All solution-processed hafnium rich hybrid dielectrics for hysteresis free metal-oxide thin-film transistors

Abstract

Organic–inorganic (O–I) hybrid materials combine the great variability and interactions at the molecular scale that have been demonstrated to have an impact on their properties, especially as gate dielectric thin films in thin-film transistors (TFTs). Solution and low-temperature processing, cost-effective and large-scale deposition, and flexibility are critical for stimulating future flexible electronic device applications. In this study, we present several HfAlO_x–PVP hybrid thin films, possessing the advantages of O–I hybrid materials, by incorporating hafnium derivatives into pristine AlO_x–PVP hybrid solution. A facile dip-coating approach was used to deposit the hybrid thin films at a low processing temperature of 200 °C. We further studied the effect of Hf derivatives in hybrid thin films and their dielectric properties by varying the Hf/Al molar ratios. This study showed that the addition of Hf into hybrid thin films increased their dielectric characteristics more than those of AlO_x–PVP hybrid thin films. The dielectric properties measured on MIM capacitor structures showed a low leakage current density of the order of 10⁻⁸ A cm⁻². The frequency-dependent capacitance shows a high capacitance density of up to 70 nF cm⁻² with low dielectric dispersion. These hybrid thin films are further used as dielectric gate layers in solution-processed In₂O₃ TFTs to validate their electrical performance. The analysis of transfer curves of TFTs, revealing that the devices containing Hf-rich hybrid dielectric films, showed significant electrical performance with very low hysteresis, including a saturation mobility of 0.25 cm² V⁻¹ s⁻¹, a threshold voltage of 1.3 V, a subthreshold swing of 0.37 V dec⁻¹ and a high I_on/I_off current ratio of 10⁶. Furthermore, we presented the feasibility of employing these hybrid dielectric layers in the fabrication of a-IGZO TFTs by RF magnetron sputtering rather than In₂O₃ TFTs to examine the electrical characteristics such as electrical charge transport with other electrical parameters and demonstrated TFTs with a mobility of 3.39 cm² V⁻¹ s⁻¹, a threshold voltage of 2.2 V, a subthreshold swing of 0.89 V dec⁻¹ and a high I_on/I_off ratio of 10⁶. In conclusion, the solution derived HfAlO_x–PVP hybrid dielectric thin films manifest potential for dielectric materials for future low-cost and low-temperature solution-based metal oxide TFT applications.