The VLSI I took for my EE degree was the hardest course by far. I did a digital logic project and the amount of time I spent looking at my traces and trying to figure out what went wrong, only to forget to ground my P-wells or make one of transistors too small. Maybe I just wasn't good at it but have a lot of respect for people who do it professionally.

There's also MEMS which is basically making sensors (even motors) out of Silicon.