Title :
Stability Constraints Define the Minimum Subthreshold Swing of a Negative Capacitance Field-Effect Transistor
Author :
Jain, Abhishek ; Alam, Md. Ashraful
Author_Institution :
Sch. of Electr. & Comput. Eng., Purdue Univ., West Lafayette, IN, USA
Abstract :
The current-voltage characteristics of a classical field-effect transistor (FET) is dictated by thermal injection of charge carriers over a gate-controlled energy barrier. It is well known that the subthreshold swing (S) associated with these transistors cannot be reduced below the Boltzmann limit of 60 mV/decade, which in turn defines the lower limit of power dissipation. Therefore, a number of groups have recently proposed to use negative capacitance (NC) gate insulators in FETs to reduce S below the Boltzmann limit. The ferroelectric-FET (FE-FET) and suspended-gate FET (SG-FET) are two examples. It is now well accepted that NC-FETs can lower S, but given a specific device architecture, the question of whether there is a lower limit of S (and if so, the conditions that define the limit) has not been answered. In this paper, we: 1) demonstrate that the fundamental constraints of stability and hysteresis-free operation dictate that there is a lower limit of S associated with each NC-FET technology; 2) provide a general algorithm to calculate the minimum subthreshold swing (Smin); and 3) illustrate the concept using SG-FET and FE-FET for two different channel configurations, namely, a bulk FET and an FET with constant channel capacitance. Our results broaden the understanding of field-effect action in NC-FETs and should inform research on these devices.
Keywords :
Poisson equation; capacitance; electric properties; ferroelectric devices; field effect transistors; Boltzmann limit; FE-FET; NC gate insulators; NC-FET technology; SG-FET; bulk FET; channel configurations; charge carriers; constant channel capacitance; current-voltage characteristics; ferroelectric-FET; field-effect action; gate-controlled energy barrier; hysteresis-free operation; minimum subthreshold swing; negative capacitance field-effect transistor; negative capacitance gate insulators; power dissipation; stability constraints; suspended-gate FET; thermal injection; Capacitance; Capacitors; Ferroelectric materials; Field effect transistors; Insulators; Logic gates; Materials; Body factor; field-effect action; instability; negative capacitance; sub-60 mV/decade switching; two well energy landscape; two well energy landscape.;
Journal_Title :
Electron Devices, IEEE Transactions on
DOI :
10.1109/TED.2014.2316167