Improved charge pump for flash memory applications in triple well CMOS technology

Abstract

Flash memories, which are key components for non-volatile storage in many portable applications, require high voltages for correct operation. These voltage have to be generated by using on-chip voltage elevators. This article presents an improved scheme for charge-pump voltage elevators suitable for use in triple-well CMOS fabrication technology. A direct drain-bulk connection is realized for the pass transistor which implements the charge transfer device in each pump stage. This results in placing a P-N diode in parallel with the pass transistor, thereby improving the charge transfer process between adjacent stages. The proposed charge pump provides smaller output resistance (and, hence, larger current drive capability and shorter recovery time) and higher power efficiency as compared to conventional solutions. An experimental comparison between two charge pump modules (based on the traditional and on the presented scheme, respectively) integrated in 0.13-μm CMOS Flash technology, demonstrated the effectiveness of the proposed approach.