Semiconductors & ICs

HEMT Amplifiers and Equipment for Their On-Wafer Testing

Power levels in CPW circuits can be measured without packaging. Power amplifiers comprising InP-based high-electron-mobility transistors (HEMTs) in coplanar-waveguide (CPW) circuits designed for operation at frequencies of hundreds of gigahertz, and a test set for on-wafer measurement of their power levels have been developed. These amplifiers utilize an advanced 35-nm HEMT monolithic microwave integrated-circuit (MMIC) technology and have potential utility as local- oscillator drivers and power sources in future submillimeter-wavelength heterodyne receivers and imaging systems. The test set can reduce development time by enabling rapid output power characterization, not only of these and similar amplifiers, but also of other coplanar-waveguide power circuits, without the necessity of packaging the circuits.

Posted in: Semiconductors & ICs, Briefs

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Lower-Dark-Current, Higher-Blue-Response CMOS Imagers

Semiconductor junctions are relocated away from Si/SiO2 interfaces. Several improved designs for complementary metal oxide/semiconductor (CMOS) integrated- circuit image detectors have been developed, primarily to reduce dark currents (leakage currents) and secondarily to increase responses to blue light and increase signal- handling capacities, relative to those of prior CMOS imagers. The main conclusion that can be drawn from a study of the causes of dark currents in prior CMOS imagers is that dark currents could be reduced by relocating p/n junctions away from Si/SiO2 interfaces. In addition to reflecting this conclusion, the improved designs include several other features to counteract dark-current mechanisms and enhance performance.

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Compact, Single-Stage MMIC InP HEMT Amplifier

This amplifier exhibits gain of 5 dB at 340 GHz. Figure 1 depicts a monolithic microwave integrated-circuit (MMIC) single-stage amplifier containing an InP-based high- electron-mobility transistor (HEMT) plus coplanar-waveguide (CPW) transmission lines for impedance matching and input and output coupling, all in a highly miniaturized layout as needed for high performance at operating frequencies of hundreds of gigahertz. This is one in a series of devices that are intermediate products of a continuing effort to develop advanced MMIC amplifiers for sub-millimeter-wavelength imaging systems, scientific instrumentation, heterodyne receivers, and other applications.

Posted in: Semiconductors & ICs, Briefs, TSP

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MEMS/ECD Method for Making Bi2–xSbxTe3 Thermoelectric Devices

Devices containing diverse materials in complex three-dimensional shapes can be fabricated. A method of fabricating Bi2–xSbxTe3-based thermoelectric microdevices involves a combination of (1) techniques used previously in the fabrication of integrated circuits and of microelectromechanical systems (MEMS) and (2) a relatively inexpensive MEMS-oriented electrochemical- deposition (ECD) technique. The devices and the method of fabrication at an earlier stage of development were reported in “Sub milli meter-Sized Bi2–xSbxTe3 Thermoelectric Devices” (NPO-20472), NASA Tech Briefs, Vol. 24, No. 5 (May 2000), page 44. To recapitulate: A device of this type generally contains multiple pairs of n- and p-type Bi2–xSbxTe3 legs connected in series electrically and in parallel thermally. The Bi2–xSbxTe3 legs have typical dimensions of the order of tens of microns. Metal contact pads and other non-thermoelectric parts of the devices are fabricated by conventional integrated-circuit and MEMS fabrication techniques. The Bi2–xSbxTe3 thermoelectric legs are formed by electrodeposition, through holes in photoresist masks, onto the contact pads.

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Low-Temperature Supercapacitors

Electrolyte compositions are designed to extend the low-temperature operational limit. An effort to extend the low-temperature operational limit of supercapacitors is currently underway. At present, commercially available non-aqueous supercapacitors are rated for a minimum operating temperature of –40 °C. A capability to operate at lower temperatures would be desirable for delivering power to systems that must operate in outer space or in the Polar Regions on Earth.

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Radiation-Insensitive Inverse Majority Gates

These gates would be implemented as microscopic vacuum electronic devices. To help satisfy a need for high-density logic circuits insensitive to radiation, it has been proposed to realize inverse majority gates as microscopic vacuum electronic devices. In comparison with solid-state electronic devices ordinarily used in logic circuits, vacuum electronic devices are inherently much less adversely affected by radiation and extreme temperatures.

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Dual-Input AND Gate From Single-Channel Thin-Film FET

These transistors show potential as large-area, low-cost electronic circuitry on rigid and flexible substrates. A regio-regular poly (3-hexylthiophene) (RRP3HT) thin-film transistor having a split-gate architecture has been fabricated on a doped silicon/silicon nitride substrate and characterized. RRP3HT is a semiconducting polymer that has a carrier mobility and on/off ratio when used in a field effect transistor (FET) configuration. This commercially available polymer is very soluble in common organic solvents and is easily processed to form uniform thin films. The most important polymer-based device fabricated and studied is the FET, since it forms the building block in logic circuits and switches for active matrix (light-emitting-diode) (LED) displays, smart cards, and radio frequency identification (RFID) cards.

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