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Fabrication of a MOS Memory Device Containing Metal Nanoparticles and a high-k Control Oxide Layer Ch. Sargentis 1* , K. Giannakopoulos 2 , A. Travlos 2 and D. Tsamakis 1 1 Department of Electrical and Computer Engineering, National Technical University of Athens, Iroon Polytechniou 9 Zografou,157 73 Athens, Greece 2 Institute of Materials Science, National Center for Scientific Research `Demokritos`, 153 10 Ag. Paraskevi Attikis, Athens, Greece *sargent@central.ntua.gr Today many electronic devices, such as laptops, palmtops, cellular phones and digital cameras use non-volatile memories that have a very short access time, low power consumption, high memory density and long retention times. Most efforts on improving these devices are focused on the developement of MOSFET floating gate devices embedded with semiconductor nanoparticles [1-7]. Recently, similar devices, embedded with metallic nanoparticles, have been fabricated [2-5]. These devices [2] are relatively immune to the Fermi level fluctuations caused by contamination and have smaller energy perturbation than those based on semiconductor nanoparticles. Since metals can have a wide range of work functions, it is possible to use them for improving the relationship between the retention time and the speed of the write-erase process, parameters that one needs to balance during device design. Memory devices embedded with nanoparticles have been fabricated with various methods, such as: Chemical Vapor Deposition [6], ion beam synthesis [7], sputtering [3] and recently Molecular Beam Epitaxy (MBE) [4]. In this work we use the MBE method in order to fabricate MOS memory structures embedded with platinum (Pt) nanoparticles on a SiO 2 /HfO 2 interface. We have chosen to work with Pt nanoparticles due to the fact that Pt has a large work function. Initially we grew thermally a 3.5 nm dry SiO 2 layer (tunneling oxide) on a n-Si (001) substrate. This oxide layer is fabricated in a furnace with dry thermal oxidation at 850 ºC. We have chosen such a low temperature in order to have good thickness control. Immediately after, the sample is annealed at 920 ºC in nitrogen ambient for 20 minutes in order to remove any states in the SiO 2 layer. Then, 1 nm of Pt is deposited at room temperature; the Pt is evaporated with the use of an electron gun in the MBE system. Next, 37 nm of a HfO 2 control oxide layer are deposited at 200 º C in an oxygen rich ambient, so that it becomes as stoichiometric as possible. An advantage of the MBE method is its control over the Pt nanoparticle size and density, and of the HfO 2 layer thickness. Most importantly, this method leaves the SiO 2 tunnelling layer unaffected, as shown in Figure 1(a) (cross-sectional TEM image). From the plan view image (Figure 1(b)) we find that the average diameter of Pt nanoparticles is 4,9 nm and the sheet density is 3.2x10 12 cm -2 . Figure 1: (a) Cross-section image of Pt nanoparticles embedded in the HfO 2 / SiO 2 interface and (b) Plan-view image of Pt nanoparticles fabricated on SiO 2 oxide The fabricated structure shows a clear hysteresis behaviour on C-V (capacitance-voltage, Figure 2) and G-V (conductancevoltage, not shown here) measurements; a reference structure (one fabricated under exactly the same conditions but without nanoparticles) shows no hysteresis. The flat band voltage shift increases gradually with the increase of the applied electric field. From these C-V measurements, and the assumption that in our structure there are two capacitors in series (one for each oxide), we can find the number of carriers which are stored in every nanoparticle. We have calculated [8] that in every nanoparticles one to two carriers are stored. Furthermore, from the above data, we have calculated that we obtain a flat-band voltage shift (ΔV FB ) equal to +0.257 V for average electric field equal to 0.65 MV/cm. We observe a shift at the position of the flat band voltage when the gate voltage is swept from inversion to accumulation and inverse; there is no shift in the sample without nanoparticles. Figure 3 shows the shift of the flat-band voltage versus the amplitude of a 100ms positive and negative voltage square pulse, applied to the gate of the Pt nanoparticle MOS structures. Immediately after each pulse, C-V measurements were performed by sweeping the gate voltage (V gate ) in a small region near flat-band conditions in order to avoid any charging or discharging effects. 76
