Mathieu J. E. Ulenaers

Stresses in Pt/Pb(Zr,Ti)O3/Pt thin‐film stacks for integrated ferroelectric capacitors

A study of the stresses in a ferroelectric capacitor stack deposited on an oxidized silicon substrate is presented. The capacitor stack was prepared with sputtered Pt bottom and top electrodes and a ferroelectric film of composition PbZrxTi1−xO3 (PZT) with x≊0.5 which was deposited using a modified sol‐gel technique. The stresses were determined by the changes in the radius of curvature of the wafer following the deposition steps, during and after annealing treatments, and after etching steps in which the top electrode, the PZT film, and the bottom electrode were successively removed. The largest stress effects are found in the Pt electrodes which are deposited under conditions giving an intrinsic compressive stress. An annealing treatment exceeding 500 °C changed the stress of the bottom electrode from ≊−750 MPa (compressive) to a large tensile stress (≊1 GPa). This stress is largely thermal and is caused by the differences in thermal‐expansion coefficients of the Pt film and the Si substrate. The stress...

Nanosecond switching of thin ferroelectric films

The switching time (ts) for polarization reversal in ferroelectric films of PbZr0.53Ti0.47O3 and La‐substituted PbTiO3 has been investigated. The films were prepared by spin‐on and metalorganic decomposition followed by processing into ferroelectric capacitors having electrode areas ranging from 9 to 50 000 μm2. Pulse measurements show that under all our experimental conditions ts is instrumentally limited and that therefore the true switching time is smaller than the experimental resolution of 1.8 ns. This very fast polarization reversal can be explained by a nucleation‐rate‐controlled switching mechanism.

Dynamics and squeeze film gas damping of a capacitive RF MEMS switch

We report on measurements of the time-dependent capacitance of an RF MEMS shunt switch. A high time-resolution detection set-up is used to determine switching time and motion of the device. From the equation of motion the damping force is extracted. The measured damping force is found to be approximately proportional to the speed over the gap to the third power (FD v/z3), in good agreement with squeeze film damping theory. Significant influence of slip–flow effects on the motion is observed. Measurements at low pressure show underdamped harmonic oscillations in the opening motion and contact bounce effects in the closing motion. Effects of dielectric charging on the C–V curves are discussed. Experimental results are compared with electromechanical and damping simulations.

RF MEMS tunable capacitors with large tuning ratio

MEMS tunable capacitors have been fabricated in a thin-film technology for passive integration. Using a dual-gap relay-type design, continuous and reversible capacitance tuning with a tuning ratio up to 17 has been demonstrated, while requiring an actuation voltage of only 20 V. A quality factor of 150 to 500 has been measured in the frequency range of 1 to 6 GHz, making these devices very suitable as building blocks in many RF applications. These are the highest tuning ratio and quality factor reported to date for parallel-plate tunable capacitors.

Microelectromechanical tunable capacitors for reconfigurable RF architectures

This paper reports on metal-based MEMS tunable capacitors, fabricated in a thin-film process on high-ohmic silicon. Continuous and reversible tuning has been demonstrated with an average tuning ratio of 4.5. A quality factor between 100 and 300 has been obtained in a frequency range of 0.5 to 4 GHz. The combination of a high quality factor and large tuning range makes these tunable capacitors very suitable as building blocks in many radio-frequency (RF) applications. The tuning speed, temperature stability and RF power handling have been studied in terms of self-actuation. Finally, the need for a hermetic package as well as a packaging concept which can potentially provide this has been demonstrated. After packaging, the devices can be handled as standard silicon dies, making them fit very well with a system-in-package approach.

Reactive ion Etching of Pt/PbZr x Ti 1−x O 3 /Pt Integrated Ferroelectric Capacitors

Dry etching of a Pt/PbZr x Ti 1−x O 3 /Pt (Pt/PZT/Pt) ferroelectric capacitor stack with CF 4 /Ar plasmas with a reactive ion etching process for the fabrication of micrometer-sized integrated ferroelectric capacitors is described. The etch rate for both Pt and PZT is determined as a function of the process settings: Power, pressure and CF 4 -Ar gas flow ratio. A chemical enhancement of the etch rate is found for PZT. It is shown that it is possible to etch the Pt/PZT/Pt ferroelectric capacitor stack in a CF 4 /Ar plasma in a single lithographic process using patterning by photoresist masking. Redeposition processes occurring during etching are described.

High-Q integrated RF passives and RF-MEMS on silicon

A technology platform is described for the integration of low-loss inductors, capacitors, and MEMS capacitors on a high-resistivity Si substrate. Using this platform the board space area taken up by e.g. a DCS PA output impedance matching circuit can be reduced by 50%. The losses of passive components that are induced by the semi-conducting Si substrate can effectively be suppressed using a combination of surface amorphisation and the use of poly crystalline Si substrates. A MEM switchable capacitor with a capacitance switching factor of 40 and an actuation voltage of 5V is demonstrated. A continuous tuneable dual-gap capacitor is demonstrated with a tuning ratio of 9 using actuation voltages below 15V.

Processing and performance of integrated ferroelectric and CMOS test structures for memory applications

Abstract The feasibility of integrating ferroelectric thin films with silicon CMOS technology was investigated by processing a ferroelectric process evaluation module which contains ferroelectric and CMOS test structures and some memory cells. The smallest cells have a ferroelectric capacitor (FECAP) of 25 μm2. The FECAPs were made with Pt/Ti electrodes and with Pb(Zr,Ti)O3 deposited by a modified sol-gel technique or by organometallic chemical vapour deposition. The back-end processing includes the insulation and interconnection of the FECAPs and the MOS transistors. The ferroelectric processing has only a slight influence on the CMOS properties. The properties of the FECAPs improve significantly by an additional anneal in oxygen. Both CMOS and FECAP properties allow a proper functioning of the memory cells. These can be reliably operated at supply voltages as low as 3 V and pulse widths down to 20 ns. The endurance of the memory cells exceeds 1013 read/write cycles.

MEMS tunable capacitors and switches for RF applications

RF MEMS capacitive switches and tunable capacitors have been realized in an industrialized thin-film process developed for manufacturing high-quality inductors and capacitors. Combining integrated passives with high-performance tuning and switching elements on the same die offers a potential for building a new generation of RF front-ends for hand-held mobile communication. Capacitive switches with an insertion loss of 0.4 dB and an isolation of 17 dB at 1 GHz have been demonstrated. Dual-gap relay type tunable capacitors have been fabricated that show a continuous and reversible tuning ratio of 12 together with a quality factor larger than 150 at frequencies higher than 0.5 GHz. These are the highest tuning ratio and quality factor reported to date. A 0-level packaging concept that is compatible with the fabrication technology has been adopted.

Passive integration and RF MEMS: a toolkit for adaptive LC circuits

RF MEMS variable capacitors have been realized in an industrialized thin-film process for manufacturing high-quality inductors and capacitors on high-ohmic silicon. The fixed as well as the moveable electrode consists of aluminium, the native aluminium oxide is used as a dielectric. A tuning ratio of 1.35 and a switching ratio up to 29 have been measured. At RF frequencies they show low ohmic losses, which make them very suitable for use in high-quality adaptive LC networks. The feasibility of the application of switched capacitors for load switching in GSM power amplifiers has been demonstrated through simulations based on experimentally derived components and systems parameters.