| 摘要 |
1,211,745. Semi-conductor controlled rectifiers. GENERAL ELECTRIC CO. 27 Nov., 1967 [19 Dec., 19661, No. 53971/67. Heading H1K. In a PNPN switching device one of the outermost zones consists of a main region to which the anode or cathode is ohmically connected and an auxiliary region carrying a non-ohmic gate contactor having an area arranged for exposure to a controllable illumination source, the construction being such that the resistance between the gate contact or area and the anode or cathode is higher than that of any current path of the same length in the main region. This accelerates the spread of current of firing thus reducing the turn on delay and rise times and is achieved either by making the auxiliary region thinner or by isolating it from the main region. Where a thinned region is used may be circular and disposed, preferably centrally, within the main region or segmental or annular and disposed at or near the edge of the main region, or there may be plurality of regions each provided with a gate contact. If the region is annular or segmental it may have a similarly shaped gate contact or a plurality of interconnected contacts. The contact may form a Schottky barrier with the auxiliary region e.g. it may be an aluminium wire ultrasonically bonded thereto, or may consist of an ohmically contacted epitaxial layer forming a PN junction with the region. A typical device is made from a 60 ohm. cm. phosphorus doped N type silicon wafer by diffusing into its faces to form P type layers. Then a gold-antimony foil is alloyed to one face to form an ohmically contacted N type cathode layer, and an aluminium foil attached to a tungsten or molybdenum plate alloyed to the other to form an ohmic anode contact. The thinned region is then formed by etching away part of the goldantimony contact and part of the region beneath it, and an aluminium wire bonded to it ultrasonically. The resulting device can be triggered by a positive pulse on the gate. Alternatively the aluminium wire is bonded to the region prior to thinning so that after etching it is disposed on a mesa. In this case as explained in the Specification in this embodiment triggering can be effected by either a positive or a negative pulse. |
