Capacitance and admittance spectroscopy analysis of hydrogen-degraded Pt/(Ba, Sr)TiO3/Pt thin-film capacitors

Abstract

One of the problems occurring in conjunction with the integration of Ba 0.7 Sr 0.3 TiO 3 ͑BST͒ thin film capacitors into the Si technology is the large increase of leakage current after a forming gas heat treatment. In order to reveal the underlying mechanism, we studied the electric properties of Pt/ BST/Pt ͑metal-insulator-metal͒ ͑MIM͒ structures after annealing in atmospheres containing hydrogen (H 2 ) or carbon monoxide by means of admittance spectroscopy. Frequency-dependent capacitance measurements on these MIM structures revealed a thermally activated relaxation step at low frequencies with an activation energy of 0.62 eV. Admittance spectroscopy, in which the conductance is monitored as a function of temperature and frequency, verifies the Schottky barrier heights at the Pt/BST interface revealed by dc measurements. We found that the Schottky barrier height decreased by 0.4 eV after annealing in a reducing atmosphere, independent of the presence of protons. © 2000 American Institute of Physics. ͓S0003-6951͑00͒00139-X͔ Because of rapid evolution in the integration technology of high-dielectric-constant ferroelectric materials like Ba 0.7 Sr 0.3 TiO 3 ͑BST͒, the integration of ferroelectric capacitors in complementary metal-oxide-semiconductor ͑CMOS͒-based devices is one of the most important challenges. 1,2 For practical device applications of these new materials, their electrical properties must be understood properly with respect to dependence on the CMOSintegration processes. One of the most serious problems that Pt/BST/Pt ferroelectric capacitors suffer from during integration is the large increase of the leakage current by more than four orders of magnitude after annealing in a strongly reducing atmosphere, 3,4 e.g., a typical forming gas anneal (N 2 95% and H 2 5%͒. To avoid dramatical resistance degradation it is important to determine its origin.BST films, typically 130 nm thick, were deposited by chemical solution deposition ͑CSD͒ 3,5 on a platinized Si wafer. The Pt top electrodes ͑100 nm͒ were deposited by rf magnetron sputtering and patterned by a lift off process. The surface area of the top electrodes is 0.19 mm 2 . The resulting capacitors were postannealed under an oxygen atmosphere at Tϭ550-600°C for 30 min, and are referred to as the reference capacitors. Additionally, some capacitors were annealed at Tϭ450°C under a forming gas atmosphere ͑FGA͒ or a mixture of CO 5% and argon 95% ͑COA͒. These atmospheres have comparable oxygen partial pressure p O 2 , which are lower than 10 Ϫ15 bar. The electrical data were acquired using a Keithley 617 electrometer as the voltage source and picoamperemeter. A voltage-step technique is used to precisely reveal the leakage currents and to eliminate dielectric charging currents of the capacitor. For ac measurements a frequency response analyzer SI1260 from Schlumberger Ltd. was used in combination with a Solatron 1296 dielectric interface. Figure 1͑a͒ shows comparison of the leakage current for a Pt/BST/Pt capacitor before and after a reducing atmosphere...

Impedance spectroscopy of Na and Nd doped strontium bismuth titanate

“…On the low-frequency (<100 kHz) side, the ac conductivity increases with temperature, and it shows little frequency dependence. At high frequencies, the dielectric behavior is related to the short range hopping of charge carriers through trap sites separated by barriers, while the behavior at a low-frequency plateau is attributed to dc conductivity generated by Schottky emission from the metal oxide-metal junction [19][20][21][22]. Two slopes can be drawn, one in the high frequency region above 100kHz and the other in the lower frequency region.…”

Low-frequency dielectric relaxation and ac conduction of SrBi2Ta2O9 thin film grown by pulsed laser deposition

“…10,17 For the similar experiments of Pt/(Ba, Sr)TiO 3 /Pt thin film, it was reported that the activation energy determined by a low-frequency ac measurement agreed well with the 0 Schottky barrier heights by a dc measurement. 9 For Pt/ SBN/Pt junction, characteristics of electrical conduction were previously reported by I -V analysis, and conduction mechanisms were explained by the Schottky emission. Then the barrier height for conduction process was estimated to be 0.9 eV by Watanabe et al 10 and 1.0-1.2 eV by Seong et al 17 from the slope of leakage current density J vs 1/T plot.…”

“…8,9 It is well known that the electrical properties of the SBT, (Ba, Sr)TiO 3 (BST), and Pb(Zr, Ti)O 3 ͑PZT͒ thin films on electrodes strongly depend on the state of the surface, and impurities or defects may act as traps or donors. [10][11][12][13] Waser et al suggested that the oxygen vacancy plays an important role in the resistance degradation and dielectric degradation of thin polycrystalline (Ba, Sr)TiO 3 films.…”

Characterization of (Ba, Sr)RuO3 films deposited by metal organic chemical vapor deposition

“…Not only BST itself but also the electrode material for the BST film has been extensively studied since the properties of BST films such as the dielectric constant and leakage current density are strongly affected by the bottom electrode [4][5][6]. In this work, we propose a (Ba, Sr)RuO 3 [BSR] oxide electrode which has an outstanding structural match with BST and which is chemically compatible with BST.…”