P. F. Lee

Growth and characterization of Hf-aluminate high-k gate dielectric ultrathin films with equivalent oxide thickness less than 10 Å

Ultrathin amorphous Hf–aluminate (Hf–Al–O) films have been deposited on p-type (100) Si substrates by pulsed-laser deposition using a composite target containing HfO2 and Al2O3 plates. Transmission electron microscopy observation of Hf–Al–O films showed that the amorphous structure of Hf–Al–O films was stable under rapid thermal annealing at temperatures up to at least 1000 °C. Capacitance–voltage measurement of a 38 A Hf–Al–O film revealed that the relative permittivity of the film was about 16. Such a film showed very low leakage current density of 4.6×10−3 A/cm2 at 1 V gate bias. The Hf–Al–O film under optimized condition did not show any significant interfacial layer at the interface and an equivalent oxide thickness of less than 10 A has been achieved. The formation of Hf–O and Al–O bonds in the film was revealed by x-ray photoelectron spectroscopy.

Synthesis and memory effect study of Ge nanocrystals embedded in LaAlO3 high-k dielectrics

A floating gate memory structure utilizing Ge nanocrystals embedded in LaAlO3 (LAO) high-k dielectric films has been fabricated by pulsed-laser deposition. A cross-sectional high-resolution transmission electron microscopy study revealed that the floating gate structure contains 5-nm-diam spherelike Ge nanocrystals embedded in amorphous LAO. A significant memory effect with a very high density of charge storage up to 2×1013∕cm2 in the Ge nanocrystals and a maximum flat band voltage shift of 3.2 V have been achieved for the trilayer structure of LAO(8nm)∕Ge∕LAO(3nm)∕Si. The memory structure utilizing the Ge nanocrystals grown in 1 min showed excellent charge retention characteristics, whereas the decay in memory capacitance after 104s of stress under a flat band voltage was only 8%. These results suggest that this memory structure utilizing Ge nanocrystals embedded in a LAO dielectric offers a high potential for the further scaling of floating gate memory devices. In addition, the effects of Ge growth time...

Study of interfacial reaction and its impact on electric properties of Hf-Al-O high-k gate dielectric thin films grown on Si

Amorphous thin films of Hf–Al–O (with atomic ratio of Al/Hf of about 1.4) were deposited on (100) p-Si substrates by pulsed-laser deposition using a HfO2 and Al2O3 composite target. Transmission electron microscopy was employed for a detailed study of the interfacial reaction between the Hf–Al–O films and the Si substrates. Islands of Hf silicide formed from interfacial reaction were observed on the surface of the Si substrate. The formation of Hf silicide is attributed to the presence of Al oxide in the films that triggers the reaction between Hf atoms in the amorphous Hf–Al–O films and Si under an oxygen deficient condition. The impact of silicide formation on the electrical properties was revealed by high-frequency capacitance–voltage (C–V) measurements on metal–oxide–semiconductor capacitors. The observed abnormal C–V curve due to interfacial reaction was discussed.

Comparison of interfacial and electrical characteristics of HfO2 and HfAlO high-k dielectrics on compressively strained Si1-xGex

Interfacial reactions and electrical properties of HfO2 and HfAlO high-k gate dielectric films on strained Si1−xGex (x=17%) fabricated by pulsed-laser deposition were investigated. The dielectric films were characterized by x-ray photoelectron spectroscopy, transmission electron microscopy, and electrical measurements. We found that alloying of HfO2 with alumina can reduce the GeOx formation at the interfacial layer and thus reduce the Ge diffusion during the film post-thermal annealing process. Such suppression effect significantly improved the electrical properties of the dielectric films.

Epitaxial growth of yttrium-stabilized HfO2 high-k gate dielectric thin films on Si

Epitaxial yttrium-stabilized HfO2 thin films were deposited on p-type (100) Si substrates by pulsed laser deposition at a relatively lower substrate temperature of 550 °C. Transmission electron microscopy observation revealed a fixed orientation relationship between the epitaxial film and Si; that is, (100)Si//(100)HfO2 and [001]Si//[001]HfO2. The film/Si interface is not atomically flat, suggesting possible interfacial reaction and diffusion. X-ray photoelectron spectrum analysis also revealed the interfacial reaction and diffusion evidenced by Hf silicate and Hf–Si bond formation at the interface. The epitaxial growth of the yttrium stabilized HfO2 thin film on bare Si is via a direct growth mechanism without involving the reaction between Hf atoms and SiO2 layer. High-frequency capacitance–voltage measurement on an as-grown 40-A yttrium-stabilized HfO2 epitaxial film yielded an effective dielectric constant of about 14 and equivalent oxide thickness to SiO2 of 12 A. The leakage current density is 7.0×1...

