Saeed Abadei

Na0.5K0.5NbO3/SiO2/Si thin film varactor

Perfectly c-axis oriented micrometer thickNa 0.5 K 0.5 NbO 3 (NKN) films have been prepared on a thermally grown ultrathinSiO 2 template layer onto a Si(001) wafer by the pulsed laser deposition technique. A x-ray diffraction θ–2θ scan reveals multiple-cell structuring of single phase NKN film along the polar axis, while filmsgrown onto amorphous ceramic (Corning) glass show a mixture of slightly c-axis oriented NKN and pyrochlore phases. This implies a small amount ofSiO 2 crystallites distributed in an amorphous matrix inherit Si(001) orientation and promotes highly oriented NKN film growth. NKN filmdielectric permittivitye ′ was found to vary from 114.0 to 107.2 in the frequency range 1 kHz–1 MHz, while the resistivity was on the order of2.6×10 10  Ω cm @ 20 kV/cm. The planar interdigital variable reactance device (varactor) based on theNKN/SiO 2 /Si thin film structure possesses a dissipation factor of 0.8% at 1 MHz and zero bias, electrical tunability of 3.1%, and nA order leakage current at 20 V bias at room temperature.

Low-frequency and microwave performances of laser-ablated epitaxial Na0.5K0.5NbO3 films on high-resistivity SiO2/Si substrates

The dielectric properties of laser-ablated 0.5-μm-thick c-axis epitaxialNa 0.5 K 0.5 NbO 3 (NKN) films on high-resistivity (>7.7 kΩ cm) siliconSiO 2 /Si substrates are studied experimentally in the temperature interval of 30–320 K and at frequencies of 1.0 MHz–40 GHz. The films are grown by laser ablation from a stoichiometric target. For the measurements, planar 0.5-μm-thick gold electrodes (interdigital and straight slot) are photolithography defined on the top surface of NKN films. The slot width between the electrodes is 2.0 or 4.0 μm. At low frequencies(f 1. At microwave frequencies(f>10 GHz), the voltage dependence of the capacitance is given by the NKN film. More than a 13% capacitance change at 40 V dc bias and a Q factor of more than 15 are observed at 40 GHz, which make the structure useful for applications in electrically tunable millimeter-wave devices

Tunable ferroelectric filter-phase shifter

Design of a tuneable filter-phase shifter is presented. Thin ferroelectric film varactors are used to provide voltage tuneable phase shift in a silicon coplanar waveguide (CPW). Varactors with zero bias capacitance 0.17pF, loss tangent tan/spl delta/-0.04 and 20% tuneability provide continuous voltage tuneable phase shift up to 90/spl deg//spl plusmn/5/spl deg/ at 19 GHz with 10% bandwidth. The figure of merit is about 30/spl deg//dB. The sizes of the phase shifter silicon chip are less than 2/spl times/5.5mm. The phase shifter is designed for possible integration in silicon MMICs.

DC field dependent properties of Na0.5K0.5NbO3/SiO2/Si structures at millimeter-wave frequencies

Dielectric properties of laser-ablated 0.5-μm-thick c-axis epitaxial Na0.5K0.5NbO3 films on high-resistivity (7.7 Ω cm) silicon SiO2/Si substrate are studied experimentally at frequencies up to 40 ...

Microwave characterization of thin ferroelectric films

A simple technique for characterization of dielectrics at high microwave frequencies is proposed and verified experimentally. The technique makes use of the measured impedance of a test structure. The latter is a simple capacitor, formed on the top of a substrate with an arbitrary number of dielectric/conductor layers and contains a material under test (MUT) layer with unknown loss tangent and dielectric constant. Assuming that all other layers are specified, a simple method is given to calculate RF impedance of such a structure enabling extraction of MUT properties

Strain induced ferroelectrosity in epitaxial SrTiO3 films

Abstract Microwave performances of planar capacitors formed on epitaxial SrTiO 3 (STO) films reveal that two-dimensional, in-plane strain in the film lead to a formation of a stable non-cubic, low symmetry ferroelectric phase. The residual polarization vector has two stable states, normal to the film surface, and may be switched under applied DC bias. Due to the charges in surface/interface levels, the films may contain either a single or opposing domains.

Analytic approximations for multilayer substrate coplanar-plate capacitors

Closed form analytic approximations are proposed for complex impedance (capacitance and Q-factor) of capacitors formed by two coplanar rectangular conducting patches sandwiched between dielectric layers. The computations using proposed formulas are at least an order of magnitude faster in comparison with the commercially available softwares, and can be used in optimisation procedures. The formulas are reversible, i.e. from measured impedance one can compute permittivity and losses of one of the dielectric layers.

Silicon substrate integrated ferroelectric microwave components

Advantages of ferroelectrics integrated with silicon substrate for tunable microwave applications are discussed. Tunable microwave devices based on coplanar-plate and parallel-plate ferroelectric varactors are considered. It is shown that tunable ferroelectric devices integrated with silicon substrate may be considered for commercial applications above 10–20 GHz.

Thin Na0.5K0.5NbO3 Films for Varactor Applications

Single phase Na 0.5 K 0.5 NbO 3 (NKN) thin films have been pulsed laser deposited on SiO 2 /Si(C-01) wafers and LaAlO 3 (001) and MgO(001) single crystals. Radio frequency (up to 1 MHz) and microwave (up to 50 GHz) dielectric spectroscopy studies have been carried out to characterize thin NKN films for electrically tunable microwave device applications. Films on single crystal oxide substrates showed tunabilities as high as 30-40 % at 40 V bias and dissipation factor of 0.01-0.02 at 1 MHz. The films on Si substrates showed low dielectric losses of

Microwave properties of tunable capacitors basee on magnetron sputtered ferroelectric Na0.5K0.5NbO3 film on low and high resistivity silicon substrates

Abstract In this work, small signal DC voltage dependent dielectric permittivity, loss tangent, and tuneability of magnetron sputtered epitaxial Na0.5K0.5NO3 films are studied experimentally. (100)-oriented Na0.5K0.5NbO3 films are deposited onto SiO2-buffered CMOS grade low resistivity (p = 10–20 Ωcm) and high resistivity (p = 15–45 kΩcm) silicon substrates. Planar capacitors with 2 or 4 μm gaps between electrodes have been fabricated on top of ferroelectric films. These devices have been characterized in the frequency range 1.0 MHz to 50 GHz at temperatures 30 – 300K. Na0.5K0.5NbO3/SiO2/Si structures on high resistivity silicon substrate exhibit C-V performances typical for Metal-Insulator-Semiconductor (MIS) capacitors. At low frequencies, f< 1.0 GHz, the large tuneability and large losses are associated with the MIS structure, while at higher microwave frequencies the tuneability is mainly associated with the ferroelectric, film. At 1.0 MHz and room temperature, the tuneability of Na0.5K0.5NbO3/SiO2/Si structures more than 90%, reducing to 10–15 % at 50 GHz. The losses decrease with increasing the DC bias and frequency. A Q-factor more than 15 at 50 GHz is observed. The dielectric permittivity of the Na0.5K0.5NbO3 film is in the range 50–150 at frequencies 0.045–50 GHz. On low resistivity substrate the performance of Na0.5K0.5NbO3 films is completely screened by the high losses in silicon, and the tuneability is negligible.