Technology commentary - In perspective: The tunnel diode

In the late 50s and early 60´s, speed was an important concern in electronics. Then, bipolar was the dominant transistor technology, although MOS was on the way and CMOS was soon to be proposed. Even though little yet existed in the way of integrated circuit technology, the foundations were already laid for most of the popular bipolar IC logic configurations of today. Propagation delays for RTL and diode-resistor-transistor type logic were on the order of 50ns, although certain novel configurations based on high performance bipolar discretes had operating speeds 10 times faster. Solid-state microwave circuits were based largely on varactor diode parametric amplifiers and negative resistance oscillators with operating frequencies in the range of 1-1OGHz.