Freddy Ponchel

Microwave properties of epitaxial (111)-oriented Ba0.6Sr0.4TiO3 thin films on Al2O3(0001) up to 40 GHz

Perovskite Ba0.6Sr0.4TiO3 (BST) thin films have been grown on Al2O3(0001) substrates without/with inserting an ultrathin TiOx seeding layer by rf magnetron sputtering. X-ray diffraction and pole figure studies reveal that the film with the TiOx layer (12-A-thick) is highly oriented along the (111) direction and exhibits a good in-plane relationship of BST(111)∥Al2O3(0001). The high frequency dielectric measurements demonstrate that the complex permittivity (e=e′−je″) is well described by a Curie–von Scheidler dispersion with an exponent of 0.40. The resulting epitaxial BST films show high permittivity (∼428) and tunability (∼41%, at 300 kV/cm and 40 GHz) and their microwave properties (1–40 GHz) potentially could be made suitable for tunable devices.

Dielectric microwave characterizations of (Ba,Sr)TiO3 film deposited on high resistivity silicon substrate: Analysis by two-dimensional tangential finite element method

(Ba,Sr)TiO3 (BST) thin films were deposited on high resistivity silicon substrates by in situ rf magnetron sputtering. A buffer layer was used to improve the cristallinity of the films, the composition was fixed to Ba/Sr=30/70. The relative permittivity and the losses were measured up to 60 GHz using coplanar strip lines. The dispersion of the permittivity and the losses has been determined with a home made numerical code based on finite elements: ELFI. We show that, with the measurements of the scattering parameters coupled with ELFI, it is possible to know the BST complex permittivity over a very broad frequency band. The BST films deposited by in situ (700 °C) present excellent properties between 1 to 60 GHz. The relative permittivity is in the order of 270 and the losses are very small 0.09 at 60 GHz. These structures BST/silicon high resistivity show good potentialities for devices microwaves applications which need future integration in a silicon environment.

Microwave evaluation of Pb0.4Sr0.6TiO3 thin films prepared by magnetron sputtering on silicon: Performance comparison with Ba0.3Sr0.7TiO3 thin films

Pb0.4Sr0.6TiO3 (PST) thin films were deposited on high resistivity silicon substrate by radio frequency magnetron sputtering. A pure perovskite phase was obtained at a low post annealing temperature of 650 °C. The relative dielectric constant, loss factor, tenability, and figure of merit were determined over a large frequency range of 1 GHz to 60 GHz. A large tunability about 60% and a relatively low loss of 16% at 60 GHz were obtained. PST is an alternative material for microwave agile devices integrated with silicon and this is discussed from the standpoint of monolithic integration with a low thermal budget.

Broadband Dielectric Characterization of Sapphire/TiO x /Ba 0.3 Sr 0.7 TiO 3 (111)-Oriented Thin Films for the Realization of a Tunable Interdigitated Capacitor

A complete microwave characterization up to 67 GHz using specific coplanar waveguides was performed to determine the dielectric properties (permittivity, losses, and tunability) of sapphire/TiOx/Ba0.3Sr0.7TiO3 (BST) (111)-oriented thin films. To that end, BaxSr1-xTiO3 thin films were deposited by RF magnetron sputtering on sapphire (0001) substrate. To control the preferred (111) orientation, a TiOx buffer layer was deposited on sapphire. According to the detailed knowledge of the material properties, it has been possible to conceive, fabricate, and test interdigitated capacitors, the basic element for future microwave tunable applications. Retention of capacitive behavior up to 67 GHz and a tunability of 32% at 67 GHz at an applied voltage of 30 V (150 kV/cm) were observed. The Q-factor remains greater than 30 over the entire frequency band. The possibility of a complete characterization of the material for the realization of high-performance interdigitated capacitors opens the door to microwave device fabrication.

X-ray combined analysis of fiber-textured and epitaxial Ba(Sr,Ti)O3 thin films deposited by radio frequency sputtering

A complete study is given in this paper on the structural properties of Ba(Sr,Ti)O3 (BST) thin films which present various preferred orientations: (111) and (001) fiber and epitaxial textures. The films are deposited in situ at 800 °C by sputtering on Si/SiO2/TiOx/Pt substrates and the orientation is controlled by monitoring the concentration of O2 in the reactive plasma or by prior deposition of a very thin TiOx buffer layer between BST films and substrates. The epitaxial films are obtained on (001)-alpha-Al2O3 substrates covered with TiOx buffer layers. In order to analyze finely the preferred orientations, the texture, the microstructural features, and the anisotropy-related quantities such as residual stresses in the films, the conventional Bragg−Brentano θ - 2θ x-ray diffraction diagrams is shown not to be sufficient. So, we systematically used x-ray combined analysis, a recently developed methodology which gives access to precise determination of the structure (cell parameters and space group) of th...

