The charge storage in the a-Si:H PIN photodiode under different light wavelength illuminations has been studied. The leakage current-voltage and capacitance-voltage curves under three fundamental visible light wavelengths, i.e., red, green and blue light were measured. The apparent charge storage density in the negative voltage range was quantified from the capacitance-voltage curve; charges in the positive voltage range were estimated from the leakage current-voltage curve. The measurement was verified with a pre-fabricated circuit which is a charge storage readout device. The diode under the long wavelength light illumination condition stored more charges than that under the short wavelength light illumination condition because the former could penetrate the intrinsic a-Si:H layer deeper than the latter could. The leakage current and charge storage capacity of the diode are determined by the generation of electron-hole pairs and the depletion of charges in the intrinsic layer as well as the supply of charges from the electrodes. A comparison of charge storage capacities of diodes with different intrinsic layer thicknesses is also presented. The number of photogenerated carriers increases with the thickness of the i-layer due to the long penetration depth, but the junction capacitance decreases which results in the decrease of the charge storage capacity. The tradeoff between the photogenerated carriers and the capacitance, combined with thickness-dependent recombination mechanisms increases the complexity of the PIN diode charge storage capacity. The n+- and p+-contact region should be heavily doped so that the storage charge can be confined in the i-layer without diffusing and recombining in the contact region. The n+ and p+ films, prepared by plasma enhanced chemical vapor deposition (PECVD) of a wide range of doping concentration, were fabricated to achieve low bulk resistivity and ohmic contacts with the metal electrodes. Charge storage density was improved after the optimization doped layers in both positive gate voltage and negative gate voltage. The low resistivity contact layers, reduced density of state in the intrinsic layer, and graded p+/i layer account for the enhancement of the charge storage density in the optimized diode.

RF magnetron sputtering has been employed to deposit n-type epitaxial zinc oxide thin films on p-type silicon substrates to form p-n diode structures. Commonly found on silicon, native SiOx layers, typically of a few nanometer thick, would hinder the epitaxial growth of ZnO. In this thesis work, a crystalline metal oxide layer was introduced as a buffer layer by redox reaction between a metal layer and the native SiO2. Aluminum was first sputtered for 20 seconds (4 nm), 40 seconds (8 nm), 60 seconds (12 nm) to produce three sets of samples. Each set was then annealed in situ at 450¢J for 20 minutes, 40 minutes, 60 minutes, respectively, to generate 9 different fabrication conditions meant to ignite a redox reaction between aluminum and the silicon oxide. All samples were treated for comparison by rapid thermal annealing to 900¢J, intended to improve the crystalline quality of the buffer layer and thus the epitaxial zinc oxide. Means to characterize the samples included (1) cross-sectional TEM (Transmission Electron Microscopy) observations of the interfaces and defects in various regions of the formed material or device structures; (2) x-ray crystallography via £s-2£c and rocking scans in regards to the perfection of the crystal structures and the relative film-substrate orientations; (3) photoluminescence spectroscopy, which showed oxygen deficiency in the ZnO epitaxial thin films as judged by the peaks of near-edge luminescence and mid-gap impurity states. The resulted material structure is a pin diode with a transparent n-ZnO layer sandwiching in the middle an aluminum oxide insulating layer with the p-Si substrate. The electrically insulating aluminum oxide layer serves to increase the minority carrier accumulation effect, extending carriers¡¦ effective life times and hence enhancing the light emission efficiency. Measuring the current-voltage characteristics of the pin device structures provides insights into the interface charges, while high-frequency capacitance-voltage curves helps give a glimpse of the interfaces between ZnO and Al2O3 or AlOx, as well as those between Al2O3 or AlOx and silicon, all concerning the electronic accumulations at each interface. Keywords: sputtering, ZnO, Al2O3 , pin diode.

