CARBON NANOTUBE TRANSISTORS INTRODUCTION In recent years development
CARBON NANOTUBE TRANSISTORS INTRODUCTION In recent years, development in Carbon nanotube transistors have been explored and experimented on as a viable replacement for traditional silicon transistors due to its atomic properties. Recent advancements to overcome the dilemma of the small scaling of the contact metals by placing the interfaces at the ends of the tubes allowed for high electrical performance with less than 10 nm of tubing length. EXAMPLES Fig. 1. Diagram of the Wrap-around Gate CNTFET in which the entire circumference of the nanotube is gated to improve the electrical and on/off ratio performance, as well as reducing leaking current [2]. Fig. 2. Diagram of the Suspended CNTFETs. As, the name suggests, it uses a nanotube suspended over the trench to limit contact with the gate oxide. This allows for improved performance since there is less scattering [2]. Fig. 5. Molybdenum end-contacted quasiballistic SWNT transistors with Lc defined by contact trenches. In these schematics and graphs, The Mo end-bonded contact can maintain its total contact resistance, allowing the device to be applied as a contact scaling solution for future scaled device technologies. Fig. 4. Molybdenum endcontacted Single-Walled Carbon Nanotube (SWNT) Transistor. The diagrams and graphs display how its output characteristics allow for electrical reliability and contact resistance independent of its size. In addition, even though various widths of contact metal was tested, there was no off-state performances caused by the variations [3]. Although CNTs boast attractive features for improved electronic and computer hardware, there are practical and physical limitations to overcome. In order to optimize voltage usage and current flow in the CNTs, researchers considered the following problems: Some of the conducted projects for CNTs such as scaling the CNT gate length to as low as 5 nm and developing end-bonded contacts with low size independent resistance demonstrate the ability to increase electrical current efficiency and different chemical interactions between the carbon nanotubes and metals for new configurations. Limited technology necessary for mass production and adapting future hardware from silicon chips is currently expensive and is time consuming [1], [2]. • For billions of nanotubes to be placed precisely where they are need most, a reliable, nonlithographic method needs to be established [1]. • Developing end-bonded contacts for n-type FETS and to limit increasing contact resistance for size downscaling [3]. Fig 3. Structure and Performance of 5 nm CNTFETs. the schematics and graphs indicate the high-performance transfer characteristics of a gate length at 5 nm compared to 10 nm [3]. • Overall, the silicon complementary metal-oxide semiconductor (CMOS) FETs have been outclassed by the more innovative top-gated CNTFETs with a gate length of 5 nm at the same scale proving to be more efficient for electronics. Also, the SWNT transistor technology solved the issue of the increasing contact resistance with decreasing size due to the design scheme using Molybdenum end contacts. The next stages to improve transistor technology is to determine a way for functional end-bonded contact for ntype FETS as current research has only proven successful for p -type FETs. CONCLUSIONS In summary, advancements to reduce contact resistance at the endbonds of CNTs under increasing small gate lengths have proven to be a valuable alternative to conventional MOSFET systems [2]. In addition, this will lead to further progress in developing nanotubes for further metallic and semiconducting experiments [1]. WORKS CITED RESEARCH DEVELOPMENTS CHALLENGES RESULTS & FUTURE PROGRESS [1] “IBM Reports Breakthrough on Carbon Nanotube Transistors” MIT Technology Review, Oct. 1, 2015 [Online]. Available: https: //www. technologyreview. com/s/541921/ibm-reports-breakthrough-on-carbonnanotube-transistors/ [Accessed: Jan. 26, 2019]. [2] “Carbon nanotube field-effect transistor” Wikipedia. com. [Online]. Available: https: //en. wikipedia. org/wiki/Carbon_nanotube_field-effect_transistor#Key_advantages [Accessed Jan. 28, 2019]. [3] C. Qiu, Z. Zhang, M. Xiao, Y. Yang, D. Zhong, L. Peng, “Scaling carbon nanotube complementary transistors to 5 -nm gate lengths” Research Gate, Jan. 19, 2017 [Online Serial]. Available: https: //www. researchgate. net/profile/Lian. Mao_Peng/publication/312558907_Scaling_carbon_nanotube_complementary_transistors_to_5 nm_gate_lengths/links/5 a 024 cce 0 f 7 e 9 b 688749328 d/Scaling-carbon-nanotube-complementarytransistors-to-5 -nm-gate-lengths. pdf [Accessed Jan. 26, 2019]. [4] Q. Cao, S. Han, J. Tersoff, A. Franklin, Y. Zhu, Z. Zhang, G. Tulevski, J. Tang, W. Haensch, “Endbonded contacts for carbon nanotube transistors with low, size-independent resistance” Research. Gate, Nov. 18, 2015. [0 nline Serial]. Available: https: //www. researchgate. net/profile/Shu_Jen_Han/publication/282437194_Endbonded_contacts_for_carbon_nanotube_transistors_with_low_sizeindependent_resistance/links/56 cbd 6 e 708 ae 5488 f 0 db 1 cd 0. pdf [Accessed Jan 27, 2019].
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