One day in July, Jack Kilby was working at Texas Instruments when it occurred to him that all parts of a circuit, not just the transistor, could be made out of silicon. At the time, nobody was putting capacitors and resistors into ICs. This would change the future and make it easier to produce and sell integrated circuits. Kilby's boss liked the idea, and told him to get to work. By September 12, Kilby had built a working model, and on February 6, Texas Instruments filed a patent. Their first ""Solid Circuit"" was the size of a fingertip. 