No abstract

Metal oxide resistive switching memories have been a crucial component for the requirements of the Internet of Things, which demands ultra‐low power and high‐density devices with new computing principles, exploiting low cost green products and technologies. Most of the reported resistive switching devices use conventional methods (physical and chemical vapor deposition), which are quite expensive due to their up‐scale production. Solution‐processing methods have been improved, being now a reliable technology that offers many advantages for resistive random‐access memory (RRAM) such as high versatility, large area uniformity, transparency, low‐cost and a simple fabrication of two‐terminal structures. Solution‐based metal oxide RRAM devices are emergent and promising non‐volatile memories for future electronics. In this review, a brief history of non‐volatile memories is highlighted as well as the present status of solution‐based metal oxide resistive random‐access memory (S‐RRAM). Then, a focus on describing the solution synthesis parameters of S‐RRAMs which induce a massive influence in the overall performance of these devices is discussed. Next, a precise analysis is performed on the metal oxide thin film and electrode interface and the recent advances on S‐RRAM that will allow their large‐area manufacturing. Finally, the figures of merit and the main challenges in S‐RRAMs are discussed and future trends are proposed.

Solution processing of amorphous metal oxides has lately been used as an option to implement in flexible electronics, allowing a reduction of the associated costs and high performance. However, the research has focused more on the semiconductor layer rather than on the insulator layer, which is related to the stability and performance of the devices. This work aims to evaluate amorphous aluminum oxide thin films produced by combustion synthesis and the influence of far-ultraviolet (FUV) irradiation on the properties of the insulator on thin-film transistors (TFTs) using different semiconductors, in order to have compatibility with flexible substrates. An optimized dielectric layer was obtained for an annealing of 30 min assisted by FUV exposure. These thin films were applied in gallium-indium-zinc oxide TFTs as dielectrics showing the best results for TFTs annealed at 180 °C with FUV irradiation: good reproducibility with a subthreshold slope of 0.11 ± 0.01 V dec and a turn-on voltage of -0.12 ± 0.05 V, low operating voltage, and good stability over time. Finally, the dielectric layer was applied in solution-processed indium oxide (InO) TFTs at low temperature, 180 °C, with a short processing time being compatible with flexible electronic applications.

In the past decade, solution-based dielectric oxides have been widely studied in electronic applications enabling the use of low-cost processing technologies and device improvement. The most promising are the high-κ dielectrics, like aluminum (AlO) and hafnium oxide (HfO), that allow an easier trap filling in the semiconductor and the use of low operation voltage. However, in the case of HfO, a high temperature usually is needed to induce a uniform and condensed film, which limits its applications in flexible electronics. This paper describes how to obtain HfO dielectric thin films and the effect of their implementation in multilayer dielectrics (MLD) at low temperatures (150 °C) to apply in thin film transistors (TFTs) using the combination of solution combustion synthesis (SCS) and ultraviolet (UV) treatment. The single layers and multilayers did not show any trace of residual organics and exhibited a small surface roughness (<1.2 nm) and a high breakdown voltage (>2.7 MV·cm). The resulting TFTs presented a high performance at a low operation voltage (<3 V), with high saturation mobility (43.9 ± 1.1 cm·V·s), a small subthreshold slope (0.066 ± 0.010 V·dec), current ratio of 1 × 10 and a good idle shelf life stability after 2 months. To our knowledge, the results achieved surpass the actual state-of-the-art. Finally, we demonstrated a low-voltage diode-connected inverter using MLD/IGZO TFTs working with a maximum gain of 1 at 2 V.

Solution combustion synthesis (SCS) has been widely used to produce simple and complex oxides with a desired morphology (size and shape). SCS is valuable due to low cost, simplicity and energy efficient synthesis. To guarantee the best molecular‐level mixing of reactants in an aqueous or solvent‐based solution some parameters need to be controlled, such as fuel type, metal cations precursors, stoichiometry ratio (φ), pH effect, atmosphere and initiation type. These determine the final properties of the oxide materials, providing the potential to reach different morphologies, which are essential for their final applications. This Review article focuses on the crucial parameters in SCS and how these affect the overall materials properties from nanostructures to thin films. To finalize, special attention is given to the application of SCS to form metal oxide thin films at low temperature and their application in thin film transistors (TFTs).