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Role of bismuth precursor in crystallization of SrBi 2 Ta 2 O 9 thin films
| Content Provider | Semantic Scholar |
|---|---|
| Author | Tirumala, S. Desu, Seshu Babu Rastogi, Alok C. |
| Abstract | Crystallization of SrBi2Ta2O9 (SBT) thin films was studied as a function of viscosity of bismuth precursor and baking temperature, in order to fabricate capacitors with improved ferroelectric properties. SBT thin films were deposited on toPt substrates using a chemical solution deposition (CSD) technique. Post-deposition anneal at750◦C for 1 h in oxygen atmosphere revealed a significant influence of baking temperature and the viscosity of bismuth precursor on the microstructure and the ferroelectric properties of SBT thin films. A high baking temperature ( 350◦C) and a low viscosity of bismuth precursor (8 cp) yielded larger amounts of Bi2O3 secondary phase, smaller SBT grains ( 104 nm), and lower remanent polarization (Pr = 2.0μc/cm2). Additionally, these films exhibited a very high rate of ageing ( > 45% reduction in Pr after 7 days). A modified CSD process is suggested, which could suppress the formation of Bi2O3 secondary phase. Films fabricated using modified CSD technique exhibited a much larger grain size of 165 nm, higher Pr of 7.2μc/cm2, and significantly improved ageing characteristics (< 1% reduction in Pr after 7 days). A qualitative model to describe the ageing in SBT-based capacitors is also suggested. PACS: 71.20Nr; 71.20Ps; 71.55-i Chemical solution deposition process (CSD) is one of the commonly used techniques to deposit fatigue-free SrBi2Ta2O9 (SBT) thin films [1]. In the literature, several processing parameters such as annealing temperature and annealing method, annealing gas, stoichiometry, and the chemical formula of the precursors were studied extensively and were reported to affect the ferroelectric properties [2–12]. However, there is a wide variation in the reported remanent polarization (Pr ranging from4μc/cm2 to 10μc/cm2) of SBT thin film capacitors deposited under almost identical processing conditions. Even within our own group, we earlier reported a Pr of 6.5μc/cm2 for SBT thin film capacitors fabricated using a room-temperature stable precursor solution [2]. However, we have significant variations in these results when a different batch of bismuth precursor, from the same vendor was used. Additionally, SBT thin film capacitors fabricated using Bi precursors bought from different vendors, exhibited even wider variations in their ferroelectric properties. The only difference was in the viscosity of the Bi precursor. Therefore, the viscosity of theBi precursor is an important processing parameter that could affect the ferroelectric properties of SBT thin films. Viscosity may be indicative of the molecular nature, more importantly of the extent of Bi precursor oligemerization. The extent of oligemerization of Bi precursor could influence the crystallization ofBi2O3. PureBi precursors, when coated on Pt substrates and baked, revealed a dependence of the crystallization of Bi2O3 on the viscosity of the precursor. Since, the crystallization temperature of Bi2O3 is close to the typical baking temperatures of SBT thin films ( ≈ 450◦C), a Bi2O3 secondary phase could be formed in the SBT thin films during baking. Hence, viscosity of Bi precursor and baking temperature could influence the formation of Bi2O3 secondary phase in SBT thin films prior to high-temperature crystallization anneal. Presence of the Bi2O3 secondary phase could effect the crystallization kinetics of the SBT thin films during hightemperature annealing. There have been reports of the presence of Bi2O3 secondary phase in crystallized SBT thin films [13]. However, no correlation was established between the amount of the Bi2O3 secondary phase and the ferroelectric properties of the capacitors. In this study, we investigated the dependence of the amount of theBi2O3 secondary phase on the Bi precursor viscosity and on the baking temperature. The sensitivity of the ferroelectric properties of SBT thin films on the amount of secondaryBi2O3 phase was also studied. A modified CSD technique was developed in order to minimize this secondary phase in the crystallized SBT thin films, and thereby obtain improved ferroelectric properties. Additionally, we also examined the ageing characteristics of SBT thin films as a function of the amount of theBi2O3 secondary phase. A qualitative model to explain ageing in SBT thin films is proposed. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://page-one.springer.com/pdf/preview/10.1007/s003390050044 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
