7 research outputs found
Geometrical magnetoresistance effect and mobility in graphene field-effect transistors
Further development of the graphene field-effect transistors (GFETs) for
high-frequency electronics requires accurate evaluation and study of the
mobility of charge carriers in a specific device. Here, we demonstrate that the
mobility in the GFETs can be directly characterized and studied using the
geometrical magnetoresistance (gMR) effect. The method is free from the
limitations of other approaches since it does not require an assumption of the
constant mobility and the knowledge of the gate capacitance. Studies of a few
sets of GFETs in the wide range of transverse magnetic fields indicate that the
gMR effect dominates up to approximately 0.55 T. In higher fields, the physical
magnetoresistance effect starts to contribute. The advantages of the gMR
approach allowed us to interpret the measured dependencies of mobility on the
gate voltage, i.e., carrier concentration, and identify the corresponding
scattering mechanisms. In particular, the range of the fairly constant mobility
is associated with the dominating Coulomb scattering. The decrease in mobility
at higher carrier concentrations is associated with the contribution of the
phonon scattering. Analysis shows that the gMR mobility is typically 2-3 times
higher than that found via the commonly used drain resistance model. The latter
underestimates the mobility since it does not take the interfacial capacitance
into account.Comment: The following article has been submitted to Applied Physics Letters.
After it is published, the DOI will be found her
High-performance silicon-based nano-thermoelectric bolometers for uncooled infrared sensing
Infrared (IR) sensors and photodetector arrays are employed in various imaging applications (such as night vision), remote temperature measurement, and chemical analysis. These applications are in space and environmental sensing, transport, health and medicine, safety, security, defense, industry, agriculture, etc. Optical chemical analysis employs IR absorption spectroscopy which enables the identification and quantification of gases, liquids, and materials based on their unique absorption spectra which are feature-rich in the IR region. State-of-the-art (SoA) quantum photodetectors utilize either photoconductivity or the photovoltaic effect. Commercial quantum photodetectors are widely available in the spectral range from UV to short-wave infrared (SWIR), but in mid-wave IR (MWIR) and long-wave IR (LWIR), they require exotic materials and cooling to maintain high sensitivity. Thermal detectors (bolometers) are a competing technology that can reach high sensitivities in IR without the need for cooling and can be manufactured using widely available semiconductor technologies. SoA bolometers include resistive bolometers, diode- or transistor-based bolometers, and thermoelectric bolometers. By utilizing nanomaterials and integrated design, we have minimized the thermal mass and demonstrated fast and sensitive nano-thermoelectric IR bolometers with high thermoelectric efficiency. We review the application and development of the silicon-based nano-thermoelectric infrared bolometers: modelling, design, fabrication, and electro-optical characteristics. The enabling materials, silicon nanomembranes, are also discussed, and the first devices used to test the potential of these nanomembranes, the electro-thermal devices, are reviewed and new experimental results are presented.</p
Uncooled nano-thermoelectric bolometers for infrared imaging and sensing
The state-of-the-art quantum infrared photodetectors have high performance, but obtaining high sensitivity in mid- and long-wavelength infrared (MWIR and LWIR) requires cooling and exotic materials. Whereas thermal detectors offer lower cost without the need for cooling but are typically slower and less sensitive than cooled quantum infrared detectors. Nano-thermoelectrics and nanomembranes offer opportunities for enhancing the performance of uncooled MWIR and LWIR imaging and sensing. Similar to thermoelectric detectors, the infrared sensitive signal in those is generated by the thermoelectric effect, providing advantages over resistive bolometers, i.e. less noise sources and zero power consumption in the detector itself. We have recently demonstrated that nano-thermoelectrics provides a route towards high-sensitivity and cost-effective LWIR detection. When the thickness of the thermoelectric polysilicon membrane is reduced, increased phonon scattering leads to reduced thermal conductivity. This gives rise to the high thermoelectric figures of merit determining the detector sensitivity. The speed stems from the low-thermal-mass device design with an integrated metal nanomembrane absorber and the lack of separate support structures. We report integrated circuit concept for the readout of these detectors, and study how the absorber grid geometry determines the device performance. The fabricated devices have thermal time constants, responsivities and specific detectivities D* in the ranges of 190 – 208 µs, 334 – 494 V/W, and (7.9 – 8.7)·107 cmHz1/2/W, respectively. The differences in the device performance originate from the differences in the thermal mass, total resistance, and impedance matching of the absorber grid. By optimization, we expect that D* = 8.3·108 cmHz1/2/W can be reached.</p
Wafer-Scale Graphene Field-Effect Transistor Biosensor Arrays with Monolithic CMOS Readout
The reliability of analysis is becoming increasingly important as point-of-care diagnostics are transitioning from single-analyte detection toward multiplexed multianalyte detection. Multianalyte detection benefits greatly from complementary metal-oxide semiconductor (CMOS) integrated sensing solutions, offering miniaturized multiplexed sensing arrays with integrated readout electronics and extremely large sensor counts. The development of CMOS back end of line integration compatible graphene field-effect transistor (GFET)-based biosensing has been rapid during the past few years, in terms of both the fabrication scale-up and functionalization toward biorecognition from real sample matrices. The next steps in industrialization relate to improving reliability and require increased statistics. Regarding functionalization toward truly quantitative sensors, on-chip bioassays with improved statistics require sensor arrays with reduced variability in functionalization. Such multiplexed bioassays, whether based on graphene or on other sensitive nanomaterials, are among the most promising technologies for label-free electrical biosensing. As an important step toward that, we report wafer-scale fabrication of CMOS-integrated GFET arrays with high yield and uniformity, designed especially for biosensing applications. We demonstrate the operation of the sensing platform array with 512 GFETs in simultaneous detection for the sodium chloride concentration series. This platform offers a truly statistical approach on GFET-based biosensing and further to quantitative and multianalyte sensing. The reported techniques can also be applied to other fields relying on functionalized GFETs, such as gas or chemical sensing or infrared imaging
Wafer-scale graphene field-effect transistor biosensor arrays with monolithic CMOS readout
The reliability of analysis is becoming increasingly important as
point-of-care diagnostics are transitioning from single analyte detection
towards multiplexed multianalyte detection. Multianalyte detection benefits
greatly from complementary metal-oxide semiconductor (CMOS) integrated sensing
solutions, offering miniaturized multiplexed sensing arrays with integrated
readout electronics and extremely large sensor counts. The development of CMOS
back end of line integration compatible graphene field-effect transistor (GFET)
based biosensing has been rapid during the last few years, both in terms of the
fabrication scale-up and functionalization towards biorecognition from real
sample matrices. The next steps in industrialization relate to improving
reliability and require increased statistics. Regarding functionalization
towards truly quantitative sensors and on-chip bioassays with improved
statistics require sensor arrays with reduced variability in functionalization.
Such multiplexed bioassays, whether based on graphene or on other sensitive
nanomaterials, are among the most promising technologies for label-free
electrical biosensing. As an important step towards that, we report wafer-scale
fabrication of CMOS integrated GFET arrays with high yield and uniformity,
designed especially for biosensing applications. We demonstrate the operation
of the sensing platform array with 512 GFETs in simultaneous detection for
sodium chloride concentration series. This platform offers a truly statistical
approach on GFET based biosensing and further to quantitative and multi-analyte
sensing. The reported techniques can also be applied to other fields relying on
functionalized GFETs, such as gas or chemical sensing or infrared imaging