Design of auto-store circuit for nvSRAM with SONOS access transistor

Abstract

In this paper, an auto-store circuit that can perform a store and restore operation of non-volatile SRAM (nvSRAM) with access transistor whose gate stack is Silicon-Oxide-Nitride-Oxide-Silicon (SONOS) is designed. The suggested auto-store circuit is consisted by two small circuit parts of a store and restore circuit. The store circuit moves data in SRAM cell into SONOS device before power turns off while a restore circuit recalls the data to SRAM cell when the power is resupplied. When the nvSRAM replaces its conventional access transistor with the SONOS flash memory device, higher word line voltage is needed for a store operation. It demands much energy and additional voltage source to store a data. To overcome this disadvantage, the capacitor component is added in the store and restore circuit which is charged during the normal operation mode. At the moment of the power-off, the store circuit discharges the capacitors and applies higher voltage to the word line for the store operation. When the power is supplied again, the restore circuit discharges the capacitor and applies pre-charge voltage and restore the data to the bit line and word line. The simulation results show that the suggested auto store circuit can perform the store, restore operation in the sudden power off without an additional voltage source.