Silicon-germanium Heterojunction Bipolar Transistors Research Articles

A Physics-Based Circuit Aging Model for Mixed-Mode Degradation in SiGe HBTs

A physics-based silicon-germanium (SiGe) heterojunction bipolar transistor (HBT) aging model for mixed-mode stress based on the lucky-electron model and reaction-diffusion theory is developed for integration with compact models. An effective aging parameter extraction method is described, and the aging model parameters are fit for a modern SiGe HBT platform. The aging model is implemented as a wrapper in the Cadence Spectre circuit simulator. Device-level aging simulations are shown to be well-matched to measured degradation data. The aging model is further used to explore the effects of aging on a simple current mirror circuit, showing a decrease in mirror ratio with degradation.

Analytic Estimation of Thermal Resistance in HBTs

In this paper, we propose a new method for estimating the peak junction temperature and thermal resistance in modern heterojunction bipolar transistors (HBTs). The proposed method uses the temperature dependence of thermal conductivity of the material. The method is analytic in nature and does not require any iteration as opposed to the existing state-of-the-art model. This analytic method can easily include the available scaling relations relevant to specific technology to estimate the junction temperatures and thermal resistances of the corresponding transistors. The analytic model is tested against iterative self-consistent solutions for simple structures without any trench isolation and for structures corresponding to the ST Microelectronics B9MW technology that includes shallow and deep trench isolations. The model is slightly modified in order to include the effects from the back-end-of-line metal layers. The resulting analytic model is validated against the measured results for silicon germanium HBTs fabricated in ST Microelectronics B9MW technology.

Innovative SiGe HBT Topologies With Improved Electrothermal Behavior

This paper investigates alternative topologies of silicon germanium heterojunction bipolar transistors designed and fabricated in the state-of-the-art BiCMOS process from STMicroelectronics for improved safe-operating characteristics. Electrical and thermal behaviors of various structures are analyzed and compared, along with a detailed discussion on drawbacks and advantages. The test structures under study are different in terms of emitter-finger layouts as well as the metal stacks in the back-end-of-line. It is observed that the multifinger transistor structures having nonuniform finger lengths with wider area enclosed by the deep trench and higher metallization stacks yield an improved thermal behavior. Therefore, the safe-operating area of multifinger transistors can be extended without degrading the RF performances.

Analysis of temperature dependence of linearity for SiGe HBTs in the avalanche region using Volterra series

In this paper, linearity characteristic of silicon germanium (SiGe) heterojunction bipolar transistors (HBTs) at different temperatures in the avalanche regime is investigated by the Volterra approach incorporating with a physics-based breakdown network for the first time. Third-order intermodulation distortion (IMD3) decreases with increasing temperature in the impact ionization region due to lower nonlinear contributions from individual nonlinearity according to the Volterra analysis results. Calculated gain, output power, and efficiency of SiGe HBTs are in good agreement with measurement results in the avalanche region. This analysis with respect to temperature can benefit the reliability study of linearity for SiGe HBTs in the avalanche regime.

Impact of Bias Conditions on Total Ionizing Dose Effects of <inline-formula> <tex-math notation="LaTeX">$^{60}{\hbox{Co}}\gamma $</tex-math> </inline-formula> in SiGe HBT

The effect of bias condition on total ionizing dose (TID) of Silicon–Germanium heterojunction bipolar transistors (SiGe HBTs) is investigated. The SiGe HBTs are set at forward, saturated, cutoff, and all-grounded biases during $^{60}{\hbox{Co}}\gamma $ irradiation. After each irradiation stops, the forward Gummel characteristic and inverse Gummel characteristic are measured, and a 3-D simulation of TID for SiGe HBT is performed. The mechanism of TID in different bias conditions is obtained by analyzing normalized excess base current. The results show that the TID damages are different at various irradiation biases of the SiGe HBT, and the worst bias between forward and inverse Gummel characteristics exhibits inconsistently. The reason could be attributed to different defects produced and accumulated in oxide layers by irradiation at various bias conditions. To be specific, the oxide trap charges ( ${{\hbox{N}}_{\rm ot}}$ ) in emitter/base (E/B) Spacer is important to the forward Gummel characteristic, yet the ${{\hbox{N}}_{\rm ot}}$ in LOCOS determines the inverse Gummel characteristic. However, after long time irradiation, the interface states ( ${{\hbox{N}}_{\rm it}}$ ) both in E/B Spacer and LOCOS dominate the damage to the SiGe HBT despite in forward Gummel mode or inverse Gummel mode.

