Propagation delay time dependence on gate geometry for the self-aligned I2L

The gate geometry dependence of the minimum pro.- pagation delay time (tpdm) was investigated for the self-aligned I²L. Switching characteristics were measured by using I²L test patterns with different base contact geometries and collector widths (Wc); tpdm=0.9 nS for a double base contact and Wc= 4µm I²L gate and ftoggle-max= 150 MHz for a divide-by two circuit with Wc= 7 µm I²L gates. Experimental results suggest that the resistance of the intrinsic base area for the n-p-n transistor has strong influence on tpdm. An analysis based on a charge control model which includes this base resistance effect was carried out and the experimental results were explained very well.