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_____________________________________________________________ EE 666 April 14, 2005 Molecular quantum-dot cellular automata Yuhui Lu Department of Electrical.

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Presentation on theme: "_____________________________________________________________ EE 666 April 14, 2005 Molecular quantum-dot cellular automata Yuhui Lu Department of Electrical."— Presentation transcript:

1 _____________________________________________________________ EE 666 April 14, 2005 Molecular quantum-dot cellular automata Yuhui Lu Department of Electrical Engineering University of Notre Dame

2 _____________________________________________________________ EE 666 April 14, 2005 Outline of presentation QCA overview Metal-dot QCA devices Molecular QCA Clocking molecular QCA Summary

3 _____________________________________________________________ EE 666 April 14, 2005 Quantum-dot Cellular Automata Represent binary information by charge configuration A cell with 4 dots Tunneling between dots Polarization P = +1 Bit value “1” 2 extra electrons Polarization P = -1 Bit value “0” Bistable, nonlinear cell-cell response Restoration of signal levels cell1cell2 cell1cell2 Cell-cell response function Neighboring cells tend to align. Coulombic coupling

4 _____________________________________________________________ EE 666 April 14, 2005 0011 0110 Binary wire Inverter A B C Out Majority gate M A B C Programmable 2-input AND or OR gate. QCA devices

5 _____________________________________________________________ EE 666 April 14, 2005 Metal-dot QCA cells and devices “dot” = metal island electrometers 70 mK Al/AlO x on SiO 2 Metal-dot QCA implementation Greg Snider, Alexei Orlov, and Gary Bernstein

6 _____________________________________________________________ EE 666 April 14, 2005 Metal-dot QCA cells and devices Demonstrated 4-dot cell A.O. Orlov, I. Amlani, G.H. Bernstein, C.S. Lent, and G.L. Snider, Science, 277, pp. 928-930, (1997). 1 2 3 4

7 _____________________________________________________________ EE 666 April 14, 2005 Metal-dot QCA cells and devices Majority Gate M A B C Amlani, A. Orlov, G. Toth, G. H. Bernstein, C. S. Lent, G. L. Snider, Science 284, pp. 289-291 (1999).

8 _____________________________________________________________ EE 666 April 14, 2005 From metal-dot to molecular QCA Key strategy: use nonbonding orbitals (  or d) to act as dots. “dot” = redox center Mixed valence compounds Why molecule? 1. Natural, uniform quantum dots. 2. Small. High density. 3. Room temperature operation.

9 _____________________________________________________________ EE 666 April 14, 2005 Binary information encoded in the molecular charge configuration “0”“1”“0”“1” “0” “1” Mobile charges are created by chemical oxidation or reduction.

10 _____________________________________________________________ EE 666 April 14, 2005 Experiments on molecular double-dot Fehlner, Snider, et al. (Notre Dame QCA group) Journal of American Chemical Society, 125:15250, 2003 Ru Fe “0” “1” Fe group and Ru group act as two unequal quantum dots. trans-Ru-(dppm) 2 (C≡CFc)(NCCH 2 CH 2 NH 2 ) dication

11 _____________________________________________________________ EE 666 April 14, 2005 Surface attachment and orientation PHENYL GROUPS “TOUCHING” SILICON Molecule is covalent bonded to Si and oriented vertically by “struts.” Si(111) molecule Si-N bonds “struts”

12 _____________________________________________________________ EE 666 April 14, 2005 Applied field equalizes the energy of the two dots When equalized, capacitance peaks. applied potential Measurement of molecular bistability layer of molecules Ru Fe Ru Fe 2 counterion charge configurations on surface

13 _____________________________________________________________ EE 666 April 14, 2005 Charge configurations HOMO orbitals from quantum chemistry calculation show the localization of mobile electron. “1” “0” Bistable charge configuration. Ru Fe Ru Fe

14 _____________________________________________________________ EE 666 April 14, 2005 Switching by an applied field Mobile electron driven by electric field, the effect of counterions shift the response function. Click-clack correspond to:

15 _____________________________________________________________ EE 666 April 14, 2005 4-dot molecule Each ferrocene acts as a quantum dot, the Co group connects 4 dots. Fehlner et al (Notre Dame chemistry group) Journal of American Chemical Society 125:7522, 2003 6 Å Advantage: neighboring molecules have the same charge configurations. No need to keep track on the numbers in the array.

