# Patent

## Title
Metal-free integrated circuits comprising graphene and carbon nanotubes

## Abstract

An integrated circuit includes a graphene layer, the graphene layer comprising a region of undoped graphene, the undoped graphene comprising a channel of a transistor, and a region of doped graphene, the doped graphene comprising a contact of the transistor; and a gate of the transistor, the gate comprising a carbon nanotube film. A method of fabricating an integrated circuit comprising graphene and carbon nanotubes, includes forming a graphene layer; doping a portion of the graphene layer, resulting in doped graphene and undoped graphene; forming a carbon nanotube film; and etching the carbon nanotube film to form a gate of a transistor, wherein the transistor further comprises a channel comprising the undoped graphene and a contact comprising the doped graphene. A transistor includes a gate, the gate comprising a carbon nanotube film; a channel, the channel comprising undoped graphene; and a contact, the contact comprising doped graphene.

## Background
FIELD OF INVENTION
This disclosure relates generally to the field of semiconductor chip fabrication.
BACKGROUND OF RELATED ART
In semiconductor chips comprising complementary metal oxide on semiconductor (CMOS) integrated circuits, circuit contacts and interconnects may be fabricated from various metals, such as lead (Pb) or gold (Au). High volume production of semiconductor chips containing these metals may result in environmental pollution, as such metals may be inherently environmentally unfriendly, and may be hazardous to the environment if discarded products containing the semiconductor chips are not disposed of properly. The use of metal in semiconductor chips may also constrain fabrication process conditions, for example, limiting maximum process temperatures and presenting problems with tool cross-contamination.
SUMMARY
In one aspect, an integrated circuit includes a graphene layer, the graphene layer comprising a region of undoped graphene, the undoped graphene comprising a channel of a transistor, and a region of doped graphene, the doped graphene comprising a contact of the transistor; and a gate of the transistor, the gate comprising a carbon nanotube film.
In one aspect, a method of fabricating an integrated circuit comprising graphene and carbon nanotubes, includes forming a graphene layer; doping a portion of the graphene layer, resulting in doped graphene and undoped graphene; forming a carbon nanotube film; and etching the carbon nanotube film to form a gate of a transistor, wherein the transistor further comprises a channel comprising the undoped graphene and a contact comprising the doped graphene.
In one aspect, a transistor includes a gate, the gate comprising a carbon nanotube film; a channel, the channel comprising undoped graphene; and a contact, the contact comprising doped graphene.
Additional features are realized through the techniques of the present exemplary embodiment. Other embodiments are described in detail herein and are considered a part of what is claimed. For a better understanding of the features of the exemplary embodiment, refer to the description and to the drawings.



BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
Referring now to the drawings wherein like elements are numbered alike in the several FIGURES:
FIGS. 1A and 1B illustrate a cross section and a top view, respectively, of an embodiment of an integrated circuit comprising graphene and carbon nanotubes after formation of a graphene layer(s).
FIG. 2 illustrates a top view of an embodiment of an integrated circuit comprising graphene and carbon nanotubes after application of mask material.
FIG. 3 illustrates a top view of an embodiment of an integrated circuit comprising graphene and carbon nanotubes after etching regions of the graphene layer(s) and removal of the mask material.
FIG. 4 illustrates a top view of an embodiment of an integrated circuit comprising graphene and carbon nanotubes after doping of a portion of the graphene.
FIG. 5 illustrates a cross section of an embodiment of an integrated circuit comprising graphene and carbon nanotubes after formation of a dielectric layer.
FIG. 6 illustrates a cross section of an embodiment of an integrated circuit comprising graphene and carbon nanotubes after application of mask material to the dielectric layer.
FIGS. 7A and 7B illustrate a cross section and a top view, respectively, of an embodiment of an integrated circuit comprising graphene and carbon nanotubes after etching of the dielectric layer and removal of the mask material.
FIG. 8 illustrates a cross section of an embodiment of an integrated circuit comprising graphene and carbon nanotubes after formation of a carbon nanotube film.
FIG. 9A illustrates a cross section of an embodiment of an integrated circuit comprising graphene and carbon nanotubes after etching of the carbon nanotube film.
FIG. 9B illustrates an embodiment of a transistor comprising graphene and carbon nanotubes.
FIG. 10 illustrates a method of fabricating of an integrated circuit comprising graphene and carbon nanotubes.



