Browsing by Author "Ezhilvalavan, S"

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Conduction mechanisms in amorphous and crystalline Ta2O5 thin films
(1998-05-01)
Ezhilvalavan, S
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Electrical properties and leakage current mechanisms of amorphous and polycrystalline tantalum pentoxide (Ta2O5) films were studied. Ta2O5 thin films were deposited on Pt/SiO2/n-Si substrate by reactive magnetron sputtering and then annealed at temperatures ranging from 500 to 800 degrees C for 30 min in O-2. The as-deposited films were amorphous and showed good electrical properties in terms of a dielectric constant of about 31 and leakage current density of 10(-10) A/cm(2) at 100 kV/cm. The leakage current flowing through Ta2O5 film increases from 10(-10) to 10(-7) A/cm(2) following the annealing. The conduction mechanism at low electric fields (100 kV/cm) is due to Ohmic conduction. On the other hand Schottky mechanism dominates at the intermediate fields (100-350 kV/cm) and Poole-Frenkel becomes predominant at high fields (>350 kV/cm). The increase in leakage current density in the crystallized film is due to Si penetrated into the Ta2O5 grain and grain boundary from the underlying SiO2/n-Si substrate. (C) 1998 American Institute of Physics.
Dielectric relaxation and defect analysis of Ta2O5 thin films
(2000-05-21)
Ezhilvalavan, S
;
Tsai, MS
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The presence of defects in thin-film dielectrics often leads to dielectric relaxation as a function of frequency, in which the dielectric constant decreases and the loss tangent increases with increasing frequency. Dielectric relaxation results in charge storage capacity reduction under dynamic random access memory operating conditions. In this work, the dielectric relaxation behaviour of de reactive sputtered Ta2O5 thin film was investigated. Using dielectric dispersion measurements as a function of frequency (100 Hz less than or equal to f less than or equal to 10 MHz) and temperature (27 degrees C less than or equal to T less than or equal to 150 degrees C), we determined the dielectric relaxation and defect quantity of the films and propose an equivalent circuit on the basis of complex capacitance, admittance and impedance spectral studies.
Electrical properties of rapid thermal-enhanced low pressure chemical vapor deposited Ta2O5 thin films
(1999-03-01)
Lee, CJ
;
Huang, LT
;
Ezhilvalavan, S
;
Tseng, TY
;
電子工程學系及電子研究所
Electrical properties of rapid thermal-enhanced low pressure chemical vapor deposited Ta2O5 thin films subjected to an in situ two-step postannealing process were studied. Films treated by rapid thermal annealing in O-2 at 550 degrees C for 90 s followed by plasma O-2 at 550 degrees C for 30 s exhibit a leakage current density of 7.91 x 10(-9) A/cm(2) at an applied electric field of 100 kV/cm and a dielectric constant of similar to 38. The decrease in leakage current density of the annealed Ta2O5 films in comparison to the as-deposited films is attributed mainly to the effective reduction of carbon impurities and oxygen vacancies by the two-step postannealing process. (C) 1999 The Electrochemical Society. S1099-0062(98)08-064-X. All rights reserved.
Electrical properties of Ta2O5 thin films deposited on Cu
(2000-02-01)
Ezhilvalavan, S
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The electrical and dielectric properties of reactively sputtered Ta2O5 thin films with Cu as the top and bottom electrodes forming a simple metal insulator metal (MIM) structure, Cu/Ta2O5/Cu/n-Si, were studied. Ta2O5 films subjected to rapid thermal annealing (RTA) at 800 degrees C for 30 s in N-2 ambient crystallized the film, decreased the leakage current density and resulted in reliable time-dependent dielectric breakdown characteristics. The conduction mechanism at low electric fields (<100 kV/cm) is due to Ohmic conduction; however, the Schottky mechanism becomes predominant at high fields (>100 kV/cm). Present studies demonstrate the use of Cu as a potential electrode material to replace the conventional precious metal electrodes for Ta2O5 storage capacitors. (C) 2000 Elsevier Science S.A. All rights reserved.
Electrical properties of Ta2O5 thin films deposited on Ta
(1999-04-26)
Ezhilvalavan, S
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The electrical properties of reactively sputtered Ta2O5 thin films with Ta as the bottom electrodes were investigated. Ta films were deposited onto SiO2/n-Si substrates by sputtering in Ar and in situ annealed at 700 degrees C for 10 min in N-2 at a chamber pressure of 20 mTorr. We compared the effectiveness of both as-deposited and annealed Ta bottom electrodes on the leakage characteristics of Ta2O5 thin films. We also envisaged the influence of the surface roughness and morphology of the Ta bottom electrode in modifying the resultant microstructure of the annealed Ta2O5 films. Present studies demonstrate the use of Ta as a potential bottom electrode material to replace the precious metal electrodes and to simplify the fabrication process of the Ta2O5 storage capacitor. (C) 1999 American Institute of Physics. [S0003-6951(99)03317-3].
