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Charge Storage Into Metallic Nanoparticles E. Verrelli 1 , D. Tsoukalas 1 , K. Giannakopoulos 2 , D. Kouvatsos 3 , P. Normand 3 and D.E. Ioannou 4 1 National Technical University of Athens School of Applied Sciences, 15780 Zografou, Greece 2 Inst. of Materials Science, NCSR Demokritos, NCSR “Demokritos”,153 10, Ag.Paraskevi, Greece 3 Institute of Microelectronics, NCSR Demokritos 4 George Mason Univ., Fairfax VA 22030, USA * Tel: 30-210-7721679, email: verrelli@central.ntua.gr 1. Introduction Nanoparticle memories have made their point during last years as a possible solution to overcome the scaling issue of nonvolatile memories. Metallic nanoparticles have been less explored than semiconductor nanoparticles as charge storage elements [1, 2]. In principle metal nanoparticles should present advantages over silicon nanocrystal memories. The higher electron affinity of several metals as compared with Si allows for engineering the potential well of the storage nodes in order to create an asymmetric barrier between Si channel and the storage nodes. The usual method to form metallic nanoparticles is based on the deposition of thin metallic films using evaporation on top of a tunneling thermal oxide followed by thermal annealing resulting in the formation of metallic nanoparticles. The density and size distributions of the nanoparticles depend on annealing conditions and the thickness of the deposited thin film [3]. The drawback of this technique is the need for relatively high temperature treatment that involves the risk for contamination of the silicon substrate. It also results in uncontrolled size distribution of the nanoparticles. In this work we are presenting results on the formation of nickel nanoparticles on a thin tunneling thermal SiO 2 layer using a new room temperature nanoparticle manufacturing technique. 2. Experimental The nanoparticle deposition technique is based on a physical vacuum deposition process. Particles are generated using a highpressure magnetron sputtering device and carried away from the target area by the discharge gas into a condensation zone where nanoparticles are grown (fig. 1). The nanoparticles after being swept through this zone enter the chamber through a final aperture and they are soft-landed on the oxide surface. Using such a technique room temperature formation of nanoparticles becomes possible under high purity vacuum conditions. The tunneling oxide used in the present experiment is a thermal oxide of 4 nm formed after dry oxidation of p-type silicon wafers at 850˚C. Then a layer consisting of nickel nanoparticles was deposited followed by the deposition of an insulating layer of HfO 2 by RF reactive sputtering. High purity HfO 2 target was used and deposition was performed either at room temperature or 300˚C under either argon flow or a mixture of argon/oxygen flow to a ratio 1:6. Deposition was performed at a pressure 8.10 -3 mbar using an r.f. power of 200 W. Aluminum metal contacts were e-beam evaporated onto the backside of the silicon substrates and on the top of the deposited layers through a shadow mask to form MIS capacitors. An annealing step at 320˚C for 20 min in N 2 was performed after finalizing fabrication for all samples. For each sample containing nanoparticles a reference sample with the same SiO 2 /HfO 2 gate dielectric stack but without the nanoparticle layer was also fabricated. Characterization of charge storage within the layers was subsequently performed by C-V sweeps at 1 MHz using an Agilent 4284A capacitance meter. 3. Discussion-Results Nanoparticles with size distributions of ±20% and density distributions that can vary between 10 10 cm -2 and 10 12 cm -2 are formed. Minimum achieved size of the nanoparticles is 2 nm and maximum size 14 nm by proper variation of process parameters. These results have been obtained by Transmission Electron Microscopy imaging. Representative plane view images of deposited nickel nanoparticles with different size and density distributions are shown in fig.2. C-V measurements of reference samples -not shown here- demonstrate that sputtering conditions at 300˚C under oxygen flow induce negligible hysteresis. Room- temperature or 300˚C deposited HfO 2 without any