Self-organized Ge nanocrystals embedded in HfAlO fabricated by pulsed-laser deposition and application to floating gate memory

A trilayer metal-oxide-semiconductor structure containing a HfAlO tunnel layer, isolated Ge nanocrystals, and a HfAlO control layer, was obtained using pulsed-laser deposition (PLD). Self-organized Ge nanocrystals were formed by PLD at 600°C, suggesting a useful low-temperature process for fabricating Ge nanocrystals embedded in dielectric materials. The self-organized Ge nanocrystals so formed were uniform in size and distribution with a density approaching 1012cm−2. The effects of deposition temperature and growth rate in forming Ge nanocrystals were investigated and it was revealed that a relatively low temperature and growth rate are favorable for the formation of Ge nanocrystals. The memory effect of the Ge nanocrystals with storage charge density of up to 1012cm−2 has been demonstrated by the presence of hysteresis in the capacitance-voltage curves.

Effects of AlOx-cap layer on the luminescence and photoconductivity of ZnO thin films

The effects of AlOx-cap layer on the optical and photoelectrical properties of ZnO films have been studied by cathodoluminescence (CL), photoluminescence (PL), and photoconductivity (PC). Both the PL and CL show that the cap layer improves the emission characteristics of ZnO by enhancing the band-edge emission while at the same time reducing the deep-level emissions. To study the origin of improvement, depth-resolved CL has been carried out to map out the emissions at different depths. It shows that the improvement occurs primarily at the film surface, which indicates the cap layer acts as a passivation layer that suppresses the detrimental surface states. The PC measurement on the capped ZnO at room temperature shows a distinctive excitonic feature at 3.29 eV and an overall increment of photoresponse above the band gap. Therefore, our results suggest a higher sensitivity of UV detection can be achieved in ZnO simply be employing a thin AlOx-cap layer.

Spontaneous recovery of hydrogen-degraded TiO2 ceramic capacitors

Degradation of TiO2-based ceramic capacitors was observed after hydrogen incorporation on the termination electrodes of the capacitors via electrolysis of water. Fourier-transform infrared (FTIR) absorption spectra analysis of polished rutile single crystals clearly showed that hydrogen was incorporated into the TiO2 lattice through the treatment. Hydrogen reduces Ti4+ to Ti3+ and increases the concentration of charge carriers. The degradation was found to exhibit a strong dependence on time at room temperature. The degraded properties were spontaneously recovered through an aging process, showing a spontaneous recovery unique to TiO2-based ceramic capacitors. It is proposed that hydrogen is metastable in TiO2 and that hydrogen-induced degradation has different stabilities among various oxide-based components and devices.

Effects of Al addition on the native defects in hafnia

Two occupied native defect bands are experimentally detected in pure HfO2. The density of states of band one in the middle of the band gap reduces drastically with the Al addition, while that of band two slightly above the valence-band maximum remains rather unaffected. We attribute the two bands to the charged oxygen vacancy, and the oxygen-interstitial-related defect states of the HfO2, respectively. We demonstrate that the added Al passivates the VO+ induced midgap states but has little effect on other aspects of the electronic structure of the material.

Investigation of Ge nanocrytals in a metal-insulator-semiconductor structure with a HfO2∕SiO2 stack as the tunnel dielectric

A metal-insulator-semiconductor (MIS) structure containing a HfO2 control gate, a Ge nanocrystal-embedded HfO2 dielectric and a HfO2∕SiO2 stack layer as tunnel oxide, was fabricated by an electron-beam evaporation method. High-resolution transmission electron microscopy study revealed that the HfO2∕SiO2 stack layer minimized Ge penetration, leading to the formation of Ge nanocrystals that are self-aligned between the tunnel oxide and the capping HfO2 layer. Influence of different annealing conditions on the formation and distribution of Ge nanocrystals was studied. Current–voltage (I–V) and capacitance–voltage (C–V) measurements revealed promising electrical characteristics of the MIS structure, and relatively high stored charge density of 1012cm−2 was achieved.