Thin films could enable future ReRAM

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A way to control oxygen concentration in tantalum oxide films has been found by researchers from Moscow Institute of Physics and Technology (MIPT). Produced by atomic layer deposition, these thin films could be the basis for creating new forms of non-volatile memory.

A promising technology for creating such a device is resistive switching memory, or ReRAM. It works by changing the resistance across a memory cell through applied voltage.

A ReRAM cell can be realised as a metal-dielectric-metal structure. Oxides of transition metals such as hafnium and tantalum have proved useful as the dielectric component of this layered structure. Applying voltage to a memory cell that is based on these materials causes oxygen migration, changing its resistance.

However, oxygen-deficient film deposition techniques normally used in ReRAM design are not applicable to functional 3D architectures.

To find a solution, MIPT researchers turned to atomic layer deposition (ALD). ALD enables conformal coating of 3D structures.

"The hardest part in depositing oxygen-deficient films was finding the right reactants that would make it possible to both eliminate the ligands contained in the metallic precursor and control oxygen content in the resulting coating," said lead researcher Andrey Markeev.

"We achieved this by using a tantalum precursor, which by itself contains oxygen, and a reactant in the form of plasma-activated hydrogen."

However, as soon as the experimental sample was removed from the vacuum chamber and exposed to the atmosphere, the top layer of the dielectric was modified, making it impossible to detect oxygen deficiency.

“Our team worked with a unique experimental cluster, which allowed us to grow films and study them without breaking the vacuum,” concluded PhD student Konstantin Egorov.