Total ionizing dose effects of domestic SiGe HBTs under different dose rates

The total ionizing radiation (TID) response of commercial NPN silicon germanium hetero-junction bipolar transistors (SiGe HBTs) produced domestically are investigated under dose rates of 800 mGy(Si)/s and 1.3 mGy(Si)/s with a Co-60 gamma irradiation source. The changes of transistor parameters such as Gummel characteristics, and excess base current before and after irradiation, are examined. The results of the experiments show that for the KT1151, the radiation damage is slightly different under the different dose rates after prolonged annealing, and shows a time dependent effect (TDE). For the KT9041, however, the degradations of low dose rate irradiation is higher than for the high dose rate, demonstrating that there is a potential enhanced low dose rate sensitivity (ELDRS) effect for the KT9041. The possible underlying physical mechanisms of the different dose rates responses induced by the gamma rays are discussed.

Influence of temperature on transit times and microwave noise performances of SiGe HBT

The influence of temperature (300 K and 40 K) on intrinsic transit times and microwave noise performances of silicon germanium (SiGe) heterojunction bipolar transistors (HBTs) is investigated. At 300 K, we compared measured and modelled S-parameters and four noise parameters, and we found a good agreement. At 40 K, we compared measured and modelled S-parameters, and we deduced noise performances from the S-parameter measurements. The electric model includes correlated junction noise sources and a proper extraction of the transit times involved in these sources. Moreover, the microwave noise model considers all the physical phenomena that impact noise performances in SiGe HBTs. We analysed three devices having different Ge content (10%–20%, 10%–25% and 10%–30%). At 40 K, the device with 10%–25% reaches one of the lowest base transit times (τB), the lowest minimum noise figure (NFmin), and the lowest equivalent noise resistance (Rn), for operation frequencies up to the maximum device dynamic performances (f ≈ fT) These results demonstrate the excellent potential to develop cryogenic applications of SiGe HBTs.

Noise Parameter Analysis of SiGe HBTs for Different Sizes in the Breakdown Region

Noise parameters of silicon germanium (SiGe) heterojunction bipolar transistors (HBTs) for different sizes are investigated in the breakdown region for the first time. When the emitter length of SiGe HBTs shortens, minimum noise figure at breakdown decreases. In addition, narrower emitter width also decreases noise figure of SiGe HBTs in the avalanche region. Reduction of noise performance for smaller emitter length and width of SiGe HBTs at breakdown resulted from the lower noise spectral density resulting from the breakdown mechanism. Good agreement between experimental and simulated noise performance at breakdown is achieved for different sized SiGe HBTs. The presented analysis can benefit the RF circuits operating in the breakdown region.

An Improved Noise Model for SiGe HBT With an Inductive Breakdown Network in the Avalanche Region

In this paper, an improved radio-frequency (RF) noise model is extended for silicon germanium (SiGe) heterojunction bipolar transistors (HBTs) by applying RF avalanche delay mechanism to investigate noise performance in the breakdown region where reliability is a concern. The impact of inductive feedback due to base–collector (BC) junction avalanche breakdown on noise performance is analyzed and explained by utilizing this improved noise model incorporating an inductive network. The avalanche effects on noise sources are verified and explained physically by the dead-space theory. The contributions of electrons and holes to the avalanche noise are taken into account by including an electron- and hole-breakdown network in the presented noise model. The presented method is compared with the conventional approach. When the avalanche noise is absorbed by base and collector noise sources as in the conventional RF noise model without a breakdown network, simulated noise parameters deviate from experimental data at breakdown. Instead, good agreement between measured and simulated noise parameters and $S$ -parameters from the presented RF noise model is achieved in the inductive breakdown and active regions. The presented noise model and the obtained parameters can be applied to SiGe HBT circuits for reliability investigation.

Effects of BEOL on self-heating and thermal coupling in SiGe multi-finger HBTs under real operating condition

Effects of the back-end-of-line layers up to metal-1 on the self-heating and thermal coupling in a multi-finger silicon germanium heterojunction bipolar transistor (SiGe MFT) are investigated. It is observed that the rise in junction temperature is overestimated if the BEOL effects are not considered. A new method for estimating the thermal coupling coefficients is proposed emulating the real operating condition. The proposed methodology demonstrates that the thermal coupling is increased in real operating condition and the estimated coupling coefficients are almost independent of the dissipated power. Further an empirical closed-form formulation is proposed for estimating the coupling coefficients analytically and for subsequently using in compact model simulation. The formulation is found to predict the coefficients quite accurately. Compact model simulations using the analytically obtained coupling coefficients show excellent model agreement with the static and dynamic 3D TCAD simulation data for junction temperature. Finally the model is validated against the measured data corresponding to an SiGe MFT fabricated using B55 technology from ST microelectronics.

Laser-Induced Single Event Transients in Local Oxidation of Silicon and Deep Trench Isolation Silicon-Germanium Heterojunction Bipolar Transistors**Supported by the National Natural Science Foundation of China under Grant Nos 61274106.

