Fabrication and characterization of silicon position sensitive particle detectors

Position sensitive particle detectors are needed in high energy physics research. This thesis describes the development of fabrication processes and characterization techniques of silicon microstrip detectors used in the work for searching elementary particles in the European center for nuclear research, CERN. The detectors give an electrical signal along the particles trajectory after a collision in the particle accelerator. The trajectories give information about the nature of the particle in the struggle to reveal the structure of the matter and the universe. Detectors made of semiconductors have a better position resolution than conventional wire chamber detectors. Silicon semiconductor is overwhelmingly used as a detector material because of its cheapness and standard usage in integrated circuit industry. After a short spread sheet analysis of the basic building block of radiation detectors, the pn junction, the operation of a silicon radiation detector is discussed in general. The microstrip detector is then introduced and the detailed structure of a double-sided ac-coupled strip detector revealed. The fabrication aspects of strip detectors are discussedstarting from the process development and general principles ending up to the description of the double-sided ac-coupled strip detector process. Recombination and generation lifetime measurements in radiation detectors are discussed shortly. The results of electrical tests, ie. measuring the leakage currents and bias resistors, are displayed. The beam test setups and the results, the signal to noise ratio and the position accuracy, are then described. It was found out in earlier research that a heavy irradiation changes the properties of radiation detectors dramatically. A scanning electron microscope method was developed to measure the electric potential and field inside irradiated detectorsto see how a high radiation fluence changes them. The method and the most important results are discussed shortly.

Development of advanced silicon radiation detectors for harsh radiation environment

This thesis describes the development of advanced silicon radiation detectors and their characterization by simulations, used in the work for searching elementary particles in the European Organization for Nuclear Research, CERN. Silicon particle detectors will face extremely harsh radiation in the proposed upgrade of the Large Hadron Collider, the future high-energy physics experiment Super-LHC. The increase in the maximal fluence and the beam luminosity up to 1016 neq / cm2 and 1035 cm-2s-1 will require detectors with a dramatic improvement in radiation hardness, when such a fluence will be far beyond the operational limits of the present silicon detectors. The main goals of detector development concentrate on minimizing the radiation degradation. This study contributes mainly to the device engineering technology for developing more radiation hard particle detectors with better characteristics. Also the defect engineering technology is discussed. In the nearest region of the beam in Super-LHC, the only detector choice is 3D detectors, or alternatively replacing other types of detectors every two years. The interest in the 3D silicon detectors is continuously growing because of their many advantages as compared to conventional planar detectors: the devices can be fully depleted at low bias voltages, the speed of the charge collection is high, and the collection distances are about one order of magnitude less than those of planar technology strip and pixel detectors with electrodes limited to the detector surface. Also the 3D detectors exhibit high radiation tolerance, and thus the ability of the silicon detectors to operate after irradiation is increased. Two parameters, full depletion voltage and electric field distribution, is discussed in more detail in this study. The full depletion of the detector is important because the only depleted area in the detector is active for the particle tracking. Similarly, the high electric field in the detector makes the detector volume sensitive, while low-field areas are non-sensitive to particles. This study shows the simulation results of full depletion voltage and the electric field distribution for the various types of 3D detectors. First, the 3D detector with the n-type substrate and partial-penetrating p-type electrodes are researched. A detector of this type has a low electric field on the pixel side and it suffers from type inversion. Next, the substrate is changed to p-type and the detectors having electrodes with one doping type and the dual doping type are examined. The electric field profile in a dual-column 3D Si detector is more uniform than that in the single-type column 3D detector. The dual-column detectors are the best in radiation hardness because of their low depletion voltages and short drift distances.

