Ferroelectric and Conductance Characterization of SrTiO3 Thin Films Grown on Silicon

Student Author(s)

Andrew Johnson

Faculty Mentor(s)

Dr. Joshua Veazey

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Thin-film ferroelectric/semiconductor heterostructures are regarded as potential platforms for high-density data storage. In certain structures, the local ferroelectric polarization state of the film has been shown to modulate conductivity with nanoscale precision [Maksymovych et al., Science 324, 1421-5 (2009), Gajek, et al., Nature 6, 296-297 (2007)]. Thus, information could in principle be encoded into the local polarization states of the thin film, creating nanoscale bits. SrTiO3 (STO) thin films exhibit epitaxial strain-induced ferroelectricity when deposited directly onto the surface of n-type Si(001) [Warusawithana, et al., Science 324, 367-369 (2009)]. In the work presented here, local probes were used to investigate the nanoscale ferroelectric and conductive properties of STO thin films (thicknesses ranging t = 2-10 nm) deposited on p-type Si(001) via molecular beam epitaxy, with a SrO interfacial layer. We observe classic signatures of ferroelectricity for samples having STO thicknesses of t < 5 nm. We patterned ferroelectric domains lithographically by applying voltages via a conductiveatomic force microscopy (c-AFM) tip. Domains were subsequently imaged with piezoresponse force microscopy (PFM), which indicated the ability to pole ferroelectric features with length scales of order 100 nm. Ferroelectric hysteresis loops revealed stable switching characteristics, with coercive voltages Vc≈1-2 V. In addition, preliminary evidence suggests a correlation between polarization direction and conductivity (determined via current-voltage, I-V curves) through the sample. Conclusive evidence of such ferroelectric-modulated conductivity, however, would require simultaneous measurement of conductivity and ferroelectric switching. Current work is focusing on this prospect.


This work was generously supported by the Hope College Department of Physics Frissel Research Fund and the National Science Foundation under NSFMRI Grant No. CHE-1126462. Portions of this work were conducted in the CMP group facilities at Michigan State University.

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