Silicon carbide (SiC) has been used for centuries as an industrial abrasive and has been
actively researched since the 1960's as a robust material for power electronic applications.
Despite being the first semiconductor to emit blue light in 1907, it has only recently been
discovered that the material has crucial properties ideal for long-term, implantable biomedical
devices. This is due to the fact that the material offers superior biocompatibility and
hemocompatibility while providing rigid mechanical and chemical stability. In addition, the material
is a wide-bandgap semiconductor that can be used for optoelectronics, light delivery, and optical
sensors, which is the focus of this dissertation research.
In this work, we build on past accomplishments of the USF-SiC Group to develop active
SiC-based Brain Machine Interfaces (BMIs) and develop techniques for coating other biomaterials
with amorphous SiC (a-SiC) to improve device longevity. The work is undertaken to move the
state of the art in in vivo biomedical devices towards long term functionality. In this document we
also explore the use of SiC in other bio photonics work, as demonstrated by the creation of the
first reported photosensitive capacitor in semi-insulating 4H-SiC, thus providing the mechanism
for a simple, biocompatible, UV sensor that may be used for biomedical applications.
Amorphous silicon carbide coatings are extremely useful in developing agile biomaterial
strategies. We show that by improving current a-SiC technology we provide a way that SiC
biomaterials can coexist with other materials as a biocompatible encapsulation strategy. We
present the development of a plasma enhanced chemical vapor deposition (PECVD) a-SIC
process and include material characterization analysis. The process has shown good adhesion
to a wide variety of substrates and cell viability tests confirm that it is a highly biocompatible
coating whereby it passed the strict ISO 10993 standard tests for biomaterials and biodevices.
In related work, we present a 64-channel microelectrode array (MEA) fabricated on a cubic
3C-SiC polytype substrate as a preliminary step in making more complex neurological devices.
The electrode-electrolyte system electrical impedance is studied, and the device is tested against
the model. The system is wire-bonded and packaged to provide a full neural test bed that will be
used in future work to compare substrate materials during long-term testing.
Expanding on this new MEA technology, we then use 3C-SiC to develop an active,
implantable, BMI interface. New processes were developed for the dry etching of SiC neural
probes. The developed 7 mm long implantable devices were designed to offer four channels of
single-unit electrical recording with concurrent optical stimulation, a combination of device
properties that is indeed at the state-of-the-art in neural probes at this time.
Finally, work in SiC photocapacitance is presented as it relates to radio-frequency tuning
circuits as well as bio photonics. A planar geometry UV tunable photocapacitor is fabricated to
demonstrate the effect of below-bandgap optical tuning. The device can be used in a number of
applications ranging from fluorescence sensing to the tuning of antennas for low-power
communications.
While technology exists for a wide variety of in vivo interfaces and sensors, few active
devices last in the implantable environment for more than a few months. If these devices are
going to reach a long-term implant capability, use of better materials and processing strategies
will need to be developed. Potential devices and strategies for harnessing the SiC materials family
for this very important application are reviewed and presented in this dissertation to serve as a
possible roadmap to the development of advanced SiC-based biomedical devices.
| Identifer | oai:union.ndltd.org:USF/oai:scholarcommons.usf.edu:etd-6309 |
| Date | 18 March 2014 |
| Creators | Register, Joseph |
| Publisher | Scholar Commons |
| Source Sets | University of South Flordia |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Graduate Theses and Dissertations |
| Rights | default |
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