Browse Prior Art Database

Three State MNOS FET Memory Array

IP.com Disclosure Number: IPCOM000085743D
Original Publication Date: 1976-May-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Krick, PJ: AUTHOR

Abstract

Because of the analog nature of the switching characteristics of metal nitride-oxide semiconductor (MNOS) variable threshold field-effect transistors (FET's), it is possible to use them as 3-state memory elements. As a result the effective density of the memory array is increased by 50%.

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Three State MNOS FET Memory Array

Because of the analog nature of the switching characteristics of metal nitride-oxide semiconductor (MNOS) variable threshold field-effect transistors (FET's), it is possible to use them as 3-state memory elements. As a result the effective density of the memory array is increased by 50%.

The 3 states of an MNOS FET memory element are illustrated in Fig. 1. Here the "0" or erased state (V(T) = 1 volt) of the MNOS FET is the same as when the device is operated as a binary memory element. The "2" state corresponds to the high (V(T) = 8 volts) threshold state of the device and is the same as the high-threshold state when the device is operated in the conventional manner. The third state is called the "1" state (V(T) = 4 volts) and corresponds to an intermediate threshold state.

In a word organized memory array similar to the array shown in IBM Technical Disclosure Bulletin, Vol.17, No.6, November 1974, pp. 1811-1813, information is written into a device by first erasing it with the application of a positive potential, +V, to the substrate while the device's gate voltage is held at ground potential. Then, the device is written into one of three states (0, 1, or 2) depending upon the bit line potential during the write half of the erase-write cycle.

To leave the device in the 0 state the bit line potential is held at approximately the word line potential so that the net voltage across the gate insulator is zero volts. To put the device...