The authors performed a study to determine whether silicon very large-scale integrated circuits (VLSICs) can survive the high temperature (up to 300 degrees C) and total-dose radiation environments (up to 10 Mrad over a 7-10-y system life) projected for a very-high power space nuclear reactor platform. It is shown that circuits built on bulk epitaxial silicon cannot meet the temperature requirement because of excessive junction leakage currents. However, circuits built on silicon-on-insulator (SOI) material can meet both the radiation and temperature requirements. It is also found that the temperature dependence of the threshold voltage of the SOI transistors is less than that of bulk transistors. Survivability of high-temperature SOI VLSICs in space, including immunity to transient and single-event upset, is also addressed. >

High-temperature silicon-on-insulator electronics for space nuclear power systems: requirements and feasibility

Several industrial applications require specific electronic systems installed in harsh environments to perform measurements, monitoring, and control tasks such as in space exploration, aerospace missions, automotive industries, down-hole oil and gas industry, and geothermal power plants. The extreme environment could be surrounding high-, low-, and wide-range temperature, intense radiation, or even a combination of above conditions. We review, in this paper, the main leading applications that demand advanced technologies to fit the unconventional requirements of extreme operating conditions, discussing their main merits and limits compared to established and emerging technologies in this field, including silicon (Si), silicon on insulator (SOI), silicon germanium (SiGe), silicon carbide (SiC) as well as III–V semiconductors particularly the gallium nitride (GaN) semiconductor. In spite of successfully exceeding extreme conditions borders by developing advanced semiconductor devices dedicated for harsh environments, especially in high-temperature applications, the packaging challenges are still limiting the reliability of the developed technologies. Those challenges are examined in this review in terms of limitations and proposed solutions.

Electronics and Packaging Intended for Emerging Harsh Environment Applications: A Review

To enhance ultrasonic bond development, an improved understanding is needed of the processes taking place at the bond interface. This work is designed to determine the role that bonding parameters play in contributing to bond development. Of particular concern are the effects created by the machine variables, i.e., load, power, and time. Silicon was selected as a bond surface for aluminum wire bonds. The brittle nature of silicon provides a permanent record of the bonding history. With both the crystal orientation and defects of the silicon well characterized prior to bonding, features such as the location of residual bonding strains in the silicon were determined. The pattern of partially bonded material exposed by peeling underdeveloped bonds simulates a torus (or doughnut) with an unbonded central region. Features of aluminum wire bonds to aluminum, glass, beryllium, and silicon were compared to show that a common mechanism exists independent of the bond surface material. The ability to bond to silicon varies with wire composition. For example, both Al-0.5% Mg and pure Al wires bond readily, while Al-l% Si wire does not. Two modes of material flow characterize interfacial behavior. Ultrasonic energy promotes a material softening which, in conjunction with the applied load, results in a gross flow to expose fresh material for bonding. In the second stage of material flow, a wave form is propagated through the wire to the periphery of the wire-silicon interface. This wave form is observed as a periodic cutting action into the silicon perpendicular to the pulsing direction. A fine ball-like formation in the grooves of the wave region at the bond zone was a feature common to the different bonding surfaces. The wavelength and wave amplitude vary linearly with the applied power as does the tip-to-tip displacement of the wedge. The groove spacings are of the same magnitude as the wedge displacement. For constant power and time, increased load increases the size of the central bond region that does not experience the wave action. For constant load and power, the width of the wave affected periphery increases toward the center of the bond with time. The method of thermally induced stacking faults by steam oxidation was used to characterize the residual bond strains in the silicon. Faulting was found in the peripheral region of the bond where the wave action was operable. This faulting correlated to stresses generated in the pulsing direction and not to the directions of gross material flow. Reliable bonding depends upon a proper control of the gross and wave flow processes by optimizing material properties as well as machine variables. A model has been developed to qualitatively relate the influence of these variables and the manner in which a change in one parameter affects the response of the remaining variables.

Enhancing Ultrasonic Bond Development

The thin films of gold which are applied so extensively in electronic devices are normally deposited over thin films of other metals in two, three or even four component metallization systems. The problems arising in such systems are vividly illustrated in this article on the gold/chromium metallization system developed in large measure at the Sandia Laboratories in Albuquerque, New Mexico.

