Charge conduction and breakdown mechanisms in self-assembled nanodielectrics

Developing alternative high dielectric constant (k) materialsfor use as gate dielectrics Is essential for continued advances In conventional Inorganic CMOS and organic thin film transistors (OTFTs). Thicker films of high-kmaterials supprestunneling leakage currents while providing effective capacitances comparable to those of thin films of lower-kmaterials. Self-assembled monolayers (SAMs) and multilayers offer attractive options for alternative OTFT gate dielectrics. One class of materials, organosilane-basedself-assembled nanodielectrics(SANDs), has been shown to form robust films with excellent Insulating and surface passivation properties, enhancing both organic and Inorganic TFT performance and lowering device operating voltages. Since gate leakage current through the dielectric Is one factor limiting continued TFT performance Improvements, we Investigate here the current (voltage, temperature) (/(V,T))transport characteristics of SAND types II(πconjugated layer) and III (δsaturated + π-conjugated layers) In SI/native SIO ₂/SAND/Au metal-lnsulator-metal (MIS) devices over the temperature range -60 to +100 ^0C. It Is found that the location of the π-conjugated layer with respect to the SI/SIO ₂ substrate surface In combination with a saturated alkylsiane tunneling barrier Is crucial In controlling the overall leakage current through the various SAND structures. For small applied voltages, hopping transport dominates at all temperatures for the π-conjugated system (type II). However, for type III SANDs, the δ- and π- monolayers dominate the transport In two different transport regimes; hopping between +25 ^0C and +100 ^0C, and an apparent switch to tunneling for temperatures below 25 ^0C. The δ-saturated alkylsilanetunneling barrier functions to reduce type III current leakage by blocking Injected electrons, and by enabling bulk-dominated (Poole-Frenkel) transport vs electrode-dominated (Schottky) transport In type II SANDs. These observations provide Insights for designing next-generation self-assembled gate dielectrics, since the bulk-dominated transport resulting from combining δ- and π-layers should enable realization of gate dielectrics with further enhanced performance. 2009 American Chemical Society.