TCAD analysis of wide-spectrum waveguide in high-voltage SOI CMOS

A TCAD based analysis is presented on the transmission efficiency η of silicon-on-insulator (SOI) and silicon nitride slab waveguides in a high-voltage standard SOI-CMOS technology, for the spectral range of 480 nm - 1300 nm, and isotropic optical excitation via monolithic Si-based LEDs. The effects of geometry, wavelength and galvanic isolation on η are reported

CO-INFECTION OF BRUCELLA AND DENGUE VIRUS

Objective: Brucellosis is an important zoonotic infection having a worldwide distribution. In South East Asian developing countries like India, brucellosis is yet well-known but often neglected disease. Although dengue fever has a global distribution, South East Asian region together with the Western Pacific region represents 75% of the current global disease burden. Frequent dengue fever outbreaks have been encountered in different parts of India. Both brucellosis and dengue fever may present with many nonspecific symptoms. This study was designed to identify the trend of their co-infection.Methods: The study was carried out from February 2015 to July 2016 in Eastern India. Blood samples collected from clinically suspected dengue fever cases were confirmed serologically by dengue specific NS1, IgM, and IgG capture ELISA methods. The confirmed dengue samples were further subjected to Brucella specific serological and molecular investigations.Results: Out of 37 serologically confirmed dengue cases, 8 (21.6%) showed co-infection of brucellosis and dengue fever. Female predominance was observed among the co-infection cases. Most of these cases belonged to the age group 21-40 years and resided in and around Kolkata.Conclusion: This study portrays the simultaneous acquisition of these two pathogens in a few patients. Co-infection of these two pathogens, while feasible, has not been accounted previously in this part of India. Thus, this report highlights the significance of studying the possibility of occurrence of dual infection of these two diseases and its outcome in patients with febrile illness thereby providing future scope of preventing case fatalitiesKeywords: Brucellosis, Dengue, Co-infection, ELISA, Polymerase chain reaction

COMPARISON OF SEROLOGICAL TESTS AND PCR FOR DIAGNOSIS OF HUMAN BRUCELLOSIS SUFFERING FROM FEVER

Objective: Brucellosis is an important zoonotic disease throughout the globe and other developing countries. The present study was aimed to compare results of different serological tests and PCR for diagnosis of brucellosis in patients sufferings from fever in Kolkata and in adjoining districts.Methods: A total of 2088 serum samples were collected from the patients suffering from fever from January, 2013 to September, 2015. The samples were tested by serological tests STAT, RBPT, ELISA(IgM,IgG) and Brucella genus specific PCR. Results: The study revealed decreasing positive results by STAT (18.43%, N=385), RBPT (12.59%, N=263), IgM ELISA (7.71%, N=161), PCR (4.21%, N=88) and IgG ELISA (1.43%, N=30). When serological tests were compared with PCR, it was found that both STAT and PCR were positive in 84 samples( 4.02%), both RBPT and PCR were positive in 65 samples(3.11%), both IgM and PCR were positive in 51 samples(2.44%) and both IgG and PCR were positive in 9 samples(0.43%). Conclusion: In this cross sectional study in a zonal population of India it was found that STAT was the most sensitive test for diagnosis of brucellosis followed by RBPT when compared to PCR test results. Four STAT negative samples showed positive results in PCR, which were positive by RBPT test. This indicates that if we combine STAT and RBPT for diagnosis of brucellosis then both sensitivity and specificity of the combined test will increase.Â

BRUCELLAR UVEITIS IN EASTERN INDIA

Objective: Brucellosis- one of the major zoonotic diseases, still remains an uncontrolled problem, in regions of high endemicity. Ophthalmic brucellosis is not studied and overlooked in most developing countries.  Considering the severe outcome of undiagnosed ophthalmic brucellosis, in this paper we made attempts to find out whether this disease still remains a health problem in a South East Asian developing country, where study of this disease is largely neglected.  Methods This study was carried out over a one year period from January 2015 to December 2015. Blood samples were collected from clinically confirmed cases of uveitis and they were subjected to five serological and one genus specific molecular investigations, for the detection of Brucella infection.Results Out of 20 uveitis cases, 4 (20%) cases confirmed as brucellar uveitis, by serological tests followed by PCR confirmation. After treatment of brucellosis all the four patients were recovered uneventfully.Conclusion: Brucella infection involving the eye is still a significant problem in South East Asian countries; hence in all uveitis cases in this reason brucellosis should be excluded by available laboratory tests.Government of India (Dept. of Biotechnology the major zoonotic diseases, still remains an uncontrolled problem, in regions of high endemicity. Ophthalmic brucellosis is not studied and overlooked in most developing countries.  Considering the severe outcome of undiagnosed ophthalmic brucellosis, in this paper we made attempts to find out whether this disease still remains a health problem in a South East Asian developing country, where study of this disease is largely neglected.   Methods This study was carried out over a one year period from January 2015 to December 2015. Blood samples were collected from clinically confirmed cases of uveitis and they were subjected to five serological and one genus specific molecular investigations, for the detection of Brucella infection.Results Out of 20 uveitis cases, 4 (20%) cases confirmed as brucellar uveitis, by serological tests followed by PCR confirmation. After treatment of brucellosis all the four patients were recovered uneventfully.Conclusion: Brucella infection involving the eye is still a significant problem in South East Asian countries; hence in all uveitis cases in this reason brucellosis should be excluded by available laboratory tests

