A Comparative Numerical Study of Junctionless and p-i-n Tunneling Carbon Nanotube Field Effect Transistor

In this paper, a gate-all-around junctionless tunnel field effect transistor (JL-TFET) based on carbon nanotube (CNT) material is introduced and simulated. The JL-TFET is a CNT-channel heavily n-type-doped junctionless field effect transistor (JLFET) which utilizes two insulated gates (Control-Gate, P-Gate) with two different metal workfunctions in order to treat like tunnel field effect transistor (TFET). In this design, the privileges of JLTFET and TFET are mixed together. The numerical comparative study on the performance characteristics of JL-TFET and conventional p-i-n TFET demonstrated that the proposed JL-TFET has a higher ON-state current driveability (ION), a larger ON/OFF-current ratio (I-ON/I-OFF), a lower drain induced barrier lowering (DIBL), a shorter delay time (tau), and also a superior cut-off frequency (f(T)). Moreover, in order to further performance improvement of proposed JLTFET, three novel device structures namely as junctionless linear descending gate workfunction TFET (JL-LDWTFET), junctionless linear ascending gate workfunction TFET (JL-LAWTFET) and junctionless triple metal gate TFET (JL-TMGTFET) are proposed by gate workfunction engineering approach. According to simulation results, the JL-TMGTFET with the gate composed of three segments of different work functions shows excellent characteristics with high ION/IOFF ratio, a superior ambipolar characteristic, a shorter delay time and a better cut-off frequency compared to conventional p-i-n TFET and other proposed junctionless-based features. All the simulations are done with the full quantum mechanical simulator for a channel length of 60-nm using nonequilibrium Green's function (NEGF) method.