Low-Voltage IGZO TFTs Using Solution-Deposited OTS-Modified Ta<sub>2</sub>O<sub>5</sub> Dielectric
Navid Mohammadian, Bikas C. Das, Leszek A. Majewski
Abstract
Low-voltage, high-performance thin film transistors (TFTs) that use amorphous metal oxide (MO) semiconductors as the active layer have been getting tremendous attention due to their essential role in future portable electronic-devices and systems. However, reducing the operating voltage of these devices to or below 1 V is a very challenging task because it is very difficult to obtain low threshold voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> ) and small subthreshold swing (SS) MO TFTs. In this article, indium gallium zinc oxide (IGZO) TFTs that use solution-deposited Ta <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> operating at 1 V are demonstrated. To enhance the dielectric properties of the fabricated ultrathin (d ~ 22 nm + 2 nm) tantalum pentoxide films, n-octadecyltrichlorosilane (OTS) self-assembled monolayer (SAM) was used. The morphology and electrical properties of both pristine and OTS-treated Ta <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> films have been studied. The optimized Ta <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> /OTS IGZO TFTs operate at 1 V with saturation field-effect mobility larger than 2.3 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V·s, threshold voltage of around 400 mV, SSs below 90 mV/dec, and current ON-OFF ratios well above 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> . The performance of the presented TFTs is high enough for many commercial applications such as disposable sensors or throwaway, low-end electronics significantly reducing the cost of their production.