/pdf/gold-chromium-metallizations-for-electronic-devices-3t5t7zhwcq.pdf

Gold/chromium metallizations for electronic devices

A key issue associated with the wider adoption of hybrid-electric vehicles (HEV) and plug in hybrid-electric vehicles (PHEV) is the implementation of the power electronic systems that are required in these products [1]. To date, many consumers find the adoption of these technologies problematic based on a financial analysis of the initial cost versus the savings available from reduced fuel consumption. Therefore, one of the primary industry goals is the reduction in the price of these vehicles relative to the cost of traditional gasoline powered vehicles. Part of this cost reduction must come through optimization of the power electronics required by these vehicles. In addition, the efficiency of the systems must be optimized in order to provide the greatest range possible. For some drivers, any reduction in the range associated with a potential HEV or PHEV solution in comparison to a gasoline powered vehicle represents a significant barrier to adoption and the efficiency of the power electronics plays an important role in this range. Likewise, high efficiencies are also important since lost power further complicates the thermal management of these systems. Reliability is also an important concern since most drivers have a high level of comfort with gasoline powered vehiclesmore » and are somewhat reluctant to switch to a less proven technology. Reliability problems in the power electronics or associated components could not only cause a high warranty cost to the manufacturer, but may also taint these technologies in the consumer's eyes. A larger vehicle offering in HEVs is another important consideration from a power electronics point of view. A larger vehicle will need more horsepower, or a larger rated drive. In some ways this will be more difficult to implement from a cost and size point of view. Both the packaging of these modules and the thermal management of these systems at competitive price points create significant challenges. One way in which significant cost reduction of these systems could be achieved is through the use of a single coolant loop for both the power electronics as well as the internal combustion engine (ICE) [2]. This change would reduce the complexity of the cooling system which currently relies on two loops to a single loop [3]. However, the current nominal coolant temperature entering these inverters is 65 C [3], whereas a normal ICE coolant temperature would be much higher at approximately 100 C. This change in coolant temperature significantly increases the junction temperatures of the devices and creates a number of challenges for both device fabrication and the assembly of these devices into inverters and converters for HEV and PHEV applications. With this change in mind, significant progress has been made on the use of SiC devices for inverters that can withstand much higher junction temperatures than traditional Si based inverters [4,5,6]. However, a key problem which the single coolant loop and high temperature devices is the effective packaging of these devices and related components into a high temperature inverter. The elevated junction temperatures that exist in these modules are not compatible with reliable inverters based on existing packaging technology. This report seeks to provide a literature survey of high temperature packaging and to highlight the issues related to the implementation of high temperature power electronic modules for HEV and PHEV applications. For purposes of discussion, it will be assumed in this report that 200 C is the targeted maximum junction temperature.« less

/pdf/high-temperature-high-power-packaging-techniques-for-hev-nu8ra5szbi.pdf

High-Temperature High-Power Packaging Techniques for HEV Traction Applications

Hybrid microcircuits in geothermal instrumentation must operate from room temperature to 300°C. Bond failure occurred during operation of initial geothermal circuits due to intermetallic growth at the aluminum wire-to-gold conductor interface. To remedy this problem, two wire bonding techniques have been qualified in high-temperature aging tests: 1) ultrasonic bonding of aluminum wire directly to modified fritless gold conductor inks (DuPont 9910, AVX 3520, and TFS A328) and 2) insertion of a I mil diffusion barrier pad between the thick film and the aluminum wire. Both systems allow 100-1000 h operation at 300°C. Three alloys of wire were tested: pure aluminum, aluminum with I percent silicon, and aluminum with 1 percent magnesium. The degradation rates differed greatly with pure aluminum being the least tolerant to temperature aging and wire with 1 percent silicon faring best. Because thick-film surfaces tend to be harder than thin-film surfaces, hardened aluminum wire (elongation 0.5 percent) formed bonds with less pad deformation and, consequently, with higher pull strengths than standard bonding wire (elongation 1-3 percent). Comparison of wire bonds aged at three temperatures (250, 300, and 350°C) demonstrated several orders of magnitude spread in degradation rates; for 1000-h bond lifetime, 300°C was found to be about the highest allowed operational temperature for direct bonding to gold. Disks of kovar and nickel of l-mil thickness and 30 mils diam were used as diffusion barriers between the gold and aluminum. Evaporated on one side of each disk was a 1 µm gold thin film for thermocompression bonding to the thick film; the other side received an evaporated aluminum film for wire bonding. Aging for 1000 h up to 350°C produced no increase in bond resistance for any of the three wire alloys tested. Some decrease in pull strength with time was noticed but was attributed to annealing of the wire.

Aluminum Wire to Thick-Film Connections for High-Temperature Operation

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Aluminum Wire to Thick-Film Connections for High-Temperature Operation