Interface trap densities at gate oxide/silicon substrate (SiO2/Si) interfaces of metal oxide semiconductor field-effect transistors (MOSFETs) were determined measuring the substrate bias dependence of the subthreshold slope. This method enables the characterization of interface traps residing between the midgap and strong inversion (2 times the Fermi potential) of small MOSFETs. In consequence of the high accuracy of this method, the energy dependence of the interface trap density is more reliable. The application of this technique to a MOSFET showed good agreement with the result obtained through the high-frequency/quasi-static capacitance-voltage (C-V) technique for a MOS capacitor. Furthermore, substrate dopant concentration obtained as a by-product through this technique also showed good agreement with the result obtained through the body effect measurement.
A method to determine the flat-band voltage, V
FB, in silicon-on-insulator (SOI) metal-oxide semiconductor (MOS) structures has been proposed. It is based on the measurement of the back channel threshold voltages of SOI MOS field-effect transistors (MOSFET's) as a function of the front gate bias. This method is very useful for fully depleted SOI MOSFET's with a low channel dopant concentration. Mean values of V
FB's obtained from this method were -0.79 V for n+ polysilicon gate SOI n-MOSFET's with a gate oxide of 205 Å and an acceptor concentration of 4×1015 cm-3, and -0.12 V for n+ polysilicon gate SOI p-MOSFET's with a gate oxide of 205 Å and a donor concentration of 5×1015 cm-3. The accuracy in the determination of V
FB is mainly dependent on precise evaluations of the front gate oxide thickness, the surface silicon thickness, and the channel dopant concentration.
An analytical model for SO1 nMOSFET with a floating body is developed to describe the I d s-I>, characteristics. Considering all current components in MOSFET as well as parasitic BJT, this study evaluates body potential, investigates the correlations among many device parameters, and characterizes the various phenomena in floating body: threshold voltage reduction, kink effect, output conductance increment, and breakdown voltage reduction. This study also provides a good physical insight on the role of the parasitic current components in the overall device operation. Our model explains the dependence of the channel length on the Ids-l;ls characteristics with parasitic BJT current gain. Results obtained from this model are in good agreement with the experimental I d s-Ik, curves for various bias and geometry conditions.
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