Physical design automation at transistor level

The research and development of the design automation of integrated circuits started by the layout level and it evolved to higher levels of abstraction. At physical design level the evolution of automation was remained at the standard cell approach, where the layout of the cells are designed and included in a cell library. So, the design of the cell layout is not really automated. A cell library is also limited to small number of logic combinations. This limitation doesn't allow reaching an optimization of the circuit at the physical design level.