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Novel materials are needed for intracortical neural implants (INI) to extend their reliability and functionality beyond a few years. Cubic silicon carbide (3C-SiC) is a chemically inert, physically robust semiconductor that has shown, through extensive in vitro testing, a high biocompatibility with neural cells. Recently we have shown that 3C-SiC does not attract a negative immune response from microglia in vivo, but the implants size did not allow adequate investigation of tissue response [1]. We produced a passive implant to test the in vivo tissue reaction of C57BL/6J mice to 3C-SiC and compare to our positive control of silicon (Si). Dual, triangular shanks were fabricated from each material and combined into a single device which was then implanted simultaneously into three C57BL/6J mouse brains for 35 days. The mice were perfused with 4% paraformaldehyde and the brains treated using immunohistochemistry. Fluorescence microscopy indicated that Si produced the expected increased inflammatory response from both microglia/ macrophage and astrocyte cells, whereas 3C-SiC shows minimal inflammatory reaction from these glial cells. Si also created tissue voids larger than the implants themselves whereas 3C-SiC showed minimal voids and even still had neuronal processes in contact with the implant. Our conclusion is that 3C-SiC shows great potential for use within the neural environment and should be fashioned into active INI to evaluate signal quality over time.

Single crystal silicon carbide (SiC) is a wide band-gap semiconductor which has shown both bio- and hemo-compatibility [1-5]. Although single crystalline SiC has appealing bio-sensing potential, the material has not been extensively characterized. Cubic silicon carbide (3C-SiC) has superior in vitro biocompatibility compared to its hexagonal counterparts [3, 5]. Brain machine interface (BMI) systems using implantable neuronal prosthetics offer the possibility of bi-directional signaling, which allow sensory feedback and closed loop control. Existing implantable neural interfaces have limited long-term reliability, and 3C-SiC may be a material that may improve that reliability. In the present study, we investigated in vivo 3C-SiC biocompatibility in the CNS of C56BL/6 mice. 3C-SiC was compared against the known immunoreactive response of silicon (Si) at 5, 10, and 35 days. The material was examined to detect CD45, a protein tyrosine phosphatase (PTP) expressed by activated microglia and macrophages. The 3C-SiC surface revealed limited immunoresponse and significantly reduced microglia compared to Si substrate.

Chemical vapor deposition in the low pressure regime of a high quality 3C-SiC film on silicon ͑100͒-oriented substrates was carried out using silane ͑SiH 4 ͒, propane ͑C 3 H 8 ͒, and hydrogen ͑H 2 ͒ as the silicon supply, carbon supply, and gas carrier, respectively. The resulting bow in the freestanding cantilever structures was evaluated by an optical profilometer, and the residual gradient stress ͑ 1 ͒ in the films was calculated to be approximately between 15 and 20 MPa, which is significantly lower than the previously reported 3C-SiC on Si films. Finite element simulations of the stress field in the cantilever have been carried out to separate the uniform contribution ͑ 0 ͒, related to the SiC/Si interface, from the gradient one ͑ 1 ͒, related to the defects present in the SiC epilayer.There is an increasing demand for sensors that can operate at temperatures well above 300°C and in severe environments such as automotive and aerospace applications. In particular, combustion process and gas turbine control have stimulated the search for alternatives to silicon. Silicon carbide ͑SiC͒ is a material that has attracted much attention for a long time, particularly due to its wide bandgap, its ability to operate at high temperatures, its mechanical strength, and its inertness to exposure in corrosive environments. However, the difficulty in growing high quality crystalline material and processing electronic devices has limited its use to very specific application areas, such as high temperature, high power, and high frequency applications that are not suitable for Si-based devices. For other applications, and particularly for SiC-microelectromechanical systems ͑MEMS͒ devices, large-area substrates are essential. 1 The cubic polytype, namely, 3C-SiC but also known as ␤-SiC, is the only polytype with a cubic crystal structure which crystallizes in a ZnS lattice structure and hence it can be deposited on silicon substrates. This allows the growth of cubic silicon carbide layers on large-area silicon substrates and paves the way for this suitable and important material to be applied to MEMS or nanoelectromechanical systems. 2 The use of large-area substrates offers the possibility for economical and low cost batch processing, which makes SiC more attractive for sensors and device applications. The heteroepitaxy of SiC on Si substrates results in the heterostructure 3C-SiC/Si, which is a very interesting material system for MEMS and nanoelectromechanical systems.With respect to the mechanical properties of the silicon carbide films for use in sensors or freestanding MEMS structures, one important issue is the residual stress field, which is normally created during the growth process and which can result in the unwanted deformation or failure of these structures. Stress varies from point to point within the crystal lattice, altering the lattice spacing and consequently changing the properties of the material.For example, the built-in stress may change the mechanical response, the resonant frequency of the thin-film struc...

Abstract. Single crystal 3C-SiC films were grown on (100) and (111) Si substrate orientations in order to study the resulting mechanical properties of this material. In addition, poly-crystalline 3C-SiC was also grown on (100)Si so that a comparison with monocrystaline 3C-SiC, also grown on (100)Si, could be made. The mechanical properties of single crystal and polycrystalline 3C-SiC films grown on Si substrates were measured by means of nanoindentation using a Berkovich diamond tip. These results indicate that polycrystalline SiC thin films are attractive for MEMS applications when compared with the single crystal 3C-SiC, which is promising since growing single crystal 3C-SiC films is more challenging. MEMS cantilevers and membranes fabricated from a 2 µm thick single crystal 3C-SiC grown on (100)Si under similar conditions resulted in a small degree of bow with only 9 µm of deflection for a cantilever of 700 µm length with an estimated tensile film stress of 300 MPa. Single crystal 3C-SiC films on (111)Si substrates have the highest elastic and plastic properties, although due to high residual stress they tend to crack and delaminate.