MID-IR LED-based, Photoacoustic CO2 Sensor

AbstractThe technology used to implement CO2 sensors depends on the requirements in terms of sensitivity, price and robustness. The most common technology for highly sensitive tasks are based on tunable diode laser spectroscopy, while so-called non-dispersive infrared (NDIR) photometers [2] are used in less demanding scenarios such as control air conditioning systems. Most NDIR systems use thermal emitters as light source which are readily available at low cost but require compensation for cross-sensitivities toward other gas species. The detector technology employed in these systems ranges from photodiodes to thermopiles and pyroelectric detectors, all of which require the use of spectral filters to avoid cross sensitivities. Here we present a low-cost photoacoustic-based detector comprised of a microphone in a hermetically sealed chamber filled with CO2. To excite sound waves a MID-IR LED emitting radiation in the strong CO2 absorption region around 4.2μm is used for the first time

Geometry-based tunability enhancement of flexible thin-film varactors

In this letter, flexible voltage-controlled capacitors (varactors) based on an amorphous Indium–Gallium–Zinc–Oxide (a-IGZO) semiconductor are presented. Two different varactor designs and their influence on the capacitance tuning characteristics are investigated. The first design consists of a top electrode finger structure which yields a maximum capacitance tunability of 6.9 at 10 kHz. Second, a novel interdigitated varactor structure results in a maximum tunability of 93.7 at 100 kHz. The design- and frequency-dependencies of the devices are evaluated through C–V measurements. Furthermore, we show bending stability of the devices down to a tensile radius of 6 mm without altering the performance. Finally, a varactor is combined with a thin-film resistor to demonstrate a tunable RC-circuit for impedance matching and low-pass filtering applications. The device fabrication flow and material stack are compatible with standard flexible thin-film transistor fabrication which enables parallel implementation of analog or logic circuitry and varactor devices

Improvement of contact resistance in flexible a-IGZO thin-film transistors by CF4/O2 plasma treatment

In this work, we analyze the effect of CF4/O2 plasma treatment on the contact interface between the amorphous Indium-Gallium-Zinc-Oxide (a-IGZO) semiconductor and Titanium-Gold electrodes. First, the influence of CF4/O2 plasma treatment is evaluated using transmission line structures and compared to pure O2 and CF4 plasma, resulting in a reduction of the contact resistance RC by a factor of 24.2 compared to untreated interfaces. Subsequently, the CF4/O2 plasma treatment is integrated in the a-IGZO thin-film transistor (TFT) fabrication process flow. We achieve a reduction of the gate bias dependent RC by a factor up to 13.4, which results in an increased current drive capability. Combined with an associated channel length reduction, the effective linear field-effect mobility is increased by up to 74.6% for the CF4/O2 plasma treated TFTs compared to untreated reference devices

Hyperleptinemia Is Required for the Development of Leptin Resistance

Leptin regulates body weight by signaling to the brain the availability of energy stored as fat. This negative feedback loop becomes disrupted in most obese individuals, resulting in a state known as leptin resistance. The physiological causes of leptin resistance remain poorly understood. Here we test the hypothesis that hyperleptinemia is required for the development of leptin resistance in diet-induced obese mice. We show that mice whose plasma leptin has been clamped to lean levels develop obesity in response to a high-fat diet, and the magnitude of this obesity is indistinguishable from wild-type controls. Yet these obese animals with constant low levels of plasma leptin remain highly sensitive to exogenous leptin even after long-term exposure to a high fat diet. This shows that dietary fats alone are insufficient to block the response to leptin. The data also suggest that hyperleptinemia itself can contribute to leptin resistance by downregulating cellular response to leptin as has been shown for other hormones

Disposable sensors in diagnostics, food and environmental monitoring

Disposable sensors are low‐cost and easy‐to‐use sensing devices intended for short‐term or rapid single‐point measurements. The growing demand for fast, accessible, and reliable information in a vastly connected world makes disposable sensors increasingly important. The areas of application for such devices are numerous, ranging from pharmaceutical, agricultural, environmental, forensic, and food sciences to wearables and clinical diagnostics, especially in resource‐limited settings. The capabilities of disposable sensors can extend beyond measuring traditional physical quantities (for example, temperature or pressure); they can provide critical chemical and biological information (chemo‐ and biosensors) that can be digitized and made available to users and centralized/decentralized facilities for data storage, remotely. These features could pave the way for new classes of low‐cost systems for health, food, and environmental monitoring that can democratize sensing across the globe. Here, a brief insight into the materials and basics of sensors (methods of transduction, molecular recognition, and amplification) is provided followed by a comprehensive and critical overview of the disposable sensors currently used for medical diagnostics, food, and environmental analysis. Finally, views on how the field of disposable sensing devices will continue its evolution are discussed, including the future trends, challenges, and opportunities

