(705B) Phase-Change Based TCAM Architecture and Cell (17-Sep-2009)

(705B) Phase-Change Based TCAM Architecture and Cell

Background of PCM Element:PCM devices use the unique behavior of chalcogenide glass, which can be "switched" between two states,
crystalline or amorphous, with the application of heat.The crystalline and amorphous states of chalcogenide glass have dramatically different
electrical resistivity values, and this forms the basis by which data is stored.The amorphous,high resistance state is used to represent a binary 1,
and the crystalline, low resistance state represents a 0.PCM devices mostly make use of a mixture of germanium, antimony and tellurium called
GST (Ge2Se2Tb5).Under high temperature (over 600°C), the chalcogenide becomes liquid. Once cooled, it is frozen into an amorphous glass-like
state and its electrical resistance is high.By heating the chalcogenide to a temperature above its crystallization point, but below the melting point,
it will transform into a crystalline state with a much lower resistance.This phase transition process can be completed in as quickly as 5
nanoseconds.Proposed architecture of the PCM based TCAM Cell: BL (Bit line), SL(Search Line) and ML(Match Line)

B L x B L y

S L x S L y

M L

Description of operations of PCM based TCAM cell : Reading, Searching and Writing

SL0x SL0y

BL0x BL0y

Write Operation:

One way to write the 2T-2P TCAM cell is by driving the selected ML high and keeping all other ML low (BLUE DRIVERS)

Write data is then driven on the...