Limits...
Current rectifying and resistive switching in high density BiFeO3 nanocapacitor arrays on Nb-SrTiO3 substrates.

Zhao L, Lu Z, Zhang F, Tian G, Song X, Li Z, Huang K, Zhang Z, Qin M - Sci Rep (2015)

Bottom Line: These capacitors also show reversible polarization domain structures, and well-established piezoresponse hysteresis loops.Moreover, apparent current-rectification and resistive switching behaviors were identified in these nanocapacitor cells using conductive-AFM technique, which are attributed to the polarization modulated p-n junctions.These make it possible to utilize these nanocapacitors in high-density (>100 Gbit/inch(2)) nonvolatile memories and other oxide nanoelectronic devices.

View Article: PubMed Central - PubMed

Affiliation: Institute for Advanced Materials and Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials, South China Normal University, Guangzhou 510006, China.

ABSTRACT
Ultrahigh density well-registered oxide nanocapacitors are very essential for large scale integrated microelectronic devices. We report the fabrication of well-ordered multiferroic BiFeO3 nanocapacitor arrays by a combination of pulsed laser deposition (PLD) method and anodic aluminum oxide (AAO) template method. The capacitor cells consist of BiFeO3/SrRuO3 (BFO/SRO) heterostructural nanodots on conductive Nb-doped SrTiO3 (Nb-STO) substrates with a lateral size of ~60 nm. These capacitors also show reversible polarization domain structures, and well-established piezoresponse hysteresis loops. Moreover, apparent current-rectification and resistive switching behaviors were identified in these nanocapacitor cells using conductive-AFM technique, which are attributed to the polarization modulated p-n junctions. These make it possible to utilize these nanocapacitors in high-density (>100 Gbit/inch(2)) nonvolatile memories and other oxide nanoelectronic devices.

No MeSH data available.


Related in: MedlinePlus

Cross-section TEM images for the SRO/BFO/Nb-STO nanodot heterostructure.(a) Relative smaller magnification image as a overview for a nanocapacitor structure, and (b) larger magnification image; (c) selected area electron diffraction (SAED) alone the <010> direction, showing diffraction spots of STO, BFO, and SRO, along with minor impurity phases.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4389717&req=5

f2: Cross-section TEM images for the SRO/BFO/Nb-STO nanodot heterostructure.(a) Relative smaller magnification image as a overview for a nanocapacitor structure, and (b) larger magnification image; (c) selected area electron diffraction (SAED) alone the <010> direction, showing diffraction spots of STO, BFO, and SRO, along with minor impurity phases.

Mentions: The Nb-STO/BFO/SRO nanoscale features were also examined by the cross-section TEM observations shown in Fig. 2. The cross-section image demonstrates that each cell is composed of well-epitaxial BFO thin layer of ~10 nm in thickness, covered with a SRO capping layer as top electrode. It is also worthy of mention that the interface between BFO and SRO nanodots is not very flat, which is limited by our fabrication method. The individual layers were also checked by Energy Dispersive X-Ray Spectroscopic Analysis (EDX). From the transmission electron microscopy (TEM) cross-section images, it is seen that both BFO and SRO show well-established single crystalline with the same orientation as the substrate. The epitaxial quality was further examined by selected area electron diffraction (SAED) along the <010> direction (Fig. 2(c)), where apparent diffraction spots of STO/SRO and BFO, along with minor amount of impurity phase, can be identified. It should be mentioned here that, the diffraction spots of SRO and STO are well overlapped, as their lattice parameters are very close. By carefully examining the reciprocal lattices from the STO and BFO, we can derive a large BFO c/a ratio of ~1.14, corresponding to an out-of-plane lattice parameter c ~ 4.45 Å, close to that of tetragonal BFO nanostructure on LaAlO3 substrate reported by Zhang et al (c = 4.65 Å)11. We have checked carefully the lattice space and have found that the c-parameter is not very uniform spatially. Most areas show a small c-lattice space ~4.5 Å, while there are some locations exhibiting smaller c ~ 4.0 to 4.2 Å. The diffraction spots can well reflect the average of the lattice spaces, consistent with our HRTEM image analysis. We also notice that the angle between the a and c is 89–90°, slightly deviated from the rectangular angle. Therefore, it is safe to conclude that the structure is monoclinic or most likely psuedotetragonal, similar to reported results for BFO/SRO/STO by Chu et al19. The large c/a ratio may be attributed to the big in-plane compressive strain imposed by the substrate, noting the lattice mismatch of 1.7% between strain-free BFO and Nb-STO. Due to the small thickness (~10 nm) of BFO, the strain imposed from the Nb-STO is almost over the whole BFO nanostructures, which may be higher than that with a SRO buffer layer. From the literature, BFO directly deposited on Nb-STO has a much bigger c/a ratio than that with a SRO layer1920, supporting our assumption. Furthermore, our deposition oxygen pressure (2 Pa) is lower than that commonly used for film deposition (10 Pa), which may introduce high density oxygen vacancies and also bring more distortion into the BFO lattice. While the nonuniformity in lattice space may be related to the defects such as dislocations, which can partially relax the local strains, further study is still needed to throw light on the reason for the large lattice distortion in our BFO nanostructures.


