In-Sung Park

Improved electrical properties of Pt/HfO2/Ge using in situ water vapor treatment and atomic layer deposition

The effects of water vapor treatment (WVT) on a Ge substrate were investigated in order to understand the improved electrical properties of Pt/HfO2/Ge metal-oxide-semiconductor (MOS) capacitors. The WVT and HfO2 deposition were performed in situ using an atomic layer deposition technique to avoid air exposure. As a result, the WVT on cleaned Ge substrates reduced the native oxide effectively and enhanced the initial growth of the HfO2 film. The improved interface qualities with WVT enhanced Ge-based device performance through a smoother capacitance-voltage curve, less increase in the inversion capacitance, and lower density of interface states.

Layer-by-layer photonic crystal fabricated by low-temperature atomic layer deposition

Layer-by-layer three-dimensional photonic crystals are fabricated by low-temperature atomic layer deposition of titanium dioxide on a polymer template created by soft lithography. With a highly conformal layer of titanium dioxide, a significantly enhanced photonic band gap effect appears at 3.1μm in transmittance and reflectance. From optical investigations of systematically shifted structures, the robust nature of the photonic band gap with respect to structural fluctuations is confirmed experimentally. With angle-resolved Fourier-transform spectroscopy, the authors also demonstrate that the fabricated photonic crystal can be a diffraction-free device as the photonic band gap exists over the diffracting regime.

Atomic layer deposition of Y2O3 films using heteroleptic liquid (iPrCp)2Y(iPr-amd) precursor

Y2O3 films grown with a new liquid Y precursor, (iPrCp)2Y(iPr-amd), have been investigated in terms of the chemical properties of the precursor, atomic layer deposition (ALD) process, and material characterization of the deposited film, as well as its non-volatile resistive switching behavior has been investigated. A heteroleptic (iPrCp)2Y(iPr-amd) has been synthesized because it exists in a liquid phase at room temperature. A vapor pressure of 1 Torr is obtained at 168 °C, and thermal evaporation and decomposition begins from 250 °C and 425 °C, respectively. The Y2O3 film is fabricated by ALD technique using (iPrCp)2Y(iPr-amd) and water as the precursors. The growth of the Y2O3 films is self-limited with an ALD window from 350 °C to 450 °C and a growth rate of 0.06 nm per cycle. The deposited Y2O3 film shows a polycrystalline cubic structure, higher refractive index of over 1.8 at 632.8 nm, and a high dielectric constant of 24. The as-deposited Y2O3 film is highly stoichiometric and constant in terms of Y and O through the depth, and it also includes small –OH bonds in the film without any additional processes. The Ru/Y2O3/Ru resistor shows resistance switching between the low and high resistance states with voltage sweeping, and the resistance ratio between the two states is more than 1000 times, which is preferable for non-volatile memory operation.

Anode dependence of set voltage in resistive switching of metal/HfO2/metal resistors

The anode dependence of set voltage in resistive switching behaviors of metal/HfO2/metal resistors is investigated by applying positive and negative voltage polarity, and by changing the location of the electrodes made of various metals including Al, Pt, Mo, and Ru. When the same anode is applied to resistors whatever cathodes are, their set voltages in high resistance state are very similar. The strong anode dependence on set voltage is related to the potential near the anode domain owing to the partial rupture of the conducting filament. This rupture of filaments makes the thick insulator film thinner with a small potential barrier.

Uniform dehydrogenation of amorphous silicon thin films using a wide thermal annealing system

To prevent ablation caused by sudden hydrogen eruption during crystallization of hydrogenated amorphous Si (a-Si:H) thin films, a wide dehydrogenation thermal annealing (wDTA) system was developed to reduce hydrogen content in a-Si:H film prior to its crystallization process. The annealed a-Si:H films were fully dehydrogenated and nanocrystallized by the wDTA system. Raman scattering measurement revealed that the dehydrogenation process lowers the hydrogen content through disappearance of the peak intensity at 2000 cm−1. The a-Si:H film was transformed into nanocrystallized Si with lower residual stress. The major advantage of this wDTA was the large area uniformity of the thermal and the resulting material properties for 8 generation display. The uniform material characteristics of the hydrogen content, thickness, energy bandgap, and transmittance of the annealed Si films in the overall area was confirmed by Raman spectroscopy, spectroscopic ellipsometry, and UV–vis spectrometer measurement.

