High-performance sol–gel processed a-IGZO TFTs with low-melting point metal electrodes

Abstract

Sol–gel-based amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs) have gained widespread attention due to their simple process and low cost. Herein, a-IGZO thin films with In : Ga : Zn = 4 : 1 : 4 were fabricated at 400 °C using a sol–gel process, and high-performance a-IGZO TFTs were successfully demonstrated through contact engineering following the guidance of the Schottky–Mott rule, i.e., low work function metals In and Ga with low melting points were employed as contact electrodes. The Ga-contacted and In-contacted devices exhibit superior performance. Specifically, at V_ds = 1 V, the performance of Ga-contacted devices and In-contacted devices exhibited an increased from μ_FE = 5.67 cm² V⁻¹ s⁻¹, V_th = 2.19 V, SS = 0.91 V dec⁻¹, and I_ON/I_OFF = 7.9 × 10⁵ in Cr-contacted devices to μ_FE = 11.40 cm² V⁻¹ s⁻¹, V_th = 1.17 V, SS = 0.56 V dec⁻¹, and I_ON/I_OFF = 2.5 × 10⁶ as well as μ_FE = 12.67 cm² V⁻¹ s⁻¹, V_th = 0.17 V, SS = 0.47 V dec⁻¹, and I_ON/I_OFF = 5.4 × 10⁶. Meanwhile, the contact resistance of Ga-contacted a-IGZO TFTs (1088 kΩ μm) and In-contacted a-IGZO TFTs (403 kΩ μm) are much lower than that of Cr-contacted devices (1890 kΩ μm). The improvement of device performance can be attributed to lower metal work function and superior contact interface quality, which can inhibit the Fermi level pinning effect and maximize the performance of N-channel a-IGZO TFTs. Furthermore, both the positive and negative bias stability of the devices with the different contact were systematically studied. At 3600 s for NBS (V_gs = −20 V) and PBS (V_gs = +20 V), the Ga-contacted and In-contacted devices are shifted by −3.5 V and 11.5 V and −3.1 V and 9.1 V, respectively, which are better than the −10.6 V and 17 V of the Cr-contacted ones. These results further confirm that In and Ga can form high-quality interfaces with a-IGZO. Our results demonstrate a simple and effective strategy to fabricate high-performance sol–gel-based a-IGZO TFTs and provide a solid foundation for its practical application.