Intrinsic dead layer effect and the performance of ferroelectric thin film capacitors

Zhou, Changjian; Newns, Dennis M.

doi:10.1063/1.366147

Cited by 297 publications

(180 citation statements)

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“…In both the above studies then, the thesis would be that size-related permittivity suppression is largely unavoidable as it is an intrinsic feature of the electrode-dielectric boundary. The inevitability of reduced size leading to intrinsic permittivity suppression would also be the conclusion from other well-known investigations: Zhou and Newns [32] applied Thomas theory to demonstrate that 'dead-layers' were intrinsic; Sirenko et al [33] saw clear evidence, in far infra-red ellipsometry measurements, that modes which soften in bulk SrTiO 3 do not soften in thin films, even when as thick as 2 µm. Figure 5 (online colour at: www.pss-a.com) Calculated spatial distribution of the inverse permittivity profile through a cross-section of an idealised parallel-plate thin film capacitor structure [31].…”

Section: Figurementioning

confidence: 89%

Ferroelectrics at the nanoscale

Gregg¹

2009

Physica Status Solidi (a)

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There are several factors which make the investigation and understanding of nanoscale ferroelectrics particularly timely and important. Firstly, there is a market pressure, primarily from the electronics industry, to integrate ferroelectrics into devices with progressive decreases in size and increases in morphological complexity. This is perhaps best illustrated through the roadmaps for product development in FeRAM (Ferroelectric Random Access Memory) where the need for increases in bit density will require a move from 2D planar capacitor structures to 3D trenched capacitors in the next few years. Secondly, there is opportunity for novel exploration, as it is only relatively recently that developments in thin film growth of complex oxides, self‐assembly techniques and high‐resolution ‘top–down’ patterning have converged to allow the fabrication of isolated and well‐defined ferroelectric nanoshapes, the properties of which are not known. Thirdly, there is an expectation that the behaviour of small scale ferroelectrics will be different from bulk, as this group of functional materials is highly sensitive to boundary/surface conditions, which are expected to dominate the overall response when sizes are reduced into the nanoscale regime.This feature article attempts to introduce some of the current areas of discovery and debate surrounding studies on ferroelectrics at the nanoscale. The focus is directed primarily at the search for novel size‐related properties and behaviour which are not necessarily observed in bulk. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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Section: Figurementioning

confidence: 89%

Ferroelectrics at the nanoscale

Gregg¹

2009

Physica Status Solidi (a)

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“…Such a "dead" layer not necessarily has a different microstructure ͑e.g., due to reconstruction or high density of defects͒, because the intrinsic surface effect on the polarization 16 may also reduce the local dielectric permittivity. 17,18 The existence of a built-in electric field at the film/electrode interface represents another possible origin of suppressed dielectric response in the subsurface layer. 2,18 On the other hand, the interfacial capacitance may mostly originate in the finite electronic screening length of metallic electrodes.…”

Section: Introductionmentioning

confidence: 99%

“…17,18 The existence of a built-in electric field at the film/electrode interface represents another possible origin of suppressed dielectric response in the subsurface layer. 2,18 On the other hand, the interfacial capacitance may mostly originate in the finite electronic screening length of metallic electrodes. 19,20 This would be in agreement with the results of recent first-principles calculations 21 and the latest experimental data on high quality BaTiO 3 thin films, 4 which indicate that the observed polarization relaxation can be attributed to the depolarizing field determined solely by imperfect compensation of ferroelectric polarization charges by electron density variations in SrRuO 3 electrodes.…”

Section: Introductionmentioning

confidence: 99%

Thickness dependence of intrinsic dielectric response and apparent interfacial capacitance in ferroelectric thin films

Pertsev

Dittmann

Plonka

et al. 2007

Journal of Applied Physics

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We studied theoretically the influence of the progressive strain relaxation and the depolarizing-field effect on the thickness dependence of the out-of-plane dielectric response of epitaxial ferroelectric thin films sandwiched between extended metal electrodes. The calculations show that the inverse of the measured capacitance varies with the film thickness almost linearly in the most part of the thickness range at the majority of temperatures. Extrapolation of this linear dependence to zero thickness usually gives considerable nonzero intercept even in the absence of nonferroelectric interfacial layers. Remarkably, such apparent “interfacial capacitance” in a certain temperature range becomes negative. The physical meaning of the effective dielectric constant, which can be extracted from the slope of the reciprocal capacitance thickness dependence, is also analyzed. The theoretical predictions are compared with the experimental data obtained for single-crystalline SrRuO3∕Ba0.7Sr0.3TiO3∕SrRuO3 and Pt∕Ba0.7Sr0.3TiO3∕SrRuO3 thin-film capacitors.

