Voltage-controlled oscillators (VCOs) are key components in providing periodic signals that are used in RF communications systems for time synchronization and signal processing. However, the stand-alone VCOs can have poor phase noise performance and experience frequency drift; therefore, injection locking can be implemented in a VCO to stabilize these performance metrics. Injection-locked VCOs (ILVCOs) in satellite communications or radar systems can be subject to total-ionizing dose (TID) effects, which could alter the performance of the oscillator. The present work analyzes the effects of TID in a 5-GHz ILVCO using an X-ray source and demonstrates that the locking range increases and phase noise of the ILVCO improves with total dose. This unexpected result was analyzed using circuit simulations and shows that the negative threshold voltage shifts induced by TID may be posited to the increase of the ratio of injection signal current to oscillator signal current, which may ultimately extend the locking range. Consequently, the increase in the strength of the injection signal due to TID may also lead to the decrease of phase noise. These results suggest that the use of ILVCOs in satellite systems may be favorable as they are TID radiation tolerant compared to stand-alone oscillators.

Space exploration to “Ocean World” environments, such as Europa, that seek to find biosignatures of extraterrestrial life requires robust and reliable electronics for sensing, data processing, motor/actuator control, and communication. Commercial-off-the-shelf (COTS) components are designed for commercial or military-spec (milspec) temperature ranges. Wide-temperature applications require a shielded “Warm Electronics Box (WEB)” to keep COTS components operational. However, COTS components are also designed with little to no regard for radiation tolerance. In addition, size, weight, and power constraints may limit the use of “WEB” based approaches. Electronic system designs must be tailored to the extreme conditions under which they will operate. The presence of extreme cold temperatures and high radiation adversely affects the parameters of CMOS and bipolar junction transistor devices over time, compromising the reliability of electronic systems. This paper reviews device performance degradation issues induced by extreme cold and high-ionizing irradiation and promotes a strategic circuit design philosophy that exclusively uses silicon germanium heterojunction bipolar transistors and silicon P-channel MOSFETs to capitalize on their favorable performances in cryogenic and high-radiation environments.

We investigate silicon-germanium heterojunction bipolar transistor (SiGe HBT) collector region impact ionization and transit time performance limits at 300 and 100 K using a commercially available Boltzmann transport equation (BTE) solver based on the Monte Carlo (MC) method. We demonstrate that the carrier energies computed by the solver can be used to accurately predict measured device multiplication factors (M-1) at both temperatures using the simple Okuto-Crowell model. We then use computed electron velocity and energy profiles to automatically discover a Pareto front using Bayesian optimization techniques. Finally, we investigate collector profiles along the Pareto front to provide insight into optimal collector profile design for both 300 and 100-K operation. The results suggest that collector profiles designed along the Pareto front at 300 K will likely lie along the Pareto front at 100 K.

This work investigates single-event effects (SEEs) in integrated optical transceivers by experimentally examining subsystem-level vulnerabilities and their contributions to system-level upsets using pulsed-laser testing. A silicon-on-insulator (SOI) electronic-photonic integrated circuit (ePIC) implementing an on-off keying (OOK), intensity-modulated direct-detection (IM/DD) link is used as a test platform. Individual subsystems are selectively targeted to study single-event transient (SET) generation and propagation across electrical and optical domains. An analytical model is developed to describe electrical-to-optical SET propagation and identify subsystem-specific parameters influencing transient behavior. Experimental results show that, within this platform, SET duration is a key factor in single-event upset (SEU) severity, as long transients lead to extended multi-bit upsets (MBUs). The results of this work highlight the importance of subsystem-level transient characterization to guide targeted radiation-hardened-by-design (RHBD) strategies for robust optical communications in space environments.

