Emerging Technologies of Computation

1. Emerging Technologies of Computation Montek Singh COMP790-084 Aug 30, 2011

2. Today: Quantum Dot Cellular Automata (part 2) • Gain/amplification • restoring logic • clock gain • QCA Implementation • Experimental results

3. Gain/amplification in QCA • What is gain/amplification? • Why is gain important in digital systems? • Gain in QCA • small electrostatic forcetips electron over • clocking provides furtheramplification

4. QCA clocking • QCA clocking • “freeze” cell when clock low • equivalent to latching • free it up when clock high • equivalent to computing • Often use 4 or more clock phases

5. QCA: Fabrication • Metal-island • aluminum dots • 1 micron, so very low temperatures • Semiconductor • 20-50 nm, so still very low temperatures • most common • Molecular • single molecules, so very fast • future, not yet • Magnetic • magnetic exchange interactions instead of electron tunneling • room temperature

6. QCA: Semiconductor type • Al-AlOx-Al type • Aluminum dots • Aluminum Oxide barriers • fabricated on Silicon substrate • using electron beam lithography • Example: Notre Dame group

7. Experimental results • Notre Dame group • 6-dot cell • D1-D4 are two double-dots for QCA • E1-E2 are electrometers for reading out

8. Experimental results • Majority-gate experiment • V1-V4 “simulate” inputs A, B and C • Electrometers read output

9. Experimental results

10. Experimental results

11. Practical considerations • For clearer separation between output ‘1’ and ‘0’, we need • lower temperatures (70mK) • or, smaller capacitances (molecular-scale sizes)