If you could go back in time and do, or bring, one thing to mess up the timeline what would it be?

Even if it had infinite power and was unbreakable, it would end up being fought over and coveted as holy relic, instead of being played with and studied

Hardly. The miniaturization required to make modern chips is ages ahead of anything possible in the 50s or 60s. Hell, them even getting some x-ray microscope to see the stupidly small transistors we have today would be a challenge in itself!