Low temperature crystallization of SrBi2Ta2O9 (SBT) films

Uchiyama, Kiyoshi; Arita, Koji; Shimada, Yasuhiro; Hayashi, Shigenori; Fujii, Eiji; Otsuki, T.; Solayappan, N.; Joshi, V. K.; Araújo, Carlos A. Paz de

doi:10.1080/10584580008222258

Cited by 16 publications

(11 citation statements)

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“…The results indicate that the dominant process is the occupation of the Sr vacancies by the Bi excess, more than the diffusion of the Bi toward the Pt bottom electrode or to the grain boundary. Other authors 22 have shown that SBT compositions with Bi in Sr positions produce a structural distortion of the pseudo-perovskite that results in maximum values of spontaneous and remanent polarizations, P s and P r . But, this also decreases the reaction interface between Pt and Bi.…”

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confidence: 98%

Crystallization, Heterostructure, Microstructure, and Properties of Ferroelectric Strontium Bismuth Tantalate Films Derived from Tantalum Glycolate Solutions

et al. 2003

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Strontium bismuth tantalate (SBT) films were prepared by chemical solution deposition (CSD) onto Pt/TiO 2 /SiO 2 /(100)Si substrates. Nominal chemical compositions of the precursor solutions of SrBi 2 Ta 2 O 9 , SrBi 2.2 Ta 2 O 9 , Sr 0.8 Bi 2 Ta 2 O 9 , and Sr 0.8 Bi 2.2 Ta 2 O 9 were tested for the deposition of the films. Crystallization of the films was carried out by a two-step process (TS) or a single-step process (SS). The TS treatment consisted of thermal treatment of the films in oxygen atmosphere at 550°C for 7200 s, with a heating rate of 8°C/s, followed by a rapid thermal processing (RTP) in oxygen at a temperature of 650°C for 3600 s, using a heating rate of 200°C/s. The SS process was just the RTP treatment of the films. The X-ray diffraction (XRD) patterns of the crystalline films showed the formation of the layered perovskite together with a second phase. Analysis of the films by means of Rutherford backscattering spectroscopy (RBS) showed that this second phase was placed at the interface and it was formed by the reaction of the film and the substrate. Composition and thickness of this interface as well as profile composition of the SBT layer were also analyzed by RBS. These studies indicated that the heterostructure of the films was related with their nominal composition and with the type of thermal treatment used for their crystallization. Both parameters, composition and treatment, also determined the surface microstructures of the films. Dielectric and ferroelectric properties of the films were measured and related with their composition, heterostructure, and microstructure. The best hysteresis loops with the maximum values of remanent polarization, P r , were obtained for the films with nominal composition of Sr 0.8 Bi 2.2 Ta 2 O 9 and crystallized with the SS treatment. These films have a low fatigue up to ∼10 11 cycles, a retention of the polarization over 10 5 seconds, and leakages of <10 -7 µA/cm 2 at 300 kV/cm.

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confidence: 98%

Crystallization, Heterostructure, Microstructure, and Properties of Ferroelectric Strontium Bismuth Tantalate Films Derived from Tantalum Glycolate Solutions

et al. 2003

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“…3, and it shows two-step weight losses. [15][16][17][18][19][20] Therefore, the first exotherm (approximately 650°C) appearing in the DTA curve corresponds to the crystallization of the intermediate fluorite phase, while the second exotherm (approximately 780°C) indicates the formation of the Aurivillius phase. From the TGA data the pyrolysis temperature is fixed as 450°C, to obtain the noncrystalline SBT film.…”

Section: Resultsmentioning

confidence: 99%

“…8,9,15 However, the high-temperature processing has been a major limiting factor. Several optimized processes, including the rapid thermal annealing and annealing of SBT thin films under the oxygen flow, have been successful to lower the crystallization temperature to approximately 650°C [16][17][18][19][20] and to improve the properties of SBT thin films as well. Several optimized processes, including the rapid thermal annealing and annealing of SBT thin films under the oxygen flow, have been successful to lower the crystallization temperature to approximately 650°C [16][17][18][19][20] and to improve the properties of SBT thin films as well.…”

Section: Introductionmentioning

confidence: 99%

Influence of nanoparticle seeding on the phase formation kinetics of sol-gel-derived Sr_0.7Bi_2.4Ta₂O₉thin films

2003

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Sr 0.7 Bi 2.4 Ta 2 O 9 (SBT) thin films were deposited on unseeded and SBT nanoparticle (approximately 60-80 nm) seeded Pt/Ti/SiO 2 /Si substrates via sol-gel and spin-coating techniques. The SBT thin films were heated at 600°C for 1 h to form the fluorite phase, and these fluorite films were further heated at 730-760°C for fluorite-to-Aurivillius phase transformation. The volume fractions of Aurivillius phase formation obtained through quantitative x-ray diffraction analyses showed highly enhanced kinetics in seeded SBT thin films. Johnson-Mehl-Avrami isothermal kinetic analyses were performed for the characterization of Aurivillius phase formation in unseeded and seeded SBT thin films using the volume fraction values. The Avrami exponents were determined as approximately 1.4 and approximately 0.9 for unseeded and seeded SBT films, respectively, which reveals different nucleation modes. By using Arrhenius-type plots, the activation energy values for the phase transformation of unseeded and seeded SBT thin films were determined to be approximately 264 and approximately 168 kJ/mol, respectively. This gives a key reason for the enhanced kinetics in seeded films. Microstructural analyses on unseeded SBT thin films showed formation of randomly oriented needlelike crystals, while those on seeded ones showed formation of domains comprising directionally grown wormlike crystals. On the basis of the phase formation kinetics and microstructural development, a model representing different nucleation and crystal growth mechanisms for the unseeded and seeded SBT thin films was proposed.

