UCLA researchers have invented a novel nanotechnology probe based telegraph signal microscope (TSM). When TSM is combined with atomic force microscopy, real-time characterization of single atom spins and detection of defects in carbon nanotubes (CNTs)/ nanowires is possible.
For more than half a century, the number of transistors per chip has increased exponentially according to Moores law. As traditional CMOS technologies are beginning to reach their limit, the semiconductor industry is looking to carbon nanotubes (CNTs) and nanowire field-effect transistors (FETs) to answer the need for increased minimization. CNTs are beginning to have applications in electronics, optics, material science, and medicine. However, large-scale integration of nanowire based FETs remains a problem because defects like oxide traps become a major concern at the nano level. Traditional defect characterization relies on capacitance based methods such as deep level transient microscopy (DLTM) and electron paramagnetic resonance (EPR). However these methods cannot be applied to CNTs, due to their inherently low capacitance. There is a clear need for development of a robust defect detection system in the nanotechnology industry.
Researchers at UCLA have demonstrated that random telegraph signal (RTS) noise is a sensitive and nondestructive measure related to trapping and detrapping of single defect centers in CNT channels. Although the RTS signal has been observed in other systems, it does not become the dominant signal until the nano level, when channel size is sufficiently small. UCLA researchers have exploited the RTS phenomena and created a telegraph signal microscope (TSM) that uses RTS with CNTs/nanowires as a probe. TSM can be used to detect defects in nanotechnology based devices with ultra-high sensitivity. Furthermore, TSM can be integrated with atomic force microscopy to acquire image and single atom information simultaneously. At low temperature, TSM can map single spin and manipulating spin when used with EPR. Finally, Fermi energy of the RTS probe is sensitive to incidence of a single photon, enabling use of this technology as a photon detector as well.
A complete device has been assembled and tested with single wall carbon nanotubes and Indium Oxide nanowire FETs. RTS amplitudes up to 60% total current were observed, demonstrating good sensitivity and signal to noise ratio. Defect information, material damage, bandgap calculation for CNT and transition coefficients due to single defect Coulomb potential have been detected.
|United States Of America||Issued Patent||7,427,754||09/23/2008||2005-439|