Characterization and modeling of proton radiation effects in linear bipolar devices and circuits

Linear microcircuits (e.g., operational amplifiers) manufactured with bipolar junction transistors (BJTs) are susceptible to radiation damage caused by protons. System engineers must consider this susceptibility when implementing electronics for use in the proton-rich space environment. In order to develop reliable, low-cost techniques for qualifying linear circuits for use in space applications, mechanisms of proton radiation effects at the circuit and device level must be understood and characterized in detail. Through an analysis of experimental data, degradation mechanisms for transistors and circuits are identified and analytical models for proton radiation effects are presented.; The BJTs used in linear circuits are vulnerable to protons because exposure to these particles increases bulk recombination, caused by displacement damage, and surface recombination, caused by ionization damage, and subsequently decreases current gain. Low-cost x-ray irradiations give good estimates of the ionization damage caused by protons. However, since x-ray sources cause relatively insignificant amounts of displacement damage, neutron irradiations can be used to analyze the susceptibility of BJTs to proton-induced lattice displacement. In this work, the results of proton, neutron, and x-ray irradiations on operational amplifier circuits are compared. The data reveal that the circuits' susceptibilities to either displacement or ionization damage are strong functions of processing variables related to the circuits' input transistors. Analytical models that describe the functional relationship between the electrical response of BJTs and processing parameters are used to determine whether transistor degradation is caused primarily by bulk displacement, ionization damage, or a combination of both. Furthermore, in this work, a previously unidentified proton radiation effects mechanism, non-linear proton defect interaction, is characterized. The data show that the sum of independent measurements of ionization- and displacement-induced degradation in bipolar parts does not equal the degradation due to an equivalent amount of proton damage. Device simulations and analytical modeling on BJTs demonstrate that a primary cause for these non-linear characteristics is the combined effects of ionization-induced oxide charge and displacement-induced bulk traps on subsurface bulk recombination.