Role of oxygen vacancies on the bias illumination stress stability of solution-processed zinc tin oxide thin film transistors

Abstract

Solution-processed ultra-thin (∼3 nm) zinc tin oxide (ZTO) thin film transistors (TFTs) with a mobility of 8 cm2/Vs are obtained with post spin-coating annealing at only 350 °C. The effect of light illumination (at wavelengths of 405 nm or 532 nm) on the stability of TFT transfer characteristics under various gate bias stress conditions (zero, positive, and negative) is investigated. It is found that the ΔVth (Vthstress 3400 s − stress 0 s) window is significantly positive when ZTO TFTs are under positive bias stress (PBS, ΔVth = 9.98 V) and positive bias illumination stress (λ = 405 nm and ΔVth = 6.96 V), but ΔVth is slightly negative under only light illumination stress (λ = 405 nm and ΔVth = −2.02 V) or negative bias stress (ΔVth = −2.27 V). However, the ΔVth of ZTO TFT under negative bias illumination stress is substantial, and it will efficiently recover the ΔVth caused by PBS. The result is attributed to the photo-ionization and subsequent transition of electronic states of oxygen vacancies (i.e., Vo, Vo+, and Vo++) in ZTO. A detailed mechanism is discussed to better understand the bias stress stability of solution processed ZTO TFTs.

The Impact of Solvents on the Performances of Solution‐Processed Indium Gallium Zinc Oxide Thin‐Film Transistors Using Nitrate Ligands

“…Hence, DIW‐based IGZO film shows a lower amount of oxygen deficiency compared with the organic solvent (Figure ). Hence, oxygen vacancies act as trap sites, it resulted in a larger amount of V th shift that occurred in 2‐ME‐based IGZO due to the presence of a greater amount of oxygen vacancy when compared with the DIW …”

P‐5.2: Aqueous Sr‐doped In2O3 TFT stability under negative bias illumination stress

“…It can be assumed that the enhanced stability is related to the Sr content. Many researches have stated the mechanism of the NBIS instability of oxide TFTs [10,11], when under the negative bias stress, the V o is more easily ionized into the positive divalent oxygen vacancy (V o 2+ ). The conversion of the V o to V o 2+ releases two free electrons, causing the shift of the threshold voltage in the negative direction.…”

Improvement of the long-term stability of ZnSnO thin film transistors by tungsten incorporation using a solution-process method

“…7,8 Compared with other indium-free binary compounds, ZTO has emerged as a promising candidate semiconductor due to its high charge carrier mobility and comparable device performance with its counterparts. [6][7][8][9][10] In spite of the above-mentioned advantages of ZTO TFTs, they seem to suffer from severe bias-stress instability, 11,12 and the electron density of the back channel surface is susceptible to H 2 O and O 2 molecules in ambient air. 7,13 Recent studies have shown that doping third metal ions into ZTO can solve these issues, for example Nb-doped ZTO, 7 Zr-doped ZTO, 14 Hf-doped ZTO 15 and TI-doped ZTO.…”