On-Chip Thermoelectric Hotspot Cooling

Increased power density and non-uniform heat dissipation present a thermal management challenge in modern electronic devices. The non-homogeneous heating in chips results in areas of elevated temperature, which even if small and localized, limit overall device performance and reliability. In power electronics, hotspot heat fluxes can be in excess of 1kW/cm2. Although novel package-level and chip-level cooling systems capable of removing the large amounts of dissipated heat are under development, such “global” cooling systems typically reduce the chip temperature uniformly, leaving the temperature non-uniformity unaddressed. Thus, advanced hotspot cooling techniques, which provide localized cooling to areas of elevated heat flux, are required to supplement the new “global” cooling systems and unlock the full potential of cutting-edge power devices. Thermoelectric coolers have previously been demonstrated as an effective method of producing on-demand, localized cooling for semiconductor photonic and logic devices. The growing need for the removal of localized hotspots has turned renewed attention to on-chip thermoelectric cooling, seeking to raise the maximum allowable heat flux of thermoelectrically-cooled semiconductor device hotspots. This dissertation focused on the numerical and empirical determination of the operational characteristics and performance limits of two specific thermoelectric methods for high heat flux hotspot cooling: monolithic thermoelectric hotspot cooling and micro-contact enhanced thermoelectric hotspot cooling. The monolithic cooling configuration uses the underlying electronic substrate as the thermoelectric material, eliminating the need for a discrete cooler and its associated thermal interface resistance. Micro-contact enhanced cooling uses a contact structure to concentrate the cooling produced by the thermoelectric module, enabling the direct removal of kW/cm2 level heat fluxes from on-chip hotspots. To facilitate empirical validation of on-chip thermoelectric coolers and characterization of advanced thin film thermoelectric coolers, it was found necessary to develop a novel laser heating system, using a high power laser and short-focal length optics. The design and use of this illumination system, capable of creating kW/cm2-level, mm-sized hotspots, will also be described

Partnership for Research on Ebola VACcination (PREVAC): protocol of a randomized, double-blind, placebo-controlled phase 2 clinical trial evaluating three vaccine strategies against Ebola in healthy volunteers in four West African countries

International audienceAbstract Introduction The Ebola virus disease (EVD) outbreak in 2014–2016 in West Africa was the largest on record and provided an opportunity for large clinical trials and accelerated efforts to develop an effective and safe preventative vaccine. Multiple questions regarding the safety, immunogenicity, and efficacy of EVD vaccines remain unanswered. To address these gaps in the evidence base, the Partnership for Research on Ebola Vaccines (PREVAC) trial was designed. This paper describes the design, methods, and baseline results of the PREVAC trial and discusses challenges that led to different protocol amendments. Methods This is a randomized, double-blind, placebo-controlled phase 2 clinical trial of three vaccine strategies against the Ebola virus in healthy volunteers 1 year of age and above. The three vaccine strategies being studied are the rVSVΔG-ZEBOV-GP vaccine, with and without a booster dose at 56 days, and the Ad26.ZEBOV,MVA-FN-Filo vaccine regimen with Ad26.ZEBOV given as the first dose and the MVA-FN-Filo vaccination given 56 days later. There have been 4 versions of the protocol with those enrolled in Version 4.0 comprising the primary analysis cohort. The primary endpoint is based on the antibody titer against the Ebola virus surface glycoprotein measured 12 months following the final injection. Results From April 2017 to December 2018, a total of 5002 volunteers were screened and 4789 enrolled. Participants were enrolled at 6 sites in four countries (Guinea, Liberia, Sierra Leone, and Mali). Of the 4789 participants, 2560 (53%) were adults and 2229 (47%) were children. Those < 18 years of age included 549 (12%) aged 1 to 4 years, 750 (16%) 5 to 11 years, and 930 (19%) aged 12–17 years. At baseline, the median (25th, 75th percentile) antibody titer to Ebola virus glycoprotein for 1090 participants was 72 (50, 116) EU/mL. Discussion The PREVAC trial is evaluating—placebo-controlled—two promising Ebola candidate vaccines in advanced stages of development. The results will address unanswered questions related to short- and long-term safety and immunogenicity for three vaccine strategies in adults and children. Trial registration ClinicalTrials.gov NCT02876328 . Registered on 23 August 2016