The work principle of a Nothing On Insulator nanotransistors with a cavity was presented in a previous work [1, 2]. The encountered problems were: atypically traces for ID-VGS. They still change the monotony when VGS rises from +0,3V to +3V. The explanations came from simulations that surprised the tunneling of the oxide. The premature breakdown is predicable for 10nm oxide. In the real case, the nanodevice body is placed on a hard support that reaches 100um.
This paper has two targets: the breakdown limitation through the Back-Gate terminal; the real effects including in the nanotransistor simulations.
The Atlas simulations have taken into account in the MODEL statement the parameters: BBT – Band to Band Tunneling, Fermi distribution, mobility’s models and eventually schro – to activate the Schrodinger equation solving. Now, the simulations overcome step by step the problems: (1) the support thickness was selected 100um. In this way the premature breakdown is avoided; (2) two materials of the insulator support were simulated: oxide and sapphire; (3) the real effects of interfaces were introduced: Si/oxide interface charge Qf=5x1010e/cm2 is simulated; secondly, an n-type poly as source and drain real contacts are defined, workfunction=-0,55V. To increase the simulations accuracy with this test nanodevice versus prior case were modified: (a) the Ox, Oy mesh at inter-atomic distance 0,3nm in Si film. The self-consisting solving of the Poisson and Schrodinger equations is possible along nodes, assumed now as atoms; (b) the Si islands sizes are changed at 10nmx4nmx10nm and the doping concentration in Si film was increased at 2x1021cm-3, so that the number of impurities in Si reaches to 800/ islands volume.
Results: The gate current is zero for all voltages ranges. The back-gate tunneling is completely removed. At VD=4V, VG=4V ID=7.6nA and 33nA for oxide and for sapphire with ideal interfaces. After the Qf2 considering besides to the real contacts ID becomes 5546nA. Interesting new quantum effects occurred in source and drain regions, where different electron concentrations arise and distinct currents ID, IS consequently appear.
1. IEEE Int. Conf.Proc. CAS’Sinaia, Romania, 2005, p.65-68.
2. IEEE Int. Conf.Proc. MSM’2005, USA, Anaheim, p.111-114. |