• Daniyar Kylyzhov

A new type of DRAM will help accelerate the development of AI


Today the memory wall remains the main problem in computing systems. This is the difference between the processing time and the time it takes to transfer data to the processor from individual DRAM chips. With the growing popularity of artificial intelligence applications, the problem has become even more acute.



Research teams in the United States and Belgium have stated that a new kind of oxide semiconductor DRAM can store bits hundreds or thousands of times longer. In conventional DRAM, reading will drain the capacitor and the value must be written back to memory. In addition, the charge leaves the capacitor through the transistor. Therefore, all memory cells need to be updated periodically. In modern DRAM chips, this happens every 64 milliseconds.


Embedding DRAM in a processor chip has limitations. The challenge lies in making the capacitor and ultra-low leakage transistor.


However, the new type of DRAM has only two transistors, no capacitor (2T0C). The gate of the transistor itself is a natural small capacitor. Thus, the charge representing the bit can be stored right there.


The advantage of this design for AI is that separate devices are used for writing and reading.


However, the 2T0C circuit does not work well with silicon logic transistors. Bits may disappear because the gate capacitance of the transistor is too low and the leakage through the transistors is too high. So the researchers decided to turn to devices made from amorphous oxide semiconductors. Semiconductors regulate the current, which speeds up writing, but allows very little charge to pass through, which increases the life of the bits.


The US team used indium oxide doped with up to 1% tungsten.


The capacitorless DRAM transistors developed by the US researchers include a tungsten-doped indium oxide semiconductor [orange], palladium top and bottom gates (yellow), nickel source and drain electrodes [green], and hafnium oxide dielectrics [blue].

The capacitors DRAM transistors developed by the US researchers include a tungsten-doped indium oxide semiconductor [orange], palladium top and bottom gates (yellow), nickel source and drain electrodes [green], and hafnium oxide dielectrics [blue].

The capacitors DRAM transistors developed by the US researchers include a tungsten-doped indium oxide semiconductor [orange], palladium top and bottom gates (yellow), nickel source and drain electrodes [green], and hafnium oxide dielectrics [blue].

Researchers at the Belgian company Imec have presented a similar embedded 2T0C circuit in an IEDM using indium gallium and zinc oxide as a semiconductor.


Such oxides can be processed at relatively low temperatures. This means that devices made from them can be embedded in the interconnect layers above the silicon of the processor without damaging the silicon devices below.



Thus, a 4-layer 2T0C DRAM reduced the chip area required for built-in memory by about 3.5 times, and for an 8-layer - by 7.3 times. It also demonstrated a performance advantage over onboard 1T1C DRAM.


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