Abstract
Memory structures with an embedded sheet of separated Si or Ge nanocrystals were prepared by low pressure chemical vapour deposition using a Si3N4 control and SiO2 tunnel layers. It was obtained that a properly located layer of semiconductor nanocrystals can improve both the charging and retention behaviour of the MNOS structures simultaneously. Memory window width of above 6 V and retention time of 272 years was achieved for charging pulses of 15 V, 10 ms.
Highlights
Information storage in non-volatile memories is based on changing the threshold voltage of memory field effect transistors (FETs) by appropriate voltage pulses
X-ray photoelectron spectroscopy (XPS) results obtained on the MNOS structures after removing the upper part of the control silicon nitride layer clearly indicate the presence of NCs at the oxide/nitride interface, as it is presented in Fig. 1 for the structures with Si NC deposition duration of 30 s and 60 s
The memory window is somewhat wider for memory structures with NCs than in the reference sample
Summary
Information storage in non-volatile memories is based on changing the threshold voltage of memory field effect transistors (FETs) by appropriate voltage pulses. The actual mechanism is injection of charge by tunneling and its storage in a floating gate, or in traps in metal-nitride-oxide-semiconductor (MNOS) or silicon-oxidenitride-oxide-silicon (SONOS) devices located in the nitride layer close to the SiO2/Si3N4 interface [1,2,3,4,5,6,7,8]. One of the possible solutions is to replace floating gate with separated semiconductor nanocrystals (NCs), which are electrically isolated In this case the loss of information via local defects can be avoided [3,4,5,6,7,8]. Another possible way to avoid the above difficulties is the application of SONOS or MNOS devices In these structures the charge holding the information is stored in the traps of nitride layer, which are electrically isolated by their nature. Two earlier works were devoted to the study the effect of semiconductor NCs in SONOS structures [9, 11], to the best of our knowledge we are the only group studying this effect in MNOS structures
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