Jean-François Legier

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.

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.

Crosstalk Phenomenon in Coupled Microstrip Lines Laid on Semi-Conducting Substrates

Crosstalk phenomena and pulse propagation in coupled microstrip lines on insulating and semiconducting substrates are analysed. Propagation characteristics of these lines are obtained by Spectral Domain Analysis in order to avoid any error involved by the use of analytical model and T.E.M. approximation. Time domain results are calculated by a conventional fast Fourier transform. Effects of semiconducting layer, substrate thickness, lines spacing and length, loading impedances, on crosstalk and transfer are investigated.

Full Wave Analysis of Conductor and Substrate Losses in High Speed VLSI Interconnects

The determination of electrical properties of interconnects represents a critical design and analysis problem in the high-speed integrated very large-scale integration (VLSI) circuit in order to minimize signal distortion due to propagation delay and dispersion. In order to accomplish this, it is necessary to analyze and model the broad-band characteristics of submicrometer interconnects since the signals tend to exhibit both the short rising and falling times. Today, most extraction and delay analysis tools are limited to RC networks leaving an inherent unpredictability in the design process where inductive and substrate effects are suspected. However, the effect of a silicon substrate, which is negligible at low frequency, has a prevalent effect on the characteristics of lines during the operation of high-speed chips. One result of this study is to give a criteria that can be used to determine that a range exist for which inductance and substrate effects are not negligible, and which nets require a complete transmission line model.

Analysis of planar transmission lines and microshield lines with arbitrary metallization cross sections using finite elements methods

Propagation analysis is proposed to determine with much accuracy as possible, the dispersion characteristics for classical planar structures as well as for the new microstrip and coplanar membrane microshield lines both for microwave and millimeter wave ranges. These transmissions lines present an arbitrary cross section for the metallization of the strips and a finite value of the conductivity. We have developed two formulations of finite element methods in order to simulate such structures in the considered frequency range, showing the influence of lossy strips corner angles.<<ETX>>

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.

Microwave characteristics of planar electrooptic modulator

An attempt is made to model traveling-wave optical modulators in the microwave frequency range by two methods: a desktop computer method based on the effective complex dielectric constant and a more rigorous method, i.e. the mode-matching technique. The aim is to quantify both bulk microwave and metallic losses and to determine the phase velocity in the microwave frequency range. This study takes into account the geometry of the cross section of the structure, the multilayered nature of the waveguide, and the hybrid nature of the mode. The two methods are compared for moderately lossy structures and shown to give quite similar results. However, when more realistic structures with highly doped multilayered substrates are considered, only the rigorous method can be used.<<ETX>>

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).

Comparison of the benefits, from S i O 2 to ultralow-K dielectric and air spacing introduction, in term of interconnects performances, for the future high speed Ic’s in a multicoupled lines system

Introduction of different low-K to ultra low-K dielectric material in the spacing between neighbour copper interconnects localised on the same level of metallization is analyzed. It is done to evaluate signal integrity such as crosstalk, propagation delay and rise time on a set of several unintentionally coupled Cu lines of micron and nanometer sizes. A full wave analysis based on tangential vector finite element method is implemented in MATLAB environment in order to extract, via a transmission multicoupled line model, the electrically R, L, C, G, Lm, Cm coupled elementary cell. This model with all the mutual impedance and admittance is necessary and more convenient for transient analysis by using commercial software such as Spice or other transient tool. We show that the improvement due to the introduction of low dielectric material can reach more than 200% for the crosstalk and 25% on propagation delay for 1 mm interconnect length. This work also highlights that it is not always realistic to study only a set of two or three lines because some signals appears at the far end of the second or the third interconnect located at the both sides of an attacker.