【作者】 柏自奎；

【导师】 谢长生；

【作者基本信息】 华中科技大学 ， 材料学， 2008， 博士

【摘要】 金属氧化物气敏传感器作为“气—电”信息转换器件，实现对气体的检测和生产过程控制，同其它方法相比，具有结构简单、廉价、反应迅速等优点，因而成为应用最广、发展最快的气敏传感器之一。随着现代工农业及信息技术的发展，人们对气体的检测不再满足于监控和报警，而提出了更高的要求，不仅要具有定性判别，还要具有定量指示功能。而满足这种技术要求色不再是一个传感器所能胜任的。在现阶段，金属氧化物半导体气体传感器都是单个器件，普遍存在着体积大、能耗高、灵敏度低、热稳定性差、可靠性、选择性和抗干扰性不够强以及一致性差等缺点，简单的多元件组合不能满足生产中的要求，因而限制了金属氧化物半导体气体传感器的进一步广泛应用。本文从ZnO基半导体气体传感器的微型集成阵列的制备技术出发，以提高传感器阵列的灵敏度、选择性、稳定性为目的，着重研究ZnO的掺杂、粉体预处理、厚膜预处理、烧结工艺等对传感器阵列元件的敏感性和稳定性的影响，并采用复阻抗分析的方法研究传感器稳定性变化对应的厚膜微结构变化。首先，介绍了气敏传感器阵列的应用背景，阐述了金属氧化物半导体气敏传感器阵列的结构及原理，综述了金属氧化物微结构气体传感器及其阵列的制备技术研究进展及最新动态，分析了气敏传感器的性能指标，最后详细论述了影响稳定性的因素、改善稳定性的措施及稳定性的研究方法。其次，采用了激光微加工方法与丝网印刷制备气敏传感器阵列，对比了各自的特点，并着重研究了气敏浆料的配置及丝网印刷工艺对厚膜的表面形貌及边缘平整度的影响。激光微加工和丝网印刷平面制备工艺都具有很好的稳定性和可靠性。相比之下，激光微加工制备工艺简单，但阵列基片上的温度分布有微小的波动；丝网印刷制备工艺更适合大批量生产，阵列基片上温度分布均匀，基片的机械强度高。配制气敏浆料的有机载体对浆料的稳定性和印刷性、印刷厚膜的一致性有重要影响。由松油醇、丁基卡必醇醋酸酯和邻苯二甲酸二丁酯按6：3：1的质量比组成有机载体的混合溶剂，能获得具有较好层次挥发特性，配以1wt．％1，4-丁内酯，4wt．％司班85、0．5wt．％氢化蓖麻油作流变剂、表面活性剂、触变剂，以7：3的固体粉体与有机载体质量比制备气敏浆料可获得均匀、稳定的、满足印刷工艺要求的气敏浆料。最佳固体粉体与有机载体的质量比因粉体特性的差异应有小的变化。印刷速度、网距、刮板压力、刮板角分别为60 mm/s、3．5mm、2．0kgf、72°时，印刷厚膜具有最高的边缘平整度。第三，从四针状纳米ZnO厚膜的烧结工艺、粉体预处理和厚膜预处理工艺研究了纳米ZnO传感器的敏感性和稳定性。烧结温度对敏感性的影响因测试气体种类不同有不同的特点，烧结温度越高，传感器越稳定。环境湿度是传感器稳定性的重要影响因素，在50％RH的测试和存储环境中，传感器能保持最佳的敏感性和稳定性。700℃，3小时预处理四针状纳米ZnO粉体、200℃水浴处理印刷厚膜对元件的敏感性有较强的调控作用，也提高了稳定性。第四，采用单一掺杂和复合掺杂的ZnO，结合不同的烧结工艺制备气敏传感器阵列，并研究了气敏性和稳定性。依据掺杂改善敏感性、提高稳定性的原则，选择了Ni、Bi₂O₃和Cu₂O作单一掺杂材料，Al₂O₃、TiO₂、V₂O₅为复合掺杂材料。平行于厚膜表面的磁场诱导5wt．％Ni掺杂的ZnO厚膜对100 ppm甲醛具有最好的敏感性和选择性，同时具有很好的稳定性。一元掺杂ZnO+5wt．％Al₂O₃元件对甲醇、甲醛和丙酮气体具有较好的敏感性；三元复合掺杂ZnO+5wt．％Al₂O₃+10wt．％TiO₂+1wt．％V₂O₅元件对苯、甲苯和二甲苯具有较好的敏感性，也改善了元件的稳定性。10wt．％Cu₂O掺杂的纳米ZnO厚膜元件对各种气体都具有最好的敏感性，分别掺杂5wt．％Bi₂O₃和Cu₂O的纳米ZnO元件敏感性次之，但稳定性更好。第五，引入微波烧结工艺研究了单一掺杂和复合掺杂ZnO厚膜阵列元件的气敏性和稳定性。微波烧结ZnO及掺杂ZnO厚膜时间越长，厚膜电导和敏感性越小。在20、40、60min三个烧结工艺中，20min烧结的元件具有最好的敏感性和最低的最佳敏感温度，60min烧结的元件具有最好的稳定性。一元Al₂O₃和三元Al₂O₃、TiO₂、V₂O₅复合掺杂ZnO厚膜改善了稳定性的同时提高了对甲醇的敏感性，二元Al₂O₃和TiO₂复合掺杂ZnO，则降低厚膜的敏感性。微波烧结可以有效调控气敏传感器的敏感性和稳定性，是一种值得深入探索的新的烧结工艺。第六，采用复阻抗分析的方法研究了传感器阵列厚膜的微结构及其阵列稳定性变化对应的厚膜微结构变化特征。在恒定高温和热循环中，初期元件的谱线随时间波动较大，阻抗谱对应的相位-频率特性曲线向高频移动。随热循环的进行，晶界电阻逐渐减小，晶界电容逐渐增大。ZnO+5wt．％Cu₂O厚膜中引入了p-n结结构，抑制了元件阻抗谱线和相位-频率特性谱线出现大的波动，使元件表现出相对稳定的特性；微波烧结纯ZnO和ZnO+5wt．％Bi₂O₃厚膜元件具有相同的特征阻抗谱曲线，曲线由两个不同直径的四分之一圆弧组成的压扁的半圆弧，曲线随时间波动较小，表明厚膜中颗粒具有更好的烧结状态，元件稳定性好，Cu₂O掺杂ZnO抑制了厚膜颗粒的烧结，阻抗谱曲线随时间的波动较小，元件稳定性差；水浴处理使纯ZnO和掺杂ZnO厚膜谱线稳定，厚膜具有更均匀，更稳定的晶粒及晶界结构，元件在恒定的高温中具有良好的稳定性，但元件在热循环作用中，阻抗谱线持续波动，厚膜不能有效的释放热循环在厚膜中产生的应力，使厚膜颗粒的烧结结构被损坏，稳定性变差。更多还原

【Abstract】 Metal oxide gas sensors as the "gas-electricity" transducer to detect gas and control industry production are one of the most widely researched and used gas sensors due to their advantageous features, such as low price, prompt response and simple structure. However, with the development of modern industry and information technology, the use of gas sensors is no longer only limited to annunciating and alarming. Gas sensors are called for not only qualitative discrimination but also quantitative analysis of gas in applications. A single sensor can not competent to do it. At present, metal oxide semiconductor sensors are single devices which have the defects and deficiency as big bulk, high power consumption, poor sensitivity, thermal stability, reliability, selectivity, anti-interference and coherency. Simple multi-devices combined can not meet the needs of industry production. In this dissertation, to increase the sensitivity, selectivity