The number of applications in which infrared radiation sensors are used is increasing. In some applications, the cost of the sensor itself is an issue, and simple solutions are thus required. In this thesis, the investigations have related to the use of thin polymer membranes in thermal infrared sensors, such as bolometers and thermopiles. Infrared sensors are usually subcategorized into photonic sensors and thermal sensors. For detection of infrared radiation using a photodetector, there is a requirement for low band-gap material. The need of cooling makes infrared photodetectors rather expensive, and not an alternative for low-cost applications. In thermal sensors, the heat generated from the incident infrared radiation is converted into an electrical output by means of a heat sensitive element. Thermal sensors operate at room temperature, which makes them a low-cost alternative. The basic structure of thermal sensors consists of a temperature sensitive element connected to a heat sink through a structure with low thermal conductance. It is common to use thin membranes of Silicon or Silicon Nitride as thermal insulation between the heat sink and the sensitive element. In comparison, polymers have a thermal conductance that is lower than in these materials, and this increases the generated temperature in the sensitive element. A polymer such as SU-8 has a low thermal conductivity and is applied using a spin coater. This reduces the number of complex processing steps. This thesis presents a new application of SU-8 as a closed membrane in a thermal sensor. The concept was initially demonstrated by fabricating a nickel bolometer and titanium/nickel thermopile structure with a 5 µm SU-8 / SiO2 membrane. However, for the sensor responsivity to be able to compete with commercial thermal sensors the structures, some optimization was required. Since the thermopile generates its own voltage output and requires no external bias, the optimizations were focused on this structure. There exist a number available software tools for thermal simulation of components. However, to the author’s best knowledge, there exist no tool for design optimization of thermopiles with closed membranes. An optimization tool using iterative thermal simulations was developed and evaluated. A new thermopile structure, based on the optimization results, was both fabricated and characterized. Using an infrared laser with a small spot, the measured responsivity of the manufactured thermopile was higher than that of a commercial sensor. In the case of a defocused spot and for longer wavelengths, the infrared absorption in the absorption layer reduces and degrades the responsivity. The thermopile was further evaluated as a sensor in a carbon dioxide meter application based on the NDIR principle. An increase in the CO2 concentration demonstrated a clear decrease in the thermopile voltage response, as was expected. By normalizing the voltage response and comparing it with a commercial sensor, this showed that the SU-8 based thermopile is relatively more sensitive to changes in the CO2 concentration. / STC

Goal of this thesis is to study infrared detection by means of thermal. Theoretical part of this work gives an introduction to thermal detectors.

Diamond is a promising material for high-power, high-frequency and high- temperature electronics applications, where its outstanding physical properties can be fully exploited. It exhibits an extremely high bandgap, very high carrier mobilities, high breakdown field strength, and the highest thermal conductivity of any wide bandgap material. It is therefore an outstanding candidate for the fastest switching, the highest power density, and the most efficient electronic devices obtainable, with applications in the RF power, automotive and aerospace industries. Lightweight diamond devices, capable of high temperature operation in harsh environments, could also be used in radiation detectors and particle physics applications where no other semiconductor devices would survive. The high defect and impurity concentration in natural diamond or high-pressure-high-temperature (HPHT) diamond substrates has made it difficult to obtain reliable results when studying the electronic properties of diamond. However, progress in the growth of high purity Single Crystal Chemical Vapor Deposited (SC-CVD) diamond has opened the perspective of applications under such extreme conditions based on this type of synthetic diamond. Despite the improvements, there are still many open questions. This work will focus on the electrical characterization of SC-CVD diamond by different measurement techniques such as internal photo-emission, I-V, C-V, Hall measurements and in particular, Time-of-Flight (ToF) carrier drift velocity measurements. With these mentioned techniques, some important properties of diamond such as drift mobilities, lateral carrier transit velocities, compensation ratio and Schottky barrier heights have been investigated. Low compensation ratios (ND/NA) < 10-4 have been achieved in boron-doped diamond and a drift mobility of about 860 cm2/Vs for the hole transit near the surface in a lateral ToF configuration could be measured. The carrier drift velocity was studied for electrons and holes at the temperature interval of 80-460 K. The study is performed in the low-injection regime and includes low-field drift mobilities. The hole mobility was further investigated at low temperatures (10-80 K) and as expected a very high mobility was observed. In the case of electrons, a negative differential mobility was seen in the temperature interval of 100-150K. An explanation for this phenomenon is given by the intervally scattering and the relation between hot and cold conduction band valleys. This was observed in direct bandgap semiconductors with non-equivalent valleys such as GaAs but has not been seen in diamond before. Furthermore, first steps have been taken to utilize diamond for infrared (IR) radiation detection. To understand the fundamentals of the thermal response of diamond, Temperature Coefficient of Resistance (TCR) measurements were performed on diamond Schottky diodes which are a candidate for high temperature sensors. As a result, very high TCR values in combination with a low noise constant (K1/f) was observed.

The maximum sensitivity of a thermal IR sensor can be available either by means of the sensor material, having its own absorbing properties, or by the deposition of an additional absorber structure on the detector surface. In this thesis, the theory of two absorption structures is discussed. The first is called the interferometric absorber structure. The second structure under investigation uses a lead selenide layer for the IR absorption. In the interferometric structure, a new epoxy material SU8-2002 was used as a dielectric medium. This material has a very low thermal conductivity of 0.3 W/mK, which makes it suitable for thermal detectors. The interferometric structure is based on three layers, a 40–60 Å thick Ti layer, a SU8–2002 layer with a thickness of 2000 Å thick and a 2000Å Al layer. Using standard cleanroom processing an interferometric structure was fabricated. Transfer matrix theory was used in order to simulate the interferometric structure and the lead selenide was fabricated by means of an argon-plasma sputtering process. Both fabricated samples were characterized through Fourier transfer infrared (FTIR) spectroscopy together with a specular reflectance accessory. The thicknesses of the added layers were measured using Atomic force microscopy (AFM) for both the interferometric and lead selenide structure.  It was determined  that by changing the reflective index value of the SU8-2002 from the reported value of 1.575 to about 2.40 that this provided a better agreement with the experimental results. The absorption results for the interferometric structure were determined to be approximately 82–98% for the wavelength region of 2-20µm at 30 degree. The PbSe absorption spectra showed 30%–50% absorption for the wavelength region 2.5 – 6.67μm.

Infrared detector technologies have been developing each day. Thermal detectors take great attention in commercial applications due to their low power consumption and low costs. The active material selection and the deposition of the material are highly important performance effective factors for microbolometer detector applications. In that sense, developing vanadium oxide (VOx) microbolometer active material by sol-gel method might be feasible approach to achieve good performance microbolometer detectors. In this study, vanadium oxide thin films are prepared by sol-gel method is deposited on silicon or silicon nitride wafers as active material by spin coating. The films are annealed under different hydrogen concentration of H2/N2 environments at 410