In this thesis, n-type ZnO thin films are grown on buffered p-type Si substrates by RF sputtering. The buffer is a pure nanometer-thick Al layer deposited onto a Si substrate that has a native SiOx over-layer. The Al- layer is meant to react with the native oxide and reduce it back to the pure Si formation when the Al-layer is itself oxidized into AlOx. The pin diodes with ZnO grown on AlOx are expected to outperform those with ZnO on SiOx on the aspects of electrical quality and crystallographic orientations. The transmission electron microscopy was employed to study the epitaxial relationship between the ZnO layers and the Si substrates, the crystal structure, and defects at the ZnO-Al or Al-SiOx interfaces. X-ray diffraction studies through £s-2£c, rocking curve, GIXRD and pole-figure scans were also conducted to see the differences between as-deposited and post-annealing treated samples concerning with the ZnO crystallographic orientations and general qualities. Through comparisons of the leakage current and the tunneling behaviors , the electrical measurements can be used to analyze the pin devices.

Mit der Entdeckung des Gleichrichter-Effekts 1873 wurde der theoretische Grundstein für die Halbleiter-Diode gelegt. Heutzutage sind Dioden auf nahezu allen elektronischen Schaltungen zu finden. Sie erfüllen dabei unterschiedlichste Aufgaben und finden Anwendung zum Beispiel als Gleichrichter, RF-Widerstand oder ESD-Schutzstruktur. Dioden basieren auf einem p/n-Übergang, welcher den Stromfluss in eine Richtung passieren lässt und in die andere Richtung sperrt. Bei PIN-Dioden wird zwischen der p-dotierten und der n-dotierten Zone noch ein intrinsisches bzw. niedrig dotiertes Gebiet eingefügt. Im Rahmen dieser Arbeit wurden Silizium- und GaAs- basierte PIN-Dioden für den Einsatz als ESD-Schutzstruktur und für Anwendungen in der Leistungselektronik untersucht. Mit Hilfe von TCAD-Simulationen wurden verschiedene Eigenschaften der PIN-Dioden unter Einwirkung eines ESD-Ereignisses analysiert. Die Bildung und Bewegung von Stromfilamenten konnte dabei beobachtet werden. Es stellte sich heraus, dass die Geometrie der Schutzdiode einen direkten Einfluss auf deren Lebensdauer hat. Es konnten Designvorschläge für ein optimiertes ESD-Schutzverhalten gemacht werden. Zur Validierung der Ergebnisse wurden verschiedene PIN-Dioden hergestellt und mittels TLP-Messung charakterisiert. Bei sehr schmalen Strukturgrößen konnten mehrere Spannungsabfälle beobachtet werden, was auf das Vorhandensein mehrerer Stromfilamente hindeutet. Diese Vermutung konnte anhand von TCAD-Simulationen bestätigt werden. Zur Analyse eines Layouts auf dessen ESD-Robustheit sind zeitintensive TCAD-Simulationen ungeeignet. Aus diesem Grund wurden auf Basis der TLP-Messungen und TCAD-Simulationen layoutabhängige Kompaktmodelle entwickelt. Diese ermöglichen eine schnelle Simulation der rückläufigen Kennlinie einer in Sperrrichtung vorgespannten PIN-Diode. Zusätzlich konnten die Bildung und Bewegung eines Stromfilaments nachgebildet werden. Im Hinblick auf Anwendungsmöglichkeiten in der Leistungselektronik, wurden Untersuchungen an GaAs-basierten PIN-Dioden durchgeführt. Diese zeichnen sich vor allem durch deutlich höhere Durchbruchspannungen aus. Mit TCAD-Simulationen und Hochspannungsmessungen wurden die Dioden charakterisiert. Aus den gewonnenen Erkenntnissen konnte ein analytisches Modell abgeleitet werden, was eine Optimierung der Diodenstruktur im Hinblick auf die Durchbruchspannung ermöglichte.