Effects of vacancy-type defects in silicon based particle detectors

The semiconductor particle detectors used at CERN experiments are exposed to radiation. Under radiation, the formation of lattice defects is unavoidable. The defects affect the depletion voltage and leakage current of the detectors, and hence affect on the signal-to-noise ratio of the detectors. This shortens the operational lifetime of the detectors. For this reason, the understanding of the formation and the effects of radiation induced defects is crucial for the development of radiation hard detectors. In this work, I have studied the effects of radiation induced defects-mostly vacancy related defects-with a simulation package, Silvaco. Thus, this work essentially concerns the effects of radiation induced defects, and native defects, on leakage currents in particle detectors. Impurity donor atom-vacancy complexes have been proved to cause insignificant increase of leakage current compared with the trivacancy and divacancy-oxygen centres. Native defects and divacancies have proven to cause some of the leakage current, which is relatively small compared with trivacancy and divacancy-oxygen.

Simulations of 3D Stripixel Detectors

Large Hadron Collider (LHC) is the main particle accelerator at CERN. LHC is created with main goal to search elementary particles and help science investigate our universe. Radiation in LHC is caused by charged particles circular acceleration, therefore detectors tracing particles in existed severe conditions during the experiments must be radiation tolerant. Moreover, further upgrade of luminosity (up to 1035 cm-2s-1) requires development of particle detector’s structure. This work is dedicated to show the new type 3D stripixel detector with serious structural improvement. The new type of radiation-hard detector has a three-dimensional (3D) array of the p+ and n+ electrodes that penetrate into the detector bulk. The electrons and holes are then collected at oppositely biased electrodes. Proposed 3D stripixel detector demonstrates that full depletion voltage is lower that that for planar detectors. Low depletion voltage is one of the main advantages because only depleted part of the device is active are. Because of small spacing between electrodes, charge collection distances are smaller which results in high speed of the detector’s response. In this work is also briefly discussed dual-column type detectors, meaning consisting both n+ and p+ type columnar electrodes in its structure, and was declared that dual-column detectors show better electric filed distribution then single sided radiation detectors. The dead space or in other words low electric field region in significantly suppressed. Simulations were carried out by using Atlas device simulation software. As a simulation results in this work are represented the electric field distribution under different bias voltages.

3D Stripixel Detectors Simulation

Solid-state silicon detectors have replaced conventional ones in almost all recent high-energy physics experiments. Pixel silicon sensors don't have any alternative in the area near the interaction point because of their high resolution and fast operation speed. However, present detectors hardly withstand high radiation doses. Forthcoming upgrade of the LHC in 2014 requires development of a new generation of pixel detectors which will be able to operate under ten times increased luminosity. A planar fabrication technique has some physical limitations; an improvement of the radiation hardness will reduce sensitivity of a detector. In that case a 3D pixel detector seems to be the most promising device which can overcome these difficulties. The objective of this work was to model a structure of the 3D stripixel detector and to simulate electrical characteristics of the device. Silvaco Atlas software has been used for these purposes. The structures of single and double sided dual column detectors with active edges were described using special command language. Simulations of these detectors have shown that electric field inside an active area has more uniform distribution in comparison to the planar structure. A smaller interelectrode space leads to a stronger field and also decreases the collection time. This makes the new type of detectors more radiation resistant. Other discovered advantages are the lower full depletion voltage and increased charge collection efficiency. So the 3D stripixel detectors have demonstrated improved characteristics and will be a suitable replacement for the planar ones.

Comparison of Local Feature Detectors and Descriptors for Visual Object Categorization

Local features are used in many computer vision tasks including visual object categorization, content-based image retrieval and object recognition to mention a few. Local features are points, blobs or regions in images that are extracted using a local feature detector. To make use of extracted local features the localized interest points are described using a local feature descriptor. A descriptor histogram vector is a compact representation of an image and can be used for searching and matching images in databases. In this thesis the performance of local feature detectors and descriptors is evaluated for object class detection task. Features are extracted from image samples belonging to several object classes. Matching features are then searched using random image pairs of a same class. The goal of this thesis is to find out what are the best detector and descriptor methods for such task in terms of detector repeatability and descriptor matching rate.

