Browsing by Author "Leu, CC"

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Characterization of NH3 plasma-treated Ba0.7Sr0.3TiO3 thin films
(2000-04-01)
Wuu, DS
;
Horng, RH
;
Liao, FC
;
Leu, CC
;
Huang, TY
The effects of plasma surface treatment, using NH3 gas, of Ba0.7Sr0.3TiO3 (BST) films on the leakage and dielectric characteristics of a Pt/BST/Pt capacitor were investigated. As a result of the exposure of BST to the plasma, the leakage current density of the BST capacitor can be improved by three orders of magnitude as compared to that of the nonplasma-treated sample at an applied voltage of 1.5 V. Nevertheless, the surface morphology of BST was also changed by the NH3 plasma, as explored by atomic force microscopy. From the X-ray photoelectron spectroscopy examination, the existence of the N 1 s peak was observed in the plasma-treated sample. It induces the additional space charge and results in the reduction of the dielectric constant. (C) 2000 Elsevier Science Ltd. All rights reserved.
Effects of O-2 plasma treatment on the electric and dielectric characteristics of Ba0.7Sr0.3TiO3 thin films
(2000-04-01)
Leu, CC
;
Chan, SH
;
Chen, HY
;
Horng, RH
;
Wuu, DS
The effects of the O-2 plasma treatment on the electric and dielectric characteristics of Ba0.7Sr0.3TiO3 (BST) thin films were investigated. As a result of the exposure of the as-deposited or the annealed BST films to the O-2 plasma, the leakage current density of the BST films can be improved. Typically, the leakage current density can decrease by three orders of magnitude as compared that of the non-plasma treated sample at an applied voltage of 1.5 V. It is found that the plasma treatment changes the surface morphology. The capacitance of the BST films was reduced by 10%similar to 30%. The improvement of the leakage current density and the reduction of a dielectric constant for the plasma treated samples could be attributed to the reduction of carbon contaminations of BST thin films. The 10 year life time of the time-dependent dielectric breakdown (TDDB) studies indicates that all the samples have a life time of over 10 years of operation at a voltage bias of 1 V. (C) 2000 Elsevier Science Ltd. Al rights reserved.
Electrical properties of metal-ferroelectric-insulator-semiconductor using sol-gel derived SrBi2Ta2O9 film and ultra-thin Si3N4 buffer layer
(2002-12-02)
Huang, CH
;
Tseng, TY
;
Chien, CH
;
Yang, MJ
;
Leu, CC
The electrical properties of the metal-ferroelectric-insulator-silicon memories with stacked gate configuration of Pt/ SrBi2Ta2O9 (SBT)/Si3N4/p-Si (1 0 0) were investigated. In an attempt to operate at low voltage with sufficient large memory window, various ultra-thin Si3N4 buffer layers in thickness of 3.5, 2, and 0.9 nm were employed. From the results of C-V measurements, the memory window can be as large as 0.8 V at the bias amplitude of 5 V for the sample with 0.9 nm SixNy buffer layer. Well-crystallized perovskite structures have been further confirmed by the spectra of X-ray diffraction measurements. The leakage current, which plays a very important role in the data retention, of Pt/SBT (245 nm)/Si3N4 (0.9 nm)/p-Si (10 0) can be as low as 2.5 X 10(-8) A/cm(2) at 200 kV/cm. Excellent fatigue-free performance with up to 10(10) read/write cycles and good retention time of > 2 h have been obtained. Optimization and scaling of SBT thin films are believed to be effective in pursuing extremely low voltage operation, high-density and liable 1T nonvolatile ferroelectric random access memories. (C) 2002 Elsevier Science B.V. All rights reserved.
High-performance Pt/SrBi2Ta2O9/HfO2/Si structure for nondestructive readout memory
(2003-09-01)
Chien, CH
;
Wang, DY
;
Yang, MJ
;
Lehnen, P
;
Leu, CC
Metal-ferroelectric-insulator-semiconductor (MFIS) capacitors with 390-nm-thick SrBi2Ta2O9 (SBT) ferroelectric film and 8-nm-thick hafnium. oxide (HfO2) layer on silicon substrate have been fabricated and characterized. It is demonstrated for the first time that the MFIS stack exhibits a large memory window of around 1.08 V at an operation voltage of 3.5 V. Moreover, the MFIS memory structure suffers only 18% degradation in the memory window after 10(9) switching cycles. The excellent performance is attributed to the formation of well-crystallized SBT perovskite thin film on top of the HfO2 buffer layer, as evidenced by the distinctive sharp peaks in X-ray diffraction (XRD) spectra. In addition to its relatively high kappa value, HfO2 also serves as a good seed layer for SBT crystallization, making the proposed Pt/SrBi2Ta2O9/HfO2/Si structure ideally suitable for low-voltage and high-performance ferroelectric memories.