DETAILED DESCRIPTION
Embodiments of systems and methods for integrated circuits comprising graphene and carbon nanotubes are provided, with exemplary embodiments being discussed below in detail.
Integrated circuits comprising graphene and carbon nanotubes allow fabrication of metal-free monolithic electronic devices. Graphene comprises a one-atom thick sheet of carbon atoms packed in a honeycomb lattice structure, and has a relatively high carrier mobility and current capacity. Doped graphene possesses a conductivity that is higher than the conductivity of undoped graphene. Undoped graphene may form a channel region of a transistor, and doped graphene may form contacts and interconnects. Graphene circuit interconnects may have a lower stray capacitance than metal wires. A dielectric and a carbon nanotube thin film may be disposed on a graphene layer. The carbon nanotubes may form circuit vias and top-layer interconnects. The completed integrated circuit comprises carbon and oxide materials, resulting in transparent and flexible circuits that may be easily stacked to produce multilayer circuits that are environmentally friendly. In addition, constraints on process integration caused by use of metals, such as limited thermal budget and tool cross-contamination, may be eliminated.
FIGS. 1A and 1B illustrate a cross section 100a and a top view 100b of an embodiment of an integrated circuit comprising graphene and carbon nanotubes after formation (e.g., by growing, deposition, etc.) of a graphene layer or few graphene layers 101. Graphene layer 101 is disposed on substrate 102. Graphene 101 may be formed in any appropriate manner, including, but not limited to, heating of silicon carbide. Graphene layer 101 may comprise between about 1 and 20 sheets of graphene stacked on top of each other in some embodiments; therefore, the thickness of graphene layer 101 may range from about 1 atom thick to about 20 atoms thick, equivalent to a range of about 0.35 nanometers (nm) to about 7 nm thick. Substrate 102 may comprise any appropriate oxide material, including, but not limited to, hafnium oxide, silicon oxide, or aluminum oxide.
FIG. 2 illustrates a top view 200 of an embodiment of an integrated circuit comprising graphene and carbon nanotubes after a mask material 201 is applied on top of graphene layer 101 and substrate 102, and lithographically patterned. Mask material 201 may comprise polymethyl methacrylate (PMMA) in some embodiments. The unmasked graphene 101 is then etched. Etching may be performed using oxygen plasma in some embodiments.
FIG. 3 illustrates a top view 300 of an embodiment of an integrated circuit comprising graphene and carbon nanotubes after etching of the exposed graphene 101 and removal of the mask material 201. The mask material 201 of FIG. 2 has been removed, resulting in etched graphene region 301 disposed on substrate 102.
FIG. 4 illustrates a top view 400 of an embodiment of an integrated circuit comprising graphene and carbon nanotubes after doping of a portion of graphene region 301. A mask (not shown) has been applied to a portion of etched graphene region 301, and the uncovered portion of the etched graphene region 301 has been doped, resulting in undoped graphene 401 and doped graphene 402. The mask (not shown) is then removed. Doped graphene 402 may be doped with any appropriate material, including but not limited to organic molecules such as polyethyleneimine (PEI) or diazonium. Doped graphene 402 has a higher conductivity than undoped graphene 401. Doped graphene 402 comprises transistor contacts and interconnects, and undoped graphene 401 comprises transistor channel regions.
FIG. 5 illustrates a cross section 500 of an embodiment of an integrated circuit with graphene and carbon nanotubes after formation (e.g., by growing, deposition, etc.) of a dielectric layer 501 on the graphene layer, which comprises doped graphene 402 and undoped graphene 401. Dielectric layer 501 may be formed by any appropriate method, including, but not limited to, atomic layer deposition (ALD) or low-temperature chemical vapor disposition (CVD). Dielectric layer 501 may comprise any appropriate oxide material, including, but not limited to, hafnium oxide, silicon oxide, or aluminum oxide.
FIG. 6 illustrates a cross section 600 of an embodiment of an integrated circuit comprising graphene and carbon nanotubes after application of mask material 601 to dielectric layer 501. Mask material 601 defines via regions for the integrated circuit. Mask material 601 may comprise any appropriate masking material, including but not limited to PMMA.
FIGS. 7A and 7B illustrate a cross section 700a and a top view 700b of an embodiment of an integrated circuit comprising graphene and carbon nanotubes after etching of dielectric layer 501 and removal of the mask material 601. The exposed regions of dielectric layer 501 have been etched down to expose doped graphene regions 402. Etching mask 601 is removed after etching of dielectric layer 501 is completed, resulting in dielectric regions 701.
FIG. 8 illustrates a cross section 800 of an embodiment of an integrated circuit comprising graphene and carbon nanotubes after formation (e.g., by growing, deposition, etc.) of a carbon nanotube film 801. Carbon nanotube film 801 is disposed on dielectric regions 701 and exposed doped graphene regions 402. Carbon nanotube film 801 may comprise vias and top layer interconnects for the integrated circuit. Carbon nanotube film 801 may be formed by any appropriate process, including but not limited to deposition from a solution or CVD growth.
FIG. 9A illustrates a cross section of an embodiment of an integrated circuit comprising graphene and carbon nanotubes after etching of carbon nanotube film 801. A mask material (not shown) is applied to carbon nanotube film 801, and the exposed regions of carbon nanotube film 801 are etched down to the top of dielectric regions 701. The mask material (not shown) is then removed. Area 901, which is shown in further detail in FIG. 9B, illustrates an embodiment of a transistor 900b comprising graphene and carbon nanotubes. Transistor 900b comprises a gate 902 comprising carbon nanotube film 801, a channel 903 comprising undoped graphene 401, and contacts 904 comprising doped graphene 402 and carbon nanotube film 801.
FIG. 10 illustrates a method for fabrication of an integrated circuit comprising graphene and carbon nanotubes. In block 1001, a graphene layer is formed on a substrate, as is shown in FIGS. 1A-B. In block 1002, the graphene is etched, as is shown in FIGS. 2 and 3. In block 1003, a portion of the etched graphene region is doped, as is shown in FIG. 4. In block 1004, a dielectric layer is formed on the graphene layer, as is shown in FIG. 5. In block 1005, the dielectric layer is etched, as is shown in FIGS. 6 and 7A-B. In block 1006, a carbon nanotube film is formed, as is shown in FIG. 8. In block 1007, the carbon nanotube film is etched, as is shown in FIG. 9A, resulting in a completed transistor, as is shown in FIG. 9B.
The technical effects and benefits of exemplary embodiments include an environmentally friendly high performance semiconductor chip that may be transparent and flexible.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.

