Graded ferroelectric capacitors with robust temperature characteristics

El‐Naggar, Mohamed Y.; Dayal, Kaushik; Goodwin, David G.; Bhattacharya, Kaushik

doi:10.1063/1.2369650

Cited by 35 publications

(22 citation statements)

References 21 publications

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“…209,210 Some important device geometries of interest include settings with partially electroded surfaces, 211 or with surface features such as notches, islands, and surface tips. 212,213 In the former case, the partially electrode surfaces lead to a problem posed on all-space because of existence of stray fields outside the device. In the latter case, a highly resolved calculation is required near regions where geometry and/or electric field changes abruptly, but a coarse discretization can be used away from these regions.…”

Section: Challenges For Modeling Of Complex Oxide Heterostructuresmentioning

confidence: 99%

Challenges and opportunities for multi-functional oxide thin films for voltage tunable radio frequency/microwave components

Subramanyam¹,

Cole²,

Sun³

et al. 2013

Journal of Applied Physics

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147

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There has been significant progress on the fundamental science and technological applications of complex oxides and multiferroics. Among complex oxide thin films, barium strontium titanate (BST) has become the material of choice for room-temperature-based voltage-tunable dielectric thin films, due to its large dielectric tunability and low microwave loss at room temperature. BST thin film varactor technology based reconfigurable radio frequency (RF)/microwave components have been demonstrated with the potential to lower the size, weight, and power needs of a future generation of communication and radar systems. Low-power multiferroic devices have also been recently demonstrated. Strong magneto-electric coupling has also been demonstrated in different multiferroic heterostructures, which show giant voltage control of the ferromagnetic resonance frequency of more than two octaves. This manuscript reviews recent advances in the processing, and application development for the complex oxides and multiferroics, with the focus on voltage tunable RF/microwave components. The over-arching goal of this review is to provide a synopsis of the current state-of the-art of complex oxide and multiferroic thin film materials and devices, identify technical issues and technical challenges that need to be overcome for successful insertion of the technology for both military and commercial applications, and provide mitigation strategies to address these technical challenges. V C 2013 AIP Publishing LLC.

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Section: Challenges For Modeling Of Complex Oxide Heterostructuresmentioning

confidence: 99%

Challenges and opportunities for multi-functional oxide thin films for voltage tunable radio frequency/microwave components

Subramanyam¹,

Cole²,

Sun³

et al. 2013

Journal of Applied Physics

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147

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“…Further, a is both position-and temperature-dependent, and we assume the variation a ij ðx; TÞ ¼ a 0 T À T c ðxÞ ð Þ d ij following. 23 The governing equations can now be obtained by minimizing the free energy while subject to the electrostatic constraint…”

Section: Fig 2 Functionally Graded Thin Film Constructed From Bariumentioning

confidence: 99%

“…Key elements of this strategy follow. 23 Additionally, even when the entire film is above the local T c , the use of heterogeneous films provides a simple route to applying an inhomogeneous strain that is required for flexoelectricity. Figure 1 presents a schematic description of the dielectric permittivity variation within each layer.…”

mentioning

confidence: 99%

Piezoelectricity above the Curie temperature? Combining flexoelectricity and functional grading to enable high-temperature electromechanical coupling

