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Natural semiconducting diamond samples (Class 11-b) were used to develop techniques for the production of reproducible lowresistivity ohmic contacts for diamond devices. Annealed tantalum/gold and titanium/gold deposits on { 100) polished diamond surfaces reduced the resistance by seven orders of magnitude relative to the as-received samples. The interfaces were characterized using metallography, scanning electron microscopy, and secondary ion mass spectrometry.

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The Tactical Signal Intelligence (SIGINT) Technology (TST) program objective was to develop optically controlled PIN-diode radio frequency (RF) switches and demonstrate their feasibility to enhance electromagnetic interference (EMI) immunity, sensitivity, speed, and reliability in front-end SIGINT systems. APPROACHProject members performed the following tasks to reach the project objective:• Surveyed, analyzed, and selected U.S. Army, Air Force, and Navy SIGINT systems for optoelectronic (OE) switch development goals.• Developed switch circuit designs for these applications.• Developed switch technology to implement these designs and to assess its present performance and limitations.• Demonstrated feasibility in the laboratory and in SIGINT system equipment where possible. RESULTSThe TST Program developed optically controlled PIN-diode-based RF switches for potential TST applications. Applications included EMI immunity, bias-free operation, switching speed, low noise, power handling, and reliability. A U.S. Air Force Common Aperture RF (CARF) and a U.S. Army tactical jammer (TACJAM) system provided performance goals. CARF featured very high ON-OFF ratios at X-band. These ON-OFF ratios were provided by current mechanical switches. TACJAM featured high RF power handling and isolation. For these applications, the TST Program designed, built, and tested switch circuits based upon the photovoltaic (PV)-PIN switch and the PIPINS. For the CARF case, a PV-PIN circuit yielded suitable isolation, but not insertion loss. The shortfall was caused by inherent semiconductor-based switch properties and microwave packaging techniques. For the TACJAM case, which used a T/R switch, the PIPINS circuit reached the performance goals up to 100-W cw (instrument-limited). Single PIPINS later handled 200-W cw in cold switching (instrument-limited) and 175-W cw in hot switching.The TST Program studied the potential advantages of SIGINT applications for three Services. These applications guided OE switch development. The U.S. Air Force CARF X-band bypass switch and the U.S. Navy Combat Direction Finding (CDF) very high frequency/ultra high frequency (VHF/UHF) commutating antenna feed switch were typical examples of low-power, receive, and RF switching applications. High-power RF switching applications were exemplified in the Army (and Marine Corps) TACJAM VHF/UHF T/R switch. The optical PIN diode switches (OPDS) program accomplished the following tasks:• Analyzed optical PIN diode switches. The PV-PIN switch (figure 1) is based upon conventional OPDS concepts for TST.