Ge2Sb2Te5 p-Type Thin-Film Transistors on Flexible Plastic Foil

In this work, we show the performance improvement of p-type thin-film transistors (TFTs) with Ge2Sb2Te5 (GST) semiconductor layers on flexible polyimide substrates, achieved by downscaling of the GST thickness. Prior works on GST TFTs have typically shown poor current modulation capabilities with ON/OFF ratios ≤20 and non-saturating output characteristics. By reducing the GST thickness to 5 nm, we achieve ON/OFF ratios up to ≈300 and a channel pinch-off leading to drain current saturation. We compare the GST TFTs in their amorphous (as deposited) state and in their crystalline (annealed at 200 °C) state. The highest effective field-effect mobility of 6.7 cm2/Vs is achieved for 10-nm-thick crystalline GST TFTs, which have an ON/OFF ratio of ≈16. The highest effective field-effect mobility in amorphous GST TFTs is 0.04 cm2/Vs, which is obtained in devices with a GST thickness of 5 nm. The devices remain fully operational upon bending to a radius of 6 mm. Furthermore, we find that the TFTs with amorphous channels are more sensitive to bias stress than the ones with crystallized channels. These results show that GST semiconductors are compatible with flexible electronics technology, where high-performance p-type TFTs are strongly needed for the realization of hybrid complementary metal-oxide-semiconductor (CMOS) technology in conjunction with popular n-type oxide semiconductor materials

N-type to p-type transition upon phase change in Ge6Sb1Te2 compounds

In this work, we study the electronic properties of Ge6Sb1Te2 compounds in thin-film transistor architectures on plastic substrates, which enable the extraction of field-effect mobility μFE, carrier density, and polarity in highly resistive thin-films. We find that the Ge-rich compound exhibits n-type conductivity in the amorphous phase with a gradual transition to p-type behavior upon thermal annealing. At a temperature of 350 °C, the material undergoes a phase change, which is confirmed by x-ray diffraction measurements. After the phase change, μFE and the conductivity increase and the polarity becomes p-type, while the carrier density does not change significantly. Furthermore, we compare the properties of Ge6Sb1Te2 to the commonly studied material composition of Ge2Sb2Te5 in the Hall measurement and find that the carrier density of the Ge-rich compound is reduced by 2 orders of magnitude, which indicates that the significantly lower concentration of Ge vacancies leads to a reduction of p-type doping

Flexible CMOS electronics based on p-type Ge2Sb2Te5 and n-type InGaZnO4 semiconductors

Ultra-thin p-type chalcogenide glass Ge2Sb2Te5 (GST) semiconductor layers are employed to form flexible thin-film transistors (TFTs). For the first time, TFTs based on GST show saturating output characteristics and an ON/OFF ratio up to 388, exceeding present reports by a factor of ∼20. The channel current modulation is greatly enhanced by using ultra-thin 5 nm thick amorphous GST layers and 20 nm thick high-k Al2O3 gate dielectrics. Flexible CMOS circuits are realized in combination with the n-type oxide semiconductor InGaZnO4 (IGZO). The CMOS inverters show voltage gain of up to 69. Furthermore, flexible NAND gates are presented. The bending stability is shown for a tensile radius of 6 mm. U.S. Government work not protected by U.S

Improvement of contact resistance in flexible a-IGZO thin-film transistors by CF4/O-2 plasma treatment

In this work, we analyze the effect of CF4/O-2 plasma treatment on the contact interface between the amorphous Indium-Gallium-Zinc-Oxide (a-IGZO) semiconductor and Titanium-Gold electrodes. First, the influence of CF4/O-2 plasma treatment is evaluated using transmission line structures and compared to pure O-2 and CF4 plasma, resulting in a reduction of the contact resistance RC by a factor of 24.2 compared to untreated interfaces. Subsequently, the CF4/O-2 plasma treatment is integrated in the a-IGZO thin-film transistor (TFT) fabrication process flow. We achieve a reduction of the gate bias dependent RC by a factor up to 13.4, which results in an increased current drive capability. Combined with an associated channel length reduction, the effective linear field-effect mobility mu(lin,FE,eff) is increased by up to 74.6% for the CF4/O-2 plasma treated TFTs compared to untreated reference devices