| 1. |
- Chen, Si, 1982-, et al.
(författare)
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Current gain enhancement for silicon-on-insulator lateral bipolar junction transistors operating at liquid-helium temperature
- 2020
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Ingår i: IEEE Electron Device Letters. - 0741-3106 .- 1558-0563. ; 41:6, s. 800-803
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Tidskriftsartikel (refereegranskat)abstract
- Conventional homojunction bipolar junction transistors (BJTs) are not suitable for cryogenic operation due to heavy doping-induced emitter band-gap narrowing and strong degradation in current gain (β) at low temperature. In this letter, we show that, on lateral version of the BJTs (LBJTs) fabricated on silicon-on-insulator (SOI) substrate, such β degradation can be mitigated by applying a substrate bias (V sub ), and a β over unity is achieved in a base current (I B ) range over 5 orders of magnitudes at 4.2 K, with a peak β ~ 100 demonstrated. The β improvement is explained by the enhanced electron tunneling through base region as a result of base barrier lowering and thinning by a positive Vsub, which leads to dramatic increase of collector current (IC) while IB is negligibly affected.
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| 2. |
- Chen, Xi, et al.
(författare)
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Device noise reduction for Silicon nanowire field-effect-transistor based sensors by using a Schottky junction gate
- 2019
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Ingår i: ACS Sensors. - : American Chemical Society (ACS). - 2379-3694. ; 4:2, s. 427-433
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Tidskriftsartikel (refereegranskat)abstract
- The sensitivity of metal-oxide-semiconductor field-effect transistor (MOSFET) based nanoscale sensors is ultimately limited by noise induced by carrier trapping/detrapping processes at the gate oxide/semiconductor interfaces. We have designed a Schottky junction gated silicon nanowire field-effect transistor (SiNW-SJGFET) sensor, where the Schottky junction replaces the noisy oxide/semiconductor interface. Our sensor exhibits significantly reduced noise, 2.1×10-9 V2µm2/Hz at 1 Hz, compared to reference devices with the oxide/semiconductor interface operated at both inversion and depletion modes. Further improvement can be anticipated by wrapping the nanowire by such a Schottky junction thereby eliminating all oxide/semiconductor interfaces. Hence, a combination of the low-noise SiNW-SJGFET sensor device with a sensing surface of the Nernstian response limit holds promises for future high signal-to-noise ratio sensor applications.
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| 3. |
- Chen, Xi, et al.
(författare)
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Multiplexed analysis of molecular and elemental ions using nanowire transistor sensors
- 2018
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Ingår i: Sensors and actuators. B, Chemical. - : Elsevier BV. - 0925-4005 .- 1873-3077. ; 270, s. 89-96
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Tidskriftsartikel (refereegranskat)abstract
- An integrated sensor chip with silicon nanowire ion-sensitive field-effect transistors for simultaneous and selective detection of both molecular and elemental ions in a single sample solution is demonstrated. The sensing selectivity is realized by functionalizing the sensor surface with tailor-made mixed-matrix membranes (MMM) incorporated with specific ionophores for the target ions. A biomimetic container molecule, named metal-organic supercontainer (MOSC), is selected as the ionophore for detection of methylene blue (MB+), a molecular ion, while a commercially available Na-ionophore is used for Na+, an elemental ion. The sensors show a near-Nernstian response with 56.4 ± 1.8 mV/dec down to a concentration limit of ∌1 ΌM for MB+ and 57.9 ± 0.7 mV/dec down to ∌60 ΌM for Na+, both with excellent reproducibility. Extensive control experiments on the MB+ sensor lead to identification of the critical role of the MOSC molecules in achieving a stable and reproducible potentiometric response. Moreover, the MB+-specific sensor shows remarkable selectivity against common interfering elemental ions in physiological samples, e.g., H+, Na+, and K+. Although the Na+-specific sensor is currently characterized by insufficient immunity to the interference by MB+, the root cause is identified and remedies generally applicable for hydrophobic molecular ions are discussed. River water experiments are also conducted to prove the efficacy of our sensors.
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| 4. |
- Hu, Qitao, et al.
(författare)
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Current gain and low-frequency noise of symmetric lateral bipolar junction transistors on SOI
- 2018
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Ingår i: 2018 48th European Solid-State Device Research Conference (ESSDERC). - 9781538654019 - 9781538654002 - 9781538654026 ; , s. 258-261
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Konferensbidrag (refereegranskat)abstract
- This paper presents a comprehensive study of symmetric lateral bipolar junction transistors (LBJTs) fabricated on SOI substrate using a CMOS-compatible process; LBJTs find many applications including being a local signal amplifier for silicon-nanowire sensors. Our LBJTs are characterized by a peak gain (β) over 50 and low-frequency noise two orders of magnitude lower than what typically is of the SiO 2 /Si interface for a MOSFET. β is found to decrease at low base current due to recombination in the space charge region at the emitter-base junction and at the surrounding SiO 2 /Si interfaces. This decrease can be mitigated by properly biasing the substrate.
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| 5. |
- Hu, Qitao, et al.
(författare)
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Effects of Substrate Bias on Low-Frequency Noise in Lateral Bipolar Transistors Fabricated on Silicon-on-Insulator Substrate
- 2020
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Ingår i: IEEE Electron Device Letters. - 0741-3106 .- 1558-0563. ; 41:1, s. 4-7
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Tidskriftsartikel (refereegranskat)abstract
- This letter presents a systematic study of how the substrate bias (Vsub) modulation affects the current-voltage (I-V) characteristics and low-frequency noise (LFN) of lateral bipolar junction transistors (LBJTs) fabricated on a silicon-on-insulator(SOI) substrate. The current gain (β) of npn LBJTs at low base voltage can be greatly improved bya positive Vsub as a result of enhanced electron injection into the base near the buried oxide (BOX)/silicon interface. However, an excessive positive Vsub may also adversely affect the LFN performance by amplifying the noise generated as a result of carrier trapping and detrapping at that interface. Our results provide a practical guideline for improving both β and the overall noise performance when using our LBJT as a local signal amplifier.