Variable attenuators are important circuits that can be employed in many radio frequency (RF) applications, e.g., in automatic gain control (AGC) amplifiers, broadband gain-control blocks at RF frequencies or as broadband vector modulators. For any applications, low insertion phase shift and low power consumption are of interest. A way to implement variable attenuators is using the RF PIN diode. The PIN diode is characterized by a low doped (I = intrinsic) semiconductor region between p- (P) and n-type (N) semiconductor regions. Besides the variable attenuators, the PIN-diode is used in other RF circuits, such as RF switches, limiters and phase shifters. This project presents the design of variable attenuators at 7.5 GHz and 500 MHz frequency bandwidth for ultra-wideband (UWB) applications using two different PIN diodes. The variable attenuators have a topology based on 90° hybrid couplers. The design is performed using Advance Design Systems (ADS) from Agilent Technologies Inc. After presenting the PIN diode and its equivalent circuit, the theory of the 90° passive directional branch line coupler and the operation principle of the variable attenuators are presented. As the selection of the appropriate PIN diode is a critical step in the design, special attention is dedicated to this aspect. It follows the design of the variable attenuators with extensive descriptions of the simulations in ADS. Firstly, both series and shunt attenuators are presented. However, as these circuits normally offer narrow band variable attenuation, the 900 directional branch line coupler is used in the attenuator for broader band operation. At the end, a double hybrid coupler is found to eliminate the ripple in the high attenuation state of the single hybrid coupled attenuator. So the final topology of the variable attenuator is a double hybrid coupler variable attenuator- Moreover, in this project, different PIN diodes are investigated for variable attenuator applications. Different manufacture companies are currently providing different kinds of PIN diodes in terms of parameters and packages. Every type of PIN diodes are providing different sort of advantages to the designers. That is why it has become more difficult for the RF designers to choose the right device for the specified application. Beside the design of the variable attenuator using PIN diodes, some considerations in form of a guide line to the designers while they are using the PIN diode for designing the variable attenuator. In this work, the used PIN diodes are a beam lead PIN diode and chip PIN diode. The beam lead PIN diode is used because it is manufactured for high frequency and it produces excellent electrical performance and isolation at high frequencies. On the other hand, the chip PIN diode eliminates the problem of package parasitics. However, printed circuit board (PCB) manufacturing limitations at the university laboratory incline the balance in the favor of the beam lead PIN diode, HPND- 4005 from Avagotech, instead of the also considered chip diode MA-COM MA4P202.

Zugl.: Duisburg, Essen, Univ., Diss., 2008

Yes / This paper presented a new circular polarization reconfigurable antenna for 5G wireless communications. The antenna, containing a semicircular slot, was compact in size and had a good axial ratio and frequency response. Two PIN diode switches controlled the reconfiguration for both the right-hand and left-hand circular polarization. Reconfigurable orthogonal polarizations were achieved by changing the states of the two PIN diode switches, and the reflection coefficient |S11| was maintained, which is a strong benefit of this design. The proposed polarization-reconfigurable antenna was modeled using the Computer Simulation Technology (CST) software. It had a 3.4 GHz resonance frequency in both states of reconfiguration, with a good axial ratio below 1.8 dB, and good gain of 4.8 dBic for both modes of operation. The proposed microstrip antenna was fabricated on an FR-4 substrate with a loss tangent of 0.02, and relative dielectric constant of 4.3. The radiating layer had a maximum size of 18.3 18.3 mm2, with 50 W coaxial probe feeding. / European Union’s Horizon 2020 research and innovation programme under grant agreement H2020-MSCA-ITN-2016 SECRET-722424.

This Thesis presents the design and development of a reconfigurable both in frequency and radiation pattern Annular Slot Antenna (ASA). The antenna is fabricated on Duroid with dielectric constant 6.15. The ASA operates in three different frequencies: 5.2, 5.8 and 6.4 GHz. The matching at those frequencies is achieved using linear stubs. PIN diodes are used as switches to connect/disconnect the stubs to the microstip feed line. The use of PIN diodes along the slot allows the steering of the radiation pattern and therefore the position of a radiation pattern null is directed in three pre-selected directions.

University, Diss., 2001--Bonn.

The master's thesis deals with the design and implementation of a reconfigurable patch antenna. The antenna is fed by a microstrip transmission line. To the microstrip feeder, tuning stubs are connected. Each stub matches the input impedance of the antenna to 50 ? for different operation frequencies. Stubs can be individually connected to the feeder by PIN diodes; operation frequency of the antenna can be switched that way. In the project, the antenna is initially designed for antenna substrate RO3006. Then, the design will be converted to the substrate ARLON AD600 selected for the realization. In the project, modifications of stubs will be proposed to properly connect the PIN diodes. Functionality of the designed antenna will be verified by modeling in Ansoft Designer. The last part will be dealt with implementation of the antenna and the experimental measurement of their properties.