Thesis Examination Committee

Prof Kevin CHEN, ECE/HKUST (Chairperson)
Prof Zhiyong FAN, ECE/HKUST (Thesis Supervisor)
Prof Levent YOBAS, ECE/HKUST

Abstract

With strikingly high speed, data retention ability and memory density, Resistive RAMs have emerged as a forerunning non-volatile memory. In this work, we report an ultra-fast switching electron-transport-assisted ECM (E2CM) cell using three-dimensional arrays of quantum wires (QWs) made of methyl ammonium lead iodide (MAPbI3) perovskite as solid electrolyte and silver (Ag) as AE. The QWs have diameter ~ 10 nm approaching exciton Bohr radius thus demonstrating optical band-gap widening due to quantum confinement. The mechanistic study confirmed that the electrical switching behavior in MAPbI3 QWs and nanowires (NWs) originates from electrochemical reduction of Ag cation at aluminum (Al) CE and in body of QWs assisted by electron transport, leading to fast formation of Ag filament in material resulting in drastic conductivity increase. Intriguingly, it was also discovered that when downscaling the wire diameter from NW to QW, the device ON/OFF ratio was increased by 1,000 times rendering QWs much more energy efficient than NW and thin film devices. Careful switching speed measurement shows that the QW device has ~ 1.5 ns ultra-fast switching speed, which is 20,000 times faster than the commercially available Phase–Change Memory (PCM) based R-RAM system and also much faster than many conventional oxide, sulphide and selenide based ECM devices. The devices made with the electrically isolated QWs with density up to 2×1011 /cm2 demonstrated unprecedented scalability down to 14 nm memory cell lateral dimension and 76.5 nm2 effective device area for single bit storage, which is even smaller than the effective single bit storage area of the state-of-the-art tri-layered-cell (TLC) based 3D NAND and PCMs. Moreover, the QW based device exhibited multi-bit storage and hence the unparalleled ultra-high storage density of 13.07 Giga-bit (Gb) /mm2 is potentially achievable. The memory device also demonstrated optical response to light illumination, thus enabling optical programmability among different levels of LRSs.