Charge trap flash

Charge trap flash (CTF) is a semiconductor memory technology used in creating non-volatile NOR and NAND flash memory. The technology differs from the more conventional floating-gate MOSFET technology in that it uses a silicon nitride film to store electrons rather than the doped polycrystalline silicon typical of a floating gate structure. This approach allows memory manufacturers to reduce manufacturing costs five ways:The charge trapping mechanism, first observed in the 1960s, was used as a storage mechanism in EEPROM before it became popular for use in flash memory.Like the floating gate memory cell, a charge trapping cell uses a variable charge between the control gate and the channel to change the threshold voltage of the transistor. The mechanisms to modify this charge are relatively similar between the floating gate and the charge trap, and the read mechanisms are also very similar.Charge trapping flash is similar in manufacture to floating gate flash with certain exceptions that serve to simplify manufacturing.Spansion's MirrorBit Flash and Saifun's NROM are two flash memories that use a charge trapping mechanism in nitride to store two bits onto the same cell effectively doubling the memory capacity of a chip. This is done by placing charges on either side of the charge trap layer. The cell is read by using forward and reverse currents through the channel to read either side of the charge trap.Samsung Electronics in 2006 disclosed its research into the use of Charge Trapping Flash to allow continued scaling of NAND technology using cell structures similar to the planar structures in use at that time. The technology depends on a SONOS (semiconductor-oxide-nitride-oxide-semiconductor) or MONOS (metal-ONOS) capacitor structure, storing the information in charge traps in the nitride layer.