Browsing by Author "Dauchy, Florent"

Now showing 1 - 4 of 4
  • Thumbnail Image
    ItemOpen Access
    New Advances in Forming Functional Ceramics for Micro Devices
    (2006-10-10T00:00:00Z) Dorey, Robert A.; Rocks, Sophie A.; Dauchy, Florent; Navarro, A.
    Micro electromechanical systems (MEMS) are finding uses in an increasing number of diverse applications. Currently the fabrication techniques used to produce such MEMS devices are primarily based on 2-D processing of thin films. The challenges faced by producing more complex structures (e.g. high aspect ratio, spans, and multi-material structures) require the development of new processing techniques. Potential solutions to these challenges based on low temperature processing of functional ceramics, selective chemical patterning, and micro-moulding are presented to show that it is possible to create complex functional ceramic structures which incorporate non-ceramic conducting and support structures. The capabilities of both techniques are compared and the relative advantages of each explored.
  • Thumbnail Image
    ItemOpen Access
    Patterned crack-free PZT thick films for micro-electromechanical system applications
    (Springer Science Business Media, 2007-05-01T00:00:00Z) Dauchy, Florent; Dorey, Robert A.
    The fabrication and structuring of multilayer-thick film piezoelectric (PZT-lead zirconate titanate) structures, using composite sol-gel techniques and wet etching is described. The composite sol-gel technique involves producing a PZT powder/sol composite slurry which when spun down, yields films a few micrometres thick. Repeated layering and infiltration has been used to produce PZT films between 10 and 40 μm thick. Due to the low firing temperature (<720°C), it has also been possible to produce PZT films with embedded thin (ca. 100 nm thick) metal electrodes. The PZT thick films have also been structured using a wet etching technique. Examples of features and cavities with lateral dimensions in the order of tens of micrometres are presented. The ability to fabricate and structure thick functional films with embedded metal electrode structures offers the possibility to create novel micro-device structures suitable for use in micro-electromechanical systems (MEMS
  • Thumbnail Image
    ItemOpen Access
    Stress analysis, dielectric, piezoelectric, and ferroelectric properties of PZT thick films. Fabrication of a 50MHz Tm-pMUT annular array
    (Cranfield University, 2007) Dauchy, Florent; Dorey, Robert A.
    PZT films up to 35 μm thick were fabricated, using a composite sol gel route combining a PZT powder and a PZT sol. The maximum temperature for the process was 710°C. A demonstration of single layer and multilayer structures was given to show the flexibility of this technology. With Stoney’s Equation, studies of the in-situ film stress development as a function of the film thickness and density was effectuated. It helped to understand that the internal forces increase considerably with the film thickness and density. This study yields to set up experimental conditions in which a crack free surface finish of a 28μm thick film revealed the adaptability of the spin coating technique to fabricate thick films. The wet etching technology revealed the possibility of a great adaptability to pattern and shape innovative devices such as bars 10 μm wide of 21μm PZT thick film. The results open the way to a wide range of new industrial application requiring small features and/or multilayer PZT thick film with embedded electrodes. The single element and annular array devices have been shown to resonate at approximately 60MHz in air and 50 MHz in water. Three types of the composite thick film – 2C+4S, 2C+5S and 2C+6S – were used to fabricate the Tm-pMUT devices. In each case the most effective poling was obtained by maintaining the poling field of 8.4V/μm during cooling from the poling temperature (200ºC) to ‘freeze’ poled domains in place. This ‘freezing’ was required to prevent the tensile stresses within the film from reorienting the domains at high temperatures when the poling field is removed. Increasing values of thickness mode coupling coefficient (kt) were observed with increasing levels of sol infiltration (decreasing density). Such behaviour is thought to be due to non linear effects on the piezoelectric coefficient (e33) at high levels of porosity. For very dense thick film material a kt of 0.47 was observed which is comparable to that observed for the bulk material.
  • Thumbnail Image
    ItemOpen Access
    Thickness mode high frequency MEMS piezoelectric micro ultrasound transducers
    (Springer Science Business Media, 2007-12-01T00:00:00Z) Dauchy, Florent; Dorey, Robert A.
    Thickness mode piezoelectric micro-electromechanical system (MEMS) ultrasound transducers, operating in the 50–75 MHz range, have been fabricated using a composite sol gel technique in combination with wet etching. The composite sol gel technique involves producing a PZT powder/sol composite slurry, which when spun down yields films a few micrometers thick. Repeated layering, and infiltration, has been used to produce PZT films between 20 and 40 μm thick. Due to the low firing temperature (<720°C) it has also been possible to integrate these PZT films with a micro-machined silicon support wafer. These PZT thick films have been structured using a wet etching technique to create free standing pillars that have been shown to resonate in thickness mode in the frequency range of 50–75 MHz. Examples of these structures and their resonant behaviour are pres