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CopyrightWILEYVCHVerlagGmbH&Co.KGaA,69469Weinheim,Germany,2011

SupportingInformation

forAdv. Mater.,DOI: 10.1002/adma.201101115

Fabrication and Characterization of MIM Diodes Based on

Nb/Nb 2 O 5 Via a Rapid Screening Technique

Prakash Periasamy, Joseph J. Berry, Arrelaine A. Dameron,

Jeremy D. Bergeson, David S. Ginley, Ryan P. OHayre, and

Philip A. Parilla*

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DOI: 10.1002/adma.201101115

Fabrication and characterization of MIM diodes based on Nb/Nb2O5 via a rapid screening

technique

By Prakash Periasamy, Joseph J. Berry, Arrelaine A. Dameron, Jeremy D. Bergeson, David S.

Ginley, Ryan P. OHayre, and Philip A. Parilla*

E-mail: philip.parilla@nrel.gov, Phone: 303-384-6506, Fax: 303-384-6564

National Renewable Energy Laboratory, Golden, CO 80401 (USA)

Supporting Information

Table of Contents

S.No. DescriptionPage

No.1 Plot of Nb2O5 thickness as a function of anodization voltage. 2

2 XPS spectrum of Nb2O5 surface in the Nb/Nb2O5 bilayer. 3

3Photograph of the custom I-V station built specifically to test bent-wire point-

contact MIM devices.4

4

Note on statistical analysis done to calculate the asymmetry (fASYM) and

nonlinearity (fNL) reported in Figs 3(a) and (b) in the main text. 5

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1. Plot of Nb2O5 thickness as a function of anodization voltage.

Figure S1. Plot of thickness of anodized Nb2O5 layer as a function of anodization voltage.

Thickness was measured via x-ray reflectivity (XRR). A Philips XPert five-circle diffractometer

was used for XRR measurements. Anodization of Nb metal film to Nb2O5 was done in a 1MH2SO4 electrolyte solution at atmosphere conditions for an anodization time of 60 seconds. Fresh

H2SO4 solution was used for each data point. The growth coefficient (thickness/anodizationvoltage) is estimated to be 2.7 nm/V. Very similar growth coefficient was also obtained for longer

anodization time. Under similar conditions, the variation in thickness is found to be less than 1

nm.

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2. XPS spectrum of Nb2O5 surface in the Nb/Nb2O5 bilayer.

XPS analysis was carried out on the anodized surface to ascertain the oxidation state of theanodized layer. Figure S2 shows the high-resolution XPS spectrum of the Nb 3d region. A

survey scan was also taken (not shown here) that identified peaks of Nb and O in addition to traceimpurities of C.

Peak positions of the Nb 3d5/2 and Nb 3d 3/2 after corrections for the peak shift (0.7 eV based on

C 1S peak) are 207.3 and 210 eV, respectively. These peak positions match very well with the

reported (listed below) Nb 3d peak for Nb2O5.

The range for Nb 3d5/2 peak of Nb2O5 is between 207-208 eV.[Supp. Ref. 1]

Ozer et al.,[Supp. Ref. 2]

reported that the peak positions of Nb 3d5/2 and Nb 3d3/2 of Nb2O5 films (prepared by sol-gel, RF

magnetron sputtering) close to 207.2 and 210.1 eV, respectively.

Figure S2. High-resolution XPS spectrum showing the Nb 3d region of the anodized niobiumoxide surface. Peak positions of the Nb 3d5/2 and Nb 3d 3/2 after corrections for the peak shift

(0.679 eV based on C 1S peak) are 207.271 and 210.018 eV, respectively. These peak positionsmatches very well with the reported Nb 3d peak for Nb2O5.

Supplemental Reference (Supp. Ref.)[1] W. F. S. John F.Moulder, Peter E. Sobol and Kenneth D. Bomben, Ed.Handbook of X-ray Photoelectron

Spectroscopy, Physical Electronics, Minnesota 1995.

[2] N. Ozer, D. G. Chen, C. M. Lampert, Thin Solid Films1996, 277, 162.

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3. Photograph of the custom I-V station built specifically to test bent-wire point-contact

MIM devices.

Figure S3. Photograph of the custom I-V station for characterizing bent-wire point-contact MIM

devices. The metal 1 (M1)/insulator (I) bilayer on a silicon substrate (with native oxide) wasmounted to the supporting post. The metal 2 (M2) bent-wire was contacted to the M1/I bilayer

using a differential micrometer. In this study Nb/Nb2O5 is used as the M1/I bilayer. Pressed

indium wire was used to glue the copper wire contact to the un-anodized M1 surface. DC bias is

applied between M1 and M2 bent-wire and the resulting current is measured using a Keithley

2636 source measure unit. Current-Voltage data were recorded in a computer via LabTracer 2.0

software provided by Keithley.

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5. Note on statistical analysis done to calculate the asymmetry (fASYM) and nonlinearity (fNL)

reported in Figs 3(a) and (b) in the main paper.

For each MIM configuration, thirty I-V curves were collected by positioning the metal 2 wire(M2) in (at least) three different locations on the Nb2O5 surface. fASYMand fNLwere calculated

from the individual I-V data. As expected, fASYMwas found to be dependent on the bias voltage,whereas fNL was nearly independent on the bias voltage above the turn-on voltage (TOV). TOV is

defined as the knee of the I-V curve [Reference [3] in the main paper].

fASYMreported in Fig 3(a) (see main paper) is the average of thirty asymmetry values calculated

for each MIM configuration at 0.5V bias voltage. Very similar trends were seen for other bias

voltages. Error bars indicate the standard deviation in the distribution of fASYMat a bias of 0.5V.

Outliers were determined by evaluating the 25th

and 75th

quartiles after which the average

asymmetry values are calculated.

Since fNL is independent on bias voltage above the TOV, all the fNL values beyond TOV are

included for the calculations in each of the thirty I-V curves for every MIM configuration. The

TOV values for all the MIM configurations studied range from 0.1 to 0.25 V. To ensure that only

points beyond TOV were evaluated, the fNL values for each of the MIM configurations were takenbetween 0.3 to 0.5 V for the calculations. For the example of the Nb/Nb2O5/Cu MIMconfiguration, 30 I-V curves are collected. In each of the 30 I-V curves, 20 fNL values between 0.3

and 0.5V are considered. Hence the total number of fNL data points for the Nb/Nb2O5/Cu

configuration is 600 (30 X 20). Histograms are plotted using the data population (600 points) of

fNL values for each MIM configuration were used to analyze the distribution of the data. A typicalhistogram plot is shown in Figure S4 for the fNL values of Nb/Nb2O5/Cu. Figure S4 indicates a

typical histogram and fit to a normal distribution. This approach was applied to the other MIMconfigurations. Using this analysis the box and whisker plot of fNL values for each of the MIM

configuration was constructed based on the values obtained fitting the normal distribution to the

histograms.

Figure S4. Histogram plot of fNL values of Nb/Nb2O5/Cu. A normal distribution fit is also shown.