Integrated-circuit Schottky polarity guard

An aluminium Schottky-diode bridge, fabricated using a standard linear integrated-circuit process, is described. The Schottky-barrier structure effectively eliminates parasitic p-n-p transistor action, which is troublesome when collector-base diodes are used. A `guard-ring¿ geometry enables a reverse breakdown of 70 V to be achieved. Comparable devices made with `metal-overlap¿ geometry have reduced breakdowns of 36 V. A further advantage of using Schottky diodes in the bridge is their low forward drop, which for this device is 0.42 V at 10 mA. The intended area of application is in hybrid microcircuits for telephone sets.