A 512 Kbit low-voltage NV-SRAM with the size of a conventional SRAM

This paper describes two new circuit techniques for nonvolatile SRAMs with back-up ferroelectric capacitors (NV-SRAMs). These circuits are able to overcome the size and low-voltage-reliability problems faced by the original NV-SRAM. A new 0.25-/spl mu/m-design-rule four-metal-layer NV-SRAM cell occupies 9.7 /spl mu/m/sup 2/, that is the same area as a 0.25-/spl mu/m three-metal-layer SRAM cell. A high-voltage/negative-voltage plate line driver allows a low-voltage-operation NV-SRAM array to improve its nonvolatile retention characteristics. A 512 Kbit test macro has also been designed with only one percent area overhead from a conventional SRAM macro.