16 _____________________________________________________________ EE 666 April 14, 2005 Bistable configurations “0” “1” Guassian-98 UHF/STO-3G/LANL2DZ HOMO orbital show the localization of mobile electron.

17 _____________________________________________________________ EE 666 April 14, 2005 Can one molecule switch the other ?

18 _____________________________________________________________ EE 666 April 14, 2005 Switching molecule by a neighboring molecule Coulomb interaction is sufficient to couple molecular states. driver response

19 _____________________________________________________________ EE 666 April 14, 2005 Intermolecular Interaction E kink =0.25 eV Kink energy is greater than k B T, thus room temperature operation is possible. “1” Ground State “1”“0” Excited State Energy

20 _____________________________________________________________ EE 666 April 14, 2005 Kroemer’s lemma If, in discussing a semiconductor problem, you cannot draw an Energy-Band-Diagram, this shows that you don't know what you are talking about. If you can draw one, but don't, then your audience won't know what you are talking about. There is no energy band for single molecule. Single molecule only has discrete energy levels.

21 _____________________________________________________________ EE 666 April 14, 2005 Origin of energy band Bonding orbital Anti-bonding orbital …. Atomic orbital The interaction between two atomic orbitals form a bonding orbital and an anti-bonding orbital. band Band originated from the interaction of large number of atomic orbitals in the periodic potential. In single molecules, energy levels are discrete.

22 _____________________________________________________________ EE 666 April 14, 2005 Ground state First excited state The ground and first excited energy levels “1” “0” 1,4-diallyl butane radical cation

23 _____________________________________________________________ EE 666 April 14, 2005 Discrete energy levels under the switching field Ground state First excited state +

24 _____________________________________________________________ EE 666 April 14, 2005 Discrete energy levels under the switching field Ground state First excited state +

25 _____________________________________________________________ EE 666 April 14, 2005 Discrete energy levels under the switching field Ground state First excited state +

26 _____________________________________________________________ EE 666 April 14, 2005 Clocked QCA input How to control the information flow? Clocking: 1.Control of information flow around the circuit. 2. Restore the dissipative energy. Cells fully polarized to be “0” or “1”.

27 _____________________________________________________________ EE 666 April 14, 2005 Clocking field “1” “0” null E E E or Use local electric field to switch molecule between active and null states. active “null”

28 _____________________________________________________________ EE 666 April 14, 2005 Adiabatic switching 01 01 null energy x

29 _____________________________________________________________ EE 666 April 14, 2005 Clocked molecular QCA

30 _____________________________________________________________ EE 666 April 14, 2005 Model clock QCA Clocking field Switching field “null”“1” “0” 1,5,9 decatriene Using ethene as quantum dot.

31 _____________________________________________________________ EE 666 April 14, 2005 Molecular energy “0” “1” “null” Gaussian 03 CASSCF(5,6) 6-31G* “0” “1” “null” The molecule is locked in “null” state, thus carries no information. ground state first excited state second excited state

32 _____________________________________________________________ EE 666 April 14, 2005 Molecular energy “0”“1” “null” A clock voltage “turns on” the devices. “0” “null”“1” ground state first excited state second excited state

33 _____________________________________________________________ EE 666 April 14, 2005 Molecular energy “0” “1” “null” “0” “1” “null” Large enough clock voltage “pins” the mobile charge. ground state first excited state second excited state

34 _____________________________________________________________ EE 666 April 14, 2005 Summary The binary information is encoded in the molecular charge configuration. Coulomb interaction couples the information transport. Room temperature operation. Clocking controls the information flow.

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