World’s First Dynamic and Local Temperature Profiling in a Carbon Nanotube Interconnect
2011.08.10
(2011.08.22 Update)
National Institute for Materials Science
A research group headed by Prof. Dmitri Golberg, who is a MANA Principal Investigator, Dr. Pedro Costa (a former ICYS-MANA postdoctoral researcher, currently of Aveiro University, Portugal), and Dr. Ujjal K. Gautam (a former ICYS-MANA postdoctoral researcher, currently of the Jawaharlal Nehru Centre for Advanced Scientific Research, JNCASR, India) at the International Center for Materials Nanoarchitectonics, National Institute for Materials Science succeeded for the first time in the world in dynamic observation of the local temperature distribution in an individual carbon nanotube (CNT) interconnect when a current is passed through it.
Abstract
- A research group headed by Prof. Dmitri Golberg, who is a MANA Principal Investigator, Dr. Pedro Costa (a former ICYS-MANA postdoctoral researcher, currently of Aveiro University, Portugal), and Dr. Ujjal K. Gautam (a former ICYS-MANA postdoctoral researcher, currently of the Jawaharlal Nehru Centre for Advanced Scientific Research, JNCASR, India) at the International Center for Materials Nanoarchitectonics (MANA; Director-General: Masakazu Aono), National Institute for Materials Science (President: Sukekatsu Ushioda) succeeded for the first time in the world in dynamic observation of the local temperature distribution in an individual carbon nanotube (CNT) interconnect when a current is passed through it. Observations were made using a transmission electron microscope (TEM) equipped with a scanning tunneling microscope (STM) probe.
- CNT have excellent electrical response characteristics due to their small size, and are considered to be one of the most promising candidates as a material for next-generation electronic devices. When configuring a device, electrical junctions must keep their integrity and maintain a satisfactory performance even under long-term electrical stress. For this, high thermal and structural stability are required. Similarly, high stability is also necessary in junctions/interconnects made of CNTs. As there are cases in which local temperature rise in the junction causes substantial deterioration in device performance, a dynamic elucidation of the temperature and its profiling over the electrical interconnect is necessary. However, until now, the nature of the temperature distribution and structural changes which occur when an electric current passes through a CNT junction were basically unknown.
- In this research, the MANA group succeeded in dynamic observation of the phenomena which occur when a current passes through an individual CNT junction. The ends of a carbon nanotube (diameter: 130 nm, length: 3.1μm, tube wall thickness: 5 nm), which had been filled with a sublimable sulfide (Zn0.92Ga0.08S, sublimation temperature: Tsub=928 K=655°C), were connected to electrodes in the TEM and a current was passed through the tube. First, a tube tip that was in poor physical contact with the electrode was solely Joule heated, forming a high temperature region called a “hot spot.” Thereafter, through a sort on “nanowelding” process, the nanotube was firmly and uniformly joined with the electrode. Then, as the current was kept passing, uniform heating occurred in the nanotube body itself, and the position of the hot spot shifted to approximately the center of the tube. The sulfide in the tube sublimated in the hot spot region and disappeared, forming a hollow. Because the electrodes were kept at room temperature during heating, sharp temperature gradients formed in the nanotube longitudinal and cross-sectional directions, with the distance between the edge of the hot spot and the electrode as a marker, and temperature profiling became possible. Observation can be performed over the full process until electrical destruction of the interconnect. As an example, this research confirmed that the temperature may reach 928 K (655°C) at the tube center and 1052 K (779°C) in the tube wall.
- Using this technique, the temperature changes in CNT junctions can be observed with nanometer level spatial and millisecond order temporal resolutions. High expectations are placed on application of measurement and imaging of local temperature distribution using this technique as a method for evaluating nanodevice junctions.
- The results of this research will be published in the online edition of the English science journal “Nature Communications” on August 10, 2011 at 0:00 Japan time (August 9, 16:00 local time).
Figure:Results of TEM observations when the ends of a carbon nanotube filled with a sulfide were connected to gold electrodes and the CNT was resistively heated.
From left to right, Fig. shows the shift of the hot spot from the CNT tip to the tube center. The insets are enlargements of the hot spot regions in the nanotube. The hollow formed by sublimation of the sulfide serves as a marker pointing at the actual temperature. After the tube was firmly and uniformly connected to the electrode, the electrodes on the two ends of the tube started to act as massive heat sinks which reduced the temperature of the tube by enabling effective heat dissipation. The electrode temperature was then held to normal (room) temperature and the temperature gradients along and across the CNT were determined.
