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Study of Nano Spherical-shell TiO2Oxygen Sensor Based on PN Junction Substrate

Author: ZhangHuiJun
Tutor: WenDianZhong
School: Heilongjiang University
Course: Microelectronics and Solid State Electronics
Keywords: Titanium dioxide oxygen sensor nano spherical shell doping sensitivecharacteristic
CLC: TP212
Type: PhD thesis
Year: 2013
Downloads: 47
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Abstract


With the rapid development of science and technology, it is necessary to effectivelydetect oxygen in the field of aerospace, biomedical, food processing, environmentalmonitoring etc. In different application fields, due to the limits to adapting environment,function, size and cost, we need to pay more attention to measurement precision,sensitive range, high environmental adaptability, miniaturization, easy integration etc.The TiO2has unique physical and chemical properties, so it has important applicationvalue in gas sensor. Since the90’s of20th century, nanometer science has become thenew content of basic theory and applied research based on TiO2material. Due to thequantum size effect, surface effect of nanometer materials, structure and properties ofnano-materials TiO2have great difference with the conventional materials, researchingnanostructured films is helpful to improve the performance and design of gas sensor. Inthis work, we applied nano spherical-shell TiO2film as the sensitive films, the TiO2/Siheterostructure as the sensitive electrodes to design and fabricat TiO2oxygen sensor andachieved the following theoretical analysis and research:1. Using the method of atomic scale Ti metal particle size deposition, separationuder liquid phase, self-assembly by sphere and shell, extraction separation, and stepoxidation, TiO2spherical shell structure which was approximately250nm in diameterwas preparated. Oxygen sensing films were made of TiO2spherical shells and transitivePt-TiO2or W-TiO2thin films which achieved by reactive sputtering. The typicalsynthesis procedure of hollow nanospheres was as follows. The Ti particals of ultrafinemetal atoms in oill were deposited by physical deposition. The Ti particals and carbonspheres (170-200nm in diameter) were evenly dispersed in the mixed solution ofdichloromethane and alcohol, and completed sphere and shell self-assembly. Core-shellstructure of Ti particles was achieved, and then removed the oil solution by extraction.Under oxygen-enriched air, Ti metal Core-shell was echelon oxidated to form TiO2hollow nanospheres, and at the same time, carbon spheres were oxidated and evaporated.Oxygen sensing films were made of TiO2spherical shells and transitive TiO2thin films.2. The prepared sensing films were characterized by XRD, AFM, XPS, and TEM. The diameter of TiO2hollow nanospheres is about250nm and integrity of the structure,wall of TiO2nanospheres is about between35nm-50nm. Shell TiO2particles on spheresshowed regular, uniform distribution and the size is about15nm-25nm.Two-dimensional lattice image showed anatase phase TiO2(101) and (004) crystal andthe spacing of crystal surface is0.35nm,0.24nm, separately. Thin films of TiO2nanospheres can be well covered on the surface of transition layers, no discontinuity orthe crack. It was Obvious to improve the surface adsorption of detected gases and obtainexcellent gas sensitivity.3. TiO2oxygen sensor was designed and fabricated based on the sensitivemechanism of TiO2films and TiO2/Si heterostructure. Longitudinal surface currenttransmission of TiO2/Si heterostructure was used to improve sensor performance. Thesensor is composed of three parts: TiO2sensitive active region and the detectingelectrode, the heating resistor and the heating electrode, and temperature control diodeand the detecting electrode. PN junction was fabricated on silicon cup surface activeregion, non active area was covered by SiO2, the Pt detection electrode was fabricatedon p+-Si and n+-Si neutral zone, Pt heating electrode was fabricated on region of theSiO2layer, doped-TiO2sensing film which was made of TiO2spherical shells andtransitive TiO2thin films was fabricated on active region and Pt detection electrode, sothe sensor is compatible with the Si integrated-process.4. Combined with the microstructure of gas sensitive materials, the physical andchemical adsorption characteristics, sensitive properties of TiO2/Si heterostructure,effects of temperatureand environmental humidity on the gas sensing properties of thesensor was discussed based on the structure design to improve the sensing mechanismand to systematically test the sensitivity of the sensor, selectivity, response time andrecovery time, and hysteresis characteristics.

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