Browsing by Subject "Silicon nanoparticles"

Now showing 1 - 9 of 9

Open Access
2-nm laser-synthesized Si nanoparticles for low-power charge trapping memory devices
(IEEE, 2014-08) El-Atab, N.; Özcan, Ayşe; Alkış, Sabri; Okyay, Ali Kemal; Nayfeh, A.
In this work, the effect of embedding Silicon Nanoparticles (Si-NPs) in ZnO based charge trapping memory devices is studied. Si-NPs are fabricated by laser ablation of a silicon wafer in deionized water followed by sonication and filtration. The active layer of the memory was deposited by Atomic Layer Deposition (ALD) and spin coating technique was used to deliver the Si-NPs across the sample. The nanoparticles provided a good retention of charges (>10 years) in the memory cells and allowed for a large threshold voltage (Vt) shift (3.4 V) at reduced programming voltages (1 V). The addition of ZnO to the charge trapping media enhanced the electric field across the tunnel oxide and allowed for larger memory window at lower operating voltages. © 2014 IEEE.
Open Access
Enhanced non-volatile memory characteristics with quattro-layer graphene nanoplatelets vs. 2.85-nm Si nanoparticles with asymmetric Al2O3/HfO2 tunnel oxide
(Springer New York LLC, 2015) El-Atab, N.; Turgut, B. B.; Okyay, Ali Kemal; Nayfeh, M.; Nayfeh, A.
In this work, we demonstrate a non-volatile metal-oxide semiconductor (MOS) memory with Quattro-layer graphene nanoplatelets as charge storage layer with asymmetric Al2O3/HfO2 tunnel oxide and we compare it to the same memory structure with 2.85-nm Si nanoparticles charge trapping layer. The results show that graphene nanoplatelets with Al2O3/HfO2 tunnel oxide allow for larger memory windows at the same operating voltages, enhanced retention, and endurance characteristics. The measurements are further confirmed by plotting the energy band diagram of the structures, calculating the quantum tunneling probabilities, and analyzing the charge transport mechanism. Also, the required program time of the memory with ultra-thin asymmetric Al2O3/HfO2 tunnel oxide with graphene nanoplatelets storage layer is calculated under Fowler-Nordheim tunneling regime and found to be 4.1 ns making it the fastest fully programmed MOS memory due to the observed pure electrons storage in the graphene nanoplatelets. With Si nanoparticles, however, the program time is larger due to the mixed charge storage. The results confirm that band-engineering of both tunnel oxide and charge trapping layer is required to enhance the current non-volatile memory characteristics.
Open Access
Low power Zinc-Oxide based charge trapping memory with embedded silicon nanoparticles
(ECS, 2014) Nayfeh, A.; Okyay, Ali Kemal; El-Atab, N.; Özcan, Ayşe; Alkış, Sabri
In this work, a bottom-gate charge trapping memory device with Zinc-Oxide (ZnO) channel and 2-nm Si nanoparticles (Si-NPs) embedded in ZnO charge trapping layer is demonstrated. The active layers of the memory device are deposited by atomic layer deposition (ALD) and the Si-NPs are deposited by spin coating. The Si-NPs memory exhibits a threshold voltage (Vt) shift of 6.3 V at an operating voltage of -10/10 V while 2.6 V Vt shift is obtained without nanoparticles confirming that the Si-NPs act as energy states within the bandgap of the ZnO layer. In addition, a 3.4 V Vt is achieved at a very low operating voltage of -1 V/1 V due to the charging of the Si-NPs through Poole-Frenkel emission mechanism at an electric field across the tunnel oxide E > 0.36 MV/cm. The results highlight a promising technology for future ultra-low power memory devices.
Open Access
Low power zinc-oxide based charge trapping memory with embedded silicon nanoparticles via poole-frenkel hole emission
(2014) El-Atab, N.; Ozcan, A.; Alkis, S.; Okyay, Ali Kemal; Nayfeh, A.
