Ferroelectric transistors with improved characteristics at high temperature

We report on the temperature dependence of ferroelectric metal-oxide-semiconductor (MOS) transistors and explain the observed improved characteristics based on the dielectric response of ferroelectric materials close to the Curie temperature. The hysteretic current-voltage static characteristics of a fully depleted silicon-on-insulator transistor, with 40 nm vinylidene fluoride trifluorethylene, and 10 nm SiO2 gate stack, are measured from 300 to 400 K. In contrast with conventional MOS field effect transistors (MOSFETs), the subthreshold swing and the transconductance show, respectively, a minimum and a maximum near the Curie temperature (355 K) of the ferroelectric material. A phenomenological model is proposed based on the Landau-Ginzburg theory. This work demonstrates that a MOSFET with a ferroelectric layer integrated in the gate stack could have nondegraded or even improved subthreshold swing and transconductance at high temperature even though the hysteresis window is reduced. As a consequence, we suggest that for ferroelectric transistors with appropriately designed Curie temperatures, the performance degradation of logic or analog circuits, nowadays operating near 100 °C, could be avoided. © 2010 American Institute of Physics.