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The origin of multilevel resistances of In3Sb1Te2 (IST) phase-change random access memory cell has been investigated with high-resolution transmission electron microscopy (HR-TEM). The HR-TEM indicates that the microstructure of IST in the programming volume changes from amorphous to InSb and amorphous at the first state, and InSb and InTe at the second state, and IST at the third state, which are fairly consistent with four different levels of resistance. The resistance difference between the amorphous and the IST is about four orders of magnitude. [ABSTRACT FROM AUTHOR]

Structural transformation of the Ge2Sb2Te5 was investigated by a high resolution transmission electron microscopy (HRTEM). It was found that Ge atoms undergo umbrella-flip motion from a tetrahedral site into an octahedral site in transforming from the amorphous to the metastable phase of Ge2Sb2Te5. The presence of a twin boundary between fcc and hexagonal structured Ge2Sb2Te5 was also confirmed through the HRTEM observations. These results support the umbrella-flip model proposed by Kolobov et al. [Nat. Mater. 3, 703 (2004)] and the epitaxial growth model proposed by Park et al. [Appl. Surf. Sci. 256, 8102 (2006)]. [ABSTRACT FROM AUTHOR]

The microstructures of once melt-quenched Ge2Sb2Te5 (GST) phase change contact dimensions are directly investigated with high resolution transmission electron microscopy (HR-TEM) by applying reset pulse of 7–13 V. The ovonic threshold switching voltage is decreased from 4.1 to 2.8 V when the as-deposited GST cells are once melt quenched by 10 V. HR-TEM reveals that there are hexagonal nuclei in the once melt-quenched GST and the GST can be partially left in not the amorphous but the crystalline state when the molten GST is not swiftly quenched, which is an origin of the switching failure. [ABSTRACT FROM AUTHOR]

During the crystallization of amorphous YMnO[sub 3] thin film on Si (100) at 870 °C in a dry O[sub 2] ambient, a nanoprecipitate layer was found between the YMnO[sub 3] and the Si substrate. Lattice image processing as well as high-resolution transmission electron microscopy showed that the nanoprecipitate layer was a cubic Y[sub 2]O[sub 3] phase. Also, it showed that a native oxide was consumed by the reaction with the Y atoms. This [111] Y[sub 2]O[sub 3] layer exhibited a local epitaxial relationship to the c-axis oriented (0001) YMnO[sub 3]. The formation of Y[sub 2]O[sub 3] phase and the consumption of native oxide at the YMnO[sub 3]/Si interface are due to the Y atom which is better than Mn in its ability to oxidize during heat treatment in O[sub 2] ambient. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

For the ferroelectric gate-type capacitors, we have fabricated Pt/YMnO[sub 3](YMO)/Si and Pt/SrBi[sub 2]Ta[sub 2]O[sub 9](SBT)/Si structures. We have used the highly c-axis oriented hexagonal YMO thin films (ε[sub r]approx. 19) and the polycrystalline SBT thin films (ε[sub r]approx. 150) with a dominant (115) orientation, respectively. The memory effect resulting from the ferroelectric switching properties is investigated as a function of the dielectric constant of ferroelectric thin films with 150 nm in thickness. About 3 times wider memory window is obtained by using a relatively low dielectric constant of YMO than that using a relatively high dielectric constant of SBT. Typical memory windows of the Pt/YMO/Si and the Pt/SBT/Si capacitors are 1.24 and 0.34 V, respectively, at a gate voltage of 5 V. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]