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SCR Cross-Coupled Memory Cell

IP.com Disclosure Number: IPCOM000047532D
Original Publication Date: 1983-Dec-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 54K

Publishing Venue

IBM

Related People

Hulvey, MD: AUTHOR [+3]

Abstract

The current hogging problem in silicon-controlled rectifier (SCR) cross-coupled memory cells is minimized by minimizing the negative resistance characteristic in the cells. The negative resistance characteristic may be minimized by (1) reducing the resistance in series with the Schottky barrier diodes of the cell, indicated in Fig. 1 as resistors R1 and R2, (2) reducing the current I through the collector of the PNP transistors of the cells, and (3) by increasing the base-to-emitter voltage of the PNP transistors. The electrical circuit of the SCR cell is shown in Fig. 1. The circuit includes first and second cross-coupled bipolar NPN transistors T1 and T2, each having a pair of dual emitters, first and second PNP transistors T3 and T4, and first and second Schottky barrier diodes D1 and D2.

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SCR Cross-Coupled Memory Cell

The current hogging problem in silicon-controlled rectifier (SCR) cross-coupled memory cells is minimized by minimizing the negative resistance characteristic in the cells. The negative resistance characteristic may be minimized by (1) reducing the resistance in series with the Schottky barrier diodes of the cell, indicated in Fig. 1 as resistors R1 and R2, (2) reducing the current I through the collector of the PNP transistors of the cells, and (3) by increasing the base-to- emitter voltage of the PNP transistors. The electrical circuit of the SCR cell is shown in Fig. 1. The circuit includes first and second cross-coupled bipolar NPN transistors T1 and T2, each having a pair of dual emitters, first and second PNP transistors T3 and T4, and first and second Schottky barrier diodes D1 and D2. A cross-section of the layout of the half cell, i.e., devices T1, T3 and D1, is illustrated in Fig. 2. The negative resistance characteristic in SCR cells occurs when the base-emitter voltage of a PNP transistor plus the base-emitter voltage of an NPN transistor is less than the voltage across the Schottky barrier diode connected between the base-collectors of these two transistors plus the voltage drop across resistors R1 and R2. In this current-hogging condition, one selected cell conducts all available read current. Hence, multi-cell reading is not possible and unselected cell data could be destroyed. The base-to-emitter voltage of the PNP transistor may be increased by reducing the lateral PNP hole injection length which will increase the injection current density and this high injection effect will lower the PNP beta. The lateral hole injection length may be conveniently ad...