Design and characterization of large area position sensitive radiation detectors

Planar, large area, position sensitive silicon detectors are widely utilized in high energy physics research and in medical, computed tomography (CT). This thesis describes author's research work relating to development of such detector components. The key motivation and objective for the research work has been the development of novel, position sensitive detectors improving the performance of the instruments they are intended for. Silicon strip detectors are the key components of barrel-shaped tracking instruments which are typically the innermost structures of high energy physics experimental stations. Particle colliders such as the former LEP collider or present LHC produce particle collisions and the silicon strip detector based trackers locate the trajectories of particles emanating from such collisions. Medical CT has become a regular part of everyday medical care in all developed countries. CT scanning enables x-ray imaging of all parts of the human body with an outstanding structural resolution and contrast. Brain, chest and abdomen slice images with a resolution of 0.5 mm are possible and latest CT machines are able to image whole human heart between heart beats. The two application areas are presented shortly and the radiation detection properties of planar silicon detectors are discussed. Fabrication methods and preamplifier electronics of the planar detectors are presented. Designs of the developed, large area silicon detectors are presented and measurement results of the key operating parameters are discussed. Static and dynamic performance of the developed silicon strip detectors are shown to be very satisfactory for experimental physics applications. Results relating to the developed, novel CT detector chips are found to be very promising for further development and all key performance goals are met.

Readout Electronics for Gas Electron Multiplier Detectors

The European Organization for Nuclear Research (CERN) operates the largest particle collider in the world. This particle collider is called the Large Hadron Collider (LHC) and it will undergo a maintenance break sometime in 2017 or 2018. During the break, the particle detectors, which operate around the particle collider, will be serviced and upgraded. Following the improvement in performance of the particle collider, the requirements for the detector electronics will be more demanding. In particular, the high amount of radiation during the operation of the particle collider sets requirements for the electronics that are uncommon in commercial electronics. Electronics that are built to function in the challenging environment of the collider have been designed at CERN. In order to meet the future challenges of data transmission, a GigaBit Transceiver data transmission module and an E-Link data bus have been developed. The next generation of readout electronics is designed to benefit from these technologies. However, the current readout electronics chips are not compatible with these technologies. As a result, in addition to new Gas Electron Multiplier (GEM) detectors and other technology, a new compatible chip is developed to function within the GEMs for the Compact Muon Solenoid (CMS) project. In this thesis, the objective was to study a data transmission interface that will be located on the readout chip between the E-Link bus and the control logic of the chip. The function of the module is to handle data transmission between the chip and the E-Link. In the study, a model of the interface was implemented with the Verilog hardware description language. This process was simulated by using chip design software by Cadence. State machines and operating principles with alternative possibilities for implementation are introduced in the E-Link interface design procedure. The functionality of the designed logic is demonstrated in simulation results, in which the implemented model is proven to be suitable for its task. Finally, suggestions that should be considered for improving the design have been presented.

Transient current technique simulation of semiconductor detectors

Nowadays advanced simulation technologies of semiconductor devices occupies an important place in microelectronics production process. Simulation helps to understand devices internal processes physics, detect new effects and find directions for optimization. Computer calculation reduces manufacturing costs and time. Modern simulation suits such as Silcaco TCAD allow simulating not only individual semiconductor structures, but also these structures in the circuit. For that purpose TCAD include MixedMode tool. That tool can simulate circuits using compact circuit models including semiconductor structures with their physical models. In this work, MixedMode is used for simulating transient current technique setup, which include detector and supporting electrical circuit. This technique was developed by RD39 collaboration project for investigation radiation detectors radiation hard properties.

Coarse Global Visual Localization of a Mobile Robot

Localization, which is the ability of a mobile robot to estimate its position within its environment, is a key capability for autonomous operation of any mobile robot. This thesis presents a system for indoor coarse and global localization of a mobile robot based on visual information. The system is based on image matching and uses SIFT features as natural landmarks. Features extracted from training images arestored in a database for use in localization later. During localization an image of the scene is captured using the on-board camera of the robot, features are extracted from the image and the best match is searched from the database. Feature matching is done using the k-d tree algorithm. Experimental results showed that localization accuracy increases with the number of training features used in the training database, while, on the other hand, increasing number of features tended to have a negative impact on the computational time. For some parts of the environment the error rate was relatively high due to a strong correlation of features taken from those places across the environment.

