Saeed Moghaddam

An inorganic–organic proton exchange membrane for fuel cells with a controlled nanoscale pore structure

Proton exchange membrane fuel cells have the potential for applications in energy conversion and energy storage, but their development has been impeded by problems with the membrane electrode assembly. Here, we demonstrate that a silicon-based inorganic-organic membrane offers a number of advantages over Nafion--the membrane widely used as a proton exchange membrane in hydrogen fuel cells--including higher proton conductivity, a lack of volumetric size change, and membrane electrode assembly construction capabilities. Key to achieving these advantages is fabricating a silicon membrane with pores with diameters of approximately 5-7 nm, adding a self-assembled molecular monolayer on the pore surface, and then capping the pores with a layer of porous silica. The silica layer reduces the diameter of the pores and ensures their hydration, resulting in a proton conductivity that is two to three orders of magnitude higher than that of Nafion at low humidity. A membrane electrode assembly constructed with this proton exchange membrane delivered an order of magnitude higher power density than that achieved previously with a dry hydrogen feed and an air-breathing cathode.

Ferroelectric phenomena in Si-doped HfO2 thin films with TiN and Ir electrodes

Ferroelectric HfO2 is an attractive candidate for future ferroelectric random access memory devices due to its compatibility with the complementary metal-oxide-semiconductor process, conformal deposition, and scaling ability. Crystallization of HfO2 with different dopants and annealing conditions can produce the stabilization of the monoclinic, tetragonal, cubic, or orthorhombic crystal phases. In this work, the authors observe ferroelectric behavior in Si-doped hafnium oxide with TiN and Ir electrodes. Atomic layer deposited 10 nm HfO2 capacitors doped with varying concentrations of SiO2 have been fabricated in the metal–ferroelectric–insulator–semiconductor (MFIS) structure. The ferroelectric characteristics of thin film HfO2 are compared in the MFIS and metal–ferroelectric–metal configurations. Post-metallization anneals were applied to all thin film ferroelectric HfO2 capacitors, resulting in a remanent polarization of up to 22 μC/cm2 and a range of observed coercive voltages, emphasizing the importan...

TaN interface properties and electric field cycling effects on ferroelectric Si-doped HfO2 thin films

Ferroelectric HfO2-based thin films, which can exhibit ferroelectric properties down to sub-10 nm thicknesses, are a promising candidate for emerging high density memory technologies. As the ferroelectric thickness continues to shrink, the electrode-ferroelectric interface properties play an increasingly important role. We investigate the TaN interface properties on 10 nm thick Si-doped HfO2 thin films fabricated in a TaN metal-ferroelectric-metal stack which exhibit highly asymmetric ferroelectric characteristics. To understand the asymmetric behavior of the ferroelectric characteristics of the Si-doped HfO2 thin films, the chemical interface properties of sputtered TaN bottom and top electrodes are probed with x-ray photoelectron spectroscopy. Ta-O bonds at the bottom electrode interface and a significant presence of Hf-N bonds at both electrode interfaces are identified. It is shown that the chemical heterogeneity of the bottom and top electrode interfaces gives rise to an internal electric field, whic...

The effects of layering in ferroelectric Si-doped HfO2 thin films

Atomic layer deposited Si-doped HfO2 thin films approximately 10 nm thick are deposited with various Si-dopant concentrations and distributions. The ferroelectric behavior of the HfO2 thin films are shown to be dependent on both the Si mol. % and the distribution of Si-dopants. Metal-ferroelectric-insulator-semiconductor capacitors are shown to exhibit a tunable remanent polarization through the adjustment of the Si-dopant distribution at a constant Si concentration. Inhomogeneous layering of Si-dopants within the thin films effectively lowers the remanent polarization. A pinched hysteresis loop is observed for higher Si-dopant concentrations and found to be dependent on the Si layering distribution.

Effect of electrode geometry on performance of an EHD thin-film evaporator

This paper presents details of an optimization process of electrode geometry for an electrohydrodynamically (EHD) driven thin-film evaporator. The operation principle of the device is based on the action of the EHD force on the molecules of a dielectric liquid in a highly convergent electric field. The force starts at the end of a pair of electrodes, where the electric field changes from zero far from the electrodes to a finite value in between the electrodes. This force drives the liquid up into the spacing between the electrodes. The electrodes in this study were deposited thinly on a SiO/sub 2//Si wafer, so the liquid could be held within micrometers of thickness over the surface. Since the performance of the device in removing heat from the surface is a function of its pumping head and consequently its electrode geometry, the performances of different electrodes were evaluated by testing twelve sets of electrode pairs with different geometries. Then the optimum electrode design was incorporated into the design of a large size (32/spl times/32 mm/sup 2/) EHD thin-film evaporator. The device was fabricated, and its pumping and heat transfer performances were tested. A pumping head equal to the full height of the electrodes and a heat transfer coefficient of 1.9 W/cm/sup 2/./spl deg/C was achieved using HFE-7100 liquid.

