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It is well known that earthquakes cause hydrological changes, such as drying or flooding of water wells, fluctuations in ground-water levels in wells, changes in water quality, and formation of new springs. Significant drops in ground-water levels in wells were recorded during recent earthquakes in NW Turkey on August 17, 1999 in İzmit and on November 12, 1999 in Düzce. The İzmit earthquake (Ms 7.4) caused pre-seismic water-level changes in wells at Eskişehir, located 118-216 km away from the epicentre. Well-level changes in the Eskişehir, Sakarya, Bursa, Yalova, Yenişehir and İnegöl basins were recorded prior to and after the Düzce earthquake (Ms 7.2) as well. These changes are due to strain on the southern Marmara segments of the Thrace-Eskişehir Fault Zone (TEFZ), which is affected by deformation of the North Anatolian Fault Zone (NAFZ). Ground-water-level changes in wells prior to and after the earthquake away from the epicentre and the position of Eastern Marmara-Eskişehir region indicate a possible connection between well-level changes that respond to compressive and tensile stresses and shear strain away from active strike-slip faults. The wells, located in basins having an angular connection with the earthquake-producing main faults, completely activate only during major earthquakes. The wells showing anomalies prior to earthquakes are generally found near epicentres or in basins having an angular connection as stated above. The data collected after the 1999 anomalies up to September 2004 indicate that the 1999 anomalies are unique to that year. It was not difficult to separate the seasonal fluctuations of the water levels from the earthquake anomalies. In this context, it is concluded that the 1999 water level anomalies prior to the earthquake were the fast- and short-period signature of slow but long-term deformations that occurred over a large area.

In this study, we deal with the design and implementation of microsystems for electron spin resonance (ESR) applications. Three different microsystems are designed with different approaches for microwave magnetic field generation, ESR detection and sample handling. To the best of our knowledge, these microsystems are the first ever realized fully integrated solutions providing X-band ESR spectroscopy functionality on a single silicon chip. The first microsystem implements absorption mode ESR detection by means of a differential approach. It consists of two pairs of planar excitation/detection coils, a voltage controlled oscillator (VCO), a low noise amplifier (LNA) and a mixer. The excitation/detection coil pairs are identical. The excitation coil has a diameter of 300 microns, and it also functions as the LC-tank inductor of the VCO. The detection coil, which is placed in the middle of the excitation coil, has a diameter of 100 microns. The ESR sample is placed over one of the detection coils. This coil functions as the sample coil, while the empty coil functions as the reference coil. The excitation coils generate the microwave magnetic field acting on the detection coils. In the presence of ESR, the induced voltage on the sample coil differs from the induced voltage on the reference coil. This difference is amplified by the LNA and down-converted by the mixer. Two such microsystems with operating frequencies at 6 and 8 GHz are prototyped on a single standard CMOS chip with an area of 8.6 mm2. The ESR spin sensitivities achieved with the 6 and 8 GHz microsystems are 6.7×1010 and 3.9×1010 spins/GHz1/2, respectively. The second microsystem is an improved version of the first microsystem, with a slightly different topology. Furthermore, LNAs are implemented with SiGe bipolar transistors for higher gain with lower noise figure. It is also prototyped on a single silicon chip with an area of 4 mm2. The ESR spin sensitivity achieved with this microsystem is 3×1010 spins/GHz1/2. The third microsystem implements dispersion mode ESR detection by means of a differential approach in frequency domain. It consists of two VCOs, a mixer, a high frequency buffer, and a frequency divider. The VCO LC-tank inductor has a diameter of 100 microns, and it functions both as the excitation and detection coil. The two coils are placed perpendicularly in order to prevent injection locking. The VCO outputs are multiplied by the mixer, and a difference frequency output is generated. This output is amplified by the high frequency buffer. Its frequency is then divided by the frequency divider, and a 1-bit digital frequency output is generated. In the presence of ESR, the center frequencies of one of the VCOs changes slightly. This change is observed at the output in the form of frequency. This microsystem is prototyped on a standard CMOS chip with an area of 1 mm2. The ESR spin sensitivity achieved with this microsystem is 2×1010 spins/GHz1/2. The realized microsystems already have performances comparable to commercial systems. Their performances can further be improved; and they may be used in different micro scale applications of ESR spectroscopy and imaging.

