Interfaces in Epitaxial Ferroelectric Layers/Multilayers and Their Effect on the Macroscopic Electrical Properties

Pintilie, L.; Boni, Georgia Andra; Chirilă, Cristina; Hrib, Luminiţa; Iuga, A.; Trupina, L.; Pintilie, I.; Pasuk, Iuliana; Negrea, Raluca; Ghica, Corneliu; Botea, Mihaela; Apostol, Nicoleta G.; Teodorescu, Cristian M.

doi:10.1002/9781118935743.ch20

Cited by 2 publications

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“…Considering the switched area of the ferroelectric thin film in Figure 4, the polarization charge density was calculated to be around 120 µC/cm 2 . The average value for fifteen times measurements obtained through PU waveform is 119.0±8.3 µC/cm 2 for the positive bias branch, which is close to the previously reported values (albeit, slightly higher), [46][47] as shown in Figures 4(d,e). Because we obtained the switched area from the PFM phase images, this area value may be slightly underestimated.…”

Section: Figures S3 S4 and S5supporting

confidence: 91%

Direct Probing of Polarization Charge at Nanoscale Level

et al. 2017

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based on the detection of the polarization switching current. [7][8][9] However, owing to an important long-term development for reducing the sizes of the electronic devices, the preparation of ferroelectric materials such as nanostructures and thin films is entering nanometer-scale regime and accordingly it requires the investigation of the ferroelectricity at the nanoscale level. Even though piezoresponse force microscopy (PFM) has been used extensively to explore nanoscale ferroelectricity over the past two decades, [10][11][12] it was recently revealed that several nonferroelectric effects, e.g., the electrostatic effect and electrochemical strain, can also contribute to the PFM response, which often leads to a misinterpretation of the measured PFM response. [13][14][15] In particular, it was reported that PFM hysteresis loops can be generated even in nonferroelectric materials. [16,17] Furthermore, new types of ferroelectric materials, e.g., HfO 2 -based materials, [18][19][20] have been recently studied by many different research groups and industries to gain a fundamental understanding as well as to investigate practical applications of new ferroelectrics. Considering the current situation, an alternative approach is necessary to examine the existence of the ferroelectricity at the nanoscale level.In this study, we demonstrate the direct probing of a polarization charge at the nanoscale level using a combination of conventional conductive atomic force microscopy (CAFM) and PFM. It has been generally accepted that the detection of polarization charge using a conventional CAFM setup without a top Ferroelectric materials possess spontaneous polarization that can be used for multiple applications. Owing to a long-term development of reducing the sizes of devices, the preparation of ferroelectric materials and devices is entering the nanometer-scale regime. Accordingly, to evaluate the ferroelectricity, there is a need to investigate the polarization charge at the nanoscale. Nonetheless, it is generally accepted that the detection of polarization charges using a conventional conductive atomic force microscopy (CAFM) without a top electrode is not feasible because the nanometer-scale radius of an atomic force microscopy (AFM) tip yields a very low signal-to-noise ratio. However, the detection is unrelated to the radius of an AFM tip and, in fact, a matter of the switched area. In this work, the direct probing of the polarization charge at the nanoscale is demonstrated using the positive-up-negativedown method based on the conventional CAFM approach without additional corrections or circuits to reduce the parasitic capacitance. The polarization charge densities of 73.7 and 119.0 µC cm −2 are successfully probed in ferroelectric nanocapacitors and thin films, respectively. The obtained results show the feasibility of the evaluation of polarization charge at the nanoscale and provide a new guideline for evaluating the ferroelectricity at the nanoscale. Polarization ChargeFerroelectric materials possess spontaneous...

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Section: Figures S3 S4 and S5supporting

confidence: 91%

Direct Probing of Polarization Charge at Nanoscale Level

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“…Here, we have used C-V measurements to study the free carrier density inside the ferroelectric film and their temperature dependence and the interface trap density. Below we describe each one of them briefly13, 24,53,54 .…”

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Engineering ferroelectric switching dynamics

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The word dynamics roots from the Greek word δύναμις (dynamis) which means "power" 1. Consequently, this branch of science deals with the effects of forces on motion such as aerodynamics which deals with the motion of gas, and thermodynamics which describes the relationship between thermal and mechanical energy etc. In ferroelectrics, switching dynamics deals with the study of domain wall motion under an applied electric field 2-4. But in order to understand a physical system fully it is not only important to understand the dynamical behaviour of the system, but also the degrees of freedom of the system which determine the number of independent ways in which a system can move. For an ensemble the degrees of freedom are determined by its stochastic variables. Apropos, within systems at real device scale (present day ferroelectric based devices are 130 nm in lateral dimension), it is pertinent to treat them as an ensemble rather than as a single entity. Ferroelectrics, because of their non-volatility and bi-stability and, most importantly, their switchability between the two states using an applied electric field, have found applications such as non-volatile random access memory (NVRAM) devices 3, 5. Ferroelectric RAM (FeRAM) devices were first proposed by Dudley Allen Buck in his master's thesis in 1952 at MIT 6. It was shown that ferroelectrics can not only be used for storing memory but also for logic operations. Field effect transistors based on ferroelectrics (FeFET), as well as ferroelectric tunnel junctions (FTJ) based devices in recent years have also been realized for the realization of non-destructive read out memories 7-12. Even though the crystal structure and internal chemical environment renders the bi-stability in ferroelectrics 13, 14 , the actual switching in ferroelectrics takes place through nucleation and growth mechanisms 3, 4, 15, 16 of ferroelectric domains. In FeRAM and FeFET, the device performance characterised by the switching speed, remnant polarization, coercive voltages, leakage current, reliability and stability, is of paramount importance. For the above devices, since domain wall switching dynamics determines the switching speed, coercive voltages, operating voltages and energy consumption etc., it gave rise to a plethora of research into the domain wall switching dynamics and statistics treating the ferroelectrics as ideal insulators. On the other hand, ferroelectrics were also treated as semiconductors to explain

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Interfaces in Epitaxial Ferroelectric Layers/Multilayers and Their Effect on the Macroscopic Electrical Properties

Cited by 2 publications

References 72 publications

Direct Probing of Polarization Charge at Nanoscale Level

Direct Probing of Polarization Charge at Nanoscale Level

Engineering ferroelectric switching dynamics

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