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This investigation examines the physical mechanisms that can increase the variability of both p-n junctions and silicon–germanium heterojunction bipolar transistors (SiGe HBTs) at cryogenic temperatures. The important operative mechanisms responsible for device parameter variability include bandgap narrowing due to heavy doping, mechanical stress, and the Ge profile. The impact of direct tunneling on cryogenic parameter variability in SiGe HBTs is also examined. Measurement results are compared with TCAD simulations to provide additional insights, and possible mitigation methods are discussed.

This paper provides insight into the transport mechanisms of the collector current in SiGe HBTs operating at cryogenic temperatures and compares three technology generations of devices. Based on the experimental data, a method to differentiate direct tunneling from quasi-ballistic transport is proposed. Measurements indicate that direct tunneling becomes more significant at cryogenic temperatures. The effects of technology scaling on the direct tunneling were investigated using TCAD. Direct tunneling was found to be sensitive to the base width and the Ge profile. It is predicted that without an increase in the Ge content, direct tunneling may dominate over quasi-ballistic transport at the limits of technology scaling.

We investigate high current stress mechanisms and demonstrate how Auger hot carriers can damage both oxide interfaces and polysilicon regions of the emitter and base. A new current gain enhancement (CGE) effect is proposed, which involves hot-carrier damage to the polysilicon emitter and extrinsic base leading to the degradation of the associated minority carrier mobilities. We demonstrate the different CGE mechanisms in SiGe HBTs under forward and inverse modes of operation. The hot-carrier damage responsible for CGE at high injection is explored in depth with the help of TCAD simulations. Evidence for this effect has been gathered with good statistical significance from various stress conditions, various technologies, complimentary (NPN + PNP) devices, and from dc and ac measurements. The new polysilicon degradation mechanism proposed in this paper has been generalized and is important for accurately modeling the changes in base resistance and current gain ( $\beta$ ) at high injection, where circuits are typically biased to extract maximum device performance.

The implementation of a “superjunction” collector design in a silicon–germanium heterojunction bipolar transistor technology is explored for enhancing breakdown performance. The superjunction collector is formed via the placement of a series of alternating the p/xn-doped layers in the collector-base space charge region and is used to reduce avalanche generation leading to breakdown. An overview of the physics underlying superjunction collector operation is presented, together with TCAD simulations, and a parameterization methodology is developed to explore the limits of the superjunction collector performance. Measured data demonstrate the limitations explored in simulation.

The doping profile of silicon-germanium heterojunction bipolar transistors (SiGe HBTs) is modified to enhance inverse-mode (IM) device operation. Device improvements are presented in this paper, along with the impact the alterations have on the radiation effects response. This investigation represents the first published occurrence of a radiation-hardening-by-process approach in a SiGe HBT technology. Results show that improving IM performance can degrade the radiation tolerance of the structure. Total ionizing dose and single-event transient (SET) results are provided along with an analysis that utilizes TCAD simulation. An additional profile modification using an implanted vertical superjunction is included in this paper to expand upon how nonradiation specific device modifications can impact SETs.

Safe-operating-area (SOA) in a high-voltage complementary silicon–germanium (SiGe) (= n-p-n + p-n-p) on silicon-on-insulator (SOI) technology is investigated from 24 °C to 300 °C. Three key reliability degradation regions are identified, including: 1) high-current; 2) mixed-mode; and 3) high-power. The degradation mechanisms, which are operative, including Auger damage, mixed-mode damage, and electrothermal runaway as well as their temperature dependences are identified. Mixed-mode damage exhibits a strong negative temperature coefficient for both n-p-n and p-n-p SiGe heterojunction bipolar transistors (HBTs) up to 300 °C, which leads to an increase in the SOA from a high-voltage perspective. Electrothermal boundaries are also explored by finding ${J}_{C,{\textsf {crit}}}$ and ${V}_{{\textsf {CB}},{\textsf {crit}}}$ across the ${J}_{C}$ – ${V}_{\textsf {CB}}$ plane up to 300 °C. Both n-p-n and p-n-p SiGe HBTs show an increase in the SOA for the electrothermal boundary as temperature increases. High-current-induced damage, on the other hand, exhibits a positive temperature coefficient, which implies that high current drive should carefully be considered when using SiGe HBT circuits operated in a high-temperature environment. However, at very high temperatures (>200°C), the high current damage processes show annealing properties, which implies that at sufficiently high temperatures, annealing can dominate over Auger damage and potentially extend the SOA of the technology.

