3. Consider a MOS structure as sketched in the figure below. For t<0, the structure is at zero bias. In this condition, there is a depletion region in the semiconductor with a charge density of Qa= -3.4×10 C/cm². A = 10 μm² W-4.04 eV Xox4.5 nm NA-6x10¹7 cm³ At t=0, a current source is switched on with the sign indicated in the figure. Estimate the time that it takes for the MOS structure to be brought to the onset of inversion for the three cases below. The generation lifetime in the depletion region is tg=1 μs. a) If I -100 nA. b) If I 100 nA. c) If I = 1 nA.