Publications by Nicolas Ledermann

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This work dealt with the establishment of a reproducible and industrially exploitable fabrication technology for piezoelectric MEMS based on PZT thin films. {100}-textured piezoelectric 1-4 μm thick films were found to be the most suited materials for MEMS applications where a strong transverse e31,f coefficient is required. Values of 11.5 to 12.5 C/m2 throughout the investigated thickness range have been obtained. PZT MEMS requires some special microfabrication processes. The patterning of platinum electro

This paper describes fabrication and characterization results of piezoelectric micromachined ultrasonic transducers (pMUTs) based on 2-mu m-thick Pb(Zr0.53Ti0.47O3) (PZT) thin films. The applied structures are circular plates held at four bridges, thus par ...

Novel, highly sensitive piezoelectric acoustic sensors based on partially unclamped Pb(Zr-x, Ti1-x)O-3 (PZT) coated cantilever and bridge have been fabricated by silicon micromachining. High sensitivity at low frequencies (5-100 Hz) has been achieved by patterning very narrow slits (3 to 5 mum) around the structures. A typical response of 100 mV Pa-1 and a noise equivalent pressure of 1.6 mPa Hz(1/2) at 20 Hz have been measured using a 10 pF charge amplifier. Stress compensation, dry etching and integration

Ferroelectric capacitive devices for memory and MEMS applications require patterned ferroelectric thin films with high anisotropic etched features. In this paper, physical and chemical parameters during etching of Pb(Zr0.53Ti0.47)O-3 (PZT) by a dual frequency ECR/RF reactor have been investigated. The removal characteristics of blanket films and films with a patterned mask were investigated as a function of gas chemistry (Ar, halogen gases), substrate bias RF power and working pressure (from 5 x 10(-4) Pa t

Ferroelectric thin films for memory and MEMS applications require noble metal or refractory metal oxide electrodes. In this paper, physical and chemical mechanisms during platinum etching by a dual frequency ECR/RF reactor have been investigated. An ion beam was generated by means of a 50 mm diameter ECR-gun directed towards the substrate. The latter was placed on a RF powered electrode for discharging and local activation of reactive gas species. The removal characteristics of blanket platinum films and pl

Ferroelectric thin films for memory and MEMS applications require noble metal or refractory metal oxide electrodes. In this paper, physical and chemical parameters during etching of RuO2 and Pr by a dual frequency ECR/RF reactor have been investigated. The removal characteristics of blanket films and films with a patterned mask (photoresist or SiO2 masks) were investigated as a function of gas chemistry (Ar, O-2, halogen gases), ion beam energy (ion extraction/acceleration voltages), substrate bias RF power

PZT (PbZrx Ti1-xO3) thin films have been locally grown by means of sol-gel deposition and local annealing on microhotplates. The microhotplates were based on a stress compensated Si3N4 /SiO2 membranes as structural elements and contained tantalum silicide filaments (Ta5Si3) for resistive heating. Above the filaments, a passivation layer of SiO2, an adhesion layer of Ti/TiO2 and a bottom electrode of Pt were deposited. Due to the low heat conductivity of the membrane, crystallization of the PZT film occurs e

Piezoelectric micromachined ultrasonic transducers for airborne and immersed applications working in the frequency range from 20 kHz in liquid to 750 kHz in air have been fabricated and characterized, as well as simulated by finite element modelling. The basic element consisted of a oxidized and platinized silicon membrane coated with a 2 mum thick (100)-textured Pb(Zr,Ti)O-3 (PZT) thin film deposited by sol-gel techniques. SOI wafers have been applied to obtain a good definition of the silicon part of the

There is a need for chemically resistant coatings that protect the exposed surface of microfluidics components. Pinhole free films with low stress and a good uniformity on flat and inclined surfaces are required. In this study, amorphous silicon carbide (SiC) thin films have been deposited by RF magnetron sputtering on hat surfaces and into micromachined cavities of Si (100). The variation of RF power, deposition pressure and substrate bias voltage have been studied. Depending on the deposition conditions,

PZT thin films for memory applications are known to lack sufficient resistance versus polarization fatigue when used together with platinum. One possible solution for this problem is to use conductive oxides like La1-xSrxCoO3 (LSCO) as an electrode. In this paper LSCO thin films were deposited via RF magnetron sputter deposition (face to face configuration) from a single oxide target. Changing the layer beneath LSCO at 750 degrees C and an RF Power of 50 W on SiO2/Si, the film is slightly (100) textured. A.

