Reliability of 1×5 μm2 emitter InAlAs/InGaAs HBTs under bias and thermal stress

InAlAs/InGaAs heterojunction bipolar transistors with emitter dimensions of 1×5 μm² were subjected to elevated temperature, bias stress lifetests. The devices were stressed under DC bias at three elevated temperatures to allow the activation energy to be calculated. The devices were different from HBTs previously reported on by HRL in that the emitter width was reduced to 1 μm, the collector thickness was decreased from 700 to 200 nm, and the Be doping level was increased to decrease the sheet resistivity. Three separate failure criterion were considered with the most pessimistic predicting a MTTF of 3.6×10⁷ hours at a junction temperature of 125°C.