Silicon (Si) photonic integrated circuits (PICs) allow for the combination of high-speed Si electronics with integrated photonic components on a single chip. However, integrated photonic modulator designs are often limited by the driving electronics since, modulators often require large voltage swings from high-speed electrical driving circuits. Due to inherent gain-bandwidth trade-offs, creating high-speed voltage drivers with large voltage swings is difficult without considerable design effort. The use of Ring-assisted Mach-Zehnder Modulator (RA-MZM) schema allows for compact modulator design while decreasing V pi, resulting in less restrictive driving voltage requirements. Electronic requirements can be further reduced by employing a single-ended push-pull scheme for the RA-MZMs and exploiting intentionally over- and under-coupled RA-MZM designs targeting phase or amplitude cancellation operation. RA-MZM design optimization allows for more lenient voltage swing design requirements at the electronic-photonic interface, facilitating modulation at higher speeds while still preserving data fidelity.

single-event-effect (SEE) responses of microring modulators (MRMs) are evaluated. Charge was introduced using a pulsed-laser system capable of locally injecting electron-hole pairs (EHPs) via two-photon absorption (TPA). Both electrical single-event transients (SETs) and optical SETs (OSETs) were collected for different input wavelengths, anode biases, and laser pulse energies (PEs). Laser-equivalent linear energy transfer (LETL) threshold sensitivity, SET amplitude, and SET duration, were found to be highly dependent on the operational bias. Wavelengths near resonance conditions often used in MRM applications exhibit the highest OSET sensitivity. Reasons for, and implications of, these bias dependencies are analyzed through free-carrier-plasma-dispersion (FCPD) theory and literature on pump-probe experiments. Analysis supports transients occur due to changes in the refractive index incurred during carrier injection, as well as thermal generation from free-carrier absorption (FCA). OSETs are observed down to a minimum PE = 207 pJ, corresponding to an LETL of 5.2 MeV & centerdot; cm(2)& centerdot; mg(-1), relevant for space environments and orbital applications. Contrary to existing literature claims, the theory, data, and analysis presented in this work suggest that not all photonic components are SEE-resilient, with MRMs exhibiting the highest OSET sensitivity of any photonic component reported to date.

Previous work suggests that optimization of a signal constellation could be used to reduce single-event upset (SEU) likelihood, but focuses on isolated circuit components, not systems. The present work extends the process of digital modulation scheme selection for SEU-resilience to a generalized procedure for a full radio frequency (RF) receiver. Two custom modulation schemes are optimized for Manhattan or Euclidean distance to minimize the system-level SEU impact of an single-event transient (SET) within individual circuits. Pulsed-laser single-event effect (SEE) testing is utilized to evaluate SEU-hardening of a silicon-germanium (SiGe) wireless receiver operating on these custom modulation schemes. Basic receiver archetypes are used as test cases to determine the efficacy of system-level radiation hardening through modulation scheme selection. Results demonstrate that intentionally selecting modulation schemes based on known component sensitivity can reduce system-level SEU rates.

The single-event effect (SEE) and total ionizing dose (TID) responses of thermally activated vanadium dioxide (VO2) radio frequency (RF) switches are investigated for use in radiation-intense environments. Experimental results demonstrate that VO2 switches maintain stable switching behavior and RF performance after exposure to 1 Mrad(SiO2) of $\gamma $ -ray TID, with marginal change in resistance in the insulating state and low change in resistance in the conductive state. No substantial degradation in insertion loss or isolation was observed. TID damage originates from the creation of oxide traps, whose creation is a strong function of exposure temperature, and while the traps are evident in the insulating (drift-based transport) state, they are less prevalent in the conductive state. Heavy-ion testing was conducted using 16 MeV/amu ions, with linear energy transfer (LET) values up to 55 MeV-cm2/mg, and no transient events or performance perturbations were observed in either the insulating or conducting states. Simulations incorporating carrier injection support the SEE results, indicating that localized phase changes or trap accumulation have limited influence on system-level operation. The results highlight the intrinsic radiation resilience of these VO2-based switches and support their potential for high-frequency space-borne communications systems.

The present work investigates the performance of SiGe heterojunction phototransistors (HPTs) fabricated in a commercially available 130-nm SiGe BiCMOS (8XP) technology, with emphasis on their unique ability to function not only as photodetectors, but also as the core active devices within an optical receiver. Detailed characterization demonstrates that electrical and optical figures-of-merit track closely, highlighting the transistor-like nature of SiGe HPTs and enabling compact modeling within standard circuit frameworks. The dependence of responsivity on external base resistance and bias conditions is quantified, showing that responsivity is not a fixed parameter, but can be engineered through circuit-level choices. Geometry and layout tradeoffs are also explored across multiple SiGe HPT variants, where optical window size and contact configuration determine the balance between responsivity, bandwidth, and fill factor. The results highlight the expanded design space available when SiGe HPTs are integrated directly into optical receiver front ends, offering application-specific tradeoffs not accessible with conventional photodiode (PD)-plus-transimpedance amplifier (TIA) architectures.

