Markus Siegert

Spin Torque Induced Magnetization Switching Variations

Spin torque induced magnetization switching variations are studied using experimental measurement and theoretical modeling. The study covers a wide time range, from the short time dynamic switching (10 ns) to the long time thermal switching (0.1 s). The modeling results agree well with the measurement data on switching mean and variation. Both data and model show different scaling behaviors of switching current variation and switching time variation as time scales down from the second to the nanosecond region. This study not only provides understanding of the physics involved, but also tools for making design tradeoffs between current switching magnitude, switching variation, switching speed, and thermal stability.

Charge-based scanning probe readback of nanometer-scale ferroelectric domain patterns at megahertz rates

We present a method for data storage in continuous ferroelectric (FE) media, applicable to storage systems based on one or more scanning probes. Written FE domains are read back in a destructive fashion by applying a constant voltage of magnitude greater than the coercive voltage, as is done in FE random access memory (FeRAM). The resulting flow of screening charges through the readback amplifier provides sufficient signal to allow readback of domains of minimum dimension of the order of 10 nm at MHz rates, orders of magnitude faster than previously demonstrated techniques for readback of domains in continuous FE media.

Correlating structural and resistive changes in Ti:NiO resistive memory elements

Structural and resistive changes in Ti-doped NiO resistive random access memory structures that occur upon electroforming have been investigated using hard x-ray microscopy. Electroforming leads to structural changes in regions of size up to about one micrometer, much larger than the grain size of the structure. Such changes are consistent with a migration of ionic species or defects during electroforming over regions containing many crystalline grains.