Ferroelectricity of low thermal-budget HfAlO: X for devices with metal-ferroelectric-insulator-semiconductor structure

Abstract

The effect of annealing temperature on the ferroelectricity of HfAlOx with Al concentration of 4.5% is physically and electrically investigated by metal-ferroelectric-insulator-semiconductor (MFIS) platform. HfAlOx with 600 °C annealing is confirmed to possess ferroelectricity by the formation of non-centrosymmetry orthorhombic III phase, clockwise capacitance-voltage hysteresis, significant polarization-electric field hysteresis curve, and in-depth analysis of current component as compared with non-ferroelectric HfO2. Compared to commonly discussed MFM devices from which thermal annealing of 800 °C is required to induce ferroelectricity, the relatively lower thermal budget to form ferroelectric HfAlOx in MFIS devices can be attributed to the compressive thermal stress caused by the difference in thermal expansion between the Si substrate and HfAlOx during thermal annealing, and it is the stress that helps lower the annealing temperature to crystallize HfAlOx in the orthorhombic phase. In addition, MFIS devices with 600 °C-annealed HfAlOx hold the prospect of becoming a promising candidate for memory applications by demonstrating a memory window of 0.6 V with 3 V operation voltage which is comparable with or superior to those with conventional ferroelectric films. Furthermore, the process to from ferroelectric HfAlOx-based devices can be fully integrated into incumbent mass production fabs, empowering next-generation memory technology.