Zhihong Wang

Ferroelectric and Domain Properties of 0.55Pb(Sc1/2Ta1/2)O3-0.45PbTiO3 Thin Films

Highly oriented 0.55Pb(Sc 1/2 Ta 1/2 )O3-0.45PbTiO 3 (PSTT) thin films were prepared by RF magnetron sputtering. The x-ray diffraction patterns show that the films were highly (220) preferred orientation. The piezoresponse force microscopy observations show that both in-plane and out-of-plane polarization exist in the same areas of the film. This films possess dielectric constant ϵ r = 570 with loss tg δ = 0.03 at 1 kHz. Ferroelectric hysteresis loop of this film showed the remanent polarization 2P r and the coercive field 2E c were 52 μC/cm2, 172 kV/cm, respectively. The leakage currents of the films at ± 200 kV/cm were in the order of 10−7A/cm2.

Nanoscale capacitance spectroscopy characterization of AlGaN/GaN heterostructure by current-sensing atomic force microscopy

A current-sensing atomic force microscopy was set up to measure the nanoscale capacitance spectroscopy of the two-dimensional electron gas (2DEG) of AlGaN/GaN heterostructures. The variation in the contact radius of the probe, which is important for the quantitative characterization of 2DEG, was experimentally determined by monitoring the resistive variation of the probe-sample contact and theoretically studied by numerical calculation. The current-sensing method is able to detect the change in Schottky barriers of the probe-sample contact, which affects the measurement of the threshold voltage of 2DEG. By fitting the nanoscale capacitance spectroscopy with numerical calculations, the concentration of 2DEG was quantitatively characterized. The result was comparable with that of macroscopic measurements.

The Domain Structure and Pyroelectric Properties of (111) Preferred Oriented PLT Thin Films Prepared By RF Magnetron Sputtering

The Pb0.9La0.1Ti0.975O3 (PLT10) thin films were grown on Pt/Ti/SiO2/Si(100) substrates by using RF magnetron sputtering. The crystalline and domain properties of PLT 10 thin films were studied by using X-ray diffraction (XRD) and piezoresponse force microscopy (PFM). It was found that the head-to-tail polarization configurations exist constantly in PLT thin films, indicating that the low electrical energy configurations are quite common in PLT thin films. Nanoscale banded 90deg a-a domain patterns as small as 30 to 60 nm in width were clearly visualized in the PLT thin films. The banded domain alternated in adjacent lamellae which are a result of mechanical strains at the surface and the interface between the substrate and the PLT thin films is more stable. The PLT films have relatively large pyroelectric coefficient gamma=2.20times10-8 Cldr(cm2ldrK)-1 and relatively high figures of merit. Hence PLT10 thin films could be applied widely in IR detectors or uncooled focus plane arrays.

Nanoscale banded 90° domain patterns in (111) oriented (Pb,La)TiO3 thin films

Lanthanum doped lead titanate ferroelectric thin films were grown on Pt∕Ti∕SiO2∕Si(100) substrates using rf magnetron sputtering. X-ray diffraction patterns show that the main phase of the films is tetragonal perovskite with preferred orientation of (111) perpendicular to the substrate. We investigated the ferroelectric domain patterns and the corresponding polarization arrangements of the films using piezoresponse force microscopy. Head-to-tail polarization configurations were often found to exist, indicating that the low electrical energy configurations are quite common in these thin films. Nanoscale banded 90° a-a domain patterns as small as 30–60nm in width were observed. The banded domains alternated with adjacent lamellae can be attributed to mechanical strains at the surface and at the interface between the substrate and the film.