Solution-Processed HfO_x for Half-Volt Operation of InGaZnO Thin-Film Transistors

Abstract

Solution-processed high-κ gate dielectrics, such as Al 2 O 3 and HfO 2 , show great potential for use in low-cost electronics. However, high-temperature treatments are generally needed to cure the film, limiting the use in flexible electronics. Here we use anodization, a simple, low-cost, solution-based method, to form thin, conformal, high quality HfO x layers at room temperature. Several anodization voltages were studied, and the relative quantity of Hf−O bonding was found to increase by 10% when increasing anodization voltage from 2 to 3 V, while maintaining almost the same when further increasing the anodization voltage. Conduction mechanisms were analyzed, showing that Schottky emission dominates even for the thinnest oxides. HfO x layers formed by anodization voltages of 2, 3, and 4 V show high capacitance density of 1290, 1160, and 1060 nF/cm 2 , which are equivalent to 2.68, 2.97, and 3.26 nm of thermally grown SiO 2 . Using such high capacitance density insulators, we fabricated InGaZnO (IGZO) thin-film transistors (TFTs) at room temperature, showing a low operating voltage of 0.5 V, one of the lowest for oxide−semiconductor-based TFTs. TFTs gated with HfO x anodized at the optimal voltage, 3 V, show a high current on/off ratio of >10 5 , a mobility approaching 10 cm 2 /(V s), and a subthreshold swing as low as 69 mV/dec, close to the theoretical limit at 300 K. The interface trap density was found to be highly related to the quality of the HfO x film, showing a 50% decrease with the increase of anodization voltage from 2 to 3 V. The devices show negligible change after storage in air for 6 months and favorable stability under both positive and negative gate bias stress. Finally, we demonstrate TFTs on plastic substrates, maintaining high quality performance even under a bending radius of 9 mm. As a result, such devices have potential applications in low-cost, low-voltageoperation, low-power electronics.

Ultralow-Voltage Field-Effect Transistors Using Nanometer-Thick Transparent Amorphous Indium–Gallium–Zinc Oxide Films

“…Eventually, a clear correlation is found between mobility and D it compared with the reported literature data based on sputter-coated a-IGZO thin films for which D it is at least 1 order of magnitude less than the values obtained in this work. 20 Therefore, our perception here is that the higher D it along with the very long channel width (18 mm) in this work actually results in quite low mobility values, which can be enhanced further by optimizing the interface between a solution-processed nanometer-thick dielectric and a-IGZO thin film and reducing the channel width. Drain current degradation under positive gate bias stress (PBS) has also been studied to demonstrate the performance stability.…”

“…However, the anodization process is a very efficient and cost-effective technique to form insulating metal oxides with precise control over the film thickness down to the nanometer level. 20 Anodization is an electrochemical process that needs a pair of electrodes, an anode and a cathode, dipped inside a suitable electrolyte solution. Typically, the metal that needs to be anodized is used as the anode and a constant bias is applied to it for anodization.…”

Digital Electrochemistry for On‐Chip Heterogeneous Material Integration

“…[ 13 ] The low SS of (140.9 ± 8.6) mV dec −1 is due to the high dielectric constant of the dielectric layer and the good quality of the dielectric–semiconductor interface. [ 27 ] Ultralow voltage conditions are highly desirable in some applications, such as wearable or electrochemical devices to avoid parasitic electrochemical reactions, and promote safe and low power operation. [ 28 ] Due to the ultrathin dielectric layer, our a‐IGZO TFT active‐matrix could work at a low voltage of 1.8 V. The electrical performance of the a‐IGZO TFTs and active‐matrix up to 1.8 V gate bias is shown in Figures S6–S8 in the Supporting Information.…”

Graphene-Oxide-Based Fluoro- and Chromo-Genic Materials and Their Applications

“…These properties make graphene have a very wide range of applications in flexible electronics, protective coatings, solar cells, etc. [ 15 , 16 , 17 , 18 , 19 , 20 , 21 ]. However, graphene is a hydrophobic material and it has no noticeable solubility in molecular solvents, which greatly limits its application.…”