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Successive Layer Charging of Si Nanocrystals in a Double-Layer Nanocrystal Structure within SiO 2 M. Theodoropoulou, A. Salonidou and A. G. Nassiopoulou* IMEL/NCSR Demokritos, Terma Patriarchou Grigoriou, Aghia Paraskevi, 153 10 Athens, Greece *A.Nassiopoulou@imel.demokritos.gr Two-dimensional arrays of Si nanocrystals within SiO 2 constitute a distributed charge storage medium with better immunity to tunnel oxide defects compared with the polycrystalline silicon continuous charging medium used in conventional non-volatile memory devices [1]. However, when tunnel oxide thickness goes below ~5 nm, data retention fails to fulfill the 10-years criterion set for non-volatility. In order to overcome this problem, a two-layer structure, with one layer composed of very small nanocrystals (diameter below ~3 nm) and a second one on top with larger nanocrystals (diameter above ~5 nm) was proposed [2]. In this case, due to quantum confinement, the small dots show a band offset compared with the larger dots, which acts as a barrier for carrier leakage to the substrate. In this work we fabricated such a structure using low pressure chemical vapor deposition of amorphous silicon (α-Si) on a thin tunnel oxide on Si, followed by high temperature-thermal oxidation/annealing and we investigated its charging properties. The fabrication conditions were presented in detail elsewhere [3]. The following processing steps were used. First, p-type silicon wafers with a resistivity of 1-2 Ω.cm were oxidized at 850 o C for 8 min producing an approximately 3.5 nm thick thermal oxide. An approximately 9.5 nm thick silicon film was deposited on top of the thermal oxide, by LPCVD at 580 o C, 300 mTorr, for 3 min. The samples were oxidized at 900 o C for 25 min producing an approximately 13 nm thick thermal oxide, on top of a 2.5 nm thick silicon nanocrystal layer. In order to reduce the thickness of the top oxide layer, the samples were chemically etched in a 2% HF solution, resulting in a 1.5 nm thick top oxide layer. High temperature annealing was performed in N 2 at 900 o C for 30 min. The resulting structure contains one layer of silicon nanocrystal within two SiO 2 layers. By repeating the same procedure, a second silicon nanocrystal layer is grown, with a size of 3.5 nm and a control oxide of 10 nm. Finally the samples were annealed in N 2 at 900 o C for 30 min. For electrical characterization an aluminum gate metal was deposited and patterned and an ohmic contact was formed on the back side of the wafer. The two-layered silicon nanocrystal MOS structure is shown schematically in Fig.1. To investigate the charging properties of the silicon nanocrystal layers, capacitance-voltage (C-V) measurements were performed at 1MHz, at room temperature, by applying positive and negative gate pulses of different height and width on the gate without discharging the structure between applied pulses. Fig. 2 shows C-V curves of a fresh capacitor compared to those obtained after application of positive and negative gate pulses. The pulse width was 15 s and the pulse height step 0.5 V. When a positive or a negative gate pulse is applied, a positive or negative shift in the flatband voltage is obtained, indicative of charging the silicon nanocrystal layers with electrons (holes) respectively. This charging is due to injection of electrons (holes) from the silicon substrate to the nanocrystal layers through the tunnel oxide. In the presence of the two layers, charging of the first layer is first completed, resulting in a first saturation step in the flat band voltage shift ΔV FB , and charging of the second layer (second saturation step) occurs at a higher voltage. The same occurs at negative applied pulses, corresponding to hole charging. A maximum positive shift of 2.1 V and negative shift of -2.8 V were obtained for maximum end voltages of ±8 V. Fig. 3 shows the flatband voltage shift ΔV FB as a function of the applied positive or negative gate pulse height. The pulse width was 15 s and the gate pulse step was 0.5 V. Two very distinct steps separated by about 1.5 V and 2.5 V are observed. These steps correspond to the successive charging of the first and second nanocrystal layer [4]. We see that full charging of the first nanocrystal layer is completed at approximately +4 V/-4 V, while the second nanocrystal layer is fully charged at approximately +8V/-8V. In conclusion, we demonstrated multilevel charge storage (+4V/-4V, +8V/-8V) in a doublelayer Si nanocrystal MOS structure, fabricated by LPCVD deposition of α-Si and subsequent thermal oxidation. The flatband voltage shift of the structure as a function of the applied positive/negative gate pulse height indicated the successive charging of the two silicon nanocrystal layers by electron(hole) injection respectively. These results are very promising for application in multi-bit memory devices. 10
FIG 1. Schematic representation of the silicon nanocrystal MOS structure. 2.5 6.0x10 -11 fresh pulse width 15s 2.0 1.5 pulse width 15s 5.0x10 -11 1.0 0.5 C(F) 7.0x10 -11 ΔV FB =-2.8V 4.0x10 -11 3.0x10 -11 ΔV FB =2.1V ΔV FB (V) 0.0 -0.5 -1.0 -1.5 2.0x10 -11 -2.0 1.0x10 -11 -8V -6V -5V -3V 3V 5V 6V 8V -2.5 -3.0 -4.5 -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 V(V) 3 4 5 6 7 8 V(V) FIG 2. C-V curves at 1 MHz for positive and negative gate pulses and 15 s pulse width. FIG 3. Flatband voltage shift as a function of positive and negative gate pulses and 15 s pulse width. [1] S. Tiwari, F. Rana, H. Hafani, A. Hartstein, E. F. Crabbe, and K. Chan, Appl. Phys. Lett. 68, 1377 (1996). [2] R. Ohba, N. Sugiyama, K. Uchida, J. Koga and A. Toriumi, IEEE Trans. Elect. Dev. 49 (2002). [3] A. Salonidou, A.G.Nassiopoulou, K. Giannakopoulos, A. Travlos, V. Ioannou-Sougleridis and E. Tsoi, Nanotechnology 15, 1233 (2004). [4] T. Z. Lu, M. Alexe, R. Scholz, V. Talelaev and M. Zacharias, Appl. Phys. Lett. 87, 202110 (2005). 11
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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Page 15 and 16: Ανοιχτή Συνεδρία «
Page 17 and 18: «NανοΥλικά και Νανο
Page 19 and 20: New materials and MOS device concep
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Page 25: Thus the mean R In-In is expected t
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Page 35 and 36: Electrical Spin Injection from Fe i
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Page 39 and 40: References [1] CH Lee, J. Meteer, V
Page 41 and 42: Σχήμα 1: Φωτογραφία
Page 43 and 44: SEM Image Layout Simulation Εικ
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Optical Properties of CuIn 1-x Ga x
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ανοπτημένο με λέιζ
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Στο σχήμα 3 φαίνοντ
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Id (mA) -0,3 -0,2 -0,1 Vg=0 Vg=-1 V
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Strained-Si Si 1-x Ge x graded Si 1
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Fig. 1. Laser mask movement during
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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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Μετασχηματισμοί φά
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Μελέτη της Επίδρασ
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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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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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Κομπίτσας Μ…………
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ΕΥΡΕΤΗΡΙΟ ΣΥΓΓΡΑΦΕ
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W Watson I.M………………4 Weg
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xxiii ÏÎ±Î½ÎµÎ»Î»Î·Î½Î¹Î¿ ÏÏÎ½ÎµÎ´ÏÎ¹Î¿ ÏÏÏÎ¹ÎºÎ·Ï ÏÏÎµÏÎµÎ±Ï ÎºÎ±ÏÎ±ÏÏÎ±ÏÎ·Ï & ÎµÏÎ¹ÏÏÎ·Î¼Î·Ï ...