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Due to the complexity of device processing, the trade-off between yield and area has resulted in diminishing rate of scaling for the high-density static random access memory (SRAM) cell at advanced CMOS nodes. An introduction of extreme ultraviolet (EUV) and multipatterning has added additional cost to technology in order to realize 3-D device structure and ultrascaled metal routing. In this era, spin-transfer torque (STT)-MRAM technology can provide an alternative to high-density SRAM and for the last level cache (LLC) applications. In this article, we discuss the memory design and technology tradeoff to enable the STT-MRAM as a viable option. We have realized the technology over 300-mm wafer, measuring 1 million samples to build a SPICE model for circuit simulation. Occupying up to 83.3% of an area that of SRAM macro has been designed and simulated for the scaled 5-nm CMOS node. The simulated MRAM macro shows the best read and write access time of 3.1 and 6.2 ns, respectively. Magnetic tunneling junction (MTJ) pillar of 38-nm diameter is realized at 90-nm pitch, measuring resistance area (RA) of 5.2-Ω ⋅ μm2, Jsw of 5.5 MA/cm2 with improved Δ avg of 70, and breakdown voltage of 0.99 V. The energy comparison shows increasing gains versus SRAM for the increasing cache sizes crossing over at of 0.3 and 4 MB for the single-cycle read and write operations, respectively. [ABSTRACT FROM AUTHOR]

In this paper, we present an intensive study of 6T-SRAM designs for vertical gate-all-around (GAA) transistors (VFETs) and lateral GAA transistors (LFETs) using 5-nm node design rules. Optimizations of the nanowire (NW) diameter and the gate length are also conducted to enhance the SRAM performance. Device VT retargeting has been proposed for improving the minimum operating voltage ( V\min ) of SRAMs. The isoperformance and isoyield have been performed to assess and determine the benefits provided by LFET and VFET architectures, respectively. Our results show that the VFET bitcells are denser than the LFET bitcells by 20%–30%. The SRAM read stability (read static noise margin) is significantly improved using the NW channel. For a $6\sigma $ yield target and an isoarea of SRAM bitcells, V\min of the VFET bitcell is 80 mV lower than LFET designs. Applying the proposed VT retargeting technique can allow the VFET 122 bitcell to operate at 0.57 V without using assist circuits. A standby leakage below 10 pA/cell can be achieved for both architectures. At isoperformance, the standby leakage of VFET bitcells is $2.6\times $ lower than LFET bitcells. [ABSTRACT FROM AUTHOR]

For the first time, we present complete device threshold voltage (VT)-targeting methodology for FinFET SRAM in 10-nm technology, considering capacitance due to metal pattering and device variability to set target read current for different variants of SRAM architecture to determine technology high-density (HD) SRAM cell. The VT-targeting methodology brings into play the worst case read and write margins available for SRAM cell to determine nominal device VT by tuning the work function of metal gate. Analysis shows that for minimum leakage current, 112 SRAM cell is optimum, whereas for the same area of 0.0546~\mu \mathrm{m}^{\mathrm {2}} with 50% higher leakage, 122 SRAM outperform by 5% and 20% improved read and write margins, respectively. The 122 SRAM as HD cell reduces the cost of the technology by sharing P-channel field effect transistor (PFET) and N-channel field effect transistor (NFET) VT mask with the high threshold voltage logic devices, whereas the 112 SRAM device shares only NFET VT mask. The 111 SRAM can achieve target performance at lesser area of 0.048~\mu \mathrmm^\mathrm 2 by compromising read stability, which will result in lower yield. At 64-nm pitch, litho-etch litho-etch (LELE) double-patterned gate impacts device performance and alleviates variability; hence the read margin of SRAM cell should consider an additional 1\sigma \mathrm {\mathbf {rsnm}} margin to retain the same yield in 10-nm-technology era. [ABSTRACT FROM AUTHOR]