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M. Schneider, A. Bittner, U. Schmid:
"Impact of film thickness on the temperature-activated leakagecurrent behavior of sputtered aluminum nitride thin films";
Sensors and Actuators A: Physical, 224 (2015), S. 177 - 184.

Aluminum nitride (AlN) is a material of significant importance in the field of micro electro-mechanicalsystems (MEMS) due to its piezoelectric properties and its use as passivation layer. This work pro-vides a comprehensive study on the film thickness dependence of the temperature activated leakagecurrent behavior of sputtered aluminum nitride thin films. The thickness ranges from 40 to 400 nm, pro-viding insight into the electrical characteristic of AlN thin films for thickness values typically used inMEMS devices. The leakage current shows a highly symmetrical behavior for both positive and negativebias directions due to a tailored silicon substrate pre-treatment process. At low electric field strengthsE ≤ 0.1 MV/cm, the leakage current is dominated by ohmic behavior, while for E ≥ 0.3 MV/cm, the leak-age current is controlled by a Poole-Frenkel mechanism. Both the defect-related barrier height and thedefect density for the Poole-Frenkel regime can be extracted from arranging the data in an Arrheniusconfiguration. The barrier height shows no significant influence of film thickness. However, the defectdensity correlates directly with the leakage current level of the film and thus dominates the electri-cal behavior. The defect density increases significantly with increasing film thickness. As the thin filmswere deposited under nominally unheated substrate conditions the substrate temperature increases withincreasing sputter time. A simple model is proposed in order to provide a qualitative understanding ofthe observed effect by assuming a substrate temperature driven redistribution of defect states within theband gap of aluminum nitride thin films.

Aluminum nitride (AlN) is a material of significant importance in the field of micro electro-mechanicalsystems (MEMS) due to its piezoelectric properties and its use as passivation layer. This work pro-vides a comprehensive study on the film thickness dependence of the temperature activated leakagecurrent behavior of sputtered aluminum nitride thin films. The thickness ranges from 40 to 400 nm, pro-viding insight into the electrical characteristic of AlN thin films for thickness values typically used inMEMS devices. The leakage current shows a highly symmetrical behavior for both positive and negativebias directions due to a tailored silicon substrate pre-treatment process. At low electric field strengthsE ≤ 0.1 MV/cm, the leakage current is dominated by ohmic behavior, while for E ≥ 0.3 MV/cm, the leak-age current is controlled by a Poole-Frenkel mechanism. Both the defect-related barrier height and thedefect density for the Poole-Frenkel regime can be extracted from arranging the data in an Arrheniusconfiguration. The barrier height shows no significant influence of film thickness. However, the defectdensity correlates directly with the leakage current level of the film and thus dominates the electri-cal behavior. The defect density increases significantly with increasing film thickness. As the thin filmswere deposited under nominally unheated substrate conditions the substrate temperature increases withincreasing sputter time. A simple model is proposed in order to provide a qualitative understanding ofthe observed effect by assuming a substrate temperature driven redistribution of defect states within theband gap of aluminum nitride thin films.

Aluminum nitride; Sputter deposition; Leakage current; Poole-Frenkel

http://dx.doi.org/10.1016/j.sna.2015.01.032