Tech Briefs

A Bistable Microelectronic Circuit for Sensing an Extremely Low Electric Field

Bistable systems are prevalently found in many sensor systems. It is well established that a well-designed coupling scheme, together with an appropriate choice of initial conditions, can induce oscillations (i.e. periodic switching between stable fixed points) in over-damped bistable dynamical systems when a control parameter exceeds a threshold value. This behavior was demonstrated in a specific prototype system comprised of three unidirectionally coupled ferromagnetic cores, the basis of a coupled core fluxgate magnetometer. Another prototypical (quartic potential based) system of coupled over-damped Duffing elements has been applied to describe the dynamics of the polarization inside a ferroelectric material, the basis of an electric-field sensor currently under development.

Posted in: Briefs, Electronics & Computers, Architecture, Microelectricmechanical device, Sensors and actuators, Electric power, Product development
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Fiber-Optic Seismic Sensor for Unattended Ground Sensing

Seismic military sensors are required to be robust, reliable, compact, and easy to install and operate to be effective in the battlefield environment. Three types of sensor technologies were addressed that provide improved design and novel signal processing techniques: (a) a wavelength scanning, pulsed-laser-based demodulation system; (b) digital lock-in amplifier and field-programmable gate array (techniques) for weak signal detection and processing; and (c) improved seismic sensitivity based on carbon fiber optic composite cantilever and fiber-Bragg-grating (FBG).

Posted in: Briefs, Physical Sciences, Fiber optics, Sensors and actuators, Defense industry
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Reflected Signal Analysis

Forensic characterization of a wireless device is useful in many applications. An example of this is in the testing of Federal Communications Commission (FCC) Part 15 devices that must adhere to strict guidelines with regard to RF interference; one reason being problems with Portable Electronic Devices (PEDs) carried onboard aircraft. The operation of PEDs aboard U.S.-registered civil aircraft is limited. These rules also permit the use of specific PEDs after the aircraft operator has determined that the PED will not interfere with the operations of the aircraft. However, how can the aircraft operator know which PEDs are approved, or if the approved devices are being operated at inappropriate times? Compliance can be verified by detecting the operation of transmitting PEDs (T-PEDs) using an onboard monitoring system, or it could be verified by characterizing the device at a gate entry point, whether powered on or off, using specially designed probe signals and forensic techniques to classify the returned signal. In a more general setting, forensic characterization allows determination of the type of device, make, model, configuration, and other characteristics based on observation of the data that the device produces. The unique characteristics of the device are known as device signatures or device fingerprints.

Posted in: Briefs, Electronics & Computers, Electromagnetic compatibility, Wireless communication systems, Aircraft operations, Regulations, Identification
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Threshold Voltage Tuning of Metal-Gate MOSFETs Using an Excimer Laser

This work presents a localized method for tuning the threshold voltages (Vt) of multilayer metal-gate metal-oxide-semiconductor field-effect transistor (MOSFET) devices with a spatial area theoretically limited by the wavelength of the laser beam. This technique allows an independent means to tailor threshold voltage on a device-to-device basis that provides greater design flexibility. This maskless technique allows tailoring of thresholds by tuning the work function of the gate by intermixing titanium and titanium nitride using a laser pulse. The source and drains of the MOSFET are simultaneously annealed by the laser.

Posted in: Briefs, Photonics, Calibration, Lasers, Semiconductor devices, Transistors, Titanium
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Development of GaN-Based Nanostructure Photon Emitters

Gallium nitride (GaN)-based wide bandgap semiconductors are very important material systems for fabrication of photon emitters in a wide range of wavelengths. In particular, the light emitters in ultraviolet (UV), blue, and green wavelengths have been developed and demonstrated in recent years. Besides these UV and visible light emitters, the unique properties of a GaN material system such as large exciton energy and large LO phonon energy, have been proposed as a very suitable material candidate for realization of various photon emitters such as single-photon emitters, LEDs, vertical cavity surface emitting lasers (VCSELs), and quantum cascade lasers (QCL) at room temperature.

Posted in: Briefs, Photonics, Lasers, Fabrication, Materials properties, Semiconductors
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Solution Deposition Methods for Carbon Nanotube Field-Effect Transistors

Extensive research has been done on carbon nanotube field-effect transistors (CNTFETs), which may revolutionize electronics. Single-walled carbon nano-tubes (SWNTs) act as the channel between the source and the drain of the transistor device. CNTFETs can have very high on/off current ratios, but the presence of metallic CNTs, in addition to semiconducting CNTs, reduces the on/off ratio significantly. Therefore, the CNT thin film has a major influence on the transistor behavior and must be carefully developed.

Posted in: Briefs, Manufacturing & Prototyping, Transistors, Nanomaterials
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Micro-Propulsion Devices Made of Low-Temperature Co-Fired Ceramics

In the satellite industry, the trend is towards decreasing the size of satellites and clustering of small satellites. Technological advancements in microelectronics have made it more economical to launch a cluster of satellites with a single vehicle rather than the traditional one satellite per vehicle. A small satellite cannot carry a large quantity of fuel or batteries for power so it will require an alternative propulsion system for station-keeping and orbital corrections. The current micro-propulsion alternatives include miniaturized versions of Hall Effect thrusters, plasma thrusters, and chemical devices. These devices are commonly fabricated as microelectromechanical system (MEMS) devices using silicon.

Posted in: Briefs, Manufacturing & Prototyping, Downsizing, Microelectricmechanical device, Product development, Ceramics, Silicon alloys, Satellites
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