Reliability of large periphery GaN-on-Si HFETs

GaN devices exhibit excellent potential for use in many RF applications. However, commercial acceptance of the technology has been hindered by the scarcity and non-statistical nature of reliability results. In this work we present a full device level reliability study of GaN-on-Si HFETs. Reliability results on this technology include three-temperature DC data that show an activation energy of 1.7 eV and an average failure time >10⁷ h at 150 °C. Additionally, long duration DC lifetest (30 000 device hours) and RF lifetest (4000 device hours) results demonstrate a repeatable low drift process. Environmental tests such as autoclave and ESD demonstrate the ruggedness of the material system and technology. Finally, initial failure analysis is discussed.     

To Your Health: Self‐Regulation of Health Behavior Through Selective Exposure to Online Health Messages

Reaching target audiences is of crucial importance for the success of health communication campaigns, but individuals may avoid health messages if they challenge their beliefs or behaviors. A lab study (N = 419) examined effects of messages' consistency with participants' behavior and source credibility on selective exposure for 4 health lifestyle topics. Drawing on self‐regulation theory and dissonance theory, 3 motivations were examined: self‐bolstering, self‐motivating, and self‐defending. Prior behavior predicted selective exposure across topics, reflecting self‐bolstering. Standard‐behavior discrepancies also affected selective exposure, consistent with self‐motivating rather than self‐defending. Selective exposure to high‐credibility sources advocating for organic food, fruits and vegetable consumption, exercise, and limiting coffee all fostered accessibility of related standards, whereas messages from low‐credibility sources showed no such impact.     

Impact of the injection‐level‐dependent lifetime on Voc,FF, ideality m,J02, and the dim light response in a commercial PERC cell

The injection‐level‐dependent (ILD) lifetime of the silicon wafer impacts many characteristics of the final photovoltaic cell. While efficiency is commonly understood to be impacted by the silicon bulk lifetime (at the maximum power point injection level), this work demonstrates the wide ranging impacts of ILD lifetime on the V_oc, the fill factor (FF), the diode ideality factor m, and the dim light response. Instead of a two‐diode model, we utilize a boundary + ILD bulk lifetime model to analyze a commercial passivated emitter rear contact (PERC) cell featuring an AlO_x dielectric rear passivation. The ILD lifetime is directly measured and used to calculate the bulk recombination current across injection levels. With this boundary + ILD lifetime model, we demonstrate the role of the ILD lifetime on many cell parameters in this PERC cell. For most high efficiency commercial p‐type monocrystalline solar cells, the typically lower bulk lifetime at the maximum power point versus the lifetime at the open circuit point reduces the measured FF and pseudo‐FF. This work illustrates that for a commercial PERC cell with AlO_x rear passivation, the ILD lifetime is the primary mechanism behind reduced FF, ideality factors greater than 1, and the source of the J₀₂ term in the two‐diode model. The crucial implications of this work are not only to better understand commercial PERC cell loss mechanisms but also to encourage a focus on different metrics in cell diagnostics. One such metric is the V_oc at 0.1 or 0.05 suns. Copyright © 2016 John Wiley & Sons, Ltd.     

HF chemical etching of SiO2 on 4H and 6H SiC

Thickness and etch rate of SiO₂ films thermally grown on hexagonal SiC substrates were compared to results obtained from SiO₂/Si samples. The data confirm that profilometry and ellipsometry yield the same thickness values for oxides grown on Si and SiC. Within the accuracy of our measurements, oxides grown on different polytypes and faces of SiC etch at the same rate in a HF acid solution. The etch rate using a 50:1 H₂O:HF(50%) solution at room temperature is 0.1 nm/s and is uniform throughout the thickness of the SiO₂ films. The rate is the same as that obtained for SiO₂ grown on Si.     

采用MUF的倒装芯片封装技术

业界对信号完整性和电学性能提出了越来越高的要求,因而开始向更薄基板的方向发展,Amkor Technology Inc.开发出一种使用模塑底部填充（MUF）而非毛细底部填充（CUF）的倒装芯片模塑球栅阵列（FCMBGA）封装技术,使得无源器件与倒装芯片的间距更小,同时还提供了更优的薄芯基板变形控制,并可以获得更好的焊料连接可靠性。     

Cons and pros: prison education through the eyes of the prison educated*

ABSTRACT

While much has been written within academic journals about prisoners, rarely is there anything written by prisoners. In this essay, we, a group of prisoners who are earning or have earned college degrees while incarcerated in Texas, address the purpose, merits, and pitfalls of prison education and reform. Written as a response to the essays appearing in this special issue, we discuss our experiences of being othered as inmates, the impact of societal bias against us, our perspectives on prison education, and our own ideas for reforming prisons and making them more humane.     

