Tunneling, Current Gain, and Transconductance in Silicon-Germanium Heterojunction Bipolar Transistors Operating at Millikelvin Temperatures

Davidović, Dragomir; Ying, Hanbin; Dark, Jason; Wier, Brian R.; Ge, L.; Lourenco, Nelson E.; Omprakash, Anup P.; Mourigal, Martin; Cressler, John D.

doi:10.1103/physrevapplied.8.024015

Cited by 20 publications

(9 citation statements)

References 45 publications

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“…Lastly, the asymptotic solution is restricted to values of average Knudsen number such that 2 c 1 < 1, which limits our analysis to a minimum base width of 40 nm for the chosen scattering rates. However, DC non-idealities were reported in devices with base widths on this order, [25][26][27] and again our analysis applies. Given these considerations, we conclude that quasiballistic transport is not responsible for non-ideal cryogenic DC characteristics of SiGe HBTs.…”

Section: Discussionsupporting

confidence: 62%

“…Finally, we discuss alternate explanations for the cryogenic non-idealities. Prior works have suggested that direct tunneling from the emitter to the collector is a possible origin of non-idealities in devices with narrow base widths ∼ 10 nm [25,26]. However, non-ideal cryogenic transconductance has been observed in first-generation SiGe HBTs with base widths on the order of 100 nm [24,27] for which the direct tunneling current is expected to be negligible.…”

Section: Discussionmentioning

confidence: 99%

“…Further, non-idealities observed in the hole current cannot be explained by direct tunneling as the hole potential barrier terminates at the poly-Si emitter contact, which is hundreds of nanometers away from the base-emitter junction. Lastly, abrupt changes in the slope of I-V characteristics have been attributed to a switch from trap-assisted transport to a tunneling or quasiballistic mechanism [26,27]. However, similar trends are observed in p-n diodes [52][53][54] for which direct tunneling or quasiballistic transport is not relevant, and the possibility of a similar mechanism occurring in SiGe HBTs has not been excluded.…”

Section: Discussionmentioning

confidence: 99%

“…The latter effect has been phenomenologically described using an elevated electron temperature that is taken as the effective temperature for thermionic emission at the base-emitter junction [10,11,24]. As base widths were scaled further down to ∼ 20 nm in recent years, direct tunneling of electrons was reported to contribute to the collector current at biases approaching the built-in potential [25][26][27].…”

Section: Introductionmentioning

confidence: 99%

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Quasiballistic electron transport in cryogenic SiGe HBTs studied using an exact, semi-analytic solution to the Boltzmann equation

Naik

Minnich

2021

Journal of Applied Physics

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Silicon–germanium heterojunction bipolar transistors (HBTs) are of interest as low-noise microwave amplifiers due to their competitive noise performance and low cost relative to III–V devices. The fundamental noise performance limits of HBTs are thus of interest, and several studies report that quasiballistic electron transport across the base is a mechanism leading to cryogenic non-ideal IV characteristics that affect these limits. However, this conclusion has not been rigorously tested against theoretical predictions because prior studies modeled electron transport with empirical approaches or approximate solutions of the Boltzmann equation. Here, we study non-diffusive transport in narrow-base SiGe HBTs using an exact, semi-analytic solution of the Boltzmann equation based on an asymptotic expansion approach. We find that the computed transport characteristics are inconsistent with experiments, implying that quasiballistic electron transport is unlikely to be the origin of cryogenic non-ideal IV characteristics. Our work helps to identify the mechanisms governing the lower limits of the microwave noise figure of cryogenic HBT amplifiers.

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Section: Discussionsupporting

confidence: 62%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Quasiballistic electron transport in cryogenic SiGe HBTs studied using an exact, semi-analytic solution to the Boltzmann equation

Naik

Minnich

2021

Journal of Applied Physics

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“…SiGe HBTs have recently been shown to operate at milliKelvin temperatures 23 , and a theory of their cryogenic operation has begun to develop 24,25 . Although other technologies can also operate at cryogenic temperatures 26 , SiGe HBTs have a better scaling potential 27 .…”

Section: Introductionmentioning

confidence: 99%

Probing the Magnetodynamics of Magnetic Tunnel Junctions with the Aid of SiGe HBTs

Dark,

Ying,

Nunn

et al. 2018

Preprint

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High impedance (∼1 MΩ) magnetic tunnel junctions (MTJs) are used to observe and record the magnetodynamics of the nanomagnets that form the junctions themselves. To counteract the bandwidth limitations caused by the high impedance of the junction and the parasitic capacitance intrinsic to any cryogenic system, silicon-germanium heterojunction bipolar transistors (SiGe HBTs) are used as cryogenic preamplifiers for the MTJs. The resulting measurement improvements include an increase in bandwidth by a factor of 3.89, an increase in signal-to-noise ratio by a factor of 6.62, and a gain of 7.75 of the TMR signal produced by the MTJ. The limitation to the measurement system was found to be from the external, room temperature electronics. Despite this limitation, these improvements allow for better time-resolved magnetodynamics measurements of the MTJs. These experiments pave the way for future cryogenic, magnetodynamics measurement improvements, and could even be useful in cryogenic memory applications.

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Synthesis of Wafer‐Scale Graphene with Chemical Vapor Deposition for Electronic Device Applications

Sun

Pang

Cheng

et al. 2021

Adv Materials Technologies

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The first isolation of graphene opens the avenue for new platforms for physics, electronic engineering, and materials sciences. Among several kinds of synthesis approaches, chemical vapor deposition is most promising for the growth at wafer‐scale, which is compatible with the Si‐based electronic device integration protocols. In this review, the types, properties, and synthesis methods of graphene are first introduced. Many details of wafer‐scale graphene synthesis by chemical vapor deposition strategies are given, including the wafer‐scale single crystal metal and alloy preparation, roll to roll synthesis over Cu, roll to roll electrochemical transfer technique. Besides, the batch‐to‐batch synthesis are highlighted for direct graphene over dielectric substrates such as sapphire and Si/SiO2. The electronic transport and transparent conductance of the wafer‐scale graphene are compared with high‐quality single crystal. The progress and proof‐of‐the‐concept are briefly recalled in graphene‐based electronics such as transistors, sensors, integrated circuits, and spin transport valves. Eventually, the readers are provoked with the current challenges as well as the future opportunities.

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Tunneling, Current Gain, and Transconductance in Silicon-Germanium Heterojunction Bipolar Transistors Operating at Millikelvin Temperatures

Cited by 20 publications

References 45 publications

Quasiballistic electron transport in cryogenic SiGe HBTs studied using an exact, semi-analytic solution to the Boltzmann equation

Quasiballistic electron transport in cryogenic SiGe HBTs studied using an exact, semi-analytic solution to the Boltzmann equation

Probing the Magnetodynamics of Magnetic Tunnel Junctions with the Aid of SiGe HBTs

Synthesis of Wafer‐Scale Graphene with Chemical Vapor Deposition for Electronic Device Applications

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