Self-Assembled Ultra-Thin Dielectrics: The Quest for Defect-Less Interfaces

The concept of “bottom-up” fabrication seeks to construct functional devices via self-driven organization employing weak chemical forces. A natural choice for realization of bottom-up approach is the use of alkyl-based monolayers for ultra-thin (∼2 nm thick) dielectric. Such insulating films are an essential component of field-effect transistors (FET), represented by the “O” (oxide) in the well known CMOS acronym. While this quest has started already half a century ago, the extreme sensitivity of electronic properties to minute amount of defects (e.g., the concept of dopants) calls for ultimate structural perfection. The widespread availability of surface characterization tools (SPM, XPS) and fabrication tools (lithography, clean rooms, and glove boxes) shed new light on the fundamental processes that still hamper the reproducibility and reliability of monolayer for electronic applications. In my talk I will focus on three basic dilemma confronting a technological realization of monolayer-based dielectric:

• Long-range order vs. homogeneity of the alkyl tails: while ordered systems are more robust, fluid-like tail could fill voids and serve as ‘defect healing’;
• Binding strength to the substrate: although weak binding is less durable it improves homogenous coverage by facile lateral diffusion;
• Mass penetration vs. charge leakage: structural disorder (liquid-like tails) increases the resistance to charge transport yet is more prone to diffusion of metallic atoms from one electrode to the other, constructing shorts;

Optimizing these apparent contradicting requirements by judicious chemical design is a major challenge for our ability to harness supramolecular chemistry into viable technology.