Solution Combustion Synthesis: Low‐Temperature Processing for p‐Type Cu:NiO Thin Films for Transparent Electronics

Abstract

Low-temperature solution processing opens a new window for the fabrication of oxide semiconductors due to its simple, low cost, and large-area uniformity. Herein, by using solution combustion synthesis (SCS), p-type Cu-doped NiO (Cu:NiO) thin films are fabricated at a temperature lower than 150 °C. The light doping of Cu substitutes the Ni site and disperses the valence band of the NiO matrix, leading to an enhanced p-type conductivity. Their integration into thin-film transistors (TFTs) demonstrates typical p-type semiconducting behavior. The optimized Cu NiO TFT exhibits outstanding electrical performance with a hole mobility of 1.5 cm V s , a large on/off current ratio of ≈10 , and clear switching characteristics under dynamic measurements. The employment of a high-k ZrO gate dielectric enables a low operating voltage (≤2 V) of the TFTs, which is critical for portable and battery-driven devices. The construction of a light-emitting-diode driving circuit demonstrates the high current control capability of the resultant TFTs. The achievement of the low-temperature-processed Cu:NiO thin films via SCS not only provides a feasible approach for low-cost flexible p-type oxide electronics but also represents a significant step toward the development of complementary metal-oxide semiconductor circuits.

A Review of Low‐Temperature Solution‐Processed Metal Oxide Thin‐Film Transistors for Flexible Electronics

“…Research in this area has focused mainly on improving the field effect mobility of p‐type oxide semiconductor‐based TFTs. Especially, most of p‐type solution‐processed oxide TFTs show field‐effect mobility, <1 cm 2 V −1 s −1 ( Figure ), which is still very low compared with n‐type solution‐processed oxide TFTs . In general, oxide semiconductors have a high formation energy regarding metal defects that contribute to hole concentration.…”

“…(Data compiled from refs. ) The p‐type solution‐processed oxide TFT papers published from 2010 to 2019.…”

“…Therefore, NiO has been studied relatively slowly as p‐type solution‐processed oxide semiconductors compared with Cu 2 O and SnO. Recently, several studies have been conducted to solve this problem of low conductivity of NiO by doping with Sn or Cu atoms …”

“…NiO has been used as a p‐type oxide material by varying microstructure or electrical performance through various post treatment or metal doping (e.g., Li, Cu, Zn, Al, and others) . In general, it is known that doped metals in NiO substitute Ni sites and disperse the valence band of the NiO matrix to improve p‐type conductivity . Jang and co‐workers fabricated p‐type solution‐processed NiO x TFTs with high performance at low‐temperatures of 280 °C through Sn doping.…”

“…Combustion process is a simple and time‐saving method for forming oxide films at low‐temperature among various methods for the above‐mentioned low‐temperature process. Shan and co‐workers formed a Cu‐doped NiO thin‐film through a spin‐coating process and achieved a low‐temperature process by generating combustion reaction with involving acetylacetone and urea as fuel materials in NiO solution . TG‐differential scanning calorimetry (DSC) analysis showed that the low thermal decomposition temperature of acetylacetone‐assisted precursors.…”