Low-pressure crystallization of sol-gel-derived PbZr0.52Ti0.48O3 thin films at low temperature for low-voltage operation
(2003-05-01)
Wang, DY
;
Chien, CH
;
Chang, CY
;
Leu, CC
;
Yang, JY
The properties of sol-gel-derived 120-nm PbZr0.52Ti0.48O3 thin films crystallized in low-pressure O-2 ambient at 500degreesC have been investigated. it is found that PbZr0.52Ti0.48O3 films crystallized in low-pressure oxygen ambient exhibit higher remanent polarization as well as a lower coercive field, compared to those annealed in O-2 atmosphere. The remanent polarization (i.e., 2P(r)) for samples annealed in 60 mbar O-2 ambient is as high as 36 muC/cm(2), and the coercive field (2E(C)) is 99.9 kV/cm at an applied voltage of 2 V. The improvement of P-E hysteresis loops by low-pressure oxygen annealing is ascribed to less incorporation of oxygen and other residues in the resultant PbZr0.52Ti0.48O3 films, since the reductions in the amount of these residual species are beneficial for the complete transformation of the perovskite structure. The reductions in oxygen content and amounts of other residues such as CO2 and H2O are confirmed based on Auger depth profiles and thermal desorption spectra (TDS), respectively.
Low-temperature growth of polycrystalline ge films on SiO2 substrate by HDPCVD
(2005)
Yang, MJ
;
Shieh, J
;
Hsu, SL
;
Huang, IJ
;
Leu, CC
Pure and high-quality polycrystalline Ge films have been deposited directly onto fully SiO2 covered substrates by high-density plasma chemical vapor deposition (HDPCVD) system. Only a tiny amount of O and C near the surface has been observed from X-ray photoelectron spectroscopy and Auger electron spectroscopy data, which may come from surface oxidation and contamination. Very pure Ge composition has been achieved in the bulk of the films. The cubic structure with primarily (111), (220), and (311) orientations of the Ge films is mainly composed of fine grains and can be unambiguously identified from X-ray diffraction patterns. Furthermore, successful Ge film depositions with nearly no incubation time are demonstrated using a mixture of GeH4/H-2 as process gas at 400 degrees C. Thickness vs. time analysis was performed by high-resolution transmission electron microscopy. The HDPCVD technique used was able to provide a simple, powerful, and reliable approach in the fabrication of polycrystalline Ge thin film transistors. (C) 2005 The Electrochemical Society.
Study of thermal stability of nickel monogermanide on single- and polycrystalline germanium substrates
(2005-06-20)
Hsu, SL
;
Chien, CH
;
Yang, MJ
;
Huang, RH
;
Leu, CC
We have investigated the thermal stability of nickel monogermanide (NiGe) films formed by rapid thermal annealing on both single- and polycrystalline Ge substrates. We found that the NiGe phase is the only one present after nickel germanidation in the temperature range 400-700 degrees C. A fairly uniform NiGe film formed on the single-crystalline Ge; it possessed excellent resistivity (15.6 mu Omega cm) and was thermally stable up to 550 degrees C, but it degraded rapidly at higher temperatures as a result of agglomeration. In contrast, the NiGe film formed on the polycrystalline Ge exhibited much poorer thermal stability, possibly because of polycrystalline Ge grain growth, which resulted in columnar NiGe grains interlaced with Ge grains that had a dramatically increased sheet resistance. As a result, we observed that the sheet resistances of NiGe lines subjected to annealing at 500 degrees C depended strongly on the linewidth when this width was comparable with the grain size of the polycrystalline Ge. (c) 2005 American Institute of Physic's.
The effects of low-pressure rapid thermal post-annealing on the properties of (Ba,Sr)TiO3 thin films deposited by liquid source misted chemical deposition
(2001-12-01)
Yang, MJ
;
Chien, CH
;
Leu, CC
;
Zhang, RJ
;
Wu, SC
The technique of low-pressure post-annealing process with additional second-step annealing for preparation of the Ba0.7Sr0.3TiO3 thin films deposited by liquid source misted chemical deposition (LSMCD) has been proposed. With employing this annealing procedure, the leakage current density can be significantly eliminated by approximately one order of magnitude at 2 V. In particular, process temperature can be reduced from 650 degreesC to 600 degreesC without suffering deteriorated crystallinity issue, which is identified by both C-V measurement and X-ray diffraction spectrum. The extracted dielectric constant is 310 with extreamly low loss tangent of 0.005. The spectrum of atomic force microscopy (AFM) shows that this low-pressure process results in smoother surface topography. Moreover, thermal desorption spectrums assure that less residual organics and contaminations were left after low pressure post-annealing. This may be one of the reasons for lowering crystallization temperature and the improved electrical properties.
Variations of differential capacitance in SrBi2Ta2O9 ferroelectric films induced by photoperturbation
(2005-02-28)
Leu, CC
;
Chien, CH
;
Chen, CY
;
Chang, MN
;
Hsu, FY
In this letter, we demonstrated the impact of illumination on the differential capacitance variation of a strontium bismuth tantalite (SBT) capacitor during scanning capacitance microscopy measurements. It was found that illumination with a stray light of laser in an atomic force microscope could perturb the dC/dV signals of the samples. We attribute this phenomenon to the generation of free carriers by the photon absorptions via defect traps in the SBT thin film. Therefore, this present work suggests that the effect of laser illumination must be carefully taken into consideration whenever a field-sensitive technique is employed to analyze the properties of a ferroelectric material. (C) 2005 American Institute of Physics.