O 2 flow during sputtering exhibit strong hysteresis and cannot be used efficiently as control dielectrics. On fig.3 and fig.4 we present C-V measurements obtained using the same tunneling oxide (4 nm thickness) and nanoparticle layer but with different thickness of HfO 2 (10 nm and 25 nm respectively) deposited at 300˚C under Ar/O 2 flow. In each of these figures the corresponding reference sample is presented for comparison. A clear effect resulting from the presence of nanoparticles is observed in both figures. From these data the corresponding memory windows are estimated and drawn in fig. 5 and 6 as a function of voltage sweeps. As it can be seen the 25 nm thick HfO 2 sample shows a larger and more symmetric window compared to the 10 nm HfO 2 sample as a result of less leakage current from nanoparticles to the gate electrode. This is also confirmed by I-V measurements. 4. Conclusions We have demonstrated charge storage in nickel nanoparticles deposited on thin SiO 2 films at room temperature by a PVD technique through the fabrication and electrical measurements of MIS structures in which HfO 2 is used as the control insulator. Memory windows of 2 V for applied gate voltages less than 7 V have been measured. The results reported herein show the potential of the PVD technique for controlled growth of nanoparticles for use in non-volatile memory applications. 21
References [1] CH Lee, J. Meteer, V. Narayanan, EC Kan, J. Electronic Mater. 34 (2005) 1 [2] JJ Lee, Y. Harada, JW Pyun, DL Kwong, Appl. Phys. Lett. 86 103505 (2005) [3] J. Dufourcq, P. Mur, M.J. Gordon, S. Minoret, R. Coppard and T. Baron, Materials Science and Engineering: C, in press (available in sciencedirect) Fig 1: Nanoparticle source schematic. Fig.2 TEM plane view images of as deposited nanoparticles. The bar corresponds to 20 nm. C/C ox 1.0 0.8 0.6 0.4 -6 -4 -2 0 2 4 Gate Bias (V) 0.2 1V/-1V/1V 3V/-3V/3V 5V/-5V/5V 0.0 -6 -4 -2 0 2 4 C/C ox 1.0 0.8 0.6 0.4 0.2 Gate Bias (V) 1V/-1V/1V 3V/-3V/3V 5V/-5V/5V Flat-Band Voltage Shift (V) 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 1 2 3 4 5 6 7 Gate Sweep Bias (V) Fig 3: C-V characteristics for 10nm thick HfO 2 memory device. In the inset the C-V curves for the reference sample are shown. Fig.4: Flat-band voltage shifts for 10nm thick HfO 2 memory device under sweep bias operation. C/C ox 1.0 0.8 0.6 0.4 0.0 -6 -4 -2 0 2 4 Gate Bias (V) 1V/-1V/1V 0.2 3V/-3V/3V 5V/-5V/5V 7V/-7V/7V 0.0 -6 -4 -2 0 2 4 C/C ox 1.0 0.8 0.6 0.4 0.2 Gate Bias (V) 1V/-1V/1V 3V/-3V/3V 5V/-5V/5V Flat-Band Voltage Shift (V) 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 1 2 3 4 5 6 7 Gate Sweep Bias (V) Fig 5: C-V characteristics for 25nm thick HfO 2 memory device. In the inset the C-V curves for the reference sample are shown. Fig 6: Flat-band voltage shifts for 25nm thick HfO 2 memory device under sweep bias operation. 22
Page 1 and 2: XXIII ΠΑΝΕΛΛΗΝΙΟ ΣΥΝΕ
Page 3 and 4: Κοιτώντας τα πρακτ
Page 5 and 6: ΕΠΙΤΡΟΠΕΣ Οργανωτι
Page 7 and 8: ΠΡΟΓΡΑΜΜΑ ΣΥΝΕΔΡΙΟ
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forwarded to the back interface dur
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Σχήμα 2: Εκθετική εξ
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V th (V) G m,max /G m,max0 (%) I d
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C/ C ox 1,0 0,8 0,6 0,4 0,2 0,0 -4
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και Ta 2 O 5 , των οποίω
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κατασκευή της. Η πα
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ΔP (mW) 12 10 8 6 4 2 0 0 500 1000
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υπολογίσουμε θεωρη
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Σχήμα 2 Σύστημα ηλε
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Μελέτη των Μηχανισ
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Ανάπτυξη και Μελέτ
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Structure and Magnetic Properties o
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Δομή και Μαγνητικέ
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Μετρήσεις Ειδικής
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Further, almost all of the observed
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g-factor 2.019 2.016 2.013 2.010 2.