We present a study on the single event transient (SET) induced by a pulsed laser in different silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) with the structure of local oxidation of silicon (LOCOS) and deep trench isolation (DTI). The experimental results are discussed in detail and it is demonstrated that a SiGe HBT with the structure of LOCOS is more sensitive than the DTI SiGe HBT in the SET. Because of the limitation of the DTI structure, the charge collection of diffusion in the DTI SiGe HBT is less than that of the LOCOS SiGe HBT. The SET sensitive area of the LOCOS SiGe HBT is located in the collector-substrate (C/S) junction, while the sensitive area of the DTI SiGe HBT is located near to the collector electrodes.

Application of Pelletron Accelerator to Study High Total Dose Radiation Effects on Semiconductor Devices

Silicon bipolar junction transistors (BJTs), Silicon-germanium heterojunction bipolar transistors (SiGe HBTs) and metal oxide semiconductor (MOS) devices are the key components of BiCMOS integrated circuits. The semiconductor devices need to withstand very high total doses (100’s of Mrad) for reliable operation of electronic circuits for 8-10 years of LHC operation. The study of radiation tolerance of semiconductor devices up to 100 Mrad of total dose takes longer time with conventional60Co gamma, proton and electron irradiation facilities and the effects due to these radiations are well understood. Hence it is important to study the effects of heavy ion irradiation on various semiconductor devices. The irradiation time decreases with increasing linear energy transfer (LET) of incident radiation and LET increases with atomic number of the impinging ions. But it is essential to understand the mechanism of energy transfer by different heavy ions in semiconductor devices. Therefore, here we give an overview of different heavy ion interactions with Si BJTs, MOSFETs and SiGe HBTs by primarily focusing on the electrical characteristics of these devices before and after ion irradiation. We show that the irradiation time needed to reach very high total dose can be reduced by using Pelletron accelerator facilities instead of conventional irradiation facilities.

3-D simulation study of single event effects of SiGe heterojunction bipolar transistor in extreme environment

A 3-D simulation of single event effects (SEEs) for domestic Silicon–Germanium heterojunction bipolar transistor (SiGe HBT) in extreme environment is performed with TCAD simulation tools. The influences of environment temperature and linear energy transfer (LET) on SEE are investigated. The combined effects of temperature and LET are also discussed. The results show some interesting phenomena by analyzing collected charges and transient current. The collected charges increase as temperature rises, but the current peaks decline with temperature increasing at base, collector and substrate. However, the peak of emitter transient current rises up and then declines. As LET rises, the collected charges go up linearly, and the transient current peaks also increase but their growth trends are slow. Mobility, carrier ionization and recombination of various regions at different conditions are the main causes of these differences. Current transient is very severe at low temperature. But charge collection is sensitive to high temperature and high LET. Transient pulse caused by diffusion mechanism may have a serious effect on SEEs.

Single-event response of the SiGe HBT in TCAD simulations and laser microbeam experiment**Project supported by the National Natural Science Foundation of China (Grant No. 61274106).

In this paper the single-event responses of the silicon germanium heterojunction bipolar transistors (SiGe HBTs) are investigated by TCAD simulations and laser microbeam experiment. A three-dimensional (3D) simulation model is established, the single event effect (SEE) simulation is further carried out on the basis of SiGe HBT devices, and then, together with the laser microbeam test, the charge collection behaviors are analyzed, including the single event transient (SET) induced transient terminal currents, and the sensitive area of SEE charge collection. The simulations and experimental results are discussed in detail and it is demonstrated that the nature of the current transient is controlled by the behaviors of the collector–substrate (C/S) junction and charge collection by sensitive electrodes, thereby giving out the sensitive area and electrode of SiGe HBT in SEE.

Cryogenic preamplification of a single-electron-transistor using a silicon-germanium heterojunction-bipolar-transistor

We examine a silicon-germanium heterojunction bipolar transistor (HBT) for cryogenic pre-amplification of a single electron transistor (SET). The SET current modulates the base current of the HBT directly. The HBT-SET circuit is immersed in liquid helium, and its frequency response from low frequency to several MHz is measured. The current gain and the noise spectrum with the HBT result in a signal-to-noise-ratio (SNR) that is a factor of 10–100 larger than without the HBT at lower frequencies. The transition frequency defined by SNR = 1 has been extended by as much as a factor of 10 compared to without the HBT amplification. The power dissipated by the HBT cryogenic pre-amplifier is approximately 5 nW to 5 μW for the investigated range of operation. The circuit is also operated in a single electron charge read-out configuration in the time-domain as a proof-of-principle demonstration of the amplification approach for single spin read-out.

