Nanostructured molecular switch and memory Hyoyoung Lee US-Korea - PowerPoint PPT Presentation

Nanostructured molecular switch and memory Hyoyoung Lee US-Korea NanoForum, 27-30Apr2009 The center of Smart molecular memory @ Dept. of Chem. , SKKU

Why working on molecular memory? Tera-bit Molecular Memory Device Current Commercial Memory ME, High Density - Digital-Camera, mp3, Cellular phone, Hand-held PDA, Notebook 2009. 02. 04, 500G, $170

Possible applications of the molecular memory Molecular Memory Metal electrode Random Access Memory (RAM) Au SiO 2 /Si substrate - Volatile Memory - Non-Volatile Memory Flash D-, S-RAM Memory Molecular Computer - Highly density memory - Cheap (Low-end product) - Various and flexible

Technology Performance Evaluation for Molecular Monolayer Memory 2007 년 ITRS Roadmap

What is the major drawback? Operational reliability! What is the major issue for improving a reliability? That is directly related to......device yield! Summary of results for the fabricated devices. (Note: working and non-working devices were defined by statistical analysis with Gaussian fitting on histograms) Tae-Wook Kim, Gunuk Wang, Hyoyoung Lee,and Takhee Lee*, Nanotechnology 18 (2007) 315204

What are the major issues when using SAMs? Metal electrode SAMs, thin films of molecules Metal electrode 1. Stability of SAMs, thin films of organic molecules - Compactness, robustness, and film thickness of the SAMs - Stability of SAMs having functional groups vs only alkane (di)thiol 2. Bottom/top Electrodes (metal) - Surface roughness of bottom metal electrode (btm) - Penetration of metal particles into the SAMs (top) - Surface area contacted on metal electrode

Real world in small, tiny land! Surface roughness , RMS of bottom electrode: ~1.4 nm ~2 nm ~1.4 nm (Btm) The length of SAM molecules, film thickness of SAMs: ~2 nm (Btm) <0.5 nm Unavoidable Penetration! Top Vapor deposition What is your suggestion to improve our device yield? What do you say about film thickness?

Self-Assembled Monolayer of RB I I I I O O O O NaO NaO NaO H 2 N NaO I I I I I I I I Cl C Cl C NH ONa SAc Cl Cl O O O O Cl Cl Cl Cl SAc I Cl Cl I Cl Cl Cl Cl C C O O O O Cl Cl SH SH S I S I Bi-layer OH I N H N H N H OH N H I H H H H H H H H Cl Cl I Cl H N Cl H N H N H N I Cl O Cl O Cl O C I Cl O C I NH NH I O I O S S S S S S Gold Gold RB-(CH 2 ) 2 SH RB-TUA-AUT Surface : Au(800 Å )/Ti(50 Å )/Si

Thickness of RB-(CH2) 2 SH, AUT-AUT and RB-AUT-AUT using Ellipsometer RB-(CH 2 ) 2 SH OH OH I I Cl Cl Cl Cl I I Cl Cl O O 15 Å Cl O Cl O C C I I NH NH I I O O S S Gold NaO NaO I I I I 12 Å Cl Cl O O Cl Cl I Observed I Theoretical Cl Cl C C O O O O Cl Cl SH S I SH SAMs S I value/ Å value/ Å RB-(CH 2 ) 2 SH 17 20 N H N H N H N H H H H H 34 Å H H H H H N H N H N H N AUT-AUT 34 35 S S S S RB-AUT-AUT 46 45 Gold RB-AUT-AUT

I-V curves by using CP-AFM RB-(CH 2 ) 2 SH AUT-AUT RB-AUT-AUT 1. RB-(CH 2 ) 2 SH film show ohmic behavior 2. AUT-AUT film show insulating behavior 3. RB monolayer on the bilayered AUT exhibit hysteresis. G. S. Bang, … H. Lee* , Langmuir (IF. 4.0) 23 , 5195-5199 (2007) 10

What do you say about…in device? - Preventing the penetration of Au NPs Focused ion beam - Increasing the film thickness - Introducing H boning to overcome the RMS of Au btm 11

Current density-voltage (J-V) - Current density-voltage ( J-V ) characteristics of semi-log scale Current density-voltage (J-V) characteristics; Normalized I-V curves between – 0.5 V and + 0.5 V (the inset) for the TUA-AUT device (black line) and the RB-TUA-AUT device (red line) in the nano via-hole with 170 nm diameter. 12

Device yields depending on the length of molecules NaO I I Cl O Cl I Cl C H O O Cl S I S NaO I I 4.5 nm Cl O Cl I N H N H H Cl 3.8 nm C H H H H S O O Cl S I H N H N 2.9 nm 1.9 nm S S S S 13

High Reproducibility Current density-voltage ( J-V ) characteristics for the RB-TUA-AUT device G. S. Bang, …,… H Lee* , Small (IF 6.4 ), 4, 1399-1405 (2008). 14

Molecular switch/memory i i V t

Possible molecules for molecular switches/memory N N Zn Fe N N Fullerene, N-type Ferrocene Porphyrin What are other possible molecules for molecular switch/memory device?

