Stabilized Platinum Electrodes for Ferroelectric Film Deposition using   Ti, Ta and Zr Adhesion Layers

Maeder, Thomas; Sagalowicz, Laurent; Muralt, Paul

doi:10.1143/jjap.37.2007

Cited by 113 publications

(58 citation statements)

References 17 publications

(28 reference statements)

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“…Previously, a similar but much stronger density decrease of the Pt layer in Pt/ Ti bilayer electrode upon the annealing was reported and attributed to the strong diffusion of Ti and its following oxidation. 21,22 Though the diffusion at the Pt/ TiO x interface was not strong 6,11 or even undetectable as reported, 18 the limited diffusion and incorporation of Ti and O into Pt have been observed previously [23][24][25][26] and confirmed by scanning transmission electron microscopy. 16 Ti and O can migrate along the grain boundaries of Pt when the sample is annealed.…”

Section: A Formation Of Pt Hillocks On the Bare Pt Electrodesupporting

confidence: 61%

“…However, the Pt/ Ti metallic electrode shows poor thermal stability and reliability including the formation of Pt hillocks [5][6][7][8] or bumps under thermal conditions, 9 surface morphology evolution during aging, 7 short circuit of ferroelectric capacitors caused by the Pt hillocks, 10 severe diffusion of Ti into Pt, and even encapsulation of Pt hillocks with TiO x during annealing. 6,[9][10][11] In contrast, Sreenivas et al reported that the Pt/ TiO x electrode structure shows an improved thermal stability. 6 For a given ferroelectric medium with a certain chemistry and structure, the ferroelectricity is dependent on the electrical and mechanical boundary conditions to a great extent.…”

Section: Introductionmentioning

confidence: 99%

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Structural investigations of Pt∕TiOx electrode stacks for ferroelectric thin film devices

Cao

Solbach

Klemradt

et al. 2006

Journal of Applied Physics

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Effects of the thermal treatment and the fabrication process of Pb͑Zr 0.3 Ti 0.7 ͒O 3 ͑PZT͒ thin films using chemical solution deposition on Pt/ TiO x electrode stacks were investigated using complementary analytical techniques including atomic force microscopy ͑AFM͒, x-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and grazing incidence x-ray reflectivity of synchrotron radiation. The surface and interface structures of the Pt/ TiO x electrode stacks with different thermal treatments, and the PZT/ Pt/ TiO x sample were examined. The propagation of Pt hillocks on the bare Pt/ TiO x electrode stacks upon the annealing was observed. AFM observations also revealed that the upper surface of the Pt bottom electrode under PZT thin film became rougher than that of the bare Pt electrode with the same thermal history. Global structural information including the density, surface or interface root-mean-square roughness, and thickness of each constituent layer in the samples were determined using x-ray reflectivity. A density decrease of the Pt layer upon the annealing or during the fabrication of PZT thin films was found from fitting the specular reflectivity, and further confirmed by the negative shift of the Yoneda peak of Pt in the diffuse reflectivity. The formation of Pt hillocks on the bare Pt electrodes was attributed to the compressive stress during the high-temperature annealing caused by the limited incorporation of Ti and O into the Pt layer. Roughening of the PZT/Pt interface was ascribed to the interaction between the compressive stress in Pt and the indentation by the PZT crystallization and grain growth during the annealing.

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Section: A Formation Of Pt Hillocks On the Bare Pt Electrodesupporting

confidence: 61%

Section: Introductionmentioning

confidence: 99%

Structural investigations of Pt∕TiOx electrode stacks for ferroelectric thin film devices

Cao

Solbach

Klemradt

et al. 2006

Journal of Applied Physics

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“…As Cr 2 O 3 is found both below and above Ru, one can conclude that Ru is neither a good barrier against oxygen, nor against Cr diffusion. This might be generalized to any noble metal / reactive metal stack: in a recent paper [20], we show the oxidation behavior of Ti, Zr and Ta adhesion layers for Pt metallizations (whether the adhesion layer oxidizes in and above the Pt or below it) is determined by the respective cation and oxygen mobilities in the corresponding oxide. Finally, one should note that pure Cr was chosen rather than an alloy for simplicity in this study.…”

