氧化鎳熱敏電阻於溫度感測微陣列之應用

Abstract

首先以有機金屬分解墨水噴製鋰鎳氧化物薄膜。將前驅物氫氧化鎳與氫氧化鋰溶解於醋酸水溶液中，並使用壓電式噴墨印機將墨水沉積在石英基材上。液膜在經過500 °C高溫燒結後，所形成的氧化物薄膜中含有Ni2O3，這使得薄膜電阻率降低許多。此外，鋰鎳氧化物薄膜的電阻率對溫度的變化會遵循Arrhenius關係式，其中的活化能約為0.38 eV，非常適合用作溫度感測的材料。不過，製程中的液膜燒結程序，溫度高達500°C，限制了基材的選擇。若要在低溫下進行薄膜製程，便得先出氧化鎳粉末。 接著，為了避免繁複的參雜程序，改以碳黑作為摻雜物來降低氧化鎳的電阻率。利用化學沉澱形成的Ni(OH)2/CB粉前驅物僅需經過300°C的燒結程序便能夠製備出NiO/CB複合物，在溫度範圍50至200°C之間，其B值大於4000 K，對溫度的敏感度極高，也十分適合用作溫度感測材料，與溶劑混合成膠即可進行塗佈作業。不過，由於合成的複合物粉末是經由人工研磨而得，其粒徑過大，無法用於噴墨印刷系統。 最終則是以奈米粒子墨水噴製氧化鎳薄膜。藉由pH值的調整將市售的氧化鎳奈米粒子穩定地懸浮於10 vol%的乙二醇水溶液，再利用壓電式噴墨印機將墨水沉積在玻璃基材上。液膜僅需經過200°C的後續熱處理，便會於玻璃基材上沉積成氧化鎳薄膜，因此，相較於有機金屬分解墨水的製程，此方法能夠應用至更廣泛的基材。此研究所製作的溫度感測元件不僅具有極高的敏感度(於溫度範圍50至200°C之間的B值為4544 K)，同時還具有極短的反應時間(<1秒鐘)。

In this research, the negative temperature coefficients (NTC) of resistance of nickel oxide and nickel oxide based materials were investigated and nickel oxide micro temperature sensing arrays were fabricated via inkjet printing technology. First, to create conductive nickel oxide micro patterns with metal-organic decomposition inks, nickel/lithium hydroxides dissolved in acetic acid were printed on quartz plates. After thermal pyrolysis at 500°C, the existence of Ni2O3 was observed in the synthesized thin films and contributes to better electrical conductivity. The synthesized thin films are promising materials for temperature sensing applications due to the high activation energy of 0.38 eV for conduction. However, the 500°C sintering process limited the choice of substrates. In order to fabricate nickel oxide thin films at lower temperature, nickel oxide based powders supposed to be synthesized on priority. To prevent complicated dopant formulations and sintering processes, carbon black was used as the dopant to increase the conductivity of nickel oxide. The NiO/CB composites with a large temperature coefficient of resistance (TCR) were prepared by a chemical precipitation followed by thermal annealing. After dispersed in solvents, the NiO/CB composite gels can be applied to thin film deposition. In the range of 50 to 200°C, the deposit composites possessed high temperature sensitivity with B-values more than 4000 K. Nevertheless, the composite powders can’t be used in inkjet printing system because of micro scale sizes. Finally, micro NiO thermistor arrays for temperature sensing applications were fabricated with nanoparticle inks. The NiO nanoparticles were well suspended in 10 vol% EG aqueous solution by adjusting the pH value and inkjet-printed on glass substrates. Nickel oxide thin films were deposited on the glass substrate after a thermal treatment only at 200°C. Compared to processes with metal-organic decomposition inks, this process can be applied to more substrates. The fabricated temperature sensing elements not only have a great temperature sensitivity with B-values of 4544 K but also a short response time less than 1 second.