Synthesis of Ru(tpy) 2 Derivatives RuCl 3 -3H 2 O N H 2 C (CH 2 ) n SAc N N N N N 1 equiv. Ru N N N Cl Cl Cl NH 4 PF 6 H 2 C (CH 2 ) n SAc RuCl 3 -3H 2 O NH 4 PF 6 N 0.5 equiv. N N N N R 1 (H 2 C) m N (CH 2 ) n R 2 N RU +2 R 1 =R 2 =SAc, m=n=0 N R 1 =SAc, R 2 =H, m=n=0 N - 2PF 6 R 1 =R 2 =SAc, m=n=7 R 1 =SAc, R 2 =H, m=7, n=0 R 1 =R 2 =SAc, m=n=13 R 1 =SAc, R 2 =H, m=13, n=0 Electron Donor (metal)-Acceptor (Ligand, tpy) Ru 2+ ---> Co 2+ , Fe 2+ (got now) e - 17

Measurement system (STM) of the solid state Scheme of Ru II complexes incorporated in an ordered n -alkanethiol SAM on Au(111) X X = H, SAc, and S-AuNP N AuNP N N i Ru 2+ SAc N N N N N N or 2+ Ru N N N SH SH n SAc n = 0, 7, and 13 S S S S S A voltage-driven molecular switch Au (111) 18

I-V characteristics of a Au-NP/Ru II (tpyS) 2 incorporated 1- octanethiol (OT) SAM on Au(111), Dithiol Current-voltage ( I-V ) characteristics 3 STM image at a constant tunneling current 2 of 20 pA with a tip bias of 1.2 V 3 4 2 1 C u rre n t/n A 0 Bundles of AuNPs 5 -1 1 6 -2 -3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 Histograms of threshold voltage for current switch-on 25 in the single Au-NP/Ru II (tpyS) 2 junctions A single AuNP 20 15 Count 71nm 10 5 0 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 Tip bias voltage/V 19

Redox formal potentials to the vacuum levels Cyclic voltammogram for a 3 mM RuII(tpy)(tpyC 13 SAc) solution in acetonitrile using a glassy carbon electrode. 60 Ligand-centered redox reaction, -1.2 V SCE (Ru II (tpy)(tpy)] 2+ + e - � (Ru II (tpy)(tpy) - ] 2+ 40 20 Current/ µ A E 0 0 π * LUMO, L -20 Ru-centered redox reaction, - 3.4 eV +1.2 V SCE (Ru II – e - � Ru III ) -40 2.0 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 E/V vs. SCE HOMO, π M - 6.74 eV The redox formal potentials can be converted to the vacuum levels; Hipps et al. [4.7 eV + (1.7)E ox (SCE) 1/2 ] and Armstrong et al [4.7 eV + E red (SCE) 1/2 ] 1.Energy levels of the first metal-centered oxidation, 6.74 ( V ox = 4.7 eV + (1.7) x 1.2 = 6.74 eV ) 2.Energy levels of the first ligand-centered reduction are 3.4 V ( V red = 4.7 eV - 1.2 = 3.4 eV) below the vacuum. 20

Proposed charging process into the ligand-centered LUMO of Ru II terpyridine complexes Current-voltage ( I-V ) characteristics E 0 3 e - LUMO, π * L 2 3 V bias = ∆ r 2 4 - 3.4 eV 1 C u rre n t/n A 1.7 V 0 5 - 5.6 eV - 5.1 eV -1 1 HOMO, π M 6 -2 Sample - 6.74 eV -3 Tip -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 Negative Bias -Typical I-V characteristics through molecular junctions of Ru II (tpy)(tpyC 7 S) showed significant conductance switching to a high conductance state approximately at 1.7 V. -The threshold voltage of switch-on is comparable to the first redox formal potential of the terpyridine ligand supported on gold. K. Seo, … H. Lee* , J. Am. Chem. Soc. (IF 7.9), 130(8), 2553-2559, 2008 1 st understanding of the charging Process of the molecules at the solid state Electron Tunneling through an Alkyl Chain-Tethered Metal Complex Molecular Switch Junction K. Seo, … H. Lee* , Chem. of Mater., submitted, 2009 Molecular Electron Transport on Structural Phase Transition in a Large Area Junction K. Seo, H. Lee* , ACS Nano., accepted, 2009 21

Fabrication of Molecular Monolayer Non-Volatile Memory (MMMVM) 단분자막 22

Write-multiple read-erase-multiple read (WRER) cycles 1 st Molecular Monolayer Non-Volatile Memory (MMMVM) w/ voltage-driven J. Lee, … H. Lee * , will be submitted to Adv, Func. Mater, , 200 23

Intrinsic Properties of Ru complexes and memory w/NW Schematic diagram of the In 2 O 3 nanowire SEM image of an In 2 O 3 FET device nanowire FET 1. M. Jung … H Lee* and J. Kim*, Quantum interference in radial heterostructure nanowires, Nano Letters , 8 , 3189, 2008 2. M Jung, H Lee* …, Short-channel effect and single-electron transport in individual indium oxide Nanowires, Nanotechnology , 18, 435403, 2007 . 24

Electron Transport through Individual Indium Oxide Nanowire I DS - V G characteristics of the In 2 O 3 nanowire FET I DS - V G characteristics of the In 2 O 3 nanowire FET device device modified with Ru SAM 25

Electron Transport through Individual Indium Oxide Nanowire I DS versus retention time for the In 2 O 3 nanowire Reversible switching operations in the write, read, erase and read FET in an ON current state (red line) and an voltage cycles; writing, reading and erasing voltages ( V G pulses for 1 s) OFF current state (black line). are − 15 V, − 6 V and 15 V, respectively. I, Choi, … H Lee* , Charge Storage Effect on In 2 O 3 Nanowires with Ruthenium Complex Molecules, Applied physics express, 2, 015001, 2009 26

Electrode patterning w/soft Lithography Decal Transfer Light Stamp Nanoinprinting µ -Contact Printing Mold PDMS PDMS Resist Substrate Imprint(press mold) substrate substrate UV UV Remove mold substrate substrate Pattern transfer (reactive ion etching) 27