Dielectric behavior related to TiO x phase change to TiO 2 in TiO x /Al 2 O 3 nanolaminate thin films
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esearch Letters
Dielectric behavior related to TiOx phase change to TiO2 in TiOx/Al2O3 nanolaminate thin films Geunhee Lee, Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080; Institute for Functional Nanomaterials, University of Puerto Rico, San Juan, Puerto Rico 00931-3343 Ram S. Katiyar, Institute for Functional Nanomaterials, University of Puerto Rico, San Juan, Puerto Rico 00931-3343 Bo-Kuai Lai, Lake Shore Cryotronics, Westerville, Ohio 43082 Charudatta Phatak, Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 Orlando Auciello, Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080 Address all correspondence to Geunhee Lee at [email protected] and Orlando Auciello [email protected] (Received 9 January 2014; accepted 22 April 2014)
Abstract We previously demonstrated that TiOx/Al2O3 nanolaminates (TAO NL) exhibit abnormally high-dielectric constant k (800–1000), due to Maxwell–Wagner polarization, via charge accumulation at insulating Al2O3/semiconducting TiOx interfaces. Here, we report TAO NL dielectric properties related to TiOx phase change in TiOx (0.9 nm)/Al2O3 (0.1 nm) NL. High-resolution transmission electron microscopy shows amorphous TiOx phase change to crystalline anatase TiO2 due to free-energy minimization. The phase change induce reduction in leakage current and dielectric loss (J = 10−2 to 10−4 A/cm2, tan δ = 10 to 10−1), still with k ∼ 600 up to MHz, compared to amorphous TAO NLs.
Dielectric materials having high-dielectric constant (k ∼ 10– 1000 s) are critical to enable the next generation of electronic devices [e.g., Complementary metal-oxide-semiconductor (CMOS)] in which the dielectric constant will ultimately decide the degree of scaling following Moore’s law.[1] In addition, high-k materials may greatly impact the development of a new generation of supercapacitors for high-frequency devices[2] and energy storage systems.[3] Very high-dielectric constants (k ≥ 1000) has been observed in ferroelectric materials that exhibit spontaneously created dipole moments,[4] or in an oxide with relaxor behavior characterized by a ferroelectric response under high-electric fields at low temperature but without macroscopic spontaneous polarization,[5] or some oxides with colossal dielectric constant such as La1.875Sr0.125NiO[6] and CaCu3Ti4O[127] in which the giant 4 dielectric constant has been generally characterized by a semiconducting bulk and highly resistive grain boundary.[6,7] Recently, our group reported the development of nanolaminates (NLs) thin-film structure consisting of Al2O3 and TiOx layers (TAO) with sublayer thickness of below 1 nm.[8,9] The TAO NL structure exhibited k values of up to 1000 at lower frequencies (0.1–1 MHz), induced by the tailored materials and interfaces.[8,9] The recent research on the TAO NL[8,9] revealed that the relatively high leakage currents (∼10−3 A/cm2) observed in the initial TAO NL[10] can be reduced by orde
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