Designing Ultrahard Bipolar Transistors

Calculations are presented for a bipolar transistor which indicate the relative importance of the device regions in establishing the neutron tolerance. For conventionally diffused profiles with a fixed set of device parameters, the calculations indicate that an optimum base width may occur which will yield the maximum neutron hardness. The analysis indicates that the neutron hardness can be increased substantially by using a device profile with a shallow, abrupt emitter and a narrow base region. Devices utilizing these criteria are extremely tolerant to neutron irradiation and show a current gain greater than 10 after a neutron fluence of 1016 n/cm2 (E > 10 keV). This represents an order of magnitude increase in hardness over devices presently available.