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ρυθμό 4 C.min -1 , έπειτ
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ΜΕΛΕΤΗ ΤΟΥ ΦΑΙΝΟΜΕ
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Νέοι Εξαφερίτες Ba µ
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Crystal Structure of a new Supramol
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Magnetic Phase Transition in Synthe
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Συσχέτιση πλαστική
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Resonant Spin Transfer Torque in Do
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3 η Προφορική Συνεδ
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technology, and e-beam lithography.
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ecause it reduces the calculation o
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The thermodynamic average is obtain
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ΑΠΟΤΕΛΕΣΜΑΤΑ Στην
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προερχόµενη είτε α
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Combining Magnetism and Ferroelectr
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υµένια LCMO/STO (100) πολ
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Our scheme is illustrated in Fig. 1
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[6] . Η μελέτη του υλι
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τα πειραµατικά µας
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συµπύκνωµα. Αυτό επ
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και αναδεικνύει τρ
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P P P P P power P copolymers P and
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Αυτο-οργάνωση και Μ
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Viscoelastic Response of Micelles w
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Διηλεκτρική απόκρι
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Light - induced Reversible Hydrophi
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Οι παραπάνω τρεις κ
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AP-PH (a.u.) 0.4 0.3 0.2 0.1 0.0 0
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Synthesis of Polymer Brushes onto I
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Conformational Properties of Dendri
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Structure and Dynamics of Branched
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∆οµή και ∆υναµική
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Επίδραση της Τοπολ
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(α) (β) Σχήμα 2: (α) Απε
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Figure 3. Generation 4 PAMAM-H 2 O
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Από όλα τα παραπάνω
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Το PHEGMA είναι άμορφο
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PS HAuCl 4 P2VP Ion loading PSP2VP
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The nonlinear optical response of A
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νανοσωµατίδια. Όπω
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Bioactive Glass/Nanodiamonds system
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Energy Loss Rates of Hot Electrons
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Σύνθεση και Χαρακτ
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μπορεί να ερμηνευτ
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Nανοσυνθέτα Εποξει
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[1] S. Iijima, Nature 354, 56 (1991
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Figure 3: GCMC calculations for und
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μερών, εμφανίζοντα
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1.0 Reflectance 1.1 1.0 0.9 0.8 0.7
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στο συντελεστή διέ
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¿ÔÖØÑÒØÓÐØÖÐÒÒÖÒ¸
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Συναπόθεση Cr - Ni σε
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Investigation of the Structural, Mo
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Modification of Perlite Cementitiou
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Templated Sol-Gel Synthesis Of TiO
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Παρασκευή Υμενίων
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Preparation of YSZ Solid Electrolyt
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Σύνθεση, Ανισοτροπ
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Μελέτη ανθρώπινων
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Local Coordination of Zn and Fe in
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Επίδραση της Προσθ
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Αλκαλική Σύνθεση κ
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Μηχανικές Iδιότητε
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The Influence of Thermal Aging on t
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Modeling and quantitative phase ana
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Συμβολή στη Συντήρ
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Κρυσταλλική Συµπερ
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Σύνθεση Στερεών ∆ι
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Fabrication and Characterization of
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∆ιερεύνηση δυνατό
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Συγκριτική αξιολόγ
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6 η Προφορική Συνεδ
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Ηλεκτρομαγνητική Α
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Φασματοσκοπική Μελ
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Thermal and Electrical Properties o
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Structure, Mechanical, and Optoelec
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Designing Nanoporous Materials for
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This program was developed to serve
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Νέα Αυτό-οργανούμε
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A Physical Model to Interpret the E
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FIR study of Ag x (As 33 S 33 Se 33
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Mελέτη Μεικτών Γυαλ
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The Structural Role of Fe and Zn in
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ΕΥΡΕΤΗΡΙΟ ΣΥΓΓΡΑΦΕ
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Κομπίτσας Μ…………
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ΕΥΡΕΤΗΡΙΟ ΣΥΓΓΡΑΦΕ
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