On-chip hv and lv capacitors acting as the second back-up supplies for nvsram auto-store operation

Abstract

Two on-chip capacitors including one HV capacitor VPPcap and one LV VCC capacitor VCCcap are built over a NVSRAM memory chip as a back-up second power supplies for each NVSRAM cell, regardless of 1-poly, 2-poly, PMOS or NMOS flash cell structures therein. The on-chip HV and LV capacitors are preferably made from one or more MIM or MIP layers for achieving required capacitance. A simplified VCC power system circuit without a need of a State machine designed for performing only one NVSRAM Program operation without Erase operations is proposed for initiating NVSRAM's Auto-Store operation without using any off-chip Vbat and Vcap. During the Auto-Store operation, all HV pumps and oscillators associated with the two on-chip capacitors are shut off once VCC voltage drop is detected by a VCC detector to be below 80% of regular VDD level.