Hysteresis-Free High-Performance Pentacene Organic Thin-Film Transistor by Sputtering Amorphous Barium Titanate as Ultrathin High-<i>k</i> Gate Dielectric

In this work, low-voltage pentacene organic thin-film transistors (OTFTs) are fabricated using 12-nm ultrathin barium titanate (BTO) gate dielectric sputtered at various temperatures (room temperature (RT), <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$200~^{\circ }$ </tex-math></inline-formula>C, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$350~^{\circ }$ </tex-math></inline-formula>C) with and without subsequent annealing at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$400~^{\circ }$ </tex-math></inline-formula>C in N<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>. Among the samples, the sample with BTO sputtered at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$200~^{\circ }$ </tex-math></inline-formula>C without the N<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> annealing shows the best performance: smallest and negligible hysteresis of 18 mV, highest carrier mobility of 2.91 cm<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{{2}}\cdot $ </tex-math></inline-formula>V<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-{1}}\cdot $ </tex-math></inline-formula>s<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-{1}}$ </tex-math></inline-formula>, highest ON-/OFF-current ratio of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.16\times 10^{{6}}$ </tex-math></inline-formula>, low threshold voltage of −1.09 V, and small subthreshold swing (SS) of 140 mV/dec. In addition, the leakage current density of the BTO dielectric can be achieved at a low level of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$9.75\times 10^{-{8}}$ </tex-math></inline-formula> A/cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at an electric field of −1 MV/cm. The best matching in surface energy between the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$200~^{\circ }$ </tex-math></inline-formula>C-sputtered BTO dielectric and pentacene leads to the growth of the largest grains during the pentacene deposition, resulting in the least grain-boundary scattering on the carrier transport in pentacene film and thus the highest carrier mobility in the OTFT. Moreover, the smallest hysteresis of this sample implies the lowest trap density at the pentacene/BTO interface and thus the weakest Coulomb scattering, which is another reason for its highest carrier mobility.