Future Bipolar Device Structures

Recently developed bipolar device structures including their problems and future trends are reviewed. Polysilicon emitter-base self-aligned structures and trench isolation techniques are becoming key elements for high performance bipolaw ECL device structures, by which parasitic capacitances and resistances have been reduced drastically. In order to get further improved performance, smaller parasitic capacitances associated with the pull-up resistor as well as high cutoff frequency are required. Wafer-direct-bonded SOI structures are the promising candidate, while the base resistance and the cutoff frequency should be optimized moderately. The most serious problem is the power dissipation of ECL-type circuits. Smaller logic swings and low temperature operation should be also considered.