Fysica van niet-lineaire selectorelementen voor hoge-dichtheid cross-point geheugenarrays: Toegangstoestellen en selector-enkel geheugen

Cross-point array architecture is an attractive solution for high-density low-cost memory. A critical component in this design is a two-terminal non-linear selector device, necessary to suppress the undesired leakage through half-selected cells. This work investigates various selector options, with a particular focus on amorphous chalcogenide-based ovonic threshold switches (OTS). Moreover, it goes beyond its original selector application and explores the use of OTS as a self-selective memory device. This is enabled by the polarity effect, manifested as a modulation of threshold voltage, depending on the programming pulse polarity. An in-depth investigation of the physics of the polarity effect is provided, proposing two possible mechanisms: (i) field-driven atomic segregation and (ii) anisotropic defect switching linked to local structural rearrangement. Furthermore, the application potential of this phenomenon is explored, demonstrating successful selector-only memory (SOM) with excellent characteristics. A comprehensive assessment of SOM operation is presented, establishing fundamental performance-reliability trade-offs and identifying further optimization pathways. Additionally, this work also investigates alternative selector concepts, targeting magnetic memory applications. This includes bipolar metal-semiconductor-metal (MSM) selectors with various amorphous semiconductor layers (a-Si, a-Ge and a-InGaZnO), as well as unipolar InGaZnO-based Schottky diodes. Finally, a novel cross-point architecture utilizing a distributed Schottky diode selector is proposed, capable of overcoming the issue of read margin degradation.