AVS 46th International Symposium
    Electronic Materials and Processing Division Wednesday Sessions
       Session EM-WeA

Invited Paper EM-WeA3
Nano-Crystal and Quantum-Dot Memories: Implications Small Dimensions, Quantum Confinement and Interface States

Wednesday, October 27, 1999, 2:40 pm, Room 608

Session: Novel Materials and Devices for Computation and Communication
Presenter: S. Tiwari, Cornell University
Authors: S. Tiwari, Cornell University
A. Kumar, IBM T.J. Watson Research Center
J.J. Welser, IBM T.J. Watson Research Center
Correspondent: Click to Email
For field-effect devices, one of the most significant effects of scaling of critical dimensions to the 1--10~nm range is a reduction in collective effects whose reproducibility has been so profitably applied over the last many decades. Examples of such collective phenomena are the number of electrons flowing through the channel, the number of electrons transferred during a CMOS switching event, and the number of dopants used to control the threshold voltage. A larger number of electrons flowing in the channel leads to smaller fluctuations in the current, a larger number of electrons transferred during switching leads to smaller fluctuations in the switching voltage levels, and a larger number of dopants leads to smaller fluctuations in the threshold voltage. The scaling of device dimensions has been driven by higher function and lower cost gained from an increase of device density and performance, a lowering of power density, and mixing of logic and memory technologies. Logic and memory have to co-exist at such small dimensions, and the various forms of memory have to be capable of providing a range of performance from high speed to low power and non-volatility. Nano-crystal and Quantum-Dot memories, examples of flash memories, are small dimension structures that utilize quantum-dot(s) between the gate and the channel of a field-effect transistor to store electron(s), which screen the mobile charge in the channel and thus induce a change in the threshold-voltage or conductivity. These quantum-dots are transmissively coupled to the channel and isolated from the gate. Their reduced dimension and confinement brings forth two important features that are absent in the conventional silicon field-effect transistors: a reduced density of states, restricting the states available for electrons and holes to tunnel, and the Coulomb blockade effect, arising from a larger electrostatic energy associated with placing a charged particle onto a smaller capacitance.