Browse Prior Art Database

Compact Stacked DRAM Cell with Vertical Transfer Device

IP.com Disclosure Number: IPCOM000112322D
Original Publication Date: 1994-Apr-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Bronner, GB: AUTHOR [+2]

Abstract

A new stacked DRAM cell with vertical transfer device is proposed. The proposed cell structure achieves a high degree of integration suitable for 64 Mb and beyond, has good surface topography and avoids problems related to planarization of the stacked capacitor as well as short channel effects of the transfer device.

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Compact Stacked DRAM Cell with Vertical Transfer Device

      A new stacked DRAM cell with vertical transfer device is
proposed.  The proposed cell structure achieves a high degree of
integration suitable for 64 Mb and beyond, has good surface
topography and avoids problems related to planarization of the
stacked capacitor as well as short channel effects of the transfer
device.

      A schematic vertical cross-section and top view of the proposed
new cell are shown in the Figure.  A three polysilicon layer process
is necessary to realize this structure.  The stacked capacitor is
placed in a medium depth trench (2-3&mu.m).  Poly I is the gate of
the transfer device.  The access device length is determined by the
depth of the trench.  Poly II and Poly III form the capacitor
electrodes.  Poly II makes contact with the source of the access
device and Poly III is capacitor plate common to all the cells in the
array.  A layer of silicon nitride isolates the access device from
the stacked capacitor.  A self-aligned contact process is used to
make contact with the drain and the bitline.  The bitlines are formed
after the storage capacitor has been introduced.

      Both open bitline and folded bitline architecture can be
achieved using the stacked cell.  Cell area and capacitance values
for the open and folded bitline structures are summarized below.
Larger storage capacitance can be obtained at the expense of cell
area.