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, 7 (1), 932

Recovery of Alumina Nanocapacitors After High Voltage Breakdown

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Recovery of Alumina Nanocapacitors After High Voltage Breakdown

A Belkin et al. Sci Rep.

Abstract

Breakdown of a dielectric material at high electric fields significantly limits the applicability of metal-dielectric-metal capacitors for energy storage applications. Here we demonstrate that the insulating properties of atomic-layer-deposited Al2O3 thin films in Al/Al2O3/Al trilayers can recover after the breakdown. The recovery has been observed in samples with the dielectric thickness spanning from 4 to 9 nm. This phenomenon holds promise for a new generation of capacitors capable of restoring their properties after the dielectric breakdown. Also, if employed in capacitor banks, the recovery process will ensure that the bank remains operational even if a breakdown occurs.

Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1
Figure 1
(a) Schematic of the sample (not to scale) and electrical diagram of the measurement setup. All the layers are labeled explicitly. The measurement setup includes electrometer Keithley 6517B serving as the voltage source and the ammeter, and the series resistor R0 ≈ 10 MΩ. (b) An example of an electric breakdown measurement. Black line shows how the source voltage changes over time, the blue line depicts the corresponding voltage drop on the sample. The thickness of the insulating layer in this example was 4 nm. The sample voltage at first follows the source voltage. In this example, at voltage about 5 V dielectric breakdown happens. The sample resistance gets reduced by orders of magnitude, thus the voltage on the capacitor (blue curve) also drops.
Figure 2
Figure 2
Current-voltage dependences of samples with alumina thicknesses equal to (a) 4 nm, (b) 6.5 nm and (c) 9 nm. The data plotted here corresponds to the first full period of the voltage curve (see Fig. 1(b)). Source voltage amplitude is (a) 6 V, (b) 9 V and (c) 12 V. Arrows serve as a guide to an eye. Vs is the voltage between capacitor plates.
Figure 3
Figure 3
The dependence of the absolute value of the leakage current density, |J|, on the sample voltage, VS, for the nanocapacitor with 9 nm Al2O3 layer. Black arrows indicate the sections of the dependence corresponding to forward and backward voltage ramp. Each half cycle lasts 1800 s. Inset (a) is the dependence of the capacitance on the frequency of the voltage signal with the amplitude equal 1 V. Inset (b) shows the dependence of the normalized capacitance ΔC/C0 = (C − C0)/C0 on the applied constant bias voltage (black circles). To exclude the hysteresis from the analysis, we use data points obtained during the voltage sweep from +5 V to −5 V. Blue dashed line corresponds to the parabolic fit of the data.
Figure 4
Figure 4
The time dependence of the source voltage U (red dashed line) and sample resistance Rs (blue line) for the nanocapacitor with 4 nm Al2O3 layer. Initial and successive global breakdown jumps are marked with black arrows.
Figure 5
Figure 5
The capacitance of the samples before (black squares) and after (blue circles) the initial global breakdown. The thickness of the dielectric is 6.5 nm. Dashed line depicts the average value of the capacitance obtained before breakdown.
Figure 6
Figure 6
Optical image of a test MDM nanocapacitor after a high-voltage breakdown. Small black specks on the surface of the top electrode constitute local breakdowns (marked as “Local BD”). Scale bar corresponds to 20 μm.
Figure 7
Figure 7
Scanning electron microscope images of the top surface of a test MDM nanocapacitor after a high-voltage breakdown made at (a) 5 k magnification, scale bar is 2 μm, (b) 20 k magnification, scale bar is 500 nm, and (c) 50 k magnification, scale bar is 200 nm.

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