A low power zinc-oxide (ZnO) charge trapping memory with embedded silicon (Si) nanoparticles is demonstrated. The charge trapping layer is formed by spin coating 2 nm silicon nanoparticles between Atomic Layer Deposited ZnO steps. The threshold voltage shift (ΔVt) vs. programming voltage is studied with and without the silicon nanoparticles. Applying -1 V for 5 s at the gate of the memory with nanoparticles results in a ΔVt of 3.4 V, and the memory window can be up to 8 V with an excellent retention characteristic (>10 yr). Without nanoparticles, at -1 V programming voltage, the ΔVt is negligible. In order to get ΔVt of 3.4 V without nanoparticles, programming voltage in excess of 10 V is required. The negative voltage on the gate programs the memory indicating that holes are being trapped in the charge trapping layer. In addition, at 1 V the electric field across the 3.6 nm tunnel oxide is calculated to be 0.36 MV/cm, which is too small for significant tunneling. Moreover, the ΔVt vs. electric field across the tunnel oxide shows square root dependence at low fields (E 1 MV/cm) and a square dependence at higher fields (E > 2.7 MV/cm). This indicates that Poole-Frenkel Effect is the main mechanism for holes emission at low fields and Phonon Assisted Tunneling at higher fields. © 2014 AIP Publishing LLC.
Open Access
Memory effect by charging of ultra‐small 2‐nm laser‐synthesized solution processable Si‐nanoparticles embedded in Si–Al2O3–SiO2 structure
(Wiley-VCH Verlag, 2015) El-Atab, N.; Rizk, A.; Tekcan, B.; Alkis, S.; Okyay, Ali Kemal; Nayfeh, A.
A memory structure containing ultra-small 2-nm laser-synthesized silicon nanoparticles is demonstrated. The Si-nanoparticles are embedded between an atomic layer deposited high-κ dielectric Al2O3 layer and a sputtered SiO2 layer. A memory effect due to charging of the Si nanoparticles is observed using high frequency C-V measurements. The shift of the threshold voltage obtained from the hysteresis measurements is around 3.3V at 10/-10V gate voltage sweeping. The analysis of the energy band diagram of the memory structure and the negative shift of the programmed C-V curve indicate that holes are tunneling from p-type Si via Fowler-Nordheim tunneling and are being trapped in the Si nanoparticles. In addition, the structures show good endurance characteristic (>105program/erase cycles) and long retention time (>10 years), which make them promising for applications in non-volatile memory devices. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Open Access
Nanosecond pulsed laser ablated sub-10 nm silicon nanoparticles for improving photovoltaic conversion efficiency of commercial solar cells
(Institute of Physics Publishing Ltd., 2017) Rasouli, H. R.; Ghobadi, A.; Ghobadi, T. G. U.; Ates, H.; Topalli, K.; Okyay, Ali Kemal
In this paper, we demonstrate the enhancement of photovoltaic (PV) solar cell efficiency using luminescent silicon nanoparticles (Si-NPs). Sub-10 nm Si-NPs are synthesized via pulsed laser ablation technique. These ultra-small Si nanoparticles exhibit photoluminescence (PL) character tics at 425 and 517 nm upon excitation by ultra-violet (UV) light. Therefore, they can act as secondary light sources that convert high energetic photons to ones at visible range. This down-shifting property can be a promising approach to enhance PV performance of the solar cell, regardless of its type. As proof-of-concept, polycrystalline commercial solar cells with an efficiency of ca 10% are coated with these luminescent Si-NPs. The nanoparticle-decorated solar cells exhibit up to 1.64% increase in the external quantum efficiency with respect to the uncoated reference cells. According to spectral photo-responsivity characterizations, the efficiency enhancement is stronger in wavelengths below 550 nm. As expected, this is attributed to down-shifting via Si-NPs, which is verified by their PL characteristics. The results presented here can serve as a beacon for future performance enhanced devices in a wide range of applications based on Si-NPs including PVs and LED applications.
