Large magnetic field induced by carbon nanotube current -proposal of carbon nanotube inductors

New concepts of electronic components are needed to fabricate further high-performance integrated circuit. One of the new concepts is the incorporation of inductors into integrated circuits. The incorporation into integrated circuits, however, has the difficulty in three dimensional nano-fabrication technique, and the small effect due to the small quantity of magnetic permeability of o = 4 it x10-7 H/m and the large diameter of the inductor's wires. We have proposed the inductors made of carbon nanotube [1, 2]. Ihough the fabrication of the proposed inductor is still challenging and has many problems, merits of the proposed inductor are following, 1. Since the radius (r) of carbon nanotube are several nm, the magnetic field (H) induced by the current (1) in carbon nanotube is about one thousand times larger than that induced by the current in normal copper wire whose radius is about several gm. (H = I/2;zr) 2. According to the relation between magnetic field (I) in the inductor and inductance (L) of the inductor, 1/2 JPOH2dV = 1/2LI2, the large magnetic field (A) results in the large inductance (L). 3. Since the carbon nanotube can be bent with small curvature, the inductor made of carbon nanotube is smaller than the inductor made of copper or gold. In this paper, we have observed the large magnetic field induced by the small current in carbon nanotube using magnetic force microscope [31. The used carbon nanotube was made by laser ablation method. After the dispersing the carbon nanotube on the SiO 2/Si substrate, gold/nickel metal interconnects to the carbon nanotube. By applying the alternating current in carbon nanotube, we have obtained the images of synchronized component in the force signal using lock' in measurement. Since the images were the convolution of Kelvin force microscopy and magnetic force microscopy images, we extracted the magnetic field distribution using the symmetry difference between the magnetic and electric field. Observed magnetic fields were proportional to the amplitude of the alternating current. The estimated magnetic field near the carbon nanotube of 8 mT at 250 pA roughly agrees with the theoretical one. This magnetic field is also very large compared with that produced by the copper wire in the normal inductor. Since the inductance of 1.0 ,um long carbon nanotube is estimated to be about 1 pH, normalized inductance is found to be larger than that of normal inductance [21. Therefore, carbon nanotube inductors are promising passive electric component for the integrated circuit Reference [1]Y. Sakurada, S. Irako, Y. Nakajima, T. Hanajiri, K. Tsubaki, Ext. Abstr. (51st Spring meet 2004); Japan Society of Applied Physics and Related Societies, 29p-F-16. 121S. Irako, Y. Sakurada, Y. Nakajima, T. Hanajiri, T. Toyabe, K. Tsubaki, Ext. Abstr. (51st Spring meet. 2004); Japan Society of Applied Physics and Related Societies, 29p-F-15. 13]D. Saida and T. Takahashi, Jpn. J. Appl. Phys. Vol. 42, pp.4874, 2003.