Total ionizing dose (TID) effects are evaluated for a high-voltage (>30 V) complementary SiGe on SOI technology. Devices are irradiated with 10-keV X-rays at doses up to 5 Mrad(SiO2). The results depend strongly on collector-to-emitter bias, in both forward- and inverse-mode. An anomalous reduction in current gain at high injection in forward-mode operation is observed at doses >500 krad(SiO2). Calibrated 2-D TCAD simulations suggest that this high injection phenomenon is primarily due to interface traps near the STI/Si interface, which is exhibited as a collector resistance increase in the forward Gummel characteristics. Additionally, a strong collector doping dependence is observed, which indicates that this is primarily driven by the thick and lightly doped collector used in this technology. These results illustrate, that high concentrations of interface traps at the STI can have a strong impact on the forward-mode TID response of SiGe HBTs.

This paper examines the fundamental reliability differences between n-p-n and p-n-p SiGe HBTs. The device profile, hot carrier transport, and oxide interface differences between the two device types are explored in detail as they relate to device reliability. After careful analysis under identical electrical stress conditions for n-p-n and p-n-p, the differences in activation energies for the damage of the oxide interfaces of the two devices is determined to be the primary cause for accelerated degradation seen in p-n-p SiGe HBTs. An analytical model has been adapted for simulating these aging differences between p-n-p and n-p-n devices. This paper has significant implications for predicting the degradation of complementary SiGe HBTs and even engineering future generations with well-matched n-p-n and p-n-p device-level reliability.

The capability of inverse-mode (IM) silicon- germanium (SiGe) heterojunction bipolar transistors (HBTs) for the mitigation of single-event transients (SETs) under large-signal operation was investigated in an RF down-conversion single- balanced mixer using a through-wafer, two-photon absorption pulsed-laser beam experiment and TCAD heavy-ion simulations. The IM SiGe HBTs replace conventional forward-mode (FM) SiGe HBTs in the differential pair, which provides full current steering for frequency mixing operation. Under steady-state conditions, the IM SiGe HBT differential pair exhibits smaller transient peaks with shorter durations compared to the FM SiGe HBTs. In addition, under the injection of a local oscillator (LO) signal with large swing, the IM SiGe HBTs show faster recovery (50% reduction in the best case) from the impact of SETs. In the frequency domain, it is observed that IM SiGe HBTs produce less distortion at the output for an intermediate frequency below 1 GHz. Based on the performance comparison between FM and IM SiGe HBT down-conversion mixers, system design guidelines to compensate the noise figure degradation associated with using IM SiGe HBTs are discussed.

This paper investigates single-event effects in a W-Band (75-110 GHz) SiGe HBT down-conversion mixer intended for use in a space-based remote sensing radar system. Transient pulse propagation to the output of the mixer as a linear time variant system is analyzed theoretically. This study facilitates the understanding of transient propagation in RF receivers. Device- and circuit-level simulations were conducted to verify the results of the proposed theory. A two photon absorption laser was used to induce transients on different SiGe HBTs within the circuit to assess the impact of SETs on performance. This study shows that significant transients can be produced at the output of the mixer, which can potentially corrupt the received data or received pulse of the radar. It is shown that a differential double-balanced structure can effectively eliminate some of the transients at the output of the mixer. To the authors' best knowledge this is the first study of single event transients conducted on a millimeter-wave SiGe circuit.

The effects of negative feedback, both external and internal, on single event transients (SETs) in SiGe HBT analog circuits are investigated. In order to examine internal negative feedback effects, basic common-emitter NPN current mirrors, with and without emitter degeneration resistors, are utilized. A Wilson current mirror and a Wilson mirror with its intrinsic external feedback removed are used to study external negative feedback effects under the influence of laser-induced single events. The measurement data clearly show notable improvements in SET response that can be made by employing both internal and external negative feedback. The peak transient in the output current is reduced, and the settling time upon a laser strike is shortened significantly by negative feedback. All four investigated current mirrors were fabricated with IBM 8HP 130 nm SiGe BiCMOS technology.

