LONDON – European research institute IMEC has reported a Resistive RAM (RRAM) memory cell that measures 10-nm by 10-nm at the International Electron Devices Meeting, which took place Dec. 5 to 7 in Washington DC. The organization claims this is the smallest such cell and that it shows the potential to replace NAND flash memory.
RRAM is one of a number of emerging non-volatile memory technologies being researched as a potential replacement for NAND flash, which is based on charge-storage and which in its present form is thought will not scale below about 18-nm planar dimensions.
RRAM is based on the electronic switching of a resistor element material between two stable resistive states and can be contained in a cross-bar array. IMEC has focused on hafnium/hafnium-oxide as the switching material sandwiched between conventional titanium-nitride contacts.
Cross-section of 10-nm Hf/HfOx RRAM element.
The major strengths of RRAM technology, sometimes also labeled as memristor, are its potential density due to cross-bar formation and speed. IMEC researchers have previously stated that they feel they have a good understanding of the filamentary switching mechanism based on the movement of oxygen vacancies in the material.
The reported Hf/HfOx resistive stack has an area of less than 10-nm x 10-nm (100 square nanometers) and has demonsrated an endurance of more than 10^9 (1 billion) cycles. It has nanosecond on/off switching times at low voltages and a resistive window of a factor 50 that shows no closure after functioning at 200 degrees C for 30 hours, IMEC said. This gives an exprapolated data retention of 10 years at 100 degrees C.
The switching energy per bit is below 0.1pJ, and AC operating voltages are well below 3 volts.
In addition, IMEC has also looked into the impact of film crystallinity on the operation of RRAM cells, especially with a view to further scaling. It also sheds light on the role of the cap layer and on the switching mechanisms.
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