1. Montek Singh COMP790-084 Aug 30, 2011

2.  Gain/amplification ◦ restoring logic ◦ clock gain  QCA Implementation  Experimental results

3.  What is gain/amplification?  Why is gain important in digital systems?  Gain in QCA ◦ small electrostatic force tips electron over ◦ clocking provides further amplification

4.  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.  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.  Al-AlOx-Al type ◦ Aluminum dots ◦ Aluminum Oxide barriers ◦ fabricated on Silicon substrate ◦ using electron beam lithography  Example: Notre Dame group

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

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

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