FABRICATING digital circuits due to LOW power loss gate structures and massive integration in a small area.CMOS Fabrication technology requires both n-channel (nMOS) and p-channel (pMOS) transistors to be built on the same chip substrate.To accommodate both nMOS and PMOS devices, SPECIAL regions must be created in which the semiconductor type is opposite to the substrate type.These regions are called wells or tubs.Advantages of CMOS device:High input impedance.CMOS gates are very simpleCMOS logic takes very little powerLess AFFECTED by noiseLow power consumption Transmission gate:The switch is considered closed when the voltage applied to the gate is logic high and is considered as open when the voltage applied to the gate is logic low.The output (y) is logic high, when the input (A) is logic high & switch controlled signal (B) is logic high & it is not logic high for all other combinations.Features of PTL INCLUDES:Gate is static.‘N’ transistor used instead of 2NNo static power dissipation.It is ratioless and Bidirectional. Pass transistor:Pass transistor uses an NMOS or PMOS transistor to transfer charge from the input node to the output node, under the control of gate voltage.The output remains in high input impedance state when the gate voltage is zero.Pass transistors logic is widely used in ROM, PLA's, Multiplexers, etc.