PZT making waves in MEMS
Lead zirconate titanate (PZT) is adding capabilities, accuracy and resilience to microelectromechanical systems (MEMS) with the latest announcement that STMicroelectronics NV is offering a customizable PZT-based piezoMEMS process to allow work with development partners (see ST adds piezoelectric MEMS to process portfolio).
It would reasonable to assume that ST also has its own piezoMEMS components that make use of this process and that it will be producing in volume.
But the directions in which ST could take the process are broad. PZT is a ceramic perovskite material that is ferroelectric, pyroelectric and also displays a strong piezoelectric effect. The piezoelectric effect means that a voltage across the material produces mechanical movement while the application of force to the crystal structure produces a voltage difference. Thin films of PZT have been used to produce various types of component, from ferroelectric memories through to IR imaging sensors and for microfluidic heads in inkjet printers. It has also shown promise for energy harvesting type applications.
But in general the additional complexity of laying down and patterning a film of PZT – or alternative piezoelectric materials such as aluminum nitride and zinc oxide – has tended to restrict use to applications where there was no alternative approach.
According to a report on ferroelectric films from Yole Developpement inkjet head and capacitors in integrated passive devices were responsible for 90 percent of the use of such ferroelectric thin films in 2010 but with MEMS use expected to grow strongly.
What is changing is more processes knowledge and broader availability – which affects the implementation price point – as well as better understanding amongst design engineers. Those engineers are starting to see the benefit of using the high resonant frequency and dynamic range of piezoelectric transducers to not only make the special devices listed above and different types of RF type devices and energy harvest machines, but also to enhance mainstream MEMS that have previously been of a capacitively-operated electrostatic design.
It is also noticeable that a startup called Vesper Technologies Inc. (Boston, Mass) is claiming superior dynamic range specifications for a piezoelectric MEMS microphone of its design over a conventional silicon membrane MEMS microphone.
ST is by no means the first company to declare it can make piezoelectric MEMS. The market has been developing gradually for many years. But ST is a MEMS market leader and has a well-honed procedure for working with high volume customers in a MEMS manufacturing role. In this context ST doesn’t see itself as a MEMS foundry as a development and manufacturing partner.
And developments in this area have been coming thick and fast in recent months and years. It is notable that Microgen Systems, a vendor of piezoelectric energy harvest components is backed by X-Fab and has presumably transferred its process to X-Fab which acts as its manufacturing partner. And recently Rohm said its newly created foundry in Kyoto would offer piezoelectric MEMS capability.
Related links and articles:
Peter Clarke’s opinion compendium updated
ST adds piezoelectric MEMS to process portfolio
Silex funded to develop PZT energy harvest process
Rohm opens MEMS foundry operation
Startup’s piezoelectric MEMS mics show superior dynamic range
Piezoelectric energy harvesters get a lift
STMicroelectronics to develop next-generation MEMS pilot line with Lab4MEMS
MicroGen’s piezoMEMS energy harvesters enable wireless sensor network
IR sensor startup preps smartphone bid
MEMS applications are broadening the traditional scope of ferroelectric thin films
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