Tukkilajittelun röntgenmittauksen hyödyntäminen, tapaus Korkeakosken saha

Diplomityön tavoitteena oli selvittää työn toimeksiantajan UPM, Korkeakosken sahan röntgenmittauslaitteen oksaindeksilajitteluparametrille lukuarvo, jolla päästään A-tukkien osalta tavoiteltuun sydänsahatavaralaatujakaumaan eli saadaan siirrettyä VI- sydänsahatavaralaatu B-tukkien joukkoon. Lisäksi työssä tutkittiin sahan tukkilajittelun röntgenmittauslaitteen mittauksen toimivuutta ja sen tehokkaampaa hyödyntämistä. Korkeakosken sahan käyttämä röntgenmittauslaite on Bintec Oy:n kehittämä ja on tyypiltään Wood-X-4D. Laitteen mittaus perustuu tukin kuvaamiseen viipaleinaeli tomografiamittaukseen. Laite mittaa tukista useita ominaisuuksia ja antaa niiden perusteella lajitteluparametreille lukuarvoja. Lajitteluparametriarvojen muuttaminen vaikuttaa syntyvään sydänsahatavaralaatujakaumaan. Työ suoritettiin röntgenmittauslaitteella tekemällä tukeille toistomittauksia ja lajittelukokeita. Kokeissa käytettävät tukit olivat halkaisijaltaan 230 mm - tukkiluokasta. Tukkeja lajiteltiin eri tukkilaatulajitteluasetuksilla, jolloin seurattiin niistä sahattavia sahatavaralaatuja. Sahatavaralaatujen määrityksessä käytettiin sahaosastolla olevaa Finscan Oy:n kehittämää BoardMaster-NT-lajittelumittalaitetta. Tutkimus osoitti, että oksaindeksin pudottamisella, ei päästy työnantajan asettamaan sydänsahatavaran laatulajittelutavoitteeseen sallituissa oksaindeksirajoissa. Tavoitteen saavuttaminen olisi edellyttänyt oksaindeksin arvon pudottamista selkeästi alle asetetun 28 rajan. Tutkimustulokset osoittivat, että röntgenmittalaitteen lajitteluparametrien toiminnan varmuus vaihteli merkittävästi riippuen käytettävästä parametrista ja että laitteen mittaustarkkuus kärsi laitteen yleiseksi viaksi todetun detektorivian myötä. Täten tarkka laatulajittelu edellyttää röntgenmittalaitteen kaikkia neljää toimivaa detektoria. Tämä pystytään varmistamaanvaradetektorilla.

Moment Operators of Observables in Quantum Mechanics, with Applications to Quantization and Homodyne Detection

The questions studied in this thesis are centered around the moment operators of a quantum observable, the latter being represented by a normalized positive operator measure. The moment operators of an observable are physically relevant, in the sense that these operators give, as averages, the moments of the outcome statistics for the measurement of the observable. The main questions under consideration in this work arise from the fact that, unlike a projection valued observable of the von Neumann formulation, a general positive operator measure cannot be characterized by its first moment operator. The possibility of characterizing certain observables by also involving higher moment operators is investigated and utilized in three different cases: a characterization of projection valued measures among all the observables is given, a quantization scheme for unbounded classical variables using translation covariant phase space operator measures is presented, and, finally, a mathematically rigorous description is obtained for the measurements of rotated quadratures and phase space observables via the high amplitude limit in the balanced homodyne and eight-port homodyne detectors, respectively. In addition, the structure of the covariant phase space operator measures, which is essential for the above quantization, is analyzed in detail in the context of a (not necessarily unimodular) locally compact group as the phase space.

