Amorphous In–Ga–Zn Oxide Semiconducting Thin Films with High Mobility from Electrochemically Generated Aqueous Nanocluster Inks

Abstract

Solution processing is a scalable means of depositing large-area electronics for applications in displays, sensors, smart windows, and photovoltaics. However, solution routes typically yield films with electronic quality inferior to traditional vacuum deposition, as the solution precursors contain excess organic ligands, counterions, and/or solvent that leads to porosity in the final film. We show that electrolysis of aq. mixed metal nitrate salt solutions drives the formation of indium gallium zinc oxide (IGZO) precursor solutions, without purification, that consist of ∼1 nm radii metal−hydroxo clusters, minimal nitrate counterions, and no organic ligands. Films deposited from cluster precursors over a wide range of composition are smooth (roughness of 0.24 nm), homogeneous, dense (80% of crystalline phase), and crack-free. The transistor performance of IGZO films deposited from electrochemically synthesized clusters is compared to those from the starting nitrate salt solution, sol−gel precursors, and, as a control, vacuum-sputter-deposited films. The average channel mobility (μ AVE ) of air-annealed cluster films (In:Ga:Zn = 69:12:19) at 400°C was ∼9 cm 2 V −1 s −1 , whereas those of control nitrate salt and sol−gel precursor films were ∼5 and ∼2 cm 2 V −1 s −1 , respectively. By incorporating an ultrathin indium−tin−zinc oxide interface layer prior to IGZO film deposition and airannealing at 550°C, a μ AVE of ∼30 cm 2 V −1 s −1 was achieved, exceeding that of sputtered IGZO control films. These data show that electrochemically derived cluster precursors yield films that are structurally and electrically superior to those deposited from metal nitrate salt and related organic sol−gel precursor solutions and approach the quality of sputtered films.

High Quality Magnetic Oxide Thin Films Prepared via Aqueous Solution Processing

“…This method, recently coined "Prompt Inorganic Condensation", or PIC, has been used to make high quality films of a number of oxides, including dielectrics, [53][54][55][56][57][58] transparent conducting oxides, 59,60 and high-resolution inorganic resists. 61,62 In these examples using PIC, dehydration and nitrate removal are shown to occur without negatively affecting film morphology, allowing the preparation of dense, smooth films at relatively low temperatures.…”

Aqueous Solution Processing of Combustible Precursor Compounds into Amorphous Indium Gallium Zinc Oxide (IGZO) Semiconductors for Thin Film Transistor Applications

“…Interestingly,g allium oxide exhibits aw eakc rystalline phase with broad reflexes which corresponds to the "d-Ga 2 O 3 "p hase. [26] The homogeneity of the coated films from the urea nitrate precursors on aS i/SiO 2 substrate as well as their microstructure was investigated via high-resolution transmission electron mi- (Figure 7a,b) revealed that films annealed at both temperatures are amorphous in nature with the absence of anyp artial film crystallinity amorphous matrix. It is known that gallium oxide displays ab road phase distribution depending on the type of precursor used and the thermalc alcination history under which this material is obtained.T his allows to form different crystalline phases or even mixtures therefrom.…”

Design, Properties, and TFT Application of Solution‐Processed In‐Ga‐Cd‐O Thin Films

“…In recent two decades, solution‐processed semiconductors and their devices have attracted increasing attentions, because the solution method allows deposition of thin films in air via a roll‐to‐roll process and/or by the directly patterning printing without incorporating photolithography for mass production, and possesses some other beneficial features such as the precise control of the cation‐anion stoichiometry together with metal cation ratios . To date, a variety of solution‐processable metal oxide semiconductors such as indium zinc oxide (In‐Zn‐O), zinc tin oxide (Zn‐Sn‐O), indium gallium zinc oxide (In‐Ga‐Zn‐O), and zinc indium tin oxide (Zn‐In‐Sn‐O), have been extensively explored as potential channel materials for thin‐film transistor (TFT) application providing reasonable electrical characteristics. Among all of these oxide semiconductors, amorphous/nanocrystalline In‐Ga‐Zn‐O is investigated most frequently, because it demonstrates outstanding electrical performance and meter‐scale uniformity in vacuum‐based processing, and has been commercially used as the channel material of TFTs for backbone electronics of active matrix liquid crystal displays (AMLCDs) and active‐matrix organic light‐emitting diode displays (AMOLEDs) .…”

“…This indicates that a small change is reflected in the thermal‐driven condensation processes substituting Zn with Cd. In this work, the final annealing temperature for InGaCd x O samples is fixed at a frequently used 400 °C in the solution‐processed In‐Ga‐Zn‐O films …”