Improved Performance of Bottom-Contact Organic Thin-Film Transistor Using Al Doped HfO2 Gate Dielectric (2014)

Aluminum doped HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (HfAlO) prepared by atomic layer deposition is investigated as gate dielectric for low-voltage organic thin-film transistors (OTFTs). The HfAlO film exhibits a low leakage current density of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(4.92 \times 10^{-8}\) </tex-math></inline-formula> A/cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(^{2}\) </tex-math></inline-formula> at −3 MV/cm, which is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(\sim 70\) </tex-math></inline-formula> % smaller than its HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> counterpart. In addition, copper phthalocyanine (CuPc) OTFT with HfAlO dielectric has an average mobility <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(\mu ~(2.58\pm 0.32\times 10^{-3}\) </tex-math></inline-formula> cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(^{2}\) </tex-math></inline-formula> /Vs) increased by 58%, sub-threshold slope SS (0.9 ± 0.11 V/decade) decreased by 11%, and ON/OFF ratio <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(I_{\mathrm{{\scriptstyle ON}}}/I_{\mathrm{{\scriptstyle OFF}}}\) </tex-math></inline-formula> (3.1 ± 1.3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(\times \) </tex-math></inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\( 10^{3}\) </tex-math></inline-formula> ) increased by 86% as compared with those with HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> as gate dielectric ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(\mu =1.63\pm 0.27\times 10^{-3}\) </tex-math></inline-formula> cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(^{2}\) </tex-math></inline-formula> /Vs; <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\({\rm SS}=1.01\) </tex-math></inline-formula> ±0.1 V/decade; <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(I_{\mathrm{{\scriptstyle ON}}}/I_{\mathrm{{\scriptstyle OFF}}}=1.7\pm 0.77\times 10^{3}\) </tex-math></inline-formula> ). All these could be ascribed to the inclusion of Al in the HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> film, which increases the conduction band offset and the bandgap and improves the dielectric and interface quality. The temperature effect on the performance of OTFTs is also investigated.