At
this week’s 2011 IEEE International Electron Devices Meeting (IEDM),
imec presented the world’s smallest, fully-functional HfO2-based
Resistive RAM (RRAM) cell, with an area of less than 10×10 nm². The new
cell shows potential to meet the major requirements for future
device-level nonvolatile memory. RRAM is an emerging technology for
nonvolatile memory, a candidate to replace NAND Flash technology in the
scaling race to sub-10nm memories.
Current
charge storage based Flash memory technologies are believed to face
scaling limitations beyond 18 nm. To overcome these, a variety of
innovative cell and memory concepts are investigated worldwide. One of
the most promising memory concepts is the resistive RAM or RRAM. It is
based on the electronic switching of a resistor element material between
two stable (low/high) resistive states. The major strengths of RRAM
technology are its potential density and speed.
Imec’s
RRAM cell features a novel Hf/HfOx resistive element stack. It couples a
cell area of less than 10x10nm² with an excellent reliability
(endurance of more than 109 cycles). The cell has fast nanosecond-range
on/off switching times at low-voltages. It has a large resistive window
(>50) and shows no closure of the on/off window after functioning at
200 C for 30 hours. The device even remained operating failure-free
functioning for 30 hours with a thermal stress of 250 C. The switching
energy per bit is below 0.1 pJ, and AC operating voltages are well below
3 V. With these characteristics, imec’s cell meets the major
requirements for device-level nonvolatile memory.
In
addition, imec has also further clarified the impact of film
crystallinity on the operation of RRAM cells, especially with a view on
further scaling. It also sheds light on the role of the cap layer and on
the switching mechanisms.
These
results were obtained in cooperation with imec’s key partners in its
core CMOS programs Globalfoundries, INTEL, Micron, Panasonic, Samsung,
TSMC, Elpida, Hynix, Fujitsu and Sony.
