Molecular Scale Switching Junction
Growth and shrinkage of nanoscale metal protrusions in solid electrolytes such as metal sulphides were recently found to controllably generate high and low conducting states with varying electrical bias voltages [1-3]. This nonvolatile switch has been coined the atomic switch due to the atomic size of the metal protrusions. It consists of two electrodes, one made of a solid electrolyte and the other made of an inert metal such as Pt, separated by a nanometer-sized gap. Typical solid electrolytes are chalcogenide s, like the metal sulfides Ag2S and Cu2S, which have become two of the most widely, studied systems. Upon a large enough applied bias, metal ions ease out of the solution and bridge the nanometer-sized gap where they combine with electrons to form the metal protrusions. It is also believed that the electrons from the opposite electrode tunnel across the gap causing metal precipitation of the solid electrolyte thus forming the metal bridge.
As soon as the two electrodes are bridged, the device switches from a non conducting state to that of conduction. By reversing the bias, the metal bridge dissolves back into the solid electrolyte thus reverting back to its normal state. Several metals were found to demonstrate this property when solid electrolytes are formed and sandwiched between two nano-scale electrodes.
This atomic mechanics has the potential of reducing the size of the switching devices to nano-scale dimensions ensuring above 100GB/cm2 of cell density and ultra-low energy consumption in transistors. The devices have the potential to go beyond the allowable density limit of current and future silicon based CMOS devices. The eventual success of this research will offer solutions to some of the challenges that silicon CMOS industry is likely to face in the next decade.
Along with atomic switch, molecular switching is among the many alternatives being explored as replacement for the current charge storage memory. Soon scaling of charge based storage will reach a critical size in which unacceptable state detection and retention times will render them obsolete. Using organic molecules sandwiched between two inert electrodes can further reduce the physical dimensions into the nanometer range, with the ultimate goal being the ability to control conduction through a single molecule.
Our group in collaboration with Hewlett Packard is interested in developing novel techniques for separating and keeping a precise gap between the two electrodes. We also look to find new novel materials that exhibit the same switching characteristics as the well study Ag2S and Cu2S electrolytes.
Our group's interest is to explore the high speed switching characteristics of various organic compounds. A great deal of work has been done by many groups concerning the DC switching characterization [4-8] of these organic molecules, but little has been done with sending high speed signals through the devices. Part of the limitations that we are attempting to solve is reducing the high frequency losses and obtaining the desired nanometer-sized electrodes [9,10]. Nanoimprinting offers a way to reach the critical dimensions with the hope of eventually confining a single molecule. In order to improve the device yields, We are also developing techniques for generating ultra-flat metal surfaces and applying the for interfacing molecular devices.[11,12] Other interests include alternatives to interfacing between the electrodes and molecules.
We are currently working on nanoscale structures for measuring the Casimir force and assessing its role in molecular electronics  and also investigating sensors for single molecule detection via surface enhanced Raman spectroscopy.
- Hewlett-Packard Labs
- Army Research Labs
- Sandia National Labs
- Terabe, K., Hasegawa, T., Nakayama, T. & Aono, M., "Quantized conductance atomicswitch", Nature 433, 47-50 (2005).
- Terabe, K., Hasegawa, T., Nakayama, T. & Aono, M., "Quantum point contact switch realized by solid electrochemical reaction", RIKEN Review 37 (July, 2001).
- Sakamoto, T., Sunamura, H., Kawaura, H., Nakayama, T., Hasegawa, T. & Aono, M.,"Nanometer-scale switches using copper sulfide", Appl. Phys. Lett., 82, 18,(2003).
- Stewart, D. R., Ohlberg, D. A. A., Beck, P. A., Lau, C. N. & Williams, R. S. ,"Exponential temperature dependence and low-bias conductance anomaly in transport through Langmuir-Blodgett monolayer devices", Applied Physics a-Materials Science & Processing80, 1379-1383 (2005).
- Richter, C. A., Stewart, D. R., Ohlberg, D. A. A. & Williams, R. S. , "Electrical characterization of Al/AlOx/molecule
Ti/Al devices", Applied Physics a-Materials Science & Processing 80, 1355-1362 (2005).
- Lau, C. N., Stewart, D. R., Bockrath, M. & Williams, R. S. , "Scanned probe imaging of nanoscale conducting channels in Pt/alkanoic acid monolayer/Ti devices", Applied Physics a-Materials Science & Processing 80, 1373-1378 (2005).
- Stewart, D. R. et al., "Molecule-independent electrical switching in Pt/organicmonolayer/Tidevices", Nano Letters 4, 133-136 (2004).
- Chen, Y. et al., "Fabrication of electronic molecular devices for memory application", Abstracts of Papers of the American Chemical Society 221, U308-U308 (2001).
- M. Saif Islam, G.Y. Jung, T. Ha, D.R. Stewart, Y. Chen, S.Y. Wang, R. Stanley Williams,"Ultra-smooth platinum surfaces for nanoscale devices fabricated using chemicalmechanical polishing", Applied Physics A, Special Issue on Nanotechnology, 80, (6), pp1385-1389, 2005.
- M. Saif Islam, G.Y. Jung, T. Ha, D.R. Stewart, Y. Chen, S.Y. Wang, R. Stanley Williams, "Ultra smooth platinum surfaces for nanoscale devices fabricated using chemical mechanical polishing", Applied Physics A, Special Issue on Nanotechnology, 80, (6), pg1385-1389, 2005
- M. Saif Islam, Z. Li, S-C Chang, D.A.A. Ohlberg, D.R. Stewart, S.Y. Wang, and R.S. Williams, "Dramatically Improved Yields in Molecular Scale Electronic Devices using Ultra-Smooth Platinum Electrodes prepared by Chemical Mechanical Polishing" IEEE Nano, Nagoya, Japan, July 15, 2005.
- Chad Johns and M. Saif Islam , Doug A. A. Ohlberg, Duncan R. Stewart, Philip J. Kuekes, Shih-Yuan Wang and R. Stanley Williams, "Atomic Switching Junctions Based on Solid Electrolytes and an Organic Monolayer of molecules", Submitted to Nanoletters, 2007.
- C. Johns, I. Kimukin, M. Saif Islam , D. A. A. Ohlberg, D. R. Stewart, C. Donley, S.-Y. Wang and R. S. Williams, "A novel non-destructive interfacing technique for molecular scale switching junctions", Mater. Res. Soc. Symp. Proc. Vol. 938, 2006 (0938-N08-01).
- "Impact of Casimir force in molecular electronic switching junctions." Aaron Katzenmeyer, Logeeswaran VJ, Bayram Tekin, M. Saif Islam. IEEE INEC, 24-27 March 2008