Quantum-dot Cellular Automata (QCA) demands to be a promising alternative of CMOS in ultra large scale circuit integration.Arithmetic and logic unit designs using QCA are of high research interest.A layout of four and eight bit universal shift register (USR) has been proposed.Initially QCA layouts of D Mens Hats flip-flop with clear and 4 to 1 multiplexer are designed, which are extended to design 4 and 8-bit parallel in parallel out (PIPO) shift register.Finally the PIPO is utilized to design 4-bit and 8-bit USR.
By the comparative analysis it is observed that the proposed D Flip-flop Racquet Sports - Squash achieved 40% clock delay improvement, whereas the modified layout of 4 to 1 multiplexer achieved 30% cell count reduction and 17% clock delay reduction from the previous works.This results in 31% reduction in cell count, 45% reduction in area and 55% reduction in clock cycle delay in 8 bit USR layout.