Research On Gate Current Of Uniaxial Strained Si MOS Device

Si-based strained material （strained-Si, strained-SiGe） can improve the deviceperformance due to the enhanced carrier mobility, and has great application prospects inhigh-speed/high-performance devices and circuits. And, gate current has an importanteffect on devices and IC, however, there is little research about strained silicon device’sgate current. So, the gate current of strained Si MOS is investigated in this paper.In this paper, the mechanism of gate leakage current is firstly analyzed. Based oncarriers’ transfer vertically，combined with the main component of gate leakage current，the conclusion is obtained that the gate leakage current is mainly induced by carriers’gate tunneling and thermal emission. For gate tunneling，now most MOS devices’ gatedielectric thickness is smaller than3nm，so the main tunneling is direct tunneling. Aboutcarrier’s thermal emission mainly induced by hot carrier effect.Secondly，starting with the quantum mechanical theory，the tunneling gate currentmodel of uniaxial strained silicon is built. The relationships of the tunneling current todevices’ structure parameters, biased voltages and stress are analyzed. After undergoingsimulation quantitatively using Matlab, it is found that the simulation result greatlyagrees with the reported experimental result, indicated the correct of our model. Andthen our result is compared with the result of biaxial stressed silicon nMOSFETs, whichshows the current of uniaxial strained Si nMOSFETs is lower than that of biaxialstressed silicon nMOSFETs, and so uniaxial devices have advantages over biaxialdevices.Finally，from the hot carrier effect and lucky hot carrier modeling， the hot carriergate current model of uniaxial strained silicon is built. The relationships of the tunnelingcurrent to devices’ structure parameters, biased voltages and stress are analyzed. Afterundergoing simulation quantitatively using Matlab, it is found that the simulation resultgreatly agrees with the reported experimental result, indicated the correct of our model.And then，the simulation results shows the current of uniaxial strained Si nMOSFETs islower than that of body silicon MOS device, having a good stability in hot carrier. InTDDB（timing-dependent dielectric breakdown）, the uniaxial strained silicon MOSdevice’s lifetime is longer. These results above show the uniaxial strained devices haveadvantages.