PARMENIDE: Piezoelectric array for medical imaging and non destructive control using integrated micromechanica devices

• Unité de recherche: PCRD EU
• Numéro de projet: 99.0691
• Titre du projet anglais: PARMENIDE: Piezoelectric array for medical imaging and non destructive control using integrated micromechanica devices

Mots-clé (Anglais)

MEMS; piezoelectric thin films; medical imaging; micromachining

Autre Numéro de projet (Anglais)

EU project number: G1RD-1999-00174

Programme de recherche (Anglais)

EU-programme: 5. Frame Research Programme - 1.3.1 Innovative products, processes and organization

Description succincte (Anglais)

See abstract

Partenaires et organisations internationales (Anglais)

Coordinator: LCR, Orsay (F)

Résumé des résultats (Abstract) (Anglais)

Since a few years, micromachined ultrasonic transducers (MUT) are investigated for phased arrays in high frequency acoustic imaging to overcome resolution and frequency limits of reticulated bulk PZT transducers applied today. The basic element consists of a micromachined membrane that is driven by either capacitive or piezoelectric actuation (pMUT). In this project, thin membranes coated with Pb(ZrxTi1-x)O3 (PZT) thin films are studied for pMUT applications. The first part of this project is devoted to fabrication processes. Major issues are the quality of the PZT films, the overall low stress of the membranes, and the precision of the patterning processes. A second part deals with the characterization of cantilever and membrane structures. Measurements and finite element simulations are compared to deduce important material parameters such as in-plane stiffness and effective e31 of PZT. The obtained database serves for later design optimization by finite element calculations. Fluid-acoustic elements added to the membrane models allow the fluidic load and acoustic emission in immersion applications to be taken into account. Experimental and simulation results are used to design a transducer for high frequency medical imaging.
Micromachined ultrasonic transducer cells and arrays containing 2 µm thick, textured PZT thin films have been fabricated and demonstrated in the frequency range of 60 kHz (1 mm diameter) to 1.8 MHz (300 µm diameter). Effect of membrane shape, top electrode size and liberation of structure on coupling factor was evaluated. Coupling factors up to 25 percent have been obtained for round, suspended membranes operating at 800kHz. Parasitic capacitance has been suppressed by adding an isolation layer in non-active part of transducer. Strong effect of dc bias on resonance frequency and coupling factor has been observed for low frequency transducers. Linear and 2D arrays were evaluated in frequencies between 1 and 2 MHz. Important reproducibility of resonance frequencies has been obtained.
Finite element modeling with experimentally verified piezoelectric coefficients indicate that pMUT devices of 140 µm diameter working at 4 to 6 MHz could achieve satisfying pressure amplitudes.

Références bases de données (Anglais)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 99.0691