistor of any claims 1, or 3-20 inclusive, wherein the conductor is configured to induce strain in the region of the transistor in which the charge is formed.

40. A device of claim 39, wherein the induced strain enhances effective carrier mobility in the region of the transistor in which the charge is formed.

41. A method, comprising inducing a layer of charge in a conduction path of a transistor between a semiconductor channel and a channel tap, the conduction path being proximate to a conductor locally insulated from the layer of induced charge and from a gate of the transistor, the conductor possessing a workfunction outside of a bandgap of a semiconductor in a region of the transistor in which the charge is induced.