NER: Nanowire Non-Volatile Memory

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We propose to investigate and develop a new type of non-volatile electronic memory based on a novel conduction bistability observed in regimented arrays of self assembled semiconductor nanowires [Appl. Phys. Lett., 76, 460 (2000)]. The wires have two stable conductance states that differ in conductance by four orders of magnitude at room temperature. These two states can be used to encode binary bits 0 and 1. When a sample is left in the high conductance state at room temperature, it remains in that state for 1 year before reverting to the low conductance state, and when it is left in the low conductance state, it persists in that state for longer than the monitoring period of 1 year. The long retention time may be partially a result of quantum confinement and the phonon bottleneck effect. This system is a promising candidate for non-volatile random access memory with excellent packing density. Apart from the retention time, two important figures of merit for memory devices are the access speed for reading/writing and the dynamic power dissipation during the read/write operation. The measured writing time (the reading time is much smaller) is ~ 2 msec, which we believe can be reduced significantly with appropriate device design. The threshold voltage for switching is a few tens of volt, which too can be reduced significantly using the same design. However, the unavoidable penalty involved in reducing the access time and power dissipation is a concomitant reduction of the retention time. In order to develop a truly advanced memory, these contradictory requirements must be met in an optimal manner which makes this research high risk and exploratory. A secondary purpose of the NER is to identify unequivocally the mechanism responsible for the bistability. Virginia Commonwealth University has an active outreach program involving high school students (the RAPME program for minorities and the QUESTERS program). Students from both programs will be involved in this research (K-12 education). This research will be carried out in collaboration with a group in Kurchatov Institute, Moscow, Russia.