Who: Ryoma Hayakawa (NIMS, Tsukuba, Japan)
Place: Donostia International Physics Center
Date: Monday, 4 September 2017, 12:00
Vertical resonant tunneling transistors with molecular quantum dots
International Center for Materials Nanoarchitectonics (WPI-MANA)
National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba 305-0044, Japan
Quantum molecular devices hold considerable promise for the construction of new data processing architectures that cannot be achieved using current Si technology. Although the relevant basic quantum transport properties have been examined by specific methods such as scanning probe and break-junction techniques, these methodologies are not compatible with current complementary metal-oxide?semiconductor (CMOS) applications.
In this regard, we have proposed to use organic molecules as quantum dots in double tunnel junctions.1-3 A striking feature of the proposed system is that the tunnel junction is composed of a MOS structure, which is the heart of current Si transistors. Thus, the structure satisfies both requirements above, namely, the integration of molecular functions and close affinity with current CMOS devices. The molecules are embedded in the insulating layers, which consist of a silicon oxide (SiO2) layer and an aluminum oxide (Al2O3) layer (Fig. (a)). The number density of molecules was estimated in the order of 1012-1013 cm-2, and we have observed clear resonant tunneling through discrete energy levels of the embedded molecules.1 This finding enabled the following attractive manipulations of the tunneling currents, which are unique features of organic molecules: the employment of binary molecules, including copper phthalocyanine and fluorinated phthalocyanine, produced multilevel control of the resonant tunneling;2 and the adoption of diarylethene photochromic molecules allowed for optical manipulation of the tunneling, with the current being reversed by alternating ultraviolet and visible light irradiation.3
Futhermore, we employed abovementioned double tunnel junctions as the transistor channels in vertical resonant tunneling transistor.4 The transistors enabled multilevel operations induced by the discrete energy levels of the molecules. The effective gate modulation of the resonant tunneling currents was produced by depletion layers in the Si substrates. Thus, the proposed device has potential to integrate molecular functions into future CMOS devices, and to deliver unique device operations unobtainable with inorganic quantum dots.
1) R. Hayakawa and Y. Wakayama et al., Adv. Funct. Mater. 2011, 21, 2933-2937.
2) R. Hayakawa and Y. Wakayama et al., ACS Appl. Matter. Interfaces 2013, 5, 11371-11376.
3) H.-S. Seo , R. Hayakawa and Y. Wakayama et al., J. Phys. Chem. C 2014, 118, 6467-6472.
4) R. Hayakawa and Y. Wakayama et al., Nanoscale 2017 (under review).