MOCVD Emitter Regrowth Technology for Scaling InGaAs/InP HBTs to Sub-100nm Emitter Width

By scaling semiconductor thicknesses, lithographic dimensions, and contactresistivities, the bandwidth of InGaAs/InP Hetero-junction Bipolar Transistors(HBTs) has reached 550/1100 GHz ft/fmax at 128 nm emitter width (wE). Primary challenges faced in scaling the emitter width are: developing high aspectratio emitter metal process for wE < 100nm, reducing base contact resistivityρb,c, and maintaining high DC current gain β.The existing W/TiW emitter process for RF HBTs cannot scale below 100nm. Process modules for scaling the emitter width to 60 nm are demonstrated.High aspect ratio trenches are etched into a sacrificial Si layer and then filledwith metal via Atomic Layer Deposition (ALD). Metals with high melting pointsare chosen to withstand high emitter current densities (JE) at elevated junctiontemperatures without suffering from electromigration or thermal decompositionand is thus manufacturable. ALD deposition of TiN, Pt, and Ru are explored.Novel base epi designs are proposed for reducing Auger recombination current(IB,Auger). A dual doping layer in the base is proposed with a higher doping in theupper 5 nm of the base for lower ρb,c and a lower doping in the remainder of thebase for reducing IB,Auger. Presence of a quasi-electric field (4EC) in the upperdoping grade accelerates electrons away from the region towards the collector,thus further reducing IB,Auger.Selective regrowth of the emitter semiconductor via Metal-Organic ChemicalVapour Deposition (MOCVD) is proposed for decoupling the extrinsic base regionunder the base metal from the intrinsic region under the emitter-base junction,for increasing β,ft, and improving ρb,c. Carbon p-dopants in the InGaAs base arepassivated by H+ during regrowth. Annealing to reactivate carbon induces surfacedamage and increases base sheet resistance (Rb,sh) and ρb,c. Process techniquesfor minimizing Rb,sh and ρb,c in an emitter regrowth process are demonstratedand compared. ρb,c of 5.5 Ω.µm2 on p-InGaAs is demonstrated on TransmissionLine Measurement (TLM) structures after regrowth and anneal, by protecting thesemiconductor surface with tungsten. This is comparable to 2.9 Ω.µm2 measuredon TLM structures that do not undergo regrowth and anneal.Feasibility of emitter regrowth is demonstrated on Large Area Devices (LADs)with SiO2 as regrowth mask, and W cap during anneal. Emitter-regrowth andnon-regrowth devices of identical dimensions and epi design are compared. Emitterregrown HBTs yield higher β of 28 as compared to 13 for non-regrowth devices.Benefits of emitter regrowth cannot be ascertained on LADs due to high seriesresistance and large gap spacings between base metal and emitter-base junction.A process flow is proposed for scaling regrown HBTs to 60 nm emitter widths.The process incorporates ALD emitter metal technology that is demonstrated inthe first half of the dissertation. New epi designs for regrown-emitter HBTs areoptimized for maximizing β, ft. Scaling regrown-emitter HBTs is essential forrealizing their benefit over non-regrowth HBTs

Clinico-demographic profile of young people presenting with refractive errors to a medical college hospital of Bihar, India

Background: Refractive errors are the second most important cause of blindness and account for 18% of the burden. An estimated 123.7 million people suffer from visual impairment due to unaddressed refractive errors worldwide. International agencies recognize that globally, there is insufficient data on the prevalence and types of refractive errors in different populations and age groups. The present study evaluated the proportion of refractive errors with their clinico-demographic context among 10–24-year old patients, presenting to the Ophthalmology Outpatient Department (OPD) of a tertiary hospital of Bihar state of India. Material and methods: This prospective, descriptive study collected information about refractive errors in 2739 eyes of 1482 young people. The association between the refractive errors and clinico-demographic variables such as age group, gender, residential background and educational status was evaluated using the chi-square test (taking p < 0.05 as significant). Results: Hypermetropic errors were more common (51%) comprising of hypermetropia (32%) and hypermetropic astigmatism (19%). They marginally exceeded myopic errors (about 49%), comprising myopic astigmatism (26%) and myopia (22%) while mixed astigmatism was the least common (0.4%). Myopic errors were significantly more common in the 10–14 years age group (76%) while hypermetropic errors predominated in older age-groups (54%, p < 0.001). Myopia predominated in females (39%) and in rural young people (53%), myopic astigmatism in the illiterate (45%) but hypermetropia in males (37%, p < 0.001), urban (35%, p < 0.001) and literate young people (31%, p < 0.001). Conclusions: This study revealed a broad picture of proportion and predominance of different refractive errors and their associations with clinico-demographic profile of the patients

