Abstract
The miniaturization of electronic devices has been the principal driving force behind the semiconductor industry, and has brought about major improvements in computational power and energy efficiency. Although advances with silicon-based electronics continue to be made, alternative technologies are being explored. Digital circuits based on transistors fabricated from carbon nanotubes (CNTs) have the potential to outperform silicon by improving the energyâdelay product, a metric of energy efficiency, by more than an order of magnitude. Hence, CNTs are an exciting complement to existing semiconductor technologies1,2. Owing to substantial fundamental imperfections inherent in CNTs, however, only very basic circuit blocks have been demonstrated. Here we show how these imperfections can be overcome, and demonstrate the first computer built entirely using CNT-based transistors. The CNT computer runs an operating system that is capable of multitasking: as a demonstration, we perform counting and integer-sorting simultaneously. In addition, we implement 20 different instructions from the commercial MIPS instruction set to demonstrate the generality of our CNT computer. This experimental demonstration is the most complex carbon-based electronic system yet realized. It is a considerable advance because CNTs are prominent among a variety of emerging technologies that are being considered for the next generation of highly energy-efficient electronic systems3,4.
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Acknowledgements
We acknowledge the support of the NSF (CISE) (CNS-1059020, CCF-0726791, CCF-0702343, CCF-0643319), FCRP C2S2, FCRP FENA, STARNet SONIC and the Stanford Graduate Fellowship and the Hertz Foundation Fellowship (M.M.S.). We also acknowledge Z. Bao, A. Lin, H. (D.) Lin, M. Rosenblum, and J. Zhang for their advice and collaborations.
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M.M.S. led and was involved in all aspects of the project, did all of the fabrication and layout designs, and contributed to the design and testing. G.H. wrote the SUBNEG and testing programs, and contributed to the design and testing. N.P. contributed to the design, and N.P., H.W. and H.-Y.C. contributed to developing fabrication processes. H.-S.P.W. and S.M. were in charge and advised on all parts of the project.
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Extended data figures and tables
Extended Data Figure 1 Fabrication flow for the CNT computer.
Steps 1â4 prepare the final substrate for circuit fabrication. Steps 5â8 transfer the CNTs from the quartz wafer (where highly aligned CNTs are grown) to the final SiO2 substrate. Steps 9â11 continue final device fabrication on the final substrate.
Extended Data Figure 2 Multibit arithmetic unit.
a, Schematic of a two-bit arithmetic unit, comprising six individual arithmetic logic units (ALU) as shown in Fig. 3b. b, Measured and expected output waveforms testing all possible input combinations of the two-bit arithmetic unit, showing correct operation.
Extended Data Figure 3 Internal versus external connections of CNT computer.
a, Schematic of the CNT computer, showing that all connections are fabricated on-chip and that only signals reading or writing to or from an external memory are connected off-chip. b, SEM of the CNT computer, showing which connections are made to and from the CNT computer from the probe pads. The SEM is colour-coded to match the coloured wires in a.
Extended Data Figure 4 PMOS-only logic schematics.
a, Schematic of PMOS-only inverter. b, Schematic of PMOS-only NAND gate.
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Shulaker, M., Hills, G., Patil, N. et al. Carbon nanotube computer. Nature 501, 526â530 (2013). https://doi.org/10.1038/nature12502
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DOI: https://doi.org/10.1038/nature12502
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