Thyristor Ram

1627 Words Mar 18th, 2012 7 Pages
THYRISTOR RAM
Muktesh Waghmare, Raman Gaikwad

1: Principle:
Thyristor is well-known for its high-current drive capability and its bi-stable characteristics. It has been widely used in power electronics applications. With the exponential advances in CMOS technology tiny thyristor devices can now be easily embedded into conventional nano-scale CMOS. This enables the creation of a memory cell technology with features that include small cell size, high performance, reliable device operation, and good scalability. Use of thyristor provides a positive regenerative feedback that results in very large bit cell operation margins. The difference is that the four-transistor CMOS latch of a 6T-SRAM is replaced by the PNP-NPN bipolar latch of a
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Indium is known to have an acceptor level which is 156 meV above the top of the valence band of silicon. As a result, the fraction of ionized indium atoms increases with temperature, resulting in reduced gain. Such a thyristor (TCCT) that has good thermal stability, large switching speed and a small fabrication size is used to create memory cells. Two possible thyristor cell structures for memory devices are as follows:
3.1: Thyristor based S-RAM: T-RAM consists of a thin vertical thyristor with a surrounding MOS gate as the bi stable element and a planar NMOSFET as the access transistor. A novel gate-assisted switching mechanism is used in T-RAM which enables the thyristor to switch at a high speed and a low voltage level. [5]

: Write operation:
Both WL1 and WL2 are high. The first word-line will control the access gate while the second word-line will control the thyristor gate. When writing a "high", the bit-line BL is set at low, and both word-lines WL1, WL2 are switched on. At this moment, the thyristor behaves like a forward biased PN diode. After a write operation, both gates are shut off, and a "high" state is stored in the thyristor.
When writing a "low", the bit-line BL is set at "high" state, and both word-lines WL1, WL2 are switched on. At this moment, the thyristor behaves like a reverse biased diode. After the write operation, both gates are shut off, and a "low" state is stored in the thyristor
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