Der-Chi Shye

Low Temperature Radio-Frequency-Sputtered ( Ba , Sr ) TiO3 Films on Pt/TiN/Ti/Si Substrates with Various Oxygen/Argon Mixing Ratios

(Ba,Sr)TiO 3 (BST) films were fabricated on Pt/TiN/Ti/Si substrates by low temperature radio frequency magnetron cosputtering at 300°C. Material and electrical properties of BST films sputtered at low temperatures are significantly affected by the O 2 /(Ar + O 2 ) mixing ratio (OMR). Plasma emission spectra indicate that the deposition rate declines at a higher OMR due to oxide formation on the target surface. The dielectric constant of the BST films can reach a maximum of 364 at 5% OMR. The ten-year lifetime of the time-dependent dielectric breakdown implies that the reliability of the capacitor can be enhanced at a higher OMR due to compensation of oxygen vacancies and smaller grain sizes. Current-voltage analysis indicates that the leakage current of the Pt/BST/Pt capacitor is limited by Schottky emission (SE)/Poole-Frenkel emission (PF) at a lower/higher applied field. The applied field boundary between SE and PF shifts toward higher field as OMR increases. Moreover, an energy band model was proposed and this leakage mechanism was discussed.

Effects of post-oxygen plasma treatment on Pt/(Ba,Sr)TiO3/Pt capacitors at low substrate temperatures

We investigated how oxygen plasma post-treatment improves leakage characteristics of Pt/(Ba,Sr)TiO3 (BST)/Pt capacitors prepared by the radio-frequency (RF) cosputtering technique. Experimental results indicate that oxygen plasma treatment can effectively passivate the oxygen vacancies of (Ba,Sr)TiO3 (BST) films, thus decreasing the electric conduction paths of leakage currents. By this low-temperature (250°C), and short-duration (~5 min) process, the leakage current is reduced by as many as two orders of magnitude. The reliability characteristics of time-dependent dielectric breakdown (TDDB) are improved as well. However, the usage of oxygen plasma treatment is not unrestricted. Plasma treatment for an extended period (more than 10 min) degrades both the leakage and reliability characteristics, due to plasma damage. Excellent electrical characteristics, including low leakage current (1.5 ×10-8 A/cm2) under 0.1 MV/cm, high dielectric constant (288), and a lifetime longer than 10 years under 2 MV/cm can be achieved. Therefore, the proposed technique for as-deposited BST films is a highly promising means of improving the electrical characteristics of BST thin films.

The Effects of Post Excimer Laser Annealing on (Ba,Sr)TiO3 Thin Films at Low Substrate Temperatures

The amorphous (Ba,Sr)TiO3 (α-BST) films sputtered onto the Pt/TiN/Ti/Si substrates are greatly improved using the excimer laser annealing (ELA) technique of wavelength 248 nm at low substrate temperature 300°C. The dielectric constant of the α-BST film is remarkably enhanced from 80 to over 250 after ELA treatment. The heat conduction analysis indicates that a very shallow light absorption depth of the wavelength 248 nm for the BST film behaves an excellent thermal property, which doesnt damage the underlayer films during ELA treatment. Besides, the leakage current of ELA-BST films is strongly influenced by the laser energy fluence (LEF). The detailed mechanisms of the crystallinity and the electric properties are systematically studied in this report.

Dependence of polarization on temperature coefficient resistance of (Ba, Sr)TiO3 thin films post-treated by RTA

The temperature coefficient of resistance (TCR) characteristics of Pt/(Ba 0 . 8 Sr 0 . 2 )TiO 3 (BST)/Pt thin-film resistors are studied for the BST films with rapid thermal annealing (RTA) treatments. The polarizations induced by bias voltages greatly influence the TCR characteristics. The RTA-treated BST thin film exhibits negative TCR (NTCR) behavior at a negative voltage, but, intriguingly, positive TCR (PTCR) behavior at a positive voltage. According to the leakage current analysis, Schottky emission dominates the negatively biased current at the upper interface, but Heywang barrier scattering confines the positive biased current.