We explore different vertical profile designs with optimized emitter-base (EB) junctions targeting both constant current gain $(\beta)$ across temperature and broadened $\mathbf{f}_{\mathbf{T}}/\mathbf{f}_{\max}$ curves for improved large-signal linearity. This work explicitly examines achieving a temperature-independent $\beta$ via profile design in SiGe HBTs, and explores the limitations using triangular and ledge-based Ge profiles at the EB junction. The effects of base width and the EB junction separation length are also investigated for reduced parasitic capacitance and improved frequency response at low-bias currents. This work presents the underlying theory, along with the measured results for the two optimization targets, both of which should aid in designing circuits with better linearity and stability across bias and temperature corners.

We investigate and compare the hot-carrier degradation of SiGe HBTs under both traditional mixed-mode electrical stress conditions and high-current electrical stress conditions using measured stress data and an in-depth analysis of the underlying degradation mechanisms. While large electric fields are the driving force in mixed-mode hot-carrier degradation, the Auger recombination process is shown to be the hot-carrier source under high-current stress conditions. Auger hot-carrier degradation shows a positive temperature dependence, unlike mixed-mode degradation, due to the temperature dependence of Auger recombination and its energy distribution function. We also use calibrated TCAD simulations to explain an unexpected stress threshold behavior that occurs due to the formation of a potential well in the neutral base region, and to explore a field-compression effect at the collector/subcollector junction that contributes to trap formation at the shallow trench isolation oxide interface.

This paper presents the results of an investigation of the steady-state safe operating conditions for large-signal silicon-germanium (SiGe) heterojunction bipolar transistor (HBT) circuits. By calculating capacitive currents within the intrinsic transistor, avalanche inducing currents through the transistor junctions are isolated and then compared with dc instability points established through simulation and measurement. In addition, calibrated technology computer-aided design simulations are used to provide further insight into the differences between RF and dc operation and stress conditions. The ability to swing the terminals of a SiGe HBT beyond the static $I$ – $V$ conditions coincident with catastrophic breakdown is explained. Furthermore, hot-carrier effects are also compared from multiple perspectives, with supporting data taken from fully realized $X$ -band and $C$ -band cascode driver amplifiers. This analysis provides microwave circuit designers with the framework necessary to better understand the full-voltage-swing potential of a given SiGe HBT technology and the resultant hot carrier damage under RF operation.

The implementation of a “superjunction” collector design in a silicon-germanium heterojunction bipolar transistor is explored for enhancing breakdown performance. The superjunction collector is formed through the placement of a series of alternating pn-junction layers in the collector-base space charge region to modify the carrier energy profile and reduce avalanche generation. An overview of the physics underlying superjunction collector operation is presented with TCAD simulations, and practical superjunction design techniques are discussed. The first measured data on a superjunction collector is also presented and shows a 57% improvement in breakdown performance.

We study mixed-mode stress degradation in SiGe HBTs using a novel physical TCAD model in which the processes of hot carrier generation within the semiconductor, carrier propagation to the oxide interface, and formation of interface traps are directly modeled. Transient degradation simulations using a calibrated 2-D SiGe HBT model correlate well with measured data. With this novel simulation tool, we investigate the bias dependence and location of interface traps and show that secondary holes produced by impact ionization are the dominant carrier to damage the emitter-base (EB) spacer oxide interface, confirming previously reported results. We also compare in detail trap formation at the EB spacer and shallow-trench-isolation (STI) oxide interfaces as a function of time and stress condition. At the STI oxide interfaces, we find that hot electrons and holes each dominate trap formation in different regions, and the hot carriers that reach the STI predominately originate outside of the selectively implanted collector, revealing the important role played by dopant diffusion from the extrinsic base of quasi-self-aligned SiGe HBTs.

Profile optimization techniques are investigated for silicon-germanium heterojunction bipolar transistors (SiGe HBTs) intended for inverse-mode (IM) operation. IM device operation, also known as inverse active, involves electrically swapping the emitter and collector terminals and has been shown to improve the radiation tolerance of SiGe HBTs to single event transients (SETs). Multiple profile design variations are explored and trade-offs are analyzed with support of TCAD simulation. Modest design variations show marked improvement on IM performance while having minor impact on forward-mode (normal active) operation.