Combination of reversible resistive and ferroelectric switching demonstrated in HfO₂

Already popular as a high-k dielectric material (i.e., semiconductor) in devices such as MOSFETs, hafnium oxide was also proposed by some for new memory technologies because it displays ferroelectric and resistive switching behavior. This could make it suitable for both ferroelectric random access memory (FeRAM) and resistive random access memory (RRAM) devices. New work published in the Journal of Applied Physics describes for the first time a combination of reversible resistive and ferroelectric switching within a single capacitor cell.

Researchers studied both amorphous and polycrystalline TiN/Sr:HfO₂/Pt metal-oxide-metal samples, deposited on a standard Si wafer to create an asymmetric single metal insulator metal (MIM) capacitor stack. They first compared resistive switching differences in both amorphous and crystalline stacks, typically used for resistive-only and ferroelectric-only switching, respectively.

In the crystalline case, they found that an increased filament-forming voltage, when migrating oxygen vacancies form a conductive filament, corresponded to a decreasing reset voltage.

The experimenters then achieved resistive and ferroelectric switching within a single cell, inducing an initial ferroelectric state followed by a resistive state with low resistance and soft breakdown. A second reset restored the high resistance state with a ruptured filament in the capacitor, resetting the whole oxide layer. This then enabled further ferroelectric switching operation. Deep reset behavior was critical to achieving the resistive/ferroelectric combination. Both the ferroelectric and the resistive switching states depend chiefly on the distribution and concentration of oxygen vacancies in the oxide layer.

With the basic principle of combined ferroelectric and resistive switching demonstrated, future experiments to provide more insight into these HfO₂-based devices may lead to their practical use in memory storage.

Source: “Interplay between ferroelectric and resistive switching in doped crystalline HfO₂,” by Benjamin Max, Milan Pešić, Stefan Slesazeck, and Thomas Mikolajick, Journal of Applied Physics (2018). The article can be accessed at https://doi.org/10.1063/1.5015985 .