PbS colloidal quantum dots based photodetectors for integrated SWIR detection

Due to the low water absorption and nightglow, sensing in short wave infrared (SWIR) is very attractive in applications such as; passive night vision, biomedical imaging and remote sensing. The monolithic integration of photodetectors to the readout circuits is desirable in many applications to increase density of detectors and reduce costs, system size and power consumption. Solution-processed semiconductors are a promising alternative to conventional bulk crystalline photodetectors since their production is low cost and easy, their bandgap can be tuned depending on their sizes, and they can be easily integrated on any substrate. In this work, PbS colloidal quantum dot based photodiodes are realized that are compatible with the integration on Read Out Integrated Circuits (ROIC). Various kinds of PbS quantum dots based schottky diodes are designed on glass and silicon substrates. Spin deposition steps and solid state ligand exchange processes are optimized to create pinhole free and high mobility PbS quantum dot layers. In addition to that Integrated Circuit (IC) compatible versions of PbS colloidal quantum dot (CQD) photodiodes are realized. ROIC chip surface is mimicked on Si substrates and fabrication steps are optimized for integration. Special importance is given to optimize highly conductive and transparent indium tin oxide layer using DC magnetron sputtering. Sensitivities of 1.4x1012 Jones, comparable to the conventionally used crystalline, bulk photodetectors is achieved. Also, plasmonic scattering effects of metal nanoparticles in PbS CQD layer are studied. Absorption and responsivity enhancement of 6 fold is presented using gold nanoparticles in PbS CQD based photoconductors

Realization of micromachined-electromechanical devices for wireless communication applications

As the communication technology evolves day by day, the demands for low cost, low power, multifunctional and higher-speed data communication circuits are increasing enormously. All these essential requirements enforce significant challenges on the current technology and illustrate the need for new designs and advanced architectures. The challenges of reconfigurability, spectrum efficiency, security, miniaturization and cost minimization can only be met by ensuring that the transceiver/receiver is comprised of low-energy, low-cost, adaptive and high performance RF devices. With the potential to enable wide operational bandwidths, eliminate off-chip passive components, make interconnect losses negligible, and produce almost ideal switches and resonators in the context of a planar fabrication process compatible with existing IC processes, micromachining and Micro-Electro-Mechanical Systems (MEMS) has emerged to overcome the aforementioned problems of communication circuits. Up to date RF MEMS technology prove that on-chip switches with zero standby power consumption, low switching power and low actuation voltage; high quality inductors, capacitors and varactors; highly stable (quartz-like) oscillators and high performance filters operating in the tens of MHz to several GHz frequency range can be realized. The availability of such RF and microwave components will provide designers with the elements they have long hoped for to create novel and simple, but powerful, reconfigurable systems. In this thesis, realization of RF MEMS components such as capacitive switches, parallel plate variable capacitors, micromachined inductors and resonators for wireless communication applications are presented. The design and fabrication of each component are given in detail. The performance improvement of some blocks by integrating RF MEMS devices is demonstrated. Also the fabrication process problems limiting the performance parameters of RF MEMS components are addressed

A novel single-chip RF-voltage-controlled oscillator for bio-sensing applications

A novel interdigiated capacitance (IDC) based affinity biosensor system is presented that detects C-Reactive Protein (CRP), a risk marker for cardiovascular diseases, and transmit the information to a distance location wirelessly. The biosensor system consist of a voltage controlled oscillator (VCO) and an IDC. In the presence of CRP the capacitance of the IDC changes and this directly reflects to the oscillation frequency of the VCO. In the presence of 800 ng/ml antigen the frequency of the system shifts from 1.9438 GHz to 1.94175 GHz and with 64 ug/ml frequency shifts from 1.95975 GHz to 1.94875 GHz with -120 dBc/Hz phase noise

Realisation of radio frequency microelectromechanical devices for multiband, tunable circuit applications

In this work a microelectromechanical-based parallel plate variable capacitor, a micromachined-inductor and an LC resonator that is formed by combining these two are presented. The parallel plate variable capacitor has curvature due to compressive stress and this allows the theoretical 50% tuning range to be exceeded. By changing the tuning voltage from 0 to 55 V, the varactor can achieve capacitance values from 90 to 260 fF. Additionally, inductors are designed and fabricated using the same process steps. Inductance values of 1.5 to 2 nH and quality factors from 5 to 10 are achieved. An inductor and variable capacitor are combined to form an LC resonator whose centre frequency changes from 8.194 to 6.192 GHz with applied voltages from 0 to 30 V

