Enabling Ferroelectric Memories in BEoL-towards advanced neuromorphic computing architectures
Advanced non-volatile memory concepts such as the 1T1C ferroelectric (FE) random-access memory (FeRAM) and the 1T1C FE field-effect transistor (FeFET) can be realized by connecting a metal-ferroelectric-metal (MFM) capacitor placed in the back end of line (BEoL) of a microchip to the drain and gate contacts of a standard logic device, respectively. With the vertical distributed select devices in the front-end of line (FEoL) and the storage elements in the BEoL, both concepts increase the effective memory density of a microchip without introducing major changes in the FEoL fabrication technology. However, for advanced neuromorphic computing architectures, the 1T1C FeFET is the device of choice, since it provides non-destructive readout. The most promising material for the integration of FE non-volatile memory functionalities into the BEoL is Zr doped HfO2 (HZO). It crystallizes at low temperatures in the orthorhombic phase (the one with FE properties) and with a polycrys talline structure. The latter is important to enable analogue like switching in synaptic devices. Herein, the above-mentioned memory concepts are introduced and key steps to optimize the HZO films for the BEoL integration and for the neuromorphic computing use case are described.