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| 6. |
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| 7. |
- Hu, Qitao, et al.
(författare)
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Improving Selectivity of Ion-Sensitive Membrane by Polyethylene Glycol Doping
- 2021
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Ingår i: Sensors and actuators. B, Chemical. - : Elsevier. - 0925-4005 .- 1873-3077. ; 328
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Tidskriftsartikel (refereegranskat)abstract
- Hydrophobic ions can generate considerable interference to ion detection in a complex analyte with membrane-based ion-selective sensors, due to the hydrophobic interaction. In this paper, we demonstrate that the interference from the hydrophobic interaction to the sensors can be significantly reduced by incorporating hydrophilic polyethylene glycol (PEG) into the membrane. The sensor is a silicon nanowire field-effect transistor (SiNWFET) with its surface functionalized with an ionophore-doped mixed-matrix membrane (MMM), where the ionophore is either a commercial Na-ionophore Ⅲ or a novel synthetic metal-organic supercontainer. The incorporation of PEG suppresses the partitioning of hydrophobic ions into the MMM and thus reduces their interference to the detection of target ions. This is evidenced with an improvement in selectivity for Na+ detection in the presence of interfering methylene blue (MB+) ion by more than an order of magnitude. It further enables detection of Na+ and MB+ using a SiNWFET sensor array in a multiplexed manner with controlled susceptivity to cross-interference and a greatly expanded dynamic range.
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| 8. |
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| 9. |
- Hu, Qitao, et al.
(författare)
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Ion sensing with single charge resolution using sub-10-nm electrical double layer-gated silicon nanowire transistors
- 2021
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Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 7:49
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Tidskriftsartikel (refereegranskat)abstract
- Electrical sensors have been widely explored for the analysis of chemical/biological species. Ion detection with single charge resolution is the ultimate sensitivity goal of such sensors, which is yet to be experimentally demonstrated. Here, the events of capturing and emitting a single hydrogen ion (H+) at the solid/liquid interface are directly detected using sub-10-nm electrical double layer-gated silicon nanowire field-effect transistors (SiNWFETs). The SiNWFETs are fabricated using a complementary metal-oxide-semiconductor compatible process, with a surface reassembling step to minimize the device noise. An individually activated surface Si dangling bond (DB) acts as the single H+ receptor. Discrete current signals, generated by the single H+-DB interactions via local Coulomb scattering, are directly detected by the SiNWFETs. The single H+-DB interaction kinetics is systematically investigated. Our SiNWFETs demonstrate unprecedented capability for electrical sensing applications, especially for investigating the physics of solid/liquid interfacial interactions at the single charge level.
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| 10. |
- Hu, Qitao
(författare)
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Silicon Nanowire Based Electronic Devices for Sensing Applications
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Silicon nanowire (SiNW) based electronic devices fabricated with a complementary metal-oxide-semiconductor (CMOS) compatible process have wide-range and promising applications in sensing area. These SiNW sensors own high sensitivity, low-cost mass production possibility, and high integration density. In this thesis, we design and fabricate SiNW electronic devices with the CMOS-compatible process on silicon-on-insulator (SOI) substrates and explore their applications for ion sensing and quantum sensing. The thesis starts with ion sensing using SiNW field-effect transistors (SiNWFETs). The specific interaction between a sensing layer and analyte generates a change of local charge density and electrical potential, which can effectively modulate the conductance of SiNW channel. Multiplexed detection of molecular (MB+) and elemental (Na+) ions is demonstrated using a SiNWFET array, which is functionalized with ionophore-incorporated mixed-matrix membranes (MMMs). As a follow-up, polyethylene glycol (PEG) doping strategy is explored to suppress interference from the hydrophobic molecular ion and expand the multiplexed detection range. Then, the SiNW is downscaled to sub-10 nm with a gate-oxide-free configuration for single charge detection in liquid. We directly observe the capture and emission of a single H+ ion with individually activated Si dangling bonds (DBs) on the SiNW surface. This work demonstrates the unprecedented ability of the sub-10 nm SiNWFET for investigating the physics of the solid/liquid interface at single charge level.Apart from ion sensing, the SiNWFET can be suspended and act as a nanoelectromechanical resonator aiming for electrically detecting potential quantized mechanical vibration at low temperature. A suspended SiNW based single-hole transistor (SHT) is explored as a nanoelectromechanical resonator at 20 mK. Mechanical vibration is transduced to electrical readout by the SHT, and the transduction mechanism is dominated by piezoresistive effect. A giant effective piezoresistive gauge factor (~6000) with a strong correlation to the single-hole tunneling is also estimated. This hybrid device is demonstrated as a promising system to investigate macroscopic quantum behaviors of vibration phonon modes.Noise, including intrinsic device noise and environmental interference, is a serious concern for sensing applications of SiNW electronic devices. A H2 annealing process is explored to repair the SiNW surface defects and thus reduce the intrinsic noise by one order of magnitude. To suppress the external interference, lateral bipolar junction transistors (LBJTs) are fabricated on SOI substrate for local signal amplification of the SiNW sensors. Current gain and overall signal-to-noise ratio of the LBJTs are also optimized with an appropriate substrate voltage.
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