Saturday, September 13, 2014

Study on band-gaps of a variety of classic ALD high-k´s via REELS

A good investigation on band-gaps of a variety of classic ALD high-k´s  - all amorphous NbO, TaO, ZrO, HfO, AlO, and SiO School of Electrical Engineering and Computer Science at Oregon State University and Intel. One of the key aspects of this work is that  the MIM devices have been fabricated on ultra-smooth ZrCuAlNi (ZCAN) amorphous metal bottom electrodes.

All high-k materials were deposited in a Picosun SUNALE R-150B reactor and SiO were deposited in a Cambridge NanoTech Fiji PEALD reactor. 

Investigation of the impact of insulator material on the performance of dissimilar electrode metal-insulator-metal diodes
Nasir Alimardani, Sean W. King, Benjamin L. French, Cheng Tan, Benjamin P. Lampert and John F. Conley Jr.
J. Appl. Phys. 116, 024508 (2014)

The performance of thin film metal-insulator-metal (MIM) diodes is investigated for a variety of large and small electron affinity insulators using ultrasmooth amorphous metal as the bottom electrode. Nb 2O5, Ta 2O5, ZrO2, HfO2, Al2O3, and SiO2 amorphous insulators are deposited via atomic layer deposition (ALD). Reflection electron energy loss spectroscopy (REELS) is utilized to measure the band-gap energy (EG) and energy position of intrinsic sub-gap defect states for each insulator. EG of as-deposited ALD insulators are found to be Nb 2O5 = 3.8 eV, Ta 2O5 = 4.4 eV, ZrO2 = 5.4 eV, HfO2 = 5.6 eV, Al2O3 = 6.4 eV, and SiO2 = 8.8 eV with uncertainty of ±0.2 eV. Current vs. voltage asymmetry, non-linearity, turn-on voltage, and dominant conduction mechanisms are compared. Al2O3 and SiO2 are found to operate based on Fowler-Nordheim tunneling. Al2O3 shows the highest asymmetry. ZrO2, Nb 2O5, and Ta 2O5 based diodes are found to be dominated by Frenkel-Poole emission at large biases and exhibit lower asymmetry. The electrically estimated trap energy levels for defects that dominate Frenkel-Poole conduction are found to be consistent with the energy levels of surface oxygen vacancy defects observed in REELS measurements. For HfO2, conduction is found to be a mix of trap assisted tunneling and Frenkel-Poole emission. Insulator selection criteria in regards to MIM diodes applications are discussed.

Equilibrium energy band diagrams with defect levels indicated. Dotted lines in (a) SiO and (b) AlO indicate distinct energy levels peaks determined by REELS. The shaded region in (c) HfO, (d) ZrO, (e) TaO, and (f) NbO represents the extended range of oxygen vacancy related defect levels as determined by REELS. Darker shading is meant to represent higher densities of defects. Finally, the thick dashed lines in (d) ZrO, (e) TaO, and (f) NbO indicate defect levels extracted from electrical measurements. (J. Appl. Phys. 116, 024508 (2014))

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