ng .c om Design and Implementation of VLSI Systems Lecture02 cu u du on g th an co CMOS logic Impact of doping on silicon resistivity .c om silicon 4.9951022 atoms in cm3 Resistivity 3.2  105 Ωcm dope with boron  p-type cu u du on g th an co ng dope with phosphorous or arsenic  n-type 1 atom in billion  1 atom in million  1 atom in thousand  1 atom in billion  1 atom in million  1 atom in thousand   Electrons are more mobile/faster than holes What happens if we sandwich p & n types? A Al om p ng .c n B cu u du on g th an co One-dimensional representation ➢I n equi l i br i um, th edr i f ta nddi f f usi on components ofcur r ent a r eba l a nced;th er ef or eth enetcur r entf l ow i nga cr oss th e j uncti on i s zer o. du on g th an co ng .c om PN-junction regions of operation cu u In reverse bias, the width of the depletion region increases. The diode acts as voltage-controlled capacitor. A forward bias decreases the potential drop across the junction. As a result, the magnitude of the electric field decreases and the width of the depletion region narrows. nMOS and pMOS transistors om Each transistor consists of a stack of a conducting gate, an insulating layer of silicon dioxide and a semiconductor substrate (body or bulk) Gate Drain ng Source .c nMOS transistor Polysilicon co SiO2 pMOS transistor Source Gate Drain Polysilicon SiO2 n+ n+ p tox bulk Si n+ th an polysilicon gate L W n+ p+ SiO2 gate oxide (good insulator, ox = 3.9) p+ n bulk Si cu u du on g p-type body Body is