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dc.rights.licenseRestricted to current Rensselaer faculty, staff and students. Access inquiries may be directed to the Rensselaer Libraries.
dc.contributorBhat, Ishwara B.
dc.contributorDahal, Rajendra
dc.contributorLu, James
dc.contributor.authorRahman, Muktadir
dc.date.accessioned2021-11-03T08:25:29Z
dc.date.available2021-11-03T08:25:29Z
dc.date.created2015-06-09T13:46:17Z
dc.date.issued2015-05
dc.identifier.urihttps://hdl.handle.net/20.500.13015/1456
dc.descriptionMay 2015
dc.descriptionSchool of Engineering
dc.description.abstractThere has been a lot of interest in the design and fabrication of high efficiency solid- state neutron detectors during the last few years. This interest is mainly attributed to the necessity of detecting special nuclear materials (SNM) to prevent its illicit transportation through different port of entries around the country. Robust, compact and portable neutron detectors requiring a low bias voltage are much better suited for mass deployment and detection of SNM compared to the currently used gas filled tube detectors which are very expensive and lack portability. Initial designs utilized a planar silicon diode with a thin layer (~2-5 µm) of neutron sensitive material in the form of enriched boron 10B on top. Neutron-boron reaction produces α particles that can be detected by Si p-n junction. But the devices displayed low efficiency due to the two conflicting facts that the boron layer needs to be thin enough for the generated α particles to escape boron and to reach the silicon p-n junction, but thick enough for efficient absorption of neutrons.
dc.description.abstractIn summary, this thesis was able to provide a proof of concept for EPD as a viable process to fill high aspect ratio semiconductor trenches. First order results for different suspensions displayed encouraging results in the form of very good fillings. Simulation results also provided a better understanding related to the deposition parameters and were used to optimize the experiments.
dc.description.abstractColloidal silica demonstrated excellent filling and the results were reproducible. It also provided a proof of the initial concept that EPD can become an industry standard process for filling high aspect ratio semiconductor trenches. The B4C-IPA suspension also demonstrated reasonably good filling. The use of commercial B4C-H2O slurry also displayed excellent fill and was stable compared to the B4C-IPA suspension, which made the deposition process reproducible.
dc.description.abstractAs a first step to demonstrate a proof of concept, silica (SiO2) nanoparticle was chosen to be deposited in high aspect ratio trenches, as colloidal silica nanoparticles in suspension form is readily available. Then, boron carbide nanoparticles (B4C) were used for deposition by dispersing them in isopropanol. Multiple simulations as well as experiments were carried out to determine the optimum applied voltage, the electrode separation and nanoparticle concentration by weight to achieve a high packaging fraction of nanoparticles in the trenches. Best condition was when the applied voltage was fixed at 50 volts and the electrode separation was kept at ~0.5 cm. The boron carbide nanoparticles were analyzed to find the zeta potential, the deposition rate, and the density of deposited B4C film. The density of deposited B4C film was found to be ~1.5 g/cm3 and the deposition rate was found to be almost 0.001 mg/cm2/s. Both constant DC and pulsed voltage were applied for deposition. A commercially obtained form of the B4C nanoparticles, namely a B4C-H2O slurry was also used. The filling inside the trenches was studied through cross-sectional SEM images.
dc.description.abstractIn order to achieve high efficiency, researchers have shown that one needs to etch deep holes or trenches in silicon and then fill them with boron. The high aspect ratio holes are fabricated with deep reactive ion etching (DRIE) through Bosch process and filled with 10B using low-pressure chemical vapor deposition process (LPCVD), which resulted in the best detectors as far as efficiency and detector area are concerned. However, this process requires use of expensive equipments such as DRIE and LPCVD reactors. To reduce the cost of fabrication significantly, high aspect ratio trenches can be anisotropically etched in (110) silicon using KOH or TMAH. To fill the trenches with boron or compound of boron, an alternative deposition process called electrophoretic deposition (EPD) has been is considered instead of LPCVD process.
dc.description.abstractThis thesis provides a theoretical background of EPD and demonstrates the applicability of the technique to fill high aspect ratio semiconductor trenches for specialized purposes. Finite element analysis based simulations for electric field lines and electrostatic potentials are performed for different aspect ratios of the trenches ranging from 20:1 to 3:1.
dc.description.abstractElectrophoretic Deposition is a colloidal process that utilizes an external electric field to influence charged micro or nanoparticles in a suspension to deposit onto a material surface. It is hypothesized that EPD can be used to fill the high aspect ratio trench-patterned microstructures with boron carbide (B4C) nanoparticles. EPD has been used in the ceramic industry for a long time and recently has found numerous applications due to its low cost, reduced formation time, simple apparatus requirement and versatility in numerous unique applications. It is expected that the fabrication cost of a trench patterned microstructure using wet etching process and filled with B4C nanoparticles through EPD process is significantly lower compared to patterns etched using DRIE and filled through the LPCVD process.
dc.language.isoENG
dc.publisherRensselaer Polytechnic Institute, Troy, NY
dc.relation.ispartofRensselaer Theses and Dissertations Online Collection
dc.subjectElectrical engineering
dc.titleElectrophorteic deposition of boron carbide in high aspect ratio trenches in silicon for neutron detector application
dc.typeElectronic thesis
dc.typeThesis
dc.digitool.pid175938
dc.digitool.pid175939
dc.digitool.pid175940
dc.rights.holderThis electronic version is a licensed copy owned by Rensselaer Polytechnic Institute, Troy, NY. Copyright of original work retained by author.
dc.description.degreeMS
dc.relation.departmentDept. of Electrical, Computer, and Systems Engineering


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