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To: NightOwl who wrote (13941)	4/19/2008 9:48:17 PM
From: NightOwl	Read Replies (1) of 14464

Well. Speaking of the devil in the nano-details... We (Jun Zhu and co-workers) are studying non-volatile memory device behavior based on thin graphite field effect transistors (FETs) with a ferroelectric film Pb(Zr0.2Ti0.8)O3 (PZT) as gate oxide. With a remnant polarization field of ~ 40 ?C/cm2, PZT can potentially induce an enormous 2D carrier density in graphite ~ 3x1014cm-2. The electric-field controlled polarization switching of PZT provides a natural mechanism to implement memory functions. Below the coercive field, PZT displays a high dielectric constant of ~100. We have deposited and identified 3-5 nm graphite pieces on epitaxial single crystal PZT thin films grown on Nb doped SrTiO3 (STO) substrates (backgate) and fabricated FET devices (Fig.1) using e-beam lithography. Our thin graphite FETs show pronounced hysteresis in carrier density and resistivity as a function of the applied backgate voltage and sweeping direction (Fig. 3), with long retention time of ~10 hours at room temperature, suggesting possible applications as memories. This phenomenon has been observed in multiple devices. We also measure 2D carrier density as high as 2x1013/cm2 in these FETs, with just a few volts on the backgate, demonstrating the efficient charge injection of PZT gate dielectric. Our current investigation focuses on identifying the origins and the mechanisms of the surface states which play important role in the screening of bulk polarization of the PZT and give rise to the direction of the observed hysteresis. We are also experimenting with sample preparation techniques to eliminate such states to achieve yet high density 2D conduction channels and non-volatile memory effect due to the switching of the PZT polarization. nseresearch.org 0\|0

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