| Abstract |
To investigate memory properties of GaN QDs, MOS capacitors were realized with GaN nanocrystals embedded in the SiO2 dielectric. Samples were grown on n-type Si and Al was used as the metal gate. A reference sample with no QDs was also developed. High-frequency capacitance-voltage measurements were performed which revealed a wide hysteresis for all the samples except for the reference which exhibited no hysteresis for a full voltage sweep. C-V characteristics suggest electron injection that takes place from the substrate but limited hole injection. The width of the hysteresis was found to increase with the quantity of GaN embedded in the oxide. Pulse measurements confirm an asymmetry between electron and hole injection and suggest that erasing is more challenging than programming for these devices. Retention measurements at room temperature revealed good retention properties meeting the ten-year threshold for non-volatility. Finally, transient current measurements were performed to further investigate injection mechanisms.
The continuous floating gate transistor faces several challenges, the most significant of which is its scalability problem, and this does not allow NVMs to follow the rate of shrinkage of other integrated circuits. For that reason, several alternatives to the FG-MOSFET have been proposed in literature with the nanoparticle FG-MOSFET being a very prominent candidate. In this direction, GaN QDs could present two key advantages: compared to Si, GaN is considered to have a negative conduction band offset which could result in improved retention characteristics; in addition, it is fully compatible with current CMOS manufacture technologies. The current thesis investigates the potential of GaN QDs in NVMs.
The first chapter introduces the reader in the basic concepts of NVM, as well as the fundamental operation of the FG-MOSFET. The second chapter includes the theoretical background that is necessary for the understanding of this work. Physics of the MOS system are first described with emphasis on the capacitance of the device. The paragraphs that follow look into the properties of both the continuous and the nanoparticle floating gate respectively. Finally, chapter 3 describes the experimental process, the results and the analysis in full detail.
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CMOS compatible non-volatile memory devices based on III-N quantum dots
