can anyone explain these terms??

[tension885]

hello,
some elementary terms used in CMOS
p-substrate , n substrate
n channel
n+ region , p+ region

can anyone here explain these terms??? their basic definitions and difference??

 

[layoutmaster]

p-substrate : when you start the fab process from p-type silicon

n-substrate: Exactly the same, but with N-type silicon

n+ region / P+ region: Silicon area with high doping of N or P material (these areas are generated by difusion of N or P type elements into silicon.

n-channel: As the name indicates is the channel formed below the MOS gate once its Vthreshold is reached. The channel creates a current path between MOS source and drain.

 

[vlsi_whiz]

VLSI processes make use of a substrate, a base Si material from which the layers that form the transistor are grown. This layer is called the SUBSTRATE and can be of "p" type or "n" type. If we use a p-type substrate we get a n-channel MOSFET (NMOS) device and when we use a n-type substrate we get a p-channel MOSFET (PMOS). To fabricate both PMOS and NMOS on a single die/substrate, we use only one type, ie, the p-type substrate. Here when the source and drain regions are fabricated, we get the NMOS device. To fabricate a PMOS, we will make a N+ region in the p-substrate and then fabricate the PMOS in it.

When you fabricate a MOS transistor, there are 3 regions - Source, Drain and Gate. The Gate separates the Source and Drain regions. When a voltage is applied at the gate of a MOS using p-substrate (NMOS), a channel is formed between the Source and Drain. This channel is made up of electrons and hence called N-channel. If the channel is made up of holes, it will be called a p-channel for PMOS transistors.

N+ and P+ are regions of higher doping than normal N and P regions. These regions contain more electrons(N) and holes (P) and exhibit a slightly different electrical characteristic. These N+ and P+ regions are used to fabricate the Source and Drain regions for NMOS and PMOS transistors.