Mbarki¹,

Baccam²,

Dayal³

et al. 2014

Applied Physics Letters

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Most technologically relevant ferroelectrics typically lose piezoelectricity above the Curie temperature. This limits their use to relatively low temperatures. In this Letter, exploiting a combination of flexoelectricity and simple functional grading, we propose a strategy for high-temperature electromechanical coupling in a standard thin film configuration. We use continuum modeling to quantitatively demonstrate the possibility of achieving apparent piezoelectric materials with large and temperature-stable electromechanical coupling across a wide temperature range that extends significantly above the Curie temperature. With Barium and Strontium Titanate, as example materials, a significant electromechanical coupling that is potentially temperature-stable up to 900 C is possible. A piezoelectric material couples electric fields with mechanical stress and deformation. It enables the conversion of stimuli and energy between electromagnetism and mechanics, and has important applications that range from energy harvesting to artificial muscles.1 Perovskites such as Barium Titanate (BaTiO 3 ) and Lead Titanate (PbTiO 3 ) are two widely used materials that exhibit a fairly high electromechanical coupling.2-4 The piezoelectricity in these materials, which are also ferroelectric, are driven by an asymmetric distribution of charges in the atomic unit cell. Above the Curie temperature (T c ), the crystal structure transforms to a centrosymmetric state, and both ferroelectricity and piezoelectricity disappear. For example, at T c ¼ 120 C in BaTiO 3 , it transforms from a non-centrosymmetric tetragonal crystal to a centrosymmetric cubic crystal. The loss of piezoelectricity at such (relatively) low temperatures hinders their potential application to areas ranging from hypersonics to oil extraction, which require high-temperature energy harvesting, harsh environment sensing, and actuation, among others.We exploit flexoelectricity as the first element of our strategy to go beyond this limitation. Flexoelectricity denotes the coupling between polarization and strain gradients; this is in contrast to piezoelectricity that relates polarization to strains. The difference between piezoelectricity and flexoelectricity can be readily observed from the following equation:where, P i is the electric polarization, S jk is the strain tensor, e ijk is the third order piezoelectric tensor, and f ijkl is the fourth order flexoelectric tensor. Flexoelectricity is a property that is displayed by all dielectrics to some degree. Thus, in a centrosymmetric material, where the piezoelectric tensor e vanishes, non-uniform strains can still induce a polarization. Flexoelectricity is mediated through the fourth-order tensor f, and unlike e, symmetry principles permit its existence in all types of crystal structure and not just non-centrosymmetric crystals. For instance, while BaTiO 3 will cease to be piezoelectric above T c ¼ 120 C, it can still display flexoelectricity. Flexoelectricity has recently received much attention, e.g., it suggests tantali...

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“…1,2 More recently, they have found applications in high-speed memories, 3 and have been proposed as elements of microwave circuits 4,5 and as photonic switches at small length scales. 6 Many of these modern applications use thinfilm geometries with surface electrodes.…”

Section: Introductionmentioning

confidence: 99%

Free surface domain nucleation in a ferroelectric under an electrically charged tip

Yang

Dayal

2012

Journal of Applied Physics

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This paper examines the process of domain nucleation in ferroelectric perovskites at a free surface due to electrical fields applied through a charged tip above the surface. We use a real-space phase-field model to model the ferroelectric, and apply a boundary element-based numerical method that enables us to accurately account for the stray electric fields outside the ferroelectric and the interactions through electric fields between the external tip and ferroelectric. We calculate the induced domain patterns, the stress and internal electric fields, and the induced surface displacement for various relative orientations of the crystal lattice with respect to the free surface. The effect of the external spatially inhomogeneous electric field leads to the formation of complex domain patterns and nominally incompatible microstructures. Two key findings are: first, in c axis films, a new domain forms beneath the tip through 180 switching and this new domain has the opposite piezo-response as the original domain, leading to a distinct displacement signature on the surface; and second, in a axis films, domain nucleation occurs at lower applied field because polarization rotates to align with the applied field, whereas in c axis films, the polarization magnitude reduces until 180 switching occurs at a higher applied field. We also see that the calculated domain patterns differ significantly from analytical approximations that are often used.

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Graded ferroelectric capacitors with robust temperature characteristics

Cited by 35 publications

References 21 publications

Challenges and opportunities for multi-functional oxide thin films for voltage tunable radio frequency/microwave components

Challenges and opportunities for multi-functional oxide thin films for voltage tunable radio frequency/microwave components

Piezoelectricity above the Curie temperature? Combining flexoelectricity and functional grading to enable high-temperature electromechanical coupling

Free surface domain nucleation in a ferroelectric under an electrically charged tip

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