Open Access
Silicon nanoparticle charge trapping memory cell
(Wiley-VCH Verlag, 2014) El-Atab, N.; Ozcan, A.; Alkis, S.; Okyay, Ali Kemal; Nayfeh, A.
A charge trapping memory with 2 nm silicon nanoparticles (Si NPs) is demonstrated. A zinc oxide (ZnO) active layer is deposited by atomic layer deposition (ALD), preceded by Al2O3 which acts as the gate, blocking and tunneling oxide. Spin coating technique is used to deposit Si NPs across the sample between Al2O3 steps. The Si nanoparticle memory exhibits a threshold voltage (Vt) shift of 2.9 V at a negative programming voltage of -10 V indicating that holes are emitted from channel to charge trapping layer. The negligible measured Vt shift without the nanoparticles and the good re- tention of charges (>10 years) with Si NPs confirm that the Si NPs act as deep energy states within the bandgap of the Al2O3 layer. In order to determine the mechanism for hole emission, we study the effect of the electric field across the tunnel oxide on the magnitude and trend of the Vt shift. The Vt shift is only achieved at electric fields above 1 MV/cm. This high field indicates that tunneling is the main mechanism. More specifically, phonon-assisted tunneling (PAT) dominates at electric fields between 1.2 MV/cm < E < 2.1 MV/cm, while Fowler-Nordheim tunneling leads at higher fields (E > 2.1 MV/cm). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Open Access
Silicon nanoparticles from pulsed laser ablation
(CRC Press, 2017) Kurşungöz, Canan; Şimşek, Elif U.; Ortaç, Bülend; Sattler, K. D.
The research on silicon nanocrystals (SiNCs) has been considerably attractive for the scientist in the last decades due to the SiNCs’ significant size-dependent optical properties, and their potential for stimulated emission (Pavesi et al. 2000). The bright photoluminescence (PL) properties of SiNCs is mainly observed in visible regions of the spectrum (Wolkin et al. 1999). On the other hand, blue-luminescent SiNCs would provide a decrease in free carrier absorption and an increase in the stimulated emission (Švrček et al. 2006). These excellent properties and their biocompatible nature make SiNCs a promising candidate for applications such as light-emitting devices or energy sources, in biomedicine and photodynamic therapy (Walters et al. 2005; Stupca et al. 2007; Wang et al. 2008). Moreover, it was suggested that the production of SiNCs in colloidal suspension provides considerable advantages in optoelectronics applications due to the increased stimulated emission process (Luterova et al. 2016).
Open Access
Two-nanometer laser synthesized Si-nanoparticles for low power memory applications
(Springer International Publishing, 2016) El-Atab, N.; Okyay, Ali Kemal; Nayfeh, A.
Current flash memory devices are expected to face two major challenges in the near future: density and voltage scaling. The density of the memory is related to the gate length scaling which is constrained by the gate stack, namely, the tunnel oxide thickness. In fact, the gate length is required to be commensurate with the gate stack in order to maintain a good gate control and to avoid short channel effects. However, in conventional flash memories, the tunnel oxide thickness has a lower limit of 6-7 nm (depending on NOR or NAND structure) in order to avoid back-tunneling and thus leakage of charges which destroys the necessary retention characteristic of the memory (>10 years). The second problem which needs to be solved is the high program and erase operating voltages. Once again, the limitation to operating voltage scaling is the inability to reduce gate stack thickness. Therefore, it is imperative to find novel structures and materials to be incorporated in the memory cells which would allow tunnel oxide and voltage scaling. In this study, MOSFET- and MOSCAP-based memory devices are investigated along with the use of 2-nm silicon nanoparticles (Si-NPs) for charge storage. Atomic layer deposition is used to deposit the active layer of the memory and the spin coating is performed to deliver the Si-nanoparticles across the sample.