Joseph Ya-min Lee

Leakage currents in amorphous Ta2O5 thin films

Tantalum oxide (Ta2O5) is an important material for future dynamic random access memory application owing to its high dielectric constant. This work examines the structural and electrical properties of Ta2O5 thin films deposited by plasma-enhanced chemical vapor deposition using a penta ethoxy tantalum Ta(OC2H5)5 liquid source. The x-ray diffraction patterns indicate that the as-deposited thin films are amorphous and become polycrystalline after rapid thermal annealing above 650 °C. The level of carbon contamination is below that which can be detected by Auger electron spectroscopy measurement. Electrical measurements performed on amorphous Ta2O5 using a Au/Ta2O5/Pt/Ti/Si metal-tantalum oxide-metal structure exhibit a low leakage current, reasonable breakdown field (5.4 MV/cm), and high dielectric constant (23–25). The leakage current is 2×10−8 A/cm2 at 1 MV/cm. In addition, the leakage current mechanism of amorphous Ta2O5 capacitors is investigated by plotting the ln(J) vs E1/2 curves at a low electric f...

Electrical conduction mechanism in high-dielectric-constant (Ba0.5,Sr0.5)TiO3 thin films

The electrical conduction mechanism of (Ba0.5,Sr0.5)TiO3 (BST) as a function of the temperature was studied. Au/BST/Pt metal–insulator–metal capacitors were fabricated. The temperature range was from 300 to 423 K. The conduction current depended on the voltage polarity. At high electrical field (>800 kV/cm) and with the Pt electrode biased negatively, the Pt/BST interface forms a Schottky barrier with a barrier height of 0.58 eV from 300 to 373 K. The Au/BST interface forms an ohmic contact. The conduction current when the Au electrode is biased negatively shows space-charge-limited-current behavior. An energy band diagram is proposed to explain the experimental results.

Electrical conduction mechanisms of metal∕La2O3∕Si structure

Metal-oxide-semiconductor capacitors that incorporate La2O3 dielectric films were deposited by radio frequency magnetron sputtering. In this work, the essential structures and electrical properties of La2O3 thin films were investigated. Capacitance–voltage, energy dispersive x-ray spectrometry, and transmission electron microscopy analyses reveal that an interfacial layer was formed, subsequently reducing the effective dielectric constant of the 700°C annealed La2O3 thin films. The dominant conduction mechanism of the Al∕La2O3∕p-Si metal-lanthanum oxide-semiconductor capacitor is space-charge-limited current from 300to465K in the accumulation mode. Three different regions, Ohm’s law region, trap-filled-limited region, and Child’s law region, were observed in the current-density–voltage (J–V) characteristics at room temperature. The activation energy of traps calculated from the Arrhenius plots was about 0.21±0.01eV. The electronic mobility, trap density, dielectric relaxation time, and density of states i...

Fabrication and Characterization of Metal–Ferroelectric (PbZr0.53Ti0.47O3)–Insulator (Dy2O3)–Semiconductor Capacitors for Nonvolatile Memory Applications

Metal-ferroelectric-insulator-semiconductor capacitors with Pb(Zr0.53,Ti0.47)O3 (PZT) ferroelectric layer and dysprosium oxide (Dy2O3) insulator layer were fabricated and characterized. The measured memory window of 0.86V was close to the theoretical value ΔW≈2dfEc≈0.78V at a sweep voltage of 8V. The size of the memory window as a function of PZT film thickness was discussed. The C-V flatband voltage shift (ΔVFB) as function of charge injection was also studied. An energy band diagram of the Al∕PZT∕Dy2O3∕p-Si system was proposed to explain the memory window and flatband voltage shift. The charge injection is mainly due to electrons.

Electron conduction mechanism and band diagram of sputter-deposited Al/ZrO2/Si structure

Metal-oxide-semiconductor capacitors that incorporate ZrO2 gate dielectrics were fabricated by radio frequency magnetron sputtering. In this work, the essential structures and electrical properties of ZrO2 thin films were investigated. C-V, energy dispersive x-ray spectrometry, and transmission electron microscopy analyses reveal that an interfacial layer was formed, subsequently reducing the k value of the annealed ZrO2 thin films. Additionally, the mechanisms of conduction of the Al∕ZrO2∕p-Si metal/zirconium oxide/semiconductor structure were studied with reference to plots of standard Schottky emission, modified Schottky emission, and Poole–Frenkel emission. According to those results, the dominant mechanisms at high temperatures (>425K) are Poole–Frenkel emission and Schottky emission in low electric fields ( 1MV∕cm), respectively. Experimental results indicate that the Al∕ZrO2 barrier height is 0.92eV and the extracted trap level is about 1.1eV from the conduction...

Temperature dependence of the current conduction mechanisms in ferroelectric Pb(Zr0.53,Ti0.47)O3 thin films

The temperature dependence of the current conduction mechanisms in Au/Pb(Zr0.53,Ti0.47)O3/Pt (Au/PZT/Pt) metal–insulator–metal thin-film capacitors was investigated. The dominant current conduction mechanism from 300 to 375 K is space-charge-limited current (SCLC) due to holes and changes to Schottky emission in the temperature range of 400 to 500 K above the electric field of 0.2 MV/cm. It is observed that the transition voltage (Vtr) of SCLC conduction decreases with increasing temperature. Shallow hole trap levels vary from 0.3 to 0.19 eV above the valence-band edge as the temperature varies from 300 to 375 K. The trap-filled-limited voltage (VTFL) increases with increasing temperature. The deep trap level extracted from VTFL is positioned at 0.39 eV above the valence-band edge. The Au/PZT barrier height extracted from Schottky emission is 0.85 eV. An energy band diagram of the Au/PZT/Pt system is proposed to explain the current–voltage characteristics.

A New Metal–Ferroelectric

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