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Reduction of the Small Channel Effect in an IGFET Structure

IP.com Disclosure Number: IPCOM000079566D
Original Publication Date: 1973-Jul-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Kroell, KE: AUTHOR

Abstract

Small channel or small L effect (IBM Technical Disclosure Bulletin, Vol. 12, No. 9, February 1970, p. 1391) provides a typical limitation to the application of insulated gate field-effect transistors (IGFETs) in integrated circuits. The effect occurs when the channel length becomes so small that the space-charge zones of source and drain overlap. In this case, the FET threshold voltage decreases substantially, so that the FET may become unserviceable as a component.

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Reduction of the Small Channel Effect in an IGFET Structure

Small channel or small L effect (IBM Technical Disclosure Bulletin, Vol. 12, No. 9, February 1970, p. 1391) provides a typical limitation to the application of insulated gate field-effect transistors (IGFETs) in integrated circuits. The effect occurs when the channel length becomes so small that the space-charge zones of source and drain overlap. In this case, the FET threshold voltage decreases substantially, so that the FET may become unserviceable as a component.

Fig. 1 is a plan view of a standard IGFET and Fig. 2 shows the corresponding structure as proposed. The boundaries of the space-charge zones occurring as a result of the operating voltages are marked by dotted lines.

The wedge-shaped design of the source and drain region ensures that the space-charge zones are narrower towards the wedge ends than along the straight boundaries, i.e., d1>d2. This permits choosing a smaller source/drain spacing than was possible with previous arrangements (L2<L1), without the space-charge zones of source and drain touching each other. For this reason, the small channel effect occurs only with shorter gate lengths. The source/drain wedges are preferably realized by ion implantation.

The advantages obtainable are:
1) FET components having higher switching speeds because of

shorter gate length.
2) Reduced punch-through tendency permitting higher operating

voltages.
3) Reduced space requirements for the component be...