Conducting atomic force microscopy studies on doped CuInO2 thin films for resistive memory
device applications
B.R. Mehta
Thin Film Laboratory
Department of Physics
Indian Institute of Technology Delhi
Hauz Khas, New Delhi -110016, India
brmehta@physics.iitd.ernet.in
Delafosite thin films have interesting structural, optical and electronic properties due to the highly
anisotropic crystal structure and possibility of bipolar conductivity. In this presentation, optical, structural
and electrical properties of Sn (n type) and Ca (p type) doped CuInO2 layers grown by rf magnetron
sputtering technique will be discussed. Depending on doping and deposition temperature, these films show
nanocolumnar structure with (110) and (006) preferred orientations. The observed decrease in activation
energy from 0.9 eV to about 0.10 eV and a large decrease in conductivity from 2.11 × 10 -10 Scm-1 to 1.66 ×
10-1 Scm-1 on Sn doping has been explained due to the change in preferred orientation along with efficient
doping. Our results show that crystallite orientation is the most important factor controlling the electrical
conduction in delafossite thin films. The anisotropy of electrical conduction along (006) and (110) directions
in tin doped samples has been further established using conducting atomic force microscopy (CAFM)
measurements. The CAFM measurements shows the presence of nanoconducting region when the current
flow direction is aligned along the BO6 layer and complete absence of conducting regions when the current
direction is perpendicular to the film surface. Resitive memory devices based on Sn and Ca doped CuInO2
films show stable and reproducible ‘on’ and ‘off’ states. CAFM measurement on these devices carried out
before and after ‘forming’ show the growth of nanoconducting filaments on the application of a threshold
voltage. It is possible to control resistance in the ‘on’ and ‘off’ states and magnitute of the forming and
switching voltages by controlling the doping concentration and crystallite orientation in CuInO2 layers.
Applied Physics Letters, 93, 192104 (2008)
Journal of Applied Physics (2009)