Abstract
The in vitro and vivo behavior and tissue reaction to ultrananocrystalline diamond has been evaluated for periods of up to 3 months in BALB/c mice. In this work, ultrananocrystalline diamond (UNCD) thin films were evaluated for use as hermetic and bioinert encapsulating coatings for implantable microchip. These films were conformally deposited on highly conductive silicon dies using microwave plasma enhanced chemical vapor deposition with Ar-rich/CH4 gas mixtures with different relative amounts of hydrogen (0-4%). Scanning electron microscopy studies showed that all the films are dense and continuous on the edges of the diced microchip as well as the center regions. Results of cyclic voltammetry test revealed that when there was 1% of hydrogen in the plasma, the coatings obtained renders the surface electrochemically inactive, with very low leakage currents (1.4x10-5 A/cm2 at 0.5 V; 9x10-4 A/cm2 at 5 V) ex vivo. On the other hand, the current density elicited by the electrochemical activity on silicon chips with O-UNCD coatings keeps around 9x10-4 A/cm2 or even lower up to 3 months in vivo. In addition, microchip with UNCD coatings were implanted subcutaneously into BALB/c for up to 3 months in vivo, and tissue reaction and capsule formation were evaluated at various time points, shown in Figure 1. These results were supported and concluded that O-UNCD is a promising candidate for use as the encapsulating coatings for implantable microelectronic devices.