What the problem is, the whole display or controller?

Hi guys! I have an iPad Air 2, everything worked well, I’ve updated to iOS 11, everything was right. A few days later the touchscreen didn’t work (the iPad didn’t fall into water or something else, it just stopped responsing to the touches), the display is working (no defects), but doesn’t response to the touches, every button works....only the touchscreen doesn’t work. I have done hard reset (entered the recovery mode and then restored), it didn’t help.

The question:

What the problem is? Do I have to replace the whole display or maybe there is a chip or other electronic element that controls just touchscreen? I think there will be a big difference at price between replacing the whole screen and replacing a little chip.

Thank you