Aluminium gallium nitride (AlGaN) is a semiconductor material. Other semiconductor materials include germanium, silicon carbide, and gallium nitride and have various applications. Binary compounds such as tungsten carbide or boron nitride can be very refractory. Atomically thin boron nitride is one of the strongest electrically insulating materials. Atomically thin boron nitride has much better oxidation resistance than graphene. Yttria is used as a sintering additive in the production of porous silicon nitride. Cu atoms forms hexagonal layers reminiscent of the boron nitride (graphite structure). Once ignited, beryllium burns brilliantly forming a mixture of beryllium oxide and beryllium nitride. It is any alloy of aluminium nitride and gallium nitride. The most important example is gallium nitride, a semiconductor. Low-pressure deposition of thin films of cubic boron nitride is possible. MEMS cantilevers are commonly fabricated from silicon (Si), silicon nitride (SiN), or polymers. All other forms of boron nitride are crystalline. Layers of amorphous boron nitride (a-BN) are used in some semiconductor devices, e.g. MOSFETs. Copper can be directly electroplated onto ruthenium, in contrast to tantalum nitride.