Nanoscale Lateral switchable rectifiers fabricated by Local Anodic Oxidation
Pablo F. Siles 1,2, B. S. Archanjo3, D. L. Baptista3, V. L. Pimentel1, J. Joshua Yang4, B. R. A. Neves5, G.
Medeiros-Ribeiro4
1 Laboratório Nacional de Luz Síncrotron, Caixa Postal 6192, CEP 13083-970, Campinas, SP, Brazil
2 Instituto de Física Gleb Wataghin, Universidade Estadual de Campinas, UNICAMP, SP, Brazil
3 Divisão de Metrologia de Materiais, Instituto Nacional de Metrologia, Normalização e Qualidade
Industrial (INMETRO), Duque de Caxias, RJ, 25250-020, Brazil
4 Hewlett-Packard Laboratories, 1501 Page Mill Road, Palo Alto, California 94304
5 Departamento de Física, Universidade Federal de Minas Gerais, Belo Horizonte, MG, 30123-970, Brazil
Supplementary Information
Humidity Control System:
Figure S1 shows the schematic diagram of the home-made humidity control system.
Figure S1. Schematic diagram of a home-made humidity control system for local anodic oxidation processes in the
Ti films. The oxidation takes place in a well controlled humidity environment (better than 1%). In order to obtain
an specific humidity inside the main chamber, the main humidity controller set the temperature in the H2O vapor
chamber and opens the solenoid valve permitting the flux of N 2 (to decrease humidity) or N2+H2O hot vapor (to
increase humidity) to the main chamber where the LAO process is performed. Since it able to perform all the
experiments in-situ, this humidity control is of great importance. LAO processes are performed in a relatively high
humidity values while electrical measurements requires low values inside the chamber in order to reduce any
influence of the environment during the switching processes of the device. Sample structure corresponds to
sample A.
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Structural and chemical analysis:
The structural and chemical analysis was performed via high resolution analytical transmission electron
microscopy (HRTEM) of the LAO oxide patterns before the step formation. Initially, a 50 nm-thick Ti film
is evaporated, by DC sputtering, on a SiO2 substrate. Ti thin film is then patterned by LAO processes, in a
60% relative humidity atmosphere, by applying 10V bias voltage and typical tip-sample velocity within 110 µm/s (figure S2 (a) shows a schematic diagram of the structure). Using a dual beam (focused ion
beam and electron beam) TEM sample preparation technique, we could take the oxidized Ti film and
attach it to a TEM grid. Figures S2 (a), (b) and (c) show the sample preparation steps. First, a platinum
layer is deposited using the electron beam in order to protect the oxidized Ti surface. Ion beam is used
to mill material from both sides of the protected area and the micromanipulator is used to transport the
sample to a TEM grid. The sample is then thinned and cleaned (figure S2 (d)), in other to become
electron-transparent, and presents a thickness between 10 and 100 nm.
(a)
(b)
Ti oxidized LAO pattern
Pt
Ti thin film
Si+SiO2 substrate
(c)
(d)
Figure S2. Steps of dual beam TEM sample preparation technique of a local anodized area of Ti film. Sample
structure in (a) corresponds to sample B.
HRTEM cross section images of the oxidized Ti film are presented in figures S3 (a) and (b). Figure S3 (a)
presents a general lateral view of the layer structure of the sample. The granular Pt protection layer is
observed on the top of the image. The TiOx/Ti film is situated just below the protection layer, above the
SiO2 substrate. A bright stripe representing the TiOx layer is clearly observed in the figure S3 (b).
However, a well-defined interface between TiOx and Ti is not evidenced. The analysis of the HRTEM
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images show that the Ti film is constituted by a nanometric polycrystalline structure, while in the TiOx
layer an amorphous phase seems to dominate.
a)
b)
Pt
TiOx
Ti
Ti
SiO2
Figure S3 (a), (b) High resolution TEM cross section images.
Ti
Electrical Models for IV characteristics:
Figure S4 shows experimental IV characteristics of the switchable rectifiers in Ti-TiOx-Ti junctions and
their respective fitting using a Frenkel-Poole model.
Figure S4. Switchable rectifiers in a MIM junction. Solid lines represent the fitted IV characteristics assuming
Frenkel-Poole emission (dominant for high fields and high temperatures [1]). Dashed lines represent the
experimental data.
[1] S.M. Sze, Physics of semiconductor devices (Wiley, New York, 1981, pp. 403).
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