Design, fabrication, and integration of a fuel cell for a hybrid micro power system

The purpose of this research was to design, fabricate, and evaluate a CMOS compatible micro fuel cell (PEMFC) that incorporates an electrode with integrated heaters and temperature sensors. This device would later be incorporated into a UM-muPower Supply coupled with a wireless interface, control circuitry, a micro-electrochemical system (MEMS) device, and an energy storage device.; The device was fabricated starting with a standard single side polished (N or P) type 4 inch <100> silicon wafer, supported by a 1 micron stress relieved stack comprised of three LPCVD (low pressure chemical vapor deposition) layers (Oxide/Nitride/Oxide: 4000/2000/4000 A). The heaters and temperature sensors were fabricated on top of this stack and were made out of a 6000 A layer of phosphorous doped LPCVD polysilicon. Typical sensor and heater resistance measurements are ∼1--4 KO and 16--17 KO respectively. The heaters and temperature sensors are isolated from the thin film fuel cell device by an LPCVD 5000 A oxide layer.; The anode and cathode layers are made out of electron beam (E-beam) evaporated titanium (2000 A) and the catalyst layers are made out of 50 A of E-beam platinum. The electrodes are separated by a 5000 A spin-casted NafionRTM layer cured at 150°C for 45 minutes. The fuel cell electrode and catalyst layers differ from previous work in material and design. The Triple Phase Boundary (TPD) is optimized in this design to increase the perimeter to area ratio (interfacial area) and packing density by using triangular instead of circular vias.; The best performance of the micro fuel cell was 0.2 mW/cm2. The following parameters were used in the operation of the micro fuel cell: integrated heater temperature 80C°, H2 and O2 flow rates of 5 sccm, saturator temperatures of 90°C or 69.2 RHM, and catalyst loading of 9.06 mug/cm2 (anode and cathode). The power density of a conventional PEMFC was found to be 400 mW/cm2 under the following parameters: fuel cell temperature was 80°C, H2 and O2 flow rates were 60 sccm, saturator temperatures were 90°C, and catalyst loading was 0.5 mg/cm2 (anode and cathode). From examining the power density on a per volume basis, the conventional fuel cell had a power density of 8 mW/cm3 while the UM-muPEMFC had a power density of 7 mW/cm3.; None of the following chemical compounds had deleterious effects on the performance of the UM-muPEMFC: Shipley(TM) photoresists (1812, 1827, 9260), MF319 Developer, AZ400K Developer, Baker Photoresist strip (1000 and 2000), Acetone, Hexamethyl Disilane Solution, and Tetramethylammonium hydroxide. Further experiments were performed to optimize the adhesion of spin casted NafionRTM onto the substrate. Under the correct thin film curing conditions (avoiding basic compounds), Acetone could be used as a solvent for metal lift-off on top of the NafionRTM layer.