Book Description

This dissertation, "A study of integrated semiconductor thin-film sensors on sio2/si substrate" by Bin, Li, 李斌, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled A STUDY OF INTERGATED SEMICONDUCTOR THIN-FILM SENSORS ON SiO /Si SUBSTRATE submitted by Bin Li for the degree of Doctor of Philosophy at the University of Hong Kong in April 2001 With the development of the information technology, the need for miniaturized, intelligent and programmable sensors is rapidly increasing. To meet this trend, developing thin-film sensors on silicon substrate is of great importance. In this thesis, two areas are focused on. One is spreading-resistance temperature (SRT) sensor on silicon on insulator (SOI), while the other is the multi-function thin-film microsensor on SiO /Si substrate. Based on the principle of minority-carrier exclusion effect, SRT sensor on bulk Si is intensively studied. Optimizations of structural parameters and processing conditions on thermal characteristics of SRT sensors are carried out. With appropriately small electrode and high substrate doping, bulk SRT sensor can function at temperatures up to 400 C at a low current of 2 mA. ii SRT sensor on SOI is then investigated with emphasis on its resistance versus temperature (R-T), low-temperature and AC characteristics. Moreover, the effect of Si- film thickness on the maximum operating temperature (T ) is simulated and verified by max experiment results. When the silicon film is sufficiently thin, i.e. 0.1 μm, T can be max significantly raised up to 550 C, even at a very low bias current of 1 μA. Measurements under low-temperature or AC condition reveal that SRT sensor behaves like a conventional resistor. A new microsensor consisting of a thin-film resistor and a metal-insulator- semiconductor (MIS) capacitor is developed by depositing perovskite-type thin film on SiO /Si substrate. SrNb Ti O, Ba La TiO and Ba La Nb Ti O chosen as the 2 x 1-x 3 1-x x 3 1-x x y 1-y 3 sensing film present reasonable multi-function sensitivities to light, heat and humidity. Differences in the sensing properties of the films are related to their chemical compositions and grain boundaries. It is hoped that by varying the chemical composition, processing conditions of the film, better performance could be obtained. Finally, the effects of device structure on the sensitivities of perovskite thin-film microsensors are discussed. A new physical model is proposed for humidity-sensitive MIS capacitor with a metal-perovskite-SiO -Si structure. Based on this model, it is deduced that higher sensitivity of thinner film is due to higher porosity of the film. However, thinner film results in lower sensitivity to illumination due to poorer absorption, iii while the film thickness only has minor effects on the thermal sensitivity. The effects of SiO thickness are studied and experimental results demonstrate that an optimal value of 250 A gives rise to good multi-function sensitivities. The dependence of electrical properties of photoresistor on device dimension is investigated. Devices with smaller electrode spacings show reasonably linear I-V characteristics. Moreover, heat treatment in O for an optimal time can increase the photo sensitivity by suppressing dark current. In conclusion, SOI SRT sensors and perovskite-oxide thin-film microsensors are promising candidates for integrated sensor applications.