Nauka i proces industrijalizacije u Srbiji

Predavanje na Inženjerskom forumu 4: Nacionalne tehnološke platforme Srbije. 160 godina industrije i fabrike za budućnost Srbije Beograd, Srpska akademija nauka i umetnosti, 5. decembar 2013

The Influence of Mechanical Deformation on Some Characteristics of Bipolar Semiconductor Devices

Rad je posvećen proučavanju elektronskih karakteristika germanijuma i silicijuma i bipolarnih poluprovodni čkih naprava podvrgnutih elastičnoj mehaničkoj deformaciji. Cilj prve dve glave ovog rada bio je da formuliše opštu teoriju pomoću koje bi se mogli razmatrati fenomeni prenosa naelektrisanja kod poluprovoclnika i problemi injekcije manjinskih nosilaca kod bipolarnih poluprovodničkih naprava, podvrgnutih deformaciji koja je nastala spoljašnjom primenom sile ili je poslediea mehaničkih napona uvedenih u toku tehnoloških procesa njihovog dobijanja. Pri formulaciji ove teorije korišćen je model deformacionog potencijala i Kroemerov dokaz egzistencije kvazielektričnih sila u nehomogenim poluprovodnicima. Tako razvijena teorija primenjena je u trećoj glavi, na proučavanje uticaja nehomogene deformacije na statičke karakteristike bipolarnih poluprovodničkih naprava. Posebna pažnja posvećena je smanjenju pojačanja tranzistora, pod uticajem lokalizovane, spolja primenjene deformacije i deformacije nastale pri difuziji visokih koncentracija primesa u emiteru. Pri razmatranju problema smanjenja pojačanja pod uticajem lokalizovane deformacije, bilo je potrebno da se pored teorije razvijene u prve dve glave razmotri i uticaj efekta „visoke injekcije“ u deformisanoj oblasti. Ovi uslovi nastaju pri dovoljno velikim kompresionim deformacijama, pošto su injektovane struje manjinskih nosilaca, eksponencijalno povezane sa mehaničkim naponima u toj oblasti. Ovde dato razmatranje, pretstavlja proširenje našeg ranije objavljenog rada, s tim što su pored naših eksperimentalnih rezultata za silicijumske tranzistore uključeni i novi eksperimentalni rezultati Sirkina i Feokistove koji pokazuju da se navedena teorija može sasvim dobro primeniti i na germanijumske i na silicijumske tranzistore. Osim tog, ovde je data teorija i eksperimentalni rezultati otkrivenog efekta povećanja probojnog napona kolektor-emiter usled primene lokalizovane deformacije na emiter planarnog tranzistora. Praktičan značaj proučavanja uticaja lokalizovane deformacije na pojačanje tranzistora sa uzemljenim emitorom povezan je sa činjenicom da je ovaj efekat najčešće korišćen pri konstrukciji pretvarača pritiska poznatih pod nazivom „Pitran“, poluprovodničkih mikrofona itd. Proučavanje uticaja mehaničkih napona nastalih u toku tehnoloških procesa izrade bipolarnih poluprovodničkih naprava na njihove karakteristike, inspirisano je ranije eksperimentalno ustanovljenom činjenicom da se pojačanje tranzistora sa uzemljenim emiterom smanjuje pri povećanju koncentracije primesa kojima se dopinguju emiter i baza. Ovaj efekat, kao i efekti anomalne difuzije bora i fosfora i silicijum predstavljaju ograničenje daljeg razvoja visokofrekventnih silicijumskih tranzistora, jer se pri njihovoj fabrikaciji, radi postizanja visokih graničnih frekvencija koriste visoke koncentracije primesa. Mada se razmatranje ovog efekta komplikuje činjenicom da je pri analizi potrebno koristiti nedovoljno razvijenu teoriju p-n spojeva, formiranih od degenerisanih poluprovodnika, i uračunati efekat politropije primesa, mi smo pokazali da se pomoću teorije razvijene u prve dve glave ovog rada, mogu kvalitativno, a u nekim slučajevima i kvantitativno objasniti navedeni efekti. Kraj treće glave posvećen je teoriji anomalnih ili kooperativnih efekata difuzije. Mi smatramo, da je teorija data u prvom delu ovog rada ovde našla jednu od najpotpunijih primen