and stability of gas sensor arrays, the effect of doping, pretreatment of powders, pretreatment of thick films and sintering craft were discussed and complex impedance analysis was used to study the thick film micro-structure change according to the sensor stability change, on the basis of the technology to manufacture ZnO based semiconductor gas sensor arrays.Firstly, the application and development trend of gas sensors array were introduced in this paper. The structure and gas-sensing mechanisms of metal oxide semiconductor sensor arrays were expatiated. Improvements and current research evolvements of technology to manufacture metal oxide micro-structure gas sensors and their arrays were summarized. Sensor Performance was analyzed. At last, factors to effect stability, ways to improve stability and methods to research it were particularly discussed.Secondly, gas sensor arrays were manufactured by laser micromachining and screen-printing technique and features of each method were compared. Research was focused on effects of the preparation of gas-sensing materials paste and screen-printing techniques to the morphology of thick films and the resolution of samples. Both laser micromachining and the screen-printing techniques have good stability and reliability. The laser micromachining technique is a simple preparation method and a tiny fluctuation of temperature distribution was brought out on array substrate. The resistance heater on the array substrate prepared by screen-printing technique provides even temperature distribution, and the screen-printing technique is more suitable for volume-produce. The organic vehicle mixed in the paste has important effects to the stability, the printing property of the paste, and coherency of thick film. The main solvent composed of terpineol. butyl-carbitol-acetate and di-n-butyl phthalate with the ration of each 6:3:1 can meet the real needs with gradual volatility. 1wt.% 1,4-butyrolactone, 4wt.% span-85, 0.5wt.% hydrogenated castor oil added serve as rheological agent, surfactant, thixotropic agent. Well-proportioned and stable paste was then prepared by mixing solid powders and organic vehicle together with the weight ration 7:3. The most appropriate ration of solid powders and organic vehicle has small adjustments according to the difference of powder properties. The results show that highest resolution of the printing films can be achieved with printing speed 60mm/s, nets high 3.5mm, pressure of scraper 2.0kgf, and scraping angle 72°.Thirdly, sensitivity and stability of nano-ZnO sensors were researched in aspects as sintering temperature of thick films, pretreatment of powder, and hydrothermal treatment of thick films. Effects of sintering temperature to sensitivity have different features according to different kinds of gas. The higher sintering temperature is, the more stable sensitivity is. Relative humidity （RH） is another important factor to sensor stability. In testing and storage circumstance of 50%RH, sensors show best sensitivity and stability. Pretreatment of nano-ZnO at 700℃for 3h and hydrothermal treatment of thick films at 200℃have control function to the sensitivity of sensors and also increase their stability.Fourthly, single-doped and multi-doped ZnO sensor arrays were fabricated with different sintering craft. And the corresponding sensitivity and stability were studied. The results show that the sensors based on 5wt.