Analytical Extraction Method for Density of States in Metal Oxide Thin-Film Transistors by Using Low-Frequency Capacitance–Voltage Characteristics

Abstract

An analytical expression for density of trap states (DOS) related to the surface potential is derived from the Poisson's equation and the surface potential corresponding to certain gate-source voltage is obtained by integrating the low-frequency capacitance-voltage characteristic. It is shown that the DOS for indium-zinc-oxide thin-film transistors (IZO TFTs) may be represented by the superposition of exponential deep states and exponential tail states with the density of deep/tail states (N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DA</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TA</sub> ) at the conduction edge as 1.2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> ·eV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> /9.0 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> ·eV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and the characteristics energy of deep/tail states (E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DA</sub> /E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TA</sub> ) as 5.0 eV/0.182 eV. These extracted parameters are further verified by the comparison of the measured transfer and output characteristics of IZO TFTs with the simulation results by a 2D device simulator ATLAS (Silvaco). Hence, this extraction method of DOS may be very useful for characterizing metal oxide TFTs since it is analytical, fast, and accurate.