I- Introduction

II- Experiment

III- Parametric Degradation

IV- Mechanisms

V- Source Dependence

VI- Implications

VII- Summary

VIII- Acknowledgment

References

Abstract 

Irradiation of 2N5339 NPN Bipolar Junction Transistors with either 250-MeV protons or 10-keV X-rays shifts the input characteristics to lower values of VBE while degrading the current gain and drive current. The degradation is consistent with increased recombination in the neutral base and emitterbase depletion region. A decrease in collector current following proton irradiation suggests that recombination in the neutral base is significant. At a given ionizing dose, degradation is worse for proton irradiation than for X-ray irradiation due to the presence of displacement damage and a higher charge yield. A comparison of degradation produced by the two radiation sources suggests that ~40% of the excess base current resulting from 250-MeV proton irradiation is due to ionization damage. When compared with previous results for other devices, these results suggest that ionization-to-displacement damage ratios in bipolar devices may increase with proton energy in a way that is consistent with trends in charge yield and NIEL.

INTRODUCTION

THE current gain of bipolar junction transistors is important in satellite amplification applications such as radio transmitters and RF power generation [1]. Energetic protons in space degrade bipolar current gain by producing both ionization damage in the oxide overlying the emitter-base (E-B) junction and displacement damage in the semiconductor bulk [2]. In contrast, 10-keV X-rays produce only ionization damage, since the secondary electrons that they produce have energies below the displacement damage threshold [3]. Consistent with an approach for damage separation outlined in ASTM E1855-15 [4], Arutt, et al. have estimated the contributions of ionization damage to 4-MeV proton-induced degradation of bipolar devices from several technologies by comparing the proton responses to those of 10-keV X-rays [5], [6]. To date, however, ratios of ionization damage and displacement damage at larger proton energies, characteristic of radiation environments in low-earth orbits [7], have not been examined. In this work, the portion of proton-induced degradation due to ionization damage is estimated for a commercial bipolar transistor following irradiation with 250-MeV protons. The amount of ionization damage at the larger proton energy is greater than that reported for 4-MeV protons by a factor of more than two, suggesting that ionization-to-displacement damage ratios in bipolar devices may depend strongly on proton energy. The trend in damage ratios is consistent with the dependencies of charge yield and NIEL on proton energy. Mechanisms leading to current gain degradation through increased base recombination are reviewed. Differences in degradation due to radiation source type are related to the relative amounts of ionization damage and displacement damage accumulated in each case. Finally, implications for using proton irradiation to screen bipolar devices for displacement damage are discussed.