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HRL develops InAs/GaAlSb mm-wave sensor

HRL Laboratories has developed a zero-bias InAs/AlSb/AlGaSb detector that is expected to dramatically improve the effectiveness of millimeter-wave imaging systems.
HRL Laboratories, the Malibu-based research organization, has developed a novel device operating at zero bias that enables an order-of-magnitude improvement in the sensitivity of millimeter-wave imaging systems.

The millimeter-wave spectrum allows detectors to “see through” obstructions much more effectively than other imaging bands such as the infrared. Prototype millimeter-wave cameras are already being developed to detect concealed weapons and explosives hidden beneath clothing. Navigation applications include enhanced air, land, and sea guidance through poor visibility conditions such as fog, rain, smoke, and sandstorms.

The sensor, using HRL-proprietary technology, is based on an inexpensive antimonide-based semiconductor fabrication process. The device is an innovative “square-law” detector diode.

The current device of choice for millimeter-wave imagers is the Schottky diode, with each diode making up a single pixel of the camera. For low levels of input power, such as occur in the applications suggested above, the Schottky diode must be biased in order for the incoming millimeter-wave signal to generate a current.

The HRL device uses the staggered (Type II) band gap line-up of InAs and GaAlSb layers separated by an AlSb barrier. The structures are grown at HRL by MBE. By careful design, the device is able to function as a “square-law” detector at zero bias.

Both shot and 1/f noise, which derive from and are proportional to the bias, are totally absent in the HRL zero-bias device. The result is an order-of-magnitude improvement in the noise-equivalent-power (NEP), the key sensitivity figure-of-merit. HRL says that this has recently been confirmed by measurements at the National Institute of Standards and Technology (NIST) ini Boulder, Colorado.

HRL has produced and delivered several hundred thousand diodes to Trex Enterprises in San Diego, California, for its advanced camera now under development.

The HRL diode is expected to enable the practical implementation of millimeter-wave imaging for a wide range of military and commercial applications in the near future.

HRL Laboratories LLC is a corporate R&D laboratory owned by Boeing, General Motors and Raytheon. HRL performs custom R&D activities and contract services for its three owners, for the US government, and for other commercial entities.

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