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“…It has been proposed that the reduction of r in ferroelectric thin films can be explained by the existence of interfacial "dead layer" at one or both metal electrodes with poor dielectric properties. 2,[19][20][21] They may arise from the oxygen interdiffusion, chemical reaction, structural defects, or Schottky barriers at the interfaces. Treating the dead layer as a capacitance C i in series with bulk film capacitance C b , the measured capacitance may be expressed as 1 / C =1/C b +1/C i , and the dielectric constant of the dead layer increases as the film thickness decreases.…”

Section: -2mentioning

confidence: 99%

Effect of CaRuO3 interlayer on the dielectric properties of Ba(Zr,Ti)O3 thin films prepared by pulsed laser deposition

Tang

Tian

Wang

et al. 2006

Applied Physics Letters

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Ba͑Zr 0.2 Ti 0.8 ͒O 3 ͑BZT͒ thin films on Pt͑111͒ / Ti/ SiO 2 /Si͑100͒ substrates without and with CaRuO 3 ͑CRO͒ buffer layer were fabricated at 650°C in situ by pulsed laser deposition. The BZT thin films showed a dense morphology, many clusters are found on the surface images of BZT/Pt films, which are composed by nanosized grains of 25-35 nm; the average grain size of BZT/CRO films is about 80 nm, which lager than that of BZT/Pt thin film. The dielectric constants and dissipation factors of BZT/Pt and BZT/CRO thin films were 392 and 0.019 and 479 and 0.021 at 1 MHz, respectively. The dielectric constant of BZT/Pt and BZT/CRO thin films changes significantly with applied dc bias field and has high tunabilities and figures of merit of ϳ70% and 37 and 75% and 36, respectively, under an applied field of 400 kV/ cm. The possible microstructural background responsible for the high dielectric constant and tunability was discussed. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2360177͔ Barium strontium titanate ͑Ba, Sr͒TiO 3 ͑BST͒ thin films have currently become very attractive for applications in decoupling capacitors, storage capacitors, dynamic randomaccess memory, and tunable microwave devices. 1,2 The large electric field-depended dielectric constant can be used for devices such as tunable oscillators, filters, and phase shifters. In such devices, it is desirable to have a high dielectric tunability in a certain electric field range and low dielectric loss. Ba͑Zr y Ti 1−y ͒O 3 ͑BZT͒ is a possible choice as an alternative to BST in the fabrication of ceramic capacitors 3,4 because Zr 4+ is chemically more stable than Ti 4+ . The ferroelectric phase transition at the Curie temperature ͑T C ͒ in BZT bulk ceramics is known to change significantly with Zr content. BZT ceramics exhibit a diffuse phase transition and have high tunability in compositions with y ജ 0.20. [3][4][5][6] The fabrication of BZT thin films by rf-magnetron sputtering, 7 sol-gel method, 8 and pulsed laser disposition ͑PLD͒, 9 and their dielectric properties have been reported recently. Many efforts have been made to improve the dielectric properties of the BST thin film capacitors, including using conductive oxide electrodes such as ͑Ba, Sr͒RuO 3 , 10 ͑La 0.7 Sr 0.3 ͒MnO 3 , 11 LaNiO 3 , 12 and yttrium barrium copper oxide ͑YBCO͒. 13 The effects of CaRuO 3 buffer layer on the dielectric properties and tunability of BZT films have not yet been reported. In this work, Ba͑Zr 0.2 Ti 0.8 ͒O 3 thin films growth on Pt/ Ti/ SiO 2 / Si substrate without and with CaRuO 3 buffer layer were prepared by pulsed laser disposition. The orientation characteristics of grains, dielectric properties, tunability, and figure of merit of the columnar-grained Ba͑Zr 0.2 Ti 0.8 ͒O 3 thin films on Pt/ Ti/ SiO 2 / Si substrate without and with CaRuO 3 buffer layer are also reported.CaRuO 3 ͑CRO͒ bottom electrode layer was grown on Pt/ Ti/ SiO 2 / Si substrates at 750°C by rf-magnetron sputtering and using a CRO target. Ba͑Zr 0.2 Ti 0.8 ͒O 3 ͑BZT͒ thin films were gr...

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Intrinsic dead layer effect and the performance of ferroelectric thin film capacitors

Cited by 297 publications

References 8 publications

Ferroelectrics at the nanoscale

Ferroelectrics at the nanoscale

Thickness dependence of intrinsic dielectric response and apparent interfacial capacitance in ferroelectric thin films

Effect of CaRuO3 interlayer on the dielectric properties of Ba(Zr,Ti)O3 thin films prepared by pulsed laser deposition

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