Scott Harada

Sputtering of (001)AlN thin films: Control of polarity by a seed layer

The authors report on the ability to control the polarity of sputter deposited AlN(001) thin films using seed layers. Reactive sputter deposition leads to N-polarity on any substrate hitherto applied, i.e., Si(111), sapphire, SiO2, and polycrystalline metals such as Pt(111), Mo(110), and W(110). A site-controlled polarity allows for an efficient excitation of shear modes of surface, bulk, and Lamb waves by interdigitated electrodes. The authors were able to introduce the Al-polarity through a metal-organic chemical-vapor deposition seed layer. By subsequently patterning the substrate surface, it was possible to define the desired film polarity of sputter deposited AlN film. Polarities were determined by selective etching with KOH solutions and by piezoresponse force microscopy.

Strong improvement in the photonic stop-band edge sharpness of a lithium niobate photonic crystal slab

We report on a photonic crystal (PhC) etched into a 380 nm thick lithium niobate (LN) thin film deposited on a MgO substrate by pulsed laser deposition. The transmission properties of this device were assessed by optical near-field measurements and compared to the transmission spectra of the same PhC drilled into bulk LN and calculated by a two dimensional finite-difference time domain method. We show a strong improvement in the transmission properties of the LN PhC by etching it into a thin layer rather than into a 500 µm thick wafer. This result appears to be very promising for applications based on LN tunable PhCs.

Combinatorial Discovery and Optimization of Amorphous HfO2-Nb2O5 Mixture with Improved Transparency

Combinatorial high vacuum chemical vapor deposition (HV-CVD) of mixed HfO2-Nb2O5 thin films has been demonstrated to yield amorphous layers at substrate temperatures where individually deposited pure HfO2 and Nb2O5 films are polycrystalline. Spectroscopic ellipsometry of the films shows that adding HfO2 to Nb2O5 improves the transparency of the films while still maintaining a high refractive index. Atomic force microscopy measurements show that the root-mean-square surface roughness of the films is about 1.2 nm

Combinatorial Chemical Beam Epitaxy of Lithium Niobate Thin Films on Sapphire

A combinatorial chemical beam epitaxy technique was used to optimize deposition of (001) lithium niobate thin films on {001} sapphire substrates. Lithium tert-butoxide [Li(OBut)] and niobium tetra-ethoxy di-methyl-amino-ethoxide [Nb(OEt)(4)(dmac)] were used as precursors. The highest quality films obtained exhibited rocking curve full-width at half-maximum values of about 0.03 degrees and lithium contents {[Li]/[(Li)) + (Nb)]} larger than 48 (mol %) estimated by Raman spectroscopy. High-resolution transmission electron microscopy observations revealed that the lithium niobate film consists of a buffer layer (thickness <8 nm) with a high density of defects above which the epitaxial lithium niobate film was obtained

Pulsed laser deposition of KNN-based ferroelectric thin films on platinised Si substrates

In this paper we report work on a modified potassium sodium niobate composition that has the potential to replace PZT for piezoelectric thin film applications. Pulsed laser depositions were undertaken on platinised Si substrates. The resultant films were found to be well-oriented in the [100] direction and almost phase-pure. TEM analysis of film cross-sections revealed the grain structure to be highly columnar. Values for P-s = 3.8 mu C/cm(2) and E-c = 20 kV/cm were derived from polarisation hysteresis measurements for a 32 mu m thick film. Finally, piezoresponse force microscopy was used to map the local piezoelectric activity down to the level of individual grains in the film.

Geometry of Chemical Beam Vapor Deposition System for Efficient Combinatorial Investigations of Thin Oxide Films: Deposited Film Properties versus Precursor Flow Simulations

An innovative deposition system has been developed to construct complex material thin films from single-element precursors by chemical beam vapor deposition (CBVD). It relies on well distributed punctual sources that emit individually controlled precursor beams toward the substrate under high vacuum conditions combined with well designed cryo-panel surfaces that avoid secondary precursor sources. In this configuration the impinging flows of all precursors can be calculated at any substrate point considering the controlled angular distribution of the emitted beams and the ballistic trajectory of the molecules. The flow simulation is described in details. The major advantage of the deposition system is its ability to switch between several possible controlled combinatorial configurations, in which the substrate is exposed to a wide range of flow compositions from the different precursors, and a uniform configuration, in which the substrate is exposed to a homogeneous flow, even on large substrates, with high precursor use efficiency. Agreement between calculations and depositions carried out in various system configurations and for single, binary, or ternary oxides in mass transfer limited regime confirms that the distribution of incoming precursors on the substrate follows the theoretical models. Additionally, for some selected precursors and in some selected conditions, almost 100% of the precursor impinging on the substrate is incorporated to the deposit. The results of this work confirm the potentialities of CBVD both as a research tool to investigate efficiently deposition processes and as a fabrication tool to deposit on large surfaces.

Efficient optimization of high vacuum chemical vapor deposition of niobium oxide on full wafer scale

A systematic study of niobium oxide deposition using niobium tetraethoxy-dimethyl- amino-ethoxide (Nb(OEt)4(dmae)) precursor is presented. The deposition process was conducted in a high-vacuum chemical vapor deposition machine with precursor flux gradient capability. An efficient optimization of the deposition process was achieved and both mass-transport- and chemical-reaction-limited regimes were identified.