Nonuniform RF Overstress in High-Power Transistors and Amplifiers

Nonuniform light emission from power transistors at 2-3-dB compression levels has been imaged using a microscope- mounted camera. The nonuniformity depends on the device lateral geometry, load impedance, dc and radio frequency (RF) conditions, and the negative gate current, which is a result of the RF-induced impact ionization in the transistors. Numerical simulations demonstrated a nonuniform distribution of the RF overstress in the transistors under the same conditions. The simulations indicate that the nonuniformity in the light intensity may be attributed to the RF-induced voltage overstress. Therefore, the observed light emission may be used as a direct and contactless monitor of the RF-induced overstress in transistors and power amplifiers.