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Flash Memory Cell using the RSTI (Raised Shallow Trench Isolation)

IP.com Disclosure Number: IPCOM000123119D
Original Publication Date: 1998-May-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 3 page(s) / 141K

Publishing Venue

IBM

Related People

Fujisawa, K: AUTHOR [+3]

Abstract

Disclosed is a Flash memory cell using the Raised Shallow Trench Isolation (RSTI) achieving the high coupling ratio, which contributes to the scaling of the cell size and higher performance of program and erase efficiency at lower voltage. And also the diffusion leakage at the corner of shallow trench isolation (STI) is solved by this RSTI technology. The coupling ratio is given by the formula Coupling ratio = (capacitance between CG and FG) / (capacitance of FG)

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Flash Memory Cell using the RSTI (Raised Shallow Trench Isolation)

   Disclosed is a Flash memory cell using the Raised Shallow
Trench Isolation (RSTI) achieving the high coupling ratio, which
contributes to the scaling of the cell size and higher performance
of program and erase efficiency at lower voltage.  And also the
diffusion leakage at the corner of shallow trench isolation (STI) is
solved by this RSTI technology.  The coupling ratio is given by the
formula
  Coupling ratio = (capacitance between CG and FG) /
                    (capacitance of FG)

   Where, CG indicates the control gate and FG indicates the
floating gate.  The capacitance of FG is consisted with the
capacitance between FG and silicon substrate and the other parasitic
capacitance, besides the capacitance between CG and FG.
Conventionally, the coupling ratio is around 0.5 - 0.6 but it is
likely to be smaller when STI is used for cell isolation comparing
with LOCOS due to the planalization of silicon substrate and STI
surface.  Most conventional method for achieving the high coupling
ratio is to shrink the channel width (b in the Figure 1) or thinning
the thickness between the FG and CG (one in Figure 1).  In this
conventional method, some disadvantages are exposed, such as data
retention problem and reliability of the film for thinning the
thickness between FG and CG, and insufficient drain current for cell
state sensing for smaller channel width.  The proposed flash cell
...