Hi I'm simulating a digital inverter and wondering if the power dissipation looks reasonable(any recommendation for the width?). I also notice some oscitation after the output is stable, any suggestion to fix that?

The oscillations are numerical errors. Try

.option method=gear

before the .control line to use a higher order integration method. Also use a smaller step size in the .tran command. If your input signal rise time is 100ps use a smaller tstep, like:

.tran 2p 1.6u