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The cryosar is a high-speed two-terminal computer component whose operation, at liquid helium temperature (4.2Â°K), is based on impact ionization of impurities in germanium. Two types of cryosars are discussed: the first, fabricated using uncompensated germanium, exhibits a high resistivity (~107 ohm-cm) until a critical field (~10 volts/cm) is reached, after which the current increases by as much as seven orders of magnitude; the second, fabricated using compensated p-type germanium, has similar electrical characteristics except that a negative resistance region occurs between the high- and low-impedance states, making bistable operation possible. These properties are due to bulk effects, and since both contacts are ohmic, the device is bilateral. The first type of cryosar can perform the functions of an ordinary diode; the bistable cryosar can be used as a memory element, multivibrator or flip-flop. Both types are very fast, the speed being limited by the turn-on time of 10-8 seconds or less. Since the active region of each cryosar is limited to the volume directly between its two contacts, a large number of independent cryosars may be placed on one wafer of germanium. Present results point to excellent reliability and reproducibility of the individual elements, making feasible the plating or evaporation of large arrays, possibly integrated into microprinted circuits. If one requires the cryosars alone, it should be possible to fit 200,000 into a cubic inch.