Field effect transistors constructed by coating carbon nanotubes with dielectrics and metals by ALD
The invention solves this problem, allowing SWCNTs to be uniformly coated with dielectrics using ALD. With its exquisite control over the thickness and conformality of the coating, the technique allows the formation of coaxial coatings. The technique involves the use of a compound such as nitrous oxide to adsorb to the SWCNT which gives a surface that is now receptive to ALD precursors.
Developed in the lab of Professor Roy Gordon, this technique allows for the deposition of thin films on the surface of nanotubes using atomic layer deposition (ALD) without affecting their electronic properties. The invention is a key insight into the functionalization of carbon nanotube surfaces, allowing chemical precursors to absorb to the surface of the nanotube, forming receptor sites for the deposition of coaxial thin films (dielectrics, metals etc.) by ALD that are exceptionally thin, continuous, and radially isotropic. The thin film coatings can be functionalized with binding partners of analytes (i.e., antibody/antigens) to form biosensors. Coaxial metallic layers can also be deposited on the suspended nanotubes, allowing the fabrication of coaxial field-effect transistors.
The invention opens up the use of SWCNTs as the active heart of transistors for IC chips and for sensors. The inventors have demonstrated the formation of SWCNT transistors using techniques compatible with chip fabrication. Another potentially valuable finding is that the carbon nanotubes can be oxidized away, leaving behind hollow tubes of the coating layer. This allows a simple process for forming nanotubes composed of any materials that can be formed by ALD.
Intellectual Property Status: Patent(s) Pending
Since their discovery over a decade ago, carbon nanotubes have been the subject of intense study because of their unique electrical, thermal, and mechanical properties. They have been proposed as the basis of new sensors, nanoscale electrical circuits, molecular delivery systems, photonic sources, thermal conductors, mechanical fibers, chemical catalysts, and as critical components for a wide variety of other applications.
A wide range of nanoscale devices and structures can be produced using this invention's non-covalent functionalization technique. For example, a functionalized carbon nanotube may be coaxially coated with a high-K dielectric layer and a selected conducting layer, to form a surround-gate transistor with large charging energies. In addition, the single-walled carbon nanotube's(SWCNT) functionalization layer will enable highly customizable coatings (e.g. hydrophilic surfaces for medical application) as well as rapid, templated manufacture of hollow nanotube structures.
SWCNTs have remarkable electrical and optical properties that have not yet been extensively commercialized because of difficulties making robust and high quality devices containing them. One current difficulty is the lack of a good technique for uniformly coating SWCNTs with dielectrics, which is required to make devices such as transistors, while retaining the SWCNTs remarkable electrical and optical properties. Atomic layer deposition (ALD), a promising technique for making thin films for next generation chips, has previously not been available for coating SWCNTs because their surface is not receptive to ALD precursors.
“ALD on Suspended Single-Walled Carbon Nanotubes via Gas-Phase Noncovalent Functionalization”, Damon Farmer and Roy G Gordon, Nano Letters., (2006), 6(4): 699-703.