C/ C ox 1,0 0,8 0,6 0,4 0,2 0,0 -4 -2 0 2 4 V gate [V] Figure 2: High frequency C-V curves of a MOS device containing Pt nanoparticles embedded in the HfO 2 /SiO 2 interface for V gate =(-1.5)-(+1.5) V (●), (-2)-(+2) V (▲), (-2.5)-(+2.5) V (▼), (-3)-(+3) V (►), (-3.5)-(+3.5) (*) and sample without dots for V gate =(-4)-(+4) V (■). V FB (V) 3.0 square pulse 2.5 2.0 1.5 1.0 0.5 DV max =4.43 V 0.0 -0.5 -1.0 -1.5 -2.0 -2.5 2 4 6 8 10 (V) V gate-pulse Figure 3: Flat-band voltage shift versus gate voltage pulse (Vgate-pulse). Pulse duration was 100ms. It is assumed that the extracted ΔV FB is only due to the application of the square pulse. Electron (hole) charging initiates at voltage pulses of about +5 V (–5 V) and further increases until +9 V (–9 V). The maximum memory window obtained is ΔV FB =4.43V. We have fabricated MOS device stacks that are composed of: a thin injection SiO 2 layer, high-density of Pt nanoparticles deposited thereon and a 37nm-thick HfO 2 control oxide. Structural and electrical studies reveal that these structures are suitable for non-volatile memory devices with low-voltage injection. [1] S. Tiwari, J.A. Wahl, H. Silva, F. Rana, J.J. Welser: Appl. Phys A 71 (2000) 403-414 [2] Zengtao Liu, Chungho Lee, Venkat Narayanan, Gen Pei, Edwin Chihchuan Kan: IEEE Trans. El. Devices 49 9 (2002) 1606-1613 [3] Z. Tan, S. K. Samanta, W. J. Yoo, S. Lee: Appl. Phys. Letters 86 1 (2005) 1-3 [4] Q. Wang, Z. T. Song, W.L. Liu, C.L. Lin, T.H. Wang: Applied Surface Science 230 1-4 (2004) 8-11 [5] S. Kolliopoulou, P. Dimitrakis, P. Normand, Hao-Li Zhang, N. Cant, S. D. Evans, S. Paul, C. Pearson, A. Molloy, M. C. Petty, D. Tsoukalas: J. Appl. Physics 94 8 (2003) 5234-5239 [6] Y. Xiaoli, S. Yi, G. Shulin, Z. Jianmin, Z. Youdou, S. Kenichi, I. Hiroki, H. Toshiro: Physica E: (2000) 189-193 [7] P. Normand, P. Dimitrakis, E. Kapetanakis, D. Skarlatos, K Beltsios, D. Tsoukalas, C. Bonafos, H. Coffin, G. Benassayag, A. Claverie, V. Soncini, A. Agarwal, Ch. Sohl, M. Ameen: Microelectronic Engineering 73-74 (2004) 730-735 [8] Ch. Sargentis, K. Giannakopoulos, A. Travlos, D. Tsamakis, Mater. Res. Soc. Symp. Proc. Vol. 830, D6.4.1, (2005) 77
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XXIII ΠΑΝΕΛΛΗΝΙΟ ΣΥΝΕ
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Κοιτώντας τα πρακτ
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ΕΠΙΤΡΟΠΕΣ Οργανωτι
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ΠΡΟΓΡΑΜΜΑ ΣΥΝΕΔΡΙΟ
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21. Οργανικά τρανζίσ
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15:30 15:45 16:00 16:15 16:30 16:45
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41. Modeling and quantitative phase
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Ανοιχτή Συνεδρία «
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«NανοΥλικά και Νανο
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New materials and MOS device concep
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Reliability Characteristics of Rare
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Ο λόγος των ταχυτήτ
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Thus the mean R In-In is expected t
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FIG 1. Schematic representation of
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με 0.80 eV στη διεπιφά
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Εντοπισµός Φορέων
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Παρασκευή και Xαρακ
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Electrical Spin Injection from Fe i
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Electrical Spin Injection of Spin-P
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References [1] CH Lee, J. Meteer, V
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Σχήμα 1: Φωτογραφία
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Υπολογισμός Υψηλής
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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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ΕΥΡΕΤΗΡΙΟ ΣΥΓΓΡΑΦΕ
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