Fred Mitlitsky

Wafer‐scale laser pantography: Fabrication of n‐metal‐oxide‐semiconductor transistors and small‐scale integrated circuits by direct‐write laser‐induced pyrolytic reactions

A complete set of processes sufficient for manufacture of n‐metal‐oxide‐semiconductor (n‐MOS) transistors by a laser‐induced direct‐write process has been demonstrated separately, and integrated to yield functional transistors. Gates and interconnects were fabricated of various combinations of n‐doped and intrinsic polysilicon, tungsten, and tungsten silicide compounds. Both 0.1‐μm and 1‐μm‐thick gate oxides were micromachined with and without etchant gas, and the exposed p‐Si [100] substrate was cleaned and, at times, etched. Diffusion regions were doped by laser‐induced pyrolytic decomposition of phosphine followed by laser annealing. Along with the successful manufacture of working n‐MOS transistors and a set of elementary digital logic gates, this letter reports the successful use of several laser‐induced surface reactions that have not been reported previously.

Reversible (unitised) PEM fuel cell devices

Regenerative fuel cells (RFCs) are enabling for many weight-critical portable applications, since the packaged specific energy (>400 Wh/kg) of properly designed lightweight RFC systems is several-fold higher than that of the lightest-weight rechargeable batteries. RFC systems can be rapidly refueled (like primary fuel cells), or can be electrically recharged (like secondary batteries) if a refueling infrastructure is not conveniently available. Higher energy capacity systems with higher performance, reduced weight and freedom from fueling infrastructure are the features that RFCs promise for portable applications. Reversible proton exchange membrane (PEM) fuel cells, also known as unitised regenerative fuel cells (URFCs), or reversible regenerative fuel cells, are RFC systems which use reversible PEM cells, where each cell is capable of operating both as a fuel cell and as an electrolyser. URFCs further economise portable device weight, volume and complexity by combining the functions of fuel cells and electrolysers in the same hardware, generally without any system performance or efficiency reduction. URFCs are being made in many forms, some of which are already small enough to be portable. Lawrence Livermore National Laboratory (LLNL) has worked with industrial partners to design, develop and demonstrate high-performance and high-cycle-life URFC systems. LLNL is also working with industrial partners to develop breakthroughs in lightweight pressure vessels that are necessary for URFC systems to achieve the specific energy advantages over rechargeable batteries. Proton Energy Systems Inc is concurrently developing and commercialising URFC systems (its Unigen ; product lproduct line), in addition to PEM electrolyser systems (the Hogen ; product lproduct line), and primary PEM fuel cell systems. LLNL is constructing demonstration URFC units in order to persuade potential sponsors, often in their own conference rooms, that advanced applications based on URFCs are feasible. Safety and logistics force these URFC demonstration units to be small, transportable and easily set up, hence they already prove the viability of URFC systems for portable applications.

Electrolysis Propulsion for Spacecraft Applications

Electrolysis propulsion has been recognized over the last several decades as a viable option to meet many satellite and spacecraft propulsion requirements. This technology, however, was never used for in-space missions. In the same time frame, water based fuel cells have flown in a number of missions. These systems have many components similar to electrolysis propulsion systems. Recent advances in component technology include: lightweight tankage, water vapor feed electrolysis, fuel cell technology, and thrust chamber materials for propulsion. Taken together, these developments make propulsion and/or power using electrolysis/fuel cell technology very attractive as separate or integrated systems. A water electrolysis propulsion testbed was constructed and tested in a joint NASA/Hamilton Standard/Lawrence Livermore National Laboratories program to demonstrate these technology developments for propulsion. The results from these testbed experiments using a 1-N thruster are presented. A concept to integrate a propulsion system and a

Wafer-Scale Laser Pantography: IV. Physics of Direct Laser-Writing Micron-Dimension Transistors

The processes involved in the fabrication of micron-dimension transistors and small-scale integrated circuits using only the technique of direct laser-writing by localized pyrolytic surface reactions are discussed. New experimental findings in the deposition of tungsten by silicon. surface reduction of tungsten hexafluoride and doped polysilicon are presented. The techniques used to fabricate laser beam-written n-MOSFETs are being extended to make unipolar JFETs and bipolar lateral pnp transistors.

Optimization and Demonstration of a Solid Oxide Regenerative Fuel Cell System

Single cell solid oxide regenerative fuel cells (SORFCs) have been demonstrated for over 1000 hours of operation at degradation rates as low as 0.5% per thousand hours for current densities as high as 300mA/cm{sup 2}. Efficiency levels (fuel cell power out vs. electrolysis power in) have been demonstrated in excess of 80% at 100mA/cm{sup 2}. All testing has been performed with metallic based interconnects and non-noble metal electrodes in order to limit fabrication costs for commercial considerations. The SORFC cell technology will be scaled up to a 1kW sized stack which will be demonstrated in Year 2 of the program. A self contained SORFC system requires efficient thermal management in order to maintain operating temperatures during exothermic and endothermic operational modes. The use of LiF as a phase change material (PCM) was selected as the optimum thermal storage medium by virtue of its superior thermal energy density by volume. Thermal storage experiments were performed using LiF and a simulated SORFC stack. The thermal storage concept was deemed to be technically viable for larger well insulated systems, although it would not enable a high efficiency thermally self-sufficient SORFC system at the 1 kW level.