Electron paramagnetic resonance and luminescence study of sol-gel derived YAG : Cr powder
(1999-03-01)
Lo, JR
;
Ezhilvalavan, S
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Electron paramagnetic resonance (EPR) and luminescence studies were carried out for the sol-gel-derived YAG:Cr powders subjected to three kinds of heat treatment processes. The results show that powders processed using the two-step heat treatment process with the addition of 20 wt% LiCl and by direct heat treatment at 1500 degrees C exhibit good luminescence properties. The emission spectrum for the powders obtained by the two-step process shows the R-line at 688 nm, whereas the powders directly heat treated at 1500 degrees C display an additional R-line of Al2O3 : Cr at 694 nm: EPR measurements show that the presence or absence of absorption peaks depends on the Cr3+ environment in-the host lattice resulting from the different methods of heat treatment of the powder. The EPR spectra of YAG:Cr3+ phosphors were interpreted to indicate both Cr3+ single ion and Cr3+-Cr3+ pair (with spin three) transitions.
Preparation and properties of tantalum pentoxide (Ta2O5) thin films for ultra large scale integrated circuits (ULSIs) application - A review
(1999-03-01)
Ezhilvalavan, S
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Tantalum pentoxide (Ta2O5) thin films have rapidly evolved into an important field of research/development for both basic and applied science with the promise of creating a new generation of advanced micro devices for electronics applications. This paper provides a broad review of the current status and future trends of Ta2O5 thin films as a high ly promising storage dielectric material for high-density dynamic random access memory applications. Various methods of thin film material processing are briefly reviewed. The physical, electrical and dielectric characteristics of Ta2O5 thin films with specific examples from recent literature and the associated conduction mechanisms are summarized and discussed. Some suggestions to improve the electrical properties of the films are finally included. (C) 1998 Kluwer Academic Publishers.
Progress in the developments of (Ba,Sr)TiO3 (BST) thin films for Gigabit era DRAMs
(2000-08-15)
Ezhilvalavan, S
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
This paper reviews the recent developments of (Ba,Sr)TiO3 (BST) thin films for future Gbit era dynamic random access memory (DRAM) applications. The trends of DRAM capacitors in the last decade are briefly described first. Then the technological aspects of BST films such as deposition techniques, post-annealing, physical, electrical and dielectric characteristics of the films, effects of electrode materials, dielectric relaxation and defect analysis and the reliability phenomena associated with the films are briefly reviewed with specific examples from recent literature. The basic mechanisms that control the bulk electrical conduction and the origin of leakage currents in BST films are also discussed. Finally, possible developments of gigabit era DRAM technology are summarized. (C) 2000 Elsevier Science S.A. All rights reserved.
Properties and reliability of Ta2O5 thin films deposited on Ta
(1999)
Ezhilvalavan, S
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The electrical and reliability properties of reactively sputtered Ta2O5 thin films with Ta as the bottom electrodes forming simple metal insulator metal (MIM) structure. Pt/Ta2O5/Ta/SiO2/n-Si were studied. Ta films were deposited on SiO2/n-Si substrates by sputtering in Ar and in situ annealed at 700 degrees C for 10 min in N-2 at a chamber pressure of 20 mTorr. We compared the effectiveness of both as-deposited and annealed Ta bottom electrode on the leakage characteristics of Ta2O5 thin films. Ta2O5 films subjected to rapid thermal annealing (RTA) process at 800 degrees C for 30s in O-2 crystallized the film, decreased the leakage current density and resulted in reliable time-dependent dielectric breakdown characteristics. We also envisaged the influence of the surface roughness and morphology of the Ta bottom electrode in modifying the resultant microstructure of the annealed Ta2O5 films. Present studies demonstrate the use of Ta as a potential bottom electrode material replaces the precious metal electrodes and simplifies the fabrication process of the Ta2O5 storage capacitor.
Short-duration rapid-thermal-annealing processing of tantalum oxide thin films
(1999-03-01)
Ezhilvalavan, S
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The effect of the rapid thermal annealing (RTA) processing time on the electrical properties of reactively sputtered tantalum oxide (Ta2O5) films that was deposited onto Pt/SiO2/ n-Si substrates, which resulted in the formation of a metal-insulator-metal (MIM) planar capacitor structure, was studied, The Ta2O5 MIM capacitors were subjected to different RTA processing times (30 s to 30 min) at temperatures in the range of 600 degrees-800 degrees C in an ambient oxygen-gas atmosphere. A very-short-duration RTA process at a temperature of 800 degrees C in oxygen gas for 30 s crystallized the films, decreased the leakage current density (to 10(-10) A/cm(2) at a stress field of 100 kV/cm), increased the dielectric constant (to 52), and resulted in the most-reliable time-dependent dielectric-breakdown characteristics. The decrease in leakage current density was attributed to the reduction of oxygen vacancies and the suppression of silicon diffusion from the SiO2/n-Si substrate into the Ta2O5 grain and the grain boundary, because of the shorter-duration annealing, Increasing the annealing time to >30 s increased the leakage current density. The annealing duration of the RTA process was more crucial in regard to obtaining optimum dielectric properties and low leakage current densities. Time-dependent dielectric-breakdown characteristics indicated that Ta2O5 MIM film capacitors that were subjected to an RTA process at a temperature of 800 degrees C for 30 s in oxygen gas can survive a stress field of 1.5 MV/cm for 10 years. The electrical and dielectric measurements in the MIM configuration showed that Ta2O5 is a good dielectric material and is suitable for use in future dynamic random-access memories.