Atomic layer deposition based titanium alloying of zno for microbolometer applications
Microbolometers are attractive candidates for both military applications and consumer electronics among the uncooled thermal detectors due to their compactness, low cost, comparable performance with photon detectors and CMOS compatibility. The temperature sensitive active material is the most important part of resistive type microbolometers where change in electrical response occurs upon IR radiation. Typical active materials used for this purpose are YBCO and VOx. It was reported in several studies that ZnO has higher TCR value than commercially available active materials. However a temperature insensitive TCR property has not been achieved yet. To improve the TCR property of ZnO, doping with Titanium is proposed in this work. According to Ellingham diagram of oxides which is used generally in extractive metallurgy, it is obvious that titanium oxide is more stable than zinc oxide . Therefore doping with Titanium may reduce oxygen related defects and improve TCR property. Atomic layer deposition (ALD) is used for digital alloying of ZnO with Titanium. Titanium doped ZnO (TZO) films with Ti concentrations 2.5%, 5.9% and 12.2% were deposited using precursors diethylzinc, mili-Q water and tetrekis(dimethylamido)titanium. Then intrinsic defect related elemental characterization were made. Effect of Titanium doping on structure of TZO thin films was discussed. After material characterization, planar microresistors were fabricated in UNAM cleanroom facility. Piranha-HF and solvent cleaning of silicon substrate were performed before microfabrication. Vaksis Handy Plasma Enhanced Chemical Vapor Deposition (PECVD) was used to deposit insulation layer on silicon wafer. Photolithograpy steps were performed using Laurell Spinner system and EVG 620 mask aligner to pattern TZO thin film. Then contact material metallization was performed using Vaksis MIDAS Thermal Evaporator system. Current-voltage characterization of microfabricated resistors was performed before Temperature Coefficient of Resistance (TCR) measurements to see the contact type resistors. Then TCR measurements were done between 15oC and 25oC by applying constant current to the contact pads of resistor. Approximate resistivity values of 5 different samples were calculated. It is shown that proposed TZO active material for resistive type microbolometers has a temperature insensitive and high TCR value.