Engineering MSMFM Structure Composed of Compound Bi-Directional Selector and Ferroelectric Capacitor for High Density Capacitor Arrays

Ferroelectric hafnium oxide (HfO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>) thin films have the potential to enable high density, non-volatile memory that can further the advancement of compute in memory (CiM) architectures [1]. The metal-ferroelectric-metal (MFM) capacitor is such a device that is highly scalable and easily integrated into crossbar arrays, where the bit line (BL) runs perpendicular to the word line (WL) in a different vertical plane. However, ferroelectric MFMs are vulnerable to polarization disturb during read and write cycles in crossbar arrays, as other capacitors that share the common WL or BL experience a potential difference that can alter the current polarization state of the ferroelectric material (Fig. 1a and Fig. 1b) [2]. To counteract this polarization disturb effect, a highly non-linear, bi-directional metal-semiconductor-metal (MSM) device, originally explored in resistive random-access memories (ReRAM) [3], is fabricated in series with an MFM (Fig. 2c). The resulting “MSMFM” stack is subsequently explored as a possible alternative in crossbar arrays (Fig. 3b) by analyzing the performance of discrete MSMFM devices. In this work, we explore the effectiveness of the MSMFM stack at mitigating polarization disturb when the MFM portion of the device is exclusively subjected to Rapid Thermal Annealing (RTA) and when the entire compound device is annealed, and further demonstrate the importance of annealing the selector to optimize the MSMFM stack for high density configurations.