Low-temperature fabrication of sputtered high-k HfO2 gate dielectric for flexible a-IGZO thin film transistors

Abstract

In this work, low temperature fabrication of a sputtered high-k HfO2 gate dielectric for flexible a-IGZO thin film transistors (TFTs) on polyimide substrates was investigated. The effects of Ar-pressure during the sputtering process and then especially the post-annealing treatments at low temperature (≤200 °C) for HfO2 on reducing the density of defects in the bulk and on the surface were systematically studied. X-ray reflectivity, UV-vis and X-ray photoelectron spectroscopy, and micro-wave photoconductivity decay measurements were carried out and indicated that the high quality of optimized HfO2 film and its high dielectric properties contributed to the low concentration of structural defects and shallow localized defects such as oxygen vacancies. As a result, the well-structured HfO2 gate dielectric exhibited a high density of 9.7 g/cm3, a high dielectric constant of 28.5, a wide optical bandgap of 4.75 eV, and relatively low leakage current. The corresponding flexible a-IGZO TFT on polyimide exhibited an optimal device performance with a saturation mobility of 10.3 cm2 V−1 s−1, an Ion/Ioff ratio of 4.3 × 107, a SS value of 0.28 V dec−1, and a threshold voltage (Vth) of 1.1 V, as well as favorable stability under NBS/PBS gate bias and bending stress.

The Effect of Zirconium Doping on Solution-Processed Indium Oxide Thin Films Measured by a Novel Nondestructive Testing Method (Microwave Photoconductivity Decay)

“…Microwave photoconductivity decay (µ-PCD) is a noncontact and nondestructive technology with low cost and short time [33][34][35]. Information regarding the defect state density can be obtained by the microwave reflectivity of the photo-carrier trapping and recombination, this being an important parameter for the evaluation of the quality of the semiconductor thin films.…”

Improvement in Bias Stability of IGZO TFT With Etching Stop Structure by UV Irradiation Treatment of Active Layer Island

“…Because the active layer and the insulating layer were prepared in the same process for all samples during the experiment. Therefore, the reason for the decrease in the subthreshold swing may be the reduction of bulk defects in the active layer [32]. This bulk defects are mainly oxygen vacancies.…”

Recent progress in the development of backplane thin film transistors for information displays

“…Vacuum-processes. Research trends (Table 1) for vacuum-processed oxide TFTs are as follows: (1) variation in oxide semiconductor materials and use of high-k dielectrics to achieve high µ [6][7][8][9][10][11][12][13]; (2) low-cost and non-toxic implementation using indium-free compositions [14][15][16]; (3) high-reliability components based on flexible substrates [17]; and (4) vacuum-deposition technology that uses non-sputtering methods (e.g. atomiclayer deposition (ALD) or metalorganic chemical-vapor deposition (MOCVD)) [14,16,18].…”