Large-Signal Reliability Analysis of SiGe HBT Cascode Driver Amplifiers

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.

On the Cryogenic RF Linearity of SiGe HBTs in a Fourth-Generation 90-nm SiGe BiCMOS Technology

Large-signal ( $P_{\rm 1\,dB}$ ) and small-signal (OIP3) radio frequency (RF) linearities of silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) fabricated in a new fourth-generation 90-nm SiGe BiCMOS technology operating at cryogenic temperatures are investigated. The SiGe BiCMOS process technology has an $f_{T}$ / $f_{\rm max}$ of 300/350 GHz. SiGe HBTs with two different layout configurations, collector-base-emitter (CBE) and CBE-base-collector (CBEBC), were characterized over temperature. Both dc and ac figures-of-merit are presented to aid in understanding the linearity, and to provide an overall performance comparison between the two layout configurations. The extracted peak $f_{T}$ / $f_{\rm max}$ for CBE and CBEBC at 78 K are 387/350 and 420/410 GHz, respectively. The $P_{\rm 1\,dB}$ and OIP3 linearity metrics for both configurations are comparable. Source- and load-pull measurements were performed at each temperature at 8 and 18 GHz, with the devices biased at a $J_{C}$ of 18 mA/ $\mu \text{m}^{2}$ . Two-tone measurements over bias were also performed at 300 and 78 K with 50- $\Omega $ terminations for the source and load impedances. The 50 $\Omega $ results follow a similar response to the source- and load-pull measurements at 300 and 78 K, and demonstrate that the small-signal linearity of the SiGe HBTs is not adversely impacted by operation at cryogenic temperatures. The CBEBC configuration demonstrated the most consistent RF linearity performance at cryogenic temperature out of the two layout options.

A comparison of 100 MeV oxygen ion and 60Co gamma irradiation effects on advanced 200 GHz SiGe heterojunction bipolar transistors

The third-generation (200 GHz) silicon–germanium heterojunction bipolar transistors were irradiated with 100 MeV oxygen [O7+] ions in the dose range from 1 to 100 Mrad. The different electrical characteristics like forward-mode and inverse-mode Gummel characteristics, the normalized base current, excess base current, the current gain, damage constant, neutral base recombination, avalanche multiplication and the output characteristics were measured before and after irradiation. The ion irradiation results were compared with 60Co gamma irradiation results to understand the linear energy transfer effects on the electrical characteristics on silicon–germanium heterojunction bipolar transistors. The stopping range of ions in matter simulation study was conducted to understand the energy loss of 100 MeV O7+ ions in silicon–germanium heterojunction bipolar transistor structure.

80 MeV Carbon Ion Irradiation Effects On Advanced 200 GHz Silicon-germanium Heterojunction Bipolar Transitors

The total dose effects of 80 MeV carbon ions and 60 Co gamma radiation in the dose range from 1 Mrad to 100 Mrad on advanced 200 GHz Silicon-Germanium heterojunction bipolar transistors (SiGe HBTs) are investigated. The stopping and range of ions in matter (SRIM) simulation study was conducted to understand the energy loss of 80 MeV carbon ions in SiGe HBT structure. Pre- and post-radiation DC figure of merits such as Gummel characteristics, excess base current, ideality factor, DC current gain, damage constant, neutral base recombination, avalanche multiplication of carriers and output characteristics were used to quantify the radiation tolerance of the devices. The excess base current, current gain and damage constant for 80 MeV carbon irradiated SiGe HBTs show more degradation when compared to 60 Co gamma irradiation. The ideality factor for 80 MeV carbon ions irradiated SiGe HBTs is also more when compared to 60 Co gamma irradiated SiGe HBTs. The SiGe HBTs shows minimal degradation in current gain at collector current levels (~ 1 mA) where the circuits are biased even after 100 Mrad of total dose. Therefore SiGe HBTs are became the reliable candidate for deep space exploration programs and high energy physics experiments (HEP) like large hadron colliders (LHCs). Copyright © 2015 VBRI press.

SiGe HBT Large-Signal Table-Based Model With the Avalanche Breakdown Effect Considered

In this paper, a table-based large-signal model for silicon germanium heterojunction bipolar transistors with the introduction of a breakdown network is presented to describe the avalanche breakdown effect of the base-collector junction on direct current and RF characteristics completely. Input oscillation and output inductive behaviors in the breakdown regime are found to be due to impact ionization induced holes and electrons, respectively. The avalanche breakdown effect and early effect modeled by the breakdown network and output resistance, respectively, can be distinguished in the presented model. In addition, a good agreement between the extracted total input and output resistances at RF and dc is obtained. The validity of this presented large-signal table-based model with multibias intrinsic parameters has been verified through the measured output spectrum and waveform.