Advanced Device Laboratory

Outline

To explore future nanoelectronics, we develop fabrication processes of sub-10 nm structures, and study their electronic properties to apply them to functional nanodevices. We use carbon nanotubes, semiconductor (Si, Ge, InAs, et al.) nanowires, graphene and functional molecules as building blocks of those nanostructures. Besides, we are interested in the THz properties of solid-state materials and development of a near-field THz imaging system. Surface analysis with medium energy ion beam scattering is also our research target. With a combination of the top-down and bottom-up technologies, we fabricate quantum dots, CNT/molecule heterostructures, and semiconductor/superconductor hybrid nanostructures for use in single electron devices, quantum computing devices, new quantum THz detectors and so on.

Recent Research Topic

Nanoelectronics research beyond CMOS transistors

Fig. 1 Single electron inverter fabricated with an individual carbon nanotube

Fig. 2 Quantum dot devices with an individual Si nanowire

We develop sub-10 nm scale nanostructures and study their electronic properties to explore possible applications to future nanoelectronics beyond CMOS. For that purpose, we use materials such as carbon nanotubes, semiconductor nanowires (Si, Ge and compound), graphene and molecules that are self-assembled in a size that is difficult to achieve with conventional top-down technology. The nanodevices we currently study are single electron devices where ultra-low power consumption is expected, quantum computing devices (qubits) composed of charge, spin and flux, and functional THz detectors based on the quantum response of the nanodevices to THz waves.

Quantum dots are basic nanostructures we use for nanodevices, where electrons are confined in small spaces. They are often called “artificial atoms,” and the one-dimensional hard wall potential well is an appropriate model of the carbon nanotube quantum dot. The single particle states are designed there with the Zeeman splitting in magnetic fields. This means that a single spin is created, which is a spin quantum bit. Coherent control of the artificial quantum state is one of our main research targets. It could be a spin state in the quantum dot, or the superconducting state in superconductor/ normal material hybrid nanostructures. The carbon nanotube and molecule heterostructures are ultimate nanostructures with a molecular scale. In those very small nanostructures, quantum effects could be observable even at room temperature.

In addition to developing discrete quantum devices, developing techniques to integrate those devices is also an important research target.

Fig. 3 Zeeman splitting of single particle levels in the carbon nanotube artificial atom

Fig. 4 THz photon assisted tunneling in carbon nanotube quantum dots