![]() ![]() ![]() The depletion layer will be flat along the length of the device because there is no horizontal voltage gradient to slant it. There will be a depletion region at the oxide contact surface, but because it is below the threshold voltage, not enough carriers are drawn to the surface to create an inversion layer. A2:The inversion layer will not be present.A1:If the metal gate made direct contact to the semiconductor, when voltage was applied it would conduct current directly from the source, and the device would not operate properly.Q3: How does the device fail if it gets too hot? Will it be pinned open or closed?.Q2: If the gate voltage is nonzero but below the threshold voltage, and the source to drain voltage is zero, what does the inversion layer look like?.Q1: Why is the insulator present? What would happen to the device if it were absent?.This minimizes over-lap capacitance between the n+ regions and the gate. The gate itself shields the doping so that the regions are defined by the gate. Finally, arsenic atoms are doped to form the n+ drain and source regions. A poly silicon layer is deposited on top of the gate and heavily doped to be conductive. Next, the field oxide is removed over the active device area and the gate oxide is grown in the center. ![]() This is to modify the doping concentration in the channel. Next, the SiO2 is etched away and a layer of field oxide is deposited, and more boron is doped in. This creates heavily doped p channel stop which prevent conduction between devices. The device region is protected by a layer of photo-resist, and then the surface is heavily doped with boron through the \(Si_3N_4\) and \(SiO_2\) into the wafer surface. ![]() \(SiO_2\) is grown over this and \(Si_3N_4\) is then deposited over that. In making a MOSFET, first a lightly doped p-type Silicon wafer is used. ![]()
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