Carbon Based Electronics:
Carbon nanotube based electronic devices, photoelectronic devices and system integration
Extensive efforts have been made to explore alternative channel materials to push the Moore’s Law forward. Carbon nanotubes (CNTs), as an ultrathin and one-dimensional semiconductor material, have ultra-high carrier mobility (for both electrons and holes), large saturation speed, large mean free path under strong electric field and large transconductance. Meanwhile, carbon nanotube based FETs have a strong gate control ability even if with a short channel, which plays an important role in the next-generation information processing. A series of research works have been done to explore the feasibility of carbon nanotubes to implement the next-generation devices and ICs. The main contributions are included as follows.
1) Initiated the doping-free carbon nanotube CMOS integrated circuits technology.
Compared with the traditional silicon based CMOS integrated circuit, the doping-free carbon nanotube CMOS integrated circuits technology gives up the traditional concept of using chemical doping to control the transistor’s polarity. According to the characteristics of carbon nanotubes, adopting a suitable metal as contact can define the type of carriers injected into CNT, and hence control the polarity of FETs. Based on this principle, a doping free technique for CNT CMOS fabrication is developed with greatly simplified fabrication process. Carbon nanotube device is more than 5 times faster than Si based devices at similar size, while the power consumption is only 1/10. Based on single semiconducting single-walled CNTs, a 1-bit full adder with the supply voltage as low as 0.4 V have been demonstrated, which is the world record. For comparison, the target minimum supply voltage for silicon-based device is 0.6 V, which is expected to be achieved around 2020. Carbon nanotube based integrated circuits can work at as low as -200 °C and as high as 300 °C. This technology also enable a new generation of flexible and transparent chips with grealy extanded applications.
2) Implemented carbon nanotube CMOS devices in 3 nm technology node.
High-performance top-gated CNT complementary transistors with a gate length of 5 nm have been fabricated on a single semiconducting CNT. The results revealed that with the carbon nanotube technology, only through the planar process, the CMOS integrated circuit at 3 nm technology node can be achieved. The device has more than 10 times advantages over the state-of-the-art silicon technology in terms of performance and power consumption. In addition, it is close to the theoretical limit of the electronic devices determined by the quantum uncertainty principle. In January 2017, the work was published in the journal of Science. At the same time, this work has been wildly reported by various domestic and foreign media, including IEEE Spectrum (Institute of electrical and electronic engineers flagship journal), Science and Technology Daily, Scientific Computing World, Chinese electronic newspaper, Financial Time, etc.
3) Developed carbon nanotube large scale integrated circuits technology.
The team developed a modularized construction method of general integrated circuits on individual carbon nanotubes. By using this technology, an 8-bit bus system has been demonstrated, which is by far the most complex integrated circuit based on a single CNT. This work is highlighted by Nature as a hot spot subject with a title of “Nanotubes form a complex circuit”. Through the optimization of carbon nanotubes materials, devices’ size and structure, and fabrication process, a mass production approach has been developed for carbon nanotube integrated circuits. Batch preparation of high performance devices with a yield of 100% has been demonstrated. The obtained device is highly uniform. A standard deviation of threshold voltage of 34 mV is obtained, which is approaching the 25.58 mV deviation in 65 nm technology node Si CMOS. A 4-bit adder and a 2-bit multiplier has been realized for the first time. The 4-bit adder consists of 140 p-type CNT FETs with 12 stages logical depth, which is the most complex carbon nanotube based integrated circuits with the highest integration degree so far.
4) Developed high performance carbon nanotube photoelectronic devices integration technology.
Compared with silicon devices, semiconducting CNT presents direct band gap, which leads to good photoelectronic property and is another advantage for CNT devices. High performance diode can be realized by using Sc and Pd as contacts on two terminals of a CNT respectively. Electrons and holes can be injected into CNT channel with a zero barrier (forward biased situation) or maximum barrier that equals to the band gap of CNT (reversed biased situation). When the device is forward biased, efficient injection of electrons and holes into CNT results in combination of excitons. The first CNT based infrared light emission diode (LED) was realized. What’s more, a novel CNT cascaded photo-battery (virtual contact) technique was developed through fabricating 4 pairs of virtual electrodes on a CNT with length of 10 micrometer. The photovoltage is increased by 5 times to over 1 V, which is the necessary voltage for practical use. The related work was published in Nature Photonics, which was chosen as ‘Ten Advances in Science of China’ in 2011. The work was selected as the "Ten major scientific and technological progress in China in 2011" by the Ministry of Science and Technology, and into the "2012 scientific development report" issued by the Chinese Academy of Sciences. It was considered one of the most representative work of Chinese scientists in that year. Another representative work is that the demonstration of an electrically driven carbon nanotube based on chip three-dimensional optoelectronic integrated circuit (OEIC). This single material-based monolithic optoelectronic integration with CMOS compatible signal processing circuits is significant to realize rapid data communication and functional diversification in the post-Moore era.
The development of carbon based information technology is expected to bring a new boom for electronics in the post-Moore era, and further promote the development of information technology with great prospect value. The team led by Prof. Lian-Mao Peng has solved the basic problems and key technologies of carbon nanotube electronics, which greatly promoted the development of carbon-nanotube based integrated circuit. The carbon nanotube technology is expected to become the future mainstream chip technology, driven by major changes in the field of information devices. The work of the team in the field of carbon based integrated circuit research is in the international frontier, which enhance our country's core competitiveness in the field of information technology in the future. More than 100 SCI papers have been published in related field in Science, Nature Photonics, Nature Communication, Advanced Materials, Nano Letter, ACS Nano and other journals with 4,000+ Google Scholar citations. Six of these papers are selected as Thompson ESI Highly Cited Papers of related fields (top 1%). The project of carbon-based nanoelectronic devices and integration was awarded as the second prize in China's State Natural Science Award at 2016, and was also awarded as Ministry of Education national sciences first award at 2013. The related works were cited by International Technology Roadmap of Semiconductor (ITRS) with 13 times in Emerging Research Materials and Emerging Research Devices. At the end of 2015, Prof. Lian-Mao Peng and his carbon based integrated circuit research was selected as one of the two representative and significant contributions to the Nature Index of Beijing in "Nature Index 2015 China" published by Nature, which evaluated their work of the construction of high-performance carbon nanotube transistors and integrated circuits as “represents the future of computer processors”. The Carbon Based Electronics research project has been supported by funding of the Ministry of Science and Technology, the National Key Research & Development Program and other sources with over 2 hundred million.
Besides the academic achievements reported in the published publications, over 20 patent applications have been submitted, while 15 of them have been granted, including 3 United States patents. In addition to the ongoing research activities, the team also focuses on the achievement transformation and establishes a depth of the cooperative partnership with the industry, such as Beijing Oriental Electronics (BOE) and Huawei Technologies Co., Ltd. Prof. Lian-Mao Peng was awarded the title of “Top ten science and technology figures to promote Beijing Creation” in 2015.