Metal-HfO2-Ge capacitor: Its enhanced charge trapping properties with S-treated substrate and atomic-layer-deposited HfO2 layer

The charge trapping properties of metal-HfO2-Ge capacitor as a nonvolatile memory have been investigated with (NH4)2S-treated Ge substrate and atomic-layer-deposited HfO2 layer. The interfacial layer generated by (NH4)2S-treated Ge substrate reveals a trace of -S- bonding, very sharp interface edges, and smooth surface morphology. The Ru-HfO2-Ge capacitor with (NH4)2S-treated Ge substrate shows an enhanced interface state with little frequency dispersion, a lower leakage current, and very reliable properties with the enhanced endurance and retention than Ru-HfO2-Ge capacitor with cyclic-cleaned Ge substrate.

Dielectric function of Si1−xGex films grown on silicon-on-insulator substrates

The dielectric functions of undoped and P-doped Si1−xGex (SiGe) films with a compressive strain on silicon-on-insulator (SOI) substrates are obtained by using spectroscopic ellipsometry. The respective Kato–Adachi and Tauc–Lorentz models are best fitted to the undoped and P-doped SiGe films to obtain their complex dielectric functions. The undoped SiGe films are characterized by multimodal peaks in the dielectric function, whereas the P-doped SiGe films exhibit only a broad peak. Further, the E0 and E1 critical points (CPs) of the undoped SiGe films are strongly dependent on the Ge concentration, whereas the E2 CPs are independent of concentration. The E0 and E2 CPs in the undoped SiGe films on an SOI substrate are lower than those of SiGe on a bulk-Si substrate owing to the higher strain. For P doping in SiGe, its dose causes non-monotonic variations in Eg and E0.

GeOx interfacial layer scavenging remotely induced by metal electrode in metal/HfO2/GeOx/Ge capacitors

The metal gate electrodes of Ni, W, and Pt have been investigated for their scavenging effect: a reduction of the GeOx interfacial layer (IL) between HfO2 dielectric and Ge substrate in metal/HfO2/GeOx/Ge capacitors. All the capacitors were fabricated using the same process except for the material used in the metal electrodes. Capacitance-voltage measurements, scanning transmission electron microscopy, and electron energy loss spectroscopy were conducted to confirm the scavenging of GeOx IL. Interestingly, these metals are observed to remotely scavenge the interfacial layer, reducing its thickness in the order of Ni, W, and then Pt. The capacitance equivalent thickness of these capacitors with Ni, W, and Pt electrodes are evaluated to be 2.7u2009nm, 3.0u2009nm, and 3.5u2009nm, and each final remnant physical thickness of GeOx IL layer is 1.1u2009nm 1.4u2009nm, and 1.9u2009nm, respectively. It is suggested that the scavenging effect induced by the metal electrodes is related to the concentration of oxygen vacancies generated by o...

Strain modified/enhanced ferromagnetism in Mn3Ge2 thin films on GaAs(001) and GaSb(001)

Ferromagnetic Mn3Ge2 thin films were successfully grown on GaAs(001) and GaSb(001) substrates using molecular beam epitaxy. The results of our work revealed that the substrate facilitates to modify magnetic and electrical properties of Mn3Ge2 films due to tensile/compressive strain effect between films and substrates. The characteristic spin-flopping transition at around 150u2009K for the bulk Mn3Ge2 disappeared completely for both samples. The antiferromagnetism below 150u2009K changed to ferromagnetism and retained above room temperature. The saturation magnetization was found to be 0.23 and 1.32u2009μB/Mn atom at 10u2009K for the samples grown on GaSb(001) and GaAs(001), respectively.

Effect of Growth Temperature on the Structural and Electrical Properties of ZrO2 Films Fabricated by Atomic Layer Deposition Using a CpZr[N(CH3)2]3/C7H8 Cocktail Precursor

The effect of growth temperature on the atomic layer deposition of zirconium oxide (ZrO2) dielectric thin films that were fabricated using a CpZr[N(CH3)2]3/C7H8 cocktail precursor with ozone was investigated. The chemical, structural, and electrical properties of ZrO2 films grown at temperatures from 250 to 350 °C were characterized. Stoichiometric ZrO2 films formed at 250–350 °C with an atomic ratio of O to Zr of 1.8–1.9 and a low content of carbon impurities. The film formed at 300 °C was predominantly the tetragonal crystalline phase, whereas that formed at 350 °C was a mixture of tetragonal and monoclinic phases. Electrical properties, such as capacitance, leakage current, and voltage linearity of TiN/ZrO2/TiN capacitors fabricated using the thin ZrO2 films grown at different temperatures were compared capacitor applications. The ZrO2 film grown at 300 °C exhibited low impurity content, predominantly tetragonal crystalline structure, a high dielectric permittivity of 38.3, a low leakage current of below 10−7 A/cm2 at 2 V, and low-voltage linearity.