Full-swing local bitline SRAM architecture based on the 22-nm FinFET technology for low-voltage operation

The previously proposed average-8T static random access memory (SRAM) has a competitive area and does not require a write-back scheme. In the case of an average-8T SRAM architecture, a full-swing local bitline (BL) that is connected to the gate of the read buffer can be achieved with a boosted wordline (WL) voltage. However, in the case of an average-8T SRAM based on an advanced technology, such as a 22-nm FinFET technology, where the variation in threshold voltage is large, the boosted WL voltage cannot be used, because it degrades the read stability of the SRAM. Thus, a full-swing local BL cannot be achieved, and the gate of the read buffer cannot be driven by the full supply voltage (V_DD), resulting in a considerably large read delay. To overcome the above disadvantage, in this paper, a differential SRAM architecture with a full-swing local BL is proposed. In the proposed SRAM architecture, full swing of the local BL is ensured by the use of cross-coupled pMOSs, and the gate of the read buffer is driven by a full V_DD, without the need for the boosted WL voltage. Various configurations of the proposed SRAM architecture, which stores multiple bits, are analyzed in terms of the minimum operating voltage and area per bit. The proposed SRAM that stores four bits in one block can achieve a minimum voltage of 0.42 V and a read delay that is 62.6 times lesser than that of the average-8T SRAM based on the 22-nm FinFET technology.