SOLID STATE DEVICES

Author: BENMESSAOUD ALI.
Year: 2001.
University: AUTÓNOMA DE BARCELONA [www.uab.es].
Place of defense: CENTRO NACIONAL DE MICROELECTRÓNICA.
Place of preparation: ESCUELA DE DOCTORADO Y DE FORMACIÓN CONTINUADA.

Summary: It has chosen the technical PECVD to obtain deposits subóxido silicon, SiOx, thickness of the order of micron, substratros Si two inches. We have made deposits with contenildos oxygen between 1.3 and 2.0, and a range of refractive indices between 1.96 (next to Si2N4) and 1.46 (SiO2). The structure (in particular, the porosity), and tension uniformity of the layers are better the lower the oxygen content. Moreover, the layers contain floods impurities in the form of links Si-H, NH, Si-OH and H2O. The contents of impurities varies gradually from layers pobles oxygen with a lot of links Si-Hy NH, and zero content Si-OH H2O, and layers of the oxide structure next estequiométrico with zero content links Si-Hy NH, and high content of Si-OH and H2O. It has investigated the conditions of temperature, pressure and power of the processes of deposit, for improvement of the quality of the layers floods. Increasing the temperature of deposit (up 350Â ° C) and power (up to 50 W, limited by the decline of uniformity), reduces the content of impurities in the layers, but the gradual increase in tension with the rise the content of oxygen layers, advised that the deposits grow minors valroes temperature and power in obtaining layers rich in oxygen. As regards to pressure, low values (100 m Torr), favoring the reduction of impurities, but the increase in the structural involved in the increased pressure (up to 300 m Torr), inhibits the accommodation of impurities in oxygen-rich layers, so that the quality of deposits will be enhanced procedure to an increase in pressure as they grow layers with a predictable higher content of Si-OH and H2O. Improving conditions for the deposit does not solve two fundamental problems, on the one hand, have not been able to remove impurities or tension of layers and on the other, the oxygen-rich layers are unstable compared to the humidity. The study of the action of moisture and the subsequent efforts to stabilize the layers, to carry out a thermal annealing at a temperature below 350Â ° C, the results are paraciales, with the effects reversible. As a solution has been proposed to carry out a rapid thermal annealing at high temperatures (950Â ° C) of the layers. The layers are estructuralemente compact treated and insensitive to the external action of the humidity, do not contain significant amounts of impurities, except low links Si-H environments O3-SiH addition, the level of tension disappears in rich layers If and gradually increases with the oxygen content, becoming a 50% lower than in the layers deposited without subsequent treatment. The refractive index is extended to the interval 2.32-2.00.

Author: AMIROLA SANZ JORGE.
Year: 2004.
University: POLITÉCNICA DE CATALUÑA [www.upc.edu].
Place of defense: aula de telensenyament, edifici B3, campus nord.
Place of preparation: C4 Despatx Direcció nord.

Summary: During recent times has emerged the concept of Systems Micro-Electro-Mecánicos (MEMS). Such systems may provide a solution to many problems of size (miniaturization), consumption, etc., but in turn are a huge source of new solutions and applications. Among the most versatile structures within the world of MEMS are voladizos (or cantilevers) and bridges suspended. Such structures have proven to be very useful for a large number of applications, as well as sensing and action. The work carried out in this thesis are designed and manufactured different types cantilever structures and bridge through manufacturing processes developed specifically for this work. One of the fields in which they have developed more efforts since the emergence of such structures is the sensing of gas, so in this work we have demonstrated the operation of devices manufactured for this application. It first presents a study of the state of art from the point of view of the structure itself, as gas sensors in general. Below is an overview of the theoretical foundations underlying the behavior of electro devices that plan to manufacture. These are cantilevers both resonant and non-resonant sensing where the gas will be based on its funcionalización through a polymer coating sensitive. The early detection proposed are: change in the resonance frequency due to absorption (resonant devices, electrostatic detection) and deflection due to the stress induced by differential surface absorption (Non resonant electrostatic detection (variation of capacity) or piezoresistiva). It presents a study by theoretical simulations of the performance of these devices in order to dimensionarlos correctly at the time of manufacture. We present a new method for cantilevers resonant excitation based on electromechanical coupling, which will allow us to achieve good levels of signal from devices with low quality factor. In the chapter devoted to the manufacture presents the different processes developed in this work. The major differences in all of them lie in the type of micromecanización employed (volume or surface), the type used in the detection device (electrostatic or piezoresistiva), and the type of wafers used in their manufacture (normal attack by unemployment or electrochemical BESOI). It describes in detail all the processes and the development thereof. Below are the techniques of measurement proposals for the application of gas sensing and characterization of devices manufactured. It then describes the measurement system used as the deposit system polymer developed in this work. The following are the measures undertaken so as to gas as relative humidity, as well as the results and their analysis. The Limits of detection obtained, as well as response times and its linearity, are within the current state of the art for the type of measured gases, leading to measure concentrations well below the levels dangerous to health. Finally, it presents the findings of the thesis as well as a future line of work to improve outcomes. The avenues of inquiry would be the most notable of eliminating drift of the measure temperature through theft or inclusion of a reference cantilever, and the implementation of arrays of cantilevers to detect gas mixtures.