Design trade space for a Mars ascent vehicle for a Mars sample return mission

Abstract The design of an ascent vehicle for Mars sample return is one of the most challenging problems to be addressed for this type of mission. This paper identifies the spectrum of performance requirements that could be required of a Mars ascent vehicle for a sample return mission. With this understanding of performance requirements, an investigation of technology requirements is presented. These technology requirements are compared to past and existing technology in order to identify which are the lagging technologies and where development investment should be made. Mars ascent approaches which include storable propellants and in-situ production of propellants are considered. Several technology comparisons are performed to illustrate performance regions that are appropriate for different technologies. Several promising propulsion technologies are identified: miniature constant displacement pumps, bladder lined composite tankage, thin wall metal tankage and advanced propellants. Technologies that have been designed, built, tested and flown are emphasized.

Wafer-Scale Laser Pantography: VI. Direct-Write Interconnection Of VLSI Gate Arrays

General principles of laser direct-write deposition processes are reviewed. Device interconnection of CMOS gate arrays by means of computer-controlled, laser-induced thermochemical surface reactions is described. Interconnection quality parameters are related, and processing rate considerations are discussed.

Fabrication of Gate Array Interconnect Structures Using Direct-Write Deposition Processes

General principles of laser direct-write deposition processes are reviewed. Device interconnection of CMOS gate arrays by means of computer-controlled, laser-induced thermochemical surface reactions is described. Maskless, automated, five-minute interconnection of 1000 gate CMOS array dies is described using discretionary laser-induced chemical vapor deposition. Eight 125-stage ring oscillators written on a single CMOS gate array die were shown to have the device-limited performance of similar patterns manufactured by a photolithographically patterned aluminum-silicon alloy. These results suggest the feasibility of using this method, Laser Pantography (LP), for rapid implementation of prototype and limited volume semi-custom VLSI circuits immediately after their design is completed.

Preliminary demonstration of power beaming with non-coherent laser diode arrays

A preliminary demonstration of free-space electric power transmission has been conducted using non-coherent laser diode arrays as the transmitter and standard silicon photovoltaic cell arrays as the receiver. The transmitter assembly used a high-power-density array of infrared laser diode bars, water cooled via integrated microchannel heat sinks and focused by cylindrical microlenses. The diode array composite beam was refocused by a parabolic mirror over a 10 meter path, and received on a ∼15×25 cm panel of thin film high efficiency silicon solar cells. The maximum cell output obtained was several watts, and the cell output was used to drive a small motor. Due to operating constraints and unexpected effects, particularly the high nonuniformity of the output beam, both the distance and total received power in this demonstration were modest. However, the existing transmitter is capable of supplying several hundred watts of light output, with a projected received electric power in excess of 200 watts. The source radiance is approximately 5×109 W/m2-steradian. With the existing 20 cm aperture, useful power transmission over ranges to ∼100 meters should be achievable with a DC to DC efficiency of greater than 10%. Non-coherent sources of this type are readily scalable to powers of tens of kilowatts, and with larger apertures can be used directly for power transmission up to several kilometers. Future non-coherent diode laser sources may be suitable for power transmission over hundreds of kilometers. Also, the experience gained with non-coherent arrays will be directly applicable to power beaming systems using coherent diode arrays or other array-type laser sources.A preliminary demonstration of free-space electric power transmission has been conducted using non-coherent laser diode arrays as the transmitter and standard silicon photovoltaic cell arrays as the receiver. The transmitter assembly used a high-power-density array of infrared laser diode bars, water cooled via integrated microchannel heat sinks and focused by cylindrical microlenses. The diode array composite beam was refocused by a parabolic mirror over a 10 meter path, and received on a ∼15×25 cm panel of thin film high efficiency silicon solar cells. The maximum cell output obtained was several watts, and the cell output was used to drive a small motor. Due to operating constraints and unexpected effects, particularly the high nonuniformity of the output beam, both the distance and total received power in this demonstration were modest. However, the existing transmitter is capable of supplying several hundred watts of light output, with a projected received electric power in excess of 200 watts. The s...

Low-Cost Co-Production of Hydrogen and Electricity

A study to further the efforts of low-cost co-production of hydrogen and electricity through the use of a distributed approach on a planar solid oxide fuel cell platform.