## Claims

1. A method of fabricating an integrated circuit comprising graphene and carbon nanotubes, the method comprising:
forming a graphene layer on a substrate;
doping a portion of the graphene layer, resulting in a region of doped graphene adjacent a region of undoped graphene;
forming a dielectric layer on top of the graphene layer;
a via formed through the dielectric layer;
forming a carbon nanotube film in the via and over the region of undoped graphene;
etching the carbon nanotube film to form a gate of a transistor, wherein the transistor further comprises a channel comprising the undoped graphene and a contact comprising the doped graphene, the gate comprising a first portion of the etched carbon nanotube film that is isolated from the undoped graphene channel by the dielectric layer; and
wherein etching the carbon nanotube film also forms a top level interconnect on top of the dielectric layer and in contact with the via, the top level interconnect comprising a second portion of the etched carbon nanotube film that is separated from the first portion of the etched carbon nanotube film.

2. The method of claim 1, wherein the dielectric layer comprises an oxide material.

3. The method of claim 1, wherein the graphene layer is between about 0.35 nanometers (nm) and about 7 nm thick.

4. The method of claim 1, wherein the substrate comprises an oxide material.

5. The method of claim 1, further comprising patterning the graphene layer by etching, and doping the etched graphene layer with an organic molecule.

6. The method of claim 5, wherein the organic molecule comprises polyethylemneimine.

7. The method of claim 5, wherein the organic molecule comprises diazonium.