Section: Discussionmentioning

confidence: 84%

Conducting Barriers for Direct Contact of PZT Thin Films on Reactive Substrates

Maeder

Muralt

Sagalowicz

et al. 1999

J. Electrochem. Soc.

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Several bottom electrode systems for ferroelectric oxide thin film deposition onto reactive substrates or reactive metal films have been investigated with respect to chemical barrier properties and contact resistivity. Such electrode systems should not deteriorate by oxidation, and should prevent oxygen diffusion into the underlying base metal. First, the protective performance of Pt, Ru, RuO 2 / Ru and Cr has been evaluated on reactive substances such as W, Zr, Mo and TiN. On most materials, a reactive and passivating metal such as Cr offers protection up to a higher temperature than noble metals. This is explained by preferential oxidation. On Cr, a RuO 2 electrode allowed oxidation resistance to more than 800°C without any Cr diffusion: the RuO 2 serves both as an electrode and as a barrier to Cr. In order to reduce the contact resistance due to the formation of a Cr 2 O 3 film at the RuO 2 / Cr interface, a Ru interlayer was inserted, giving a RuO 2 / Ru / Cr. This combination allowed to maintain a low contact resistance up to 700°C.

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“…The difference in behavior might be understood when one knows that in the oxide Ti diffuses more than oxygen while Ta diffuses slower than oxygen. 9 In a previous study, 9 we showed that when one oxidizes the electrode (without depositing the PZT), almost all the Ti comes to the Pt surface while most of the tantalum stays under the Pt. In the case of Ti, there is upward diffusion of Ti, which leaves a lot of vacancies and voids, which are at least partially filled by downward diffusion of oxygen, lead and Pt.…”

Section: Discussionmentioning

confidence: 95%

Stoichiometry and Interdiffusion in PZT Thin Films Studied by Transmission Electron Microscopy

et al. 1999

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Electrode stability, interdiffusion, phase purity and deviation from stoichiometry at the PZT-electrode interface are key issues in PZT thin film integration. This article highlights the use of transmission electron imaging combined with energy dispersive spectroscopy (EDS) for the investigation of these phenomena. The accuracy of the EDS analysis is discussed. It will be shown that using a standard PZT sample and controlled conditions, reliable analysis can be performed.Diffusion mechanisms have been studied for Pt based electrode systems and RuO 2 -based electrode systems developed for direct integration onto silicon. The materials studied were composed of stacks of silicon-silicon oxide, an adhesion layer (Ti, Ta or TiOJ), an electrode (Pt or RuG 2 ) and PZT (45/55). The PZT was deposited by sol gel using the same parameters to allow for comparison of the different electrodes. Four different electrode / adhesion layer materials were compared (Pt/Ti, Pt/TiOx, Pt/Ta and RuO 2 / TiO 2 ). In the case of Pt, lead and oxygen diffusion through the electrode is observed. While the initial Ta layer transforms into a homogeneous pyrochlore phase, the Ti adhesion layer is heavily deformed. In the case of TiO, the lead is mainly incorporated at the interfaces with Pt and with Si0 2 . No lead diffusion to the adhesion layer is observed for the Ru0 2 electrode. In-situ sputtering and sol-gel deposition of PZT are also compared. The sol-gel films are close to the right stoichiometry for the perovskite while the sputtered films contained an excess of lead. No sign of second phase is found by X-ray diffraction (XRD), by ElS and by high resolution transmission electron microscopy (HRTEM) which suggests that the excess lead is accommodated in the perovskite lattice.

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Stabilized Platinum Electrodes for Ferroelectric Film Deposition using Ti, Ta and Zr Adhesion Layers

Cited by 113 publications

References 17 publications

Structural investigations of Pt∕TiOx electrode stacks for ferroelectric thin film devices

Structural investigations of Pt∕TiOx electrode stacks for ferroelectric thin film devices

Conducting Barriers for Direct Contact of PZT Thin Films on Reactive Substrates

Stoichiometry and Interdiffusion in PZT Thin Films Studied by Transmission Electron Microscopy

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