To date, the fabrication of molecular electronics devices has been complicated by the need for imprecise processing steps. The invention described here enables lithographic processing of a molecular thin film with greater precision while continuing to utilize standard lithographic methods and equipment, representing a key technology for enabling molecular electronics cross-point memory and logic circuits.

BACKGROUND:  The current methods of fabricating molecular electronics devices involve the following simplified steps:

1. A wafer (or chip) that has been prepatterned with an electrode pattern
2. Is coated with a molecular monolayer or multilayer thin film
3. A very thin protective metal film that uniformly wets the molecular layer is then deposited on top of the molecular layer
4. A photolithography or electron beam resist solution is then deposited on top of the metal film
5. The resist material is lithographically patterned using optical or electron-beam lithographic techniques and a shadow mask
6. Top conducting electrodes are patterned
7. The resist material is "washed" away, leaving behind the molecular film sandwiched between the bottom electrodes, the protective metal film, and the top electrodes

INNOVATION:  Instead of Step 3 in the above process, a protective film of Titanium was deposited on the molecular monolayer using electron-beam evaporation. All processing steps are subsequently carried out on this layer - protecting the fragile molecular monolayer from the potentially damaging photoresist application and lithography process.

Instead of step 6 above, a 100 nanometer thick film of aluminum was deposited through the patterns in the resist material onto the titanium film to create the top electrode.

After the lithographic processing has been completed and wiring connections have been established, the protective metal thin film layer is selectively removed using a wet or dry etching process.

To validate the process, an isolated molecular switch tunnel junction device was fabricated, as was a 16-bit molecular switch tunnel junction crosspoint memory circuit.

BENEFITS OF THE INVENTION: 

1. Enables economically feasible mass production of molecular electronics devices
2. Utilizes current production techniques
3. Key enabler of molecular electronics

Reference: UCLA Case No. 2001-218

PCT Publication Number: WO 03/050877 A1