% Ni-doped T-ZnO with magnetic-field induced in parallel direction to the thick film surface have the optimized sensitivity and selectivity to 100ppm formaldehyde together with nice stability. ZnO+5wt% Al₂O₃ sensors have comparatively higher sensitivity to methanol, formaldehyde, and acetone; the trinary doped ZnO+5wt.% Al₂O₃+10wt.% TiO₂+1wt.% V₂O₅ sensors are more sensitive to benzene, toluene and xylene and the stability of thick films is also increased; binary doped ZnO+5wt. % Al₂O₃+10wt. % TiO₂ sensors have comparatively lower sensitivity and stability. 10wt.% Cu₂O doped nano-ZnO have optimized sensitivity to all kinds of gas. 5wt.% Bi₂O₃ and Cu₂O each doped ones improve sensitivity and stability.Fifthly, microwave sintering technique was employed to study the sensing property and stability of single doped or multi-doped ZnO sensor arrays. The longer the ZnO and doped ZnO thick films are sintered, the lower the sensor conductivity and sensitivity are. The sensors sintered by microwave for 20min have the highest sensitivity and lowest temperature for optimized sensitivity. Those sintered for 60min have the best stability. The single Al₂O₃ and trinary Al₃O₂, TiO₂ and V₂O₅ doped nano-ZnO sensors have higher sensitivity and stability to 100ppm formaldehyde. Microwave sintering technique can effectively modify and control sensibility and stability of gas sensors and thus is worth further research.Sixthly, complex impedance analysis was employed to study the microstructure of thick films and its change according to the change of stability of sensors. For the ZnO and 5wt.% Bi₂O₃ doped ZnO sensors sintered in electric cooker, the Impedance curve have comparatively large fluctuation In the early continuous high temperature and heating cycle operation, and the phase-frequency characteristics curve tends to high frequencies. The grain boundary resistance and capacitance of the corresponding sensors decrease and increase gradually, respectively. The impedance curve and phase-frequency curve of the 5wt.% Cu₂O doped ZnO sensors is stable in stability testing process, which are contributed to p-n junction micro-structure in the thick films. The stability of the sensors is improved. The ZnO and ZnO+Bi₂O₃ sensors sintered by microwave have the same characteristics of impedance curve, which is a flat half circular arc composed of two quarters of circular arc with different diameters. The thick films are sintered well, so the sensors resistance is stable. For Cu₂O doped ZnO thick film, Cu₂O suppress of the ZnO particle agglomeration, which lower the sensor stability. The impedance curve of the ZnO and doped ZnO sensors by the hydrothermal treatment had remained unchanged in continuous high temperature operation, which was a quarter of circular arc. It indicated that the more uniform, more stable grain and grain boundary structure in the thick films are obtained. However, in the heating cycle operation, the impedance curves are fluctuant. It indicated that the thick films can not effectively absorb stress from themselves and the substrate. The grain boundary micro-structure in the thick films is spoiled and the stability of the sensors is decreased.更多还原