Promising Engineering Approaches for Improving the Reliability of HfZrO_x2-D and 3-D Ferroelectric Random Access Memories

The main challenge in ferroelectric (FE) random access memory (FRAM) scaling is to maintain a high polarization density on the vertical sidewall of 3-D FE capacitors. Two simple and effective methods - stress engineering and optimized interface orientation - are proposed to facilitate the preferential transition from the tetragonal to the orthorhombic phase for ferroelectricity. Four FE phase-progressive experiments were conducted for 2-D/3-D FRAMs with external stress sources and an interfacial layer (IL). Both 2-D and 3-D FRAMs show the wake-up free feature with the presence of both the external stressor and the optimized IL. To extract the sidewall polarization of 3-D FRAM, a set of testkeys was designed and studied. The 3-D FRAM shows an initial sidewall with good reliability and durability with ${P} _{r} = {18}\,\,\mu \text{C}$ /cm2 and endurance of up to 109 cycles. Furthermore, the retention test with the read mode of ${P} _{\text {0,switch}}$ and ${P} _{\text {1,switch}}$ at 85 °C was investigated, and the imprint effect was proved to be the main cause of retention loss.