1. MOS Capacitor Lecture #5

2. Transistor Voltage controlled switch or amplifier : control the output by the input to achieve switch or amplifier Two types of Transistors: Bipolar junction transistor (BJT), uses both diffusion and recombination of electron and hole charge carriers Field effect transistor (FET) uses an electric field and drift to control the conductivity. FETs are also known as unipolar transistors as they involve single- carrier-type operation

3. Field Effect Transistor FET Transistor consists of Metal-oxide-silicon (MOS) capacitor and two pn-junction one in forward bias and the second in reverse bias n channel MOSFET p channel MOSFET Metal is a conductor Oxide is an insulator

4. Field Effect Transistor FET Transistor consists of Metal-oxide-silicon (MOS) capacitor and two pn-junction one in forward bias and the second in reverse bias Channel is the region under the oxide

5. Field Effect Transistor We talk about two states: V GS is very low  Accumulation of holes in the channel  No current I DS =0 (Cut- off) VGS is high  Accumulation of electrons (inversion) in the channel  high current I DS >0 (ON) There is no a vertical current I GS I GD I GB OFF ON

6. Summary for MOS with p-type bulk State Accumulation Surface potential Gate voltage Charges in the surface Holes Flat band Weak inversion Inversion Intrinsic Depletion Holes Electrons Acceptors

7. Summary for MOS with p-type bulk Accumulation Flat band Depletion Intrinsic Inversion

9. MOS C-V Characteristic Experimental set-up for C-V measurement: 1.D.C voltage V GB 2.A.C periodic function with amplitude of V a and frequency f=1/T (T is period). General V GB >>V a, therefore the A.C power supply will not change the state of the device and under this condition, we can: The D.C voltage will set the bias or operating point of the device and A.C will measure the capacitance of the device. It is important to have slow ramping or rising time between the different values of the D.C operating point

10. MOS C-V Characteristic - Summary

11. MOSFET Transistor

12. (1) - linear (2) - triode (3) - triode (4) - triode (5) - triode (6) - saturation (7) - saturation

13. MOSFET Transistor Explanation to pinched-off: When V DS biomes larger than V DS,sat (V GS -V T ), the point in the channel at which the inversion charge is just zero moves toward source terminal. 1.In this case, electrons enter the channel at the source, travel though the channel toward the drain, and then, at the point where the charges goes to zero, are injected into the depletion region, where they are swept by the electric field (E) to drain contact. 2.We can consider the space between the source and drain as two regions with two resistors in serial (R cahnnel Channel or inversion and R depletion). The R depl >>R channel, and therefore most of the voltage (V DS -V DS,sat )=(V DS -V GS -V T ) is dropped only on the R dep and therefore there is no change in the resistance of the channel.

14. Gauss's Law Two plates are identical, but one has a charge of +Q and the other has a charge of -Q, the field in the region between them will point from the positive plate to the negative plate and will have a value of : In the region outside the plates, the two fields will exactly cancel. This arrangement is known as a parallel-plate capacitor. We'll look at that again as a device used to store charge.

15. Gauss's Law In case a constant electric field