Browse Prior Art Database

Single FET Memory Cell With Buried Extended Source

IP.com Disclosure Number: IPCOM000080668D
Original Publication Date: 1974-Jan-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 67K

Publishing Venue

IBM

Related People

Anantha, NG: AUTHOR [+3]

Abstract

The area required by a one-device field-effect transistor (FET) memory cell is reduced by extending the FET source below the FET channel to a point near the FET drain. The buried extended source functions as a storage capacitor connected between the FET source and the substrate.

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Single FET Memory Cell With Buried Extended Source

The area required by a one-device field-effect transistor (FET) memory cell is reduced by extending the FET source below the FET channel to a point near the FET drain. The buried extended source functions as a storage capacitor connected between the FET source and the substrate.

Referring to Fig. 1, N+ subcollector 1 is placed in a selected location of P substrate 2. Epitaxial p layer 3 is placed on substrate 2 and N+ reach-through diffusion 4 is made in epitaxial layer 3. The shape of subcollector 1 and reach- through diffusion 4 is shown more clearly in the exploded perspective view of Fig.
4.

The FET is completed, as shown in Fig. 2, by the provision of N+ drain diffusion 5 gate, dielectric 6, metal word line 7, and oxide isolation 8 which penetrates through the epitaxial layer 3 to a point in substrate 2 below buried region 1. Gate dielectric 6 and source and drain regions 4 and 5 are formed either by a self-aligned gate process or by a nonaligned gate process.

Relatively high-diffusion capacitance can be obtained by making the impurity concentration high in the P substrate 2,.in the buried region 1 and in the lower region of epitaxial layer 3. The impurity concentration preferably is at a level of about 10/16/ atoms/cc adjacent to the top surface of the epitaxial layer 3, to preserve the desired qualities of the FET. The graded impurity concentration is achieved during the growth of the epitaxial layer 3.

A...