Effects of Thermal Stabilities for the Ultra Thin Chromium Layers Applied on (Ba, Sr)TiO3 Thin Films

This work reports the temperature-electric properties for the (Ba, Sr)TiO3(BST) thin film capacitor using the multi-film structure of BST/ultra-thin-chromium(Cr) layer/BST. The BST(200 nm)/Cr(1–3 nm)/BST(200 nm) multi-films reveal excellent properties in the thermal stabilities of dielectric property, low leakage current and less power dissipation.

Dependence of Ferroelectric Characteristics on the Deposition Temperature of (Pb,Sr)TiO3 Films

The pulsed laser deposition (PLD) of (Pb,Sr)TiO3 (PSrT) films on Pt/SiO2/Si at low substrate temperatures (Ts), ranging from 300 to 450 °C, has been investigated. The PLD PSrT films prepared at low Ts exhibit ferroelectric properties, good crystallinity, and no significant interdiffusion between the PSrT film and the Pt bottom electrode. The conduction mechanism is identified as Schottky emission at low electric fields and as Poole–Frenkel emission at high electric fields. PSrT films grown at appropriate Ts yield fewer interface states and fewer trapping states, leading to a smaller leakage current. The enhanced (100) preferred orientation of PSrT films deposited at Ts=350–400 °C exhibits optimum ferroelectricity. In addition, the dielectric constant and ferroelectricity are associated with the preferred orientation. This shows that the electrical characteristics strongly rely on the preferred orientation and trapping states, which could be controlled by varying the substrate temperature (Ts≤450 °C) during PLD.

Effects of Laser Treatment for the Pb(Zr, Ti)O3/(La, Sr)MnO3 Heterostructure Prepared onto the Stainless Steel Substrate

Amorphous multifilm—Pb(Zr,Ti)O 3 (PZT)/(La, Sr)MnO 3 (LSMO)—prepared onto stainless-steel substrates can be greatly improved using the CO 2 laser annealing technique. The conductive thin film LSMO of 200 nm is sputtered onto a standard industrial stainless steel (SUS430) substrate as a buffer layer, effectively improving the adhesion and prohibiting the interdiffusion of chrome and manganese atoms from stainless steel substrate. As the experimental results show, the LSMO and PZT thin films treated in a two-stage sequential process by CO 2 laser exhibit better crystallinity and electric properties than the PZT/LSMO heterostructure treated by one-shot laser annealing due to heat conduction. The mechanisms of the crystallinity and the electric properties are systematically studied in this report.

Polarization Degradation and Breakdown of Pulse-Laser-Deposited (Pb,Sr)TiO3 Films at Low Temperatures

(Pb,Sr)TiO3 (PST) films were deposited on Pt/SiO2/Si by pulsed laser deposition at low substrate temperatures (Ts) ranging from 300 to 450 °C. The loss in remnant polarization (Pr) and coercive field (Ec) is found to be less than 17% after 1010 switching cycles when Ts is higher than 350 °C. It is also suggested that the leakage current is reduced when Ts increases up to a temperature of 400 °C. However, PST films deposited at 450 °C may produce serious Pb–O volatilization, resulting in the deterioration of the crystallinity and high leakage currents. As a result, the 400 °C-deposited PST film reveals the lowest leakage current, nearly fatigued-free J–E characteristics after 1010 switching cycles, and the best breakdown property, attributed to the enhanced crystallinity and low concentration of defects.

Characteristics of low-temperature-prepared (Ba,Sr)TiO/sub 3/ films post treated by novel excimer laser annealing

Thin (Ba/sub 0.5/Sr/sub 0.5/)TiO/sub 3/ (BST) films were sputtered on Pt/TiN/Ti/Si multilayer substrates at very low temperature (150/spl deg/C). A novel process, using wavelength 248-nm KrF excimer laser annealing (ELA), has been undertaken to implement barium strontium titanate (BST) films at a low process temperature of 300/spl deg/C. The crystallinity and dielectric constant are greatly improved after ELA treatment. In this work, the variation of texture was investigated. Besides, the escaped oxygen atoms from BST films were detected in-situ using a residual gas analyzer (RGA) during ELA process. Thus, the degradation of upper surface is strongly influenced by the laser energy fluence for an ELA-BST film.