Direct Probing of Polarization Charge at Nanoscale Level

Abstract

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...

Designing functional ferroelectric interfaces from first-principles: dipoles and band bending at oxide heterojunctions

“…Multilayered structures incorporating ferroelectric perovskites and metal/oxide electrodes have extensively been investigated for their use in a wide range of advanced applications, including but not limited to (multiple state) ferroelectric memories [1][2][3][4][5], quantum tunneling junctions [6][7][8][9][10][11][12][13][14], photo-ferroic solar cells [15][16][17][18][19][20][21][22][23][24], and various multilevel architectures with coupled ferroic modes [25][26][27][28][29][30][31][32][33][34]. Also, new experimental methods have been envisaged for acquiring an accurate control of polarization when the ferroelectric layer is situated deep into these structures [35][36][37][38]. Ferroelectric interfaces are key elements for the functionality of these heterostructures.…”

Gamma‐Ray Irradiation Effect on Ferroelectric Devices with Hafnium Aluminum Oxides

“…In this section, we further investigate the shift of polarization current under different PMA conditions to clarify the influence of grain size effect. The previous study had revealed that the polarization current shifts toward longer switching time are due to the contribution of film leakage . Therefore, we can differentiate the leakage component contributed by radiation‐induced defect from the ferroelectric polarization switching.…”

Recent Progress in the Nanoscale Evaluation of Piezoelectric and Ferroelectric Properties via Scanning Probe Microscopy

“…Kwon et al suggested a similar approach to obtain the actual switched area by further combination with PFM, which is referred to as AFM-PUND. [38] In their work, they focused on the switched area rather than the contact area because the amount of polarization charge is eventually determined by the switched area in ferroelectric materials. In this case, quantitative evaluation of polarization charge density is possible because the switched area is measurable by PFM.…”

“…However, if this is combined with SPM, a P-E hysteresis loop can be obtained over less than one micrometer for the top electrode; furthermore, it is possible to measure the P-E hysteresis loop on the film surface without the top electrode. [37][38][39] In this progress report, we summarize recent achievements in the evaluation of piezoelectric and ferroelectric properties on the nanoscale based on SPM techniques. Among the various SPM methods presented in Table 1, we first discuss the recent progress and some issues such as quantification methods and non-piezoelectric contributions made in piezoresponse force microscopy (PFM); this is because PFM is the most well-known SPM technique for elucidating the piezoelectric and ferroelectric properties.…”