MOSFET OPERATIONS and its types Enhancement and Depletion types

Analog circuits.
Mosfet types and its operations

1. KARPAGAM INSTITUTE OF TECHNOLOGY COIMBATORE – 641 105. DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING MOSFET Prof G.mani sankar AP/ECE Karpagam institutions coimbatore 5/16/2024

2. MOSFET The metal oxide semiconductor field effect transistor is a semiconductor device widely used for switching purposes and for the amplification of electronic, signals. It has three terminals source(s), gate(G) and drain (D). The MOSFET can function in two ways (i) Depletion mode. (ii) Enhancement mode. 5/16/2024

3. Construction and operation of depletion type MOSFET n-channel depletion MOSFET Fig shows N-channel depletion MOSFET It operates both depletion mode and enhancement mode. Construction A type material is formed silicon base it is referred as substrate The substrate internally connected to the source terminal Two heavy depend region n+ are diffused in p-type substrate One n+ region act as source(s) and another n+ region act as drain(D) 5/16/2024

4. Cont.. 5/16/2024

5. Cont.. • A thin insulating layer SiO2 is grown over the surface. • The primary difference between the construction of depletion type and enhancement type MOSFET is that there is absence of channel in two enhancement type. Where as there is a diffused channel in the depletion type 5/16/2024

6. Operation When V gs = 0, V Ds  voltage is applied across two drain to source As a result is an attraction for the positive potential at the drain by two free electrons of n-channel and current is established through the channel. 5/16/2024

7. Cont.. 5/16/2024

8. • When V gs  = + ve voltage • The positive gate voltage will draw additional electrons from the p-type substrate due reverse leakage current. As two V Gs  continues to increase in the positive direction. The drain current will increase at a rapid rate • [ V gs  = V e ↑, I D ↑] when V gs  = - V e  voltage. The negative potential at the gate will tend to pressure electrons toward to the p-substrate and attract holes. From the p-type substrate. The more negative voltage, the increase the rate of recombination. The resulting drain current reduced. [ V gs  = - V e ↑, I D  ↓] 5/16/2024

9. Characteristics of n-channel depletion type MOSFET 5/16/2024

10. Construction and working of n-channel enhancement type MOSFET 5/16/2024

11. Cont.. It operates only in enhancement mode No physical channel between two n-region as shown in Fig. A p-type material is formed as substrate. It is internally connected to source terminal Two n+ highly doped regions are diffused in p-substrate One n+ region act as drain (D) and one n+ region act as source(S) Insulating layer Sio 2  is grown over the surface of the structure. No-channel between the two n+ regions. 5/16/2024

12. Operation • when V gs  = 0, voltage is applied between drain and source , the absence of n- channel will result in a zero drain current ( V gs  = 0, V Ds = + ve I D =0 ). 5/16/2024

13. If both V gs  and V ds  is + ve voltage is + ve voltage When + ve voltage to gate repelled the holes to p-type substrate As V gs  increases it will induced the n-type channel between the two n+ region V gs  is increased beyond the threshold level, the density of free carriers induced channel will increases, I D  current increases. If r gs  is constants and v Ds  increases the pinching off process occurs, and narrow channel at the drain end. 5/16/2024

14. Cont.. 5/16/2024 I D  = k(V Gs  – V T ) 2

15. Thank you 5/16/2024