Lawrence Ludwig

Effect of ultraviolet radiation exposure on room-temperature hydrogen sensitivity of nanocrystalline doped tin oxide sensor incorporated into microelectromechanical systems device

The effect of ultraviolet (UV) radiation exposure on the room-temperature hydrogen (H2) sensitivity of nanocrystalline indium oxide (In2O3)-doped tin oxide (SnO2) thin-film gas sensor is investigated in this article. The present sensor is incorporated into microelectromechanical systems device using sol-gel dip-coating technique. The present sensor exhibits a very high sensitivity, as high as 65 000–110 000, at room temperature, for 900ppm of H2 under the dynamic test condition without UV exposure. The H2 sensitivity is, however, observed to reduce to 200 under UV radiation, which is contrary to the literature data, where an enhanced room-temperature gas sensitivity has been reported under UV radiation. The observed phenomenon is attributed to the reduced surface coverage by the chemisorbed oxygen ions under UV radiation, which is in consonance with the prediction of the constitutive equation, proposed recently by the authors, for the gas sensitivity of nanocrystalline semiconductor oxide thin-film sensors.

Hydrogen-discriminating nanocrystalline doped-tin-oxide room-temperature microsensor

Highly hydrogen (H2)-selective [relative to carbon monoxide (CO)] sensor, operating at room temperature, has been fabricated using the micronanointegration approach involving the deposition of the nanocrystalline indium oxide (In2O3)-doped tin oxide (SnO2) thin film on microelectromechanical systems device. The present microsensor exhibits high room-temperature sensitivity towards H2 (S=12700); however, it is insensitive to CO at room temperature. In view of the different gas selectivity mechanisms proposed in the literature, it is deduced that the In2O3 doping, the presence of InSn4 phase, the low operating temperature (room temperature), the mesostructure, the small sizes of H2 and H2O molecules, the bulky intermediate and final reaction products for CO, and the electrode placement at the bottom are the critical parameters, which significantly contribute to the high room-temperature H2 selectivity of the present microsensor over CO. The constitutive equation for the gas sensitivity of the semiconductor ...

Tin Whisker Electrical Short Circuit Characteristics—Part II

Existing risk simulations make the assumption that when a free tin whisker has bridged two adjacent exposed electrical conductors, the result is an electrical short circuit. This conservative assumption is made because shorting is a random event that has an unknown probability associated with it. Note however that due to contact resistance, electrical shorts may not occur at lower voltage levels. In our first paper, we developed an empirical probability model for tin whisker shorting. In this paper, we develop a more comprehensive empirical model using a refined experiment with a larger sample size, in which we studied the effect of varying voltage on the breakdown of the contact resistance which leads to a short circuit. From the resulting data, we estimated the probability distribution of an electrical short, as a function of voltage. In addition, the unexpected polycrystalline structure seen in the focused ion beam (FIB) cross section in the first experiment was confirmed in this experiment using transmission electron microscopy (TEM). The FIB was also used to cross section two card guides to facilitate the measurement of the grain size of each card guides tin plating to determine its finish.

High Temperature Boost (HTB) Anode Power Supply for a modular and scalable power processing unit

A concept of a modular and scalable 10kW to 80kW High Temperature Boost (HTB) Power Processing Unit (PPU) capable of operating at temperatures beyond the standard military temperature range was proposed for solar electric in-space propulsion. Within the PPU, the Anode Power Supply (APS) module is a 10kW modular power stage and is the key to the HTB PPU. This paper is to present the design, development, fabrication, testing and thermal demonstration of the 10kW HTB APS. The system architecture and the paradigm shift of the HTB PPU is also to be described. In addition, the extreme environments electronic and packaging technologies are addressed as the fundamental technology path. The HTB PPU is intended for power processing in the area of space solar electric propulsion, where reduction of inspace mass and volume are desired, and sometimes even critical, to achieve the goals of future space flight missions. The concept of the HTB PPU can also be applied to other extreme environment applications, such as geothermal and petroleum deep-well drilling, where higher temperature operation is required.

A nanoparticle-based microsensor for room temperature hydrogen detection

In this work, we report a novel micromachined hydrogen sensor operating at room temperature. The sensor has been successfully designed and fabricated, based on interdigitated conductometric microelectrodes integrating indium oxide (In/sub 2/O/sub 3/)-doped tin oxide (SnO/sub 2/) semiconductor nanocrystalline particles with platinum (Pt) nanoclusters. Very high H/sub 2/ sensitivity (110/spl times/10/sup 3/) with fast response and recovery has been observed for the presented sensor at room temperature and low hydrogen gas concentration. The nanomaterial/microdevice integration for a highly efficient sensor device with unprecedented functions has been explored and investigated systematically.

Room Temperature Hydrogen Gas Sensitivity of Nanocrystalline-Doped Tin Oxide Sensor Incorporated into MEMS Device

Nanocrystalline indium oxide (In 2 O 3 )-doped tin oxide (SnO 2 ) thin film sensor has been sol-gel dip-coated on a microelectromechanical systems (MEMS) device. The micro-sensor device is successfully utilized to sense ppm level H 2 at room temperature with high sensitivity. The chamber pressure has no pronounce effect on the room temperature H 2 sensitivity.

High temperature anode power supply parts and packaging reliability and survivability

The power processing unit (PPU) of a solar electrical propulsion system for in-space propulsion is developed as a high power, temperature, and efficiency, modular, high specific impulse, and non-isolated converter topology unit for future deep space and manned missions. Overall, the High Temperature Boost (HTB) PPU has 87% improvement in PPU specific power/mass and 38% improvement in-space solar electric system mass saving. The objectives of this Phase 1 study are to develop a High Temperature Anode Power Supply 10kW Prototype module with new extreme environment component and packaging technology and determine the component reliability and packaging survivability for at least 50 cycles in the temperature range of -55°C to +160°C. After cycling, the functionality is tested at room temperature and elevated temperature (base plate at 100°C). Selection of high temperature components and advanced packaging techniques enables operation at a higher base plate temperature of 100°C. SiC MOSFETS and diodes were chosen as well as high temperature capacitors designed to operate at 1kV and 2μF at 150°C.