Ydinvoimalaitoksen nuklidijakauma vaikutus kontaminaatiomittauksiin

Tässä diplomityössä kuvataan Loviisan voimalaitoksen vaihtelevien kontaminaation nuklidijakaumien vaikutusta kontaminaatiomittausten tuloksiin. Nuklidikohtaisten tietojen ja kontaminaation nuklidikoostumuksen selvittämiseen käytettiin epäsuoraa kontaminaationmittausmenetelmää. Valvonta-alueen eri huonetiloista kerättiin pyyhintänäytteitä. Näytteet mitattiin kontaminaatiomittareilla sekä gammaspektrometrisesti radiokemian laboratoriossa. Gamma-analyysissä saatiin selville nuklidikohtaiset aktiivisuudet ja suhteelliset nuklidijakaumat. Kirjallisuudesta etsittiin tiedot kunkin kontaminaatiosta löytyneen nuklidin aktiivisuusominaisuuksille. Säteilyn ilmaisimien havaitsemistehokkuuden energiariippuvuus vaikuttaa kunkin nuklidin mittaustulokseen. Nuklidikohtaisten tietojen sekä tunnettujen energiariippuvuuksien perusteella arvioitiin hiukkasten energiajakauman aiheuttaman mittausvirheen osuutta kullekin nuklidijakaumalle. Tässä tutkimuksessa tarkastellaan lisäksi eri kontaminaatiomittausmenetelmien hyviä ja huonoja puolia. Säteilysuojelutyössä käytetyt kontaminaation mittalaitteet on työssä esitelty ja mittaustarkkuuteen vaikuttavia seikkoja on käsitelty operatiivisen säteilysuojelun kannalta.

Päällystettyä hienopaperia valmistavan tuotantolinjan tuotannon tehokkuuden kehittäminen

Diplomityön tavoitteena on selvittää paperivioista aiheutuvien katkojen syyt paperikoneella ja pyrkiä löytämään ratkaisu ongelmiin erilaisia vianilmaisujärjestelmiä apuna käyttäen. Työssä analysoidaan laatuhylyn synty tuotantolinjan eri kohteissa. Lisäksi tilastoidaan häiriöseisokkisyyt ja sitä kautta pyritään painottamaan kunnossa-pidon tärkeyttä tuotantolinjan tehokkuudessa. Kirjallisuusosassa tutustutaan hyötysuhteen määritelmään ja käsitellään tuotantolinjan hyötysuhteeseen vaikuttavia tekijöitä. Kirjallisuusosassa selvitetään päällystetyn hienopaperin tuoteanalyysin avulla ominaisuudet, joilla on vaikutusta ajettavuuteen ja katkoherkkyyteen on-line päällystävällä hienopaperikoneella. Kokeellisessa osassa selvitetään tuotantoaikaa vähentävien tekijöiden syyt ja mahdolli-set aiheuttajat erilaisten vikaprofiilien avulla. Kokeellisessa osassa analysoidaan myös tuotantolinjan hylyn syntyyn vaikuttavat tekijät ja pyritään minimoimaan hylyn määrä. Pohjapaperin täplät aiheuttivat reikäkatkoja ja hylyn syntymistä kalanterin aukaisujen takia. Reunaviat ja kireysheitot aiheuttivat myös runsaasti katkoja. Lukuisat häiriöseisokit aiheuttivat aikahävikkiä. Häiriöseisokkeja aiheuttivat viat mekaanisissa laitteissa, narujen vaihdot ja rullausruuhkat. Telasuojelun aiheuttamat kalanterin aukaisut olivat työn alussa suurin paperin hylkäyssyy. Telasuojelun optimoinnin ja pohjapaperin täplien määrän vähenemisen myötä telasuojeluaukaisut vähenivät. Lajinvaihdot ja katkot olivat suurimmat hylyn aiheuttajat työn loppuaikana.