Epidemiology and Clinicopathological Profile of Renal Cell Carcinoma: A Review from Tertiary Care Referral Centre

Renal cell carcinoma (RCC) accounts for 3% of all adult cancers and 85% of all kidney tumours. Incidence of RCC is lower in Asian region, particularly in India, probably due to lack of reporting. Most of the data about RCC are from Western countries; and data from India are scarce, especially regarding para-neoplastic syndromes. We sought to determine the epidemiology, clinicopathological profile and management of RCCin a tertiary care centre in Western India. This was a retrospective study that involved data analysis of records of RCC patients who presented to our institution from April 2016 to February 2020. Laboratory investigations, including tests for paraneoplastic syndrome (PNS), and relevant radiologic investigations were performed and treatment was offered according to the stage, patient factors and available modalities. A total 142 RCC patients were included in the study. The median age of presentation was 58 years. Most of the patients (67%) were symptomatic, and 33% of the patients were asymptomatic, and the RCC was diagnosed incidentally. A large number of patients (56.3%) had PNS. The most common histopathologic type of RCC was clear cell carcinoma (68.8%), followed by papillary (20%) and chromophobe (8%) carcinoma. 40% of carcinomas with sarcomatoid differentiation were seen in patients under 50 years of age. Two cases of multicystic RCC were both seen in patients less than 50 years of age. 65.5% of the patients presented at Stage 1 and 2. Most surgeries (71.2%) were done in a minimally invasive manner. A significant number of patients were asymptomatic, in which RCC was detected incidentally. The age of presentation was earlier, yet the patients had a higher tumour stage. More than half of the patients had PNSs. Despite growing trend towards Western data, the significantly higher number of patients with PNSs and early age of presentation suggest inherent differences in tumour biology, possibly related to differences in genetic and environmental factors

Radar sounding evidence for buried glaciers in the southern mid-latitudes of Mars

Lobate features abutting massifs and escarpments in the middle latitudes of Mars have been recognized in images for decades, but their true nature has been controversial, with hypotheses of origin such as ice-lubricated debris flows or glaciers covered by a layer of surface debris. These models imply an ice content ranging from minor and interstitial to massive and relatively pure. Soundings of these deposits in the eastern Hellas region by the Shallow Radar on the Mars Reconnaissance Orbiter reveal radar properties entirely consistent with massive water ice, supporting the debris-covered glacier hypothesis. The results imply that these glaciers formed in a previous climate conducive to glaciation at middle latitudes. Such features may collectively represent the most extensive nonpolar ice yet recognized on Mars

Assessment of humoral immune responses to blood-stage malaria antigens following ChAd63-MVA immunization, controlled human malaria infection and natural exposure.