Lead-Free α-La2WO6 Ferroelectric Thin Films

(001)-Epitaxial La2WO6 (LWO) thin films are grown by pulsed laser deposition on (001)-oriented SrTiO3 (STO) substrates. The α-phase (high-temperature phase in bulk) is successfully stabilized with an orthorhombic structure (a = 16.585(1) Å, b = 5.717(2) Å, c = 8.865(5) Å). X-ray-diffraction pole-figure measurements suggest that crystallographic relationships between the film and substrate are [100]LWO ∥ [110]STO, [010]LWO ∥ [11̅0]STO and [001]LWO ∥ [001]STO. From optical properties, investigated by spectroscopic ellipsometry, we extract a refractive-index value around 2 (at 500 nm) along with the presence of two absorption bands situated, respectively at 3.07 and 6.32 eV. Ferroelectricity is evidenced as well on macroscale (standard polarization measurements) as on nanoscale, calling for experiments based on piezo-response force-microscopy, and confirmed with in situ scanning-and-tunneling measurements performed with a transmission electron microscope. This work highlights the ferroelectric behavior, at room temperature, in high-temperature LWO phase when stabilized in thin film and opens the way to new functional oxide thin films dedicated to advanced electronic devices.

Ferroelectric thin films working at microwave frequency for reconfigurable devices on silicon substrate: performances comparison between BST, PST

The dielectric microwave performance of BST and PST films is studied via tunability. The films are deposited onto silicon wafer with high resistivity using radio frequency magnetron sputtering with an in situ process for BST films and ex situ for PST films. In order to improve the crystalline quality of the films a buffer layer is introduced systematically. The films have a pure perovskite structure. The microwave test structures are coplanar line waveguides that give a complete microwave characterisation up to 67 GHz. The determination of the tunability properties at microwave frequency is obtained by measurements of the scattering parameters coupled with software, written by the authors, based on a two-dimensional vector finite element method. At 67 GHz, the BST tunability reaches a value of 29% with 30 V maximum applied voltage and the PST attains a value of 60% at the same condition. PST appears as a promising alternative material to BST for microwave tunable devices.

Proximity Effect of Neighbour Victim Lossy Interconnects on a Single Attacker and Vice Versa

Signal integrity on a set from three to eight lossy copper interconnects of less than one square micron is determined from a transient simulation based on electrical circuit representation. This circuit is deduced from a full wave finite element method. Our signal integrity results on numerous possible excitations show that two neighbour interconnects on both sides of a reference aggressor or victim is sufficient to predict more complex situation on largest number of wires. This means that the five interconnects case is also well appropriate. We have verified that it is the best compromise whatever the permittivity of dielectric material which filled the spacing between interconnects, as well as the width of this spacing.

Tunable Interdigitated Capacitances on Ba0.3Sr0.7TiO3 Thin-Film

BaxSr1-xTiO3 thin films were deposited by rf magnetron sputtering on sapphire substrate. A TiOx buffer layer was deposited on sapphire in order to control the (111)-preferred orientation. Specific coplanar waveguides have been fabricated on this structure and used to achieve a microwave characterization of the Ba0.3Sr0.7TiO3 up to 67 GHz. Interdigitated capacitors (IDC) were then realized on 350 nm of BST deposited on sapphire substrate. The capacitive aspect is retained up to 67 GHz. Tunablity of 35% under a low electric field (150 kV/cm) was measured up to 67 GHz.

Parasitic influence, on signal integrity, of several victim lines placed asymmetrically beside and symmetrically at both sides of an attacker interconnect and mutually

Far end crosstalk on victim lines located near an aggressor as well as rise time and propagation delay at the end of the attacker are evaluated. It is done thanks to a home made software based on full wave electromagnetic finite element and transient analysis simulation. These investigations are carried out when the aggressor lossy interconnect of less than one micron square area is symmetrically and asymmetrically placed in an arrangement of three, five and eight copper lossy lines, in case of low, medium and strong mutual effects. Our signal integrity points out that two neighbour lines on both sides of an active interconnect (i.e. the aggressor) are a good compromise to understand more complicated situation on greatest number of unintentionally coupled interconnects. We have verified this fact even in case of small spacing or high permittivity material which filled partially the spacing between interconnects (i.e. strong mutual effects).