50 Amp silicon titanium junction Schottky power diode - is heat treated during fabrication to freely grow cpds. in boundary layer and make device stable to 650 degrees C

摘要

A Schottky power diode capable of passing 50 A or more has previously been made using N type silicon and chromium with a forward voltage drop of 0.35 V. These diodes deteriorate rapidly as a result of surges and thermal shock because of the formation of chromium silicon cpds. in the boundary layer at temps. exceeding 350 deg. C. By substituting titanium for chrome and subjecting the diode to heat treatment at 600 deg. C and allowing silicon titanium cpds. to form freely in the bonding layer a diode is produced which is more stable, withstanding temps. to 650 deg. C. It has a forward voltage drop of 0.4 V and a lower reverse leakage current at 40 V reverse bias than the chromium diode. The diode is made by epitaxial growth of an N type layer on an N+ substrate with a P+ annular guard ring. This is covered by a resin layer with holes for the Schottky contacts. A 3 micron layer of titanium is laid down by vacuum evaporation and the resin layer dissolved away taking with it the unwanted titanium. A silver layer is deposited on the remaining titanium and the device heat treated at 600 deg. C in a non oxidising atmosphere, for about 30 mins. The rear surface of the device is then metalised by deposition of layers of molybdenum, phosphorous doped nickel and then silver.