The electrical characteristics and reliability of Hf-In-Zn-O (HIZO) metal-oxide-semiconductor capacitors (MOSCAPs) with a microporous SiO2-based electric-double-layer (EDL) dielectric were investigated. Experimental results indicated that the HfO2 interlayer could effectively improve the interface quality, thus leading to reduced interface states, suppressed hysteresis and decreased gate leakage current. Improved performance was achieved for the HIZO MOSCAPs with HfO2/EDL stack gate dielectrics (HECAPs), such as a large capacitance density of 0.7 mu F/cm(2), an interface state density of 5.7 x 10(11) eV(-1)/cm(2), a fixed charge density of 1.9 x 10(12) cm(-2), a hysteresis voltage of 230 mV and a gate leakage current density of 3 x 10(-6) A/cm(2) at +1 V. Moreover, enhanced reliability of the HECAPs was obtained with an elevated dielectric breakdown voltage of 4.8 V and a small increase (<15 %) of gate leakage after gate bias stressing at 2 V for 3600 s. (C) 2013 Elsevier B.V. All rights reserved.