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NONVOLATILE MEMORY DEVICE USING RESONANT TUNNELING FOR LOW VOLTAGE APPLICATIONS

IP.com Disclosure Number: IPCOM000007221D
Original Publication Date: 1994-Jun-01
Included in the Prior Art Database: 2002-Mar-06
Document File: 4 page(s) / 176K

Publishing Venue

Motorola

Related People

Marius Orlowski: AUTHOR [+4]

Abstract

We propose a new programming mechanism for non-volatile devices using the resonant tunneling mechanism for efftcient charging of the floating gate at much lower control gate and drain bias than used presently. The resonant tunneling path through the insulator can be achieved by introduction, either by deposition or by implantation, of appropriate impu- rity energy levels within the forbidden band-gap of the dielectric. No retention problems during the read operation are anticipated.

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Technical Developments Volume 22 June 1994

NONVOLATILE MEMORY DEVICE USING RESONANT TUNNELING FOR LOW VOLTAGE APPLICATIONS

by Marius Orlowski, Jack Higman, Karl Hess* and Matthew Noel1

~BFSLM" InsMM* "nhenity of Illin.ai* aI "lbaM.cham~,*n

ABSTRACT

  We propose a new programming mechanism for non-volatile devices using the resonant tunneling mechanism for efftcient charging of the floating gate at much lower control gate and drain bias than used presently. The resonant tunneling path through the insulator can be achieved by introduction, either by deposition or by implantation, of appropriate impu- rity energy levels within the forbidden band-gap of the dielectric. No retention problems during the read operation are anticipated.

where ESi02 is the dielectric constant of the SiO,. Usually the voltage applied on the control gate is in excess of 12 V The high energy electrons are achieved by heating (accelerating) them in large lateral fields in the channel. The larger the lateral field the more electrons attain high enough energy to surmount the potential barrier, This channel heating requires high voltages at the drain, usually in excess of 8 V The potential barrier between silicon and silicon diox- ide imposes a severe boundary condition on the bias that must be used for the programming (write) oper- ation. Nonvolatile memory devices are therefore dif- ficult to design for low voltage applications. This difficulty may be overcome by our proposal which is discussed in the next section.

INTRODUCTION

NEW PROGRAMMING MECHANISM

USING RESONANT TUNNELING

  In conventional floating gate devices the write operation consists ofapplying a positive voltage VC to the control gate which establishes electric field across the two insulators, one between the silicon substrate and floating gate and the other between the floating and control gate, see Figure 1. During the application of the bias at the control gate VC electrons from silicon substrate can tunnel through the oxide (t,, = d,) into the floating gate and thus store charge on it. In most of the applications the tunneling through the SiO, can be described by the Fowler-Nordheim equation for the tunneling cur- rent density:

J = CE2 exp(-Eo/E) (1)

where C is a constant, E is the electric field, and E, is a function of the carrier effective mass m* and of the barrier height $ only. In many non-volatile devices presently in use, the programming is enhanced by means of hot carrier injection through relatively thick oxides (g 100 A). Afier some time I of charging the floating gate, the applied bias VC is removed and the stored charge Q causes a shift of the threshold voltage VT:

AVT = -dJ&SiO2 Q (2)

  It is known that various impurities introduce energy levels in the forbidden energy band-gap of the dielectric. If the thickness of the dielectric is large enough an isolated energy level acts as a trap for electrons, In fact, this phenomenon is used in all types of MIOS-like devices [l]. For t...