Development of embedded graphitic-sandwich structures in single-crystal synthetic diamond via ultrafast laser micromachining

We discuss the direct fabrication of embedded, graphitized features within high-purity, synthetic single-crystal diamond through ultrafast laser micromachining for the purpose of developing diamond-based capacitive structures. As an incorporating substrate, carbon in the form of highly pure synthetic diamond offers numerous advantageous physicochemical properties, including hardness, durability, optical transparency, and extremely high electrical resistance. On the other hand, graphitic carbon can exhibit exceptionally low electrical resistance. A simple sandwich structure of a thin sheet of diamond between two sheets of graphite could, therefore, form a simple plate-type capacitive structure. For a single structure consisting of 1 μm thick plates with areal dimensions of 5 × 1 mm2 and 1 μm gaps between plates, we estimate a capacitance of 240 pF, with a 3 kV/μm breakdown voltage in diamond. ∼2500 plates thus fabricated in a ∼5 × 5 × 1 mm3 diamond chip could, therefore, store ∼300 mJ of energy. To realize this kind of structure, we employ ultrafast laser micromachining with high numerical aperture focusing and precise positioning control to disrupt the crystalline matrix of a well-confined volume within single-crystal synthetic diamond, forming embedded graphitic features. Graphitized plate regions 1 μm thick with 1 μm separations can be fabricated in this manner, and empirical I–V measurements indicate resistances in the plates as low as ∼kΩ. We also address challenges involved with fabricating closely parallel, embedded graphitic plates in thick diamond substrates, including aberration, machining time, and cracking.