Open AccessThis article is
- freely available
Exploration of Sub-VT and Near-VT 2T Gain-Cell Memories for Ultra-Low Power Applications under Technology Scaling
Institute of Electrical Engineering, Ecole Polytechnique Fédérale de Lausanne, Station 11, Lausanne,VD 1015, Switzerland
VLSI Systems Center, Ben-Gurion University of the Negev, POB 653, Be'er Sheva 84105, Israel
Faculty of Engineering, Bar-Ilan University, Ramat-Gan 52900, Israel
* Author to whom correspondence should be addressed.
Received: 4 February 2013; in revised form: 16 March 2013 / Accepted: 19 March 2013 / Published: 29 April 2013
Abstract: Ultra-low power applications often require several kb of embedded memory and are typically operated at the lowest possible operating voltage (VDD) to minimize both dynamic and static power consumption. Embedded memories can easily dominate the overall silicon area of these systems, and their leakage currents often dominate the total power consumption. Gain-cell based embedded DRAM arrays provide a high-density, low-leakage alternative to SRAM for such systems; however, they are typically designed for operation at nominal or only slightly scaled supply voltages. This paper presents a gain-cell array which, for the first time, targets aggressively scaled supply voltages, down into the subthreshold (sub-VT) domain. Minimum VDD design of gain-cell arrays is evaluated in light of technology scaling, considering both a mature 0.18 μm CMOS node, as well as a scaled 40 nm node. We first analyze the trade-offs that characterize the bitcell design in both nodes, arriving at a best-practice design methodology for both mature and scaled technologies. Following this analysis, we propose full gain-cell arrays for each of the nodes, operated at a minimum VDD. We find that an 0.18 μm gain-cell array can be robustly operated at a sub-VT supply voltage of 400mV, providing read/write availability over 99% of the time, despite refresh cycles. This is demonstrated on a 2 kb array, operated at 1 MHz, exhibiting full functionality under parametric variations. As opposed to sub-VT operation at the mature node, we find that the scaled 40 nm node requires a near-threshold 600mV supply to achieve at least 97% read/write availability due to higher leakage currents that limit the bitcell’s retention time. Monte Carlo simulations show that a 600mV 2 kb 40 nm gain-cell array is fully functional at frequencies higher than 50 MHz.
Keywords: embedded memory; gain cell; energy efficiency; subthreshold operation; near-threshold operation; retention time; access speed; technology scaling
Citations to this Article
Cite This Article
MDPI and ACS Style
Meinerzhagen, P.; Teman, A.; Giterman, R.; Burg, A.; Fish, A. Exploration of Sub-VT and Near-VT 2T Gain-Cell Memories for Ultra-Low Power Applications under Technology Scaling. J. Low Power Electron. Appl. 2013, 3, 54-72.
Meinerzhagen P, Teman A, Giterman R, Burg A, Fish A. Exploration of Sub-VT and Near-VT 2T Gain-Cell Memories for Ultra-Low Power Applications under Technology Scaling. Journal of Low Power Electronics and Applications. 2013; 3(2):54-72.
Meinerzhagen, Pascal; Teman, Adam; Giterman, Robert; Burg, Andreas; Fish, Alexander. 2013. "Exploration of Sub-VT and Near-VT 2T Gain-Cell Memories for Ultra-Low Power Applications under Technology Scaling." J. Low Power Electron. Appl. 3, no. 2: 54-72.