EFFECT OF PROCESS PARAMETERS ON THE PERFOMANCE OF POROUS SILICON HYDROGEN SENSORS *P.K.Sekhar, A.G.Sine and S.Bhansali BioMEMS and Microfabrication Laboratory, Dept. of Electrical Engineering, University of South Florida, Tampa, FL 33620 *Corresponding author: Praveen Kumar Sekhar, 813-454-3691, psekhar@eng.usf.edu Abstract: The process parameters of impedance based Pd doped porous silicon sensor were varied to optimize the sensitivity towards hydrogen detection. The active (Pd) layer thickness and pore depth were found to critically influence the sensitivity. The sensor was tested in the range of 0-1.5% H 2 . The optimized Pd thickness was found to be 8 nm with pore depth correlating to an etching time of 30 mins. Keywords: Hydrogen Sensor, Palladium Nanoclusters, Nanowires, Morphology INTRODUCTION Hydrogen, the clean energy of tomorrow has been in extensive use for commercial and technological applications such as in feedstock & transportation industries and recently for space explorations. It serves as an efficient clean energy alternative with high thermal enthalpy defacto commanding the attention of common people as well as the scientific community. Concurrently, in the next 20 years, concerns about global climate change and energy deficit will support hydrogen as a cost-effective alternative for fossil fuels. However, the frequent use of H 2 has raised concerns over safety. The explosive limits of hydrogen in air ranges between 4.65 and 93.9% in volume. The need of the hour being accurate monitoring and rapid sensing of this odorless, colorless gas in the vicinity of the storage facilities and general user environment. Especially, it is critical to develop a safe and reliable sensor to monitor hydrogen targeting this range. Numerous companies and organizations such as NASA and DOE, that use large quantities of hydrogen and oversee the development of the technology, have outlined a detailed performance criterion for an acceptable hydrogen sensor [1]. Multitude of approaches is being investigated including sol–gel-based sensors [2], semiconductor sensors [3], oxide-based sensors, thin-film-based sensors, optical sensors [4] (Surface Plasmon Resonance) and acoustic wave sensors [5]. Existing techniques either saturate at low levels of H 2 , have slower response, consume more power or exhibit poor sensitivity. In the case of nanostructures based H 2 sensing, even though the sensors respond in real-time, fabricating these nanowire sensors entail complex procedures, such as the transfer of the nanomoieties and their organized assembly. Exploiting the novel features at nanoscale while adhering to NASA guidelines, porous silicon (PSi) substrates as sensing platforms have been explored [6]. Impedance based palladium doped porous silicon sensors offer several advantages which include (a) batch fabrication, (b) high electroactive interaction (response to minor perturbations) with the desired analyte, (c) tunability towards targeting specific sensing needs and (d) easy integration with microelectronic circuitry with flexibility of achieving System-On-Chip (SoC) configuration. Porous silicon etching variables such as silicon crystal orientation, dopant type, dopant level, current density, etching solution and etching time are found to influence the structure and morphology of the pores, thereby affecting the sensor performance. Another critical parameter of investigation is the active layer (Pd) thickness which dictates the H 2 absorption and desorption cycles. This work examines the influence of a sub-set of process variables such as etching time (pore depth) and Pd thickness relating to the structure and morphology of the pores, which in turn is correlated to performance and stability of the nanostructured H 2 sensor. EXPERIMENTAL Figure 1. Cross Sectional View of Sample Etched for 30 mins, with 8nm of Pd Annealed at 900ºC in N2 Coated Finally with 8 nm of Pd. Porous Silicon was fabricated by electrochemical etch of a p-type Silicon wafer with 50 nm