Nominal structure of the surface channel wafer (with shaded layers omitted) and the buried channel wafer (entire structure).
C-V, G-V, and characteristics. The gate voltage sweep rate is 0.3 V/min in the C-V and G-V data, and is 0.03 V/min in the data. Included in the C-V plots are quasistatic (QS) data and ideal P-S simulations. The simulations are used to estimate the oxide capacitance, and are offset along the voltage axis by an arbitrary amount to aid clarity. In all admittance measurements, a full gate voltage sweep of was used to minimize non-equilibrium effects. The full C-V hysteresis loops are included at the highest frequency. The arrows indicate the direction of the hysteresis. In the surface plots, the thick line marks the locus of the peaks, which are proportional to the .
Gate voltage dependence of (column 1) the drain current, (column 2) the subthreshold swing, and (column 3) the P-S calculated channel carrier concentration and trap energy for (a)-(c) the surface, and (d)-(f) buried channel wafers. Note the highly non-linear trap energy scale in (c) and (f) applies to the single curve in each figure. is defined as zero at the conduction band edge and negative within the bandgap. The gate length, drain bias, and sweep rate were 1 μm, 50 mV, and 22 V/min, respectively. The gate sweep was .
Conduction band edge energy, , and electron volume density, n, profiles for the surface and buried channel MOSFETs, showing the trap energy at the oxide semiconductor interface at the same channel carrier concentration, approximately corresponding to the point of minimum SS of Fig. 3.
Comparison of the of the surface and buried channel Al2O3 MOSFETs (open symbols) at 22 V/min. Included for comparison are the 22V/min SS and Terman from a buried channel GGO/GO/InGaAs interface MOSFET.3 The low-high frequency from n+ GGO/GO/InGaAs MOS capacitors4 over a range of sweep rates is included as a shaded region. The data points for the two Al2O3 wafers and for the GGO/GO/InGaAs interface MOSFET (Ref. 3) are shown as solid symbols. The extracted from a 50 mV SS measurement of Egard et al. 5 assuming the nominal structure and 50% donor activation are labelled Lund. Portions of the figure are Reprinted with permission from Paterson et al., J. Appl. Phys. 110, 54103 (2011). Copyright © 2011 American Institute of Physics.
Minimum subthreshold swing and interface state density versus gate voltage sweep rate. The lines are fits of Eq. (2) to the data.
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