Browse Prior Art Database

Vertical EEPROM Cell

IP.com Disclosure Number: IPCOM000109706D
Original Publication Date: 1992-Sep-01
Included in the Prior Art Database: 2005-Mar-24
Document File: 2 page(s) / 64K

Publishing Venue

IBM

Related People

Acovic, A: AUTHOR [+3]

Abstract

Disclosed is a vertical EEPROM cell with a common source of two devices buried underneath the active area to improve density.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 65% of the total text.

Vertical EEPROM Cell

       Disclosed is a vertical EEPROM cell with a common source
of two devices buried underneath the active area to improve density.

      The vertical EEPROM cell is built inside a trench (Fig. 1).  By
utilizing a vertical structure, the density of EEPROM is increased
and the coupling factor is improved, and operating voltage can be
reduced accordingly.  Since the Fowler-Nordheim tunneling oxide (50
o) between source (bottom of trench, Fig. 1) and floating gate is
decoupled from gate oxide (100 o), the program/erase speed of the
vertical EEPROM is also improved.  The advantages of the vertical
EEPROM are summarized on the next page:
     1.  HIGH DENSITY: By embedding the device vertically into a
trench, the channel length and the size of source region will not
affect the cell size.  Hence, the density of EEPROM can be increased.
     2.  LOW VOLTAGE: Since the tunneling oxide is decoupled from the
gate oxide, the thickness of tunneling oxide (on the bottom of the
trench) can be reduce to achieve the same tunneling current at lower
voltage.
     3.  HIGH PROGRAM/ERASE SPEED: Performance of the vertical EEPROM
is improved because the FN tunneling mechanism occurring at the
bottom of the trench is used to program/erase the cell.
     4.  HIGH COUPLING FACTOR: Since the floating gate is butted to
isolation oxide on 3 sides of the trench, the coupling factor between
floating gate and control gate is high.  As a result of...