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“…As discussed by Uchiyama et al,9 the suppression of quasi-stable fluorite formation during the heat-up process after the coating was one of the key process factors to obtain the ferroelectric SBT phase, especially for low-temperature processing. This can be achieved by the adoption of rapid thermal annealing ͑RTA͒.…”

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confidence: 97%

“…1 Among the many candidate ferroelectric materials, the SrBi 2 Ta 2 O 9 ͑SBT͒ thin film appears to be one of the most promising ferroelectric layer materials in the FeRAM due to its excellent reliability properties, such as fatigue and retention endurances, even with conventional Pt electrodes. 2 However, there are three major problems related to SBT material.…”

mentioning

confidence: 99%

Performance and Reliability of Low-Temperature Processed SrBi[sub 2]Ta[sub 2]O[sub 9] Capacitors for FeRAM Applications

Oh¹,

Noh²,

Lee³

et al. 2004

J. Electrochem. Soc.

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Low-temperature processed SrBi 2 Ta 2 O 9 ͑SBT͒ capacitors were tested as the ferroelectric memory cells of fully functional ferroelectric random access memory ͑FeRAM͒ devices. The 100 nm thick SBT films were deposited by the spin-on coating technique using a metallorganic decomposition source and crystallized by rapid thermal annealing at 700°C for 1 min followed by a furnace annealing at 650°C for 1 h under oxygen atmosphere, considered a low thermal budget process. The fabricated Pt/SBT/Pt capacitors showed reasonable ferroelectric performances with a ⌬ P ͑switching polarization-nonswitching polarization͒ of approximately 10 C/cm 2 after the full process integration. The FeRAM chip-level reliability analysis showed that the major reason for the function failure was from the opposite state retention characteristics due mainly to the small ⌬ P values. A 10-year guaranteed lifetime can be achieved when the operation voltage is higher than approximately 4 V at the test condition of 85°C operation and 125°C storage.Ferroelectric random access memory ͑FeRAM͒ has attracted considerable attention due to its advantages of nonvolatile data retention, low power consumption, and fast write/read speed. 1 Among the many candidate ferroelectric materials, the SrBi 2 Ta 2 O 9 ͑SBT͒ thin film appears to be one of the most promising ferroelectric layer materials in the FeRAM due to its excellent reliability properties, such as fatigue and retention endurances, even with conventional Pt electrodes. 2 However, there are three major problems related to SBT material. The first is the high processing temperature ͑ϳ800°C͒ required for the crystallization of the material and recovery of the dry etching damage for integrated circuit formation. 3 The high processing temperature of the SBT material imposes various problems in FeRAM fabrication, especially for the merged memory-logic application, because the high temperature of the capacitor process adversely affects the transistor performances. This is true regardless of the integration density. When a high-density application is considered, the hightemperature annealing under the oxidizing atmosphere seriously oxidizes the buried contact of the capacitor having a capacitor-over-bit line structure, and malfunction of the device results.The second problem is the relatively small remanent polarization value ( P r , Ͻ10 C/cm 2 at 5 V applied voltage͒ compared to the Pb(Zr,Ti)O 3 ͑PZT͒ material, which shows a typical P r value of ϳ30 C/cm 2 at the same applied voltage. 4,5 Because the operation of FeRAM relies upon the amount of extracted charge from the cell capacitor, as in the case of dynamic random access memory, a smaller P r value, in principle, could induce a small sensing margin issue. Furthermore, unfortunately, the integration processes used for the FeRAM device after the ferroelectric capacitor fabrication generally degrade its performance. Usually, the P r decreases by the chemical interactions or the mechanical stresses imposed by the interlayer dielectric ͑ILD͒ and intermetal d...

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Low temperature crystallization of SrBi₂Ta₂O₉ (SBT) films

Cited by 16 publications

References 4 publications

Crystallization, Heterostructure, Microstructure, and Properties of Ferroelectric Strontium Bismuth Tantalate Films Derived from Tantalum Glycolate Solutions

Crystallization, Heterostructure, Microstructure, and Properties of Ferroelectric Strontium Bismuth Tantalate Films Derived from Tantalum Glycolate Solutions

Influence of nanoparticle seeding on the phase formation kinetics of sol-gel-derived Sr_0.7Bi_2.4Ta₂O₉thin films

Performance and Reliability of Low-Temperature Processed SrBi[sub 2]Ta[sub 2]O[sub 9] Capacitors for FeRAM Applications

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Low temperature crystallization of SrBi2Ta2O9 (SBT) films

Cited by 16 publications

References 4 publications

Crystallization, Heterostructure, Microstructure, and Properties of Ferroelectric Strontium Bismuth Tantalate Films Derived from Tantalum Glycolate Solutions

Crystallization, Heterostructure, Microstructure, and Properties of Ferroelectric Strontium Bismuth Tantalate Films Derived from Tantalum Glycolate Solutions

Influence of nanoparticle seeding on the phase formation kinetics of sol-gel-derived Sr0.7Bi2.4Ta2O9thin films

Performance and Reliability of Low-Temperature Processed SrBi[sub 2]Ta[sub 2]O[sub 9] Capacitors for FeRAM Applications

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Low temperature crystallization of SrBi₂Ta₂O₉ (SBT) films

Influence of nanoparticle seeding on the phase formation kinetics of sol-gel-derived Sr_0.7Bi_2.4Ta₂O₉thin films