J. Mater. Sci. Technol. ›› 2020, Vol. 42: 28-37.DOI: 10.1016/j.jmst.2019.12.006
• Orginal Article • Previous Articles Next Articles
Ji-Ye Baeka, Duy Le Thaib, Lee Sang Yeona, Hyungtak Seoab*()
Received:
2019-07-15
Revised:
2019-09-22
Accepted:
2019-10-27
Published:
2020-04-01
Online:
2020-04-16
Contact:
Seo Hyungtak
Ji-Ye Baek, Duy Le Thai, Lee Sang Yeon, Hyungtak Seo. Aluminum doping for optimization of ultrathin and high-k dielectric layer based on SrTiO3[J]. J. Mater. Sci. Technol., 2020, 42: 28-37.
Fig. 1. Schematic diagrams of (a) co-sputtering Al and SrTiO3 via RF magnetron sputtering and (b) MOS capacitor structure with top and bottom Pt electrodes, Al-doped SrTiO3 insulator, and Si semiconductor. (c) TEM images of SrTiO3 and Al-doped SrTiO3 (sp = 40 and 100 W); inset images are captured at a magnification of 600,000 times. (d) TEM-EDS elemental mapping image of Al40:STO layer.
Sputtering power (W) | Al content (%) | |
---|---|---|
TEM-EDS | AES | |
40 | 5.33 | 4.8 |
100 | 10.26 | 9.5 |
Table 1 Atomic percentage of Al in STO layers.
Sputtering power (W) | Al content (%) | |
---|---|---|
TEM-EDS | AES | |
40 | 5.33 | 4.8 |
100 | 10.26 | 9.5 |
Fig. 2. (a) XRD result of pristine SrTiO3: as-deposited and after PDA. (b) XRD patterns of annealed Al:STO samples (sp = 0, 20, 40, 60, 80, and 100 W). (c) AFM image of SrTiO3 layers (before and after PDA and Al:STO layers (sp = 40 and 100 W)).
Fig. 4. XPS spectra of (a) Sr 3d, (b) Ti 2p, (c) O 1s, and (d) Al 2p of SrTiO3 and Al:STO samples (sp = 40 and 100 W). Here, peaks (1) and (2) represent the Sr-O bonds on the surface; peak (3) represents Ti-OOH (Ti4+δ), peak (4) represents Ti-O (Ti3+), and peak (5) represents Al-O bond (in SrAl2O4).
Fig. 5. AES depth profiles of O, Ti, Sr, and Al content as a function of depth in (a) STO layer, (b) Al40:STO layer, and (c) Al100:STO layer respectively. TOF-SIMS depth profiles near interfacial silicate region in (d) STO layer and (e) Al40:STO layer.
Fig. 6. (a) EOT values of Al:STO layers (corresponding to different thicknesses) measured at a frequency of 1 MHz. (b) Comparison of the current density and EOT values of 8-nm-thick insulating layers. (c) Shift of flat band voltage through C-V measurement of the MOS devices (STO and Al:STO) with temperature variation from 80 to 300 K. (d) Variation of fixed charge density from the C-V measurement of the MOS devices (STO and Al:STO) with temperature variation from 80 to 300 K. Change in the leakage current tunneling model according to the electric field of (e) Al-doped STO film and (f) STO film at low temperature (80-280 K). Leakage current plots as a function of Arrhenius input with an increase in temperature (80-400 K) at (g) -0.5 V and (h) 0.5 V.
Sample (8 nm thick) | Leakage Current Density (A/cm2) (@1 MV/cm) | Capacitance Density (μF/cm2) | EOT (nm) | Dielectric constant |
---|---|---|---|---|
SrTiO3 | 1.02 × 10-5 | 7.67 | 0.45 | 86.7 |
Al20:STO | 1.68 × 10-6 | 7.40 | 0.47 | 83.6 |
Al40:STO | 2.53 × 10-9 | 7.20 | 0.48 | 81.3 |
Al60:STO | 6.69 × 10-8 | 6.93 | 0.50 | 78.2 |
Al80:STO | 1.67 × 10-7 | 6.64 | 0.52 | 75.0 |
Al100:STO | 4.84 × 10-8 | 6.40 | 0.54 | 72.3 |
Table 2 Summary of the leakage current density, maximum capacitance density, EOT, and dielectric constant of SrTiO3 and Al:STO thin films.
Sample (8 nm thick) | Leakage Current Density (A/cm2) (@1 MV/cm) | Capacitance Density (μF/cm2) | EOT (nm) | Dielectric constant |
---|---|---|---|---|
SrTiO3 | 1.02 × 10-5 | 7.67 | 0.45 | 86.7 |
Al20:STO | 1.68 × 10-6 | 7.40 | 0.47 | 83.6 |
Al40:STO | 2.53 × 10-9 | 7.20 | 0.48 | 81.3 |
Al60:STO | 6.69 × 10-8 | 6.93 | 0.50 | 78.2 |
Al80:STO | 1.67 × 10-7 | 6.64 | 0.52 | 75.0 |
Al100:STO | 4.84 × 10-8 | 6.40 | 0.54 | 72.3 |
Fig. 7. (a) Imaginary dielectric constant plot as a function of photon energy obtained from SE measurement and 3-phase optical modeling, (b) VB edge spectra obtained through XPS analysis for STO and Al:STO dielectric layers. (c) Schematic band alignment model constructed through electrical and spectroscopic analyses for STO and Al:STO MOS capacitors.
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