In this paper we report on progress made in optical logic planes consisting of hybrid electrically assisted thermo-optic resonators fabricated with standard Silicon technology. As a starting point, the features and shortcomings of a first generation of these bistable elements, based on double-sided polished Silicon wafers, are reviewed. Consecutively we demonstrate, both with modeling and experimental results, that some of the shortcomings of the first generation can be remedied using a Silicon on Sapphire based device. Finally we propose a novel structure, based on Silicon Implanted Oxide substrates, that combines the advantages of the two pervious structures. We show via a heat transfer model that these devices can display bistability at multi-microwatt optical bias power and that, when adequately dimensioned, crosstalk can be avoided such that they can be packed into dense arrays. Both these characteristics and their stability, wavelength flexibility, hybrid mode of operation, and the potentialities for microsecond switching times, can turn these low-cost devices into work- horses for prototype digital optical parallel computing circuitry.