Evaluation of analytical models for thermal analysis and design of electronic packages

The objective of this study is to evaluate the use of several analytical compact heat transfer models for thermal design, optimization, and performance evaluation in electronic packaging. A model for heat spreading in orthotropic materials is developed. The developed model is used in conjunction with the other available heat transfer models in a resistance network for calculation of heat transfer rate and junction temperatures in a multi-chip module (MCM). Refrigeration cooled MCM of an IBM server is used to illustrate the methodology. Results of the analytical model and resistance network analysis are compared with a numerical solution. Capability of the analytical model in predicting the thermal field is discussed and effectiveness of using the analytical models in thermal design and optimization of electronic packages is demonstrated.

Novel Method for Measurement of Total Hemispherical Emissivity

Abstract : This report was developed under a SBIR contract. This paper describes a heat flux-based method for measuring emissivity of a surface. In this method the emissivity of a surface is calculated using direct measurement of the heat flux passing through the surface. Unlike storage-based calorimetric methods, this method does not require application of known amounts of heat to the surface or the temperature history of a known amount of thermal mass to calculate the surface emissivity. Application and operation of this method is much simpler than calorimetric methods as it does not require careful thermal insulation of the heat radiating body from the surroundings. This technique allows emissivity measurements of the newly developed variable emissivity surfaces with significantly lighter and energy efficient measurement equipment that can operate for long term space missions. In this study, a commercially available thermopile heat flux sensor was used to measure the emissivity of a black paint and a variable emissivity surface, Electrostatic Switched Radiator (ESR). This paper details the concept, experimental setup, and the experiment results.

Measurement of Corona Wind Velocity and Calculation of Energy Conversion Efficiency for Air-Side Heat Transfer Enhancement in Compact Heat Exchangers

Corona discharge utilizes the effect of electrically induced secondary motions to enhance the air-side heat transfer coefficients between high-density fins in a fin structure. The objective of this study was to measure the velocity associated with the air jet generated by corona discharge for parametric ranges of interest to air-side heat transfer enhancement in compact heat exchangers. This is the first study of its kind where the nonintrusive laser Doppler velocimetry (LDV) technique was used to measure the velocity, with careful attention paid to correction for the electric field effects on the particles and the resulting slip velocity. Experiments were conducted with a prototypical wire-to-plate geometry (positively charged wire and grounded plate). In two series of experiments, the flow was seeded with 2.5 μm glass microspheres and 0.5 μm polystyrene nanospheres. The corrected velocity measurements were used to calculate the kinetic energy flux to the fluid and the resulting efficiency of the electric-to-kinetic energy conversion.

Ferroelectric Si-Doped HfO 2 Device Properties on Highly Doped Germanium

Ferroelectric Si-doped HfO2 thin films are integrated into three different device stacks with a p+ Ge substrate, a p+ Si substrate, and a TaN bottom metal gate. The ferroelectric behavior of the Si-doped HfO2 thin films is strongly dependent on the bottom interfaces. The Si-doped HfO2 thin films have favorably improved ferroelectric properties on the p+ Ge substrate due to the lack of a dielectric interfacial layer between HfO2 and Ge. The low-voltage operation and cycling stability of Si-doped HfO2 ferroelectric thin films on Ge can lead to the realization of high performance, robust Ge ferroelectric field-effect transistors for nonvolatile memory applications.

Performance Analysis of an Electrostatic Switched Radiator Using Heat-Flux-Based Emissivity Measurement

The heat-flux-based emissivity measurement technique developed in our earlier work has been used to study the performance of an electrostatic switched radiator. The capability of fast and accurate measurement of the real-time changes in emissivity enabled by this technique allowed understanding of the transient behavior during activation, as well as identification of a major failure mode of the second-generation electrostatic radiator. A solution for resolution of this failure mode was then proposed and successfully tested, producing accurate and repeatable results over many cycles. A change in emissivity of 0.52 was achieved with 280 V applied, among the best consistent results achieved through electrostatic technology. The current work offers further understanding of electrostatic radiator performance and its application to space vehicles.