High-Speed Electron Devices Using Nanometer-thick Metal/Insulator Layered Heterostructures 



Staffs:    M. Asada    M. Watanabe
Students:  T. Suemasu  N. Suzuki   Y. Kouno  W. Saitoh  H. Iwai 
           K.Mori      F. Iizuka

Superlattices and ultrathin layers with the combination of metal and insulator were proposed as one of the candidates of the material for ultrahigh- speed electronic devices and optical devices because of the low resistivity of metals, low dielectric constant and wide band gap of insulators and high conduction band offset at metal/insulator heterointerface. A novel transistor using quantum interference in metal/insulator heterostructure has been proposed and it was shown that sub-pico second response can be expected at such devices.

Results obtained up to now are as follows.


  1. Multiple negative defferential resistance (NDR) due to quantum interference of electron waves was observed for the first time in metal (CoSi2)/insulator(CaF2) resonant tunneling hot electron transistor structure. This result is considered to be a strong evidence of quantum interference of hot electron waves in the CaF2 conduction band, which is the same mechanism as the Fabry-Perot interferometer in optics.

  2. The first transistor action with negative differential resistance at room temperature (300K) of nanometer-thick metal(CoSi2)/insulator(CaF2) resonant tunneling transistor (MI-RTT) has been achieved. Observed characteristics was explained relatively well using theoretical analysis taking several parasitic elements (e.g., base resistance, substrate resistance and leak currents connected to the intrinsic transistor) into account.

  3. The formation technique of silicon and cobalt silicide nanometer particles (<10nm) in CaF2 grown on a Si(111) substrate was demonstrated using codeposition of Si, Co and CaF2. It was made clear that the size and density of silicon and silicide particles can be controlled by the substrate temperature and the evaporation rate of CaF2 and Si. At a growth temperature of around 200 degree C and a flux ratio of Co:Si:CaF2 of about 1:2:2, an average diameter of 7nm was obtained.