Memory device

With the accelerated scaling down of integrated circuits, it becomes very challenging to fabricate metal-insulator-metal (MIM) capacitors having a high capacitance density and a low leakage current for memory units

• DRAM

Cross-sectional TEM images of (a) ZrO₂/TiN and (b) ZrO₂/Ru structures and XPS depth profiles of chemical composition ratio 

with etching time for (c) ZrO₂/TiN and (d) ZrO₂/Ru structures.

We investigate effects of bottom electrodes on high-k dielectric thin films formed through atomic layer deposition (ALD) for DRAM. We focus on the correlation between interfacial layer formation and electrical properties. And dopants can change the crystallinity and can combine with oxygen vacancy in gap states of dielectric, resulting in lowering leakage currents.

• ReRAM and FeRAM

Left: 3D memristor schematic diagram, Right: 3D resistive memory.

Along with DRAM, neuromorphic memristors are being studied. For example, ReRAM and FeRAM have similar structures as metal-insulator-metal capacitors. The materials for active layer are almost same with high-k materials. Regarding ReRAM devices, I will study tuning oxygen vacancies, or combining with other materials system such as 2D materials to enhance device performance. Regarding FeRAM devices, as you can see this graph, doping leads to increase permanent polarizability of HfO₂. I will study various ternary material system to enhance device performance. Also, for both cases, 3D vertical integration study will be conducted with ASD technique.

• NAND FLASH
  

As the high capacity of NAND is required, 3D structure NAND Flash with increased density is being studied.

Accordingly, as a high quality thin film according to a 3D structure is required, a new patterning method through AS-ALD is being studed. Various processes are being developed for these logic devices.