Stable CW Operation of Gap-Coupled Silicon-On-Sapphire to LiNbO3 Acoustoelectric Amplifiers.
MASSACHUSETTS INST OF TECH LEXINGTON LINCOLN LAB
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Technological advances are detailed which improve the performance of gap-coupled acoustoelectric amplifiers for dc drift field operation. The amplifier configuration is a segmented 1-micrometer thick layer of 20 ohm cm n-type silicon-on-sapphire held in close proximity to a 21-microsecond YZ LiNbO3 delay line. The combination of ion-beam-etched spacer posts on the delay line surface and a simple packaging scheme utilizing the sapphire wafer as a pressurized diaphragm allow reproducible formation of uniform air-gaps of the order of 0.1 micrometers over a 1.5 mm x 2.5 cm area. Transverse dc fringing fields are effectively terminated both at the surface traps of the chemically-stripped and depleted Si surface and at the deep acceptor-donor pair traps within the Si film. Thus the electron-sheet homogeneity is preserved even at drift fields over 2 kVcm and the theoretical S-shaped gain characteristic is observed. For an effective coupling gap of 0.17 micrometers a typical 12-cm long segment has peak electronic gain of over 21 dB at 140 MHz with a minimum acoustic noise figure of 7 dB near 1 kV bias. Intermodulation distortion products are more than 50 dB below signal for output sheet powers under 2 dBmmm. Phase deviation relative to the delay line alone is only 0.7 deg rms for 4 cascaded segments. Author
- Electrical and Electronic Equipment