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. 2023 Apr 2;13(7):1256.
doi: 10.3390/nano13071256.

Experimental Formation and Mechanism Study for Super-High Dielectric Constant AlOx/TiOy Nanolaminates

Jiangwei Liu  1 , Masayuki Okamura  1 , Hisanori Mashiko  2 , Masataka Imura  1 , Meiyong Liao  1 , Ryosuke Kikuchi  2 , Michio Suzuka  2 , Yasuo Koide  1
Affiliations

Experimental Formation and Mechanism Study for Super-High Dielectric Constant AlOx/TiOy Nanolaminates

Jiangwei Liu et al. Nanomaterials (Basel). .

Abstract

Super-high dielectric constant (k) AlOx/TiOy nanolaminates (ATO NLs) are deposited by an atomic layer deposition technique for application in next-generation electronics. Individual multilayers with uniform thicknesses are formed for the ATO NLs. With an increase in AlOx content in each ATO sublayer, the shape of the Raman spectrum has a tendency to approach that of a single AlOx layer. The effects of ATO NL deposition conditions on the electrical properties of the metal/ATO NL/metal capacitors were investigated. A lower deposition temperature, thicker ATO NL, and lower TiOy content in each ATO sublayer can lead to a lower leakage current and smaller loss tangent at 1 kHz for the capacitors. A higher deposition temperature, larger number of ATO interfaces, and higher TiOy content in each ATO sublayer are important for obtaining higher k values for the ATO NLs. With an increase in resistance in the capacitors, the ATO NLs vary from semiconductors to insulators and their k values have a tendency to decrease. For most of the capacitors, the capacitances reduce with increments in absolute measurement voltage. There are semi-circular shapes for the impedance spectra of the capacitors. By fitting them with the equivalent circuit, it is observed that with the increase in absolute voltage, both parallel resistance and capacitance decrease. The variation in the capacitance is explained well by a novel double-Schottky electrode contact model. The formation of super-high k values for the semiconducting ATO NLs is possibly attributed to the accumulation of charges.

Keywords: ATO; atomic layer deposition; capacitor; double-Schottky contacts; nanolaminate; super-high dielectric constant.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Fabrication routines for the Si/Ti/Pt/ATO NL/Ti/Au capacitors in (a) schematic plan view and (b) schematic cross-sectional view: (i) silicon substrate cleaning, (ii) Ti/Pt evaporation, (iii) ATO NL deposition, (iv) Ti/Pt evaporation, and (v) ATO NL etching to open the windows for Ti/Pt electrodes.
Figure 2
Figure 2
(a) Schematic diagram of the Si/Ti/Pt/ATO NL/Ti/Au capacitor. (b) STEM image and (c) EDX mapping for the 1.98A/2.01T ATO NL layer.
Figure 3
Figure 3
Raman spectra for (a) AlOx and TiOy single layers and (b) 0.34A/0.73T, 0.51A/0.52T, and 0.68A/0.33T ATO NLs.
Figure 4
Figure 4
(a–d) Leakage current-voltage, capacitance-frequency, capacitance-voltage, and loss tangent-frequency characteristics of the Si/Ti/Pt/ATO NL/Ti/Au capacitors with the variation in ATO NL deposition temperature. The ATO NL and sublayer thicknesses are the same at around 50 nm and 0.5A/0.5T, respectively. Their deposition temperatures were 150 (black circle line), 200 (red circle line), and 250 °C (green circle line).
Figure 5
Figure 5
(a–d) Leakage current-voltage, capacitance-frequency, capacitance-voltage, and loss tangent-frequency characteristics for the Si/Ti/Pt/ATO NL/Ti/Au capacitors with variation in NL thickness and the number of ATO interfaces. The deposition temperature for the four ATO NL layers was the same at 200 °C. The ATO sublayer thicknesses were 0.51A/0.52T (black, red, and green circle lines) and 2.04A/2.08T (blue circle line). The numbers of ATO interfaces for the four samples were 50, 100, 194, and 25, respectively.
Figure 6
Figure 6
(a–d) Leakage current-voltage, capacitance-frequency, capacitance-voltage, and loss tangent-frequency characteristics for the Si/Ti/Pt/ATO NL/Ti/Au capacitors with the variation in AlOx and TiOy contents. The deposition temperature, total NL thickness, and each ATO sublayer thickness were kept at 200 °C, around 100 nm, and around 1 nm, respectively. The ATO sublayer thicknesses change from 0.34A/0.73T to 0.77A/0.19T.
Figure 7
Figure 7
(a) Impedance spectra of the Si/Ti/Pt/ATO NL/Ti/Au capacitors measured at 0 V in the frequency from 1 Hz to 1 MHz. The sublayer thicknesses for them are the same at 0.51A/0.52T. The total thicknesses for the ATO NL layers are 51.9 (black circle), 103.8 (red circle), and 201.3 nm (green circle). (b) Equivalent circuit for the Si/Ti/Pt/ATO NL/Ti/Au capacitors. (c,d) Rp and capacitance as functions of voltage derived from the impedance spectra, respectively.
Figure 8
Figure 8
Dielectric constants of the ATO NLs as functions of (a) deposition temperature, (b) number of ATO interfaces, (c) TiOy content, and (d) resistance of the capacitor. The open and solid circle spots in Figure 8b represent the 0.51A/0.52T and 2.04A/2.08T ATO NLs, respectively.
Figure 9
Figure 9
Schematic diagrams of the double-Schottky electrode contact model at a voltage of: (a) +V, (b) V = 0, and (c) −V, respectively.
See this image and copyright information in PMC

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