Pulsed, focused electrons are presented as a possible surrogate to single-event effect (SEE) testing. Electrons have the capability to penetrate deep into a material and provide an equivalent linear energy transfer (LET) in silicon to that of a heavy ion. Through experiment, modeling, and simulation of a large area pin photodiode, we have shown that this method can act as an alternative way to test for SEEs as long as the spot size of the electron bunch is small enough to saturate the local carrier collection dynamics. There are no known fundamental physical limitations to preclude pulsed, focused electrons as a tool to be used for predictive SEE capability.

The operability and total-ionizing-dose (TID) response of 45-nm annular RF silicon-on-insulator (SOI) nFETs are evaluated and compared with standard layouts. All devices were exposed to 10-keV X-rays, up to a dose of 1 Mrad(SiO2), at both high-gate/low-drain and low-gate/high-drain irradiation conditions. Differences in damage response to dc and small-signal performance between samples are observed as a result of TID-sensitive oxides and their proximity to key transport regions of the devices. Annular FETs are more TID tolerant than standard nFETs while showing small RF performance tradeoffs as well as lower drive currents and higher threshold voltages. Technology computer-aided design (TCAD) is used to isolate critical oxides and damage mechanisms in annular and standard layouts to help confirm experimental data and observed damage trends. Taken together, these results suggest that annular FETs represent a valid TID-hardening approach in small-lithography RF silicon-on-insulator complementary metal-oxide semiconductor technology platforms for both dc and RF applications.

Space-borne wireless communications systems have become ubiquitous with the advent of commercial space flight. To support robust wireless data transmission in Earth-orbiting and deep-space applications, a framework has been developed for radio frequency (RF) designers and radiation-effects engineers to identify, model, visualize, and test single-event effects (SEEs) in wireless receivers. Digital RF communications receivers are introduced, including the constellation diagram, an important visualization tool. Then, the generation of single-event transients (SETs) is presented in multiple layers, starting from transistors, building to SETs at the outputs of each circuit block, and culminating in the response of the full receiver system. Circuit blocks addressed in this work include a low-noise amplifier (LNA), a downconversion mixer, and a voltage-controlled oscillator (VCO). Analytical theory and numerical simulation are synthesized, accompanied by pulsed-laser SEE testing, to give an understanding of how deposited charges in constituent transistors convert to SETs and single-event upsets (SEUs). As an example case, a SiGe-BiCMOS direct-conversion receiver carrying 100-Mbaud quadrature phase shift keying (QPSK) at the X-band (8-12 GHz) is characterized using pulsed-laser SEE testing. This manuscript provides a useful review and analytical template that enable future designers and radiation-effects engineers to: 1) model SET propagation in a wireless receiver a priori, without testing full systems; 2) identify the SEE mechanisms present in a wireless receiver with knowledge of the circuit components present; and 3) determine sensitive transistors and circuits to develop informed test plans for worst case predictions.

In this work, the reliability and performance characteristics of silicon-germanium heterojunction bipolar transistor (SiGe HBT) cascode amplifier cells are investigated. In particular, this study investigates the tradeoffs of using transistors scaled for maximum performance or for increased breakdown voltage in the common-base stage of the cascode. The cascode structures are investigated for their dc operating limits, as well as their small- and large-signal performance, and their electrical reliability. Simulations and measurements are performed to determine how to minimize the performance tradeoffs and maximize the reliability improvement of each device type. It is shown that the difference in peak unity cutoff frequency (f(T)) is much smaller between the high-performance (HP) and medium breakdown (MB) cascodes than for the individual devices, and that biasing the collector-base (CB) device past its base current reversal point further increases f(T) of the cell by 10% or more. Reliability data show that more reliable cascode cell depends on the biasing condition and load line of the cell. Overall, results show that bias and load line can be changed to improve both the performance and reliability of cascode cells.