Current rectifying and resistive switching in high density BiFeO3 nanocapacitor arrays on Nb-SrTiO3 substrates.

Zhao L, Lu Z, Zhang F, Tian G, Song X, Li Z, Huang K, Zhang Z, Qin M - Sci Rep (2015)

Cross-section TEM images for the SRO/BFO/Nb-STO nanodot heterostructure.(a) Relative smaller magnification image as a overview for a nanocapacitor structure, and (b) larger magnification image; (c) selected area electron diffraction (SAED) alone the <010> direction, showing diffraction spots of STO, BFO, and SRO, along with minor impurity phases.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4389717&req=5

f2: Cross-section TEM images for the SRO/BFO/Nb-STO nanodot heterostructure.(a) Relative smaller magnification image as a overview for a nanocapacitor structure, and (b) larger magnification image; (c) selected area electron diffraction (SAED) alone the <010> direction, showing diffraction spots of STO, BFO, and SRO, along with minor impurity phases.
Mentions: The Nb-STO/BFO/SRO nanoscale features were also examined by the cross-section TEM observations shown in Fig. 2. The cross-section image demonstrates that each cell is composed of well-epitaxial BFO thin layer of ~10 nm in thickness, covered with a SRO capping layer as top electrode. It is also worthy of mention that the interface between BFO and SRO nanodots is not very flat, which is limited by our fabrication method. The individual layers were also checked by Energy Dispersive X-Ray Spectroscopic Analysis (EDX). From the transmission electron microscopy (TEM) cross-section images, it is seen that both BFO and SRO show well-established single crystalline with the same orientation as the substrate. The epitaxial quality was further examined by selected area electron diffraction (SAED) along the <010> direction (Fig. 2(c)), where apparent diffraction spots of STO/SRO and BFO, along with minor amount of impurity phase, can be identified. It should be mentioned here that, the diffraction spots of SRO and STO are well overlapped, as their lattice parameters are very close. By carefully examining the reciprocal lattices from the STO and BFO, we can derive a large BFO c/a ratio of ~1.14, corresponding to an out-of-plane lattice parameter c ~ 4.45 Å, close to that of tetragonal BFO nanostructure on LaAlO3 substrate reported by Zhang et al (c = 4.65 Å)11. We have checked carefully the lattice space and have found that the c-parameter is not very uniform spatially. Most areas show a small c-lattice space ~4.5 Å, while there are some locations exhibiting smaller c ~ 4.0 to 4.2 Å. The diffraction spots can well reflect the average of the lattice spaces, consistent with our HRTEM image analysis. We also notice that the angle between the a and c is 89–90°, slightly deviated from the rectangular angle. Therefore, it is safe to conclude that the structure is monoclinic or most likely psuedotetragonal, similar to reported results for BFO/SRO/STO by Chu et al19. The large c/a ratio may be attributed to the big in-plane compressive strain imposed by the substrate, noting the lattice mismatch of 1.7% between strain-free BFO and Nb-STO. Due to the small thickness (~10 nm) of BFO, the strain imposed from the Nb-STO is almost over the whole BFO nanostructures, which may be higher than that with a SRO buffer layer. From the literature, BFO directly deposited on Nb-STO has a much bigger c/a ratio than that with a SRO layer1920, supporting our assumption. Furthermore, our deposition oxygen pressure (2 Pa) is lower than that commonly used for film deposition (10 Pa), which may introduce high density oxygen vacancies and also bring more distortion into the BFO lattice. While the nonuniformity in lattice space may be related to the defects such as dislocations, which can partially relax the local strains, further study is still needed to throw light on the reason for the large lattice distortion in our BFO nanostructures.

Bottom Line: These capacitors also show reversible polarization domain structures, and well-established piezoresponse hysteresis loops.Moreover, apparent current-rectification and resistive switching behaviors were identified in these nanocapacitor cells using conductive-AFM technique, which are attributed to the polarization modulated p-n junctions.These make it possible to utilize these nanocapacitors in high-density (>100 Gbit/inch(2)) nonvolatile memories and other oxide nanoelectronic devices.

View Article: PubMed Central - PubMed

Affiliation: Institute for Advanced Materials and Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials, South China Normal University, Guangzhou 510006, China.

ABSTRACT
Ultrahigh density well-registered oxide nanocapacitors are very essential for large scale integrated microelectronic devices. We report the fabrication of well-ordered multiferroic BiFeO3 nanocapacitor arrays by a combination of pulsed laser deposition (PLD) method and anodic aluminum oxide (AAO) template method. The capacitor cells consist of BiFeO3/SrRuO3 (BFO/SRO) heterostructural nanodots on conductive Nb-doped SrTiO3 (Nb-STO) substrates with a lateral size of ~60 nm. These capacitors also show reversible polarization domain structures, and well-established piezoresponse hysteresis loops. Moreover, apparent current-rectification and resistive switching behaviors were identified in these nanocapacitor cells using conductive-AFM technique, which are attributed to the polarization modulated p-n junctions. These make it possible to utilize these nanocapacitors in high-density (>100 Gbit/inch(2)) nonvolatile memories and other oxide nanoelectronic devices.

No MeSH data available.


Related in: MedlinePlus