Abstract
Silicon nanowire (SiNW) metal-oxide-semiconductor (MOS) capacitors with Al2O3/TiO2/Al2O3 (ATA) stacked dielectric films were fabricated by metal-assisted chemical etching (MACE) and atomic layer deposition (ALD). High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) images revealed that SiNWs were conformally coated with ATA although the cross-sectional shapes of MACE-SiNWs were non-uniform and sharp spikes can be seen locally. The dielectric capacitance density of 5.9 μF/cm2 at V = −4 V of the perfect accumulation region was achieved due to the combination of the large surface area of the SiNW array and the high dielectric constant of ATA. The capacitance changed exponentially with the voltage at V < −4.3 V and the capacitance of 84 μF/cm2 was successfully achieved at V = −10 V. It was revealed that not only 3D structure and high-k material but also local nanostructure of SiNWs and stacked dielectric layers could contribute to the considerable high capacitance.
Highlights
Electrostatic capacitors have attractive characteristics for the application in energy storage devices
A Silicon nanowire (SiNW) MOS capacitor with the SiNW length of 2.4 μm and Al2O3 thickness of 10 nm, fabricated by metal-assisted chemical etching (MACE) achieved the maximum capacitance of 4.1 μF/cm2 [5]
Before the dielectric thin film deposition on SiNWs, the samples were cleaned by dipping in a piranha solution at 120~140 ◦C for 15 minutes and an HF (5%) solution at room temperature for 1 minute
Summary
Electrostatic capacitors have attractive characteristics for the application in energy storage devices. There are some reports of metal-oxide-semiconductor (MOS) capacitors using SiNWs. Morel et al achieved the capacitance density of 18 μF/cm2 using SiNWs and 10-nm-thickalumina (Al2O3) deposited by atomic layer deposition (ALD) as a dielectric material [7]. A SiNW MOS capacitor with the SiNW length of 2.4 μm and Al2O3 thickness of 10 nm, fabricated by MACE achieved the maximum capacitance of 4.1 μF/cm2 [5].
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