oz Gao.51Ino.49P/I1tGa1-sAs/GaAs MODÜLE KATKILI ALAN ETKİLİ TRANSİSTORLERİN FABRİKASYONU VE KARAKTERİZASYONU Yalçın, Tolga Yüksek lisans, Elektrik ve Elektronik Mühendisliği Bölümü Tez Yöneticisi: Doç. Dr. Gengiz Beşikçi Nisan 2000, 64 sayfa ALGaj-jAs/InGaj-yAs/GaAs malzeme sistemine alternatif olarak Gao51In049P/ Inx^Ga1-xAs/GaAs malzeme sisteminin MODFET uygulamaları için fizibilitesi Ga0,51In0,49p.^P/Inx^Ga1-x^As/GaAs direçlerin ve Ga0.51In 0.49P/In 0.15Ga O.85As/ GaAs MODFETlerin I-V karakterizasyonu yoluyla incelendi. Heteroyapılar Gaz Kaynaklı Işın Epitaksisi tekniği ile büyütüldü. Elde edilen sonuçlar Ga 0.51^Ino.49^P katmanında DX merkezi benzeri özellikler gösteren doğal bir tuzak olduğunu ve bu tuzağın tavlanmış örneklerde daha etkili hale geldiğini gösterdi. Ga0.51^InO.49^P/ In0.15Gao.85As/GaAs MODFETlerde görülen süreğen fotoiletkenliğe (PPC) ve eşik voltajındaki kaymalara bu tuzağın sebebiyet verdiği düşünülmektedir. Gao.51Ino.49^P/Inx^Ga1-x^^As/GaAs sistemi oldukça yüksek iki boyutlu elektron gazı yoğunluğu ve MODFET transkondüktansı (7um kapı uzunluğu için 229 mS/mm) ¦sec ıfe§M(§ĞRirrfei wwutvermesine rağmen, Ga^In^P malzemesinde aygıt üretimi sırasında oluşan bozulmalar önemli bir sorun teşkil edebilmektedir. Bununla birlikte, A^Gaj-^As/IriyGaj-yAs/ GaAs malzeme sistemiyle karşılaştırıldığında, Ga05îlıa0A9P/ Ir^Ga^j^As/GaAs malzeme sisteminin büyütülmesi ve MöDFET uygulamalarında kullanılması üzerine sınırlı sayıda çalışma yapılmıştır. Bu çalışmada elde edilen sonuçlar bu malzeme sisteminin şu anda gördüğünden daha fazla ilgiyi hak ettiğini göstermektedir. Anahtar Kelimeler: MODFET, HEMT, TEGFET, DX CENTER, PPC, ALGAAS/GAAS, GAINP/INGAAS/GAAS. vı ABSTRACT FABRICATION AND CHARACTERIZATION OF Ga0,51In0,49P/InxGa1-xAs/GaAs MODULATION DOPED FIELD EFFECT TRANSISTORS Yalçın, Tolga M.S., The Department of Electrical and Electronics Engineering Supervisor: Assoc. Prof. Dr. Cengiz Beşikçi April 2000, 64 pages The feasibility of the Ga051In049P/InxGa1_xAs/GaAs material system for MODFET applications as an alternative to A1x^Ga1-x As/InxGa1-xAs/GaAs system is investigated through I-V characterization of Ga0,51In0,49P/InxGa1-xAs/GaAs lateral resistors and Ga0,51In0,49P/InxGa1_xAs/GaAs MODFETs. The heterostructures have been grown by Gas Source Molecular Beam Epitaxy technique. The results show that a native trap with DX center like properties is present in Ga0.51In0.49P and effects of this trap become more apparent when the material is annealed. This trap seems to be responsible for the persistent photoconductivity (PPC) and threshold shift observed in the fabricated Ga0.51In0.49P/In0.15Ga0.85As/GaAs MODFETs. While theGa051In system yields reasonablly high two dimensional electron gas concentration and substantially large MODFET transconductance (229 mS/mm for 7jim gate length), degradation of Ga0.51In0.49P at temperatures typically used during fabrication seems to be an important problem. However, when compared with the AlxGa1-xAs/InxGa1-xAs/GaAs material system, limited amount of work has been done on the growth and use of G%51In049P/In015Ga085As/GaAs material system for MODFET applications. The results of this work show that this material system deserves more attention then it is currently receiving. Keywords: MODFET, HEMT, TEGFET, DX CENTER, PPC, ALGAAS/GAAS, GAINP/INGAAS/GAAS. IV 64

