(Invited) New Dielectric Nanomaterials Fabricated from Nanosheet Technique

Abstract

We present a novel procedure for fabricating high-k nanodielectrics by using of perovskite nanosheet (Ca2-xSrxNb3O10) as a building block. We synthesized Ca2-xSrxNb3O10 nanosheets by delaminating layered perovskites (KCa2-xSrxNb3O10), and fabricated multilayer nanofilms on atomically flat SrRuO3 and Pt substrates by Langmuir-Blodgett method. Various microscopy techniques showed highly ordered lamellar structures, and electron energy loss spectroscopy revealed no detectable interdiffusion and strains at the interface between the layers and substrate. These nanofilms showed both high dielectric constant (>200) and low leakage current (< 10-7 A/cm2) even in films less than 5 nm thick. Our work thus provides a new recipe for designing nanodielectrics desirable for future high-k devices.

Synthesis of Sr2Nb3O10 nanosheets and their application for growth of thin film using an electrophoretic method

“…However, when the annealing temperature exceeded 600°C, the ε r value of the film decreased, and the film annealed at 800°C showed a small ε r value of 51, probably due to the degradation of the Pt electrode (Figure B). The ε r value of the SNO film grown by the LB method is large, at approximately 240, because this film has a microstructure similar to that of the single crystal . Therefore, it can be suggested that if the crystallinity of the film was improved by controlling the process conditions, the ε r value of the SNO film deposited by the electrophoresis method could be increased.…”

“…To synthesize the nanosheets from these compounds, the alkali metal ions or [Bi 2 O 2 ] 2+ ions of these compounds should be substituted for protons in acid solution, whereas the proton ions should be replaced with organic polycations such as tetrabutylammonium ions (TBA + ) and tetramethylammonium ions (TMA + ) . Finally, these perovskite nanosheets were grown on a substrate using the layer‐by‐layer (LBL), Langmuir‐Blodgett (LB), and electrophoresis methods …”

“…A Ti 0.87 O 2 thin film with thickness of 9.4 nm deposited on the SrRuO 3 substrate exhibited a high ε r value and low leakage current density, indicating that LBL is a useful method for deposition of the nanosheets . LB has been known as a simple and effective deposition method for nanosheets . Sr 2 Nb 3 O 10 (SNO) and Ca 2 Nb 3 O 10 (CNO) thin films deposited on SrRuO 3 substrate using the LB method have a single crystal‐like microstructure, and show a large ε r value (>200), with a low loss (2%‐5%) and low leakage current density (10 −7 Acm −2 at 1 V) .…”

“…LB has been known as a simple and effective deposition method for nanosheets . Sr 2 Nb 3 O 10 (SNO) and Ca 2 Nb 3 O 10 (CNO) thin films deposited on SrRuO 3 substrate using the LB method have a single crystal‐like microstructure, and show a large ε r value (>200), with a low loss (2%‐5%) and low leakage current density (10 −7 Acm −2 at 1 V) . Moreover, a dead‐layer, which is usually present between the dielectric thin film and the metal electrode, was not observed in these thin films, indicating that with the decrease in film thickness, their high ε r values do not decrease …”

“…7,10,16 Finally, these perovskite nanosheets were grown on a substrate using the layer-by-layer (LBL), Langmuir-Blodgett (LB), and electrophoresis methods. [19][20][21][22][23][24][25][26][27] The LBL method has been used to deposit various thin films. 21,23,28 A Ti 0.87 O 2 thin film with thickness of 9.4 nm deposited on the SrRuO 3 substrate exhibited a high e r value and low leakage current density, indicating that LBL is a useful method for deposition of the nanosheets.…”