Low-Temperature, Solution-Processed ZrO₂:B Thin Film: A Bifunctional Inorganic/Organic Interfacial Glue for Flexible Thin-Film Transistors

Abstract

A solution-processed boron-doped peroxo-zirconium oxide (ZrO2:B) thin film has been found to have multifunctional characteristics, providing both hydrophobic surface modification and a chemical glue layer. Specifically, a ZrO2:B thin film deposited on a hydrophobic layer becomes superhydrophilic following ultraviolet-ozone (UVO) treatment, whereas the same treatment has no effect on the hydrophobicity of the hydrophobic layer alone. Investigation of the ZrO2:B/hydrophobic interface layer using angle-resolved X-ray photoelectron spectroscopy (AR XPS) confirmed it to be chemically bonded like glue. Using the multifunctional nature of the ZrO2:B thin film, flexible amorphous indium oxide (In2O3) thin-film transistors (TFTs) were subsequently fabricated on a polyimide substrate along with a ZrO2:B/poly-4-vinylphenol (PVP) dielectric. An aqueous In2O3 solution was successfully coated onto the ZrO2:B/PVP dielectric, and the surface and chemical properties of the PVP and ZrO2:B thin films were analyzed by contact angle measurement, atomic force microscopy (AFM), Fourier transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The surface-engineered PVP dielectric was found to have a lower leakage current density (Jleak) of 4.38 × 10(-8) A/cm(2) at 1 MV/cm, with no breakdown behavior observed up to a bending radius of 5 mm. In contrast, the electrical characteristics of the flexible amorphous In2O3 TFT such as on/off current ratio (Ion/off) and electron mobility remained similar up to 10 mm of bending without degradation, with the device being nonactivated at a bending radius of 5 mm. These results suggest that ZrO2:B thin films could be used for low-temperature, solution-processed surface-modified flexible devices.

Metal oxide semiconductor thin-film transistors for flexible electronics

“…A few examples include c-PVP layers applied to planarize and smoothen the surface of PES or PI, 191,226 as well as PVP films utilized to reduce the surface roughness of PI foils from 3.6 nm down to 0.3 nm (root mean square). 232 145,197 Nevertheless, for solution-deposited metal oxide semiconductors, it is preferable to solution process also the gate dielectric, in order to further benefit from the lowcost large-area approach offered by solution-deposition processes. Within solution-processed gate dielectrics, polymeric materials are especially suitable due to the moderate annealing temperatures needed, as well as the high bendability that can be achieved.…”

“…76,190,191,[194][195][196][197]200,224,228,233 Nevertheless, some groups have presented single bending tests (tensile and compressive) at radii between 25 and 1 mm, as well as cyclic bending up to 10 000 cycles. 83,145,192,193,199,201,[220][221][222]225,226,229,231,232 In the case of flexible TFTs with nano-scale shapes, it has been demonstrated that the application of mechanical bending causes a deformation of the particle network. In particular, tensile strain slightly increases the distance between individual particles, resulting in a lower l FE .…”

“…Device failure is often caused by strain-induced breakdown in the gate dielectric layers, e.g., in SiO 2 in combination with amorphous In 2 O 3 :Ga 199 or thin ZnO (8 nm) 222 metal oxide semiconductor. While solution-processed Al 2 O 3 layers can withstand up to 320 bending cycles without failure, 83,192 polymeric (PVP), 229 polymer-oxide hybrids (PVP with 15 nm ZrO 2 ), 232 or electrolyte 193 gate dielectrics are fully functional up to 10 000 repetitions. The contacts can also originate device failure, especially in the case of brittle ITO electrodes.…”

“…For example, Song et al attributed the failure of ZnO TFTs (50 lm PI/50 nm ITO/270 nm SiO 2 /8 nm ZnO/50 nm Al) during real time bending tests (e.g., manual crumpling of the devices) to the formation of fractures in either the electrodes or the gate dielectric. 222 Device degradation in the active layer is mostly attributed to the use of crystalline metal oxide semiconductors, 192,232 or to a high number of bending cycles paired with a small bending radius. 193 The difference between amorphous and crystalline metal oxide semiconductors is illustrated in a study by Yu et al, where crystalline In 2 O 3 and amorphous In 2 O 3 -PVP were compared (see Fig.…”

Letter : Solution-processed flexible zinc-tin oxide thin-film transistors on ultra-thin polyimide substrates

“…On the other hand, most of the oxide semiconductors include indium . But the low natural abundance of indium has made it into an increasingly expensive commodity, which has led to a large research driven to replace indium in oxide semiconductors.…”