Patent GB-1191161-A (GB)
Title: Integrated Circuits
IPC: H01L27/00
Filed: 1967-05-03
Abstract: 1,191,161. Semi-conductor devices. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 3 May, 1967 [6 May, 1966], No. 20467/67. Heading H1K. Isolation between parts of a monolithic integrated circuit is provided by a good conductor in or on the body between the elements connected to an external potential. The screening conductor may surround one or more components and the region of the body to which it is applied is held at the external potential and the regions to either side form resistors across which the p.d.s. between the active areas of the devices and the potential applied to the screening ring are dropped. The values of these resistors depend on the spacing between the device areas and the screening ring and may be selected to provide values which can form part of the desired circuit. In all the embodiments the screening rings are applied to the surface of the wafer. The circuit may comprise: (i) two independent transistors with emitter resistors provided by the paths in the substrate to the screening rings which form the ground connection, Figs. 1a and 1d (not shown); (ii) three emitter followers with their collectors regions provided by a single layer and their base regions also constituted by a single layer divided into individual areas by screening rings and also providing base biasing resistors, Figs. 2a, 2b and 2c (not shown); (iii) a function generator comprising a plurality of diodes provided by area of two common layers and associated resistors, Figs. 4a, 4b and 4c (not shown); (iv) three NPNP controlled rectifiers having one common layer and sharing parts of a second layer, Figs. 7a, 7b and 7c (not shown); (v) two NPNP controlled rectifiers and two input diodes, constructed as hereafter described, forming a bi-stable circuit, Figs. 8, 10a and 10b (not shown); (vi) a ring counter, Fig. 13 (not shown); and (vii) a shift register, Fig. 14 (not shown). The diodes for circuit (v) are provided by NPNP structures with the last two regions connected by low value resistor provided by part of the N region between the active areas and the screening ring. Two such diodes can be provided by diffusing two N-type regions into a PNP structure and surrounding by a single screening ring, and such double diodes are used in circuits (v) and (vi), single diodes being used in circuit (vii). The current in an NPNP structure is limited to the central area of the device due to the potential valley produced by the lateral resistance to the screening ring, Fig. 15a (not shown). The breakdown voltage of an NPNP structure can be reduced by combining it with a Zener diode, Fig. 16 (not shown). Connections between the top and the bottom of the wafer can be produced by etching a cavity through the upper layers to expose the bottom layer, and depositing a conductive connection from the top surface to the bottom of the cavity. The screening ring need not completely enclose the device but may have a gap through which a connection to a region inside the ring passes, Figs. 6a and 6b (not shown). In a specific embodiment an NPNP element is produced by epitaxially depositing an N- type layer on a P-type silicon substrate, diffusing-in boron to form a P-type region and then diffusing-in phosphorus to form an N-type region and to simultaneously form an annular N-type zone in the epitaxial layer surrounding the device to produce a low resistance connection for the screening ring. The electrodes and screening ring are produced by vapour depositing a layer of aluminium and selectively etching.