Haoran Zheng

Fully transparent thin-film varactors: fabrication and performance

We report the fabrication of fully transparent thin-film varactors using a dielectric material, barium strontium titanate (Ba0.6Sr0.4TiO3, BST), as an electric field tunable layer, transparent conductive oxide (Sb doped SnO2, ATO) as a bottom electrode and ATO/Ag tri-layer film as a top electrode. This kind of varactor using ATO/Ag/BST/ATO capacitors shows a transmittance of about 80% (including the substrate) in the visible region, a medium capacitance of about 463 pF, a low loss tangent of about 0.015, and superior tunable dielectric properties at room temperature. Calculations of dielectric tunability and figure of merit (FOM) display a maximum value of ∼53% at 560 kV cm−1 and ∼66, respectively. We believe that the transparent thin-film varactors using ATO/Ag/BST/ATO capacitors presented in this paper could be a milestone for future see-through electronic devices.

Low loss, high tunable BaZr0.2Ti0.8O3/BaSn0.85Ti0.15O3 heterostructure thin films

Ferroelectric BaZr0.2Ti0.8O3/BaSn0.85Ti0.15O3 (BZT/BTS) heterostructure thin films (∼200-nm-thick) have been prepared on Pt/TiOx/SiO2/Si substrates by pulsed laser deposition. The heterostructure thin films are crack free, compact, and crystallized in a perovskite structure. Dielectric measurements indicate that the BZT/BTS heterostructure thin films exhibit a low dielectric loss of below 0.007, a medium dielectric constant of ∼441, and the superior tunable dielectric properties at room temperature. Calculations of tunability and figure of merit (FOM) display a maximum value of 68.5% at 500 kV/cm and ∼101, respectively. The FOM value is higher than that of the single-layer BTS and BZT thin films. A brief discussion is given on the lower loss compared to the single-layer thin films. The results indicate that BZT/BTS heterostructure thin films are excellent candidates for electrically steerable applications.

Improved performance of transparent-conducting AZO/Cu/AZO multilayer thin films by inserting a metal Ti layer for flexible electronics

In order to improve the performance of transparent conductive Al-doped ZnO (AZO)/Cu/Al-doped ZnO multilayer thin films, multilayer thin films of titanium-embedded AZO/Cu/AZO structures have been designed and deposited onto flexible polycarbonate substrates to develop an indium-free transparent flexible electrode. The effect of Ti layer on the structural, optical, and electrical properties of multilayer thin films was investigated. The experiments reveal that the AZO/Ti/Cu/AZO fabricated in argon-oxygen mixtures has the best performance (commutation quality factor of 422.0): resistivity of 3.85×10-5  Ω·cm, sheet resistance of 4.31  Ω/sq, carrier concentration of 1.65×1022  cm-3, mobility of 9.87  cm2/Vs, and acceptable luminous transmittance of above 82% in the visible range.