Microwave bipolar silicon power transistors

The design, fabrication and evaluation of microwave bipolar silicon transistors are described for pulsed operation at power-levels up to 5 watts and frequencies in the 3.0--5.0 GHz range. Typical power gains of 4-6 dB at 3.5 GHz with 25% efficiency have been achieved with "mesh" emitter geometries. Emitter line vcidths of 2 µm and metalization stripes of 2.5 µm are employed in the mesh cell design. Steep impurity profiles are used to minimize the high injection level effects of emitter neutral capacitance and base widening. The effects of phosphorous and arsenic emitter diffusion profiles on the microwave performance are contrasted. The technology trade offs are discussed such as material orientation, emitter diffusant, contact metalization, edge breakdown and passivation. The contact metalization is silicon-doped aluminum to provide low contact resistance and prevent silicon dissolution into the aluminum on contact formation. A deep oxide base isolation is used, in contrast with the conventional guard ring diffusion, to increase breakdown voltage, lower parasitic bonding pad capacitance, and minimize oxide steps to permit high photographic resolution across large areas. The evaluation of the microwave transistors is performed with a unique "chip carrier" to provide low base lead inductance to the ground plane. Ribbon bonds are used in place of the conventional wire bonds to reduce lead inductance. Transistor performance is discussed in terms of input and output matching, maximum available gain, gain compression, and efficiency.