Integration of ferroelectric thin films into silicon based microsystems

The integration of ferroelectric materials will enhance the functionality of conventional microsystems. The converse piezoelectric effect can be used for the fabrication of integrated actuators, which will help to realize integrated high frequency switches. The aim of this thesis is the integration of ferroelectric thin films into silicon based microsystems. Therefore, PZT thin films have been deposited on platinum coated silicon substrates by chemical solution deposition (CSD) and are characterized regarding their electrical and electromechanical properties. It has been shown that PZT with a composition of 45% zirconium and 55% titanium shows a very high piezoelectric coefficient of 115 pm/V. Moreover it has been proved that no electromechanical fatigue occurs, if the material is driven with unipolar electric fields. Lead hafnate titanate (PHT) is a variation of PZT and doping with 10% lanthanum leads to an electrostrictive behavior. Thereby, the piezoelectric coefficient is around 60 pm/V and nearly independent on the applied electric field, which leads to a linear strain behavior. The investigation of the permittivity of barium strontium titanate (BST) shows a linear decrease with increasing temperatures. This effect is used for the detection of infrared radiation. For the fabrication of silicon based microsystems a variety of technologies have been developed for the structuring of ferroelectric thin films, platinum electrodes, silicon and silicon dioxide. The release of cantilevers and membranes is performed by back etching with TMAH, isotropic etching with SF6 plasma and by a sacrificial process. The latter one is based on silicon on insulator substrates, whereby the buried oxide is etched with HF-vapor. Furthermore, a process for the fabrication of freestanding copper bridges was developed. A number of cantilevers relying on the converse piezoelectric effect were fabricated and characterized with a laser vibrometer regarding the displacement and the resonance frequency. The measurement results are in good agreement with finite element simulations. A maximum displacement of 80 µm was measured at an applied voltage of only five volts. This is several times more than can be achieved with electrostatic actuation. Further development leads to the fabrication of a microrelay, which than was integrated in an high frequency switch. Simulations show that this novel piezoelectric concept reaches a switching level of more than 20 dB up to 20 GHz. Further fabricated microsystems are thin film bulk acoustic resonators (TFBAR) relying on the generation of acoustic waves due to electrostriction and showing a resonance at 6.2 GHz as well as a dielectric bolometer for the detection of infrared radiation. Beyond, experiments with PZT coated metal foils exhibit higher spontaneous polarization than obtained on platinum coated silicon. From the experiments, cantilevers using the metal foil as flexible substrate were fabricated with fine mechanical techniques showing a displacement of 35 µm.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2006

Author dc:creator

• Kügeler, Carsten

Contributors dc:contributor

• Waser, Rainer

• info:eu-repo/classification/ddc/620
• Ingenieurwissenschaften
• MEMS
• PZT
• Piezoelektrischer Aktor
• ferroelektrische Dünnschicht
• Hochfrequenzschalter
• RF switch
• TFBAR
• ferroelectric thin film

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

eng

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-123532%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:61920