Lithium Niobate Films Research Articles

Characterization of field-effect transistors with lithium niobate gates for memory applications

Abstract Thin films of lithium niobate were r.f. sputtered on device structures† which were then processed using a molybdenum based lift-off procedure. This procedure facilitated the fabrication of ferroelectric gate field-effect transistors without the use of complicated alignment and etch techniques. The resulting transistors had a .5 μm gate layer of lithium niobate. The molybdenum lift-off procedure will be described, as well as the application of the lithium niobate transistors to memory devices.

Crystallization kinetics of lithium niobate films from limited volume of melt solution

AbstractThe growth kinetics of LiNbO3 films from a limited volume of melt solution is observed. We developed crystallization models describing the character of mass transfer in the liquid phase for isothermal and non‐isothermal epitaxy. Analytical expressions have been derived connecting the film thickness with the system growth parameters. The experimental values being in good agreement with the calculated ones.

Magnetron sputtered lithium niobate films

The preparation of lithium niobate films on Corning 7059 glass by rf planar magnetron sputtering in an Ar+40% O 2 mixture has been studied at 2 mtorr. Films deposited on unheated substrates became crazed by realese of a tensile stress arising from the difference between the expansion coefficient of the glass and the coating. Improvement of surface cleanliness by discharge cleaning or solvent degreasing using iso-propyl alcohol in a Soxhlet extractor enhanced the film/substrate adhesion. This prevented crazing, but the transparent films produced were still under stress. Glass surfaces cleaned sufficiently for high film adhesion had a coefficient of static friction, glass on glass, of greater than ∼0.8. A lithium niobate powder target was used because the uneven heating arising from magnetron discharge localization resulted in fracture of single crystal material. Care was taken to remove all water vapour from the discharge atmosphere uing liquid nitrogen traps, for without these the coatings produced were optically absorbing, due to oxide reduction, presumably formed by an active hydrogen reaction. The refractive index of the films, as determined from their waveguiding characteristics, was in the region of 2.10–2.20. Trial coatings grown at 380°C and above had indices in the region of 2.19; these high temperature films were also transparent but under tensile stress. The growth rates ranged from 9.5å min −1 for a substrate temperature of 380°C to 11.5 å min −1 for a substrate temperature of 470°C.

The growth of thin films of lithium niobate by chemical vapour de position

The growth of single crystal films of LiNbO 3 on LiTaO 3 substrates of (1010) orientation by chemical vapour deposition is described. The complex of Li with 2, 2, 6, 6 tetramethylheptane 3, 5 dione is used as the volatile Li source and Nb pentamethylate is used as the Nb source. After deposition at 450°C, using Ar carrier gas and O 2 to oxidise the organometallic compounds, the layer is heated at 1000°C in O 2 to convert it into single crystal LiNbO 3. The structure functions as an optical waveguide but the losses are about 40 dB/cm.

Fabrication of Lithium Niobate Light Guiding Films

In optical communications systems lithium niobate films could play an important role due to the large electrooptic, acousto-optic and non linear coefficients of this material. In this paper we discuss two methods for preparing such films and the resultant film properties. The methods used are out diffusion and R. F. sputtering. The basic element in integrated optics is the thin film optical waveguide. A light guiding layer is one which have an index of refraction higher than that of the surounding materials. On LiNbO3 this can be achieved by varying the Li/Nb ratios by out diffusion of Li from a monocrystal, or by appropriately controlling the sputtering conditions when depositing LixNbyO3 films onto a lower index substrate such as LiNbO3, glass, etc. ... This usually leads to polycrystalline films. In out-diffusion we have an index gradient waveguide extending into the bulk material with a large depth below the surface (∼100–350 µm). Sputtered films have an abrupt index discontinuity with a lower thickness (1–10 µm). Both techniques will be discussed and compared.