Cutters are made using a combination of high heat and high pressure. Man made diamonds can be grown in 5-10 minutes. Because of this diamond content, a fixed cutter bit may also be known as a diamond drill bit.
High heat plus pressure creates a PDC (polycrystalline diamond compact) cutter.
Cutters are made from a carbide substrate and diamond grit. High heat of around 2800 degrees and high pressure of approximately 1,000,000 psi forms the compact. A cobalt alloy is also present and acts as a catalyst to the sintering process. The cobalt helps bond the carbide and diamond.
During the cooling process, the tungsten carbide shrinks at a rate of 2.5 times faster than the diamond. Controlling this stress, as with most aspects of drill bit design, is called Intellectual Property, and manufacturers rarely, if ever, share their secrets.