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The present work demonstrates, for the first time, the impact of back-end-of-line (BEOL) design on the electrical reliability of SiGe heterojunction bipolar transistors (HBTs). Mixed-mode and high-current stress were performed for four different SiGe HBT variants designed with varying levels of dummy metal over-layers. The avalanche multiplication factor was found to be insensitive to changes in the BEOL, and thus the classical mixed-mode degradation was found to be similar across all BEOL variants. Meanwhile, high-current stress showed that adding more dummy metal layers alleviated the current gain and base current density degradation by 30% and 100%, respectively. Both the mechanical stress and temperature differences due to additional dummy metal layers were investigated using calibrated technology computer-aided design (TCAD) simulations. To assess RF implications, small-signal transition frequency ( ${f}_{T}$ ) improved by about 21%, and large-signal power added efficiency (PAE) increased by about 4% while the RF breakdown remained unchanged. The present study sheds light on the impact of reliability on dummy BEOL design, as well as its potential performance enhancement for circuit design in a manner that incurs no additional concern for electrical reliability under nominal conditions.

The total-ionizing-dose (TID) responses of silicon and low-loss silicon-nitride (SiN) integrated waveguides are evaluated. Mach-Zehnder interferometers (MZIs), which allow for both TID-induced changes in effective refractive index ( $n_{\mathrm { eff}}$ ) and transmission losses to be observed, were exposed to 10-keV highly localized X-ray pulses facilitating very high dose irradiation for small exposure areas. TID-induced shifts in $n_{\mathrm { eff}}$ and transmission losses were observed for both waveguide types above 3 Mrad(Si), with the silicon waveguides exhibiting better radiation resilience for both metrics. Data collected were used to create Ansys Lumerical simulations to propose potential mechanisms of TID-induced degradation in waveguides. Furthermore, to better understand the effects of $n_{\mathrm { eff}}$ degradation on other passive components, both silicon and SiN TID-damaged ring resonators were simulated in MATLAB. Differences in $n_{\mathrm { eff}}$ changes and transmission losses imply that for high dose environments (>10 Mrad(Si)), when comparing waveguide types, silicon waveguides will provide similar loss performance and comparably smaller shifts in $n_{\mathrm { eff}}$ compared to typically lower-loss SiN waveguides.

Three third-order digital modulation schemes, rectangular 8-quadrature amplitude modulation (8-QAM), 8-phase shift keying (8-PSK), and star 8-QAM are compared for RF receiver-level single-event upset (SEU) sensitivity using laser pulses to strike the low-noise amplifier (LNA). Star 8-QAM had significantly better SEU resilience than 8-PSK and rectangular 8-QAM, suggesting that the choice of the constellation mapping could be effective for mitigating SEUs due to single-event transients (SETs) in the LNAs of RF receivers.

Radio frequency (RF) communications systems in space flight are subject to single-event upsets (SEUs) due to dropout of the local oscillator (LO) during a single-event transient (SET), named here as single-event dropout (SEDO). If the duration of the SEDO is substantial, it inevitably compromises data. To help alleviate SEUs due to SEDO, the present work compares the dropout dynamics and recovery times of two types of RF $\boldsymbol {LC}$ oscillators with matched performance: the cross-coupled and the differential-Colpitts. The SEDO responses of both oscillators were tested using a pulsed laser to deposit charge via a two-photon absorption (TPA) process. For matched electrical performance and laser excitation conditions, the Colpitts oscillator demonstrated $14\times $ faster recovery. This improved response was examined using a hybridized circuit/technology computer-aided design (TCAD) simulation approach, and it was determined that a lower impedance at the bases of critical oscillating transistors naturally reduces the SEDO sensitivity for Colpitts oscillators. While cross-coupled oscillators are widely used, the present work demonstrates that Colpitts oscillators should instead be considered in frequency synthesizers to mitigate SEUs due to SEDO in oscillators.

Standard digital modulation schemes are compared for receiver-level single-event upset (SEU) sensitivity. Single-event transients (SETs) on the wideband silicon–germanium (SiGe) low-noise amplifier (LNA) carrying on–off keying (OOK), binary phase-shift keying (BPSK), and frequency-shift keying (2-FSK) modulated data were induced using laser pulses. Both the modulation scheme and its detection method had a significant impact on the SEU sensitivity of the receiver. The SET sensitivity and noise sensitivity of the modulation schemes and demodulation techniques were correlated. Therefore, designing a receiver to be more robust to noise inherently makes it more robust to SETs. For space missions that anticipate a high flux of radiation, taking SETs into account when choosing the radio frequency (RF) modulation scheme and the demodulation method may be important to avoid underestimating the total bit-error rate (BER) when other system trade-offs are compared against the system BER.

A comparison of laser-induced single-event transients (SETs) in silicon-germanium heterojunction bipolar transistor (SiGe HBT) variants designed for high-speed (HS) applications and high-breakdown (HB) applications is presented. A significantly lower amplitude SET response at low laser pulse energies was observed in the HS device compared to the HB device. At high laser pulse energies, however, the transient amplitudes converged and produced a nearly identical response. A 3-D technology computer-aided design (TCAD) model of a SiGe HBT was used to understand the differences between the observed SET responses. During an SET produced by a low laser pulse energy, the mean electric field in the collector-base (CB) junction of a simulated HB device is shown to have a greater magnitude across the depletion region compared to that of its HS counterpart. Motivated by the proportional relationship between drift current and CB junction electric field, a greater breakdown voltage device produced a larger SET response. During an SET produced by a high laser pulse energy, the charge from the SET exceeded the collector doping in both the HS and HB SiGe HBT. This creates a conductive path to the output terminal, removing the dependence of collector doping on SET amplitude. The results of this study should help inform design choices of which device breakdown variant should be used in a given circuit if SETs are a major consideration for the application.