Browse Prior Art Database

Bit Line Leakage Screen for Directory Chips

IP.com Disclosure Number: IPCOM000102125D
Original Publication Date: 1990-Oct-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Wong, RC: AUTHOR

Abstract

Partially good directory chips incorporating current sensing and word redundancy functions have been found to contain word line defects contributing to current leakage along some bit lines, leading to later product malfunction in the field. A screening test is described in this article which detects these bit line leakage defects at a saving in time and product SPQL over existing approaches.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 95% of the total text.

Bit Line Leakage Screen for Directory Chips

       Partially good directory chips incorporating current
sensing and word redundancy functions have been found to contain word
line defects contributing to current leakage along some bit lines,
leading to later product malfunction in the field.  A screening test
is described in this article which detects these bit line leakage
defects at a saving in time and product SPQL over existing
approaches.

      The disclosed bit line defect screen test scheme is shown in
the figure.  The screen test circuit (shown in dotted enclosure) is
employed for test purposes only, allowing the chip to be operated
outside of normal limits, such as in stress testing.  Referring to
the figure,  I1 identifies the read access current; I2 the sense
current from the bit line; I3 the leakage current, and I4 the write
discharge current.  As shown, the read access current (I1), from the
lower word line, is controllable from a chip pad. The sense current
per bit line (I2) is proportional to I1. As long as I2 > I3 (leakage
current), READ is still possible except for some performance
degradation.  However, if I2 is adjusted so that I2 < I3, the sense
signal then is simply never developed.  A leakage screen test can
thus be set up with decreasing I2 (e.g., down to 10% of nominal
value).

      The disclosed leakage screen test scheme offers significant
savings in test time over power-down testing procedures and provides
a more reliable meas...