On the development of students’ attitudes towards corruption and cheating in Russian universities

Based on empirical data from selected public universities in Khabarovsk, Russia, this paper compares first and fifth year students regarding their attitudes towards corruption in general and university corruption in particular. Even after making both groups of students comparable with respect to a range of socio-economic characteristics by a matching approach, the results suggest that fifth year students are more open to a range of informal and corrupt practices than first years. Our analysis therefore points to the possibility that the Russian higher education system might ‘favor’ compliance with corruption and informal practices, with potentially detrimental consequences for the Russian society as a whole

Solution based Al/PbS and Ti-Au/PbS Schottky photodiodes for SWIR detection

In this work, PbS colloidal quantum dot based photodiodes are realized that is compatible for integration to read out electronics. Schottky photodiode topology is selected to implement PbS quantum dots as photodetector because of its fast response and moderate sensitivity. The device is formed from Indium tin oxide (ITO) anode, the photosensitive PbS layer and a schottky contact formed of both aluminum or titanium and gold stack. Ligand exchange processes optimized in order to replace long capping ligands of PbS QDs with shorter ones. Layer by layer deposition method is applied to form pinhole free PbS CQD films. For Al/PbS samples rectification ratios greater than 100 is achieved for +/- 2 V bias voltages. At 2V reverse bias and under 5mW/cm(2) illumination, 0.195 A/W responsivity and 8.19 x 10(10) Jones normalized detectivity is achieved. For Ti-Au/PbS samples, rectification ratio greater than 250 is achieved for +/- 2 V bias voltages. At 3V reverse bias, 0.667 A/W responsivity, 53.3 % quantum efficiency and 2,12 x 10(10) Jones normalized detectivity is achieved

UWB uygulamasına özgü SiGe BiCMOS karıştırıcı tasarımı=design and implementation of SiGe-BiCMOS mixer for UWB applications

Özet: Bu makalede, AMS 0.35 ´m SiGe BiCMOS teknolojisi kullanılarak, doğrudan çevirmeli UWB uygulamalarına uygun alıcı yapıları için tasarlanmış 5GHz frekans bandında çalışan tümleşik devre karıştırıcı tasarımı, anlatılmaktadır. Karıştırıcı tasarımı için uygun teknolojinin belirlenmesi ilk adım olarak seçilmiş ve çalışma frekansı olan 5 GHz frekansı için, düşük gürültü seviyesine ve ucuz maliyete sahip SiGe teknolojisi tercih edilmiştir. Devre tasarımı yüksek kazanç, düşük gürültü ve düşük güç tüketimi belirtimleri dikkate alınarak gerçekleştirilmiştir. Devrenin tüm simülasyonları, Cadence® SpectreRF simülatörü kullanılarak gerçeklenmiştir. Devre, 5GHz frekans bandında, 11 dB kazanç ve 5 dB gürültü sayısına sahiptir. 1 dB bastırma noktası -14 dBm olan devrenin, giriş üçüncü derece kesişim noktası (IIP3) -8.9 dB giriş gücü seviyesindedir. Devre, 2.5 V besleme gerilimi altında, 15 mW güç harcamaktadır.{|}This paper presents the design of UWB SiGe BiCMOS mixer block for direct-conversion type transceiver architectures which optimized for WLAN applications in the frequency range of 5 GHz using AMS 0.35 ´m SiGe BiCMOS technology. High gain, low noise figure (NF) and low power dissipation are the main considerations for optimizations. The simulations are performed using Cadence® SpectreRF environment. The simulation results shows, 11 dB gain, 5 dB NF and - 14 dBm 1-dB compression point. The circuit consumes only 15 mW under 2.5 V supply voltage

Responsivity improvement in PbS colloidal quantum dot photoconductors using colloidal gold nanoparticles

A study is presented on improving the absorption of the PbS colloidal quantum dot (CQD) films using plasmonic scattering. Unlike previous methods that include high temperature annealing, an integrated circuits (IC) compatible method of introducing colloidal gold nanoparticles to PbS film during the spin deposition process is developed. The devices are composed of eight layers of PbS and gold nanoparticles are spin cast after the fourth layer that places them in the middle, sandwiched between PbS films in order to avoid electrical shorts between the fingers. Two different solutions of gold nanoparticles in citrate, 0.1% and 0.01%, are used to fabricate two different devices. Introducing 0.01% Au nanoparticles in PbS film increases the responsivity 2.6-fold, whereas introducing 0.1% Au nanoparticles results in a 6.5-fold increase in responsivity