Cellulose acetate as a selective sorbent for limonin in orange juice

Cellulose acetate as flake or powder is an efficient and selective sorbent for removing the bitter principle limonin from orange juice. Treatment of orange juice serum with powder (10 g/litre) removed 44–70% of the limonin content in less than an hour, at the same time removing relatively negligible amounts of hesperidin and ascorbic acid. Similar amounts of limonin could be removed by agitating the whole juice with cellulose acetate flakes held in open mesh bags which allowed contact between the enclosed flakes and the juice. Other materials, including related carbohydrate derivatives and polymers, were tested but only cellulose acetate butyrate shared the unusual sorptive properties of cellulose acetate.     

Multiuser Detection for Out-of-Cell Cochannel Interference Mitigation in the IS–95 Downlink

This paper considers the application of multiuser detection techniques to improve the quality of downlink reception in a multi-cell IS–95 digital cellular communication system. In order to understand the relative performance of suboptimum multiuser detectors including the matched filter detector, optimum multiuser detection in the context of the IS–95 downlink is first considered. A reduced complexity optimum detector that takes advantage of the structural properties of the IS–95 downlink and exhibits exponentially lower complexity than the brute-force optimum detector is developed. The Group Parallel Interference Cancellation (GPIC) detector, a suboptimum, low-complexity multiuser detector that also exploits the structure of the IS–95 downlink is then developed. Simulation evidence is presented that suggests that the performance of the GPIC detector may be near-optimum in several cases. The GPIC detector is also tested on a snapshot of on-air data measured with an omnidirectional antenna in an active IS–95 system and is shown to be effective for extracting weak downlink transmissions from strong out-of-cell cochannel interference. The results of this paper suggest that the GPIC detector offers the most performance gain in scenarios where weak downlink signals are corrupted by strong out-of-cell cochannel interference.     

Controlled Growth of ZnO Nanowires and Their Optical Properties

This article surveys recent developments in the rational synthesis of single‐crystalline zinc oxide nanowires and their unique optical properties. The growth of ZnO nanowires was carried out in a simple chemical vapor transport and condensation (CVTC) system. Based on our fundamental understanding of the vapor–liquid–solid (VLS) nanowire growth mechanism, different levels of growth controls (including positional, orientational, diameter, and density control) have been achieved. Power‐dependent emission has been examined and lasing action was observed in these ZnO nanowires when the excitation intensity exceeds a threshold (∼40 kW cm^–2). These short‐wavelength nanolasers operate at room temperature and the areal density of these nanolasers on substrate readily reaches 1 × 10¹⁰ cm^–2. The observation of lasing action in these nanowire arrays without any fabricated mirrors indicates these single‐crystalline, well‐facetted nanowires can function as self‐contained optical resonance cavities. This argument is further supported by our recent near‐field scanning optical microscopy (NSOM) studies on single nanowires.     

Developments in the fabrication and performance of high-quality HgCdTe detectors grown on 4-in. Si substrates

We are continuing to develop our growth and processing capabilities for HgCdTe grown on 4-in. Si substrates by molecular beam epitaxy (MBE). Both short-wave and mid-wave infrared (SWIR and MWIR) double-layer hetero-junctions (DLHJs) have been fabricated. In order to improve the producibility of the material, we have implemented an in-situ growth composition-control system. We have explored dry etching the HgCdTe/Si wafers and seen promising results. No induced damage was observed in these samples. Detector results show that the HgCdTe/Si devices are state-of-the-art, following the diffusion-limited trend line established by other HgCdTe technologies. Focal-plane array (FPA) testing has been performed in order to assess the material over large areas. The FPA configurations range from 128×128 to 1,024×1,024, with unit cells as small as 20 μm. The MWIR responsivity and NEDT values are comparable to those of existing InSb FPAs. Pixel operabilities well in excess of 99% have been measured. We have also explored the role of growth macrodefects on diode performance and related their impact to FPA operability. The SWIR HgCdTe/Si shows similar results to the MWIR material. Short-wave IR FPA, median dark-current values of less than 0.1 e⁻/sec have been achieved.