lecture29 - Spring 2004 FET Exam Solution Calculate V T for...

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Unformatted text preview: Spring 2004 FET Exam Solution Calculate V T for aSi-MOS transistor with an n +-polysilicon gate, silicon oxide thickness of 15nm, a channel doping of N A =5 x 10 16 cm-3 , a fixed charge of 1 10 11 qC/cm 2 , and channel length L=3 m and channel width = W= 5 m. The acceptor doping makes it an n-channel device F ox B ox i ms T C Q C Q V 2 + = 1. ( ) ( ) V 960 . 398 . 562 . 10 08 . 1 10 5 ln 0259 . 2 / 124 . 1 ln 2 / 10 16 = = = = = + = = i A g f C f C s m ms n N q kT E E E E E For a n + polysilicon to a n-channel p-substrate Neglecting the band narrowing from the degenerate doping (cont.) (cont.) 1. ( ) ( ) 2-8-19-2 11 i C/cm 10 6 . 1 C 10 1.6 cm 10 1 Q = = () ( ) ( ) 2 7 7- 14 ox F/cm 10 30 . 2 cm 10 15 F/cm 10 85 . 8 9 . 3 C = = = ox i t Finding f ( ) V 398 . 10 08 . 1 10 5 ln V 0259 . ln 10 16 = = = i A f n N q kT Finding capacitance across the insulator Finding fixed charge in the insulator (cont.) 1. Finding depletion charge ( ) () ( ) ( ) ( ) ( ) 2 7 3- 16 19 14 C/cm 10 15 . 1 398 . cm 10 5 C 10 6 . 1 F/cm 10 85 . 8 8 . 11 2 2 ) 2 ( 2 2 1 2 1 2 1 = = = = = f A s A s A A B qN qN qN w qN Q (cont.) 1. ( ) V 266 . 0.795 0.4955 0.0696--0.960 V 398 . 2 F/cm 10 30 . 2 C/cm 10 15 . 1 F/cm 10 30 . 2 C/cm 10 6 . 1 V 960 . 2 2 7 2 7 2 7 2 8 = + + = +...
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lecture29 - Spring 2004 FET Exam Solution Calculate V T for...

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