oz YÜKSEK PERFORMANSLI BİR VLSI STANDART HÜCRE KÜTÜPHANESİ VE BİR DTMF GÖNDERİCİ YONGASININ GERÇEKLEŞTİRİLMESİ YALÇIN, Tolga Yüksek Lisans Tezi, Elektrik ve Elektronik Mühendisliği Anabilim Dalı Tez Yöneticisi: Prof. Dr. Murat AŞKAR Temmuz, 1994, 95 sayfa. Yüksek performanslı bir CMOS VLSI standart hücre kütüphanesi geliştirildi ve bir DTMF gönderici yongası tasarlanıp gerçekleştirildi. Hücre kütüphanesi, 1.2 /zm çift-polisilikon/çift-metal SCMOS MOSIS süreci için geliştirildi. Bu kütüphanede toplam olarak 58 tane hücre vardır. Bu hücrelerden sekiz tanesi ardışıl hücre, beş tanesi de dolgu hücresidir. Geri kalan bütün hücreler ise katışımsal mantık hücreleridir. DTMF gönderici yongası ise tama men sayısal bir yonga olup, mikroişlemciler tarafından kontrolü için gerekli olan bütün kontrol işaretlere sahiptir. Yonga, sayısal doğrusal-PCM çıktısı ürettiği için, hem doğrudan PCM hatlarına bağlanabilir, hem de ticari amaçlı sayısal- analog çeviricilerle kullanılabilir. Tasarımın fiziksel serimi bu tezde geliştirilen hücre kütüphanesi ve Mietec hücre kütüphanesi kullanılarak iki farklı yonga üzerinde gerçekleştirildi. Her iki gerçekleştirim birbiriyle karşılaştırıldı. Daha sonra prototip için, yonga IMEC'de üretildi. Üretilen yonga tam işlerlik ve per formans testlerinden geçirildi. Test sonuçlarında üretilen yonganın birçok ticari amaçlı yongadan daha yüksek performansa sahip olduğu gözlendi. Anahtar Sözcükler: CMOS, VLSI, Standart Hücre Kütüphanesi, İletişim Devreleri, Çeviriciler, DTMF. Bilim Dalı Sayısal Kodu: 609.01.01, 609.01.02 iv ABSTRACT A HIGH PERFORMANCE VLSI STANDARD CELL LIBRARY AND IMPLEMENTATION OF A DTMF SENDER CHIP YALÇIN, Tolga M. S. in Electrical and Electronics Engineering Supervisor: Prof. Dr. Murat AŞKAR July, 1994, 95 pages. A high performance Standard CMOS VLSI library is developed and a DTMF sender chip is designed and implemented. The standard cell library is developed using the 1.2 fim double-poly/double-metal SCMOS MOSIS process. It consists of 58 different cells. Eight of these cells are sequential cells, and five of them are pad cells. The rest of the cells are all combinational logic cells. The DTMF sender chip is a fully digital chip, and posses all the control sig nals required for microprocessor control. The chip produces digital linear-PCM outputs and can be either connected to PCM lines directly or operated with any commercial digital-to-analog converters. Physical layout of the design is created on two different chips using the library developed in this thesis, and the Mietec's Standard Cell Library. Both implementations are compared. Then for prototyping, the chip has been manufactured at IMEC. The manufactured chip is tested for full functionality, and performance. It has been observed that the manufactured chip has higher performance than most commercial chips. Keywords: CMOS, VLSI, Standard Cell Library, Telecommunication Circuits, Dialers, DTMF. Science Code: 609.01.01, 609.01.02 111 95