Noureddine Tayebi
Graduate Researcher, Stanford University/Intel
April 12, 2011 | 12:00 to 01:00 | 540 Cory Hall, DOP Center Conference Room
Host: John Huggins
Probe-based nonvolatile memory using ferroelectric media is an ideal candidate for future ultra-high density (> 1 Tbit/inch^2) memory devices. In such a device, an array of atomic force microscope (AFM) probes is used to write data by applying short electrical pulses to invert the polarization of local film volumes. However, no commercial product has reached the market yet. This is due to three fundamental issues that have remained a bottleneck for the development of this technology. These are ultrahigh density writing over large areas, stability of single-digit nanometer inverted domains and probe-tip mechanical wear. In this talk, we demonstrate a dual CMOS switching scheme which allows for the writing of a stable 3.6 Tbit/inch^2 storage density over a 1×1 µm2 area, which is the highest density ever written on ferroelectric films over such a large area. Using novel dielectric-sheathed single-walled carbon nanotube (SWNT) probes, we then demonstrate that single-digit nanometer domains remain stable only if they are fully inverted through the entire PZT film thickness, which is dependent on a critical ratio of electrode size to the film thickness. This understanding enables the formation of stable domains as small as 4 nm in diameter, corresponding to 10 unit cells in size. Such domain size corresponds to potential 40 Tbit/inch^2 data storage densities. Furthermore, we show that the built-in bias can be tuned and suppressed by repetitive hydrogen and oxygen plasma treatments, allowing for nanometer-size domain stability in both up and down polarizations. Finally, we show that a platinum-iridium probe-tip retains its write-read resolution on such surfaces over 5 km of sliding at a 5 mm/s velocity. This tip-wear endurance is enabled by introducing a thin water layer at the tip-media interface – thin enough to form a liquid crystal. By modulating the force at the tip-surface contact, this water crystal can act as a viscoelastic material, which reduces the stress level on atomic bonds taking part in the wear process. Furthermore, we show that the wear endurance distance can be increased by as much as two folds through the use of ultra-hard HfB2 metal coatings.
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