imec shows capacitor-free DRAM

tags10uf smd capacitor Oct. 10 , 28

Imec has developed a dynamic random access memory (DRAM) cell architecture that does not require capacitors and can therefore be stacked into a 3D structure.

Classic DRAM designs exceeding 32GB are difficult to expand as the size becomes smaller, mainly due to the result of capacitors. In contrast, imec showed a design with two low-power indium gallium zinc oxide thin film transistors (IGZO-TFT) and no storage capacitors. It is well known that IGZO-TFT has an extremely low off current, and the parasitic capacitance of the read transistor is used as a storage element.

The retention time of 2T0C (2-transistor 0 capacitor) unit is greater than 400s, which further reduces power consumption with a longer refresh rate. This can be achieved in the back end of the CMOS process (BEOL) to place the dynamic memory layer above the logic.

Imec has fabricated transistors with a gate length of 45nm on 300mm wafers, and described the architecture in a paper at the IEDM conference this week.

"In addition to the long retention time, IGZO-TFT-based DRAM cells also provide a second major advantage over current DRAM technology. Unlike silicon, IGZO-TFT transistors can be manufactured at relatively low temperatures, so they BEOL process compatible." said Gouri Sankar Kar, director of imec's planning.

"This allows us to move the periphery of the DRAM memory cell under the memory array, which greatly reduces the footprint of the memory die. In addition, BEOL processing opens up a path for stacking individual DRAM cells, thus realizing a 3D-DRAM architecture."

The expansion of DRAM memory is a key element of cloud computing and AI, which is a key area identified by the European Commission as the region, especially in the recovery of Covid-19. Many different architectures have also been proposed to eliminate capacitors in DRAM.

"Our breakthrough solution will help eliminate the so-called memory wall, allowing DRAM memory to continue to play a key role in demanding applications such as cloud computing and artificial simulation.