Sparks and flames

Question

This was bought in 2001 and has had only 2 call-outs. It started to create sparks occasionally for no apparent reason so we solved this temporarily by placing a dinner plate on the turntable. The part inside the machine which looks like a piece of card is now creating fire when microwave is selected. The rest of the machine's functions are fine.
Can you tell me what part that is and if replacement of it will solve the problem please?