A Memory Device Utilizing Resonant Tunneling in Nanocrystalline Silicon Superlattices
- PDF / 82,897 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 23 Downloads / 199 Views
A Memory Device Utilizing Resonant Tunneling in Nanocrystalline Silicon Superlattices Laurent Montès*, Galina F. Grom, Rishi Krishnan, Philippe M. Fauchet, Leonid Tsybeskov, Bruce E. White Jr.1 Department of Electrical and Computer Engineering, University of Rochester, Rochester, NY 14627, U.S.A. 1 Digital DNA Laboratories, Motorola, Austin, TX 78721, U.S.A. ABSTRACT A quantum structure based on Si/SiO2 and fabricated using standard Si technology has strong potential for applications in non-volatile and scaled dynamic memories. Among standard requirements, such as long retention time and endurance, a structure utilizing resonant tunneling offers lower bias operation and faster write/read cycle. In addition, degradation effects associated with Fowlher-Nordheim (FN) hot electron tunneling can be avoided. Superlattices of nanometer size layers of silicon and silicon dioxide were obtained by sputtering. The size of the silicon nanocrystallites (nc-Si) is fixed by the thickness of the silicon layer which limits the size dispersion. A detailed analysis of the storage of charges in the dots, as a function of the nanocrystals size, is investigated using capacitance methods. Constant voltage and constant capacitance techniques are used to monitor the discharge of the structure. Room temperature non-volatile memory with retention times as long as months is evidenced. INTRODUCTION The size reduction of transistors in the microelectronic industry and the challenges that follows lead for the search of alternative devices. Realization of silicon quantum dots is promising for new electronic devices. However many parameters play a crucial role in determining the properties of the dots. Such parameters as uniformity, size, shape, crystallographic orientation, passivation ... are difficult to control. In nc-Si memory devices writing usually occurs through a single SiO2 tunnel oxide [1], thus defects or leakage currents in the oxide can also strongly influence the properties of the device. Up to date, there is no systematical study concerning the influence of the dot size and tunnel barrier thickness on the memory properties. In this work, we present the principles of operation of an original and alternative structure for non-volatile memory operation. It relies on resonant tunneling through a superlattice composed of nc-Si and SiO2 layers, with typical thickness in the order of a few nanometers. It is possible to operate the memory even if one (or more) of the nc-Si layers is leaking. It is also less sensitive to technologically induced fluctuations such as the tunnel oxide thickness. Use of direct tunneling allows fast writing/erase while no degradation of the SiO2 is expected. The retention time could also be improved by orders of magnitude. In order to determine the influence of the size of the dots and tunnel barriers we have elaborated devices with several nc-Si sizes and tunnel oxide thickness. Capacitance methods are used to evidence the charging of the dots and the time evolution of the stored charges is studied. EXPERIMENTAL
Data Loading...