This study investigates the effects of total ionizing dose (TID) damage on silicon photonic (SiPh) phase shifters using Mach-Zehnder modulators (MZMs). By employing a microbeam X-ray source to irradiate one phase shifter in the MZM structure, we were able to isolate radiation-induced effects on phase shifter performance. The results demonstrate three key TID effects on the Si phase shifter: radiation-induced attenuation (RIA), radiation-induced refractive index change (RIRIC), and phase shifter pinch-off. Using the measured MZM transfer function, we developed formulations of radiation-induced effect, providing a quantitative tool for assessing how TID impacts SiPh modulator performance. Our findings suggest that multiple factors influence the variations in TID effects observed across different dose levels, including TID-induced changes to material structure, free carrier modulation, and band-to-band absorption due to radiation-induced defects. This study highlights the complexity of radiation effects in SiPh devices and provides insights that can guide future efforts to improve radiation tolerance in SiPh systems operating in extreme environments.

This work presents two low noise amplifiers (LNA) operating at 225 GHz utilizing a novel coupled-line coupler gain-boosting technique that achieves increased power gain compared to conventional common-emitter stages with no additional power consumption. This technique is demonstrated and fabricated in a 90 nm SiGe BiCMOS process technology. The seven-stage and 15-stage LNAs operating at 225 GHz exhibit a measured gain of 5 dB and 11.7 dB, respectively. To the best of the authors’ knowledge, this work demonstrates the first implementation of a coupled-line coupler based gain-boosting technique for use in sub-THz amplifiers operating above f max /2.

A high-performance SiGe heterojunction phototransistor (HPT) with peak responsivity of 12.5 A/W at 850 nm and an optical transition frequency of 150 GHz is developed in a commercial SiGe BiCMOS technology platform by optimizing the lateral geometry of SiGe heterojunction bipolar transistors (HBTs). An optical receiver based on the proposed SiGe HPT with >40 dBO gain and 10 GHz bandwidth is demonstrated.

The application of radiation-hardening by design (RHBD) to the low-noise amplifier (LNA) in an RF communications receiver has promise for improving data fidelity in applications subject to single-event effects (SEEs). In order to overcome the challenges of empirically modeling single-event transient (SET) propagation in RF receivers, calibrated technology computer-aided design (TCAD) is used to perform mixed-mode simulations and identify viable RHBD approaches for SiGe cascode LNAs. Example results at X-band (8-12 GHz) are used to demonstrate these approaches. Finally, the findings in the present work are organized into a proposed radiation-hardening design flow to aid circuit and system engineers who wish to consider single-event-upset (SEU) rates in the performance of their LNAs.

Spectrum scanning enables a radio receiver to adapt to a dynamic spectral environment (i.e., interferers) with minimal time delay, thereby optimizing a data link in real time. This feature allows next-generation intelligent (cognitive) radio systems to be able to make dynamic decisions such as component tuning for increased performance or reduced power consumption. With the growing deployment of satellite communications systems, spectrum sensing has also been proposed as a potential solution to mitigate signal interference while simultaneously optimizing spectral utilization in increasingly crowded channels. Recently, substantial research has been carried out using compressed sensing (CS) to perform the spectrum scanning task, since it facilitates sub-Nyquist sampling and rapid spectrum recovery with reduced overhead. The present work outlines the theory behind the Modulated Wideband Converter (MWC) compressed-sensing spectrum-scanning architecture, numerically analyzes the probability of signal recovery when receivers are subject to multi-tone inputs, and compares various sparse vector recovery algorithms, all for realistic terrestrial-to-low-earth-orbit (LEO) radio-frequency (RF) link conditions. Both cases in which the signal sparsity is known and unknown are considered. We conclude with recommendations on signal recovery techniques and provide a summary of recovery probability under various cases of signal-to-noise ratio degradation, such as antenna-pointing error, free-space path loss, and multi-path fading effects.

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.

This work investigates the automatic design of silicon-germanium (SiGe) heterojunction bipolar transistor (HBT) germanium profiles utilizing Bayesian optimization in a commercial TCAD engine. The time-intensive nature of device simulation renders standard numerical optimization strategies infeasible, as gradients are expensive to approximate, and candidate objective functions, such as device minimum noise figure (NFmin), maximum transit frequency (f(T)), or breakdown voltage (BVCEO) are often not well-behaved functions of design variables. Bayesian optimization is a strategy that seeks a global optimum of an expensive-to-evaluate function of which little underlying structure is assumed. Here, we model the output of TCAD simulations as such a function and show that Bayesian optimization is capable of exploring the Ge profile design space, providing optimized profiles in as few as 30 simulation iterations.