Polybenzimidazole as a thermally stable Langmuir–Blodgett film insulator in InP metal-insulator-semiconductor devices

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Abstract
In order to fabricate metal‐insulator‐semiconductor (MIS) devices on III‐V semiconductors it is often necessary to use deposited insulators, since these semiconductors do not form native oxides of the quality found with the Si/SiO2 system. Langmuir–Blodgett (LB) organic thin films have previously been investigated as such insulators. Unfortunately, conventional LB films have too low a melting point (about 70 °C) for practical applications. We have studied films which are spread as a monomer, then polymerize on the water surface to form poly [1,4‐phenylene‐5,5’(6,6’)‐bibenzimidazole‐2,2’‐diyl] (PBI). We show that deposited films of PBI have the repeatable and finely controllable thickness of conventional LB films, but remain fairly stable when subjected to temperatures up to 400 °C. Using PBI LB films as a gate insulator we have fabricated working depletion mode MISFET structures on n‐type indium phosphide with gate lengths down to 1.2 μm.