| 11. |
- Chen, Si, 1982-, et al.
(författare)
-
Current gain enhancement for silicon-on-insulator lateral bipolar junction transistors operating at liquid-helium temperature
- 2020
-
Ingår i: IEEE Electron Device Letters. - 0741-3106 .- 1558-0563. ; 41:6, s. 800-803
-
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.
|
|
| 12. |
- Chen, Si, 1982-
(författare)
-
Electronic Sensors Based on Nanostructured Field-Effect Devices
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Point-of-care (POC) diagnostics presents a giant market opportunity with profound societal impact. In particular, specific detection of DNA and protein markers can be essential for early diagnosis of e.g. cancer, cardiovascular disease, infections or allergies. Today, identification of these markers often requires extensive laboratory work and hence is expensive and time consuming. Current methods for recognition and detection of specific biomolecules are mostly optics based and thus impose severe limitations as to convenience, specificity, sensitivity, parallel processing and cost reduction.Electronic sensors based on silicon nanowire field-effect transistors have been reported to be able to detect biomolecules with concentrations down to femtomolar (fM) level with high specificity. Although the reported capability needs further confirmation, the CMOS-compatible fabrication process of such sensors allows for low cost production and high density integration, which are favorable for POC applications. This thesis mainly focuses on the development of a multiplex detection platform based on silicon nanowire field-effect sensors integrated with a microfluidic system for liquid sample delivery. Extensive work was dedicated to developing a top-down fabrication process of the sensors as well as an effective passivation scheme. The operation mechanism and coupling efficiencies of different gate configurations were studied experimentally with the assistance of numerical simulation and equivalent circuits. Using pH sensing as a model system, large effort was devoted to identifying sources for false responses resulting from the instability of the inert-metal gate electrode. In addition, the drift mechanism of the sensor operating in electrolyte was addressed and a calibration model was proposed. Furthermore, protein detection experiments were performed using small-sized Affibody molecules as receptors on the gate insulator to tackle the Debye screening issue. Preliminary results showed that the directionality of the current changes in the sensors was in good agreement with the charge polarities of the proteins. Finally, a graphene-based capacitor was examined as an alternative to the nanowire device for field-effect ion sensing. Our initial attempts showed some attractive features of the capacitor sensor.
|
|
| 13. |
- Fu, C., et al.
(författare)
-
Optimization of stiffness for isotropic conductive adhesives
- 2010
-
Ingår i: 2010 International Symposium on Advanced Packaging Materials: Microtech, APM '10. - 9781424467563 ; , s. 29-33
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- With the rapid developments of electronic packaging, there is an increasing demand on high performance isotropic conductive adhesives (ICAs). However, the traditional ICAs are brittle, sensitive for crack formation and delamination, which is one of the major drawbacks that limits their use in a wide range of applications. Therefore great efforts have been made to make conductive adhesives more flexible. The present work aims at studying of several chemicals in terms of flexibilizing materials to modify the stiffuess modulus of the conductive adhesives. The effect of the flexibilizers has been characterized by different methods, such as Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA), Thermogravimetric Analysis (TGA), etc. Moreover, the electrical resistance, thermal conductivity and viscosity are also measured in various conditions. Experimental results indicate that one of the flexibilizing materials using flexible ester-linkage is particular of interest as it offers low electrical resistance, high thermal performance and low modulus without decreasing glass transition temperature (Tg) and influencing curing and decomposition conditions. ©2010 IEEE.
|
|
| 14. |
- Fu, Yifeng, 1984, et al.
(författare)
-
Selective growth of double-walled carbon nanotubes on gold films
- 2012
-
Ingår i: Materials Letters. - : Elsevier BV. - 1873-4979 .- 0167-577X. ; 72, s. 78-80
-
Tidskriftsartikel (refereegranskat)abstract
- Growth of high-quality vertical aligned carbon nanotube (CNT) structures on silicon supported gold (Au) films by thermal chemical vapor deposition (TCVD) is presented. Transmission electron microscopy (TEM) images show that the growth is highly selective. Statistical study reveals that 79.4% of the as-grown CNTs are double-walled. The CNTs synthesized on Au films are more porous than that synthesized on silicon substrates under the same conditions. Raman spectroscopy and electrical characterization performed on the as-grown double-walled CNTs (DWNTs) indicate that they are competitive with those CNTs grown on silicon substrates. Field emission tests show that closed-ended DWNTs have lower threshold field than those open-ended.
|
|
| 15. |
- Hu, Qitao, et al.
(författare)
-
Effects of Substrate Bias on Low-Frequency Noise in Lateral Bipolar Transistors Fabricated on Silicon-on-Insulator Substrate
- 2020
-
Ingår i: IEEE Electron Device Letters. - 0741-3106 .- 1558-0563. ; 41:1, s. 4-7
-
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.
|
|
| 16. |
- Hu, Qitao, et al.
(författare)
-
Improving Selectivity of Ion-Sensitive Membrane by Polyethylene Glycol Doping
- 2021
-
Ingår i: Sensors and actuators. B, Chemical. - : Elsevier. - 0925-4005 .- 1873-3077. ; 328
-
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.
|
|
| 17. |
|
|
| 18. |
- Hu, Qitao, et al.
(författare)
-
Ion sensing with single charge resolution using sub-10-nm electrical double layer-gated silicon nanowire transistors
- 2021
-
Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 7:49
-
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.
|
|
| 19. |
- Hu, Qitao
(författare)
-
Silicon Nanowire Based Electronic Devices for Sensing Applications
- 2021
-
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.
|
|
| 20. |
- Hu, Qitao, et al.
(författare)
-
Single Charge Detection in Liquid Sample Using Sub-10 nm Silicon Nanowire Transistors
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Direct detection of a single charge in liquid sample is the ultimate sensitivity goal of electrical biochemical sensors. In this paper, the events of capturing and emitting a single hydrogen ion (H+) at the solid/liquid interface were directly detected for the first time using sub-10 nm gate-oxide free silicon nanowire field-effect transistors (SiNWFETs). The SiNWFETs were fabricated using CMOS-compatible process. The intrinsic device noise was minimized with a surface reassembling process. Individually activated surface Si dangling bond (DB) acted as single H+ receptor. Discrete current signals generated by single H+-DB interactions via local Coulomb scattering were detected by the SiNWFETs. The kinetics of the single H+-DB interactions was systematically investigated. Our devices demonstrate the unprecedented ability to investigate the physics of solid/liquid interface at single charge level.
|
|