Avalanche-mode silicon LEDs for monolithic optical coupling in CMOS technology

Complementary Metal-Oxide-Semiconductor (CMOS) integrated circuit (IC) technology is the most commercially successful platform in modern electronic and control systems. So called "smart power" technologies such as Bipolar CMOS DMOS (BCD), combine the computational power of CMOS with high voltage transistors (~20-100 V) to enable the monolithic integration of advanced smart power applications used in e.g. automotive (car) applications, digital audio amplifiers, and integrated analog-digital systems. Many of such systems require data communication or signal transfer with galvanic isolation, for safety and interference reasons or to interface between low voltage digital parts and high voltage (power) components on an IC. Optocouplers transfer signals optically across a galvanically isolated channel. They can be operated for a wide range of data rates (including DC), and are less prone to external electromagnetic interference. Monolithic integration of such optocouplers in CMOS ICs require research and development of suitable light emitters and light detectors for an energy efficient, high speed, and cost effective operation of the system. This PhD thesis covers two broad aspects. Firstly, it deals with the physics, design, and analysis of efficient light emitting diodes (LEDs) in silicon CMOS technology. Silicon LEDs conventionally emit infrared light (~1100 nm), which is not compatible with the spectral detection efficiency of silicon photo-detectors. This is because silicon can efficiently detect light having wavelengths of less than ~1000 nm. Therefore the focus is on a specific design solution to this problem, where the LED is biased in "avalanche breakdown". In this situation, there exists a high electric field in the device, which is responsible for light being emitted at shorter wavelengths (400 nm-900 nm). Such an emission, if properly guided laterally across the CMOS IC, would be detected by a silicon photodiode with a relatively high quantum efficiency. Wide-spectrum Si LEDs are promising for the integration of opto-electronics in CMOS. Secondly, this thesis analyzes the feasibility of realizing a monolithic optical link using silicon LEDs in a BCD silicon-on-insulator (SOI) CMOS technology, from a device physics viewpoint. The optical coupling is treated as a conversion process from electrons to photons (in the LED) and back again to electrons (in the detector). Analysis is done from the viewpoint of coupling efficiency, where also the effect of heating across such a link due to high power dissipation in the avalanche-mode LED has been considered. Optical propagation via built-in waveguides in SOI technologies is also studied using Finite difference time-domain simulations. The analysis of this link is aimed at integrating avalanche-mode LEDs, which have the potential to be driven at high speeds (~ GHz), with single-photon sensitive optical detectors (e.g. using SPADs)

Optical absorption sensing with dual-spectrum silicon LEDs in SOI-CMOS technology

Silicon p-n junction diodes emit low-intensity, broad-spectrum light near 1120 nm in forward bias and between 400-900 nm in reverse bias (avalanche). For the first time, we experimentally achieve optical absorption sensing of pigment in solution with silicon micro LEDs designed in a standard silicon-on-insulator CMOS technology. By driving a single LED in both forward and avalanche modes of operation, we steer its electroluminescent spectrum between visible and near-infrared (NIR). We then characterize the vertical optical transmission of both visible and NIR light from the LED through the same micro-droplet specimen to a vertically mounted discrete silicon photodiode. The effective absorption coefficient of carmine solution in glycerol at varying concentrations were extracted from the color ratio in optical coupling. By computing the LED-specific molar absorption coefficient of carmine, we estimate the concentration (0.040 mo/L) and validate the same with a commercial spectrophotometer (0.030 mol/L ). With a maximum observed sensitivity of 1260 /cm /mol L, the sensor is a significant step forward towards low-cost CMOS-integrated optical sensors with silicon LED as the light source intended for biochemical analyses in food sector and plant/human health.Comment: IEEE Sensors 2020, 4 pages, 5 figures (https://ieeexplore.ieee.org/document/9278700

Minority Carrier Injection in High-Barrier Si-Schottky Diodes

In this paper, we investigate the presence of minority carriers and their role in charge carrier transport in silicon (Si) Schottky diodes with a high potential barrier. Using TCAD simulations along with an analytical model, we show that an inversion charge is induced at the metal-semiconductor (MS) interface in a high-barrier Schottky diode which imparts bipolar-type current characteristics to otherwise a unipolar Schottky diode, even at low-injection operation. In such a high-barrier diode, minority diffusion also becomes important along with the majority carrier thermionic emission and therefore cannot be neglected, unlike in a conventional Schottky diode. The presence of minority carriers at low injection in a high-barrier Si Schottky diode has been experimentally verified via a prior-reported two-diode electrical test method, reverse recovery measurements, and by measuring infrared electroluminescence. It is also shown, via TCAD simulations, that the diffusion component becomes more pronounced in case of a reduced Gummel number and at elevated temperatures.</p

Figures of merit of avalanche-mode silicon LEDS

The silicon avalanche-mode light-emitting diode (AMLED) opens a route for on-chip opto-electronic applications in standard CMOS, both due to its relatively broad spectral overlap with the spectral responsivity of silicon photodiodes and due to its high speed capability. This work presents closed form models for the key figures of merit (FOMs) of AMLEDs, namely, current (or power) density, cut-off frequency, radiative efficiency, and specifically for optical data communication energy cost per photon. Their derivations are based on one-dimensional analyses of an abrupt single-sided (p+n or n+p) junction and of a p-i-n diode. TCAD simulations for optimized device structures, including the recently reported superjunction (SJ) LED, were performed to validate the model. Measurements on single-sided abrupt junctions and SJ diodes are shown to validate some of the modelled trends. The results show that a p-i-n or an SJ diode is favorable to a conventional single-sided junction diode for the AMLED design. In addition, as confirmed for conventional AMLEDs by earlier reports, the results indicate that for a yet higher efficiency the carrier supply should be increased. For this a combination of a separate minority carrier injector and SJLED is proposed, referred to as the injection-avalanche CMOS SJLED. However, more experimental optical data (e.g., absolute photon flux) are needed for a more accurate model validation