Ju-chul Park

Improvement of resistive memory switching in NiO using IrO2

For the development of resistive memory devices using NiO, improvements of several memory switching properties are required. In NiO memory cells with noble metal electrodes, broad dispersions of memory switching parameters are generally observed with continuous memory switchings. We report the improvements in minimizing the dispersions of all memory switching parameters using thin IrO2 layers between NiO and electrodes. The role of thin IrO2 layers on NiO growth and memory switching stabilization are discussed.

Observation of molecular nitrogen in N-doped Ge2Sb2Te5

Ge2Sb2Te5 (GST) film in the crystalline state was nitrogen doped using the reactive sputtering method in order to increase sheet resistance. High-resolution x-ray absorption spectroscopy revealed that molecular nitrogen (N2) existed in the N-doped GST film. This finding implies that both molecular nitrogen and atomic-state nitrogen should be taken into account in understanding the structures of N-doped GST film. The molecular nitrogen is believed to exist at interstitial and vacancy sites, and more likely at grain boundaries.

Observation of [110] surface band within {101} a-domain of heteroepitaxial PbTiO3 thin film fabricated by hydrothermal epitaxy

Heteroepitaxial PbTiO3 film on an Nb-doped (001) cubic SrTiO3 substrate was fabricated by hydrothermal epitaxy at 200°C. Piezoresponse force microscopy and x-ray Θ rocking curves confirmed that the film showed a c∕a∕c∕a multi-domain structure even though it did not undergo a cubic paraelectric (PE) to tetragonal ferroelectric (FE) phase transition. After heat treatment of this film at 600°C, we observed the [110] surface band within the a-domain, which was formed through the PE to FE phase transition. We also found that a [110] surface band existed along the (11¯1) plane within the a-domain. We predicted that the [110] surface band would be monoclinic phase due to the interaction of two different variants of a-domains in the presence of a c-domain in the heteroepitaxial PbTiO3 film.

Effects of cobalt silicidation and postannealing on void defects at the sidewall spacer edge of metal–oxide–silicon field-effect transistors

The void formation at the edge of the sidewall spacer during postannealing is favorable in reducing both the number of excess silicon vacancies generated in the silicon substrate during silicidation, and the tensile stress concentrated at the edge of the metal-oxide-silicon field-effect transistor (MOSFET) sidewall spacer. The observation of void growth with the postannealing time supports this hypothesis. The observed void shape agrees well with a numerical simulation driven by the minimization of the interfacial free energy. The void serves as a resistance in the current–voltage characteristics of MOSFET devices.