Re: Fastest Inverter
-One way is to use cascaded inverters as in the book: Digital Integrated Circuits: A Design Perspective, page 206-210 (2nd Edn), if the output capacitance is large, this should speed up your clock_bar.
-Make the clock rise and fall time 10ps.
-Another way is to use a TSPCR, which eliminates the need to use an inverted clock for your FFs, this is on page 350.
Remember, use thin lines to reduce the capacitive loading, and never use poly as a wire. I had the same problem by the way using crappy 0.18u TSMC transistors, and my clock couldn't go over 3GHz, but I didn't do any of the above because I'm lazy. Good luck.