We report an all-printed flexible carbon nanotube (CNT) thin-film transistor (TFT). All the CNT TFT components,
including the source and drain electrodes, the TFT transport channel, and the gate electrode, are printed on a flexible
substrate at room temperature. A high ON/OFF ratio of over 103 was achieved. The all printed CNT-TFT also exhibits
bias-invariant transconductance over a certain gate bias range. This all-printed process avoids the conventional
procedures in lithography, vacuum, and metallization, and offers a promising technology for low-cost, high-throughput
fabrication of large-area flexible electronics on a variety of substrates, including glass, Si, indium tin oxide and plastics.
The potential of thin film thickness variation measurement method, reflectometric interference spectroscopy (RIfS), for a
compact label-free biosensor is investigated. A model to estimate thickness variation is built based on RIfS. A set-up of
the sensor having dual Light Emitting Diodes (LEDs) and one photo detector are introduced. To verify the model,
sample chips with different thicknesses of silica film layers ranging from 2 to 20nm are used in the experiment. The
estimated values are compared with their reference values which are measured by an Atomic Force Microscopy (AFM).
Since the chosen LEDs' wavelength is not an ideal one, the comparison shows that the model underestimates the
thickness variation. By using dual LEDs and a photo detector with the reliable model, the handheld device for
transparent thin film measurement will become practical.
This paper presents a label-free biosensor using two Light Emitting Diodes (LEDs) as light sources and a photo detector
as a receiver. The sensor uses a silica-on-silicon wafer with PMMA [Poly(methyl methacrylate)] as the functional layer.
The principle of this biosensor is based on the Fabry Perot (FP) interferometer. A thickness of a 100 nm PMMA layer is
spin-coated on the silicon wafer, which has a thin thermal oxide layer of 500 nm. In such a configuration, the PMMA
layer and silica layer function as an FP cavity. When a light illuminates the surface of the sensor, the reflections from the
PMMA-air and silica-silicon interfaces will interfere with each other. Consequently, the change of the cavity length,
which is caused by biomaterial binding on the PMMA layer, will result in a red shift in the reflection spectrum. An
intensity change of the reflection light will be observed on an individual wavelength. In order to eliminate environment
noise and to enhance the sensitivity of the sensor, two LEDs, whose center wavelength is chosen on either side of the
spectrum notch, are introduced in the system. A photo detector will alternatively obtain the intensities of the two
individual reflected lights, and collect the signal via a data acquisition system. Long-term tests have shown that the
sensor is resistant to environmental fluctuation. Biolinker Protein G' was used for binding tests. The sensor shows great
potential in biosensor applications due to its compact size and low cost.
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