Peking University realizes the world's first gigahertz carbon nanotube integrated circuit

According to Moore's Law, China's instrumentation network instrument research and development has reduced the cost of transistors by reducing the size of transistors and increasing performance and integration; however, further development has been limited by physical limitations, power consumption, and manufacturing costs. Emerging information device technologies support the development of future electronics. Carbon nanotubes are considered to be ideal materials for the construction of sub-10nm transistors; theoretical and experimental studies have shown that compared with silicon-based devices, they have 5 to 10 times the intrinsic speed and power consumption advantages, performance is close to the quantum uncertainty The limit of the electronic switch determined by the principle is expected to meet the development needs of integrated circuits in the post-Moore era. However, due to the large parasitic effect, the actual fabrication of the carbon tube integrated circuit is of lower operating frequency (generally below megahertz, 1 MHz=106 Hz), which is higher than the operating frequency of the silicon-based complementary metal oxide semiconductor (CMOS) circuit (gigahertz. Gigahertz, 1 GHz = 103 MHz = 109 Hz) is several orders of magnitude lower. In the study of a carbon nanotube array-based ring oscillator published by the International Business Machines (IBM) researcher in August 2017, the oscillation frequency is 282 MHz, which is still far lower than expected. Therefore, the significant increase in the operating frequency of carbon nanotube integrated circuits has become an important challenge in the development of carbon nanotube electronics.

College of Information Science and Technology, Peking University, Key Laboratory of Nanodevice Physics and Chemistry Ministry of Education Prof. Peng Lianmao-Professor Zhang Zhiyong studied carbon nanotube electronics for more than 10 years and developed a complete set of carbon tube CMOS technology. Sub 10nm CMOS devices and medium-scale integrated circuits. Recently, through the optimization of carbon nanotube materials, device structures/processes, and circuit layouts, they have achieved the first time in the world to implement carbon nanotube integrated circuits operating at gigahertz frequency, which has strongly promoted the development of carbon nanotube electronics.

The team first improved the transconductance and drive current of carbon nanotube transistors by optimizing the carbon nanotube material, device structure, and process; for a transistor with a 120-nm gate length, the on-state current and transconductance of the transistor at a working voltage of 0.8V were achieved. 0.55 mA/μm and 0.46 mS/μm, where transconductance is the highest value for published carbon nanotube devices. Based on this performance device, a five-level ring oscillator was successfully implemented with an oscillation frequency of 680 MHz. Then, the team further optimized the device structure by introducing air spacers between the source and drain and the gate to reduce the parasitic capacitance of the source and the drain. At the same time, the thickness of the gate resistor was increased to reduce the parasitic resistance and the oscillation frequency reached 2.62 GHz. On this basis, the team further improved the five-step ring oscillator oscillation frequency to 5.54 GHz by reducing the length of the carbon nanotube transistor and optimizing the circuit layout, which is almost 20 times faster than the previously published highest record (282 MHz); and the 120 nm gate length The single-stage gate delay of the carbon tube device is only 18ps. Under the premise of not using the multi-layer interconnection technology, the speed is close to the commercial silicon-based CMOS circuit of the same technology node. More importantly, the carbon nanotube film used in this technology is used as an active region material to realize mass production of high-performance carbon tube ring oscillator circuits. The circuit yield is 60%, and the average oscillation frequency of the ring oscillator is 2.62. In GHz, the characterization difference is 0.16 GHz, which shows good performance uniformity.

"Natural Electronics" screenshots and description of the carbon nanotube ring oscillator circuit described in the article: (a) SEM photographs of five-level ring-oscillator circuits; (b) 5.54 GHz carbon ring oscillator circuits; (c) statistics of ring-oscillation frequencies Histogram; (d) Comparison of single-stage gate delays with other carbon tube materials, two-dimensional materials, and silicon-based ring oscillators.

On December 11, 2017, the paper entitled “Gigahertz integrated circuits based on carbon nanotube films” was published online in Nature Electronics. DOI:10.1038/s41928-017-0003-y), which will be officially published in the inaugural issue of the journal, and this is the first paper published by Peking University in this journal. Zhong Donglai, a doctoral student at the 2013 College of Information Science, was the first author, and Professor Zhang Zhiyong and Professor Peng Lianxi were co-authors. This research work has not only greatly promoted the development of carbon nanotube integrated circuits, but also showed that based on existing carbon nanotube materials, it is possible to achieve integrated circuits with performance comparable to that of commercial monocrystalline silicon-based CMOSs ​​through simple processes; if more The ideal materials (such as high-density carbon nanotube parallel arrays) and more advanced processing technologies are expected to promote carbon nanotube technology to exceed silicon-based CMOS technology in terms of speed and power consumption.

The study received funding from the National Key R&D Program, the National Natural Science Foundation of China, the Beijing Science and Technology Plan, and the construction of world-class universities (disciplines) and special development guides.

(Original title: Information College Peng Lian-Zhang Zhiyong's team achieved the world's first gigahertz carbon nanotube integrated circuit)