Signal-to-Noise Ratio in Adsorption-Based Microfluidic Bio/Chemical Sensors

The noise due to stochastic fluctuations of the number of adsorbed analyte particles, caused by random adsorption-desorption (AD) process coupled with analyte convection and diffusion, is inherent to adsorption-based bio/chemical sensors. It posses the fundamental limit for the detection of analyte. In this study we perform an analysis of the signal-to-noise ratio (SNR) of microfluidic sensors, taking into account their AD noise. We have shown that mass transfer significantly influences the possibility to achieve the acceptable SNR value. It also influences the minimal detectable concentration and also the time necessary to reach the SNR value that ensures reliable real-time detection and quantification of the analyte

Analysis of the low-frequency noise spectrum in graphene-based biochemical sensors and its application in analyte recognition and quantification

In this study, we use the theoretical model of low-frequency noise in an adsorption-based sensor to analyze the possibility for the recognition and quantification of the analyte based on the measured fluctuations spectrum. We have developed an analytical expression for the spectral density of the fluctuations of the number of analyte particles adsorbed onto the sensing surface which takes into account the processes of mass transfer through the sensor reaction chamber, adsorption and desorption, and surface diffusion of adsorbed particles [1,2]. The numerical calculations performed using the derived theory are in agreement with the experimental data from the literature obtained for graphene-based gas sensors [3,4]. While analyzing the dependence of specific features in the fluctuation spectra of various parameters, we investigate which type of information about the analyte and its interaction with the graphene surface can be obtained from the experimentally obtained noise spectrum. References:1. Djurić, Z., Jokić, I., Peleš, A., Microel. Eng. 124, 81-85 (2014).2. Djurić, Z., Jokić, I., Peleš, A., “Highly sensitive graphene-based chemical and biological sensors with selectivity achievable through low-frequency noise measurement – Theoretical considerations“, in Proceedings - MIEL 2014, 29th Int. Conference on Microelectronics, IEEE, 2014, pp. 153-156.3. Rumyantsev, S., Liu, G., Shur, M.S., Potyrailo, R.A., and Balandin, A.A., NanoLetters 12, 2294-2295 (2012).4. Rumyantsev, S., Liu, G., Potyrailo, R.A., Balandin, A.A., and Shur, M.S., IEEE Sensors Journal 13, 2818-2822 (2013)

Nanofabrikacija planarnih split ring rezonatora za metamaterijale sa negativnim indeksom prelamanja u infracrvenom opsegu

Experimental nanofabrication of planar structures for one-dimensional metamaterials designed to achieve a negative effective refractive index in the mid-infrared range (5-10 micrometers) was performed. Double split ring and complementary double split ring resonators (SRR and CSRR) with square and circular geometries, were chosen to be fabricated since these are the basic building blocks to achieve a negative effective dielectric permittivity and magnetic permeability. Scanning probe nanolithography with z-scanner movement was used to fabricate straight-line and curvilinear segments with a line width of 80-120 nm. The geometries were delineated in 20 nm thin silver layers sputter-deposited on a positive photoresist substrate spin-coated on polished single crystal silicon wafers, as well as on polycarbonate slabs. The morphology of the structures was characterized by atomic force microscopy. The feature repeatibility was 60-150 nm, depending on the process conditions and the feature complexity. The nanolithographic groove depth in different samples ranged from 4 nm to 80 nm.Vršena je eksperimentalna nanofabrikacija planarnih struktura za jednodimenzionalne metamaterijale projektovane da dostignu negativnu vrednost efektivnog indeksa prelamanja u srednjetalasnom infracrvenom opsegu (5-10 mikrometara). Napravljeni su dvostruki split ring i komplementarni split ring rezonatori (SRR i CSRR) sa kvadratnom i kružnom geometrijom, pošto se oni mogu koristiti kao osnovni gradivni blokovi za dostizanje negativne efektivne dielektrične permitivnosti i magnetske permeabilnosti. Korišćena je nanolitografija skanirajućom sondom u režimu z-pomeraja skanera da bi se napravili pravolinijski i zakrivljeni segmenti sa širinom linije 80 - 120 nm. Geometrija je delineirana u 20 nm debelim slojevima srebra deponovanim spaterovanjem na podlogu od fotorezista nanetu spinerom na polirane pločice monokristala silicijuma, kao i na polikarbonatnim pločicama. Morfologija struktura karakterisana je "atomic force" mikroskopom. Ponovljivost detalja bila je 60-150 nm, zavisno od procesnih uslova i složenosti detalja. Dubina nanolitografskih brazdi menjanja je u opsegu od 4 do 80 nm

