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Browse Prior Art Database

Floating Voltage Line Underpass

IP.com Disclosure Number: IPCOM000076285D
Original Publication Date: 1972-Feb-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 51K

Publishing Venue

IBM

Related People

Geller, H: AUTHOR [+2]

Abstract

In order to achieve low resistance the highest doped diffusion, isolation (P++), is used to underpass 10 crossing metal lines 11 as well as perform its usual isolation function at 12. To prevent this underpass from shorting to the P substrate, N++ subcollector 13 is used under the isolation diffusion to separate the two P materials. The junction between the subcollector 13 and isolation diffusions 12 is very highly capacitive.

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Floating Voltage Line Underpass

In order to achieve low resistance the highest doped diffusion, isolation (P++), is used to underpass 10 crossing metal lines 11 as well as perform its usual isolation function at 12. To prevent this underpass from shorting to the P substrate, N++ subcollector 13 is used under the isolation diffusion to separate the two P materials. The junction between the subcollector 13 and isolation diffusions 12 is very highly capacitive.

If the subcollector 13 were biased to a high voltage the diode junction between the subcollector 13 and the isolation 12 would be reverse biased, causing no DC current problems. However, while there is no diffusion capacitance caused by current flow, the underpass 10 still sees a large junction capacitance. The described underpasses avoid this problem by allowing the subcollector to float with respect to the grounded substrate. The capacitance between the subcollector and substrate is small, by comparison to the underpass to subcollector capacitance.

In Fig. 1, the subcollector 13 is floating. However, in the upward transition, the isolation 12 to subcollector 13 diode can forward bias bringing the subcollector voltage up to within a diode drop of the underpass 10. The openings 15 allow contact to be made to the underpass. The Fig. 2 underpass can be used where more room is available. By using collector-type contacts at 16, the subcollector 13 is shorted to the underpass 10 at both ends. This puts the conduct...