Built-in voltages and asymmetric polarization switching in Pb(Zr,Ti)O3 thin film capacitors

Abstract

Asymmetric polarization switching of Pb(Zr,Ti)O3 (PZT) thin films with different electrode configuration has been studied in (La,Sr)CoO3/Pb(Zr,Ti)O3/(La,Sr)CoO3 (LSCO) heterostructures in which the conducting oxide (La,Sr)CoO3 and/or LaCoO3 (LCO) have been used as an electrode. Polarization-voltage (P-V) hysteresis loop of LSCO/PZT/LSCO was symmetric. However, LCO/PZT/LSCO showed a largely asymmetric P-V hysteresis loop and large relaxation of the remanent polarization at the negatively poled state, eventually leading to an imprint failure. On the other hand, LSCO/PZT/LCO exhibited large relaxation of the positively poled state. The asymmetric behavior of the polarized states implies the presence of an internal electric field inside the PZT layer. It is suggested that the internal electric field is caused by built-in voltages at LCO/PZT and LSCO/PZT interfaces. The built-in voltages at LCO/PZT and LSCO/PZT interfaces were 0.6 V and 0.12 V, respectively.

Dynamic leakage current compensation in ferroelectric thin-film capacitor structures

“…The proposed method might therefore be even more interesting, if ferroelectric capacitors with different electrode materials will be studied. 11 Summarizing our results, the present contribution addresses the problematic of leakage current and leakage current compensation in ferroelectric thin-film capacitor structures. It is shown that an ohmic contribution in the current response of a leaky ferroelectric capacitor has a significant impact on the shape of the hysteresis curve and lead to nonphysical values of the remnant polarization and the coercive field.…”

Reduction-induced Fermi level pinning at the interfaces between Pb(Zr,Ti)O3 and Pt, Cu and Ag metal electrodes

“…in dynamic random access memory (DRAM), piezoelectric sensors and actuators [1,2,3,4]. For PZT thin film, the cycling stability, imprint performance and leakage current strongly depend on the used electrode material [5,6,7,8]. Electrical fatigue causes a reduction of polarization with increasing switching numbers and is a severe limitation of device operation.…”

Effect of lattice-misfit strain on the process-induced imprint behavior in epitaxial Pb(Zr0.52Ti0.48)O3 thin films

“…Since the PZT capacitors with noble metal electrodes like Pt exhibit a significant polarization loss when subject to bipolar switching pulses, in the past decade, for the growth of fatigue-free PZT capacitors and especially in the epitaxial form, various oxide electrodes such as La 0.5 Sr 0.5 CoO 3 (LSCO), SrRuO 3 (SRO), La 0.7 Sr 0.3 MnO 3 (LSMO), and LaNiO 3 (LNO) have been employed. [3][4][5][6][7][8]11,12 For epitaxial LSCO/PZT/LSCO capacitors, however, when exposed to reducing atmosphere for device fabrication, a large voltage offset was observed. [3][4][5] This process-induced imprint behavior was greatly complicated by the instability of the LSCO layer at reduced oxygen pressures, 5,13 and rarely examined for the other oxide electrodes.…”

“…However, there is a lack of understanding on the formation of the internal field. Different models, such as the aligned dipolar defect complexes and asymmetric distribution of charged defects through a bulk thin film, 2-5 and a built-in electric field or a nonswitching layer at the ferroelectric-electrode interface, [6][7][8][9] have been proposed to explain the asymmetric behavior of ferroelectric capacitors.…”

“…However, it is often observed that ferroelectric films exhibit significant imprint, or asymmetry of switching parameters, such as the coercive field ͑E c ͒ and the remnant polarization ͑P r ͒. [2][3][4][5][6][7][8][9][10] The cause of the imprint is generally attributed to the presence of an internal electric field in the capacitor which supports the given polarization state while opposing the antiparallel one. However, there is a lack of understanding on the formation of the internal field.…”