SOI MOSFET mismatch due to floating-body effects

Abstract

To distinguish small differentials in voltage, circuits such as sense amplifiers and SRAM cells require transistors having closely matched electrical characteristics. For example, a mismatch in threshold voltage between cross-coupled NMOSFETs in a sense amplifier introduces an additional noise source which hinders reliable sensing. Mismatch in V/sub T/ results from mismatched body-charge state, which is dependent on the operating history of the MOSFETs. In this paper, the effect of transient operation of cross-coupled partially-depleted SOI NMOSFETs on the mismatch of device electrical characteristics is investigated with FIELDAY device modeling. Selective use of novel "body-equilibration links" allows closely matched electrical characteristics within groups of devices without seriously degrading the performance advantages of SOI.