The development of protective vaccines against many difficult infectious pathogens will necessitate the induction of effective antibody responses. Here we assess humoral immune responses against two antigens from the blood-stage merozoite of the Plasmodium falciparum human malaria parasite--MSP1 and AMA1. These antigens were delivered to healthy malaria-naïve adult volunteers in Phase Ia clinical trials using recombinant replication-deficient viral vectors--ChAd63 to prime the immune response and MVA to boost. In subsequent Phase IIa clinical trials, immunized volunteers underwent controlled human malaria infection (CHMI) with P. falciparum to assess vaccine efficacy, whereby all but one volunteer developed low-density blood-stage parasitemia. Here we assess serum antibody responses against both the MSP1 and AMA1 antigens following i) ChAd63-MVA immunization, ii) immunization and CHMI, and iii) primary malaria exposure in the context of CHMI in unimmunized control volunteers. Responses were also assessed in a cohort of naturally-immune Kenyan adults to provide comparison with those induced by a lifetime of natural malaria exposure. Serum antibody responses against MSP1 and AMA1 were characterized in terms of i) total IgG responses before and after CHMI, ii) responses to allelic variants of MSP1 and AMA1, iii) functional growth inhibitory activity (GIA), iv) IgG avidity, and v) isotype responses (IgG1-4, IgA and IgM). These data provide the first in-depth assessment of the quality of adenovirus-MVA vaccine-induced antibody responses in humans, along with assessment of how these responses are modulated by subsequent low-density parasite exposure. Notable differences were observed in qualitative aspects of the human antibody responses against these malaria antigens depending on the means of their induction and/or exposure of the host to the malaria parasite. Given the continued clinical development of viral vectored vaccines for malaria and a range of other diseases targets, these data should help to guide further immuno-monitoring studies of vaccine-induced human antibody responses

Analysis of human B‐cell responses following ChAd63‐MVA MSP1 and AMA1 immunization and controlled malaria infection

Acquisition of non‐sterilizing natural immunity to Plasmodium falciparum malaria has been shown in low transmission areas following multiple exposures. However, conflicting data from endemic areas suggest that the parasite may interfere with the induction of effective B‐cell responses. To date, the impact of blood‐stage parasite exposure on antigen‐specific B cells has not been reported following controlled human malaria infection (CHMI). Here we analysed human B‐cell responses in a series of Phase I/IIa clinical trials, which include CHMI, using candidate virus‐vectored vaccines encoding two blood‐stage antigens: merozoite surface protein 1 (MSP1) and apical membrane antigen 1 (AMA1). Previously vaccinated volunteers show boosting of pre‐existing antigen‐specific memory B‐cell (mBC) responses following CHMI. In contrast, unvaccinated malaria‐naive control volunteers developed an mBC response against MSP1 but not AMA1. Serum IgG correlated with the mBC response after booster vaccination but this relationship was less well maintained following CHMI. A significant reduction in peripheral MSP1‐specific mBC was observed at the point of diagnosis of blood‐stage infection. This was coincident with a reduction in peripheral blood B‐cell subsets expressing CXCR3 and elevated serum levels of interferon‐γ and CXCL9, suggesting migration away from the periphery. These CHMI data confirm that mBC and antibody responses can be induced and boosted by blood‐stage parasite exposure, in support of epidemiological studies on low‐level parasite exposure

Role of Indocyanine Green Angiography in Free Flap Surgery: A Comparative Outcome Analysis of a Single-Center Large Series of 877 Consecutive Free Flaps

Purpose This study aims to assess and validate the role and cost-effectiveness of indocyanine green angiography (ICGA) in free flap surgery outcomes. A new intraoperative protocol of whole-body surface warming (WBSW) for all free flap surgeries during the strategic “microbreaks” is also described. Methods A retrospective analysis of 877 consecutive free flaps, performed over 12 years, is presented. The results of the ICGA group (n = 438) were compared with the historical No-ICGA group (n = 439), and statistical significance was calculated for three crucial flap-related adverse outcomes and cost-effectiveness. ICGA was also used as a tool to show the effect of WBSW on free flaps. Results ICGA showed a notably strong statistical significance in decreasing two outcome parameters, namely, partial flap loss and re-exploration rate. It was also cost-effective. ICGA also demonstrated the positive role of WBSW in increasing flap perfusion. Conclusions Our study shows that the usage of ICGA for intraoperative assessment of flap perfusion can significantly reduce the partial flap loss and re-exploration rate in free flap surgeries in a cost-effective manner. A new protocol of WBSW is also described and recommended to increase flap perfusion in all free flap surgeries