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) imaging is employed to characterize the surface of patterned noble metal (Pt) and titania (TiO2) thin films deposited on oxidized silicon wafers. ToF-SIMS is used to follow the different process steps during the thin films patterning as well as the post-processing cleaning. Both positive and negative ToF-SIMS modes reveal the presence of contaminants, due to the etching processes (Cl- Al-,(+)), but only on the etched surfaces. Elements due to the pos

The effective piezoelectric coefficient e(31) has been measured on sol-gel processed Pb(ZrxTi1-x)O-3 thin films with Zr concentrations ranging from 45 to 60%. The largest value was observed at 45% Zr, although dielectric constant and effective d(33) peak at 53% Zr. The findings suggest that the optimal composition for microactuators and sensors is less than or equal to 45% Zr, i.e., in the tetragonal part of the phase diagram.

Pb(Zr-x, Ti1-x)O-3 (PZT) piezoelectric thin films are of major interest in MEMS technology for their ability to provide electro-mechanical coupling. In this work, the effective transverse piezoelectric coefficient e(31,f) of sol-gel processed films was investigated as a function of composition, film texture and film thickness. Dense, textured and crack-free PZT films have been obtained on silicon substrates up to a thickness of 4 mum. Crystallization anneals have been performed for every 0.25 mum. Nucleatio

New micromachined pressure sensors based on PZT coated silicon cantilevers have been fabricated and integrated in a photoacoustic gas detector. PZT Sol-gel thin films texture and composition were optimized with respect to the transverse piezoelectric coefficient e(31,f). A best value of -12 C/m(2) was obtained with (100)/(001) textured thin films at the MPB composition. Optimum stress compensation between the different layers composing the cantilever has been studied in order to yield flat cantilevers. A hi

A micro-hotplate device, useful in catalytic high-temperature chemical sensors, micro-chemical reactors and as infra-red source, in particular at temperatures above 600 DEG C, comprises a thin film resistive heater (1) made of a refractory metal silicide selected from silicides of tantalum, zirconium, tungsten, molybdenum, niobium and hafnium, the silicide having a polycrystalline structure obtainalble at temperatures above 600 DEG C. The thin film resistive heater (1) is encapsulated between insulating lay

Processing optimization allowed the sol-gel fabrication of 1 mum thick, phase pure perovskite thin films with identical grain size and controlled texture. This made it possible to fabricate stress compensated beams to measure the transverse piezoelectric coefficient over the whole composition range of PbZr1-xTixO3. The highest value of -12.1 C/m(2) was measured for (100)/(001) textured PZT53/47. For (111) textured films the maximum value of -8.7 C/m(2) was found to be in the tetragonal phase field at 55% Ti

Unexpectedly high-longitudinal piezoelectric coefficients have recently been reported in c-axis oriented Pb(Zr,Ti)O-3 thin films with morphotropic phase boundary composition [Fu , Appl. Phys. Lett. 80, 3572 (2002)]. Our analysis and experimental results show that, in comparison with other methods commonly used to investigate piezoelectric response of thin films, the charge integration technique used by Fu may lead to an order of magnitude higher apparent piezoelectric coefficients if the substrate on which

Effective transverse piezoelectric coefficient e(31,f) has been measured on (100)/(001) sol-gel Pb(ZrXTi1-X) thin films with compositions between 30% and 45% Zr. A maximum value of 8.07 +/- 0.36 C/m(2) at 40% Zr is found. The influence of the poling field ranging from 50 kV/cm to 250 kV/cm has been evaluated.

Nicolas Ledermann

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Piezoelectric acoustic sensors and ultrasonic transducers based on textured PZT thin films

Piezoelectric micromachined ultrasonic transducers based on PZT thin films

Piezoelectric Pb(Zr-x,Ti1-x)O-3 thin film cantilever and bridge acoustic sensors for miniaturized photoacoustic gas detectors

Mechanisms of Pb(Zr0.53Ti0.47)O-3 thin film etching with ECR/RF reactor

Etching of platinum thin films with dual frequency ECR/RF reactor

Etching of RuO2 and Pt thin films with ECR/RF reactor

Local growth of sol-gel films by means of microhotplates

Simulation and characterization of piezoelectric micromachined ultrasonic transducers (PMUT's) based on PZT/SOI membranes

Sputtered silicon carbide thin films as protective coating for MEMS applications

La1-xSrxCoO3 as electrode materials for ferroelectric thin film applications

Imaging by time-of-flight secondary ion mass spectrometry of plasma patterned metal and oxide thin films

In-plane piezoelectric coefficient of PZT thin films as a function of composition

{100}-textured, piezoelectric Pb(Zr-x Ti1-x)O-3 thin films for MEMS: integration, deposition and properties

Piezoelectric cantilever microphone for photoacoustic GAS detector

High temperature micro-hotplate

Processing optimization of solution derived PbZr1-xTixO3 thin films for piezoelectric applications

Piezoelectric response of thin films determined by charge integration technique: Substrate bending effects

Effective transverse piezoelectric coefficient e(31,f) of (100)/(001) textured PZT thin films