Unravelling and controlling hidden imprint fields in ferroelectric capacitors

Abstract

Ferroelectric materials have a spontaneous polarization that can point along energetically equivalent, opposite directions. However, when ferroelectric layers are sandwiched between different metallic electrodes, asymmetric electrostatic boundary conditions may induce the appearance of an electric field (imprint field, Eimp) that breaks the degeneracy of the polarization directions, favouring one of them. This has dramatic consequences on functionality of ferroelectric-based devices such as ferroelectric memories or photodetectors. Therefore, to cancel out the Eimp, ferroelectric components are commonly built using symmetric contact configuration. Indeed, in this symmetric contact configuration, when measurements are done under time-varying electric fields of relatively low frequency, an archetypical symmetric single-step switching process is observed, indicating Eimp ≈ 0. However, we report here on the discovery that when measurements are performed at high frequency, a well-defined double-step switching is observed, indicating the presence of Eimp. We argue that this frequency dependence originates from short-living head-to-head or tail-to-tail ferroelectric capacitors in the device. We demonstrate that we can modulate Eimp and the life-time of head-to-head or tail-to-tail polarization configurations by adjusting the polarization screening charges by suitable illumination. These findings are of relevance to understand the effects of internal electric fields on pivotal ferroelectric properties, such as memory retention and photoresponse.

Complementary Resistive Switching Using Metal–Ferroelectric–Metal Tunnel Junctions

“…Sample Growth : Ferroelectric BTO thin films (4 nm thick) were epitaxially grown on (001) LSAT substrates buffered by a thin La 2/3 Sr 1/3 MnO 3 (LSMO) (20 nm) layer acting as metallic electrode. Films were grown by pulsed laser deposition (PLD) using the conditions discussed elsewhere . Structural characterization is shown in Figure S13 in the Supporting Information.…”

Tailoring Lattice Strain and Ferroelectric Polarization of Epitaxial BaTiO3 Thin Films on Si(001)

“…Platinum top electrodes, 20 nm thick and 60 μm x 60 μm in size, were deposited using dc magnetron sputtering through stencil masks. Ferroelectric polarization loops and leakage current were measured at room temperature in top-top configuration 26 (two BTO capacitors were measured in series, contacting two top Pt electrodes and using the conducting LNO buffer layer as common bottom electrode) by means of an AixACCT TFAnalyser2000 platform. Ferroelectrics loops were obtained by sweeping an electric field at a constant rate with a frequency of 10 kHz and measuring the current, using the dielectric leakage current compensation (DLCC) to minimize leakage current effects.…”

Enhancement of phase stability and optoelectronic performance of BiFeO3thin filmsviacation co-substitution

“…Ferroelectric characterization Top Pt electrodes (20 nm thick) were deposited by sputtering through a stencil mask on LSMO-buffered films, allowing to obtain arrays of contacts of 7 µm diameter. Ferroelectric polarization loops were measured at room temperature in top-top configuration 32 (two BFO capacitors were measured in series, contacting two top Pt electrodes and using the conducting LSMO buffer layer as common bottom electrode) by means of an AixACCT TFAnalyser2000 platform. Ferroelectrics loops were obtained by sweeping an electric field at a constant rate with a frequency of 1 kHz and measuring the current, using the dielectric leakage current compensation (DLCC) to minimize leakage current effects.…”