STL versus ISL: an experimental comparison

Schottky-transistor logic (STL) and integrated Schottky logic (ISL) have been fabricated in both 4-μm and 2-μm oxide isolated processes and characterized over the military temperature range (-55 to +125°C ambient). The temperature coefficient of the average propagation delay (t˜/SUB pd/) is positive for STL over the entire operating current range. For ISL, the temperature coefficient of t/SUB pd/ is negative at low currents and positive at high currents. Both the 4-μm and 2-μm ring oscillator designs studied showed this behavior. At 25°C, t/SUB pd/ data indicate no difference between STL and ISL for practical purposes. At -55°C, the STL has a slight (~0.1 ns) speed advantage over ISL. At 150°C (junction), the 2-μm STL gates with a 200 Ω/□ base sheet resistance have the lowest minimum t/SUB pd/ of the gates studied (0.9 ns at a total current of 190 μA) compared to the best for ISL at 1.0 ns and 150 μA. The ISL operates at a lower logic swing than the STL at 105°C, and has a speed advantage in the current range useful for VLSI. Additional data are presented which demonstrate the effect of the base resistance, epitaxial resistivity and substrate resistivity on delay.