Remote cutoff field effect transistor

摘要

1,098,345. Field-effect transistors. MOTOROLA Inc. June 21, 1965 [July 24, 1964], No. 26130/65. Heading H1K. The transverse cross-section of the channel of field effect transistor comprises at least two regions of different thicknesses. As shown, Fig. 3, the channel comprises a plurality of alternate thick and thin regions. The thin regions provide a high initial transconductance while the thick regions provide a high cut-off voltage. The device is produced by depositing a silicon dioxide layer (61) on a P-type silicon substrate (60), Fig. 10B (not shown), etching rectangular openings (62) in oxide layer (61), Fig. 10C (not shown), and diffusing boron into the exposed surface of the substrate, Fig. 10D (not shown). The oxide layer is removed and a layer (64) of N-type silicon is epitaxially deposited during which process the boron diffuses out of substrate (60) to form P-type regions (3111), Fig. 10E (not shown). A P-type silicon layer (67) is epitaxially deposited over the N- type layer (64), Fig. 10F (not shown), and boron is diffused through an oxide mask to produce P-type region (71) extending between the two P-type layers to surround and isolate channel region (33), Figs. 10H and 10I (not shown). Phosphorus is diffused through an oxide mask to form source and drain regions (78, 79), Fig. 10K (not shown), and aluminium is vacuum evaporated to form source and drain contacts (16, 17), Fig. 10L (not shown). A layer of gold is vacuum evaporated on to the lower face of the substrate. A plurality of transistors are formed simultaneously in a large wafer which is divided into individual dice each of which is mounted on a gold-plated header, Fig. 1 (not shown), by heating to above the gold-silicon eutectic temperature so that the gold alloys with the silicon. Aluminium films are deposited on the ends of lead-out wires (20, 21) which are joined to source and drain contacts (16, 17) by fine aluminium wires (18, 19) attached by pressure welding. Lead-out wire (23) is bent over and contacts header (14) which forms the gate contact. The encapsulation is completed by welding a cap (25) to the header. The aspect ratio of the thin regions of the channel is made large to increase the initial transconductance of the device. The transverse cross-section of the channel may alternatively comprise a single thin region flanked by two thick regions, Fig. 8 (not shown), and this may be modified by reducing the thickness of part of the thin region to produce a channel comprising regions of three different thicknesses, Fig. 9 (not shown).