Steady-state analysis of stochastic time response of chemical and biological microfluidic sensors

In this paper we first give a short review of two stochastic models describing both the expected value and variance of the random number of adsorbed particles in microfluidic adsorption-based chemical and biological sensors. One model takes into account the influence of coupling of stochastic adsorptiondesorption processes and mass transfer on the change of the number of adsorbed particles, while the other neglects the influence of mass transfer. Subsequently, by using the two models, we perform the analysis of the expected value and variance, as well as the sensor's signal-to-noise ratio, after reaching the steady state of all transient processes. We compare the results obtained by using the different models, and determine conditions for their application. We estimate the influences of the sensing surface area and the concentration of target particles on statistical parameters of sensor response and signal-to-noise ratio, considering the cases where mass transfer is significant, and those where it is not. We particularly analyze the mass transfer influence on the expected value, variance and signal-to-noise ratio. Such analysis does not exist in the available literature. The presented analysis yields new knowledge about the stochastic response of adsorption-based sensors, and it is significant for their optimization in order to achieve reliable analyte detection and improved sensing performance

Analysis of the Fundamental Detection Limit in Microfluidic Chemical and Biological Sensors

Detection limits in microfluidic chemical and biological sensors, which determine the range of analyte concentrations reliably detectable by the sensor, are important sensor parameters. The lower limit of detection, defined as the lowest concentration that can be distinguished from noise, has its minimum determined by the fundamental adsorption-desorption (AD) noise, inevitable in adsorption-based devices. In this work, we analyze this fundamental detection limit, particularly considering the influence of mass transfer processes in microfluidic devices. For that purpose, we derive the expression for the sensor’s signal-to-noise ratio (SNR), which takes into account the AD noise, and then the equation for the minimal analyte concentration at which the SNR has a sufficiently high value for reliable analyte detection. Subsequently, we analyze the mass transfer influence on the sensor’s maximal achievable signal-to-noise ratio and on the fundamental detection limit. The results of the analysis show a significant mass transfer influence on these important sensor performance metrics. They also provide guidelines for achieving the sensor’s best possible detection performance through the optimization of the sensor design and operating conditions

Steady-state analysis of stochastic time response of chemical and biological microfluidic sensors

In this paper we first give a short review of two stochastic models describing both the expected value and variance of the random number of adsorbed particles in microfluidic adsorption-based chemical and biological sensors. One model takes into account the influence of coupling of stochastic adsorptiondesorption processes and mass transfer on the change of the number of adsorbed particles, while the other neglects the influence of mass transfer. Subsequently, by using the two models, we perform the analysis of the expected value and variance, as well as the sensor's signal-to-noise ratio, after reaching the steady state of all transient processes. We compare the results obtained by using the different models, and determine conditions for their application. We estimate the influences of the sensing surface area and the concentration of target particles on statistical parameters of sensor response and signal-to-noise ratio, considering the cases where mass transfer is significant, and those where it is not. We particularly analyze the mass transfer influence on the expected value, variance and signal-to-noise ratio. Such analysis does not exist in the available literature. The presented analysis yields new knowledge about the stochastic response of adsorption-based sensors, and it is significant for their optimization in order to achieve reliable analyte detection and improved sensing performance

Analysis of Stochastic Time Response of Microfluidic Biosensors in the Case of Competitive Adsorption of Two Analytes

A model of stochastic time response of adsorption-based microfluidic biosensors is presented, that considers the competitive adsorption-desorption process coupled with mass transfer of two analytes. By using the model we analyze the expected value of the adsorbed particles number of each analyte, which determine the sensor response kinetics. The comparison with the case when only one analyte exists is used for investigation of the influence of competitive adsorption on the sensor response. The response kinetics analyzed by using the stochastic model is compared with the kinetics predicted by the deterministic response model. The results are useful for optimization of micro/nanosensors intended for detection of substances in ultra-low concentrations in complex samples

Intrinsic noise equivalent concentration of dynamic mode microcantilever biosensors

The presented theory enables systematic investigation of the dependence of the minimal detectable concentration of the target analyte, determined by the cantilever intrinsic noise, on various parameters. Inclusion of the influence of effects such as the mass transfer in noise considerations results in a more accurate noise model, which is necessary when methods based on noise measurements are developed.Poster presented at the 38th International Conference on Micro and Nano Engineering MNE, 16-20 September 2012, Toulouse, Franc