Controlling the Al-Doping Profile and Accompanying Electrical Properties of Rutile-Phased TiO₂ Thin Films

Abstract

The role of Al dopant in rutile-phased TiO2 films in the evaluation of the mechanism of leakage current reduction in Al-doped TiO2 (ATO) was studied in detail. The leakage current of the ATO film was strongly affected by the Al concentration at the interface between the ATO film and the RuO2 electrode. The conduction band offset of the interface increased with the increase in the Al dopant concentration in the rutile TiO2, which reduced the leakage current in the voltage region pertinent to the next-generation dynamic random access memory application. However, the Al doping in the anatase TiO2 did not notably increase the conduction band offset even with a higher Al concentration. The detailed analyses of the leakage conduction mechanism based on the quantum mechanical transfer-matrix method showed that Schottky emission and Fowler-Nordheim tunneling was the dominant leakage conduction mechanism in the lower and higher voltage regions, respectively. The chemical analyses using X-ray photoelectron spectroscopy corroborated the electrical test results.

Asymmetry in electrical properties of Al‐doped TiO2 film with respect to bias voltage

“…The same concentration profile of Al ion in ATO films also obtained from the time-of-flight secondary ion mass spectroscopy profile and X-ray photoemission spectroscopy analysis. These results were confirmed that Al concentration both at the interface and depth-direction can be controlled by Al 2 O 3 deposition location [5]. The capacitance density of ATO films were about 95 fF/μm 2 regard- www.pss-rapid.com status solidi physica rrl less location of Al doping.…”

“…In Ref. [5], the Schottky barrier height was taken to be 1.49-1.59 eV. However, taking the reference Schottky barrier height as 1.2 eV and assigning 0.1 eV difference between the two interfaces resulted in the much better fitting with not only the J-V curve shape but also the absolute J values.…”

“…In these two cases, the interfaces with RuO 2 BE and TE must have the highest Al concentration. According to the previous report [5], these interfaces had an Al concentration of ~2 at%, whereas the opposite interfaces had a much lower Al concentration, whose precise value could not be identified due to the limited detection limit of the analysis tool (time of flight medium energy ion scattering spectroscopy). The same concentration profile of Al ion in ATO films also obtained from the time-of-flight secondary ion mass spectroscopy profile and X-ray photoemission spectroscopy analysis.…”

“…While the pioneering work of Kim et al [4] on Al-doping effect in TiO 2 used uniform doping profile of Al, more recent work by Jeon et al [5] demonstrated that precise control of Al-doping profile in ATO is possible by changing the sequence of atomic layer deposition (ALD) of Al 2 O 3 deposition cycle among the many (250 cycles for 9 nm thickness) ALD cycles of TiO 2 . They also elucidated that locating the Al-doping profile closer to the interface with RuO 2 electrodes is more beneficial to suppress leakage current while minimizing the k degradation of the bulk TiO 2 layer.…”

Recent advances in the understanding of high-kdielectric materials deposited by atomic layer deposition for dynamic random-access memory capacitor applications

“…The dielectric constant for this ATO thin film was ;60, which was significantly smaller than the expected ;100 for a rutile phase because of the decrease in crystallinity from the Al dopant. The tremendous leakage current reduction in this report was likely because Al doping increased the CBO to its ideal value via the acceptorlike characteristics of the Al ions in the TiO 2 [52,53]. These results [53,55] showed that the electrical properties of ATO depended on the Al doping profile.…”